Gas separation – Means within gas stream for conducting concentrate to collector
Patent
1988-04-07
1989-05-30
Spitzer, Robert
Gas separation
Means within gas stream for conducting concentrate to collector
55 68, 55158, 55210, 210604, 210621, 210188, 435311, B01D 5322
Patent
active
048347795
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of separation of gas mixtures and particularly to the separation of a single component from a mixture of gases. A semipermeable membrane and a purge gas are used. The purge gas contains at least one of the gases desired to be retained on the feed side of the membrane. The purpose of this is to minimize the passage across the membrane of the gases to be retained and encourage the passage across the membrane from the feed side to the purge side of the gas component to be separated.
2. Description of the Prior Art
The prior art has separated gases from mixtures using semipermeable membranes from a feed side to a diffusion side by drawing a vacuum on the diffusion side.
Another method commonly used is to pass a feed gas on one side of a semipermeable membrane and to pass a purge gas on the opposite side. A higher pressure is used for the feed gas than for the purge gas to encourage the diffusion of molecules from the feed side to the purge side. If the concentration of the desired gases to be diffused is less on the sweep side, then the differential in pressure will cause diffusion of such gases from the feed side to the purge side. Unfortunately the method does not permit the passage of a single element from a mixture of gases since generally the partial pressure of all the components on one side of the membrane are less on the sweep side as well as the concentration thereof.
Another method includes using a very thin semipermeable membrane which is selectably permeable for a specific gas such as hydrogen. In this instance, the feed gas is passed in contact with the semipermeable membrane and only the molecule which is selectively permitted to pass will go through the membrane. This method has limited application since such highly selective membranes are limited to very few gas elements at the present time.
SUMMARY OF THE INVENTION
The present invention is based on the concept that, using a semipermeable membrane, operating under typical conditions of feed gas injection into the high pressure side of the membrane, through the use of a purge gas, the partial pressure differential across the membrane of gas components not present in the purge gas will increase, resulting in higher relative mass transfer to those gas components through the membrane. In addition, the use of the purge gas decreases the partial pressure differential across the membrane of those gas components present in the purge gas resulting in a lower relative mass transfer through the membrane. This process can be used to more selectively transfer specific gas components through the membrane.
According to another aspect of the invention, in a mixture of gases, certain gas components present in gas mixtures on both sides of a semipermeable membrane can have their respective partial pressures balanced so that there is substantially a zero partial pressure differential. The remaining gas components then will diffuse in either direction across the membrane depending upon their differential partial pressures.
This invention can find specific application in the field of fermentation sciences in which air enriched with oxygen is passed through a fermentation vat by any suitable means for purposes of speeding up the fermentation reaction. This air/oxygen enrichment produces off-gases from the fermentation vat consisting, for example, of 30% by volume of oxygen, 55% by volume of nitrogen, and 15% by volume of carbon dioxide. In the past, such gases were simply vented to the atmosphere.
According to the invention process, these gases, maintained at a pressure of for example 75 psia, are passed on one side of a semipermeable membrane and a sweep gas or purge gas comprising compressed air at preferably about 52.2 psia is passed on the opposite side of the membrane. At these two relative pressures, the partial pressure differential of nitrogen on both sides of the membrane is essentially zero. This causes the minimal passage of oxygen and nitrogen in either directio
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Deloche Daniel C.
Paganessi Joseph E.
Sauer Richard A.
Bethel George F.
Bethel Patience K.
Liquid Air Corporation
Spitzer Robert
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