Synthetic Diesel Production through Catalytic Pyrolysis of Biomass-Waste Tire Mixtures

The continuance of the modern world luxurious life-style, threatened by imminent depletion of cheap crude oil reserves, demands both the identification of alternative, sustainable, dense, cheap energy resources and means for effective waste reuse and disposal. This is of particular importance in the context of Jet fuels, for which energy demands are significant. The pyrolysis of waste tire rubber (WTR) results in the production of a pyrolytic oil (PO) in many ways similar to the crude exploited from fossil resources. PO has become a promising product since it addresses all of the aforementioned demands simultaneously. The yields and composition of this PO are strong functions of the production conditions and feedstock. In this work, the reaction conditions for PO synthesis using pulverized WTR alone and a mixture of WTR with sugarcane bagasse (30 and 70% w/w respectively) were experimentally assessed. Slow heating rates of approximately 5.5ºC/min were applied to 500 g of the feedstock in a batch reactor at a nitrogen flow rate of 2 L min^-1 with and without MgO derived catalysts. Liquid yields were obtained in the range from 50 to 56% for WTR alone and 47 to 50% for WTR+SCB, with catalyst having a negligible effect on the conversion to PO. Cetane number of PO was estimated using NIR spectra, with average values of 43 for bulk oils of both studied feedstock. For WTR pyrolysis, gas yield was observed to be close to 6% for experiments run without catalyst with a two-fold yield increase if catalyst was present. In contrast, WTR+SCB yields approximately 20% gas, with no definitive catalyst effect on gaseous phase. Pyrolytic processes require energy, which may partly come from the fuel gasses obtained during the process itself; therefore, a characterization of the gas phase comes convenient. In the experiments run within the context of this work, the obtained gas of WTR pyrolysis was composed mainly of CH₄, with a peak measured composition of over 96% CH₄. SCB addition resulted in a 75% reduction of CH₄ and a 70% increase in CO₂ concentration.