Study Of Catalyst For The Dehydration Of Methanol To Dimethyl Ether

Dimethyl ether（DME） has a wide range of uses, great market value has been arised regarding its use as a clean energy, substitute for liquefied petroleum gas（LPG）. The most widely used industrial dimethyl ether production process is methanol dehydration reactions, the process using zeolite materials and γ-Al₂O₃ catalysts. ZSH-5 catalyst has higher prices, however, γ-Al₂O₃ has been mostly employed due to its low price, easy availability and high stability but low activity at low temperatures. Hence, the modification of γ-Al₂O₃ to increase its catalytic activity for methanol dehydration has become very important.In this paper, The γ-Al₂O₃ monolith support with high surface area and wide pore size distribution was prepared by extruding of a mixture of pseudo boehmite, organic aditives, subsequent drying and roasting. On this basis, the different modifiers and the amount of active ingredient loading on the catalytic activity of dehydration were investigated, the results show that: in considering the conversion of methanol and catalyst stability, the load 7% PO₄^3-alumina catalyst was the best. The methanol dehydration process with the vaporizing chamber temperature of 200 ℃, reaction temperature of 325 ℃, reaction pressure of atmospheric pressure, liquid space velocity（LHSV） of 4 h-1, the catalytic activity has the best performance.On the basis of above research, the n（NH3）/n(PO₄^3-) of impregnation liquied and the additives of ammonia, triethanolamine（TEA）, hexamethylenetetramine（HMT） and diethylenetriamine（MSDS） on the catalytic activity were investigated, the results show that :with the rate of n（NH3）/n(PO₄^3-) = 3, the catalyst containing 7 wt.% of phosphate with the addition of diethylenetriamine demonstrated the highest activity. The catalytic activity is found to be determined mainly by the amount of weak and medium acid sites.