| Bio-oil,in which has wide variety of phenols, can be used instead of the traditional petrochemical resource of phenol to prepare phenol-derivative products, such as phenol-formaldehyde resin (PF). However, the content of phenols in bio-oil is generally low due to the different structure of biomass and the complexity of the fast pyrolysis process, which has a negative impact on its industrial application as chemical substitutes. This paper focuses on improving the content of phenols in bio-oil.The influence of different kinds of biomass on the pyrolysis products was investigated. The effects on phenolic products by two aspects of pretreatment of raw materials and catalysis of pyrolysis process were studied. Enrichment mechanism and regulation rule of the phenols derived from pyrolysis process was explored. The oriented regulation mechanism and method for refining phenols through biomass pyrolysis was achieved. The main conclusions of this paper are as follows:(1) The bio-oil yields of hardwood were higher than that of softwood. However, the content of total phenols in hardwood bio-oils was much lower than that in softwood bio-oils. The content of total phenols in bio-oil is not only related to the lignin content in raw materials, but also presents a good positive correlation with the ratio of lignin/holocellulose in woody biomass.(2) The content of phenols in bio-oil was improved by the co-pyrolysis process of larch and waste rubber. In the co-pyrolysis process, when the temperatures were lower than 366℃, the major pyrolysis was on sawdust and lots of oxygen compounds generated. As the temperatures exceeded 366℃, the major pyrolysis component would be on the rubber and the aromatics produced in this stage. Phenols in bio-oil are the results of the thermal degradation of lignin in larch and the oxidation of aromatics in waste rubber.(3) The capability of catalytic thermal cracking of alkali lignin by three metal chlorides additives was ranked as such:Fe3+> Ca2+> K+. The ability of generating small-molecule gases by the additives was in the order of K+> Fe3+> Ca2+. The additives of CaCl2 and FeCl3 significantly improved the yields of lignin bio-oil, and increased the phenols content from 79.5% to 91.9% and 91.3%, respectively.(4) Nickel formate as an additive increased the relative contents of phenol,alkylphenols and total phenols from alkali lignin pyrolysis dramatically and promoted the formation of aromatics. Moreover, the relative contents of these compounds increased as the temperature rised. The nickel formate thermally decomposed to form hydrogen resulting in hydrodeoxygenation of alkali lignin pyrolysis to produce aromatics, and Ni was in favor of producing alkylphenols by Friedel-Crafts alkylation.(5) Catalysts of Cu/C, Pd/C, Pd-Ag and HZSM-5 can improve the pyrolysis efficiency and the content of total phenols. The highest content of total phenols was obtained by HZSM-5,and increased by approximately 35% compared with the content in bio-oil without catalysis.(6) The catalyst of Cu-Zn/FPC was prepared using fast pyrolysis char (FPC) as catalyst support loading with Cu and Zn with different atomic ratio using the co-impregnation method. The catalyst significantly improved the reaction efficiency and simplified the phenolic compounds.The catalyst had the highest selectivity of phenols when the content of metal loading was 6.5wt% and molar ratio of Cu/Zn was 2:1. When the catalytic temperature was 400℃ and the carrier flow was 0.8 L/min, the content of total phenols in larch bio-oil reached 30.33wt%, and increased by over 50% than that in larch bio-oil without catalyst. |
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