Patent ID: 8853485

Claim:
A method for preparing low-carbon olefin products comprising a polymer grade ethylene and/or a polymer grade propylene comprising: (1) providing a stream of methanol pyrolysis gas comprising ethylene, propylene, C 4 hydrocarbons, and C 5 hydrocarbons, wherein the ratio of said ethylene to said propylene in said methanol pyrolysis gas is at least about 0.8 to about 1.5 by volume; (2) compressing the methanol pyrolysis gas from step (1) in a compression system for a three- to four-stage compression, to obtain a compressed methanol pyrolysis gas having a pressure of about 1.1 to about 2.5 MPaG; (3) removing at least one impurity from the compressed methanol pyrolysis gas from step (2) in an impurity removal system to obtain a refined methanol pyrolysis gas comprising a CO 2 concentration of less than 1 ppm and/or a total content of an alkyne less than about 5 ppm by volume; (4) cooling said refined methanol pyrolysis gas from step (3) with a propylene refrigerant in a pyrolysis gas cooler to obtain a cooled refined methanol pyrolysis gas; (5) passing the cooled refined methanol pyrolysis gas from step (4) into a front-end ethylene removing column comprising an upper portion and a lower portion, wherein said upper portion is maintained at a temperature ranging between about −53° C. and about −26° C., to produce an upper stream comprising ethylene and light components; (6) passing the upper stream from the front-end ethylene removing column from step (5) to an ethylene absorption column maintained at a temperature ranging between about −15° C. to about −53° C. where an absorbent comprising C 4 hydrocarbons contacts the upper stream from the front-end ethylene removing column to produce a lower liquid stream comprised of ethylene and absorbent and an upper vapor stream comprised of absorbent, ethylene and light gases; (7) passing the upper vapor stream from the ethylene absorption column from step (6) into an ethylene recovery column maintained at a temperature ranging between about −68° C. and −34° C. where the absorbent comprising C 4 hydrocarbons contacts the upper vapor stream from the ethylene absorption column to produce an upper stream comprised of absorbent and light gases and a lower stream comprised of ethylene and absorbent; (8) passing the lower liquid stream from the ethylene recovery column from step (7) to the front-end ethylene removing column; (9) passing the lower liquid stream from the ethylene absorption column from step (7) to a demethanizing column maintained at a temperature ranging between about −27° C. to about −65° C. to produce an upper stream and a lower stream; (10) passing the lower stream from the demethanizing column in step (9) into an ethylene fractionating column maintained at a temperature ranging from about −18° C. to about 128° C.; and, (11) obtaining polymer grade ethylene comprising greater than 99.95% by volume ethylene from the ethylene fractionating column.