Preparation Of Mannitol Using Electrochemical Method

Mannitol has extensive uses, especially in pharmaceutical and food industry. Now, it is mainly obtained by natural extraction and catalytic hydrogenation . Electrochemical synthesis can be finished at moderation condition and need no special reagents. The whole process is easy to operate without wastes. The process of electrochemical reduction synthesis of mannitol from fructose was investigated in this paper.According to electrolytic property, the analysis method of fructose and mannitol was proposed according to the condition of fructose, supporting electrolysis, mannitol and sorbitol coexisting. After using HPLC to determine the content of electrolytic solution, it was verified that the reduction products of fructose were mannitol and sorbitol.The factors effecting chemical synthesis of mannitol from fructose in batches such as current density, initial concentration of fructose, supporting electrolytic concentration, temperature and passed charge were discussed in a self-made cell. At selected conditions of current density 0. 5A/dm2, initial concentration of fructose at 0. 6mol/L, supporting electrolytic concentration at 0. 3mol/L, temperature at 40℃ and passed of 1. 2 times of theoretical charges, the conversion rate of fructose was 61. 8% and the current efficiency was 51. 5%.The process of chemical synthesis of mannitol catalyzed with Raney Nickel was presented. The effecting factors such as catalysis quantity, current density,initial concentration of fructose, supporting electrolytic concentration and temperature were discussed. At selected conditions of catalysis quantity 4g, current density at 0. 7A/dm2, initial concentration of fructose at 0.5mol/L, supporting electrolytic concentration at 0.2mol/L, temperature at 40℃ and passed theoretical charges, the conversion rate of fructose was 83. 5% and the current efficiency was 83. 5%.The strengthening process of chemical synthesis of mannitol in a packed bed reactor was presented. The effecting factors such as operation fashion, Raney Nickle quantity in packing, voltage, stir velocity, with and without supporting electrolyte were discussed. In the batches process, with packed Raney Nickel catalyst 200g, initial concentration of fructose at 1.0mol/L; voltage at 6V; without supporting electrolyte and reaction 2 hours, the conversion rate of fructose was 98. 5% and the current efficiency was 98. 3%. Based on the batches operation, through altering packing state of Raney Nickel catalyst, the continuum process was presented. At the conditions of inputting 2.0mol/L fructose solution at 4mL/min, voltage at 6V, the conversion rate of fructose was about 96%. In the wholly process, the average conversion rate of fructose was 87.0% and the current efficiency was 86. 6%.The recovery rate of mannitol in the electrolytic solution was 80% after separation and crystallization. The purity of mannitol was above 90% measured by HPLC. The infrared characteristic curve of production was pretty well coincided to the standard sample.