BRPI0619195A2 - corrosion inhibitor - Google Patents

Abstract

Corrosion inhibitor. A composition and method of inhibiting corrosion caused by naphthenic acid in fluids includes using a combination of a thiophosphorus compound and a hydrogen sulfide removal compound. The hydrogen sulfide removal compound enhances the performance of the thiophosphorus compound and can be included at relatively low levels in the composition. The treatment can be applied to fluids including crude oils and lighter fractions thereof.

Description

Patent Descriptive Report for "CORROSION INHIBITOR".

The present invention relates to corrosion inhibitors. The present invention is particularly directed to corrosion inhibitors useful for applications in which naphthenic acid is present.

It is well known in the art that processing crude oil in its various fractions can damage the iron containing metal surfaces of the processing equipment. This corrosion is often associated, in particular, with the presence and activity of naphthenic acid.

Corrosion occurs when the amount of naphthenic acids in the hydrocarbon reaches some critical value indicated by the total acidity index ("IA"), expressed as milligrams of potassium hydroxide required to neutralize acids in a one gram sample. Older literature generally holds that an AI greater than about 0.5 is required for a crude oil to cause naphthenic acid corrosion, but more recent experience indicates that the critical value may vary considerably from this value. When high temperatures are applied to crude oil, such as temperatures from 175 ° C (-347 ° F) to about 400 ° C (-752 ° F) commonly used to refine and distill the oil, the problem corrosion is typically more exacerbated.

Although various corrosion inhibitors are known in the art, the effectiveness of any particular corrosion inhibitor is generally known to be dependent upon the circumstances under which it is used. As a result, a variety of corrosion inhibitors have been developed and marked for use in the particular treatment of crude oils, to protect particular metals, to inhibit specific types of corrosion, and / or for use under particular temperature, ambient conditions. , and the like. For example, US 3,909,447 describes certain corrosion inhibitors as useful against corrosion in oxygenated aqueous systems at relatively low temperatures, such as water flooding, cooling towers, drilling muds, air drilling and auto-radiator systems.

As commonly used, naphthenic acid is a collective term for certain organic acids present in various crude oils. Although smaller amounts of other organic acids may also be present, it is understood that most acids in a naphthenic acid-based crude oil are naphthenic in character, that is, with a saturated ring structure that conforms to a formula. such as one of the following:

In the above formulas, m is typically 1-2, and η varies. It is basically any carboxylic acid group with at least one saturated, 5- or 6-membered ring attached. A simple example is cyclopentaenoic acid.

The molecular weight of naphthenic acid can extend over a wide range. However, most naphthenic acid in crude oils is found after distillation in the lightest fractions, including, for example, diesel oil. When hydrocarbons containing such naphthenic acid contact iron-containing metals, especially at elevated temperatures, various corrosion problems arise.

Several approaches to controlling naphthenic acid-induced corrosion have included neutralizing and / or removing naphthenic acids from the crude oil being processed; combine low acidity oils with more corrosive high acidity oils to reduce the total neutralization index; and use relatively expensive corrosion resistant alloys in the construction of the crude oil processing apparatus. Such attempts are generally disadvantageous in that they require additional processing and / or substantially increase the cost of treating crude oil. Alternatively, US Patent 4,443,609 describes certain phosphonic acids and tetrahydrothiazole esters as useful additives for inhibiting acid corrosion. Such inhibitors may be prepared by reaction of certain 2,5-dihydrothiazoles with a dialkyl phosphite. Although these phosphonic tetrahydrothiazole acids and esters offer good corrosion inhibition, they tend to rupture under high temperature conditions.

Another disadvantage of using phosphorus-based compounds is that it is claimed that phosphorus impairs the function of various catalysts used to treat crude oils such as fixed bed hydrotreaters and hydrocracking units. Thus, crude oil processors are often faced with a dilemma, as corrosion itself, if not inhibited, can result in accumulation in the hydrocarbon fluid of an amount harmful to iron catalyst, as high as 10 to 20. ppm in some cases. Unfortunately, while there are numerous commercially available non-phosphorus-based inhibitors, they are known to be generally somewhat less effective than phosphorus-based compounds.

A significant advance in phosphorus-based naphthenic acid-induced corrosion inhibitors is reported in US Patent 4,941,994. In this Patent, it is described that corrosion of metal in hot, acidic liquid hydrocarbons is inhibited by the presence of a corrosion inhibiting amount of a dialkyl and / or trialkyl phosphite with an optional thiazoline. Another patent, Patent 5,863,415 mentions that thiophosphorus compounds of a specific formula are particularly useful for corrosion inhibition in hot liquid hydrocarbons and may be used at concentrations that add less of the catalyst-damaging phosphorus to the fluid than some of the previous phosphorus-based corrosion inhibitors. Such thiophosphorus compounds also offer the advantage that they can be prepared from relatively low cost starting materials.

In view of the above, it would be desirable in the art to find additional method and compositions for inhibiting and controlling naphthenic acid-induced corrosion in crude oils which offer advantages over the prior art. In one aspect, the present invention is a method for inhibiting corrosion of naphthenic acid in a fluid containing a corrosive amount of naphthenic acid, wherein the method comprises adding to the fluid or a feed therefor a thiophosphorus compound. and a hydrogen sulfide removal compound, wherein the thiophosphorus compound and hydrogen removal compound are in effective amounts to inhibit corrosion.

In another aspect, the invention is a composition useful for inhibiting naphthenic acid corrosion in a fluid containing a corrosive amount of naphthenic acid comprising a mixture of a thiophosphorus compound and a hydrogen sulfide removal compound.

In one aspect, the present invention is a method for inhibiting naphthenic acid corrosion in a fluid containing a corrosive amount of naphthenic acid, wherein the method comprises adding to the fluid or a feed therein in sufficient amounts to effect corrosion inhibition in the fluid, a thiophosphorus compound and a hydrogen sulfide removal compound. The fluid may be, for example, a hydrocarbon such as a crude oil or a lighter fraction thereof. Thiophosphorus compounds useful with the present invention include those described in Zetlmeisl U.S. Patent 5,863,415, the contents of which are incorporated herein by reference in their entirety. For example, thiophosphorus compounds useful in the practice of the present invention include the salts of thiophosphorus compounds, alkyl and aryl esters of thiophosphorus compounds, and isomers of thiophosphorus compounds. Any thiophosphorus compounds which effect naphthenic acid-induced corrosion inhibition in fluids may be used in the present invention.

In a non-limiting embodiment, thiophosphorus compounds of the general formula are useful in the present invention: <formula> formula see original document page 6 </formula>

FORMULA 1

wherein R1 is R3 (OCH2CH2) n-, or R3 (OCH2CH2) nO-, R2 is equal to R1 or is -XH, each X is independently sulfur or oxygen, provided, however, that at least one of X is sulfur, R3 is an alkyl group of about 6 to about 18 carbon atoms, and η is an integer from O to about 12.

Hydrogen sulfide removal compounds useful in the invention include those described in US Patents 5,169,411 to Weers and US 6,663,841 to Salma et al., The contents of which are incorporated herein by reference in their entirety. Included in the compounds are the non-acidic imine compound, which is the condensation product of an amine or polyamine and an aldehyde, dialdehyde or ketone. For example, they include, in non-limiting embodiments, those compounds having the general formula:

<formula> formula see original document page 6 </formula>

where χ is an integer from about 1 to about 10; R1 is independently selected from the group consisting of

<formula> formula see original document page 6 </formula> <formula> formula see original document page 7 </formula>

FORMULA 5

cycloalkyl having from about 4 to about 7 carbon atoms, phenyl, benzyl, alkyl having from 1 to about 20 carbon atoms, and alkenyl having from 1 to about 20 carbon atoms; R3 is hydrogen, alkyl having from 1 to about 20 carbon atoms, alkenyl having from 1 to about 20 carbon atoms, or aryl; η is an integer from 1 to 6; R4, R5, and R6 are each independently selected from the group consisting of alkyl containing from 1 to about 20 carbon atoms and

<formula> formula see original document page 7 </formula>

FORMULA 6

R7 is hydrogen or alkyl having from 1 to about 20 carbon atoms, and is equal to R2 with the proviso that only one of R4, R5 and R6 can be

<formula> formula see original document page 7 </formula>

FORMULA 6

and R2 is independently selected from the group consisting of = CH2, cyclohexyl, <formula> formula see original document page 8 </formula>

FORMULA 7

alkyl containing from 1 to about 20 carbon atoms; and alkenyl containing from 1 to about 20 carbon atoms. In FORMS 5 and 6, the "S" means at least one sulfur atom in the ring, without being specific for its location or locations.

Inhibitors of the present invention have been found to be both effective and exhibit very low levels of hydrogen sulfide evolution during storage and use. The amount of the thiophosphate compound is desirably, in certain non-limiting embodiments, from about 40 to about 70% by weight of a total additive comprising both the thiophosphorus compound and the sulfide removal compound. hydrogen. In other embodiments, the hydrogen sulfide removal compound may be from 1% to 10% by weight, preferably from about 4% to about 6% by weight. The remainder of the additive may be an inert material that is compatible with the fluid, such as, for example, mineral oil. In other non-limiting modalities, the thiophosphorus compound may represent from about 90% to about 99% by weight of the total additive, and in still other non-limiting modalities, it may represent from about 90 to about 90%. 96 wt%.

The additive combination of the thiophosphorus compound and the hydrogen sulfide removal compound may be employed in the fluid containing the corrosive naphthenic acid in any amount that is effective to inhibit corrosion by the fluid / naphthenic acid. . This may be relatively low, from about 100 ppm to about 5,000 ppm, but larger or smaller amounts may be employed if they are effective. In many desirable embodiments, it has been found that a level of from about 500 ppm to about 2,000 ppm is effective, and in other desirable embodiments it may be in the range of about 750 ppm to about 1,250 ppm. The following examples are provided to illustrate the present invention. The examples are not intended to limit the scope of the present invention and should not be construed accordingly. Quantities are in parts by weight or weight percent unless otherwise indicated.

Example 1

A test of the invention is performed by first determining the corrosion level for a blank.

The procedure includes the step of adding 282 grams of mineral oil to the reaction flask. A test cell is sparged with nitrogen at a flow rate of 10 to 20 mL / min for a period of 30 to 60 minutes with continuous agitation. The heaters are set at 288 ° C and the test cell is sprayed with 1 mol% H2S nitrogen for the remainder of the test. The test procedure is performed with a total acidity index of 10 mg KOH1 temperature of 288 ° C, an operating time of 24 hours, and 1% mol of hydrogen sulfide in nitrogen, using test specimens. C1018 carbon steel. A "blank" is initially tested without corrosion inhibitor to determine the amount of corrosion that occurs. About 20 g of commercial naphthenic acids having a total acidity index of 151 are injected 30 minutes after the specimen is inserted into the test cell. Then a first test of the invention is performed using another specimen and the same procedure except that the corrosion inhibitor of the invention was included. The corrosion inhibitor is a mixture of a thiophosphorus compound and a hydrogen sulfide removal compound at a level of 1,000 ppm by volume, where the thiophosphorus compound is present at 55 wt.% And the removal compound. present at 5% by weight, with the remainder of the mixture being a mineral oil. The specimens are in all cases removed after 24 hours in the test cell for evaluation. The procedure for testing the invention is also completed with another specimen in a second test.

In the first test, and when compared to the "blank", the level of protection provided by the invention is determined to be -94.2%. In the second test of the invention, the level of protection is determined to be 99.7%. Comparative Example 2

Example 1 is repeated substantially identically except that the hydrogen sulfide removal compound was not used, but the same amount of thiophosphorus compound is used. In a first test, the protection level is determined to be 80.1%. In a second test, the protection level is determined to be -89.2%.

Claims (17)

A method for inhibiting naphthenic acid corrosion in a fluid containing a corrosive amount of naphthenic acid, wherein the method comprises adding to the fluid or feed thereof a thiophosphorus compound and a hydrogen sulfide removal compound. wherein the thiophosphorus compound and hydrogen sulfide removal compound are in such amounts that corrosion is inhibited. A method according to claim 1, wherein the thiophosphorus compound and hydrogen sulfide removal compound are added as a mixture. A method according to claim 1, wherein the thiophosphorus compound has the general formula: wherein R1 is R3 (OCH2CH2) n-, or R3 (OCH2CH2 ) nO-, R2 is equal to R1 or is -XH, each X is independently sulfur or oxygen, provided, however, that at least one X is sulfur, R3 is an alkyl group of 6 to 18 carbon atoms and n is an integer from 0 to 12. <formula> formula see original document page 11 </formula> A method according to claim 1 wherein the hydrogen sulfide removal compound has the general formula: wherein x is an integer from about 1 to about about 10; R1 is independently selected from the group consisting of <formula> formula see original document page 11 </formula> cycloalkyl having from 4 to 7 carbon atoms, phenyl, benzyl, alkyl having from 1 to 20 carbon atoms, and alkenyl having from 1 to 20 carbon atoms; R3 is hydrogen, alkyl having 1 to 20 carbon atoms, alkenyl having 1 to 20 carbon atoms, or aryl; η is an integer from 1 to 6; R4, R5, and R6 are each independently selected from the group consisting of alkyl containing from 1 to 20 carbon atoms, and R7 is hydrogen or alkyl having from 1 to 20 carbon atoms, and is equal to R2, provided that only one of R4, R5 and R6 may be and R2 is independently selected from the group consisting of = CH2, cyclohexyl, alkyl containing from 1 to 20 carbon atoms, and alkenyl containing from 1 to -20 carbon atoms; and wherein S means at least one ring sulfur atom at any location. A method according to claim 1, wherein the fluid is a crude oil or a fraction thereof. A method according to claim 2, wherein the hydrogen sulfide removal compound is present in the mixture in a quantity of 1% to 10% by weight. A composition according to claim 6 wherein the hydrogen sulfide removal compound is present in the mixture in an amount of 4% to 6% by weight. The composition of claim 2, wherein the thiophosphorus compound is present in the mixture in an amount of 40% to 70% by weight. The composition of claim 2, wherein the mixture further includes mineral oil. A composition useful for inhibiting naphthenic acid corrosion, which contains a corrosive amount of naphthenic acid, which comprises a mixture containing a thiophosphorus compound and a hydrogen sulfide removal compound. The composition of claim 10, wherein the fluid is a crude oil or a fraction thereof. The composition of claim 10, wherein the hydrogen sulfide removal compound is present in the mixture in an amount of 1% to 10% by weight. The composition of claim 12, wherein the hydrogen sulfide removal compound is present in the mixture in an amount of 4% to 6% by weight. The composition of claim 10, wherein the thiophosphorus compound is present in the mixture in an amount of 40% to 70% by weight. The composition of claim 10, wherein the mixture further includes mineral oil. The composition of claim 10, wherein the thiophosphorus compound has the general formula: wherein R1 is R3 (OCH2CH2) n-, or R3 (OCH2CH2 ) nO-, R2 is equal to R1 or is - XH1 each X is independently sulfur or oxygen, provided, however, that at least one X is sulfur, R3 is an alkyl group of 6 to 18 carbon atoms and η is an integer from 0 to 12. The composition of claim 10, wherein the hydrogen sulfide removal compound has the general formula R 30 (CH 2) n - wherein χ is an integer from about 1 to 10; R1 is independently selected from the group consisting of <formula> formula see original document page 14 </formula> cycloalkyl having from 4 to 7 carbon atoms, phenyl, benzyl, alkyl having from 1 to 20 carbon atoms, and alkenyl having from 1 to 20 carbon atoms; R3 is hydrogen, alkyl having 1 to 20 carbon atoms, alkenyl having 1 to 20 carbon atoms, or aryl; η is an integer from 1 to 6; R4, R5, and R6 are each independently selected from the group consisting of alkyl containing from 1 to 20 carbon atoms, and R7 is hydrogen or alkyl having to 1 to 20 carbon atoms, and is equal to R2 with the proviso that only one of R4, R5 and R6 can be <formula> formula see original document page 14 </formula> and R2 is independently selected from the group consisting of = CH2, cyclohexyl, <formula> formula see original document page 15 </formula> alkyl containing 1 to 20 carbon atoms, and alkenyl containing 1 to -20 carbon atoms; and wherein S means at least one ring sulfur atom at any location.