Catalytic hydrogenation of CO and CO2 in the Presence of Light Hydrocarbons Vahid Shadravan Bachelor of Chemical Engineering (Shahid Bahonar University of Kerman) A thesis submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy in Chemical Engineering School of Engineering Faculty of Engineering and Built Environment The University of Newcastle Callaghan, NSW 2308, Australia March 2018 Statement of Originality I hereby certify that the work embodied in the thesis is my own work, conducted under normal supervision. The thesis contains published scholarly work of which I am a co-author. For each such work a written statement, endorsed by the other authors, attesting to my contribution to the joint work has been included. The thesis contains no material which has been accepted, or is being examined, for the award of any other degree or diploma in any university or other tertiary institution and, to the best of my knowledge and belief, contains no material previously published or written by another person, except where due reference has been made in the text. I give consent to the final version of my thesis being made available worldwide when deposited in the University’s Digital Repository, subject to the provisions of the Copyright Act 1968 and any approved embargo. Vahid Shadravan Signature: Date: ii Statement of Contribution of Others I, the undersigned, attest that Research Higher Degree candidate, Vahid Shadravan, has carried out the experiments, results analysis and writing of paper included in this thesis. Professor Eric Kennedy Signature: Date: Professor Michael Stockenhuber Signature: Date: iii Acknowledgments Firstly, I would like to express my sincere gratitude to my supervisors Professor Eric Kennedy and Professor Michael Stockenhuber for their continuous support, meticulous supervision, patience, encouragement and immense knowledge. The life lessons that I have learnt from my supervisors are the most valuable achievements of my journey as a PhD candidate at the University of Newcastle. I would also like to thank my friends and colleagues at the Priority Research Centre for Energy, Dr Omid Mowla, Hadi Hosseini Amoli, Pedram Ghaseminejad Sadr, Luke Harvey, Dr Glenn Bryant, Matthew Drewery, Jarrod Friggieri, Dr Jerry Pui Li, Dr Sara Mosallanejad, Hamed Mootabadi, Dr Gizelle Sanchez, Dr Nasser Ahmed Khan, Dr Khalil Ahmed, Guangyu Zhao, Penghui Yan and many others for their assistance and friendship. I would like to take this opportunity to thank some influential people who helped me to find, develop and continue my interest in chemical engineering. Firstly, I thank Mr Neku Amal, my middle-school chemistry teacher; in his classes and laboratory demonstrations, I found my deep interests in chemical experiments and studies. I am also grateful for everything that I have learnt during my Bachelor studies at Shahid Bahonar University of Kerman from Dr Sattar Ghader, Dr Ali Farsi and Dr Seyed Soheil Mansouri. I would like to warmly appreciate all my friends (Ehsan, Ali, Farhad, Soheil and Shahram) and my relatives (my uncles, aunts, grandparents and my brother’s wife, Melika) in Iran; and my friends in Australia (Omid(s), Leily, Armin(s), Neda, Behzad, Esi, Mahmoud and the members of Newcastle Aikido) for their friendship, kind support and encouragements. My sincere thanks also goes to my iv inspiring instructors at Newcastle Aikido (Saku Shin Kan), Sensei Drius and Sensei Gabriel. Finally, I would like to dedicate my thesis to my dearest father and mother (Hossein and Maliheh), my lovely brother (Saeed) and my beloved fiancé (Maryam). I appreciate their patience while I was living far from them to follow my dreams. They have been continuously a source of love and support through my life. I would have not been able to accomplish this journey without their patience, love, unconditional support and sacrifice. v Abstract Carbon oxides emission, as by-products of many industrial synthetic hydrocarbon processes, causes serious environmental issues and negatively affects commercialisation of some new processes (e.g. OCM). Thus, producing CO and CO2 (COx) free (or with minimal amount of COx) synthetic hydrocarbon streams is necessary to facilitate commercialization of these new processes as large scale industrial plants. Moreover, due to the significant environmental effect of COx, it is critical to develop processes to convert COx and reduce their emission into the atmosphere. In this thesis, catalytic hydrogenation of COx in the presence of light hydrocarbons (methane, C2-C3 alkane and alkene) was studied. The feasibility of converting COx (where the residual concentration of both CO and CO2 in the product gas stream are less than 1 ppm) without reducing the inlet concentration of feed hydrocarbons was initially investigated over a bench-mark hydrogenation catalyst (Ni/Al2O3). It is found that the inlet species were consumed and converted in different temperature ranges. For feed compositions containing COx and C1-C3, the consumption of carbon monoxide, carbon dioxide and C2/C3 paraffins was observed and their maximum conversion was attained over different temperature ranges, in the following order: CO (150 – 250 °C) < CO2 (250 – 350 °C) < C2/C3 paraffins (275 – 400 °C). Moreover, Olefins were converted under all reaction conditions at lower temperatures (below 150 °C) due to the hydrogenation reaction which resulted in the formation of saturated hydrocarbons. Furthermore, the studies on COx hydrogenation in the presence of light hydrocarbons were extended to the development of catalysts to enhance the total outlet concentration of light hydrocarbons in a COx-free product stream. The vi effect of different transition metals (i.e. Fe, Co, Cu, Cr, Mn, Zn, Ru, Rh, Ag and Cd) on the catalytic performance of a Ni/Al2O3 catalyst was studied. Different and distinct promoting or inhibiting influence was observed (e.g. maximum C2-C4 yield of production increased from 6% for Ni/Al2O3 to 12% for Ni-Mn/Al2O3). The characteristics of partially charged active sites of the catalysts were studeid by employing different techniques (i.e. in situ NO-FTIR, CO-/H2-TPD and chemisorption). It is found that the addition of transition metals to Ni/Al2O3 markedly changed the structure of the active sites on the primary catalyst. For example, addition of copper resulted in increasing the ratio of Carbon-accepting to Oxygen-accepting sites (i.e. NO linear/bent adsorption increased from 7.70 for Ni/Al2O3 to 24.89 for Ni-Cu/Al2O3), which is probably increased the chance of linear CO adsorption that needs higher temperature for C – O cleavage. In contrast, by adding manganese to Ni/Al2O3 catalyst the ratio of electron accepting to donating sites balanced on the catalyst surface. Thus, most probably the number active carbon and hydrogen species increased on the surface. Promoting effect of manganese on Ni/Al2O3 was further investigated. Catalyst activity measurements as well as various characterisation techniques (such as XRD, CO and H2 chemisorption, in situ NO-FTIR and TPR) were performed for a series of Ni-Mn/Al2O3 catalysts with different nickel and manganese contents. It is considered that there is an optimum amount of Mn added (i.e. bi-metallic Ni- Mn/Al2O3 catalyst with 8 wt% of nickel and 4 wt% of manganese) to the primary catalyst which enhanced the catalyst activity and selectivity. Moreover, the more hydrogen amount in the feed stream improved the catalyst activity for COx hydrogenation and selectivity toward C2-C4 production (i.e. maximum C2-C4 yield of production increased from 1.5% for ~9.5 kPa H2 to 6.5% for ~37.8 kPa H2 in vii the feed stream over Ni/Al2O3). According to investigation of the catalysts’ electronic properties with different Ni and Mn contents, changes in catalytic activity (for COx hydrogenation) and selectivity (for light hydrocarbons formation) can be interpreted as being due to the effect of different electronic structure of the catalysts with variety of Ni/Mn ratios. The electrostatic properties of crystalline nickel and nickel-manganese particles was studied by computational methods (i.e. KS-DFT). Finally, this study continued on investigating the catalytic hydrogenation of COx in an industrial gas mixture containing light hydrocarbons. Complete removal of COx present in an ethane offgas (ExxonMobil refinery, Altona, VIC) via catalytic hydrogenation (over Ni-Mn/Al2O3) was studied. The effects of adding extra hydrogen and pre-treatment of the feed stream on the process was analysed. It is found that the addition of hydrogen gas into the feed reduced the concentration of CO and CO2 to below the detection limits. By adding 25% and 40% of extra H2 to the feed stream no COx were detected in the outlet. Moreover, pre-treatment of the offgas using molecular sieves to remove water vapour from the feed gas stream did not affect COx hydrogenation at low temperatures (below 300 °C). However, pre-treatment resulted in a significant reduction in CO and CO2 concentrations at temperatures above 300 °C. The results also confirmed the saturate gas plant ethane offgas can considerably deactivate the Ni-Mn/Al2O3 catalyst. The effect of ethane and ethylene in the feed gas stream on catalytic hydrogenation of low concentration CO and CO2 has also been investigated. Ethane addition did not influence the hydrogenation of COx at 180 °C while it inhibited the hydrogenation reaction at 320 °C. On the other hand, ethylene addition inhibited CO and CO2 hydrogenation at both 180 °C and 320 °C. viii List of Publications/Awards Conferences: . Vahid Shadravan, Eric Kennedy, Michael Stockenhuber, “The influence of the electronic structure of bi-metallic nickel-based catalysts on the catalytic hydrogenation of CO and CO2”, International Symposium on Relations between Homogeneous and Heterogeneous Catalysis, 2018. Vahid Shadravan, Eric Kennedy, Michael Stockenhuber, “Promoting effects of manganese on Ni/Al2O3 for catalytic hydrogenation of COx in presence of light hydrocarbons”, Europa-cat, 2017.