Study On Upgrading Of Bio-oil By Catalytic Esterification And Kinetics Of Model Compounds

Bio-oil produced by fast pyrolysis liquefaction of biomass is dark brown viscous mixture with a special smoky odor. It has high organic acid content, high oxygen and water content, low heating value, complex compositions and thermal instability. Crude bio-oil is primary liquid fuel; it must be upgraded in order to achieve the high value of utilization. In this paper, bio-oil was upgraded by catalytic esterification, which worked well to reduce the acidity and viscosity and improve the heating value and stability, making its performance closer to the petroleum oil.The solid acid catalyst silica sulfuric acid with good water resistance was prepared by chlorosulfonic acid and silica gel successfully, and characterized by IR, TG, XPS and BET testing. The acidic functional groups (-SO3H) on the surface played the role of solid acid centers. The effects of catalyst loading, ratio of acid to alcohol, temperature and the presence of water on the catalytic activity and reuse time of the catalyst were studied by using the model reaction of acetic acid and 1-butanol. The results showed that the silica sulfuric acid had high catalytic esterification activity and good water resistance. They can be use repeatedly and are suitable for upgrading bio-oil by catalytic esterification.The physical and chemical properties and the organic compositions of bio-oil before and after catalytic esterification which was occurred between bio oil and methanol, ethanol and 1-butanol respectively were analyzed. It was showed that the physical and chemical properties and the main component of bio-oil before and after esterification changed markedly. The acid value reduced from 40.88mgNaOH·g-1 to 5.95mgNaOH·g-1,7.35mgNaOH·g-1 and 8.12mgNaOH·g-1, respectively. The heating value increased from 14.46MJ·kg-1 to 20.79MJ·kg-1,26.14MJ·kg-1,31.44MJ·kg-1, respectively. The water content, density and viscosity also reduced. GC-MS analysis showed that the organic carboxylic acid was converted to esters efficiently. The acetic acid and formic acid were converted to the corresponding esters, besides, a variety of other esters were produced. The relative content of esters increased from 0.87% of the crude bio-oil to 12.9%,17.61%, and 22.26%, respectively. The species and content of ether compounds increased after upgrading the bio-oil. The content of aldehydes and carbohydrates decreased, while that of ketones and phenols remained unchanged.The reaction kinetics model for esterification of acetic acid and 1-butanol using silica sulfuric acid as catalysts and acetic acid as the model compound of bio-oil was investigated. Without the influence of internal and external diffusion, the reaction kinetics equation under the above experimental conditions was:-rA=X0.396×3.67×106e-56890/RT(CACB-CCCD/4.20)...