Graduation Semester and Year

2018

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Brian Dennis

Abstract

Energy demand has been rapidly increasing in the last 30 years due to the population growth and high demand by industries. However, as natural energy sources are limited, they cannot meet this increased energy demand. Therefore, alternative energies have become an option to sustain current and future energy demands. One promising and reliable alternative energy is the Fischer-Tropsch synthesis (FTS), which is a gas-to-liquid (GTL) technology that converts syngas from a low-value feedstock, for example, from coal, biomass, or natural gas, into a high-value liquid hydrocarbon. In addition, FTS is a highly exothermic catalytic reaction that requires careful thermal management during the synthesis, especially in the catalyst bed, so as to not deactivate the catalyst. One way to manage the increased temperature during synthesis is to use different type FTS reactors. However, these types of reactors do not completely manage the thermal problem of FTS because traditional catalyst materials used during synthesis, such as alumina oxide and silica oxide, do not conduct heat well unless they are specifically modified to do so. The purpose of this experiment is to increase the thermal capacity of the catalyst support in effort to increase liquid hydrocarbon selectivity. To increase heat transfer, copper, aluminum, and two sizes of graphite (0.7 and 0.9 mm), were added to the center of 3 mm traditional silica oxide catalyst support and tested individually. These modified silica oxide catalyst supports were used in a fixed bed FTS reactor to test for improvements in catalytic performance and product selectivity of the system. The results from these tests were compared with the results from using the traditional silica oxide catalyst support. Both the modified and traditional silica oxide catalyst support were loaded with design catalyst and promoters. The FTS experiment was done at 300 psig, a gas flow rate with 2:1 hydrogen to carbon monoxide ratio, and a catalyst was diluted with quartz chips diluent. The catalytic performance of the four modified and traditional silica oxide catalyst support was determined after the synthesis reaction stabilized around 18-20 h. after the activation started. The products, gas outlet, oil, and a water-alcohol mixture, were used to estimate the catalytic performance of the catalysts. The results show the increased of a catalytic performance of the modified silica oxide catalyst support with a Cu core affected by the increase in an overall heat capacity in a catalyst pellet. The improvement of the overall heat capacity showed only a small temperature swing in the system which resulted in about 30% increased in overall catalyst productivity. A spent modified silica oxide supported catalyst with a Cu will be characterized using TEM and XRD to see the synthesis reaction affect the catalyst particles

Keywords

Fischer-Tropsch synthesis, core-shell catalyst, Thermal capacity

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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