A Thermally Regenerable Composite Sorbent of Crosslinked Poly(acrylic acid) and Ethoxylated Polyethyleneimine for Water Desalination by Sirotherm Process

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(EPELXG), 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 well-known 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 degrees C but less than 0.1 meq/g (dry) sorbent, respectively, at 30 degrees C but less than 0.1 meq/g (dry) sorbent at 80-90 degrees C. The equilibrium sorption data at 30 degrees C fit well to both Langmuir and Freundlich isotherms for single-component sorption and to Butler-Ockrent and Jain-Snoeynik 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 ion-exchange process, yielding diffusivity values of 1.0-1.3 x 10(-6) cm(2)/s for NaCl and 3.0-3.5 x 10(-7) cm(2)/s for MgCl(2), in the initial period at 30 degrees C, with the diffusivity falling abruptly in both cases at higher conversions. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 2741-2750, 2009