Dimethyl Ether Production from Natural Gas & CO2 (Direct Method)

The process under analysis comprises three major sections: (1) Syngas Production; (2) DME Synthesis; and (3) Purification.

Syngas Production. Natural gas feedstock is treated in zinc oxide beds, for removing sulfur compounds, and in a pre-reformer (fixed-bed-type reactor), that converts higher hydrocarbons contained in the feed gas into a gas rich in methane and hydrogen, in order to protect the catalysts. Then, the treated gas is fed to a dry reformer, in which the methane reacts catalytically with CO2, generating CO and H2 (syngas). The reformer outlet stream is cooled, compressed and then fed to absorption column for the separation of unconverted CO2 by means of a methanol wash.

DME synthesis. The syngas is then fed to a fixed-bed synthesis reactor, in which it is directly converted to DME. Such direct synthesis of DME is carried out in the presence of a bifunctional zeolite-based catalyst system (Cu-Zn-Al/ZSM-5 catalyst). The reactor outlet gas is mainly comprised of DME, methanol, CO2 and unconverted hydrogen and CO.

Purification. The effluent from DME synthesis is cooled, and DME and methanol are separated from the gases by condensation. The separated gas is partially recycled to the DME synthesis, with a small purge. The DME-methanol condensate stream is then passed through distillation columns. In the CO2 column, carbon dioxide is removed from the DME and recycled to the dry reforming. In the DME column, DME product is purified from methanol and directed to storage facilities located outside battery limits. Finally, wastewater is separated in the methanol column and the methanol obtained is recycled to the DME synthesis.