Date of Award
Doctor of Philosophy
The conversion of synthesis gas to desirable liquid fuels in gasoline and diesel range in a single reactor process with simultaneous use of FT and cracking catalysts was investigated in this dissertation. Co-based catalyst and ZSM-5 were used as a FT and cracking catalysts, respectively. The structural and textural properties of ZSM-5 were analyzed by XRD, BET and particle size analysis. Following, commercially available FT and cracking catalyst were tested in the newly designed fixed bed dual-zone reactor under 350 psi; syngas with H2/CO ratio in the amount of 2, and flow rate of 70, 100 and 130 smL/min; and 0.5, 1.25 and 2.5 g of ZSM-5. The temperature for the FT Co-based catalyst was maintained constant at 190 °C, whereas, the temperature for the additionally implemented cracking catalyst was varied (250, 300 and 350 °C). The effect of operating reaction conditions such as syngas flow rate, Si/Al molar ratio; temperature and loading of cracking catalyst were investigated. It was shown, that in general, decrease of syngas flow rate, ipso facto increase in residence time, resulted in decrease of gasoline and diesel fuel production, whereas reduction of ZSM-5 loading improved the formation of C5 - C17 paraffins. An enhancement in gasoline and diesel paraffin range formation was also observed with the decrease of cracking temperature. In addition, the effect of variation in operating conditions was evaluated for liquid paraffin production and dominance of chain propagation reactions over cracking and/or isomerizarion reactions with cracking catalyst loading and syngas flow rate was observed. As a consequence, the results employing ZSM-5 showed increased formation of light hydrocarbons and aromatics; and reduction of heavier paraffins production. Finally, the effect of various Si/Al molar ratios in the amount of 50, 80 and 280 were studied in this research. It was found, that the decrease in acidity of ZSM-5 zeolite enhanced the selectivity towards desirable products as well as heavier paraffins, but suppressed the formation of CH4. Furthermore, the isomerization reactions became favored in expense of cracking reactions.
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