| Pyrolysis has attracted great widespread attention, since bio-oil produced from fast pyrolysis can be used as a substitute for traditional liquid fuels. However, biomass has high oxygen content, and bio-oil as the major products of pyrolysis has complex composition including ether, ester, aldehyde, ketone, phenol, organic acid, alcohol and polycyclic aromatic hydrocarbons of volatile, nonvolatile organic compounds and viscous oligomer. They belong to a number of chemical species involve of almost all of oxygen-containing organics. Thus, bio-oil is usually highly acidic, high water and oxygen content, and low heating value. Bio-oil has been restricted in the commercial development to be chemicals and fuels. Based on that, in this thesis experimental study and theoretical analysis are made systematically on pyrolysis vapors condensation and physicochemical property of bio-oils. The results may shred some light on high-value utilization of bio-oil.Firstly, fractional distillation is chosen to explore the organic species and distribution property by the difference of boiling points for each component of bio-oil derived from fast and slow pyrolysis, respectively. Then the condensation curves of light-, mid-and heavy-fractions were achieved according to the results of distillation, in order to provide guidance for fractional condensation of pyrolysis vapors. In the process of pyrolysis, different pyrolysis technologies and condensation temperatures were used to investigate the enrichment properties of high value-added fractions from bio-oil. Finally, the medium fraction separated from bio-oil with high energy density was used as the feedstock to prepare bio-slurry, and the properties of pyrolysis and gasification of bio-slurry were investigated. The results may shred some light on high efficient conversion of biomass and high-value utilization of bio-oil.Firstly, bio-oils derived from fast pyrolysis of cotton stalk and distillation of wood were selected for the study. With the two methods of distillation and extraction, bio-oil with complicated components was separated preliminarily for extensive analysis of bio-oil. Firstly, two kinds of bio-oils were distillated under different temperatures increasing in sequence (110?,110-140?,140?170?,170-200?,200-250?,250-300?), and six fractions were obtained. Based on the detailed analysis of these fractions, light fraction obtained under 170? of low boiling points has the properties of high moisture content, strong acidity, low viscosity and heating value, and poor stability, which is mainly composed of organic acids (formic acid, acetic acid and butyric acid), ketones (hydroxyl and cyclopentene), and aldehydes. In addition, acetic acid which contributes to the acidity of bio-oil was nearly all collected in the light fraction. The fraction yield of 170?250? as medium fraction accounts for small part of bio-oil, and has poor fluidity with low moisture, which is mainly composed of phenols, guaiacols and their derivatives. Heavy fraction distillated over 250? without low boiling point substances appears a similar solid of pitch at room temperature without any moisture and fluidity, which mainly consists of aromatic compounds of high molecular weight including naphthalene, fluorene and anthracene. The connection of distillation temperature and boiling points was studied according to classifying the chemical composition of each fraction based on chemical composition category. In addition, statistical calculation was performed to evaluate the role of distillation in bio-oil separation, which can provide theoretical guidance for the subsequent fractional condensation.Secondly, on the basis of the distillation results, the research on fractional condensation of pyrolysis vapors was carried out on the four condensed system (condensed by 300?? 100??0? and -20?), and the effect of condensation temperatures on the property of each fraction was studied. During the experiment of fractional condensation, liquid condensed at 0? accounts for the highest value of more than 50% of the whole bio-oil, which are mainly water and organic acids, while liquid condensed at 100? are mainly fusel phenols. The fraction collected at 300? is bitumen. Water and organic acids were well separated from bio-oil by fractional condensation, more than 80% water and nearly all the organic acids were collected in the group of 0? and -20?.Then the storage stability of bio-oils produced by fractional condensation of pyrolysis vapors was inveatigated. GC/MS,13C NMR and GPC were used to analysis the aging behaviour of each fraction. Finally, combined with literature analysis, the mechanism of bio-oil aging was summarized. Organic acids, aldehydes and ketones in bio-oil are active materials, which lead to esterification, polymerization and condensation reaction to be the main reasons of aging. And most reactions must be performed under acidic condition. Almost water and acids compounds were collected in the light fraction through fractional condensation, which can benefit to reduce the aging degrees of other fractions.Finally, the medium fraction derived from fractional condensation with high energy density was used to prepare bio-slurry by mixing with biochar and biomass powder. The property of slurry character and rheological behavior was discussed, then the pyrolysis/gasification property of bio-slurry was investigated. The results show that, high temperature of 800? under steam gasification leads to high yield of H2, and the yield of H2 was about 65%, and the yield of CO was about 17%. The syngas preparation from bioslurry has great application prospect in economy and technology. |
PDF Full Text Request