Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2000-03-07
2001-10-23
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C095S045000, C096S007000, C210S182000, C210S257200, C210S321750, C210S321840, C210S636000, C210S774000, C210S806000, C202S176000, C203S039000
Reexamination Certificate
active
06306307
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of fluid separations whereby fluid components are separated from a mixture by pervaporation or vapor permeation.
BACKGROUND OF THE INVENTION
A variety of commercial processes rely on fluid separation techniques using membranes in order to separate one or more desirable or undesirable fluid components from a mixture. Separation processes using membranes are used for the separation of water from mixtures with organic liquids, for the separation of volatile organic compounds from aqueous solutions, for the separation of organic components from mixtures of same, or for the separation of at least one volatile component from a mixture with at least one nonvolatile component.
This type of membrane separation operates on the basis of differences in permeation rate through certain dense, non-porous membranes. When the mixture to be separated is brought into contact with the membrane as a liquid, the process is called pervaporation. If the mixture is gaseous, the term “vapor permeation” is often applied. The present invention applies to both processes, but in the present specification, for the sake of brevity, the word pervaporation will be used to represent both processes. In both cases, one side of the membrane faces the fluid mixture while the other side is exposed to a vacuum or a carrier gas, which reduces the partial pressure of the permeable substance and thereby provides the driving force for permeation.
In passing through the membrane, a substance is first sorbed or absorbed into the membrane, then it diffuses through the membrane, and finally emerges as a gas on the low pressure side of the membrane. Different substances will permeate at different rates according to the chemistry of the membrane material and the prevailing operating conditions interacting with it. Some membranes favor the permeation of water over organic substances: these are termed “hydrophilic”. Those favoring organics over water are termed “hydrophobic”. Other membranes are designed to separate different species of organic substances.
The components of the fluid that pass through the membrane comprise the “permeate” and those that do not pass comprise the “retentate.” The valuable fraction from the process may be the retentate or the permeate or in some cases both may be valuable.
Even mixtures such as azeotropes can be effectively separated by pervaporation, which is not possible utilizing thermodynamic vapor-liquid equilibria, such as in distillation processes. Numerous mixtures, e.g. water and ethanol, water and isopropanol, chloroform and hexane, water and tetrahydrofuran, water and dioxane, methanol and acetone, methanol and benzene, methanol and methylacetate, ethanol and ethylacetate, ethanol and cyclohexane, and butanol and heptane, which vaporize azeotropically when certain concentration limits are reached, can be separated by pervaporation.
U.S. Pat. No. 5,536,405 which issued Jul. 16, 1996 to Myrna et al. discloses a stacked membrane disk assembly which is located in a pressure vessel. This is typical of many commercial apparatus, which require pressure vessels to operate. Additionally, many pervaporation processes are operated at elevated temperatures, e.g. 100° C. Apart from the capital expense of pressure vessels, one of the disadvantages of having a pressure vessel is that the vessel needs to be dismantled when repairs are required to be performed on the membrane disk assembly which is inside the vessel. The down-time for dismantling, replacing disks or the disk assembly and then reassembling the apparatus can be as long a day or more.
U.S. Pat. No. 5,620,605 which issued Apr. 15, 1997 to Jens K. Moller discloses an apparatus having membrane cassettes which may be operated with vacuum on the permeate side of the membrane and atmospheric pressure on the retentate side of the membrane. However, this is a huge and complex apparatus that would be very difficult and time consuming to repair should some of the membrane cassettes fail.
SUMMARY OF THE INVENTION
The present invention concerns an apparatus for the arrangement of membranes in a module and, in particular, a plate module for the separation of mixtures by a pervaporation process, wherein the module is simple and inexpensive and very easily and quickly replaced if required.
According to one aspect of the invention, there is provided a module for pervaporation or vapor permeation comprising a central, axial permeate removal tube having a wall with at least one inlet opening therein. At least one separator element is mounted on the permeate removal tube adjacent to the inlet opening. The separator element includes a permeate transport plate having a transverse opening therethrough for the passage of the permeate removal tube through the permeate transport plate. The permeate transport plate also defines fluid passages disposed radially relative to the permeate removal tube and communicating with the inlet opening therein. A pervaporation membrane envelops the permeate transport plate. Annular sealing rings are located concentrically about the permeate removal tube in engagement with the pervaporation membrane, so that fluid has to pass through the pervaporation membrane to enter the permeate removal tube inlet opening.
According to another aspect of the invention, there is provided apparatus for performing pervaporation or vapor permeation separation of fluids. The apparatus comprises a solution tank for containing fluid to be separated. A separator module is located in the tank. The separator module has a central, axial permeate removal tube extending from the tank. The permeate removal tube has a wall with at least one inlet opening therein. At least one separator element is mounted on the permeate removal tube adjacent to the inlet opening. The separator element includes a permeate transport plate having fluid passages communicating with the inlet opening. A pervaporation membrane envelops the permeate transport plate and sealing rings engage the pervaporation membrane, so that fluid entering the permeate removal tube has to pass through the pervaporation membrane. A permeate tank is located outside the solution tank and is connected to the permeate removal tube, and a vacuum pump is connected to the permeate tank to apply vacuum to the tank and the permeate removal tube.
According to yet another aspect of the invention, there is provided a method of separating fluids by pervaporation or vapor permeation comprising the steps of providing a separator module having an envelope of pervaporation material with a supporting permeate transport located therein and a permeate removal tube communicating with the inside of the envelope. The envelope is surrounded with fluid to be separated, the fluid being neither pressurized nor under vacuum. Vacuum is applied to the permeate removal tube to extract vapor permeate from the module.
REFERENCES:
patent: 3948778 (1976-04-01), Muller
patent: 4897192 (1990-01-01), Lawrence
patent: 4936954 (1990-06-01), Sander
patent: 5227064 (1993-07-01), Strid
patent: 5389255 (1995-02-01), Danziger et al.
patent: 5437796 (1995-08-01), Bruschke et al.
patent: 5445731 (1995-08-01), Tuohey et al.
patent: 5536405 (1996-07-01), Myrna et al.
patent: 5620605 (1997-04-01), Moller
patent: 5641402 (1997-06-01), Kohonen et al.
A Break-Even Analysis of Distillation—Membrane Hybrids, AIChE Journal, Jan. 1998, vol. 44, No. 1, pp. 93-105.
Separating Azeotropic Mixtures, pp. 12-15 Sulzer Technical Review 3/98.
Hamza Alia A.
McGregor Ian R.
Nye Mark E.
Wilson John G.
Drodge Joseph W.
Fielding Chemical Technologies, Inc.
Young & Basile
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