Catalytic Steam Pyrolysis of Biomass for Production of Liquid Feedstock

Detta är en avhandling från Stockholm : KTH Royal Institute of Technology

Sammanfattning: The current societal needs for fuels and chemical commodities strongly depend on fossil resources. This dependence can lead to economic instabilities, political problems and insecurity of supplies. Moreover, global warming, which is associated with the massive use of fossil resources, is a dramatic “collateral damage” that endangers the future of the planet.Biomass is the main renewable source available today that can, produce various liquid, gaseous and solid products. Due to their lignocellulosic origin are considered CO2 neutral and thus can generate CO2 credits. Biomass processing can meet to the challenge of reducing of fossil resources by producing a liquid feedstock that can lessen the “fossil dependence” and /or meet the increased demand via a rapidly emerging thermochemical technology: pyrolysis.The ultimate goal of this process is to produce liquid with improved properties that could directly be used as liquid fuel, fuel additive and/or feedstock in modern oil refineries and petrochemical complexes.However, the liquids derived from biomass thermal processing are problematic with respect to their handling and end use applications. Thus, alternative routes of advanced liquid feedstock production are needed. Heterogeneous catalysis has long served the oil refining and petrochemical industries to produce a wide range of fuels and products. The combination of biomass pyrolysis and heterogeneous catalysis (by bringing in contact the produced vapours/liquids with suitable catalysts) is a very promising route.In this dissertation, the exploitation of biomass to produce of liquid feedstock via pyrolysis over a multifunctional catalyst and in a steam atmosphere is investigated. Steam pyrolysis in a fixed bed reactor demonstrated that steam can be considered a reactive agent even at lower temperatures affecting the yields and the composition of all the products. The devolatilisation accelerates and the amount of final volatile matter in the char.Fast pyrolysis in the presence of steam results in improved and controlled thermal decomposition of the biomass; higher liquid yields and slightly deoxygenated liquid products are also obtained.Steam pyrolysis over a bi-metallic Ni-V catalyst can produce liquids of improved quality (lower O content) and also provide routes for selective deoxygenation. However, a decrease in liquid yield was observed.The combination of metal and acid catalysts (Ni-V/HZSM5) shows enhanced deoxygenation activity and increased H preservation in the produced liquid. The final O content in the liquid was 12.83wt% at a zeolite (HZSM5) loading of~75wt%; however, the yield of the obtained liquid was substantially decreased. Moreover, increased coke formation on the catalyst was observed at highest zeolite rate.The increased catalyst space time (?) results in a lower liquid yield with reduced oxygen (7.79 wt% at ? =2h) and increased aromatic content. The coke deposited per unit mass of catalyst is lower for longer catalyst space times, while the char yield seems to be unaffected.The evaluation of the stability of the hybrid catalyst showed no significant structural defects and activity loss when the catalyst was regenerated at a low temperature (550?C).