Dimethyl Ether from CO2-Rich Natural Gas (Steam & CO2 Reforming)

The process under analysis comprises three major sections: (1) syngas production; (2) methanol synthesis; and (3) DME synthesis.

Syngas production. Initially, the CO2-rich natural gas is mixed with steam and an additional carbon dioxide feed stream and fed to a reformer, which is a tubular fired heater filled with a catalyst based on nickel oxide on magnesium oxide (NiO/MgO). In the reformer, the methane reacts with the carbon dioxide and water, yielding carbon monoxide and hydrogen in a highly endothermic reforming reaction. The reformer outlet stream is cooled and then compressed to 70 - 80 bar.

Methanol synthesis. The compressed syngas is mixed with recycle gas and fed to the methanol synthesis reaction system, where CO reacts with hydrogen to generate methanol. The system outlet gas is mainly comprised of methanol, water vapor, unconverted hydrogen, CO and CO2. This stream is cooled, and methanol and water are separated from the gases by condensation. The separated gas is recycled with a small purge. The water/methanol condensate (crude methanol) stream is forwarded to three distillation columns for methanol purification. Purified methanol is split in two streams: part is sent to storage facilities outside battery limits to be sold as co-product and the remaining part is forwarded to DME synthesis.

DME Synthesis. Part of the purified methanol is vaporized, superheated and then fed to an adiabatic fixed-bed reactor, in which it is dehydrated to yield DME. The catalyst used to promote the methanol dehydration is an activated alumina. The reactor effluent, mainly comprising DME product, water and unreacted methanol, is cooled in a series of heat exchangers by heat integrations with methanol feed heating and superheating and finally sent to a last distillation column, where DME product is obtained from the column top. The unconverted methanol and water are removed by the column bottoms and recycled to the methanol synthesis section for methanol recovery.