Ethanol Production By Microbe Based On Cotton Stalk

The pretreatment methods based on cotton stalk and screened strains for alcohol fermentation were evaluated. Then the technics of alcohol fermentation based on cotton stalk hydrolysis liquid were systematically investigated.1. Effect of alkali pretreatment of cotton stalk was evaluated. It was showed that alkali pretreatment destroyed the structure of cotton stalk lignocellulosic by dissolved hemicellulose and lignin. The content of lignin and hemicellulose of cotton stalk were decreased 49.83% and 55.75% at the following conditions: concentration of NaOH(2%), solid to liquid ratio(1:20), temperature(120℃), time(75min). And they decreased 51.76% and 56.76% after alkali/microwave pretreated 15min at 700W. Microwave power has less influence on concentration of cellulose in cotton stalk and reclaim rate of carbohydrate(cellulose + hemicellulose). But it has greater influence on pretreatment time, higher power needs shorter time. And the optimal enzymic hydrolysis conditions were temperature (45℃) , pH (4.6) and enzyme(Celluclast 1.5L) loading (4μL/g substrate). Hydrolysis rate was reached 20.01% after enzymic hydrolysed 96h for alkali pretreatment cotton stalk. But it was reached 20.05% for alkali/microwave pretreatment cotton stalk after 48-h hydrolysis.2. Effect of acid pretreatment of cotton stalk was also investigated. It was showed that acid pretreatment destroyed the structure of cotton stalk lignocellulosic by hydrolysed hemicellulose and partial cellulose. It was determined that the hydrolyzing rate reached 29.61% at the following conditions: c(H2SO4)=2.0%, the hydrolyzing temperature 120℃, hydrolyzing time 4h, and the solid to liquid ratio 1:12. But it was only reached 14.32% after acid/microwave treated cotton stalk 45min at 300W. Increased microwave power could decrease pretreated time, but in the same time it would weaken degree of hydrolysis of hemicellulose. The enzymic hydrolysis rate was equivalent to 49.1 percent of it in acid pretreatment cotton stalk enzymic hydrolyzed process.3. The enzymic hydrolysis kinetics studies were carried out for acid pretreated cotton stalk, alkali pretreated cotton stalk and alkali/microwave pretreated cotton stalk. Their hydrolysis was all competitively inhibited by their product (reducing sugar) and could be described as follows:4. There are 31 strains which could convert xylose into alcohol seperated from suburb of Shihezi. It could increase 3.7 times capacity of ethanol produce by yeast Y68 which was obtained through UV mutation than primitive stain. Its characters of growth and fermentation were investigated, and it was applied in fermentation process of different pretreated cotton stalk hydrolysis liquid. It showed that temperature(35℃-38℃),pH(5.5) are the optimal culture conditions for Y68. It could still grow in culture medium with 14 % (V/ V) alcohol. Inoculum(5%), temperature(35℃-38℃), pH(5.5) and flask speed 80r/min are the optimal fermentation conditions. It spent more time in acid pretreated cotton stalk saccharification liquid fermentation than alkali pretreated cotton stalk. But, the conversion of alcohol concentration from different pretreated cotton stalk saccharification liquid were above 56.81%.