Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2002-06-27
2004-12-14
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C095S045000, C095S050000
Reexamination Certificate
active
06830691
ABSTRACT:
TECHNICAL FIELD
The present invention relates to novel processes for separation of fluid mixtures. Broadly, intergrated processes of the invention comprise a plurality of separations using solid perm-selective membranes. More particularly, the invention relates to recovery of specified products using a plurality of membrane modules disposed in a first product group, a second product group, and optionally one or more intermediate group. Processes of the invention with the membrane modules in multiple groups are beneficially useful for simultaneous recovery of a very pure permeate product and a desired non-permeate product from a mixture containing organic compounds.
BACKGROUND OF THE INVENTION
Light hydrocarbons serve as the building blocks for the production of numerous chemicals. Ethylene, a light olefin composed of two carbon atoms joined by a double bond, is used in the production of several chemicals including polyethylene, ethylene oxide, ethylene dichloride, and ethylbenzene. Propylene, a light olefin composed of three carbon atoms where two of the carbon atoms are joined by a double bond, is used in the manufacture of polypropylene, acrylonitrile, oxo alcohols, cumene, and propylene oxide. Light hydrocarbons composed of four carbon atoms are used, for example, in the production of synthetic rubbers and elastomers, sec-butyl alcohols, maleic anhydrides, polybutenes, and clean motor fuels (e.g. alkylate).
These light hydrocarbons have traditionally been produced by steam or catalytic cracking. Oxygenate conversion (e.g. methanol to olefins), dehydrogenation, and isomerization routes have also grown in recent years as important production routes. Separation costs are a significant fraction of the overall costs of making these petrochemicals. When the valuable light hydrocarbons are produced, they are often accompanied by the production of other compounds that must be removed. For example, when propylene is produced in the presence of hydrogen, it is often produced in conjunction with propane. Generally, it is required to remove the propane before propylene can be used to produce more valuable products. However, many of the desirable light hydrocarbons are produced with compounds that have boiling points that are very similar to those of the desirable light hydrocarbons. These separations then become very expensive and energy intensive. For example, a typical ethylene separation section of an ethylene plant requires cryogenic conditions to achieve the required ethylene purity. A propane/propylene splitter requires so many separation stages that it is typically done in two large towers each containing more than 100 trays.
Processes that enable the concentration and recovery of these desirable light hydrocarbons without expensive distillation steps have been sought for many years.
In U.S. Pat. No. 3,758,603 and 3,864,418 R. Hughes and E. Steigelmann describe the use of membranes in conjunction with metal complexing techniques to facilitate the separation of ethylene from ethane and methane. Similar metal complex and membrane hybrid processes have been described by R. Yahnke in U.S. Pat. No. 4,060,566, by M. Kraus in U.S. Pat. No. 4,614,524, and by R. Valus in U.S. Pat. No. 5,057,641. These processes utilize a separation unit containing a membrane having a feed side and a permeate side with a liquid between them that contains a metal-containing ion complexing agent. Transport of the desired component is described as occurring by a) dissolving the component in the facilitator liquid on the feed side of the membrane; b) forming a component-carrier complex; c) diffusing the complex to the permeate side of the membrane; and d) releasing the component from the carrier. The selectivity of the membrane is maximized by choosing a complexing agent with a high affinity for the desired component. The agent facilitates the transport of the desired component from the feed stream to the permeate.
Evaluation of a facilitated transport membrane process for the separation of propylene from propane is described by J. Davis et al. in an article entitled “Facilitated Transport Membrane Hybrid Systems for Olefin Purification” published in Sep. Sci. Tech 28, 463-476 (1993). Davis et al. used a silver nitrate solution in a hybrid membrane system to obtain selectivities for propylene transport that were in excess of 150.
D. Gottschlich and D. Roberts examined hybrid systems consisting of a distillation column and a facilitated transport membrane separation module in paper for SRI Project 6519 and DOE Contract Number DE-AC07-761D01570 entitled “Energy Minimization of Separation Process Using Conventional/Membrane Systems” (1990). They compare the effectiveness of several arrangements of facilitated transport membranes and distillation processes.
R. Noble and co-workers in two articles entitled “Analysis of a Membrane/Distillation Column Hybrid Process” published in J. Memb. Sci. 93, 31-44 (1994) and “Design Methodology for a Membrane/Distillation Column Hybrid Process” published in J. Memb. Sci.99, 259-272 (1995) discuss the design and optimization of several combined membrane and distillation processes for the separation of propylene and propane. Their work focuses on the placement of the membrane around the distillation column in order to obtain an efficient process that accomplishes the desired separation.
Friesen et al. describe the use of a membrane system to separate propylene from propane in European Patent Application 0701856A1 where the flux of propylene through the membrane has been enhanced by the use of a condensable sweep gas on the permeate side of the membrane. They present examples for a membrane that illustrate the effect of sweep gas rate on propylene flux.
Handbooks and review articles on membrane separation processes extol the simplicity and efficiency of membranes. However, the prior art for using membranes to separate desirable hydrocarbons (e.g. olefins) out of complex mixtures only considers the use of membranes in hybrid systems, where membranes have been combined with facilitating liquids or distillation columns. These other separation processes have inherent difficulties that could undermine their coupling with membranes. For example, the metal complexing agents described above are often very susceptible to poisoning. A. Sungpet et al. state in an article entitled “Separation of Ethylene from Ethane Using Perfluorosulfonic Acid Ion-Exchange Membranes” published in ACS Symposium Series “Chemical Separations with Liquid Membranes,” 270-285 (1996) that the selectivity and permeability of membranes for the separation of hydrocarbon mixtures, such as olefins from paraffins, is too low to be attractive, so membranes have been combined with other separation processes to achieve the desired separation. However if a membrane material was developed with sufficient permeability and selectivity where it could be used without other separation steps, it is not clear how to utilize the material in an industrial process. Detailed designs and evaluations of processes where the separation of desirable hydrocarbons is accomplished only by membranes are lacking. An understanding of the effect of membrane selectivity and process configuration on the energy and amount of membrane area required to separate desirable hydrocarbons out of complex mixtures is needed.
There is a present need for processes and apparatus using perm-selective membranes for simultaneous recovery of a very pure permeate product and a desired non-permeate product, in contrast to by-product, waste streams, in particular, processes which do not have the above disadvantages. A further object of the invention is to provide inexpensive processes and apparatus for the efficient separation of chemical compounds from mixtures which are difficult to separate, e.g., separation of propane-propylene by fractional distillation.
Improved processes should provide for an integrated sequence, carried out with streams in gas and/or liquid state, using a suitable perm-selective membranes, preferably a solid perm-selective membrane which under
Bartels John V.
Colling Craig W.
Huff, Jr. George A.
BP Corporation North America Inc.
Fortuna Ana
Jerome Fred S.
Schoettle Ekkhard
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