Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2002-11-25
2004-09-28
Therkorn, Ernest G. (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S653000, C210S654000, C426S490000, C426S492000, C426S495000, C554S175000
Reexamination Certificate
active
06797172
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for refining and degumming edible, industrial and specialty oils by ultrafiltration, leading to a permeate fraction with reduced phosphatide content and a retentate with increased phosphatide content, wherein the ultrafiltration membrane is composed of a polymer or copolymer of a vinylidene difluoride monomer.
2. Background of the Related Technology
Crude vegetable, nuts and animal oils and fats are produced by a large variety of processes (J. M. Fils,
The production of oils in Edible Oil Processing
, eds. W. Hamm and R. J. Hamilton, Sheffield Academic Press, Sheffield, 2000) and extraction with an organic solvent such as hexane, is one of these processes. This extraction process utilizes an organic solvent, such as hexane, and produces a solution of crude oil and the organic solvent, which is commonly referred to as “miscella.”
Another process involves pressing the oil-bearing material in, for example, a mechanical screw press. This leads to crude pressed oil and a press cake which still contains appreciable amounts of residual oil. It is common practice to recover this residual oil by extracting the press cake with solvent.
In known processes, crude oils typically are degummed, refined, bleached and deodorized to remove undesirable compounds including: free fatty acids (FFAs), phosphatides, particulate matter like meal residues, coloring materials like chlorophylls and xanthophylol, and miscellaneous non-saponifiable materials. For example, in processing soybean oils, the first step is degumming to remove the phosphatides for the production of lecithin. Water degumming is a conventional degumming method. When water is added to crude oil, most of the phosphatides in the oil are hydrated and become insoluble in oil. The hydrated gums are then separated from the oil by centrifugation. Next, the FFAs are reacted with sodium hydroxide to produce soaps, which are then removed along with residual phosphatides by centrifugation. Some pigments and destabilizing peroxides are then adsorbed by, for example, acid-activated bleaching clay; and finally, the oil is heated under high vacuum with steam sparging to strip trace amounts of FFAs, aldehydes and ketones, and other volatile compounds.
Considerable amounts of energy in the form of steam or electricity are required in these processes, and each step of the process of making edible oil only removes one or two types of undesirable components. If crude oil is not properly processed, treatment during the following steps will be more difficult and time and labor consuming. In addition to the energy costs, caustic refining, water washing and bleaching steps produce various streams such as high biological oxygen demand (BOD) acidic waste water and spent bleaching clay that either need to be treated or recovered due to economical or environmental reasons.
In conventional refining processes, free fatty acids, undesirable flavors, odor and color compounds, and other natural components like the phosphatides, must be removed from crude vegetable oils before they are used for food. Unfortunately, a “refining loss” 3-4 times greater than the free fatty acids content is often experienced, and considerable quantities of salable “neutral oil” is lost.
Processes for refining glyceride oils utilizing semi-permeable membranes have been disclosed in literature. U.S. Pat. Nos. 4,062,882 and 4,093,540 to A. K. Sen Gupta describe a process for refining a crude glyceride oil composition by passing a solution of this oil in an organic solvent under pressure over a semi-permeable membrane. In this process, the membrane retains the phosphatides present in the oil solution as a result of which the oil solution passing through the membrane shows a reduced phosphatide content. The membranes described in U.S. Pat. No. 4,093,540 are made of polyacrylnitrile. The membranes described in U.S. Pat. No. 4,062,882 are made of polyacrylonitrile, a polysulphone and a polyamide.
In U.S. Pat. No. 4,553,501 to Sen Gupta, a membrane filtration process is described that not only removes the phosphatides present in the crude triglyceride oil but also the free fatty acids present therein by the addition of a base to the miscella. In addition to the polyacrylonitrile, polysulphone, and polyamide membranes mentioned above, polyimide anisotropic membranes are also used for this purpose. Membranes made of these polymers are also described in PCT 00/42138 to Jirjis et al.
Polyimide membranes are also described in U.S. Pat. No. 4,414,157 to Iwama et al. U.S. Pat. No. 4,545,940 to Mutoh et al. describes a membrane used for the dewaxing of triglyceride oils that consists of a copolymer of ethylene and tetrafluoroethylene. In addition to waxes, phospholipids and free fatty acids were also retained by this membrane, but the disclosed flux is too low to be economic.
A subsequent paper (S. S. Köseo{haeck over (g)}lu, J. T. Lawhon and E. W. Lusas,
Journal American Oil Chemists' Society
, 67 (5), 315-322, 1990) on the suitability of a number of ultrafiltration membranes, reported that membranes made of polyamide were the least affected by hexane, but that a membrane made from a fluorinated polymer was deteriorated by hexane.
SUMMARY OF THE INVENTION
Accordingly, a need has arisen for refining and degumming oils in a process which has improved separation and which is more economical and more environmentally suitable than known methods.
In accordance with the present invention, a process for refining and degumming oils by ultrafiltration is provided that significantly improves the quality of the edible oils and lecithin products and is more economical and environmentally suitable than known methods. The inventive process contacts oil with an ultrafiltration membrane, wherein the ultrafiltration membrane comprises a polymer or copolymer of a vinylidene difluoride monomer, and separates the oil into a permeate fraction having a reduced phosphatide, color and free fatty acids content and a retentate fraction having an increased phosphatide content.
Accordingly, an object of the present invention is to provide ultrafiltration membranes that can be profitably used in the refining and degumming of solutions of oils in organic solvents by an ultrafiltration process.
It is a further object of the invention to provide membranes for the refining and degumming by ultrafiltration of pressed oils, conducted in the absence of solvent.
A further object of the invention is to provide edible oil products and lecithin products prepared by ultrafiltration which have significantly improved qualities over known edible oil products and lecithin products.
The ultrafiltration membranes according to the present invention (i.e., comprised of a polymer or copolymer of a vinylidene difluoride monomer): (1) are hexane-resistant, i.e., they retain their strength and do not swell in hexane so that they retain their permeability and selectivity, (2) withstand the pressure drop over the membrane during ultrafiltration; (3) have a good permeability for triglyceride oil and its solvents, which results in a relatively high flux through the membrane during the ultrafiltration process; (4) retain free fatty acids, coloring pigments and phosphatides from pressed oil and/or miscella and thus show a high selectivity, (5) do not unduly suffer from fouling, i.e., rinsing the membrane with solvent, permeate or miscella at regular (but not too frequent) intervals restores the membrane flux to a fully acceptable and constant level.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
In the process of the present invention, “crude oil” (substantially unrefined, unprocessed oil) is contacted with an ultrafiltration membrane. If the crude oil is combined with a solvent, either as a result of extracting the crude oil from vegetable products or from the addition of solvent to improve separation, it is referred to as “miscella.” If crude oil is recovered from vegetable products using physical methods, such as pressing, expellers, expanders, and/or extruders, a
De Greyt Wim F. S.
Farr Walter E.
Kellens Marc
Koseoglu Semih Sefa
Baker & Botts L.L.P.
The Texas A&M University System
Therkorn Ernest G.
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