Catalysts in Biomass Pyrolysis

Abstract

One of the most promising suggested methods either to improve the quality of bio-oil (the liquid or oil fraction produced via biomass pyrolysis) by minimizing its undesirable properties (high viscosity, corrosivity, instability, etc.) or to increase the production of valuable chemical products is the application of heterogeneous catalysis. The most appropriate process for biomass catalytic pyrolysis should be based on the circulating fluid bed (CFB) technology, overviewed in this study. Upgrading of bio-oil can be achieved either during or after its production process. The first case refers to the application of heterogeneous catalysis in biomass pyrolysis (in-situ catalytic upgrading), which decreases organic yield but significantly improves bio-oil composition. A plethora of micro- (zeolitic) or meso-porous (Al-MCM-41) acid materials have been tested, either promoted or not with several transition metals. Lately basic materials are also suggested as promising candidate catalysts for biomass catalytic pyrolysis, however tailoring of their acidity/basicity and porosity characteristics is still needed to develop an optimized catalyst. Conversion of biomass compounds (e.g., aqueous glucose feedstocks) to aromatics is also studied using metal-promoted catalysts. Downstream upgrading of the pyrolytic oils, mainly focusing on their deoxygenation, is attempted either by a typical catalytic hydrotreatment with hydrogen and carbon monoxide under high pressure and/or in the presence of hydrogen donor solvents or utilizing zeolitic cracking catalysts. Lately, integration of bio-oil upgrading in a conventional petrochemical refinery is approached via co-processing bio-oil with conventional oil refinery feedstocks; this approach has received great interest both from research groups and big oil companies.