Field of the Invention

V

^' 5 The present invention relates to a process for refining glyceride oil in which glyceride oil is treated with an acid and alkali, and contacted with a amorphous silica.

Background of the Invention

10

EP-A-478090 relates to a process for the refining of glyceride oil, and in particular to a refining process in which glyceride oil is treated with an acid and an alkali in the form of an aqueous solution, and contacted with 15 amorphous silica. Optimal results are obtained if the alkali is added in a 10% by weight aqueous solution. Thereafter water is removed slowly. This operation is preferably done under vacuum.

20 Whilst this process works very well, producing refined oils with very low phosphorus levels, without the need for an aqueous/oil phase separation, the levels of reagent additions required to refine high phosphorus containing oils result in high levels of water in the oil requiring

25 excessively long drying periods prior to removal of the adsorbent by filtration. Furthermore, during the drying stage, foaming can occur resulting in vigorous drying which can lead to leaching of the contaminants from the adsorbent back into the oil.

30

There is therefore a need for a refining process for glyceride oil for the removal of impurities such as phosphatides, metals, oxidised materials and soaps resulting in the production of less effluents, such as sludges and

35 soapstock, in which the drying stage is minimized.

It has now been found that it is possible to achieve good phosphorus removal without the addition of high levels of water, thus eliminating the need for excessive water removal.

General Description of the Invention

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

i) acidifying the oil with an acid,

ii) partially neutralizing the acidified oil with solid alkali,

iii) contacting the partially neutralised oil with an adsorbent,

iv) removing solids from the glyceride oil.

The starting glyceride oil may be crude or partially degummed. Examples of glyceride oil that may be refined with the process according to the invention 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. The acid may be inorganic, 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°, 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% w/w, preferably 0.15-0.5% w/w is sufficient. In practice, using citric acid 0.7% of

50% w/w concentration is enough for glyceride oil comprising up to 250 mg/kg phosphorous in phosphorous containing compounds.

After the acid treatment the oil is partially neutralised by contact with a solid alkali. The degree of neutralisation should be less than 90% of the acid added during acid treatment. Preferably, the degree of neutralisation is less than 80% of the added acid. In practice, optimal results are obtained if the degree of neutralisation lies within the range of about 50 to about 75% of the added acid.

Generally, any alkali might be used for the partial neutralisation 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. Alternatively, base treated inorganic porous adsorbents such as those described in EP 0 507 217 Al may also be used in the partial neutralisation step.

During the alkali treatment, the oil temperature can be in the range of 5 to 95°C. Higher temperatures are generally avoided so as to eliminate the possible need for a cooling stage prior to the addition of adsorption.

After the partial neutralisation of the with alkali, the oil is contacted with an adsorbent. This adsorbent is may be an amorphous silica or a bleaching clay. The preferred

adsorbent is an amorphous silica selected from silica gels, silica hydrogels, precipitated silicas, dialytic silicas and fumed silicas. Optimum results are obtained if the amorphous silica used is a silica hydrogel. Before, during or after the addition of the adsorbent to the partially neutralised oil, the temperature should be increased to above 70°C, preferably above 80°C. If a base treated inorganic porous adsorbent, such as those described in EP 0 507 217 Al, is added during the neutralisation stage, further addition of adsorbent at this stage may not be necessary, depending on the level of contaminants in the oil.

Finally, the solids are removed from the oil by some convenient means, for example filtration. Depending on the level of water added to the oil during the acid addition, it may be necessary to dry the oil slightly if it is to be filtered. The water content of the oil prior to a filtration step should preferably be less than 0.3%wt. In most cases a drying stage will not be necessary.

Thereafter, depending on the oil quality, it may be necessary to further refine the oil. If necessary, the oil can be subjected to a bleaching treatment using a bleaching earth. In such cases, an intermediate removal of the adsorbent in the process of the present invention is not necessary and the bleaching earth may be added to the neutralised oil containing the adsorbent. Subsequently, the bleaching earth and adsorbent are removed simultaneously during a filtration stage.

Detailed Description of the Invention

The present invention will be further described in the following examples.

Control

.

300g of crude rapeseed oil, phosphorus content 23δppm, were J heated to 80°C. A l%wt(wet basis) loading of silica hydrogel 5 (obtainable under the trade name Sorbsil R20 from Joseph

Crosfield & Sons - Warrington - England) , was added and the oil stirred for 10 minutes. The filtered oil was found to contain 212ppm of residual phosphorus.

10 Example 1

A 0.75%wt loading of a 50%wt concentration citric acid solution was added to 450g of crude rapeseed oil, initial phosphorus content 238ppm, at ambient temperature. The

15 acidified oil was stirred vigorously for 10 minutes then moderately for 20 minutes. A 0.45%wt loading of sodium silicate powder (obtainable under the trade name Metso 510 from Joseph Crosfield & Sons - Warrington - England) was then added to the oil at ambient temperature with vigorous

20 stirring for 5 minutes and moderate stirring for 10 minutes. The temperature of the oil was then increased to 80°C, l%wt (wet basis) silica hydrogel (obtainable under the trade name Sorbsil R20 from Joseph Crosfield & Sons - Warrington - England)added, and the oil stirred for a further 10 minutes.

25 The filtered oil was found to contain 23ppm of residual phosphorus.

Example 2

30 Example 1 was repeated using 500g of a crude rapeseed oil

♦ with an initial phosphorus content of 225ppm, 1.5%wt of 50%wt citric acid solution, 0.89%wt of Metso 510 and 1.5%wt silica hydrogel (obtainable under the trade name Sorbsil R20

from Joseph Crosfield & Sons - Warrington - England) . The filtered oil was found to contain 8ppm of residual phosphorus.

Example 3

Example 1 was repeated using 450g of a crude rapeseed oil with an initial phosphorus content of 217ppm and 0.47%wt of Soluble C sodium silicate powder (obtainable from Joseph Crosfield & Sons - Warrington - England) . The filtered oil was found to contain 14ppm of residual phosphorus.

Example 4

Example 1 was repeated using 450g of a crude rapeseed oil with an initial phosphorus content of 249ppm and 0.69%wt of Soluble M sodium silicate powder (obtainable from Joseph Crosfield & Sons - Warrington - England) . The filtered oil was found to contain lδppm of residual phosphorus.

Metso 510, Soluble C and Soluble M sodium silicates are all obtainable from Joseph Crosfield & sons - Warrington - England and have the following general composition.

Grade Mean Wt ratio Total Solids Mean Na ₂ 0/ Si0 ₂ :Na ₂ 0 (approx) /%wt %wt

Metso 510 1.0 58 29

Soluble C 2.0 80 27

Soluble M 3.3 80 18.5

Example 5

Example 1 was repeated using 500g of a crude rapeseed oil with an initial phosphorus content of 66ppm, 0.5%wt of 50%wt citric acid solution, 0.17%wt of solid sodium hydroxide and 0.5%wt silica hydrogel (obtainable under the trade name Sorbsil R20 from Joseph Crosfield & Sons - Warrington - England) . The filtered oil was found to contain 19ppm of residual phosphorus.

Example Initial Type of Sorbsil Final %wt P/ppm Base* R20 P/ppm Phospho- loading lipid on %wt (wb) adsorbent

(db)**.

Control 238 None 1.0 212 24

1 238 Sodium 1.0 23 195 silicate

(1:1)

2 225 Sodium 1.5 8 132 silicate

(1:1)

3 217 Sodium 1.0 14 185 silicate

(2:1)

4 249 Sodium 1.0 18 210 silicate

(3.3:1)

5 66 Sodium 0.5 19 86 hydroxide

in each case sufficient base was added to neutralise 70% of the acid added.

** The phospholipid adsorption capacity of the adsorbents has been calculated as follows:

%wt Phospholipid on Solid (dry basis) = PL (ppm) * 10 ^'2 silica (db)

where PL(ppm) is the amount of phospholipid adsorbed, which is equal to 30 x the amount of phosphorus removed (delta P) in ppm, and silica (db, %wt) is the dry basis loading of silica. Therefore, equation 1 can be rewritten:

%wt Phospholipid on Solid (dry basis)=

delta P(ppm) x 30 x 10' ² silica(wb, %wt) x (100-TV) 100

where silica(wb.%wt) is wet basis loading of silica and TV is its total volatile content in %wt, which is equal to 67%wt for silica hydrogel (obtainable under the trade name Sorbsil R20 from Joseph Crosfield & Sons - Warrington -. England) .

The above examples demonstrate that the process of the present invention is capable of removing high levels of phosphorus from the oil using acceptably low loadings of adsorbent. The phospholipid adsorption capacity of silica hydrogel is greatly enhanced by the combined partial neutralisation and adsorbent treatment. The addition of solid base during the neutralisation stage eliminates the need for a lengthy drying step prior to removal of the solids by filtration. The results show that sodium silicate produces better results than other bases such as sodium hydroxide.