Process for separating CO.sub.2 from other gases

• US 4,659,343 A
• Filed: 09/09/1985
• Issued: 04/21/1987
• Est. Priority Date: 09/09/1985
• Status: Expired due to Term

• Current Assignee: Cynara Co. (Schlumberger NV)
• Original Assignee: Cynara Co. (Schlumberger NV)
• Inventors: Kelly, Ralph M.
• Primary Examiner(s): Spitzer, Robert
• Application Number:
  US06/774,251
• Time in Patent Office: 589 Days
• Field of Search: 55/16, 55/68, 55/73, 55/158, 210/640, 210/649-651
• US Class Current: 95/46
• CPC Class Codes: B01D 2319/04 Elements in parallel
• CPC Class Codes: B01D 53/22 by diffusion manufacturing semi-permeable membranes B01D67/00; form, structure or properties of semi-permeable membranes B01D69/00; material for semi-permeable membranes B01D71/00
• CPC Class Codes: B01D 53/226 in serial connexion
• CPC Class Codes: B01D 63/02 Hollow fibre modules
• CPC Class Codes: B01D 63/031 Two or more types of hollow fibres within one bundle or within one potting or tube-sheet
• CPC Class Codes: B01D 63/04 comprising multiple hollow fibre assemblies
• CPC Class Codes: Y02C 20/40 of CO2

Abstract

An improved process is described for separating carbon dioxide from light hydrocarbons by means of a membrane. The membrane separation is operated so that hydrocarbon liquids are condensed in contact with the membrane. This process is particularly valuable for the separation of gas mixtures into separate acid gas, gaseous hydrocarbon and liquid hydrocarbon streams.

Claims

1. An improved process for separating carbon dioxide from a fluid mixture with hydrocarbons comprising the steps of:

(a) contacting a liquid-hydrocarbon tolerant membrane selectively permeable to carbon dioxide with a fluid mixture comprising carbon dioxide and at least one C₃ to C₈ hydrocarbon;

(b) permeating carbon dioxide from the fluid mixture through the membrane at conditions which result in the presence of at least one condensed liquid hydrocarbon in the fluid mixture in contact with the membrane; and

(c) separating the condensed liquid hydrocarbon from the gases which do not permeate the membrane.

2. The process as described in claim 1 wherein the hydrocarbon fluid mixture in Step (a) comprises C₁ through C₅ hydrocarbons.

3. The process as described in claim 2 wherein the hydrocarbon fluid comprises 1 to 20 percent hydrogen sulfide.

4. The process as described in claim 2 wherein the membrane is a water-dry cellulose ester membrane.

5. The process as described in claim 2 wherein the membrane is a hollow fiber membrane.

6. The process as described in claim 5 wherein the membrane is a water-dry cellulose acetate membrane.

7. The process as described in claim 5 wherein the membrane includes a pressure case and said pressure case has separate outlets for removal of non-permeate liquids and non-permeate gases.

8. The process as described in claim 2 wherein a plurality of membranes are employed in series.

9. The process as described in claim 2 further comprising:

(d) contacting the non-permeate gases from Step (c) with a membrane selectively permeable to carbon dioxide, (e) permeating carbon dioxide through the membrane to produce permeate and non-permeate gas streams, and (f) recovering gaseous hydrocarbons from the non-permeate.

10. The process as described in claim 9 wherein the permeate or non-permeate gas from Step (e) is employed to cool feed gas introduced to the membrane in Step (a).

11. The process as described in claim 2 further comprising separating the non-permeate from Step (c) in a distillation column to remove in the distillate essentially all methane and carbon dioxide present and essentially all the C₄ and heavier hydrocarbons in the bottoms.

12. The process as described in claim 11 further comprising:

(d) contacting the overheads from the distillation column with a membrane selectively permeable to carbon dioxide, (e) permeating carbon dioxide through the membrane to produce permeate and non-permeate gas streams and (f) recovering a gaseous non-permeate consisting predominantly of methane and ethane.

13. The process as described in claim 12 wherein the non-permeate or permeate gas from Step (e) is employed to cool feed gas introduced to the membrane in Step (a).

14. The process as described in claim 11 wherein the non-permeate or permeate gas from Step (e) is used to cool fluids in process steps.

15. The process as described in claim 2 wherein the membrane exhibits a CO₂ flux with pure CO₂ of at least about 1×

10^-6 cm³ /(sec cm² cm of Hg) at 10°

C. and 50 psig.

16. The process as described in claim 15 wherein the membrane is a water-dry cellulose triacetate membrane.