CA2015939A1 - Method for controlling silica/silicate deposition in aqueous systems using phosphonates and carboxylic/sulfonic polymers - Google Patents

Abstract

TITLE OF THE INVENTION
"METHOD FOR CONTROLLING SILICA/
SILICATE DEPOSITION IN AQUEOUS SYSTEMS
USING PHOSPHONATES AND CARBOXYLIC/SULFONIC POLYMERS"
ABSTRACT OF THE INVENTION

This invention is directed to a method for controlling the formation of silica/silicate deposits in aqueous systems by adding an effective amount, preferably at least 0.1 ppm, of a designated phosphonate and, optionally, a carboxylic/sulfonic polymer or salt thereof to the aqueous system being treated. Borate or molybdate ion sources may also be added.

Description

C~1456 TITLE F TH~ INVENTION
"METHOD FOR CONTROLLIMG SILICA/
SILICATE DEPOSITION IN AQUEOVS SYSTEMS
USING PHOSPHONATES AND CARBOXYLIC/SULFONIC POLYMERSn BACKGROUND OF THE INVENTION
U~S. Pat~ No. 3,~28~196 discloses th~ use of copolymers of 2 acrylamido-2-methylpropylsulfonic acid and acrylic acid as scale inhibitors.

U.SO Pat. No. 4,640~793 discloses the use of admixtures containing carboxylic acid/sulfonic acid polymers and phosphonates as scale and corrosion inhibitors.

U.S. Pat. NoO 4,618,448 discloses th use of polymers comprising an unsaturated carboxylic acid, an un~aturated sulfonic acid and an unsa~urated polyalkylene oxi~e as scale inhlbi~ors.

Japanese No. 57-084794 discloses the use of copolymers of acrylic acid and allyl polyethylene glycol as scale inhibitorsO

European patent applica~ion 84301450.7 discloses carboxylic acid/sulfonic acid copolymers in combination with organic phosphonates as scale inhibitors.

U D S ~ Patent 4,510,059 discloses the use of carboxylic funtional polyampholytes to reduce silica deposits in aqueous systems.

U.S. Patent ~,532tO47 discloses a method of inhibiting amorphous silica scale formation using polypolar organic compounds and borate ion sourcesO

U.S. Patent 4,584,104 discloses a method of inhibiting amorphous silica scale fo~mation usi~g a source of orthoborate ions.

Silica/silicate deposition in aqueous systems, for example boilers, cooling towers and sys~ems containiny hypersaline geothermal brines, is a continuing problemO Traditionally, depositic~n has been controlled by softening the makeup water to the system being treated, by blowdown, or by both. If deposition ocCurs~ mechanical removal or washing with ammonium fluoride or hydrofluoric acid is generally the method of control. Obviously, mechanical or chemical cleaning causes down time and increased energy and labor costs~

p~ affects the ionization of silanol groups and, therefore, affects the polymerization rate. Silica first forms, then three dimensional networks form.

~t,~ rf~3 Eventually, colloidal particles grow through condensation. At pH 7, nuclei formation and particle growth is very rapid. The pH of cooling ~atPr is generally 6.0 to 8.5 and the water temperature is generally about 30 to 70C~ The pH of geothermal brines is generally 4.0 to 6.0 and the brine temperature is generally about 100 to 210C.

It is known to use cationic polymers or cationic surfactants as silica scale inhibitors in hypersaline geothermal brines (Harrar. J.E. et al, "Final Report on Tests of Proprietary Chemical Additives as Anti-scalants for Hypersaline Geothermal Brine", January 1980 d Lawrence Livermore Laboratory, Harrar, J.E, et al , "On Line Tests of Organic Additiv~s for the Inhibition of the Precipitation of Silica from Hypersaline Geothermal Brine IV, Final tests of Candidate Additives", February 1980. Lawrence Livermore Laboratories; and ~arrar, J~E. et al, "Studies o~ Scale Formation and Scale Inhibitors at the Salton Sea Geothermal Field"~ Corrosion/80. Paper No. 225, International Corrosion Forum, devoted exclusively to the Protection and Performance of Materials, Mar. 3-7, 1980. Chicago, IL).

The inventors have discovered a method for controlling the deposition of silica and silicates in an aqueous sy~tem using a phosphonate selected from the group consisting of hexamethylene diamine tetra(methylene phosphonic acid)~ diethylene triamine penta (methylenephosphonic acid), ~lts of ~heqe compounds and combinations thereof, alone or optionally in combination with a water soluble polymer prepared ~rom at least one carboxylic acid moiety, at least one sulfonic acid moiety and~ optionally, at lea~t one polyalkylene oxide moiety. While the de3i~nated phosphonates alone are effective inhibitors, the de~ignated polymers enhance performance. The instant pho~phonates; when added to waters containing silica and hardness at a pH of about 9.0, prevent the formation of silicates and their deposition. The instant method has been shown to effectively maintain up to 300 mg/L SiO2 and greater than 200 mg/L hardness without substa~tial deposition on heat exchange-r surfaces~

DE:TAILED DESCRIPTION OF ~HE INVE NTION

The instant invention is directed to a method for controlling silica/silicate deposition in a~ aqueous system comprising adding an effective amount of A) a water soluble phosphonate selected from the group consisting of hexamethylenediamine tetra~methylene phosphonic acid), diethylene triamine penta (methylene phosphonic acid), salts of these compounds and combinations thereof; and optionally, B; a water soluble polymer having an intrinsic viscosity of about O.OS to 2.5 dl/g to the system being treated, wherein polymer B) is prepared from:

(a) 35 to 95%, by weight, of an unsaturated carboxylic acid, or salt thereof;

(b) 5 to 65%, by weight, of an unsaturated sulfonic acid, or salt thereof; and, (c) 0 to 40~, by weightl o~ an unsaturated polyalkylene oxide compound.

- 5 - C-1~56 Low molecular weight polymers of acr~lic acid and/or methacrylic acid can also be used as B)o The preferred polymers of this type have molecular weights less than about 20,000.

I B~ is used, the ratio o A):~), by wei~ht, should range from about 1:10 to about 10:1, preferably from about 1:3 to about 3O1~

Additionally/ if B) is used, a molybdate ion or a borate ion source may be added. Molybdate ions are pre~erred, as molybdate-containing compositions unexpectedly solubilize species such as calcium ions~ .
magnesium ions and SiO2. Any source of molybdate or borate ions can be used. The preferred molybdate source is ammonium molybdate, and the preferred borate sources are described in U.S. Patents 4,504,104 and 4,532,047, which are hereby incorporated into this specifica~ion by referenceO If a molybdate or borate is used as component C), the weight ratio of components A) and C) should range from about 1:5 to about 5:1. The preferred compositions contain A:B:C
weight ratios of about 1:1:2.

An effective amount of the phosphonate should be added to the aqueous system being treated. As used herein, the term "effec~iv~ amount'l is ~hat amount necessary to control silica/silicate deposition in the system being treated. Generally, the effectiYe amount will range from about 0.1 to about 200 ppm, on an active basis, based on the total weight of ~he aqueous system being treated, preferably from about 1 to about 200 ppm.

~ ~ ~J~
- ~ - C 1~56 A~ used herein, the kerm "controlling silica/silicate deposition" is meant to include inhibition of silica polymerization, threshold precipitation inhibition, stabilization, dispersion, solubili2ationt and/or particle size reduction of silica, silicates, especially calcium and magnesium silicates, and silicon ions. Clearly, the instant additives are threshold silicate precipitation inhibitors, but they also stabilize, disperse and solubilize silica and silicates. ~hus~ ~he inven~ors have discovered that the designated phosphonates, alon0 or in combination with the designated polymers and, optionally, a molybdate or borate source~
inhibit, minimize or prevent silica deposition under severe operating conditions, and intend that the in~tant specifica~ion describe this discovery, without attempting to describe the specific mechanism by which silica/silicate deposition is prevented or inhibited.

The term "aqueous system", a~, used herein, is meant to include any type of syst:em containing water, including, but not limited to, cooling water systems, boiler water systems, desalinations systems, gas scrubber water systems, blast furnace water systems, reverse osmosis sys~ems, evapora~:or systems, paper m~nufacturing systems, mining systems and the like.

If a polymer is used with the instant phosphonates, any unsaturated water soluble carboxylic acid or salt may be used as component (a) to prepare the polymer. Examples include, but are not limited to, acrylic acid~ methacrylic acidi ~-halo acrylic acid, maleic acid, itaconic acid, vinyl acetic acid, 7 - C~ 6 allyl acetic acid, fumaric acid~ ~-carboxyethyl acrylate, their ~alts and admixtures thereof. The preferred carboxylic acids are acrylic acid and methacrylic acid and their salts. The most preferred carboxylic acid is acrylic acid.

Any water--soluble unsaturated sulfonic acid or salt ~hereof may be used as moiety (b). Examples include, but are not limited to, 2-acrylamido-2-methylpropyls~lfonlc acid, 2-methacrylamido-2 methylpropylsulfonic acid, styrene sulfonic acid, vinyl sulfonlc acid, sulfo alkyl acrylate or methacrylate, allyl sulfonic acid, methallyl sulfonic acid, 3-methacrylamido-2-hydroxy propyl sulfonic acid, their salts and mixtures thereo~. The preferred sulfonic compounds are 2~acrylamido-2-methylpropyLsulfonic acid, 2-methacrylamido-2-methylpropylsulfonic acid and their salts. The most pre~erred sulfonic compound is 2-acrylamido-2-methylpropyl sulfonic acid.

If moiety (c) is present~ any water-soluble unsaturated polyalkylene oxide compound may be used.
Examples i~clude, but are not limited to, allyl polyalkylene glycols, methallyl polyalkylene glycolc, polyalkylene glycol acrylates, polyalkylene glycol methacrylates, and methoxy allyl polyalkylene glycols. The preferred unsaturated polyalkylene oxide compounds are unsaturated polyethylene compound~ and unsaturated polypropylene equivalents thereof, and their ether derivatives. More preferably, unsaturated polyethylene compounds are u~ed. Also, mixtures of polyethers formed from unsaturated polyethyelene oxide wlth other polyalkylene oxides, such as propylene or butylene oxide, may be used. The unsaturated polyether chain may be capped with an alkyl, aralkyl, sulfonate or phosphonate group metal or ion, or uncapped~

The preferred unsaturated polyalkylene oxide compounds for use as moiety (c) are selected from the group consisting of allyl polyethylene glycols of the formula CH2 = CH CH~ ~OCH2 CH2)n OH or CH2 = C~ - CH2 (OCH2 CH2)n OCH3, wherein n is 5-10, and polyethylene glycol acrylates or methacrylates of the ~ormula C~3 CH2 = C _ (O~H2CH2)XOH

where R and Rl, which may be the same or different~
are selected from the group consisting of H and lower alkyls, preferably CH3, and wherein x is 1-20O The most preferred moieties are polyethylene glycol methacrylates of the formula c~3 CH2 = C - C (OC~2CH2~ xO~
wherein x is 1 to 10. o Mixtures of the various monomers may be used, and nonionic monomer~ such as acrylamide, methacrylamide and acrylonitrile may also be present in the polymers. Polym~rs prepared using acrylic acid; alone or in combination with methacrylic acid, may also be used. Such polymers should have molecular weights less than 20,000.

The preferred polymers ~or use with the instant phosphonates are water soluble polymers having an intrinsic viscosity of about 0.05 to 2,5 dl/g, prepared from:

~ 9 - C-145 la) 35 to 95%, by wei9ht, cf an unsaturated carboxylic compound selected from the group consisting of acrylic acid, methacrylic acid, their salts and mixtures thereof;

(b) 5 to 65%, by weight, of an unsaturated sulfonic compound selected from the group consisting of 2-acryl~mido-2-methylpropyl sulfonic acid, 2-methacrylamido 2-methylpropylsul~onic acid, their salts ~nd mixtures thereof, and (c) 0-40~, by weight, of a compound selected ~rom the group consisting of CH2 ~ CH CH2 (OCH2 CH2)n OH, CH2 = CH CH2 (OCH2 CH2)n OCH3, wherein n is 5-10, C~3 CH~ - CH - C (OCH2CH2)~ ORl a~d CH2 = C - C
1 .
(OCH2CH2)X OR , whercin x is 1-20 and R lS
H or CH3, preferably H.

More preferably, component (a) is 50 to 90%, by weight~ acrylic acid or its salt and component, (b~ is 10 to 50~, by weight, 2 acrylamido-2-methylpropylsulfvnic acid or its salt. Moiety (c) may represent 0-30%, by weight, of the more pref@rred polymers. Also, for these more preferred polymer~t the intr insic viscosity is about 0 . 05 to about 0 . 5 dl/g. The most preferred terpolymers comprise 50 to 80%, by weight~ (a) 10 ~o 30%, by weight, (b~ and 5 to 15~, by weight, (c).

3 ~

The use of at least one of the designated phosphonates is critical to the instant method in ~hat these phosphonates, alone, minimiZe, inhibit and/or prevent silica/silicate deposition under severe saturation and/or temperature conditions. These compounds are efficient up to a pH of approximately The polymers of the instant invention~ if used, are commonly ava-ilable, and may be prepared by the method described in U.S. Patent 4,680,135 whi~h is hereby incorporated by reference into this specification~ ~olybdate and borate ion sources are also commonly available.

The compositions disclosed herein effectively control silica/silicate deposition in aqueous systems which have high alkalinity, high calcite satu~ation and/or high pH values. Such ~onditions are often times encountered as cycles of concentration increase. Thus, the instant phosphonate compositions provide silica/silicate protection under severe conditions where conventional silica control agents may be ineffective.

The instant compositions may be added to the system being treated by any convenient means, and the ~omponents may be added separately or in combinationO
A preferred method of addition is via makeup water streams.

?3 ~ C-1456 Additionally, other conventi.onal water treatment agents, including corrosion inhibitors such as tolyltriazole, can be used with the in~tant polymers.

EXAMPLES

The following examples demonstrate the use of the instant compositions to inhibit silica/silicate deposition. These examples are not intended to limit the scope of th~ instant invention in any wayO

In these these examples, the following compounds were tested:

Hexamethylene diamine tetra (methylene phosphonic acid), which i5 commercially available from Monsanto as Dequest 2051.

Diethylene triamine penta (methylene phosphonic acid), which is commercially available from Mon~anto as Dequest 2060.

Ammonium molybdate, which is as a source of MoO4 ions.

Boric Acid, which is a source of borate ions~

~AMæS~l, which is a 60/40 (w/w~ polymer of acrylic acid and 2-acrylamido~2-methylpropyl sulfonic acid having a weight average molecular weight of about 8200, as determined by gel permeation chromatography ~GPC).

1. AMPS is a registered trademark of The Lubrizol Corporation.

. ~' - 12 ~ C-1456 AA/AMPSA/POE, which i~ a 70/20/10 (w/w/w) polymer of acrylic acid, 2-acrylamido-2 methylpropyl ~ulfonic acid and polyethylene glycol methacrylate o~ the formula:

CH2 = C - C (ocH2cH235 OH;
o having a weight average molecular weight of approximately 10,000, as determined by GPC.

PAA, which i~ a homopolymer of acrylic acid having a molecular weight of approximately 2200.

Te~ e Method The following procedure wa~ used to evaluate the ability of the instant polymers to prevent the formation and deposition of calcium and magnesium silicates.

A two-liter polypropylene flask having a side arm was filled to the 1500 ml level with makeup water as described in Table I . The temperature of the makeup water wa~ controlled and maintained by immersing an ~lectrically heated 304 stainless steel heat-exchangar in~o the polypropylene 1ask. A refractive index liquid level sensor was placed in the side arm to maintain a constant volume in the f lask by controlling a solenoid valve on inlet line from the makeup water reser~oir.

Evaporation was achieved by passing filterad dry air or nitrogen at a resulated and measured rate through a teflon tube placed at the bottom of the flask. The makeup water was concentrated to various - 13 C-1~5~

levels (i.e~ cycled-up) by controlling the rate of aeration~ The p~ of the system was controlled by feeding acid or alkali as required by the set point pH
on a pH-st~t device.

After reaching the targeted cycles of concentration, the cycles were maintained constant for several days. This simulated the operating procedure commonly used in industrial cooling towers~ In this case the makeup water in the reservoir was replaced by distilLed water to stop further concen ration. The makeup water described in Table I was selec~ed because it is stable at room temperature and it givPs a sufficie~t induction time to establish the concentration process before any mineral precipitation occurs. The pH of the makeup water was adjusted to 8-9 and was maintained at the se:Lected pH in the flask during the entire cycling up process. The makeup water contained 10 mg/L of the designated inhibitor.
Aliquots were withdrawn at various time intervals, filtered, and analyzed for chloride, calcium, magnesium and silica. The cycles of concentration were determined based on the chloride concentration in the cycled up water. The expec~led concentration o~
the other species in 501ution was then calculated based on the cycles of concentration. The amount of deposit on the heat exchanger was determined by weighing the heat exchanger at the beginning and at the end of each run.

The results are shown in Ta~les II, III and IV.

TABLE I

Tot~l COtlCQa~r~ 0~
~ L~--Caloiu~ 100 Magn2~:Lus~ 7 . 5 Sodiu~R l.S3 Chlo~l~s 199 S~lf a~ 219 Slllca 150 2q~

TABLE II
~nhlblelon of Silic~lsilleat~s ae pH 9-0 ~ U~lng Alr or Nlerogen For Cycllng-Up ~nd aoldlng Conqta~t Cycle8 (1-8-2.0) for 2-3 Days Inhibitor Cyclln~- 2 Retentlon in Do~ag~ up ~ Inhi~ition Solutlon ~g/L~
Additiv~ Met~um _ Depo31tSiO2 Ca Mg Dequest 205110 Air 82 82 4033 Alr 85 88 21 0 Dequest 206010 Alr 95 82 8372 AA/AMPSA 2 Air * 80 3 62 ~0 Air 80 ~8 5662 M/AMPSA/POE 2 Air * 82 317 Air * 84 032 Alr 29 81 2 0 Deque~t 20515/5 Air 71 70 31 0 + M/AMPSA 20/5 Air 87 85 5068 Deque3e 206020/5 Air 91 72 7265 + AA/~5PS~

* Depo~i~ Weight Is Higher Than On Control 2~ ?~

TA.BLE I I I

osl of 51îic~/Sllicate~ at p~ 8.8 ~ 0.2 Uslng Al~
For Cycling-Up and ~loldlng Con~t~nt Cycles (1.8-2.0) ~or 7-8 D~yY
2 Reten~loQ ln DosageX Inhibltion Solutlon (mg/L) Additive (m~/L) Depo~lt S192 Ca Mg Dequest 2051 10 87 Dequest 2060 lO

Dequest 2060 ~ 10/10 lOO 68 69 . 23 AA/AMPSA/POE

D¢que~ 2060 + 10/10/20 lOO 85 91 76 M/AMPSA/PQE ~ S/5/10 93 80 36 20 MoO4~ 100 42 22 0 10/10/lO 100 64 56 35 ~A~L~ IV

I~hlblti~n of Slllc~/Silirate8 at pH 8.8 ~ 0.2 Uslng Air For Cycliu~-Up Make-up Water* and ~oldl~g Con~tant Cycls (1.8-2.0) For 7-8 Days .
% RQt~n~lon in D~R~ Z I~hlbltio~ Solution (mg/L) ~dt1Ei~ z~ _ SlO~~a Dequest 2060 10 98 67 6~ 52 MoO4 20 16 58 3 O

Dequest 2060 + 10/20 87 46 8 9 MoO4 Dequ@Rt 2060 + 10/10 94 79 65 51 AA/AMPSA/POE
Deques~ 2060 ~ 10/10/20 99 79 82 78 AA/AMPSA/POE +
MoO4 Dequest 2060 ~ 10/lOJ20 97 47 21 17 PAA ~ MoO4 De~ue~ 2060 ~ 10/10/20 98 67 45 60 A~/A~S~/~O~ +

~ .

* wle~l 100 ~g/L XCO3 alkalinity added to the makeup ~ater

Claims (13)

1. A method for controlling silica/silicate deposition in an aqueous system comprising adding to said system an effective amount of a phosphonate selected from the group consisting of hexamethylene diamine tetra(methylene phosphonic acid), diethylene triamine penta(methylene phosphonic acid), salts of these compounds and combinations thereof.

2. A method for controlling silica/silicate deposition in an aqueous system comprising adding to said system an effective amount of A) a phosphonate selected from the group consisting of hexamethylenediamine tetra(methylene phosphonic acid), diethylene triamine penta(methylene phosphonic acid), salts of these compounds and combinations thereof; and B) a water-soluble polymer comprising:

(a) 35 to 95%, by weight, of an unsaturated carboxylic acid, or salt thereof (b) 5 to 65%, by weight, of an unsaturated sulfonic acid, or salt thereof; and (c) 0 to 40%, by weight, of an unsaturated polyalkylene oxide compound, wherein said polymer has an intrinsic viscosity of 0.05 to 2.5 dl/g; wherein the weight ratio of A):B) ranges from about 1:10 to about 10:1.

3. The method of Claim 2, wherein the weight ratio of A):B) ranges from about 1:3 to about 3:1, and wherein (a) is about 50 to 80%, by weight, (b) is about 10 to 30%, by weight, and (c) is about 5 to 15%, of said composition.

4. The method of Claim 3, wherein (a) is a water soluble polymer prepared from:

a) an unsaturated carboxylic compound selected from the group consisting of acrylic acid, methacrylic acid, their salts and mixtures thereof; and b) an unsaturated sulfonic compound selected from the group consisting of 2-acrylamido-2-methylpropyl sulfonic acid, 2 methacrylamide-2-methylpropyl sulfonic acid, their salts and mixtures thereof; and (c) an unsaturated polyalkylene oxide compound selected from the group consisting of: CH2 = CH - CH2(OCH2 CH2)n OH, CH2 =
CH-CH2 (0CH2 CH2)n OCH3, wherein n is 5-10, and , wherein R1 is H or lower alkyl and x is 1-20.

5. The method of Claim 1, wherein said effective amount of said phosphonate is from about 1 to about 200 ppm.

6. The method of Claim 4, wherein said effective amount of said admixture is from about 1 to about 200 ppm.

7. The method of Claim 2, wherein a molybdate ion source or a borate ion source is added as component C), wherein the weight ratio of A):C) ranges from about 1:5 to about 5:1.

8. The method of Claim 7, wherein C) is a molybdate ion source.

9. The method of Claim 4, wherein a molybdate ion source or a borate ion source is added as component C), wherein the weight ratio of A):C) ranges from about 1:5 to about 5:1.

10. The method of Claim 9, wherein C) is a molybdate ion source.

11. A composition for controlling silica/silicate deposition comprising: A) 2-phosphonobutane tricarboxylic acid or a salt thereof; B) a water-soluble polymer comprising:

a) an unsaturated carboxylic compound selected from the group consisting of acrylic acid, methacrylic acid, their salts and mixtures thereof; and b) an unsaturated sulfonic compound selected from the group consisting of 2-acrylamido-2-methylpropyl sulfonic acid, 2-methacrylamide-2-methylpropyl sulfonic acid, their salts and mixtures thereof; and (c) an unsaturated polyalkylene oxide compound selected from the group consisting of: CH2 =CH - CH2(OCH2 CH2)n OH, CH2 =
CH-CH2 (OCH2 CH2)n OCH3, wherein n is 5-10; and C) a molybdate; wherein the weight ratio of A):B) is from about 1:10 to about 10:1 and wherein the weight ratio of A):C) is from about 1:5 to about 5:1.

12. The composition of Claim 11, wherein C) is a molybdate ion source.

13. The composition of Claim 12, wherein the weight ratio of A):B):C) is about 1:1:2.