Research On Pretreatment Of Ammoniation And Enzymatic Hydrolysis Of Corn Stalks

Energy shortage would be harm Chinese Economy and national security seriously.Therefore, replace traditional energy sources by new energy sources will be the development direction of the energy industry in the future. The biofuel receive national attention lately, for it has characteristics of renewable and pollution-free.The lignocellulose is the most abundant and cheapest renewable resources on the earth, and supposed to be the most important resources for fuel alcohol production. Relative to the first generation material of biofuel such as corn and bean, the straw fiber were identified as the second generation material of biofuel, which the most advantage is avoided the risk of be hard up of foodstuff. Therefore, the social and economic significance is very important to transform cellulose into ethanol by biological technology.There are two steps to convert cellulosic substrate to monosaccharide, namely,pretreatment of materials and enzymatic hydrolysis of cellulose.The technology of pretreatment is unsatisfactory at present. The development of cellulose bioconversion is limited by many problems in technology of stalks ethanol such as low rate of sugar conversion, process complication, low hydrolysis rate and large enzyme dosages. In this thesis, optimization conditions and handling methods of pretreatment of corn stalk as the fiber material, optimization conditions of enzymatic saccharification, the impact of ultrasound and metal ions on the enzyme has been studied.The results are shown as follows:Study is carried out on pretreatments of ammonia immersion, pammonolysis under pressure and ultrasound-assisted ammonia immersion to deal with corn stalks. The optimal scheme of pretreatment of ammonia immersion is shown as follows:Under the conditions of ammonia concentration is 15%,time is 39h, temperature is 40℃,substrate concentration is 162.5g/L, and stalk diameter is 0.5mm, the saccharifying efficiency is 3.23%,and lignin removal rate is 61.20%. Corresponding hydrolytic enzyme of reducing sugar is 45.28%, increases 32.77% than the unprocessed(12.51%).The optimal scheme of pretreatment of pammonolysis under pressure is shown as follows:Under the conditions of ammonia concentration is 15%.time is 6min. the pressure is 0.075MPa. substrate concentration is 150g/L, and stalk diameter is 1mm, the saccharifying efficiency is 1.74%. and lignin removal rate is 43.30%.Corresponding hydrolytic enzyme of reducing sugar is 21.36%, increases 8.85% than the unprocessed.The optimal scheme of pretreatment of ultrasound-assisted ammonia immersion is shown as follows:Under the conditions of ammonia concentration is 12.5%,ultrasonic time is 24min.ultrasonic power is 240W,substrate concentration is 187.5g/L,temperature is 70℃. and stalk diameter is 0.5mm, the saccharifying efficiency is 1.51%,and lignin removal rate is 32.20%. Corresponding hydrolytic enzyme of reducing sugar is 40.33%,increases 27.82% than the unprocessed.The results of optimal schemes and the factor of economic are considered that the pretreatment of ultrasound-assisted ammonia immersion is an ideal pretreatment method required for a short time, low energy consumption and the effect is better.Corn straw as material that deal with pretreatment of ultrasound-assisted ammonia immersion to carry out enzymatic hydrolysis under the conditions of temperature is 50℃.The factor of substrate concentration affected the reducing sugar yield significantly (p<0.01),hydrolysis time affected that as follow (p<0.05).Optimal scheme of enzymatic hydrolysis is shown as follows: Under the condition of pH value is 5,substrate concentration is 60g/L,enzyme dosage is 47mg/g (dry straw), and enzymatic hydrolysis time is 30h, the saccharifying efficiency of enzymatic hydrolysis is 49.00%, which increase 36.49% more than enzymatic hydrolysis without pretreatment.An appropriate degree of ultrasonic radiation plays an activation role in enzyme.Under condition of the substrate concentration is 60g/L, enzyme dosage is 47mg/g (dry straw),the optimal ultrasonic power is 39W. and ultrasonic time is 9min. Under the condition of these, reducing sugar yield of enzymatic is 56.55%.which increase 7.55% more than enzymatic hydrolysis without ultrasound.K+. Na+,Ca2+,Mg2+, and Zn2+ play an activation role in enzyme,improve the enzymatic hydrolysis yield of reducing sugar, of which Zn2+ is the most significant one. and the saccharifying efficiency has maximum activation when the Zn2+ concentration is 1.5mg/ml(liquid),Fe3-,Al3- play an restrain role in enzyme.