AU665534B2 - Low-sulfur reforming processes - Google Patents

Abstract

There is disclosed a catalytic reforming method in which hydrocarbons are treated in a reactor system to produce an aromatics enriched product, said reactor system comprising: (a) a series of reactors (10,20,30), containing a catalyst bed comprising a sulfur sensitive zeolite reforming catalyst, and each being associated with (b) a respective furnace (11,21,31) each comprising a plurality of furnace tubes for heating hydrocarbons to an elevated temperature in the range of from 850 to 1025 F suitable for reforming, (c) a heat exchanger (12); and (d) a separator (13) for separating an aromatics enriched product from effluent gas; said method comprising passing hydrocarbons through said reactor system to contact the hydrocarbons with the reforming catalyst in said reactors and separating said aromatics enriched product from said effluent gas; wherein: (i) hydrocarbons are reformed in each of said reactors under low sulfur reforming conditions of less than 50ppb sulfur; and (ii) at least the furnace tubes of the reactor system are protected from carburization and metal dusting. Apparatus for carrying out the process is also described. <IMAGE>

Description

j i i OPI DAT: 06/10/92 NTE AOJP DATE 12/11/92

INTER

(51) International Patent Classification 5 35/06, 9/16 APPLN. ID 15801 92 PCT NUMBER PCT/US92/01856 3N TREATY (PCT) (11) International Publication Number: WO 92/15653 S(43) International Publication Date: 17 September 1992 (17.09.92) (21) International Application Number: (22) International Filing Date: Priority data: 666,696 8 March 8-lf80282/ 6 Deceml 803,063 6 Decem 803,215 6 Deceml PCT/US92/01856 6 March 1992 (06.03.92) 1991 (08.03.91) ber 1991 (06.12.91) ber 1991 (06.12.91) ber 1991 (06.12.91) (71) Applicant: CHEVRON RESEARCH AND TECHNOLO- GY COMPANY [US/US]; Post Office Box 7141, San Francisco, CA 94120-7141 (US).

(72) Inventors: HEYSE, John, V. 190 Duperu Drive, Crockett, CA 94525 MULASKEY, Bernard, F. 18 Shemran Court, Fairfax, CA 94930 INNES, Robert, A. 15 Shannon Lane, San Rafael, CA 94901 HAGE- WIESCHE, Daniel, P. 1610 Leavenworth Street, Apt. 1, San Francisco, CA 94109 HUBRED, Gale, L.; 1324 Stonecrest Circle, Brea, CA 92621 MOORE, Steven, C. 1800 Lakeshore Avenue, Apt. 1, Oakland, CA 94606 BRYAN, Paul, F. 209 Apollo Court Hercules, CA 94547 HISE, Robert, L. 38 Segovia Drive, Fairfield, CA 94533 TRUMBULL, Steven, E. 398 Breed Avenue, San Leandro, CA 94577

(US).

(74) Agents: DeJONGHE, G. et al.; Chevron Corporation, Law Department, Post Office Box 7141, San Francisco, CA 94120-7141 (US).

(81) Designated States: AT, AT (European patent), AU, BB, BE (European patent), BF (OAPI patent), BG, BJ (OAPI patent), BR, CA, CF (OAPI patent), CG (OAPI patent), CH, CH (ELropean patent), CI (OAPI patent), CM (OAPI patent), DE, DE (European patent), DK, DK (European patent), ES, ES (European patent), FI, FR (European patent), GA (OAPI patent), GB, GB (European patent), GN (OAPI patent), GR (European patent), HU, IT (European patent), JP, KP, KR, LK, LU, LU (European patent), MC (European patent), MG, ML (OAPI patent), MR (OAPI patent), MW, NL, NL (European patent), NO, PL, RO, SD, SE, SE (European patent), SN (OAPI patent), TD (OAPI patent), TG (OAPI patent).

Published With international search report.

665534 (54)Title: LOW-SULFUR REFORMING PROCESSES 11 21 31 iO- 20-- EFFLUENT 2

GAS

(57) Abstract PRODUCT F D Disclosed is a method for reforming hydrocarbons comprising contacting the hydrocarbons with a catalyst in a reactor system (10, 20, 30) of improved resistance to carburization and metal dusting under conditions of low sulfur.

t r 1 7 WO 92/15653 PCT/US92/01856 1 1 LOW-SULFUR REFORMING PROCESSES 2 3 BACKGROUND OF THE INVENTION 4 This application is a continuation-in-part application of U.S. Application No. 07/666, 9, filed 6 March 8, 1991, the contents of which hereby 7 incorporated by reference, and .s related to U.S.

8 Application No. 802,82/ [Attorney's Docket No.

9 005950-316], and Application No. 803,215 [Attorney' Docket No. 005950-333], both filed 11 coe rrently herewith and the contents of which are S1 hereby incorporated by reference.

13 14 The present invention relates to improved techniques for catalytic reforming, particularly, 16 catalytic reforming under low-sulfur, and low-sulfur 17 and low-water conditions. More specifically, the 18 invention relates to the discovery and control of 19 problems particularly acute with low-sulfur, and lowsulfur and low-water reforming processes.

21 Catalytic reforming is well known in the S22 petroleum industry and involves the treatment of 23 naphtha fractions to improve octane rating by the 24 production of aromatics. The more important hydrocarbon reactions which occur during the

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U311i i i WO 92/15653 PCT/US92/01856 2 1 reforming operation include the dehydrogenation of 2 cyclohexanes to aromatics, dehydroisomerization of 3 alkylcyclopentanes to aromatics, and 4 dehydrocyclization of acyclic hydrocarbons to aromatics. A number of other reactions also occur, 6 including the dealkylation of alkylbenzenes, 7 isomerization of paraffins, and hydrocracking 8. reactions which produce light gaseous hydrocarbons, 9 methane, ethane, propane and butane. It is important to minimize hydrocracking reactions during 11 reforming as they decrease the yield of gasoline 12 boiling products and hydrogen.

13 14 Because there is a demand for high octane gasoline, extensive research has been devoted to the 16 development of improved reforming catalysts and 17 catalytic reforming processes. Catalysts for 18 successful reforming processes must possess good 19 selectivity. That is, they should be effective for producing high yields of liquid products in the 21 gasoline boiling range containing large 22 concentrations of high octane number aromatic 23 hydrocarbons. Likewise, there should be a low yield 24 of light gaseous hydrocarbons. The catalysts should possess good activity to minimize excessively high 26 temperatures for producing a certain quality of WO 92/15653 PCT/US92/O1856 3 1 products. It is also necessary for the catalysts to 2 either possess good stability in order that the 3 activity and selectivity characteristics can be 4 retained during prolonged periods of operation; or be sufficiently regenerable to allow frequent 6 regeneration without loss of performance.

7 8 Catalytic reforming is also an important process 9 for the chemical industry. There is an increasingly larger demand for aromatic hydrocarbons for use in 11 the manufacture of various chemical products such as 12 synthetic fibers, insecticides, adhesives, 13 detergents, plastics, synthetic rubbers, 14 pharmaceutical products, high octane gasoline, perfumes, drying oils, ion-exchange resins, and 16 various other products well known to those skilled in 17 the art.

18 19 An important technological advance in catalytic reforming has recently emerged which involves the use 21 of large-pore zeolite catalysts. These catalysts are 22 further characterized by the presence of an alkali or 23 alkaline earth metal and are charged with one or more 24 Group VIII metals. This type of catalyst has been found to advantageously provide higher selectivity 26 and longer catalytic life than those previously used.

i. i

I,

PCr/US92/01856, WO 92/15653 4 1 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 21 22 23 24 26 i Having discovered selective catalysts with acceptable cycle lives, successful commercialization seemed inevitable. Unfortunately, it was subsequently discovered that the highly selective, large pore zeolite catalysts containing a Group VIII metal were unusually susceptible to sulfur poisoning.

See U.S. Patent No. 4,456,527. Ultimately, it was found that to effectively address this problem, sulfur in the hydrocarbon feed should be at ultra-low levels, preferably less than 100 parts per billion (ppb), more preferably less than 50 ppb to achieve an acceptable stability and activity level for the catalysts.

After recognizing the sulfur sensitivity associated with these new catalysts and determining the necessary and acceptable levels of process sulfur, successful commercialization reappeared on the horizon; only to vanish with the emergence of another associated problem. It was found that certain large pore zeolite catalysts are also adversely sensitive to the presence of water under typical reaction conditions. Particularly, water was found to greatly accelerate the rate of catalyst deactivation.

L' i- WO 92/15653 PCT/US92/01856 1 Water sensitivity was found to be a serious 2 drawback which was difficult to effectively address.

3 Water is produced at the beginning of each process 4 cycle when the catalyst is reduced with hydrogen.

And, water can be produced during process upsets when K 6 water leaks into the reformer feed, or when the feed 7 becomes contaminated with an oxygen-containing 8 compound. Eventually, technologies were also 9 developed to protect the catalysts from water.

11 Again commercialization seemed practical with 12 the development of various low-sulfur, low-water 13 systems for catalytic reforming using highly 14 selective large-pore zeolite catalysts with long catalytic lives. While low-sulfur/low-water systems 16 were initially effective, it was discovered that a 17 shut down of the reactor system can be necessary 18 after only a matter of weeks. The reactor system of 19 one test plant had regularly become plugged after only such brief operating periods. The plugs were 21 found to be those associated with coking. However, 22 although coking within catalyst particles is a common ,i v, 23 problem in hydrocarbon processing, the extent and 24 rate of coke plug formation exterior to the catalyst particles associated with this particular system far 26 exceeded any expectation.

r L I I WO 92/15653 PCT/US92/01856 WO 92/15653 -6- 1 SUMMARY OF THE INVENTION 2 Accordingly, one object of the invention is to 3 provide a method for reforming hydrocarbons under 4 conditions of low sulfur which avoids the aforementioned problems found to be associated with 6 low-sulfur processes, such as brief operating 7 periods.

8 9 It is another object of the invention to provide a reactor system for reforming hydrocarbons under 11 conditions of low sulfur which permits longer 12 operating periods.

13 14 After a detailed analysis and investigation of the coke plugs of low-sulfur reactor systems, it was 16 surprisingly found that they contained particles and 17 droplets of metal; the droplets ranging in size of up 18 to a few microns. This observation led to the 19 startling realization that there are new, profoundly serious, problems which were not of concern with 21 conventional reforming techniques where process 22 sulfur and water levels were significantly higher.

23 More particularly, it was discovered that problems 24 existed which threatened the effective and economic operability of the systems, and the physical 26 integrity of the equipment as well. It was also 0'.5 I; T:~:CC a oij r PCT/US92/01856 WO 92/15653 7- 1 discovered that these problems emerged due to the 2 low-sulfur conditions, and to some extent, the low 3 levels of water.

4 For the last forty years, catalytic reforming 6 reactor systems have been constructed of ordinary 7 mild steel 2h Cr 1 Mo). Over time, experience 8 has shown that the systems can operate successfully 9 for about twenty years without significant loss of physical strength. However, the discovery of the 11 metal particles and droplets in the coke plugs 12 eventually lead to an investigation of the physical 13 characteristics of the reactor system. Quite 14 surprisingly, conditions were discovered which are symptomatic of a potentially severe physical 16 degradation of the entire reactor system, including 17 the furnace tubes, piping, reactor walls and other 18 environments such as catalysts that contain iron and 19 metal-screens in the reactors. Ultimately, it was discovered that this problem is associated with the 21 excessive carburization of the steel which causes an 22 embrittlement of the steel due to injection of 23 process carbon into the metal. Conceivably, a 24 catastrophic physical failure of the reactor system could result.

26 WO 92/15653 PCT/US92/01856 -8- 1 With conventional reforming techniques 2 carburization simply was not a problem or concern; 3 nor was it expected to be in contemporary low- 4 sulfur/low-water systems. And, it was assumed that conventional process equipment could be used.

6 Apparently, however, the sulfur present in 7 conventional systems effectively inhibits 8 carburization. Somehow in conventional processes the 9 process sulfur interferes with the carburization reaction. But with extremely low-sulfur systems, 11 this inherent protection no longer exists.

12 13 Figure 1A is a photomicrograph of a portion of 14 the inside (process side) of a mild steel furnace tube from a commercial reformer. The tube had been 16 exposed to conventional reforming conditions for 17 about 19 years. This photograph shows that the 18 surface of the tube has remained essentially 19 unaltered with the texture of the tube remaining normal after long exposure to hydrocarbons at high 21 temperatures the black portion of the photograph is 22 background).

23 24 Figure 1B is a photomicrograph of a portion of a mild steel coupon sample which was placed inside a 26 reactor of a low-sulfur/low-water demonstration plant WO 92/15653 PCT/US92/01856 -9- 1 for only 13 weeks. The photograph shows the eroded 2 surface of the sample (contrasted against a black 3 background) from which metal dusting has occurred.

4 The dark grey-like veins indicate the environmental carburization of the steel, which was carburized and 6 embrittled more than 1 mm in depth.

7 8 Of course, the problems associated with 9 carburization only begin with carburization of the physical system. The carburization of the steel 11 walls leads to "metal dusting"; a release of 12 catalytically active particles and melt droplets of 13 metal due to erosion of the metal.

14 The active metal particulates provide additional 16 sites for coke formation in the system. While 17 catalyst deactivation from coking is generally a 18 problem which must be addressed in reforming, this 19 new significant source of coke formation leads to a j 20 new problem of coke plugs which excessively 21 aggravates the problem. In fact, it was found that S 22 the mobile active metal particulates and coke 23 particles metastasize coking generally throughout the 24 system. The active metal particulates actually induce coke formation on themselves and anywhere that 26 the particles accumulate in the system resulting in I coke plugs and hot regions of exothermic demethanation reactions. As a result, an unmanageable and premature cokeplugging of the reactor system occurs which can lead to a system shut-down within weeks of start-up. Use of the process and reactor system of the present invention, however, overcomes these problems.

According to a first aspect of the present invention there is provided a method for reforming hydrocarbons comprising: providing a low sulfur hydrocarbon containing feed having a sulfur content of less than about 100 ppb sulfur; (ii) introducing said low sulfur hydrocarbon containing feed into reactor system comprising at least one furnace and at least one reforming reactor and including a portion with a carburization resistance greater than that of mild steel; and (iii) contacting hydrocarbons from the low sulfur hydrocarbon containing feed with a reforming catalyst.

5. Preferably, the first aspect of the invention relates to a method for reforming hydrocarbons comprising contacting the hydrocarbons with a reforming catalysts, more preferably a large-pore zeolite catalysts including an alkali or alkaline earth metal and charged with one or more Group VIII metals, in a reactor system having a resistance to carburization and metal dusting which is an improvement over conventional mild steel reactor systems under conditions of low sulfur and often low sulfur and low water, and upon reforming the 3 resistance being such that embrittlement from carburization will be less than about 2.5 mm/year, more preferably less than 1.5 mm/year, still more preferably less than 1 mm/year, and most preferably less than 0.1 mm/year. Preventing embrittlement to such an extent will significantly reduce metal dusting and coking in the reactor system, and permits operation for longer periods of time.

According to another aspect of the present invention 6"C. f' 95053 ,p:opedab, 15801.spe, .I -11there is provided a reactor system used in the method defined above.

Preferably, another aspect of the invention relates to a reac'or system including means for providing a resistance I to carburization and metal dusting which is an improvement over conventional mild steel systems in a method for reforming hydrocarbons using a reforming catalysts such as a large-pore zeolite catalyst including an alkaline earth metal and charged with one or more Group VIII metals under conditions of low sulfur, the resistance being such that embrittlement will be less than about 2.5 mm/year, more preferably less than 1.5 mm/year, still more preferably less S, 15 than 1 mm/year, and most preferably less than 0.1 mm/year.

Thus, among other factors, the present invation is based on the discovery that in low-sulfur, and low-sulfur and low-water reforming processes there exist significant carburization, metal dusting and coking problems, which problems do not exist to any significant <:*tent in 'conventional reforming processes where higher levels of sulfur are present. This discovery has led to intensive work and development of solutions to the problems, which h oo -;ch~f ,p.lopct~dablssol.sptl WPCT/US92/01856 WO 92/15653 12 1 solutions are novel to low-sulfur reforming and are 2 directed to the identification and selection of 3 resistant materials for low-sulfur reforming systems, 4 ways to effectively utilize and apply the resistant materials, additives (other than sulfur) for reducing 6 carburization, metal dusting and coking, various 7 process modifications and configurations, and 8 combinations thereof, which effectively address the 9 problems.

S11 More particularly, the discovery has led to the 12 search for, identification of, and selection of 13 resistant materials for low-sulfur reforming systems, 14 preferably the reactor walls, furnace tubes and screens thereof, which were previously unnecessary in 16 conventional reforming systems such as certain alloy 17 and stainless steels, aluminized and chromized 18 materials, and certain ceramic materials. Also, it 19 was discovered that other specific materials, applied as a plating, cladding, paint, etc., can be 21 effectively resistant. These materials include 22 copper, tin, arsenic, antimony, brass, lead bismuth 23 chromium, intermetallic compounds thereof, and alloys 24 thereof, as well as silica and silicon based coatings. In no prefar~ca\embodiment of the -13 invention there is provided a decomposable, reactive, tincontaining paint which is to be exposed to hydrocarbons at elevated temperatures and provides carburization resistance to a base construction material such that embrittlement will be less than 2.5 mm/year under exposure conditions, which paint reduces to a reactive tin which forms a tin complex with said construction material to which it is applied upon heating in a reducing environment.

Furthermore, the discovery led to the development of certain additives, hereinafter referred to as anticarburizing 4 and anticoking agents, which out of necessity are essentially sulfur free, preferably completely sulfur free, which are Snovel to reforming. Such additives include organo-tin compounds, organo-antimony compounds, organo-bismuth i' compounds, organo-arsenic compounds and organo-lead I11la compounds.

Also, the problems associated with low-sulfur reforming has lead to the development of certain process modifications and configurations previously unnecessary in conventional SI. reforming. These include certain temperature control techniques, the use of superheated hydrogen between reactors, S" more frequent catalysts regenerations, the use of staged A 25 heaters and tubes, the use of staged temperature zones, the use of superheated raw materials, and the use of larger tube diameters and/or higher tube velocities.

v-, 1 c 950815,p:\oper\dab, 1580 .spe,13 T~ o WO 92/15653 PCT/US92/01856 14 1 BRIEF DESCRIPTION OF THE DRAWING 2 As noted above, Figure 1A is a photomicrograph 3 of a portion of the inside (process side) of a mild 4 steel furnace tube from a commercial reformer which had been in use about 19 years; and as also noted 6 above, 7 8 Figure 1B is a photomicrograph of a portion of a 9 mild steel coupon sample which was placed inside a reactor of a low-sulfur/low-watrr demonstration plant 11 for only 13 weeks.

12 13 Figure 2 is an illustration of a suitable 14 reforming reactor system for use in the present invention.

16 17 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 18 The metallurgical terms used herein are to be 19 given their common metallurgical meanings as set forth in THE METALS HANDBOOK of the American Society' 21 of Metals. For example, "carbon steels" are those lI 22 steels having no specified minimum quantity for any os 23 alloying element (other than the commonly accepted 24 amounts of manganese, silicon and copper) and containing only an incidental amount of any element 26 other than carbon, silicon, manganese, copper, sulfur K: i. cll WO 92/15653 PCT/US92/01856 15 1 and phosphorus. "Mild steels" are those carbon 2 steels with a maximum of about 0.25% carbon. Alloy 3 steels are those steels containing specified 4 quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, 6 copper, silicon, sulfur and phosphorus) within the 7 limits recognized for constructional alloy steels, 8 added to effect changes in mechanical or physical 9 properties. Alloy steels will contain less than chromium. Stainless steels are any of several steels S11 containing at -least 10, preferably 12 to 12 chromium as the principal alloying element.

13 14 Generally, therefore, one focus of the invention is to provide an improved method for reforming 16 hydrocarbons using a reforming catalyst, particularly 17 a large pore zeolite catalyst including an alkali or 18 alkaline earth metal and charged with one or more 19 Group VIII metals which is sulfur sensitive, under conditions of low sulfur. Such a process, of course, 21 must demonstrate better resistance to carburization 22 than conventional low-sulfur reforming techniques.

d 23 24 One solution for the problem addressed by the present invention is to provide a novel reactor 26 system which can include one or more various means iI 1 ii 1 WO 92/15653 PCT/US92/01856 -16- 1 for improving resistance to carburization and metal 2 dusting during reforming using a reforming catalyst 3 such as the aforementioned sulfur sensitive large- 4 pore zeolite catalyst under conditions of low sulfur.

6 By "reactor system" as used herein there is 7 intended at least one reforming reactor and its 8 corresponding furnace means and piping. Figure 2 9 illustrates a typical reforming reactor system suitable for practice of the present invention. It 11 can include a plurality of reforming reactors 12 (20) and Each reactor contains a catalyst bed.

13 The system also includes a plurality of furnaces 14 (21) and heat exchanger and separator (13).

16 17 Through research associated with the present 18 invention, it was discovered that the aforementioned 19 problems with low-sulfur reforming can be effectively addressed by a selection of an appropriate reactor 21 system material for contact with the hydrocarbons 22 during processing. Typically, reforming reactor 23 systems have been constructed of mild steels, or 24 alloy steels such as typical chromium steels, with insignificant carburization and dusting. For 26 example, under conditions of standard reforming, 23 l WO 92/15653 PCT/US92/01856 17 1 Cr furnace tubes can last twenty years. However, it 2 was found that these steels are unsuitable under low- 3 sulfur reforming conditions. They rapidly become 4 embrittled by carburization within about one year.

For example, it was found that 2h Cr 1 Mo steel 6 carburized and embrittled more than 1 mm/year.

7 8 Furthermore, it was found that materials 9 considered under standard metallurgical practice to be resistant to coking and carburization are not 11 necessarily resistant under low-sulfur reforming 12 conditions. For example, nickel-rich alloys such as 13 Incoloy 800 and 825; Inconel 600; Marcel and Haynes 14 230, are unacceptable as they exhibit excessive coking and dusting.

16 17 However, 300 series stainless steels, preferably.

18 304, 316, 321 and 347, are acceptable as materials 19 for at least portions of the reactor system according to the present invention which contact the 21 hydrocarbons. They have been found to have a 22 resistance to carburization greater than mild steels F 23 and nickel-rich alloys.

1 2 4 Initially it was believed that aluminized 26 materials such as those sold by Alon Corporation WO 92/15653 PCT/US92/01856 18 1 ("Alonized Steels") would not provide adequate 2 protection against carburization in the reforming 3 reactor system and process of the invention. It has 4 since been discovered, however, that the application of thin aluminum or alumina films to metal surfaces 6 of the reforming reactor system, or simply the use of 7 Alonized Steels during construction, can provide 8 surfaces which are sufficiently resistant to 9 carburization and metal dusting under the low-sulfur reforming conditions. However, such materials are S11 relatively expensive, and while resistant to 12 carburization and metal dusting, tend to crack, and 13 show substantial reductions in tensile strengths.

14 Cracks expose the underlying base metal rendering it susceptible to carburization and metal dusting under 16 low sulfur reforming conditions.

17 18 While aluminized materials have been used to 19 prevent carburization in ethylene steam cracking processes, such processes are operated at 21 significantly higher temperatures t:han reforming; 22 temperatures where carburization would be expected.

23 carburization and metal dusting simply have not been 24 problems in prior reforming processes.

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WO 92/15653 PCT/US92/01856 19 1 Therefore, another solution to the problems of 2 carburization and metal dusting involves the 3 application of thin aluminum or alumina films on, or 4 the use of aluminized materials as, at least a portion of the metal surfaces in the reactor system.

6 In fact, the metal surfaces particularly susceptible 7 to carburization and metal dusting can be provided in 8 that manner. Such metal surfaces include but are not 9 limited to, the reactor walls, furnace tubes, and furnace liners.

11 12 When applying an aluminum or alumina film, it is 13 preferable that the film have a thermal expansivity 14 that is similar to that of the metal surface to which it is applied (such as a mild steel) in order to 16 withstand thermal shocks and repeated temperature 17 cycling which occur during reforming. This prevents 18 cracking or spalling of the film which could expose 19 the underlying metal surface to the carburization inducing hydrocarbon environment.

21 22 Additionally, the film should have a thermal 23 conductivity similar to that of, or exceeding, those S• 24 of metals conventionally used in the construction of reforming reactor systems. Furthermore, the aluminum 26 or alumina film should not degrade in the reforming WO 92/15653 PCT/US92/01856 20 1 environment, or in the oxidizing environment 2 associated with catalyst regeneration, nor should it 3 result in the degradation of the hydrocarbons in the 4 reactor system.

6 Suitable methods for applying aluminum or 7 alumina films to metal surfaces such as mild steels 8 include well known deposition techniques. Preferred 9 processes include powder and vapor diffusion processes such as the "Alonizing" process, which has 11 been commercialized by Alon Processing, Inc., 12 Terrytown, Pa.

14 Essentially, "Alonizing" is a high temperature diffusion process which alloys aluminum into the 16 surface of a treated metal, such as a 17 commercial grade mild steel. In this process, the 18 metal a mild steel) is positioned in a retort 19 and surrounded with a mixture of blended aluminum powders. The retort is then hermetically sealed and 21 placed in an atmosphere-controlled furnace. At 22 elevated temperatures, the aluminum deeply diffuses 23 into the treated metal resulting in an alloy. After 24 furnace cooling, the substrate is taken out of the retort and excess powder is removed. Straightening, 26 trimming, beveling and other secondary operations can I re*r an* exes pod i s reoe.Sriheig WO 92/15653 PCT/US92/01856 21 1 then be performed as required. This process can 2 render the treated ("alonized") metal resistant to 3 carburization and metal dusting under low-sulfur 4 reforming conditions according to the invention.

6 Thin chromium or chromium oxide films can also 7 be applied to metal surfaces of the reactor system to 8 render the surfaces resistant to carburization and 9 metal dusting under low-sulfur reforming conditions.

Like the use of alumina and aluminum films, and 11. aluminized materials, chromium or chromium oxide 12 coated metal surfaces have not been used to address 13 carburization problems under low-sulfur reforming 14 conditions.

16 The chromium or chromium oxide can also be 17 applied to carburization and metal dusting 18 susceptible metal surfaces such as the reactor walls, 19 furnace liners, and furnace tubes. However, any surface in the system which would show signs of 21 carburization and metal dusting under low-sulfur 22 reforming conditions would benefit from the 23 application of a thin chromium or chromium oxide 24 film.

i i WO 92/15653 PCT/US92/01856 22 1 When applying the chromium or chromium oxide 2 film, it is preferable that the chromium or chromium 3 oxide film have a thermal expansivity similar to that 4 of the metal to which it is applied. Additionally, the chromium or chromium oxide film should be able to 6 withstand thermal shocks and repeated temperature 7 cycling iwhich are common during reforming. This 8 avoids cracking or spaliing of the chromium or 9 chromium oxide film which could potentially expose the underlying metal surfaces to carburization 11 inducing environments. Furthermore, the chromium or 12 chromium oxide film should have a thermal 13 conductivity similar to or exceeding those materials 14 conventionally used in reforming reactor systems (in particular mild steels) in order to maintain 16 efficient heat transfer. The chromium or chromium 17 oxide film also should not degrade in the reforming 18 environment or in the oxidizing environment 19 associated with catalyst regeneration, nor should it induce degradation of the hydrocarbons in the reactor 21 system.

22 23 Suitable methods for applying chromium or 24 chromium oxide films to surfaces such as mild steels, include well known deposition techniques.

26 Preferred processes include powder-pack and vapor WO 92/15653 PC/US92/01856 3 S92/15653 PCT/US92/01856 WO 92/15653 23 1 diffusion processes such as the "chromizing" process, 2 which is commercialized by Alloy Surfaces, Inc., of 3 Wilmington, Delaware.

4 The "chromizing" process is essentially a vapor 6 diffusion process for application of chromium to a 7 metal surface (similar to the above described 8 "Alonizing process"). The process involves 9 contacting the metal to be coated with a powder of chromium, followed by a thermal diffusion step.

11 This, in effect, creates an alloy of the chromium 12 with the treated metal and renders the surface 13 extremely resistant to carburization and metal 14 dusting under low-sulfur reforming conditions.

16 In some areas of the reactor systems, localized 17 temperatures can become excessively high during 18 reforming 900-1250°F). This is particularly 19 the case in furnace tubes, and in catalyst beds where exothermic demethanation reactions occur within 21 normally occurring coke balls causing localized hot 22 regions. While still preferred to mild steels and 23 nickel-rich alloys, the 300 series stainless steels 24 do exhibit some coking and dusting at around 1000 0

F.

Thus, while useful, the 300 series stainless steels Attorney's Docket No. 005950-314 WO 92/15653 PCT/US92/01856 24 1 are not the most preferred material for use in the 2 present invention.

3 4 Chromium-rich stainless steels such as 446 and 430 are even more resistant to carburization than 300 6 series stainless steels. However, these steels are 7 not as desirable for heat resisting properties (they 8 tend to become brittle).

9 Resistant materials which are preferred over the 11 300 series stainless steels for use in the present 12 invention include copper, tin, arsenic, antimony, 13 bismuth, chromium and brass and intermetallic 14 compounds and all ys thereof Cu-Sn alloys, Cu- Sb alloys, stannides, antimonides, bismuthides, 16 etc.). Stecls and even nickel-rich alloys containing 17 these metals can also show reduced carburization. In 18 a preferred embodiment, these materials are provided 19 as a plating, cladding, paint (s oxide pain'') or other coating to a base cons,- uction material. This 21 is particularly advantageou since conventional 22 construction materials such as mild steels can still 23 be used with only the surface contacting the 24 hydrocarbons being treated. Of these, tin is especially preferred as it reacts with the surface to 26 provide a coating having excellent carburization r WO2 .W /15653 PCT/US92/01856 25 1 resistance at higher temperatures, and which resists 2 peeling and flaking of the coating. Also, it is 3 believed that a tin containing layer can be as thin 4 as 1/10 micron and still prevent carburization.

6 Where practical, it is preferred that the 7 resistant materials be applied in a paint-like 8 formulation (hereinafter "paint") to a new or 9 existing reactor system. Such a paint can be sprayed, brushed, pigged, etc. on reactor system 11 surfaces such as mild steels or stainless steels. It 12 is most preferred that such a paint be a 13 decomposable, reactive, tin-containing paint which 14 reduces to a reactive tin and forms metallic stannides iron stannides and nickel/iron 16 stannides) upon heating in a reducing atmosphere. 17 18 It is most preferred that the aforementioned i 19 paint contain at least four components (or their functional equivalents); a hydrogen decomposable 21 tin compound, (ii) a solvent system, (iii) a finely 22 divided tin metal and (iv) tin oxide as a reducible 23 sponge/dispersing/binding agent. The paint should 24 contain finely divided solids to minimize settling, and should not contain non-reactive materials which 7 r WO 92/15653 PCT/US92/01856 26 will prevent reaction of reactive tin with surfaces of the reactor system.

As the hydrogen decomposable tin compound, tin octanoate is particularly useful. Commercial formulations of this compound itself are available and v'ill partially dry to an almost chewing-gum-like layer on a steel surface; a layer which will not crack and/or split. This property is necessary for any coating composition used in this context because it is conceivable that the coated material will be stored for months prior to treatment with hydrogen.

Also, if parts are coated prior to assembly they must be resistant to chipping during construction. As noted above, tin octanoate is available commercially.

It is reasonably priced, and will decompose smoothly to a reactive tin layer which forms iron stannide in hydrogen at temperatures as low as 600 0

F.

Tin octanoate should not be used alone in a paint, however. It is not sufficiently viscous.

Even when the solvent is evaporated therefrom, the remaining liquid will drip and run on the coated surface. In practice, for example, if such were used to coat a horizontal furnace tube, it would pool at the bottom of the tube.

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i' WO 92/15653 PCT/US92/01856 -27- 1 Component the tin oxide 2 sponge/dispersing/binding agent, is a porous tin- 3 containing compound which can sponge-up an organo- 4 metallic tin compound, yet still be reduced to active tin in the reducing atmosphere. In addition, tin 6 oxide can be processed through a colloid mill to 7 produce very fine particles which resist rapid 8 settling. The addition of tin oxide will provide a 9 paint which becomes dry to the touch, and resists running.

11 12 Unlike typical paint thickeners, component (iv) 13 is selected such that it becomes a reactive part of 14 the coating when reduced. It is not inert like formed silica; a typical paint thickener which would 16 leave an unreactive surface coating after treatment.

17 18 Finely divided tin metal, component (iii), is 19 added to insure that metallic tin is available to 1 i 20 react with the surface to be coated at as low a 21 temperature as possible, even in a non-reducing 22 atmosphere. The particle size of the tin is l 23 preferably one to five microns which allows excellent 24 coverage of the surface to be coated with tin metal.

Non-reducing conditions can occur during drying of 26 the paint and welding of pipe joints. The presence i WO 92/15653 PCT/US92/01856 28 1 of metallic tin ensures that even when part of the 2 coating is not completely reduced, tin metal will be 3 present to react and form the desired stannide layer.

4 The solvent should be non-toxic, and effective 6 for rendering the paint sprayable and spreadable when 7 desired. It should also evaporate quickly and have 8 compatible solvent properties for the hydrogen 9 decomposable tin compound. Isopropyl alcohol is most preferred, while hexane and pentane can be useful, if 11 necessary. Acetone, however, tends to precipitate 12 organic tin compounds.

13 14 In one embodiment, there can be used a tin paint of 20 percent Tin Ten-Cem (stannous octanoate in 16 octanoic acid), stannic oxide, tin metal powder and 17 isopropyl alcohol.

19 The tin paint can be applied in many ways. For example, furnace tubes of the reactor system can be 21 painted individually or as modules. A reforming 22 reactor system according to the present invention can i 23 contain various numbers of furnace tube modules 24 about 24 furnace tube modules) of suitable width, length and height about 10 feet long, 26 about 4 feet wide, and about 40 feet in height).

WO 92/15653 PCT/US92/O 856 -29 1 Typically, each module will include two headers of 2 suitable diameter, preferably about 2 feet in 3 diameter, which are connected by about four to ten u- 4 tubes of suitable length about 42 feet long).

Therefore, the total surface area to be painted in 6 the modules can vary widely;.for example, in one 7 embodiment it can be about 16,500 ft 2 8 9 Painting modules rather than the tubes individually can be advantageous in at least four 11 respects; painting modules rather than individual i2 tubes should avoid heat destruction of the tin paint 13 as the components of the modules are usually heat 14 treated at extremely elevated temperatures during production; (ii) painting modules will likely be i 16 quicker and less expensive than painting tubes 17 individually; (iii) painting modules should be more 18 efficient during production scheduling; and (iv) 19 painting of the modules should enable painting of welds.

21 22 However, painting the modules may not enable the 23 tubes to be as completely coated with paint as if the 24 tubes were painted individually. If coating is insufficient, the tubes can be coated individually.

26 1 I WO 92/15653 PCT/US92/01856 30 1 It is preferable that the paint be sprayed into 2 the tubes and headers. Sufficient paint should be 3 applied to fully coat the tubes and headers. After a 4 module is sprayed, it should be left to dry for about 24 hours followed by application of a slow stream of 6 heated nitrogen about 150°F for about 24 7 hours). Thereafter, it is preferable that a second 8 coat of paint be applied and also dried by the 9 procedure described above. After the paint has been applied, the modules should preferably be kept under 11 a slight nitrogen pressure and should not be exposed S12 to temperatures exceeding about 200°F prior to 13 installation, nor should they be exposed to water 14 except during hydrotesting.

16 Iron bearing reactive paints are also useful in 17 the present invention. Such an iron bearing reactive 18 paint will preferably contain various tin compounds 19 to which iron has been added in amounts up to one third Fe/Sn by weight.

21 22 The addition of iron can, for example, be in the 23 form of FeO 3 The addition of iron to a tin 24 containing paint should afford noteworthy advantages; in particular: it should facilitate the 26 reaction of the paint to form iron stannides thereby 1 i WO 92/15653 PCr/US92/01856 31 1 acting as a flux; (ii) it should dilute the nickel 2 concentration in the stannide layer thereby providing 3 better protection against coking; and (iii) it 4 should result in a paint which affords the anticoking protection of iron stannides even if the 6 underlying surface does not react well.

7 8 Yet another means for preventing carburization, 9 coking, and metal dusting in the low-sulfur reactor system comprises the application of a metal coating 11 or cladding to chromium rich steels contained in the 12 reactor system. These metal coatings or claddings 13 may be comprised of tin, antimony, bismuth or 14 arsenic. Tin is especially preferred. These coatings or claddings may be applied by methods 16 including electroplating, vapor depositing, and 17 soaking of the chromium rich steel in a molten metal 18 bath.

19 It has been found that in reforming reactor 21 systems where carburization, coking, and metal I 22 dusting are particularly problematic that the coating 23 of the chromium-rich, nickel-containing steels with a 24 layer of tin in effect creates a double protective layer. There results an inner chromium rich layer 26 which is resistant to carburization, coking, and WO 92/15653

,I

32 1 metal dusting and an outer tin layer which is also 2 resistant to carburization, coking and metal dusting.

3 This occurs because when the tin coated chromium rich 4 steel is exposed to typical reforming temperatures, such as about 1200 0 F, it reacts with the steel to 6 form iron nickel stannides. Thereby, the nickel is 7 preferentially leached from the surface of the steel 8 leaving behind a layer of chromium rich steel. In 9 some instances, it may be desirable to remove the iron nickel stannide layer from the stainless steel 11 to expose the chromium rich steel layer.

12 13 For example, it was found that when a tin 14 cladding was applied to a 304 grade stainless steel and heated at about 1200°F there resulted a chromium 16 rich steel layer containing abouc 17% chromium and 17 substantially no nickel, comparable to 430 grade 18 stainless steel.

19 When applying the tin metal coating or cladding 21 to the chromium rich steel, it may be desirable to fY 22 vary the thickness of the metal coating or cladding 23 to achieve the desired resistance against S,24 carburization, coking, and metal dusting. This can be done by, adjusting the amount of time the 26 chromium rich steel is soaked in a molten tin bath.

WO 92/15653 PCT/US92/01856 33 1 This will also affect the thickness of the resulting 2 chromium rich steel layer. It may also be desirable 3 to vary the operating temperature, or to vary the 4 composition of the chromium rich steel which is coated which in order to control the chromium 6 concentration in the chromium rich steel layer 7 produced.

8 9 It has additionally been found that tin-coated steels can be further protected from carburization, 11 metal dusting, and coking by a post-treatment process S112 which involves application of a thin oxide coating, 13 preferably a chromium oxide, such as Cr20 3 This 14 coating will be thin, as thin as a few gm.

Application of such a chromium oxide will protect 16 aluminum as well as tin coated steels, such as 17 Alonized steels, under low-sulfur reforming 18 conditions. 19 The chromium oxide layer can be applied by i' 21 various methods including: application of a chromate 22 or dichromate paint followed by a reduction process; 23 vapor treatment with an organo-chromium compound; or 24 application of a chromium metal plating followed by oxidation of the resulting chromium plated steel.

26 WO 92/15653 PCT/US92/01856 34 Examination of tin-electroplated steels which have been subjected to low-sulfur reforming conditions for a substantial period of time has shown that when a chromium oxide layer is produced on the surface of the stannide layer or under the stannide layer, the chromium oxide layer does not cause deterioration of the stannide layer, but appears to render the steel further resistant to carburization, coking and metal dusting. Accordingly, application of a chromium oxide layer to either tin or aluminum coated steels will result in steels which are further resistant to carburization and coking under the lowsulfur reforming conditions. This post-treatment process has particular applications for treating tin or aluminum coated steels which, after prolonged exposure to low-sulfur reforming conditions, are in need of repair.

It has further been found that aluminized, e.g., "Alonized" steels which are resistant to carburization under the present reforming conditions of low sulfur can be rendered further resistant by post-treatment of the aluminum coated steel with a coating of tin. This results in a stael which is more carburization resistant since there are cumulative effects of carburization resistance

I

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L WO92/15653 PC/US92/01856 35 1 obtained from both the aluminum coating and the tin 2 coating. This post-treatment affords an additional 3 benefit in that it will mend any defects or cracks in 4 the aluminum, Alonized, coating. Also, such a post-treatment should result in a lower cost since a 6 thinner aluminum coating can be applied to the steel 7 surface which is to be post-treated with the tin 8 coating. Additionally, this post-treatment will 9 protect the underlying steel layer exposed by bending of aluminized steels, which can introduce cracks in 11 the aluminum layer, and expose the steel to 12 carburization induced under reforming conditions.

13 Also, this post-treatment process can prevent coke 14 formation on the treated steel surfaces and also prevent coke formation that occurs on the bottom of 16 cracks which appear on steels which have been 17 aluminized, but not additionally coated with tin.

18 19 Samples of Alonized Steels painted on one side with tin, were found to show a deposit of black coke* 21 only on the untreated side under low-sulfur reforming 22 conditions. The coke that forms on an aluminized 23 surface is a benign coke resulting from cracking on 24 acidic alumina sites. It is incapable of inducing additional coke deposition. Accordingly, a post- 26 treatment application of a tin coating to aluminized "i WO 92/15653 PCT/US92/01856 36 1 steels can provide further minimization of the 2 problems of carburization, coking, and metal dusting, 3 in reactor systems operating under reforming 4 conditions according to the invention.

6 While not wishing to be bound by theory, it is 7 believed that the suitability of various materials 8 for the present invention can be selected and 9 classified according to their responses to carburizing atmospheres. For example, iron, cobalt, 11 and nickel form relatively unstable carbides which 12 will subsequently carburize, coke and dust. Elements 13 such as chromium, niobium, vanadium, tungsten, 14 molybdenum, tantalum and zirconium, will form stable carbides which are more resistant to carburization 16 coking and dusting. Elements such as tin, antimony 17 and bismuth do not form carbides or coke. And, these 18 compounds can form stable compounds with many metals 19 such as iron, nickel and copper under reforming conditions. Stannides, antimonides and bismuthides, S21 and compounds of lead, mercury, arsenic, germanium, 22 indium, tellurium, selenium, thallium, sulfur and 23 oxygen are also resistant. A final category of 24 materials include elements such as silver, copper, gold, platinum and refractory oxides such as silica 26 and alumina. These materials are resistant and do r 26 *.ld plt*u \ercoy oie uhsslc

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iI;( PC/US92/01856 WO 92/15653 37 4 6 7 8 9 11 12 13 14 16 17 18 19 21 22 23 24 h 25 26 not form carbides, or react with other metals in a carburizing environment under reforming conditions.

As discussed above, the selection of appropriate metals which are resistant to carburization and metal dusting, and their use as coating materials for metal surfaces in the reactor system is one means for preventing the carburization and metal dusting problem. However, carburization and metal dusting can be prevalent in a wide variety of metals; and carburization resistant metals can be more costly or exotic than conventional materials mild steels) used in the construction of reforming reactor systems. Accordingly, it may be desirable in the reactor system of the invention to use ceramic materials which do not form carbides at typical reforming conditions, and thus are not susceptible to carburization, for at least a portion of the metal surfaces in the reactor system. For example, at least a portion of the furnace tubes, o: furnace liners or both may be constructed of ceramic materials.

In choosing the ceramic materials for use in the present invention, it is preferable that the ceramic material have thermal conductivities about that or L 1 '9 PCI'? I2/flTS56 WO 92/15653 P^/U92Oi5 38 exceeding those of materials conventionally used in the construction of reforming reactor systems.

Additionally, the ceramic materials should have sufficient structural strengths at the temperatures which occur within the reforming reactor system.

Further, the ceramic materials should be able to withstand thermal shocks and repeated temperature cycling which occur during operation of the reactor system. When the ceramic materials are used for constructing the furnace liners, the ceramic materials should have thermal expansivities about that of the metal outer surfaces With wA'ch the liner is in intimate contact. This avoids undue stress at the juncture during temperature cycling that occurs during start-up and shut-down. Additionally, the ceramic surface should not be susceptible to degradation in the hydrocarbon environment or in the oxidizing environment which occurs during catalyst regeneration. The selected ceramic material also should not promote the degradation of the hydrocarbons in the reactor system.

Suitable ceramic materials include, but are not restricted to, materials such as silicon carbides, silicon oxides, silicon nitrides and aluminum nitrides. Of these, silicon carbides and silicon Ih -I WO92/15653 PCF/US92/01856 39 1 nitrides are particularly preferred as they appear capable of providing complete protection for the 3 reactor system under low-sulfur reforming conditions.

4 At least a portion of the metal surfaces in the 6 reactor system can also be coated with a silicon or 7 silica film. In particular, the metal surfaces which 8 can be coated include, but are not limited to the 9 reactor walls, furnace tubes, and furnace liners.

However, any metal surface in the reactor system, 11 which shows signs of carburization and metrl dusting 12 under low-sulfur reforming conditions would benefit 13 from the application of a thin silicon or silica 14 film.

16 Conventional methods can be used for applying 17 silicon or silica films to coat metal surfaces.

18 Silica or silicon can be applied by electroplating 19 and chemical vapor deposition of an alkoxysilane in a steam carrier gas. It is preferable that the silicon 21 or silica film have a thermal expansivity about that 22 of the metal surface which it coats. Additionally, r 23 the silicon or silica film should be able to 24 withstand thermal shocks and repeated temperature cycling that occur during reforming. This avoids 26 cracking or spalling of the silicon or silica film, li 1

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WO 92/15653 PCT/US92/01856 40 1 and potential exposure of the underlying metal 2 surface to the carburization inducing hydrocarbon 3 environment. Also, the silica or silicon film should 4 have a thermal conductivity approximate to or exceeding that of metals conventionally used in 6 reforming reactor systems so as to maintain efficient 7 heat transfer. The silicon or silica film also 8 should not degrade in the reforming environment or in 9 the oxidizing environment associated with catalyst regeneration; nor should it cause degradation of the 11 hydrocarbons themselves.

12 13 Because different areas of the reactor system of 14 the invention different areas in a furnace) can be exposed to a wide range of temperatures, the 16 material selection can be staged, such that those 17 materials providing better carburization resistances 18 are used in those areas of the system experiencing 19 the highest temperatures.

21 With regard to materials selection, it was 22 discovered that oxidized Group VIII metal surfaces j 23 such as iron, nickel and cobalt are more active in R 24 terms of cokii.g and carburization than their unoxidized counterparts. For example, it was found 26 that an air roasted sample of 347 stainless steel was r c Il ji-i C L~ I W092/15653 PCIT/US92/01856 -41 1 significantly more active than an unoxidized sample 2 of the same steel. This is believed to be due to a 3 re-reduction of oxidized steels which produces very 4 fine-grained iron and/or nickel metals. Such metals are especially active for carburization and coking.

6 Thus, it is desirable to avoid these materials as 7 much as possible during oxidative regeneration 8 processes, such as those typically used in catalytic 9 reforming. However, it has been found that an air roasted 300 series stainless steel coated with tin 11 can provide similar resistances to coking and 12 carburization as unroasted samples of the same tin 13 coated 300 series stainless steel.

14 Furthermore, it will be appreciated that 16 oxidation will be a problem in systems where sulfur 17 sensitivity of the catalyst is not of concern, and 18 sulfur is used to passivate the metal surfaces. If 19 sulfur levels in such systems ever become i( insufficient, any metal sulfides which have formed on 21 metal surfaces would, after oxidation and reduction, 22 be reduced to fine-grained metal. This metal would 23 be highly reactive for coking and carburization.

24 Potentially, this can cause a catastrophic failure of the metallurgy, or a major coking event.

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i; PCT/US92/O1856 WO 92/15653 42 As noted above, excessively high temperatures can occur in the catalyst beds when exothermic demethanation reactions within cokeballs cause localized hot regions. These hot spots also pose a problem in conventional reforming reactor systems (as well as other areas of chemical and petrochemical processing).

For example, the center pipe screens of reformers have been observed to locally waste away and develop holes; ultimately resulting in catalyst migration. In conventional reforming processes the temperatures within cokeballs during formation and burning are apparently high enough to overcome the ability of process sulfur to poison coking, carburization, and dusting. The metal screens, therefore, carburize and are more sensitive to wasting by intergranular oxidation (a type of corrosion) during regeneration. The screen openings enlarge and holes develop.

Thus, the teachings of the present invention are applicable to conventional reforming, as well as other areas of chemical and petrochemical processing.

For example, the aforementioned platings, claddings and coatings can be used in the preparation of center

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L i I r :i 1_£ i; i: i PCT/US92/01856 WO 92/15653 43 pipe screens to avoid excessive hole development and catalyst migration. In addition, the teachings can be applied to any furnace tubes which are subjected to carburization, coking and metal dusting, such as furnace tubes in coker furnaces.

In addition, since the techniques described herein can be used to control carburization, coking, and metal dusting at excessively high temperatures, they can be used in cracking furnaces operating at from about 14000 to about 1700 0 F. For example, the deterioration of steel occurring in cracking furnaces operating at those temperatures can be controlled by application of various metal coatings. These metal coatings can be applied by melting, electroplating, and painting. Painting is particularly preferred.

For example, a coating of antimony applied to iron bearing steels protects these steels from carburization, coking and metal dusting under the described cracking conditions. In fact, an antimony paint applied to iron bearing steels will provide protection against carburization, coking, and metal dusting at 1600°F.

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jy ii 4 WO 92/15653 PCT/US92/01856 44 1 A coating of bismuth applied to nickel rich 2 steel alloys INCONEL 600) can protect those 3 steels against carburization, coking, and metal 4 dusting under cracking conditions. This has been demonstrated at temperatures of up to 1600 0

F.

6 7 Bismuth coatings may also be applied to iron 8 bearing steels and provide protection against 9 carburization, metal dusting, and coking under cracking conditions. Also, a metal coating 11 comprising a combination of bismuth, antimony, and/or 12 tin can be used.

13 14 Looking again to low-sulfur reforming, other techniques can also be used to address the problem 16 discovered according to the present invention. They 17 can be used in conjunction with an appropriate 18 material selection for the reactor system, or they 19 can be used alone. Preferred from among the additional techniques is the addition of non-sulfur, 21 anti-carburizing and anti-coking agent(s) during the 22 reforming process. These agents can be added 23 continuously during processing and function to 24 interact with those surfaces of the reactor system which contact the hydrocarbons, or they may be 26 applied as a pretreatment to the reactor system.

S WO92/15653 PCT/US92/01856 1 While not wishing to bound by theory it is 2 believed that these agents interact with the surfaces 3 of the reactor system by decomposition and surface 4 attack to form iron and/or nickel intermetallic compounds, such as stannides, antimonides, 6 bismuthides, plumbides, arsenides, etc. Such 7 intermetallic compounds are resistant to 8 carburization, coking and dusting and can protect the 9 underlying metallurgy.

11 The intermetallic compounds are also believed to 12 be more stable than the metal sulfides which were 13 formed in systems where H,S was used to passivate the 14 metal. These compounds are not reduced by hydrogen as are metal sulfides. As a result, they are less 16 likely to leave the system than metal sulfides.

17 Therefore, the continuous addition of a carburization 18 inhibitor with the feed can be minimized.

19 Preferred non-sulfur anti-carburizing and anti- 21 coking agents include organo-metallic compounds such 22 as organo-tin compounds, organo-antimony compounds, 23 organo-bismuth compounds, organo-arsenic compounds, 24 and organo-lead compounds. Suitable organo-lead compounds include tetraethyl and tetramethyl lead.

i WO92/15653 PCT/US92/01856 WO 92/15653 t;wi' Xi 46 Organo-tin compounds such as tetrabutyl tin and trimethyl tin hydride are especially preferred.

Additional specific organo-metallic compounds include bismuth neodecanoate, chromium octoate, copper naphthenate, manganese carboxylate, palladium neodecanoate, silver neodecanoate, tetrabutylgermanium, tributylantimony, triphenylantimony, triphenylarsine, and zirconium octoate.

How and where these agents are added to the reactor system is not critical, and will primarily depend on particular process design characteristics.

For example, they can be added continuously or discontinuously with the feed.

However, adding the agents to the feed is not preferred as they would tend to accumulate in the initial portions of the reactor system. This may not provide adequate protection in the other areas of the system.

It is preferred that the agents be provided as a coating prior to construction, prior to start-up, or in-situ in an existing system). If added inu r*~-i i WO 92/15653 PCT/US92/01856 47 1 situ, it should be done right after catalyst 2 regeneration. Very thin coatings can be applied.

3 For example, it is believed that when using organo- 4 tin compounds, iron stannide coatings as thin as 0.1 micron can be effective.

6 7 A preferred method of coating the agents on an 8 existing or new reactor surface, or a new or existing 9 furnace tube is to decompose an organometallic compound in a hydrogen atmosphere at temperatures of 11 about 900°F For organo-tin compounds, for example, 12 this produces reactive metallic tin on the tube 13 surface. At these temperatures the tin will further 14 react with the surface metal to passivate it.

16 Optimum coating temperatures will depend on the 17 particular organometallic compound, or the mixtures 18 of compounds if alloys are desired. Typically, an 19 excess of the organometallic coating agent can be pulsed into the tubes at a high hydrogen flow rate so 21 as to carry the coating agent throughout the system 22 in a mist. The flow rate can then be reduced to S23 permit the coating metal mist to coat and react with 24 the furnace tube or reactor surface. Alternatively, the compound can be introduced as a vapor which r i WO 92/15653 PCT/US92/01856 48 1 decomposes and reacts with the hot walls of the tube 2 or reactor in a reducing atmosphere.

3 4 As discussed above, reforming reactor systems susceptible to carburization, metal dusting and 6 coking can be treated by application of a 7 decomposable coating containing a decomposable 8 organometallic tin compound to those areas of the 9 reactor system most susceptible to carburization.

Such an approach works particularly well in a 11 temperature controlled furnace.

12 13 However, such control is not always present.

14 There are "hot spots" which develop in the reactor system, particularly in the furnace tubes, where the 16 organometallic compound can decompose and form 17 deposits. Therefore, another aspect of the invention 18 is a process which avoids such deposition in 19 reforming reactor systems where temperatures are not closely controlled and exhibit areas of high 21 temperature hot spots.

u 22 23 Such a process involves preheating the entire S24 reactor system to a temperature of from 750 'to 1150, preferably 900 to 1100, and most preferably about 26 1050 0 F, with a hot stream of hydrogen gas. After L: i- I- LI-

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PCT/US92/01856 WO 92/15653 49 preheating, a colder gas stream at a temperature of 400 to 800, preferably 500 to 700, and most preferably about 550 0 F, containing a vaporized organometallic tin compound and hydrogen gas is introduced into the preheated reactor system. This gas mixture is introduced upstream and can provide a decomposition "wave" which travels throughout the entire reactor system.

Essentially this process works because the hot hydrogen gas produces a uniformly heated surface which will decompose the colder organometallic gas as it travels as a wave throughout the reactor system.

The colder gas containing the organometallic tin compound will decompose on the hot surface and coat the surface. The organometallic tin vapor will continue to move as a wave to treat the hotter surfaces downstream in the reactor system. Thereby, the entire reactor system can have a uniform coating of the organometallic tin compound. It may also be desirable to conduct several of these hot-cold temperature cycles to ensure that the entire reactor system has been uniformly coated with the organometallic tin compound.

ii -i fd i i i i WO 92/15653 PCT7US92/01856 50 1 In operation of the reforming reactor system 2 according to the present invention, naphtha will be S3 reformed to form aromatics. The naphtha feed is a 4 light hydrocarbon, preferably boiling in the range of about 70 0 F to 450 0 F, more preferably about 100 to 6 350°F. The naphtha feed will contain aliphatic or 7 paraffinic hydrocarbons. These aliphatics are 8 converted, at least in part, to aromatics in the 9 reforming reaction zone.

11 In the "low-sulfur" system of the invention, the 1- 12 feed will preferably contain less than 100 ppb 13 sulfur, and more preferably, less than 50 ppb sulfur.

14 If necessary, a sulfur sorber unit can be employed to remove small excesses of sulfur.

16 17 Preferred reforming process conditions include a 18 temperature between 700 and 1050 0 F, more preferably 19 between 850 and 1025 0 F; and a pressure between 0 and 400 psig, more preferably between 15 and 150 psig; a 21 recycle hydrogen rate sufficient to yield a hydrogen 22 to hydrocarbon mole ratio for the feed to the 23 reforming reaction zone between 0.1 and 20, more 24 preferably between 0.5 and 10; and a liquid hourly

S

25 space velocity for the hydrocarbon feed over the A WO 92/15653 PCT/US92/01856 51 1 reforming catalyst of between 0.1 and 10, more 2 preferably between 0.5 and 3 4 To achieve the suitable reformer temperatures, it is often necessary to heat the furnace tubes to 6 high temperatures. These temperatures can often 7 range from 600 to 1800 0 F, usually from 850 and 8 1250 0 F, and more often from 900 and 1200 0

F.

9 As noted above, the problems of carburization, 11 coking and metal dusting in low-sulfur systems have 12 been found to associated with excessively high, 13 localized process temperatures of the reactor system, 14 and are particularly acute in the furnace tubes of the system where particularly high temperatures are 16 characteristic. In conventional reforming techniques 17 where high levels of sulfur are present, furnace tube 18 skin temperatures of up to 1175 0 F at end of run are 19 typical. Yet, excessive carburization, coking and metal dusting was not observed. In low-sulfur 21 systems, however, it has been discovered that 22 excessive and rapid carburization, coking and metal 23 dusting occurred with CrMo steels at temperatures 24 above 950 0 F, and stainless steels at temperatures above 1025 0

F.

26 ;LfV^I IL- -r r.

WO 92/15653 PC1T/US92/01856 52 1 Accordingly, another aspect of the invention is 2 to lower the temperatures oF the metal surfaces 3 inside the furnace tubes, transfer-lines and/or 4 reactors of the reforming system below the aforementioned levels. For example, temperatures can 6 be monitored using thermocouples attached at various 7 locations in the reactor system. In the case of 8 furnace tubes, thermocouples can be attached to the 9 outer walls thereof, preferably at the hottest point of the furnace (usually near the furnace outlet).

11 When necessary, adjustments in process operation can 12 be made to maintain the temperatures at desired 13 levels.

14 There are other techniques for reducing exposure 16 of system surfaces to undesirably high temperatures 17 as well. For example, heat transfer areas can be 18 used with resistant (and usually more costly) tubing 19 in the final stage where temperatures are usually the highest.

21 22 In addition, superheated hydrogen can be added 23 between reactors of the reforming system. Also, a 24 larger catalyst charge can be used. And, the catalyst can be regenerated more frequently. In the 26 case of catalyst regeneration, it is best -t 113~1~ I WO,92/15653 PCT/US92/01856 53 1 accomplished using a moving bed process where the 2 catalyst is withdrawn from the final bed, 3 regenerated, and charged to the first bed.

4 Carburization and metal dusting can also be 6 minimized in the low-sulfur reforming reactor system 7 of the invention by using certain other novel 8 equipment configurations and process conditions. For 9 example, the reactor system can be constructed with staged heaters and/or tubes. In other words, the 11 heaters or tubes which are subjected to the most P' i12 extreme temperature conditions in the reactor system 13 can be constructed of materials more resistant to 14 carburization than materials conventionally used in the construction of reforming reactor systems; 16 materials such as thcse described above. Heaters or 17 tubes which are not subjected to extreme temperatures 18 can continue to be constructed of conventional 19 materials. i 21 By using such a staged design in the reactor 22 system, it is possible to reduce the overall cost of ARI 23 the system (since carburization resistant materials 24 are generally more expensive than conventional materials) while still providing a reactor system 26 which is sufficiently resistant to carburization and .j 1 -i:i ii._ 'ii Sa

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g- ii PCI'/US92/01856 WO 92/15653 54 metal dusting under low-sulfur reforming conditions.

Additionally, this should facilitate the retrofitting of existing reforming reactor systems to render them carburization and metal dusting resistant under '.owsulfur operating conditions; since a smaller portion of the reactor system would need replacement or modification with a staged design.

The reactor system can also be operated using at least two temperature zones; at least one of higher and one of lower temperature. This approach is based on the observation that metal dusting has a temperature maximum and minimum, above and below which dusting is minimized. Therefore, by "higher" temperatures, it is meant that the temperatures are higher than those conventionally used in reforming reactor systems and higher than the temperature maximum for dusting. By "lower" temperatures it is meant that the temperature is at or about the temperatures which reforming processes are conventionally conducted, and falls below that in which dusting becomes a problem.

Operation of portions of the reactor system in different temperature zones should reduce metal dusting as less of the reactor system is at a -Im m.

F)

I1 :-w WO 92/15653 PC'/US92/01856 55 temperature conducive for metal dusting. Also, other advantages of such a design include improved heat transfer efficiencies and the ability to reduce equipment size because of the operation of portions of the system at higher temperatures. However, operating portions of the reactor system at levels below and above that conducive for metal dusting would only minimize, not completely avoid, the temperature range at which metal dusting occurs.

This is unavoidable because of temperature fluctuations which will occur during day to day operation of the reforming reactor system; particularly fluctuations during shut-down and startup of the system, temperature fluctuations during cycling, and temperature fluctuations which will occur as the process fluids are heated in the reactor system.

Another approach to minimizing metal dusting relates to providing heat to the system using superheated raw materials (such as hydrogen), thereby minimizing the need to heat the hydrocarbons through furnace walls.

Yet another process design approach involves providing a pre-existing reforming reactor system ,i r WO92/15653 PCT/US92/01856 A 56 1 with larger tube diameters and/or higher tube 2 velocities. Using larger tube diameters and/or 3 higher tube velocities will minimize the exposure of 4 the heating surfaces in the reactor system to the hydrocarbons.

6 7 As noted above, catalytic reforming is well 8 known in the petroleum industry and involves the 9 treatment of naphtha fractions to improve octane rating by the production of aromatics. The more 11 important hydrocarbon reactions which occur during 12 the reforming operation include the dehydrogenation 13 of cyclohexanes to aromatics, dehydroisomerization of 14 alkycyclopentanes to aromatics, and dehydrocyclization of acyclic hydrocarbons to 16 aromatics. In addition, a number of other reactions 17 also occur, including the dealkylation of 18 alkylbenzenes, isomerization of paraffins, and 19 hydrocracking reactions which produce light gaseous hydrocarbons, methane, ethane, propane and 21 butane, which hydrocracking reactions should be 22 minimized during reforming as they decrease the yield 23 of gasoline boiling products and hydrogen. Thus, 24 "reforming" as used herein refers to the treatment of a hydrocarbon feed through the use of one or more 26 aromatics producing reactions in order to provide an ahdoabnfe houhteueo n rmr SPC/US92/01856 SWO 92/15653 57 1 aromatics enriched product a product whose 2 aromatics content is greater than in the feed).

3 4 While the present invention is directed primarily to catalytic reforming, it will be useful 6 generally in the production of aromatic hydrocarbons 7 from various hydrocarbon feedstocks under conditions 8 of low sulfur. That is, while catalytic reforming 9 typically refers to the conversion of naphthas, other feedstocks can be treated as well to provide an 11 aromatics enriched product. Therefore, while the 12 conversion of naphthas is a praferred embodiment, the 13 present invention can be useful for the conversion or 14 aromatization of a variety of feedstocks such as paraffin hydrocarbons, olefin hydrocarbons, acetylene 16 hydrocarbons, cyclic paraffin hydrocarbons, cyclic 17 olefin hydrocarbons, and mixtures thereof, and 18 particularly saturated hydrocarbons.

19 Examples of paraffin hydrocarbons are those 21 having 6 to 10 carbons such as n-hexane, S22 methylpentane, n-haptane, methylhexane, S23 dimethylpentane and n-octane. Examples of acetylene S24 hydrocarbons are those having 6 to 10 carbon atoms such as hexyne, heptyne and octyne. Examples of 26 acyclic paraffin hydrocarbons are those having 6 to

I.

s.

-L-

SPCT/US92/01856 WO 92/15653 58 1 10 carbon atoms such as methylcyclopentane, 2 cyclohexane, methylcyclohexane and 3 dimethylcyclohexane. Typical examples of cyclic 4 olefin hydrocarbons are those having 6 to 10 carbon atoms such as methylcyclopentene, cyclohexene, 6 methylcyclohexene, and dimethylcyclohexene.

7 8 The present invention will also be useful for 9 reforming under low-sulfur conditions using a variety of different reforming catalysts. Such catalyst 11 include, but are not limited to Noble Group VIII 12 metals on refractory inorganic oxides such as 13 platinum on alumina, Pt/SN on alumina and Pt/Re on 14 alumina; Noble Group VIII metals on a zeolite such as Pt, Pt/SN and Pt/Re on zeolites such as L-zeolites, 16 ZSM-5, silicalite and beta; and Nobel Group VIII 17 metals on alkali- and alkaline-earth exchanged L- 18 zeolites.

19 A preferred embodiment of the invention involves 21 the use of a large-pore zeolite catalyst including an 22 alkali or alkaline earth metal and charged with one 23 or more Group VIII metals. Most preferred is the S24 embodiment where such a catalyst is used in reforming a naphtha feed.

26

I

1 WO 92/15653 PCr/US92/01856 59 The term "large-pore zeolite" is indicative generally of a zeolite having an effective pore diameter of 6 to 15 Angstroms. Preferable large pore crystalline zeolites which are useful in the present invention include the type L zeolite, zeolite X, zeolite Y and faujasite. These have apparent pore sizes on the order to 7 to 9 Angstroms. Most preferably the zeolite is a type L zeolite.

The composition of type L zeolite expressed in terms of mole ratios of oxides, may be represented by the following formula: (0.9-1.3)M 2 0

:AL

2 0 3 (5.2-6.9)SiO 2 :yH 2 0 In the above formula M represents a cation, n represents the valence of M, and y may be any value from 0 to about 9. Zeolite L, its X-ray diffraction pattern, its properties, and method for its preparation are described in detail in, for example, U.S. Patent No. 3,216,789, the contents of which is hereby incorporated by reference. The actual formula may vary without changing the crystalline structure.

For example, the mole ratio of silicon to aluminum (Si/Al) may vary from 1.0 to The chemical formula for zeolite Y expressed in terms of mole ratios of oxides may be written as: WO 92/15653 PC/US92/01856 11 12 13 14 16 17 18 19 21 22 23 24 26 60 (0.7-1.1)Na 2 0: A1 2 0 3 XSi 2 yH 2 In the above formula, x is a value greater than 3 and up to about 6. y may be a value up to about 9.

Zeolite Y has a characteristic X-ray powder diffraction pattern which may be employed with the above formula for identification. Zeolite Y is described in more detail in U.S.Patent No. 3,130,007 the contents of which is hereby incorporated by reference.

Zeolite X is a synthetic crystalline zeolitic molecular sieve which may be represented by the formula:

M

2 /nO:AI20 3 0)SiO 2 In the above formula, M represents a metal, particularly alkali and alkaline earth metals, n is the valence of M, and y may have any value up to about 8 depending on the identity of M and the degree of hydration of the crystalline zeolite. Zeolite X, its X-ray diffraction pattern, its properties, and method for its preparation are described in detail in U.S. Patent No. 2,882,244 the contents of which is hereby incorporated by reference.

An alkali or alkaline earth metal is preferably present in the large-pore zeolite. That alkaline WO 92/15653 PCI/US92/01856 61 1 earth metal may be either barium, strontium or 2 calcium, preferably barium. The alkaline earth metal 3 can be incorporated into the zeolite by synthesis, 4 impregnation or ion exchange. Barium is preferred to the other alkaline earths because it results in a 6 somewhat less acidic catalyst. Strong acidity is 7 undesirable in the catalyst because it promotes 8 cracking, resulting in lower selectivity.

9 In another embodiment, a: least part of the 11 alkali metal can be exchanged with barium using known 12 techniques for ion exchange of zeolites. This 13 involves contacting the zeolite with a solution 14 containing excess Ba++ions. In this embodiment the barium should preferably constitute from 0.1% to 16 by weight of the zeolite.

17 18 The large-pore zeolitic catalysts used in the 19 invention are charged with one or more Group VIII metals, nickel, ruthenium, rhodium, palladium, 21 iridium or platinum. The preferred Group VIII metals 22 are iridium and particularly platinum. These are 23 more selective with regard to dehydrocyclization and 24 are also more stable under the dehydrocyclization reaction conditions than other Group VIII metals. If WO 92/15653 PCT/US92/01856 62 1 used, the preferred weight percentage of platinum in 2 the catalyst is between 0.1% and 3 4 Group VIII metals are introduced into large-pore zeolites by synthesis, impregnation or exchange in an 6 aqueous solution of appropriate salt. When it is 7 desired to introduce two Group VIII metals into the 8 zeolite, the operation may be carried out 9 simultaneously or sequentially.

11 To obtain a more complete understanding of the 12 present invention, the following examples 13 illustrating certain aspects of the invention are set 14 forth. It should be understood, however, that the invention is not limited in any way to the specific 16 details set forth therein.

17 18 EXAMPLE 1 19 Tests were run to demonstrate the effect of sulfur and water on carburization in reforming 21 reactors.

22 23 In these tests, eight inch long, inch outside 24 diameter copper tubes were used as a reactor to study the carburization and embrittlement of 347 stainless 26 steel wires. Three of these stainless steel wires I

V

ii i WO,92/15653 PCT/US92/01856 63 having a diameter of 0.035 inches were inserted into the tube, while a four inch section of the tube was maintained at a uniform temperature of 1250OF by a furnace. The pressure of the system was maintained at 50 psig. Hexane was introduced into the reactor at a rate of 25 microliters/min. (1.5 ml/hr) with a hydrogen rate of about 25 cc/min. (ratio of H 2 to HC being Methane in the product effluent was measured to determine the existence of exothermic methane reactions.

A control run was made using essentially pure hexane containing less than 0.2 ppm sulfur. The tube was found to be completely filied with carbon after only three hours. This not only stopped the flow of the hydrogen and hexane feeds, the growth of carbon actually split the tube and produced a bulge in the reactor. Methane in the product effluent was approaching 60-80 wt% before plugging.

Another run was conducted using essentially the same conditions except that 10 ppm sulfur was added.

The run continued for 50 hours before it was shut down to examine the wires. No increase in methane was noted during the run. It remained steady at about 16 wt% due to thermal cracking. No coke plugs I'i i m WO 92/15653 PCT/US92101856 64 were found and no carburization of the steel wires was observed.

Another identical run was made except that only 1 ppm sulfur was added (10 times lower than the previous run). This run exhibited little methane formation or plugging after 48 hours. An examination of the steel wires showed a small amount of surface carbon, but no ribbons of carbon.

Another run was conducted except that 1000 ppm water was added to the hexane as methanol. No sulfur was added. The run lasted for 16 hours and no plugs occurred in the reactor. However, upon splitting the tube it was discovered that about percent of the tube was filled with carbon. But the carbon buildup was not nearly as severe as with the control run.

EXAMPLE 2 Tests were conducted to determine suitable materials for use in low-i .fur reforming reactor systems; materials which would exhibit better resistance to carburization than the mild steels conventionally used in low-sulfur reforming techniques.

II4 xi: WO 92/15653 PCr/US92/OI856 65 1 In these tests there was used an apparatus 2 including a Lindberg alumina tube furnace with 3 temperatures controlled to within one degree with a 4 thermocouple placed on the exterior of the tube in the heated zone. The furnace tube had an internal 6 diameter of 5/8 inches. Several runs were conducted 7 at an applied temperature of 1200 0 F using a 8 thermocouple suspended within the hot zone (=2 9 inches) of the tube. The internal thermocouple constantly measured temperatures from 0 to 10OF lower 11 than the external thermocouple.

13 Samples of mild steels (C steel and 2k Cr) and 14 samples of 300 series stainless steels were tested at 1100 0 F, 1150°F and 1200 0 F for twenty-four hours, and 16 1100 0 F for ninety hours, under conditions which i 17 simulate the exposure of the materials under 18 conditions of lov-sulfur reforming. The samples of 19 various materials were placed in an open quartz boat within the hot zone of the furnace tube. The boats 21 were one inch long and inch wide and fit well 22 within the two-inch hot zone of the tube. The boats 23 were attached to silica glass rods for each placement 24 and removal. No internal thermocouple was used when the boats were placed inside the tube.

26

A:

WO 92/15653 PCT/US92/01856 66 1 Prior to start up the tube was flushed with 2 nitrogen for a few minutes. A carburizing gas of a 3 commerciall bottled mixture of 7% propane in 4 hydrogen was bubbled through a liter flask of toluene at room temperature in order entrain about 1% toluene 6 in the feed gas mix- Gas flows of 25 to 30 cc/min., 7 and atmospheric pressure, were maintained in the 8 apparatus. The samples were brought to operating 9 temperatures at a rate of 144 0 F/min.

11 After exposing the materials to tie carburizing 12 gas for the desired period at the desired 13 temperature, the apparatus was r'enched with an air 14 stream applied to the exterior of the tube. When the apparatus was sufficiently cool, the hydrocarbon gas 16 was swept out with nitrogen and the boat was removed 17 for inspection and analysis.

18 19 Prior to start up the test materials were cut to a size and shape suitable for ready-visual 21 identification. After any pretreatment, such as 22 cleaning or roasting, the samples were weighed. Most 23 samples were less than 300 mg. Typically, each run 24 was conducted with three to five samples in a boat.

A sample of 347 stainless steel was present with each 26 run as an interral standard.

WO 92/15653 PCT/US92/01856 67 1 After completion of each run the condition of 2 the boat and each material was carefully noted.

3 Typically the boat was photographed. Then, each 4 material was weighed to determine changes while taking care to keep any coke deposits with the 6 appropriate substrate material. The samples were 7 then mounted in an epoxy resin, ground and polished 8 in preparation for petrographic and scanning electron 9 microscopy analysis to determine the coking, metal dusting and carburization responses of each material.

11 12 By necessity, the residence time of the 13 carburizing gas used in these tests were considerably 14 higher than in typical commercial operation. Thus, it is believed that the experimental conditions may 16 have been more severe than commercial conditions.

17 Some of the materials which failed in these tests may 18 actually be commercially reliable. Nevertheless, the 19 test provides a reliable indication of the relative I resistances of the materials to coking, carburization 21 and metal dusting.

22 23

F-

rh:7'~[q :-tii Pii PCT/US92/01856 WO 92/15653 The results 68 are iet forth in the Table below.

Table* Wt. C Gain Dusting Composition 1200 0 F; 24 hours C Steel 2 Cr 304 347 1150 0 F; 24 hours C Steel 2% Cr 304 347 1100°F; 24 hours C Steel Trace 23 Cr 304 347 1100 0 F; 90 hours C Steel 2 Cr 304 347 15% C 7 Hg 86 61 little little 63 80 1 1 0 0 0 52 62 5 1 50% C 3 Severe Severe No No 18 Cr 10 Ni 18 Cr 10 Ni Severe Severe No No Trace, localized No No No Severe Severe No No Hg H, (by weight)

VN-CI

i: s i r Of course, the above results are qualitative and depend on surface morphology, microscopic roughness of the metals. The carbon weight gain i indicative of surface coking which is autocatalytic.

EXAMPLE 3 The same techniques used above were used again to screen a wide assortment of materials at a temperature of 1200OF for 16 hours. The results are Attorney's Docket No. 005950-314 r i_ PCr/US92/01856 WO 92/15653 69 set forth below. Each group represents a side-byside comparison in a single boat under identical conditions.

TABLE (1) Group I Inconel 600 347 oxid.(2) 347 Fresh Group II Inconel 600 310 Incoloy 800 347 Group III Incoloy 825 Haynes 230 Alonized 347 347 Group IV Ni (Pure) Cu (Pure) Sn (Fused) 100 Sn Tin Can Sn C Steel Wt. C Gain 57 21 4 40 8 5 1 <1 2 3 <1 656 0 0 0 Dusting Severe Moderate No Severe Mild Moderate Trace Moderate Mild Trace Trace Severe No No Composition 15 Cr 75 Ni 18 Cr 10 Ni 15 Cr .25 Cr 21 Cr 32 22 Cr 64 Ni 100 Ni 100 Cu 15% C 7

H

8 50% C 3

H

8

H

2 (By Wt.) Roasted in air 2 hours at 1000 0 C to produce a thin oxide crust.

WO 92/15653 PCT/US92/01856 70 1 EXAMPLE 4 2 Additional materials were tested, again using 3 the techniques described in Example 2 (unless stated 4 otherwise).

6 Samples of 446 stainless stei. and 347 stainless 7 steel were placed in a sample boat and tested 8 simultaneously in the carburization apparatus at 9 1100°F for a total of two weeks. The 446 stainless steel had a thin coating of coke, but no other 11 alteration was detected. The 347 stainless steel, on S12 the other hand, had massive localized coke deposits, 13 and pits more than 4 mils deep from which coke and 14 metal dust had erupted.

16 Samples were tested of a carbon steel screen 17 electroplated with tin, silver, copper and chromium.

18 the samples had coatings of approximately 0.5 mil.

19 After 16-hour carburization screening tests at i 20 1200°F, no coke had formed on the tin-plated and 21 chromium-plated screens. Coke formed on the silver- 22 plated and copper-plated screens, but only where the 23 platings had peeled. Unplated carbon steel screens 24 run simultaneously with the plated screens, exhibited severe cok'ng carburization, and metal dusting.

26 K

I

SWO 92/15653 PCT/US92/01856 71 1 Samples were tested of a 304 stainless steel 2 screen; each sample being electroplated with one of 3 tin, silver, copper and chromium. The samples had 4 coatings with thicknesses of-approximately 0.5 mil.

After 16-hour carburization screening tests at 6 1200 0 F, no coke had formed on any of the plated 7 screens, except locally on the copper-plated screen 8 where the plating had blistered and peeled. Thin 9 coke coatings were observed on unplated samples of 304 stainless steel run simultaneously with the 11 plated screens..

12 13 Samples were tested of a 304 stainless steel 14 screen; each sample being electroplated with one of tin and chromium. These samples were tested along 16 with a sample of 446 stainless steel in a 17 carburization test at 1100°F. The samples were 18 exposed or five weeks. Each week the samples were I 19 cooled to rooi temperature for observation and photographic documentation. They were then re-heated 21 to 1100 0 F. The tin plated screen was free of coke; 22 the chromium-plated screen was also free of coke, 1 23 except locally where the chrome plate had peeled; and 24 the piece of 446 stainless steel was uniformly coated with coke.

26 WO092/15653 PCT/US92/01856 72 1 Samples of uncoated Inconel 600 (75% Ni) and 2 tin-coated (electroplated) Inconel 600 (75% Ni) were 3 tested at 1200°F for 16 hours. The tin-plated sample 4 coked and dusted, but not to the extent of the uncoated sample.

6 7 EXAMPLE 8 The following experiments were conducted to 9 study the exothermic methanization reaction occurring during the formation and burning of cokeballs during 11 reforming under conditions of low-sulfur. In 12 addition tin, as an additive to reduce methane 13 formation was studied.

14 In low-sulfur reforming reactor systems, coke 16 deposits containing molten particles of iron have 17 been found. This formation of molten iron during 18 reforming at temperatures between 900 and 1200°F is 19 believed to be due to very exothermic reactions which occur during reforming. It is believed that the only 21 way to generate such temperatures is through the 22 formation of methane which is very exothermic. The 23 high temperatures are particularly surprising since 24 reforming is generally endothermic in nature and actually tends to cool the reactor system. The high 26 temperatures may be generated inside the well i; i Pr 1W092/15653 PCT/US92/01856 73 1 insulated cokeballs by diffusion of hydrogen into the 2 interior catalytic iron dust sites where they 3 catalyze methane formation from coke and hydrogen.

4 In this experiment steel wool was used to study 6 methane formation in a micro pilot plant. A inch 7 stainless steel tube was packed with 0.14 grams of 8 steel wool and placed into a furnace at 1175 0

F.

9 Hexane and hydrogen were passed over the iron and the exit stream was analyzed for feed and products. The 11 steel wool was pretreated in hydrogen for twenty 12 hours before introduction of the hexane. Then hexane 13 was introduced into the reactor at a rate of 14 microliters/min. with a hydrogen rate of about cc/min.

16 1 17 Initially, methane formation was low, but 18 continued to increase as the run progressed; finally 19 reaching Then, 0.1 cc of tetrabutyl tin dissolved in 2 cc of hexane was injected into the 21 purified feed stream ahead of the iron. The methane 22 formation decreased to about 1% and continued to 23 remain at 1% for the next three hours. The data is 24 summarized in the Table below.

26 i WO 92/15653 PCT/US92/01856 74 1 TABLE 2 3 HOURS CH4 ETHANE PROPANE HEXANE 4 19.2 0.0 0.5 0.3 98.6 6 20.7 1.06 2.08 1.74 93.4 7 21.2 2.62 4.55 3.92 85.3 8 21.5 3.43 4.23 3.83 84.6 9 21.9 4.45 4.50 4.32 82.0 11 22 Tetrabutyl Tin Added 12 13 22.6 1.16 3.81 4.12 86.2 14 23.0 1.16 3.96 4.24 85.9 23.3 1.0 4.56 3.77 87.5 16 24.3 0.97 3.60 3.76 87.6 17 25.3 1.0 4.47 3.57 88.0 18 19 From the results above it can be seen that the 21 addition of tin to the steel wool stops the 22 acceleration of methane formation, and lowers it to 23 acceptable levels in the product.

24 EXAMPLE 6 26 Additional tests were conducted using tetrabutyl 27 tin pre-coated steel wool. In particular, as in 28 Example 5, three injections of 0.1 cc of tetrabutyl 29 tin dissolved in 2 cc of hexane were injected into a inch stainless steel tube containing 0.15 grams of 31 steel wool. The solution was carried over the steel 32 wool in a hydrogen stream of 900 0

F.

33 34 The hydrocarbon feed was then introduced at 1175 0 F at a hydrocarbon rate of 25 microliters/min L I r WO 92/15653 PCT/US92/01856 75 1 with a hydrogen rate of about 25 cc/min. The exit 2 gas was analyzed for methane and remained below 1% 3 for 24 hours. The reactor was then shut down, and 4 the reactor tube was split open and examined. Very little carburization had occurred on the steel wool.

6 7 In contrast, a control was run without 8 tetrabutyl tin pre-treatment. It was run for one day 9 under the same conditions described above. After 24 hours, no hydrogen or feed could be detected at the 11 tube exit. The inlet pressure had risen to 300 lbs.

12 from the original 50 lbs. When the reactor tube was 13 split open and examined, it was found that coke had 14 completely plugged the tube. 16 Thus, it can be seen that organo-tin compounds 17 can prevent carburization of steel wool under 18 reforming conditions.

19 S 20 EXAMPLE 7 21 Another run like the control run of Example 1 22 was conducted to investigate the effect of 23 carburization conditions on vapor tin coated 24 stainless steel wires in a gold plated reactor tube.

The only other difference from the control run was 26 that a higher hydrogen rate of 100 ml/min was used.

L 1 i -76- The run continued for eight hours with no plugging or excessive methane formation. When the tube was split and analyzed, no plugs or carbon ribbons were observed. Only one black streak of carbon appeared on one wire. This was probably due to an improper coating.

This experiment shows that tin can protect stainless steel from carburization in a manner similar to sulfur.

Unlike sulfur, however, it does not have to be continuously injected into the feed. Sulfur must be continuously injected into the feed to maintain the partial pressure of hydrogen sulfide in the system at a sufficient level to maintain a sulfide surface on the steel. Any removal of sulfur from the feedstock will lead to a start of carburization after sulfur is t~tripped from the reactor system. This usually occurs within 10 hours after cessation of sulfur.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

While the invention has been described above in terms of preferred embodiments, it is to be understood that variations and modifications may be used as will be appreciated by those skilled in the art. For example, portions of steel in the reactor system can be coated with niobium, zirconium, silica

C)

95053 1,p:b\opedab,I5801.spe,76

A-

i WO 92/15653 PCT/US92/01856 77 1 ceramics, tungsten, or chromium (chromizing), 2 although these techniques could be excessively 3 difficult to do or use, or prohibitively ex.-'nsive.

4 Or, the use of heat exchangers to heat hydrocarbons to reaction temperature could be minimized. The heat 6 could be provided by super-heated hydrogen. Or, the 7 exposure of heating surfaces to hydrocarbons can be 8 reduced by using larger tube diameters and higher 9 tube velocities. Essentially, therefore, there are many variations and modifications to the above 11 preferred embodiments which will be readily evident 12 to those skilled in the art, and which are to be 13 considered within the scope of the invention as 14 defined by the following claims.

i '1

Claims (18)

1. 2. A method according to claim 1, where upon reforming the resistance to carburization is greater than that for stainless steel and is such that embrittlement will be less than about 1.5 mm/year.
2. 3. A method according to claim 1 or claim 2, wherein the reforming catalyst is a large-pore zeolite catalyst including an alkali or alkaline earth metal and loaded with one or more Group VIII metals.
3. 4. A method according to claim 3, wherein the reforming catalyst is an L-type zeolite loaded with platinum. I A method according to any one of the preceding claims, wherein said hydrocarbons are contacted with the catalyst under conditions of low water.
4. 6. A method according to any one of the preceding claims, wherein at least a portion of the reactor system in contact with the hydrocarbons is treated with a metal coating.
5. 7. A method according to any one of the preceding claims, wherein at least a portion of the reactor system in contact with the hydrocarbons is a material selected from the group of copper, tin, arsenic, antimony, aluminum, germanium, lead, 95053 I,p:operdab, 1580 1.spe,78 r_ I -79- bismuth, chromium, intermetallic compounds thereof and alloys thereof.
6. 8. A method according to any one of the preceding claims, wherein at least a portion of the reactor system in contact with the hydrocarbons is a material selected from the group of copper, tin, antimony, aluminum, germanium, chromium, intermetallic compounds thereof and alloys thereof.
7. 9. A method according to claim 7 or claim 8, wherein said material is provided as a plating, cladding, paint or other coating to a base construction material. A method according to any one of claims 7 to 9, wherein said material is effective for retaining its resistance to carburization after oxidation.
8. 11. A method according to any one of claims 7 to 10, wherein said material is tin.
9. 12. A method according to any one of claims 7 to 11, wherein the material is a coating applied by electroplating, painting, vapor deposition, or soaking in a molten bath.
10. 13. A method according to any one of the preceding claims, wherein said portion with a carburization resistance greater than that of mild steel comprises a coating of reduced material on a base construction material, said reduced material provided by exposure to a reducing environment in situ.
11. 14. A method according to Claim 13, wherein the reducing environment is hydrogen. I 95053 1,p:\operdab, 15801.spe,79 L L' p I I 1 i I I II I A method according to claim 8, wherein said material is tin and is applied as a decomposable, reactive, tin- containing paint, which paint reduces to a reactive tin which forms a tin complex with said construction material to which it is applied upon heating in a reducing environment.
12. 16. A method according to claim 15, wherein said tin- containing paint comprises finely divided tin metal.
13. 17. A method according to claim 15 or claim 16 wherein said tin-containing paint comprises a hydrogen decomposable tin compound and a tin oxide. 15 18. A method according to claim 16 or claim 17, wherein the finely divided tin metal has a particle size of about 1 to microns.
14. 19. A method according to any one of claims 15 to 18, said 20 tin-containing paint further comprising one or more iron compounds. A method according to any one of claims 15 to 19, said tin-containing paint further comprising one or more iron 25 compounds, wherein the ratio of Fe/Sn is up to 1:3 by weight.
15. 21. A method according to claim 20, wherein the iron compound is Fe20 3
16. 22. A method according to any one of claims 15 to 21 comprising reducing said paint after it is applied.
17. 23. The reactor system used in the method according to any one of claims 1 to 22. 950815,p:pa\dab,15801.spe,80 II I; I I I U C L i: 81
18. 24. Methods for reforming hydrocarbons according to any one of Claims 1 to 22 or reactor systems used in said methods, substantially as hereinbefore described with reference to the Examples and/or drawings. DATED this 2nd day of November, 1995 Chevron Research and Technology Company By Its Patent Attorneys DAVIES COLLISON CAVE o I I r I I 951102,p:\oper\dab,1580.spe,81 mod