EP1968899A2

EP1968899A2 - Thermally regenerable salt sorbent resins

Info

Publication number: EP1968899A2
Application number: EP07716360A
Authority: EP
Inventors: Roger E. Johnson; Gerald Colombo
Original assignee: Novation Environmental Technologies Inc
Current assignee: Haws Corp
Priority date: 2006-01-05
Filing date: 2007-01-05
Publication date: 2008-09-17
Also published as: WO2007081803A2; WO2007081803A3; EP1968899A4

Abstract

Embodiments of the present invention are directed to thermally regenerable salt sorbent resins and methods of treating an aqueous fluid. Embodiments of the method of the invention comprise contacting the aqueous fluid within a first temperature range with a mass of thermally regenerable salt sorbent resin comprising weak acid groups with pKa between 4 and 6 and base groups having a pKb greater than 7.5. In certain cases, the thermally regenerable salt sorbent resin comprises a first phase comprising a host macroporous copolymer of a polyunsaturated monomer and a monoethylenically unsaturated monomer containing the weak acid groups and a second phase comprising a crosslinked guest copolymer of a polyunsaturated monomer and a monoethylenically unsaturated monomer containing the base groups.

Description

Thermally Regenerable Salt Sorbent Resins

TECHNICAL FIELD OF THE INVENTION

The invention is directed to thermally regenerable salt sorbent resins and use thereof for removing or reducing the concentration of dissolved salts contained in an aqueous fluid. Embodiments of the thermally regenerable salt sorbent of the invention comprise functional groups comprising a pKb greater than 7.5.

BACKGROUND OF THE INVENTION Conventional thermally regenerable salt sorbent resins ("TRSS resins") comprise discrete weak acid functionality and weak base functionality in resin particles. Such TRSS resins are hybrid resins comprising a macroporous copolymer, termed the "host polymer" and a polymer at least partially filling the macropores of the host polymer, termed the "guest polymer." The host polymer and the guest polymer typically are different polymers, not only with respect to the weak acid and weak base functionality, but also to the properties of the polymeric network of each copolymer.

Aqueous fluids comprising ionic contaminants may be contacted with the TRSS resin to remove the ionic contaminants or "soften" the aqueous fluid. The ionic contaminants are loaded on to the resin. Prior to the loading of ionic contaminants onto the resin, the ion- exchange groups are internally oriented with functional groups of the opposite polarity, thus maintaining a general overall electrical neutrality in the resin. This is shown on the left-hand side of Figure 1 below. When exposed to aqueous fluid comprising ionic contaminants at ambient temperature, the internal functional groups of both polarities preferentially interact with the external ionic contaminants, and the contaminants are loaded onto the resin. A loaded resin is shown on the right-hand side of Figure 1. This occurs until the available ion-exchange sites are fully occupied and the resin is fully loaded. Strictly speaking, TRSS resins are not true ion- exchangers because the counter-ions are built into the polymeric structure of the resin, and therefore, counter-ions are not released into the aqueous phase as contaminants are adsorbed.

TRSS may easily be regenerated. To regenerate TRSS resins, the adsorbed ionic contaminants are released simply by contacting the loaded TRSS resin to an aqueous fluid at elevated temperatures, typically 90-100° C. Previous research has shown that thermal regeneration is driven by the temperature dependencies of the ionization constants Ka and Kb of the respective functional groups. Thus at elevated temperatures, conditions are formed in which the carboxylic and amine functionalities are weakened such that no internal association occurs and the absorbed salt is released into the heated water. Once the TRSS resin is cooled to room temperature, internal 'self association' of the zwitterions reoccurs. During thermal regeneration, a concentrated salt regeneration effluent (brines) is produced, however, no net addition of salts to ^• the environment occurs as in normal ion exchange resins. See Figure 1.

The term "hybrid" indicates that the TRSS resins have some of the characteristics or properties of both a gel and a macropσrous copolymer. The pores of the macropσrous host copolymer are typically filled with the guest copolymer utilizing varying percentages of a crosslinking agent by introducing the guest polymer or the guest copolymer-forming monomer components in varying amounts. The resins may also be prepared by filling the pores of the macroporous host copolymer with additional macroreticular copolymers in varying amounts with varying crosslinking agents or varying amounts of phase extender. Hybrid resins are described in United States Patent Nos. 3,991,107; 4,136,067; and 4,152,496, which are hereby incorporated by reference in their entirety.

Such TRSS resins are described in United States Patent Application Publication US 2006/0054561 Al, which is hereby incorporated by reference in its entirety. In certain embodiments, the host copolymer may comprise the weak acid functionality and the guest copolymer comprises the weak base functionality. A portion of the weak acid and weak base functionality may associate in the resin to form a zwitterionic state. Thereby the resin may act as a typical ion exchange resin for the adsorption of ions, such as the adsorption of salt ions dissolved in water, without the "exchange" of ions occurring. A typical zwitterionic interaction is shown in Figure 1.

As used herein, the term "elution" refers to the removal of ions, both cations and anions, which have been loaded on to the resin during the absorption process. The term

"regeneration" refers to restoration of the functional groups in the resin to the zwitterion form. These operations are each thermally activated and essentially simultaneously occur. Therefore, elution will necessarily also involve regeneration.

SUMMARY Embodiments of the present invention are directed to thermally regenerable salt sorbent resins and methods of treating an aqueous fluid. Embodiments of the method of the invention comprise contacting the aqueous fluid within a first temperature range with a mass of thermally regenerable salt sorbent resin comprising weak acid groups with pK_a between 4 and 6 and base groups having a pKb greater than 7.5. In certain cases, the thermally regenerable salt sorbent resin comprises a first phase comprising a host macroporous copolymer of a polyunsaturated monomer and a monoethylenically unsaturated monomer containing the weak acid groups and a second phase comprising a crosslinked guest copolymer of a polyunsaturated monomer and a monoethylenically unsaturated monomer containiαg the base groups.

In embodiments of the invention the thermally regenerable salt sorbent resin comprises weak acid groups having pK_a between 4 and 6 and and base groups having a pK_b greater than 7.5, wherein the weak acid groups and the base groups form zwitterions within the resin.

It should be noted that, as used in this specification and the appended claims, the singular forms "a," "and," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a polymer" may include more than one polymer. Unless otherwise indicated, all numbers expressing quantities of ingredients, time, temperatures, and so forth used in the present specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad ^■ scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, may inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

It is to be understood that this invention is not limited to specific compositions, components or process steps disclosed herein, as such may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 shows the internal zwitterions of the TRSS resins and the loading/regeneration cycles involved in the process of the present invention;

Figure 2 is a graph of the bicarbonate ions concentration in the regeneration effluent for a test of loading/regeneration cycles for softening of water by TRSS 100 and TRSS 200; and Figure 3 is a graph of the bicarbonate ions concentration in the regeneration effluent for a test of loading/regeneration cycles for softening of water by TRSS 200 and TRSS 300. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The thermally regenerable salt sorbent resins according to the present invention comprise both weakly acidic groups and basic groups within a resin matrix. The TRSS resins may be hybrid resins in the form of beads which have as a macroporous matrix comprising a host copolymer having weak acid groups and a guest polymer comprising basic groups. In certain embodiments, the guest polymer at least partially fills the pores of the host polymer.

The resins according to the present invention may be used to remove the salts from an aqueous solution. The hybrid resins have use for deionizing water, desalination, desalting urine to a level where it may be used directly as a hydrogen source for plants, purification for water regeneration on space vehicles, decolorizing sugar solutions, and decontaminating or purifying industrial waste water.

The hybrid resins will be contacted with the liquid containing the salts to be removed at temperature range, typically from about 5° C to 25° C. To regenerate the hybrid resin, that is, to remove the cations and anions associated with the adsorbed salt from the resin, the resin may be contacted with or flushed with an aqueous liquid at a higher temperature, typically in the range of about 60-100° C. After cooling to 3-25° C, the hybrid resin returns to its original zwitterionic state.

Embodiments of the TRSS resin may be made by polymerization of a mixture of guest copolymer precursor monomers and chain extenders in the presence of a host precursor macroporous copolymer. The resultant macroporous copolymer will be a precursor of the final TRSS resin in which the weak acid groups may be protected functionalities, such as carboxylic acid esters, which are convertible to weak acids. The precursor monomers of the guest copolymer bear functional groups which are precursors that are capable of being converted to basic groups. The backbone of the host macroporous copolymer may be a crosslinked copolymer of (1) a polyunsaturated monomer containing a plurality of non-conjugated ethylenic groups (CHb=C-) and (2) a monoethylenically unsaturated monomer, either aromatic or aliphatic.

Suitable polyunsaturated monomers include divinylbenzene, divinyltolueήes, divinylnaphthalenes, diallyl phthalate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, neopentyl glycol dimethacrylate, bis-phenol A • dimethacrylate, pentaerythritol, terra- and trimethacrylates, divinylxylene, divinylethylbenzene, divinylsulfone, divinylketone, divinylsulfide, allyl acrylate, diallyl maleate, diallyl fumarate, diallyl succinate, diallyl carbonate, diallyl malonate, diallyl oxalate, diallyl adipate, diallyl sebacate, divinyl sebacate, diallyi tartrate, diallyl silicate, triallyl tricarballylate, triallyl aconitate, triallyl citrate, triallyl phosphate, N,N'-methylenediacrylamide, N,N'-methylene dimethacrylamide, N,N' ethyienediacrylamide, trivinylbenzene, trivinykiaphthalene, polyvinylanthracenes and the polylallyl and polyvinyl ethers of glycol glycerol, pentaerythritol, resorcinol and the monothio- or dithio-derivatives of glycols. Suitable monoethylenically unsaturated monomers for the macroporous host copolymer or the guest copolymer comprise esters of acrylic acid, such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, tert-butyl acrylate, ethylhexyl acrylate, cyclohexyl acrylate, isobornyl acrylate, benzyl acrylate, phenyl acrylate, alkylphenyl acrylate, ethoxymethyl acrylate, ethoxyethyl acrylate, ethoxypropyl acrylate, propoxymethyl acrylate, propoxyethyl acrylate, propoxypropyl acrylate, ethoxyphenyl acrylate, ethoxybenzyl acrylate, ethoxycyclohexyl acrylate, the corresponding esters of methacrylic acid, styrene, o-, m-, and p-methyl styrenes, and o-, m-, and p-ethyl styrenes, dimethyl itaconate, vinyl naphthalene, vinyl toluene and vinylnaphthalene. A class of monomers of particular interest consists of the esters of acrylic and methacrylic acid with Cj-Cio aliphatic alcohol. The formation of the macroporous host copolymer will result in a precursor copolymer which will contain pendant functionalities which can be converted to weak acids. For example, referring to FIG. 1, if an ester of acrylic acid is used as the monoethylenically unsaturated monomer, the resultant host precursor copolymer will contain carboxylic acid ester groups which can later be converted to carboxylic acid groups by hydrolysis. The crosslinked guest precursor copolymer may be formed from a polyunsaturated monomer and a monoethylenically unsaturated monomer containing functional groups which can be converted to weak bases. Suitable polyunsaturated monomers used to form the guest precursor copolymer are the same as the polyunsaturated monomers which may be used to form the host macroporous copolymer. The suitable monoethylenically unsaturated monomers containing a functional group which can be converted to a basic group are monoethylenically unsaturated monomers containing haloalkyl groups. Such haloalkyl groups include, but are not limited to, chloromethyl and/or bromomethyl. The groups will be attached to the monoethylenically unsaturated portion of the monomer, as in for example, p-vinyl benzyl chloride (VBC). Thus, for example, the crosslinked guest precursor copolymer may be formed by polymerization of VBC and divinylbenzene to form a guest precursor copolymer having pendant chloromethyl groups. Methods for preparing the host macroporous copolymer are known in the art. See for example U.S. Pat. Nos. 3,275,548 and 3,357,158. The formation of the crosslinked guest precursor copolymer in the presence of the macroporous host precursor copolymer is a polymerization generally carried out in the presence of a radical polymerization initiator, such as, but not limited to, benzoylperoxide, t-butyl hydroperoxide, lauroyl peroxide, cumene hydroperoxide, tetralin peroxide, acetyl peroxide, caproyl peroxide, t-butyl perbenzoate, t-butyl diperphthalate, methyl ethyl ketone peroxide, for example. The amount of initiator required is roughly proportional to the concentration of the mixture of monomers. The usual range is 0.01% to 5% by weight of initiator with reference to the weight of the monomer mixture. Another suitable class of free- radical generating initiators includes the azo catalysts, including for example, azodiisobutyronitrile, azodiisobutyramide, azobis(.alpha.,.alpha.-dimethylvaleronitrile), azobis(a- methyl-butyronitrile), dimethyl_;, diethyl, or dibutyl azobis(methyl-valerate). These and other similar azo compounds, which serve as free radical initiators, contain an -N=N-- group attached to aliphatic carbon atoms, at least one of which is tertiary. An amount of 0.01 to 2% of the weight of monomer or monomers is usually sufficient.

Conditions for forming the guest precursor copolymer in the presence of the host macroporous precursor copolymer are known in the art. Typically the polymerization to form the guest precursor copolymer is conducted in a liquid, such as water that is not a solvent for monomeric material. However, a precipitant must also be present which acts as a solvent for the monomer mixture but which is chemically inert under the polymerization conditions. The presence of the precipitant causes a phase separation of the product hybrid copolymer. The determination and selection of such precipitants are known in the art.

The relative amounts of guest precursor polymer and MP host precursor copolymer can be varied over a wide range. It is desirable, however, to use at least 50 parts by weight of guest precursor copolymer per 100 parts by weight of MP base or host precursor polymer, with the maximum amount being dictated by that amount which can be imbibed or retained in or on the MP structure. This maximum will ordinarily be about 300 parts by weight of guest precursor copolymer per 100 parts by weight of base precursor polymer, although higher amounts can also be used. Preferably, the amounts of guest precursor copolymer to MP base will be in the range of about 100 to 200 parts of guest precursor copolymer per 100 parts of MP polymer.

The hybrid resin and the methods of the present invention in which the pores of the macroporous host copolymer are filled with a crosslinked guest copolymer are prepared by adding a monomer mixture containing the components necessary to form the crosslinked guest precursor copolymer directly to the host macroporous precursor copolymer in its dry state. While not intending to be bound by a particular theory, it is believed that the monomer is adsorbed or imbibed into the pores of the macroporous copolymer and the imbibed monomers are polymerized within the macroporous host copolymer beads after heating the mixture to initiate the polymerization. Thereafter, the ionic functional groups are introduced to create the internal zwitterions relationship. United States Patent Application US 2006/0234141 describes a process for preparing TRSS resins by treating the hybrid resin with a weak base such as dialkyl amine to convert the haloalkyl groups to amine groups and by hydrolyzing the carboxylic ester groups, or other protected weak acid functionalities, on the host precursor copolymer to weak acid groups. Since the guest copolymer is held within the pores of the host copolymer, the weak base groups of the guest polymer and weak acid groups of the host polymer are in close proximity to each other and they may thus form internal zwitterions. An aqueous fluid comprising a salt may be passed over, or otherwise placed in contact with, the TRSS resin. While in contact, the cation and anion of the ionic contaminants associate with the respective weak base and weak acid groups, thus, interposing in the zwitterions. The ionic contaminants are thus loaded on the TRSS resin without a corresponding exchange of ions as in traditional ion exchange resins. Since no traditional ion exchange takes place, thermal removal of the adsorbed salt may be accomplished at relatively moderate temperatures, typically in the range of about 60- 100° C, such as by simply contacting the TRSS resin with hot water, preferably hot deionized water or hot product or softened water. The TRSS resins of the present invention provide a surprising improvement over the TRSS resins. The prior art TRSS resins produced from dimethyl amine ("DMA") to form the basic functionality on a benzyl ring may effectively soften typical residential waters. However, in certain applications, TRSS resins produced from DMA were not able to be regenerated a sufficient number of times to be practical, such as for certain high hardness residential water softening applications. While not wishing to limit the invention, it is believed that the prior art TRSS resins produced from DVB and DMA for the basic functionality are subject to fouling by bicarbonates in the water to be treated. Typical public water sources comprise bicarbonates, primarily calcium bicarbonate and to a lesser extent sodium bicarbonate. It is not certain whether the bicarbonate fouling is due to physical or chemical fouling of the TRSS resin. In the prior art TRSS resins produced from DMA, the amine functionality is connected to the polymeric network of the guest polymer through a chemical linker comprising a benzyl ring. Due to the resonance stability effects of the benzyl ring, the basicity of the tertiary amine group is reduced to a pKb of approximately 7. The inventors postulated that the fouling of the TRSS resin was predominantly due to chemical fouling rather than a physical fouling of the macropores of the host polymer. The fouling would prevent the TRSS resin from being fully regenerated and would result in decreased capacity after a number of loading/regeneration cycles. The ability of a TRSS resin to be regenerated may be tested through a series of loading/regeneration cycles. Loading/regeneration test results for the prior art TRSS resins produced from. DMA show that such resins may be commercially acceptable for some industrial and residential softening applications, however, the number of times that such TRSS resins may be loaded and regenerated may limit their use in certain other applications. Figure 2 is a graph of the bicarbonate in the regeneration effluent of two different TRSS resins, TRSS 100 (Prior art, Formula 1) and TRSS 200 (Formula 2). TRSS 100 is produced according to the methods described above, wherein the aminolysis reaction between the halogen of the guest polymer and DMA forms the weak basic functionality. Aminolysis is a chemical reaction in which a molecule reacts with a molecule of ammonia or an amine to form a basic functionality. In this case, the aminolysis reaction involves the replacement of the chlorine group on the benzyl chloride with the amine along with the corresponding elimination of hydrogen halide (HX). Another aminolysis reaction with primary or secondary amines involves a carboxylic acid group or with a carboxylic acid derivative to form an amide. TRSS 200 is produced similarly to TRSS 100 except the aminolysis reaction was between the halogen of the guest polymer and dimethyl amino propylamine ("DMAPA") to form the basic functionality. DMAPA has a higher PK_b when attached to the poiymer backbone (pK_b of approximately 7.5), considering that the resonance stabilization effects of the benzyl group in the chemical linker is diluted by the increased distance between the amine and the benzyl ring.

Host Polymer

Formula Ir TRSS 100 Formula 2: TRSS 200

The concentration of bicarbonate in the regeneration effluent for the loading/regeneration cycling of the test of TRSS 100 is shown in Figure 2. The data is from loading/regeneration experiments performed with an aqueous feed comprising a calcium bicarbonate concentration of approximately 190 ppm in aqueous fluid of the loading phase. During the loading phase, or water softening, the ionic contaminants in the aqueous feed are at normal ambient temperatures and the internal functional groups of both polarities of the zwitterions preferentially interact with the ionic species in the aqueous feed to trap the hardness of the opposite polarity, and thereby the ionic contaminants are loaded onto the TRSS resin and softened product water is produced. The TRSS 100 resin was then regenerated by passing heated softened product water over the TRSS 100 resin at a temperature of approximately 85° C to release the adsorbed contaminants and regenerate the zwitterionic state of the TRSS 100, once cooled to room temperature. The regeneration effluent was analyzed for bicarbonate ions and the concentration of bicarbonate ion is plotted in. Figure 2. There are two lines of the loading/regeneration data in Figure 2. One line is the actual bicarbonate concentration data from the loading/regeneration test; the other line is the difference between the concentration of the bicarbonate in the regeneration effluent and the bicarbonate concentration in the product water used to regenerate the TRSS resin. As can be seen, the concentration of bicarbonate ion in the regeneration effluent is lower than the original bicarbonate in the feed stream. In fact, the second line (TRSS 100 minus product water) shows that the bicarbonate ion concentration in the regeneration effluent was lower than the bicarbonate ion concentration in the softened product water used to regenerate the TRSS 100 resin. See Figure 2. The loaded bicarbonate was clearly fouling the resin by some mechanism since the bicarbonate is not found to be in the effluent product water. From the bicarbonate decomposition equation shown below, it was hypothesized that the bicarbonate may be decomposing to CO₂ and water. It was speculated that the TRSS resin was being either physically or chemically fouling the resin by the remaining calcium. A proposed mode of chemical fouling was suspected and is shown in Scheme 1.

The typical reaction scheme for the decomposition of carbonate and scale formation is shown in Scheme 2.

CO₂ + H₂O — H⁺ H- HCO₃ 2H⁴^ CO₃ 2- As shown in Scheme 1, as a result of the decomposition of the carbonate ions, the host polymer was converted to the calcium form of the polyacrylic acid. The conversion of the host polymer to the calcium form of a polyacrylic acid results in reducing the softening effectiveness of the TRSS resin by reducing the number of regenerated zwitterions. The inventors speculated that a stronger relationship between the ions in the zwitterionic state would prevent chemical fouling of the TRSS resin by such a mechanism. A stronger relationship between the ions was created by increasing the basicity of the anionic group of the guest polymer, however, the relationship between the zwitterionic groups could also be strengthened by increasing the acidity of the cationic group, changing the composition of the chemical linkage between the anionic and/or the cationic functional groups and the polymer, changing the composition of the polymer, or changing the structure of the polymer to place the cationic and anionic functional groups in closer proximity, for example. A stronger relationship between the ions may be created by changing the base functional group to one prepared from amines with higher basicity than DMA, such as, but not limited to, dimethylamino propylamine, triethylenetetramine, diethylenetriamine, tetraethylenepentamine, or ethylenediamine. Similar loading/regeneration cycling testing was performed using TRSS 200 resins produced with DMAPA. Figure 3 shows the results of this test. As can be seen, TRSS 200 performed significantly better than TRSS 100 in the loading/ regeneration testing. As may be seen in Figure 3, the bicarbonate concentration in the regeneration effluent of the TRSS 200 test continues to rise as with increasing loading/regeneration cycles. However, if the data is reviewed after consideration of the concentration of bicarbonate ions in the product water that was used to regenerate the TRSS 200 resin, it can be seen that the resin begins to foul after 30 loading/regeneration cycles and the concentration of bicarbonate ions being removed from the resin begins to drop decrease. However, the increased ionic attraction of the ionic components of the zwitterions has improved the ability of the TRSS resin to be regenerated. As can be seen in Figure 2, the relationship of the two curves showing the data related to the regeneration of TRSS 200, significantly more unloaded bicarbonate ions are present in the regeneration effluent than with TRSS 100, in fact, after compensation for the bicarbonate in the softened product water used as the regeneration feed, the curve labeled TRSS 200 minus product water indicates clearly that bicarbonate that was loaded on the resin is being released into the regeneration effluent. A third TRSS resin was prepared with a further increase in the basicity of the base functionality of the guest polymer. The base functionality of the TRSS 300 resin has a pKb of approximately 8. TRSS 300 was produced similarly except the aminolysis reaction was performed with the halogen of the guest polymer and triethylene tetramine ("TETA") to form the basic functionality. TETA has a higher PK_b when attached to the polymer backbone. Similar loading/regeneration cycling testing was performed using TRSS 300 resins produced with TETA ■ as with the other two resins, however, the regeneration cycle for the TRSS 300 was performed with deionized water instead of product water. Deionized water was used as the regeneration feed instead of softened product water to clearly show the bicarbonate ions that were unloaded from the resin. The concentration of bicarbonate in the regeneration effluent for the loading/regeneration cycling of the test of TRSS 300 is shown in Figure 3 for each cycle. The data is from experiments performed with an aqueous feed comprising a calcium bicarbonate concentration of approximately 190 ppm in the loading phase. As can be seen in Figure 3, the TRSS 300 resin with the greatest basicity in the functional groups of any of the tested resins shows a steady state concentration of bicarbonate in the regeneration effluent indicating that decomposition of the bicarbonate in the resin and fouling of the resin by bicarbonate is reduced.

It is a further advantage of the present invention, and which is unexpected, that capacities of the resins of the invention are greatly improved over similar host-guest hybrid resins known in the art. The following example will further illustrate the invention but are not intended to limit it. In the present application, parts and percentages are given by weight unless otherwise stated. EXAMPLE l

Resins according to the present invention were compared. The as resins TRSS 100 and TRSS 200 and 300 of the present invention were produced according to the process described in United States Patent Application Publication No US 2005/0234141, which is hereby incorporated by reference in its entirety.

The hybrid thermally regenerable salt sorbent (TRSS) resins are formed from a hybrid precursor hybrid resin having two relatively independent phases. The hybrid precursor resin is formed by intimately mixing at a temperature less than about 40 ⁰C. a nonaqueous solution of a polyunsaturated monomer, a monoethylenically unsaturated monomer containing a haloalkyl group and a polymerization initiation reagent with a dry, solid host crosslinked macroporous copolymer to imbibe the nonaqueous solution into the macroporous copolymer to form a polymerization mixture. The polymerization mixture is heated to a temperature between about 70 °C. to 100⁰C for a period of time sufficient to polymerize the polyunsaturated monomer with the monoethylenically unsaturated monomer containing a haloalkyl group to thereby form the hybrid precursor resin.

The precursor resin formed is a hybrid copolymer containing a crosslinked macroporous host copolymer phase containing functionalities convertible to weak acid groups, having at least some of the pores filled with a crosslinked guest copolymer phase containing haloalkyl groups. The hybrid precursor resin is then converted into the hybrid TRSS resin by treatment with DMA (TRSS 100) to at least partially convert the haloalkyl groups to weak base groups to form a heterogenous hybrid weak base resin; and treating the heterogenous hybrid weak base resin with a hydrolyzing agent to thereby at least partially convert the functionalities to weak acid groups. One phase comprises the host crosslinked macroporous copolymer having weak acid groups and the other phase comprises the crosslinked guest copolymer having weak base groups.

Other resins according to the present invention, TRSS 200 and TRSS 300 were made with the modifications as indicated above. In order to reduce the resonance stability effect of the ionic functionality of the host and guest polymers, polymers prepared without aromatic rings may provide a stronger ionic interaction between the zwitterions of the TRSS resin. One manner that this could be accomplished would be for the preparation of a host polymer from acrylate monomers only. The acrylates may be hydrolyzed to carboxylic acid functional groups and reacted with amines to form amine functionality. One method of preparing such a TRSS resin is provided below. The example below is prepared from methyl acrylate (MA), but any acrylate may be used. To prepare the acrylic host polymer, an aqueous solution containing 0.25 g NaCl, and 2.6 g of DPADMAC (10% solids) may be added in 3 necked round bottom flask fitted with thermometer, overhead stirrer and reflux condenser. The stirrer will be started to insure complete dissolution of reactaαts. The water amount may be about 100 ml. A monomer mix may be prepared in a separate beaker containing 47.5 g MA, 2.2 g DVB, 0.45 g DEGDVE, 20 gms diisobutyl ketone and 1.17g of lauroyl peroxide. The monomer mix may be added dropwise to the aqueous solution. At that point the power control on the.heating mantle may be turned on to start heating the suspension polymerization. The temperature should be controlled between 65-70° C for 2.5 hours, and after cooling the reaction mixture the resultant macroporous copolymer may be collected on a Buchner funnel and dried in an oven overnight. The guest polymer may be prepare in the macropores of the host polymer by adding 50 gms of dried MA host polymer to 47.5 gms MA, 2.2 gms DVB, 0.45 gms DEGDVE (diethylene glycol divinyl ether), 20 gms diisobutyl ketone and 1.17 gms lauroyl peroxide and rolled in rotary flask for 3 hours or until a free-flowing hybrid resin is obtained. The rotary flask containing the hybrid resin may then submerged in a water bath heated to 70° C, and held at that approximately that temperature for 3 hours to complete polymerization of the guest polymer. The resultant acrylic hybrid copolymer was collected on a Buchner funnel and dried overnight.

The process may be completed by formation of the anionic and cationic functionalities to from the acrylic TRSS resin. To form the basic functionality, 50 gms of DAMAPA, (0.5 mole) and 76 gms (1.0 mole) of AHC can be charged to a 3 necked flask fitted with thermometer, overhead stirrer and reflux condenser. DI water may be added to make a good slurry and the flask was heated to 90-95° C for 6 hours. After cooling to room temperature, 20 gms (0.5 mole) NaOH may be added, the flask may be heated to 90-95° C, and held at this temperature for 3 hours. After cooling, the resin may be rinsed with DI water until a conductivity of < 100 mohms is obtained. The resultant TRSS resin may then be acidified to pH 6.0 by adding 0. IN HCl to the resin slurry.

Claims

CLAIMS:

1. A method of treating an aqueous fluid, comprising the step of: contacting the aqueous fluid within a first temperature range with a mass of thermally regenerable salt sorbent resin comprising weak acid groups with pKa between 4 and 6 and base groups having a pK_b greater than 7.5.

2. The method of claim I₉ wherein the thermally regenerable salt sorbent resin comprises a first phase comprising a host macroporous copolymer of a polyunsaturated monomer and a monoethylenically unsaturated monomer containing the weak acid groups and a second phase comprising a crosslinked guest copolymer of a polyunsaturated monomer and a monoethylenically unsaturated monomer containing the base groups.

3. The method of claim 2, wherein the pores of said host macroporous copolymer are at least partially filled with the guest copolymer;

4. The method of claim 1, comprising: regenerating the thermally regenerable salt sorbent resin by elution with an aqueous regenerant fluid within a second temperature range wherein said second temperature range is greater than said first temperature range.

5. The method of claim 1, wherein said first temperature range is about 5° C. to 25° C.

6. The method of claim 1 , wherein the base groups have a pK_b greater than 8.0.

7. The method of claim 1, wherein the weak acid groups comprise a carboxylic acid group.

8. A thermally regenerable salt sorbent resin, comprising: weak acid groups having pKa between 4 and 6; and base groups having a pK_b greater than 7.5, wherein the weak acid groups and the base groups form zwitterions within the resin.

9. The thermally regenerable salt sorbent resin of claim 1, wherein the thermally regenerable salt sorbent resin comprises a first phase comprising a host macroporous copolymer of a polyunsaturated monomer and a monoethylenically unsaturated monomer containing the weak acid groups and a second phase comprising a crosslinked guest copolymer of a polyunsaturated monomer and a monoethylenically unsaturated monomer containing the base groups.

10. The thermally regenerable salt sorbent resin of claim 9, wherein the pores of said host macroporous copolymer are at least partially filled with the guest copolymer;

11. The thermally regenerable salt sorbent resin of claim 8, wherein the base groups have a pK_b greater than 8.0.

12. The thermally regenerable salt sorbent resin of claim 8, wherein the weak acid groups comprise a carboxylic acid group.

13. The thermally regenerable salt sorbent resin of claim 8, wherein the weak acid groups comprises at least one of carboxylate, phosphate, or sulphonate.

14. The thermally regenerable salt sorbent resiα of claim 8,- wherein the groups are derived from at least one of dimethylamino propylamine, triethylenetetramine, diethylenetriamiαe, tetraethylenepentamiαe, or ethylenediamine.