Dimethyl ether synthesis via methanol dehydration: Effect of zeolite structure

In this paper, the effects of either pore size or topology of zeolites were studied in the methanol dehydration to dimethyl ether reaction by comparing catalytic performances of BEA, MFI and FER structures in the temperature range 180 °C-300 °C. The aim of this study was to investigate how the zeolite catalyst characteristics affect the process performances in terms of methanol conversion and DME selectivity. It was found that the largest-pore 3-D framework zeolite (BEA) was very effective in converting methanol but the channel size and topological connection spaces allowed the fast formation of coke precursors that rapidly decreases the catalyst performances at higher temperatures. Even if lower in intensity, the same phenomenon was observed for MFI structure (medium pores 3-D framework) confirming stable performances in the temperature range used in the real processes. On the contrary, the 2-D small pores FER zeolite showed a very good selectivity at high temperature also exhibiting a promising conversion rate for an industrial application. Continuous catalytic tests at 300 °C, followed by coke deposition analysis, confirmed that BEA rapidly deactivates and exhibited the higher coke formation rate, on the contrary, FER structure exhibited a great stability (conversion and selectivity) as well as a reduced coke formation tendency.