WO2004067133B1

WO2004067133B1 - Cyclic membrane separation process

Info

Publication number: WO2004067133B1
Application number: PCT/US2004/001119
Authority: WO
Inventors: John Bowser; Stuart Nemser
Original assignee: Cms Technology Holdings Inc; John Bowser; Stuart Nemser
Priority date: 2003-01-24
Filing date: 2004-01-16
Publication date: 2004-10-28
Also published as: DE112004000175T5; CA2513667A1; WO2004067133A2; JP4987467B2; JP2006517146A; CA2513667C; WO2004067133A3; MXPA05007775A; GB0514299D0; GB2412887B; GB2412887A

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

AMENDED CLAIMS [Received by the International Bureau on 31 August 2004 (31.08.04)]

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 ullage 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 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 ullage gas into the feed-retentate chamber of the module so as to contact the first side of the membrane with the ullage gas, (ii) separating the ullage gas to form a low organic content gas depleted in volatile organic compounds relative to the ullage gas and a high organic content gas enriched in volatile organic compounds relative to the ullage 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 gas in the storage tank, (c) for a second length of time, stopping the conveying of the ullage gas, the separating of the ullage 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 ullage gas at a temperature below the glass transition temperature such that the volatile organic

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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.