| Recently, with lack of energy, there is an important issue which human has been facing is that how to utilize the resource reasonable. Along with the environmental problem brought by reduction of extraction of fossil energy and utilizing, the exploitation and development of renewable energy is an important tast for the researchers. Liquefaction of biomass to produce biology oil and high value-added chemicals technics are able to convert the lower energy density of biology substance to high energy density and grade liquid fuel. It is an efficiency way to utilize biology substances reasonable. However, there are several difficulties in the liquefaction conversion of biomass under high pressure to bio-oil and high value-added chemicals, such as low production of bio-oil, lower grade, and low conversion rate of lignin of bio-substances. Therefore, in this paper, the effects of several kinds of catalysts were investigated, including four kinds of alkaline catalysts (sodium carbonate, potassium carbonate, sodium hydroxide and potassium hydroxide), the industrial molecular sieve catalysts, alumina catalysts in petrochemials field, and ion-exchanging HZSM-5 zeolite catalysts applied to liquiefaction by high pressure to produce bio-oil and high value-added chemicals. The objective of this study is to improve relatively reaction conditions of high pressure liquefaction with high efficient catalyst, and then increase the conversion rate of bio-substance's lignin in order toincrease yield of bio-oil product. The most important is that how to improve the characteristics of bio-oil products with the selective catalysts.During the high pressure liquefaction process, the study of reaction conditions as the basis of further research is very necessary. The effects of reaction conditions on bio-oil yield, such as reaction temperature and holding time, were investigated. The highest total oil yield of straw and sawdust liqufection is 50.25%(280℃) and 35.96% (320℃), respectively. It was shown by the results that the yield and composition of bio-oil are determined by materials and reaction conditions.In addition, the structure of bio-oil and residues obtained from the thermochemical liquefaction of straw in hot compressed water was investigated. Those products were obtained by sampling during the experimental process at the temperature of 200,220,250,300 and 310℃, respectively. The products of liquefaction were separated into water-solution fraction, Tetrahydrofuran solubles (bio-oil) and insolubles (residues). The raw straw and residues were analyzed by SEM, FTIR, and elemental analysis, while the bio-oil and water-soluble products were analyzed by GC-MS and TOC, respectively. It was indicated by the results that the main component including cellulose and hemicellulose of straw began to decompose at 200℃, while the lignin decomposed at 250℃. The main compounds of bio-oil were butylated hydroxytoluene and dibutyl phthalate, while higher molecular compounds were produced by further repolymerization with the temperature increasing. The results might be helpful to investigate the product characteristics at different temperatures during the process of liquefaction and establish a pathway of the straw liquefaction, which can be utilized to improve the yield of goal products (bio-oil, phenols and other useful chemicals).The catalysts, which are used for the research of alkaline catalyst, were NaOH, KOH, Na2CO3 and K2CO3, respectively. The yields of three kinds of bio-oil (ether phase, ethyl acetate phase and acetone phase) of sawdust liquefaction were enhanced, while the yields of residue were reduced markedly. In the run with NaOH, the yield of residue (Oil) was 1.26%(11.87%), while the yield of residue (Oil) was 20.87% (3.40%) without catalyst. In the run of straw, the highest yield of Oill, Oil2 and lowest yield of residue were 9.895%(with Na2CO3),6.693%(with KOH) and 6.415% (with NaOH), respectively.Meanwhile, another objective of this study is to improve the quality of the bio-oil. The effect of the catalyst on yield and composition of bio-oil, and the catalytic effects differences between liquefaction of straw (cellulose) and sawdust (lignin) were investigated. The maximum bio-oil yield was obtained as 20.83%with Al2O3 catalyst (0.4g), while the minimum residue yield of 12.50%was obtained at 280℃with 0.3g Al2O3. It was shown by gas chromatography/mass spectrometry (GC-MS) analysis that the main difference between bio-oil obtained from with or without catalyst runs were the amount of heneicosane and other oxygenous compounds. In the rus of HZSM-5 and Ni, Fe ion-exchanging HZSM-5 zeolite catalysts, the total bio-oil yields were increased obviously with Ni, Fe ion-exchanging HZSM-5 zeolite. In addition, the catalytic effects of ion-exchanging HZSM-5 zeolite were differernt with the temperature. The yield of OD was increased with ion-exchanging HZSM-5 zeolite catalyst at 280℃, while the yield of HO was enhanced at 300℃.Furthermore, liquefaction of straw to produce bio-oil with mixed solvent (ethanol-water mixture) was carried out in a 1 OOOmL autoclave at 300℃. The alkalic additives selected in this research were NaOH and KOH, while catalysts in this research were Na2CO3, K2CO3 and Fe ion-exchanging HZSM-5 zeolite catalysts, respectively. It was shown by the results that the bio-oil yield was increased significantly by the addition of NaOH. In NaOH run, the bio-oil yield was enhanced from 38.64%to 53.27%, while the conversion rate of the liquefaction was increased from 85.31%to 90.54%. The hydrothermal liquefaction of straw was studied with the same alkalic additives and catalysts as the mixed solvent liquefaction. Comparing the results of the two different reaction systems (mixed solvent system and hydrothermal liquefaction system), it was indicated that alkalic additives and catalysts were more effective in the mixed solvent system. The bio-oil was analyzed by gas chromatography-mass spectrometry (GC-MS. It was indicated by the results that the component characterization of bio-oil was mainly depended on catalyst. The content of hydrocarbon was enhanced in the NaOH run, while the content of aromatic compounds was increased by FeHZSM-5.In conclusion, reaction temperature is the biggest effect for the process of biomass liquefaction with high temperature and high pressure. The hightest yield of total oil yield of staw in the high pressure liquefaction is 50.25%(280℃), while the total oil yield of sawdust liquefaction is 35.96%(320℃). In the process of biomass liquefaction with high temperature and high pressure, cellulose and hemicellulose were decomposed at 200℃, lignin was decomposed at 250℃. The addition of catalyst could improve the conversion of high pressure liquefaction of staw and sawdust. The addition of NaOH resulted in residue yield was only 1.26%, while the residues yield was 20.87%without catalyst. Oill yield was increased from 3.4%to 11.87%, Al2O3 catalyst has little effect on bio-oil yield, the major effectiveness is to increase the heneicosane to 79.50%, and efficiently reduce the oxygen content of bio-oil, but the effects of molecure sieve and ion-exchanging HZSM-5 zeolite catalysts are to increase OD phase yield, and also increase ratio heneicosane as main content in bio-oil. The decomposition of biomass was improved with catalysts. The strict conditions of biomass liquefaction was reduced, while the conversion rate of lignin and the yields of bio-oil and valuable chemicals were enhanced with HZSM-5 zeolite, Al2O3, and Ni, Fe ion-exchanging catalysts.
|
PDF Full Text Request