UCLA Electronic Theses and Dissertations

UCLA UCLA Electronic Theses and Dissertations Title Methanation of Carbon Dioxide Permalink https://escholarship.org/uc/item/3nd6n502 Author Goodman, Daniel Jacob Publication Date 2013 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California UNIVERSITY OF CALIFORNIA Los Angeles Methanation of Carbon Dioxide A thesis submitted in partial satisfaction of the requirements for the degree Master of Science in Chemical Engineering by Daniel Jacob Goodman 2013 ABSTRACT OF THE THESIS Methanation of Carbon Dioxide by Daniel Jacob Goodman Master of Science in Chemical Engineering University of California, Los Angeles, 2013 Professor Selim M. Senkan, Chair The emission of greenhouse gases into the atmosphere has been linked to global warming. Carbon dioxide’s (CO2) one of the most abundant greenhouse gases. Natural gas, mainly methane, is the cleanest fossil fuel for electricity production helping meet the United States ever growing energy needs. The methanation of CO2 has the potential to address both of these problems if a catalyst can be developed that meets the activity, economic and environmental requirements to industrialize the process. Producing methane using carbon dioxide as a reactant would have the dual effect of keeping CO2 from entering earth’s atmosphere by consuming it to produce natural gas which in turn can produce electricity to meet growing power needs. This thesis aims to introduce the current methanation of carbon dioxide research, provide guidance into what needs to be considered before entering this field and how one might go about it. ii The thesis of Daniel Jacob Goodman is approved. Yunfeng Lu Yi Tang Selim M. Senkan, Committee Chair University of California, Los Angeles 2013 iii DEDICATION I would like to dedicate this thesis and the work to produce it to the following people, for without them it would not have been completed. Thanks to my advisor, Dr. Selim Senkan, for his patience, belief in my abilities and guidance in completing this degree. As well as my family and friends for their support throughout my time in graduate school and wishing the best for me even if it took longer than intended and was not what I initially set out to do. Lastly, a great thanks to my Girls for their love, understanding, and help getting back on track toward finishing this degree. iv TABLE OF CONTENTS Abstract of the Thesis……………………………………………………………………….…….ii Committee Page…………………………………………………………..………………………iii Dedication Page…………………………………………………………..………………………iv Introduction………………………………………………………………………………………..1 Thermodynamics of the Methanation of Carbon Dioxide………………………………………...3 Methanation Catalyst.....…………………………………………………………………………..8 Experimental………..……………………………………………………………………………17 Mechanism……………………………………………………………………………………….21 Conclusions………………………………………………………………………………………26 References………………………………………………………………………………………..27 v INTRODUCTION The United States emits 6 billion tons of carbon dioxide (CO2) per year into earth’s atmosphere. Greenhouse gases are so named because of their ability to absorb and emit infrared radiation. Water vapor and CO2 are the most common greenhouse gases in earth’s atmosphere. Recent studies indicate a high probability of a link between anthropogenic greenhouse gas emissions and observed effects on global warming, precipitation patterns, ocean acidification, and weather patterns [1]. Petroleum use for transportation accounts for about 1/3 of the total annual U.S. emissions of CO2. Fossil fuel use for electricity generation accounts for more than another 1/3. For electricity generation coal emits twice as much CO2 as natural gas which emits 20-40 times what nuclear or renewable methods do [1]. Nature gas is the cleanest of the fossil fuels, based on greenhouse gas emissions. 86% of the natural gas consumed in the U.S. is produced domestically and most of the remainder from Canada. This domestic production removes dependence on foreign sources and the international market price fluctuations that come with them. Steady prices in natural gas would allow for the construction of cleaner natural gas combined cycle plants, possibly with carbon capture and storage (CCS) technology, to replace existing coal plants helping reduce emitted CO2 [1]. There are 3 main strategies for reducing CO2 emission: reduce the amount of CO2 produced, storage of CO2, and usage of CO2. Hydrogenation of CO2 is an attractive C1 building block for making organic chemicals, materials, and carbohydrates (i.e. foods) if considering reducing emissions by usage of CO2. CO2 as a chemical feedstock in current industrial processes is 1 limited: synthesis of urea and its derivatives, salicylic acid, and carbonates. This limitation is due to the thermodynamic stability of CO2, which requires high energy substances to transform it into other chemicals [2]. The hydrogenation of CO2 into more useful fuels or chemicals uses hydrogen as the required high energy material for transformation. The products of CO2 hydrogenation currently being researched include carbon monoxide, methane, methanol, ethanol and higher alcohol, hydrocarbons, dimethyl ether, formic acid, formates and formamides. Some of these products can be fuels in internal combustion engines, raw materials and intermediates in many chemical industries, easily liquefied allowing for easy storage and transportation, and in general are more desirable than CO2. Effecting the scale up of CO2 hydrogenation to industrial levels include lack of satisfactory catalysts (with desirable cost, activity, selectivity, stability, recovery, reuse, and handling), efficient and economic reactor design and the availability of hydrogen which has issues with its production, storage and transportation [2]. Methane is the main component of natural gas [3]. If a natural gas plant with carbon capture and storage technology were utilized for producing electricity using methane/natural gas produced from CO2 all 3 strategies for reducing CO2 emissions would be implemented. This is why there is great interest in producing methane from CO2. Catalytic hydrogenation of CO2 to methane, CO2(g) + 4 H2(g) CH4(g) + 2 H2O(g), also called the Sabatier reaction (named after chemist Paul Sabatier in 1902 who observed the reaction over a Nickel catalyst) [4] is a topic most recently reviewed by Wang et al [5], who also reviewed the hydrogenation of carbon dioxide into other products [2]. 2 This paper is meant as an introduction into the research being conducted on CO2 methanation: The thermodynamics of the CO2 methanation reaction; types of catalysts being explored, what factors need to be considered when choosing which to use (i.e. type of metal(s), support, metal loading, and preparation method), and a table of CO2 catalysts investigated in the literature with their relevant conditions and results; The Sabatier reaction mechanism and how to design a reactor system to test your catalyst; Characterization techniques to use to better understand and evaluate your catalyst’s performance; and some conclusions and recommendations developed from reviewing the current state of methanation technology. THERMODYNAMICS OF THE METHANATION OF CARBON DIOXIDE Thermodynamic equilibrium calculations of chemical systems can give answers to important questions, such as the type of thermodynamically stable reaction products produced along with their selectivity and yield, if a reaction proceeds endothermically or exothermically, the impact of reaction parameters like temperature, pressure and reactant ratios [6]. Comparing calculations with experimental results allows for the identification of kinetic hindrances, i.e. thermodynamically allowed but somehow suppressed chemical reactions, providing guidance in catalyst development and process control of methanation. CO2, and its Carbon-Oxygen double bonds, is a stable molecule. Both terms of the Gibbs free energy disadvantage the conversion of CO2 into other products. At atmospheric pressure and 298 K, the ΔH is about 293 kJ/mol CO2 for the dissociation of CO2 into CO and O2. The addition of the higher Gibbs free energy co-reactant H2 in the reversible and exothermic methanation o reaction makes the conversion of CO2 thermodynamically easier with a ΔH of -167 kJ/mol [7]. 3 Gao et al. conducted systematic thermodynamic analysis of carbon oxide (CO and/or CO2) methanation using the total Gibbs free energy minimization method which is without any hindrances caused by kinetics, transport phenomena, or hydrodynamics. Table 1 lists possible reactions involved in the methanation of carbon oxides. Their calculations were based on gaseous compounds containing H2, O2, N2, CO, CO2, CH4, H2O, C2H4, and solid carbon. Note that all the reactions may simultaneously happen and since 3 of the reactions produce CO2 it is difficult to completely convert it. The van’t Hoff equation was used to calculate equilibrium constants (K), which are plotted versus temperature in Figure 1. It can be seen that the exothermic CO2 methanation (R2) is suppressed as temperature increases and that it plays an important role in the methanation reaction system because of its high equilibrium constant in the 200-500 oC range [6]. Table 1. Possible reactions involved in the methanation of carbon oxides [6] 4 Figure 1. The calculated K values of the reactions involved in methanation. [6] Figure 2 shows the typical product fraction for CO2 methanation determined by Gibbs minimization at equilibrium for a stoichiometric 4:1 H2:CO2 feed at 1 atm. At low temperatures o CH4 and H2O are

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