Effect of dehydration component on the performance of bi-functional catalysts in direct synthesis of dimethyl ether from syngas

Three bi-functional catalysts have been prepared by physical mixing of a commercial methanol synthesis catalyst (CuO-ZnO-Al2O3) with three different methanol dehydration catalysts including: H-MFI90, γ-Al2O3 and H-Mordenite. The bi-functional catalysts have been characterized using BET, XRD, TPR, NH3-TPD and elemental analysis techniques and also tested in a mixed slurry bed reactor at the same operating conditions (T = 240oC, P=50bar, H2/CO=2, SV=1100 ml gcat-1h-1, weight ratio of metallic function to dehydration function = 3) for 60h time on stream. These operating conditions were chosen in such away that the rate of methanol dehydration is the rate determining step in all experiments. It is found that the acidity of dehydration components had dramatic effect on the extent of synergy of reaction system. The physical mixture of CuO-ZnO-Al2O3 andH-ZSM-5 showed better performance, which can be contributed from NH3-TPD results to more acidic sites with moderate strength. Catalyst deactivation for three bi-functional catalysts was insignificant.

Keywords:

Dimethyl ether , dehydration catalyst , synthesis gas , direct synthesis