| Biomass residues are abundant and with the characterizations of being renewable and "zero carbon emission". The effective utilization of biomass residues is of great significance in the view of resource conservation and environment protection. Hydrothermal liquefaction has advantages of mild reaction conditions, low energy consumption and high efficiency over other biomass conversion technologies for bio-oil preparation. However, bio-oil is complex in composition, of low calorific value and cost much under present conversion methods in the short term. Therefore, extracting high value-added chemicals by separating technology is currently one of the hot research topics in the field of biomass conversion.With Salix psammophila and rice straw as raw materials, based on the physical properties and chemical composition of bio-oil, this study systematically investigated the performance of solvent extraction and column chromatography on bio-oil separation. Detailed research content is as follows:Firstly, systematically studied the extracting effect of bio-oil with eight kinds of commonly used solvents, and explored the influence of three parameters of non-polarity parameter, polarity parameter and hydrogen bond parameter on bio-oil extraction capabilities and the extraction rate of specific compound families in bio-oil. The results showed that the hydrogen bond and polarity parameters were main factors influencing the solvent extraction capabilities. Phenols and ketones extraction capabilities increased with the increase of the polarity while hydrocarbons showed adverse variation; Bio-oil extraction capability among different solvents is in decreasing order:tetrahydrofuran> toluene> ethyl acetate> acetone> ether> dichloromethane> n-hexane.Secondly, on the basis of the single solvent extraction, tetrahydrofuran, ethyl acetate and n-hexane in turn were chosen to make up a multi-step extraction process and got three oil components:light oil (26.13%), mid-weight oil (54.19%), heavy oil (19.68%). Light oil can be used for further separation and extraction of high value-added chemicals, such as the cyclopentenone and phenolic compounds. Oligomers exists in middle-weight oil, which also can be re-hydrothermal reacted, or produce bio-asphalt.Finally, silica gel column chromatography was used to separate main high value-added small molecule compounds out of bio-oil. Retention time of high value-added compounds in an isocratic elution process was studied with a mixed eluent composed of ethyl acetate and petroleum ether (V/V= 1:6) to get the fraction containing different compounds. At last, in pretreatment of acid and alkali extraction, a 2,6-dimethoxy phenol fraction was obtained with purification of 91% purity by GC-MS peak area. |
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