| 其他摘要 | An ever-increasing demand for resources enforces the need of sustainability in all areas. Dimethyl ether (DME), as a clean fuel and important chemical raw materials, can be synthesized from coal, biomass and natural gas. With the developing of one-step synthesis technology of DME from syngas, the cost of dimethyl ether will be further decreased. It has triggered a growing interest in exploring the downstream of the DME. In this paper, we do some research about DME directly conversion to downstream chemicals. Our research shows that dimethyl ether can be directly converted to hexamethylbenzene(HMB) on zeolite catalysts at low temperature. In addition, we have study the influence of different zeolites and mental modified zeolites on the conversion of DME to hexamethylbenzene, and chose the catalyst with best performance on DME to hexamethylbenzene do deeply research. The catalyst regeneration performance has been investigated, and the mechanism of dimethyl ether directly to hexamethylbenzene has been discussed.
The performance of different zeolites convert DME to hexamethylbenzene have been studied, and found HBeta has good catalytic ability. The effect of Si/Al on HBeta catalyst performance have been investigated, and found that with the decrease of Si/Al, the selectivity of hexamethylbenzene become increasing. MnO2, ZnO, WO3, MoO3, K2O modified HBeta has been prepared by impregnation method, and found that MnO2/HBeta has the best performance in DME to hexamethylbenzene among all of the modified HBeta. The suitable acidity of the catalyst may be the reason for the promotion of the HMB selectivity.
The preparation parameters of Mn/HBeta have been studied, and found that with the increase of calcination temperature, the selectivity of hexamethylbenzene increases first and then decreases, the best calcination temperature is 450℃. The effect of MnO2 loads on the performance have been studied, and found that with the increase of loads, the selectivity of hexamethylbenzene increase first then decrease, the best loads is 10%. The effect of reaction conditions has been optimized, the optimized reaction conditions are as follow T= 280 ℃, P= 0.1 MPa, GHSV=100 h-1, and the dimethyl ether conversion rate can reach 76.36% and hexamethylbenzene selectivity is 25.06%.
The regeneration performance of 10%MnO2/HBeta have been studied, and found that this catalyst has good regeneration ability, after regeneration the deactivated catalyst can restore the original state. The structure and properties between fresh catalyst and used catalyst have been characterized, and found that the catalyst deactivation is mainly for the formation of coke which can cover the surface acidity and block pore channels of catalysts. Comprehensive analysis of catalysts structure properties and catalytic performance shows that weak acid center of catalysts is the activation center of dimethyl ether, appropriate amount of Bronsted acid is beneficial to the formation of hexamethylbenzene. |
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