GB2169611A

GB2169611A - Stabilization of palm kernal oil or its alkyl esters

Info

Publication number: GB2169611A
Application number: GB08600027A
Authority: GB
Inventors: Alfred Struve; Richard Schuh; Horst Baumann; Hartwig Schutt; Harald Wallis
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 1985-01-14
Filing date: 1986-01-02
Publication date: 1986-07-16
Also published as: EP0189049A1; DE3500938C2; GB2169611B; JPH0753874B2; GB8600027D0; EP0189049B2; MY102435A; EP0189049B1; DE3673027D1; DE3500938A1; BR8600103A; JPS61163999A

Description

1 GB 2 169 611 A 1

SPECIFICATION

Stabilization of palm kernel oil and palm kernel oil fatty acid methyl esters for processing into neutralcolored reaction products This invention relates to the stabilization of palm kernel oil and palm kernel oil fatty acid alkyl esters for processing into neutral-colored reaction products.

Coconut oil and palm kernel oil are both important natural starting materials for the commercial production of oleochernical products. The chemical treatment of this natural starting material is generally preceded by conversion of the triglyceride present into the corresponding fatty acid esters with lower 10 monohydric alcohols, more especially into the corresponding methyl esters. The methyl ester or the fatty acid methyl ester mixture may be obtained by direct transesterification of the triglyceride with methanol or indirectly by splitting the triglyceride into fatty acid and glycerine and subsequently esterifying the fatty acids or fatty acid mixtures to form the alkyl esters.

Comparison of quality, as determined in particular by storage behavior, by oxidation stability, by stabi- 15 lization potential and in particular by the effect on color of reaction products of these stored starting materials, shows that coconut oil or the reaction products obtained from coconut oil show considerably better behavior than palm kernel oil and its reaction products. Coconut oil is considerably more stable to oxidation than palm kernel oil. The same applies to the methyl esters or methyl ester mixtures obtained therefrom. This can only be partly attributable to the slightly higher iodine numbers of palm kernel oil 20 compared with coconut oil. Both palm kernel oil and coconut oil contain natural antioxiclants, essentially in the form of ot-tocotrienol. Coconut oil contains distinctly more antioxidant (> 30 ppm) than palm kernel oil, cf. H. Behringer et al. in Fette, Seifen, Anstrichmittel 78 (1976) pp 228-231.

Whereas coconut oil and coconut oil fatty acid methyl ester are normally stable to autoxiclation for several months at room temperature, the same does not apply to palm kernel oil and palm kernel oil 25 fatty acid methyl ester. Applicants were able to show that palm kernel oil and palm kernel oil fatty acid methyl ester take up oxygen considerably more quickly than coconut oil and coconut oil fatty acid methyl ester. Corresponding studies have shown that palm kernel oil alone takes up 10 to 25 times more oxygen than coconut oil. In the accelerated ageing test, in which the oxygen uptake of natural fats and oils and of fat and oil derivatives is measured in a Warburg manometer as a measure of their oxidation behavior, 30 the induction time of palm kernel oils, after which a significant uptake of oxygen begins, at 80'C is of the order of 10 to 20 hours, whereas in comparative studies with coconut oil there was still no measurable uptake of oxygen after periods of 50 to 90 hours.

The effect of these differences in quality between palm kernel oil and its derivatives on the one hand and coconut oil and its derivatives on the other hand is that the respective starting materials and/or their 35 reaction products are damaged to different extents during storage, transport and/or processing, and ac cordingly, occur with considerable differences in quality.

The object of the present invention is to eliminate the undesirable instability of the palm kernel oil and reaction products thereof. However, the basically obvious approach of making up the deficit of natural antioxidants; in palm kernel oil by adding known antioxidants led to the surprising discovery that satisfac- 40 tory reaction products cannot readily be obtained in that way.

Important measures of the suitability of a natural fat as a raw material are its color values as measured on soap solution - obtained by alkaline saponification of the corresponding fatty acid methyl esters or fatty acid methyl ester mixtures - or on fatty acid diethanolamides - obtained by amidating splitting of the fatty acid methyl ester starting materials. These color values are crucial parameters for the suitability 45 both of the originally used oils and of the methyl esters produced therefrom.

More specifically, therefore, the object of the present invention is to stabilize palm kernel oil and, more especially, alkyl esters of palm kernel oil fatty acids, particularly palm kernel oil fatty acid methyl ester, against harmful effects during storage in the presence of air in such a way that, when subsequently re acted, the stored oleochernical starting materials give reaction products of such color neutrality that no 50 undesirable deteriorations in color have to be accepted. In the context of the invention, the expression color neutrality' is understood to mean color stability during the individual reaction steps which substan tially corresponds to the known and accepted color stability of coconut oil of normal quality and its reac tion products. Accordingly, the invention seeks to make palm kernel oil, but especially the palm kernel oil fatty acid alkyl esters obtainable therefrom, comparable in handling and processing with the correspond- 55 ing materials based on the coconut oil.

The tests conducted with a view to accomplishing this objective have surprisingly shown that the choice of two specific oxidation stabilizers known per se guarantees the desired result. The use of other oxidation stabilizers, which may be regarded as entirely equivalent on the strength of general chemical knowledge, does not lead to the desired result of color neutrality in the reaction products of palm kernel 60 oil fatty acid methyl ester in particular.

Accordingly, the present invention relates to the use of di-3,5-tert.butyl-4-hydroxytoluene and/or toco pherols as stabilizers in palm kernel oil and palm kernel oil fatty acid alkyl esters for their processing to neutral-colored reaction products.

Di-3,5-tert.-butyl-4-hydroxytoluene, hereinafter referred to as BHT, and tocopherols may be used in ad- 65 2 GB 2 169 611 A 2 mixture, but more especially on their own for the purpose according to the invention. It has been found that, even by adding very small quantities of BHT, but especially by adding small quantities of tocopherol, palm kernel oil fatty acid methyl ester can be stabilized for prolonged periods, for example for up to two months, at room temperature to such an extent that alkanolamides or soaps produced therefrom 5 show the good color values required. More information on the desired color values can be found in the Examples.

If tocopherols are used as stabilizers in accordance with the invention, the tocopherols in question are, in particular, a.-, P-, -y- and 8tocopherol and also (x-, P-, -y- and 8-tocotrienols, above all mixtures thereof, of the type occuring as impurities in vegetable oils. Particularly suitable stabilizers of the tocopherol type are mixtures of soya oil steamer condensate rich in y-tocopherol and the a--tocopherol obtained there- 10 from by thorough methylation which can also be synthetically obtained.

Palm kernel oils which accumulate with considerable differences in quality or which are damaged to different extents during transport or storage can be stabilized to form starting materials which comply with the relevant standards by the addition of small quantities of BHT and/or tocopherol in accordance with the invention. Of greater importance is the fact that corresponding palm kernel oil fatty acid alkyl esters of different origin can also be correspondingly stabilized. In this connection, it is advisable to add the stabilizing additives used in accordance with the invention to the fatty acid methyl ester or fatty acid methyl ester mixture immediately after preparation or, alternatively, initially to purify an inadequate fatty acid alkyl ester mixture by preferably repeated distillation and directly to stabilize the distillate.

If other known antioxidants are used instead of the stabilizers used in accordance with the invention, 20 the required color neutrality in the reaction products of the palm kernel oil fatty acid methyl esters is surprisingly not obtained. For example, neither the use of 2-tert.-butyl hydroquinone nor even the use of butylated hydroxyanisole nor the use of galliG acid propyl ester shows the stabilizing effect required in accordance with the invention. The hydrolysis products and the diethanolamides of both the tert.-butyl hydroquinone derivative and of propyl gallate show high color values. The use of butylated hydroxyanisole in relatively large quantities, for example in quantities of more than 500 ppm, results only in unde sirably high saponification color numbers to begin with, although after prolonged storage undesirably high diethanolamide color numbers are also obtained.

The stabilizers used in accordance with the invention are normally active in quantities of less than 500 ppm and, more especially, in quantities of less than 300 ppm, based on stabilized starting material. BHT 30 can give entirely satisfactory results in the context of the invention in quantities of only 10 to 100 ppm and more especially in quantities of only about 20 to 50 ppm. Tocopherols added beyond the natural content can also give satisfactory color stabilization for subsequent reaction products when added in quantities of less than 100 ppm and, more especially, in quantities of at least 20 to 100 ppm. Where metal containers, for example steel tanks, are used for storage, it can be of advantage to add complexing 35 agents for metal ions to the material to be stabilized, for example citric acid, ascorbic acid or ascorbic acid fatty alcohol esters, more especially ascorbic acid palmitate.

The palm kernel oil fatty acid alkyl esters to be stabilized in accordance with the invention are obtained in known manner either by lipolysis of palm kernel oil and subsequent esterification of the fatty acid mixture obtained with the corresponding lower alcohol or by direct transesterification of palm kernel oil 40 with the corresponding alcohol. The alcohol component of the palm kernel oil fatty acid alkyl ester pref erably consists of methanol. In general, the palm kernel oil fatty acid alkyl esters intended for chemical further processing preferably contain only C,,-C,,, fatty acids as their acid component. To this end, the so called first-runnings fatty acids containing from 6 to 10 carbon atoms are normally separated off from the mixtures of the free fatty acids by fractional distillation in the case of direct esterification. If the palm kernel oil fatty acid alkyl esters are obtained by transesterification, the unwanted esters of the C,,-Cl, fatty acids are removed from the ester mixture by distillation after transesterification. In principle, this process may of course also be applied to ester mixtures of the type obtained from palm kernel oil fatty acid mixtures by direct esterification without preliminary fractionation of the fatty acids. In one particular em bodiment, therefore, the invention relates to palm kernel oil fatty acid methyl ester mixtures, more espe- 50 cially in the Cl,-C,,, fatty acid range, obtained by esterification of palm kernel oil fatty acids, especially those containing from 12 to 18 carbon atoms, with methanol or by transesterification of palm kernel oil with methanol and, if desired, isolation of the C,,-C,,, fatty acid ester cut, containing added di-3,5-tert.

butyl-4-hydroxytoluene and/or added tocopherol in quantities of less than 500 ppm for the production of neutral-colored reaction products.

Examples

In the following Examples, the following characteristics are used as a measure of the stability of the palm kernel oil fatty acid esters: peroxide number (PO No.), carbonyl number (CO No.), saponification color values (SCV) and diethanolamide color value (DEACV). These characteristics were determined as 60 follows:

Peroxide number (PO No.) The PO No. was determined by Wheeler's method, cf. DGF-Einheitsmethoden C- VI 6a (84), Wissen schaftliche Verlagsgesellchaft mbH, Stuttgart (1950 - 1984). In this method, a sample of the ester in a 65 3 CO No. - a - E 14 a = consumption of 0.5 N sodium hydroxide solution (mi) E = weight of the sample (g) GB 2 169 611 A 3 mixture of chloroform and glacial acetic acid is reacted in the cold with potassium iodide and the iodine formed by the peroxide present is determined by titration with sodium thiosulfate using starch solution as indicator. Calculation of the PO No. in mVal 02/kg is carried out in accordance with the following equation:

PO No. = a. N. 1000 E wherein a consumption of sodium thiosulfate measuring solution (mi) N normality of the sodium thiosulfate measuring solution E = weight of the sample (g) Carbonyl number (CO No.) The CO No. was also determined by a DGF-Einheitsmethode (cf. loc. cit. C- V 18 (58)). In this method, a 15 sample of the ester is heated for a relatively long time to reflux temperature with a 0.5 N aqueous-alcoholic hydroxylamine hydrochloride solution. The hydrogen chloride released is then titrated in the cooled mixture with 0.5 N alcoholic sodium hydroxide solution using a pyricline/brom phenol blue indicator. The CO No. is calculated in accordance with the following equation:

Saponification color values (SCV) To determine the SCV, 10 g of fatty acid ester are heated for 1 hour to reflux temperature with 100 ml of methanolic 1 N potassium hydroxide solution. The SCV are measured on the cooled sample with a 5 30 1/4"-cuvette in a Lovibond Tintometer. Esters of high quality should give red and yellow values of < 1.0 and < 5, respectively.

Diethanolamide color values (DEACV) To determine the DEACV, equivalent quantities of fatty acid ester and diethanolamine are reacted with 35 one another for 5 hours at 85'C in the presence of 1% by weight, based on the total quantity, of sodium methylate. The methanol released is continuously distilled off. The DEACV are measured on the cooled reaction product with a 5 1/4"-cuvette in a Lovibond Tintometer. The color of the diethanolamide may be regarded as satisfactory at < 1.5 for red and at < 15 for yellow (corresponding to a Gardner color value of < 3).

Examples 1 and 2 Palm kernel oil was split with water in an autoclave at 22WC. After the glycerine had been washed out, the C,-C,,, fatty acids were largely distilled off from the fatty acid mixture obtained, leaving a mixture consisting essentially Of C12-Cl. fatty acids. 45 The mixture of C,,-C,,, palm kernel oil fatty acid mixtures obtained was reacted with methanol (ratio by weight 1: 1) for 2 hours at 22WC in an autoclave under autogenous pressure. Methanol and water of reaction were distilled off from the resulting mixture. By repeating the reaction with methanol in excess and the distillation twice, a mixture of C12-CU, palm kernel oil fatty acid methyl esters having the following characteristics was obtained: acid number 0.3; saponification number approx. 238; iodine number 18. 50 PO No., CO No., SCV and DEACV were determined on the freshly distilled ester. 10 ppm of 3,5-di-tert.

butyi-4-hydroxytoluene (BHT; commercial product) or 50 ppm of atocopherol (DL; 99%; commercial product) were added as stabilizer to samples of the ester. These samples and a stabilizer-free sample (approx. 500 mi of each) were stored in darkness at approx. 2WC for 6 weeks in 500-mi wide necked flasks with loosened screw closures. The values mentioned above were then re-determined.

In the case of Example 2, a C,,-C,,, palm kernel oil fatty acid methyl ester prepared by the method de scribed above was again stabilized with 10 ppm of BHT.

The results obtained are shown in Table 1 below:

4 GB 2 169 611A 4 TABLE 1

Example Stabilizer Storage PONo. CONo. SCV DEACV time yellow red yellow red (weeks) 5 0 1.6 0.1 1.4 0.3 6.5 0.9 - 6 21.0 0.5 8.0 1.3 18.0 1.7 ppm BHT 6 0.8 0.1 2.0 0.5 7.0 1.2 50 ppm 6 2.2 0.1 2.0 0.4 8.0 1.3 10 a-tocopherol 2 0 0.75 0.1 0.6 0.1 4.0 0.9 - 6 9.7 0.2 2.3 0.3 10.0 1.3 10 Ppm BHT 6 0.7 0.1 0.8 0.1 4.5 0.8 15 Example 3

C12-C,, palm kernel oil fatty acid methyl ester, which had been stored for longer than 6 weeks and which had a PO No. of 40 and a CO No. of 0.6, was distilled twice, producing a total of 3.7% by weight of 20 residue. The distillate has an acid number of 0.3, a saponification number of 241 and an iodine number of 14.

PO No., CO No., SCV and DEACV were determined on the freshly distilled ester. 10 ppm and 50 ppm of 3,5-di-tert.-butyl-4-hydroxytoluene (BHT; commercial product), 50 ppm of (x-tocopherol (99%; commercial product) and 50 ppm of a mixture of tocopherols from soya oil (containing approx. 50% by weight of -y- 25 tocopherol as its main constituent; commercial product) as substances to be used in accordance with the invention and 50 ppm of 2-tert.-butyl hydroquinone (TBHQ; commercial product) and 50 ppm of 2-tert.

butyl hydroxyanisole (BHA; commercial product) as comparison substances were added to samples of the ester. These samples and a stabilizer-free sample (approx. 500 ml of each) were stored in darkness at approx. 20'C for 4 weeks in 500-ml wide-necked flasks with loosened screw closures. The values men tioned above were then re-cletermined. The results obtained are shown in Table 11 below.

TABLE 11

Stabilizer Storage PO No. CO No. SCV DEACV 35 time yellow red yellow red (weeks) - 3.0 0.3 6.0 1.2 9.0 1.7 - 4 43.0 0.8 18.0 3.0 18.0 4.4 40 ppm BHT 4 2.7 0.3 6.0 1.2 17.0 2.2 ppm BHT 4 2.3 0.2 6.0 1.2 17.0 2.2 ppm a-tocopherol 4 2.0 0.3 7.0 1.3 13.0 2.2 ppm tocopherol 4 1.6 0.3 4.5 1.0 13.0 2.5 from soya oil 45 ppm THBQ 4 1.9 0.2 8.0 2.2 27.0 9.0 ppm BHA 4 1.8 0.2 8.0 1.8 18.0 4.0 It can be seen from Table 11 that even a palm kernel oil fatty acid methyl ester which has already been damaged by oxidation can be effectively stabilized with the substances to be used in accordance with the 50 invention after re-distillation so that, after prolonged storage, reaction products of better color quality can be obtained with the stabilized ester than with the non-stabilized ester.

Example 4

Stabilized and stabilizer-free samples of the C,,-C,, palm kernel oil fatty acid methyl ester described in 55 Example 1 and, for comparison, a sample of a C,,-C,, coconut oil fatty acid methyl ester (acid number 0.3; saponification number 240; iodine number 11) were subjected to an accelerated ageing test in a Warburg manometer (see Laboratoriumstechnik fur Biochemiker, edited by B. Keil and Z. Sormova, Aka demische Verlagsgesellschaft Geest & Portig KG, Leipzig 1965, pp. 247- 249). In this test, the samples (3 g) are exposed to the effect of oxygen at WC and the oxygen uptake continuously monitored. The follow- 60 ing samples were tested:

A) palm kernel oil fatty acid methyl ester, stabilizer-free B) palm kernel oil fatty acid methyl ester + 10 ppm BHT C) palm kernel oil fatty acid methyl ester + 50 ppm BHT D) coconut oil fatty acid methyl ester, stabilizer-free GB 2 169 611 A 5 The test results obtained are shown in the form of a graph in Figure 1. It can be seen that an addition of 50 ppm of BHT was sufficient to provide the palm kernel oil fatty acid methyl ester with the stability which a comparable coconut oil fatty acid methyl ester has.

Claims

1. A process for the stabilization of palm kernel oil and palm kernel oil fatty acid alkyl esters for processing to neutral-colored reaction products which comprises incorporating di-3,5-tert.-butyl-4hydroxytoluene and/or tocopherols as stabilizers.

2. A process as claimed in Claim 1, characterized in that the stabilizers are used in quantities of less 10 than 500 ppm.

3. A process as claimed in Claim 2 characterized in that the stabilizers are used in quantities of less than 300 ppm.

4. A process as claimed in Claim 2 or Claim 3 characterized in that the stabilizers are used in quantities of from 10 to 100 ppm.

5. A process as claimed in any of Claims 1 to 4, characterized in that the palm kernel oil fatty acid alkyl esters have been obtained by reaction of palm kernel oil with lower alkanols.

6. A process as claimed in Claim 5 characterized in that the lower alkanol is methanol.

7. A process as claimed in Claim 1 substantially as herein described with reference to the Examples.

8. Palm kernel oil and palm kernel oil fatty acid alkyl esters when stabilized by a process as claimed in 20 any of Claims 1 to 7.

9. The use of di-3,5-tert.-butyl-4-hydroxytoluene and/or tocopherols as stabilizers in palm kernel oil and palm kernel oil fatty acid alkyl esters for processing to neutral- colored reaction products.

10. A mixture of palm kernel oil fatty acid methyl esters, obtained by esterification of palm kernel oil fatty acids, with methanol or by transesterification of palm kernel oil with methanol and, if desired, isola- 25 tion of the Cl,-C,, fatty acid ester cut, containing added di-3,5-tert.- butyl-4-hydroxytoluene and/or added tocopherol in quantities of less than 500 ppm, for the production of neutral-colored reaction products.

11. A mixture as claimed in Claim 10 characterized in that the fatty acid methyl ester is one within the C12-C18 fatty acid range.

12. A process as claimed in Claim 10 or Claim 11 characterized in that the palm kernel oil fatty acid 30 which is esterified contains from 12 to 18 C-atoms.

13. A mixture as claimed in Claim 10 substantially as herein described with reference to the Exam ples.

Printed in the UK for HMSO, D8818935, 5186, 7102. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.