WO1994025551A1

WO1994025551A1 - Process for refining glyceride oil

Info

Publication number: WO1994025551A1
Application number: PCT/EP1994/000991
Authority: WO
Inventors: Anthony Nock
Original assignee: Joseph Crosfield & Sons Limited
Priority date: 1993-04-23
Filing date: 1994-03-29
Publication date: 1994-11-10
Also published as: AU6537494A

Abstract

In a process for refining glyceride oils, the oil is first acidified with a degumming acid, the resulting oil is then partially neutralized with sodium silicate, the partially neutralized oil being then contacted with acid activated clay, the solids being eventually removed from the glyceride oil.

Description

Process for Refining Glvcerlde Oil

Field of the Invention

The present invention relates to a process for refining glyceride oil in which glyceride oil is treated with acid and alkali.

Background of the Invention

Glyceride oil from vegetable or animal origin are valuable raw materials for the food industry. Oil of vegetable origin, such as soybean oil, rapeseed oil, sunflower oil, cotton seed oil and the like are normally obtained from seeds and beans by pressing and/or solvent extraction. It must be understood that refined oils of which the end use is non-edible can also be processed by the process according to the present invention.

Such glyceride oils mainly consist of triglycerides components. However, they generally contain also a significant amount of non-triglyceride components, including phosphatides (gums), waxy substances, partial glycerides, free fatty acids, colouring materials, oxidized compounds and small amounts of metals which are thought to be associated with the phosphatides. Dependant upon the intended final use of the oil, many of these impurities can have an undesired effect on the quality of the stored oil, in particular taste, taste keepability and colour. It is therefore necessary to refine crude glyceride oil, i.e. to remove phosphatides and other impurities.

In general, the first step in the refining process for glyceride oil is known as the degumming step during which water is added to the crude oil in order to hydrate the phosphatides which are subsequently removed by centrifugation. This water degummed oil is further treated with acid and/or alkali to remove the residual phosphatides and to neutralize the free fatty acids. The resulting soap is separated from the oil which is then further refined using bleaching and deodorization treatments. The lower the amount of residual phosphatides after the degumming step, the easier the subsequent refining steps. For such oils, it is possible to avoid the alkali refining step altogether, in which case the oil is only further refined by means of bleaching and steam refining.

A refining process which does not involve an alkali treatment is generally referred to as physical refining and is highly desirable in terms of simplicity and yield.

The removal of phosphatides from glyceride oils using physical process steps in addition to conventional chemical processes is disclosed in the prior art.

Such processes, referred to as modified acid refining processes, are for example disclosed in US-A-4, 629, 588, in EP-A-361,622, or in EP-A-478, 090.

All these processes require the use of amorphous silica as a specific adsorbent.

Commonly used adsorbents in oil refining are bleaching earths, Kieselguhrs and synthetic silicates. Bleaching earths comprise Fuller's earths, and acid activated clay, in particular, acid treated bentonites or montmorillonites.

It is therefore a first goal of the present invention to provide a glyceride oil refining process for the removal of impurities such as phosphatides, using physical process steps in addition to conventional chemical process, which could be performed with an alternative adsorbent to amorphous silica.

General Description of the Invention

It is a first object of the present invention to provide a process for refining glyceride oils, comprising the steps of:

i) acidifying the oil with an acid; ii) partially neutralizing the acidified oil with alkali; iii) contacting the partially neutralized oil with acid activated clay; iv) removing solids from the glyceride oil.

The starting oil may be crude oil or partially degummed oil. Examples of glyceride oils that may be refined are soybean oil, rapeseed oil, sunflower oil, safflower oil, corn oil, cotton seed oil and rice bran oil.

The acid used for acidifying the oil should be an acid which complexes metal ions resulting from the decomposition of metal containing compounds in the glyceride oil, commonly known as a degumming acid. The acid may be inorganic, such as phosphoric acid, or organic, such as citric acid.

Optimal results are obtained if during the acid treatment, the temperature is as low as possible, generally less than 60°C, in practice, the oil temperature during acidification is about 10-50°C, preferably 20-40°C. The acid should be added at high concentration and under high stirring for homogeneously dispersing the acid through the oil. The amount of acid used depends on the quality of the oil to be refined and an amount of 0,05-2%, preferably 0.15-0.5% w/w is sufficient. In practice, using citric acid 0.7% w/w of 50% w/w concentration is enough for glyceride oils comprising up to 250 g/kg phosphorus in phosphorus containing compounds.

After the acid treatment, the oil is partially neutralized with an alkali. The degree of neutralization is essential, and should be less than 90% of the acid added during the acid treatment. Preferably, the degree of neutralization is less than 80% of the added acid. In practice, optimal results are obtained if the degree of neutralization lies within the range of about 50 to about 75% of the added acid.

Generally, any alkali might be used for the partial neutralization of the acid added during the acid treatment. However optimal results are obtained if the alkali is selected from the group comprising hydroxides, such as sodium and potassium hydroxide, and further silicates, such as sodium and potassium silicates, the best results being obtained with sodium silicate.

Preferably, the alkali is added in the form of an aqueous solution. Optimal results are obtained if the alkali is added in a 10% by weight aqueous solution. During the alkali treatment the oil temperature should also be as low as possible in order to avoid redissolution of the phosphatides into the glyceride oil, and further to minimize the soap formation, generally about 300 to 800 mg/kg soap is formed. It is advantageous when the oil temperature during the acid treatment and alkali treatment are comparable. Accordingly, during the alkali treatment the oil temperature is within the range of about 5 to 60°C. After the partial neutralization of the oil with alkali, the oil is contacted with the acid activated clay. Example of acid activated clay are those commonly used for bleaching vegetable oil, animal fats and mineral oils, such as Fulmont Premiere and Fulmont AA (obtainable from Laporte absorbents - England) , Tonsil ACCFF, Tonsil Optimum and Tonsil Supreme (Obtainable from Sud-Chemie AG - Germany) . Before, during or after the addition of the acid activated clay to the partially neutralised oil, the temperature of said oil should be raised above 70°C, preferably above 80°C. In practice the temperature is in the range of about 85-95°C.

In order to ease separation, particularly if the oil is to be filtered, water is gradually removed from the mixture, under the influence of vacuum (measured as absolute pressure below 500 mbar) , after treated with the acid activated clay.

The partially neutralized oil is preferably first contacted with the acid activated clay for 10-40 minutes at a temperature of about 85-95°C using 2%wt of acid activated clay, depending on the oil quality.

The removal of water may be stopped when the water content of the oil is less than 0.3% by weight.

Thereafter, the solids, generally acid activated bleaching earth with impurities, are removed from the glyceride oil.

Optionally, the oil may be subjected to a bleaching treatment to remove colouring agents using a further quantity of bleaching earth. Intermediate removal of the first added activated clay is not necessary prior to the bleaching stage.

Definitions and Standard Methods i) oil water content

Water measurements were carried out before and after drying using a Metrohm 702 Titrino for automatic Karl Fischer titration (method similar to AOCS recommended practice Ca. 2e-55) of unfiltered samples.

ii) oil phosphorus content

Phosphorus determination was carried out on hot filtered samples by colorimetric analysis according to recommended AOCS practice Ca 12-55.

iii) Degree of neutralisation of the acid

Knowing the quantity of degumming acid which has been added it is possible to calculate the required amount of alkali which is needed to complete the neutralisation of the degumming acid. The degree of neutralisation is the percentage of the required amount of alkali which has been introduced at the end of the the partial neutralisation.

Specific Description of the Invention

The present invention will be further described with reference to the following examples.

A series of well known adsorbent have been tested on the same oil (crude rapeseed oil with a phosphorus content of 380 ppm) .

The experimental conditions were as follows Acid and sodium silicate treatment were carried out at ambient temperature, i.e 20°C.

Take 600g of oil, add 1.5% w/w of a 50%w/w solution of citric acid at ambient temperature with vigorous stirring

(1200 rpm) for 10 minutes followed by moderate stirring (100 rpm) for 20 minutes. Add 10.9% w/w of a 10%w/w (solids) solution of sodium silicate in order to achieve a neutralization of 70% of the added citric acid. The solution is then strongly stirred for 5 minutes and then moderately stirred for 10 minutes. Increase temperature to 80°C, add adsorbent and stir for 10 minutes moderately. Then dry to less than 0.25% w/w water under vacuum (350 mbar absolute pressure) . Drying time will vary depending on initial water content. For these examples the drying time was typically 120 minutes.

The results are summarized in the following Table 1,

Table 1

Adsorbent Adsorbent Water P Water P added content content content content % w/w Before Before After After (wet) Drying drying drying drying (% w/w) (ppm) (% w/w) (ppm)

Sorbsil R20 0.25 7.21 28 0.23 100

0.50 8.10 92 0.24 10

1.00 7.60 18 0.24 8

1.50 8.26 5 0.20 <5

2.00 7.50 8 0.14 <5

Fulmont 0.50 7.62 10 0.18 35 Premiere

1.00 7.41 11 0.18 11

1.50 7.66 <5 0.25 16

2.00 8.27 17 0.24 <5

Fuller' s 1.50 8.35 8 0.24 59 Earth

Kieselguhr 1.50 8.12 11 0.24 70

Mg Silicate 1.50 10.5 44 0.23 79 (1.5 ratio)

Mg Silicate 1.50 7.94 59 0.22 75 (3.3 ratio)

Sorbsil R20 is an amorphous silica obtainable from Joseph Crosfield and Sons - Warrington - England. Fulmont Premiere is an acid activated bleaching earth obtainable from Laporte Absorbents - Widnes - England.

Fuller's earth is a natural bleaching earth obtainable from Laporte Absorbents - Widnes - England.

A good quality refined oil should have typically less than 5ppm residual phosphorus. The results show that this can be achieved using about twice as much acid activated bleaching earth as amorphous silica whereas natural bleaching earth (Fuller's Earth) or diatomaceous earth (Kieselguhr) or magnesium silicate prove to be ineffective.

Claims

1. Process for refining glyceride oils, comprising the steps of:

2. Process according to claim 1 wherein, after the partial neutralisation of the acidified oil, the degree of neutralisation of the acid added during the acid treatment of the oil is below 90%.

3. Process according to claim 2 wherein, after the partial neutralisation of the acidified oil, the degree of neutralisation of the acid added during the acid treatment of the oil is between 50% and 75%.