| Research Abstract |
This study aims to develop the environmentally benign heat supply system using the heats of mixing of carbon dioxide (CO_2) and diethyl carbonate (DEC), which is environmentally benign solvent, in critical region of CO_2. In this study, for the completion of the heat supply system, further examinations concerning the cycle system of the fluids were attempted, on the basis of the heat supply system designed in the previous Grant-in-Aid for Scientific Research. In addition, a search of the solvent coupled with CO_2 was performed. Details and results of this study are as follows:
1. In the previous system, it was possible to operate only in extremely small flow rate. Therefore, an improvement of the mixer was performed, aiming the increase of the flow rate of CO_2 and DEC, and the enhancement of mixing of them. In this study, two types of mixers, that is, an improved single-tube mixer (mixer A) and multi-tube mixer (mixer B) was mainly considered. Total flow rate was set to 0.2 mol/min., a
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nd 0.3-0.4 mol/min. for mixers A and B, respectively. From the experimental results of the recovery of the heats of mixing, when mixer A was applied, the largest value (about 5.8 kJ/mol) of the maximum recovered heats was obtained. The recovery ratio of the heats of mixing was maximum about 70 % compared with the maximum value of heats of mixing (about 9.0 kJ/mol) measured in our previous study. The system with mixer A is applicable as the heat supply system, by the use of the heats of mixing for CO_2 + DEC system. On the other hand, the results by mixer B indicate that the mixing efficiently will improve by making the tube length longer. These results would be useful for the improvement of the mixer.
2. A search of the solvents coupled with CO_2 was performed by the measurements of the heats of mixing, in order to obtain the solvents accompanying larger heat effects, as well as DEC. In this study, two ethers, that is, diisopropyl ether (DIPE) and methyl tert-buthyl ether (MTBE), were applied as the solvents, considering the affinity with CO_2. The heats of mixing for CO_2 + DIPE and + MTBE systems were determined at temperatures 298-308 K, and pressures 5.0-7.5 MPa, using an isothermal microcalorimeter(IMC). Maximum value of exothermic was about 8.0 kJ/mol at 298 K and 5.0 MPa for both two mixtures. This maximum value was slightly lower than that of CO_2 + DEC system. However, this maximum value of heat effects is about 1.6 times larger than that of previous mixtures of CO_2 + solvent, and it is considered to achieve positive results of the search of solvents. Less
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