The effects of temperature, pressure, and the initial composition of feed gas on the synthesis of dimethyl ether from CO hydrogenation and from CO 2 hydrogenation are investigated in a wide range of reaction conditions. By the detailed contrast between the dimethyl ether synthesis process from CO hydrogenation and that from CO 2 hydrogenation, it is seen that the former holds an advantage over the latter because of outstanding synergic effects. On the basis of the observation of the transition processes by adding CO 2 into the CO hydrogenation system through two different ways, it has been found that there are two kinds of critical states in which the equilibrium conversions of CO and CO 2 reach zero. After many critical states in the whole triangle region composed of the feed concentrations of CO, CO 2 , and H 2 are obtained, the dimethyl ether synthesis process is divided into three parts: CO hydrogenation, CO 2 hydrogenation, and parallel hydrogenation of CO and CO 2 .
The hybrid catalyst prepared by physically mixing a commercial methanol synthesis catalyst
and a solid acid dehydration catalyst was used for slurry phase dimethyl ether synthesis from
syngas. It was found that the addition of dehydration catalyst resulted in a significant synergic
effect on the overall syngas conversion. But, the excessive addition of dehydration catalyst could
not enhance the synergic effect but instead depressed the whole reaction rate. It was also proven
that this phenomenon existed when the methanol catalyst was used for low temperature water
gas shift reaction. When the fine powder in hybrid catalyst was sieved away, the special
phenomenon disappears and the conversion profile is the same with that in gas phase. It is
proved that the presence of the fine and superfine powder could be a primary cause resulting in
low catalyst activity. The better activity and stability of the hybrid catalyst can be realized by
carefully choosing the catalyst particle size and improving the catalyst strength.
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