Kinetic fractionators, and cycling processes for fractionation of gas mixtures

• US 8,921,637 B2
• Filed: 09/26/2011
• Issued: 12/30/2014
• Est. Priority Date: 11/15/2010
• Status: Active Grant

• Current Assignee: Exxonmobil Upstream Research Company (Exxon Mobil Corporation)
• Original Assignee: Exxonmobil Upstream Research Company (Exxon Mobil Corporation)
• Inventors: Sundaram, Narasimhan, Northrop, P. Scott
• Primary Examiner(s): Nguyen, Tam M
• Application Number:
  US13/877,315
• Publication Number:
  US 20130225898A1
• Time in Patent Office: 1,191 Days
• Field of Search: None
• US Class Current: 585/823
• CPC Class Codes: B01D 2252/30 Ionic liquids and zwitter-ions
• CPC Class Codes: B01D 2253/1085 characterized by a silicon-aluminium ratio
• CPC Class Codes: B01D 2256/245 Methane
• CPC Class Codes: B01D 2257/304 Hydrogen sulfide
• CPC Class Codes: B01D 2257/306 Organic sulfur compounds, e.g. mercaptans
• CPC Class Codes: B01D 2257/504 Carbon dioxide
• CPC Class Codes: B01D 2257/702 Hydrocarbons
• CPC Class Codes: B01D 2257/708 Volatile organic compounds V.O.C.'s
• CPC Class Codes: B01D 53/0407 Constructional details of adsorbing systems
• CPC Class Codes: B01D 53/0446 Means for feeding or distributing gases
• CPC Class Codes: B01D 53/047 Pressure swing adsorption
• CPC Class Codes: C07C 7/12 by adsorption, i.e. purification or separation of hydrocarbons with the aid of solids, e.g. with ion-exchangers
• CPC Class Codes: C10L 3/101 Removal of contaminants
• CPC Class Codes: C10L 3/102 of acid contaminants
• CPC Class Codes: C10L 3/106 of water
• CPC Class Codes: Y02C 20/40 of CO2

Abstract

A process for separating methane from a natural gas mixture employs pressure swing adsorption in one or more vessels. Each vessel has an adsorbent material having a kinetic selectivity for contaminants over methane greater than 5. Contaminants within the natural gas mixture become gases kinetically adsorbed within the adsorbent material. The vessel is placed under pressure to cause contaminants to be adsorbed in the surfaces and micro-pores of the adsorbent material. The process includes releasing a product stream comprised at least 95% by volume methane from a first gas outlet in the vessel, and desorbing the contaminant gases from the adsorbent material by reducing the pressure within the vessel. The desorbing step is done without applying heat to the vessel, thereby delivering a waste gas stream comprised at least 95% by volume of the contaminant gases. An improved fractionation vessel having both major and minor flow channels is also provided.

Claims

1. A process for separating methane from a natural gas mixture, the process comprising:

directing a natural gas mixture into a gas separation unit, the gas separation unit having at least one vessel comprised of;

a gas inlet for receiving the natural gas mixture,

a first gas outlet,

an adsorbent material that has a kinetic selectivity for contaminants over methane greater than 5, such that the contaminants become gases kinetically adsorbed within the adsorbent material,

at least two major flow channels through the adsorbent material placing the gas inlet and the first gas outlet in fluid communication, and

at least one minor flow channel through the adsorbent material, the minor flow channels being in fluid communication with the major flow channels;

placing the at least one vessel under pressure to cause contaminants to be adsorbed to the adsorbent material;

releasing a product stream comprised at least 95% by volume of methane from the first gas outlet; and

desorbing the contaminant gases from the adsorbent material by reducing the pressure within the at least one vessel without applying heat to the vessel, thereby delivering a waste gas stream comprised at least 95% by volume of the contaminant gases.

2. The process of claim 1, wherein the contaminant comprises CO₂, H₂S, H₂O, heavy hydrocarbons, VOC'"'"'s, mercaptans, or combinations thereof.

3. The process of claim 2, wherein the at least one vessel is configured to deliver the waste gas stream through the gas inlet.

4. The process of claim 2, wherein the at least one vessel is configured to deliver the waste gas stream through the gas outlet.

5. The process of claim 2, wherein:

the at least one adsorbent vessel further comprises a second gas outlet intermediate the gas inlet and the first gas outlet; and

desorbing the contaminant gases releases a first portion of the waste gas stream from the first gas outlet, and a second portion of the waste gas stream from the second gas outlet.

6. The process of claim 2, wherein:

the vessel further comprises a plurality of rods;

each of the at least two major flow channels is formed between, and along the major axis of, the plurality of rods; and

the plurality of rods are spaced substantially equi-distantly apart, providing the major flow channels with a substantially uniform volume.

7. The process of claim 6, wherein:

the at least one minor flow channel is formed by a plurality of stepped surfaces along the respective rods.

8. The process of claim 6, wherein:

each of the plurality of rods comprises a bore therein;

each of the plurality of rods comprises a ferromagnetic material placed along the bore; and

the method further comprises applying a magnetic field to the plurality of rods to create uniform spacing of the plurality of rods.

9. The process of claim 6, further comprising:

selecting an ionic fluid as an absorbent to enhance adsorptive properties of the adsorbent material; and

placing the selected ionic fluid onto the stepped surfaces before directing the natural gas mixture into the gas inlet.

10. The process of claim 6, wherein:

the at least one adsorbent vessel further comprises a second gas outlet intermediate the gas inlet and the first gas outlet; and

the at least one minor flow channel is formed by flow channels that intersect the at least two major flow channels and which place the gas inlet and second gas outlet in fluid communication.

11. The process of claim 10, wherein the at least one minor flow channel is transverse to the at least two major flow channels.

12. The process of claim 2, wherein:

desorbing the contaminant gases releases a first portion of the waste gas stream during a first time period, and a second portion of the waste gas stream during a second time period.

13. The process of claim 12, wherein:

the first portion of the waste gas stream comprises at least 98% by volume CO₂.

14. The process of claim 13, wherein:

the second portion of the waste gas stream comprises nitrogen, hydrogen, methane, H₂O, or combinations thereof.

15. The process of claim 2, wherein the releasing and desorbing steps take place in a combined cycle of less than one minute.

16. The process of claim 2, wherein the adsorbent material further comprises an annular ring along an inner diameter of the at least one vessel.

17. The process of claim 2, wherein the adsorbent material comprises a monolithic body having longitudinal through-openings forming the at least two major flow channels.

18. The process of claim 2, further comprising:

dehydrating the natural gas mixture before directing the natural gas mixture into the gas separating unit.