Synthesis of quaternary ammonium hydroxide from its halide salt by bipolar membrane electrodialysis (BMED): effect of molecular structure of ammonium compounds on the process performance

BACKGROUNDConventional methods for synthesis of quaternary ammonium hydroxides, such as the reaction of quaternary ammonium chloride, ion-exchange and electro-electrodialysis cannot achieve benign production of QAOH without secondary pollution. The objective of the present study was to develop bipolar membrane electrodialysis with a novel stack configuration as an improved method to prepare high purity quaternary ammonium hydroxide from its halide salt. RESULTSTo investigate the synthesis of quaternary ammonium hydroxide (QAOH) with high purity by using electrodialysis with bipolar membranes (BMED), four different types of quaternary ammonium hydroxides (tetramethylammonium hydroxide, TMAOH; tetrapropylammonium hydroxide, TPAOH; methyltriethylammonium hydroxide, MTAOH; and benzyltrimethylammonium hydroxide, BTAOH) were chosen as the target products. The effect of the molecular structure of four different types of halide salts (NR4X) on the BMED performance was studied by investigating operating parameters such as current density, feed concentration and feed flow velocity and energy consumption on the basis of ion dimensions and molecular weight, ion electrophoretic mobility and the interaction between ammoniums and membranes. The results indicate that it is feasible to obtain quaternary ammonium hydroxides with high purity (Cl-/Br- content<500ppm) by BMED with a novel four-compartment configuration in view of environmental aspects. CONCLUSIONFor converting higher molecule size halide salts, the process performance was lower, while the energy consumption increased, at similar experimental conditions, which is in line with the theory. (c) 2014 Society of Chemical Industry.