Investigation On Pretreatment Process And Enzymatic Hydrolysis Properties Of Sugarcane Bagasse For Ethanol Production

Sugarcane bagasse is a main by-product of sugar industry in China, but most of them are burnt, which will caused both environmental pollution and resources waste. So it is necessary to improve its comprehensive utilization. Natural wood fiber has "recalcitrance" and the efficiency of direct digestion is very low. In order to improve the cellulase accessibility to cellulose, it must be pretreated before enzymatic hydrolysis. In this paper, sugarcane bagasse was used as raw materials, weak alkaline sodium sulfite and weak alkaline hydrogen peroxide pretreatment before enzymatic hydrolysis have been studied. The total reducing sugar conversion rate of pretreatment and enzymatic hydrolysis liquid was used as as the evaluation index and the respective pretreatment conditions were optimized. The raw materials, pretreatment solids and enzymolysis residues were further analyzed comparatively. Meanwhile, the effect of the lignin and hemicellulose degradation rate on the weak alkaline Na2SO3 pretreatment was explored which will provide theoretical basis and technical support for the wood fiber converting to ethanol efficiently.Firstly, the composition content of raw bagasse was analyzed by using the non-wooden paper making materials composition analysis standard. The cellulose content was 48.13%, hemicellulose content was 25.81%, Klason lignin content was 20.94% and acid soluble lignin was 1.26%. Secondly, the optimal process conditions of alkaline Na2SO3 pretreatment and alkaline H2O2 pretreatment were obtained by single factor experiment and response surface experiment, and the influence of pretreatment on enzymatic hydrolysis was further investigated.The optimal pretreatment conditions of alkaline Na2SO3 pretreatment were as follows: 170 ℃, 2.5h, NaOH concentration 3.5%, Na2SO3 concentration 10%. In this condition, the total reducing sugar conversion rate was 74.95% and the reducing sugar content in the pretreatment process was just 13.32%. After pretreatment, the fiber structure was damaged greatly and the fragment of fiber surface was increased, which greatly improved the accessibility of cellulase and raised the efficiency of enzymatic hydrolysis.The optimal pretreatment conditions for alkaline H2O2 pretreatment were as follows: 73℃, 5h, H2O2 concentration 5.5%. Under this condition, the total reducing sugar conversion rate was 64.13% and only a small amount of monosaccharide was detected in the pretreatment liquid. After pretreatment, the fiber structure became loose, the specific surface area increased and the crystallinity of cellulose increased.Under the optimal pretreatment condition, the two kinds of pretreatment methods were compared. The results showed that the lignin degradation rate after alkaline Na2SO3 pretreatment was obviously higher than that after alkaline H2O2 pretreatment, which was 75%, and the degradation rate of lignin after alkaline H2O2 pretreatment was only 58.74%. After alkaline Na2SO3 pretreatment and enzymatic hydrolysis, 100 g raw materials can get 31.82 g of glucose and 22.07 g of xylose. After alkaline H2O2 pretreatment and enzyme hydrolysis, 100 g raw materials can get 26.74 g of glucose and 19.02 g of xylose.Using enough cellulase dosage and under the optimal condition of enzymatic hydrolysis, the effect of lignin and hemicellulose degradation rate on the enzymolysis properties after alkaline Na2SO3 pretreatment was also studied. The results showed that the total reducing sugar conversion rate increased along with the increase of the lignin degradation rate, which showed that the removal of lignin and hemicellulose is advantageous to the cellulase digestion. When the removal degree of lignin and hemicellulose was higher, the efficiency of enzymatic hydrolysis was also higher.