US2985699A - Isomerization of paraffin hydrocarbons - Google Patents

Description

only in small amounts; the

Patented May 23,1961

2,985,699 ISOMERIZATION F PARAFFIN HYDROCARBONS Donald Schwartz, Moorhead, Min and Paul Earl Eberly, Jr., and Elroy Merle Gladrow, Baton Rouge, La., assignors to Esso Research and Engineering Compauy, a corporation of Delaware No Drawing. Filed Dec. 29, 1958, Ser. No. 783,109

5 Claims. (Cl. 260-68355) r The present invention relates to a process wherein straight chain paraflin hydrocarbons are converted into the more desirable branched chain hydrocarbons in the presence of aluminum halides, particularly aluminum bromide. The invention is especially concerned with a liquid phase paraflin hydrocarbon isomerization process wherein undesirable cracking of the hydrocarbons is suppressed or avoided.

In general, in branched paraflin hydrocarbons are of greater commercial value than the corresponding straight chain hydrocarbons. The branched chain hydrocarbons in petroleum gasoline fractions have greater octane ratings than the corresponding straight chain hydrocarbons. This is of considerable importance in view of the increased demands for high anti-knock rating motor fuels to satisfy the requirements of modern high compression engines. One of the commercially important processes for supplying high octane motor fuels involves isomerization of the light naphtha components of such fuels.

The isomerization of normal paraflin hydrocarbons of from 4 to 7 carbon atoms into the corresponding branched chain homologs is well known. For efiecting the isomerization, it is customary to employ certain metal halides, particularly aluminum chloride or'aluminum bromide, in conjunction with certain promoters, such as hydrogen chloride, hydrogen bromide or boron fluoride. Insofar as the isomerization of light naphthas is concemed the lower the temperature of isomerization, within limits, the more favorable is theequilibrium for converting straight chain paraflin hydrocarbons into isomers of high octane rating. Aluminum bromide has been found to be more active than aluminum chloride at lower isomerization temperatures, e.g. in the range of about 40 toabout 120 F.

Although, as stated, the lower isomcrization, temperathe petroleum industry isoparatlins and tures that are possible when using aluminum bromide v favor the production of high yields of isomers of high octane rating, the system is extremely sensitive to the occurrence of cracking, which can result in poor selectivity to the desired product and which can also cause a rapid decrease in the rate of isomerization. In the past, various cracking suppressors, such as aromatic hydrocarbons and naphthene hydrocarbons, not an entirely satisfactory solution to the problem, however, because the aromatics andnaphthenes can be used use of larger amounts tends to suppress the isomerization reaction unduly. If cracking does occur during isomerization, an attempt to pre vent this by increasing the amounts of aromatics or naphthenes used simply serves to reduce the isomeri'zation activity to an undesirably low level. Thus, there has been a need for a systemfor reducing cracking tendencies during isomerization without adversely afiecting the isomerization reaction itself.

It is one obiect of the activity of aluminum bromide as an rsomerization catalyst while at the same time suppressing undesired have been employed. This is cracking of the reactants or theisomerization. products.

In accordance with the present invention, the isomerization of normalparaflinic hydrocarbons of from 4 to 7 carbon atoms is conducted in the presence of aluminum bromide or in the presence of a mixture of aluminum chloride and aluminum bromide along with a second catalyst comprising platinum'sulfide, platinum oxysulfide, or their mixtures. When the mixed aluminum bromide-aluminum chloride is used, the proportions may range up to l to 2 parts of the chloride for each part of the bromide,

by weight. The reaction is conducted at a temperature in the range of from about'40' to 120 F.

It is preferred that both the aluminum bromide and the platinum sulfides be associated with suitable supports. The support for the platinum may be the same as or may be dilferent from the aluminum halide support. Among the supports or carriers that may be used in this invention are included activated carbon, activated alumina, pumice, silica gel, fullers'earth, various activated clays and calcined bauxite. A partially dehydrated calcined bauxite known commercially as Porocel may also be used. Partial dehydration to prepare the Porocel for use may include heating for 2 to 3 hours at 1200 to 1400' F. or for from 15 to 18 hours at 900 to 1000 F. Typical bifunctional catalysts that may be used in the present invention include a mixture of platinum sulfide supported on silica gel along with aluminum bromide or mixed aluminum bromide-aluminum chloride on a suitable support or aluminum bromide supported on ferric oxide plus platinum sulfide or oxysulfide supported on silica gel or on treated bauxite.

The aluminum bromide may be placed on the support by impregnating the support with the bromide at an elevated temperature in the gas phase or, alternatively, a support can be placed in the reaction zone and the aluminum bromide can be carried into the reaction zone along with the hydrocarbon feed. .Another method of preparation is to mix the aluminum halide with the support and to heat the mixture to effect impregnation. If desired, loosely held aluminum halide may be removed from the catalyst mass by heating the mass and passing through it a gas such as carbon dioxide, methane, hydrogen or nitrogen. Alternatively solving the aluminum halide in a suitable solvent such as ethylene dichloride or dioxane, for example, and the porous carrier impregnated with this solution, followed by heating to remove the solvent and loosely heldaluminum halide. Still another alternative isto employ a powdered-support or promoter, mix the aluminum halide with it, andcompress the mixture into pellets. t, The proportion of support to aluminum halide catalyst should be at least 2 to 1 by weight but from a practical standpoint should not exceed about 50 to 1'. Stated conversely, the ratio of aluminum halide to support should be in the range of 2 to 50 parts of the halide for each 100 parts of support. The preferred range is from about percent, preferably about 0.1 to 1.0 wt. percent, of platithe present inventioa to preserve Although batch num metal on the support, and thereafter sulfiding in a manner known per se. Alternately, the supports are impregnated directly with 0.01 to 1% of. platinum sulfide or oxysulfide. The process of preparing the catalyst is not a part of the present invention.

operations may be used, the process is preferably conducted as a continuous operation using flow rates of from about 0.1 to about 2 v./v./hr. (volume the support may be impregnated by disa,ess,eee

of feed per volume of total catalyst including support per hour). The apparatus employed may be of a conventional nature and may comprise a tower containing a fixed bed of the catalyst through which the reacting hydrocarbons are circulated, using an external recycle line to send the reactants back through the bed any number of times.

Aromatics and other materials that tend to be detrimental to the isomerization reaction may be removed from. the feed by conventional means, such as acid treating, solvent extraction, mild hydrogenation or the like. Solvent extraction is preferred. promoters such as HF, HBr or .HCl are used, these may be added along with the feed. These are usually employed in amounts of about 1 to 10% based on the feed.

The following examples and data are offered to set forth the advantages of the present invention.

Example 1 Aluminum alcoholate solution was hydrolyzed in 10 volumes H and left to stand at room temperature for a week. The slurry was filtered and oven dried. This material is alumina beta trihydrate. A portion of this was calcined at 1000 F. This material will be referred to as support A in the following example.

Example 2 A portion of the alumina beta trihydrate prepared as described in Example 1 was calcined at 1000" F. This was impregnated with PtCl solution of suflicient concentration to incorporate 0.6% Pt on the alumina, oven dried and calcined at 1000 F. This material is referred to as support "B" in the following examples.

Example 3 A portion of the alumina beta trihydrate prepared as described in Example 1 was calcined at 1000 F. and then placed in a dish. In a separate vessel 51 cc. of a dilute PtCl (Pt 1.08 gr.) solution admixed with 57 cc. of a solution comprising 1 cc. of 20% ammonium sulfide solution. As the precipitate of PtS, slowly started to form, the mixture was quickly added to the alumina. Oven dried and calcined 6 hours at 1000" F. This material comprises 1% Pt (as PtS on alumina and is designated support "0 in the following examples.

Example 4 Commercial Porocel, which is an impure alumina comprising iron oxide, Was calcined at 1000 F. This material, which is the standard support in isomerization, is designated support D" in the following example.

Example Supports A," B, C and "D described above were composited with aluminum bromide and a hydrocarbon feed mixture and tested for their isomerization properties. The tests were made as follows: 2 grams of the support were placed in a bottle, 1 gram AlBr added, and then 7.4 cc. of a hydrocarbon mixture comprising 67% n-heptane and 33% methylcyclohexane. The methylcyclohexane is present as a cracking inhibitor. The bottles were each capped tightly, placed in a mechanical shaker at room temperature and shaken for two hours. At this point hydrocarbon samples were withdrawn and analyzed by gas chromatography. The results follow:

When conventional Example 6 Supports "C" and D" were examined in an isomerization operation conducted over longer periods of time. Two grams of support were placed in a bottle, 1 gram AlBr, added, and then 7.4 cc. of a hydrocarbon mixture comprising 67 n-heptane and 33% methylcyclohexane. The bottles were each tightly capped and placed in a mechanical shaker for 3 hours. The results follow.

on D

These data further attest to the fact that support C, which is the support in the present invention, is superior to Porocel, the commercial, high activity support. In addition, it was found that with support 0 in the 3 hours operation, 4.3% triptane was found in the isomerized product. This compares with 2-3% triptane in the similar run with support D.

Example 7 Further tests to evaluate platinum sulfide on a support for Friedel-Crafts isomerizations of n-parafiins totheir branched chain isomers are here presented. These tests were made in a similar manner as described in Example 6 except that they were carried out for 1 hour. The results are as follows:

7.4 ml. feed (67% n-heptane 33% methylcyclohexane) 1 gram support (20%) 1 gram AlBr, (20%) In this run, platinum sulfide on alumina was compared to Porocel and gave 41.3% conversion (no cracking) to 28.6% for Porocel. This is at a 20 wt. percent support level which is rather low for isomerization reactions. Even at this low concentration, the platinum sulfide appears to be very reactive. When cutting the AlBr, concentration to 10%, 26.8% conversion with platinum sulfide was obtained as compared to 22.5% Porocel. Thus, the use of platinum sulfide enables a 50% reduction in AlBr, to obtain the same conversion using Porocel.

It is clear from the data above that the platinum sulfide support is very much more reactive and selective for isomerization than Porocel, alumina and other supports.

What is claimed is:

1. A process for converting normal paraffin hydrocarbons of from 4 to 7 carbon atoms to the corresponding branched chain isomers which consists of contacting said hydrocarbons at a temperature in the range of from about 40 to about .120 F. with a supported bifunctional catalyst comprising an aluminum halide selected from the group consisting of aluminum bromide and aluminum bromide-aluminum chloride mixtures and a support carrying about 0.01 to 5 wt. percent of platinum, 'said platinum being in the form of a sulfide compound.

2. The process as defined by claim 1 wherein said aluminum halide is supported on calcined bauxite and admixed with said support carrying the platinum sulfide compound. I

3. Process as defined by claim 1 wherein said support carrying the platinum sulfide compound is alumina.

4. Process as defined by claim 1 wherein said support carries about 0.1 to 1 wt. percent platinum.

5 3. A 9:0? for converting normal paraflln hydro- References Cited in the file of this patent (381130080 m4to7caxbonatomatothecorresponding UNIT branched chain isomers which consists in contacting ED STATES PATENTS said hydrocarbons at a temperature in the range of from et 1953 about 40' to about 120' F. with a catalyst comprising 5 2366302 Elms 1956 a rapport carrying aluminum bromide 40.01 to 5 wt. 2,90%425 a a1 1959 percent of platinum, said platinum being in the form v FOREIGN PATENTS 555,861 Great Britain Sept. 9,. 1943

Claims (1)

1. A PROCESS FOR CONVERTING NORMAL PARAFFIN HYDROCARBONS OF FROM 4 TO 7 CARBON ATOMS TO THE CORRESPONDING BRANCHED CHAIN ISOMERS WHICH CONSISTS OF CONTACTING SAID HYDROCARBONS AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 40* TO ABOUT 120*F. WITH A SUPPORTED BIFUNCTIONAL CATALYST COMPRISING AN ALUMINUM HALIDE SELECTED FROM THE GROUP CONSISTING OF ALUMINUM BROMIDE AND ALUMINUM BROMIDE-ALUMINUM CHLORIDE MIXTURES AND A SUPPORT CARRYING ABOUT 0.01 TO 5 WT. PERCENT OF PLATINUM, SAID PLATINUM BEING IN THE FORM OF A SULFIDE COMPOUND.