Process for producing ethylene

• US 6,444,869 B2
• Filed: 07/19/2001
• Issued: 09/03/2002
• Est. Priority Date: 10/04/1999
• Status: Expired due to Term

• Current Assignee: UOP Llc (Honeywell International Inc.)
• Original Assignee: UOP Llc (Honeywell International Inc.)
• Inventors: Cheng, Linda Shi, Senetar, John J., Miller, Lawrence W., Davis, Mark M.
• Primary Examiner(s): GRIFFIN, WALTER DEAN
• Application Number:
  US09/909,249
• Publication Number:
  US 20020007101A1
• Time in Patent Office: 411 Days
• Field of Search: 585/809, 585/802, 585/638, 585/639, 585/640, 585/820, 585/822, 585/833
• US Class Current: 585/809
• CPC Class Codes: C07C 11/04 Ethylene
• CPC Class Codes: C07C 2521/04 Alumina
• CPC Class Codes: C07C 2521/08 Silica
• CPC Class Codes: C07C 2521/18 Carbon
• CPC Class Codes: C07C 2529/08 of the faujasite type, e.g. type X or Y
• CPC Class Codes: Y02P 30/20 using bio-feedstock
• CPC Class Codes: Y02P 30/40 Ethylene production

Abstract

A process is provided for the concentration and recovery of ethylene and heavier components from an oxygenate conversion process. A separation process such as a pressure swing adsorption (PSA) process is used to remove hydrogen and methane from a demethanizer overhead stream comprising hydrogen, methane and C₂ hydrocarbons and subsequently return the recovered C₂ hydrocarbons to be admixed with the effluent from the oxygenate conversion process. This integration of a separation zone with a fractionation scheme in an ethylene recovery scheme using an initial demethanizer zone resulted in significant capital and operating cost savings by the elimination of cryogenic ethylene-based refrigeration from the overall recovery scheme.

Claims

1. A process for the production of an ethylene product stream front an oxygenate conversion effluent stream comprising hydrogen, methane, ethylene, ethane, propylene, propane, and C₄-plus olefins said process comprising:

a) passing the oxygenate conversion effluent stream to a deethianizer zone to provide a light hydrocarbon feedstream comprising hydrogen, methane, ethylene and ethane, and a deethanized stream comprising propylene, propane, and C₄-plus olefins;

b) passing the light hydrocarbon stream to a demethanizer zone operating at a demethanizing temperature greater than about −

45°

C. to provide a bottom stream comprising ethylene and ethane and an overhead stream comprising hydrogen, methane, and ethylene;

c) passing the overhead stream at effective adsorption conditions to an adsorption zone containing at least two adsorption beds, each of said adsorption beds containing a selective adsorbent to adsorb the ethylene on adsorption to produce an adsorber effluent stream comprising hydrogen and methane, and on desorption to produce a desorbed stream comprising ethylene and immediately following adsorption withdrawing a vent stream comprsing hydrogen and methane in a cocurrent depressurization step which is terminated prior to the breakthrough of ethylene;

d) passing the bottom stream to a C₂ splitter zone to produce the ethylene product stream and an ethane stream; and

e) combining the desorbed stream with the oxygenate conversion effluent stream prior to passing the oxygenate conversion effluent stream to the demethanizer zone.

2. The process of claim 1 wherein the effective adsorption conditions include an adsorption temperature comprising less than about 49°

C. (120°

F.).

3. The process of claim 1 wherein the selective adsorbent is selected from the group consisting of silica gel, activated carbon, alumina, zinc X zeolite, calcium Y zeolite and mixtures thereof.

4. The process of claim 1 wherein the adsorption zone comprises a pressure swing adsorption zone.

5. The process of claim 1 wherein the demethanizing temperature comprises a temperature greater than about −

40°

C.

6. The process of claim 1 wherein the selective adsorbent comprises silica gel.

7. The process of claim 1 wherein the light hydrocarbon stream comprises a non-adsorbable molar ratio of hydrogen and methane to C₂ hydrocarbons of less than about 0.5 moles of hydrogen and methane to moles of ethylene and ethane.

8. The process of claim 1 wherein the light hydrocarbon stream comprises a non-adsorbable molar ratio of hydrogen and methane to C₂ hydrocarbons ranging from about 0.01 to about 0.5 moles of hydrogen and methane to moles of ethylene and ethane.

9. The process of claim 1 wherein the ethylene product stream is recovered at a recovery of greater than about 99.5 mol-% relative to the ethylene in the oxygenate conversion effluent stream.

10. The process of claim 1 further comprising compressing the oxygenate conversion effluent stream to an effective demethanizer pressure of between about 1050 kPa and about 2860 kPa prior to passing the oxygenate conversion effluent stream to the demethanizer zone.

11. The process of claim 1 wherein the ethylene product stream comprises about 99.5 mol-% ethylene or greater.

12. The process of claim 1 wherein the demethanizer zone comprises a primary ethylene recovery of greater than about 85 mol-% ethylene per mole of ethylene in the light hydrocarbon stream.

13. The process of claim 1 wherein the adsorption zone provides an adsorptive recovey of ethylene comprising greater than about 95 mol-% ethylene.

14. The process of claim 1 further comprising recovering a propylene product stream from the deethanized stream.

15. The process of claim 1 wherein the demethanizer zone is refrigerated to the demethanizing temperature with a refrigerant comprising propylene.

16. The process of claim 1 wherein the oxygenate conversion effluent stream comprises a reaction product of an oxygenate feedstock having been reacted at effective conversion conditions in the presence of a diluent in an oxygenate conversion reaction zone containing a small pore, non-zeolitic catalyst to convert essentially all of the oxygenate feedstock to produce the oxygenate conversion effluent stream.

17. The process of claim 1 wherein the oxygenate conversion effluent stream further comprises carbon dioxide and said process further comprises passing the oxygenate conversion effluent stream to a carbon dioxide removal zone to remove at least a portion of the carbon dioxide and subsequently passing a carbon dioxide depleted stream to a dryer zone containing a solid desiccant to remove water prior to passing the oxygenate conversion effluent stream to the demethanizer zone.