A new method of gel-coating polyethyleneimine (PEI) on organic resin beads. High capacity and fast kinetics of PEI gel-coated on polystyrene

A new process has been developed for gel-coating a high-capacity weak-base resin, polyethyleneimine (PEI), on an inert organic support, polystyrene (P S), used as macroporous spherical beads. The process produces a thin and fi rm coating of PEI, cross-linked with glutaraldehyde and chemically bonded t o the PS surface through carboxylic acid groups, created a priori by exposu re to a chromic acid solution in glacial acetic acid for 3 h at the reflux temperature. Designated as OPS . . . [PEI.XG], the spherical gel-coated bea ds afford nearly full attainment of the theoretical proton capacity of the coated resin and exhibit significantly faster attainment of equilibrium sor ption, compared to a conventional bead-form ion exchanger. Ascorbic acid an d UO2SO4 have been used as test sorbates for comparing the performance of O PS . . . [PEI.XG] with that of a commercial weak-base resin poly(4-vinylpyr idine) (PVP). In an ascorbic acid substrate solution, the gel-coat layer of OPS . . . [PEI.XG] exhibits a sorption capacity of 12 mmol/g of (dry) resi n, as compared to 2 mmol/g of(dry) PVP resin beads, while for UO22+ the cor responding capacities are 4.5 and 1.1 mmol/g of dry resin, respectively. La rge differences are also observed in sorption rates of gel-coated resin bea ds, in which the sorption is largely confined to the surface gel layer, and conventional resin beads, in which sorption occurs in the whole matrix.