Intraparticle diffusion during selective ion exchange with a macroporous exchanger

Abstract

Chlorophenols, quaternary ammonium compounds, benzene and naphthalene sulfonates and benzene carboxylates are examples of environmentally significant synthetic organic compounds which exist as ions in water over a wide range of pH values. This study discusses the sorption kinetics, and more specifically, intraparticle diffusion behaviors of trace concentrations of pentachlorophenate (PCP −) and other chlorophenates onto a commercially available macroporous polymeric anion exchanger (IRA-900). The anion exchanger is essentially biphasic, i.e. every single exchanger particle contains an enormous number of tiny microgels and an interconnected network of pores. Ion exchange functional groups reside solely within the microgels. For comparison, a gel or microporous anion exchanger is also included in the study. Experimental results reveal a distinctly different type of effect of competing chloride ion concentration on gel and macroporous ion exchangers pertaining to sorption of pentachlorophenate (PCP −). While the effective intraparticle diffusivity of PCP − for gel-type resin remained unaltered with a change in competing chloride concentration, the same increased significantly for the macroporous exchanger with an increase in chloride concentration. Pore diffusion is considered to be the predominant intraparticle transport mechanism for highly preferred PCP − inside the macroporous exchanger. Under the normal hydrodynamic conditions of a fixed bed column run, intraparticle diffusion was found to be the rate-limiting step. For various chlorophenates, the effective intraparticle diffusivities were inversely correlated to the octanol–water partition coefficients of their parent chlorophenols.