Direct dimethyl ether synthesis from synthesis gas: The influence of methanol dehydration on methanol synthesis reaction

Abstract

Direct dimethyl ether (DME) synthesis from synthesis gas is studied with regard to potential effects of methanol dehydration on methanol formation and copperbased catalyst performance. For this, the influence of the operating conditions (space velocity, temperature, pressure, time-on-stream and syngas composition) on activity, selectivity and stability of the catalyst was studied and compared for methanol synthesis and direct DME synthesis. The advantage of the direct over the two-step DME synthesis is apparent at conditions where syngas conversion to methanol is thermodynamically limited. However, under the applied operating conditions, results suggest that combining methanol synthesis and dehydration has a negative effect on the methanol formation kinetics. The origin of the observed phenomena is investigated by varying dehydration catalyst and by introducing dehydration products (DME and water) into the methanol synthesis feed. Choice of the solid acid catalyst does not seem to affect methanol formation, and DME is also found to be practically inert over the methanol synthesis catalysts. Water injection, on the other hand, led to a significant decrease in the methanol synthesis rate. Thus, formation of an additional amount of water through methanol dehydration might be an explanation for the lower methanol formation rate in the direct DME synthesis.

Enhanced Direct Dimethyl Ether Synthesis from CO2-Rich Syngas with Cu/ZnO/ZrO2 Catalysts Prepared by Continuous Co-Precipitation

“…• C and 50 bar, the productivities are generally higher for the CO 2 -rich feed composition compared to the CO-rich composition (Table 4), which agrees with results reported in the literature [70][71][72][73][74]. In preliminary experiments, we observed a decrease in productivity using CO 2 -rich feed at reaction temperatures ≥250 • C. In this context, we refer to Ruland et al [70], who studied CO 2 hydrogenation using a commercial CZA catalyst and reported a decrease in the conversion of CO 2 -rich syngas with increasing temperature.…”

Ferrierite vs. γ-Al2O3: The superiority of zeolites in terms of water-resistance in vapour-phase dehydration of methanol to dimethyl ether

“…as alternative catalysts to γ -Al 2 O 3 for both methanol dehydration process and one-pot CO/CO 2 hydrogenation, exhibiting both higher activity (even at lower reaction temperature) and higher resistance to water adsorption than γ -Al 2 O 3 [19][20][21][22][23][24][25][26][27][28][29][30][31] . In this concern, Zhi et al [22] demonstrated via both experimental and theoretical approach, that the inhibitory effect of water during alcohol dehydration over zeolites is related neither to the destruction of acid sites by water (e.g.…”

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…”

“…In literature methanol to acidic catalyst ratios of 1 : 1 up to 8 : 1 can be found. 5,6,60,[70][71][72][73][74] The rate limiting methanol synthesis is reason to choose higher amounts of methanol synthesis catalyst. However, Fig.…”

“…The single-step direct DME synthesis proceeds via intermediate methanol as well, yet offers a reduction in process steps and increased overall conversion to DME. [4][5][6][7] Although the direct DME synthesis process outperforms the indirect process in terms of efficiency, separation and recycling remain a requirement. In the direct DME synthesis, the O-surplus of the feed ends up in CO 2 , resulting in equal molar amounts of DME and CO 2 produced.…”