Studies On The Acid Hydrolysis Technology Of Corn Cob And The Ethanol Fermentation Of Hydrolysate From Corn Cob

The purpose of this research is to regard wooden cellulose material as raw materials of ethanol fermentation, study in hydrolysis craft and fermented craft, and expect to enlarge the range of material at the transformation of renewable resources to the fuel ethanol .The hydrolysis of lignocellulose is primary step for the bio-transformation fuel ethanol of it. Hemicellulose content of corncob as offal of crops is relatively high for renewable plant that has already been found at present, which is about 35%-40%. So, corncob was selected as raw materials for production of ethanol in this subject. The chemical acid solution was chosen as the hydrolysis method of raw materials. The main research included two stages acid hydrolysis, the optimization the condition of hydrolysis; the detoxification of hydrolysate, and the hydrolysate ethanol fermentation of recombinant genetic E.coli 947 (pEtac-PA) and yeast Pichia stipitis CBS5773 which can utilize xylose to produce ethanol. The main research contents are as follows.Firstly, the content of corncob total solid material, ash, acid-soluble lignin and acid-insoluble lignin was determined. which are 98.2%, 3.8%, 3.3% and 16.9% separately.Secondly, two stages of hydrolysis acid craft was carried on preliminary research. The influence factors to the conversion ratio of reducing candy and pentose include strong sulphuric acid density and the ratio of material and liquid in concentrated acid pretreatment, and sulphuric acid density, hydrolysis time and hydrolysis temperature (pressure ) in dilute sulphuric acid hydrolysis. Hydrolysis terms were optimized by single factor experiment and better process conditions were gained, which were 60% density (W/W) of strong sulphuric acid, 1:3 ratio of material and liquid in the concentrated acid pretreatment, density 4% of sulphuric acid, hydrolysis time 1.0h, hydrolysis pressure 0.1MPa in the dilute sulphuric acid hydrolysisDetoxification methods of hydrolyzates of corncob have been investigated and the detoxification craft of hydrolysate was confirmed. The detoxification process was the hydrolyzate to boil for 15 minutes, later adjusted pH value to 10 gradually with Ca (OH ) 2 neutralization , filtered, adjusted pH value to 7.0 with sulphuric acid , filtered again and then concentrated to the proper density on 25℃ by vacuum evaporation, and decoloured by the active charcoal of density 2% finally.The hydrolysate ethanol fermentation of recombinant genetic E.coli 947 (pEtac-PA) and yeast Pichia stipitis CBS5773 were studied. Fermented condition influence factors have been investigated to recombinant bacterium E.coli 947 to ethanol fermentation , fermented terms of this recombinant were optimized. The result is, while shaking the flask and fermenting, the rotational speed of the table is 100r/min, 20mL liquor in 250mL flask, 6% of inoculating etc., best pH value most worth 7.0 , able to bear most getting high density 50+50(g/L), 5g/L yeast extrac tof best addition ,fermenting 65g/L initial sugar concentration of hydrolyzate (glucose 35g/L + xylose 30g/L) to yield 0.29(g/g) ethanol yield under right best condition At the same time, the yeast Pichia stipitis CBS5773 was adapted, and the adaptation of this yeast made it adapt to the toxic environment of the hydrolyzate. Its growth situation in hydrolyzate is close to growth in simulated hydrolyzate culture. It fermented 65g/L initial sugar concentration of hydrolyzate (glucose 35g/L + xylose 30g/L) and yielded 0.26(g/g) of ethanol yield, which was 52% of theoretical ethanol yield.