WO1993023508A1

WO1993023508A1 - The refining of oils

Info

Publication number: WO1993023508A1
Application number: PCT/GB1993/001044
Authority: WO
Inventors: David Brian Shaw; Mary Elizabeth Davies; Jameel Barlas
Original assignee: Laporte Industries Limited
Priority date: 1992-05-21
Filing date: 1993-05-21
Publication date: 1993-11-25
Also published as: GB9210835D0

Abstract

A process for refining water-degummed oil comprising acid-degumming the oil, treating the acid-degummed oil with an adsorbent comprising a highly acid-treated layered clay mineral having a surface area of at least 250 m2/g, a silica content, calculated as SiO¿2?, of 80-99 % by dry weight and a bound aluminium content, calculated as Al2O3 of from 0.1 to below 3 % by dry weight, and separating the oil from the absorbent.

Description

The refininσ of oils

This invention relates to the refining of oils and more particularly to the removal of phosphorus compounds, pigments, trace metals and, in the case of alkali treated oils, soaps therefrom.

The oils with which the present invention is concerned are primarily the triglyceride oils of vegetable origin such as sunflower seed oil, soya bean oil, coconut oil, cottonseed oil, groundnut oil, rapeseed oil, canola oil and the like although oils of animal or fish origin are not excluded from the scope of the invention. It is envisaged that the raw material to be operated upon by the present invention would normally be crude water or steam degummed oil, hereafter referred to merely as "water-degummed" oil, from which a proportion of the hydratable phospholipids or phoεphatides have been removed. The phosphorus content of water-degummed oils may still be as high as 200 parts per million (pp ) .

Our copending patent application No. PCT/GB92/00241 describes the use of an adsorbent material comprising a highly acid-treated layered clay mineral to reduce the levels of phosphorus compounds in oils. It was envisaged that the use of the adsorbent in question could reduce the need for alkali refining or degumming steps.

The adsorbent described in the above identified copending patent application is, more specifically, a highly acid-treated layered clay mineral, such as a 2-layer clay mineral for example kaolin, or the halloysite-endellite structure for example attapulgite or sepiolite, or three layered clay minerals for example a smectite, the acid treated clay mineral having a surface area of at least 250 m²/g, a silicon content, calculated as Siθ2 of 80% to 99% by dry weight and a bound aluminium content, calculated as AI2O3, of from 0.1% to below 3.0% by dry weight. The adsorbent also preferably has a Hedley acidity of from 0.1% to 5.0% particularly preferably from 1% to 5%, and/or a water leachable aluminium content, calculated as AI2O3, of at least 0.05% and/or a water leachable iron content, calculated as Fe2U3, of at least 0.05%.

The adsorbent described in the above-identified copending patent application may be produced by treating a suitable clay mineral with an acid having a pKa value of below 3.0 followed by washing, so as to achieve the adsorbent properties set out above. The more detailed disclosure of said PCT/GB92/00241 specification relating to the preparations and properties of the adsorbent is . incorporated herein by reference. It has now been found that the effectiveness of oil refining can be improved by treating the water degum ed oil to an acid degumming stage preceding treatment with the said highly acid-treated layered clay mineral adsorbent, particularly if the acid-degumming is carried out under controlled conditions.

. The present invention therefore provides a process for refining water degummed oil comprising acid-degumming the oil, treating the acid-degummed oil with an adsorbent comprising a highly acid-treated layered clay mineral having _a surface area of at least 250 m g, for example from 300 m^/g to 450 m^/g, a silica content, calculated as Siθ2_/ of

80% to 99% for example from at least 82% and/or up to 95% by dry weight and a bound aluminium content, calculated as AI2O3 of from 0.1% to below 3.0% for example from at least 0.2% and/or up to 1.3% by dry weight and separating the oil from the adsorbent. Preferably the oil is further treated. simultaneously or particularly preferably sequentially, in either order, with an acid-treated layered clay mineral having a silica content, calculated as Siθ2, of below 80% by dry weight, for example from 55% to 75% by dry weight. In such a treatment process the highly acid-treated layered clay mineral can give an overall performance, in terms of phosphorus and pigment removal substantially equivalent to, and in terms of soap removal from neutralised oil superior to, an amorphous precipitated silica adsorbent which last type of adsorbent has hitherto been regarded as particularly effective in oil-refining. In contrast, reference to our copending patent specification identified above, at example 8, shows that when used to treat water-degummed but not acid-degummed oil an amorphous silica adsorbent gave a considerably more efficient phosphorus removal than a highly acid-treated clay mineral.

The acid-degumming step of the present invention may be conducted using any of the acids known to react with non- hydratable phosphatides and used for this purpose, for example phosphoric acid, malic acid or, preferably, citric acid. The acid is preferably added to oil having a temperature of from 40°C to 100°C or more particularly preferably from 50°C to 95°C and this control of temperature is found to have a considerable effect on phosphorus removal pairticularly where a relatively lower quantity of the highly acid-treated adsorbent is used. It can therefore enable the quantity of the highly acid treated adsorbent to be reduced. Another important preferred feature is to use aqueous solution of the acid having a concentration of from 10% to 50% particularly preferably from 15% to 45% by weight. This control of concentration can contribute materially to lower phosphorus and chlorophyll contents in the refined oil product. The quantity of acid used, (calculated as 100% acid) is preferably from 0.05% to 1% particularly from 0.1% to 0.5% by weight of the oil. In the three step system contemplated by the invention the efficiency of phosphorus removal is somewhat adversely affected by using larger quantities of acid in the acid-degumming step than 0.5% wt, or even, to some extent, than 0.4% wt. The acid is preferably mixed with the oil for more than 5 minutes for example from 10 minutes to 30 minutes followed by removal of the aqueous and phase, for example by centrifugation.

The acid-degummed oil is preferably treated with from up to about 2% by weight of the highly acid-treated mineral. It is found however that quantities below 1% for example from 0.25% to 0.75% can be effective in the context of the present invention. The method used to achieve contact of the.oil with the mineral may be selected according to known practice for, for example, bleaching earths. The mineral may be in the form of a bed, may be carried on a support or may be mixed into the body of the oil. The temperature at which this stage is carried out is preferably at least 40°C and up to 100°C or more but particularly preferably from 50°C to 95°C and the duration of treatment is preferably at least 10 minutes, for example from 15 minutes to 40 minutes. The particle size of the highly acid-treated mineral is preferably below 53 microns and particularly preferably below 38 microns for example substantially from 5 microns to 38 microns since phosphorus removal is found to be improved by this selection of particle size for example from 20.2% removal for >53 microns, 47.1% removal for 38-53 microns and 58.7% removal for <38 microns fractions in the absence of acid degumming or any following adsorption steps.

The oil is preferably also treated with an acid-treated clay mineral having a silica content, calculated as Siθ2_r below 80% and preferably at least 55% particularly preferably at least 60% by weight. This mineral may be produced from the same range of minerals and by the same acid treatment methods as are outlined above save that the acid elay ratio may be lower and/or the duration of contact may be lower. Typically the quantity of such acid-treated mineral may be from 0.5% to 3% by weight although in the mineral may be from 0.5% to 3% by weight although in the present process a quantity no more than about 1% by weight may be effective. The temperature and duration of treatment may be selected from the same ranges as apply to the highly acid-treated mineral. Preferably this treatment is performed after the treatment with the highly acid-treated mineral.

The invention will now be more particularly described by reference to the Examples 1 to 29 of which 1 to 12, 16 to

22, 24 and 26 are according to the invention and Examples 13 to 15, 23 and 27 to 29 are comparative Examples outside the invention.

In the following Examples the highly acid-treated clay had a surface area of at least 250 m^/g, a Siθ2 content of 86.47% and an AI2O3 content of 0.77% by dry weight, and the acid-treated clay mineral having a Siθ2 content below 80% where used had a Siθ2 content of 63.33%, an AI2O3 content of

10.02%, an iron content of 4.2% and a Hedley acidity of 1.84% by dry weight. In both cases the base clay was a calcium/magnesium montmorillonite. Examples 1-6

Water-degummed soya oil containing 90 ppm phosphorus, 0.87 ppm chlorophyll and giving a Lovibond Red (5.25" cell) reading of 11.6 was treated with a 30% w/v citric acid solution at a treatment level of 0.3% (100% acid) wt by adding the acid to the oil while at ambient temperature and then heating the oil to 70°C and holding at that temperature for 15 minutes. Then the highly acid-treated mineral was introduced into various samples of the oil at various dosage levels as indicated in the following Table and the temperature was raised to 100°C and maintained at that level for 30 minutes. The oil was removed from the mineral and subjected to analysis to determine the content of chlorophyll and phosphorus and its content of carotene as indicated by the Lovibond Red (5.25" cell) test. The results are set out below:

These examples show that the phosphorus content of the oil which still stood at over 56 ppm after acid degumming could be reduced to 1 ppm or below by the use of the highly acid-treated clay. Examples 7-15

Water-degummed soya oil containing 109 ppm of phosphorus and 1.03 ppm chlorophyll was acid-degummed using citric acid of varying concentrations, but at a standard

0.3% dosage, and at various temperatures and contact times.

This was followed by a treatment with the highly acid treated layered clay mineral at 1% dosage level for 20 minutes contact time at 50°C or 70°C depending on the acid degumming temperature and then a treatment with the acid treated layered clay mineral having a Siθ2 content of less than 80% by weight at a dosage level of 1.25% at 100°C for 30 minutes. The effect of the variation in acid-degumming conditions on phosphorus and chlorophyll contents in the treated oil is summarised in the following Table.

In the following Examples a number of the conditions were varied as indicated in the following Table. The oils used were water-degummed soya oil having phosphorus contents of either 90 ppm, or 75 ppm (Examples 17-19). In every case the dosage of citric acid was 0.3% and its concentration as used was 30% w/v. The acid-degumming with citric acid was followed by successive treatments with the highly acid- treated clay and then with the less highly acid-treated clay (<80% Siθ2 wt). In Example 19 the order of addition of the two acid-activated clay minerals was reversed.

TABLE III (a) Refining Conditions

TABLE III (b) Refined Oil Properties

* = Repitition of the indicated measurements

While Example 13 gave a good refining performance using a total mineral dosage of 2% the addition of the citric acid to oil already at elevated temperature, as in Example 17 enabled an even better refining performance to be obtained despite the use of a reduced mineral dosage. This preferred feature is clearly of some considerable importance to the efficient operation of the invention. Example 20

Soya bean oils having initial soap contents of 515 ppm, 255 ppm and 73 ppm which had been water- and acid-degummed and neutralised under standard conditions were treated with the highly acid treated clay mineral/acid treated clay mineral combination of this invention in dosages of 0.15/0.3% respectively. It was found that as the initial soap contents decreased the efficiency of soap removal increased.

TABLE IV % Soap Removed Ex No. Soap Content ppm 515 255 73

% soap removed 20 Invention 19.7% 40.7% 100%

Examples 21-23

Water-degummed soya bean oil was treated, without acid- degumming, and containing 104 ppm phosphorus and 1.06 ppm chlorophyll was treated at a level of 1.5% with various adsorbents to determine their relative efficacy in removing these materials. The results are set out in the following Table. TABLE V Ex No Adsorbent % P removed % chlorophyll removed

21 A 45.2 62.3

22 B 12.5 96.2 23 C 7.7 17.0

Adsorbent A was the highly acid-treated layered montmorillonite clay mineral, B was the acid-treated layered montmorillonite clay mineral containing less than 80% wt of S1O2, C was a layered montmorillonite clay mineral which had not been acid-treated and was in the Ca/Mg form. The results show the unique properties of the highly acid- treated clay mineral in relation to a combination of phosphorus and chlorophyll impurities.

Claims

CLAIMS :

1. A process for refining water-degummed oil comprising acid-degumming the oil, treating the acid-degummed oil with an adsorbent comprising a highly acid-treated layered clay mineral having a surface area of at least 250 m²/g, a silica content, calculated as Si0₂, of 80-99% by dry weight and a bound aluminium content, calculated as A1₂0₃ of from 0.1 to below 3% by dry weight, and separating the oil from the adsorbent.

2. A process as claimed in Claim 1 wherein the layered clay mineral is a kaolinite, attapulgite, sepiolite or smectite.

3. A process as claimed in Claim 1 or Claim 2 wherein the acid treatment is conducted to give a bound aluminium content, calculated as A1₂0₃ of at least 0.2% by dry weight.

4. A process as claimed in any one of the preceding Claims wherein the adsorbent has a Hedley acidity of from 0.1 to 5.0%.

5. A process as claimed in any one of the preceding Claims wherein the adsorbent additionally contains at least 0.05% of water leachable aluminium calculated as A1₂0₃ and/or of water leachable iron calculated as Fe₂0₃, by dry weight.

6. A process as claimed in any one of the preceding Claims wherein the adsorbent has a particle size of from

5 to 38 microns.

7. A process as claimed in any one of the preceding Claims wherein the oil is further treated simultaneously, sequentially or previously, with an acid-treated layered clay mineral having a silica content, calculated as Si0₂, of below 80% by dry weight.

8. A process as claimed in any one of the preceding Claims wherein the acid-degumming is carried out by adding the acid to oil having a temperature of 40°C to 100°C.

9. A process as claimed in any one of the preceding Claims wherein the acid-degumming is carried out by adding acid having a concentration of from 10% to 50% by weight.

10. A process as claimed in any one of the preceding Claims wherein the acid-degumming is carried out using from 0.05 to 1% acid (calculated as 100% acid) by weight of oil.

11. A process as claimed in any one of the preceding Claims wherein the acid-degummed oil is treated with from 0.25 to 0.75% by weight of adsorbent material.

12. A process as claimed in any one of the preceding Claims wherein the treatment of the oil with the adsorbent is carried out in oil having a temperature of 40°C to 100°C.