Pyrolysis of Biomass in to Fuels and Green Aromatics

Abstract

The dependence of humans on fossil resources is not limited to fuel needs. A significant amount of petroleum feedstock is also used to produce materials, from pharmaceuticals and plastics to asphalt for roads. But just like with fuels, the use of fossil resources for these purposes leads to depletion of resources and greenhouse gas emissions. The use of biomass as replacement for fossil fuel has increasing interest. Since biomass is considered a sustainable energy source, the use of biomass is regarded as a solution to environmental problems and depleting energy supplies. Benzene, toluene and the three xylenes (BTX) are bulk chemicals, which are vital for the petrochemical industry. Their major downstream products are plastics, but they are also used for solvents, additives and other specialty chemicals. Based on the environmental impacts over the lifecycle of a BTX product, the fossil resource depletion and greenhouse gas emissions make the largest impact on the environment. Because of this and the size of the market for BTX products, it is important to look for more sustainable options for BTX. Catalytic fast pyrolysis (CFP) is a promising thermochemical conversion route for lignocellulosic biomass that produces chemicals, including benzene, toluene, and xylenes (BTX), and fuels compatible with current, petrochemical infrastructure. In this single step process, solid biomass is fed into a catalytic reactor in which the biomass first thermally decomposes to form pyrolysis vapors. These pyrolysis vapors then enter the zeolite catalysts and are converted into the desired aromatics and olefins along with CO, CO2, H2O, and coke. Catalytic modifications to pyrolysis bio-oils are geared towards the elimination and substitution of oxygen and oxygen-containing functionalities in addition to increasing the hydrogen to carbon ratio of the final products. Recent progress has focused on both hydrodeoxygenation and hydrogenation of bio-oil using a variety of metal catalysts and the production of aromatics from bio-oil using cracking zeolites. Research is currently focused on developing multi-functional catalysts used in situ that benefit from the advantages of both hydrodeoxygenation and zeolite cracking. Development of robust, highly selective catalysts will help achieve the goal of producing drop-in fuels and petrochemical commodities from wood and other lignocellulosic biomass streams. The focus of this report is to study the reaction chemistry, effect of various process parameters on CFP of biomass. Biomass is thermally decomposed in a few seconds and produces dehydrated products, including anhydrosugars and furans. The dehydrated products then enter into the zeolite catalyst pore where they are converted into aromatics, CO, CO2, H2O and coke. The major competing reaction to aromatic production is the formation of coke. The main coking reaction is the polymerization of the furan intermediates on the catalyst surface.