| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 89 === The purpose of this research was to develop a heterogeneous catalyst that could convert methanol, carbon monoxide, and oxygen to dimethyl carbonate (DMC) under atmospheric pressure. Finding the optimal reaction conditions to achieve maximum DMC yield was another goal to be accomplished.
Activity of catalyst was tested under atmospheric pressure, using a continuous flow micro-reactor. The standard reaction conditions were temperature 190℃, space velocity 1468 h-1, feed composition (molar ratio) CH3OH/CO/O2 = 50/36/14, and feed rate 24 cm3/min (STP). The main product of the studied reaction was dimethyl carbonate, and the byproducts were methyl formate, dimethoxy methane and dimethyl ether.
The investigation started with a catalyst screening. After activity tests, only CuCl2/C, among CuCl2/C, CuCl/C and PdCl2/C, showed some activity. The optimal loading of CuCl2 in CuCl2/C was found to be 13.5wt%. Adding PdCl2, KOH and CH3COOK to CuCl2/C could only result in lowering the activity of CuCl2/C.
The second step took in this research was to find the optimal reaction conditions. The experimental variables were changed one at a time. The range of the variables studied were partial pressure of methanol 0.1~0.5 atm, partial pressure of CO 0.075~0.36 atm, partial pressure of oxygen 0.03~0.14 atm, reaction temperature 150~210℃, and space velocity 733~2933 h-1. In studying the influence of partial pressure of methanol on the rate of reaction, the feed rate of methanol was varied, and the change was balanced by a nitrogen flow to maintain a constant total flow rate. The same technique was also used in the studies of the influences of carbon monoxide and oxygen. The optimal reaction conditions found in this investigation were partial pressure of methanol 0.2 atm, partial pressure of CO 0.36 atm, partial pressure of oxygen 0.14 atm, reaction temperature 180℃, and space velocity 1185 h-1. Under the optimal conditions, 45% of methanol conversion and 63% of dimethyl carbonate selectivity could be achieved.
CuCl2/C catalyst deactivated seriously during the reaction. The conversion of methanol dropped about 70% in 11 hours. However, at the mean time, the selectivity of dimethyl carbonate increased was doubled, raising from 30% to 60%. The appearance of several crystalline structures containing Cu2+ and the loss of chlorine in the catalyst was thought to be the reasons for the deactivation.
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