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 (PS), used as macroporous spherical beads. The process produces a thin and firm coating of PEI, cross-linked with glutaraldehyde and chemically bonded to the PS surface through carboxylic acid groups, created a priori by exposure 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 beads afford nearly full attainment of the theoretical proton capacity of the coated resin and exhibit significantly faster attainment of equilibrium sorption, compared to a conventional bead-form ion exchanger. Ascorbic acid and UO 2 SO 4 have been used as test sorbates for comparing the performance of OPS···[PEI.XG] with that of a commercial weak-base resin poly(4-vinylpyridine) (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) resin, as compared to 2 mmol/g of (dry) PVP resin beads, while for UO 2 2+ the corresponding capacities are 4.5 and 1.1 mmol/g of dry resin, respectively. Large differences are also observed in sorption rates of gel-coated resin beads, in which the sorption is largely confined to the surface gel layer, and conventional resin beads, in which sorption occurs in the whole matrix.