EP0361592A2

EP0361592A2 - Method of inhibiting sulfide attack

Info

Publication number: EP0361592A2
Application number: EP89202360A
Authority: EP
Inventors: Bennet P. Boffardi
Original assignee: Calgon Corp
Current assignee: Calgon Corp
Priority date: 1988-09-26
Filing date: 1989-09-19
Publication date: 1990-04-04
Also published as: JPH02133587A; EP0361592A3; AU626322B2; NZ230686A; AU4175389A

Abstract

A method of inhibiting sulfide attack on carbon steel in contact with sulfide-containing waters using acrylic acid/acrylamido methylpropyl sulfonic acid-type polymers.

Description

BACKGROUND OF THE INVENTION

U.S. Patents 3,928,196 and 4,552,665 disclose the use of 2-acrylamido-2-methylpropylsulfonic acid/acrylic acid copolymers in water treatment applications as scale inhibitors and metal ion stabilizers.
U.S. Patent 4,526,728 and published EPO application 89,654 disclose the use of 2-acrylamido-2-methylpropylphosphonic acid/acrylic acid or acrylamide copolymers as scale inhibitors.
U.S. Patent 4,209,398 discloses the use of acrylic acid/2-hydroxy alkyl methacrylate-type polymers as scale and corrosion inhibitors.
U.S. Patent 4,650,591 discloses the use of acrylic acid/acrylamido methylpropyl sulfonic acid/acrylamido methylpropyl phosphonic acid-type polymers as scale and corrosion inhibitors and U.S. Patent 4,618,448 discloses the use of acrylic acid/acrylamido methylpropyl sulfonic acid/polyalkylene oxide-type polymers as scale and corrosion inhibitors.
U.S. Patent 4,640,793 discloses synergistic compositions for use as scale or corrosion inhibitors which contain acrylic acid/acrylamido methylpropyl sulfonic acid-type polymers.
U.S. Patent 4,762,626 discloses the use of hydroxyethylacrylate/acrylate copolymers to inhibit zinc sulfide scaling in oil well operations.
None of these references, however, disclose the use of the instant polymers to inhibit sulfide attack on carbon steel.
This invention relates to the inhibition of sulfide attack on metallic surfaces in contact with aqueous systems.
More particularly, this invention relates to the use of specified low molecular weight polymers to inhibit sulfide attack on metallic surfaces in contact with aqueous systems containing sulfides.
Sulfide corrosion of carbon steel is a serious problem in any water system containing sulfides. For example, a sulfide leak in a hydrocarbon processing operation can cause severe carbon steel corrosion. The inventor has discovered that certain water soluble polymers inhibit sulfide attack on carbon steel in such systems.

DESCRIPTION OF THE INVENTION

This invention is directed to a method of inhibiting sulfide attack on carbon steel which is in contact with sulfide-containing water comprising adding to said water an effective amount of a water soluble polymer selected from the group consisting of:

1. polymers having a weight average molecular weight of less than about 25,000, as determined by low angle, light scattering, comprising:
- a) about 40-90%, by weight, acrylic acid or methacrylic acid; and
- b) 10-60%, by weight, 2-acrylamido-2-methylpropyl sulfonic acid or 2-methacrylamido-2-methylpropyl sulfonic acid, and salts of such polymers;
2. polymers having a weight average molecular weight of less than about 25,000, as determined by low angle light scattering, comprising:
- a) about 35-90%, by weight, of an unsaturated carboxylic compound selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid, their salts and mixtures thereof;
- b) about 5-40%, by weight, of an unsaturated sulfonic compound selected from the group consisting of 2-acrylamido-2-methylpropyl- sulfonic acid, 2-methacrylamido-2-methylpropyl sulfonic acid, methallyl sulfonic acid, allyl sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid, their salts and mixtures thereof; and
- c) about 5-40%, by weight, of a monomer selected from the group consisting of unsaturated polyalkylene oxide compounds, 2-acrylamido-2-methylpropylphosphonic acid, acrylamide and C₁₄ alkyl acrylamides;
3. polymers having a weight average molecular weight of less than about 25,000, as determined by low angle light scattering, comprising:
- a) about 25-75%, by weight, of acrylic acid, methacrylic acid, maleic acid or itaconic acid, their salts and mixtures thereof; and
- b) about 25-75%, by weight, of a hydroxy C₁₋₄ alkyl acrylate.

For class 1, the preferred polymers contain about 50-70% of (a) and about 30-50% of (b), by weight. The most preferred polymers comprise acrylic acid and 2-acrylamide methylpropyl sulfonic acid, and have a molecular weight of from about 500 to about 15,000.
For class 2, the preferred polymers are prepared from 50-70%, by weight, of (a), 10-40%, by weight of (b) and 10-30%, by weight of (c), and have a molecular weight of from about 500 - 15,000. For (a) the preferred monomers are acrylic acid and methacrylic acid. For (b), the preferred monomers are 2-acrylamido-2-methylpropyl sulfonic acid and 2-methacrylamido-2-methyl-propyl sulfonic acid. For (c), the preferred monomers are polyalkylene oxides selected from the group consisting of allyl polyethylene glycol, methallyl polyethylene glycol, polyethylene glycol acrylate, polyethylene glycol methacrylate, methoxy allyl polyethylene oxide, alkoxyallyl polyethylene oxide and the polypropylene equivalents thereof. Also, mixtures of polyethers formed from polyethylene oxide with other polyalkylene oxides, such as propylene or butylene oxide may be used. The polyether chain may be capped with an alkyl aralkyl sulfonate or phosponate group metal or ion, or uncapped.
Also preferred is t-butyl acrylamide. The most preferred monomers are allyl PEGS defined by the formula CH₂=CH-CH₂(OCH₂CH₂)_n OH, where n is 5-10, and methoxy allyl PEGS defined by the formula CH₂=CH-CH₂(OCH₂CH₂)_nOCH₃, where n is 5-10.
For class 3, the preferred polymers contain 50-70%, by weight, acrylic acid or methacrylic acid as (a) and 30-50%, by weight, and 2-hydroxypropyl acrylate as (b). These preferred polymers have a molecular weight of from about 500 to about 15,000.
The polymers of class 1 are further defined in U.S. Patent 4,640,793, the polymers of class 2 are further defined in U.S. Patent 4,618,448 and the polymers of class 3 are further defined in U.S. Patent 4,209,398. These patents are hereby incorporated into this specification by reference.
The inventor has surprisingly found the above defined polymers to be effective sulfide corrosion inhibitors. As used herein, sulfides include any compounds of the formula M₂S or R₂S, wherein M is a monovalent metal and R is a monovalent organic radical.
An effective amount of at least one of the above polymers is required. As used herein, the term "effective amount" refers to that amount of polymer which effectively inhibits sulfide attack on carbon steel in the aqueous system being treated. The inventor has found that the effective amount of a polymer of this invention varies depending upon the concentration of sulfide present in the system being treated and upon system parameters such as temperature and pH. However, the required dosage generally ranges from about 0.1 to about 100 ppm, preferably from about 1 to about 20 ppm, based on active polymer and the total amount of water in the system being treated.
The instant polymers may be prepared by mixing the designated monomers in the presence of a free radical initiator. Any free radical initiator may be used. Examples include peroxides, azo initiators and redox systems. The polymerization may also be initiated photochemically. The preferred catalysts are sodium persulfate or a mixture of ammonium persulfate and any azo-type initiator, such as 2,2′-azobis-(2,4-dimethyl-4-methoxyvaleronitrile). The polymerization may be conducted by any of a variety of procedures. For example, solution, suspension or bulk emulsion polymerization techniques may be used.
The reaction temperature is generally not critical. Reactions will generally occur between 10 and 100^oC, preferably 40 to 60^oC. It is generally impractical to run the reaction below room temperature because it proceeds too slowly. Above a temperature of 60°C, the molecular weight of the polymer tends to decrease. The reaction, depending on the temperature, generally takes from 1 to 12 hours. Measuring for residual monomer will verify when the reaction is complete.
The pH of the reaction mixture is not critical. The pH is generally in the range of 3.5 to 9.0.
The percent solids in the reaction mixture is not critical. The preferred range is 1 to 50%, by weight, solids.
While the polymers of the instant invention have been found to be effective inhibitors of sulfide attack, they may be used in combination with other scale inhibitors (such as phosphonates) or with other corrosion inhibitors (such as zinc salts or triazoles) known in the art.
The instant polymers can be used as water treatment additives for any industrial water-containing system wherein a sulfide might contact carbon steel, such as gas scrubber systems or any hydrocarbon processing systems which contain sulfides. They can be fed alone or as part of a treatment dosage which includes, but is not limited to, biocides, scale inhibitors, dispersants, defoamers and/or other corrosion inhibitors.

EXAMPLES

The following examples demonstrate the effectiveness of the instant polymers in inhibiting sulfide attack on carbon steel. They are not, however, intended to limit the scope of the invention in any way. In these examples,
AA/AMPSA is a 60/40 w/w polymer of acrylic acid and 2-acrylamido-2-methylpropyl sulfonic acid having a molecular weight of about 8200.
AA/AMPSA/MAPEG is a 60/20/20 w/w/w polymer of acrylic acid, 2-acrylamido-2-methylpropyl sulfonic acid and methoxyallyl PEG wherein n=5, having a molecular weight of about 5,000-10,000.
AA/HPA is a copolymer of acrylic acid and 2-hydroxypropyl acrylate available from National Starch Corporation as Natrol 42.
AA/TBA/AMPSA is a 65/13/22 w/w/w polymer of acrylic acid, t-butyl acrylamide and AMPSA, commercially available from Rohm and Haas as WTP-1.

EXAMPLES 1-4

These examples demonstrate the efficacy of various polymers in controlling sulfide attack on carbon steel. The tests were run using 5X LNVA water at pH 7 and 65^oC. Banox (0.1%) pretreated steel probes were used to monitor corrosion rates. The composition of 5X LNVA water is shown below:

Test Solution (5X LNVA water)

Species Composition (mg/L)

Calcium 45

Magnesium 14

Chloride 170

Sulfate (SO₄) 100

Silica (SiO₂) 50

Bicarbonate 47 for pH 7

165 for pH 8
Corrosion tests were performed in 8 liter corrosion test cells containing the test solution. The solution was held at 65^oC via a Haake constant temperature immersion circulator. The pH of the solution was controlled at 7 with a Kruger & Eckels model 440 pH controller.
The corrosion rates were monitored using a Petrolite automatic corrosion rate meter, model 1010.
Each test solution contained 3 mg/l PO₄, 15 mg/l polyphosphate, 3 mg/l phosphate ester, and 2 mg/L sodium tolyltriazole. The carbon steel probes were preconditioned by soaking in 1000 mg/l of a calcium/zinc/polyphosphate solution (6:1:26 wt%) overnight (0.1% Banox).
The probes were placed in the test solution containing the phosphorus inhibitor and sodium tolyltriazole. Corrosion rates were monitored until steady-state was achieved, usually overnight.
The steady-state corrosion rate was 1 mpy. The addition of 5 mg/l sulfide (S²⁻) rapidly increased corrosion to 16 mpy and it remained at that rate until the test was terminated 4 hours later.

Four polymers were then tested to determine the effect on suppressing sulfide attack. The data is shown in Table 1.

TABLE I

Sulfide Attack on Carbon Steel
LNVA Water, 65^oC, pH 7

Example No.	System (Active)	Steady State Corrosion Rate (mpy)	5 mg/L Sulfide Added Peak Corrosion Rate (mpy)	Degraded Corrosion Rate (mpy) After 1.5 Hours
1	-	16	16	-
2	6 mg/L AA/AMPSA	0.8	5	1
3	6 mg/L AA/HPA	0.4	3	1.5
4	6 mg/L AA/AMPSA/MAPEG	0.8	5	0.8-1.0
5	6 mg/L AA/TBA/AMPSA	0.8	2	1.2

All the above copolymers behaved similarly in suppressing steel corrosion in the presence of sulfide.

Claims

1. A method of inhibiting sulfide attack on carbon steel in contact with sulfide-containing water comprising adding to said water an effective amount of a water soluble polymer selected from the group consisting of:

1. polymers having a weight average molecular weight of less than about 25,000, as determined by low angle light scattering, comprising:
a) about 40-90%, by weight, acrylic acid or methacrylic acid; and
b) about 10-60%, by weight, 2-acrylamido-2-methylpropyl sulfonic acid or 2-methacrylamide-2-methylpropyl sulfonic acid, and salts of such polymers;

2. polymers having a weight average molecular weight of less than about 25,000, as determined by low angle light scattering, comprising:
a) about 35-90%, by weight, of an unsaturated carboxylic compound selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid, their salts and mixtures thereof;
b) about 5-40%, by weight, of an unsaturated sulfonic compound selected from the group consisting of 2-acrylamido-2-methylpropyl-sulfonic acid, 2-methacrylamido-2- methylpropylsulfonic acid, methallyl sulfonic acid, allyl sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid, their salts and mixtures thereof; and
c) about 5-40%, by weight, of a monomer selected from the group consisting of unsaturated polyalkylene oxide compounds, 2-acrylamido-2-methylpropyl phosphonic acid, acrylamide and C₁₋₄ alkyl acrylamides; and

3. polymers having a weight average molecular weight of less than about 25,000, as determined by low angle light scattering, comprising:
a) about 25-75%, by weight, of acrylic acid, methacrylic acid, maleic acid or itaconic acid, their salts and mixtures thereof; and
b) about 25-75%, by weight, of a hydroxy C₁₋₄ alkyl acrylate.

2. The method of Claim 1, wherein about 0.1 to about 100 ppm of said polymer is added to said sulfide-containing water, based on the total amount of the water being treated.

3. The method of Claim 1, wherein polymer 1 is used and said polymer 1 is prepared from acrylic acid, and 2-acrylamido-2-methylpropyl sulfonic acid.

4. The method of Claim 2, wherein polymer 1 is used and said polymer 1 is prepared from acrylic acid and 2-acrylamido-2-methylpropyl sulfonic acid.

5. The method of Claim 3, wherein said polymer 1 is prepared from 50% to 70%, by weight, acrylic acid and 30% to 50%, by weight, 2-acrylamido-2-methylpropyl sulfonic acid.

6. The method of Claim 4, wherein said polymer 1 is prepared from 50% to 70%, by weight, acrylic acid and 30% to 50%, by weight, 2-acrylamido-2-methylpropyl sulfonic acid.