GB2145418A - Method of separating sterols from deodorisation distillates of oils - Google Patents

Abstract

A method of separating sterols in deodorisation distillates of fats and fatty oils by solvent-fractional crystallisation, which comprises centrifugal sedimentation and centrifugal filtration.

Description

SPECIFICATION Method of separating sterols from deodorisation distillates of oils The present invention relates to a method of separating sterols from the deodorisation distillates which are formed as by-products in the deodorisation step of a process for purifying fats and fatty oils (referred to herein as "oils").

In a conventional purification process, oils such as soybean, rape-seed, cotton-seed, safflower, sunflower, rice-bran, corn, coconut, palm and palm kernel oil are treated in a number of steps, one of which is deodorisation. In deodorisation, scum, slag, hotwell oil foots and other by-products (referred to herein as "deodorisation distillates" or merely "distillates") are formed, and which include, for instance, tocopherols, sterols, hydrocarbons, glycerides and/or free fatty acids.

The sterols may comprise from 1 to 35% by weight of the distillates. The sterols are good emulsifiers and stabilisers, and are good moisture-proofing agents for human skin. They are advantageously used as base materials for cosmetics, as raw materials for the synthesis of drugs such as steroid hormones, and as feed additives, e.g. for lobsters, eels and silkworms. The tocopherols may comprise from 0.1 to 20% by weight of the distillates. They may have utility as drugs, foods or anti-oxidants.

It is difficult to separate tocopherol condensates from the deodorisation distillates when sterols are present. It is therefore necessary to fractionate the sterols before the tocopherols can be isolated. Various methods are known, for the commercial-scale separation of sterols. One approach involves the addition of a material such as a dibasic organic acid, a metal chloride or urea. Another approach involves solvent fractional crystallisation.

In solvent fractional crystallisation, sterol crystals may be separated by ultra-centrifugation. However, ultra-centrifugation requires large-scale apparatus, and it is often difficult to treat the separated sterols satisfactorily. Further, it is necessary to use an amount of solvent much greater than, e.g. 15-30 times, the amount of the distillates, owing to the separational characteristics of sterols. The problem then arises that, since the sterols, accompanied by fatty acids, have some degree of solubility in the solvent, sterols remain in the distillates and may precipitate out in, and adversely affect, subsequent operations.

By way of example, methanol may be used as the solvent. The solubility of certain sterols in methanol is about 2%. The greater amount of solvent used, the larger the sterol content in the distillates after separation.

Sterols in the distillates, after separation, may be prevented from precipitation by adding a further solvent such as hexane, toluene or xylene. The fact that a further component is added, however, complicates solvent recovery.

According to the present invention, a method of separating sterols in deodorisation distillates of fats and fatty oils comprises solvent-fractional crystallisation, centrtifugal sedimentation and centrifugal filtration.

The method of the invention allows sterols to be obtained efficiently, while using only low amounts of solvent, and small-scale apparatus. Simple, manual operations only may be involved. The sterols which are obtained have good dehydration characteristics and can be handled easily.

The method of the invention may involve one or more centrifugal sedimentation operations, and one or more centrifugal filtration operations, in any order. One of each of the operations may give sufficient condensation and isolation of sterols. It is often preferred that a series of centrifugal sedimentation is followed by one centrifugal filtration. More than one of each operation can be more effective, e.g. to increase yields of other components of the distillates. The operations may be advantageously accompanied by others such as the washing of solids.

The accompanying drawing is a flow sheet illustrating a sequence of steps which may be conducted within the scope of the present invention.

With particular reference to the drawing, the deodorisation distillate is first mixed with a solvent. The solvent:distillate ratio is preferably from 1:1 to 1:3. Dissolution may be caused by heating. On complete dissolution, the solution is cooled to 10-20 C in order to precipitate primary sterol crystals. The solution is then passed to a sedimentation centrifuge, for centrifugal sedimentation, and the supernatent liquid is then taken off.

The residual liquid is mixed with further solvent. The solvent:liquid ratio may again be from 1:1 to 1:3. The liquid may again be dissolved in the solvent, by heating. On complete dissolution, the solution is gradually cooled to 0-5 C, in order to recrystallise sterols. If the temperature becomes too low, e.g. -5 to -10 C, fatty acids in the distillates may solidify and cause difficulty in subsequent separation.

The recrystallised solution is passed to a centrifugal filter. The solids thus separated are washed with the same solvent as was used in the centrifugal filtration. The washing solvent:solids ratio may be from 2:3 to 1:1. This washing step facilitates the recovery of oily substances.

The supernatantfrom the centrifugal sedimentation and the filtrate from the centrifugal filtration are combined with the wash liquor. Solids may be dissolved by heating. Cooling of the solution to 0-5 C recrystallises residual sterols which are then separated by centrifugal filtration.

If preferred, recrystallisation, at either stage of the illustrated process, may be achieved by hot filtration of the insolubles.

The sedimentation centrifuge as employed is preferably of the basket-type. The centrifugal effect is preferably from 1000 to 1500. The centrifugal filter as employed is also preferably of the basket-type. The centrifugal effect is preferably from 700 to 900. Low centrifugal effects facilitate handling and save labour.

The solvent used in the invention may be selected from the well-used solvents. Examples are C1 4 aliphatic alcohols such as methanol, ethanol, isopropyl alcohol and isobutyl alcohol, aliphatic carboxylic acid esters such as ethyl acetate, and aliphatic ketones such as methyl isobutyl ketone, methyl ethyl ketone and acetone.

Single solvents or solvent mixtures may be used.

The shape of the crystallites of sterols may vary, depending on the solvent used. However, homogeneous separation may be carried out irrespective of the crystal shape.

The following Examples illustrate the present invention.

Example I The steps in the flow sheet were followed, using methanol as solvent. The compositions of liquids as treated in each unit operation changed as follows.

(A) Primary Precipitation followed by Centrifugal Sedimentation Deodorization Distillates 38.2 kg (Rape-seed Oil) (including 10.28 kg of sterols) Methyl alcohol 9.93 kg Original Supernatant Residual Liquid Liquid Liquid Methyl alcohol 9.93 kg 7.15 kg 2.78 kg Oils* 27.92 22.66 5.26 Sterols 10.28 2.06 8.22 Total 48.13 31.87 16.26 * The ingredients other than sterols in the deodorization distillates are herein given the general term "Oils" (B) Recrystallization (1)followed by Centrifugal Filtration (1) Methanol used in the recrystallization 29.8 kg Original Solid Liquid Filtrate Fraction Methyl alcohol 32 58 keg 31.42 kg 1.16 kg Oils 5.26 4.51 0.75 Sterols 8.22 1.70 6.52 Total 46.06 37.63 8.43 (C) Washing Methanol used as a wash liquid 21.84 kg Original Solid Liquid Wash Liquid Fraction Methyl alcohol 23.0 kg 22.52 kg 0.48 kg Oils 0.75 0.61 0.14 Sterols 6.52 0.47 6.05 Total 30.27 23.60 6.67 (D) Recrystallization (2) followed by Centrifugal Filtration (2) Original Solid Liquid Filtrate Fraction Methyl alcohol 61.09 kg 60.83 kg 0.26 kg Oils 27.78 27.64 0.14 Sterols 4.23 0.49 3.74 Total 93.1 88.96 4.14 Adding up the above: Original Solid Liquid Filtrate Fraction Methyl alcohol 61.57 kg 60.83 kg 0.74 kg Oils 27.92 27.64 0.28 Sterols 10.28 0.49 9.79 Total 99.77 88.96 10.81 % Recovery of sterols 95.2% % Recovery of oils 99.0% Example 2 The method as in Example 1 was repeated, with the exception that isopropanol was used instead of methanol.

(A) Primary Precipitation followed by Centrifugal Sedimentation Deodorization Distillates 40.0 kg (Soybean oil) (including 8.8 kg of sterols) Isopropanol 50.9 kg Original Supernatant Residual Liquid Liquid Liquid Isopropanol 50.9 kg 46.2 kg 4.7 kg Oils 31.2 28.4 2.8 Sterols 8.8 1.3 7.5 Total 90.9 75.9 15.0 (B) Recrystallization (1)followed by Centrifugal Filtration (1) Isopropanol used in the recrystallization 50.9 kg Original Supernatant Residual Liquid Liquid Liquid Isopropanol 55.6 kg 50.4 kg 0.5 kg Oils 2.8 2.5 0.3 Sterols 7.5 1.5 6.0 Total 65.9 54.4 6.8 (C) Washing Isopropanol used as a wash liquid 12.7 kg Original Solid Liquid Wash Liquid Fraction Isopropanol 13.2kg 12.8kg 0.4kg Oils 0.3 0.25 0.05 Sterols 6.0 0.4 5.6 Total 19.5 13.45 6.05 (D) Recrystallization (2) followed byCentrifugal Filtration (2) Original Solid Liquid Filtrate Fraction Isopropanol 109.4kg 109.1 kg 0.3kg Oils 31.15 31.05 0.1 Sterols 3.2 0.4 2.8 Total 143.75 140.55 3.1 Adding up the above: Original Solid Liquid Filtrate Fraction Isopropanol 109.8 kg 109.1 kg 0.7 kg Oils 31.2 31.05 0.15 Sterols 8.8 0.4 8.25 Total 149.8 140.55 9.25 % Recovery of Sterols 95.5% % Recovery of Oils 99.5% Example 3 The method as in Example 1 was repeated with the exception that acetone was used instead of methanol.

(A) Primary Precipitation followed by Centrifugal Sedimentation Deodorization Distillates 45.0 kg (Cotton-seed oil) (including 7.8 kg of sterols) Acetone 113.8kg Original Supernatant Residual Liquid Liquid Liquid Acetone 113.8 kg 109.7 kg 4.1 kg Oils 37.2 36.2 1.0 Sterols 7.8 2.6 5.2 Total 158.8 148.6 10.3 (B) Recrystallization (1) followed by Centrifugal Filtration (1) Acetone used in the recrystallization 26.0 kg Original Supernatant Residual Liquid Liquid Liquid Acetone 30.1 kg 27.4 kg 2.7 kg Oils 1.0 0.2 0.8 Sterols 5.2 1.7 3.5 Total 36.3 29.3 7.0 (C) Washing Acetone used as a wash liquid 17.7 kg Original Solid Liquid Wash Liquid Fraction Acetone 20.4 kg 20.1 kg 0.3 kg Oils 0.8 0.7 0.1 Sterols 3.5 0.3 3.2 Total 24.7 21.1 3.6 (D) Recrystallization (2) followed by Centrifugal Filtration (2) Original Solid Liquid Filtrate Fraction Acetone 157.2 kg 154.9 kg 2.3 kg Oils 37.1 36.3 0.8 Sterols 4.6 1.5 3.1 Total 198.9 192.7 6.2 Adding up the above: Original Solid Liquid Filtrate Fraction Acetone 157.5 kg 154.9 kg 2.6 kg Oils 37.2 36.3 0.9 Sterols 7.8 1.5 6.3 Total 202.5 192.7 9.8 % Recovery of Sterols 97.6% % Recovery of Oils 80.8%

Claims (5)

1. A method of separating sterols in deodorisation distillates of fats and fatty oils by solvent-fractional crystallisation, which comprises centrifugal sedimentation and centrifugal filtration.

2. A method according to claim 1, in which the solvent is selected from C1.4 alkanols, aliphatic carboxylic acid esters, aliphatic ketones and mixtures thereof.

3. A method according to claim 1, in which the centrifugal sedimentation is conducted in a basket-type sedimentation centrifuge, at a centrifugal effect of from 1000 to 1500.

4. A method according to any preceding claim, in which the centrifugal filtration is conducted in a basket-type centrifugal filter, at a centrifugal effect of from 700 to 900.

5. A method according to claim 1, substantially as described in any of the Examples.