FURTHER DEVELOPMENT OF THE ISOPROPANOL-ACETONE CHEMICAL HEAT ENGINE

摘要

The performance and feasibility of a closed cycle chemical heat engine have been explored. This heat engine was designed to convert moderate temperature solar thermal energy into electricity. The solar thermo-chemical cycle comprises two processes: the dehydrogenation of isopropyl alcohol into hydrogen and acetone around 300 °C, a temperature compatible with typical parabolic trough plants, and the hydrogenation of acetone in a fuel cell at 30 °C. To evaluate the feasibility of this concept, the two processes were studied independently. First, the dehydrogenation of isopropyl alcohol was studied at a temperature of 300 °C. Isopropyl alcohol was thermally decomposed into acetone and hydrogen on a copper sponge catalyst. The products were measured using a gas chromatograph mass spectrometer (GCMS) to determine catalyst activity and byproduct formation. Conversion percentages of isopropyl alcohol to acetone were measured over an hour for each experiment. The main byproduct of the reaction was methyl isobutyl ketone (MIBK), a product of two acetone molecules. Second, the hydrogenation of acetone was studied in a Polymer Electrolyte Membrane Fuel Cell (PEMFC). At room temperature, the reaction of acetone and hydrogen to isopropyl alcohol has a standard cell potential of 0.128 volts (for an equimolar mixture of acetone and isopropyl alcohol). The fuel cell performed with an open circuit voltage of 0.12-0.14 volts for the various mixtures and had a limiting current of 42 mA/cm~2 for a 4 molar acetone mixture in water. The process was found to be feasible, but not optimal in practice due to its low cell potential.