Study Of Freeze-thaw Combined With Acid-alkali Pretreatment Process Of Wheat Straw

Fuel Ethanol has higher combustion efficiency and less environmentalpollution compared to gasoline. Ethanol has been considered a suitablealternative to fossil fuels as transportation fuel. Lignocellulosic biomass issufficient and renewable feedstock for ethanol production. Ethanol productionfrom lignocellulosic materials requires operations including pretreatment,hydrolysis and fermentation. Enzymatic degradation of raw materials obtainreducing sugar can be used to produce ethanol by microbial fermentation,pretreatment is necessary to make raw materials for efficient enzymatichydrolysis.In this paper, agricultural waste wheat straw is selected raw material forethanol production.“Two-step” pretreatment and adding bovine serum albuminin enzymatic reaction solution is attempted to efficient conversion the celluloseand hemicelluloses of straw to reducing sugar. The results are as follows:1. The sulfuric acid treatment conditions as follows: process temperature80°C, sulfuric acid concentration2wt%, liquid-solid ratio20, and process time20h.264mg reducing sugar and4.3mg furfural are released during acid treatmentof1g wheat straw.115mg reducing sugar is obtained by cellulose hydrolysis(NS22074,20U,48h). Cellulose hydrolysis rate is33%.2. First step pretreatment. The freeze-thaw treatment conditions as follows:freezing temperature-20°C, freezing time12h, liquid (water)-solid ratio10,thawing temperature25°C, thawing time1h, and freeze-thaw cycle twice. Usingsulfuric acid treat wheat straw that treated by freeze-thaw process. The sulfuricacid treatment conditions as follows: temperature80°C, sulfuric acidconcentration2wt%, liquid-solid ratio20, and process time16h.295mg reducingsugar and1.5mg furfural are released, and128mg reducing sugar is obtained by cellulose hydrolysis (NS22074,20U,48h). Cellulose hydrolysis rate is37%.Wheat Straw porosity is increased and chemical activity is enhancement throughfreeze-thaw process. Sulfuric acid treatment efficiency is improved.3. Second step pretreatment. The first step pretreatment of wheat straw assubstrate was treated by lime at the low and high temperatures, respectively. Thelow-temperature lime treatment conditions as follows: process temperature60°C,lime75mg/g, liquid (water)-solid ratio10, process time20h. After the two-steppretreatment,215.5mg reducing sugar is obtained by cellulose hydrolysis(NS22074,20U,48h). Cellulose hydrolysis rate is64%. The high-temperaturelime treatment conditions as follows: process temperature121°C, lime100mg/g,liquid (water)-solid ratio15, process time60min. After the two-step pretreatment,242.1mg reducing sugar is obtained by cellulose hydrolysis (NS22074,20U,48h). Cellulose hydrolysis rate is72%. Lignin of wheat straw is reduced;cellulose is exposing and swelling through lime treatment. So the cellulosechemical activity is enhanced. The efficiency of the high-temperature limetreatment is higher than low-temperature treatment.4. The two-step pretreatment of wheat straw as substrate is implementedenzymatic hydrolysis using cellulase.50mg/g bovine serum protein (BSA) addsto enzymatic hydrolyzate. Cellulose hydrolysis rate is80%(NS22074,20U/g,48h). Cellulose hydrolysis rate is85%(72h). The promotion mechanism of BSAto cellulase as follows: BSA can improve the stability of enzyme and reducedeactivation of enzyme due to binding with lignin.