A thermally regenerable composite sorbent of crosslinked poly(acrylic acid) and ethoxylated polyethyleneimine for water desalination by Sirotherm process

Abstract

Crosslinked poly(acrylic acid) (XPAA) made by copolymerization of acrylic acid and ethylene glycol dimethacrylate in bulk was further reacted with 80% ethoxylated polyethyleneimine, and the latter insolubilized by treatment with glutaraldehyde. The resulting composite sorbent, XPAA(EPEI.XG), containing carboxylic acid groups and weakly basic tertiary amine groups in close proximity in the same resin bead exhibited thermally regenerable desalination property, simulating the wellknown Sirotherm TM resins. For NaCl and MgCl 2 , the sorbent has saturation capacities of 0.796 and 0.839 meq/g (dry) sorbent, respectively, at 30 C but less than 0.1 meq/ g (dry) sorbent at 80-90 C. The equilibrium sorption data at 30 C fit well to both Langmuir and Freundlich isotherms for single-component sorption and to Butler-Ockrent and Jain-Snoeyink models for bicomponent sorption. Although the sorption of NaCl exhibits a plateau in the pH range of 4-5, that of MgCl 2 increases sharply above pH 4 because of additional sorption by cation exchange at the ionic sites formed at higher pH. The sorption rate data show characteristics of particle-diffusion controlled ionexchange process, yielding diffusivity values of 1.0-1.3 Â 10 À6 cm 2 /s for NaCl and 3.0-3.5 Â 10 À7 cm 2 /s for MgCl 2 , in the initial period at 30 C, with the diffusivity falling abruptly in both cases at higher conversions.

Study of a new process for the efficient regeneration of ion exchange resins

“…Recent studies [16,17] on thermally regenerable composite (Sirotherm-type) resins showed that a weak acid/weak base mixed bead resin had a substantially reduced ion adsorption capacity at higher temperatures. Heating from 30°C to 80°C reduced the capacity by a factor of 8 [16].…”

“…The "Plum pudding" resin structure, which is prepared by embedding microparticles of polyamines and microparticles of polyacids in a water and salt permeable matrix, has been discussed by Bolto and Jackson [8]; who also described the disadvantage of the presence of a high proportion of inert polymeric matrix material, which tends to limit the thermally regenerable capacity of a particular resin. Studies have been carried out by Hatch [25], Bolto and Jackson [8] and Chanda et al [16] to overcome this issue.…”

“…A thermally regenerable composite resin of crosslinked polyacrylic acid and ethoxylated polyethyleneimine was used for water desalination more recently by Chanda et al [16,17]. This type of resin, which is similar to that used in the present study, can be regenerated thermally with no apparent loss of capacity for up to 10 cycles of operation [16]. Sirotherm resins are composed of weak acid and weak base groups; thus during the exchange process a proportion of the Na + and Cl − ions remain in the solution, due to the hydrolysis of the weak resin salts.…”

“…Therefore, high purity deionized water cannot be produced using these resins and they are suitable only for partial removal of salts. Sirotherm resins are typically usable only for partial removal of salts which have salinities in the range of 2000 and 3000 mg/l [16].…”

Salt‐free softening by thermo‐reversible ion‐adsorbing hydrogels

“…1,2 The current technology to bind multivalent ions is based commonly on the use of ion exchange resins (IEX). 3,4 Regeneration of IEX typically involves high temperatures [5][6][7] or consecutive washing steps involving brine or acid and caustic, 8 leading to a large amount of waste salt. 9,10 The disposal of these salts cause salinization of surface waters and soil, which is an increasing burden for the environment.…”