Fermentation Of Pentose And Hexose To Ethanol By PVA Immobilized Cells Of Pichia Stipitis

Fermentation of xylose-glucose was investigated using immobilized cells of Pichia stipitis.The thesis studied the selection of immobilized-entrapmed materials, the technology of preparation of immobilized cells, effects of additives to intension of immobilized cells, ethanol co-fermentation and bacteriostasis , ethanol fermentation of immobilized cells in a 3L fermentor, the orderliness of xylose-glucose fermentation of immobilized cells, the concentration of substrate and effects of fed batch to fermentation .The main results of study were follows.Fermentation was compared using Calcium alginate (CA) and polyvinyl alcohol (PVA) as the immobilized-cells carriers . The results showed that the stable fermentation time was 180d and 30d for immobilized-cells with PVA and CA , respectively . Utilization rate of sugars was 80% and 94%, respectively . PVA was the better entrapment.The optimal concentration of PVA and boracic acid was 9% and 3.5%, respectively. The intension and consistency reached a better level at this concentration. The PVA could be resolved by adding CA and the optimal quantum was 1%. Adding CaCl₂ to crosslinker could crosslink CA and modulate the water absorption . The optimal quantum of CaCl₂ was 0.5%.Fermentation of PVA immobilized cells used the value model , the optimal inoculum time and volume was 18 h and 4% .In the actual fermentation ,the best ratio of broth and immobilized cells is 1:1.Utilization of glucose was faster than that of xylose when fermenting glucose-xylose mixture to ethanol by immobilized cells. It was because the metabolism of xylose was much complex than that of glucose, and the glucose and production would probably affect the utilization of xylose . The sugar conversion rate of PVA was 93.9%,better than the sugar conversion rate of CA,it was 87%Optimization of PVA resulted in more convenient operation and higher productivity. Treated with acid and freezing could reduce the water dilatability of PVA-H₃BO₃. Co-adsorption and entrapment, the 3% carbon was the right immobilized material. The optimal initial pH was 5.0. The optimal conserve method was under the plain and humid environment.Fermentation was invesgated in 3L fermentor using immobilized cells of Pichia stipitis . The conditions of ethanol fermentation were 35℃, 400r/min , air flow rate 3.0V/V·h . Comparing fermentation with free cells and immobilized cells , the results showed that the fermentation theoretical yield of free cells and immobilized cells was 90.6%, 88.7%, 85.4%, 81.3%, 76. 6% and 91.1%, 89.1%, 86.3%, 84.9%, 83.2% , respectively, when initial concentration of glucose was 20g/l, 30 g/l, 40 g/l, 50 g/l and 60 g/l . The cell endurance and ethanol yield was higher under immobilized cells. When fed-batch fermentation in 3 L fermentor, the more fed times the better productivity. The sugar conversion rate was 79.26%, 82.5%, 84.86%,and 86.92% when fed times was two, three, four and five, the ethanol yield was 85.32%, 87.4%, 88.68% and 91.73%. The result was better than batch fermentation.