| With the growing demand for energy and the decrease of fossil fuels, looking for a sustainable new energy has been the key mission for us today. Biomass energy, as a kind of renewable energy, has attracted more attention of various countries in the world. To study, exploit and utilize biomass energy has become one of research hotspots of the whole world. Although there are abundant biomass recourses in our China, its application has the problem of low utilization rate and high environmental pollution problems. So the research and application of biomass has been considered to be our pressing task and should be given our great strategic importance. Bio-ethanol is a kind of bioenergy, and can be made alone or mixed with gasoline as car fuels. To make bio-ethanol by agricultral wastes, biomass ethanol, has great advantages on saving food, saving energy, and environmental protection.it has been over 100 years since the bioethanol was studied, while the technology has not been put into practice because of the lack of practical pretreatment technology and the low conversion rate of lignocellulosic materials to fermentable sugar. As studied, lignocellulosic materials have hard structures. The facts of crystalline structure of cellulose, hemicellulose sheath and the protective seals of lignin lead to the slow enzymatic hydrolysis, so an efficient pretreatment is necessary to break the cellulose polymer and improve the conversion rate of cellulose, which is an important approach to solve the production problem of biomass ethanol and put it into industrial production.The main task of this paper included the following several aspects:ultrasonic pretreatment of corn cob, ultrasonic-assisted acid pretreatment technology of corn cob, and the ultrasonic-promotion of the following enzymatic hydrolysis. It aims to find a economical and practical pretreatment methods to solve the problem of high cost and poor effects of the now using pretreatment technologies, and reduce the enzyme dosage, improve the reducing sugar yield to finally improve the conversion rate of plant cellulose.(1) Study on the ultrasonic pretreatment technology of corn cob. Based on the yield of reducing sugar, effects of solid-liquid ratio, enzyme dosage, reaction time on the reducing sugar yield were studied respectively, and effects curves of various factors were obtained. The processing conditions were optimized by uniform and orthogonal experiments. And the regression equation were abtained as:Y=19.972+0.002X1X3+0.001X1X4.(X1, Ultrasonic power; X2, One-time irradiating time; X3, Pause time; X4, Ultrasonic irradiating time)The optimal conditions were:Ultrasonic power,260W/g, One-time irradiating time,2s, Pause time,6s, Total irradiating time,30min. Reducing sugar yield under the optimal condition is 26.71%, which showed that the ultrasonic pretreatment is too limited to break the complex structure of lignocellulose and to get an ideal reducing sugar yield.Reasons of the increase of reducing sugar yield after ultrasonic pretreatment were investigated. Scanning Eelectron Microscopy (SEM) and FTIR spectra showed that the ultrasonic irradiation did not break the internal structure of cellulose and did not damage the internal functional groups. So the reasons was deduced that ultrasonic irradiation promote the release of some internal reducing sugar to increase the whole sugar yield.(2) Study on the ultrasonic-assisted acid pretreatment technology of corn cob.Under the actions of ultrasound and dual acid, study the yield of reducing sugar after the partially hydrolyzing of wood fibers, and the promoting effects of the structural damage to the following enzymatic hydrolysis. Results of feasibility tests showed that the yield of reducing sugar obtained by this method is 30.96%,1.72,1.43, 1.22 times higher than that of boiling water bath, boiling water bath with Stirring, ultrasonic without boiling water bath, respectively.The main effect factors were screened by PB experiments as acid concentration, ultrasonic power, ultrasonic irradiating time, and regression equations were abtained by Uniform Experiment Design as:Y=-0.276-0.430X12-0.001X1X2+0.006X1X3-1.5X10-5X2X3+1.009X1+0.002X2.(X1, Acid concentration; X2, Ultrasonic power; X3, Ultrasonic irradiating time) The optimizing conditions were got from the equations as:Acid concentration, 1.20%, Ultrasonic power,121.95W/g, Ultrasonic irradiating time,60min. Reducing sugar yield under the optimal condition is 26.71%, which showed an excellent effects on reducing acid dosage and improving the reducing yield.The SEM and FTIR scanning spectra showed that the internal structure of lignocellulosic materials pretreated by this method was greatly broken and part of the function groups were damaged.(3) Based on the traditional mechanical equation and experimental data, the mass transfer and hydrolysis kinetics models in the process of ultrasonic-assisted acid pretreatment were investigated.Derived by the reaction mechanism and fitted with classical models of acid pretreatment, the model of ultrasonic-assisted acid pretreatment process has a high fitting degree with the reported classical mocel, which means acid pretreatment process did not be changed under the ultrasonic wave field. And it was found that k1 and k2 value showed the same changes in the reaction systerm and k2 was lower than k1. k1 value of the system is higher than that of other processes with a low consumption of acid, which may be related to the mass transfer enhancement of ultrasonic wave.k2 value of the system is lower than that of other reported data, indicating that ultrasonic wave, as a kind of pretreatment method, has its advantage on the degradation of products. Activation energy Ea was caculated as 31.8541kJ/mol.(4) Study on the effects of ultrasonic wave on cellulase activity and enzymatic hydrolysis process.Effects of two different ultrasonic wave (Probe Model Ultrasonic, Pulsed Frequency-Sweeping Ultrasonic) on the cellulase activity were compared, and the stability and significance of Pulsed Frequency-Sweeping Ultrasonic treatment were better than those of Probe Model Ultrasonic treatment.Conditions of Pulsed Frequency-Sweeping Ultrasonic treatment was optimized, and the optimum condition was obtained as:300kW,28kHz,2min. And the holding time showed more influence on cellulase activity that the cellulase activity decreased 68.97% after 48h. By the determination o Uv-absorption Spectroscopy, Uv differential spectrum and fluorescence, we found the treatment did not change the chemical composition or structure of the valence bond, but changed its conformation to activate the cellulase activity. The experiment result shows practical significance and application value on reducing the usages of cellulase.Effects of ultrasonic wave on cellulase hydrolysis process were studied, and it was found that reducing suger yield of the treated sample was 18.43% higher than that of samples without treatment. |
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