Catalytic pyrolysis of cellulose with oxides: effects on physical properties and reaction pathways

Fast pyrolysis is a potential technology for converting lignocellulosic biomass into bio-oil, a potential substitute for crude oil and a source of chemicals. Nevertheless, the high amounts of acid, oxygenated compounds, and water content cause the bio-oil to be unsuitable for direct usage. Catalytic fast pyrolysis (CFP) is able to improve bio-oil properties so that downstream upgrading processes may be economically feasible. The catalytic effects of calcium oxide (CaO), magnesium oxide (MgO), and zinc oxide (ZnO) on the pyrolysis of lignocellulosic biomass were investigated and were found to be attractive. However, the reaction pathways involved have not been comprehensively compiled to our knowledge. This study aimed to study the change in physical properties of bio-oils at the simplest form upon the addition of the oxides and to provide an understanding on the catalytic reaction pathways. Such study is beneficial to further explore the potential of selected oxides in enhancing the properties of bio-oil from biomass with different lignocellulosic compositions. Experiments were carried out in a fixed-bed reactor at laboratory scale to mimic large-scale processes in a controlled environment. The catalysts exhibited strengths at different bases. CaO catalyst showed the most favorable physical effects in terms of reducing the acidity of cellulose-derived bio-oils without increasing the water content significantly and without compromising with the yield. As for deoxygenation ability, ZnO catalyst exhibited better performance.