Process Options to Produce Dimethyl Ether from Syngas

Based on the demand of green and clean fuel dimethyl ether is selected as one of the promising fuel. We recently found that a survey predicts that arctic ice will completely melt out within coming next 10 years. This is because one of the big reasons is global warming due to greenhouse gases. One way to solve this problem is not to use fossil fuels. However, this cannot be done in next 10 years. We need to use alternative fuels that are produced from bio waste and biomass. First priority is occupied for biogas.

Methane content in biogas can be used to produce a Syngas, which is good raw material to produce dimethyl ether. Some of the process option would be:

Produce Dimethyl Ether from Syngas with CO2 methane reforming: 

In CO2 –methane reformer, the reforming methane produces Syngas (carbon monoxide and hydrogen) at temperature 782 to 927 degree centigrade range at pressure around 180 to 210 psig. In turn, Syngas is processed to produce dimethyl ether (DME), which the overall reaction can be written as

  • 3CH4 + CO2 → 2CO + 2H2 →2CH3OCH3

Produce Dimethyl Ether from Syngas with steam methane reforming and hydrogen production:

Water in the form of steam participates in reforming of methane to produce Syngas with ratio of 5:3 (H2: CO). The process is advantageous due to its recycle stream of carbon dioxide. Carbon dioxide is fed back to reformer without releasing out of the system. The integrated process follows the chemical reaction as below

  • 2CH4 + H2O →CH3OCH3 + 2H2
Syngas to DME with methane partial oxidation:

This process is abbreviated by POX, an integrated process developed based on partial combustion of methane. The products formed are H2, CO and CO2 in Syngas even the CO2 do not participate in DME reaction it is recycled back to the POX reaction system. However, the recycle CO2 will reverse the water shift reaction. Due to exothermic reaction in POX, the temperatures reach up to 1316 oC. 2:1 ratio of Syngas with hydrogen to carbon monoxide is produced. The overall reaction is 2CH4 + O2 →CH3OCH3 + H2O

Technologies well developed for above three processes. Pilot plant studies are conducted and they are been scaled up also. The demand in updating the process remained in reaction and reactor system.

Direct step for producing Dimethyl Ether from Syngas (carbon monoxide and hydrogen):

Natural gas or biogas treated to produce carbon monoxide and hydrogen. The treatment involves either steam reforming, partial oxidation or auto thermal reforming. The ratio of CO and H2 depend on the impurities, CO2, and H2O formation. 2 moles of CO and 4 moles of hydrogen are required to form one of DME along with water molecule. 2:4 or 1:2 ratio of CO and H2 gas is the limiting factor for this process.

As per the catalyst and its active sites, the surface reaction takes the role of rate determining step. DME synthesis chemistry explains the method of direct step

1. Syngas production is done from methane content gases (natural gas). Some of the manufacturing methods are:

  • Partial oxidation reforming: CH4+1/2O2 →CO+2H2 or
  • Steam reforming:  CH4+H2O→CO+3H2
  • Gas/water shift reaction: CO+H2O↔CO2+H2  side reaction

2. Methanol synthesis from carbon monoxide and hydrogen occurs at the active sites of the reactor bed as per the chemical reactions.

  • 2CO+4H2→2CH3OH
  • CO2+3H2→CH3OH

3. Methanol dehydration step follows along the reactor bed simultaneously. Two moles of methanol produce dimethyl ether and water, one mole of each with less heat release.

  • (Methanol) 2CH3OH → (DME) CH3OCH3+ (Water) H2O  catalyst:Al2O3 or Zeolite

The overall direct synthesis reaction produce dimethyl ether by reaction

  • 4H2+2CO→CH3OCH3+H2O

The two first scientists Franz Fischer and Hans Tropsch discovered the process for producing organic compounds from carbon monoxide and hydrogen gas. By their theory, most of the modern petrochemical industries produce dimethyl ether type liquid chemical products from gaseous raw materials. Due to their successful experiments even solid mass contain hydrocarbons compounds are gasified and converted to required liquid products. Praffins and olefins are the two main chemical entities produced by their proposed reaction mechanism. By-product like aldehydes, ketones and carboxylic acids are produced due to the complex polymerization reaction.