The Effect Of Different Pretreatment Methods On Enzymatic Hydrolysis Of Different Cellulosic Materials

Although there is lack of crude oil reserves in China,it is a vast agricultural country with abundant lignocellulosic materials.The effective utilization of lignocellulosic materials to product bioethanol can greatly reduce Chinese energy pressure. In the process of producting bioethanol, pretreatment can improve the cellulose conversion rate. Pretreatment contains three methods: physical pretreatment,chemical pretreatment and biological pretreatment.Chemical method is one of the most possible method to be applied into industrial production, including acid pretreatment, alkaline pretreatment and organosolv pretreatment.In the study, chemical method is used to pretreat Broussonetia papyrifera and Soybean straw.The optimum conditions were obtained by using the response surface methodology.It was found that:① in the process of acid pretreatment experiment, the contents of soluble matter from two kinds of materials were increased with the enhancement of pretreatment conditions. The reducing sugar yield of Broussonetia papyrifera could reach to 35.39% when the CSF(Combined severity factor) value is near 3.57. Then, Soybean straw reducing sugar yield could reach to 25.40% with CSF = 2.81. ② In alkaline pretreatment experiment, alkali concentration has the greatest influence on pretreatment yield of Broussonetia papyrifera, and the highest reaction temperature has the greatest influence on pretreatment yield of soybean straw material. Broussonetia papyrifera reducing sugar yield could reach 41.66% during the best conditions(highest reaction temperature 130 oC,holding time 60 min,alkali concentration 1%).Soybean straw reducing sugar yield could reach 39.67% during the best conditions(highest reaction temperature 130 oC,holding time 30 min,alkali concentration 1.5%).③In organosolv pretreatment experiment,the highest reaction temperature has the greatest influence on pretreatment yield of both materials. Broussonetia papyrifera reducing sugar yield could reach 50.32% during the best conditions(highest reaction temperature 160 oC,holding time 30 min,ethanol concentration 50%).Soybean straw reducing sugar yield could reach 44.17% during the best conditions(highest reaction temperature 170 oC,holding time 90 min,ethanol concentration 50%).Compared with three pretreatment methods,the reducing sugar yield of Broussonetia papyrifera is higher than the yield of Soybean straw at the same kind of pretreatment method, which suggested that Broussonetia papyrifera is more conducive to be used to prepare bioethanol.It was also found that the highest yield of reducing sugar was obtained in organic solvent pretreatment method, and the lowest yield of reducing sugar was got in acid pretreatment method.Compared with the content of hemicellose and lignin after acid pretreatment,it was found that there are more content of lignin dissolved in the solution after alkali and organosolv pretreatments.In the process of enzymatic hydrolysis,lignin is the main obstacle.Through the study of the kinetics of delignification during alkali pretreatment and organosolv pretreatment, it were found that;①In alkaline pretreatment experiment,the delignification were the first order reaction.There are two stages of delignification including bulk delignification stage and residual delignification stage.The activation energy of the two stages were also different.The activation energy of Broussonetia papyrifera were 100.23 kJ/mol in bulk delignification stage and 111.23 kJ/mol in residual delignification stage,respectively.The activation energy of Soybean straw were E=135.04 kJ/mol in bulk delignification stage and E=174.98 kJ/mol in residual delignification stage.②In ethanol pretreatment experiment,the delignification was the first order reaction.There are two stages of delignification including bulk delignification stage and residual delignification stage.The activation energy of the two stages were also different.The activation energy of Broussonetia papyrifera were 82.30 kJ/mol in bulk delignification stage and 124.73 kJ/mol in residual delignification stage.The activation energy of Soybean straw were 52.23kJ/mol in bulk delignification stage and 136.98kJ/mol in residual delignification stage.