Abstract:
Disclosed is an improved process for the preparation of tocopherol concentrates from vegetable oil distillates. Tocopherol concentrates are obtained containing 20-80% tocopherol by weight, with an overall recovery of tocopherol of 72% to 97%. The process is comprised first of an esterification reaction where the more volatile alcohols are converted to their less volatile fatty acid esters, followed by a series of distillation steps where components boiling higher and lower than the tocopherols are separated from tocopherols and other like boiling substances. Advantages of the process are that tocopherol concentrates are produced efficiently and economically in a minimum number of steps without the use of solvents and with a relatively small capital investment.

Description:
FIELD OF THE INVENTION 
     This invention belongs to the field of organic chemistry. In particular, this invention relates to a process for the manufacture of tocopherol concentrates from the by-products of vegetable oil refining. 
     BACKGROUND OF THE INVENTION 
     Alpha, beta, gamma, and delta tocopherol (hereafter referred to as tocopherols) can be found in various ratios and concentrations in crude vegetable oils such as soy bean, sunflower, canola, rapeseed, cottonseed, safflower, corn, palm, palm kernel, and rice bran oil. These tocopherols are a valuable constituent of vegetable oil as they help prevent oxidation and spoilage. During the refining of vegetable oils a large fraction of the tocopherols are lost to various by-products and waste streams. These waste and by-products streams include, but are not limited to, deodorizer distillates, steam refining distillates, and acidulated soapstocks. The vegetable oil refining by-products typically contain from less than 1% to greater than 20% tocopherol by weight. The oil refining by-products are a valuable source of raw material for the production of natural vitamin E and other tocopherol antioxidants. However, the by-product streams also contain 20 to 99% by weight free fatty acids, less than 1% to 20% by weight sterols, less than 1% to 20% by weight sterol esters of fatty acid, less than 1% to 40% by weight mono, di, and triglycerides, less than 1% to 30% by weight hydrocarbons, and several percentage by weight of other compounds, in addition to tocopherols. Thus, in order to obtain a tocopherol concentrate stream useful for production of high purity vitamin E, it is necessary to remove these substances. 
     Numerous methods have been proposed for the recovery of tocopherols from vegetable oil refining by-products. For example, U.S. Pat. No. 2,432,181 teaches that tocopherols can be recovered from vegetable oils and fats by reacting the fatty acid glycerides with an aliphatic monohydric alcohol in the presence of an alkaline alcoholysis catalyst, followed by a flash distillation of residual alcohol glycerol, and fatty acid esters. 
     U.S. Pat. No. 3,153,055 teaches a process for the isolation of sterols and tocopherols from deodorizer distillate by esterification of free fatty acids and glycerides into lower monohydric alcohol esters under strongly acidic conditions. The sterols and tocopherols are fractionally extracted from the esterification product with a combination of polar and nonpolar solvents. 
     U.S. Pat. No. 3,335,154 teaches that deodorizer distillate can be saponified and acidulated to convert glycerides and sterol esters to free fatty acids and free alcohols (glycerol, sterols respectively). The free fatty acids are esterified with a monohydric lower alcohol and mineral acid catalyst. The sterols are precipitated/crystallized by the addition of water to the mixture, and the tocopherols are concentrated by removal of the fatty acid esters by molecular distillation. 
     All of the above processes suffer from serious drawbacks. They require the addition of extraneous monohydric alcohols and result in the production of fatty acid esters which are not normally present in the vegetable oil by-product feed material. The excess monohydric alcohol must be removed in an additional processing step. In order to produce a highly concentrated tocopherol product the sterols must either be removed by crystallization or by other means. Saponification requires large amounts of caustic and acid for acidulation, thereby creating excessive salt wastes. 
     U.S. Pat. No. 4,454,329 teaches that a tocopherol concentrate can be obtained from deodorizer distillates by esterification of the free fatty acids with a dihydric or polyhydric alcohol, in the presence or absence of an acid catalyst. The esterification is preferably carried out in the presence of an aromatic solvent such as benzene, toluene, or xylene. The esterified mixture is then subjected to either a solvent extraction or a molecular distillation to produce the final tocopherol concentrate. Preferably, the solvent extraction is proceeded by a hydrogenation to convert the unsaturated triglycerides into saturated triglycerides, thereby decreasing the solubility of the triglycerides in the solvent phase of the extraction. Distillation of the esterified mixture concentrates tocopherols, sterols, hydrocarbons and other components with similar boiling points in the distillate. The triglycerides and other high-boiling components are left in the distillation residue. 
     The above process is unsatisfactory for a number of reasons. Deodorizer distillates and the like typically contain a 1/1 to 3/1 ratio of sterols to tocopherols, depending on the vegetable oil source. The tocopherols and sterols have very similar boiling points and there-fore cannot be separated by distillation alone. The esterification is not run in such a fashion to ensure that the sterols are converted into sterol esters (which have a much higher boiling point than tocopherol). The distillate containing the tocopherols and sterols produced by the above process must be further treated by other separation techniques in order to produce a tocopherol concentrate essentially free of sterols. 
     In the solvent extraction version of the process, the solvent must be removed from the tocopherol extract, adding additional cost and complication to the process. The preferred embodiment of the solvent extraction, proceeded by the hydrogenation, adds still another step, with concomitant cost and complication. In addition, typical copper and nickel hydrogenation catalysts are known to be prooxidants, which promote the destruction of tocopherol, thereby lowering the yield of tocopherol from the process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram outlining one aspect of the method of the present invention, in which an esterification reaction is conducted in reactor (2), which is then subjected to a series of distillation steps (5), (8), and (9), to provide the desired tocopherol. 
     FIG. 2 is a diagram outlining the preferred method of the present invention, in which an esterification reaction is conducted in reactor (2), and subjected to two distillation steps. 
    
    
     FIGS. 1 and 2 are more fully described below. 
     SUMMARY OF THE INVENTION 
     One object of this invention is to provide an efficient, economical process for the isolation of tocopherols from vegetable oil processing by-products. The raw material for the process can be deodorizer distillate, steam refining distillate, acidulated soapstock, or any other vegetable oil by-product containing typically from less than 1% tocopherol to upwards of 20% tocopherol by weight. 
     In this invention, the vegetable oil by-product is subjected to an esterification step, with or without an acid catalyst, in which the sterols react with the free fatty acid already present in the mixture to form high-boiling sterol esters. Any other alcoholic moieties, triterpenoid alcohols, methyl-sterols, and the like, are converted to high-boiling fatty acid esters and waxes. Moreover, any mono- and di-fatty acid glycerides are largely converted to triglycerides by reaction with the free fatty acids. The tocopherols also react to a limited extent; the extent of reaction can be controlled by proper selection of reaction time and temperature. The esterified mixture is then subjected to a series of distillation steps in which components boiling higher and lower than the tocopherols are separated from tocopherols and other like-boiling substances. The distillation steps consist of one or more separate distillation operations to remove unreacted free fatty acids overhead, along with any low-boiling compounds, from a tocopherol-rich bottoms product and one distillation operation to remove a tocopherol-rich product overhead from sterol esters, fatty acid polyesters of glycerol, waxes, and other high-boiling substances. Either the distillation operations to remove the fatty acid and low-boilers, or the distillation operation to remove the high-boilers may be done first. The resulting product of the process is a tocopherol concentrate comprised primarily of tocopherol and hydrocarbons with similar boiling points, which is essentially free of free fatty acids, sterols, sterol esters, fatty acid polyesters of glycerol, waxes, and other high-boiling compounds. 
     As a further aspect of this invention, the catalyst for the esterification step is a monoalkyl tin compound, zinc salt of an organic acid, titanium (IV) alkoxides, zinc oxide, phosphoric acid or other mild mineral acids. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a method for preparing a tocopherol concentrate which comprises the steps: 
     (a) heating a vegetable oil by-product comprised of tocopherols, fatty acids, hydrocarbons, sterol esters of fatty acids, sterols, triterpenoid alcohols, methyl-sterols, and mono-, di-, and triglycerides, optionally in the presence of an acid catalyst, said by-product optionally containing additional C 10  -C 22  fatty acids, to a temperature of about 70° C. to 300° C. and a pressure of about 50 torr to 760 torr, while continuously removing water formed thereby, to provide a mixture comprised of sterol esters, high boiling fatty acid esters, waxes, and glycerides; and 
     (b) followed by subjecting said mixture to a series of distillation operations comprising: 
     (i) one or more separate distillation operations, wherein said distillation(s) is (are) conducted at a temperature of about 200° C. to 320° C. and a pressure of about 0.01 torr to 10 torr, in series wherein unreacted fatty acids and low-boiling components are removed as a vapor effluent and a liquid effluent comprised of tocopherols is removed; and 
     (ii) wherein said liquid effluent from step (b)(i) is subjected to one or more distillations in series, wherein said distillation(s) is (are) conducted at a temperature of about 170° C. to 270° C. and a pressure of about 0.005 torr to 2 torr, wherein a tocopherol concentrate is removed as a vapor effluent and wherein a liquid effluent comprised of sterol esters, fatty acid esters, glycerides, waxes, and other high-boiling substances is removed. 
     The description of a preferred aspect of the present invention is made in reference to the process diagrams of FIGS. 1 and 2. The vegetable oil by-product is fed via line (1) to a stirred tank or batch reactor, unit (2), operating at a temperature of about 70°-300° C., preferably in the range of 150°-230° C., and at a pressure of about 50 torr to 760 torr, preferably about 100-200 torr. The residence time in the reactor is preferably from about 1 to 24 hours, most preferably 90 minutes to two hours in the presence of an acid catalyst, and from two hours to ten hours when no catalyst is used. Preferred catalysts include monoalkyl tin compounds, zinc salt of an organic acid, titanium (IV) alkoxides, zinc oxide, phosphoric acid and other mild mineral acids. 
     During the reaction step, the free fatty acid which is already present in the feed mixture reacts with the sterols to form high-boiling sterol esters and water. Any other alcoholic moieties, triterpenoid alcohols, methyl-sterols, and the like, also react with the free fatty acids to form high-boiling fatty acid esters, waxes, and water. Moreover, any mono- and di-fatty acid esters of glycerol are largely converted to triglycerides by esterification with the free fatty acids. The tocopherols also react to a limited extent with the free fatty acid to form tocopherol esters and water. The relative rates of the esterification reactions is glycerides&gt;sterols&gt;tocopherols. Thus, the reaction of tocopherols can be controlled by proper selection of reaction temperature and time. Tocopherol recovery from the reaction step is typically 80% to 97%, more typically 85% to 92%. Conversion of sterols to fatty acid sterol esters is typically 75% to 100%, more typically 85% to 95%. In a preferred embodiment, C 10  -C 22  fatty acids are added to the starting material by-product, most preferably in an amount of up to about 40% by weight, based on the total weight of the by-product starting material. 
     The reactor is provided with a means for removal of the water of esterification, line (3). As is well-known in the art, the removal of the water of esterification drives the reaction equilibrium toward the formation of the fatty acid ester products. 
     The esterification product (4) is then subjected to a series of distillation steps in which components boiling higher and lower than the tocopherol are separated from tocopherol and other like-boiling substances. The distillation steps are one or more separate distillation operations to remove unreacted free fatty acids overhead along with any low-boiling compounds from a tocopherol-rich bottoms product, and one distillation operation to remove a tocopherol-rich product overhead away from sterol esters, fatty acid polyesters of glycerol, waxes, and other high-boiling compounds. Either the distillation operations to remove the fatty acid and low-boilers, or the distillation operation to remove the high-boilers may be done first. It should be understood that the reaction and distillation operations may be accomplished in batch, semi-batch, and continuous modes of operation. 
     This process produces tocopherol concentrates efficiently and economically in a minimum of steps. No extraneous substances are added to the raw material oil, except possibly an esterification catalyst and added C 10  -C 22  fatty acids. No solvents or excess esterification alcohols need to be removed from the reaction product. The achievable tocopherol concentration in the final product is in the range of 20-80% tocopherol by weight, depending on the amount of hydrocarbons in the starting material. More typically the product will have a tocopherol concentration of 30-60% by weight of tocopherol. The overall recovery of tocopherol from the process is typically 72% to 97%, more typically 75% to 92%, most typically 80% to 85%. 
     One embodiment of the method of the present invention is illustrated by FIG. 1. The product (4) from the esterification step is distilled in unit (5) under high vacuum to remove a substantial fraction, typically 50-90%, more typically 60-80%, of the unreacted fatty acid along with a substantial fraction the low-boilers, stream (6), to leave a tocopherol-rich bottoms product (7). The distillation operation is conducted at temperatures and pressures such that the tocopherols are largely left in the bottoms product. The temperature and pressure of distillation operation (5) is in the range of 170° C. to 270° C., 0.05 to 10 torr. The preferred range is 200° C. to 240° C., 0.5 torr to 4 torr. The distillation apparatus (5) (as are all of the distillation equipment used herein) is preferably a high-vacuum design including a short path evaporator, a wiped-film evaporator, a centrifugal molecular still, or a falling film evaporator capable of low pressure operation. 
     The bottoms product (7) of the first distillation operation (5) is distilled a second time in distillation operation (8) under high vacuum to remove any remaining unreacted fatty acids and other low-boiling compounds. The temperature of distillation (8) must be higher or the pressure lower than distillation (5) in order to ensure essentially complete removal of any remaining fatty acids. The temperature and pressure of distillation (8) is in the range of 230° C. to 300° C., 0.01 to 5 torr. The preferred range is 240° C. to 280° C., 0.1 torr to 2 torr. Under these conditions a portion, typically 5-30%, of the tocopherols will distill overhead with the remaining fatty acids into stream (9), leaving an acid-free tocopherol-rich bottoms product (10). The distillate (9) containing some tocopherols and the remaining free fatty acid may be discarded or recycled to reactor (2) or the first distillation operation (5) in order to improve the overall yield of tocopherols. Since distillation (5) and distillation (8) are conducted under different temperature and pressure conditions, they act in combination as a multi-equilibrium staged device, lowering tocopherol losses and increasing fatty acid removal. The distillation apparatus (8) may be of any high-vacuum design including a short path evaporator, wiped-film evaporator, centrifugal molecular still, or falling film evaporator. 
     The tocopherol-rich bottoms product (10) of the second distillation (8) is then subjected to a third high-vacuum distillation (11). The tocopherol and other similarly boiling compounds are collected as a final tocopherol-rich distillate product (12). The triglycerides, sterol esters, other high-boiling fatty acid esters, and other high-boiling compounds are removed in the largely tocopherol-free bottoms (13) of the distillation. Tocopherol recovery to stream (12) is typically 95% to 100%, more typically 96% to 99.9%. The catalyst, if any were used, exits in the residue. The temperature and pressure of distillation operation (11) is in the range of 170° C. to 270° C., 0.005 to 2 torr. The preferred range is 200° C. to 250° C., 0.01 torr to 0.05 torr. The distillation apparatus (11) may be of any high-vacuum design including a short path evaporator, wiped-film evaporator, centrifugal molecular still, or falling film evaporator. 
     Thus, as a further aspect of the present invention, there is provided a method for preparing a tocopherol concentrate which comprises the steps: 
     (a) heating a vegetable oil by-product comprised of tocopherols, fatty acids, sterols, sterol esters of fatty acids, and mono-, di-, and triglycerides, said by-product optionally containing added C 10  -C 22  fatty acids, optionally in the presence of an acid catalyst, at a temperature of about 70° to 300° C. and a pressure of about 50 torr to 760 torr, while continuously removing water formed thereby, to form a mixture comprised of sterol esters, high boiling fatty acid esters, waxes, and glycerides; 
     (b) followed by subjecting said mixture to distillation at a temperature of about 170° C. to 270° C. and a pressure of about 0.05 to 10 torr, while removing unreacted fatty acids and low-boiling components as a vapor effluent and a liquid effluent comprised of tocopherols; 
     (c) followed by subjecting the liquid effluent from step (b) to distillation at a temperature of about 230° C. to 300° C. and a pressure of about 0.01 to 5 torr, while removing remaining fatty acids and approximately 5 to 30 percent of total tocopherols as a vapor effluent and a liquid effluent which is a tocopherol-enriched product; and 
     (d) followed by subjecting the liquid effluent from step (c) to distillation at a temperature of about 170° C. to 270° C. and a pressure of about 0.005 to 2 torr, and collection and isolation of a tocopherol concentrate as a vapor effluent. 
     As noted above, preferred apparatus for the distillation steps include any high-vacuum design including a short path evaporator, wiped-film evaporator, centrifugal molecular still, or falling film evaporator. Accordingly, as a further aspect of the present invention, there is provided a method for preparing a tocopherol concentrate which comprises the steps: 
     (a) heating a vegetable oil by-product comprised of tocopherols, fatty acids, hydrocarbons, sterol esters of fatty acids, sterols, triterpenoid alcohols, methyl-sterols, and mono-, di-, and triglycerides, optionally in the presence of an acid catalyst, said by-product optionally containing additional C 10  -C 22  fatty acids, at a temperature of about 70° C. to 300° C. and a pressure of about 50 torr to 760 torr, while continuously removing water formed thereby, to provide a mixture comprised of sterol esters, high boiling fatty acid esters, waxes, and glycerides; 
     (b) followed by feeding said mixture to a first distillation zone comprising: 
     a first distillation apparatus selected from the group consisting of a short path evaporator, a wiped film evaporator, a centrifugal molecular still, and a falling film evaporator, operated at a temperature of about 170° C. to 270° C. and a pressure of about 0.05 to 10 torr, 
     wherein a vapor effluent comprised of a substantial fraction of the unreacted free fatty acids, and low-boiling materials is removed, 
     wherein a liquid effluent which is comprised of a tocopherol-enriched mixture is removed; 
     (c) followed by feeding the liquid effluent from step (b) to a second distillation zone comprising: 
     a second distillation apparatus selected from the group consisting of a short path evaporator, a wiped film evaporator, a centrifugal molecular still, and a falling film evaporator, operated at a about 240° C. to 280° C. and a pressure of 0.01 to 2 torr, 
     wherein a vapor effluent comprised of remaining fatty acids and approximately 5 to 30 percent of total tocopherols is removed, 
     wherein a liquid effluent comprised of a tocopherol-enriched mixture is removed; and 
     (d) followed by feeding the liquid effluent from step (c) to a third distillation zone comprising: 
     a third distillation apparatus selected from the group consisting of a short path evaporator, a wiped film evaporator, a centrifugal molecular still, and a falling film evaporator, operated at a temperature of about 170° C. to 270° C. and a pressure of 0.005 to 2 torr, 
     wherein a vapor effluent which is a tocopherol concentrate is removed and isolated. 
     It should be appreciated that the order of the fatty acid removal and high-boilers distillation may be reversed, i.e., steps (b) and (d) of the above aspects of the invention would be reversed. In this embodiment, the product of the esterification reactor (4) is fed first to distillation operation (11). The free fatty acids, low-boilers and tocopherols are distilled overhead first from the sterol esters, fatty acid polyesters of glycerol, waxes, and other high-boiling compounds. The tocopherol-rich distillate is then fed to distillation operation (5) to remove a substantial fraction of the fatty acids and low-boilers and then to distillation operation (8) to remove the remaining fatty acids and low-boilers. The final tocopherol-rich concentrate is the bottoms product of distillation operation (8). The distillate of unit (8) may be recycled to the reactor (2), the first distillation (11), or the second distillation (5) in order to increase the overall tocopherol recovery. 
     A more highly preferred embodiment of present invention is illustrated by FIG. 2. The vegetable oil by-product (1) is esterified in a batch or continuous reactor (2), with or without catalyst. The water of esterification is removed continuously via line (3) during the reaction. The product of the esterification step (4) is distilled under high vacuum to remove essentially all of the unreacted fatty acid, typically 90% to 99.9%, more typically 97% to 99.9%, along with a substantial fraction of other low-boilers via stream (8) to leave a tocopherol-rich bottoms product (10). The temperature and pressure of the distillation is in the range of 220° C. to 320° C., 0.1 to 8 torr. The preferred range is 260° C. to 290° C., 0.5 torr to 4 torr. In the preferred embodiment of the invention, the distillation apparatus for the fatty acid removal step is a multistage, refluxed fractionating column. The column must contain at least one, preferably two to four, equilibrium stages of rectification (5), as well as an optional stripping section (6). The column must also have the capability of providing reflux via line (7) to the rectification section (5). The fractionating capability of the device greatly decreases the tocopherol loss to the distillate to typically less than 5%, more typically 0.2% to 2.0%, and increases the removal of the free fatty acid from the bottoms product. The optional stripping section further increases the removal of the free fatty acids from the bottoms product. The extent of tocopherol loss is highly dependent on the reflux ratio, defined as the ratio of the mass flow rate of stream (7) to the mass flow rate of stream (8). In the preferred embodiment of the invention the reflux ratio is in the range of 0.3 to 5.0, more preferably from 0.5 to 2.0. The staging in the rectification and optional stripping sections may be provided by any vapor-liquid contacting device, including bubble cap trays, sieve trays, random packing, and structured packing. In the preferred embodiment of the invention, the equilibrium staging is provided by high efficiency, low pressure drop structured packing, in order to lower residence time and reduce the temperature required for distillation. The reboiler of the distillation apparatus may be of any high-vacuum, low residence design including a short path evaporator, wiped-film evaporator, centrifugal molecular still, or falling film evaporator. 
     The tocopherol-rich bottoms product (10) of the first distillation is then subjected to a second high-vacuum distillation (11). The tocopherol and other similarly boiling compounds are collected as a tocopherol-rich distillate product (12). The triglycerides, sterol esters, other high-boiling fatty acid esters, and other high-boiling compounds are removed in the largely tocopherol-free bottoms, stream (13), of the distillation. Tocopherol recovery to stream (12) is typically 95% to 100%, more typically 96% to 99.9%. The catalyst, if any were used, exits in the residue. The temperature and pressure of the second distillation is in the range of 170° C. to 300° C., 0.005 to 2 torr. The preferred range is 200° C. to 250° C., 0.01 torr to 0.05 torr. The distillation apparatus (11) may be of any high-vacuum design including a short path evaporator, wiped-film evaporator, centrifugal molecular still, or falling film evaporator. 
     Thus, as a further aspect of the present invention, there is provided a method for preparing a tocopherol concentrate which comprises the steps: 
     (a) heating a vegetable oil by-product comprised of tocopherols, fatty acids, hydrocarbons, sterol esters of fatty acids, sterols, triterpenoid alcohols, methyl-sterols, and mono-, di-, and triglycerides, optionally in the presence of an acid catalyst, said by-product optionally containing additional C 10  -C 22  fatty acids, to a temperature of about 70° C. to 300° C. and a pressure of about 50 torr to 760 torr, while continuously removing water formed thereby, to provide a mixture comprised of sterol esters, high boiling fatty acid esters, waxes, and glycerides; 
     (b) followed by feeding the mixture from step (a) to a first distillation zone comprising: 
     a first distillation apparatus comprised of a multistage, refluxed fractionating column and a reboiler, said column having a rectification section having at least one equilibrium stage of rectification and means for providing reflux to said rectification section, and optionally a stripping section, said apparatus operated at a temperature of about 220° C. to 320° C., and a pressure of about 0.1 to 8 torr, 
     wherein a vapor effluent which is comprised of free fatty acids and low-boiling materials is removed; and 
     wherein a liquid effluent which is comprised of a tocopherol-enriched mixture is removed; 
     (c) followed by feeding the liquid effluent from step (b) to a second distillation zone comprising: 
     one or more separate distillation apparatus in series selected from the group consisting of a short path evaporator, a wiped film evaporator, a centrifugal molecular still, and a falling film evaporator, operated at a temperature of about 200° C. to 320° C. and a pressure of about 0.01 torr to 10 torr, 
     wherein a liquid effluent comprised of sterol esters, fatty acid esters, glycerides, waxes, and other high-boiling materials is removed; 
     wherein a vapor effluent which is a tocopherol concentrate is removed and isolated. 
     It should also be understood that the order of the fatty acid removal and high-boilers distillation may be reversed in this embodiment. In this embodiment, the product of the esterification reactor (4) is fed first to distillation operation (11). The free fatty acids, low-boilers and tocopherols are distilled overhead first from the sterol esters, fatty acid polyesters of glycerol, waxes, and other high-boiling compounds. The tocopherol-rich distillate is then fed to a multi-staged fractionating distillation operation to remove essentially all of the fatty acids and a substantial fraction of the low-boilers. The distillation operation consists of a refluxed rectifying section (5), a reboiler (9), and an optional stripping section (6). The final tocopherol-rich concentrate is the bottoms product of the second multi-staged distillation operation. 
     Acccordingly, as a further aspect of the present invention, there is provided a method for preparing a tocopherol concentrate which comprises the steps: 
     (a) heating a vegetable oil by-product comprised of tocopherols, fatty acids, hydrocarbons, sterol esters of fatty acids, sterols, triterpenoid alcohols, methyl-sterols, and mono-, di-, and triglycerides, optionally in the presence of an acid catalyst, said by-product optionally containing additional C 10  -C 22  fatty acids, to a temperature of about 70° C. to 300° C. and a pressure of about 50 torr to 760 torr, while continuously removing water formed thereby, to provide a mixture comprised of sterol esters, high boiling fatty acid esters, waxes, and glycerides; 
     (b) followed by feeding the mixture from step (a) to a first distillation zone comprising: 
     one or more separate distillation apparatus in series selected from the group consisting of a short path evaporator, a wiped film evaporator, a centrifugal molecular still, and a falling film evaporator, said apparatus operated at a temperature of about 200° C. to 320° C. and a pressure of about 0.01 torr to 10 torr, 
     wherein a liquid effluent comprised of sterol esters, fatty acid esters, glycerides, waxes, and other high-boiling materials is removed; and 
     wherein a vapor effluent comprised of a tocopherols, free fatty acids and low-boilers is removed; 
     (c) followed by feeding the vapor effluent from step (b) to a second distillation zone comprising: 
     a distillation apparatus comprised of a multistage, refluxed fractionating column and a reboiler, said column having a rectification section having at least one equilibrium stage of rectification and means for providing reflux to said rectification section, and optionally a stripping section, said apparatus operated at a temperature of about 220° C. to 320° C., and a pressure of about 0.1 to 8 torr, 
     wherein a vapor effluent which is comprised of free fatty acids, and low-boiling materials is removed; 
     wherein a liquid effluent which is a tocopherol concentrate is removed and isolated. 
     EXAMPLES 
     Example 1 
     A one liter 3-neck flask equipped with a mechanical stirrer, heating mantle, Dean-Stark trap, reflux condenser, N 2  inlet, and thermowell was charged with 500 g of soy oil deodorizer distillate and 0.5 g of zinc acetate. The resulting mixture was stirred and heated for three hours at 230° C. A nitrogen flow of 250 mL/min was bubbled through the mixture while it was heated. The mixture was sampled and analyzed for tocopherols, sterols, sterol esters, fatty acids, and glycerides. The results are listed in Table 1. 
     Example 2 
     The procedure outlined above was followed except that 500 g of canola oil deodorizer distillate was charged to the reactor and 0.25 g of butylstannoic acid was used as the catalyst. The results are shown in Table 2. 
     Example 3 
     The procedure outlined in example 1 was followed except that 1.8 g of phosphoric acid was used as the catalyst. The results are shown in Table 3. 
     Example 4 
     The procedure outlined in example 1 was followed except that no catalyst was added. The mixture was stirred and heated for 24 hours at 170° C. The results are listed in Table 4. 
     Example 5 
     The procedure outlined above was followed except that the reactor was charged with 500 g of sunflower deodorizer distillate. No catalyst was added. The mixture stirred and heated for three hours at 210° C. The results are listed in Table 5. 
     Example 6 
     The effect of temperature on reaction rates was examined using the same reactor equipment as outlined in example 1. The reactor was charged with 500 g of soy deodorizer distillate for each run at 132° C., 150° C., and 170° C. No catalyst was added. Each mixture was stirred and heated for 19-20 hours and maintained at temperature. The results are listed in Table 6. 
     Example 7 
     A 150 gal stainless steel reactor equipped with an anchor agitator, steam jacket, nitrogen inlet, vacuum system, and outlet pipe for water removal was charged with approximately 800 lb of canola oil deodorizer distillate for each of four reactor runs. For each run the vacuum was set at 200 mm Hg and the mixture was agitated and steam applied to the heating jacket during a three-hour heat-up to 210° C. The reactor was held at 210° C. and 200 mm Hg, with agitation, for two hours. The reactor was then rapidly cooled to below 100° C. Water of esterification was collected during the heat-up and hold times. The reactor product of each run was sampled and analyzed for tocopherols and sterols. The results for each of the four reactor runs are listed in Table 7. 
     Example 8 
     A 150 gal stainless steel reactor equipped with an anchor agitator, steam jacket, nitrogen inlet, vacuum system, and outlet pipe for water removal was charged with 310.8 lb of soy oil deodorizer distillate. No catalyst was added. The vacuum was set at 200 mm Hg and the mixture was agitated and steam applied to the heating jacket during a five-hour heat-up to 210° C. The reactor was held at 210° C. and 200 mm Hg, with agitation, for two and a half hours. The reactor was then rapidly cooled to below 100° C. Water of esterification was collected during the heat-up and hold times. The reactor product was sampled at 5 hours and 7.5 hours and analyzed for tocopherols and sterols. The results are listed in Table 8. 
     Example 9 
     A one liter 3-neck flask equipped with a mechanical stirrer, heating mantle, Dean-Stark trap, reflux condenser, N 2  inlet, and thermowell was charged with 500 g of soy triglycerides, 5.1 g of mixed soy tocopherols, and 0.5 g of dibutyl tin oxide. The resulting mixture was stirred and heated for two hours at 230° C. A nitrogen flow of 250 mL/min was bubbled through the mixture while it was heated. The mixture was sampled at one hour intervals and analyzed for tocopherols. The results are listed in Table 9. 
     Example 10 
     Referring to FIG. 1, distillation operation 5, soy deodorizer distillate was fed continuously to a single-stage 0.42 m2 thin film evaporator unit operating at 1.3 to 1.4 torr. The unit was heated by a hot oil system to a constant temperature of 238° C. The flow rate to the column was varied and timed samples of the distillate and bottoms products were collected. The flow rates of the distillate and bottoms streams were calculated from the masses of the timed samples, and a portion of each sample was analyzed for tocopherol and fatty acid content. The effect of flow rate on fatty acid removal and tocopherol recovery in the residue is shown in Table 10. 
     Example 11 
     The effect of temperature on fatty acid removal and tocopherol recovery in the residue was examined using the same thin film evaporator as outlined in example 11. 
     System pressure varied from 2.2 torr to 2.8 torr. Timed samples were collected to calculate distillate and bottoms rates and a portion of each sample was analyzed for tocopherol and fatty acid content. The results are shown in Table 11. 
     Example 12 
     A tocopherol-rich bottoms product resulting from the removal of a substantial fraction of the fatty acids was fed continuously to a 0.42 m2 short path evaporator unit operated at 0.05 to 0.099 torr. The temperature was varied from 239° C. to 279° C. and timed samples of the distillate and bottoms products were collected. The flow rates of the distillate and bottoms streams were calculated from the masses of the timed samples, and a portion of each sample was analyzed for tocopherol and fatty acid content. The effect of temperature on tocopherol recovery in the distillate is shown in Table 12. 
     Example 13 
     An one-inch diameter glass distillation column was equipped with a vacuum pump, refluxing distillation head, reflux ratio controller, metered feed pump, heated feed line, heated feed tank, and collection vessels for the distillate and bottoms products. The column consisted of a rectification section containing six inches of structured packing, a stripping section containing 18 inches of structured packing, and a reboiler section containing twelve inches of 1/8 inch spherical glass beads. The reboiler was fitted with a brass block heater, and the rectification and stripping sections were wrapped with heat tape and insulated. 
     A portion of the esterified canola deodorizer distillate from example 7 was fed continuously to the column at a rate of 300 ml/hr, while the reboiler temperature was varied from 240° C. to 300° C. and the reflux ratio from 0.33 to 2.00. The pressure at the top of the column was maintained at 0.7 torr and all column heat tapes at 220° C. At each reboiler temperature and reflux ratio setting the column was allowed to come to equilibrium and samples of the distillate and bottoms streams were collected and analyzed for fatty acids and tocopherols. The results are shown in Table 14. 
     Example 14 
     The esterified sunflower deodorizer distillate from Example 5 was fed continuously at a rate of 400 ml/hr to a single-staged 6-inch wiped film still equipped with a heating mantle, feed pump, high vacuum pump, and distillate and residue receivers. The still was maintained at a pressure of 0.1 torr and a temperature of 240° C. throughout the distillation. The distillate and bottoms product were collected and analyzed for fatty acids, tocopherols, sterols, sterol esters, and glycerides. Essentially all of the fatty acid (98.6% of that in the feed) and 78% of the tocopherol was recovered to the distillate product. 
     Example 15 
      ASPEN™ run! Esterified soy deodorizer distillate containing 34% fatty acids, 8.5% tocopherols, 9% hydrocarbons, and 40% glycerides, sterol esters, and other heavy esters is fed continuously to a three-step distillative purification system as depicted in FIG. 1. The first single-staged high vacuum still is operated at 202° C. and 2.0 torr, the second single-staged high vacuum still at 235° C., 1.2 torr, and the third single-staged high vacuum still at 220° C., 0.01 torr. The distillate product of the second still is recycled to the feed of the first still in order to increase the recovery of the tocopherol. Aspen™ computer program simulated results are shown in Table 15. Overall recovery of tocopherol was 91%, with a concentration of 32% tocopherol. 
     Example 16 
     A portion of the esterified soy deodorizer distillate from Example 8 was fed continuously to the multi-staged refluxed column described in Example 14 at a rate of 300 ml/hr, top pressure of 0.7 torr, reboiler temperature of 285° C. and reflux ratio of 2.00. The distillate and bottoms product were collected and analyzed for fatty acids, tocopherols, sterols, and sterol esters. Recovery of tocopherol to the bottoms product of the first distillation step was 99.3%. Next, the tocopherol-rich bottoms product was fed continuously to the wiped film evaporator described in example 14 at a rate of 300 ml/hr, system pressure of 0.05 torr, and temperature of 235° C. The distillate and bottoms product of this second distillation were collected and analyzed for fatty acids, tocopherols, sterols, and sterol esters. Recovery of tocopherol to the distillate product of the second distillation step was 96.2%. Overall recovery of tocopherol through both distillation steps was 95.5%. Further results are given in Table 16. 
     Example 17 
     A portion of the esterified soy deodorizer distillate from Example 8 was fed continuously to the wiped film evaporator described in Example 14 at a rate of 300 ml/hr, system pressure of 0.05 torr, and temperature of 235° C. The distillate and bottoms product were collected and analyzed for fatty acids, tocopherols, sterols, and sterol esters. Recovery of tocopherol to the distillate product of the first distillation step was 73.3%. Next, the tocopherol-rich distillate product was fed continuously to the multi-staged refluxed column described in example 14 at a rate of 300 ml/hr, top pressure of 0.7 torr, reboiler temperature of 285° C. and reflux ratio of 2.00. The distillate and bottoms product of this second distillation were collected and analyzed for fatty acids, tocopherols, sterols, and sterol esters. Recovery of tocopherol to the bottoms product of the second distillation step was 98.8%. Overall recovery of tocopherol through both distillation steps was 72.4%. Further results are given in Table 17. 
     Example 18 
     A portion of the esterified canola deodorizer distillate from Example 7 was fed continuously to the wiped film evaporator described in Example 14 at a rate of 335 ml/hr, system pressure of 0.01 torr, and temperature of 235° C. The distillate and bottoms product were collected and analyzed for fatty acids, tocopherols, sterols, and sterol esters. Recovery of tocopherol to the distillate product of the first distillation step was 84%. Next, the tocopherol-rich distillate product was fed continuously to the multi-staged refluxed column described in example 14 at a rate of 346 ml/hr, top pressure of 2.5 torr, reboiler temperature of 260° C. and reflux ratio of 0.33. The distillate and bottoms product of this second distillation were collected and analyzed for fatty acids, tocopherols, sterols, and sterol esters. Recovery of tocopherol to the bottoms product of the second distillation step was 84.6%. Overall recovery of tocopherol through both distillation steps was 71.0%. Further results are given in Table 17. 
     
                                           TABLE 1__________________________________________________________________________Esterification of Soy Deodorizer DistillateTemperature:  230° C.Pressure:  1 atmCharge of oil:  500 g                          Free                      Sterol                          FattyReference Time      Tocopherols                  Sterols                      Esters                          Acids                              Monoglycerides                                      DiglyceridesNo.   (min)     Zn(OAc).sub.2           (g)    (g) (g) (g) (g)     (g)__________________________________________________________________________1     0   0.5   38.7   42.6                      43.7                          184.6                              5.5     392     30        38.3   10.4                      105.6                          142.0                              1.5     28.53     60        36.5   5.0 120.2                          127.84     90        33.8   2.2 121.0                          113.6                              &gt;0.5    155     120       31.0   0.8 124.9                          113.66     180       25.2   0.0 124.6                          99.4                              &gt;0.5    11.5__________________________________________________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________Esterification of Canola Deodorizer DistillateTemperature:  230° C.Pressure:  1 atmCharge of oil:  500 g                         Free     Butyl           Sterol                         FattyReference Time     Stannoic          Tocopherols                 Sterols                     Esters                         Acids                             Monoglycerides                                     DiglyceridesNo.   (min)     Acid (g)          (g)    (g) (g) (g) (g)     (g)__________________________________________________________________________7     0   0.25 35.5   39.2                     26.5                         241.4                             48.5    318     30       33.1   15.8                     109.0                         170.4                             3.5     14.59     60       31.7   5.7 126.2                         156.210    90       30.3   2.3 139.5                         156.2                             4.0     8.511    120      28.7   1.0 142.0                         142.012    180      25.2   1.1 144.5                         142.0                             3.5     5.5__________________________________________________________________________ 
    
     
                                           TABLE 3__________________________________________________________________________Esterification of Soy Deodorizer DistillateTemperature:  230° C.Pressure:  1 atmCharge of oil:  500 g                          Free                      Sterol                          FattyReference Time     Phosphoric           Tocopherols                  Sterols                      Esters                          Acids                              TriglyceridesNo.   (min)     acid (g)           (g)    (g) (g) (g) (g)__________________________________________________________________________13    0   1.8   38.7   42.6                      43.7                          184.614    30        36.9   6.7 105.4                          151.2                              107.515    60        34.4   1.8 119.4                          137.216    90        31.4   0.0 122.0                          128.8                              13517    120       28.6   0.4 125.8                          123.218    180       22.3   0.4 121.3                          114.8                              260__________________________________________________________________________ 
    
     
                                           TABLE 4__________________________________________________________________________Esterification of Soy Deodorizer DistillateTemperature:  170° C.Pressure:  1 atmCharge of oil:  500 g      no catalyst                    Free                Sterol                    FattyReference Time     Tocopherols            Sterols                Esters                    Acids                        Monoglycerides                                Diglycerides                                       TriglyceridesNo.   (min)     (g)    (g) (g) (g) (g)     (g)    (g)__________________________________________________________________________19    0   39.1   41.8                53.2                    184.8                        7.5     32.5   67.520    60  38.4   32.6                66.7                    170.8                        5.5     35     7921    120 37.9   25.8                76.7                    165.2                        3.5     36     9522    240 37.5   17.6                99.5                    148.4                        2.5     34.5   10023    360 37.7   12.1                113.0                    138.9                        2.5     31.5   11024    480 37.7   8.8 115.5                    133.0                        2.0     29     11525    1440     35.9   1.5 138.1                    106.4                        0.0     14.5   150__________________________________________________________________________ 
    
     
                                           TABLE 5__________________________________________________________________________Esterification of Sunflower Deodorizer DistillateTemperature:  210° C.Pressure:  1 atmCharge of oil:  500 g      no catalyst                     Free                 Sterol                     FattyReference  Time      Tocopherols             Sterols                 Esters                     Acids                         TriglyceridesNo.    (min)      (g)    (g) (g) (g) (g)__________________________________________________________________________26     0   11.5   8.8 36.1                     211.7                         2027     30  11.7   4.0 48.1                     199.1                         11628     60  11.8   2.0 53.3                     196.029     90  11.6   0.9 54.3                     189.8                         16030     120 11.6   0.6 55.1                     187.631     180 11.4   0.0 57.1    165__________________________________________________________________________ 
    
     
                                           TABLE 6__________________________________________________________________________Effect of Temperature on Esterification of Soy Deodorizer DistillatePressure:  1 atmCharge of oil:  500 g at each temperature point                 no catalyst                           Free                       Sterol                           FattyReference Temperature        Time            Tocopherols                   Sterols                       Esters                           Acids                               TriglyceridesNo.   (°C.)        (hr)            (g)    (g) (g) (g) (g)__________________________________________________________________________Starting --     --  39.2   42.5                       47.5                           196.0                               69.0Material32    170    19  36.2   2.1 140.9                           112.0                               135.033    150    19  36.9   12.0                       119.8                           109.2                               110.034    132    20  39.7   17.7                       102.1                           151.2                               80.5__________________________________________________________________________ 
    
     
                                           TABLE 7__________________________________________________________________________Esterification of Canola Deodorizer DistillatesPressure: 200 torrno catalystReference Temperature        Time  Start End   Tocopherol                                Starts                                    EndNo.   (°C.)        (hr)  Tocopherol                    Tocopherol                          Recovery                                Sterols                                    Sterols__________________________________________________________________________canola 86 210    2.0 hr hold              6.9   6.7   97.1% 12.14                                    0.97canola 92 210    2.0 hr hold              6.4   5.94  92.8% 10.98                                    0.91canola 95 210    2.0 hr hold              7.08  6.46  91.2% 11.91                                    0.84canola 98 210    2.0 hr hold              6.78  6.19  91.3% 11.43                                    0.42__________________________________________________________________________ 
    
     
                                           TABLE 8__________________________________________________________________________Esterification of Soy Deodorizer DistillatesPressure: 200 torrno catalystReference Temperature        Time  Start End   Tocopherol                                Starts                                    EndNo.   (°C.)        (hr)  Tocopherol                    Tocopherol                          Recovery                                Sterols                                    Sterols__________________________________________________________________________Brazilian 190    5 hr sample              11.1  8.66  78%   4.0 0.18soyBrazilian 210    7.5 hr              11.1  7.43  67%   4.0 0.0soy          sample__________________________________________________________________________ 
    
     
                       TABLE 9______________________________________Equilibration of Mixed Tocopherols with TriglyceridesTemperature:      230° C.Pressure:  1 atmReactor Charge:      500 g triglycerides, 5,1 g mixed soy      tocopherolsCatalyst Charge:      0.5 g dibutyl tin oxideReference               TocopherolNo.            time (hr)                   (g)______________________________________35             0        5.136             1        2.037             2        1.9______________________________________ 
    
     
                                           TABLE 10__________________________________________________________________________Effect of Feed Flowrate on Single-Staged Thin Film Distillationof Soy Deodorizer Distillate                          Fatty Acid                                TocopherolSystem     Hot Oil            Feed                Distillate                     Distillate                          Yield to                                Yield toPressure     Temperature            Rate                Rate to Feed                          Distillate                                ResidueRun No.(torr)     °C.            (kg/hr)                (kg/hr)                     Ratio                          %     %__________________________________________________________________________38   1.4  238    176 50.4 0.29 60    9439   1.4  238    146 51.7 0.35 73    9240   1.3  238    132 49.6 0.38 77    9141   1.3  238    127 49.1 0.39 81    89__________________________________________________________________________ 
    
     
                                           TABLE 11__________________________________________________________________________Effect of Temperature on Single-Staged Thin Film Distillationof Soy Deodorizer Distillate                          Fatty Acid                                TocopherolSystem     Hot Oil            Feed                Distillate                     Distillate                          Yield to                                Yield toPressure     Temperature            Rate                Rate to Feed                          Distillate                                ResidueRun No.(torr)     °C.            (kg/hr)                (kg/hr)                     Ratio                          %     %__________________________________________________________________________42   2.2  249    120 54.2 0.45 90    8343   2.8  264    117 58.0 0.495                          95    75__________________________________________________________________________ 
    
     
                                           TABLE 12__________________________________________________________________________Effect of Temperature on Short Path Distillation of Residuefrom Example 10, 11                          TocopherolSystem     Hot Oil            Feed                Distillate                     Distillate                          Yield toPressure     Temperature            Rate                Rate to Feed                          ResidueRun No.(torr)     °C.            (kg/hr)                (kg/hr)                     Ratio                          %__________________________________________________________________________44   0.050     239    30.7                16.4 0.53 9545   0.051     264    60.9                35.3 0.58 9846   0.099     279    66.0                41.2 0.62 99__________________________________________________________________________ 
    
     
                                           TABLE 13__________________________________________________________________________Effect of Temperature and Reflux on Multi-Staged Fractionationof Esterified Canola Distillate                              Fatty Acid                                    Tocopherol   Top  Reboiler   Feed Distillate                              Yield to                                    Yield to   Pressure        Temperature               Reflux                   Rate to    Distillate                                    ResidueReference No.   (torr)        (°C.)               Ratio                   (ml/hr)                        Feed Ratio                              (%)   (%)__________________________________________________________________________47      0.7  240    0.33                   300  0.366 93.9  92.448      0.7  255    0.33                   300  0.381 96.3  91.249      0.7  270    0.33                   300  0.388 97.1  87.350      0.7  240    1.0 300  0.342 92.6  99.651      0.7  255    1.0 300  0.358 94.0  99.552      0.7  270    1.0 300  0.329 95.8  99.153      0.7  285    1.0 300  0.370 100.0 99.654      0.7  300    1.0 300  0.376 100.0 99.655      0.7  255    2.0 300  0.359 95.0  99.656      0.7  270    2.0 300  0.374 96.5  99.457      0.7  285    2.0 300  0.365 97.7  99.658      0.7  300    2.03                   300  0.358 99.4  100.0__________________________________________________________________________ 
    
     
                                           TABLE 14__________________________________________________________________________Short Path Distillation of Esterified Sunflower from Example 5                    Free                Sterol                    FattyReference Weight     Tocopherols            Sterols                Esters                    Acid                        Monoglycerides                                Diglycerides                                       TriglyceridesNo.   (g) (g)    (g) (g) (g) (g)     (g)    (g)__________________________________________________________________________59    196.48     7.8    0.0 0.0 163.8                        1.0     4.52   0.7860    255.23     2.2    0.0 51.9                    2.4 0.0     1.28   122.6__________________________________________________________________________ 
    
     
                       TABLE 15______________________________________ASPEN ™ Program-Generated Material Balance forThree-Step Recycled Distillation Scheme of Figure 1                Free Fatty  TocopherolsStream   Mass (g/hr) Acids (g/hr)                            (g/hr)______________________________________Fresh Feed    764         260         65Distillate 1    280         253         4.5Bottoms 1    1760        498         305Distillate 2    1276        492         244.5Bottoms 2    484         6.0         60.5Distillate 3    182         6.0         59.0Bottoms 3    301         0.0         1.0______________________________________ 
    
     
                                           TABLE 16__________________________________________________________________________Two-Step Distillation of Esterified Soy Deodorizer Distillate                            Free                       Sterol                            Fatty            Tocopherol                  Sterol                       Ester                            AcidReference    Mass            Content                  Content                       Content                            ContentNo.   Stream (g) (%)   (%)  (%)  (%)__________________________________________________________________________esterified feed   1063.28            6.80  &lt;0.1 25.04                            23.26soydistillate61    distillate #1        348.95            0.14  &lt;0.1 0.0  69.0962    residue #1        714.33            10.48 &lt;0.1 36.45                            0.5663    distillate #2        143.63            48.01 0.64 0.20 3.8564    residue #2        545.55            0.5   &lt;0.1 53.82                            0.66__________________________________________________________________________ 
    
     
                                           TABLE 17__________________________________________________________________________Two-Step Distillation of Esterified Soy Deodorizer Distillate                            Free                       Sterol                            Fatty            Tocopherol                  Sterol                       Ester                            AcidReference    Mass            Content                  Content                       Content                            ContentNo.   Stream (g) (%)   (%)  (%)  (%)__________________________________________________________________________esterified feed   628.74            6.80  &lt;0.1 25.04                            23.26soydistillate65    distillate #1        260 12.25 &lt;0.1 0.0  53.3766    residue #1        368.74            3.15  &lt;0.1 43.95                            0.067    distillate #2        192.9     &lt;0.1 0.0  69.5268    residue #2        64.4            45.75 0.47 0.0  0.0__________________________________________________________________________ 
    
     
                                           TABLE 18__________________________________________________________________________Two-Step Distillation of Esterified Canola Oil Distillate                            Free                       Sterol                            Fatty            Tocopherol                  Sterol                       Ester                            AcidReference    Mass            Content                  Content                       Content                            ContentNo.   Stream (g) (%)   (%)  (%)  (%)__________________________________________________________________________esterified feed   780.93            5.9   0.9  --   32.8canoladistillate69    distillate #1        409.3            9.5   0.7  0.003                            62.1570    residue #1        367.78            2.0   0.2  65.9 0.071    distillate #2        307.6            1.8   &lt;0.1 0.0  79.472    residue #2        86.24            35.0  0.1  0.6  5.3__________________________________________________________________________