US3640895A - Inhibition of corrosion using alkyl aryl ketones - Google Patents

Abstract

CORROSION OF METALS BY AQUEOUS ACIDIC SOLUTIONS IN A NON-OXIDIZING ATMOSPHERE IS MARKEDLY INGIBITED BY THE PRESENCE OF A LOWER ALKYL ARYL KETONE. A PARTICULARLY EFFECTIVE INHIBITOR OF THIS TYPE IS METHYL BETA-NAPHTHYL KETONE. CORROSION OF CHEMICAL AND PETROLEUM PROCESS EQUIPMENT HANDLING HYDROCARBON STREAMS CONTAINING ACIDIC GASES AND WATER VAPOR IS MINIMIZED BY THE PRESENCE OF THE CORROSION INHIBITOR OF THIS INVENTION.

Description

3,640,895 INHIBITION OF CORROSION USING ALKYL ARYL KETONES Zisis Andrew Foroulis, East Orange, N.J., assignor to Esso Research and Engineering Company No Drawing. Filed July 2, 1968, Ser. No. 741,869 Int. Cl. C23f11/04, 11/12 US. Cl. 252396 15 Claims ABSTRACT OF THE DISCLOSURE Corrosion of metals by aqueous acidic solutions in a non-oxidizing atmosphere is markedly inhibited by the presence of a lower alkyl aryl ketone. A particularly effective inhibitor of this type is methyl beta-naphthyl ketone. Corrosion of chemical and petroleum process equipment handling hydrocarbon streams containing acidic gases and water vapor is minimized by the presence of the corrosion inhibitor of this invention.

BACKGROUND OF THE INVENTION This invention relates to the prevention of corrosion of metals by aqueous acidic solutions, and more particularly to the prevention of corrosion of chemical and petroleum process equipment which is subjected to corrosive attack by aqueous acidic solutions in a non-oxidizing atmosphere as a result of condensation of water containing dissolved acidic substances.

Various acidic substances which are present in petroleum refining operations cause corrosion of metals with which they come in contact. Examples of destructive inorganic compounds include hydrochloric acid, sulfuric acid, sulfur dioxide, and hydrogen sulfide. Organic compounds causing corrosion include acetic acid, phenolic compounds, naphthenic acids, and aliphatic and naphthenic organic chlorides. Corrosion-causing acids enter the hydrocarbon process streams in petroleum refineries in various ways. For example, crude oils generally contain naphthenic acids. The organic chlorides do not usually occur naturally in crude oil, but are sometimes added by producers for removal of parafiin deposits in producing wells and pipelines. These tend to hydrolyze in the presence of water to produce hydrochloric acid. Hydrogen sulfide is formed in catalytic desulfurization processes using hydrogen, in which various hydrocarbon feedstocks including virgin and cracked naphthas, as well as gas oils, containing such impurities as mercaptans, disulfides, and thiophenes, are catalytically reacted with hydrogen in order to reduce their sulfur content. Sulfuric acid and sulfur dioxide are both processing reagents, the former being used as an alkylation catalyst and the latter as an extractant for the removal of aromatics from hydrocarbon feedstocks. Hydrochloric acid and hydrogen chloride may result from several sources, including the hydrolysis of organic chlorides, hydrolysis of salt which is mixed with crude oil as a result of the use of brine in oil production operations, and as a result of hydrolysis of chlorine gas which is used in the regeneration of platinum reforming catalysts.

Acidic substances such as the foregoing will cause severe corrosion of the metals from which conventional petroleum refining equipment is constructed. Carbon steels, such as 1020 carbon steel containing 0.2% carbon, are used predominantly as materials of construction. While it would be possible to fabricate refinery equipment from steels which are less prone to corrosive attack, such as stainless steel and special alloy steels, the cost of such equipment would be inordinately high and would make any proces being conducted with such equipment uneconomical.

United States Patent Corrosion in petroleum process streams is particularly troublesome in equipment, such as condensers and heat exchangers, where condensation of water takes place. Water vapor is invariably present, both in hydrocarbon process streams and in regenerator gas streams, as is well known. When this water condenses, acidic gas present in the process stream, such as hydrogen chloride, hydrogen sulfide, sulfur dioxide, and carbon dioxide, dissolve in the condensate and attack metal equipment. Such attack occurs in hydrocarbon process streams containing only trace amounts of oxygen or none at all, since the metal is oxidized by the hydrogen ions of the acid.

The overhead stream from an atmospheric pipestill is one example of a petroleum process stream containing acidic gases. Such a stream generally contains hydrogen chloride as well as organic chlorides. Upon condensation of this overhead stream, hydrogen chloride is dissolved in the water condensate and the qunatity of hydrogen chloride is augmented by hydrolysis of a portion of the organic chlorides present. This condensate attacks the condenser surfaces.

Another location where corrosion may occur is on the downstream side of a hydrotreating unit. The effluent from a hydrotreater may contain water vapor, hydrogen chloride, and hydrogen sulfide. In typical operations this eflluent is condensed and the hydrogen sulfide removed. Corrosion is prone to take place in the condenser and the hydrogen sulfide stripper.

Acidic atmopheres are also found frequently during the regeneration of catalyst for hydroforming and other catalytic hydrogenation processes. It is necessary to prevent corrosion as a result of these acid gases while at the same time avoiding any significant adverse effect on catalyst activity as a result of contact of the catalyst with a corrosion inhibitor. This is particularly important in the case of hydroforming catalysts where the catalysts are expensive and where it is extremely crucial, from 'a process economy point of view, to extend the catalyst life as long as possible.

One possible technique for inhibiting corrosion by acids is to neutralize the acid with a base. However, such a solution would not be practical because there is a tremendous daily throughput of feed streams through petroleum or chemical processes which contain acidic materials, thereby requiring a correspondingly large amount of base for neutralization. A further problem arises from the fact that the most likely bases for use in such neutralization would be either organic nitrogen compounds or ammonia. Nitrogen, however, is a severe poison for many petroleum conversion catalysts such as reforming catalysts. Its use would, therefore, be contraindicated in any fluid stream which would eventually contact such conversion catalysts. It is thus evident that a meaningful answer to the problem facing the petroleum industry would not be based on neutralization or removal of the acidic corrosive agents in the feed stream since such techniques would either be prohibitively expensive or would result in deactivation of reforming catalysts. Instead, it is necessary to provide a corrosion inhibitor whose effectiveness does not depend on neutralization of acid present and which does not adversely affect the catalyst to any significant degree, if at all.

can be inhibited to a considerable extent by the presence of a lower alkyl aryl ketone having the formula where Ar is an aryl radical containing a maximum of two rings and R is a lower alkyl radical containing from 1 to about 4 carbon atoms. Ar is preferably a bicyclic aryl radical such as beta-naphthyl or alpha-naphthyl. In a. preferred embodiment of the invention Ar is betanaphthyl and R is methyl. Compounds of the above formula are particularly useful in inhibiting corrosion by aqueous acids in non-oxidizing atmospheres.

DETAILED DESCRIPTION OF THE INVENTION A preferred corrosion inhibitor according to this invention is methyl beta--naphtha ketone, which has the formula ,-oo1-Ii k Other alkyl aryl ketones can also be used effectively as corrosion inhibitors. Such compounds include acetophenone, ethyl phenyl ketone, methyl alpha-naphthyl ketone, methyl ortho-hydroxyphenyl ketone, methyl para-hydroxyphenyl ketone, methyl cresyl ketone, and methyl 5-hydroxy-2-naphthyl ketone, and ethyl beta-naphthyl ketone. Compounds in which the aryl radical contains more than 2 rings are generally not useful since such compounds ordinarily have water solubilities too loW to provide an effective corrosion inhibiting concentration. The presence of long chain alkyl substituents which markedly decrease solubility should also be avoided. The presence of ring substituents, such as hydroxy, which tend to increase water solubility is frequently desirable, since some compounds conforming to the above general formula in which neither the alkyl nor the aryl radicals are substituted have water solubilities which are too low for maximum effectiveness as corrosion inhibitors. On the other hand, compounds having a substantial water solubility are also poor inhibitors for preventing corrosion by acids. Best results are obtained with compounds which are substantially, but not completely, water insoluble.

The inhibitors of this invention may be used elfectively in Widely varying concentrations. Effective inhibition is obtained in concentrations ranging from about moles per liter (m./l.) up to about 0.5 m./l. in the aqueous acidic phase. Actually, there is no upper limit on the effectiveness of the inhibitors of this invention, and the maximum concentration is limited only by the solubility of the compound. However, concentratons in excess of 0.5 m./l. do not give inhibitory action substantially greater than that obtained at concentrations under 0.5 m./l.

The ketones of this invention can be used eifectively in oxidizing, inert, or reducing atmospheres. These inhibitors are well suited for use in reducing atmospheres such as those encountered in petroleum process streams. A significant advantage of these inhibitors in petroleum processing is that they do not poison platinum or palladium catalysts, which are poisoned by nitrogen and sulfur compounds. However, the ketones of this invention may also be used elfectively in environments where oxygen is present. Ketones have an advantage over aldehydes as corrosion inhibitors where oxygen is present, since aldehydes are prone to oxidation while ketones are more stable to oxidation.

Any metals which are subject to acid attack can be protected with the inhibitors of this invention. These inhibitors are particularly useful for protection of ferrous metals, and especially low carbon steel, such as 1020 carbon steel (containing 0.2% carbon). Low carbon steels are ideal for construction of petroleum processing equipment from the standpoint of cost and other significant qualities such as strength and their ability to withstand the process stream temperatures. The principal drawback to low carbon steel is its susceptibility to acid corrosion, and problems arising from this are substantially obviated by the use of the inhibitors of this inventioni Non-oxidative corrosion by acids is ordinarily a problem where the pH of the acidic solution is about 4 or lower. The ketone inhibitors of this invention offer excellent protection even in solutions which are decidely on the acid side, e. g., those having a pH of l or lower.

A few types of apparatus used in the petroleum proccessing industry will be cited as examples of apparatus which may be protected against corrosion according to this invention. One such type of apparatus is the regeneration circuit used in hydroforming. It is necessary in hydroforming to use a catalyst having a small chloride content. During regeneration coke is burned from the catalyst, producing an effiuent which has a fair concentration of CO and small quantities of S0 ,and S0 During this step, the chlorides to be found in the gas vapor will increase due to an increase in water content of the gas which serves to strip chlorine olf the catalyst. The second step is to remove any water left on the catalyst. This means thorough drying of the flue gas, which is a mixture of nitrogen, CO CO, S0 S0 and HCl. After most of the water has been removed, chlorination is started in a manner such that chlorine will be progressively absorbed by the catalyst. During the subsequent rejuvenation of the catalyst to rearrange the crystal structure, some chlorine will still be carried over with the flue gas. The last step in the regeneration operation is purging the stream With nitrogen, an inert gas, to remove air and finally pressure up with hydrogen. The inhibitor of the instant invention is injected into the hydroformer regeneration gas stream either continuously throughout the regeneration cycle or by intermittent high rate injection of inhibitor at the same total amount per regeneration cycle. The presence of the inhibitor serves to reduce or minimize corrosion in heat exchange equipment and transfer lines where water condensate, containing the acidic components mentioned previously, accumulates. The inhibitor compound is adsorbed on the metal surface and minimizes corrosion by markedly lowering the rate of corrosion reactions. As indicated earlier, the prseence of alkyl aryl ketones, preferably in the absence of oxygen, serves to inhibit the corrosion effects of various acid base corrosion causing substances. An inert gas, e.g., nitrogen, is present and, in addition, corrosive substances such as hydrogen sulfide, hydrochloric acid, and sulfuric acid are present. The addition of an alkyl aryl ketone serves to minimize corrosion with no adverse elfect on the platinum or palladium catalyst. Another area where corrosion in an inert atmosphere is widespread and has a deleterious effect is hydrotreating. Substantial quantities of hydrogen sulfide are produced in the hydrotreater by reduction of sulfur compounds such as mercaptans, disulfides, and thiophene. This causes corroslon in the presence of Water condensate. Also present is hydrogen chloride, which may result from the decomposition of organic chlorides such as carbon tetrachloride and trichloroethylene in the process stream, or from the hydroformer treat gas which contains HCl from decomposition of the chlorine treated catalyst base. In any event, the hydrotreater effiuent condenser and other overhead equipment has been plagued with problems instigated by the presence of hydrogen chloride. Again, corrosion is greatly reduced by the injection of an aryl alkyl ketone into the process stream. The fact that the ketones of this invention do not poison platinum catalysts, as do inhibitors containing nitrogen or sulfur, is important because the hydrotreater efiluent is frequently passed through a platinum catalyst bed in a hydroformer, and in those cases it is imperative to avoid corrosion inhibitors which could poison the platinum catalyst.

A significant advantage of the use of corrosion inhibitors is that it is possible to use inexpensive construction materials such as low carbon steel, instead of costly corrosion resistant alloy steels which would render the cost of the process prohibitive.

While ferrous metals have been cited as an illustrative example of metals which can be protected according to this invention, it should be understood that other metals and alloys, such as nickel, zinc, brass, and copper, may also be protected. While copper is more resistant to acid attack in a non-oxidizing atmosphere than the other metals and alloys mentioned, nevertheless it may be prone to slight attack by strong acids, and such attack is mitigated by alkyl aryl ketone.

The problem of corrosion attack is most severe in those units, such as condensers, heat exchangers, and transfer lines, where water condenses. The acid gases present in the process stream are dissolved in the condensate, and attack the metal process equipment. It has been found that the corrosion inhibitors herein are efiective under the entire temperature range in which water is present in the liquid phase. Since some processes are run at high pressure, the actual temperature may be considerably above the atmospheric boiling point of water; nevertheless, the inhibitors do not lose their effectiveness at such temperatures. Likewise, they remain efiective at low temperatures down to 32 F.

The inhibitor is preferably injected into the process stream just a short distance upstream for best results. This mitigates loss of the inhibitor, and also protects the inhibitor from decomposition from high temperatures which prevail in some units of process streams.

While the mechanism for the inhibiting action of alkyl aryl ketones such as methyl beta-naphtha ketone is not completely understood, the following explanation is offered for the purpose of illustration and as an aid in understanding the invention, and should not be taken as limiting the scope of the invention in any manner. The corrosion additive is believed to be adsorbed on the metal surface in the form of a continuous or nearly continuous thin film. This film would serve to inhibit any chemical or electro-chemical interaction between the acidic corrosive material in solution and the metal surface. The very small quantities of inhibitor that are utilized to form this thin film are not believed to undergo any significant chemical reaction with the acidic corrosive material. Thus, only small amounts of additional inhibitor would be necessary to maintain long term protection on metal surfaces, these additions being possibly necessitated by attrition losses due to physical interactions of the flowing stream with the film.

As previously noted, the corrosion inhibitor should not be markedly water soluble, nor should it be substantially completely insoluble. In short, the water solubility must be enough to establish an effective concentration, which as earlier noted is generally at least m./l. in the aqueous acidic phase.

The present invention will be more fully understood with reference to the following specific examples. It is understood that these examples are illustrations of specific embodiments of this invention and are not to be taken as limitations.

Example 1 This example illustrates the effectiveness of methyl betanaphthyl ketones as an inhibitor of acid-induced corrosion of 1020 carbon steel exposed to 0.1 N hydrochloric acid, which has a pH of 1. Corrosion rates were measured by weight losses, carbon steel specimens having a size of approximately 1" x 4 x /8, and a surface area of approximately 58 square centimeters. The specimens were abraded through 40 emery paper, degreased in benzene, and washed in distilled water. Immediately after drying, the specimens were weighed and placed in a corrosion cell and immersed in the corrosive solution. Each of the corrosive solutions, except those used for control purposes, contained a predetermined concentration of methyl betanaphthyl ketone. The amount of corroded metal was determined by weight loss. The corrosion cell was basically a 2000 m./l. Erlenmeyer flask with a special top to permit entrance and exit of nitrogen for deaeration and to prevent air contamination. The cell had a removable chimney with Pyrex hooks from which the metal specimens were suspended. The corrosive solution was deaerated with nitrogen before each run. Nitrogen also was bubbled through the solution continuously during a run to prevent contamination with air. A constant temperature was achieved by the use of a constant temperature oil bath. All runs were carried out for 2 days at a constant temperature of 25 C.

The results of representative experiments utilizing the above procedure are summarized below in Table I. In this table, corrosion rate in milligrams per square decimeter per day (mg./dm. /day or m.d.d.) and percentage inhibitor efficiency (which equals where L, is the corrosion rate without inhibitor and I is the corrosion rate with inhibitor) are given for various concentrations of inhibitor in moles per liter (m./l.).

TABLE I Inhibitor con- Corrosion Percent centration, rate, inhibitor m./l. mg./drn. /day efficiency Blank 1, 555 l0- 904 41. 6 5 l0- 627 66. 1 10" 500 67. 8 10- 572 63. 2

Example 2 The protective properties of methyl beta-naphthyl ketone for inhibition of corrosion of 1020 carbon steel in a hydroformer regenerator circuit condensate at 212 F. was determined according to this example. The condensate is a highly corrosive acidic substance having a pH of 0.5. The procedure followed was the same as in Example 1. Results are given in Table II.

TABLE II Inhibitor con- Corrosion Percent centration, rat inhibitor m./l. mgJdmfl/day efiicieney Blank 41,114 10 17, 229 58. 1 10- 16, 242 60. 3

where R is a lower alkyl radical containing from 1 to about 4 carbon atoms.

2. A process according to claim 1 in which the compound is methyl beta-naphthyl ketone.

3. A process according to claim 1 in which the metal is a ferrous metal.

4. A process according to claim 1 in which said solution has a pH not greater than about 4.

5. A process according to claim 1 in which said corrosion inhibiting compound is present in a concentration of about 10- m./l. to about 0.5 m./l. in the aqueous acidic solution.

6. A process according to claim 1 in which said acidic solution is a condensate in a hydrocarbon process stream.

7. A process according to claim 1 in which said corrosion inhibiting compound is added to a hydrocarbon process stream upstream of the area to be protected.

8. A process for inhibiting corrosion of a metal by an aqueous acidic solution which comprises adding to said solution a small but effective amount of a corrosion inhibiting compound having the formula ArCR I;

where Ar is an alpha-napthyl or beta-naphthyl radical and R is a lower alkyl radical containing from 1 to about 4 carbon atoms, said solution being surrounded by an inert or reducing atmosphere.

9. A process according to claim 8 in which Ar is betanaphthyl.

10. An aqueous acidic solution inhibited against corrosive attack on metals, said solution consisting essentially of an aqueous acid normally tending to cause corrosion of metals, and a small but effective amount of a corrosion inhibiting compound having the formula where R is a lower alkyl radical containing from 1 to about 4 carbon atoms.

11. A solution according to claim 10 having a pH not greater than about 4. I

12. A solution according to claim 10 in'which said compound is present in a concentration of about 10" m./l. to about 0.5 m./l. I

13. A solution according to claim 10 in which R is methyl.

14. A solution according to claim 10 in which said compound is methyl beta-naphthyl ketone.

15. A solution according to claim 10 in which said acid is hydrochloric acid.

References Cited UNITED STATES PATENTS 2,430,058 11/1947 Klaber 252 396 3,493,510 2/1970 Chao 252 -396 OTHER REFERENCES H. H. Uhlig, The Corrosion Handbook, J. Wiley, 1948, pp. 910, 911, and 912.

RICHARD D. LOVERING, Primary Examiner I. GLUCK, Assistant Examiner