Process for removing metal from a metal-containing glyceride oil comprising a basic quaternary ammonium salt treatment

Abstract

The present invention relates to a process for removing metal from metal-containing glyceride oil comprising the steps of: (i) contacting a glyceride oil, comprising chromium, manganese, iron, cobalt, nickel and/or copper in a total amount of from 10 mg/kg to 10,000 mg/kg, with a liquid comprising a basic quaternary ammonium salt to form a treated glyceride oil; wherein the basic quaternary ammonium salt comprises a basic anion selected from hydroxide, alkoxide, alkylcarbonate, hydrogen carbonate, carbonate, serinate, prolinate, histidinate, threoninate, valinate, asparaginate, taurinate and lysinate; and (ii) separating the treated glyceride oil from a salt comprising the quaternary ammonium cation, providing a treated glyceride oil containing a reduced amount of metals.

Claims

1. A process for removing metal from a metal-containing glyceride oil comprising the steps of: (i) contacting a glyceride oil, comprising at least one metal from the group consisting of chromium, manganese, iron, cobalt, nickel and copper, with a liquid comprising a basic quaternary ammonium salt to form a treated glyceride oil; wherein said glyceride oil contains said metals in a total amount of from 10 mg/kg to 10,000 mg/kg, and wherein the basic quaternary ammonium salt comprises a basic anion selected from hydroxide, alkoxide, alkylcarbonate, hydrogen carbonate, carbonate, serinate, prolinate, histidinate, threoninate, valinate, asparaginate, taurinate and lysinate; and a quaternary ammonium cation; and (ii) separating the treated glyceride oil from a salt comprising the quaternary ammonium cation after contacting the glyceride oil with the quaternary ammonium salt, providing a treated glyceride oil containing a reduced amount of said metals compared to the glyceride oil contacted in step (i).

2. The process of claim 1, comprising the additional step of: (iii) subjecting the treated glyceride oil after the separation step to at least one further refining step.

3. The process of claim 2, wherein the at least one further refining step comprises a deodorisation step.

4. The process of claim 3, wherein the deodorisation step involves steam stripping conducted at a temperature of from 160 C. to 270 C.

5. The process of claim 3, wherein the deodorisation step involves steam stripping conducted at a temperature of from 160 C. to 240 C.

6. The process of claim 2, wherein the process further comprises at least one additional refining step of the glyceride oil conducted prior to the treatment with the basic quaternary ammonium salt in step (i), the at least one additional refining step being selected from bleaching and degumming.

7. The process of claim 2, wherein the at least one further refining step (iii) comprises a deodorisation step and the process does not comprise a step of degumming or bleaching.

8. The process of claim 1, wherein the total amount of said metals in the glyceride oil prior to contacting in step (i) is 50 mg/kg to 5,000 mg/kg.

9. The process of claim 1, wherein the treated glyceride oil separated in step (ii) contains said metals in a total amount which is less than 50% of the total amount of said metals in the untreated glyceride oil contacted in step (i).

10. The process of claim 1, wherein the treated glyceride oil separated in step (ii) contains said metals in a total amount which is less than 75% of the total amount of said metals in the untreated glyceride oil contacted in step (i).

11. The process of claim 1, wherein the salt separated in step (ii) comprises an anion of a free fatty acid.

12. The process of claim 1, wherein the contacting step is conducted at a temperature of less than 80 C.

13. The process of claim 1, wherein the contacting step is conducted at a temperature of from 35 to 55 C.

14. The process of claim 1, wherein the quaternary ammonium cation is selected from: [N(R.sup.a)(R.sup.b)(R.sup.c)(R.sup.d)].sup.+, wherein R.sup.a, R.sup.b, R.sup.c and R.sup.d are each independently selected from C.sub.1 to C.sub.8 alkyl, wherein one or more of R.sup.a, R.sup.b, R.sup.c or R.sup.d may optionally be substituted at carbon atoms that are not bonded to the nitrogen atom by one to three groups selected from: C.sub.1 to C.sub.4 alkoxy, C.sub.2 to C.sub.8 alkoxyalkoxy, C.sub.3 to C.sub.6 cycloalkyl, OH, SH, CO.sub.2R.sup.e, and OC(O)R.sup.e, where R.sup.e is C.sub.1 to C.sub.6 alkyl.

15. The process of claim 14, wherein R.sup.a, R.sup.b, R.sup.c and R.sup.d are each independently selected from C.sub.1 to C.sub.4 alkyl, wherein at least one of R.sup.a, R.sup.b, R.sup.c or R.sup.d is substituted each by a single OH group.

16. The process of claim 14, wherein the quaternary ammonium cation is choline: (CH.sub.3).sub.3N.sup.+CH.sub.2CH.sub.2OH.

17. The process of claim 1, wherein the basic anion is selected from alkylcarbonate, hydrogen carbonate and carbonate.

18. The process of claim 17, wherein the quaternary ammonium salt contacted in step (i) is choline bicarbonate: (CH.sub.3).sub.3N.sup.+CH.sub.2CH.sub.2OH HOCOO.sup..

19. The process of claim 1, wherein the basic anion is selected from hydroxide and alkoxide.

20. The process of claim 19, wherein the basic quaternary ammonium salt contacted in step (i) is choline hydroxide: (CH.sub.3).sub.3N.sup.+CH.sub.2CH.sub.2OH OH.sup..

21. The process of claim 1, wherein the liquid comprising the basic quaternary ammonium salt comprises a solvent and the concentration of quaternary ammonium salt in the liquid is 15 wt. % to 90 wt. %.

22. The process of claim 21, wherein the solvent is an aqueous solvent.

23. The process of claim 18, wherein the liquid comprising the basic quaternary ammonium salt comprises an aqueous solvent and wherein the concentration of quaternary ammonium salt in the liquid is 50 wt. % to 90 wt. %.

24. The process of claim 20, wherein the liquid comprising the basic quaternary ammonium salt comprises an aqueous solvent and wherein the concentration of quaternary ammonium salt in the liquid is 15 wt. % to 60 wt. %.

25. The process of claim 1, wherein the glyceride oil is a vegetable oil.

26. The process of claim 25, wherein the vegetable oil is selected from coconut oil, corn oil, cottonseed oil, groundnut oil, olive oil, palm oil, rapeseed oil, rice bran oil, safflower oil, soybean oil, sunflower oil, and mixtures thereof.

27. The process of claim 1, wherein the glyceride oil is palm oil.

28. A method for reducing the metal content of a metal-containing glyceride oil, comprising contacting a glyceride oil with a basic quaternary ammonium salt, said basic quaternary ammonium salt comprising a basic anion selected from hydroxide, alkoxide, alkylcarbonate, hydrogen carbonate, carbonate, serinate, prolinate, histidinate, threoninate, valinate, asparaginate, taurinate and lysinate; and a quaternary ammonium cation.

29. The method of claim 28, wherein the glyceride oil is a vegetable oil selected from coconut oil, corn oil, cottonseed oil, groundnut oil, olive oil, palm oil, rapeseed oil, rice bran oil, safflower oil, soybean oil, sunflower oil, and mixtures thereof.

30. The method of claim 28, wherein the glyceride oil is palm oil.

31. The method of claim 28, wherein the quaternary ammonium cation is selected from: [N(R.sup.a)(R.sup.b)(R.sup.c)(R.sup.d)].sup.+, wherein R.sup.a, R.sup.b, R.sup.c and R.sup.d are each independently selected from C.sub.1 to C.sub.8 alkyl, wherein one or more of R.sup.a, R.sup.b, R.sup.c or R.sup.d may optionally be substituted at carbon atoms that are not bonded to the nitrogen atom by one to three groups selected from: C.sub.1 to C.sub.4 alkoxy, C.sub.2 to C.sub.8 alkoxyalkoxy, C.sub.3 to C.sub.6 cycloalkyl, OH, SH, CO.sub.2R.sup.e, and OC(O)R.sup.e, where R.sup.e is C.sub.1 to C.sub.6 alkyl.

32. The method of claim 31, wherein R.sup.a, R.sup.b, R.sup.c and R.sup.d are each independently selected from C.sub.1 to C.sub.4 alkyl, wherein at least one of R.sup.a, R.sup.b, R.sup.c or R.sup.d is substituted each by a single OH group.

33. The method of claim 31, wherein the quaternary ammonium cation is choline: (CH.sub.3).sub.3N.sup.+CH.sub.2CH.sub.2OH.

34. The method of claim 28, wherein the quaternary ammonium salt is choline bicarbonate: (CH.sub.3).sub.3N.sup.+CH.sub.2CH.sub.2OH HOCOO.sup..

35. The method of claim 28, wherein the basic quaternary ammonium salt is choline hydroxide: (CH.sub.3).sub.3N.sup.+CH.sub.2CH.sub.2OH OH.sup..

Description

EXAMPLES

(1) General Method for Determination of Acid Value (Mg KOH/g of Oil) and FFA (Wt. %) Content of Palm Oil.

(2) To a beaker containing 60 ml of isopropanol was added 0.5 ml of phenolphthalein. This mixture was heated until boiling and 0.02 M potassium hydroxide in isopropanol was added until a faint pink colour persisted for approximately 10 s.

(3) To a glass vial was added 0.200 g of the palm oil sample which was subsequently dissolved in 50 ml of the above hot isopropanol solution. The resulting solution was titrated whilst stirring with 0.02 M potassium hydroxide solution using a 25 ml burette graduated in 0.1 ml to the end point of the phenolphthalein indicator i.e until the pink colour persisted for at least 30 s.

(4) The Acid Value (mg KOH/g of oil) was subsequently calculated using the formula:
56.1NV/m
where: 56.1 is the molecular weight (g/mol) of potassium hydroxide; V is the volume (ml) of potassium hydroxide solution used; N is the normality (mol/l) of the potassium hydroxide solution; and m is the mass (g) of the palm oil sample.

(5) Once the Acid Value has been determined, the FFA content may be derived. The FFA content for the purposes of the present disclosure is defined as a mass percentage while assuming the FFA to be an equal mixture of palmitic acid (molecular weight 256 g/mol) and oleic acid (molecular weight 282 g/mol), giving an average molecular weight of 269 g/mol. Oil with a FFA content of 1 wt. % contains 0.01 g of oleic/palmitic acid per 1 g of oil, which amount of oleic/palmitic acid corresponds to 3.17110.sup.5 mol. The amount of KOH required to neutralise this amount of oleic/palmitic acid (i.e. the Acid ValueAV) is calculated to be 2.086 mg of KOH/g of oil (3.17110.sup.556.1).

(6) Calculation of FFA content (wt. %) therefore has the following formula:
Wt. % FFA=Acid Value0.479
General Method for Physical Refining of Palm Oil

(7) The general method for a physical refining process involving degumming, bleaching, deodorisation using industry standard conditions are set out in Table 1 below.

(8) TABLE-US-00001 TABLE 1 Refining Stage Process Details Degumming Oil is heated to 60 C. and 0.06% (mass of acid per mass of oil) of citric acid (50% aqueous solution) is added to the heated oil drop-wise and reacted for 30 min. Mucilage is allowed to settle before the aqueous phase is separated. Desiccation Degummed oil is dried at 95 C. for 30 min at 10 kPa (100 mbar). Bleaching Oil is heated under atmospheric pressure and constant stirring to 95 C. Oil is then treated with 1% bleaching clay (Tonsil Supreme 118 FF) and stirred for 5 min (wet bleaching). Subsequently, the oil is stirred at a reduced pressure of 2 to 3 kPa (20 to 30 mbar) at 95 C. for 15 min (dry bleaching). The mixture of oil and bleaching clay is separated by vacuum filtration with a suction-filter and unbleached filter paper MN620. Deodorization Oil is placed in a flask and the apparatus evacuated to a pressure of 0.1 kPa (1 mbar) before being heated to a target temperature (260 C.) in a heating mantle. Water is introduced using a microliter pump when the oil temperature reaches 160 C. and at a rate of 1% by weight of water/h. The deodorization time starts when the target temperature is reached. After deodorization time (120 min) the oil is cooled by switching off the heating mantle and the water feed is shut down when the oil temperature reaches 160 C. When the deodorized oil cools down to 80 C., the pressure valve is opened to return the apparatus to atmospheric pressure.

(9) Where reference is made herein to the use of the refining stages according to Table 1 as part of an oil refining treatment, experiments were performed using laboratory scale equipment (for example, a three-necked flask with stirring device, temperature measurement and vacuum connection). With regard to the deodorization according to Table 1, as well as the two-stage deodorization reported in examples below, this step was carried out with equipment including Deso-pistons allowing for water addition for steam stripping, a vacuum generator, a condenser, a thermometer and a heating mantle.

(10) General Method for Determination of Metal Content of Crude and Treated Oils

(11) The metal content of the oils was determined by ICP-AES analysis for oils that had not been subjected to a refining stage as outlined in table 1 and by AAS analysis (ASU L 00.00-19/1) according to standard method DIN EN ISO 11885 for oils that had been subjected to one or more refining stages.

Example 1

Metal Removal by Quaternary Ammonium Salt Treatment of Crude Palm Oil

(12) A sample of 1 kg of crude palm oil (CPO) having a measured FFA content of 7.48 wt. % was heated to 50 C. in a thermostatically controlled water bath. The homogenized CPO was then added to a 2 l stirred tank reactor in which the reactor temperature was maintained at 50 C. by means of circulating heated oil. A stoichiometric amount of choline bicarbonate (80 wt. % in H2O supplied by Sigma-Aldrich UK) relative to the FFA content of the CPO was then introduced to the reaction vessel at a rate of 1-2 ml per minute. The mixture was stirred at 500 min-1 using a mechanical overhead stirrer for 1 h. Thereafter, the mixture was centrifuged at 4000 min-1 for 3 minutes to separate a phase comprising quaternary ammonium-FFA salts and a treated CPO phase. The separated oil phase was analysed and found to contain 0.18 wt. % FFA and 0.11 wt. % water. Metal concentration of the CPO and the treated oil phase were determined. Results are provided in Table 2 below.

(13) TABLE-US-00002 TABLE 2 FFA Water Metal content mg/kg Palm Oil wt. % wt. % Fe Ni Cu Cr CPO 7.48 0.18 3665 37 138 84 Example 1 0.18 0.11 1885 2 4 11

Example 2

Metal Removal by Quaternary Ammonium Salt Treatment of Crude Palm Oil

(14) Example 1 was repeated with a different crude palm oil (CPO) having a measured FFA content of 3.21 wt. %. The separated oil phase was analysed and found to contain 0.1 wt. % FFA and 0.08 wt. % water. Metal concentration of the CPO and the treated oil phase were determined. Results are provided in Table 3.

(15) TABLE-US-00003 TABLE 3 FFA Water Metal content mg/kg Palm Oil wt. % wt. % Fe Ni Cu Cr CPO 3.21 0.12 1885 0.9 2.1 1.4 Example 1 0.09 0.08 105 0.03 0.05 0.06

(16) The results for Examples 1 and 2 shown in Tables 2 and 3 demonstrate that the basic quaternary ammonium salt treatment according to the present invention is capable of significantly reducing the total metal concentration of the oil. Removal of metals from the oil is also consistent with the degumming effect illustrated in later examples.

(17) Iron, a pro-oxidant metal which has a significant impact on the colour of the oil after exposure to heat, for instance in the deodorization step, is one of the most prevalent metal contaminants in the CPO tested, as illustrated in Tables 2 and 3. Treatment with the quaternary basic ammonium salt removes significant quantities of iron whilst other common metal contaminants, including nickel, copper and chromium, may be reduced to sub-ppm levels.

Example 3

Conventional Physical Refining of Crude Palm Oil

(18) A sample of CPO having a measured FFA content of 3.97 wt. % was refined by a conventional physical refining process involving degumming, bleaching and deodorisation using the conditions set out in Table 1 above. Quality parameters were determined before and after refining of the oil. Results are provided in Table 4 below alongside the measuring methods used. Sensoric tests of the refined oil were also undertaken at KIN GmbH Lebensmittel Institute with a panel of four examiners judging color, taste, appearance and smell according to method BVL L 00.90-6 (published in the online database managed by Beuth-Verlag: Official Collection of Testing Methods according to 64 LFGB, 35 of the Draft Tobacco Regulation and pursuant to 28b of the Genetic Engineering Act). Examiners judge each parameter on a scale of from 1 to 5 (1/2=Not for consumption, 3=Sufficient, 4=Good, 5=Excellent) and mean and median values of the judgement are presented as final results for each parameter. Typically, for an oil sample to be considered commercially acceptable, values for each parameter are required to be either 4 or 5. Results are provided in Table 4 below.

Example 4

Quaternary Ammonium Salt Treatment of Crude Palm Oil Followed by Tailored Deodorization

(19) A sample of 4 kg of the same CPO as used in Example 3 was heated to 50 C. in a thermostatically controlled water bath before being added to a stirred tank reactor in which the reactor temperature was maintained at 50 C. by means of circulating heated oil. A stoichiometric amount of choline bicarbonate (80 wt. % in water supplied by Sigma-Aldrich UK) relative to the FFA content of the CPO was then introduced to the reaction vessel at a rate of 1-2 ml per minute. The mixture was stirred at 500 min.sup.1 using a mechanical overhead stirrer for 1 h. Thereafter, the mixture was centrifuged at 4000 min.sup.1 for 3 minutes to separate a phase comprising quaternary ammonium-FFA salts and a phase of treated palm oil. The separated oil phase was titrated and found to contain 0.05 wt. % FFA.

(20) The treated palm oil was then subjected to a two stage deodorization, the first stage at a temperature of 240 C. for 10 minutes and the second at a temperature of 180 C. for 120 minutes (lower than a conventional deodorization temperature) and both stages operating at 0.2 to 0.3 kPa (2 to 3 mbar). No degumming or bleaching steps were undertaken. Quality parameters were determined for the treated palm oil before and after deodorization. Results are provided in Table 4 below alongside the measuring methods used. Sensoric tests of the quaternary ammonium salt treated and deodorized oil were also undertaken at KIN GmbH Lebensmittel Institute as described for Example 3. Results are provided in Table 5 below.

Example 5

Quaternary Ammonium Salt Treatment of Crude Palm Oil Followed by Tailored Deodorization

(21) The two stage deodorization of example 4 was repeated, but the second deodorization stage was carried out with a temperature of 200 C. instead of 180 C.

Example 6

Quaternary Ammonium Salt Treatment of Crude Palm Oil Followed by Tailored Physical Refining

(22) A sample of the quaternary ammonium salt treated palm oil from Example 4 was subjected to degumming and bleaching steps as set out in Table 1 above followed by the two stage deodorization of example 4.

(23) TABLE-US-00004 TABLE 4 Measurement Unit Method CPO Ex. 3 Ex. 4.sup.1 Ex. 4.sup.2 Ex. 5 Ex. 6 Acid Value mg KOH/ DGF-C-V 2 8.3 0.0 0.1 0.1 0.0 0.1 g Oil (06) FFA content wt. % 3.97 0.0 0.05 0.05 0.0 0.05 Phosphorus mg/kg DIN EN 8.1 <0.5 2.1 1.3 1.6 <0.5 Value 14107 Diglyceride wt. % DGF-C-III 6.4 5.7 content 3c (10) Monoglyceride wt. % DGF-C-III 0.4 0.4 content 3c (10) Color Lovibond, 1.0 1.5 1.5 0.2 AOCS RY, 1 Chromium mg/kg 0.55 0.06 0.04 <0.02 0.18 0.35 Iron mg/kg 24.44 6.71 9.21 3.36 5.89 19.1 Cobalt mg/kg <0.02 <0.02 <0.02 <0.02 0.03 Nickel mg/kg 0.76 0.15 0.18 0.15 0.38 0.53 Copper mg/kg 0.63 0.28 0.46 <0.02 0.05 0.40 .sup.1= Quaternary ammonium salt treated oil prior to deodorization; .sup.2= Quaternary ammonium salt treated oil after deodorization.

(24) TABLE-US-00005 TABLE 5 Color Appearance Smell Taste Overall Example 3 4.8/5 4.8/5 4.3/4 4.3/4 Good to (mean/median Excellent values) Example 4 3.3/3 3.5/5 3.3/3 2.8/2.5 Sufficient (mean/median values) Example 5 3.5/3.5 3.5/3.5 2.0/2.0 3.0/3.0 Not for (mean/median consumption values) Example 6 5.0/5.0 5.0/5.0 4.5/4.5 4.8/5.0 Excellent (mean/median values)

(25) The results in Table 4 illustrate the advantages of the quaternary ammonium salt treatment of the present invention.

(26) The results for Example 4 (quaternary ammonium salt treated oil) in comparison with CPO demonstrate that the quaternary ammonium salt treatment removes a significant amount of FFA whilst having minimal impact on mono- and di-glyceride content of the oil. The results for Examples 4, 5 and 6 also demonstrate that when the quaternary ammonium salt treatment is followed by deodorization, substantially all of the FFA in the oil is removed.

(27) In Example 6 the quaternary ammonium salt treatment was followed by conventional degumming, bleaching and deodorization steps. In comparison, the conventional process of Example 3 differs by the absence of the quaternary ammonium salt treatment. Surprisingly, the phosphorus level observed for the oil after the quaternary ammonium salt treatment of Example 4 is significantly lower than that of crude palm oil (2.1 mg/kg compared to 8.1 mg/kg). This demonstrates that the quaternary ammonium salt treatment contributes to degumming of the oil. In Examples 4 and 5, the quaternary ammonium salt treatment is followed only by deodorization, without any intervening degumming or bleaching steps. Although the quaternary ammonium salt treatment alone is not as effective as a conventional degumming step when a comparison is made between the phosphorus values of the oils of Examples 3, 4 and 5 (<0.5 mg/kg, 1.3 and 1.6 mg/kg respectively), the quaternary ammonium salt treatment alone is nevertheless capable of producing a satisfactory level of degumming. A desirable level of degumming in the case of refined palm oil corresponds to a reduction in phosphorus value to 5 ppm or below. Therefore, values of 1.3 and 1.6 mg/kg are well inside this quality parameter. This demonstrates that the quaternary ammonium salt treatment is capable of replacing a degumming step. Since degumming may also be associated with metal removal, these results also support the metal-removing effect of the basic quaternary ammonium salt treatment.

(28) The results in Table 5 indicate that when the quaternary ammonium salt treatment is integrated into a physical refining process, including degumming and bleaching, yet with a lower temperature deodorization stage (Example 5) then results range from sufficient to excellent. The first higher temperature stage of the two-stage deodorization is intended to perform the majority of oil depigmentation. However, superior sensoric results were surprisingly obtained when the temperature of the second stage of the two-stage deodorization was lowered still further to 180 C. following quaternary ammonium salt treatment, degumming and bleaching (Example 6). The quaternary ammonium salt treatment of the invention thus offers the possibility of lowering deodorization temperatures to reduce the energy expenditure of a glyceride oil refining process whilst removing metal contaminants and still providing a product with adequate olfactory qualities.

(29) Where the quaternary ammonium salt treatment also effectively replaces degumming and bleaching steps, sensoric qualities of the oil may not be satisfactory unless a conventional prolonged high-temperature deodorization step is incorporated, as suggested by the results for Examples 4 and 5 in Table 5.