Superabsorbent polymer (SAP) hydrogels for protein enrichment

Superabsorbent polymer (SAP) hydrogels are mainly acrylic based polymer hydrogels which are capable of absorbing water around 100 times of their own weight. Thus these are supposed to be the promising material which can be incorporated as a draw agent in forward osmosis (FO) process. In this paper, superabsorbent polymer hydrogels are used as a draw agent for protein enrichment in FO process so that structure of protein remains intact during dewatering process. Though the free swelling capacity of hydrogels in aqueous medium is high, due to their slow swelling rates water fluxes obtained in FO process are much lower as compared to conventional salts used as a draw solute. Thus in this paper research emphasis was given on increasing swelling rates of hydrogels to improve water fluxes by graft copolymerizing acrylic acid monomer on carboxymethyl cellulose (CMC) polymer. Moreover, for feasible recycling of these draw agents, a thermoresponsive polymer N-isopropyl acrylamide (NIPAM) was copolymerized with superabsorbing acrylic acid monomer and thermal dewatering process was used to regenerate the hydrogels. The synthesized hydrogels were tested as a draw agent in FO for bovine serum albumin (BSA) protein enrichment experiments. As the enrichment is directly related to the absolute weight of water extracted from the feed solution, the performance was presented in terms of enrichment factors. Thermally regenerated hydrogels were again recycled back to the process, and some reduction in enrichment was observed. Further based on the results obtained with different membrane area, mass of hydrogels, swelling ratios and water recovery rates, parameters for hydrogel assisted FO process are predicted for various applications. (C) 2015 Elsevier B.V. All rights reserved.