Application of weakly basic copolymer polyacrylamide (acrylamide-co-N,N,'-dimethylaminoethyl methacrylate) gels in the recovery of citric acid

We have successfully used different crosslinked copolymer polyacrylamide gels with a variable amount of cationic copolymer, N,N-dimethylaminoethyl methacrylate (DMA), to concentrate solutions of citric acid. Gel-swelling behaviour was studied as a function of crosslinker density, monomer concentration (gel structure) and percentage of ionizable monomer (degree of gel ionization). Using experimental design, response surfaces of the swelling ratio as a function of gel composition were calculated. The results obtained were in good agreement with other experimental data as well as with the Flory-Huggins theory for ionic gels. The recovery efficacy was a function of pH, ionic strength and percentage of ionizable monomer. (C) 1997 Elsevier Science Ltd.