Research Of Chemical Pretreated Paulownia For Bioethanol Production

Recently, Bioethanol is widely studied as a kind of main petroleum substitutes,especially the technology based on lignocelluloses which we called it the second generationethanol production. It has been an important trend in energy production system that producingbioethanol from lignocellulose biomass. It includes two big steps: hydrolyzing cellulose intoreducing sugar, formatting the sugar into ethyl alcohol. There are many hydrolysis methodsincluding chemical method, mechanical method and biological methods and so on. Biologicalmethod is milder and higher selectivity while higher cost than others, so a pretreatmentprocess is necessary before enzyme hydrolysis especially the biomass is lignocellulosebecause of its tightness and complexity of structure. Degradation and removing parts of thelignocellulose biomass during the pretreatment process so that to improve the hydrolysisefficiency is the main point of this study. This paper choose a kind of hard wood namedPaulownia as the raw material which is widely distributed in west-north of our country. It islooser in structure and more fibrous than other kind of hard wood, the content ofhomocellulose is abundant so that it is regarded as one of potential lignocellulosic material.Moreover, there has been no report about Paulownia on its lignocellulosic application in thisarea.Pretreatment processes can remove the hemicellulose, reduce the crystallinity of thecellulose, improve the porosity of the biomass and increase enzyme efficiency. Dilute acidpretreatment was widely studied because of its effectiveness and low-cost, it can degradehemicellulose into monose and soluble oligomers to enhance the transformation of cellulose.The transformation from xylan to xylose is obvious during dilute acid pretreatment comparingwith other processes. Sodium hydroxide pretreatment was concerned because of its relativelymile experimental condition and high total reducing sugar; the swelling effect and destructionof lignin structure improve the hydrolysis efficiency. The research of the dilute acidpretreatment, sodium hydroxide pretreatment and hyperacoustic sodium hydroxidepretreatment are the main part of this paper. The influence of reaction temperature, reactiontime and concentration of solution are analyzed based on the yield of reducing sugar inenzyme hydrolysate and pretreatment hydrolysate in different pretreatment processes. Theoptimum technological conditions of the three different kinds of pretreatment methods arealso identified. Analyses and representations of changes of biomass structures and hydrolysatein three different pretreated processes are: the sugar and inhibitor in enzyme hydrolysate andpretreatment hydrolysate are tested by Ultraviolet and Visible Spectrophotometer (UV-Vis), High Performance Liquid Chromatography (HPLC), Ion Chromatography(IC). Themicrostructure is tested by Scanning Electron Microscope (SEM), Fourier Transform InfraredSpectroscopy (FTIR), X-ray diffraction (XRD). The kinetic models of different pretreatmentprocesses are established through the study of the dynamic of enzyme hydrolysis onpretreated biomass. Finally, we conduct a calculation of material balance of the three differentprocesses to get the highest cellulose conversion among the three processes. We can analyzethe transformation and availability of these three different pretreatment processes from kindsof different aspects such as solid loss and sugar yield during the pretreatment process, totalsugar yield and hydrolysis efficiency and so on.It turns out that in the dilute acid pretreatment process, the main factors impacting theresults are reaction time, reaction temperature, concentration of dilute acid and mesh numberof biomass, and when the reaction temperature is145.7℃, reaction time is39.3min andconcentration of solution is1.14%, we can get the maximum value of cellulose conversionratio89.48%in the process of dilute acid pretreatment. During the hyperacoustic sodiumhydroxide pretreatment process, the main factors impacting the results are reaction time,reaction temperature, concentration of dilute acid, solid-to-liquid ratio and mesh number ofbiomass, When the reaction temperature is80℃, reaction time is15min, concentration ofsolution is10%and solid to liquid ratio is1:10, we can get the maximum value of celluloseconversion ratio90.23%in the process of hyperacoustic sodium hydroxide pretreatment. Wefind out these three different pretreated processes impacting the biomass in different degrees,especially the differences between acid pretreatment and alkaline pretreatment. Dilute acidpretreated process mainly worked on hemicellulose and degraded it. Swelling effect isremarkable and degradation on lignin is main during sodium hydroxide pretreatment process.Hyperacoustic sodium hydroxide pretreatment enhanced the degradation effects comparingwith hydroxide pretreatment process. Analyses of XRD explain the changes of crystallineafter different pretreatment processes. The strength changes, generations and disappearancesof functional groups in the FTIR spectra show the different changes of chemical functionalgroups after different pretreatment methods. The kinetic models of different pretreatmentprocesses are established through the study of the dynamic of enzyme hydrolysis afterpretreatment to get the dynamic equations, which are identical with the experimental values.This is meaningful to the further study in the future. At last, the analyses and calculations ofmaterial balance of the three different processes show the transformations and availabilities ofdifferent pretreated processes intuitively: The greatest solid loss is reaching up to249.1mg/g dry biomass belongs to the dilute acid pretreatment process. The sugar yield is41.15%duringthe hyperacoustic sodium hydroxide pretreatment process, while the total sugar yield89.0%and hydrolysis efficiency91.68%are both maximum value among the three differentpretreatment. So we can conclude that hyperacoustic sodium hydroxide pretreatment is themost hopeful among these three pretreatment processes.We can come to the conclusion that Paulownia has its research value and significance asbiomass from the results above, and also dilute acid pretreatment, sodium hydroxidepretreatment and hyperacoustic sodium hydroxide pretreatment can achieve the desiredeffects that broke the tight structure of lignocellulose, remove the hemicellulose and lignin,which is beneficial to enzyme hydrolysis so that to get good pretreated results. Hyperacousticsodium hydroxide pretreatment process is the best among these three different processes.