CA2513667A1

CA2513667A1 - Cyclic membrane separation process

Info

Publication number: CA2513667A1
Application number: CA002513667A
Authority: CA
Inventors: John Bowser; Stuart Nemser
Original assignee: John Bowser; Stuart Nemser; Cms Technologies Holdings, Inc.
Current assignee: CMS TECHNOLOGIES HOLDINGS Inc
Priority date: 2003-01-24
Filing date: 2004-01-16
Publication date: 2004-08-12
Anticipated expiration: 2024-01-16
Also published as: CA2513667C; WO2004067133A3; DE112004000175T5; JP2006517146A; MXPA05007775A; GB0514299D0; WO2004067133A2; GB2412887A; WO2004067133B1; JP4987467B2; GB2412887B

Abstract

A cyclic process for controlling environmental emissions of volatile organic compounds (VOC) from vapor recovery in storage and dispensing operations of liquids maintains a vacuum in the storage tank ullage. In the first part of a two-part cyclic process ullage vapor is discharged through a vapor recovery system in which VOC are stripped from vented gas with a selectively gas permeable membrane. In the second part, the membrane is inoperative while gas pressure rises in the ullage. In one aspect of this invention, ambient air is charged to the membrane separation unit during the second part of the cycle.
In another aspect, a vacuum is drawn in the membrane separation unit. The charging of air or drawing of vacuum purges VOC from the membrane unit and thus reduces overall VOC emissions.

Claims

1. A cyclic gas separation process for separating more preferentially permeable gas components from less preferentially permeable gas components of a feed gas mixture of such components, the process comprising the steps of (a) providing a membrane module having a selectively gas permeable membrane for the more preferentially permeable gas components and the less preferentially permeable gas components, (b) simultaneously (i) feeding the feed gas mixture to the module to contact the feed gas mixture with a first side of the membrane, (ii) discharging from the module in fluid communication with a second side of the membrane a permeate gas mixture enriched in the more preferentially permeable gas components, and (iii) withdrawing from the module in fluid communication with the first side of the membrane a retentate gas mixture enriched in the less preferentially permeable gas components, (c) stopping the feeding of the gas feed mixture to the first side, stopping the discharging of the permeate gas mixture, and stopping the withdrawing of the retentate gas mixture, (d) charging a diluent gas to the module, (e) ceasing the charging of diluent gas to the module, and (f) repeating steps (b)-(e).

2. The process of claim 1 in which the membrane comprises a polymer having a glass transition temperature, the more preferentially permeable gas components are volatile organic compounds, the diluent gas is free of volatile organic compounds and in which the process comprises feeding the feed gas mixture to the module at a temperature above the glass transition temperature and charging the diluent gas in fluid communication with the first side of the membrane.

3. The process of claim 1 in which the membrane comprises a polymer having a glass transition temperature, the diluent gas is free of the less preferentially permeable gas components and in which the process comprises feeding the feed gas mixture to the module at a temperature below the glass transition temperature.

4. The process of claim 1 in which the feed gas mixture comprises volatile organic compounds and the diluent gas comprises air.

5. A process for reducing atmospheric emissions of volatile organic compound vapor from ullege gas of a liquid volatile organic compound storage tank, the process comprising (a) providing a vapor recovery system comprising a membrane module comprising a two-sided gas permeable membrane comprising a polymer having a glass transition temperature and a selectivity for permeation of air relative to permeation of volatile organic compounds, in which one side of the membrane defines a feed-retentate chamber on a first side of the membrane in fluid communication with the allege gas and the second side of the membrane defines a permeate chamber, (b) for a first length of time simultaneously and continuously (i) conveying allege gas into the feed-retentate chamber of the module so as to contact the first side of the membrane with the ullege gas, (ii) separating the allege gas to form a low organic content gas depleted in volatile organic compounds relative to the allege gas and a high organic content gas enriched in volatile organic compounds relative to the allege gas, (iii) exhausting the low organic content gas from the module to ambient atmosphere, and (iv) returning the high organic content gas from the module into the ullege gas in the storage tank, (c) for a second length of time, stopping the conveying of the ullege gas, the separating of the ullege gas, the exhausting of the low organic content gas and the returning of the high organic content gas, (d) during step (c) charging air to the vapor recovery system in a quantity effective to remove volatile organic compounds from the membrane module, and (e) repeating steps (b)-(d).

6. The process of claim 5 which further comprises separating the ullege gas at a temperature below the glass transition temperature such that the volatile organic compounds less preferentially permeate the membrane relative to air, exhausting the low organic content gas from the permeate chamber of the module and returning the high organic content gas from the feed-retentate chamber of the module.

7. The process of claim 6 which further comprises charging the air to a location in the vapor recovery system in fluid communication with the permeate chamber and causing the air to permeate through the membrane from the second side to the first side, to pass into the feed-retentate chamber and to enter into the ullage gas of the storage tank, thereby removing volatile organic compounds from the module.

8. A cyclic gas separation process for separating more preferentially permeable gas components from less preferentially permeable gas components of a feed gas mixture of such components, the process comprising the steps of (a) providing a membrane module having a selectively gas permeable membrane for the more preferentially permeable gas components and the less preferentially permeable gas components, (b) simultaneously (i) feeding the feed gas mixture to the module to contact the feed gas mixture with a first side of the membrane, (ii) discharging from the module in fluid communication with a second side of the membrane a permeate gas mixture enriched in the more preferentially permeable gas components, and (iii) withdrawing from the module in fluid communication with the first side of the membrane a retentate gas mixture enriched in the less preferentially permeable gas components, (c) stopping the feeding of the gas feed mixture to the first side, stopping the discharging of the permeate gas mixture, and stopping the withdrawal of retentate gas mixture from the first side, (d) drawing a vacuum in the module effective to remove from the module a portion of a residual gas resident in the module at the time that the feeding, discharging and withdrawing are stopped, (e) ceasing the drawing of vacuum in the module, and (f) repeating steps (b)-(e).

9. A process for reducing atmospheric emissions of volatile organic compound vapor from ullage space of a liquid volatile organic compound storage tank, the process comprising (a) providing a vapor recovery system comprising a membrane module comprising a two-sided gas permeable membrane comprising a polymer having a glass transition temperature and a selectivity for permeation of air relative to permeation of volatile organic compounds, in which one side of the membrane defines a feed-retentate chamber on a first side of the membrane in fluid communication with the ullage gas and the second side of the membrane defines a permeate chamber, (b) for a first length of time simultaneously and continuously (i) conveying a feed gas from the ullage space into the feed-retentate chamber of the module so as to contact the first side of the membrane with the feed gas, (ii) separating the feed gas to form a low organic content gas depleted in volatile organic compounds relative to the feed gas and a high organic content gas enriched in volatile organic compounds relative to the feed gas, (iii) exhausting the low organic content gas from the module to ambient atmosphere, and (iv) returning the high organic content gas from the module into the ullage space in the storage tank, (c) for a second length of time, stopping the conveying of the feed gas, the exhausting of the low organic content gas and the returning of the high organic content gas, (d) during step (c) drawing a vacuum in the membrane module to an extent effective to remove a portion of a residual gas resident in the module at the time that the conveying of the feed gas is stopped, and (e) repeating steps (b)-(d).

10. The process of claim 9 which further comprises returning the residual gas to the ullage space.