Ethylene from Ethanol (Similar to Hummingbird Process)

The process under analysis comprises three major sections: (1) Feed treatment; (2) Reaction; and (3) Purification.

Feed treatment. Fresh ethanol feed, containing about 6 wt% water, is combined with recycled ethanol and diethyl ether recovered in distillation columns downstream, and fed to a distillation column for removal of small amounts of unwanted by-products such as acetaldehyde and C4 hydrocarbons (primarily butylenes) that were generated in the reaction. The resulting overhead stream from this column is burned as fuel.

Reaction. The bottoms stream from the feed treatment column, containing mainly ethanol and diethyl ether, is vaporized and fed to the first of four superheaters. After being vaporized and superheated, the mixture is fed to the first of four adiabatic fixed-bed reactors, containing heteropolyacid catalyst supported on silica. The superheaters provide the heat consumed by the endothermic reaction that occurs in the reactors. Each superheater is located before one of the four reaction stages, ensuring that the reaction stage inlet temperature is 240 °C. While the ethanol dehydration is carried out at high temperatures, some thermal cracking reactions may occur, generating undesirable by-products such as alkanes.

Purification. The reaction outlet stream primarily consists of unreacted ethanol, Ethylene, and diethyl ether. The stream is sent to a series of columns for Ethylene purification. The first column is mainly used to separate the Ethylene from the water formed in ethanol dehydration. The second column aims to separate diethyl ether. The distillate product is polymer grade Ethylene. The diethyl ether-rich bottoms product is recycled to the feed treatment. The bottoms stream from the first column - rich in water, ethanol and diethyl ether - is transferred to the dewatering column. Water is extracted, while mostly unreacted ethanol and diethyl ether are also recycled.