Selective Adsorption Of H-acid On Polyethyleneimine Ion Exchange Resins

l-Amino-8-naphthol-3,6-disulfonic acid (H acid) is an important dye intermediate which is widely used in the production of various dyes. The wastewater derived from manufacturing H acid is difficult to deal with due to its high organic matter concentration, complex composition, strong inorganic salt content and low biodegradability.In the present study, the PEI resin was prepared via the reaction of chloromethylated PS-DVB copolymer beads with polyethyleneimine (PEI). The PEI resin was molecular imprinted using H acid as template molecule and epichlorohydrin (EGDE) as crosslinking reagent and molecular imprinted material H-PEI resin was prepared. The adsorption behaviors of both the resins for H acid, 1-amino-naphthalene-3,6,8-trisulfonic acid (T acid) and 2-naphthalene sulfuric acid in single systems were investigated, and the recognizing selectivity of resins towards H acid was analyzed. This study also researched the influences of time and sodium sulfate concentration on the adsorption performance of the resins for H acid. Further, the adsorption selectivity for H acid in composite systems and the desorption property of resins were compared.The results showed that the optimum pH for adsorption was about 3, and the adsorption isotherms could be described by Langmuir equation. Thermodynamic data indicated that the adsorption process was spontaneous and exothermic. In single and composite systems, the adsorption selectivity of H-PEI resin for H acid was higher than that of PEI resin, which illustrated that molecular imprinting was conducive to improve the selectivity of a resin and the enhanced selectivity was mainly determined by the size of imprinting holes. Kinetic studies showed that the adsorption data of H acid on the resins fitted well to the pseudo-second-order equation. The rate constant of H-PEI resin was greater than that of PEI resin, which indicated that molecular imprinting could help reach adsorption equilibrium faster. The adsorption capacity of H acid on resins decreased with the increase of the content of sodium sulfate, but it was higher on H-PEI resin than that on PEI resin among the tested range of sodium sulfate concentrations, which showed that molecular imprinting was beneficial to enhance salt-resistance of a resin. The performance of both the resins in dynamic adsorption systems was favorable and the adsorption selectivity of H-PEI resin for H acid was better. The resins could be well desorbed by using sodium hydroxide aqueous solution.