The Reasearch On Organic Quaternary Ammonium Hydroxide By Bipolar Membrane Electrodialysis

Quaternary ammonium hydroxide are organic hydroxide which have alkalinity as similar as sodium hydroxide and potassium hydroxide,and they are widely used in some fields,including microelectronics industry,large-scale integrated circuits and chemical industry.However,the traditional process of synthesis qua-ternary ammonium hydroxide is easily to introduce impurity ions such as Br-,Cl-,Na+,which caused the low purity of quaternary ammonium hydrixude.Besides that,the traditional synthetic techniques of quaternary ammonium hydroxide have some disadvantages,for example environmental pollution and the difficulty of post-processing,thus limiting its application to a great extent.Bipolar membrane electrodialysis(BMED)is a new type of electric-membrane separation process combining the composite structure of bipolar membrane(BPM)and traditional electrodialysis(ED).Under the influence of a direct current filed,water molecules will be split into OH-and H+ in the bipolar membrane.Meanwhile,in the brine solution,OH-will combine with cation to generate base in the base cell,and H+ will combine anion to produce the corresponding acid in the acid cell.There are no newly introduced ingredients and others by-products in BMED process.Compared with the traditional production process,BMED is energy-saving and environmental-protecting.Therefore,this paper chose the BMED process to synthesis quaternary ammonium hydroxide from the corresponding quaternary ammonium salt solution.In this paper,two different structure types of quaternary ammonium hydroxide were prepared by bipolar membrane electrodialysis and the operation variables for experiment were optimized.The main conclusions are as follows:(1)Using bipolar membrane electrodialysis technology to synthesis tetramethyl ammonium hydroxides(TMAH)from tetramethyl ammonium carbonate solution(TMAHC)with the main evaluation parameters of the current efficiency.The effects of the current density,the concentration of TMAHC and flow ratio on the current efficiency were evaluated by single-factor and orthogonal experiments.The optimal operating conditions for BMED were as follows: the current density of 140 A·m-2,the TMAHC concentrations of 2.00 mol·L-1 and the flow ratio of 20 L·h-1 : 40 L·h-1(1 : 2).At these conditions the current efficiency was up to 80.3% through three-parallel experiments.(2)Hexamethonium di-hydroxide(HM(OH)2)could be synthesised from hexamethonium ammonium bromide(HMBr2)solutions by bipolar membrane electrodialysis technology.The stack configuration has four-compartment.The current efficiency is the main evalutation parameters in the experiment.Experiments were designed by response surface methodology,which 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 76.3%(the hydroxide conversion was over 98.6%),with a current density of 13.2 mA·cm-2,a feed concentration of 0.27 mol·L-1 and a flow ratio of 20 L·h-1 : 26L·h-1 : 20 L·h-1 : 20 L·h-1 for feed compartment,base compartment,acid compartment,intermediate compartment,respectively.This study demonstrates the optimized parameters of manufacturing HM(OH)2 by direct splitting its halide for industrial application.