Catalytic cracking of polycyclic aromatic hydrocarbons with hydrogen transfer reaction

Significance Statement

Increasing refining capacity and expanding the processible range of heavy crude oils are both important for the efficient use of oil resources. In modern petroleum refineries, the cracking of high molecular weight components is performed with the fluid catalytic cracking (FCC) process. However, the current fluid catalytic cracking process has been considered not to be able to directly refine polycyclic aromatic hydrocarbons (PAHs), which are one of the main components of the heavy crude oils, because of difficulties in activation of aromatic rings in an atmosphere without hydrogen. Therefore, for the efficient utilization of the heavy crude oils, it has been considered necessary to hydrogenate the PAHs with pressurized hydrogen atmosphere so as to convert them into naphthenes before they are supplied to the fluid catalytic cracking process.

Our research objective in this study is to achieve direct conversion of the PAHs into monocyclic aromatic hydrocarbons (MAHs) in the fluid catalytic cracking process. For that purpose, we focused on a hydrogen transfer reaction that proceeds in the fluid catalytic cracking process. Hydrogen transfer reaction is a bimolecular reaction in which dehydrogenation of one molecule (hydrogen donor) and hydrogenation of the other (hydrogen acceptor) proceed simultaneously. Actually, this reaction has been suppressed by the recent design of the fluid catalytic cracking catalysts because it converts olefins into paraffins, which results in a lower octane number of the produced gasoline. On the other hand, we expected the hydrogen transfer reaction to contribute to the hydrogenation and decomposition of the PAHs in the fluid catalytic cracking process.

In this study, we investigated the catalytic cracking of the PAHs using an fluid catalytic cracking catalyst with rare-earth ion exchanged USY zeolite, which is known to exhibit high hydrogen transfer activity. Reaction products analysis revealed that the yield of MAHs produced from the cracking of the 3-ring PAHs/n-hexadecane mixture was higher than that from the cracking of n-hexadecane alone. This result suggests that the 3-ring PAHs were highly reactive on the fluid catalytic cracking catalyst and they were converted into MAHs. Further investigation revealed that the conversion of the 3-ring PAHs were initiated by the hydrogen transfer reaction between the 3-ring PAHs (hydrogen acceptor) and n-hexadecane derivatives (hydrogen donor). Then, the saturated ring formed by the hydrogen transfer reaction was cracked and produced MAHs.

From the results shown in this paper, we concluded that the hydrogen transfer reaction can sufficiently contribute to hydrogenate the aromatic rings of the 3-ring PAHs in the fluid catalytic cracking process. This result suggests the possibility for the direct conversion of the PAHs into MAHs in the fluid catalytic cracking process without hydrogen atmosphere, which may be achieved by controlling the hydrogen transfer activity of the fluid catalytic cracking catalysts. 

Catalytic cracking of polycyclic aromatic hydrocarbons with hydrogen transfer reaction- Advances in Engineering

About the author

Dr. Iori Shimada obtained his bachelor’s degree in chemical engineering in 2008 and master’s degree and Ph.D. in environmental studies in 2010 and 2013, respectively, from The University of Tokyo. He was a Research Fellow of the Japan Society for the Promotion of Science (JSPS) in 2011 – 2013. Since obtaining his Ph.D. in 2013, he has been an Assistant Professor and principal investigator in the Faculty of Textile Science and Technology, Shinshu University. His research interests are in the area of sustainable energy technologies and chemical reaction engineering, including catalytic conversion process of unutilized resources (heavy oils, lignocellulosic biomass, and microalgae oils), catalytic reactions with non-hazardous water solvent, and fuel cells operated with liquid biofuels.

About the author

Dr. Hiroshi Fukunaga received his bachelor’s degree, master’s degree and Ph.D. in chemical engineering in 1993, 1995 and 1999, respectively, from The University of Tokyo. He took his current position as an Associate Professor in 2009 at the Faculty of Textile Science and Technology, Shinshu University, where he served as an Assistant Professor from 1999 to 2009. His research interests are in the area of electrochemistry and chemical engineering. In particular, he is interested in multiphase reaction kinetics and transport phenomena of solid oxide fuel cells and polymer electrolyte fuel cells.

About the author

Dr. Nobuhide Takahashi got his Ph.D. in Engineering from the University of Tokyo, in 1999. He is currently Professor at Shinshu University since 2014. His interest includes thermochemical (gasification and pyrolysis) and biochemical (fermentation) conversion for energy utilization of various biomass materials. He is also interested in promotion of carbon fixation by plant in plant factory and arid-land afforestation.

About the author

Dr. Toru Takatsuka obtained B.Sc. in 1971 and Ph.D. in 1989 in chemical engineering from The University of Tokyo. He has worked for Chiyoda Corporation (1971 – 2002), Nomura Jimusho, Inc. (2002 – 2005), Shinshu University (2005 – 2014), and Nomura Jimusho, Inc./Chiyoda Corporation (2014 to date). In 1971 – 1991, he engaged in investigating reaction engineering in the fields of residual oil upgrading processes such as hydrodesulfurization, thermal cracking, fluid catalytic cracking and carbonization technology, while developing various mathematical reaction models and proposing Meso-Pore Model of fluid catalytic cracking catalyst for residual oil conversion, which is now a basic concept of FCC catalyst development. He also engaged in development of ACR Process jointly conducted with Union Carbide Co. and Kureha Chemical Co., Ltd., and in plant operation in Texas, U.S.A. In 1991 – 1997, he engaged in environmental management technologies such as process development of deep hydrodesulfurization of diesel fuel, VGO mild hydrocracking, fluidized bed PTSA for carbon dioxide removal from flue gas, C4 alkylation by solid acid catalyst and so on. Also, he developed the Advanced Control System of fluid catalytic cracking process and supervised development of the Reformer Simulation Model. In 1997 – 2001, as R & D General Manager, he supervised many petrochemical process and catalyst development: GTL (Gas to Liquid), acetic acid, bisphenol-A, dimethylcabonate, butane dehydrogenation processes and so on. Also, he engaged in refining process and catalyst development: super clean automobile fuels, bottom of barrel conversion and HS-fluid catalytic cracking Process (High Severity fluid catalytic cracking. In 2001 – 2005, he engaged in HDS and FCC catalysts sales and licensing of refining technologies. In 2005 – 2014, as Professor in Chemical Engineering Department of Shinshu University, he conducted process system and catalyst developments of heavy oil and biomass conversion processes. From 2014 to date, as technical consultant, he has solved the problems with advice in petroleum refining and petrochemical industry.

 

Journal Reference 

Fuel, Volume 161, 1 December 2015, Pages 207-214.

Iori Shimada, Kouhei Takizawa, Hiroshi Fukunaga, Nobuhide Takahashi, Toru Takatsuka

Materials and Chemical Engineering Course, Faculty of Textile Science and Technology, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan

Abstract

With the aim of enhancing oil refining processes based on fluid catalytic cracking (FCC), the catalytic cracking of polycyclic aromatic hydrocarbons (PAHs) was investigated using an fluid catalytic cracking catalyst consisting of a rare earth ion exchanged USY zeolite. In these trials, model PAHs were dissolved in n-hexadecane and were fed into a fixed bed microactivity test reactor operating at 516 °C. Reaction product analysis indicated very little cracking of the 2-ring PAH over the fluid catalytic cracking catalyst, while in contrast the 3-ring PAH was highly reactive, and was rapidly converted into monocyclic aromatic hydrocarbons, 2-ring PAHs and coke. Tests using fluid catalytic cracking catalysts with different rare earth loadings revealed that the loading amount has little effect on the conversion of the 3-ring PAH. In addition, catalysts containing USY zeolites with comparable unit cell sizes, and thus having comparable hydrogen transfer activities, exhibited similar catalytic activities for 3-ring PAH conversion, even though they contained different amounts of the rare earth metal oxide. This result suggests that the hydrogen transfer reaction plays an important role in 3-ring PAH conversion and that the main effect of rare earth loading is to maintain the hydrogen transfer activity of the catalyst by stabilizing the USY zeolite against steam deactivation. In summary, this study successfully demonstrated a potential fluid catalytic cracking process for converting PAHs into useful light fractions without the necessity of employing a pressurized hydrogen atmosphere.

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