Mixed phase front end C.sub.2 acetylene hydrogenation

• US 5,414,170 A
• Filed: 05/12/1993
• Issued: 05/09/1995
• Est. Priority Date: 05/12/1993
• Status: Expired due to Term

• Current Assignee: Stone & Webster Process Technology, Inc. (Technip Energies NV)
• Original Assignee: Stone & Webster Engineering Corporation
• Inventors: McCue, Richard H., Hicks, Edna B.
• Primary Examiner(s): McFarlane, Anthony
• Assistant Examiner(s): PHAN, NHAT
• Application Number:
  US08/060,880
• Time in Patent Office: 727 Days
• Field of Search: 585/259, 585/264, 585/265, 585/275, 585/277
• US Class Current: 585/264
• CPC Class Codes: C07C 11/02 Alkenes
• CPC Class Codes: C07C 7/005 Processes comprising at least two steps in series
• CPC Class Codes: C07C 7/167 for removal of compounds containing a triple carbon-to-carbon bond
• CPC Class Codes: C10G 70/02 by hydrogenation

Abstract

The present invention provides an improved process for selectively hydrogenating acetylenes in an olefin plant process stream by selectively hydrogenating the acetylenes downstream of a front end depropanizer and upstream of further separation zones such as a demethanizer and/or de-ethanizer.

Claims

1. A process for hydrogenating acetylene in an olefin production plant, comprising the steps of, in sequence,

(i) passing an olefin plant feedstream through a depropanizer to produce a liquid phase stream rich in C₄₊ components and a vapor phase stream rich in C₃ and lighter components and comprising acetylene;

(ii) cooling said vapor phase stream to form a mixed vapor-liquid stream and passing said mixed vapor-liquid stream through a mixed phase hydrogenation zone to selectively hydrogenate at least a portion of the acetylene in said vapor phase stream;

(iii) separating the effluent from the mixed phase hydrogenation zone into a hydrogenated vapor stream and a hydrogenated liquid stream and passing said hydrogenated vapor stream to a vapor phase hydrogenation zone;

(iv) passing the effluent from the vapor phase hydrogenation zone to zones of further separation; and

(v) recycling said hydrogenated liquid stream to said depropanizer as a reflux for said depropanizer.

2. A process as defined in claim 1 wherein said olefin plant feedstream is derived from the product stream of a steam pyrolysis facility.

3. A process as defined in claim 1 wherein said olefin plant feedstream is derived from a catalytic cracking refinery off gas.

4. A process as defined in claim 1 wherein said olefin plant feedstream comprises butane, butenes, propane, propylene, ethane, ethylene, acetylene, methane, hydrogen, carbon monoxide and mixtures thereof.

5. A process as defined in claim 1 wherein said depropanizer operates at a high pressure ranging from about 150 psia to about 300 psia.

6. A process as defined in claim 1 wherein said mixed phase hydrogenation zone operates at a temperature of from about 10°

C. to about 40°

C. and a pressure of from about 200 psia to about 600 psia over a Group VIII metal hydrogenation catalyst.

7. A process as defined in claim 6 wherein said catalyst of the mixed phase hydrogenation is selected from the group consisting of Raney nickel, palladium-on-alumina, ruthenium-on-alumina, nickel arsenide-on-alumina and mixtures thereof.

8. A process as defined in claim 1 wherein said further separation zones comprise zones of demethanization, de-ethanization and combinations thereof.

9. A process as defined in claim 1 wherein said vapor phase hydrogenation is carried out over a catalyst comprising a Group VIII metal hydrogenation catalyst.

10. A process as defined in claim 9 wherein said vapor phase hydrogenation catalyst comprises a Group VIII metal in an amount ranging from about 0.01 to about 1 percent by weight of the total catalyst on a catalyst support.

11. A process as defined in claim 10 wherein said vapor phase hydrogenation catalyst is selected from the group consisting of Raney nickel, palladium-on-alumina, ruthenium-on-alumina, nickel arsenide-on-alumina mixtures thereof.

12. A process as defined in claim 10 wherein said vapor phase hydrogenation catalyst comprises a low surface area granular alumina impregnated with about 0.1 weight percent palladium.

13. A process as defined in claim 1 wherein said vapor phase hydrogenation zone is operated at a temperature in the range of about 10°

C. to about 200°

C. and a pressure in the range of about 200 psia to about 600 psia.

14. A process for hydrogenating acetylenes in an olefin production plant comprising the steps of:

(a) passing an olefin containing feedstock through a chilling train to cool and at least partially condense said feedstock;

(b) passing said cooled and partially condensed feedstock to a separation zone to produce a first liquid stream and a first vapor stream;

(c) passing said first liquid stream to a lower end of a depropanizer;

(d) passing said first vapor stream to an upper end of said depropanizer;

(e) separating said first liquid stream and said first vapor stream in said depropanizer into a second liquid stream rich in C₄₊ components and a second vapor stream rich in C₃ and lighter components, said depropanizer operating at a pressure ranging from 150 psia to 300 psia;

(f) cooling and partially condensing said second vapor stream rich in C₃ and lighter components and passing said cooled and partially condensed stream to a mixed phase hydrogenation zone;

(g) selectively hydrogenating at least a portion of acetylene in said mixed phase hydrogenation zone;

(h) passing the effluent from said mixed phase hydrogenation zone in step (g) to a separation zone to separate said effluent into a third liquid stream and a third vapor stream;

(i) recycling said third liquid stream to the top of the depropanizer as a reflux liquid;

(j) passing said third vapor stream to a vapor phase hydrogenation zone to selectively hydrogenate substantially all of the remaining acetylene contained in said third vapor stream;

(k) chilling and partially condensing the effluent from said vapor phase hydrogenation zone;

(l) separating the chilled and partially condensed effluent from step (k) into a fourth liquid stream and a fourth vapor stream;

(m) recycling said fourth liquid stream to either said depropanizer as a reflux liquid, or to said mixed phase hydrogenation zone as a feed stream; and

(n) passing said fourth vapor stream to a downstream separation zone comprising a demethanizer, a de-ethanizer or a combination thereof.

15. A process for hydrogenating acetylenes in the front end of an olefin production plant comprising the steps of:

(a) passing an olefin containing feedstock to a mixed phase hydrogenation zone to selectively hydrogenate at least a portion of the acetylene in said olefin containing feedstock;

(b) passing the effluent from step (a) to a vapor phase hydrogenation reactor to selectively hydrogenate substantially all of the remaining acetylene in said effluent to form a second effluent;

(c) chilling and partially condensing said second effluent from step (b) to form a vapor phase and a liquid phase;

(d) separating said vapor phase and said liquid phase; and

(e) recycling at least a portion of said liquid phase to said mixed phase hydrogenation zone.

16. A process for hydrogenating acetylene in an olefin production plant comprising the steps of:

(i) separating an olefin plant feedstream in a depropanizer to produce a liquid phase stream rich in C₄₊ components and a vapor phase stream rich in C₃ and lighter components and comprising acetylene;

(ii) combining said vapor phase stream from step (i) with a second hydrogenated liquid stream to form a mixed phase stream;

(iii) selectively hydrogenating a portion of the acetylene in said mixed phase stream in a mixed phase hydrogenation zone to form a first hydrogenated mixed phase stream;

(iv) separating said first hydrogenated mixed phase stream into a first hydrogenated vapor stream and a first hydrogenated liquid stream;

(v) selectively hydrogenating at least a portion of the remaining acetylene in said first hydrogenated vapor stream to form a second hydrogenated vapor stream;

(vi) cooling and partially condensing said second hydrogenated vapor stream to form a second hydrogenated mixed phase stream;

(vii) separating said second hydrogenated mixed phase stream into a second hydrogenated vapor stream and said second hydrogenated liquid stream;

(viii) recycling said second hydrogenated liquid stream to step (ii); and

(ix) recycling said first hydrogenated liquid stream to said depropanizer as reflux for said depropanizer.