Research On Pretreatment And Enzymolysis Of Lignocellulosic Materials

Lignocellulosic materials are the most widely distributed and abundant organic compounds in the world. One of the most effective ways to use these materials is to transfer them into reducing sugars for further production of some valuable chemicals, such as ethanol and other organic acids. In this process, pretreatment of the materials is a key step to lower the cost and increase the availability of these materials.First of all, this paper summarized the research progress of ethanol production by lignocellulosic materials and briefly introduced the ethanol production technics by lignocellulosic materials. The theory of lignocellulose pretreatment was explained and also the pretreatment methods were classified and compared with each other.And then, the mechanism of mild alkaline/oxidative pretreatment in which bagasse acts as raw material was explored. Factors influencing the experiment results including the reaction time, ratio of liquid to solid, NaOH and H₂O₂ concentration were studied, and the influence law of every factor was found. The experiment conditions of bagasse pretreatment were optimized by orthogonal experiment and the optimal pretreatment conditions were as follows: reaction time was 20h, ratio of liquid to solid was 25: 1, NaOH concentration was 1% and H₂O₂ concentration was 0.6 %. Under the above conditions, the rates of solubilization of hemicellulose and lignin were 27.2% and 77.6 %, respectively. In order to lower the experiment cost and environmental pollution, recycling of the pretreatment solution was performed.The effects of reaction time, temperature, ratio of liquid to solid and sulfuric acid concentration on the experiment results were discussed. Various factors of the bagasse hemicellulose hydrolysis were significantly high, which order is reaction time, temperature, ratio of liquid to solid and sulfuric acid concentration from big to small according to the importance. Response surface methodology was performed and obtained the reaction model. The maximum of hemicellulose hydrolysis rate forecasted at the stable condition was 59.3%, and the optimal experiment conditions were as follows: sulfuric acid concentration was 1.24%,time was 2.64h and temperature was 123℃. The hydrolysis rate of hemicellulose in bagasse was 60.3% in the experimental verification , which was very close to the forecasta. The bagasse hydrolysis solution was used repeatedly, and the increase rate of the xylose concentration slowed with the increase of the recycling time. The xylose concentration could increased to 1.6 times after the solution was used repeatedly three times. Other hydrolysis product had the same trend with the xylose that the concentration would become saturated when the solution was used repeatedly three times.One-step and two-step hydrolysis of the bagasse were performed and the content and recovery of each component of the bagasse after each pretreatment were compared with each other. The results showed that the two-step hydrolysis could raise the hemicellulose hydrolysis rate of bagasse, and acetic acid was not found in the hydrolysis products.In order to test the results of each pretreatment, the effect of different pretreatment on the bagasse enzymolysis was investigated. It was found that different pretreatment effected the bagasse enzymolysis rate greatly, the bagasse enzymolysis rate after mild alkaline/oxidative was the highest and the two-step method followed, the enzymolysis rate after dilute sulfuric acid was the lowest. And the effect of the recycling times of the pretreatment filtrate on the enzymolysis was investigated primarily. The results showed that the enzymolysis rate declined gradually with the increase of the filtrate recycling times. The enzymolysis rate of the bagasse was lowered significantly after the filtrate was recycled four times and it was more appropriate to recycle the filtrate four times.