CA2066081A1 - Phosphonate-containing polymers used as scale and corrosion inhibitors - Google Patents

Abstract

ABSTRACT OF DISCLOSURE
A method of inhibiting scale and corrosion of metal surfaces in contact with scale forming and/or corrosive industrial process waters. The process comprises treating these waters with an acrylic acid polymer which contains from 0-95 mole percent of acrylamide groups and from 1-30 mole percent of amido(Cl-C6 alkyl)phosphonate groups from the group consisting of:
a. amidomethylphosphonate groups, b. alpha-hydroxy-beta-amidoethylphosphonate groups, c. alpha-hydroxy-beta-amidoisopropylphosphonate groups, and:
d. amidopropylphosphonate groups.
These polymers have a molecular weight range between 1,000-100,000.

Description

INTRODUCTION
The present invention relates to using acrylic acid polymers which contain amidoalkylphosphonate groups for preventing the formation of scale and corrosion on metal surfaces in contac~ with corrosive and/or scale forming industrial process waters.

BACKGROUND OF THE: IPJVENTION
The utilization of water which contains certain inorganic impurities, and the production and processing of crude oil-water mixtures containing such impurities, is plagued by the precipitat,ion of these impurities with subsequent scale formation. In the case of water which contains these contaminants the harm~ul effects of scale formation are generally confined to the reduction of the capacity or bore of receptacles and conduits employed to store and convey the contaminated water. In ~he case of conduits, the impedance of flow is an obvious consequence. However, a number of equally consequential problems are realized in specific utilizations of contaminated water. For example, scale formed upon the surfaces of storage vessels and conveying lines for process water may break loose and these large masses of deposit are entrained in and conveyed by the process water to damage and clog equipment through which the water is passed, e.g., tubes, valves, filters and screens. In addltion, these crystalline deposits may appear in, and detract from, the final product which is derived from the process, e.g., paper formed from an aqueous suspension of pulp. Furthermore, when the contaminated water i5 involved in a heat exchange process, as either the "hot" or "cold" medium, scale will be formed upon the heat exchange surfaces which are contacted by the water. Such scale formation forms an insulating or thenmal opacifying barrier which impairs heat trans~er e~iciency as well as impeding flow through the system.
While calcium sulfate and calcium carbonate are primary contributors to scale formation, other salts of alkaline-earth metals and the aluminum silicates are also offenders, e.g., magnesium carbonate, barium sulfate, the aluminum silicates provided by silts of the ben~onitic, illitic, kaolinitic, etc., types.
Many other industrial waters, while not being scale forming, tend to be corrosive. Such watars, when in contact with a variety of metal surfaces such as ferrous metals, aluminum, copper and its alloys, tend to corrode one or more of such me~als, or alloys. A variety of compounds have been suggested to alleviate these problems. Such materials are lew molecular weight polyacrylic acid polymers. Corrosive waters o~ thi~ type are usually acidic in pH and are commonly found in closed recirculating systems.
Numerous compounds have been added to these industrial waters in an at~empt to prevent or reduce scale and corrosion.

One such class of materials are the well known organophosphonates which are illustrated by the compounds hydroxyethylidene diphosphonic acid (HEDP) and phosphonobutane tr.icaxboxylic acid (PBTC). Another group of active scale and corrosion inhibitors are the monosodium phosphinicobis (succinic acids) which are described in U.S. 4,08~,678.
Prior Art U.S. 4,678,~40 teaches polymers of ~he type described in this invention and broadly suggests that they may be useful as dispersants and as scale inhibitors. In U.S. 4,675,359, it is suggested that polymers of the type used in this inventicn hav~
a variety of uses. It is broadly suggested that they would be usaful as water ~reating agen~s. U.S. 4,526,728 shows that co-polymers of acrylic acid or acrylamide with 2-(meth)acrylamide-2-methylpropanephosphonic acids are useful as scale inhibitors. This proper~y of these polymers is illustrated in Examples 4 and 6 of this patent.
Summary_of the Invention The present invention relates to preventing scale and corrosion of metal surfaces in contac~ with scale ~orming or corrosive industrial process waters by using as the inhibitor a small, y~t effective, amount of an acrylamide pol~mer which contains from 1 to 30 mole percent of an amido(Cl-C6)alkylphosphonate groups. These polymers also contain amounts of acrylic acid which make up the halance of the composition thereof.
THE INVENTION
The invention comprises a method of inhibiting scale and corrosion of metal surfaces in con~act with scale forming and/or corrosive industrial process waters which comprises treating such waters with at least one part per million of an acrylic acid polymer which contains from 0-95 mole percent of acrylamide groups and from 1-30 mole percent of amido(Cl-C6)alkylphosphonate groups from the group consisting of:
a. amidom thylphosphonate groups, b. alpha-hydroxy-beta-amidoethylphosphonate groups c. alpha-hydroxy-beta-amidoisopropylphosphonate groups, and;
d. amidopropylphosphonate groups with said polymer having a molecular weight range between 1-100,000.
In a preferred em~odlment of the invention the acrylamide poly~mer contains from 5-50 mole percent of acrylamide groups.
Th~ molecular weigh~ o~ the po:Lymers may be between 1,000-100,000. P-eferably i~ is within the range of 1,000-20,000 and most preferably within the range of 1,000-10,000.
The amount of polymers required to reduce scale and corrosion will vary depending upon the severity of the system in which they are employed, and whether the condition prevalent i5 scale and/or corrosion. Dosage~ range from between as little as one part per million up to as much as 400 ppm.
Typical dosages, however, are within the range of 3-20 ppm.
Routine experiment~tion can determine the exact amount of polymer that is necessary to achieve optimum results. These dosages relate to the dosages of the active polymer which are oftentimes supplied commercially in ~he form of aqueous solutions or as water-in-oil emuls1on.

The polymers used in the practice of the invention, are described in prior publications. Their method of preparation is described in U.S. 4,678,840 and U.S. 4,675,359. The disclosures of these patents are incorporated herein by reference.
In U.S. 4,678,840 there is shown a transamidation reaction whereby the amide groups of an acrylamide polymer are substituted by reacting them with an aminoalkylpho~phonate.
Another method of producing the pol~mers resides in the reaction of an amino(Cl-C6 alkyl)phosphonate directly with an acrylic acid polymer under conditions whereby the amino radical is amidated with the carboxylic acid groups of the acrylic acid polymer. ~his technique which has been used ~o amidate aminoalkylsulfonic acld is the subject of U.S. 4,604,431, the disclosure o which is incorporated harein by reference.
Yet another method of producing the pol~mers of the invention is to oxidi~e phosphinate polymers, e.g., polymers corresponding exactly to those used in the invention, to the corresponding phosphinate polymers. These polymers are readily oxidized using peroxides and other well known oxidizing agents used to oxidize the phosphinate groups to the phosphonate groups.
It is to be understood that in the practice of the invention the term "phosphonate groups" or the term "phosphona~e" is intended to include, both in the specification and in the claims, not only the water soluble salts of the phosphonic acid groups, e.g. the alkali metal such as sodium or potassium, but also the ammonium or amine salts. Also included is the free acid form of the phosphonic acid.
EVALUATION OF T~E INVENTION
A series of laboratory screening tests were undertaken to evaluate a number of phosphonate containing polymers.
Table 1 (Backbone Polymers) lists a number of acrylic acid, acrylamide and acrylamide-acrylic acid co-polymers that were modified with aminoalkylphosphonates. It should be noted that certain of these backbone polymers contain minor amounts of diluent monomers such as acrylonitrile (AN), methacrylic acid (~AA) and vinyl acetate (vAc); when used such diluent monomers may be present in amounts ranging between 1-15 mole percent. The amount used should not be such so as to diminish water solubility of ~he polymer. In Table 1 AA is acrylic acid and AAm is acrylamide.
Tables 2-5 shows several of the backbone polymers modified with various phosphonate groups evaluated as scale and corrosion inhibitors.

2 Q ~ ~ r~ ~ ~

Backbone Polymers NO COMPOSITION ~W ~ POLYMER
1 100~ AA 4500 32.5 2 100% AA 7100 35 3 100~ A~ 5000 35 4 50/50 AA-AAm 6000 35 50/50 AA-A~m 4750 35 6 50/50 AA-AAm 6450 35 7 50/50 AA-AAm 15700 32.5 50/30/20 AA/AAm/MAA 11200 35 9 4S/50/5 AA/~Am/AN 6500 35 45/50/5 AA/AAm/VAc 7050 35 11 100% A~ 5400 3~
12 50/50 AA/AAm 2500 35 2 ~ ~

T~3LE 2 POLYMERS MODIFIED WITH AMINOMETHANE PHOSPHONIC ACID

SAMPLE BACKBONEPRODUCT COMPOSITION
NUMBER POLYMER(PO3/CO2H)a %POLYMER

1 4/96 31.0 094 1 2.5/97.5 31.9 23 2 2.2/97.8 3~.2 34 2 2.1/97.9 32.4 107 3 2/98 34.1 7A 4 12/66 29.5 095 5 8/75 34.~3 24 6 3.1/61 34.6 6 5.3/47 33.8 6A 7 18/69 29.1 076 4 4.3/69 34.7 078 4 11.1/56 34.9 8 ~.3/53 34.3 37 8 5.5/53 33.2 27 9 3.7/58 34.8 42 9 4.9/56 33.6 26 ~ 10 3.8/63 34.9 04~ 10 4.7/60 33.6 a. mole percen~ ba~ed on~ total mer uni~5~ as de~ennined by colloid titration 2 ~

TA~LE 2 (CONTINUED) POLYMERS MODIFIED WITH ALPHA-HYDROXY-BETA-AMINOETHYLPHOSPHINIC
ACID AND THEN OXIDIZED

~ ( C -- C )--O-C-NH-CH2-C(OH)-P(O) (OH)(H or OH) H
S~MPLE 8ACK~ONE PHOSPHINATE CHARGE
NUMBER POLYMER (MOLE ~) ~POLYMER
027 11 10 33 . 7 031-A (Oxidized 027 ) 32 . 3 031-13 11 25 33 . O
033 (Oxldized 031~ 30.4 0~8 12 10 34 . 1 032 A (Oxidized 02~) 32.7 032 B 12 25 33.1 034 ( Oxidized 032 ) 30 . 5 POL~MERS MODIFIED WITH ALPHA-HYDROXY-BETA--AMINOISOPROPYLPXOSPHINIC ACID AND THEN OXIDIZED
__ _ '- (C -- C)--O=C-NH-CH2-C(OH)-P(O) (OH)(H or OH) % ~

SAMPLEBACKBONE PHOSP:HINATE CHARGE %
NIJMBERPOLYMhR ( MOLE ~ )POLYMER
039 11 10 33 . 9 035 (Oxidized 039) 32.6 045 11 25 33 . 4 036 (Oxidized 045 ) 30 . 8 040 12 10 34 . 3 037 (Oxidized 040) 32 . 9 046 12 25 33 . 5 038 (Oxidized 046) 30.9 POLYMEE~ MODI~IED WIT~ ALLYL AMINE , THEN NaH2 PO2, AI13N , AND THEN OXIDIZED
--( C -- C )--O-C-NH-CH2-CH2-CH2-P(O) (OH) (H or OH) SAMP~EBACKBONE AMINE CH~RGE %
NIJ~IBERPOLYMER _ (MOLE % ~ _POLYMER
014 11 10 ~1 . 9 027 (Oxidized 014) 21. 3 025 11 25 21 . 7 029 (Oxidized 025 ) 20 . 3 015 12 10 21 . 9 028 ( Oxidized 015 ) 21. 3 026 12 25 21 . 6 030 ( Oxidized 026 ) 20 . 2 ~ $ `~ 3 ~

Benchtop Screening Test for Calcium Carbonate Scale Inhibitlon of Several Aminoalkylphosphonic Acid Modified Polymers Water Chemistry / Conditions:
360 ppm Ca/200~ppm ~g/500 ppm ~C03 (as CaCO3) Temperature: 60C, Stir rate: 300 rpm Titrant: 0.10 Normal NaOH
Dosage: 5,10 and 15 ppm actives Standard Deviation of Saturation Ratio: +/- 6.6 Saturation ratio of blank: 3.0 Poly_~rs modified with aminomethanephosphonic acid Saturation Ratio Inhibitor 5 ppm 10 p~ 15 -l(b.b) 74.8 91.1 113.7-125.9131.9-140.5 97.1 113.7143.2 94 69.9 118.6136.5 2(b.b.) --- --- 142.1 23 --- --- 144.3 34 --- --- 145.9 3(b.b.) --- --- ~~~
107 97.1 116.8131.9 4~b.b.) 31.9 48.9 48.9 7A 97.1 119.9137.7 76 53.9 121.7112.3 78 66.9 112.3136.9 5(b.b.) 21.7 28.630.9 70.0 116.8131.9 6(b.b~ --- --- 35.1 24 --- --- 131.9 --- 128.9 7(b.b.) 42.1 47.548.9 6A 65.2 97.1110.6 8(b.b.) --- --- 127.4 --- --- 109.1 37 ~ -- 107.9 Inhibitor ~ _p~ 15 ppm -9(b.b) --- -- 30 9 27 ~~ 137.7 4~ 133.1 10(b.b) --- --- 35.1 26 --- --- 131.9 43 --- --- 143.2 Backbone Inhibitor 5 ppm ~_ee~15 ppm Oxidized Samples of alpha-hydroxy-beta-aminoe~hylphosphinic aci modified ~ymers:

11 031A 76. a 124.8 142.6 11 033 7~.~ 112.3 136.3 12 032A 24.6 71.8 93.9 12 034 4~.9 71.8 11~.6 Oxidized Samples of alpha~y~roxY-beta-aminoisoe~py~lphosphinic aci mo i ied polYmers:
11 035 65.2 122.9 137.7 11 036 57.9 106.0 124.~
12 037 34.0 82.3 g9.5 12 038 36.8 71.8 106.0 Oxidized Samples of ~oly~ers modified with allyl amine, then NaH2PO2, AIBN: *
11 027 62.3 121.8 130.9 11 029 34.0 46.4 30.9 12 028 39.1 39.1 30.g 12 030 16.1 30.9 22.

~/C/~/ (bb: polymer backbone)yQ
* - 2,2' azobis(2-met~apropanenitrile) catalyst ? ~

~enchtop Screening Test for Calcium Carbonate Scale Inhibition of Several ~minoalkylphosphonic Acid ~odified Poly~ers Stir and S~ttle Test Water_Chemistry / Conditions:
360 ppm Ca / 200 ppm Mg / 500 ~C03 (a5 CaC03 ) Temperature: 60OC, Stir Rate: 250 rpm Titrant: 0.10 ~ormal NaOH, pH: 9.0 for two hours Blank: 0.6 % inhibition, 1.3 ~ dispersancy Inhibitor 5 ppm ~ 15 ppm Aminomethane~hosphonic acid modified polymers % inhibition: 55.3% 65.9% 99.5%
% dispersancy: 54.5% 77.3% 99.3%
094 % inhibition: 46.4% 47.1~ 68.4%
% dispersancy: 50.1% 53.9% 82.5%
09S ~ inhibition: 44.8% 62.3% 100%
% dispersancy: 44.8% 76.7% 93.3~
076 % inhibition: 49.5% 66.8% 74.0%
~ dispersancy: 47.5% 79.4~ 80.0%
107 % inhibition: 45.4% 65.3% 74.4%
% dispersancy: 45.8% 69.6% 85.7%
078 % inhibition: 49.6% 72.4% 79.7%
% dispersancy: 49.4% 71.4~ 88.3 043 % inhibition: 44.8% 57.5% 75.0%
% dispersancy: 44.8% 59.4% 81.3~
Ox dized Sample of alpha-hydroxy-beta-aminoethylphosphinic acid mo i ie po ymer 033 % inhibition: 42.4% 46.3% 52.3%
% dispersancy: 35.6~ 46.7% 57.7%

$ :~

Electrochemical Screening Test for Mild Steel Corrosion Inhibition of Several Aminoalkylphosphonic Acid Modified PolYmers.
.
Water Chemistry / Conditions:
360 ppm Ca / 200 ppm Mg / 440 HC03 (as CaC03) Temperature: 120 F, pH: uncontrolled, air agitation, Pre-polished Mild Steel specimen, 30 minute delay time, 500 rpm Standard deviation of corrosion rate: t-/- 0.345 mpy Inhibitor_Combination:
(A). 20 ppm inhibitor, 0 ppm PBTCl, 15 ppm of a sulfonated solution polymer (B). 10 ppm inhibitor, 10 ppm PBTC, 15 ppm of a sulfonated solution polymer (C). 10 ppm inhibitor, 10 ppm PBTC, 15 ppm substituted acrylamide, acrylate polymer Corrosion Rate (mpy) Inhibitor (A) (B) (C) Blank 8.63 .975 1.92 Aminomethanephosphonic acid modified polymers:
094 .650 2.09 2.07 095 1.03 1.57 1.05 023 1.44 .81~ xxx 034 1.85 1.28 xxx 024 1.16 1.45 xx~
035 4.29 .997 xxx 02~ 1.52 .828 xxx 037 1.18 5.75 x~x 026 5.16 2.94 xxx ~43 .978 4.22 1.38 Phosphonobutane tricarboxylic acid T~BLE 5 CONTINUED:

027 2.11 1.24 xxx 042 1.47 4.46 xxx Corrosion Rate (mpy) Inhi (A) (B) (C) Oxidized Samples of alpha-hydroxy-beta-aminoethyl~hosphinic acid modified polymers:
031 xxx .715 xxx 032 xx~ .453 xxx Oxidized Samples of alpha-h~droxy-beta-aminoisopropylphosphinic acid modifie polymers:
035 xxx 2.05 xxx 037 xxx .67g xxx Oxidized Sam~le of ~olym~r modified with allyl amine, then NaH2PO2 AIBN*:
_ !
027 xx~ 1.59 xxx 2 ~

* AI~N: 2,2' azobis(2-methylpropananitrile) catalyst 2 ~

The test methods used to generate the above data are set forth below.
Saturation Ratio Test A test solution was prepared by adding calcium, magnesium, inhibitor and bicarbonate to deionized water. Initial concentrations of the salts should be: 360 ppm Ca+2, 200 ppm Mg+2, 500 ppm HC03-. ~as CaCO3) and 5, 10, or 15 ppm of inhibitor as actives/solids. The temperature was maintained at 140F (60OC), the solution was stirred at all times, and the pH
was continuously monitored. The solution was titrated with dilute NaOH at a constant rate. With the addition of NaOH, the p~ of the test solution slowly increased, then decreased slightly, and increased again. The maximum pH prior to the slight decrease at supersaturation was the breaXpoint pH. A
mineral solubiLity computer program was then used to calculate the calcium carbonate supersaturatic)n ratio based on test conditions at the breakpoint pH. T~lis supersaturation ratio is related to the calcium carbonate inhibi~ion performance. The test procedure was repeated for difi-`erent inhibitor solutions and dosages. All precipitated calcium carbona~e must be removed from the test apparatus with dilute HCl prior to the next test run.
Benchtop Screening_Test or Calcium Carbonate Inhibition Calcium, magnesium, inhibitor and bicarbonate were added to deionized water to prepare a test solution with 360 ppm la Ca+2, 200 ppm Mg+2, 500 ppm HC03- ~as CaC03) and 5, 10 or lS
ppm inhibitor as actives/solids. An initial sample of the test water was collected for calcium analysis by atomic absorption.
The test temperature was malntained at 140F (600C). Using dilute NaOH, the p~ of the solution was slowly increased to 9.0, and maintained during ~he two hour dura~ion of the test.
At the conclusion of the test, a small sample of the solution was filtered (0.45 um) and the calcium concentration was / determin~ by atomic absorption. The remainder of the 6l~/~J unfiltered sample was allowed to settle, undisturbed for 24 hours, at room temperature. Water was th~n collected from the top of the flask after 24 hours and analyzed for calcium. The % inhibition and % dispersancy are calculated in the following manner:

% inhibition = ppm Ca+ 2 filtered ppm Ca~ 2 initial dispe~sancy = ppm Ca+2 unfiltered, settled ppm Ca+ 2 initial Electrochemical Test Both the Ta~el plo~s and linear polarization resistance te~ts ware conducted in the same water chemistry and conditions. The test solution ~or the electrochemical corrosion cell was prepared by adding calcium, magnesium, 2 ~ n3 ~

various inhibitors and bicarbonate to deionized water to obtain 360 ppm Ca+2, Z00 ppm Mg+2, 440 ppm HC03- (as CaC03).
Temperature was maintained at 120F and the solution was aerated throughout the test period. pH wa~ uncontrolled. A
standard three elec~rode cell was assembled for the polarization studies. Pre-polished mild steel specimens were used as the rotating working electrode, at a speed of 500 rpm.
All potential measurements were made against a saturated calomel reference electrode. Two graphite rods were used as the counter electrode. Polarization resistance measurements were conducted within +~- 20 mV of the corrosion potential at a scan rate of 0.1 mV/sec. Tafel plots were performed by polarizins the mild steel specimen at 250 mV cathodically and anodically from the corrosion potential.

Claims (6)

1. A method of inhibiting scale and corrosion of metal surfaces in contact with scale forming and/or corrosive industrial process waters which comprises treating such waters with at least one part per million of an acrylic acid which contains from 0-95 mole percent of acrylamide groups and from 1-30 mole percent of amido(C1-C6 alkyl)phosphonate groups from the group consisting of:
a) Amidomethylphosphonate groups, b) Alpha-hydroxy-beta-amidoethylphosphonate groups, c) Alpha-hydroxy-beta-amidoisopropylphosphonate groups, and, d) Amidopropylphosphonate groups with said polymer having a molecular weight range between 1,000-100,000.

2. The method of Claim 1 where the acrylamide polymer contains from 5-50 mole percent of acrylamide groups, and the molecular weight of the polymer is within the range of 1,000 20,000.

3. The method of Claim 2 where the amido(C1-C6 alkyl)phosphonate group is amidomethylphosphonate.

4. The method of Claim 2 where the amido(C1-C6 alkyl)phosphonate group is alpha-hydroxy-beta-amidoethylphosphonate.

5. The method of Claim 2 where the amido(Cl-C6 alkyl)phosphonate group is alpha-hydroxy-beta-amidoisopropylphosphonate.

6. The method of Claim 2 where the amido(C1-C6 alkyl)phosphonate group is amidopropylphosphonate.