590
• As methanol is formed in situ and converts to DME within the same reactor,
methanol purification can be eliminated which increases the cost-effectiveness of
the process.
The zeolite-based catalysts are preferred over other solid acid catalysts, due to
stability and easy tuning of acidic sites. The combination of various methanol synthesis components like Cu/ZnO/Al 2 O 3 , Cu/ZnO/ZrO 2 , and Cu/ZnO/Ga 2 O 3 with zeolites is reported in literature for single-step DME synthesis. The water produced
using DME synthesis deactivates conventional Cu/ZnO/Al 2 O 3 catalyst. Thus,
Zr-modified Cu/ZnO/Al 2 O 3 hybridized with HZSM 5; DME yield of 18.3% was
obtained at 220 °C and 27.6 bar [128]. Frusteri et al. [129] reported Cu-Zn-Zr/FER
catalyst prepared by gel oxalate coprecipitation of Cu/Zn/Zr precursors in FER
slurry. The CO 2 conversion of 26% with 55.7% DME selectivity was observed at
260 °C and 50 bar. The specific features of zeolites alter surface chemistry of the
Cu-Zn-Zr catalyst. In addition, the acidity of the Cu-Zn-Zr/zeolites is also altered
[130]. Temvuttirjon et al. [131] reported Cu-Zn-Zr catalyst admixed with solid
SO 4
2− -ZrO 2 catalyst. The solid SO 4
2− -ZrO 2 was synthesized by impregnation of
ZrO 2 with H 2 SO 4 . The sulfur loading influences the physicochemical properties of
sulfated ZrO 2 catalyst and DME synthesis. At monolayer coverage of S (3.63 wt%),
the DME yield was highest (4.54% at 260 °C and 20 bar).
Parallel to the process development, catalytic design of DME synthesis catalysts
remains important. Special aspects are the improvement of activity, selectivity, and
resistance to sintering and deactivation. Most recent research deals with exclusively
copper-based catalysts.
The focus will be on the detailed study of the physicochemical foundations of
direct DME synthesis from syngas, resulting in the development of the appropriate
catalyst and process technology. Development of the rigorous catalytic system
which can work at lower pressures and temperatures (lower than that of the current
industrial processes) is aimed in near future.
6 Conclusions and Future Trends
Despite several amendments in the catalytic technologies for conversion of carbon
oxides, there is still a scope for improvement. More research in process system
engineering in particular for heat integration is the main avenue towards overcoming the economic limitation. Since the main drawback of the methanol synthesis
process is the thermodynamic limitation, the use of membrane reactors finds a
potential to separate the reaction products, thereby shifting the equilibrium in the
forward direction and increasing the conversion. The future research should focus
on scaling up these membrane reactors so that they can be applied industrially. From
catalyst point of view, the major shortcomings are the early deactivation, formation
of water, easy metal sintering, hot spot formation, etc. which results in the degraded
efficiency of the process. Use of reproducible water permeable membranes seems to
K. Tripathi et al.
• As methanol is formed in situ and converts to DME within the same reactor,
methanol purification can be eliminated which increases the cost-effectiveness of
the process.
The zeolite-based catalysts are preferred over other solid acid catalysts, due to
stability and easy tuning of acidic sites. The combination of various methanol synthesis components like Cu/ZnO/Al 2 O 3 , Cu/ZnO/ZrO 2 , and Cu/ZnO/Ga 2 O 3 with zeolites is reported in literature for single-step DME synthesis. The water produced
using DME synthesis deactivates conventional Cu/ZnO/Al 2 O 3 catalyst. Thus,
Zr-modified Cu/ZnO/Al 2 O 3 hybridized with HZSM 5; DME yield of 18.3% was
obtained at 220 °C and 27.6 bar [128]. Frusteri et al. [129] reported Cu-Zn-Zr/FER
catalyst prepared by gel oxalate coprecipitation of Cu/Zn/Zr precursors in FER
slurry. The CO 2 conversion of 26% with 55.7% DME selectivity was observed at
260 °C and 50 bar. The specific features of zeolites alter surface chemistry of the
Cu-Zn-Zr catalyst. In addition, the acidity of the Cu-Zn-Zr/zeolites is also altered
[130]. Temvuttirjon et al. [131] reported Cu-Zn-Zr catalyst admixed with solid
SO 4
2− -ZrO 2 catalyst. The solid SO 4
2− -ZrO 2 was synthesized by impregnation of
ZrO 2 with H 2 SO 4 . The sulfur loading influences the physicochemical properties of
sulfated ZrO 2 catalyst and DME synthesis. At monolayer coverage of S (3.63 wt%),
the DME yield was highest (4.54% at 260 °C and 20 bar).
Parallel to the process development, catalytic design of DME synthesis catalysts
remains important. Special aspects are the improvement of activity, selectivity, and
resistance to sintering and deactivation. Most recent research deals with exclusively
copper-based catalysts.
The focus will be on the detailed study of the physicochemical foundations of
direct DME synthesis from syngas, resulting in the development of the appropriate
catalyst and process technology. Development of the rigorous catalytic system
which can work at lower pressures and temperatures (lower than that of the current
industrial processes) is aimed in near future.
6 Conclusions and Future Trends
Despite several amendments in the catalytic technologies for conversion of carbon
oxides, there is still a scope for improvement. More research in process system
engineering in particular for heat integration is the main avenue towards overcoming the economic limitation. Since the main drawback of the methanol synthesis
process is the thermodynamic limitation, the use of membrane reactors finds a
potential to separate the reaction products, thereby shifting the equilibrium in the
forward direction and increasing the conversion. The future research should focus
on scaling up these membrane reactors so that they can be applied industrially. From
catalyst point of view, the major shortcomings are the early deactivation, formation
of water, easy metal sintering, hot spot formation, etc. which results in the degraded
efficiency of the process. Use of reproducible water permeable membranes seems to
K. Tripathi et al.