Process for purifying vegetable oil

Abstract: The present invention relates to improved methods for refining vegetable oils and byproducts thereof. In an organic acid refining process, vegetable oil (1) is combined with a dilute aqueous organic acid solution (4) and subjected to high shear (6) to finely disperse the acid solution in the oil. The resulting acid-and-oil mixture is mixed at low shear (7) for a time sufficient to sequester contaminants into a hydrated impurities phase, producing a purified vegetable oil phase.

Description: Field of the Invention This invention relays to improved methods for refining vegetable oils. More particularly, this invention relates to improved processes for producing vegetable oils having reduced content of impurities such as free fatty acids and phosphatides. Background of the Invention Organic Acid Refining Vegetable oils are typically obtained by pressing or extracting the oil seeds of plants such as corn or soybeans. Properly processed vegetable oils are suitable for use in many edible oil and fat compositions destined for human consumption. Such edible oils and fats include salad oils, cooking oils, frying fats, baking shortenings, and margerines. In addition to being widely used in edible oils and fats, vegetable oils are also increasingly utilized in important industrial products such as caulking compounds, disinfectants, fungicides, printing inks, and plasticizers. Vegetable oils primarily consist of triglycerides, but several other compounds are also present. Some of these additional compounds, such as diglycerides, tocopherols, sterols, and sterol esters, need not necessarily be removed during processing. Other compounds and impurities such as phosphatides, free fatty acids, odiferous volatiles, colorants, waxes, and metal compounds negatively affect taste, smell, appearance and storage stability of the refined oil, and hence must be removed. Carefully separated, however, some of these additional compounds, particularly the phosphatides, are valuable raw materials. It is therefore important to select a vegetable oil purifying method that maximizes removal of impurities but does so in a way that least impacts the compounds removed. Vegetable oil impurities are typically removed in four distinct steps of degumming, refining, bleaching, and deodorizing. Of these four steps, degumming removes the largest amount of impurities, the bulk of which are hydratable phosphatides. Refining primarily removes non-hydratable phosphatides, soaps created from the neutralization of free fatty acids, and other impurities such as metals. Bleaching then improves the color and flavor of refined oil by decomposing peroxides and removing oxidation products, trace phosphatides, and trace soaps. Soybean oil bleaching materials include neutral earth (commonly termed natural clay or fuller's earth), acid-activated earth, activated carbon, and silicates. Deodorizing is the final processing step and prepares the oil for use as an ingredient in many edible products including salad oils, cooking oils, frying fats, baking shortenings, and margerines. The deodorizing process generally comprises passing steam through refined oil at high temperature and under near vacuum conditions to vaporize and carry away objectionable volatile components. Vegetable oil refining, also known as neutralization or deacidification, essentially involves removing free fatty acids (FFA) and phosphatides from the vegetable oil. Most refining operations employ either alkali refining (also termed caustic refining) or physical refining (also termed steam refining). Of these two refining methods, alkali refining predominates. For either refining method, an optional but preferred first step is a conventional water degumming process. Degumming refers to the process of removing hydratable phosphatides and other impurities such as metals from vegetable oils. Crude vegetable oils contain both hydratable phosphatides (HPs) and non-hydratable phosphatides (NHPs). A simple degumming process comprises admixing soft water with the vegetable oil and separating the resulting mixture into an oil component and an oil-insoluble hydrated phosphatides component (frequently referred to as a "wet gum" or "wet lecithin"). The NHPs, generally considered to be calcium and magnesium salts of phosphatidic acids, are largely unaffected by water and remain soluble in the oil component. Normally, refiners also must introduce chelating agents following degumming processes to remove metal compounds from crude vegetable oil, which typically contains calcium, potassium, magnesium, aluminum, iron and copper. Left in place, these metal impurities form salts of phosphatidic acid, thereby contributing to the NHP content. Moreover, metal contaminants, especially iron, can darken oil during deodorization, and even small amounts of iron that do not affect the oil's color can nevertheless dramatically reduce stability of refined oil. Treating crude vegetable oil with soft water produces a degummed oil and a phosphatide concentrate containing the hydratable phosphatide fraction. This phosphatide concentrate subsequently can be removed from the degummed oil by a convenient method such as centrifugal separation. Phosphatide concentrates coming from centrifugal separation will generally contain up to about fifty percent by weight water, and typically will contain from about twenty-five to about thirty percent by weight water. In order to minimize chances of microbial contamination, phosphatide concentrates must be dried or otherwise treated immediately. Dried phosphatide concentrates can be profitably sold as commercial lecithin. Degummed oil is further refined to remove NHPs and other unwanted compounds. Mineral acid also is sometimes added during the water degumming process to help minimize the NHP content of degummed oil. The acid combines with calcium and magnesium salts, enabling phosphatidic acids to migrate from the oil to the water phase, thus eliminating them from the crude oil. However, using mineral acid during degumming is inappropriate when seeking to recover gums intended for use as lecithin because the presence of mineral acid will cause darkening of the lecithin. In alkali refining, free fatty acids and gums are removed from crude or degummed oil by mixing the oil with a hot, aqueous alkali solution, producing a mixture of so-called neutral oil and soapstock (also termed refining byproduct lipid), which is an alkaline mixture of saponified free fatty acids and gums. The neutral oil is then separated from the soapstock, typically by centrifugation. The soapstock has commerical value due to its fatty acid content but must be processed further in order to render it salable. The neutral oil is further processed to remove residual soap. Soapstock is treated in a process called acidulation, which involves breaking or splitting the soap into separate oil and aqueous phases through addition of a mineral acid such as sulfuric acid to reduce the pH to approximately 1.5, followed by thorough heating and mixing. Because the aqueous phase is heavier than the oil phase, the acidulated soapstock is separated from the oil by gravity or centrifugation. The separated oil (termed acid oil) has essentially the composition of the neutral oil and is drawn off, washed with water to completely remove mineral acid and sludge, and sold, usually as an animal feed supplement. The remaining aqueous phase termed acid water) is the final waste product and can either be used in other processes or neutralized before being discarded. The alkali refining process has several drawbacks, however, mainly related to soapstock formation. One drawback is refining losses that occur due to the soapstock's emulsifying effect, wherein soapstock acts to take up a portion of the valuable neutral oil into the aqueous soapstock solution. To minimize such emulsification losses, the crude or degummed oil is usually heated to between 70°C (158°F) and 90°C (194°F) prior to being contacted with the hot alkali solution. However, heating will not completely prevent emulsions from forming, nor will it entirely break emulsions once formed. Centrifugation forces also are insufficient to completely break emulsions of neutral oil in soapstock. Another drawback to alkali refining is losses that occur when a portion of the neutral oil undergoes alkaline hydrolysis, often referred to as saponification, to produce undesirable fatty acid salts. Allowing the alkali solution and the crude or degummed oil to remain in contact for only short times can minimize saponification losses but is often insufficient to remove impurities other than fatty acids, especially impurities such as phosphatides and metal compounds. Consequently, short contact times can make it necessary to conduct a second round of refining. Yet another alkali refining drawback is that raw soapstock is troublesome to handle. Soapstock solidifies quickly upon cooling, so heated holding tanks and transfer lines are required to maintain temperatures above 60°C (140°F). Elevated temperatures also are required to prevent fermentation. On the other hand, overly heating soapstock causes it to boil, producing excessive and troublesome foaming. Still another drawback is the difficulty in disposing of the acid water created during soapstock splitting. Acid water is high in biochemical oxygen demand (BOD) and low in pH. Disposal regulations require at minimum that the acid water be neutralized before the waste can be dumped. Many states have much more stringent pollution controls, requiring often costly solutions to ensure effluent biodegradability. Thus, alkali refining involves many processing steps and has many drawbacks. In attempting to address the problems associated with alkali refining, operators must simultaneously vary many factors including the amount of heat applied, the amount and concentration of alkali, and retention times. Successfully balancing all these factors is a complex and difficult task. Furthermore, successful balancing of factors nevertheless can leave the need for additional refining cycles. An alternative to alkali refining is physical refining. Physical refining is a steam distillation process essentially the same as that used in conventional vegetable oil deodorization processes, where steam passing through vegetable oil vaporizes and carries away free fatty acids. The main advantage of physical refining over alkali refining is that no soapstock is generated. A second advantage is lower refining losses because there is no saponification of oil and no oil emulsifaction by soapstock. Accordingly, there is significant interest in physical refining due to its economic advantages and friendliness compared to alkali refining. But because physical refining does not remove NHPs, any oils to be physically refined must be free of NHPs in order to ensure stable refined oils. Oils such as palm oil and tallow, which have low NHP content, can be successfully physically refined. But oils such as soybean oil and sunflower seed oil, which are relatively high in NHPs, are not commonly physically refined because the pre-refining step of water degumming does not remove NHPs. Moreover, physically refined soybean oils have only limited acceptance in the U.S. market due to their lack of flavor stability. Thus, although present methods exist for refining vegetable oils, significant drawbacks remain. Alkali refining can substantially remove phosphatides and other impurities but presents economic challenges and water pollution concerns. Physical refining is economically and environmentally less challenging, but many vegetable oils including soybean oil which are high in NHPs cannot be acceptably physically refined. Consequently, there is a need for an improved process for purifying vegetable oils, and especially soybean oil. A prior method for refining vegetable oils is disclosed in U.S. Pat. No. 2,410,926 comprising mixing strong aqueous acid solutions with oils, adding filter aid material to absorb the aqueous phase, and separating purified oil from the residue. Typically, 1.5 to 2 percent by weight of a saturated aqueous organic acid solution is added to crude vegetable oil. The amount of water is kept low and is limited to the amount that can be absorbed by the filter aid. Solid acids are used so that any excess above the solubility limit of the small amount of water employed will be retained in the filter cake, and will not pass with the refined oil. A disadvantage of this method is the need to filter out absorbent before the oil can be used. U.S. Pat. No. 4,698,185 describes a vegetable oil refining method comprising the steps of finely dispersing an aqueous organic acid in a water-degummed oil to form an acid-in-oil dispersion, allowing the phases to remain in contact for a time sufficient to decompose metal salts of phosphatidic acid, adding a base to the acid-in-oil dispersion to increase pH to above 2.5 without substantial formation of soap, and finally separating the dispersion into an oil phase and an aqueous phase containing the phosphatides. The method typically utilizes 0.4 to 2 percent by weight of a 20 to 60 percent by weight organic acid solution and requires a degree of dispersion of at least 10 million droplets of aqueous acid per gram of oil. A disadvantage of this method is that pH basic materials like those used in alkali refining must -be added in order to remove NHPs. A somewhat similar method disclosed in U.S. Pat. No. 4,240,972 comprises adding an acid to a heated stream of crude vegetable oil and then immediately passing the mixture through a static mixer, intensively mixing for a fraction of a second to produce an acid-in-oil dispersion having acid droplets smaller than 10 µm (10 microns) and then separating the dispersion into an oil phase and an aqueous phase containing the phosphatides. This method claims that producing ultrafine acid droplets eliminates the need for lengthy acid-oil contact times. However, acid-oil contact times of less than about 15 minutes are generally insufficient to sequester substantial amounts of metal impurities. U.S. Pat. No. 4,049,686 describes a method of removing phosphatides from vegetable oils comprising dispersing an aqueous solution of an acid or acid anhydride into a heated vegetable oil, chilling the mixture to a temperature below 40°C (104°F) adding a small amount of additional water, allowing the phases to remain in contact for a time sufficient to decompose metal salts of phosphatidic acid, and separating the dispersion into an oil phase and an aqueous phase containing the phosphatides. This method claims that by cooling to a temperature below 40°C (104°F) and adding water in a step separate from the aqueous acid addition, the phosphatides are converted into a semi-crystalline phase. Disadvantages of this method include the need to add aqueous acid and water in separate steps and the need for a chilling step, both being aspects that increase overall processing complexity. U.S. Pat. No. 5,696,278 describes a process for refining crude glyceride oil and in particular a degumming process comprising the hydration and subsequent separation of phospholipids in glyceride oil. WO 94/12596 discloses a method for refining edible oils with the aim to avoid any refining step which is not considered natural. WO 96/41852 describes a process for refining a triglyceride oil comprising stripping a triglyceride oil with an inert gas, characterized in that the refining process further comprises the preceding exposure of the triglyceride oil to an aqueous solution of ascorbic acid. Further improvements in purifying vegetable oil have been sought, particularly with regard to obtaining purified vegetable oil low in free fatty acids, phosphatides, and other impurities such as metals in an environmentally friendly manner. The present invention relates to an improved process having advantages over those previously disclosed. In particular, this invention relates to a non-alkali process for purifying vegetable oil employing a dilute aqueous organic acid solution. SUMMARY OF THE INVENTION The present invention relates to an improved process for refining vegetable oil using organic acid. Specifically, the present invention relates to a process for purifying vegetable oil, the improvement comprising admixing a dilute aqueous organic acid solution with a heated stream of vegetable oil to give an acid-oil blend; mixing the acid-oil blend at high shear that generates a flow velocity of at least 14 m per second [45 feet per second] for a time sufficient to finely disperse the dilute aqueous organic acid solution in the vegetable oil and give an acid-and-oil mixture; and mixing the acid-and-oil mixture at low shear for a time sufficient to sequester contaminants into a hydrated impurities phase and produce a purified vegetable oil phase. In one embodiment the process of the present invention further comprises the step of separating the hydrated impurities phase and the purified vegetable oil phase. The organic acid refining process of the present invention effectively removes phosphatides, and other impurities such as metals from crude or degummed vegetable oil in an environmentally friendly way. The organic acid refining process of the present invention also minimizes the risk of degrading the removed impurities, some of which are valuable raw materials. The organic acid refining process of the present invention produces refined vegetable oil having improved odor, flavor, and storage stability, and characterized by a reduced content of free fatty acids, phosphatides, and other impurities such as metals, and provides a hydrated impurities phase comprising a phosphatide concentrate which is a hydrolyzed lecithin. The invention will become apparent in light of the detailed description below. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process flow scheme suitable for carrying out the improved vegetable oil refining process of the invention. DESCRIPTION OF A PREFERRED EMBODIMENT Organic Acid Refining The improved process for purifying vegetable oils can be conducted as a batch or a continuous process. As illustrated in Fig. 1, crude or degummed vegetable oil is supplied from a storage tank 1 through pump 2 to a pre-heater 3 wherein the vegetable oil is heated to a temperature of from about 88°C (190°F) to about 104°C (220°F). Suitable vegetable oils include but are not limited to those derived from soybean oil, corn oil, cottonseed oil, palm oil, peanut oil, rapeseed oil, safflower oil, sunflower seed oil, sesame seed oil, rice bran oil, coconut oil, canola oil, and mixtures thereof. A particularly preferred vegetable oil is soybean oil. The vegetable oil to be purified can be either crude or "degummed" oil. Degumming refers to the process of removing hydratable phosphatides from crude vegetable oils during refining. Crude vegetable oils contain both hydratable and non-hydratable phosphatides. A simple degumming process comprises admixing water with the vegetable oil and separating the resulting mixture into an oil component and an oil-insoluble hydrated phosphatides component (frequently referred to as a "wet gum" or "wet lecithin"). Non-hydratable phosphatides, generally considered to be calcium and magnesium salts of phosphatidic acids, are largely unaffected by water and remain soluble in the oil component. Treating crude vegetable oil with water thus produces a phosphatide concentrate containing the hydratable phosphatide fraction and a degummed oil containing the non-hydratable phosphatide fraction. This degummed oil can be removed from the phosphatide concentrate by a convenient method such as centrifugal separation. The vegetable oil is heated in pre-heater 3 to a temperature of from about 88°C (190°F) to about 104°C (220°F), preferably from about 91°C (195°F) to about 102°C (215°F), and most preferably from about 93°C (200°F) to about 99°C (210°F) depending on the source from which the vegetable oil was derived. Heating the vegetable oil minimizes the potential for losses due to emulsification when the oil is later contacted with an aqueous phase. Heating the vegetable oil also produces preferred handling viscosities and facilitates later mixing steps. Pre-heater 3 can be constructed according to many designs and can impart heat directly or indirectly to the vegetable oil. A preferred pre-heater 3 is a shell and tube heat exchanger available from Doyle & Roth and having an overall heat transfer coefficient of 965 w/m 2 °C (170 BTU/h/ft 2 /°F). The heated vegetable oil is introduced into high shear mixer 6 wherein it is combined with a dilute aqueous organic acid solution supplied from a source 4 via pump 5, thereby producing an acid-oil blend. When the present invention is carried out as a batch process, the heated vegetable oil and the dilute aqueous organic acid solution can be introduced sequentially or simultaneously and in any order into high shear mixer 6. When the present invention is carried out as a continuous process, the heated vegetable oil and the dilute aqueous organic acid solution are introduced simultaneously into high shear mixer 6. The dilute aqueous organic acid solution optionally can be heated prior to its addition into high shear mixer 6. The dilute aqueous organic acid solution may be prepared from any food grade organic acid, including but not limited to phosphoric acid, acetic acid, citric acid, tartaric acid, succinic acid, or combinations thereof. A particularly preferred organic acid is citric acid. Using a food grade organic acid, as opposed to a mineral acid, ensures that phosphatides removed during the purifying process can be purified and sold as commercial lecithin to the food industry. Using an organic acid also enables sequestering metal contaminants without the need to add other chelating agents. The dilute aqueous organic acid solution can be prepared by dissolving an appropriate amount of a solid organic acid in water, or it can be prepared by further diluting a previously prepared aqueous organic acid solution of greater strength. In preparing the dilute aqueous organic acid solution, demineralized water is preferably used. Using demineralized water avoids the possibility of converting hydratable phosphatides to non-hydratable phosphatides. As used herein, the term demineralized water means water substantially devoid of calcium and magnesium ions. The dilute aqueous organic acid solution has a concentration based on the combined weight of organic acid and water of from about 1 to about 5 percent by weight, preferably from about 2 to about 4 percent by weight, and most preferably from about 2 to about 3.5 percent by weight. The dilute aqueous organic solution is combined with the heated vegetable oil in a ratio of from about 3:97 to about 20:80, preferably from about 5:95 to about 15:85, and most preferably from about 8:92 to about 12:88, depending on the source from which the vegetable oil is derived and on whether the vegetable oil has been degummed. The acid-oil blend is mixed at high shear in the high shear mixer 6 for a time sufficient to finely disperse the dilute aqueous organic acid solution in the vegetable oil and give an acid-and-oil mixture. Generally, the acid-oil blend is mixed for a time of less than about 30 seconds, preferably less than about 15 seconds, and most preferably less than about 5 seconds. Mixing parameters are selected according to the mechanical design of the high shear mixer. Important mixer design criteria include the ratio of tank height to tank diameter, the ratio of impeller diameter to tank diameter, and the number and positioning of individual blades on the impeller. A preferred high shear mixer 6 is a High Shear Mixer MX100 available from Alfa Laval and having a tank height to tank diameter ratio of about 4:1. Preferably, high shear mixer 6 employs 5 impellers, 2 of which are radial flow impellers and 3 of which are axial flow impellers, disposed along a mixing shaft connected to a motor generating from about 22 kw (30) to about 29 kw (40 horsepower). High shear as used herein means mixer design criteria and impeller operating conditions combining to produce flow velocities of at least 14 m (45 feet) per second. High shear mixing according to the invention generally requires at least one impeller rotating at a speed of from about 900 to about 1500 rpm and having a blade tip speed of from about 1219 to about 2743 m/min (4000 to about 9000 ft/min), thereby generating high shear flow velocities of at least 14 m (45 feet) per second. The acid-and-oil mixture is pumped to a low shear mixer 7 wherein it is mixed at low shear for a time sufficient to sequester contaminants into a hydrated impurities phase and produce a purified vegetable oil phase. Generally, the mixing design criteria requiring consideration in producing low shear are the same as those discussed above in the context of producing high shear. A preferred low shear mixer 6 is a 945 or 1890 L (250 or 500 gallon) Retention Mixer available from Alfa Laval and having a tank height to tank diameter ratio of about 4:1. Preferably, low shear mixer 7 employs from about 40 to about 60 axial flow impellers disposed along a mixing shaft connected to a motor generating from about 4 to about 5.5 kw (5 to about 7.5 horsepower) Low shear as used herein means mixer design criteria and impeller operating conditions combining to produce flow velocities of less than about 6 m/s (20 feet per second). Preferably, low shear mixing of the acid-and-oil mixture occurs with at least one impeller rotating at a speed of from about 68 to about 600 rpm and having a blade tip speed of from about 183 to about 230 m/min (600 to about 950 ft/min), thereby generating low shear flow velocities of less than about 6 m/s (20 feet per second) The acid-and-oil mixture is mixed at low shear for a time of less than about 16 minutes to allow sequestering of contaminants, especially metals, into the hydrated impurities phase. The acid-and-oil mixture is preferably mixed at low shear mixing for a time of from about 6 to about 14 minutes, and most preferably from about 8 to about 12 minutes. The term sequestering as used herein refers to the process wherein contaminants are either directly or indirectly (through chemical conversion into water-soluble forms) taken up into the hydrated impurities phase. Following low shear mixing, the combined hydrated impurities and purified vegetable oil phases are advantageously pumped to a centrifuge 9 via pump 8 wherein the two phases undergo centrifugal separation and exit in separate physical streams 14 and 15. A preferred centrifuge 9 is a PX 90 available from Alfa Laval. The hydrated impurities stream 14 is sent to a holding vessel 13 and stored for subsequent processing into commercial lecithin. Water can be separated from the hydrated impurities stream and can be recycled without other treatment for use in earlier steps of the organic acid refining process. Because water can be recycled without the need for additional and expensive treatment, such as neutralization, the organic acid refining process of the invention generates substantially no discharge water. The purified vegetable oil stream 15 is sent to dryer 10 operating at less than atmospheric pressure and an elevated temperature sufficient to vaporize any residual water or objectionable volatile components at the operating pressure. A preferred dryer 10 is a Votator Thin Film Dryer available from L.C.I. Corp. Preferably, dryer 10 operates at a temperature of from about 71°C (160°F) to about 88°C (190°F) and at a vacuum of about 628 mbar to about 867 mbar (about 21 to about 29 feet of water) operating conditions which effectively remove residual water. The dried purified vegetable oil is then sent to holding vessel 12 via pump 11 and stored for subsequent use or sale. The hydrated impurities phase produced by the organic acid refining process of the invention is a phosphatide concentrate commonly termed wet lecithin. Surprisingly, however, the phosphatide concentrate produced by the organic acid refining process of the invention is a hydrolyzed lecithin containing at least about 5 percent by weight combined lyso and monoacyl forms of glyceryl phospholipids and containing a ratio of hydratable phosphatides to non-hydratable phosphatides in a ratio of at least about 9:1. Obtaining a hydrolyzed lecithin directly from a crude vegetable oil is a novel and unexpected benefit provided by the improved organic acid refining process of the invention. According to known processes, hydrolyzed lecithin is normally obtained either via acidic or basic hydrolysis or via enzymatic action. A typical acidic hydrolysis process for producing hydrolyzed lecithin comprises multiple processing steps of adding water and an acid such as hydrochloric acid to a dried lecithin, subsequently neutralizing with a base such as sodium hydroxide, and then redrying the lecithin. J. C. Schmidt and F.T. Orthoefer, Modified Lecithins , in LECITHINS 203, 206 (Bernard F. Szuhaj & Gary R. List eds., 1985). A typical enzymatic process for producing hydrolyzed lecithin comprises adding costly animal-derived or synthetic enzymes to a wet lecithin to catalyze conversion of the lecithin into a hydrolyzed lecithin. Moreover, enzymatic processes for producing hydrolyzed lecithin require that the enzymes be filtered out after lecithin conversion, adding further expense. Thus, previously known methods for obtaining hydrolyzed lecithin have required complex and expensive processing steps. Surprisingly, the organic acid refining process of the invention produces hydrolyzed lecithin directly and simply from a phosphatide-containing vegetable oil without the need for subsequent and expensive processing. The invention is illustrated further by the following examples, which are not to be construed as limiting the invention. EXAMPLE 1 Organic Acid Refining An aqueous citric acid solution containing 3 percent by weight citric acid based on the combined weight of citric acid and water was admixed with a crude filtered vegetable oil in a ratio of 10:90. The resulting acid-oil blend was mixed in a high shear mixer for 30 seconds to give an acid-and-oil mixture. The acid-and-oil mixture was then transferred to a low shear mixer and mixed for 15 minutes, and then was centifuged to separate the purified vegetable oil phase from the hydrated impurities phase. The resultant purified vegetable oil had the characteristics shown in Table I. Table I demonstrates that the organic acid refining process of the present invention effectively removes metal contaminants from crude vegetable oil. Vegetable oil purified by the organic acid refining process contains dramatically lower residual metal levels as compared to vegetable oil obtained via conventional water-degumming. The vegetable oil produced by the invention is unique among vegetable oils because it contains less than about 10 ppm phosphorous and less than about 0.1 ppm iron. EXAMPLE 2 Organic Acid Refining The hydrated impurities phase obtained in Example 1 was a hydrolyzed lecithin containing hydratable phosphatides and non-hydratable phosphatides in a ratio of about 9:1. Further analysis produced the results shown in Table II. Table II demonstrates that the lecithin produced by the organic acid refining process of the invention is a hydrolyzed lecithin because it contains greater than about 5 percent by weight combined lyso and monoacyl forms of glyceryl phospholipids. Moreover, the hydrolyzed lecithin produced is unique among hydrolyzed lecithins because it contains a ratio of hydratable phosphatides to non-hydratable phosphatides of at least about 9:1. The invention and the manner and process of making and using it, are now described in such full, clear, concise and exact terms as to enable any person skilled in the an to which it pertains, to make and use the same. Although the foregoing describes preferred embodiments of the present invention, modifications may be made therein. To particularly point out and distinctly claim the subject matter regarded as invention, the following claims conclude this specification.

Claims: Process for purifying vegetable oil, the improvement comprising: (a) admixing a dilute aqueous organic acid solution with a heated stream of vegetable oil to give an acid-oil blend; (b) mixing the acid-oil blend at high shear that generates a flow velocity of at least 14 m per second [45 feel per second] for a time sufficient to finely disperse the dilute aqueous organic acid solution in the vegetable oil and give an acid-and-oil mixture; and (c) mixing the acid-and-oil mixture at low shear for a time sufficient to sequester contaminants into a hydrated impurities phase and produce a purified vegetable oil phase. The process according to claim 1, further comprising step (d) separating the hydrated impurities phase and the purified vegetable oil phase. The process according to claim 1, wherein the dilute aqueous organic acid solution is prepared from an organic acid selected from the group consisting of phosphoric acid, acetic acid, citric acid, tartaric acid, succinic acid, and mixtures thereof. The process according to claim 3, wherein the dilute aqueous organic acid solution is a dilute aqueous citric acid solution. The process according to claim 4, the dilute aqueous citric acid solution contains less than about 5 percent by weight citric acid based on the combined weight of citric acid and water. The process according to claim 1, wherein the vegetable oil is heated to a temperature of from about 88°C (190°F) to about 104°C (220°F) prior to being contacted with the dilute aqueous organic acid solution. The process according to claim 1, wherein the dilute aqueous organic acid solution is admixed with the vegetable oil in a ratio of from about 3:97 to about 20:80. The process according to claim 1, wherein step (b) high shear mixing occurs for a time of less than about 30 seconds. The process according to claim 1, wherein step (c) low shear mixing produces a flow velocity of less than about 6m (20 feet) per second. The process according to claim 1, wherein step (c) low shear mixing occurs for a time of less than about 16 minutes. The process according to claim 2, wherein step (d) separating occurs by centrifuging the acid-and-oil mixture. The process according to claim 2, wherein step (d) separating produces a purified vegetable oil containing less than about 25 ppm metal ions. The process according to claim 12, wherein the purified vegetable oil contains less than about 1 ppm iron. The process according to claim 2, further comprising step (e) bleaching the purified vegetable oil using bleaching earth. The process according to claim 2, further comprising step (e) drying the purified vegetable oil in a dryer utilizing an operating pressure of less than about 40 mbar (30 mm Hg) and a drying temperature sufficient to vaporize water and objectionable volatile components at the operating pressure. The process according to claim 1, wherein the process generates substantially no discharge water.

Inventors: BLECHER MAURICE W, COPELAND RICHARD, BLECHER, MAURICE W., COPELAND, RICHARD
Applicants: IP HOLDINGS L L C, IP HOLDINGS L.L.C.
Application year: 1999
Main classification: C11B3
IPC codes: C11B3, A23D9, A23J7