Membrane separation of components in a fluid mixture

Details Membrane separation of components in a fluid mixture Membrane separation of components in a fluid mixture

1999-05-24

2001-02-13

Fortuna, Ana (Department: 1723)

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

C210S651000, C210S653000, C095S045000, C095S050000

Reexamination Certificate

active

06187196

ABSTRACT:

FIELD OF THE INVENTION
The present invention involves membrane separation of components in a fluid mixture, and is particularly well suited for separation of a more highly unsaturated organic compound from a less highly unsaturated organic compound or a saturated organic compound. Example separations include alkenes from alkanes, alkynes from alkenes and alkanes, dialkenes from monoalkenes, and styrene monomer from ethyl benzene.
BACKGROUND OF THE INVENTION
Many chemical manufacture and refining processes involve a difficult separation of a desired product compound from a fluid mixture containing one or more other compounds having physical properties in close proximity to those of the product compound. Examples of such difficult separations include separation of alkenes, such as ethylene or propylene, from the corresponding alkane, such as ethane or propane, and separation of styrene monomer from ethyl benzene. Currently, these difficult separations are typically performed by distillation. Distillation separation of such compounds, however, requires tall distillation towers and extensive heating to make a satisfactory separation, due to the close proximity of boiling points of the compounds being separated.
These difficult distillation separations consume a significant quantity of energy. For example, separation of alkenes from alkanes by distillation has been estimated to consume 0.12 quad per year of energy (1 quad equals one trillion billion BTU). This large energy consumption is largely due to distillation of the light olefins ethylene and propylene, which are two of the largest volume chemicals produced worldwide.
One method that has been proposed for separating olefins in a manner to avoid the high energy consumption of distillation is to make the separation with a facilitated transport membrane. A facilitated transport membrane is a thin film membrane that includes a carrier specie in the membrane that preferentially chemically interacts with a desired component to facilitate transport of that component across the membrane, thereby separating the desired component from an undesired component. In that regard, it is known that many alkenes undergo complexation reactions with silver(I) cations and that alkanes typically do not. Therefore, facilitated transport membranes including a silver(I) cationic carrier have been extensively researched at a laboratory scale with some success. Despite such extensive research, however, the use of facilitated transport membranes has not found industrial acceptance for olefin separation applications. This failure to gain industrial acceptance is largely due to problems associated with membrane and carrier stability in industrial settings.
For example, one class of membranes that have been proposed for alkene/alkane separations are the so-called immobilized liquid membranes. Immobilized liquid membranes involve a thin liquid film containing the ionic carrier. A major problem with the use of immobilized liquid membranes in industrial applications is that it is difficult to keep the liquid immobile and to keep the liquid of the membrane from evaporating. Another class of membranes that has been proposed are ion exchange membranes. With ion exchange membranes, the ionic carriers are contained within a polymeric material. A major problem with ion exchange membranes, however, is that they have been ineffective as transport membranes for alkenes unless the polymeric material is swollen with water. To address this problem, it is generally required to saturate the feed and permeate streams with water to prevent drying of the swollen membrane. Although such a procedure works well on a laboratory scale, it is impractical for most industrial applications. Immobilized liquid membranes and water-swollen ion exchange membranes, therefore, both suffer from a need to prevent liquid losses from the membranes during operation.
There is a significant need for improved membrane separation techniques to address the foregoing problems.
SUMMARY OF THE INVENTION
The present invention provides a membrane separation method in which a facilitated transport membrane is used to separate from a fluid mixture a variety of components, and particularly unsaturated organic compounds such as alkenes, alkynes, styrene monomer, etc. The membrane separation method uses a facilitated transport membrane that does not require the presence of water or other solvent during operation. The membrane includes a polymeric matrix having a chemical group that interacts with ion exchange sites in the polymer matrix to modify the electronic environment of the ion exchange sites to permit facilitated membrane transport of unsaturated organic compounds in the absence of water. It is believed that the presence of water in the water-swollen ion exchange membranes of the prior art affects the electronic environment of ion exchange sites in a manner to permit the ionic carrier of the membrane to participate in a complexation reaction with an unsaturated organic compound. Inclusion in the membrane of the present invention of a chemical group to modify the electronic environment of the ion exchange sites is believed to at least partially replace the beneficial effects that otherwise would be provided if water were present.
A preferred class of membrane materials for the present invention include two polymers. The first polymer is an ion exchange polymer similar to those that have been previously used in a water-swollen state for alkene separations. The second polymer includes the chemical group that modifies the electronic properties of ion exchange sites associated with the ion exchange polymer. The ion exchange polymer preferably includes anionic groups for cation exchange at the ion exchange sites and the second polymer includes positively charged groups that act at least partially as counter ions to the anionic groups of the first polymer, thereby modifying the electronic properties of the ion exchange sites. An example of a membrane used with present invention is one including a perfluorosulfonic acid polymer as the first polymer and oxidized poly(pyrrole) as the second polymer, with the ion exchange sites of the first polymer being occupied by an appropriate cationic carrier for the facilitated transport.
It is an object of the present invention to provide a membrane separation method for separating unsaturated organic compounds from fluid mixtures without requiring the presence of water during the separation.
It is another object of the present invention to provide a membrane for separation of unsaturated organic compounds from fluid mixtures without requiring the presence of water during the separation.
It is a further object of the present invention to provide an apparatus for use in membrane separation of unsaturated organic compounds from fluid mixtures.
It is a further object of the present invention to provide a method for manufacturing membranes useful in the separation of unsaturated organic compounds.


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