US3676327A - Inhibition of corrosion by hydrotreater effluent - Google Patents

Abstract

Corrosion of metals by aqueous hydrochloric acid condensates in petroleum processing equipment is markedly inhibited by the addition of a lower aliphatic amine to the system. The operative amines are primary aliphatic amines having four to 10 carbon atoms. Octylamine is a preferred inhibitor.

Description

Unite States aiei Forouhs [451 July 1 1, 1972 [54] INHIBITION OF CORROSION BY References Cited HYDROTREATER EFFLUENT UNITED STATES PATENTS [72] Inventor: Zisis Andrew Foroulis, East Orange, NJ. 2,938,851 5/1960 Stedman et a], ..208/47 2,920,030 1/ 1960 Thompson 73 l i Research and Engmeer'ng cmpany 3,447,891 6/1969 Crawford ..21/2.5 [22] Filed: Feb. 19, 1970 Primary Examiner-Delbert E Gantz [21] Appl 12340 Assistant Examiner-G. E. Schmitkons AttorneyPearlman and Stahl and Louis F. Kreek, Jr. [52] US. Cl ..208/47, 21/2.7, 21/58,

106/14, 203/7, 208/209, 208/262, 252/148, ABSTRACT 252/390 1 2;} Elsi-fear -;,,g ;g gg;v;g;;g 532;:rgzsilxzeiozzsig sgi:iiizirizzrkssiiizziifa; 5 2 2 by the addition of a lower aliphatic amine to the system. The

operative amines are primary aliphatic amines having four to 10 carbon atoms. Octylamine is a preferred inhibitor.

6Claims,NoDrawings INHIBITION OF CORROSION BY HYDROTREATER EFFLUENT BACKGROUND OF THE INVENTION This invention relates to the inhibition of corrosion of metal vessels used in petroleum processing operations by aqueous acidic constituents of the petroleum process stream. More especially, this invention relates to the inhibition of corrosion in the effluent from a hydrotreating unit caused by condensation of corrosive aqueous acidic constituents in said effluent.

Hydrotreating is an operation which is used widely in the petroleum process industry for reducing the sulfur content of a feedstock and for improving various properties of the feedstock such as color, odor, and stability. Basically, hydrotreating comprises treating a hydrocarbonaceous feedstock with hydrogen in the presence of a catalyst under comparatively mild conditions which will not cause significant rupture of carbon to carbon linkages as is characteristic of hydrocracking and reforming. Typical reactions taking place include the conversion of mercaptans and disulfides to hydrogen sulfide and hydrogenation of olefins to paraffins. Solvent hydrocarbons are among the feedstocks which can be treated in this manner. Hydrotreated solvent stocks must generally meet severe standards of color, odor, and corrosiveness. Such solvents may be used for various purposes, including use as an extractant in food processing. Use in food processing requires that the solvent be nontoxic, in addition to the aforementioned properties.

A great problem in hydrotreating is the condensation of aqueous hydrochloric acid in the effluent from the hydrotreater. Petroleum producing operations frequently utilize organic chlorinated compounds as carbon tetrachloride and trichloroethylene. These compounds distill overhead into the naphtha stream in petroleum processing operations which precede or hydrotreating unit and thus are contained in the hydrotreater feedstock. It is common practice to cool the hydrotreater effluent, which results in the condensation of water on metal surfaces of heat exchangers, condensers, and the like. Sufficient hydrolysis of the chlorinated carbon compounds occurs to form hydrogen chloride, which dissolves in the water condensate to form highly acidic and highly corrosive aqueous hydrochloric acid condensate. These condensates usually have a pH of less than about 4, and frequently may have a pH AS low as 1 OR even less. Since the corrosion rate of metals, and particularly ferrous metals, by acids rises rapidly as the pH is decreased below 4, it will be appreciated that a very severe corrosion problem exists in the effluent circuit of a hydrotreater.

Acidic substances such as aqueous hydrochloric acid condensates will cause severe corrosion of metals from which conventional petroleum refining equipment is constructed. Carbon steels, such as 1020 carbon steel containing 0.2 percent 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 steels and special alloy steels, the cost of such equipment would be inordinately high and would make any process being conducted with such equipment uneconomical.

It is therefore essential to provide a corrosion inhibitor which will control corrosion and make possible the use of carbon steel as construction material for equipment such as piping, heat exchangers, and the like.

The choice of a corrosion inhibitor for the effluent circuit of a solvent hydrotreater is restricted by the fact that the hydrotreated solvent must be nontoxic, colorless and odorlesss for many industrial applications of said solvents. This rules out a number of inhibitors which give effective corrosion inhibition. It is therefore essential to provide a corrosion inhibitor which not only gives effective corrosion inhibition, but

which is also either nontoxic, colorless and odorless, or is removable from the hydrotreated effluent by simple procedures such as washing, which will yield an acceptable quality of hydrotreated solvent.

SUMMARY OF THE INVENTION It has been found that corrosion of metal vessels containing a petroleum process stream by aqueous acidic condensates in said stream can be inhibited by adding to the process stream a corrosion inhibiting amount of a primary aliphatic amine containing from 4 to 10 carbon atoms.

DETAILED DESCRIPTION OF THE INVENTION The corrosion inhibitors of the present invention, as above indicated, are the primary aliphatic amines having from 4 to 10 carbon atoms. The alkyl amines are preferred. The effective inhibitors of this invention have boiling points of at least 50 C. (144 F.) to about 300 C. (572 F.). The inhibitors of the present invention may be represented by the structural formula RNH Where R is an alkyl radical containing from four to 10 carbon atoms.

The aliphatic amines containing four to 10 carbon atoms are unexpectedly better corrosion inhibitors than higher molecular weight primary amines, such as dodecyl amine. Furthermore, the aliphatic amines containing four to 10 carbon atoms do not impart any odor or color to the hydrocarbon product when used in a hydrocarbon processing system. Furthermore, these amines are nontoxic and are easily removable from the hydrocarbon product by acid washing, which permits them to be used as corrosion inhibitors even when the product hydrocarbon is to be used as an extracting agent or solvent in many industrial applications where these properties are desirable.

The preferred corrosion inhibitor of this invention is n-octylamine. Its boiling point is above that of water, so that it condenses before corrosive condensates form and thereby protects metal surfaces from corrosion. Other primary aliphatic amines having from four to 10 carbon atoms can also be used advantageously as corrosion inhibitors. Butylamine, for example, gives outstanding corrosion protection; it is less preferred than octylamine because its boiling point is below that of water, and therefore it does not condense with corrosive condensates as effectively as do the higher molecular weight amines.

Primary amines having more than 10 carbon atoms are avoided, because they are less effective as corrosion inhibitors than the primary amines having four to 10 carbon atoms, and because they impart an undesirable odor, and in the case of the higher molecular weight amines (e.g., octadecylamine), impart an undesirable color also to hydrocarbon products.

Any metals which are subject to acid attack can be protected with the inhibitors of this invention. This inhibitors are particularly useful for protection of ferrous metals, and especially low carbon steel, such as 1020 carbon steel (containing 0.2 percent 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 invention.

Nonoxidative corrosion by acids is ordinarily a problem where the pH of the acidic solution is about 4 or lower. The amine inhibitors of this invention offer excellent protection even in solutions which are decidedly on the acid side, e.g., those having a pH of 1 or lower.

The inhibitors of the present invention are particularly useful in inhibiting corrosion in hydrotreating operations. The inhibitor is introduced into the hydrotreater effluent prior to cooling thereof. When the effluent is cooled and condensation takes place, the corrosion inhibitor protects the equipment against corrosion caused by such condensates.

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 and stainless steels, may also be protected.

The problem of corrosion attack is most severe in those vessels, 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 effective 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 effective at low temperatures down to 32 F.

The present invention will be more fully described with reference to the following specific example. It is understood than this example is an illustration of a specific embodiment of this invention and is not to be taken as limiting.

EXAMPLE This example will illustrate the effectiveness of aliphatic amines as inhibitors of acid induced corrosion of 1020 carbon steel exposed to 0.1 N hydrochloric acid, having a pH of 1.1. Corrosion tests in this example were conducted at 200 F. Corrosion rates were measured by weight losses, carbon steel specimens having a size of approximately 1 inch X 4 inches X Va inch, and a surface area of approximately 58 square centimeters. The specimens were abraded through 4-0 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 an aliphatic amine. 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 provident 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 con stant 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 200 F.

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 mdd.) and percentage inhibitor efficiency which equals (l,,-I,)/(L,) X 100, where i is the corrosion rate without inhibitor and l, is the corrosion rate with inhibitor) are given for various concentrations of inhibitor. Concentration in Table I below is given as the weight percentage of the inhibitor in the corrosive test solution. All corrosion rates are the average of two runs.

TABLE I Concen- Corrosion 7: ln- Adverse tration Rate hibitor Efiect on inhibitor Wt. mg./dm."'/ effic- Odor Color day iency Blank 2160 Butylamine 1.5 5.0 99.8 No No Octylamine 1.5 32.5 98.7 No No Octylamine 3.0 14.2 99.3 No No *Dodecylamine 1.5 463 78.5 Yes No *Dodecylamine 3.0 33.3 98.1 Yes No *Octadecylamine 3.0 274 87.: Yes Yes *Given for comparison purposes.

What is claimed is: 1. A process for inhibiting corrosion of metal vessels by aqueous acidic condensates having a pH not greater than about 4 m a hydrotreater effluent stream, which comprises adding to said stream a corrosion inhibiting amount of a saturated primary aliphatic amine containing from 4 to 10 carbon atoms.

2. A process according to claim 1 in which said aqueous acidic condensate is aqueous hydrochloric acid.

3. A process according to claim 1 in which said amine is octylamine.

4. A process according to claim 1 in which the concentration of said amine is at least about l.5 percent by weight of the acidic condensate.

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

6. A process according to claim 5 in which said ferrous metal is carbon steel.

Claims (5)

1. 2. A process according to claim 1 in which said aqueous acidic condensate is aqueous hydrochloric acid.
2. 3. A process according to claim 1 in which said amine is octylamine.
3. 4. A process according to claim 1 in which the concentration of said amine is at least about 1.5 percent by weight of the acidic condensate.
4. 5. A process according to claim 1 in which the metal is a ferrous metal.
5. 6. A process according to claim 5 in which said ferrous metal is carbon steel.