DK2361298T3

DK2361298T3 - Process for reducing the 3-MCPD content in refined plant oils

Info

Publication number: DK2361298T3
Application number: DK09771302.8T
Authority: DK
Inventors: Klaus Schurz
Original assignee: Süd-Chemie IP GmbH & Co KG
Priority date: 2008-12-02
Filing date: 2009-12-01
Publication date: 2017-07-24
Also published as: PT2361298T; EP2361298B1; DE102008060059A1; EP2361298A1; HUE035623T2; WO2010063450A1; PL2361298T3; ES2637347T3

Description

The invention relates to a process for reducing the 3-monochloropropane-l,2-diol content in refined vegetable oils, where a crude oil is firstly degummed so as to give a degummed oil, the degummed oil is mixed with bleaching earth and bleached, giving a bleached oil, the bleaching earth is separated from the bleached oil so as to give a filter oil, and the filter oil is deodorized.

In the industrial production of oils and fats, bleaching earths are used for removing turbidity, discoloration or else for removing oxidation accelerators. Taste, colour and storage stability of the oils and fats can be significantly improved by the adsorptive purification. Various classes of bleaching earths are used for purification. A first group forms the class of highly active bleaching earths which are usually based on montmorillonite (HPBE = high performance bleaching earth). This group comprises, in particular, acid-activated montmorillonites, with the acid activation being carried out in a complicated process by dealuminizing the cmde clays by means of concentrated acids at high temperatures, usually at the boiling point. This process gives a bleaching earth product having a very large specific surface area and large pore volume. The use of even small amounts of this highly active bleaching earth leads to appreciable purification of the cmde oils. The use of small amounts in the bleaching process is therefore desirable because the used bleaching earth firstly binds residual amounts of oil amounts of oil, which reduces the yield, and secondly the used bleaching earth has to be disposed of according to applicable regulations. A disadvantage of these highly active bleaching earths is the fact that large amounts of acidic salt-rich wastewater arise during the production process from the dealumination by means of acid, and these can be treated or disposed of only in complicated processes. The high costs for disposal of the wastes and also the complicated production process bring about the comparably high price of such highly active bleaching earths. A further group forms the class of natural active clays (NABE = natural active bleaching earth). These naturally occurring bleaching earths have been used for hundreds of years for purifying fats and oils. These natural active systems (also referred to as Fullers earth or Fuller earths) can be made available very inexpensively. However, they have only a low bleaching power so that they are usually not suitable for purifying difficult-to-bleach oils and fats. Furthermore, significantly larger amounts of the adsorbent compared to highly active bleaching earths have to be used in order to achieve the desired bleaching result. However, higher losses of oil or fat have to be accepted as a result since the bleaching earths cannot be separated off in pure form and certain amounts of oil or fat remain in the bleaching earth.

The third bleaching earth class, namely surface-activated systems (SMBE = surface modified bleaching earth; surface-activated bleaching earths), represents a compromise between low production costs and acceptable activity. Here, a natural active raw clay is treated with small amounts of acid and "in-situ activation" is thus achieved. Raw clays containing attapulgite and hormite have been found to be particularly useful for this process. These have a quite high specific surface area for natural raw clays of from about 100 to 180 m2/g and a pore volume of from about 0.2 to 0.35 ml/g. However, since salts formed in the acid activation or unreacted proportions of the acid are not washed out, these remain in the product and are at least sometimes also deposited in the pores. As a result, these acid-activated bleaching earths generally do not attain the same efficiency as is achieved by highly active bleaching earths (HPBE) produced by dealumination by means of acid. However, the simple production process makes comparatively cheap production possible, and, as a particular advantage, no acidic wastewater is obtained.

The DMBE ("dry milled bleaching earth") represents a subgroup of the SMBEs. For the production of SMBE, the raw clay is generally treated with an aqueous solution of the acid. In the case of the DMBE, a solid acid, usually citric acid, is used for the activation and the solid acid is milled together with the raw clay. US 5,004,570 describes a process for bleaching oils, wherein a slurry comprising the oil to be bleached, a neutral bleaching earth and a chelating polybasic carboxylic acid is produced in a suitable vessel. The carboxylic acid has an even number of carboxyl groups, with the carboxyl groups being arranged in pairs and the carboxyl groups of each pair being able to assume an eclipsed confirmation. US 5,151,211 claims a bleaching earth composition comprising a neutral bleaching earth which comprises attapulgite and smectite in a ratio in the range from 0.3:1 to 1.5:1, with the proportion of attapulgite and smectite corresponding to at least 65% by weight of the bleaching earth. The composition additionally contains a polybasic carboxylic acid having an even number of carboxyl groups which are arranged in pairs, with the carboxyl groups in each case being able to assume an eclipsed arrangement. US 6,346,286 D1 claims a bleaching earth composition which comprises a mixture of a particulate clay and a particulate polybasic carboxylic acid, with the carboxylic acid having a pKa in the range from 1 to 7 and being essentially free of salts of organic acids. The clay has a moisture content of not more than 8% by weight, based on the clay. Furthermore, the polybasic carboxylic acid is present in the composition in a proportion in the range from 1 to 8% by weight, based on the composition. US 6,346,286 B1 also describes a bleaching process in which the oil to be bleached is brought into contact with a particulate composition comprising particles of a clay mineral and particles of at least one organic acid, with the organic acid being substantially free of salts of the organic acid. Citric acid, inter alia, is mentioned as a suitable organic acid.

After bleaching, the refined oil should satisfy particular requirements in respect of colour, taste and shelf life. Thus, the oil must not be too dark and, depending on the type of oil, have a yellow to green colour shade. Furthermore, the oil should be able to be kept without a deterioration in taste, i.e. not taste rancid, over a prolonged period of time. US 7,179,491 B1 describes a process for bleaching oils, which process does not require any degumming of the oil or the use of alkali or other chemicals such as acids or bases. The oil is obtained from marine sources, mammals or fish. The crude oil is firstly degassed under reduced pressure. After the vacuum has been broken by means of gaseous nitrogen, silica is firstly added to the oil and vacuum is again applied to the reactor. The vacuum is broken again and bleaching earth is added to the mixture. After vacuum has again been applied to the reactor, the mixture is bleached. The vacuum is broken again and the solid constituents are then separated off from the bleached oil by filtration. WO 2006/052974 A1 relates to seed oil compositions containing linoleic acid. A process for refining crude oil in which the crude oil is degummed by addition of water or alternatively of phosphoric acid and/or citric acid is described. The degummed oil is bleached by adding bleaching agents such as bleaching earth to the heated degummed oil. US 4,939,115 A describes a method for removing phospholipids and impurities such as metal ions Ca, Mg, Fe and Cu in oil. Here, degumming using 1% of water firstly takes place at 70°C. Bleaching of the degummed oil is carried out using amorphous silicon oxide. WO 2006/131136 A1 discloses a process for refining fats and oils, wherein the crude oil is subjected to bleaching by being treated with a bleaching earth product containing a raw clay. The crude oil is also introduced into a degumming stage which can comprise preliminary degumming by means of water and also acid degumming.

In the treatment customary at present, the oil is, after pressing, firstly degassed and dried in order to remove, for example, dissolved oxygen. Mucilaginous materials, in particular phospholipids, are subsequently removed. For this purpose, the dried and degassed oil is admixed with phosphoric acid and stirred at about 95°C. at atmospheric pressure for from about 15 to 20 minutes. In order to be able to separate off the mucilaginous materials more readily, further water is added, for example in a proportion of 0.2% by weight, towards the end of the. After brief stilling, the lecithin phase is separated off, for example by centrifugation. The subsequent bleaching of the degummed oil comprises two stages, wet bleaching and vacuum bleaching. For wet bleaching, the degummed oil is admixed with from 0.1 to 0.5% by weight of water and, after the oil has been heated to 95°C, from 0.3 to 2% by weight of bleaching earth is added. The mixture is then stirred at atmospheric pressure for about 20 minutes. Vacuum (for example 100 mbar) is subsequently applied and the oil is stirred at 95°C for another 30 minutes. After bleaching, the used bleaching earth is separated off, for example by filtering the mixture through a filter unit provided with a paper filter.

After bleaching, the oil is additionally deodorized. For this purpose, superheated steam having an exit temperature of about 240°C is passed through the oil in order to remove free fatty acids and also unpleasant flavours and odours. Deodorization is carried out under a reduced pressure in the range of less than 5 mbar, preferably from 1 to 3 mbar.

After refining, the oil has to satisfy particular requirements in respect of, for example, colour, taste and shelf life. For example, the oil should not appear brown but, depending on the type, have a yellow to green colour shade. A measure of this is the Lovibond colour number red, which should be as low as possible. In order to increase the shelf life, the oil should have a very low iron or phosphorus content.

Furthermore, the oil should be as insensitive as possible to oxidation in order to prevent development of a rancid odour and taste.

Apart from the type of bleaching earth used, the process conditions during degumming and during bleaching also have a significant influence on the result of oil refining. Thus, DE 10 2006 035 064 A1 describes a process for bleaching oils and fats, wherein - a crude oil obtained from a vegetable or animal source is provided; - the crude oil is heated to a temperature in the range from 35 to 55°C; - a bleaching earth is added to the heated crude oil; - the heated crude oil is bleached; and - the bleaching earth is separated off from the bleached crude oil.

This process makes it possible to achieve lower Lovibond colour numbers red and yellow than in the case of addition of the bleaching earth at 95°C under otherwise identical conditions, i.e. at the same amount of bleaching earth added and the same bleaching conditions. Thus, a smaller amount of bleaching earth is sufficient for achieving a given colour of the oil in the bleaching operation. The process has the advantage that the oil does not have to be heated to high temperatures for addition of the bleaching earth and the amount of bleaching earth can also be reduced.

However, undesirable accompanying materials which can be harmful to health when consumed by human beings can also be produced during oil refining. 3-Monochloropropane-l,2-diol (3-MCPD) can be formed in the production of foodstuffs, e.g. in the production of soya sauce, during baking and toasting and also in the refining of vegetable oils and fats. In animal experiments, 3-MCPD has been found to be carcinogenic. In addition, mutagenic properties of 3-MCPD have been observed in vitro but not in vivo. Furthermore, there are also indications that 3-MCPD impairs the fertility of mammals. 3-MCPD can be present both in free or in bound form, for example in the form of an ester, in foodstuffs. 3-MCPD has been found in various fats and oils. The concentration in vegetable fats and oils can extend into the range of several hundred through to several thousand ppm, in each case calculated as free 3-MCPD. The mechanism by which 3-MCPD is formed in refining of fats and oils has not yet been fully elucidated. However, in modelling studies, it has been found that chloride ions and also glycerol and monoglycerides, diglycerides and triglycerides are possible as potential starting materials in the formation of 3-MCPD.

Limit values for the content of 3-MCPD in various foods have already been prescribed in the EU. Thus, a maximum of 20 ppm of 3-MCPD are allowed to be present in soya sauce or hydrolysed vegetable proteins. A tolerable daily intake (TDI) of 2 micrograms per kilogram of body weight has been set down for human beings by the scientific expert committees of the EU and the WHO/FAO.

It was an object of the present invention to provide a process for refining oils, which comprises firstly degumming a crude oil so as to give a degummed oil, admixing the degummed oil with a bleaching earth and bleaching it, giving a bleached oil, separating the bleaching earth from the bleached oil so as to give a filter oil, and deodorizing the filter oil, which leads to a very low formation of 3-MCPD.

This object is achieved by a process having the features of Claim 1. Advantageous embodiments of the process of the invention are subject-matter of the dependent claims.

In the process of the invention, the degumming of the crude oil is carried out using only water without addition of acids. The oil is subsequently bleached at a temperature in the range from 80 to 100°C, preferably at a temperature of about 95°C. It has surprisingly been found that degumming has a significant influence on the concentration of the 3-MCPD formed in the refining of oils and fats, while bleaching exerts a significantly smaller influence and the concentration of 3-MCPD in the refined oil or fat after degumming is reduced by the addition of bleaching earth. This was particularly surprising because even when using highly active bleaching earths (HPBE), which are produced by extraction of raw clays with hydrochloric acid and therefore contain chloride ions, lower concentrations of 3-MCPD were found than after degumming and subsequent bleaching of the degummed oil, without bleaching earth having been added during bleaching. The inventors assume that precursors of 3-MCPD are formed during degumming and are then converted into 3-MCPD during deodorization.

The invention therefore provides a process for reducing the 3-monochloropropane-1,2-diol content in refined vegetable oils, where a crude oil is firstly degummed so as to give a degummed oil, the degummed oil is mixed with a bleaching earth and bleached, giving a bleached oil, the bleaching earth is separated from the bleached oil so as to give a filter oil, and the filter oil is deodorized, wherein: - water is added to the crude oil for degumming and degumming is carried out without addition of acid at a temperature of less than 70°C, and the degummed oil is preferably separated off from an aqueous phase, - the degummed oil is heated to a temperature in the range from 80 to 100°C and the bleaching earth is added in an amount of more than 1.5% by weight to the heated degummed oil, and - the bleaching is carried out at a temperature in the range from 80 to 100°C.

In the process of the invention, a crude oil is firstly provided in a customary way. This can be obtained, for example, by pressing in an oil mill. The crude oil can also be degassed and dried in the usual way.

The cmde oil is then mixed with water and stirred at a relatively low temperature.

The degumming is preferably carried out by mixing the cmde oil with water before bleaching. The amount of water added for degumming is preferably less than 15% by weight, more preferably less than 10% by weight. In one embodiment, the amount of water added is at least 0.2% by weight, while in a further embodiment is at least 0.5% by weight and in yet another embodiment is at least 1% by weight. The percentages indicated are in each case based on the cmde oil used. Degumming is carried out without addition of acids.

Degumming is carried out at a relatively low temperature of less than 70°C, preferably less than 60°C, more preferably in the range from 35 to 55°C, even more preferably in the range from 40 to 50°C.

The selected time for which the oil is treated for degumming is preferably in the range from 10 to 30 minutes, particularly preferably from 15 to 25 minutes. After degumming, the lecithin phase is separated off from the degummed oil, for example by centrifugation, decantation or by filtration. If the amount of water is less than 0.5% by weight, removal of the aqueous phase can be omitted. However, preference is given to the aqueous phase being separated off from the degummed oil even in the case of relatively small amounts of water.

The degummed oil is heated to a temperature in the range from 80 to 100°C, preferably from 90 to 98°C, more preferably about 95°C. It has been found that excessively high temperatures during bleaching lead to an increase in the concentration of 3-MCPD in the refined oil. Overheating of the oil should therefore be avoided. The bleaching earth is then added to the heated degummed oil. It has been found that when the amount of bleaching earth is too low, the concentration of 3-MCPD or 3-MCPD precursors which have been formed during degumming cannot be reduced satisfactorily. The bleaching earth is therefore added in an amount of more than 1.5% by weight, preferably in an amount in the range from 2.0 to 3.0% by weight, based on the crude oil, to the heated degummed oil. The inventors assume that the bleaching earth has only a low adsorption power for 3-MCPD and precursors thereof. It has been found that although 3-MCPD and precursors thereof are present only in amounts in the ppm range in the oil, an increase in the amount of bleaching earth used for bleaching above an amount of 1.5% by weight leads to a significant decrease in the amount of 3-MCPD in the refined oil.

After addition of the bleaching earth to the heated oil, the oil is then bleached in a manner known per se.

Bleaching can be carried out by applying a vacuum immediately after addition of the bleaching earth, i.e. without having added water to the crude oil beforehand. Bleaching then occurs as pure vacuum bleaching. The vacuum bleaching is carried out at elevated temperature, particularly preferably at temperatures of from 80 to 110°C.

In one embodiment, bleaching is carried out in at least two stages, with wet bleaching firstly being carried out and vacuum bleaching being carried out subsequently.

For wet bleaching, the crude oil is firstly admixed with water. The amount of water selected is preferably in the range from 0.05 to 1.5% by weight, particularly preferably from 0.1 to 1% by weight. The mixture is then stirred at from 80 to 100°C, particularly preferably from 90 to 95°C.

Vacuum bleaching is subsequently carried out under the conditions indicated above, i.e. preferably at temperatures of from 80 to 95°C and a pressure in the region of about 100 mbar.

After bleaching, the bleaching earth is separated off from the bleached oil. Conventional methods can be used for this purpose. The bleaching earth can be allowed to sediment and the supernatant clear oil can be decanted off. The bleached oil is usually filtered, for example through a paper filter, so as to give a filter oil. The oil obtained after separation of the bleaching earth from the bleached oil is here referred to as filter oil regardless of the method used for separating off the bleaching earth. The filter oil is finally deodorized. Conventional methods under the usual conditions are employed for this purpose.

For this purpose, superheated steam is passed through the oil, giving a full raffinate. The superheated steam preferably has an exit temperature in the range from 200 to 290°C. Deodorization is preferably carried out for a period of from 30 minutes to 2 hours. Deodorization can be carried out in a single stage, with the exit temperature of the superheated steam being kept substantially constant. However, it is also possible to carry out the deodorization in a plurality of stages, with the temperature of the superheated steam being altered during the deodorization. Here, preference is given to firstly introducing superheated steam having a temperature in the range from 250 to 290°C. This first step is preferably carried out for a period of from 20 to 45 minutes. The exit temperature of the steam is subsequently reduced, preferably into a range from 200 to 240°C. The superheated steam is then preferably passed through the oil for a further 30 to 120 minutes. On the basis of observations by the inventors, 3-MCPD is liberated during deodorization, from which the inventors presume that it was previously bound in precursors, for example in glycerides or in compounds derived therefrom.

The process of the invention makes it possible to achieve a low concentration of 3-MCPD in the refined oil when using essentially all bleaching earths, i.e. both in the case of HPBE and also in the case of SMBE and NABE.

However, a further lowering of the concentration of 3-MCPD in the refined oil can be achieved by careful selection of the bleaching earths used for bleaching.

Preference is given to using high-surface-area bleaching earths for bleaching.

One embodiment provides for the bleaching earth a specific surface area of more than 175 m2/g, while in a further embodiment the specific surface area is more than 220 m /g and in a further embodiment the specific surface area is more than 300 m /g. In one embodiment, the bleaching earth has a specific surface area of less than 400 m2/g.

Furthermore, the bleaching earths used in the process of the invention have, in a preferred embodiment, a specific pore volume of more than 0.2 ml/g, more preferably of more than 0.3 ml/g, particularly preferably a specific pore volume of more than 0.4 ml/g. In one embodiment, the bleaching earth has a pore volume of more than 0.45 ml/g and in a further embodiment a pore volume of less than 0.95 ml/g. In one embodiment, a bleaching earth which has a pore volume in the range from 0.4 to 1.0 ml/g is selected.

The specific surface area (BET surface area) and the specific pore volume are determined by means of nitrogen porosimetry in accordance with DIN 66131 and evaluation by the BJH method. The total pore volume relates to pores having a diameter of from 2 to 130 nm.

The ion exchange capacity of the bleaching earths is preferably more than 15 meq/100 g, more preferably more than 25 meq/100 g and in one embodiment more than 40 meq/100 g.

It is in principle possible to use all conventional bleaching earths in the process of the invention. It is thus possible to use both natural active bleaching earths (NABE) and acid-activated bleaching earths as bleaching earths. As acid-activated bleaching earths, it is possible to use both surface-activated bleaching earths (SMBE) and highly active bleaching earths (HPBE) obtained by extraction of a raw clay with strong acids.

However, it has been found that the type of activation of the bleaching earth used in the process of the invention has an influence on the amount of 3-MCPD present in the refined oil. It has surprisingly been found that acid-activated bleaching earths lead to lower concentrations of 3-MCPD in the refined oil. This is particularly surprising because the addition of acid during degumming leads to an increase in the concentration of 3-MCPD in the refined oil, i.e. the formation of 3-MCPD and precursors of this compound is presumably catalysed by acid.

The acid-activated bleaching earth has, as a 10% strength slurry in water, a pH of preferably less than 5 and more preferably less than 4. In one embodiment, the pH of the slurry is more than 2. In one embodiment, the slurry has a pH of less than 8.5, while in a further embodiment it has a pH of less than 4. The pH is determined by means of a pH electrode.

As acid-activated bleaching earths, it is possible firstly to use surface-activated bleaching earths (SMBE). These surface-activated bleaching earths are obtained by treating a natural raw clay with acid, with excess acid remaining on the clay. Thus, no washing step is carried out after activation.

Before activation, the raw clay can be prepared in a conventional manner and, for example, be dried or milled.

The surface activation of the raw clay can be carried out by treating the raw clay with a preferably aqueous solution of the acid used for activation.

The treatment can, for example, be carried out by moving the raw clay and spraying the solution of the acid onto the raw clay. However, other methods are also possible for applying the solution of the acid to the raw clay, for example steeping.

The activation of the raw clay can, for example, be carried out in the aqueous phase. For this purpose, the acid is brought into contact as aqueous solution with the raw clay. Here, the raw clay, which is preferably provided in the form of a powder, can firstly be slurried in water. The acid is subsequently added in concentrated form. However, the raw clay can also be slurried directly in an aqueous solution of the acid, or the aqueous solution of the acid can be added to the raw clay. In an advantageous embodiment, the aqueous acid solution can, for example, be sprayed onto a preferably crushed or pulverulent raw clay, with the amount of water preferably being selected to be very small and, for example, a concentrated acid or acid solution being used. The amount of acid can preferably be selected in the range from 1 to 10% by weight, particularly preferably from 2 to 6% by weight, of a strong acid, in particular a mineral acid such as sulphuric acid, based on the water-free raw clay (absolutely dry). If necessary, excess water can be evaporated and the activated raw clay can then be milled to the desired fineness. As already mentioned above, no washing step is required in this embodiment of the process of the invention, too. After addition of the aqueous solution of the acid, the clay is merely, if necessary, dried until the desired moisture content has been reached. The water content of the bleaching earth product obtained is usually set to a proportion of less than 20% by weight, preferably less than 10% by weight.

The activation can be carried out using either inorganic or organic acids. Suitable inorganic acids are, for example, sulphuric acid, phosphoric acid or hydrochloric acid. A suitable organic acid is, for example, citric acid.

The excess acid and the salts formed during activation are preferably not washed out. Rather, a washing step after addition of the acid, as is customary in acid activation, is preferably not carried out; instead, the treated raw clay is dried and then milled to the desired particle size.

However, it is also possible to activate the raw clay dry and, for example, mill the raw clay together with a solid acid. A suitable acid is, for example, citric acid. During milling, the particle size is set to the desired range.

The amount of acid used for activation is preferably selected to be greater than the ion exchange capacity of the raw clay, preferably in the range from 100 to 140% of the ion exchange capacity of the raw clay. A highly active bleaching earth (HPBE) is preferably used as acid-activated bleaching earth. These highly active bleaching earths are obtained by extracting a raw clay with a strong acid at elevated temperature, preferably at about the boiling point. Here, aluminium ions are basically leached from the crystal structure. After the extraction, the bleaching earth is separated off from the aqueous phase, for example by filtration, and then washed with water. This process is known per se to those skilled in the art. The highly activated bleaching earth is likewise milled to the desired particle size.

The particle size or the average particle size of the bleaching earth should preferably be selected so that complete and simple separation of the used bleaching earth from the refined product is possible. The average particle size of the pulverulent raw clay is preferably selected in a range from 10 to 63 pm. The fineness is typically selected so that from about 20 to 40% by weight of the mixture is retained (as sieve residue) on a sieve having a mesh opening of 63 pm and from about 50 to 65% by weight of the mixture is retained on a sieve having a mesh opening of 25 pm. This can be designated as typical bleaching earth fineness.

The process of the invention is suitable in principle for the refining of any oils and fats. However, the process of the invention is particularly suitable for refining vegetable oils.

Furthermore, the bleaching process of the invention is particularly suitable for low-phosphorus oils which preferably have a phosphorus content of less than 100 ppm.

In particular, the process of the invention is preferably suitable for bleaching palm oil.

The invention is illustrated in more detail below with the aid of examples. Examples:

The following analytical methods were employed:

Surface area/pore volume:

The specific surface area was carried out on a fully automated nitrogen porosimeter from Micromeritics, model ASAP 2010, in accordance with DIN 66131. The pore volume was determined using the BJH method (E.P. Barrett, L.G. Joyner, P.P. Haienda, J. Am. Chem. Soc. 73 (1951) 373). Pore volumes in particular pore size ranges are determined by adding up incremental pore volumes obtained from the evaluation of the adsorption isotherms by the BJH method. The total pore volume obtained by the BJH method relates to pores having a diameter of from 2 to 130 nm.

Oil analysis:

The colour numbers in oils (Lovibond colour numbers) were determined in accordance with AOCS Cc 13b-45. The chlorophyll A determination was carried out in accordance with AOCS Cc 13d-55.

Ion exchange capacity:

To determine the ion exchange capacity (IUF), the raw clay to be examined was dried at 105°C for a period of two hours. The dried material was then reacted with an excess of aqueous 2N NH4CI solution under reflux for one hour. After standing for 16 hours at room temperature, the mixture was filtered, after which the filter cake was washed, dried and milled and the NH4 content of the raw clay was measured by nitrogen determination (CHN analyser from Leco) according to the manufacturer's instructions. The proportion and type of the exchanged metal ions were determined in the filtrate by ICP spectroscopy.

Determination of the dry sieve residue:

About 50 g of the air-dried mineral to be examined are weighed onto a sieve having the desired mesh opening. The sieve is connected to a vacuum cleaner which sucks all fractions finer than the sieve through the sieve via a suction slit moving in a circular fashion under the bottom of the sieve. The sieve is covered with a plastic lid and the vacuum cleaner is switched on. After 5 minutes, the vacuum cleaner is switched off and the amount of coarser material remaining on the sieve is determined by difference weighing.

Loss on ignition:

About 1 g of dried sample is weighed to within 0.1 mg in an ignited, weighed porcelain crucible with lid and ignited at 1000°C for 2 hours in a muffle furnace. The crucible is then cooled in a desiccator and weighed.

Determination of the 3-MCPD content

An aliquot of the oil to be examined is dissolved in t-BME/ethyl acetate and admixed with a deuterated standard solution and also an NaOCEE solution. The fatty acids are subsequently separated from the aqueous phase using hexane. The aqueous phase is admixed with phenylboronic acid and derivatized at 80°C in a water bath for 20 minutes. After cooling, the 3-MCPD derivative is extracted with n-hexane and measured by means of GC-MS (EH+, SIM mode). Chromatography column: fused silica capillary coated with methyl silicone/phenyl silicone.

Example 1

Bleaching of a palm oil A sample of a crude palm oil is firstly heated to the temperature indicated in Table 1 for degumming and then dried and degassed at 100 mbar for 15 minutes. After degassing, the palm oil was admixed with the amount of 50% strength phosphoric acid or water indicated in Table 1 and stirred at ambient pressure for 15 minutes.

The aqueous phase was then separated off where indicated (index "f" in Table 1), the oil was brought to the temperature indicated in Table 1 for bleaching and the amount of bleaching earth indicated in Table 1 was then added. The oil was firstly bleached at atmospheric pressure for 20 minutes and subsequently at a reduced pressure of 100 mbar for 30 minutes. The oil was filtered hot through a paper filter. The filtered oil was then deodorized by firstly passing superheated steam having an exit temperature of 270°C through the oil for 30 minutes and subsequently passing superheated steam having an exit temperature of 240°C through the oil for 60 minutes. Finally, the concentration of 3-MCPD was determined. The results are summarized in Table 1.

Table 1: Refining of palm oil

The bleaching earths used in the examples have the properties indicated in Table 2: Table 2: Properties of bleaching earths

As can be seen from Table 1, a relatively large amount of 3-MCPD of 5500 ppm is formed in the case of a blank in which the palm oil is not degummed and bleaching is carried out as a blank, i.e. without addition of bleaching earth. If degumming is additionally carried out, the amount of 3-MCPD increases to 6150 ppm when water is added and a very high concentration of 3-MCPD of 11 800 ppm is found when phosphoric acid is added.

If a bleaching earth is added during bleaching after degumming, significantly lower concentrations of 3-MCPD are measured in the full raffinate. The use of bleaching earth thus does not increase the concentration of 3-MCPD in the full raffinate but instead adsorbs 3-MCPD and precursors of this compound formed during refining of the oil.

If acid is added during degumming, higher values for 3-MCPD in the full raffinate compared to degumming using only water are measured. Here, the amount of 3-MCPD decreases with decreasing amount of acid added during degumming (at a constant concentration of the acid) and also with decreasing acidity of the aqueous solution. However, larger amounts of 3-MCPD are measured than in the case of degumming carried out only with addition of water.

If the temperature during degumming is also decreased and/or the amount of water added during degumming is reduced, this likewise leads to a decrease in the measured amount of 3-MCPD.

Claims

A process for reducing the 3-monochloropropane-1,2-diol content of refined plant oils, wherein a crude oil is first evaporated so as to obtain a stripped oil, the stripped oil is blended with a bleaching soil and bleached to give a bleached oil, the bleaching soil is separated from the bleached oil so that a filter oil is obtained and the filter oil is deodorized, characterized in that - to the slimming water is added to the crude oil and the slimming is carried out without the addition of acid at a temperature of less than 70 ° C, - the skimmed oil is heated to a temperature in the range of 80 to 110 ° C, and the bleaching soil is added to the heated skimmed oil in an amount of more than 1.5% by weight, - the bleaching is carried out at a temperature in the range of 80 to 100 ° C.

Process according to claim 1, characterized in that, for the purpose of slimming, water is added to the crude oil in an amount of less than 15% by weight.

Process according to claim 1 or 2, characterized in that the scraped oil is separated from an aqueous phase.

Process according to one of the preceding claims, characterized in that the bleaching soil has a specific surface area of more than 175 m2 / g.

Process according to one of the preceding claims, characterized in that the bleaching soil has a pore volume of more than 0.2 ml / g.

Process according to one of the preceding claims, characterized in that the ion exchange capacity of the bleaching soil is more than 15 meq / 100g.

Process according to one of the preceding claims, characterized in that the bleaching soil is an acid-activated bleaching soil.

Process according to claim 7, characterized in that the acid-activated bleaching soil is an HPBE.

Process according to one of the preceding claims, characterized in that the oil is a plant oil.

Process according to one of the preceding claims, characterized in that the oil is palm oil.