The purpose of this research project was to evaluate the feasibility of producing hydrocarbons by liquid phase hydrogenation of carbon dioxide. Initial studies dealt with the evaluation of ruthenium (III) chloride over a wide range of reaction conditions. High conversions were observed and were found to vary with catalyst concentration, temperature and time. Conversion of carbon dioxide reached 73% after twenty-four hours at a catalyst concentration of 0.75g/mole of CO₂ feed. The hydrogen to carbon dioxide ratio was found to have a significant effect on product distribution and amount of methane produced. For example, low ratios of H₂/CO₂ gave large amounts of high molecular weight hydrocarbons, while relatively more methane was formed at high H₂/CO₂ ratios. An attempt was made to determine whether the reaction was taking place in the gas phase or the liquid phase or both. A number of solutions were tested, with sodium hydroxide solutions exhibiting the best results. Since the carbon dioxide feed gas dissolves in this solution immediately to form carbonate species, it is assumed that the hydrogenation reaction takes place through a carbonate species in solution. This mechanism is supported by the observation that the carbonate molarity in solution strongly affected the conversion. The conversion of carbon dioxide over different molarities of sodium hydroxide was observed to exhibit a maximum at the concentration of sodium hydroxide, which give the maximum NaHCO3 concentration. Sodium carbonate and sodium bicarbonate solutions were also tested as starting reagents in the hydrogenation reaction. Conversion was found to be 10.68% for sodium carbonate and 15.88% for sodium bicarbonate, compared with 19% conversion of carbon dioxide under the same reaction conditions. These data suggest that the major part of the hydrogenation reaction takes place through a HCO3 species in solution. The rate of hydrogenation of sodium bicarbonate and sodium carbonate were found to be first order in catalyst concentration. A linear relationship was also found to exist between conversion of carbonate species and temperature in the range of 150-300°C. Three catalyst systems; RuCl3, Ru metal and 1% Ru supported on graphite were tested in the hydrogenation of carbon dioxide over sodium hydroxide solutions. One percent Ru on graphite exhibited the fastest rate at which equilibrium was achieved, with a 76-77% conversion of carbon dioxide to methane, and higher hydrocarbons being observed after 24 hours. Thea activity of Ru metal catalysts was observed to decrease during the course of the reaction, probably because of the loss of active catalyst sites, due to fusing of the catalyst on the surface of the glass liner. The rate of reaction between carbon dioxide and hydrogen over RuCl3 in the gas phase was found to be faster than the rate of this reaction in the liquid phase. In the gas phase reaction, equilibrium was achieved after 24 hours, with 89% conversion of carbon dioxide to methane and higher hydrocarbons, compared with 70% conversion in the liquid phase, under the same reaction conditions. One percent Ru supported on graphite exhibited a faster rate of reaction in the gas phase than in the liquid phase. But the rate of the reaction over Ru metal was faster in the liquid phase than in the gas phase. Table I summarized the comparison between the gas phase and the liquid phase hydrogenation reaction for the three catalytic systems under the same reaction conditions.
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Clausen, Chris A.
Master of Science (M.S.)
College of Natural Sciences
Length of Campus-only Access
Masters Thesis (Open Access)
Akbarnejad, Mohammad M., "The Liquid Phase Conversion of Carbon Dioxide to Hydrocarbons Over Ruthenium Catalyst Systems" (1977). Retrospective Theses and Dissertations. 317.