Using bipolar membrane electrodialysis to synthesize di-quaternary ammonium hydroxide and optimization design by response surface methodology

Bipolar membrane electrodialysis (BMED) has already been described for the preparation of quaternary ammonium hydroxide. However, compared to quaternary ammonium hydroxide, di-quaternary ammonium hydroxide has raised great interest due to its high thermal stability and good oriented performance. In order to synthesize N,N-hexamethylenebis(trimethyl ammonium hydroxide) (HM(OH)2) by EDBM, experiments designed by response surface methodology were carried out on the basis of single-factor experiments. The factors include current density, feed concentration and flow ratio of each compartment (feed compartment: base compartment: acid compartment: buffer compartment). The relationship between current efficiency and the above-mentioned three factors was quantitatively described by a multivariate regression model. According to the results, the feed concentration was the most significant factor and the optimum conditions were as follows: the current efficiency was up to 76.2% (the hydroxide conversion was over 98.6%), with a current density of 13.15 mA·cm− 2, a feed concentration of 0.27 mol·L− 1 and a flow ratio of 20 L·h− 1:26 L·h− 1:20 L·h− 1:20 L·h− 1 for feed compartment, base compartment, acid compartment, and intermediate compartment, respectively. This study demonstrates the optimized parameters of manufacturing HM(OH)2 by direct splitting its halide for industrial application.