New Bifunctional Catalysts Offers Improved Performance and Stability for Direct Synthesis of Dimethyl Ether from Syngas
06 January 2010
| Catalytic performance on the bifunctional catalysts. CZA is unpromoted, CZA-Zr is promoted with Zr; CZA-Ga is promoted with Ga. Credit: ACS. Click to enlarge. |
Researchers at the Petroleum Displacement Technology Research Center, Korea Research Institute of Chemical Technology (KRICT), have developed new bi-functional catalysts, promoted with Zr (Zirconium) or Ga (Gallium), that offer higher catalytic performance and stability for the direct synthesis of dimethyl ether (DME) from syngas. A paper on their work was published 5 January in the ACS journal Energy & Fuels.
Used as an alternative diesel fuel, dimethyl ether, which is produced by the conversion of syngas derived from coal, biomass, or natural gas, offers lower NOx emissions and near-zero smoke evolution compared to conventional petroleum diesel fuel in addition to being a non-petroleum-sourced fuel. Conventional commercial production of DME from syngas is a two step process involving first the synthesis of methanol from syngas and the subsequent dehydration of the methanol to DME.
A single-step synthesis of DME from syngas on a bifunctional catalyst is receiving attention because of the simplicity and increased cost-effectiveness of a process that uses just one fixed bed or a slurry reactor, the study authors note. The direct synthesis of DME from syngas involves three important reactions:
- Methanol formation by CO hydrogenation and/or CO2 hydrogenation,
- Dehydration of methanol to DME and H2O
- Reaction of H2O with CO to form CO2 and H2 by the water-gas shift (WGS) reaction
In the case of using a bifunctional catalyst that is usually containing simultaneously two active sites for methanol synthesis and subsequent dehydration to DME, reactions of (i) and (iii) occur simultaneously on the methanol synthesis component of Cu-ZnO-Al2O3 and reaction (ii) occurs for methanol dehydration on solid acid catalysts, such as γ-alumina, ZSM-5, and modified alumina.
—Kang et al.
The researchers modified a bifunctional catalyst to enhance DME selectivity by adding Zr or Ga promoters on a Cu-ZnO-Al2O3 (CZA) methanol synthesis catalyst, and compared their performance to an unpromoted CZA catalyst.
While the unpromoted CZA catalyst showed a low DME yield around 27% and CO conversion of 61.1%, the CZA-Zr catalyst—which showed the best catalytic activity—showed DME yield of 40.3% and CO conversion of around 72.3%.
| CO Conversion and Product Distribution on Bifunctional Catalysts | ||||||
|---|---|---|---|---|---|---|
| Notation | CO conversion (mol %) |
Product distribution (mol %) | DME yield (mol %) | |||
| CH3OH | DME | CO2 | BPs | |||
| CZA | 61.1 | 23.5 | 44.2 | 29.5 | 2.8 | 27.0 |
| CZA-Zr | 72.3 | 18.1 | 55.7 | 25.2 | 1.0 | 40.3 |
| CZA-Ga | 63.9 | 19.9 | 53.1 | 25.1 | 1.9 | 33.9 |
The Cu-ZnO-Al2O3/γ-Al2O3 bifunctional catalyst promoted with Zr or Ga showed a higher catalytic performance with respect to high CO conversion and DME selectivity than that of an unpromoted catalyst...The promoters, such as Zr and Ga, play an important role in augmenting the dispersion of copper species with an appropriate electronic state and acidity of γ-Al2O3, which results in showing a high formation rate for methanol and consecutive dehydration rate to DME.
—Kang et al.
Resources
Suk-Hwan Kang, Jong Wook Bae, Hyo-Sik Kim, G. Murali Dhar and Ki-Won Jun (2010) Enhanced Catalytic Performance for Dimethyl Ether Synthesis from Syngas with the Addition of Zr or Ga on a Cu-ZnO-Al2O3/γ-Al2O3 Bifunctional Catalyst. Energy Fuels, Article ASAP doi: 10.1021/ef901133z
Methanol and DME (dimethyl ether) production from syn-gas from coal, biomass or even natural gas is the chief way for countries to stop spending excess money on imported automotive fuels even if coal must be imported itself. The factories for such products can be assured a profit by an import duty on imported liquid fuels. There may not be an actual increase of CO2 release by the manufacture and use of such fuels, but the present cost of imported liquid fuels allows for the sequestation of CO2 anyway. Wind and nuclear electricity can also reduce the release of CO2 for electrical production to also compensate for any increase due to synthetic production.
Methanol can be converted to gasoline for compatibility to existing systems. Methanol can also be directly injected into the intake air of many present diesel engines to replace up to 90 percent of diesel fuel. Methanol can also reduce soot formation. Synthetic gasoline can also be directly injected into the intake air of diesel engines to reduce fuel costs as can propane and butane or the mix called autogas. Filters and other exhaust treatments can also sufficiently reduce diesel particulates.
Because of its high efficiency and low total CO2 release, the diesel engine should become the only engine used for trucks and automobiles of any size. High performance alloys are available to keep the weight low enough, and the weight issue vanishes in comparison to the weight of the lightest lithium batteries even.
Hybrid and especially plug-in-hybrid vehicles further reduce CO2 release per mile and are a good combination with small diesel engines.
If the cost of DME can be made low, all diesel train locomotives should be converted to operate on it and autogas as well as diesel. There can also be arguments made for operation of locomotives on compressed or liquified natural gas along with diesel or DME.
Hybrid battery Diesel electric locomotives have already been tested, and when large production volumes and more automated production of Sodium-nickel-Chloride batteries reduce the cost of the batteries the locomotives will be very economic to operate.
Stationary and vehicle mounted liquid sodium batteries can reduce the operational cost of all rail vehicles with electric motors and increase the reliability. ..HG..
Posted by: Henry Gibson | 06 January 2010 at 08:09 AM
Very interesting, but well to wheels is around 13%
coal-> syngas (~80%) -> DME (~40%) -> motion (~40%)
You would probably be better just using the coal to charge an EV, but the above method would fit with current infrastructure.
IGCC charging EV's would have ~3 times better WTW and you could chuck a mix of biomass in the gasifier or use a natural gas turbine or solar thermal to add more heat for the steam cycle.
Posted by: 3PeaceSweet | 06 January 2010 at 03:12 PM
Biomass to fuel sounds good, the sooner we get on with using renewable energy, the better off we will be. Conserve the fossil fuels as reserves and use as many renewable energy sources as possible. The one great use for fossil fuels is creating renewable energy resources.
Posted by: SJC | 06 January 2010 at 08:50 PM