Fundamentals of Pyrolysis of Pretreated Biomass

Fast pyrolysis of lignocellulosic biomass has been extensively studied as a method for producing renewable fuels and chemicals. Issues with quality and stability of the resulting oil, due to its high oxygen content, have prevented commercial viability of the technology. Development of efficient oxygen removal strategies is critical for technological advancement of biomass pyrolysis. In this work, hot gas filtration was studied as a method for producing deoxygenated, stabilized pyrolysis oil. Detailed chemical analysis indicated that the increase in stability of the oil was a result of changes in the chemical composition of biooil. Specifically, hot gas filtration was found to eliminate compounds that are known participants in molecular weight-building reactions during aging. Based on experimental results, we demonstrate that hot gas filtration has the potential to reduce the oxygen content in pyrolysis oil by 30%. In order to further improve the quality of pyrolysis oil, calcium compounds were employed as in-situ catalysts. In this work, pretreatment of biomass with several calcium salts was explored, with a particular focus on calcium formate. Several calcium compounds, including calcium carbonate, formate and oxide, were found to have deoxygenating activity. The relative amount of deoxygenation was correlated with the basicity of the calcium pretreatment compound. Fast pyrolysis of pine sawdust pretreated with these compounds produces high quality, stable oils with oxygen contents ranging from 10-16 wt%. This improvement in oil quality was accompanied by a decrease in oil yield for all pretreatment compounds with the exception of calcium formate. Biomass model compounds were also pretreated with calcium oxide and calcium formate and then pyrolyzed. Based on experimental evidence, potential mechanisms for base-catalyzed deoxygenation of both lignin-type compounds and carbohydrates are proposed