Study On Concentration And Detoxification Of Glucose Solution By Vacuum Membrane Distillation

In order to improve the efficiency of lignocellulosic ethanol production, the concentration of lignocellulosic hydrolyzates and removal of inhibitors were critically important. As a new membrane separation technology, vacuum membrane distillation(VMD) could increase the concentration of nonvolatile chemicals and remove the volatile components at low operating temperature, thus the concentration of lignocellulosic hydrolyzates and removal of inhibitors by VMD was investigated.Firstly, the operation parameters, including feed temperature, flow rate and sugar concentration on the process were optimized, and the result showed that the rejection of the glucose was over99.5%for concentrating the glucose solution of ten times at the optimal condition of the velocity of1.0m/s, temperature of65℃and downstream pressure of5kPa. It was also found that the membrane flux increased as the flow rate and temperature increased, but decreased as the glucose concentration increased.Secondly, the removal of furfural and acetic acid were studied. For the relative volatility of furfural-water was much higher than that of acetic acid-water during the low concentration, the removal efficiencies of furfural and acetic acid were quite different at the conditions of glucose concentration of5g/L, furfural and acetic acid concentration of1.25g/L, temperature of65℃and downstream pressure of5kPa, that were96.25%and24.79%, respectively. In order to improve the removal efficiency of acetic acid, salts and adsorbents were added to change the vapor liquid equilibrium of acetic acid-water system. The results showed that the adding of salts in solution didn’t work while the adding of adsorbents in downstream had great effect. The removal efficiency of acetic acid increased from28.9%to42.8%for activatedcharcoal and73.2%for resin, respectively, which were1.48and2.53times than that without adsorbent.Finally, the fermentation of lignocellulosic hydrolyzates which were concentrated and detoxified by VMD was investigated, and it was found that origin and twice broths achieved a lower ethanol production and reached the maximum value of15.99g/L and28.69g/L while the maximum ethanol concentration of three times concentrated broths was42.18g/L, that was2.64and1.47times than the formers. These results indicated VMD process was effective in concentration of hydrolyzates and detoxification to increase the efficiency of ethanol fermentation.