Optimizing Catalytic Fast Pyrolysis of Biomass for Hydrocarbon Yield
Many studies have demonstrated that fast pyrolysis can turn the organic components (mainly macromolecules) in biomass into various low molecular weight chemicals that can be used directly as fuel or indirectly as building blocks for other more valuable industrial chemicals. In this study, we employed the Taguchi approach to optimize catalytic fast pyrolysis conditions for maximum hydrocarbon production. We tested four different zeolite catalysts, three biomass materials, three different catalyst-to-biomass ratios, three pyrolysis temperatures, and three pyrolysis reaction times in two experimental stages. Our results showed that the type of catalyst and the catalyst-to-biomass ratio had the biggest effects on hydrocarbon yields from catalytic pyrolysis of sorghum biomass. ZSM-5 catalysts performed better than those of zeolite Y. Zeolite CBV5524 was a better catalyst than CBV2314 in terms of hydrocarbon yield, and the amount of biochar generated during pyrolysis decreased significantly as the catalyst-to-biomass ratio increased from 10:1 to 20:1. The identified optimal catalytic pyrolysis conditions for hydrocarbon production were catalyst zeolite CBV5524, catalyst-to-biomass ratio of 20:1, and holding time of 20 s at 650°C. Under optimal catalytic pyrolysis conditions, hydrocarbon yield from sorghum biomass reached 18.3% of biomass (dry mass) with approximately 5% biochar residues. Aromatic hydrocarbons accounted for a majority of the hydrocarbon products, which included benzene (13.9% of total hydrocarbons), toluene (27.3%), ethylbenzene (1.4%), m-xylene (18.1%), p-xylene (5.2%), o-xylene (0.1%), 1,3,5-trimethylbenzene (0.8%), 1,2,4-trimethylbenzene (3.2%), naphthalene (6.3%), 2-methylnaphthalene (16%), 2-ethylnaphthalene (0.3%), and 1,7-dimethylnaphthalene (7.5%).