Improved productivity in direct dimethyl ether synthesis and sorption enhanced DME synthesis using tungstosilicic acid as the acidic function

Abstract

Renewable dimethyl ether (DME) can reduce the carbon footprint in LPG and transportation sectors. The direct synthesis of DME (DDMES) is attracting a great deal of attention because it is possible to increase the productivity of DME. However, DDMES is hindered by the formation of a high amount of water, which promotes the deactivation of both catalytic phases used in the DDMES, namely Cu/ZnO/Al₂O₃ and γ-Al₂O₃. This is particularly relevant when CO₂-rich syngas is used, since it leads to a higher production of H₂O. In this work we show that heteropolyacids such as HSiW are a suitable alternative to state-of-the-art γ-Al₂O₃ for the dehydration of methanol during the DDMES. This is because HSiW is not deactivated by the presence of water in the reaction medium. Thus, catalytic beds with HSiW reach up to four times higher DME productivity than those containing γ-Al₂O₃. This feature is further exacerbated when water is removed from the reactor by means of a sorbent, i.e., during the sorption enhanced direct DME synthesis (SEDMES). Thus, the total carbon conversion is higher for SEDMES than for DDMES regardless of the actual nature of the acid catalyst.