MXPA00005749A

MXPA00005749A - Anionic polymer products and processes

Info

Publication number: MXPA00005749A
Application number: MXPA/A/2000/005749A
Authority: MX
Inventors: Haunnlin Chen
Original assignee: Cytec Technology Corp
Priority date: 1997-12-10
Filing date: 2000-06-09
Publication date: 2001-07-09

Abstract

Aqueous dispersions of anionic water-soluble or water-swellable polymers are provided, where the polymers have an anionic charge of greater than 16%and where the dispersions maintain their form at a pH of 5.1 or greater. Processes for making these dispersions are also disclosed, as well as methods of using these dispersions to treat water containing various types of suspended materials. Dry polymers, preferably formed by drying these aqueous dispersions, are also disclosed.

Description

PROJJUC OS OF ANIONIC POLYMERS AND PROCESSES Field of the Invention The present invention relates to aqueous dispersions comprised of water soluble or swelling polymers, to processes for making the dispersions, and to the methods of using the dispersions in water treatment, dehydration, water clarification. , paper manufacturing, oil fields, soil conditioning, food processing, mineral processing and biotechnological applications.

Background of the Invention The U.S. patent No. 3,658,772 discloses a process of copolymerization of a monomeric composition of ethylenically unsaturated water-soluble mnomers in an aqueous solution containing inorganic salts at a pH in the range of from about 1 to 3.2 to produce a fluid suspension of the particles of dispersed polymers-solids. According to this patent, the polymers are comprised of at least 30 percent to about 95 percent acrylic acid and REF .: 121032 from O percent to 70 percent of recurrent acrylamide units. The inorganic salt is present in an amount sufficient to precipitate the polymer when it is polymerized in solution. It is critical that the pH be within the stated range because the salt form of the polymer is more easily soluble. This patent is related to U.S. Pat. No. 3,493,500 which also discloses the aqueous dispersions of the acrylic acid / acrylamide copolymers in a continuous aqueous salt phase, wherein the critical pH is within the range of about 1 to about 4. According to the Description of the Application from Japanese Patent No. HEI 6-25540, an anionic dispersion in the aqueous salt solution can be obtained using the dispersion polymerization to copolymerize no more than 15 mol% of an acid neutralized alkali metal (meth) acrylic, 2-acrylamide-2-methylpropanesulfonic acid, or the like, and a polymerizable nonionic monomer such as (meth) acrylamide in a solution of the aqueous salt. An anionic dispersion can also be obtained by copolymerizing the unneutralized (meth) acrylic acid or the like and the (meth) acrylamide in a solution of the aqueous salt while stirring. According to Japanese Patent Description No. SHO 50-70489, there is a relationship between the sodium acrylate content of an acrylic acid / acrylamide copolymer and its solubility in an ammonium sulfate salt solution. Specifically, when the sodium acrylate content of the polymer is about 3 mol%, it is soluble in a solution having an ammonium sulfate concentration in weight% greater than 22 percent. However, when the sodium acrylate content of the polymer becomes larger, higher and higher ammonium sulfate concentrations are required to precipitate the polymer. For example, at a sodium acrylate content of about 16 mol% the concentration of the ammonium sulfate in the solution must be greater than 35 percent to precipitate the polymer. It appears that there will be recognition in the art that the aqueous dispersions of the anionic acrylamide copolymers can be formed at a low pH without limitation on the content of the anionic monomer, but that the content of the anionic monomer is limited to about 15 per cent. cent to a higher pH where the anionic monomer is in the salt form. ' When the dispersed polymer contains more than 15 mole percent of anionic recurring units, the art recognizes that the pH of the aqueous dispersion must be low so as to maintain the anionic units in their non-neutralized less soluble form. The 15 percent limitation is recognized in the Japanese Kokai Patent Number SHO 62 (1987) -100548, SHO 62 (1987) -20502, SHO 62 (1987) -20511 and in EPO 183 466 Bl. The technique generally recognizes that the pH should be about 4 or less, see U.S. Pat. Number 3,658,772 and 3,493,500 described above. International Publication No. WO 97/34933 mentions a pH of from about 2 to about 5, but the highest pH set in the examples is only 3.63 (Example 4). European Patent Applications EPO 604 109 A2 and EPO 630 909 Al as well as U.S. Pat. No. 5,498,678 only exemplify cationic polymers. Accordingly, there is a problem in that the aqueous dispersions of the anionic water-swelling and water-soluble polymers, which have an anion content greater than 15 percent, are generally not available unless the pH of the dispersion is maintained down to about 4. An aqueous anionic dispersion of a water-soluble or water-swellable polymer having a pH greater than 4 and an anion content greater than 15 mole percent could be desirable because of these dispersions are generally used by mixing with water to disperse or dissolve the polymer, then using the resulting diluted mixture in the desired application. It can be readily appreciated that the pH of the water can significantly affect the performance of these mixtures because of the pH sensitivity of the polymer. The problem is particularly acute when the anionic aqueous dispersion is mixed with water that is not highly alkaline, for example neutral or slightly acidic water, because the acidity of the dispersion itself can make the resulting mixture even more acidic than water. Therefore, it may be desirable to have an anionic aqueous dispersion with an anion content greater than 15 mol percent which remains in the form of an aqueous dispersion at a pH greater than 4, preferably greater than 5, even more preferably higher than 6, so that the operation of the polymer could be increased materially. The previous approaches to this problem have serious disadvantages. For example, EPO 717 056 A2 describes amphoteric copolymers of the anionic monomers and cationic monomers containing the benzyl group in which it is preferred that the resulting polymer contains more cationic groups than the anionic groups. Even if a person skilled in the art would proceed contrary to this preference and prepare a polymer in which the anionic groups are more numerous than the cationic groups, the inclusion of the cationic groups could tend to dilute the anionic effect and add a extra cost. A similar dilution and a cost disadvantage may result from copolymerization with a hydrophobic monomer such as in U.S. Pat. No. 5,605,970. Dilution and extra cost may also result when the anionic polymer is precipitated by a combination of the cosmotropic salt and the cationic organic salt as in U.S. Pat. No. 5,725,779. The disadvantages may also be evident when a different kind of aqueous dispersion is prepared for example one in which the droplets of the anionic polymer are not formed because of the insolubility in a salted solution, but instead they are the result of a process of separation of the phases that involves a second incompatible polymer. In these aqueous dispersions, the salt is not necessary but instead the continuous phase contains a second polymer which is generally immiscible with the anionic polymer. For example, in some cases the second polymer may be diluent of the effect of the first polymer in a particular application, or may tend to viscosify the continuous phase to an undesirable degree. In this regard, the following U.S. Patents: 4,380,600 5,403,883 can be mentioned.; 5,480,934; 5,541,252; 4,778,836; 4,522,968; and 4,673,704. In this respect, the following European publications can also be mentioned: EPO 573 793 Al; 624 617 Al; 169 674 Bl; and 170 394 A2; as well as PCT document WO 95-11269. Despite the effort to make satisfactory anionic aqueous dispersions, the problem remains of producing anionic aqueous dispersions of water-soluble or water-swollen polymers of high molecular weight, which remain in the form of aqueous dispersions, ie the The dispersed polymer remains insoluble at a high loading and at a high pH and having advantageously low volumetric viscosities, a high content of active polymer solids, minimal amounts of dilutable material, and which dissolve or disperse easily regardless of the pH of the dilution water for give polymer blends which have the performance characteristics that are acceptable to the industry.

Brief Description of the Invention This problem is solved in the present invention by providing novel anionic aqueous dispersions of water-soluble or water-swellable polymers of generally high molecular weight, which remain in the form of an aqueous dispersion at pH 5.1 or greater and which have an anionic content of 16% by mol or greater, as well as manufacturing processes and methods of using aqueous dispersions. Accordingly, an aqueous dispersion of polymers is provided, which comprises (a) the solution of the salt comprised from about 5% to about 35% of the inorganic salt, by weight, based on the aqueous dispersion; and (b) a water soluble or swellable, anionic vinyl addition polymer, which is comprised of more than 16 mol% of anionic recurring units, based on the total moles of the recurring units in the polymer, and that it is insoluble in the salt solution; wherein the polymer is comprised of a number of anionic recurring units selected from the group consisting of methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, vinyl sulfuric acid, vinylphosphonic acid, ester sulfonic acid, styrene sulfuric acid, ammonium and alkali metal salts thereof, and mixtures thereof, which are effective in rendering the polymer insoluble in the salt solution at a pH of 5.1; and wherein the aqueous dispersion is substantially free of an amount of the cationic organic salt that is effective to precipitate the polymer.

In another embodiment there is provided a process for making an aqueous dispersion which comprises polymerizing the vinyl addition monomers to form a water soluble or swellable polymer with water having more than 16 mol% of anionic recurring units, with base in the total moles of the recurring units in the polymer; wherein the polymerization is carried out in an aqueous solution comprised from about 5% to about 35% of the inorganic salt, by weight, based on the aqueous dispersion; wherein the anionic vinyl addition monomers are comprised of an amount of anionic monomers, selected from the group consisting of methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, vinylsulfuric acid , vinylphosphonic acid, styrenesulfonic acid, styrene sulfuric acid, ammonium and alkali metal salts thereof, and mixtures thereof, which is effective to render the polymer insoluble in the salt solution at a pH of 5.1; and wherein the aqueous solution is substantially free of an amount of the cationic organic salt that is effective to precipitate the polymer. In another embodiment, there is provided a method of dehydrating a suspension of dispersed solids, comprising the intermixing of an aqueous dispersion of polymers, or an aqueous mixture thereof, in an amount effective for flocculation, with a suspension of dispersed solids. , and dehydrating the suspension of the dispersed solids, wherein the aqueous dispersion is comprised of (a) the salt solution comprised from about 5% to about 35% of the inorganic salt, by weight based on the aqueous dispersion; and (b) a water soluble or swellable, anionic vinyl addition polymer, which is comprised of more than 16 mol% of anionic recurring units, based on the total moles of the recurring units in the polymer, and that it is insoluble in the salt solution; wherein the polymer is comprised of the group consisting of methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, vinylsulfuric acid, vinylphosphonic acid, styrenesulfonic acid, styrenesulfuric acid, ammonium and alkali metal salts thereof, and mixtures thereof, which is effective to render the polymer insoluble in the salt solution at a pH of 5.1; and wherein the aqueous solution is substantially free of an amount of the cationic organic salt that is effective to precipitate the polymer.

In another embodiment, there is provided a process for producing water-soluble or water-swollen, anionic, substantially dry polymer particles comprising (a) spray drying an aqueous dispersion containing the water soluble polymer or it can be inflated with anionic water in a gas stream with a residence time of about 8 to about 120 seconds and an outlet temperature of about 70 ° C to about 150 ° C and (b) collecting the resulting anionic polymer particles . In another embodiment, there is provided a process for producing particles of a water soluble or water swellable polymer, anionic, substantially dry, comprising (1) spray drying an aqueous dispersion containing a water soluble polymer or it can be inflated with water, anionic, in a gaseous stream with a residence time of about 8 to about 120 seconds and an outlet temperature of about 70 ° C to about 150 ° C and (2) collecting the anionic polymer particles, wherein the anionic aqueous dispersion is comprised of (a) the salt solution comprised from about 5% to about 35% of the inorganic salt, by weight, based on the aqueous dispersion; and (b) a water soluble or swellable, anionic vinyl addition polymer, which is comprised of more than 16 mol% of anionic recurring units, based on the total moles of the recurring units in the polymer, and that it is insoluble in the salt solution; wherein the polymer is comprised of a number of anionic recurring units, selected from the group consisting of methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, vinylsulfuric acid, vinylphosphonic acid, styrenesulfonic acid, styrenesulfuric acid, ammonium and alkali metal salts thereof, and mixtures thereof, which is effective to render the polymer insoluble in the salt solution at a pH of 5.1; and wherein the aqueous solution is substantially free of an amount of the cationic organic salt that is effective to precipitate the polymer, as well as the substantially dry polymer particles that can be obtained by this process. In another embodiment, agglomerates or substantially dry polymer particles are provided, comprised of a water-soluble or anionic, water-soluble, vinyl-addition polymer, which is comprised of more than 16 mol% of anionic recurring units, based on the total moles of the recurring units in the polymer; wherein the polymer is comprised of a number of anionic recurring units, selected from the group consisting of methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinyl sulfonic acid, vinyl sulfuric acid, vinyl phosphonic acid, styrenesulfonic acid, styrenesulfuric acid, ammonium and alkali metal salts thereof, and mixtures thereof, which is effective to render the polymer insoluble in the salt solution at a pH of 5.1; wherein the salt solution is comprised from about 5% to about 35% of the inorganic salt, by weight based on the total weight of the polymer and the salt solution; and wherein the aqueous solution is substantially free of an amount of the cationic organic salt that is effective to precipitate the polymer.

Detailed Description of the Preferred Modalities The anionic aqueous dispersions of the present invention contain a water soluble or swellable polymer, anionic, preferably a vinyl addition polymer. The anionic charge of the anionic polymer can vary over a wide range because it contains from about 1 percent to about 100 percent anionic recurring units, based on the total moles of the recurring units. The advantages of the present invention are particularly evident when the anionic charge is about 16 mole percent or more than 16 mole percent, preferably about 17 mole percent or more, 18 mole percent or more , or 19 percent by mole or greater, even more preferably approximately 20 percent by mole or greater, 22 percent by mole or greater, or 25 percent by mole or greater, even more preferably approximately 26 percent in mol or greater, based on the total moles of the recurring units in the anionic polymer. The anionic polymer may contain 100 mole percent of recurring units or preferably about 90 mole percent or less, or more preferably about 80 mole percent or less, based on the total moles of the units recurrent The anionic recurring units can be formed by the postreaction of the polymer, for example the hydrolysis of polyacrylamide to form the carboxylic acid or the salt groups, or by hydroxylation with hydroxylamine or the hydroxylamine salt to form the hydroxamated polymer which contains the hydroxamic acid and / or hydroxamic acid salt groups, see for example US Pat. No. 4,767,540. Preferably, the anionic recurring units are formed by polymerization of the anionic monomers. The anionic monomers can include any anionic monomer including methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, vinylsulfuric acid, vinylphosphonic acid, styrenesulfonic acid, styrenesulfuric acid, ammonium and salts of alkali metal of the same. Preferred anionic monomers include acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and ammonium and alkali metal salts thereof. The water-soluble or water-swellable, anionic polymer can be a copolymer and can contain other anionic recurring units, cationic recurring units, or non-ionic recurring units. The cationic recurring units may be quaternary salts or dialkylaminoalkyl (ale) acrylate or dialkylaminoalkyl- (ale) acrylamide acid salts, or they may be dialkyldiallylammonium halides and may be formed by the copolymerization of the corresponding monomers or by post-reaction. To maintain a net anionic charge, the anionic polymers of the present invention generally contain a smaller amount of cationic recurring units than the anionic recurring units, and in general do not contain an amount of cationic recurring units that is effective to render the polymer insoluble. the salt solution at a pH of 5.1 or higher. The anionic polymers of the present invention preferably contain 5 mole% or a lesser amount of the cationic recurring units, more preferably they are substantially free of cationic recurring units, and they are even more preferably substantially free of the cationic recurring units that have been quaternized with large alkyl or aryl groups for example quaternized with alkyl halides with C3-C? 2. Even more preferably, the anionic polymers of the present invention are substantially free of cationic recurring units containing the benzyl group. The non-ionic recurring units can be formed from the water-soluble monomers such as (ale) acrylamide, N-vinylpyridine, hydroxyalkyl (meth) acrylates, N-vinylpyrrolidone, etc., preferably (meth) acrylamide, or they can be formed from hydrophobic monomers that have a low solubility in water since the inclusion of recurring units, for example hydrophobic, poorly soluble in water, they do not make the resulting polymer soluble in water or that is not inflatable with water. The non-ionic recurring units can be formed by the post-reaction of the polymer. The anionic polymer may contain amounts of recurring units of the water-soluble nonionic monomers ranging from 0 percent to about 99 percent, preferably about 10 percent or more, more preferably about 15 percent or more, even more preferably about 30 percent or greater, preferably about 90 percent or less, more preferably about 80 percent or less, even more preferably about 70 percent or less, per mole, based on in the total moles of the recurring units in the polymer. Hydrophobic monomers may be hydrocarbon monomers, for example styrene, butadiene, 1-alkene, etc., other vinyl monomers, such as vinyl halide, other mainly aliphatic or aromatic compounds with polymerizable double bonds, or monomers with only one solubility in moderate water such as acrylonitrile. Preferably, the hydrophobic monomers are alkyl (ale) acrylates or aryl (ale) acrylates in which the alkyl or aryl groups contain about 1 to about 12 carbon atoms such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, ethylhexyl (meth) acrylate, or alkyl or aryl (ale) acrylamides in which the alkyl or aryl groups contain about 1 to 12 carbon atoms, such as methyl (meth) acrylamide, ethyl (meth) acrylamide, tributyl (meth) acrylamide, dimethyl (meth) acrylamide, hexyl (meth) acrylamide, ethylhexyl (meth) acrylamide, or aromatic (meth) acrylamide. The most preferred hydrophobic monomers are acrylonitrile, ethyl acrylate and t-butylacrylamide. The water-soluble or water-swellable, anionic polymer may contain amounts of the non-ionic, hydrophobic recurring units, ranging from about 0 percent to about 15 percent, preferably about 2 percent to about 10 percent. percent, per mole based on the total moles of the recurring units in the polymer. Although the hydrophobic recurring units may be diluents of the effect of the polymer in certain applications, inclusion in controlled quantities may advantageously affect a particular characteristic of the aqueous dispersion, for example, the rate of solubility, the volumetric viscosity, the cost, the ease of processing, operation, etc. Depending on the specific modality, it may be preferable for the polymer to be free of hydrophobic recurring units, or to contain selected amounts of the hydrophobic recurring units to achieve an advantageous effect without disadvantageously increasing the diluting effect. Surprisingly, the present inventors have discovered that the inclusion of certain recurring units, which can be referred to herein as insolubilizing anionic recurring units, in the water-soluble or water-swellable, anionic polymers of the present invention, causes the resulting polymer is insoluble in the solutions of the salt, even when the total anionic content of the polymer is 16 percent or higher and even when the pH is 5.1 or higher. Accordingly, the water-soluble or anionic water-swelling polymers of the present invention generally contain an amount of anionic, insolubilizing recurring units which is effective to render the polymer in the salt solution insoluble to a pH of 5.1 or above this value. Acrylic acid is not an insoluble anionic recurring anionic unit but, surprisingly, other anionic recurring units can have an insolubilizing effect. The anionic insolubilizing recurring units can be any anionic recurring units which have the effect of rendering the anionic polymer insoluble at a pH of 5.1 or higher in a solution of the salt. Preferably, the anionic insolubilizing recurring units are selected from the group consisting of methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, vinylsulfuric acid, vinylphosphonic acid, styrenesulfonic acid, styrenesulfuric acid, ammonium and alkali metal salts thereof, and mixtures thereof. In general, at least about 20 percent of the anionic recurring units in the water soluble or water swellable, anionic polymers of the present invention are comprised of anionic insolubilizing recurring units, preferably about 25 percent or more, more preferably approximately 30 percent or more. For example, if the anionic polymer contains 50 mol% of the anionic recurring units and 50 mol% of the nonionic recurring units, it is preferred that at least about 20 mol% of these anionic recurring units, ie 10% in mole of the total recurring units in the polymer, are insoluble anionic recurring units. The larger amounts of the anionic insolubilising recurring units generally make the resulting anionic polymer more insoluble in the salt solution at a pH of 5.1, so that for example higher pH levels or lower salt levels can be achievable with larger amounts of anionic insolubilizing recurring units than with smaller amounts. The inclusion of these anionic insolubilizing recurring units also allows the water soluble or swellable polymer, anionic, resulting, to contain an even greater level of the anionic charge so that when larger amounts of insolubilizing recurring units are incorporated into the polymer, even higher levels of the anionic charge can be achieved. The effective level of the anionic insolubilizing recurring unit is generally found by routine experimentation, and can be chosen according to the selection of the total anionic charge in the polymer and the level of the salt in the aqueous dispersion. Methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid or alkali metal salts thereof, and mixtures thereof, are preferred anionic insolubilizing recurring units, and methacrylic acids and their salts are preferred. particularly. The anionic charge of the anionic polymer that is contained in the aqueous dispersions of the present invention can result from a combination of the polymerization and post-reaction of the anionic monomer. For example, an aqueous dispersion containing a polymer having an anionic charge of more than 16 mol% can be first formed by copolymerizing the acrylamide and an anionic monomer insolubilizers such as methacrylic acid to form a copolymer containing for example 95% in mol of recurring acrylamide units and 5 mol% of methacrylic acid units, then reacting the polymer subsequently by hydrolyzing a portion of the recurring acrylamide units to form the recurring acrylic acid units, so that the resulting polymer has a charge total anionic mass of more than 16% in mol. Accordingly, the process of making the aqueous dispersions present which comprises polymerizing the vinyl addition monomers to form a water soluble or swellable polymer, anionic, having more than 16 mol% of the recurring units Anionic, can be achieved by first forming a polymer which has less than 16 mol% of the anionic recurring units, then subsequently reacting this polymer to produce a polymer having more than 16 mol% of the anionic recurring units. The amount of the polymer soluble in water or that can be swollen with water, anionic, in the aqueous dispersion, is generally as high as practicable, taking into account the effect of the elevated polymer solids on the volumetric viscosity, preferably about 5 percent or more, more preferably about 10 percent or more, greater, even more preferably approximately 20 percent or greater, by weight based on the total weight of the aqueous dispersion. In general, polymer solids are not increased above a quantity which increases the volumetric viscosity to an unusable level. Practically the amount of the anionic polymer in the aqueous dispersion is about 75 percent or less, preferably about 60 percent or less, more preferably about 50 percent or less, by weight based on the total weight. The weight average molecular weight of the aryonic polymer in the aqueous dispersion is not critical and depends on the application, but in general is higher than about 100,000, preferably greater than about 1 million, more preferably greater than about 2 million, even more preferably higher that approximately 5 million. As described herein, the molecular weights of the polymers are a weighted average and can be determined by means known to those skilled in the art, preferably by light scattering or by high pressure size exclusion chromatography using a detector of Light scattering or calibrated appropriately with known molecular weight standards. The aqueous dispersions of the present invention are generally comprised of a discontinuous phase of small polymer-containing droplets, which are dispersed in the continuous aqueous phase, although, of course, smaller amounts of the polymer can be found in the continuous phase. Accordingly, the water soluble or swellable polymer, anionic, constitutes more than 25 percent, preferably more than 50 percent, of the total weight of a typical small aqueous droplet. The aqueous dispersions of the present invention are preferably formed by the polymerization of the corresponding monomers in the solution of the aqueous salt, but can also be formed by adding a gelled polymer or dry polymer for example a spray-dried polymer or agglomerates to a solution of the aqueous salt. Although the aqueous dispersions prepared by the polymerization of the monomers as described herein can sometimes have an average droplet size of about 30 microns or more, the size of the average droplet is generally less than about 30 microns, preferably less than about 20 microns. microns, more preferably approximately 15 microns or less. The size of the droplet of a non-spherical droplet is the length along a major axis. The size and shape of the droplet can be a function of the reactor conditions, such as the stirring speed, the reactor configuration, the agitator type, etc. Preferably the size of the droplets is chosen by carrying out the polymerization in the presence of one or more seeds or seeds of insoluble polymer, the seeds or seeds of the polymer are insoluble in an aqueous solution having the same concentration of the inorganic salt as said aqueous dispersion. The increase in the concentration of the seed or seed tends to reduce the maximum volumetric viscosity observed during the polymerization process and / or the reduction of the size of the droplet. Preferably the seeds or polymer seeds are the residue of a previous polymerization. The aqueous dispersions of the present invention may contain a second water-soluble polymer, preferably a vinyl addition polymer that is different from the first water soluble or swellable anionic polymer. with water. The second polymer has a tendency to stabilize the aqueous droplets of the first anionic polymer when it is soluble or partially soluble in the solution of the aqueous salt. The second water-soluble polymer can be referred to herein as a polymeric dispersant or dispersant. The dispersant may be a nonionic polymer but is preferably an anionic polymer or copolymer. The dispersant in general has the same characteristics as the anionic polymer that is contained in the dispersed phase as described above., except that it preferably has a greater solubility in the aqueous salt solution. The larger solubility generally results from the lower molecular weight and / or the greater incorporation of the anionic recurring units and / or the lesser inclusion of hydrophobic recurring units. Even more preferably the second polymer is a copolymer of acrylamide and acrylic acid or a homopolymer of acrylic acid. The characteristics of the dispersant are generally chosen by means of routine experimentation to provide the most advantageous effect, for example volumetric density, performance, costs, etc. The molecular weights of the dispersant are generally higher than about 10,000, preferably greater than about 50,000, more preferably greater than about 100,000 and even more preferably greater than about 200,000. In general, the molecular weight of the dispersant should not be so high that it viscosifies the continuous phase to an unacceptable level. Preferably, the molecular weight of the dispersant is less than about 5,000,000, more preferably less than about 3,000,000. The dispersant generally dissolves in the continuous aqueous phase of the anionic aqueous dispersion, although of course smaller amounts can be found in the discontinuous phase. The amount of dispersant in the aqueous dispersions present is generally chosen to control the properties of the aqueous dispersion, for example the operation, the volumetric viscosity, the filler, the molecular weight, the speed of solubility, the physical stability, for example , sedimentation, etc. The present anionic aqueous dispersions do not require a dispersant, but aqueous dispersions containing the dispersants are preferred. In general, the preferred aqueous dispersions contain about 1 percent or more, preferably about 2 percent or more, even more preferably about 5 percent or more, of a dispersant, by weight, based on the amount of the dispersion. first polymer soluble in water or swollen with water, anionic. The second polymer should not be present in amounts which could cause precipitation or separation of the first polymer phase in the absence of the salt. In other words, the first anionic polymer soluble in water or swellable with water is insolubilized by the action of the salt and not because of the incompatibility with the second anionic polymer. Even in the absence of the second polymer, the first polymer is still insoluble in the salt solution. Practically, this often means that the amount of the dispersant in the aqueous dispersion is about 20 percent or less, preferably about 15 percent or less, by weight, based on the amount of the first water-soluble polymer or that is It can be inflated with water, anionic. In practice, the amount of the dispersant can be found by routine experimentation, and different amounts could ordinarily be used depending on the identity of the first and second polymers, the level of the total polymeric solids, the volumetric viscosity, the ease of production, product operation, etc. The aqueous dispersions of the present invention may contain water-soluble or water-swellable, anionic, additional polymers, which are different from the first or second polymers. The additional polymer (s) may also be contained in droplets dispersed in the solution of the aqueous salt, in which case it may be described as described above for the first anionic polymer . The additional polymer (s) may also be (are) dissolved in the aqueous solution in the presence of the dispersant, in which case they may be described as mentioned above for the second polymer. Preferably the additional polymers are anionic. The aqueous dispersions of the present invention can be formed by combining two or more aqueous dispersions. Mixing can be advantageous to achieve a balance of the properties exhibited by the individual aqueous dispersions, for example the operation, the load, the total polymeric solids, the costs, the molecular weight, etc. A molecular weight of the aqueous dispersion, when such a term is used herein, is simply the weighted average molecular weight of the polymers contained therein, obtained by subjecting the complete dispersion to a suitable molecular weight characterization technique, for example the dispersion of light . Since such an aqueous dispersion contains two or more different polymers, each of which can have a molecular weight and a molecular weight distribution different from the others, the molecular weight distribution of the aqueous dispersion can be multimodal. The molecular weight of the aqueous dispersion is generally about 500,000 or greater, preferably greater than 1 million, more preferably about 2 million or more, more preferably about 3 million or more. In some cases it may be more convenient to characterize the aqueous polymers or dispersions described herein in terms of the standard viscosity rather than the molecular weight. When used here the "standard viscosity" is determined by: the dilution of an aqueous dispersion with water to form an aqueous mixture (in the case of polymers that can be swollen with water) or a solution (in the case of water-soluble polymers) that have a polymer concentration of about 0.2 percent; mixing together 8.0 grams of this aqueous mixture or solution with 8.6 grams of the 2 molar NaCl solution and then measuring the viscosity of the resulting mixture at 20 ° C using a rotating cylinder viscometer, for example the Brookfield viscometer, equipped with a UL adapter at 60 rpm. The standard viscosities of the aqueous dispersions and the anionic polymers of the present invention are generally about 1.1 centipoise or greater, preferably about 1.5 centipoise or greater, more preferably about 2.0 centipoise or greater, still more preferably Approximately 2.5 centipoise or higher depending on the application.

The aqueous dispersions of the present invention generally contain an inorganic salt. The type and amount of the salt are generally chosen to be effective to precipitate the water-soluble or water-swellable polymer, anionic, to form the aqueous droplets of the aqueous dispersion. In general, the amount of the salt is about 5 percent or more, preferably about 10 percent or more, more preferably about 15 percent or more, and even more preferably about 20 percent. one hundred or greater, by weight, based on the weight of the aqueous dispersion. The upper limit for the concentration of the salt is generally the saturation limit for the particular salt in question, because it is generally undesirable for the aqueous dispersion containing large amounts of the undissolved salt, although small amounts can be tolerated. Accordingly, the anionic aqueous dispersions of the present invention generally contain 40% or less, preferably 35% or less, still more preferably 30% or less of the inorganic salt, by weight based on the weight of the aqueous dispersion. The salt levels are generally chosen to have a favorable influence on the attributes of the product such as cost, volumetric viscosity, etc. In practice, the level of the salt is generally that which is effective to produce a desired result such as a particular volumetric viscosity or level of solids, and can be determined by routine experimentation, for example the balance of the trend for the . positive attributes of the product against the negative aspects of the use of salt, for example the cost and the diluting effect. The inorganic salt can be any inorganic salt, preferably a cosmotropic salt, for example the chloride, sulfate, phosphate or acid phosphate salt, more preferably ammonium sulfate, sodium chloride, and sodium sulfate, even more preferably sodium sulfate and ammonium sulphate. The counter ion can be any opposite ion, for example the metal ions of group IA and group IIA, ammonium, etc., preferably ammonium, sodium, potassium and magnesium. The mixtures of the salts can be used. The pH of the aqueous dispersion can be determined by any convenient means, for example a pH meter, as described in the following examples. In general, the process for making the aqueous dispersion of the present invention can be carried out at any convenient pH, preferably between pH 1 and pH 7, more preferably at a pH of 5.0 or greater or 5.1 or greater, even more preferably at a pH of 5.3 or greater or 5.5 or greater, more preferably at a pH of 6.0 or greater. When the pH of the aqueous dispersions of the present invention is 5.1 or is adjusted to a test pH of 5.1, the aqueous dispersions maintain their shape, ie they remain in the form of an aqueous dispersion in which the water-soluble polymer or that can be swollen with water, anionic, remains insoluble. Preferably, the polymer remains insoluble at a test pH of 5.3 or 5.5, or even more preferably at a pH of 5.8 or 6.0. For purposes of the present invention, a polymer that can swell in water is insoluble in a solution of the particular salt at a particular pH when the polymer that can swell with water is substantially non-swellable. For comparison, an anionic water swellable polymer having an anionic charge of more than 15 mol% and containing no effective amounts of insolubilizing recurring units as described above, is generally substantially swellable at a pH of 5.1 or greater, for the same reason that the corresponding water-soluble polymer is soluble under the same conditions. When the polymer soluble in water or swellable with water is insoluble, the aqueous dispersion generally appears opaque, for example, it appears milky white and is not clear or translucent. For the purposes of the present invention, a convenient means for determining whether the water soluble or swellable polymer, anionic, is insoluble at a particular pH to adjust the pH of the aqueous dispersion to the test pH, and then to measure the bulk viscosity of the dispersion aqueous at this pH. In general, the pH adjustment will not lead to a large change in volumetric viscosity, preferably less than 50 percent change, more preferably less than 25 percent change, more preferably less than 10 percent change. Preferably, the volumetric viscosity of the aqueous dispersion at the test pH is between about 100 centipoise and about 100,000 centipoise, still more preferably between about 500 centipoise and about 50,000 centipoise, and even more preferably between about 1,000 and about 30,000 centipoise. The volumetric viscosity can be measured by any convenient means, preferably using a rotating cylinder viscometer, for example a Brookfield viscometer, at a temperature of 20 ° C as described in the following examples. The aqueous dispersions of the water-soluble polymers are preferably formed by the polymerization of the corresponding monomers in a solution of the aqueous inorganic salt to form the first anionic water-soluble polymer, preferably in the presence of at least one second water-soluble polymer. , anionic The polymerization can be carried out by any means of initiation, including the redox, thermal or irradiation types. Examples of the preferred initiators are 2, 2'-azobis (2-amino-propan) dihydrochloride, 2,2'-azobis (isobutyronitrile), sodium bromate / sulfur dioxide, potassium persulfate / sodium sulfite, and ammonium persulfate / sodium sulfite, as well as peroxy redox initiators, for example those described in US Pat. No. 4,473,689. The levels of the initiator are chosen in a known manner to create the polymers of the desired molecular weight. The amounts of chain transfer agents, for example isopropanol, lactic acid, mercaptoethanol, etc., and branching or crosslinking agents, for example methylenebisacrylamide, glycidyl methacrylate, etc., can be added. in a known manner for further adjusting the properties of the water-soluble or anionic water-swelling polymer. Depending on the production conditions, for example the types and relative amounts of the chain transfer agent and the branching agent, water-soluble, branched or swellable polymers can be formed with water. In general, the use of larger amounts of the branching or cross-linking agent increases the tendency of the product to be water-swellable rather than water-soluble, and the increased amounts of the chain transfer agent tend to reduce molecular weight. When the chain transfer agent and the branching agent are used together, the products that can be swollen with water are more likely to be obtained at high levels of the branching agent and low levels of the chain transfer agent, while branched, water-soluble polymers can be obtained at high levels of the chain transfer agent and low levels of the branching agent. The components of the polymerization process can be added at any time; for example all of the monomers may be present from the start of the polymerization, or the monomers may be added during the course of the polymerization. In some cases it may be preferred to add the monomers during the course of the polymerization to reduce the compositional shift and / or because the monomers themselves have a solubilizing effect on the polymer. Preferably, about 10-60 weight percent, more preferably 20-50 weight percent, of the total monomer charge is present at the start of the polymerization, and the remaining monomer is added either continuously or batchwise, preferably from continuously, during the course of the polymerization. Similarly, all of the salt may be present from the start of the polymerization, or the salt may be added during the course of the polymerization or after the polymerization is supplemented. Typical parameters of the polymerization, for example temperature and time, can be chosen in a known manner, and can be varied during the course of the polymerization. The polymerization is generally carried out in the presence of an inert gas, for example nitrogen. Conventional processing aids, for example chelating agents, sequestering agents, etc., may be added when required. The aqueous dispersions of the present invention have advantageous aspects in that they are substantially free of diluents such as the surfactant, the emulsifier, the oil, the hydrocarbon liquids, the organic solvents, etc. Although viscosity reducing additives, for example glycerin, glycerol, alcohol, glycol, etc., may be present in the aqueous dispersions, the amounts should be 2% or less, more preferably 1% or less , still more preferably 0.1% or less, to maintain the advantageous properties of the invention. Although small amounts of the surfactants or emulsifiers can be added, their presence in general is unnecessary for the formation of the present aqueous dispersions. Preferably, the present aqueous dispersions contain less than 1% of the surfactant or emulsifier, and more preferably are substantially free of the surfactant or emulsifier. Small amounts of the small organic salts can be added to make the anionic polymer less soluble, which can have the effect of allowing higher polymer solids levels, reduced inorganic salt levels, etc. Since the cationic organic salt can have a diluting effect and can add a cost to the formulation, it is generally preferred that the aqueous dispersions of the present invention contain less than about 1% of the cationic organic salt, based on the total weight of the aqueous dispersion, and more preferably less than the amount which is effective to precipitate the anionic polymer. Even more preferably, the aqueous dispersions of the present invention are substantially free of the cationic organic salt. In some cases, oil-in-water emulsions or water-soluble, or water-swellable, conventional polymer emulsions may present a problem in which the presence of the oil and the surfactants and / or the emulsifier may present a secondary pollution problem for the end user. The present aqueous dispersions can provide a solution to this problem because they generally do not contain oil and a small amount or nothing of the surfactant. The present aqueous dispersions can be combined with conventional oil-in-water emulsions or microemulsions of water-soluble or water-swellable polymers to produce a product having a low oil and / or surfactant content and / or of the emulsifier than the corresponding oil-in-water emulsions or microemulsions. The waters used in the present invention can be from any source, for example, process water, river water, distilled water, tap water, etc. Preferably, the polymerizations are carried out in aqueous solutions which do not contain substantial amounts of materials which detrimentally affect the polymerization. Advantageously, the aqueous dispersions of the present invention tend to dissolve rapidly when diluted with water.

The aqueous dispersion of the present invention can be dehydrated to increase the solids content of the total polymers, or to create substantially dry products. Any means known in the art, for example distillation, spray dewatering, solvent precipitation, etc., can be used to reduce the water content. Surprisingly, partial dehydration can reduce the volumetric viscosity of an aqueous dispersion, although the tendency to dehydration increases the polymer solids. The dehydration can be effected by heating, preferably under reduced pressure, although of course excessive heating can be detrimental to the properties of the polymer. A substantially dry mass of the polymer can be obtained by the removal of water, and the mass can be shredded to create a dusty, particulate, or granular product. Water-soluble or water-swellable, anionic, dry polymers can have the useful property that they are redispersible in a saline solution at a buffered pH to form an aqueous dispersion or mixture. This may appropriately be of particular value to an end user because the dry product may be less expensive to ship to a remote site and store at this site than the corresponding aqueous dispersion because the dry product typically has a weight and lower volume. The advantageous handling properties of the aqueous dispersion can be obtained at the site simply by mixing the dried polymer with a solution of the salt, under the conditions described above for example the concentration of the salt and the pH, to form an aqueous dispersion or mixture which can be pumped or conveniently worked before it is used in the application. Surprisingly, substantially dry polymer products can be obtained by spray drying the aqueous dispersions of the present invention. The emulsions and polymer dispersions containing oil have been dehydrated by spray, see for example U.S. 4,035,317; U.S. Patent Application Serial No. 08 / 668,288; 08 / 667,782; 08 / 670,194; and the references therein, as well as the cationic aqueous dispersions, see U.S. 5,696,228. However, spray drying of anionic aqueous dispersions has not been previously reported. According to the present invention, aqueous anionic dispersions can be dewatered by spray by suitable means in a large chamber through which a hot gas is blown, whereby most or all of the volatile substances are removed and the recovery of the dry anionic polymer becomes possible. Surprisingly, the means for spraying the anionic aqueous dispersion in the gas stream are not particularly critical and are not limited to pressurized nozzles having specific orifice sizes; in effect, any device for known spray dehydration can be used. For example, means that are well known in the art such as rotary atomizers, pressure nozzles, pneumatic nozzles, sonic nozzles, etc., can all be used to spray-dry the aqueous dispersion in the gas stream. . The feed rate, the feed viscosity, the desired particle size of the spray dried product, the droplet size of the aqueous dispersion, etc., are factors which are typically considered when the media is selected. sprayed The size and shape of the chamber, the number and type of the spraying means, and other typical operating parameters can be selected to suit the conditions of the dryer using the common knowledge of those skilled in the art. Although closed cycle dehydrators can be used, open cycle sprinkler dewatering systems are preferred. The gas flow can be parallel, in mixed stream counterflow, parallel flow is preferred. The hot gas, or the inlet gas, can be any gas that does not react or forms explosive mixtures with the feed and / or the polymer dehydrated by spraying. Suitable gases used as the inlet gas are gases known to those skilled in the art, including air, nitrogen, and other gases which will not undesirably cause degradation or contamination of the polymer, preferably gases containing about 20% or less oxygen, more preferably approximately 15% or less oxygen. Even more preferably, inert gases such as nitrogen, helium, etc., which contain about 5% or less of oxygen should be used. The dried anionic polymer can be collected by various means such as a simple outlet, a sorting cone, a bag filter, etc., or the polymer can be subjected to additional drying steps, such as fluid beds, or agglomeration . The means for the collection of the dry polymer product are not critical. There are four operational parameters interrelated in the present process of spray dehydration; the gas inlet temperature, the gas outlet temperature, the volatile substances of the product and the residence time in the dryer. The outlet temperature should generally be about 150 ° C or less, preferably about 120 ° C or less, more preferably less than 100 ° C, even more preferably about 95 ° C or less, more preferably roughly 90 ° C or lower. The outlet temperature is generally approximately 70 ° C or higher, preferably approximately 75 ° C or higher. Therefore, the outlet temperatures are generally about 70 ° C to about 150 ° C, preferably about 70 ° C to about 120 ° C, more preferably about 70 ° C to less than 100 ° C. , even more preferably from about 70 ° C to about 95 ° C, even more preferably from about 75 ° C to about 90 ° C. The outlet temperatures below about 70 ° C may be adequate in certain cases, although generally this is less preferred. For example, at the expense of efficiency, spray dewatering could be carried out at extended residence times, high gas flow velocities, and low exit temperatures. In general, the dryer or dehydrator should be operated at the lowest possible exit temperature, consistent with obtaining a satisfactory product.

Preferably, the polymers that are not degraded by the present spray-drying process, for example the standard viscosity of the spray-dried polymer, are reduced by less than 15%, preferably less than 10%, still more preferably less than 5%, by the spray dewatering process, when compared to the standard viscosity of the aqueous dispersion from which the spray-dried polymer is derived. The inlet temperature, the feed rate, and the composition of the anionic aqueous dispersions can affect all exit temperatures. These parameters can be varied to provide a desired exit temperature. Feed rates are not critical, and will generally vary depending on the size of the dryer or dehydrator and the gas flow rate. The temperature of the inlet gas is less critical than the outlet gas temperature, and is generally about 140 ° C or higher, preferably about 160 ° C or higher. The gas inlet temperature is preferably about 200 ° C or less and more preferably about 180 ° C or less. Accordingly, the temperature of the inlet gas varies from about 140 ° C to about 200 ° C, more preferably from about 160 ° C to about 180 ° C. Appropriate inlet gas temperatures tend to avoid degradation of the product on the upper side and to avoid inadequate drying or dehydration on the underside. The residence time is a nominal value obtained by dividing the volume of the dryer or dehydrator by dividing the volume of the dryer or dehydrator between the flow of the volumetric gas. The residence time is generally at least about 8 seconds, preferably at least about 10 seconds. The residence time is generally not greater than about 120 seconds, preferably not more than about 90 seconds, more preferably not more than about 60 seconds, and even more preferably not more than about 30 seconds. Therefore, the general range of residence time is from about 8 to about 120 seconds, preferably from about 10 to about 90 seconds, more preferably from about 10 to about 60 seconds, and even more preferably from about 10 to about approximately 30 seconds. It is known to those skilled in the art that longer residence times are expected when larger dryers or dehydrators are used or when the dryer or dehydrator is operated in a less efficient manner. For example, at the expense of efficiency, longer residence times could be expected at very low inlet temperatures and slow gas flow rates. As a practical matter, the residence times useful in the present invention may vary from the values described above, depending on the size and type of the spray dryer or dehydrator used, the efficiency at which it is operated, and other operating parameters. . Accordingly, the residence times specified herein can be modified to suit the conditions of the dryer or dehydrator using the common knowledge of those skilled in the art. When produced according to the spray dehydration processes described herein, the particles of the anionic polymer of the present invention are generally about 10 microns or larger in diameter, preferably about 40 microns or more, more preferably about 100 microns or more, even more preferably about 200 microns or more. It is preferred that the particles of the anionic polymer do not convert to powder. The problems of dust formation and flow without aggravating typically when the polymer particles are small, so that the larger polymer particles are generally undesirable. However, very large particles can dissolve more slowly. Therefore, it is generally desirable for the anionic polymer particles to be about 1200 microns or smaller in diameter, preferably about 800 microns or smaller in diameter, more preferably about 600 microns or less, even more preferably approximately 400 microns or less. In general, at least about 90% of the polymer particles vary in size from about 10 microns to about 1200 microns, preferably at least about 95%, more preferably at least about 98%. The size of the particles of the anionic polymer can be varied somewhat to alter the operating parameters for example the configuration of the spray or spray, the viscosity of the aqueous dispersion, the feed rate, etc. The particles can be substantially spherical or non-spherical; The "diameter" of a non-spherical particle is the dimension along a principal axis. Although in some cases the anionic polymer particles are porous, hollow structures having at least one opening in their walls, it has been found that these characteristics are not always necessary to obtain the particles having desirable properties, for example, fast times of dissolution . In many cases, the parameters of the spray dehydration for example the type of the nozzle, the size of the nozzle, the exit temperature, etc., necessary to produce particles that are porous, hollow structures, having at least one opening on their walls, they are inconvenient or uneconomical, and it is advantageous to produce particles that lack some or all of these characteristics. The anionic polymeric particles formed by the spray-drying processes of the present invention can be selected to remove a larger or smaller size fraction. The larger sized particles can be fragmented for example by milling, while the smaller sized particles are generally agglomerated. The sizes can be determined by methods known to those skilled in the art, for example screening, screening, scattering of light, microscopy, microscopic automated image analysis, etc. Surprisingly, the volumetric densities of the spray-dried anionic polymeric particles of the present invention are generally larger than the volumetric densities of the dry polymers prepared by the precipitation for example of the water-in-oil emulsions of the same polymer. The anionic polymer particles having a greater density can be advantageous because they occupy a smaller volume, leading for example to lower shipping and storage costs. Although the densities of the precipitated polymers are usually less than about 0.35 grams per cubic centimeter (g / cc), the volumetric densities of the spray-dried anionic polymer particles are generally about 0.35 g / cc or greater, preferably in a manner approximately 0.4 g / cc or greater, more preferably approximately 0.45 g / cc or greater, even more preferably approximately 0.50 g / cc or greater. The volumetric densities of the spray-dried anionic polymeric particles of the present invention are generally about 1.1 g / cc or less, preferably about 1.0 g / cc or less, more preferably about 0.95 g / cc or about smaller, even more preferably approximately 0.90 g / cc or less. Therefore, the volumetric densities of the spray-dried anionic polymeric particles of the present invention generally vary from about 0.35 to about 1.1 g / cc, preferably from about 0.4 to about 1.0 g / cc, more preferably approximately 0.45 to about 0.95 g / cc, even more preferably about 0.50 to about 0.90 g / cc. Under the drying conditions described herein, the anionic polymer particles produced herein, "substantially dry" generally means that the polymer contains about 12% or less of volatile substances, preferably about 10% or less by weight, based on the weight of the dehydrated polymer by spray. The polymer generally contains about 2% or more volatile substances, preferably about 5% or more, by weight based on the total weight, and even more preferably contains from about 8 to about 10% volatile substances by weight , on the same basis. The volatile substances are measured by determining the weight loss during drying of the polymer product at about 105 ° C for about 30 minutes. It has also been found that the agglomeration of the anionic polymer particles of the present invention can improve the flow properties and the dissolution times of the polymers. Agglomeration is a known process for increasing the particle size and various methods for agglomerating the particles are known to those skilled in the art., for example "Successfully Use Agglomeration for Size Enlargement", by Wolfgang Pietsch, Chemical Engineering Progress, April 1996, p. 29-45; "Speeding up Continuous Mixing Agglomeration with Fast Agitation and Short Residence Times", by Peter Koenig, Powder and Bulk Engineering, February 1996, p. 67-84. Known agglomeration methods such as natural agglomeration, mechanical agglomeration, drum agglomeration or growth, pressure agglomeration, agglomeration without binders, agglomeration with binders, etc., can be used to agglomerate the polymer particles of the 'present invention. The agglomeration can optionally be followed by drying, for example drying in a fluid bed, to remove the binder, for example water. Pressure agglomeration is preferred, and mechanical agglomeration using a binder for water, followed by drying in a fluid bed is more preferred. The agglomerates formed by the agglomeration of the anionic polymer particles of the present invention tend to have improved flow properties and faster dissolution times when compared to the non-agglomerated polymer particles. Preferably, the agglomerates are not converted to powder. Typically, about 90% of the agglomerates of the present invention have an agglomerate size of about 120 microns or greater, preferably about 160 microns or more, more preferably about 200 microns or more, even more preferably Approximately 300 microns or more. In general, about 90% of the agglomerates have an agglomerate size of about 1500 microns or less, preferably about 1200 microns or less, more preferably about 1100 microns or less, even more preferably about 1000 microns or less . Accordingly, approximately 90%, preferably 95%, of the agglomerates have a size in the range of from about 120 to about 1500 microns, preferably from about 160 microns to about 1200 microns, more preferably from about 200 microns to about 1100 microns. , even more preferably approximately 300 microns to approximately 1000 microns. Usually, at least about 5% of the agglomerates, preferably at least about 10%, even more preferably at least about 15%, are larger than about 900 microns. The agglomerates formed by the agglomeration of the spray-dried anionic polymer particles of the present invention can be screened to remove a larger or smaller size fraction. Preferably, agglomerates larger than about 1200 microns and smaller than about 175 microns are removed for example by screening. The larger sized agglomerates are generally fragmented for example by milling, while the smaller sized agglomerates are generally recycled to the agglomerator. The density values of the agglomerates of the present invention tend to be lower than the volumetric density values of the spray-dried anionic polymer particles from which they are formed. The volumetric densities of the agglomerates of the present invention are generally about 0.35 g / cc or greater, preferably about 0.4 g / cc or greater, more preferably about 0.45 g / cc or more, more preferably preferably approximately 0.50 g / cc or greater. The volumetric densities of the agglomerates of the present invention are generally about 1.0 g / cc or less, preferably about 0.95 g / cc or less, more preferably about 0.90 g / cc or less, even more preferably approximately 0.85 g / cc or less. Therefore, the volumetric densities of the agglomerates of the present invention generally vary from about 0.35 to about 1.0 g / cc., preferably from about 0.4 to about 0.95 g / cc, more preferably from about 0.45 to about 0.90 g / cc, even more preferably from about 0.50 to about 0.85 g / cc. In order to obtain the agglomerates of a preferred size, it is preferred that the polymer particles themselves be of such a size that they are agglomerable. The agglomeration obviously tends to the multiplication of the average particle size, so that it is often easier to cause large increases in particle size than to cause small increases in the size of the particle. Therefore, to produce agglomerates of a preferred size or size range, it is generally preferred to agglomerate particles that are much smaller than the size of the desired agglomerate, rather than the particles that are only slightly smaller. The agglomerable particles are generally those that can be conveniently agglomerated to produce agglomerates having a preferred size. It is possible, but less preferred, to agglomerate larger particles to produce agglomerates that are larger than desired, then remove the larger sized agglomerates as described above. The agglomerates and substantially dry polymer particles of the present invention are generally comprised of the polymer that was contained in the anionic aqueous dispersion that was dehydrated by spraying, as described hereinabove. As described above, the anionic aqueous dispersions of the present invention may contain more than one anionic polymer, for example they may contain a polymeric dispersant and may result from the combination of two or more aqueous anionic dispersions. Spray dehydration of these anionic aqueous dispersions can be advantageous because of typically 90% or more, preferably 95% or more, even more preferably substantially all, of the resulting spray-dried polymer particles each individually containing two or more water-soluble or water-swelling vinyl addition polymers, so that the effects of stratification can be minimized. Stratification can occur when two different dry polymers having different particle sizes or different particle size distributions are mixed together, because of the tendency for larger particles to settle to the bottom of the container. The stratification during storage can affect the operation of the combined product because the top of the container tends to become enriched in the polymer having the smallest particle size. For obvious reasons, changes in the performance of the product as a function of the storage depth are to be avoided, and it is generally preferred that each polymer in a mixture be of a similar particle size, see for example EP 479 616 Al and the US Patent No. 5,213,693. A dry blend of the two different polymers is likely to exhibit a larger stratification than a dry mixture obtained by spray drying the anionic aqueous dispersions comprised of the same two anionic polymers because the majority of the spray dried polymer particles will contain each one individually two or more water-soluble or water-swelling polymers, anionic. The suspensions of the dispersed solids can be dehydrated advantageously by the practice of the present invention. The dehydration process can be carried out by the intermixing of an aqueous dispersion of the polymers, or the dry polymer, or the aqueous mixture of the dispersion, or the aqueous mixture of the dried polymer, in an amount effective for flocculation, with a suspension of the dispersed solids, and dehydrate the suspension of the dispersed solids. Surprisingly, both the anionic aqueous dispersions of the present invention and the spray-dried anionic polymeric particles and agglomerates of the present invention tend to disperse and / or dissolve faster than the corresponding, conventional water-in-oil emulsions of similar polymers or dehydrated polymers by spray from them, respectively. Typically, the aqueous dispersion of the polymers, or the dry polymer, or an aqueous mixture of the dispersion, or the aqueous mixture of the dry polymer, acts to flocculate the dispersed solids so that the rate of dehydration is increased materially compared when the polymer It is not used. The dosages of the polymer are generally chosen to be effective for flocculating the solids and can be found by routine experimentation in a manner known to those skilled in the art. Typical polymer dosages range from about 0.0454 to about 2.27 kg (0.01-5 pounds), preferably about 0.454 to about 1362 kg (1-3 pounds) of the polymer, per dry ton of the flocculated solids. Examples of the suspensions of the dispersed solids which can be dehydrated by means of the present invention are dispersed mineral solids, dispersed cellulosic solids, and dispersed biological solids. Dirty or oily water can also be clarified by the practice of the present invention. Preferably, the dispersed solids are comprised of alumina, red mud, or silica; paper solids, or municipal or industrial wastewater. Because of the advantageous aspects of the invention for example minimal, substantially oil-free amounts, of the inactive diluents, a small amount or not of the surfactant, etc., the polymers can be especially well suited for situations where part or all dehydrated solids or clarified water is returned to the environment, such as mud mulches, application to mud soil, pelletizing for fertilizer application, clarified water release or recycling, paper making, etc. The present polymers can be used to flocculate food waste and can be additives for food. Other applications which can benefit from the advantageous aspects of the present inventions include soil composting, reforestation, erosion control, protection / growth of crops, etc., where the aqueous dispersion or the dry polymer, preferably an aqueous mixture thereof, is advantageously applied to the soil. Other examples of the suspensions of the dispersed solids which can be dehydrated by means of the present invention are found in the area of papermaking, for example aqueous dispersions or dry polymer can be used as retention aids, adjuvants drainage, adjuvants for formation, an auxiliary for the production of a scrubber / thickener / drainage (application for DNT bleaching), load control agents, thickeners, or for clarification, fading, clarification of the water from the bleaching process, sedimentation, color removal, or dehydration of the mud. The polymers of the present invention can also be used in field applications such as oil refining, water clarification, dewatering of debris, oil removal and oil production. Dehydration and clarification applications for the aqueous dispersions and dry polymers of the present invention can also be found in the food processing area, including the dehydration of the waste, preferably the dehydration of the waste from the beef, of the birds, of the pig and potatoes, as well as the discoloration of the sugar, the clarification of the processing of the sugar, and the clarification of the sugar of beet. Flocculated feed solids are not necessarily waste, and may find additional use for example as animal feed. Mining and mineral applications for aqueous dispersions and dry polymers of the present invention include dewatering and thickening of coal waste, thickened waste, and applications of the Bayer process such as sedimentation of red mud, washing of red mud, the filtration of the Bayer process, the flocculation of the hydrate, and the precipitation. Biotechnological applications for the aqueous dispersions and dry polymers of the present invention include dehydration and clarification of the waste and preferably, dehydration and clarification of the fermentation broths. The present aqueous dispersions can also be used as thickeners, for example as thickeners for printing inks.

The aqueous dispersions of the present invention can be employed in the above applications alone, in conjunction with, or in series with, other known treatments. All patents, patent applications, and publications mentioned above are incorporated herein by reference. Unless otherwise specified, all percentages mentioned herein are understood to be on a weight basis. The values of the volumetric viscosity (BV) in the following examples were measured at 20 ° C using a Brookfield Viscometer equipped with the spindle of the appropriate size. Viscosity values are reported in units of centipoise (cps). The Standard Viscosity (SV) values in the following Examples were determined by diluting the polymer composition for example the aqueous dispersion with water to form a 0.2 wt% polymer blend in water, by mixing together 8.0 g of this mixture and 8.6 g of NaCl 2M, then measuring the viscosity of the resulting mixture at 20 ° C using a rotary cylinder viscometer (Brookfield Viscometer) equipped with a UL adapter at 60 rpm. Molecular weights were determined by high resolution size exclusion chromatography using a light scattering detector or ultraviolet detector calibrated with polyacrylic acid standards. All pH values in the subsequent Examples were measured with a Combined pH Electrode from ROSS 8102BN connected to a Orion Model 520A pH meter, immersing the electrode in the sample. The calibration of the pH meter was carried out with buffer solutions of both pH 4.0 and pH 7.0.

Example 1C Preparation of Dispersant A (~ 25% by weight of the polymer solution of a 5% acrylamide in mol and 95% in mol of the acrylic acid copolymer): To a suitable reaction vessel equipped with stirring means, a thermocouple, and a nitrogen spray system is charged approximately 774.57 grams (g) of deionized water, approximately 38.49 grams of a 54.5% solution of acrylamide (AMD), approximately 15 grams of the disodium salt solution, of ethylenediaminetetraacetic acid to the 5% (EDTA) (chelating agent), and approximately 408.11 grams of 99% acrylic acid (AA). The pH of the resulting monomer solution was adjusted to about 5.75 by the addition of about 303.66 grams of a 30% ammonium hydroxide solution. The monomer solution was then sprayed with nitrogen while gradually cooling to about 6 ° C. After about 40 minutes, approximately 67.29 grams of a 30% ammonium persulfate solution and approximately 67.29 grams of 30% sodium metabisulfite solution, both of which have been sprayed separately with nitrogen, were added simultaneously. the reaction vessel with agitation. The temperature of the reaction rose rapidly to about 60 ° C. When the temperature of the reaction was lowered to about 52 ° C, the reactor was placed in a 63 ° C water bath and the polymerization was continued at this temperature for about four hours. The product was a viscous solution with a volumetric viscosity (Brookfield) of approximately 1420 cps. The polymer had a number average molecular weight of about 211,000 and a polydispersity of about 9.7 as determined by high pressure size exclusion chromatography (HPSEC) with an ultraviolet detector, calibrated with poly (acrylic acid) standards.

Examples 2 to 6C The following was added to a suitable reaction vessel equipped with agitation means, a thermocouple, and a nitrogen spray system: Approximately 60.52 grams of a 54% acrylamide solution, approximately 94.84 grams of deionized water, approximately 15.06 grams of a 50% solution of sodium 2-acrylamido-2-methyl-l-propanesulfonate (AMPS), approximately 0.61 grams of a pentasodium salt (chelating agent) of the 40% solution of diethyltriaminpentaacetic acid, approximately 0.24 grams of 89% lactic acid, approximately 13.82 grams of Dispersant A, approximately 9.56 grams of 99% acrylic acid, and approximately 2.86 grams of 99% methacrylic acid (MAA). After total mixing, the pH of the monomer solution was measured to be 4.03 at room temperature. The solution is stirred while its pH is adjusted to 5.3 with 8.2 grams of a 30% ammonium hydroxide solution. The temperature was maintained between 25 ° C and 30 ° C during the pH adjustment. After pH adjustment, approximately 69.7 grams of the ammonium sulfate were added and the solution was stirred to dissolve the salt. The pH was remeasured after the salt had dissolved and readjusted to 5.3 with 0.15 grams of a 30% ammonium hydroxide. It was found that in most cases, for example in this example and the following examples, that the pH did not change more than + 0.1 unit before and after the addition of the salt. The reaction vessel was then sprayed with nitrogen while stirring. After about 40 minutes, about 2.1 grams of a 2.5% solution of 2,2-azobis (2-amidinopropane) dihydrochloride (0.1% over the weight of the monomer) was added and the reaction temperature was raised to about 40 °. C. After about one hour, approximately 22.5 grams of a 40% ammonium sulfate solution was added through a syringe pump at a rate of approximately 0.28 milliliters / minute (ml / minute). The solution gradually became a white dispersion within the course of two hours. Six hours later, the temperature of the reaction was raised to about 50 ° C and maintained at 50 ° C for a total polymerization time of about ten hours. After polymerization, the product of the aqueous dispersion was discharged and its viscosity was measured with a Brookfield viscometer at 20 ° C. Examples 3 to 6C were prepared by a similar process except that the monomer compositions were varied as shown in Table 1 and the amounts of the ammonium sulfate were also varied slightly. Table 1 provides the volumetric viscosities (BV, in units of centipoises) of the resulting dispersions, as measured with a Brookfield viscometer at 20 ° C. All final concentrations of ammonium sulfate were calculated after taking into account any water loss during the process. The pH values of the products of the final aqueous dispersion were measured and it was generally found that they will be within + 0.1 unit before and after the polymerization. The results in Table 1 show the effect of varying the level of the salt and the polymer composition on the volumetric viscosity of the resulting aqueous dispersion.

Table 1 AMD: acrylamide AA: acrylic acid AMPS: sodium 2-acrylamido-2-methyl-l-propanesulfonate MAA: methacrylic acid Examples 7 to 9 The following was added to a suitable reaction vessel equipped with agitation means, a thermocouple, and a nitrogen spray system: Approximately 112.08 grams of a 50.4% solution of acrylamide, approximately 155.54 grams of deionized water, approximately 15.61 grams of a 50% solution of sodium 2-acrylamido-2-methyl-l-propanesulfonate, approximately 1.12 grams of a pentasodium salt (chelating agent) of a 40% solution of diethyltriaminpentaacetic acid, approximately 0.39 grams of lactic acid 89%, approximately 29.05 grams of Dispersant A, approximately 16.53 grams of 99% acrylic acid, and approximately 6.91 grams of 99% methacrylic acid. After total mixing, the pH of the monomer solution was measured to be 4.17 at room temperature. The solution is stirred while its pH is adjusted to 5.35 with approximately 16.61 grams of a 30% ammonium hydroxide solution. The temperature was maintained between 25 ° C and 30 ° C during the pH adjustment. After pH adjustment, approximately 131.31 grams of ammonium sulfate (~ 26% on the weight of the total batch) were added and the solution was stirred to dissolve the salt. The pH was measured again after the salt had dissolved and readjusted to 5.3 with approximately 0.1 grams of a 30% ammonium hydroxide. The reaction vessel was then placed in a water bath at 35 ° C and sprayed with nitrogen while about 29.1 grams of a dispersion (polymeric seed) prepared in the manner described in Example 4 was added with stirring. After approximately 50 minutes, approximately 3.2 grams of a 3% solution of ammonium persulfate and approximately 3.2 grams of a 3% sodium metabisulfite solution were added simultaneously with a syringe pump in the reaction vessel at a speed of approximately 0.0125 ml / min. The solution gradually became a white dispersion within the course of two to three hours, having dispersed polymer droplets of approximately 2 micrometers in size as observed under an optical microscope. Six hours later, the temperature of the reaction was raised to about 50 ° C and maintained at about 50 ° C for a total polymerization time of about ten hours. The product of the aqueous dispersion was then discharged and its volumetric viscosity was measured with a Brookfield viscometer at 20 ° C. Examples 8 and 9 were prepared by a similar process except that the monomeric compositions were varied and the total amount of the ammonium sulfate added was also slightly increased as shown in Table 2. The total ammonium sulfate concentrations as a whole were calculated after counting any water loss during the process. The pH values of the products of the final aqueous dispersion were found to be within + 0.1 unit before and after the polymerization. The results in Table 2 show the effect of varying the level of the salt and the polymer composition on the polymeric viscosity of the resulting aqueous dispersion and also demonstrate the use of a polymeric seed.

Table 2 AMD: acrylamide AA: acrylic acid AMPS: sodium 2-acrylamido-2-methyl-l-propanesulfonate MAA: methacrylic acid Examples 10 to 14C These examples were carried out in a manner similar to Example 7 except that sodium 2-acrylamido-2-methyl-l-propanesulfonate was not included and an additional 7.5 grams of ammonium sulfate was added to the monomer solutions. An aqueous dispersion prepared in a manner similar to Example 7 was used as the seed. Table 3 lists the volumetric viscosities of the resulting aqueous dispersions as a function of the polymer composition and the concentration of the salt.

Table 3 AMD: acrylamide AA: acrylic acid MAA: methacrylic acid Examples 15 to 18 (These examples were carried out in a manner similar to Example 2 except that the methacrylic acid was not included and the ammonium sulfate solution was not added during the polymerization.Also, the pH was adjusted to 5.5 (instead of 5.3 as in Example 2) The polymerization was continued at 40 ° C for 16 hours and at 50 ° C for four hours Table 4 lists the volumetric viscosities of the resulting aqueous dispersions as a function of the polymer composition and the level of the salt .

Table 4 AMD: acrylamide AA: acrylic acid AMPS: sodium 2-acrylamido-2-methyl-l-propanesulfonate Examples 19 to 20 These examples were carried out in a manner similar to Example 10 except that the pH was raised to 5.6 and 5.9, and the salt concentrations were slightly increased. Table 5 lists the volumetric viscosities of the resulting aqueous dispersions. These examples demonstrate that aqueous anionic dispersions having an apionic charge of not more than 16% and having advantageously low volumetric viscosities can be prepared by the practice of the present invention which remain in the form of aqueous dispersions even at pH 5.6 and 5.9.

Table 5 AMD: acrylamide AA: acrylic acid MAA: methacrylic acid Examples 21 to 23 These examples were carried out in a manner similar to Example 2 except that sodium 2-acrylamido-2-methyl-l-propanesulfonate was replaced with sodium 4-styrenesulfonate (SSNa) and neither acrylic acid nor lactic acid They were added. Also, about 0.16 grams (3.050 ppm over the total monomers) and 0.05 grams (740 ppm over the total monomers) of the glycidyl methacrylate crosslinking agent (GMA) were added to the monomer solutions in Example 22 and Example 23, respectively. In addition, the salt concentrations were slightly increased and 0.4% on the weight of the monomer of 2,2-azobis (2-amidinopropane) dihydrochloride was added as the initiator. The polymerizations were carried out at about 55 ° C for four hours and about 60 ° C for an additional four hours. Table 6 lists the volumetric viscosities of the resulting aqueous dispersions.

Table 6 AMD: acrylamide AA: acrylic acid SSNa: sodium 4-styrenesulfonate Examples 24 to 25 These examples were carried out in a manner similar to Example 7 except that the total anionicity of the polymers was 40% in Example 24 and 50% in Example 25. The concentration of sodium sulfate was 21.5%. An additional 29.8 grams of 42% ammonium sulfate solution (2.5% by weight of the total batch) were added at a rate of 0.3 ml / min during the polymerization. After the polymerization, approximately 15 grams (Example 24) or 20 grams (Example 25) of the ammonium sulfate were added. Table 7 provides the volumetric viscosities of the resulting anionic aqueous dispersions.

Table 7 AMD: acrylamide AA: acrylic acid AMPS: sodium 2-acrylamido-2-methyl-l-propanesulfonate MAA: methacrylic acid Example 26 These examples were carried out in a manner similar to Example 7 except that the total anionicity of the polymer was increased to 80%, the concentration of the total monomer was reduced from 17.5% to 15% and the weight of the total was reduced from 500 grams to 400 grams. The pH of the dispersion was 5.3. The polymer composition was, on a mole percent base, AMD / AA / AMPS = 20/40/40. Seed was added and a lower initial ammonium sulfate concentration (23% over the weight of the total lot) was used. Additional ammonium sulfate was added during the polymerization to lower the viscosity while increasing the concentration of the salt to the appropriate level. The final ammonium sulfate concentration was 29.3% and the volumetric viscosity of this anionic aqueous dispersion was 2.060 cps. This example demonstrates that an aqueous dispersion containing a polymer with an anionic charge of 80% can be prepared at a pH of 5.3.

Example 27 This example illustrates the preparation of an anionic aqueous dispersion at pH 6.3 at a batch scale of 1.8 kilograms. The polymer composition was, on a mole percent base, AMD / AA / AMPS = 35/5/60. The example was carried out in a manner similar to Example 26 except that the concentration of the total monomer was 17.5% and the initial ammonium sulfate concentration was 10% on the weight of the total batch. Additional ammonium sulfate was added during the polymerization to lower the viscosity while increasing the concentration of the salt to the appropriate level. The final ammonium sulfate concentration was 19.3% and the volumetric viscosity of the resulting anionic aqueous dispersion was about 2.125 cps.

Example 28 This example illustrates the incorporation of a hydrophobic monomer in an anionic aqueous dispersion at pH 5.3 for a batch scale of 400 grams. The hydrophobic monomer used was acrylonitrile (AN). The polymer composition was, on a mole percent base, AMD / AA / AMPS / AN = 65/15/15/5. The example was carried out in a manner similar to Example 26 except that the concentration of the initial ammonium sulfate was 21.5% on the weight of the total batch. Additional ammonium sulfate was added during the polymerization to reduce the volumetric viscosity while increasing the concentration of the salt to an appropriate level. The final ammonium sulfate concentration was 26.2% and the volumetric viscosity of the resulting anionic aqueous dispersion was about 4,000 cps.

Example 29 In this example, an aqueous anionic dispersion was prepared at pH 6.5 having an anionic polymer composition of AMD / AA / AMPS = 70/20/10. The monomer concentration was 10% and the ammonium sulfate concentration was 27.5% based on a total lot weight of 300 grams. The dispersant was a copolymer of 50 mol% acrylamide and 50 mol% acrylic acid and was prepared by a process similar to Example 1, except that the weight% of the polymer was 15%. The polymerization was carried out in a manner similar to Example 26, using a ratio of monomer to dispersant (M / D) of 12: 1 (based on the actual polymer, except that approximately 1.2 grams of a persulfate solution of 2.5% ammonium were added initially to the monomer solution, followed by the addition of approximately 4.5 grams of a 0.75% sodium metabisulfite solution at a rate of approximately 0.02 ml / min to initiate the polymerization, and no acid was added The polymerization was carried out at about 35 ° C for about 16 hours, then at about 45 ° C for about four hours.The volumetric viscosity of the resulting aqueous dispersion was about 3.660 cps.

Example 30 In this example, an anionic aqueous dispersion was prepared having an anionic polymer with an AMD / AA / AMPS composition = 73.95 / 14.55 / 11.5 and also containing an additional 15 ppm (based on total monomer weight) of N, N '-methylenebisacrylamide (MBA). The concentration of the monomer was about 15% and the concentration of the ammonium sulfate was about 22% based on a total lot weight of 300 grams. The dispersant was a copolymer of 20 mol% acrylamide and 80 mol% acrylic acid, and was prepared by a process similar to Example 1 (except that the weight% of the polymer was 15%), and had a weight Weighted average molecular weight of approximately 442,000 and a polydispersity of approximately 11.3. The preparation of the dispersion was similar to that of Example 26 at a pH of 5.3, using a ratio of monomer to dispersant (M / D) of 15: 1 (based on the actual polymer), except that approximately 1.87 grams of a 2.5% ammonium persulfate was initially added to the monomer solution, followed by the addition of about 7.0 grams of a 0.75% sodium metabisulfite solution at a rate of about 0.02 ml / min to initiate the polymerization. The polymerization was carried out at about 40 ° C for about 16 hours, then at about 50 ° C for about four hours. The resulting anionic aqueous dispersion had a volumetric viscosity of about 65,000 cps.

Examples 31-35 These examples illustrate the effect of the concentration of the salt on the volumetric viscosity of the anionic aqueous dispersions. The dispersion was prepared at pH 5.3 on a batch scale of 1.5 kilograms. The polymer composition was, on a mole percent base, AMD / AA / AMPS / MAA = 70/20/5/5. The polymerization process was similar to Example 7 except that the initial ammonium sulfate concentration was about 21.5% over the weight of the total batch and about 107.14 grams of a 42% ammonium sulfate solution was added at a rate of about 0.3 ml / min during the polymerization to reduce the viscosity while raising the concentration of the salt to the appropriate level. The final ammonium sulfate concentration was 24.9% and the volumetric viscosity of the resulting aqueous dispersion was about 7,700 cps. Additional ammonium sulfate was added progressively to reduce the volumetric viscosity. Table 8 gives the total ammonium sulfate concentrations after each addition of the salt and the corresponding volumetric viscosities.

Table 8 / AMD: acrylamide AA: acrylic acid AMPS: sodium 2-acrylamido-2-methyl-l-propanesulfonate MAA: methacrylic acid Examples 36-40 These examples illustrate the effect of the level of the dispersant on the volumetric viscosity of the anionic aqueous dispersion. The polymerization process was conducted in a manner similar to Example 24 except that the polymer composition was AMD / AA / AMPS / MAA = 70/20/3/7 and the batch weight was about 400 grams. The amount of the dispersant is shown in Table 9 as a function of the weight ratio of the monomer to the dispersant (M / D). Table 9 lists the M / D ratio and the final salt concentrations of these anionic aqueous dispersions and their corresponding volumetric viscosities.

Table 9 Example 41 This example illustrates the preparation of an anionic aqueous dispersion subsequently reacted. A dispersion containing an anionic polymer having an AMD / AA / AMPS = 74 / 14.5 / 11.5 composition was prepared at a pH of 5.3 in a manner similar to that described in Example 30, except that the MBA was not added and an M / D of 15: 1 was used. The monomer concentration was about 17.5% and the ammonium sulfate concentration was about 22% based on a total lot weight of 300 grams. The dispersant was a copolymer of 5 mol% acrylamide and 95 mol% acrylic acid prepared as in Example 1C, which has a weight average molecular weight of 163,000 and a polydispersity of 9.3. The aqueous dispersion had a volumetric viscosity of 5.280 cps which was reduced to 544 cps after adding the ammonium sulfate to increase the concentration of the salt from 22% to 23.1%. The post-hydroxaction reaction was carried out on a 50 gram sample of the dispersion sample in which the pH was adjusted to 6.0 with the sodium hydroxide solution. Approximately 0.68 grams of the sulfuric acid hydroxylamine salt was added to this sample, the sample was thoroughly mixed, and the resulting mixture was placed in an oven at 50 ° C overnight. The hydroxamated aqueous anionic dispersion did not show any significant change in the characteristics of the dispersion. A ferric ion test on the anionic polymer showed the existence of the hydroxamic acid salt groups.

Example 42 This example illustrates a method of using an anionic aqueous dispersion to dehydrate a suspension of dispersed mineral solids. An anionic aqueous dispersion with an anionic polymeric composition of AMP / AA / AMPS = 74 / 14.5 / 11.5 was prepared at pH 5.3 by a process similar to that described in Example 30, except that the MBA was not added, the concentration of the monomer it was 17.5%, the dispersant was a copolymer containing 95% acrylic acid and 5% acrylamide, and the polymerization was carried out at 35 ° C for 16 hours and at 45 ° C for an additional 4 hours. The resulting aqueous dispersion had a volumetric viscosity of about 403 cps. A suspension of mineral coal was obtained having a solids level of approximately 5%. The aqueous dispersion is diluted with water to make three dosage solutions. Each of the dosing solutions was then intermixed vigorously with the respective samples of the mineral carbon suspension at a dose of about 1.5 parts of the polymer by weight per parts in million by volume of the mineral carbon suspension (ppm), 2.0 ppm and 2.5 ppm, respectively. The flocculated mineral carbon solids were allowed to settle and the sedimentation rate and clarity of the supernatant were measured. These velocities and clarities of sedimentation were comparable with those achieved with mineral, anionic, commercial dehydration products.

Example 43 This example demonstrates a method of using an anionic aqueous dispersion to dehydrate a suspension of the dispersed paper solids. An aqueous dispersion containing an anionic polymer with an AMD / AA / MAA = 70/20/10 composition was prepared at pH 5.3 by a process similar to that described in Example 10 except that approximately 126.26 grams of the ammonium sulfate % on the weight of the total batch) were added and a redox initiator was used (3% sodium bromate / 0.4% S02). The resulting aqueous dispersion had a volumetric viscosity of about 3.940 cps. A paper retention test was carried out on an alkaline paper raw material having a concentration of 3.52 grams per liter. The raw materials were first treated with an alum solution (5 ppm, based on paper solids) and a cationic starch solution (10 ppm, paper based) to form a pretreated suspension of the paper solids. Three polymer dosing solutions were prepared by diluting the aqueous dispersion so that the polymer dosage was 2 ppm, 4 ppm and 6 ppm (based on paper solids) for the three dosage solutions, respectively. Each dosing solution was then intermixed vigorously with a respective sample of the pretreated suspension of the paper solids to produce flocculated paper solids, then the drainage rates were determined through the flocculated paper solids. Drain times were 51, 59 and 67 seconds for the dosing solutions of 2 ppm, 4 ppm and 6 ppm, respectively. These drainage speeds are comparable with those achieved with anionic, commercial, retention aids.

Example 44 This example demonstrates a method for using an aqueous anionic dispersion to dehydrate a suspension of the dispersed solids in a paper fading process. An aqueous anionic dispersion containing an anionic polymer with a composition of 7? MD / AA / MAA = 70/20/10 was prepared at pH 5.1 by a process similar to that described in Example 10 except that the weight of the total batch was of 2.18 kilograms, the level of ammonium sulfate was 28% by weight, the dispersant was a commercial AMD / AA copolymer containing 70% acrylic acid and 30% acrylamide (made by hydrolysis of polyacrylonitrile), an aqueous dispersion prepared in a manner similar to Example 12 was used as the seeding, and a redox initiator (3% sodium bromate / 0.4% sulfur dioxide) was used to initiate the polymerization. The resulting anionic aqueous dispersion had a volumetric viscosity of about 1440 cps. A paper suspension containing approximately 0.25% of the magazine and newsprint was obtained. Three polymer dosage solutions were prepared by diluting the aqueous dispersion so that the polymer dosage was 1 ppm, 1.5 ppm and 2 ppm (based on paper solids) for the three dosage solutions, respectively. The test was carried out on three samples of the paper suspension by adding 8 ppm (based on paper solids) of a low molecular weight cationic polymer to each suspension, followed by the three dosage solutions, respectively. The resulting mixtures were stirred, the solids allowed to settle for 30 seconds, and the clarity of the supernatant was measured. In a control sample without the anionic polymer, the turbidity of the supernatant was approximately 1,970 NTU. For each of the dosage solutions containing the anionic polymer, improved clarity was obtained as evidenced by the turbidity values which were below about 500 NTU. At the doses of 1.5 ppm and 2.0 ppm, the turbidity values were below 300 ppm. These results of clarity are comparable with those achieved with anionic, commercial desizing products.

Example 45 This example demonstrates the preparation of an aqueous anionic dispersion which contains a polymer that can be swollen with water with the composition AMD / AA / SSNa = 77.5 / 15 / 7.5. In addition to the three monomers, 500 ppm (based on the total monomer weight) of the N, N'-methylenebisacrylamide (MBA) is also added. The monomer concentration was about 10% and the ammonium sulfate concentration was about 27.5% based on the total batch weight of 300 grams. The dispersant was a copolymer of 50 mol% acrylamide and 50 mol% acrylic acid prepared by a process similar to that described in Example 1. The aqueous dispersion was prepared in a similar manner to Example 26 except that the pH of the dispersion was 6.6, and 1.2 grams of the 2.5% ammonium persulfate solution were initially added to the monomer solution, followed by the addition of 4.5 grams of 0.75% sodium metabisulfite solution at a rate of 0.02 ml / min to start the polymerization. The polymerization was carried out at about 35 ° C for about 16 hours, then at about 50 ° C for about four hours. The volumetric viscosity of the resulting anionic aqueous dispersion at pH 6.6 was 40,500 cps. The dispersion is diluted with water to form a mixture with a polymer concentration of about 0.2%. This mixture had a cloudy appearance, indicating the presence of the polymer that can be swollen with water.

Example 46 This example demonstrates the preparation of an aqueous anionic dispersion which contains a water soluble polymer with the composition AMD / AA / MAA = 67.5 / 20 / 12.5 at pH 5.2. The process was carried out in a manner similar to Example 44, except that the sodium bromate was added to the monomer solution instead of being added during the polymerization. The resulting anionic aqueous dispersion contained 28.4% ammonium sulfate and had a volumetric viscosity of 3.560 cps.

Example 47 This example was carried out in the same manner as Example 46, except that only 40% of the methacrylic acid charge was present when the polymerization was started and the polymerization time was 6 hours. A solution of 20% acrylic acid in 10% ammonium sulfate with pH adjusted to 5.2 was prepared using the remaining 60% methacrylic acid. Thirty minutes later the polymerization was started, this methacrylic acid solution was continuously added to the reaction vessel by means of a syringe pump during the course of about six hours. The resulting anionic aqueous dispersion prepared by this monomer feed process had a volumetric viscosity of 810 cps, when compared to the volumetric viscosity of 3.560 cps achieved in Example 46. This example demonstrates that a monomer feed process can be used to significantly reduce the volumetric viscosity of an anionic aqueous dispersion.

Example 48 The aqueous dispersion of Example 27 was dehydrated by spraying on a commercially available laboratory spray drier. The laboratory spray dehydrator chamber was 760 millimeters (mm) in diameter with a vertical side of 860 mm and a conical bottom of 65 degrees. The nominal gas flow through the dehydrator was approximately 180 cubic meters per hour. The aqueous dispersion feed was fed in the center of the upper part of the chamber using a variable speed pump, through a nozzle for two fluids using air for atomization. The temperature of the exit gas was 86 ° C and was controlled by varying the inlet gas temperature (165 ° C) and the feed rate (60 milliliters / minute) To provide an inert atmosphere, the spray drier was supplied with the nitrogen gas from a cryogenic storage tank The dried polymer product was discharged through the bottom of the dehydrator cone to a cyclone where the dried product was removed and collected. about 15 seconds, the resulting spray-dried polymer particles, were agglomerated to provide the agglomerates of the anionic polymer, readily soluble in water, having a volatile substance content of 3.2% and a bulk density of approximately 0.40 grams per cubic centimeter (g / cc).

Examples 49 to 50 An aqueous dispersion having a volumetric viscosity of about 2920 cps was prepared in the same manner as Example 42, except that the dispersant was a 15% solution of a poly (acrylic acid) having a molecular weight of about 124,000. The ratio of the monomer to the dispersant (M / D, based on the actual polymer) was 15. This aqueous dispersion was concentrated by placing approximately 114 grams in a suitable vessel and heating to 45 ° C under flowing nitrogen. A total of 23.2 grams of water were removed by this process of dehydration. The aqueous dispersion remained stable demonstrating that dehydration is effective to achieve aqueous dispersions of low volumetric viscosity, with a high level of solids, as shown in Table 10.

Table 10 Viscosity Solids Example No. Polymer > (%) Volumetric (cps) 49 (as polymerized) 18.6 2920 50 23.4 880 It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following

Claims

1. An aqueous dispersion, characterized in that it is comprised of: (a) a solution of the salt comprised from about 5% to about 35% of the inorganic salt, by weight based on the aqueous dispersion; and (b) a water-soluble or water-swellable, anionic vinyl addition polymer, which is comprised of more than 16 mole percent of anionic recurring units, based on the total moles of the recurring units in the polymer, and which is insoluble in the salt solution; wherein the polymer is comprised of a number of anionic recurring units, selected from the group consisting of methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, vinyl sulfuric acid, vinylphosphonic acid , styrenesulfonic acid, styrenesulfuric acid, ammonium and alkali metal salts thereof, and mixtures thereof, which is effective in rendering the polymer insoluble in the salt solution at a pH of 5.1; and wherein the aqueous dispersion is substantially free of an amount of the cationic organic salt that is effective to precipitate the polymer.

2. An aqueous dispersion according to claim 1, characterized in that at least about 20% of the anionic recurring units are methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, or ammonium or an alkali metal salt thereof.

3. An aqueous dispersion according to claim 1, characterized in that it also comprises a second water-soluble, anionic polymer, which is soluble in the salt solution.

4. An aqueous dispersion according to claim 1, characterized in that the anionic polymer is also comprised of recurrent hydrophobic units.

5. An aqueous dispersion according to claim 1, characterized in that the polymer is substantially free of the cationic recurring units containing the benzyl group.

6. An aqueous dispersion according to claim 1, characterized in that the anionic polymer contains the hydroxamic acid or the hydroxamic acid salt groups.

7. A process for making an aqueous dispersion, characterized in that it comprises polymerizing the anionic vinyl addition monomers to form a water-soluble or swellable polymer with water having more than 16 mol% of anionic recurring units, based on in the total moles of the recurring units in the polymer; wherein the polymerization is carried out in an aqueous solution comprised from about 5% to about 35% of the inorganic salt, by weight based on the aqueous dispersion; wherein the anionic vinyl addition monomers are comprised of an amount of the anionic monomers, selected from the group consisting of methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, acid vinyl sulfuric acid, vinyl phosphonic acid, styrenesulfonic acid, styrene sulfuric acid, ammonium and alkali metal salts thereof, and mixtures thereof, which is effective in rendering the polymer insoluble in the salt solution at a pH of 5.1; and wherein the aqueous solution is substantially free of an amount of the cationic organic salt that is effective to precipitate the polymer.

8. A process according to claim 7, characterized in that the anionic recurring units are comprised of 20 mol% or more of the recurring units selected from the group consisting of methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, and ammonium and alkali metal salts thereof.

9. A process according to claim 7, characterized in that the aqueous solution is further comprised of a second water-soluble, anionic polymer, which is soluble in the aqueous solution.

10. A process according to claim 7, characterized in that the anionic polymer is substantially free of the cationic recurring units containing the benzyl group.

11. A process according to claim 7, characterized in that a portion of the inorganic salt is added to the aqueous solution during the course of the polymerization.

12. A process according to claim 7, characterized in that a portion of the anionic vinyl addition monomers is added to the aqueous solution during the course of the polymerization.

13. A process according to claim 7, characterized in that the aqueous solution comprises a seed polymer.

14. A process according to claim 13, characterized in that the seed polymer is comprised of the residue of a previous polymerization batch.

15. A process according to claim 7, characterized in that it also comprises the subsequent reaction of the anionic polymer.

16. A process according to claim 7, characterized in that it further comprises dehydrating the aqueous dispersion to form a concentrated aqueous dispersion.

17. A method of dehydrating a suspension of dispersed solids, characterized in that it comprises intermixing an aqueous dispersion of polymers, or an aqueous mixture thereof, in an amount effective for flocculation, with a suspension of the dispersed solids, and dehydrating the slurry suspension. the dispersed solids, wherein the aqueous dispersion is comprised of (a) the salt solution comprised from about 5% to about 35% of the inorganic salt, by weight based on the aqueous dispersion; and (b) a water soluble or swellable, anionic vinyl addition polymer, which is comprised of more than 16 mol% of anionic recurring units, based on the total moles of the recurring units in the polymer, and because it is insoluble in the salt solution; wherein the polymer is comprised of a number of anionic recurring units, selected from the group consisting of methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, vinyl sulfuric acid, vinylphosphonic acid , styrenesulfonic acid, styrenesulfuric acid, ammonium and alkali metal salts thereof, and mixtures thereof, which is effective in rendering the polymer insoluble in the salt solution at a pH of 5.1; and wherein the aqueous dispersion is substantially free of an amount of the cationic organic salt that is effective to precipitate the polymer.

18. A method according to claim 17, characterized in that the suspension of the dispersed solids is comprised of paper solids, biologically treated solids or mineral solids.

19. A method according to claim 17, characterized in that the polymer contains hydroxamic acid or groups of the hydroxamic acid salt and wherein the dispersed solids are comprised of red mud.

20. A process for producing particles of water-soluble or water-swellable polymer, anionic, substantially dry, characterized in that it comprises: (a) spray-drying an aqueous dispersion containing the water-soluble or swellable polymer water, anionic, in a gas stream with a residence time of about 8 to about 120 seconds and an outlet temperature of about 70 ° C to about 150 ° C; and (b) collecting the resulting anionic polymer particles.

21. A process according to claim 20, characterized in that it also comprises agglomerating the anionic polymer particles.

22. A process according to claim 20, characterized in that the aqueous dispersion is comprised of two or more water-soluble or water-swellable, anionic polymers.

23. The anionic polymer particles, characterized in that they can be obtained by the process according to claim 20.

24. The agglomerates of the anionic polymer, characterized in that they can be obtained by agglomerating the anionic polymer particles according to claim 23.