Phosphinate oligomers, compositions containing them and methods of making and using them

Abstract: A predominantly phosphinate containing composition which has as its major ingredient more than 32 mole percent of a phosphinicosuccinic acid oligomer having the probable structural formula: M is H, Na, K, NH₄, or mixtures thereof; and m and n are either 0 or a small whole number with the proviso that either m or n is a small whole number and the sum of m plus n is greater than 2. Also disclosed is a method of making these compositions which involves reacting a water-soluble hypophosphite excess maleic acid, in a molar ratio of 2.3 to 3, and the use of these compositions and of the oligomer in the prevention or inhibition of formation of scale in aqueous media, particularly alkaline cooling water.

Description: The invention relates to compositions useful in prevention or inhibition of scale formation, especially in cooling water systems, and to methods of making and using them. The term "cooling water" is applied wherever water is circulated through equipment to absorb and carry away heat. This includes air conditioning systems, engine jacket systems, refrigeration systems, as well as the multitude of industrial heat exchange operations, such as found in oil refineries, chemical plants and steel mills. The once-through system, as the name implies, is one in which the water is passed through the heat exchange equipment and the cooling water is then discharged to waste. Usually, a once-through system is employed only where water at suitably low temperature is readily available in large volume and at low cost. The usual source of once-through cooling water is from wells, rivers, and lakes, where the cost involved is that of pumping only. In a once-through system, no evaporation takes place and consequently the water does not concentrate. Circulating water characteristics are the same as the makeup water. The use of a recirculating system, in which a cooling tower, spray pond, evaporative condenser, and the like serve to dissipate heat, permits great economy in makeup water requirements. With dwindling supplies of fresh cold water available for industry's cooling requirements, increased use must be made of recirculating systems in which the cooling water is used over and over again. After passage of the circulating water through the heat exchange equipment, the water is cooled in passing over the cooling tower. This cooling effect is produced by evaporation of a portion of the circulating water in passing over the tower. By virtue of the evaporation which takes place in cooling, the dissolved solids and suspended solids in the water become concentrated. The circulating water becomes more concentrated than the makeup water due to this evaporation loss. Cycles of concentration is the term employed to indicate the degree of concentration of the circulating water as compared with the makeup. For example, 2.0 cycles of concentration indicates the circulating water is twice the concentration of the makeup water. The precipitation of calcium carbonate and calcium phosphate may form scale, particularly on heat exchange surfaces. In general, the term "scale" applies to deposits which result from crystallization or precipitation of salts from solution. Some of the factors which affect scale formation are temperature, rate of heat transfer, pH and alkalinity of the water, and concentration of ions including calcium, sulfate, magnesium, silica, and phosphate. In the past, in order to minimize the formation of the scale forming salts, the cooling water systems were operated at pHs where the solubility of the "hardness" or "scale forming" ions was the greatest. Because the pHs of the systems were acidic, corrosion inhibitors, together with dispersants, were the normal treatment. With the advent of tight controls as regards toxic pollutant discharge, operating parameters of cooling water systems had to be changed in an attempt to utilize non-chromate treatment. The development of high pH and/or non-chromate corrosion programs over the past few years has concurrently enhanced the potential for heat exchange fouling due to chemical precipitation. Most of the currently used scale preventative treatments include phosphate and/or phosphonic acid compounds such as the alkali metal polyphosphates, organo-phosphates, e.g., phosphate esters, etc., aminotrimethylene phosphonic acid, hydroxy ethylidene disphosphonic acid, and the water-soluble salts thereof. Many of the organophosphorus compositions used as scale control agents are effective, but suffer from the drawback that they are relatively expensive to use. This is usually due to the costly synthetic methods used to produce them. In the prior art relevant to the preparation and composition aspects of the invention, relatively inexpensive organophosphorus compositions are those disclosed in US-A-4,088,678. This patent purports to disclose a method for the preparation of monosodium phosphinicobis (succinic acid). It also purports to show this compound as possessing activity as a scale inhibitor. The same concepts are shown in more detail in its British counterpart, GB-A-1,512,440. Both patents teach preparing a phosphinicobis (succinate) composition by reacting maleic acid with sodium hypophosphite in the presence of a water soluble initiator. The patents demonstrate that the optimum molar ratio of maleic acid to hypophosphite is 2.2. They clearly indicate that further excesses of the maleic acid do not result in an improved product. The present invention is based on several discoveries which arose from investigating the experimental work described in the US and British patents. In the first instance, it was ascertained the products formed using a molar ratio of maleic acid: hypophosphite of 2.0 were, in fact, mixtures of products. An important discovery is that the active species that prevent scale formation are oligomers. Further, if the oligomeric species are not present in the compositions, there is poor scale inhibition or chelation. Finally, the invention is based on the discovery that the yield of oligomeric species can be improved by increasing the molar amount of the maleic acid used in the preparative procedure. In the presence of free-radical initiators, phosphorus compounds having at least one P-H linkage will react with unsaturated substrates to form various organo-phosphorus products. The nature of the product formed can be varied as a function of the number of reactive P-H bonds and stiochiometry of reagents, as referenced in: Houben-Weyl, "Methoden der Organischen Chemie" 4th Ed., Vol. XII/I, Stuttgart, 1963, 228-229; Bataafsche (Shell), "Process for the Production of Phosphorus-containing Organic Compounds and the Compounds so Produced", E.P. 660,918, 1949 [C.A. 46,8145 (1952)]; L.A. Hamilton, R.H. Williams, "Synthesis of Compounds having a Carbon-Phosphorus Linkage", U.S. 2,957,931, (1960); and E.E. Nifant'ev, M.P. Koroteev, "Synthesis of Alkyl (Cycloalkyl) dichlorophosphines and their conversion into Derivatives of Phosphinic Acids", J. Gen. Chem. (U.S.S.R.) 37,1293 (1967) [C.A. 68,39739b]. US-A-2,724,718 also describes the preparation of organophosphorus compounds by reaction of olefinic substances with sodium hypophosphite or dialkyl phosphinates (HP (O) (OR)₂). Such reactions were conducted in alcohol in an autoclave at elevated temperatures (above 120°C), employing free-radical initiators, such as peroxides. The choice of initiator is not limited to peroxides and peroxyesters. Monoalkyl phosphinic acids (phosphonous acids) have also been prepared employing azo initiators, such as azobisisobutyronitrile, which is referenced in J.K. Thottathil's, "Process for preparing Phosphonous Acids", EP App. 246,015 (1987). These reactions were conducted in alcoholic solution, maintaining acidic conditions. In the case of activated olefins, hypophosphorous acid could be made to react in the absence of catalyst. By prolonged heating of hypophosphorous acid with diethyl maleate (1:1 molar ratio) in ethanol, 1,2-dicarboethoxyethyl phosphinic acid was prepared, by A.N. Pudovik, T.M. Moshkina, I.V. Knovalova's, "New Method of Synthesis of Esters of Phosphinic and Thiophosphonic Acids XXXI. Addition of Phosphorous and Hypophosphorous Acids, Dialkyl Hydrogen Phosphites and Esters of Phosphonoacetic Acid to Esters of Maleic Acid", Zh. Obshsch. Khim. 29, 3338 (1959) [C.A. 54,15223g]. M.G. Imaev, I.S. Akhmetzhanov, I.V. Tikunova, I.I. Lyubarskaya, V.V. Rozhkova, T.M. Alakasandrova, "Phosphinosuccinic Acid Monoester Disalts", U.S.S.R. 376,388 (1973) [C.A. 79,53557z] also describes the reaction of the monoalkyl ester of maleic acid in a similar fashion. Formation of the free succinic acid or related salts were not disclosed. Conversion of the intermediate ester to phosphinico (mono) succinic acid would require subsequent hydrolysis of the intermediate ester. This is a costly and time-consuming process. Dialkylphosphinic acids are typically isolated in poor yield (9-40%) from the peroxide catalyzed addition of hypophosphorous acid to terminal olefins. The desired bis-adduct could only be isolated by careful recrystallization of the product mixture, to separate this product from the monoalkylphosphinic acid. The preferred route was oxidation of di-n-alkylphosphine oxides, which is discussed in R.H. Williams and L.A. Hamilton's "Di-n-alkylphosphine Oxides. I. Synthesis", J. Am. Chem. Soc. 74:5418 (1952). These were prepared by Grignard reaction of magnesium alkyl halides (RMgX) with di-n-butyl phosphite. Subsequent to the work described in US-A-4,088,678, another patent, US-A-4,445,983, describes the use of phosphinocarboxylic acids for sealing anodically produced oxide layers on aluminum and aluminum alloys. The materials were produced by reaction of hypophosphorous acid with unsaturated carboxylic acids, such as maleic, itaconic, and citraconic acids. US-A-4,590,014 describes an "improved" method for the formation of alkali metal phosphinate salts. The process involves simultaneous addition of olefinic material and peroxide catalyst to an aqueous alcoholic solution of alkali metal hypophosphite salt. The composition of the mixed water/alcohol solvent system was such that the reaction temperature could be conveniently maintained at or slightly above the decomposition temperature of the free-radical initiator. These conditions favor formation of the monoalkyl phosphinate over competing side-reactions such as telomerization, double bond polymerization, or oxidation of hypophosphorous acids. By this process, sodium phosphinosuccinic acid dimethyl ester was prepared by addition of dimethyl maleate and t-butyl peroctoate to a solution of sodium hypophosphite in ethanol/water (2/1) at 80°C over 4.5 hours. One aspect of the present invention is based on the realisation that a phosphinicosuccinic acid oligomer having the structural formula (I): wherein M is one or more of H, Na, K and NH₄, and m and n are independently integers of 0 to 9, provided that m + n > 2 may be used as a scale preventative or inhibitor. In another aspect, the invention comprises a composition comprising: wherein C exceeds 32 mole percent, M is H, Na, K, NH₄, or mixtures thereof; and m and n are independently integers of 0 to 9 and the sum of m plus n is greater than 2. Optionally the composition may further contain Mole Percent-Less Than D. Sodium phosphonosuccinic acid (optional) 12 E. Sodium phosphate (optional) 5 F. Sodium phosphite (optional) 6 G. Sodium hypophosphite 6 In each case, total percentage being 100. In a preferred embodiment of the composition C is about between 35-40 mole percent. In most instances, M will be one or more of H and Na. Most preferably m and n are single digit numbers, i.e. up to 9. Preferred molecular weights for the oligomer are in the region of 2,500 to 3,000, more preferably about 2,700, as determined by using polysaccharide standards on a gel permeation chromatography system. The above structure (I) is considered to be probable, since due to the nature of the reactants, there is a possibility that a small amount would contain random phosphorus atoms in the chain. Also, it is known that compounds related to the above oligomer tend to decarboxylate in the presence of strong oxidizing agents such as peroxides, or at low pH. It has been demonstrated that such decarboxylation can be minimized by neutralization of the final product or decomposition of residual oxidant at production. One of the most surprising discoveries upon which the invention is predicated is that the active chelant or scale inhibitor is the oligomer. As will be shown hereafter, when compositions are prepared without oligomer present, they possess poor scale inhibiting properties. As previously stated, the improved scale inhibiting compositions afforded by the invention should contain more than 32 mole percent of the oligomer. Higher oligomer content, e.g. between 35-40 mole percent, gives the best scale inhibition results. The preferred method of making the compositions with high oligomer contents seems to be limited to producing materials having an oligomer content not much greater than 40 mole percent. In another aspect, the compositions containing substantial quantities of oligomer are obtainable by reacting a water soluble hypophosphite with and in the presence of an excess of maleic acid using a water soluble initiator at a temperature ranging between 50°C-70°C for a period of time ranging between four to eight hours with the molar ratio of maleic acid to water soluble hypophosphite being at least 2.5, but less than 3. In a further aspect, the present invention provides a method as set out in claim 7. Either hypophosphorous acid, alkali metal hypophosphites or other water soluble ammonium, alkali metal or amine hypophosphite salts may be used. By far the most preferred is sodium hypophosphite which is the most reactive yet, at the same time, is relatively inexpensive, and is readily available commercially. The most preferred initiators are the water-soluble persulfates, particularly ammonium persulfate. It is possible to use other free-radical initiators such as the well-known inorganic peroxides and hydroperoxides. Also useful are the so-called Vazo initiators as well as certain bisulfites. In any event, it is necessary that the initiator be water-soluble. The amount of the initiator ranges from as little as 0.1 up to as much as 10%. A preferred range is 7.5%. These percentages are based on the weight of the reactants. The reaction time may vary from between two to ten hours with good results being achieved within the range of four to eight hours. While maleic acid is the preferred material, maleic anhydride, the water-soluble maleate salts such as the alkali metal, ammonium, or amine salts, as well as certain maleate esters also may be used. It is understood that the term maleic acid when used herein and in the claims is intended to include these equivalents. It should be noted that the anhydride under the conditions of the reaction will hydrolyze to the acid. As indicated, the moles of maleic acid to the hypophosphite should be at least 2.5, but less than 3. Products of the invention containing high percentages of oligomer are only capable of being produced when the maleic acid is in excess to the hypophosphite during the course of the reaction. When the maleic acid is added to the hypophosphite simultaneously with the initiator, poor yields of the oligomer are obtained. The preparative technique set forth in US-A-4,088,678 may be used. The compositions as produced are aqueous solutions containing between about 35-40 percent solids. Whether and to what extent (up to the stated maximum) ingredients D-G are present in the product will depend on reaction conditions/proportions. Furthermore such ingredients or some of them may be removed from the product. The compositions used in the scale inhibition methods of the invention are in the form of aqueous solutions which have been neutralized with a water-soluble base such as sodium hydroxide to prevent decarboxylation from occurring. These neutralized compositions usually will be neutralized to a pH of around 7-7.5. While these compositions are capable of providing good scale protection in a variety of industrial areas, they are most effective in providing protection to the surfaces in contact with alkaline cooling waters. These waters are most often cooled by means of large atmospheric cooling towers. Such waters are treated so that their pHs are within the range of between 8.2-9.5. Higher or lower alkaline pHs can be found in certain systems. The dosage at which the compositions provide scale protection will vary depending upon the environment at which they are used. Based on total solids of the compositions, the dosage can be varied between 0.1-500 ppm based on the water being treated. A typically preferred dosage range is between 2.5-100 ppm. Example 1 - Preparative Technique Maleic anhydride (306.25 g, 3.125 moles) briquettes were crushed and added to a 1.5 litre reaction flask along with about 516.9 g of water. The suspension was stirred for about fifteen (15) minutes as the maleic anhydride dissolved and hydrolyzed, raising the temperature of the solution from 21°C to 32°C. After stirring for forty-five (45) minutes longer, the mild exotherm began to subside and sodium hypophosphite monohydrate (132.5 g, 1.25 moles) was added. A second mild exotherm occurred as sodium hypophosphite dissolved. Nitrogen purging was begun and the reaction mixture was heated to 60°C over thirty (30) minutes. Ammonium persulfate solution was added (99.75 g of a 37.22% aqueous solution) over about four hours. Temperature was controlled at 60°C-61°C using heating or cooling as needed. When addition of the catalyst was complete, heating at 60°C was continued for two and one-half (2.5) hours longer. Heating was continued and incrementally increased to 80°C until oxidant was consumed or destroyed, as indicated by a negative starch-iodide test. The clear, yellow solution was highly acidic (pH 1). The concentration of the final product before neutralization was 44.77% (assuming complete incorporation of maleic acid and sodium hypophosphite). Analysis of the reaction mixture was done using ³¹P and ¹³C NMR showing the absence of maleic acid in the final product mixture. A sample (100.0 g of the 44.77% solution described above) was neutralized to pH 7.0 by dropwise addition of the 50% sodium hydroxide. Temperature of the solution was observed and maintained at 60°C or less with ice-water bath cooling. The concentration of the resultant solution was 30.79% (calculated based on dilution). Using the above preparative technique, as well as what may be referred to as a semi-batch procedure, in which the maleic acid was added simultaneously with APS initiator, a variety of product compositions were prepared. The results of these preparations are set forth in Table I. This table illustrates both comparative examples and examples falling within the present invention. GLOSSARY M.A. - Maleic acid APS = Ammonium persulfate Hypo = sodium hypophosphite monohydrate 2:1 = Monosodium phosphinicobis (succinate) OLIG = Oligomeric phosphinicosuccinates 1:1 = Monosodium phosphinicosuccinate V-50 = 2,2'-azobis (2-amidopropane) hydrochloride PSA = Monosodium phosphonosuccinate Other Phosphonics = Unknown phosphonic compounds Resid. = Unreacted sodium hypophosphite and phosphorus acids Example 2: Evaluation as scale inhibitors Several of the compositions set forth in the above table were evaluated as scale inhibitors using the following test method, referred to as the DEAL technique, i.e. the Dynamic Equilibrium Alkalinity Limit ("DEAL"). The apparatus is a recirculating system with a stainless steel heat transfer surface, outfitted with an automatic sampling system. The concentration of the ionic species is increased by evaporative water loss over a period of twenty-four (24) hours. On the basis of the chloride concentration, the cycles of concentration are determined. By comparison of the observed soluble (filtered) calcium concentration with the theoretical concentration of calcium, an index of precipitation can be evaluated. Two parameters are employed to characterize performance. The area of deviation between the theoretical and observed soluble calcium levels is integrated, as a measure of the total amount of precipitation. In addition, the maximum number of cycles which can be obtained before precipitation occurs characterizes inhibitor performance. A model has been developed to predict the potential CaCO₃ precipitation as a function of increasing concentration under the conditions of the test. The maximum CaCO₃ concentration where 95% of this precipitation has been inhibited is reported as the second measurement of the inhibitor's performance. Using the DEAL method described above, the following test results were obtained and are set forth in Table II. CaCO₃ Scale Inhibition for Phosphinico- and Phosphonosuccinate Mixtures Sample Number Mole % Oligomer Precipitation Area Max CaCO₃ Inhibition (mg/l) 15 0 307 <268 13 0 306 <273 17 3 164 342 7 14 148 352 3 32 78 374 9 40 60 393 It is evident from a study of the data in Table II that unless the oligomer is present in the composition, there is poor scale inhibition. As a corollary, as the oligomer content increases, the scale inhibition increases. Example 3: Optimization of effects in cooling systems When the oligomeric phosphinicosuccinic acid compound content is maximized, CaCO₃ inhibition activity of this mixture is equal to or better than the commercial low molecular weight polyacrylic acid, Goodrite K-752. This conclusion is reported in Table III. The compositions after neutralization are concentrated solutions containing substantial quantities of the oligomer and having a nearly neutral pH. These solutions may be used alone to prevent or to remove scale, but in many instances it is desirable to combine them with other treatments to provide a more versatile product. Thus, they may be combined with other scale inhibitors and/or dispersants such as the low molecular weight polyacrylic acids. They may be combined with corrosion inhibitors such as the inorganic molecularly dehydrated phosphates. Similarly, they can be fortified with scale inhibiting organophosphonates to provide products having synergistic properties. The oligomer-containing compositions described, in addition to preventing scale, have the potential for dispersing scale-forming components in scale-forming waters. This is so since the oligomers are low molecular weight and polymeric in nature. Also, they should be capable of removing existing scale when it is present on equipment surfaces, particularly heat transfer surfaces. When this use of composition is contemplated, high dosages should be employed.

Claims: A composition comprising A, B and C: wherein M is one or more of H, Na, K, and NH₄, and m and n are independently integers of 0 to 9 with the proviso that the sum of m plus n is greater than 2, the total percentage of the composition being 100. A composition according to claim 1 additionally comprising at least one of D, E, F and G: D. Sodium phosphonosuccinic acid less than 12 E. Sodium phosphate less than 5 F. Sodium phosphite less than 6 G. Sodium hypophosphite. less than 6 with the proviso that the total percentage of the composition is 100. A composition according to claim 1 where C is 35-40 mole percent. A composition according to claim 1 or claim 2 where M is one or more of H and Na. A composition comprising A, B and C: Ingredients Mole Percent A. Monosodium phosphinicobis-(succinic acid) less than 22 B. Monosodium phosphinicosuccinic acid, and less than 26 C. A phosphinicosuccinic acid oligomer, greater than 32 the total percentage being 100, obtainable by reacting a water-soluble hypophosphite with and in the presence of an excess of maleic acid, anhydride, salts or esters using a water-soluble initiator at a temperature ranging between 50°C-70°C for a period of time ranging between four (4) to eight (8) hours with the molar ratio of maleic acid to water-soluble hypophosphite being at least 2.5 but less than 3. A composition according to claim 5 wherein ammonium persulfate was added to the maleic acid and hypophosphite during the course of the reaction. A method for producing the composition of claim 5 which comprises reacting a water-soluble hypophosphite with and in the presence of an excess of maleic acid, anhydride, salts or esters using a water-soluble initiator at a temperature ranging between 50°C-70°C for a period of time ranging between four (4) to eight (8) hours with the molar ratio of maleic acid to water-soluble hypophosphite being at least 2.5, but less than 3, and wherein ammonium persulfate is added to the maleic acid and hypophosphite during the course of the reaction. A method of preventing or inhibiting scale deposition from an aqueous medium which consists of adding to the medium a composition as claimed in any one of claims 1 to 6. A method according to claim 8 wherein the aqueous medium is alkaline cooling water. The use of a composition as claimed in any one of claims 1 to 6, as a scale-deposition inhibitor or preventer.

Inventors: DI SIMONE I SERGIO, FAIR BARBARA E, JOHNSON DONALD A, KNELLER JAMES F, MAZZANI GIANFRANCO F, NARUTIS VYTAS, DI SIMONE, I. SERGIO, FAIR, BARBARA E., JOHNSON, DONALD A., KNELLER, JAMES F., MAZZANI, GIANFRANCO F., NARUTIS, VYTAS
Applicants: NALCO CHEMICAL CO, NALCO CHEMICAL COMPANY
Application year: 1991
Main classification: C07F9
IPC codes: C02F5