Study On The Preparation Of Choline Hydroxide And D-2-aminobutanol Via Bipolar Membrane Electrodialysis

The bipolar membrane is a kind of ion exchange membrane,which is composed of an anion exchange layer,a cation exchange layer and an intermediate catalytic layer.Under the reverse bias,the water molecule can be splitted into H⁺and OH^-by bipolar membrane.Due to its features,bipolar membrane can be introduced into electrodialysis technique and achieve the separation and conversion of the salts without adding any other reagents.Therefore,bipolar membrane electrodialysis can be applied in the production of acids and bases without generation of by-products.In this paper,bipolar membrane electrodialysis is used to produce choline hydroxide and D-2-aminobutanol.The feasibility of bipolar membrane electrodialysis to produce choline hydroxide and D-2-aminobutanol is explored.In addition,the preparation process is optimized.The conclusions are as follows:?1?The traditional three-compartment configuration bipolar membrane electrodialysis membrane stack was improved.The membrane stack with four-compartment was used for the preparation of choline hydroxide,which effectively reduced the content of choline hydroxide in the product.The Cl^-content was reduced from 1175 ppm to 418.8 ppm?converted to 45 wt.%choline hydroxide?,making it reach the industrial standard.The BMED process was evaluated by investigating the operation parameters of cation exchange membrane,initial feed concentration and voltage drop.With the optimized conditions?the constant voltage drop of 12.5 V,the initial feed concentration of 0.4 M and cation exchange membrane JCM-?-05?,the BMED process demonstrated an exceptional high conversion rate?86.84%?,low energy consumption(0.74 k Wh·kg^-1)and high current efficiency?84.60%?.In addition,the Cl^-content of the choline hydroxide converted to 45 wt.%aqueous solution could be achieved as low as 321.8 ppm.?2?The bipolar membrane electrodialysis technology was integrated into the synthetic route for the preparation of D-2-aminobutanol by chemical resolution.In the experiment,the effects of different membrane stack configurations,ion exchange membranes,initial feed concentrations and voltages on the bipolar membrane electrodialysis to produce D-2-aminobutanol were investigated,and the parameters such as yield,energy consumption and current efficiency were investigated.An evaluation is performed to determine the optimal conditions for the experiment.The optimized operating conditions are as follows:the initial concentration of the D-2-aminobutanol-L-tartaric acid solution in the feed chamber is 1.0 mol·L^-1,and the two-compartment configuration membrane stack with cation exchange membrane CMX is used at a constant voltage of 17.5 V.Under the optimized situation,the obtained D-2-aminobutanol is 1.04 mol·L^-1.The conversion rate was92.28%.The energy consumption and current efficiency were 1.88 k Wh·kg^-1D-2-aminobutanol and 54.05%,respectively.In addition,the bipolar membrane electrodialysis was used for the preparation of another chiral compound?L-2-aminobutyramide?,the successful separation of L-2-aminobutyramide and L-tartaric acid was achieved.The bipolar membrane electrodialysis technology has an application prospects in the preparation of chiral compounds by chemical resolution.