LOW PRESSURE ETHYLENE RECOVERY PROCESS

• US 3,675,435 A
• Filed: 11/07/1969
• Issued: 07/11/1972
• Est. Priority Date: 11/07/1969
• Status: Expired due to Term

• Current Assignee: Ernest Freireich, James D. Hammond, Steven B. Jackson
• Original Assignee: Ernest Freireich, James D. Hammond, Steven B. Jackson
• Inventors: Jackson, Steven B., Freireich, Ernest, Hammond, James D.
• Primary Examiner(s): Yudkoff, Norman
• Assistant Examiner(s): Purcell, A. F.
• Application Number:
  US04/874,842
• Time in Patent Office: 977 Days
• Field of Search: 62/23,24,26,27,28,30,39,40
• US Class Current: 62/622
• CPC Class Codes: C07C 7/09 by fractional condensation
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/70 Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 2200/76 Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
• CPC Class Codes: F25J 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• CPC Class Codes: F25J 2270/02 Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/06 with multiple gas expansion loops
• CPC Class Codes: F25J 2270/90 External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• CPC Class Codes: F25J 2290/40 Vertical layout or arrangement of cold equipments within in the cold box, e.g. columns, condensers, heat exchangers etc.
• CPC Class Codes: F25J 3/0219 Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
• CPC Class Codes: F25J 3/0233 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0238 separation of CnHm with 2 carbon atoms or more
• CPC Class Codes: F25J 3/0252 separation of hydrogen production of hydrogen containing gas in general C01B3/00, e.g. separation of hydrogen or hydrogen containing gases form gaseous mixtures at low temperatures C01B3/506
• CPC Class Codes: Y02P 30/40 Ethylene production

Abstract

Process for the removal of methane from a hydrocarbon feed containing ethylene, methane and higher boiling hydrocarbons with minimum loss of ethylene. Methane is separated overhead from the feed in a separation zone at a first lower pressure; a first portion of this overhead vapor is expanded through an expansion motor producing an energy output, a second portion of the overhead vapor is compressed to a second pressure greater than the first pressure in a compressor driven by the motor output. The compressed vapor portion is then cooled to condense the major portion of the methane and the condensed methane is returned to the separation zone as reflux and recovering ethylene as bottoms from the separation zone. The methane vapor is recovered as fuel gas.

Claims

2. Process according to claim 1 in which said expansion of the first overhead vapor portion is carried out to produce an energy output equal to the energy required to effect said compression of the second overhead vapor portion.

3. Process according to claim 1 in which first vapor portion comprises not less than 50 percent by volume of the methane separation overhead.

4. Process according to claim 1 in which said second portion of the overhead vapor is compressed to a pressure above about 450 psia.

5. Process according to claim 1 in which said first portion of the overhead vapor is expanded to a pressure less than about 150 psia.

6. Process according to claim 5 in which said second vapor portion is compressed to a pressure above about 450 psia and is thereafter cooled by external refrigeration to a temperature below about -135*F to effect liquefaction of from 50 to 95 percent of the methane in said portion.

7. Process according to claim 6 including also returning the liquid methane obtained from said second vapor portion to the methane separation zone as reflux.

8. Process according to claim 7 in which said first vapor portion comprises not less than 50 percent by volume of the methane separation zone overhead.

9. Process accordinG to claim 8 and including also compressing said second vapor portion sufficiently to utilize the energy output of the expansion.

10. Process according to claim 1 including also centrifugally expanding said first vapor portion through a turbine.

11. Process according to claim 9 including also centrifugally expanding said first vapor portion through a turbine.

12. Process according to claim 11 including also cooling the compressed second vapor portion to a temperature liquefying the methane therein.

13. Process according to claim 1 in which said feed contains hydrogen and including also flashing hydrogen and methane from said feed in advance of said methane separation zone and heat exchanging the flash vapor and flash liquid with incoming feed to cool the feed before flashing hydrogen and methane therefrom.

14. Process according to claim 13 including also heat exchanging said expanded overhead vapor portion with said feed to cool said feed prior to said flashing.

15. Process according to claim 13 including also heat exchanging the bottoms from the methane separation zone with said feed to cool the feed prior to said flashing.

16. Process for the removal of methane from a hydrocarbon feed containing ethylene, hydrogen, methane and higher boiling hydrocarbon components with low loss of ethylene which includes hydrogen removal from the feed, fractionating said feed in a column having a bottoms temperature less than about 10*F and a bottoms pressure between 250 and 275 psia to provide a methane-rich overhead vapor comprising methane, up to 4 percent by volume hydrogen and not more then 2 percent by volume ethylene at a temperature below about -140*F and a bottoms stream essentially free of methane;

dividing said overhead vapor into a first portion equal to not less than 50 percent by volume of said overhead vapor and a second portion conversely equal to less than 50 percent of said overhead vapor;

expanding said first portion through a turbine to lower the pressure of said first portion to less than about 150 psia and to lower the temperature of said first portion to less than about -200*F producing an energy output from said vapor expansion, heat exchanging said expanded first portion with said feed to cool the feed to temperature about -120*F and a portion of the feed to -200*F or lower suitable for hydrogen removal therefrom, and recovering the heat exchanged expanded first portion as fuel gas;

compressing the second portion of the overhead vapor to a pressure greater than about 450 psia. in a compressor driven by said energy output of said turbine, cooling said compressed second vapor portion to a temperature less than about -135*F at which at least 50 to 95 percent by weight of the methane therein condenses separating condensed methane from the compressed second vapor portion and returning the condensed methane to the column as reflux; and

recovering ethylene and higher boiling hydrocarbons as bottoms from said column.