The influence of catalyst type on the composition of upgraded biomass pyrolysis oils

摘要

The composition of oils derived from the on-line, low pressure upgrading of biomass pyrolysis oils from a fluidised bed pyrolysis unit have been investigated in relation to catalyst type. Na-ZSM-5 (partially exchanged), H-ZSM-5 and Y type zeolite catalysts, and activated alumina were used. In addition, a blank run was undertaken in which the catalyst bed was replaced by a bed of stainless steel ball-bearings to determine the influence of thermal cracking. The composition of the oils before catalysis and after catalyst upgrading were analysed by liquid chromatography fractionation, followed by coupled gas chromatography/ mass spectrometry analysis of each fraction. In particular, the aromatic and oxygenated aromatic species were identified and quantified. There were only small differences in the product yields and compositions from the catalysis of biomass derived pyrolysis oils for the Na-ZSM-5 and H-ZSM-5 catalysts. All of the catalysts were effective in deoxygenating the biomass pyrolysis oils; however, there were still significant concentrations of oxygenated compounds in the upgraded oils. The ZSM-5 catalysts gave the highest yields of hydrocarbon products when compared to the Y-zeolite and activated alumina catalysts. Significant concentrations of polycyclic aromatic hydrocarbons (PAH) were formed by all the catalysts. Some of the PAH have been shown to be carcinogenic in biological studies. The formation of coke was increased for Y-zeohte and alumina compared to the Na-ZSM-5 and H-ZSM-5 catalysts.