Catalyst Deactivation During One-Step Dimethyl Ether Synthesis from Synthesis Gas

Abstract

Catalysts for direct synthesis of dimethyl ether (DME) from synthesis gas should essentially contain two functions, i.e. methanol synthesis and methanol dehydration. In the present work, the deactivation of both functions of hybrid catalysts during direct DME synthesis under industrially relevant conditions has been investigated with special focus on the influence of each reaction step on the deactivation of the catalyst function corresponding to the other step. A physical mixture of a Cu-Zn-based methanol synthesis catalyst and a ZSM-5 methanol dehydration catalyst was used. The metallic catalyst appears to deactivate due to Cu sintering, with no apparent effect from the methanol dehydration step under the conditions applied. The acid catalyst deactivates due to accumulation of hydrocarbon species formed in its pores.Synthesis gas composition, i.e. H 2 /CO ratio and CO 2 -content (which directly affects partial pressure of water), seems to influence the zeolite deactivation.

Reversible deactivation of γ-alumina by steam in the gas-phase dehydration of methanol to dimethyl ether

“…https://doi.org/10.1016/j.catcom.2018.10.008 Received 20 July 2018; Received in revised form 14 September 2018; Accepted 8 October 2018 γ-Al 2 O 3 as a solid acid remains the catalyst of choice for the industrial production of DME, due to its low cost, high surface area, good thermal and mechanical stability, and high selectivity to DME because its relatively weak Lewis acid sites do not promote side reactions [2]. In fact, the reduced water content in SEDMES will likely promote coking of more acidic catalysts such as zeolites [7,8]. SEDMES uses a typical CuO/ZnO/Al 2 O 3 catalyst, catalysing both the methanol synthesis and the methanol dehydration reactions.…”

Sorption enhanced dimethyl ether synthesis under industrially relevant conditions: experimental validation of pressure swing regeneration

“…The optimum temperature for methanol synthesis shifts by dilution of the CZA catalyst from 230 to 250°C, which is well aligned with temperatures reported for methanol and direct DME synthesis in literature. 5,6,26,30,[59][60][61][62][63][64][65][66][67] DME synthesis, however, is far from equilibrium for all catalyst compositions and the DME yield keeps increasing with temperature. 6,68 Despite the fact that the temperature for methanol dehydration is generally higher, 4,27,31,69 direct DME synthesis is often performed at temperatures of around 250°C, 5,6,26,[59][60][61][62] not only because the methanol synthesis is considered to be the rate determining step in direct DME…”

“…This deactivation can be caused by the competing adsorption of water, dimers, trimers, or even larger alcohol-water clusters, but also the (reversible) formation of (surface) boehmite was shown. 27 Despite the large attention for more active low-temperature methanol dehydration catalysts, 4,6,59,69,71,73,74,[76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95] γ-Al 2 O 3 remains the catalyst of choice for industrial DME production, due to its low cost, high surface area, good thermal and mechanical stability, and high selectivity to DME because its relatively weak Lewis acid sites do not promote side reactions. 4,70,96,97 In contrast to direct DME synthesis, SEDMES offers two specific advantages for the (γ-Al 2 O 3 ) catalyst: the system is operated at low steam pressures and is periodically regenerated due to its adsorptive nature.…”

“…In fact, the reduced steam content will likely promote deactivation (coking) of other, more acidic, dehydration catalysts. 59,76 Reaction kinetics for the used materials are determined by fitting the parameters in the methanol synthesis and dehydration reaction models from Graaf et al (1988) and Berčič et al (1992) respectively. 26,30,31 The new parameters are given in Table 4 and their good predictive capability of the observed concentrations is shown in Fig.…”

“…An advantage of the sorption enhanced reaction conditions include the extremely low water concentration, protecting the catalyst from hydrothermal sintering. 59,70 However, water has also shown to have a positive influence in catalyst deactivation (by coking) for a CO-rich feed. The cause of the observed small decrease in catalyst activity is subject of follow-up work.…”