Deposit control method

A water system deposit control method and composition of high calcium tolerance are herein disclosed. The composition comprises a reaction product formed from acrylic acid, hydroxylated lower alkyl acrylate and hypophosphorous acid. In accordance with the method herein, an effective amount, from about 0.1-500 ppm of the composition is added to the water system, e.g., cooling water system, so as to inhibit the build-up or agglomeration of undesirable deposits along the metal surfaces on contact with the water.

FIELD OF THE INVENTION 
The present invention pertains to a method for controlling undesirable 
deposit formation in water systems and along metal surfaces and the like 
in contact with such systems. 
BACKGROUND OF THE PRESENT INVENTION 
As is well known in the art, water systems contain ingredients, either 
naturally occurring, as contaminants, or formed by the combination of 
anions and cations, which can and often do cause deposition problems. 
For example, depending on the water source and process conditions, 
industrial water can contain alkaline earth metal or transition metal 
cations such as calcium, barium, magnesium, iron, etc. and such anions as 
carbonate, phosphate, sulphate, oxalate, silicate, etc. The combination of 
these anions and cations could, accordingly, form such potential 
depositing salts as calcium carbonate, calcium sulphate, calcium 
phosphate, magnesium carbonate, magnesium sulphate, etc. When the 
concentration of any of such salts which are formed exceeds their 
solubility limit, they precipitate out of the water in the form of scale. 
The concentration of these scale forming salts can increase as a result of 
partial water evaporation, or changes in pH, temperature or pressure of 
the water. The amount of scale formation generally depends on pH, 
temperature and type of salt formed. The scale thus formed will deposit on 
surfaces in contact with the aqueous medium, such as flow pipes, storage 
tanks, heat exchanger surfaces, etc. These deposits can prevent effective 
heat transfer, interfere with fluid flow through pipes, facilitate 
corrosion, and harbor bacteria. 
Deposit control agents, such as phosphates, phosphonates, and 
polyacrylates, show similar responses as the concentration of calcium is 
increased in cooling waters and the like with the potential for 
precipitation of slightly soluble calcium salts. At very low 
(substoichiometric) treatment levels, these deposit control materials 
inhibit the nucleation and growth of crystals of calcium salts. The 
mechanism for this activity involves adsorption of the deposit control 
agent at the active growth site of the forming microcrystallites. If the 
concentration of calcium is increased, turbidity develops in the cooling 
water, indicating the formation of insoluble, calcium-deposit control 
agent adducts. If the deposit control agent concentration is increased to 
stoichiometric concentrations, this turbidity can be removed by chelation 
of the calcium ion to produce soluble calcium-containing species. 
Because of the economics of water treatment in cooling systems, deposit 
control agents must function at substoichiometric concentrations. In 
waters containing high calcium concentrations, such as might be found in 
cooling systems operating at high cycles of concentration, calcium 
tolerant deposit control agents offer a distinct advantage. The 
concentration of these materials can be increased to meet the deposit 
control demands of the system without concern for their removal by 
formation of calcium containing adducts. 
Formation of calcium-deposit control agent adducts has obvious negative 
consequences. The active or "free" deposit control agent concentration is 
limited, thus limiting deposition and corrosion control. Also, the adduct 
itself may foul the cooling system through the formation of an adduct 
deposit. 
To alleviate this problem, the calcium concentration is often controlled by 
operating at lower cycles of concentration. However, such procedure also 
has obvious economic disadvantages. 
Thus, a deposit control agent that is tolerant to high calcium 
concentrations provides definite advantages when used in cooling water 
systems and the like. The high treatment concentrations that may be 
required due to the deposition potential created by high calcium 
concentrations can be used without fear of fouling or loss of corrosion 
protection. Cycles of concentration need not be limited, providing 
economic benefits and conservation of water. 
Accordingly, there is a need in the art for a method of controlling 
deposition in high calcium ion content waters, which method does not 
result in the substantial formation of adducts comprised of calcium ions 
and the deposit control agent. 
Most of the present-day corrosion inhibitor treatments comprise a phosphate 
and/or phosphonic acid constituent. Phosphate may also be contained within 
the makeup water, e.g., tertiary sewage treatment effluent. The reversion 
of the polyphosphates and the organic phosphates plus the use of alkaline 
operating conditions leads to the formation and deposition of highly 
insoluble calcium phosphate. Accordingly, there is a need in the art for a 
deposit control treatment which inhibits the formation of calcium 
phosphate deposits. 
PRIOR ART 
Acrylic acid deposit control agents are well known in the art. In addition, 
acrylic acid/orthophosphorous acid reaction products and acrylic 
acid/hypophosphorous acid reaction products have been suggested for use as 
deposit control treatment agents. U.S. Pat. Nos. 4,239,648 (Marshall et 
al); 4,159,946 (Smith et al), 4,277,359 (Lipinski) and 4,207,405 (Masler) 
exemplify such treatments. 
The use of acrylic acid/hydroxylated lower alkyl acrylate copolymers as 
deposit control agents has been taught by U.S. Pat. No. 4,029,577 
(Godlewski et al). Similarly, U.S. Pat. No. 4,209,398 (Ii et al) discloses 
utilization, as water treating compounds, of a polymer containing a 
structural unit that is derived from a monomer having an ethylenically 
unsaturated bond and has one or more carboxyl radicals, at least a part of 
the carboxyl radicals being modified by the inclusion therein of an 
oxyalkylene radical. One copolymer specifically disclosed by Ii et al is 
the sodium salt of acrylic 
acid/2-hydroxypropylacrylate/2-hydroxypropylacrylate monophosphate. 
Despite the advent and use of the above-noted acrylic acid based water 
treatment agents, there remains a need in the art for a deposit control 
agent that is highly calcium tolerant and which is effective, especially, 
in inhibiting calcium phosphate scale. To my knowledge, an acrylic 
acid/hydroxylated lower alkyl acrylate/hypophosphorous acid reaction 
product has not been proposed or used by others heretofore. I have found 
that, surprisingly, such reaction product efficiently inhibits calcium 
phosphate deposition and is highly calcium tolerant. This is in fact 
surprising since, as the following examples indicate, the acrylic 
acid/hydroxylated lower alkyl acrylate/hypophosphorous acid reaction 
products I have discovered exhibit enhanced activity in calcium tolerance 
and calcium phosphate inhibition tests in sharp contrast to the results 
attendant upon use of either the acrylic acid/hypophosphorous acid 
reaction products exemplified in U.S. Pat. No. 4,239,648 (Marshall et al) 
and U.S. Pat. No. 4,159,946 (Smith et al) or the acrylic 
acid/2-hydroxypropylacrylate copolymers disclosed in U.S. Pat. No. 
4,029,577 (Godlewski et al). 
DETAILED DESCRIPTION 
The acrylic acid/hydroxylated lower acrylate/hypophosphorous (H.sub.3 
PO.sub.2) reaction products of the present invention are "calcium 
tolerant". This phrase is used to signify the fact that the reaction 
product remains in solution in waters having calcium ion concentrations of 
300 ppm and greater without forming an undesirable precipitate. 
Accordingly, the reaction product can exert its deposit control function 
in such waters without interference due to formation of calcium-deposit 
control agent adducts. 
Although few naturally occurring waters possess calcium ion concentrations 
on the order of 300 ppm and greater, such water systems are typically 
encountered in recirculating-type cooling water systems, which for 
economical and environmental purposes, are forced to operate at high 
levels of concentration. Although the present method is ideally suited to 
provide effective deposit control protection in these particular systems, 
the method is equally applicable to all water systems for which deposit 
control protection is sought that possess such high calcium ion 
concentrations. For instance, boiler water systems, scrubber systems, salt 
water desalination, dust collecting systems, reverse osmosis, and other 
water systems may benefit from the present invention. 
It is noted that the term "reaction product" as used herein should be 
construed to encompass the acrylic acid/hydroxylated lower 
acrylate/H.sub.3 PO.sub.2 reaction products of the present invention and 
all water soluble salt forms of this reaction product. 
The reaction product is formed via reaction of acrylic acid, the desired 
hydroxylated lower alkyl acrylate, and hypophosphorous acid (H.sub.3 
PO.sub.2), in a solvent which is inert under the reaction conditions. An 
initiator which decomposes to yield free radicals is also added to the 
solvent. Suitable solvents include water, aqueous ethanol or dioxan. 
Suitable initiators include bisazoisobutyronitrile, organic peroxides such 
as benzoyl peroxide, methyl ethyl ketone peroxide, ditertiary butyl 
peroxide and monobutyl hydroperoxide, and oxidizing agents such as 
hydrogen peroxide, sodium perborate and sodium persulphate. 
The reaction products of the present invention are obtained as solutions. 
The reaction products can then be isolated via conventional techniques 
including partial or complete evaporation of the solvent. It is to be 
understood, however, that the reaction products of the invention can be 
used in their "unpurified" form. 
Salts of the reaction products, in which some or all of the acidic hydrogen 
atoms have been replaced by cations such as alkali metal ions, ammonium 
ions or quaternized amine radicals, may also be used. Such salts may be 
prepared by mixing an aqueous or alcoholic solution of the reaction 
product with an aqueous or alcoholic solution containing an amount of the 
requisite base in excess of, equal to or less than the stoichiometric 
requirement. The solvent may then be removed by evaporation. It is noted 
that in many of the water systems in which the reaction products of the 
present invention will be used, the water is sufficiently alkaline to 
effect neutralization. 
The exact structure of the reaction product is not entirely clear. Indeed, 
the lack of sufficient model compounds, with which the instant reaction 
product could be compared, renders n.m.r. examination speculative. 
As to the reactants themselves, acrylic acid may be readily prepared by 
hydrolysis of acrylonitrile. It is commercially available from many 
sources. 
The phrase hydroxylated lower alkyl acrylate relates to an acrylate moiety 
containing from one to about four carbon atoms in the pendant alkyl group. 
Any of the carbon atoms of the alkyl group may be provided with an hydroxy 
function. The hydroxylated lower alkyl acrylate may be prepared via 
addition reaction between acrylic acid or its derivatives or water soluble 
salts and the oxide of the alkylene derivative desired. The preferred 
hydroxylated lower alkyl acrylate is 2-hydroxypropylacrylate. This may be 
prepared by reacting acrylic acid with propylene oxide. 
Hypophosphorous acid, H.sub.3 PO.sub.2, may be prepared by treating 
NaH.sub.2 PO.sub.2 with an ion-exchange resin. It is commercially marketed 
in aqueous solutions of varying concentration. 
The reaction product of the present invention may be effectively utilized 
as a highly calcium tolerant deposit control inhibition agent by adding an 
effective amount thereof, between about 0.1-500 parts of the reaction 
product per one million parts of the aqueous medium, to the desired water 
system. Preferably, the reaction product is added in an amount of between 
about 2.5-100 parts per million of water contained within the aqueous 
system to be treated. 
It is thought that the present reaction product may be used in conjunction 
with the process parameters noted in U.S. Pat. No. 4,303,568 (May et al) 
to attain the desired but elusive passivated oxide film on metal surfaces 
in contact with the treated aqueous medium. It is postulated that the 
reaction product may be combined with, or used in lieu of, the copolymer 
specified in the '568 May et al patent. The entire disclosure of U.S. Pat. 
No. 4,303,568 (May et al) is accordingly herein incorporated by reference. 
The reaction products of the present invention can also be used with other 
components in order to enhance the corrosion inhibition and scale 
controlling properties thereof. For instance, the reaction products may be 
used in combination with one or more kinds of compounds selected from the 
group consisting of inorganic phosphoric acids, phosphonic acid salts, 
organic phosphoric acid esters, and polyvalent metal salts. 
Examples of such inorganic phosphoric acids include condensed phosphoric 
acids and water soluble salts thereof. The phosphoric acids include an 
orthophosphoric acid, a primary phosphoric acid and a secondary phosphoric 
acid. Inorganic condensed phosphoric acids include polyphosphoric acids 
such as pyrophosphoric acid, tripolyphosphoric acid and the like, 
metaphosphoric acids such as trimetaphosphoric acid, and 
tetrametaphosphoric acid. 
As to the other phosphonic acid derivatives which are to be added in 
addition to the reaction products of the present invention, there may be 
mentioned aminopolyphosphonic acids such as aminotrimethylene phosphonic 
acid, ethylene diamine tetramethylene phosphonic acid and the like, 
methylene diphosphonic acid, hydroxy ethylidene-1,1-diphosphonic acid, 
2-phosphonobutane-1,2,4-tricarboxylic acid, etc. 
Exemplary organic phosphoric acid esters which may be combined with the 
reaction products of the present invention include phosphoric acid esters 
of alkyl alcohols such as methyl phosphoric acid ester, ethyl phosphoric 
acid ester, etc., phosphoric acid esters of methyl cellosolve and ethyl 
cellosolve, and phosphoric acid esters of polyoxyalkylated polyhydroxy 
compounds obtained by adding ethylene oxide to polyhydroxy compounds such 
as glycerol, mannitol, sorbitol, etc. Other suitable organic phosphoric 
esters are the phosphoric acid esters of amino alcohols such as mono, di, 
and tri-ethanol amines. 
Inorganic phosphoric acid, phosphonic acid, and organic phosphoric acid 
esters may be salts, preferably salts of alkali metal, ammonia, amine and 
so forth. 
Exemplary polyvalent metal salts which may be combined with the reaction 
products above include those capable of dissociating polyvalent metal 
cations in water such as Zn.sup.++ Ni.sup.++ etc., which include zinc 
chloride, zinc sulfate, nickel sulfate, nickel chloride and so forth. 
When the reaction product is added to the aqueous system in combination 
with an additional component selected from the group consisting of 
inorganic phosphoric acids, phosphonic acids, organic phosphoric acid 
esters, or their water-soluble salts (all being referred to hereinafter as 
phosphoric compounds), and polyvalent metal salts, a fixed quantity of 
said reaction product may be added separately and in the state of aqueous 
solution into the system. The reaction product may be added either 
continuously or intermittently. Alternatively, the reaction product may be 
blended with the above noted phosphoric compounds or polyvalent metal 
salts and then added in the state of aqueous solution into the water 
system either continuously or intermittently. The phosphoric compounds or 
polyvalent metal salts are utilized in the usual manner for corrosion and 
scale preventing purposes. For instance, the phosphoric compounds or 
polyvalent metal salts may be added to a water system continuously or 
intermittently to maintain their necessary concentrations. 
Generally, the phosphoric compounds should be present in the aqueous system 
in an amount of about 1-100 ppm (as PO.sub.4) or the polyvalent metal 
salts should be present in an amount of about 1 to 50 ppm (as metal 
cation). 
As is conventional in the art, the phosphoric compounds or polyvalent metal 
salts may be added, as pretreatment dosages, to the water system in an 
amount of about 20 to about 500 ppm, and thereafter a small quantity of 
chemicals may be added, as maintenance dosages. 
The reaction product may be used in combination with conventional corrosion 
inhibitors for iron, steel, copper, copper alloys or other metals, 
conventional scale and contamination inhibitors, metal ion sequestering 
agents, and other conventional water treating agents. Exemplary corrosion 
inhibitors comprise chromates, bichromates, tungstate, molybdates, 
nitrites, borates, silicates, oxycarboxylic acids, amino acids, catechols, 
aliphatic amino surface active agents, benzotriazole, and 
mercaptobenzothiazole. Other scale and contamination inhibitors include 
lignin derivatives, tannic acids, starch, polyacrylic soda, polyacrylic 
amide, etc. Metal ion sequestering agents include ethylene diamine, 
diethylene triamine and the like and polyamino carboxylic acids including 
nitrilo triacetic acid, ethylene diamine tetraacetic acid, and diethylene 
triamine pentaacetic acid.

SPECIFIC EMBODIMENTS 
The invention will now be further described with reference to a number of 
specific examples which are to be regarded solely as illustrative, and not 
as restricting the scope of the invention. 
Example One--Reaction Product Preparation 
A mixture of 22.5 g. hydroxypropylacrylate (0.173 mole) and 37.9 g. acrylic 
acid (0.521 mole) was first prepared. Six grams of this mixture was then 
added to a reaction flask containing 40.1 g. H.sub.2 O, 13.2 g. 
hypophosphorous acid (H.sub.3 PO.sub.2), and 0.38 g. benzoyl peroxide. The 
reaction flask was equipped with a magnet, condenser, N.sub.2 sparge, 
addition funnel and thermometer. The mixture was heated to about 
95.degree.-98.degree. C. No clear cut exotherm to reflux could be 
observed. At reflux (100.degree. C.), the remainder of the 
hydroxypropylacrylate-acrylic acid mixture was added to the reaction flask 
in dropwise manner through the addition funnel. After approximately 5-10 
ml of this dropwise addition, rapid refluxing was observed. The solution 
in the reaction flask appeared more viscous. The remainder of the 
hydroxypropylacrylate-acrylic acid mixture was added slowly over a period 
of about 10 minutes. Refluxing was noted to increase as the addition rate 
was increased. This indicated that polymerization was occurring. Refluxing 
(100.degree. C.) was continued for another 3 hours. The reaction product 
was then allowed to remain at ambient overnight. The product obtained was 
a solution containing about 54.5% solids. The molecular weight (Mw) of the 
solids was determined by gel permeation chromatography to be about 47,000 
with the Mn value being determined to be 4,400. 
Example Two--Calcium Tolerance Efficacy 
As previously mentioned, in treated aqueous systems containing high calcium 
hardness conditions, the potential exists for the uncontrolled 
precipitation of calcium-deposit control agent adducts. As the need is 
created to add more deposit control agent to prevent deposit agglomeration 
throughout the treated water system, this problem of uncontrolled 
calcium-deposit control agent adduct formation is exacerbated. 
The following table demonstrates the ability of the AA/HPA/H.sub.3 PO.sub.2 
reaction product, in contrast with other well known deposit control 
agents, in withstanding various calcium concentrations at 60.degree. C. 
The test procedure used to determine calcium tolerance of the materials 
was as follows: solutions containing 400 ppm Ca.sup.+2 and 2,000 ppm 
Ca.sup.+2 were prepared at pH=9. To these solutions, 20 ppm (actives) of 
each desired treatment were added and the pH was readjusted to 9 with NaOH 
if necessary. The solutions were placed in a water bath at 60.degree. C. 
for 10 minutes. The presence of precipitation was detected by the Tyndall 
effect. 
______________________________________ 
Calcium Tolerance 
Treatment 400 ppm Ca.sup.+2 
2,000 ppm Ca.sup.+2 
______________________________________ 
AA/HPA/H.sub.3 PO.sub.2 reaction 
Clear Clear 
product - product of 
Example One 
Copolymer acrylic acid/ 
Clear Clear 
2-hydroxypropylacrylate, 
AA:HPA mole ratio 2:1, 
nominal molecular weight 
6,000 
Dequest 2010 Very cloudy Very cloudy 
Dequest 2000 Very cloudy Very cloudy 
AA/HPA/H.sub.3 PO.sub.2 
Slight turbidity 
Slight turbidity 
reaction product - (worse than at 
Example One - second 400 ppm) 
run 
Beclene 500 Slight turbidity 
Slight turbidity 
(worse than (equivalent to AA/ 
AA/HPA/ HPA/H.sub.3 PO.sub.2 reac- 
H.sub.3 PO.sub.2 reaction 
tion product - 
product - sec- 
second run at 2000 
ond run at 400 
ppm Ca.sup.+2) 
ppm Ca.sup.+2) 
______________________________________ 
Dequest 2010 = hydroxyethylidenediphosphonic acid; available Monsanto 
Dequest 2000 = nitrilotris (methylene phosphonic acid); available Monsant 
Beclene 500 = phosphinocarboxylic acid having structure 
##STR1## 
wherein Z is H or a cation, and wherein the sum of n & m is about 2 to 6. 
See U.S. Pat. No. 4,239,648 and U.S. Pat. No. 4,159,946. This product is 
commercially available from CibaGeigy. 
Example Three--Calcium Phosphate Inhibition 
To evaluate the deposit control efficacy of the AA/HPA/H.sub.2 PO.sub.3 
reaction product of the present invention, tests were undertaken to 
measure the product's ability to prevent bulk phase precipitation of 
calcium phosphate, under conditions which would normally result in the 
precipitation of this particular salt. In this respect, it is important to 
recognize that the AA/HPA/H.sub.2 PO.sub.3 reaction product was evaluated 
at "substoichiometric" concentrations. Prevention of bulk phase 
precipitation at such "substoichiometric" levels is known in the art as 
"threshold" treatment. 
The results in the following table are expressed as "percent inhibition" 
with positive values indicating that the stated percentage of precipitate 
was prevented from being formed. 
The following conditions, solutions, and testing precedure were utilized to 
perform the calcium phosphate inhibition test. 
______________________________________ 
CALCIUM PHOSPHATE INHIBITION PROCEDURE 
Conditions Solutions 
______________________________________ 
T = 70.degree. C. 
36.76 CaCl.sub.2.2H.sub.2 O/liter DIH.sub.2 O 
pH 7.5 0.4482 g Na.sub.2 HPO.sub.4 /liter DIH.sub.2 O 
17 hour equilibrium 
Ca.sup.+2 = 100 ppm (as Ca.sup.+2) 
PO.sub.4.sup.-3 = 6 ppm 
______________________________________ 
Procedure 
(1) To about 1800 ml DIH.sub.2 O in a 2 liter volumetric flask, add 20 ml 
of CaCl.sub.2.2H.sub.2 O solution followed by 2 drops of conc HCl. 
(2) Add 40 ml of Na.sub.2 HPO.sub.4 solution. 
(3) Bring volume to 2 liters with DI water. 
(4) Place 100 ml aliquots of solution in 4 oz. glass bottles. 
(5) Add treatment. 
(6) Adjust pH as desired. 
(7) Place in 70.degree. C. water bath and equilibrate for 17 hours. 
(8) Remove samples and filter while hot through 0.2 filters. 
(9) Cool to room temperature and take Absorbance measurements using Leitz 
photometer (640 nm). 
Preparation for Leitz: 
a. 5 mls filtrate 
b. 10 mls Molybdate Reagent 
c. 1 dipper Stannous Reagent 
d. Swirl 1 minute, pour into Leitz cuvette; wait 1 minute before reading. 
(10) Using current calibration curve (Absorbance vs. ppm PO.sub.4.sup.-3) 
find ppm PO.sub.4.sup.-3 of each sample. 
Calculation 
##EQU1## 
TABLE 
______________________________________ 
Calcium Phosphate 
Inhibition 
% Inhibition 
5 ppm 10 ppm 20 ppm 
Treatment Actives Actives Actives 
______________________________________ 
AA/HPA/H.sub.2 PO.sub.3 reaction 
13 46 87 
product of Example One 
Belclene 500 0 9.4 12 
Copolymer acrylic acid/2- 
40 59 60 
hydroxypropylacrylate, 
AA:HPA mole ratio 2:1, 
nominal molecular 
weight .apprxeq. 6,000 
______________________________________ 
Example Two demonstrates that the AA/HPA/H.sub.3 PO.sub.2 reaction product 
of the present invention is comparable to the Belclene 500 and copolymer 
treatments listed in the example insofar as calcium tolerance is 
concerned. The reaction product of the present invention is clearly 
superior to the well known Dequest 2010 and Dequest 2000 materials in this 
characteristic. 
Example Three is indicative of the enhanced calcium phosphate inhibition 
characteristics afforded by the reaction product. In contrast, Belclene 
500, a well-known deposit control agent falls far short in this category. 
In fact, the performance of the reaction product, with regard to this 
inhibition trait, is even better than the noted copolymeric treatment at 
20 ppm. It is to be noted that this particular copolymeric treatment is 
widely regarded as presently providing optimal scale control inhibition. 
Accordingly, it is apparent that the reaction product of the present 
invention is a highly effective threshold agent for deposit inhibition. 
While I have shown and described herein certain embodiments of the present 
invention, it is intended that there be covered as well any change or 
modification therein which may be made without departing from the spirit 
and scope of the invention as defined in the appended claims.