Ethylene Production from Methanol

The process under analysis comprises three major sections: (1) Reaction and regeneration; (2) Quench, compresion and caustic wash; and (3) Product fractionation.

Reaction and regeneration. Methanol feed is vaporized, mixed with recovered methanol, superheated and sent to the fluidized-bed reactor. In the reactor, methanol is first converted to dimethylether (DME) intermediate and then converted to olefins with a very high selectivity to ethylene and propylene. During the reaction, coke accumulates on the catalyst, which is circulated to the fluidized-bed regenerator system. In the regenerator, the coke is removed by combustion with air to keep the catalyst activity.

Quench, compression and caustic wash. The output from the reaction and regeneration is quenched, where most of water and non-reacted methanol is removed. The vapor stream from the quench stage is compressed and sent to a caustic wash column for CO2 removal. The gas stream free of CO2 is then dried and sent to next section.

Product fractionation. The dried stream is sent to the deethanizer column, where ethylene is separated from C3+ hydrocarbons as the overhead product. The ethylene rich stream is compressed and fed to the acetylene reactor for selective acetylene hydrogenation to ethane. The acetylene reactor effluent is sent to the demethanizer column, where an ethylene-ethane mixture is separated from a light stream. The C2 mixture is then routed to the C2 splitter, to obtain polymer grade (PG) ethylene product as the overhead. The C3+ stream is fed to the depropanizer column. The bottom product, composed mainly by C4+ hydrocarbons is sent to a debutanizer for recovering of mixed C4 and pyrolysis gasoline. The depropanizer column distillate, mainly containing a propylene-propane mixture, is fed to the C3 splitter column. In the C3 splitter, PG propylene is obtained as the overhead product.