METHOD FOR EXTRACTING STEROL FROM SOYBEAN DEODORIZER SLUDGE

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for preparing sterols by extracting and purifying sterols from deodorizer sludge remaining after removal of tocopherols from soybean oils. More specifically, the present invention relates to a method for preparing sterols from soybean oil deodorizer sludge which ensures a high yield and purity of sterols.

Description of the Related Art Vegetable sterols are generally used as an emulsifier

(surfactant) in preparation of cosmetics or inks owing to their superior emulsion-stabilizing capacities. In particular, stigma sterol and β-sitosterol are useful as raw materials for pharmaceutical products. Such sterols can be obtained by various methods. Of the methods, separation of sterols from deodorizer sludge derived from soybean oil preparation is available.

When fats and oils contained in soybean oils are blown with steam under vacuum, a by-product material separates from the steam and condenses in traps. The by-product material is

referred to as "Soybean oil deodorizer sludge (distillate)". The soybean oil deodorizer sludge contains tocopherols, sterols, sterol esters, glycerides, free fat acids, hydrocarbons, etc. There have been suggested various processes for separating tocopherols and sterols from the soybean oil deodorization sludge.

US Patent No. 3,153,054 discloses a method for separating tocopherols and sterols from deodorizer sludge which uses liquid-liquid extraction due to extreme lability of tocopherols to alkali (i.e., basic pH conditions). In accordance with the method, a polar solvent is mixed with a non-polar solvent at an optimum ratio, to prepare an extraction solvent. Deodorizer sludge is extracted twice with the extraction solvent. The extract fraction is dissolved in other solvent and is cooled, to obtain tocopherols as a solid and sterols as a liquid, separately.

KR Patent Laid-open No. 1992-0004554 suggests a method for preparing tocopherol concentrates from soybean oil deodorization sludge. In this method, soybean oil deodorizer sludge is dissolved in a mixed solvent of N-hexane and methanol, followed by cooling, to obtain sterols. The remaining reactant is subjected to methyl esterification, and the solvent is distilled with a molecular distiller, to obtain a tocopherol concentrate. US Patent No. 3,335,154 discloses a method for

separating tocopherols and sterols. According to the method, deodorizer sludge is sequentially subjected to saponification and esterification. Acetone is added thereto to separate sterols from the composition. The solvent is distilled with a molecular distiller, to yield a tocopherol concentrate.

GB Patent No. 774,855 suggests a method for preparing a tocopherol concentrate. This method comprises the steps of saponifying vegetable oil deodorizer sludge with sodium hydroxide, acidifying the resulting composition, removing an aqueous phase to separate an oil phase from the composition, reacting the oil phase with a catalyst selected from lower monohydric alcohols (e.g., methanol), ' fatty alcohols and hydrochloric acid to esterify the fatty acids in the remaining composition, and separating sterols from the resulting composition by recrystallization.

However, there is a very low purity and yield problem associated with the above-mentioned methods for separating tocopherols and sterols from soybean oil deodorization sludge. In particular, sterols prepared by methods disclosed in US Patent No. 3,335,154 and GB Patent No. 774,855 are reacted with fatty esters, and are then converted into sterol esters, thus causing reduction in yield of final products.

SUMMARY OF THE INVENTION

Therefore, it is one object of the present invention to provide a method for preparing sterols by using deodorizer sludge remaining after removal of tocopherols from soybean oils which ensures a high yield and purity of sterols. In accordance with one aspect of the present invention, there is provided a method for preparing sterols from soybean oils deodorizer sludge, the method comprising the steps of: saponifying tocopherol-free soybean oil deodorizer sludge with a sodium hydroxide solution (saponifiation) ; neutralizing the saponificate with a sulfuric acid solution; removing an aqueous phase from the composition to obtain an oily phase; washing the oily phase two to three times with distilled water; distilling off a non-aqueous organic solvent under reduced pressure, followed by filtering (neutralization) ; and recrystallizing the resulting filtrate from methanol, followed by filtering and drying (recrystallization) , wherein the saponifying is carried out by adding 80 to 120 parts by weight of the non-aqueous organic solvent to 100 parts by weight of the tocopherol-free soybean oil deodorizer sludge, elevating a reaction temperature to 85 to 95 ^° C with stirring, and slowly adding 150 to 300 parts by weight of a 25% sodium hydroxide solution (w/w) to the reaction mixture, followed by reacting for 2 to 4 hours.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a cross-sectional view schematically showing the structure of a stirrer equipped with a baffle plate used in preparation of sterols.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail. Sludge remaining after removal of tocopherols from soybean oils, which is commercially available, is used as soybean oil deodorizer sludge for the preparation of sterols of the present invention. The soybean oil deodorizer sludge generally contains about 25 to 30% of sterols.

A method for preparing sterols of the present invention, first, involves saponification of a raw material with a sodium hydroxide solution. The saponification .allows ester sterols contained in the soybean oil deodorizer sludge to be converted into alcohol sterols.

Generally, saponification of soybean oil deodorizer sludge is conducted with water or other aqueous organic solvents. However, since sterol ester residues remaining

after removal of tocopherols from soybean oils are very oily and viscous sludge, it is difficult to be completely- saponified with water or other aqueous organic solvents, thus leading to disadvantages of very poor yield and purity. To overcome the disadvantages, a non-aqueous solvent capable of completely dissolving sterol esters is used for the saponification of the present invention. That is, saponification according to the present invention is carried out by completely dissolving sterol esters contained in the soybean oil deodorizer sludge in a non-aqueous organic solvent together with stirring, prior to addition of a sodium hydroxide solution thereto. More specifically, the saponification involves adding 80 to 120 parts by weight of the non-aqueous organic solvent to 100 parts by weight of the sludge, elevating a reaction temperature to 85-95 ^° C with stirring, and slowly adding 150 to 300 parts by weight of a 25% sodium hydroxide solution (w/w) _ thereto, followed by reacting for 2-4 hours.

The non-aqueous organic solvent may be selected from various organic solvents that can favorably dissolve sterol esters as well as be readily separated with water. Preferred is toluene or benzene. The non-aqueous organic solvent is added in an amount enough to completely dissolve sterol esters. Preferably, 80 or more parts by weight of the non- aqueous organic solvent are added, based on 100 parts by

weight of the sludge. More preferably, 80 to 120 parts by- weight of the non-aqueous organic solvent is added, based on 100 parts by weight of the sludge. The content of the solvent lower than 80 parts by weight induces saponification involving formation of a solid soup. Meanwhile, the content of the solvent exceeding 120 parts by weight induces a decrease in reaction efficiency, thereby causing a deterioration in yield and purity of final products.

After completely dissolving sterol ester contained in the sludge in the non-aqueous organic ^' solvent, when the sodium hydroxide solution is slowly added thereto, saponification is favorably carried out in a water-in-oil . system, thereby causing an increase in yield. To make the reaction more favorable, the sodium hydroxide solution is preferably added dropwise thereto for 20-40 min. When the time required for the dropwise addition is shorter than 20 min, saponification involving formation of a solid soup is occurred and a yield is disadvantageously decreased. Meanwhile, when the time required for the dropwise addition . is exceeding 40 min, productivity is disadvantageously decreased. Thus, it is preferred that the dropwise addition be conducted for the time within the range defined above.

The concentration of the sodium hydroxide solution according to the present invention is not particularly

limited. The content of the sodium hydroxide solution is not particularly limited. The sodium hydroxide solution is used in a sufficient amount for complete reaction. According to the present invention, 150 to 300 parts by weight of a 25% (w/w) sodium hydroxide solution is used.

During the saponification in a water-in-oil system with dropwise addition of the sodium hydroxide solution, phase separation may occur. To prevent occurrence of the phase separation, stirring rate is preferably in a range of 200 to 300 rpm ^' . The stirring rate within the range defined above causes an increase in contact area, and improvement of reaction efficiency, thus leading to ah increase in yield. When the stirring rate is lower than 200 rpm, a yield and purity are disadvantageously decreased. ■ Meanwhile, when the stirring rate is 300 rpm, improvement in yield cannot be expected any more. Thus, it is preferred that the stirring rate be maintained within the range defined above.

During the saponification with addition of the sodium hydroxide solution, it is preferable to use a stirrer 100 provided with a baffle plate 110 therein as shown in FIG. 1. The baffle plate 110 is generally arranged in a stirring reactor for promotion of reactions. The reaction of the present invention is promoted by employing the baffle plate. When the stirrer 100 provided with a baffle plate 110 is used,

the baffle plate 110 allows turbulence • within the reaction solution to be formed, thereby accelerating the diffusion rate of reactants.

After completion of the saponification, the resulting saponificate is neutralized with a sulfuric acid solution, and an aqueous phase is removed, thereby separating an oily phase from the composition. The oily phase is washed three to four times with distilled water. The non-aqueous organic solvent is distilled off under reduced pressure. The resulting residue was filtered.

The concentration of the sulfuric acid solution used for the neutralization is not particularly limited. In the present invention, to ensure more ^• efficient neutralization, 100 to 200 parts by weight of a 50% (w/w) sodium hydroxide solution is dropwise added for 20-40 min, followed by reacting 10 to 30 min, while the saponificate is stirred at a rate of 300 to 400 rpm and 70 to 9O ⁰ C. That i's, the neutralization involves dropwise adding and stirring, thereby enabling an increase in yield of sterols. After the neutralization, the resulting filtrate is recrystallized from methanol, followed by filtering and drying. The recrystallization of sterols with a lower monohydric alcohol (e.g., methanol) is commonly used in purification of sterols from soybean oil deodorization

distillates. In accordance with the present invention, to remove fatty constituents contained in the residue obtained from the neutralization and improve the color of products, 300 to 400 -parts ;by weight of methanol is :added, based on 100 parts by weight of the filtrate. The temperature is elevated at 65 to 80 ^° C, followed by reacting for 30 min. After the temperature was allowed to cool to room temperature, the mixture is stirred for 24 hours. The solid product is filtered and dried. The recrystallization of the present invention enables preparation of sterols with a high yield and purity from tocopherol-free and sterol ester-containing soybean oil deodorizer sludge. Particularly, the yield and purity of sterols prepared in the present invention is" higher than 70% or more, and 90% or more, respectively.

The present invention will be better understood from the following examples. These examples are not to be construed as limiting the scope of the invention.

EXAMPLES

Example 1

200 g of tocopherol-free soybean oil deodorizer sludge and 200 g of toluene were put in a stirrer equipped with a baffle plate, and the mixture was heated to a temperature of 9O ⁰ C with stirring at 300 rpm. 200 g of a 25% (w/w) sodium

hydroxide (NaOH) solution was dropwise added thereto over 30 min and was then reacted for 2.5 hours .

150 g of a 50% (w/w) sulfuric acid solution was dropwise added to the reaction mixture at 80 °C over 20 min with stirring. The mixture was further stirred for 15 min and was then stood. An aqueous phase was removed from the mixture, to obtain an oily phase. The oily phase ^' was washed three times with distilled water. The solvent was distilled off under reduced pressure at 110 ¹ C. The resulting residue was filtered.

300 parts by weight of methanol was mixed with the filtrate, and the mixture was put in a reactor. The mixture was heated to 65 ^° C and was reacted for 30 min. After the temperature was allowed to cool to room temperature, the reaction mixture was stirred for 24 hours. The solid product was filtered and washed with 200 g of methanol. The solvent was completely distilled off under reduced pressure, to prepare sterols. The yield and purity of the prepared sterols are shown in Table 1.

Example 2

Sterols were prepared in the same manner as in Example

1, except that 160 g of toluene was used. The yield and purity of the prepared sterols are shown in Table 1.

Example 3

Sterols were prepared in the same _ manner as in Example

1, except that 240 g of toluene was used. The yield and purity of the prepared sterols are shown in Table 1.

Comparative Example 1

Sterols were prepared in the same manner as in Example 1, except that 100 g of toluene was used. The yield and purity of the prepared sterols are shown in Table 1.

Comparative Example 2

Sterols were prepared in the same manner as in Example 1, except that 300 g of toluene was used. The yield and purity of the prepared sterols are shown in Table 1.

Comparative Example 3

«

Sterols were prepared in the same manner as in Example 1, except that 200 g of methanol was added to the soybean oil deodorizer sludge, instead of toluene. The ^' yield and purity of the- prepared sterols are shown in Table 1.

TABLE 1

As can be seen from the results of Table 1, sterols prepared by the saponification with toluene as a non-aqueous organic solvent added within the desired range defined in the present invention (Examples 1 to 3) exhibited considerably high yield and purity, as compared to sterols prepared by the saponification with methanol as a non-aqueous organic solvent (Comparative Example 1) . In Comparative Example 1, a solid soup was formed during reaction, thus making it difficult to maintain stirring and impossible to conduct the reaction. In Comparative Example 2, sterols exhibited considerably high yield and purity. However, improved effects corresponding to the toluene excess could not be obtained and preparation costs disadvantageously increased.

Example 4

Sterols were prepared in the same manner as in Example

1, except that the content of the NaOH solution was 150 g. The yield and purity of the prepared sterols are shown in Table 2.

Example 5

Sterols were prepared in the same _. manner as in Example

1, except that the content of the NaOH solution was 300 g. The yield and purity of the prepared sterols are shown in Table 2.

Comparative Example 4

Sterols .were prepared in the same manner as in Example

1, except that the content of the NaOH solution was 100 g. The yield and- purity of the prepared sterols are shown in Table 2.

Comparative Example 5

Sterols were prepared in the same manner as in Example

1, except that the content of the NaOH solution was 400 g. The yield and purity of the prepared sterols are shown in Table 2.

TABLE 2

As can be seen from the results .of Table 2, sterols prepared by the NaOH solution used within the desired range defined in the present invention (Examples 4 and 5) exhibited considerably high yield and purity, as compared to sterols prepared by the NaOH solution used out of the desired range (Comparative Example 4). In Comparative- Example 5, a solid soup was formed during reaction, thus making it difficult to maintain stirring and impossible to conduct the reaction.

Example ,6

Sterols were prepared in the same manner as in Example

1, except that the stirring was conducted at a rate of 200 rpm, upon addition of NaOH solution. The yield and purity of the prepared sterols are shown in Table 3.

Comparative Example 6

Sterols were prepared in the same manner as in Example

1, except that the stirring was conducted at a rate of 150 rpm, upon addition of NaOH solution. The yield and purity of the prepared sterols are shown in Table 3.

Comparative Example 7

Sterols were prepared in the same manner as in Example

1, except that the stirring was conducted at a rate of 350 rpm, upon addition of NaOH solution. The yield and purity of the prepared sterols are shown in Table 3..

TABLE 3

As can be seen from the results of Table 3, sterols prepared by stirring at a rate within the desired range defined in the present invention (Example 6) exhibited a high purity, as compared to sterols prepared by stirring at a low rate (Comparative Example 6) . Sterols prepared in Comparative Example 7 exhibited high yield and purity. However, these

sterols showed no improved effect, when compared to sterols prepared by stirring at a rate of 300 rpm (Example 1) .

Example 7 Sterols were prepared in the same manner as in Example

1, except that the NaOH solution was added over 20 min. The yield and purity of the prepared sterols are shown in Table 4.

Example 8 Sterols were prepared in the same manner as in Example

1, except that the NaOH solution was added over 40 min. The yield and purity of the prepared sterols are shown in Table 4.

Comparative Example 8 Sterols were prepared in the same manner as in Example

1, except that the NaOH solution was added over 10 min. The yield and purity of the prepared sterols are shown in Table 4.

Comparative Example 9 Sterols .were prepared in the same manner as in Example

1, except that the NaOH solution was added over 50 min. The yield and purity of the prepared sterols are shown in Table 4.

TABLE 4

As can be seen from the results of Table 4, sterols prepared by adding the NaOH solution for the time within the desired range defined in the present invention (Examples 7 and 8) exhibited considerably high yield and purity. In comparative Example 8 associated with addition of the NaOH solution for a, very short time, a solid soup was formed during reaction. Meanwhile, in comparative Example 9 associated with addition of the NaOH solution for a relatively long time, improved effects could not be obtained any more.

INDUSTRIAL APPLICABILITY

As apparent from the above description, the method of the present invention uses deodorizer sludge remaining after removal of tocopherols from soybean oil as a raw material.

According to the method, the soybean oils deodorizer sludge is completely dissolved in a non-aqueous organic solvent, prior

to saponification, thereby causing an increase in yield. In particular, the saponification involves ^' adding dropwise the sodium hydroxide solution over 20-40 min with stirring at a rate of 200 to 300 rpra in a stirrer provided with a baffle. Accordingly, there is provided a method for preparing sterols from soybean oil deodorizer sludge which maximizes a yield and purity.