Catalytic cracking of fast and tail gas reactive pyrolysis bio-oils over HZSM-5

Authors: Choi, Yongsuck; Elkasabi, Yaseen; Tarves, Paul; Mullen, Charles; Boateng, Akwasi

Submitted to: Fuel Processing Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2017
Publication Date: 3/27/2017
Citation: Choi, Y., Elkasabi, Y.M., Tarves, P.C., Mullen, C.A., Boateng, A.A. 2017. Catalytic cracking of fast and tail gas reactive pyrolysis bio-oils over HZSM-5. Fuel Processing Technology. 161:132-138.

Interpretive Summary: Various methods of making fuels from renewable sources exist, but their profitability depends on their method of production. Fast pyrolysis of crops and crop byproducts (biomass) involves a high-temperature breakdown in the absence of oxygen. After pyrolysis, a black crude oil (‘bio-oil’) that resembles crude petroleum is produced, except that it contains high levels of oxygen, a characteristic highly undesired for fuels like gasoline. Common techniques for refining the bio-oil into fuel usually rely on high pressure hydrogen reactions, which can be costly for refineries. Another technique, termed ‘catalytic cracking’ uses standard atmospheric pressures, albeit at higher temperatures. Catalytic cracking can more easily remove oxygen due to the lower pressures being used. While cracking of bio-oil has been investigated, the quality of different types of bio-oil can have an impact on the efficiency of cracking reactions. Our study investigated the efficiency of cracking reactions on bio-oil from two types of pyrolysis processes 1) traditional pyrolysis, and 2) tail-gas reactive pyrolysis (TGRP), a process which can produce better quality oil with reduced levels of oxygen. While cracking reactions on TGRP oil did produce fuel-grade molecules to a similar extent as those on traditional bio-oil, the process experienced some critical differences in concentrations of different molecules. Namely, the cracking produced higher concentrations of heavier molecules, and the catalyst experienced a loss of activity more quickly with TGRP oils. This new research will be valuable to companies trying to improve the economics of conversion of biomass to biofuels that can be blended with gasoline, diesel, and jet fuels.

Technical Abstract: While hydrodeoxygenation (HDO) of pyrolysis oil is well understood as an upgrading method, the high processing pressures associated with it alone justify the exploration of alternative upgrading solutions, especially those that could adapt pyrolysis oils into the existing refinery infrastructure. Catalytic cracking is one such alternative industrial practice that is carried out at near-atmospheric pressure using zeolite-based FCC catalysts. The present study focuses on the catalytic cracking of pyrolysis oil of different starting compositions over HZSM-5 to inform the extent of upgrading in the liquid phase. After establishing a catalyst bed temperature of 500 degrees C as optimum operating condition with regard to deoxygenation and yield of mono-aromatics in the products obtained the performance of the use of conventional pyrolysis and TGRP bio-oils as starting liquids for the cracking were compared. The results indicate that the formation of naphthalenes was favored, while the formation of BTEX compounds was slightly depressed in the case of the TGRP oil. We attribute this finding to the formation of naphthalenes from BTEX molecules already found in the TGRP oil. Subsequent reuse of the catalysts showed that the cracking of TGRP bio-oil exhibited slightly greater deactivation after a third cycle, likely due to the increased formation of naphthalenes and coke which block HZSM-5 pores. The results obtained from this study will help determine the issues that need to be addressed when developing a catalytic cracker with HZSM-5 for regular pyrolysis oil and TGRP oil.