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WO2000064923A1 - Process for the isolation of phytosterols from neutral substances using hydrocarbon and alcohol based solvent systems - Google Patents

Process for the isolation of phytosterols from neutral substances using hydrocarbon and alcohol based solvent systems Download PDF

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Publication number
WO2000064923A1
WO2000064923A1 PCT/IB2000/000541 IB0000541W WO0064923A1 WO 2000064923 A1 WO2000064923 A1 WO 2000064923A1 IB 0000541 W IB0000541 W IB 0000541W WO 0064923 A1 WO0064923 A1 WO 0064923A1
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Prior art keywords
solvent system
sterols
purification step
washing
hydrocarbon
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PCT/IB2000/000541
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French (fr)
Inventor
Antti Hamunen
Pertti Karinen
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Sterol Technologies Ltd.
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Publication date
Application filed by Sterol Technologies Ltd. filed Critical Sterol Technologies Ltd.
Priority to AU39841/00A priority Critical patent/AU3984100A/en
Publication of WO2000064923A1 publication Critical patent/WO2000064923A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
    • C11B—PRODUCING, e.g. BY PRESSING RAW MATERIALS OR BY EXTRACTION FROM WASTE MATERIALS, REFINING OR PRESERVING FATS, FATTY SUBSTANCES, e.g. LANOLIN, FATTY OILS OR WAXES; ESSENTIAL OILS; PERFUMES
    • C11B13/00—Recovery of fats, fatty oils or fatty acids from waste materials
    • C11B13/005—Recovery of fats, fatty oils or fatty acids from waste materials of residues of the fabrication of wood-cellulose (in particular tall-oil)
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07J—STEROIDS
    • C07J9/00—Normal steroids containing carbon, hydrogen, halogen or oxygen substituted in position 17 beta by a chain of more than two carbon atoms, e.g. cholane, cholestane, coprostane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/74—Recovery of fats, fatty oils, fatty acids or other fatty substances, e.g. lanolin or waxes

Definitions

  • the present invention relates to an improved method for separation of commercially important sterols from neutral substances or refined neutral substances, which have been separated from soaps.
  • Sterols useable in pharmaceuticals and foods need to be purified to quite a high degree to exclude undesired components, such as inorganic salts and soap residues existing in the neutral substances. Although usually present in low concentrations, a part of these impurities usually tend to remain in the sterol fraction, if the isolation of sterols has been performed by known straight crystallization processes, without any particular purification steps.
  • the neutral substances in most cases also contain organic impurities, which usually make direct crystallization of sterols in pure form difficult.
  • One kind of impurity is a group of compounds which typically cannot be seen in gas chromatographic analyses usually used in sterol assay.
  • Sterols have prior been crystallized from sterol containing materials, typically from neutral substances, using alcohol, ketone or hydrocarbon solvents, without or with water (U.S. 2,704,764, U.S. 2,843,610, U.S. 2,870,176, U.S. 4,420,427). None of these methods work quite satisfactorily in the most usual cases where the substance that contains sterols also contains said impurities.
  • U.S. 2,729,655 discloses a sterol purification method in which a residue obtained by distilling soybean oil soap stock, which had been acidified and hydrolyzed under pressure, was saponified by refluxing with sodium hydroxide and methanol. After further refining, the mixture was dissolved in petroleum ether and washed with water. Evaporation of the petroleum ether gave a crude product, which was further processed by dissolving in petroleum ether and treating with water. The solution was cooled, and sterol crystals were obtained. These impure crystals were recrystallized in isopropanol to yield pure crystalline sterols.
  • a stigmasterol enriched product is obtained in the following manner: a deodorizer distillate is saponified with an alkali hydroxide in the presence of a C r C 6 alkanol solvent, the saponified distillate is esterified with a strong mineral acid in the presence of a C r C 6 alkanol solvent, and the esterified distillate is crystallized from a solvent system comprising a C r C 6 alkanol, water and a non-polar hydrocarbon solvent.
  • the obtained precipitate enriched with stigmasterol is washed with a C 5 -C 10 hydrocarbon solvent.
  • U.S. 5,770,749 discloses a phytosterol purification process whereby a soap is extracted with a ketone, a water solution and a hydrocarbon, and the extraction product is dried to a creamy precipitate. This precipitate is thereafter dissolved in a lower alcohol and crystallized to produce sterol crystals. These crystals are then washed several times with cold alcohol and dried to produce the final product.
  • U.S. 5,670,669 discloses a sterol crystallization procedure whereby a mixture of two parts tocopherols and one part sterols was combined with a crystallization solvent.
  • hexane is used as the crystallization solvent, and the crystals thus obtained were recrystallized several times, twice with a hexane solvent including methanol/ water (1 : 1) ratio, at a 1 % concentration and a 4 % concentration, respectively, and twice more with a pure hexane solvent.
  • This invention relates to a method for producing in good yields high quality, high purity sterols, the method comprising preparing a hydrocarbon fraction rich in neutral substances from soaps, removing components interfering with sterol separation from the neutrals (e.g. impurities), and preferably crystallizing sterols from the purified neutral substances.
  • a method for the separation of sterols from soaps comprising (a) providing a hydrocarbon fraction rich in neutral substances,
  • step (d) optionally further purifying the solid product enriched in sterols by means of at least one of the steps: washing, crystallizing and recrystallizing, wherein the method optionally comprises one or more intermediate washing steps between any of the steps (a) through (d), and wherein at least two of the above steps (b) through (d) are carried out by using solvent systems of different polarities, the first solvent system comprising a hydrocarbon as the main component and the second, more polar solvent system comprising a lower alkanol as the main component.
  • solvent systems of different polarities the first solvent system comprising a hydrocarbon as the main component and the second, more polar solvent system comprising a lower alkanol as the main component.
  • the separated sterol product obtained by the method according to the invention contains practically pure sterol components without any interfering salts or organic impurities, which would make crystallization purification more difficult.
  • a further advantage of the process according to the invention is that in addition to the high purity, simultaneously high sterol yields are obtained.
  • the neutral substances can be obtained from soaps by known methods e.g. by distillation fractionation or extraction. Any soap of vegetable origin may be used in the method of the present invention.
  • a fraction rich in neutral substances suitable as raw material in the method according to the present invention may therefore be obtained from extracts of vegetable origin such as soaps from vegetable oils, or preferably from crude soap from the sulfate cellulose process or pitch soap obtained from tall oil.
  • the method according to the present invention is preferably suitable for neutral substances obtained from soap originated from wood pulping.
  • the neutral substances can be obtained from soaps typically by extraction. Extraction of the neutral substances from soaps can be performed, for example, by using mixtures of hydrocarbons and ketones and/or lower alcohols as extraction solvents. It is well known that the emulsions easily formed during the extraction procedure can be avoided by using ketones or lower alcohols together with hydrocarbons as the extraction solvents, see for example U.S. 3,965,085, hereby incorporated by reference. In this case the solvent recoveries will become more complicated in industrial applications.
  • the preparation of the hydrocarbon fraction rich in neutral substances is preferably performed by extracting the soap with a hydrocarbon solvent. If sole hydrocarbon is used as solvent, the extraction is preferably performed at elevated temperatures (and pressures) in order to break the emulsions otherwise easily formed.
  • the temperature is preferably at least 140°C, and more preferably between 140°C and 190°C.
  • This hydrocarbon extract containing neutral substances can be used as such or can be reduced or concentrated by partial evaporation before the first purification step.
  • Typical extraction conditions are, for example: the hydrocarbon used as extraction solvent is heptane, the solids content in the soap to be extracted is about 25-40 % , the amount of solvent used in the extraction is more than one part per one part dry soap by weight, the extraction temperature is higher than 140°C, and the pressure will be typically more than 10 bars.
  • the extraction can be performed using any known extraction method, such as batch extraction, column, mixer-settler, etc.
  • the obtained extract can be evaporated to dryness followed by dissolving the neutrals in a hydrocarbon solvent to prepare the hydrocarbon fraction rich in neutral substances.
  • Neutrals obtained by distillation fractionation processes can also be dissolved in a hydrocarbon solvent to prepare the hydrocarbon fraction rich in neutral substances.
  • the hydrocarbon solvent used for the hydrocarbon fraction is a short chain, aliphatic or cycloaliphatic hydrocarbon containing 1 to 10 carbon atoms, preferably 5 to 8 carbon atoms.
  • Preferred hydrocarbon solvents include hexane, heptane, octane, cyclohexane, methylcyclohexane and mixtures thereof.
  • the first solvent system which in this specification is also referred to as the "nonpolar solvent” or “low polar solvent”, comprises a hydrocarbon as the main component.
  • the hydrocarbon of the first solvent system is preferably a short chain, aliphatic or cycloaliphatic hydrocarbon containing 1 to 10 carbon atoms, preferably 5 to 8 carbon atoms, with preferred hydrocarbon solvents including hexane, heptane, octane, cyclohexane, methylcyclohexane and mixtures thereof.
  • the first solvent system can also contain a lower alkanol (preferably methanol), and optionally also water.
  • the weight ratio of hydrocarbon : lower alkanol is at least 2.3 : 1.
  • Said second solvent system which in this specification is also referred to as the "more polar solvent” or “high polar solvent", comprises a lower alkanol as the main component.
  • the term “lower alkanol” is intended to include C r C 6 alkanol.
  • the second solvent system can also contain a hydrocarbon, and optionally also water. Preferably the weight ratio of lower alkanol : hydrocarbon is at least 1.5 : 1.
  • Said hydrocarbon solvent can be the same as the above-defined hydrocarbon solvent used in the first solvent system.
  • the lower alkanol is preferably methanol.
  • solvent systems of different polarity is intended to include two subsequent steps in the purification of sterols which are performed using the first solvent system in a first step and the second solvent system in a second step, or vice versa. Further purification steps, before said first step and/or after said second step, may naturally be included in the purification process.
  • the weight ratio of solids i.e. , neutral substances, crude sterol product or solid product enriched in sterols
  • nonpolar solvent is about 1 : 1.5- 6.5.
  • the amount of water needed varies advantageously between 0 and 1 part per 1 part of solids by weight.
  • water has a significant role in the separation of sterols from neutral substances.
  • the preferable amount of optional lower alkanol in the first solvent system is 0-0.5 parts per 1 part of solids by weight.
  • a preferred weight ratio of solids : hydrocarbon : lower alkanol : water is 1 : 1.5-5 : 0-0.5 : 0-1.
  • the weight ratio of solids : second solvent system is 1 : 5-23.
  • a preferred weight ratio of solids : lower alkanol : hydrocarbon : water is 1 : 4-20 : 1-2 : 0-1.
  • the crystallization, recrystallization and/or washing operations where solvent systems of different polarity in successive process steps are used, are performed in such a manner that in the first purification step, crude sterols are separated by a crystallization or washing process, and in the second purification step the crude sterols are further purified by a crystallization, washing or recrystallization process.
  • the first purification step is performed by using the first solvent system and the second purification step is performed by using the second solvent system.
  • a typical separation process of the crude sterol fraction comprises dissolving the neutral substances into the solvent system by heating the mixture to reflux temperature, and cooling slowly to the temperature where sterols are crystallized from the mixture in reasonable yields, usually between about 0°C and 40°C. After this, the crystallized crude sterols are separated using known separation methods, e.g. filtration or centrifugation. At this stage it is advantageous to wash this crude sterol fraction, preferably with fresh crystallization solvent.
  • the separation of the crude sterol in the first purification step can also be performed by using a washing procedure where the neutral substances are slurried into the solvent system, and the insoluble sterol fraction is separated by using known methods, e.g. decanting or centrifugation.
  • the sterol purity in the crude sterol fraction varies between 75 and 96 % depending on the separation conditions and the quality of the neutral substances.
  • the first purification step can also comprise a washing operation, where the hydrocarbon fraction is washed with hot water, e.g. above 80°C, preferably 130-190°C. In this case the high temperature water wash is followed by the second purification step and a further purification step.
  • the high temperature water wash of the neutrals should preferably be performed in a closed system at high temperature, e.g. above 130°C, and high pressure, e.g. at a pressure equal to or greater than the vapor pressure of the water at the temperature, if there is any tendency of emulsion formation during the wash.
  • the process can be performed as an extraction of neutral substances dissolved in hydrocarbon solvent with water by using any suitable known extraction technique.
  • the water wash may be done directly after a high temperature hydrocarbon extraction of soap (if this technique is applied for producing the neutral substances) and applying approximately the same conditions, i.e. temperature between about 120°C and 190°C and the pressure prevailing at that temperature.
  • the amounts of water to neutral substance (hydrocarbon) phase may vary in a broad range; e.g. weight ratios from 1:10 to 10:1 can be applied depending on the amount of impurities present. It has been shown that the water wash removes only undesired impurity components, practically not at all affecting the sterol content of the neutral substances.
  • the water wash made prior to crystallization purifications makes particularly the filtration operations much easier and also guarantees a high quality final product with a low amount of inorganic "ash" content.
  • the final purification of the crude sterol fraction according to a preferred embodiment of the invention is performed by using a crystallization process, where the crystallization solvent is more polar than in the crude fraction production (in other words, the crystallization solvent is the high polar solvent).
  • the main component in the preferred solvent system in this case is methanol.
  • a nonpolar solvent preferably the same hydrocarbon solvent used in the production of crude sterol, into the solvent system.
  • this purification crystallization solvent there may be also water present in small amounts.
  • the preferred amount of methanol is between 4 and 20 parts per part of crude sterols
  • the preferred amount of hydrocarbon solvent is from 1 to 2 parts per 1 part of crude sterols
  • the preferred amount of water between 0 and OJ parts per one part of crude sterols (although, when the total solvent amount is high, even as high as 1 part water may be tolerable).
  • An optional way to purify sterols by sequential use of solvent systems with different polarities is the use of an opposite order of the solvent systems, i.e. , the first separation of crude sterols is possible to perform by using the second solvent system, i.e. the more polar solvent (preferably a methanol and hydrocarbon mixture described above with regard to the crystallization solvent), after which the final purification can be performed by washing with the nonpolar or low polar solvent, or recrystallizing from the nonpolar or low polar solvent composition described above.
  • the second solvent system i.e. the more polar solvent (preferably a methanol and hydrocarbon mixture described above with regard to the crystallization solvent)
  • the first purification step comprises crystallization of the crude sterol product from said hydrocarbon fraction using the first solvent system, optionally followed by washing with the first solvent system
  • the second purification step comprises recrystallization from the second solvent system, optionally followed by washing with the second solvent system.
  • the first purification step comprises crystallization of the crude sterol product from said hydrocarbon fraction using the first solvent system, optionally followed by washing with the first solvent system, and the second purification step comprises washing with the second solvent system.
  • the first purification step comprises crystallization of the crude sterol product from said hydrocarbon fraction using the second solvent system, optionally followed by washing with the second solvent system, and the second purification step comprises recrystallization from the first solvent system, optionally followed by washing with the first solvent system.
  • the first purification step comprises crystallization of the crude sterol product from said hydrocarbon fraction using the second solvent system, optionally followed by washing with the second solvent system, and the second purification step comprises washing with the first solvent system.
  • the first purification step comprises washing said hydrocarbon fraction with said first solvent system
  • the second purification step comprises crystallization from the second solvent system, optionally followed by washing with the second solvent system.
  • the first purification step comprises washing said hydrocarbon fraction with said second solvent system, and the second purification step comprises crystallization from the first solvent system optionally followed by washing with the first solvent system.
  • the first purification step comprises washing said hydrocarbon fraction with hot water, i.e. having the same temperature range as disclosed above, and the second purification step comprises crystallization from the first solvent system, optionally followed by washing with the first solvent system, and the further purification step comprises recrystallization from the second solvent system, optionally followed by washing with the second solvent system.
  • the first purification step comprises washing said hydrocarbon fraction with hot water
  • the second purification step comprises crystallization from the second solvent system, optionally followed by washing with the second solvent system
  • the further purification step comprises recrystallization from the first solvent system, optionally followed by washing with the first solvent system.
  • the first purification step comprises washing said hydrocarbon fraction with hot water
  • the second purification step comprises crystallization from the first solvent system, optionally followed by washing with the first solvent system
  • the further purification step comprises washing with the second solvent system.
  • the first purification step comprises washing said hydrocarbon fraction with hot water
  • the second purification step comprises crystallization from the second solvent system, optionally followed by washing with the second solvent system
  • the further purification step comprises washing with the first solvent system
  • the unsaponifiables (from Pinus taeda based pitch soap) used in this crystallization were in a hydrocarbon solvent (a mixture of aliphatic and cycloaliphatic hydrocarbons, LI A V HO, delivered by Neste Oy).
  • the mixture of solvent and unsaponifiables was brought directly from the soap extraction, which was performed at 170°C and 18 bar pressure.
  • Solids content of the hydrocarbon phase was 11.3 % and the sterols content was 35% of the solids.
  • the hydrocarbon phase was allowed to cool slowly to 20 °C. The precipitated sterols were filtered and washed with fresh solvent.
  • a water washed hydrocarbon phase equal to the one disclosed in example 2 was evaporated to a concentration where the neutrals/LIAVHO ratio was 1 : 2.0. 0.05 parts of MeOH was added calculated on the amount of neutrals and the blend was refluxed resulting in a clear solution. After cooling to 25 °C under gentle magnetic stirring, the formed crystals were filtered and washed with crystallization solvent (LIAV:MeOH 2.0:0.05). The sterol yield was 67.3% of the sterol content in the neutrals and the purity 94 % . The product was white and the ash content was 0.08 % .
  • This example describes the situation where the water needed for the formation of sterol crystals is originated from the extraction and water wash phases during the prepartion and refining of the neutral substance.
  • the solvent composition described in this example adjusted after that, no crystal formation was observed at 25 °C end temperature.
  • the water washed hydrocarbon phase disclosed in example 2 was evaporated to the concentration neutrals/LIAVl 10 of 1 :3.0. 0.35 parts of MeOH and 1 part of water calculated on the amount of neutrals (by weight) was added, and the mixture was refluxed to yield a clear solution. After crystallization, filtration and washing with the crystallization solvent, 69% of a 93 % pure sterol blend was obtained.
  • the starting material was the hydrocarbon extract that contained unsaponifiables from Pinus radiata wood based black liquor soap skimmings extracted in the same way as in example 1.
  • the solvent was evaporated so that the neutrals:LIAV ratio was 1 :0.1.
  • the crystallization was accomplished by cooling, the crystals were filtered and washed with pure LIAVl 10.
  • the dried product was a 97.5 % pure sterol blend.
  • the sterol recovery was 63.5 % of the original sterol content in the feed.
  • the unsaponifiables (mainly from Pinus taeda wood origin) were extracted from saponified pitch using a hexane-acetone method (as described in U.S. 3 ,965 ,085 , hereby incorportated by reference) .

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Abstract

A method for separating sterols from neutral substances containing the sterols, the method comprising: a) providing a hydrocarbon fraction containing the neutral substances; b) subjecting the hydrocarbon fraction to a first purification step to obtain a crude sterol product; c) subjecting the crude sterol product to a second purification step to obtain a solid product enriched in sterols; and d) optionally subjecting the solid product enriched in sterols to a further purification step, wherein said further purification step comprises at least one of the following steps: crystallization, washing and recrystallization, wherein the method optionally comprises one or more intermediate washing steps between any of the steps (a) through (d), and wherein at least one of the steps (b) through (d) is carried out using a first solvent system comprising a hydrocarbon and at least another of the steps (b) through (d) is carried out using a second solvent system comprising a C1-C6 alkanol, wherein the second solvent system is more polar than the first solvent system.

Description

PROCESS FOR THE ISOLATION OF PHYTOSTEROLS FROM NEUTRAL SUBSTANCES USING HYDROCARBON AND ALCOHOL BASED SOLVENT SYSTEMS
This application claims priority under 35 USC § 119(e) of U.S. Provisional Application Serial No . 60/ 131 , 306 , which is hereby incorporated by reference.
Field of the Invention
The present invention relates to an improved method for separation of commercially important sterols from neutral substances or refined neutral substances, which have been separated from soaps.
Background of the Invention Sterols useable in pharmaceuticals and foods need to be purified to quite a high degree to exclude undesired components, such as inorganic salts and soap residues existing in the neutral substances. Although usually present in low concentrations, a part of these impurities usually tend to remain in the sterol fraction, if the isolation of sterols has been performed by known straight crystallization processes, without any particular purification steps. The neutral substances in most cases also contain organic impurities, which usually make direct crystallization of sterols in pure form difficult. One kind of impurity is a group of compounds which typically cannot be seen in gas chromatographic analyses usually used in sterol assay. The exact nature of these compounds is not known, but there is some evidence that this group consists of a wide molecular weight range hydrocarbon-type material. Because of its invisibility in gas chromatographic analysis, the material is often called "non-elutable compounds" or "nonelutables". Also the lighter components of the neutral substances may sometimes interfere with the crystallization of sterols. In a typical case, when the neutral substances are originated from wood pulping, this light fraction typically consists of impurities such as di- and sesquiterpene compounds, stilbenes and wax alcohols.
Sterols have prior been crystallized from sterol containing materials, typically from neutral substances, using alcohol, ketone or hydrocarbon solvents, without or with water (U.S. 2,704,764, U.S. 2,843,610, U.S. 2,870,176, U.S. 4,420,427). None of these methods work quite satisfactorily in the most usual cases where the substance that contains sterols also contains said impurities.
U.S. 2,729,655 discloses a sterol purification method in which a residue obtained by distilling soybean oil soap stock, which had been acidified and hydrolyzed under pressure, was saponified by refluxing with sodium hydroxide and methanol. After further refining, the mixture was dissolved in petroleum ether and washed with water. Evaporation of the petroleum ether gave a crude product, which was further processed by dissolving in petroleum ether and treating with water. The solution was cooled, and sterol crystals were obtained. These impure crystals were recrystallized in isopropanol to yield pure crystalline sterols.
In U.S. 5,117,016, a stigmasterol enriched product is obtained in the following manner: a deodorizer distillate is saponified with an alkali hydroxide in the presence of a CrC6 alkanol solvent, the saponified distillate is esterified with a strong mineral acid in the presence of a CrC6 alkanol solvent, and the esterified distillate is crystallized from a solvent system comprising a CrC6 alkanol, water and a non-polar hydrocarbon solvent. Optionally, the obtained precipitate enriched with stigmasterol is washed with a C5-C10 hydrocarbon solvent.
U.S. 5,770,749 discloses a phytosterol purification process whereby a soap is extracted with a ketone, a water solution and a hydrocarbon, and the extraction product is dried to a creamy precipitate. This precipitate is thereafter dissolved in a lower alcohol and crystallized to produce sterol crystals. These crystals are then washed several times with cold alcohol and dried to produce the final product. U.S. 5,670,669 discloses a sterol crystallization procedure whereby a mixture of two parts tocopherols and one part sterols was combined with a crystallization solvent. In one example, hexane is used as the crystallization solvent, and the crystals thus obtained were recrystallized several times, twice with a hexane solvent including methanol/ water (1 : 1) ratio, at a 1 % concentration and a 4 % concentration, respectively, and twice more with a pure hexane solvent.
Summary of the Invention It has now been realized that in order to remove the impurities interfering with sterol crystallization from the hydrocarbon fraction rich in neutral substances , it may be necessary to apply various processes/process combinations depending on the type of impurity to be removed. The unit operations in question connected with the present invention include washing, crystallization and/or recrystallization operations using solvent systems of different polarity in at least two successive process steps. This invention relates to a method for producing in good yields high quality, high purity sterols, the method comprising preparing a hydrocarbon fraction rich in neutral substances from soaps, removing components interfering with sterol separation from the neutrals (e.g. impurities), and preferably crystallizing sterols from the purified neutral substances. In one aspect of the invention there is provided a method for the separation of sterols from soaps comprising (a) providing a hydrocarbon fraction rich in neutral substances,
(b) subjecting said hydrocarbon fraction to a first purification step to obtain a crude sterol product,
(c) subjecting the crude sterol product to a second purification step to obtain a solid product enriched in sterols,
(d) optionally further purifying the solid product enriched in sterols by means of at least one of the steps: washing, crystallizing and recrystallizing, wherein the method optionally comprises one or more intermediate washing steps between any of the steps (a) through (d), and wherein at least two of the above steps (b) through (d) are carried out by using solvent systems of different polarities, the first solvent system comprising a hydrocarbon as the main component and the second, more polar solvent system comprising a lower alkanol as the main component.
The separated sterol product obtained by the method according to the invention contains practically pure sterol components without any interfering salts or organic impurities, which would make crystallization purification more difficult. A further advantage of the process according to the invention is that in addition to the high purity, simultaneously high sterol yields are obtained.
Description of the Preferred Embodiments The neutral substances (unsaponifiables or neutrals) can be obtained from soaps by known methods e.g. by distillation fractionation or extraction. Any soap of vegetable origin may be used in the method of the present invention. A fraction rich in neutral substances suitable as raw material in the method according to the present invention may therefore be obtained from extracts of vegetable origin such as soaps from vegetable oils, or preferably from crude soap from the sulfate cellulose process or pitch soap obtained from tall oil. The method according to the present invention is preferably suitable for neutral substances obtained from soap originated from wood pulping.
The neutral substances can be obtained from soaps typically by extraction. Extraction of the neutral substances from soaps can be performed, for example, by using mixtures of hydrocarbons and ketones and/or lower alcohols as extraction solvents. It is well known that the emulsions easily formed during the extraction procedure can be avoided by using ketones or lower alcohols together with hydrocarbons as the extraction solvents, see for example U.S. 3,965,085, hereby incorporated by reference. In this case the solvent recoveries will become more complicated in industrial applications.
The preparation of the hydrocarbon fraction rich in neutral substances is preferably performed by extracting the soap with a hydrocarbon solvent. If sole hydrocarbon is used as solvent, the extraction is preferably performed at elevated temperatures (and pressures) in order to break the emulsions otherwise easily formed. The temperature is preferably at least 140°C, and more preferably between 140°C and 190°C. This hydrocarbon extract containing neutral substances can be used as such or can be reduced or concentrated by partial evaporation before the first purification step.
Typical extraction conditions are, for example: the hydrocarbon used as extraction solvent is heptane, the solids content in the soap to be extracted is about 25-40 % , the amount of solvent used in the extraction is more than one part per one part dry soap by weight, the extraction temperature is higher than 140°C, and the pressure will be typically more than 10 bars. The extraction can be performed using any known extraction method, such as batch extraction, column, mixer-settler, etc.
If other solvents or solvent mixtures are used for the extraction of neutral substances from the soap, the obtained extract can be evaporated to dryness followed by dissolving the neutrals in a hydrocarbon solvent to prepare the hydrocarbon fraction rich in neutral substances. Neutrals obtained by distillation fractionation processes can also be dissolved in a hydrocarbon solvent to prepare the hydrocarbon fraction rich in neutral substances. Preferably the hydrocarbon solvent used for the hydrocarbon fraction is a short chain, aliphatic or cycloaliphatic hydrocarbon containing 1 to 10 carbon atoms, preferably 5 to 8 carbon atoms. Preferred hydrocarbon solvents include hexane, heptane, octane, cyclohexane, methylcyclohexane and mixtures thereof.
The first solvent system, which in this specification is also referred to as the "nonpolar solvent" or "low polar solvent", comprises a hydrocarbon as the main component. As above, the hydrocarbon of the first solvent system is preferably a short chain, aliphatic or cycloaliphatic hydrocarbon containing 1 to 10 carbon atoms, preferably 5 to 8 carbon atoms, with preferred hydrocarbon solvents including hexane, heptane, octane, cyclohexane, methylcyclohexane and mixtures thereof. The first solvent system can also contain a lower alkanol (preferably methanol), and optionally also water. Preferably the weight ratio of hydrocarbon : lower alkanol is at least 2.3 : 1. Said second solvent system, which in this specification is also referred to as the "more polar solvent" or "high polar solvent", comprises a lower alkanol as the main component. The term "lower alkanol" is intended to include CrC6 alkanol. The second solvent system can also contain a hydrocarbon, and optionally also water. Preferably the weight ratio of lower alkanol : hydrocarbon is at least 1.5 : 1. Said hydrocarbon solvent can be the same as the above-defined hydrocarbon solvent used in the first solvent system. The lower alkanol is preferably methanol. The phrase "solvent systems of different polarity" is intended to include two subsequent steps in the purification of sterols which are performed using the first solvent system in a first step and the second solvent system in a second step, or vice versa. Further purification steps, before said first step and/or after said second step, may naturally be included in the purification process.
Preferably the weight ratio of solids (i.e. , neutral substances, crude sterol product or solid product enriched in sterols) : nonpolar solvent is about 1 : 1.5- 6.5. The amount of water needed varies advantageously between 0 and 1 part per 1 part of solids by weight. However, it has been shown that water has a significant role in the separation of sterols from neutral substances. Thus, the situation where no water is added to the systems usually is possible only in cases where the neutral substances already contain some water from the previous process steps in the preparation of the neutral substances, such as from the extraction or the high temperature and pressure water wash. The preferable amount of optional lower alkanol in the first solvent system is 0-0.5 parts per 1 part of solids by weight. Thus a preferred weight ratio of solids : hydrocarbon : lower alkanol : water is 1 : 1.5-5 : 0-0.5 : 0-1. Preferably the weight ratio of solids : second solvent system is 1 : 5-23.
By using a second solvent system in which a hydrocarbon and water are also included, a preferred weight ratio of solids : lower alkanol : hydrocarbon : water is 1 : 4-20 : 1-2 : 0-1.
According to the present invention the crystallization, recrystallization and/or washing operations, where solvent systems of different polarity in successive process steps are used, are performed in such a manner that in the first purification step, crude sterols are separated by a crystallization or washing process, and in the second purification step the crude sterols are further purified by a crystallization, washing or recrystallization process. According to a preferred embodiment of the invention the first purification step is performed by using the first solvent system and the second purification step is performed by using the second solvent system. A typical separation process of the crude sterol fraction comprises dissolving the neutral substances into the solvent system by heating the mixture to reflux temperature, and cooling slowly to the temperature where sterols are crystallized from the mixture in reasonable yields, usually between about 0°C and 40°C. After this, the crystallized crude sterols are separated using known separation methods, e.g. filtration or centrifugation. At this stage it is advantageous to wash this crude sterol fraction, preferably with fresh crystallization solvent.
The separation of the crude sterol in the first purification step can also be performed by using a washing procedure where the neutral substances are slurried into the solvent system, and the insoluble sterol fraction is separated by using known methods, e.g. decanting or centrifugation. Typically, the sterol purity in the crude sterol fraction varies between 75 and 96 % depending on the separation conditions and the quality of the neutral substances. According to the invention the first purification step can also comprise a washing operation, where the hydrocarbon fraction is washed with hot water, e.g. above 80°C, preferably 130-190°C. In this case the high temperature water wash is followed by the second purification step and a further purification step.
By use of the high temperature water wash, the traces of inorganic salts and soap residues can be removed. These impurities typically exist only in low concentrations, but give the sterol product, if crystallized without removing them, an ugly gray or brownish color. The soaps present in the neutrals usually also make filtration of the crystallized sterols difficult. The high temperature water wash of the neutrals should preferably be performed in a closed system at high temperature, e.g. above 130°C, and high pressure, e.g. at a pressure equal to or greater than the vapor pressure of the water at the temperature, if there is any tendency of emulsion formation during the wash. The process can be performed as an extraction of neutral substances dissolved in hydrocarbon solvent with water by using any suitable known extraction technique. Preferably, the water wash may be done directly after a high temperature hydrocarbon extraction of soap (if this technique is applied for producing the neutral substances) and applying approximately the same conditions, i.e. temperature between about 120°C and 190°C and the pressure prevailing at that temperature. The amounts of water to neutral substance (hydrocarbon) phase may vary in a broad range; e.g. weight ratios from 1:10 to 10:1 can be applied depending on the amount of impurities present. It has been shown that the water wash removes only undesired impurity components, practically not at all affecting the sterol content of the neutral substances.
By removing salts and soap residues, the water wash made prior to crystallization purifications makes particularly the filtration operations much easier and also guarantees a high quality final product with a low amount of inorganic "ash" content.
The final purification of the crude sterol fraction according to a preferred embodiment of the invention is performed by using a crystallization process, where the crystallization solvent is more polar than in the crude fraction production (in other words, the crystallization solvent is the high polar solvent). The main component in the preferred solvent system in this case is methanol. However, to improve the solubility of the sterols into the solvent, it is advantageous to add some amounts of a nonpolar solvent, preferably the same hydrocarbon solvent used in the production of crude sterol, into the solvent system. In this purification crystallization solvent there may be also water present in small amounts. The preferred amount of methanol is between 4 and 20 parts per part of crude sterols, the preferred amount of hydrocarbon solvent is from 1 to 2 parts per 1 part of crude sterols, and the preferred amount of water between 0 and OJ parts per one part of crude sterols (although, when the total solvent amount is high, even as high as 1 part water may be tolerable).
An optional way to purify sterols by sequential use of solvent systems with different polarities is the use of an opposite order of the solvent systems, i.e. , the first separation of crude sterols is possible to perform by using the second solvent system, i.e. the more polar solvent (preferably a methanol and hydrocarbon mixture described above with regard to the crystallization solvent), after which the final purification can be performed by washing with the nonpolar or low polar solvent, or recrystallizing from the nonpolar or low polar solvent composition described above.
The following specific purification methods are preferred in the present invention:
1. The first purification step comprises crystallization of the crude sterol product from said hydrocarbon fraction using the first solvent system, optionally followed by washing with the first solvent system, and the second purification step comprises recrystallization from the second solvent system, optionally followed by washing with the second solvent system.
2. The first purification step comprises crystallization of the crude sterol product from said hydrocarbon fraction using the first solvent system, optionally followed by washing with the first solvent system, and the second purification step comprises washing with the second solvent system.
3. The first purification step comprises crystallization of the crude sterol product from said hydrocarbon fraction using the second solvent system, optionally followed by washing with the second solvent system, and the second purification step comprises recrystallization from the first solvent system, optionally followed by washing with the first solvent system.
4. The first purification step comprises crystallization of the crude sterol product from said hydrocarbon fraction using the second solvent system, optionally followed by washing with the second solvent system, and the second purification step comprises washing with the first solvent system.
5. The first purification step comprises washing said hydrocarbon fraction with said first solvent system, and the second purification step comprises crystallization from the second solvent system, optionally followed by washing with the second solvent system.
6. The first purification step comprises washing said hydrocarbon fraction with said second solvent system, and the second purification step comprises crystallization from the first solvent system optionally followed by washing with the first solvent system. 7. The first purification step comprises washing said hydrocarbon fraction with hot water, i.e. having the same temperature range as disclosed above, and the second purification step comprises crystallization from the first solvent system, optionally followed by washing with the first solvent system, and the further purification step comprises recrystallization from the second solvent system, optionally followed by washing with the second solvent system.
8. The first purification step comprises washing said hydrocarbon fraction with hot water, and the second purification step comprises crystallization from the second solvent system, optionally followed by washing with the second solvent system, and the further purification step comprises recrystallization from the first solvent system, optionally followed by washing with the first solvent system. . The first purification step comprises washing said hydrocarbon fraction with hot water, and the second purification step comprises crystallization from the first solvent system, optionally followed by washing with the first solvent system, and the further purification step comprises washing with the second solvent system.
10. The first purification step comprises washing said hydrocarbon fraction with hot water, and the second purification step comprises crystallization from the second solvent system, optionally followed by washing with the second solvent system, and the further purification step comprises washing with the first solvent system.
The following examples illustrate the invention in more detail. All the % given in the examples are calculated as weight- % .
Example 1
The unsaponifiables (from Pinus taeda based pitch soap) used in this crystallization were in a hydrocarbon solvent (a mixture of aliphatic and cycloaliphatic hydrocarbons, LI A V HO, delivered by Neste Oy). The mixture of solvent and unsaponifiables was brought directly from the soap extraction, which was performed at 170°C and 18 bar pressure. Solids content of the hydrocarbon phase was 11.3 % and the sterols content was 35% of the solids. The hydrocarbon phase was allowed to cool slowly to 20 °C. The precipitated sterols were filtered and washed with fresh solvent. When 100 g dry neutrals was used as starting material, 22.5 g of a sterol blend consisting of sitosterol, sitostanol, campesterol and campestanol and nonelutable impurities were obtained. The color of the product was light grey /brown. The ash content describing the amount of inorganic salts was 0.4% . The sterol content was 80 % . Example 2
2 1 of the hydrocarbon phase of example 1 was put into an autoclave and 1 1 water was added. The autoclave was closed and the temperature was raised to 130°C, simultaneously stirring the contents. After 5 minutes at 130°C, the stirring was stopped and the lower water phase was separated through a water cooled sampling bomb. The hydrocarbon phase was let to cool to 20°C. The crystallized material was filtered and washed with fresh hydrocarbon. The color of the resulted crystalline crude sterol was white and the ash content was 0.09% . Purity of the sterols was 82% and the yield was 23 g/100 g feed neutral substances.
The positive effect of water wash of the hydrocarbon phase rich in neutrals is shown in example 2, in comparison with example 1.
Example 3
A water washed hydrocarbon phase equal to the one disclosed in example 2 was evaporated to a concentration where the neutrals/LIAVHO ratio was 1 : 2.0. 0.05 parts of MeOH was added calculated on the amount of neutrals and the blend was refluxed resulting in a clear solution. After cooling to 25 °C under gentle magnetic stirring, the formed crystals were filtered and washed with crystallization solvent (LIAV:MeOH 2.0:0.05). The sterol yield was 67.3% of the sterol content in the neutrals and the purity 94 % . The product was white and the ash content was 0.08 % .
This example describes the situation where the water needed for the formation of sterol crystals is originated from the extraction and water wash phases during the prepartion and refining of the neutral substance. When the same experiment was done using neutral substances from which the solvent was removed by vacuum evaporation, and the solvent composition described in this example adjusted after that, no crystal formation was observed at 25 °C end temperature.
The effect of methanol as part of the crystallization solvent is shown in example 3, in comparison with example 2.
Example 4
The water washed hydrocarbon phase disclosed in example 2 was evaporated to the concentration neutrals/LIAVl 10 of 1 :3.0. 0.35 parts of MeOH and 1 part of water calculated on the amount of neutrals (by weight) was added, and the mixture was refluxed to yield a clear solution. After crystallization, filtration and washing with the crystallization solvent, 69% of a 93 % pure sterol blend was obtained.
The positive effect on the sterol yield by adding water to dried neutrals is shown in example 4, in comparation with example 3.
Example 5
10 g sterols (purity 82%) from example 2 were dissolved in a solvent consisting of 20 g LIAV110 and 90 g methanol by refluxing. The sterols were recrystallized, separated and washed with fresh recrystallization solvent. The amount of crystallized product was 6.9 g of 97% pure very white sterols, ash content 0.02% .
Example 6
The starting material was the hydrocarbon extract that contained unsaponifiables from Pinus radiata wood based black liquor soap skimmings extracted in the same way as in example 1. The solvent was evaporated so that the neutrals:LIAV ratio was 1 :0.1. 2.5 parts of methanol, calculated on the amount of neutrals, was added and the mixture was heated (reflux). The crystallization was accomplished by cooling, the crystals were filtered and washed with pure LIAVl 10. The dried product was a 97.5 % pure sterol blend. The sterol recovery was 63.5 % of the original sterol content in the feed.
Example 7
The same procedure as described in example 5 was performed. The difference in this case was that the methanol used contained 1.5 % water. The sterol purity was 95.8 % and the yield was 74.9% of the original sterol content in the hydrocarbon phase.
Example 8
The unsaponifiables (mainly from Pinus taeda wood origin) were extracted from saponified pitch using a hexane-acetone method (as described in U.S. 3 ,965 ,085 , hereby incorportated by reference) . The solvent was evaporated and the solids were dissolved by refluxing into a LIAVl 10/MeOH/ water mixture (90/7/3) in a ratio of solvent/solids = 3/1. After crystallization at 25 °C, filtration and washing with the same solvent composition (the same amount as used in the crystallization), a sterol cake was obtained. The purity of this sterol was 89% and the sterol recovery was 79% of the original sterol content in the feed (which was 35 % of the dry unsaponifiables). 10 g of the obtained crude sterols were dissolved in a solvent mixture which consisted of 20 g heptane, 90 g methanol and 1 g water by refluxing. The solution was let to cool to 20°C, crystallized sterols were filtered, washed with 50 g of a pure recrystallization solvent blend, and dried. The sterol yield was 82% of the sterol content in the crude sterol, and the purity was 98 % . Ash content (no water wash in the original neutral substances) was 0.17% .

Claims

What is claimed is:
1. A method for separating sterols from neutral substances containing the sterols, the method comprising
(a) providing a hydrocarbon fraction containing the neutral substances ; (b) subjecting the hydrocarbon fraction to a first purification step to obtain a crude sterol product;
(c) subjecting the crude sterol product to a second purification step to obtain a solid product enriched in sterols; and
(d) optionally subjecting the solid product enriched in sterols to a further purification step , wherein said further purification step comprises at least one of the following steps: crystallization, washing and recrystallization, wherein the method optionally comprises one or more intermediate washing steps between any of the steps (a) through (d), and wherein at least one of the steps (b) through (d) is carried out using a first solvent system comprising a hydrocarbon and at least another of the steps (b) through (d) is carried out using a second solvent system comprising a CrC6 alkanol, wherein the second solvent system is more polar than the first solvent system.
2. The method of claim 1 , wherein the first solvent system further comprises a CrC6 alkanol and water.
3. The method of claim 2, wherein the hydrocarbon and the CrC6 alkanol are present in a weight ratio of at least 2.3 : 1.
4. The method of claim 2, wherein the hydrocarbon, the CrC6 alkanol and the water are present in a weight ratio of about 1.5-5 : < 0.5 : < 1.
5. The method of claim 1 , wherein in the step which is carried out using the first solvent system, the neutral substances, the crude sterol product or the solid product enriched in sterols to be purified and the first solvent system are present in a weight ratio of about 1 : 1.5-6.5.
6. The method of claim 1 , wherein the second solvent system further comprises a hydrocarbon and water.
7. The method of claim 6, wherein the C,-C6 alkanol and the hydrocarbon are present in a weight ratio of at least 1.5 : 1.
8. The method of claim 6, wherein the CrC6 alkanol, the hydrocarbon and the water are present in a weight ratio of about 4-20 : 1-2 : < 1.
9. The method of claim 6, wherein in the step which is carried out using the second solvent system, the neutral substances, the crude sterol product or the solid product enriched in sterols to be purified and the second solvent system are present in a weight ratio of about 1 : 5-23.
10. The method of claim 1 , wherein the hydrocarbon fraction is provided by extracting a soap with a hydrocarbon to provide a hydrocarbon phase and a soap phase and thereafter separating the hydrocarbon phase from the soap phase.
11. The method of claim 1 , wherein the hydrocarbon fraction is provided by extracting a soap with an organic solvent or organic solvent mixture to provide an organic phase and a soap phase, thereafter separating the organic phase from the soap phase, evaporating the organic phase to dryness to obtain the neutral substances and dissolving the neutral substances in a hydrocarbon.
12. The method of claim 1 , wherein the hydrocarbon in the first solvent system is selected from the group consisting of hexane, heptane, octane, cyclohexane, methylcyclohexane and mixtures thereof.
13. The method of claim 1 , wherein the CrC6 alkanol is methanol.
14. The method of claim 1 , wherein the first purification step comprises crystallizing the crude sterol product from the hydrocarbon fraction using the first solvent system, optionally followed by washing the crude sterol product with the first solvent system, and the second purification step comprises crystallizing the solid product enriched in sterols from the second solvent system, optionally followed by washing the solid product enriched in sterols with the second solvent system.
15. The method of claim 1 , wherein the first purification step comprises crystallizing the crude sterol product from the hydrocarbon fraction using the first solvent system, optionally followed by washing the crude sterol product with the first solvent system, and the second purification step comprises washing the crude sterol product with the second solvent system.
16. The method of claim 1, wherein the first purification step comprises crystallizing the crude sterol product from the hydrocarbon fraction using the second solvent system, optionally followed by washing the crude sterol product with the second solvent system, and the second purification step comprises crystallizing the solid product enriched with sterols from the first solvent system, optionally followed by washing the solid product enriched in sterols with the first solvent system.
17. The method of claim 1, wherein the first purification step comprises ϊ crystallizing the crude sterol product from the hydrocarbon fraction using the second solvent system, optionally followed by washing the crude sterol product with the second solvent system, and the second purification step comprises washing the crude sterol product with the first solvent system.
18. The method of claim 1, wherein the first purification step comprises ) washing the hydrocarbon fraction with the first solvent system, and the second purification step comprises crystallizing the solid product enriched in sterols from the second solvent system, optionally followed by washing the solid product enriched in sterols with the second solvent system.
19. The method of claim 1, wherein the first purification step comprises washing the hydrocarbon fraction with the second solvent system, and the second purification step comprises crystallizing the solid product enriched in sterols from the first solvent system, optionally followed by washing the solid product enriched in sterols with the first solvent system.
20. The method of claim 1, wherein the first purification step comprises washing the hydrocarbon fraction with hot water, the second purification step comprises crystallizing the solid product enriched in sterols from the first solvent system, optionally followed by washing the solid product enriched in sterols with the first solvent system, and the further purification step comprises recrystallizing the solid product enriched in sterols from the second solvent system, optionally followed by washing the recrystallized product with the second solvent system.
21. The method of claim 1 , wherein the first purification step comprises washing the hydrocarbon fraction with hot water, the second purification step comprises crystallizing the solid product enriched in sterols from the second solvent system, optionally followed by washing the solid product enriched in sterols with the second solvent system, and the further purification step comprises recrystallizing the solid product enriched in sterols from the first solvent system, optionally followed by washing the recrystallized product with the first solvent system.
22. The method of claim 1, wherein the first purification step comprises washing the hydrocarbon fraction with hot water, the second purification step comprises crystallizing the solid product enriched in sterols from the first solvent system, optionally followed by washing the solid product enriched in sterols with the first solvent system, and the further purification step comprises washing the solid product enriched in sterols with the second solvent system.
23. The method of claim 1 , wherein the first purification step comprises washing the hydrocarbon fraction with hot water, the second purification step comprises crystallizing the solid product enriched in sterols from the second solvent system, optionally followed by washing the solid product enriched in sterols with the second solvent system, and the further purification step comprises washing the solid product enriched in sterols with the first solvent system.
PCT/IB2000/000541 1999-04-27 2000-04-27 Process for the isolation of phytosterols from neutral substances using hydrocarbon and alcohol based solvent systems WO2000064923A1 (en)

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