Study On Mild Pretreatment And Liquefaction Of Biomass And The Mechanism Of Biomass Liquefaction

The biomass liquefaction has many advantages such as (1) the presence of solventdilutes the concentration of the products preventing the cross linked reactions and reversereactions and (2) relative low temperature in comparison with pyrolysis. As one of the mostpromising technologies for biomass conversion, biomass liquefaction is attracted muchattention over the world. Therefore, investigations on the process and mechanism of newbiomass liquefaction will provide a theoretical basis and fundamental data for the furtherdevelopment of biomass liquefaction. The main research contents and results weresummarized as follows:(1) The term ‘mild pretreatment and liquefaction instead of ‘liquefaction’ was used todescribe the thermal conversion process of biomass. The liquefaction of biomass to bio-oilconsisted of two main steps: first, the biomass was pretreated using the method ofacid-chlorite or alkali delignification; second, the liquefaction of the pretreated biomass wasperformed in a stainless steel reactor in ethanol or water. The results showed that thepretreatment could markedly enhance the bio-oil yield and decrease the optimum temperature.The bio-oil yield obtained from acid-chlorite pretreatment cornstalk liquefaction in ethanolincreased from23.4%to31.4%and the optimum reaction temperature decreased from340°C to260°C. The maximum bio-oil yield from hydrothermal liquefaction ofun-pretreated cornstalk was36.2%(260°C). Comparatively, the pretreated cornstalkconversions showed higher bio-oil yields, and the maximum bio-oil yields obtainedhydrothermal liquefaction pretreated cornstalks were39.1%(1.5h) and39.6%(3h),respectively. Mild alkali pretreatment enhanced the bio-oil yield and decreased the optimumreaction temperature compared to the untreated and strongly alkali pretreated cypress samplesin which the bio-oil yield increased from15.5to23.5%and the optimum reactiontemperature decreased from300to240°C. The pretreatment changed the main chemicalcomponents, physical structure and thermo-chemical character of biomass.(2) The method of lump analysis has been applied to study the complexity of biomassliquefaction by lumping the large number of chemical compounds into groups ofpseudo-components, and an8-lump reaction system of cornstalk liquefaction in ethanol and a 7-lump reaction system of hydrothermal liquefaction cornstalk have been defined. The resultsshowed that there was reversible reaction between the heavy oil and volatile organiccompounds occurred in the liquefaction process, and the decrease in the water-soluble oilyield was mainly attributed to the conversion of water-soluble oil to gas in the cornstalkliquefaction process. The bio-oil was converted into solid residue as the form of C and N afterthe reaction temperatures reached to300and260°C in the sub-and super-ethanolliquefaction process, respectively.(3) The solid residues were characterized by FT/IR, X-ray diffraction, sugar analysis,elemental analysis, and NMR analysis to help understand the mechanism of the hydrothermalliquefaction process. Results showed that the process of cypress degradation consists of threesteps: firstly, the amorphic structure of the hemicelluloses and cellulose was decomposed.Secondly, the crystalline cellulose was decomposed by hydrolysis and the acid-insoluble solidresidue was formed by polymerization reactions. Finally, reactive fragments recombined toform more acid-insoluble solid residue. Thermal stability of the β-O-4chemical bond inlignin was more stable as compared to β-β′and β-5′bonds.