KR20080070833A - Corrosion inhibitor - Google Patents

Abstract

A composition and method of inhibiting corrosion caused by naphthe'ic acid in fluids includes using a combination of a thiophosphorus compound and a hydrogen sulfide scavenging compound. The hydrogen sulfide scavenging compound significantly enhances the performance of the thiophosphorus compound and may be included at relatively low levels in the composition. The treatment may be applied to fluids including crude oils and lighter fractions thereof.

Description

Corrosion Inhibitor {CORROSION INHIBITOR}

The present invention relates to corrosion inhibitors. The present invention relates in particular to corrosion inhibitors useful for applications involving naphthenic acid.

It is well known in the art that the processing of crude oil in various fractions can cause damage to the iron-containing metal surface of the processing equipment. This corrosion is particularly often associated with the presence and activity of naphthenic acid. Corrosion occurs when the amount of naphthenic acid in a hydrocarbon reaches a certain threshold, expressed in total acid number (TAN) in milligrams of potassium hydroxide required to neutralize the acid in a 1 g sample. Older documents generally indicate that at least about 0.5 TAN is needed for crude oil to cause naphthenic acid corrosion, but more recent experiments indicate that the threshold may deviate significantly from this value. Corrosion problems generally worsen when elevated temperatures are applied to crude oil, such as 175 ° C. (−347 ° F.) to about 400 ° C. (-752 ° F.), which is commonly used to purify and distill oil.

While various corrosion inhibitors are known in the art, the effectiveness of any particular corrosion inhibitor is generally known to depend on the environment in which it is used. As a result, various corrosion inhibitors have been developed and targeted for specific crude oil processing to protect certain metals, to inhibit certain types of corrosion and / or to be used under certain temperature, environmental and other conditions. For example, US Pat. No. 3,909,447 discloses certain corrosion inhibitors useful for corrosion in relatively low temperature oxidized aqueous systems such as water floods, cooling towers, digging digging, air digging and automatic spinning systems.

As commonly used, naphthenic acid is a term that collectively refers to certain organic acids present in various crude oils. Although small amounts of other organic acids are also present, the majority of the acids in naphthenic acid base crudes are considered to have naphthenic, ie saturated ring structures according to the following formula:

Wherein m is generally 1-2 and n is different. It is basically any carboxylic acid group to which a ring consisting of at least one saturated 5 or 6 atoms is attached. One simple example is cyclopentanoic acid.

The molecular weight of naphthenic acid can be broadly extended. However, the majority of naphthenic acid in crude oil is found after distillation, for example in lighter fractions comprising gas oils. Serious corrosion problems arise when such naphthenic acid-containing hydrocarbons come into contact with iron-containing metals, especially at elevated temperatures.

Various approaches to controlling naphthenic acid induced corrosion include neutralizing and / or removing naphthenic acid from the crude oil being processed; Blending the low acid oil with the higher corrosive high acid oil to reduce the overall neutralization number; And the use of relatively expensive corrosion-resistant alloys within the structure of crude oil processing equipment. Such attempts are generally disadvantageous in that they require additional processing and / or add significant cost to crude oil processing. Alternatively, US Pat. No. 4,443,609 discloses certain tetrahydrothiazole phosphonic acids and esters as additives useful for inhibiting acid corrosion. Such inhibitors can be prepared by reacting certain 2,5-dihydrothiazoles with dialkyl phosphites. These tetrahydrothiazole phosphonic acids or esters inhibit corrosion well, but tend to decompose at high temperature conditions.

Another disadvantage of using phosphorus-based compounds as corrosion inhibitors is that phosphorus has been believed to impair the action of various catalysts used in crude oil processing, such as fixed bed hydrotreaters and hydrocracking units. Therefore, crude oil processing machines often face serious problems because, if corrosion itself is not suppressed, in some cases catalyst-damage amounts of iron as high as 10 to 20 ppm can accumulate in hydrocarbon fluids. Unfortunately, there are a number of commercially available non-phosphorus-based inhibitors, but they are generally known to be somewhat less effective than phosphorus-based compounds.

U.S. Patent 4,941,994 reports significant progress in phosphorus-based naphthenic acid induced corrosion inhibitors. The document states that corrosion of metals in hot acidic liquid hydrocarbons is inhibited by the presence of corrosion inhibiting amounts of dialkyl and / or trialkyl phosphites with any thiazolin. Another U.S. Pat.No. 5,863,415 discloses that certain types of thioin compounds are particularly useful for inhibiting corrosion in hot liquid hydrocarbons and at concentrations that add less catalyst-damaged phosphorus to the fluid than some previous phosphorus-based corrosion inhibitors. It is disclosed that it can. Such thiophosphorus compounds also provide the advantage that they can be prepared from relatively inexpensive starting materials.

In view of the above, it is desirable in the art to find additional methods or compositions for inhibiting or controlling naphthenic acid induced corrosion in crude oil that provide advantages over the prior art.

In one embodiment, the present invention provides a method for inhibiting naphthenic acid corrosion in a fluid comprising a corrosive amount of naphthenic acid, the method comprising adding a thioine compound and a hydrogen sulfide scavenging compound to the fluid or fluid supply device. Wherein the thioin compound and the hydrogen sulfide scavenging compound are in an amount effective to inhibit corrosion.

In another embodiment, the present invention is a compound useful for inhibiting naphthenic acid corrosion in a fluid comprising a corrosive amount of naphthenic acid comprising a mixture of a thioine compound and a hydrogen sulfide scavenging compound.

In one embodiment, the invention is a method of inhibiting naphthenic acid corrosion in a fluid comprising a corrosive amount of naphthenic acid, said method scavenging a thioin compound and hydrogen sulfide in an amount sufficient to affect corrosion inhibition in the fluid. Adding a compound to the fluid or fluid supply device. The fluid can be, for example, a hydrocarbon such as crude oil or a lighter fraction therefrom. Thioin compounds useful in the present invention include those described in US Pat. No. 5,863,415 to Zetlmeisl, which is incorporated herein by reference in its entirety. For example, thioine compounds useful in practicing the present invention include salts of thioine compounds, alkyl and aryl esters of thioine compounds, and isomers of thioine compounds. Any thioin compound that is effective in inhibiting naphthenic acid induced corrosion in a fluid can be used in the present invention.

Thioin compounds having the following general formula are useful in the present invention in one non-limiting embodiment:

식 1

Equation 1

Wherein R ¹ is R ³ (OCH ₂ CH ₂ ) _n- , or R ³ (OCH ₂ CH ₂ ) _n O-, R ² is the same as R ¹ or -XH, and each X is independently sulfur or oxygen , At least one X is sulfur, R ³ is an alkyl group of about 6 to about 18 carbon atoms, and n is an integer from 0 to about 12.

Hydrogen sulfide scavenging compounds useful in the present invention include those described in US Pat. No. 5,169,411 to Weers and US Pat. No. 6,663,841 to Salma et al., The contents of which are incorporated herein by reference in their entirety. Non-acidic imine compounds which are condensation products of amines or polyamines with aldehydes, dialdehydes or ketones are included in these compounds. For example, the compound includes compounds having the following general formula in a non-limiting embodiment:

, 식 2

, Expression 2

Wherein x is an integer from about 1 to about 10; R ¹ is

, 식 3

, Expression 3

, 식 4

, Expression 4

, 식 5

, Equation 5

Independently selected from the group consisting of 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; R ³ is hydrogen, alkyl having 1 to about 20 carbon atoms, alkenyl having 1 to about 20 carbon atoms, or aryl; n is an integer from 1 to 6; R ⁴ , R ⁵ and R ⁶ are alkyl containing from 1 to about 20 carbons and

식 6

Equation 6

Each independently selected from the group consisting of; R ⁷ is hydrogen or alkyl having 1 to about 20 carbon atoms and is the same as R ² provided that only one of R ⁴ , R ⁵ and R ⁶ can be:

; 식 6

; Equation 6

R ² is = CH ₂ , cyclohexyl,

, 식 7

, Equation 7

Independently selected from the group consisting of alkyl comprising 1 to about 20 carbon atoms and alkenyl containing 1 to about 20 carbon atoms. "S" in Equations 5 and 6 is not specified for that position or positions and indicates the presence of at least one sulfur atom in the ring.

It has been found that the inhibitors of the present invention are all effective and generate very low levels of hydrogen sulfide during storage and use. The amount of the thioin compound is, in certain non-limiting embodiments, preferably about 40 to about 70 weight percent of the total additive, including both the thioine compound and the hydrogen sulfide scavenging compound. In other embodiments, the hydrogen sulfide scavenging compound may be from 1 to 10 weight percent, preferably from about 4 to about 6 weight percent. The remainder of the additive may be an inert material which is compatible with the fluid, for example mineral oil. In another non-limiting embodiment, the thioin compound can represent about 90 to about 99 weight percent of the total additive, and in another non-limiting embodiment, about 94 to about 96 weight percent.

Additive combinations of thioin compounds and hydrogen sulfide scavenging compounds may be used in fluids containing corrosive naphthenic acid in any amount effective to inhibit corrosion affected by fluid / naphthenic acid. It may be relatively low, from about 100 ppm to about 5,000 ppm, although more or less amounts may be used if effective. In many preferred embodiments, it has been found that levels of about 500 ppm to 2,000 ppm are effective and in other preferred embodiments it may range from about 750 ppm to about 1250 ppm.

The following examples are provided to illustrate the present invention. The above examples are not intended to limit the scope of the present invention and should not be construed as such. Amounts are in parts by weight or weight percent unless otherwise indicated.

Example  One

The test of the present invention may be performed by first measuring the level.

The step includes adding 282 g of mineral oil to the reaction flask. Test cells are sparged with nitrogen while continuing to stir at a rate of 10-20 ml / min for 30 to 60 minutes. The heater is set at 288 ° C. and the test cells are sparged with 1 mol-percent H ₂ S in nitrogen for the remaining test. The test procedure was run in nitrogen using a C1018 carbon steel coupon specimen, with a total acid value of 10 mg KOH, a temperature of 288 ° C., a 24 hour run time and 1 mol-percent hydrogen sulfide. The "blank" is first tested without corrosion inhibitor to determine the amount of corrosion that occurs. Thirty minutes after the coupon specimen is inserted into the test cells, approximately 20 g of commercial naphthenic acid with a total acid value of 151 is injected. Then, the first test of the present invention is carried out using other coupon specimens and the same procedure, except that the corrosion inhibitor of the present invention is included. The corrosion inhibitor is a mixture of a thioine compound and a hydrogen sulfide scavenging compound at a volume of 1000 ppm, wherein the thioine compound is present at 55% by weight, the scavenging compound is present at 5% by weight and the remainder of the mixture is a mineral oil. . In all cases the coupon specimens are removed after 24 hours in the test cells for evaluation. The procedure for testing the present invention can also be performed with another coupon specimen in a second test.

In the first test and when compared to "blank", the level of protection provided by the present invention is measured at 94.2 percent. In the second test of the invention, the protection level is measured at 99.7 percent.

Comparative example  2

Example 1 is repeated substantially the same except that no hydrogen sulfide scavenger is used, but the same amount of thioyne compound is used. In the first test, the protection level is measured at 80.1 percent. In the second test, the protection level is measured at 89.2 percent.

Claims (17)

A method for inhibiting naphthenic acid corrosion in a fluid comprising a corrosive amount of naphthenic acid, the method comprising adding a thiophosphorus compound and a hydrogen sulfide scavenging compound to the fluid or fluid supply device. The phosphorus compound and the hydrogen sulfide scavenging compound are present in an amount capable of inhibiting corrosion. The method according to claim 1, Wherein said thioine compound and said hydrogen sulfide scavenging compound are added in a mixture. The method according to claim 1, The thioin compound has the general formula

Wherein R ¹ is R ³ (OCH ₂ CH ₂ ) _n −, or R ³ (OCH ₂ CH ₂ ) _n O—, R ² is equal to or R ¹ -XH, and each X is independently sulfur or oxygen However, at least one X is sulfur, R ³ is an alkyl group of 6 to 18 carbon atoms and n is an integer from 0 to 12. The method according to claim 1, Wherein said hydrogen sulfide scavenging compound has the general formula:

, Wherein x is an integer from 1 to about 10; R ¹ is

,

,

, Independently selected from the group consisting of cycloalkyl having 4 to 7 carbon atoms, phenyl, benzyl, alkyl having 1 to 20 carbon atoms and alkenyl having 1 to 20 carbon atoms; R ³ is hydrogen, alkyl having 1 to 20 carbon atoms, alkenyl having 1 to 20 carbon atoms, or aryl; n is an integer from 1 to 6; R ⁴ , R ⁵ and R ⁶ are alkyl containing 1 to 20 carbons and

Each independently selected from the group consisting of; R ⁷ is hydrogen or alkyl having 1 to 20 carbon atoms and is the same as R ² provided that only one of R ⁴ , R ⁵ and R ⁶ can be:

; R ² is = CH ₂ , cyclohexyl,

, Independently selected from the group consisting of alkyl comprising 1 to about 20 carbon atoms and alkenyl containing 1 to 20 carbon atoms; Where S represents the presence of at least one sulfur atom at any position in the ring. The method according to claim 1, Said fluid is crude oil or fractions thereof. The method according to claim 2, The hydrogen sulfide scavenging compound is present in the mixture in an amount of 1 to 10% by weight. The method according to claim 6, The hydrogen sulfide scavenging compound is present in the mixture in an amount of 4 to 6% by weight. The method according to claim 2, The thioine compound is present in the mixture in an amount of from 40 to 70% by weight. The method according to claim 2, Said mixture further comprising mineral oil. A composition useful for inhibiting naphthenic acid corrosion in a fluid form comprising a corrosive amount of naphthenic acid comprising a mixture comprising a thioin compound and a hydrogen sulfide scavenging compound. The method according to claim 10, Said fluid is crude oil or fractions. The method according to claim 10, The hydrogen sulfide scavenging compound is present in the mixture in an amount of 1 to 10% by weight. The method according to claim 12, The hydrogen sulfide scavenging compound is present in the mixture in an amount of 4 to 6% by weight. The method according to claim 10, The thioine compound is present in the mixture in an amount of from 40 to 70% by weight. The method according to claim 10, Said mixture further comprising mineral oil. The method according to claim 10, The thioin compound is a composition having the following general formula:

Wherein R ¹ is R ³ (OCH ₂ CH ₂ ) _n −, or R ³ (OCH ₂ CH ₂ ) _n O—, R ² is equal to or R ¹ -XH, and each X is independently sulfur or oxygen However, at least one X is sulfur, R ³ is an alkyl group of 6 to 18 carbon atoms and n is an integer from 0 to 12. The method according to claim 10, The hydrogen sulfide scavenging compound has a composition having the following general formula:

, Wherein x is an integer from 1 to about 10; R ¹ is

,

,

, Independently selected from the group consisting of cycloalkyl having 4 to 7 carbon atoms, phenyl, benzyl, alkyl having 1 to 20 carbon atoms and alkenyl having 1 to 20 carbon atoms; R ³ is hydrogen, alkyl having 1 to 20 carbon atoms, alkenyl having 1 to 20 carbon atoms, or aryl; n is an integer from 1 to 6; R ⁴ , R ⁵ and R ⁶ are alkyl containing 1 to 20 carbons and

Each independently selected from the group consisting of; R ⁷ is hydrogen or alkyl having 1 to 20 carbon atoms and is the same as R ² provided that only one of R ⁴ , R ⁵ and R ⁶ can be:

; R ² is = CH ₂ , cyclohexyl,

, Independently selected from the group consisting of alkyl comprising 1 to about 20 carbon atoms and alkenyl containing 1 to about 20 carbon atoms; Where S represents the presence of at least one sulfur atom at any position in the ring.