The Changes Of Different Materials Cell Morphological Features In Pretreatments And The Effects On The Enzymatic Hydrolysis Of Cellulose

Accompanied by increasingly serious crisis of coal, oil, natural gas and other non-renewable energy, renewable biomass energy development has been under the spotlight. The fuel ethanol produced by bio-conversion with the use of lignocellulosic material can be used to supplement or partly replace non-renewable resources, alleviating the crisis of energy shortage, reducing carbon dioxide emissions and reducing the greenhouse effect to a certain extent. Lignocellulose is a kind of renewable resources in the world with its advantages of multiple sources, large amount and low cost. And the second generation bioethanol produced by lignocellulose can avoid food security problems using grain as raw materials in the first generation of ethanol. So cellulosic ethanol has become a hotspot in the current bio-ethanol energy research area. Pretreatment is one of the key steps in the production of bioethanol. Pretreatment can break down biomass recalcitrance effectively to improve the performance of cellulosic enzymatic hydrolysis. But the mechanism of pretreatment improving the performance of cellulosic enzymatic hydrolysis is complicated.The paper attempts to analyze the influence mechanism of different pretreatments to the enzymatic hydrolysis performance of different cellulosic materials from the points of fibre morphology and biological structure.The corn strover and poplar were chosen as raw material in the article, respectively pretreated by hot water, sodium hydroxide and sodium hydroxide-Anthraquinone, acidic sulphite pretreatments followed by sieving to abtain five sieving fractions expressed by Rl, R2, R3,R4,R5. The different sieving fractions were hydrolyzed by cellulose.The effects of different pretreatments on the cellulase hydrolysis performance of different materials were researched from the perspective of chemical composition and morphological features. In addition, the cell walls of the fibrous raw materials and pretreated materials were hydrolyzed by cellulase to investigate their enzymatic hydrolysis performance. The main results obtained are as follows.(1) In terms of chemical compositions, the content of the tiny components in corn stover pretreated by NaOH was higher than that of hydrothermal pretreatment. While for poplar, the content of the tiny components pretreated by Na2SO3-H2SO4 was higher than that of NaOH-AQ pretreatment. NaOH-AQ pretreatment was prior to pretreatment on the degradation of lignin under the condition of less degradation of cellulose and hemicellulose. For corn stover and poplar, in accordance with the sequence of sieving R1, R2, R3, R4, R5, the hemicellulose content increased gradually, but the lignin content reduced in turn. Different rules were presented in the changes of cellulose content of different materials and different pretreatments. The content of cellulose in corn stover sieving increased, however the cellulose content increased first and then decreased, with the highest content of R3 and R4 for NaOH-AQ pretreatment and Na2SO3-H2SO4 pretreatment respectively. Generally, the extractive content was higher and ash content was lower in relatively longer fibre.(2) In terms of the changes of fibre morphology, in accordance with the sequence of R1, R2, R3, R4, R5, the fiber average length, fiber average width, aspect ratio, and fiber roughness decreased, while tiny fiber content decreased firstly and then increased, achieving the minimum value at R3. The average curl indexes, kink angle and kink number of the sieving groups pretreated by hot water were higher than that of NaOH pretreated corn stover. The average curl indexes, kink angle and kink number of the sieving groups pretreated by Na2SO3-H2SO4 were higher than that of NaOH-AQ pretreated poplar. This may be related to hemicellulose content in fiber. In accordance with the sequence of R1, R2, R3, R4, R5, fiber cell length and average width of hot water pretreated and NaOH pretreated corn stover reduced, while fiber cell aspect ratio increased first and then decreased, achieving largest at R2. The fiber cell length and aspect ratio of NaOH-AQ pretreated and Na2SO3-H2SO4 pretreated poplar reduced. But there was little difference in the cell average width. The fiber cell lumen diameter of NaOH-AQ pretreated poplar fiber were smaller than that of Na2SO3-H2SO4 pretreated.(3) In terms of the performance of cellulose enzymatic hydrolysis, the cellulose conversion rate of hydrothermal pretreated corn stover, NaOH pretreated corn stover, NaOH-AQ pretreated poplar and Na2SO3-H2SO4 pretreated poplar, was R5> R4> R3> R2>R1. The mass concentration of glucose and cellulose conversion curves of each sieving group were consistent, which changed remarkably at the beginning and then gradually leveled off.(4) It was found that according to the sequence of Rl, R2, R3, R4, R5, the degree of the fiber surface stripping significantly increased and the amount of fiber cells in the fiber bundle reduced in turn through the observe of the changes of cell wall in pretreatments and enzymatic hydrolysis. Parenchyma cells were more susceptible to damage and degradation than thick-walled cells in pretreatment. The fiber cell walls of corn leaf raw material, the pretreated corn stover and pretreated poplar had obvious changes after enzymatic hydrolysis for 2 h, whereas fiber cell walls of corn stover raw material and poplar raw material had changes for 8 h.