Process of esterification

The invention relates to a process for the catalytic transesterification of glyceride oils with the aid of alkali metals.

The use of alkali metals to carry out catalytic transesterification reactions is known from US Pat. No. 2,878,274. In this US patent, according to which the use of pulverulent and therefore easily metered alkali metal alcoholates is preferred, the manner of metering of alkali metals is not discussed.

Under the usual reaction conditions used in the transesterification of glyceride oils, various catalytic agents have disadvantages. Alcoholates, such as sodium ethylate and sodium methylate, lead to the formation of ethyl and methyl esters, resulting in a loss of transesterified product. In addition, these ethyl and methyl esters can not be completely removed during the subsequent conventional deodorization usually.

From US Pat. Nos. 2,442,531 to 2,442,537 it is known to carry out transesterification processes in the presence of alkali metals previously dissolved in an inert liquid such as a mineral oil or an aromatic hydrocarbon, e.g. As xylene, had been dispersed. This procedure has the disadvantage that one must later remove this indifferent liquid from the reaction mixture again.

It is also known to use alkali metal hydroxides as catalysts in the transesterification of glyceride oils. The hydroxides, such as. As sodium hydroxide, are generally introduced in the form of an aqueous solution, which, however, at conventional reaction temperatures, considerable losses by saponification of the esters.

The object of the invention is to provide a process for the catalytic transesterification of glyceride oils using alkali metals, in its implementation no longer the disadvantages of the known processes are present and products are obtained which are completely transesterified, contain no foreign substances and easily purified and into an edible Product can be transferred.

The process according to the invention for the catalytic transesterification of glyceride oils, whose water content is below 0.05% in the presence of an alkali metal dispersion at elevated temperature is characterized in that the alkali metal is pressed directly into the liquid glyceride oil having a temperature of 100 to 275 ° C wherein the alkali metal at the point of contact between an extrusion unit and the oil is in the solid state and dispersed the molten metal by means of shear forces in the liquid

Due to the presence of solid alkali metal at its interface with the liquid glyceride oil, a natural seal is formed between the oil and the squeezing unit or extrusion unit so that no liquid can enter a sizing tube through which the alkali metal is supplied. In the sizing tube, the alkali metal may be supplied in the liquid state, however, it is preferably supplied in the solid state by direct displacement by means of a piston which fits exactly into the sizing tube.

Regardless of the manner in which the alkali metal is added to the metering tube, it is essential that at the point where the tube enters the disperse glyceride oil, the alkali metal be in the solid state. Therefore, when alkali metal is supplied in the liquid state, it should be cooled to a temperature below its melting point at the pressure prevailing at least at the point where it is discharged into the liquid. When the alkali metal is fed to the tube in the solid state, the tube should be sufficiently thermally insulated or provided with similar cooling to keep the alkali metal in a solid state when contacted with the dispersed liquid.

The alkali metal may be forced into the disperse fluid through one or more holes in the sizing tube.

Preferably, the solid rod of alkali metal pressed into the tube does not extend entirely over the tube. The choice of the number and diameter of the holes in the sizing pipe should therefore be determined with respect to the diameter of the tube to which the alkali metal is metered, as well as the flow rate of the liquid therein, since alkali metal is easier to make holes of fine bore than holes hole is dispersed.

If the alkali metal is supplied in the solid state, the tube can be previously filled by melting solid alkali metal in the tube and then, before pressing, the tube to a temperature below the melting point of Alkalime-

«Tails cools.

In the execution of completely continuous operations by the method according to the invention, therefore, the alternating use of

two or more distribution tubes are preferred, wherein the alkali metal in the liquid glyceride of a odtf^r a plurality of tubes is continuously introduced while the remaining tube or the remaining tubes are filled or cooled.

Although the presence of solid alkali metal in the manifold at the location where it is first contacted with the liquid prevents seepage of all types of particulate liquids to the supply of alkali metal, the invention is particularly advantageous when dispersions Alkali metal must be prepared in Estennisdiungen intended for transesterification reactions, since the natural interlocking of the solid alkali metal also prevents the formation of undesirable reaction products in the tube, which could reduce the effective inner diameter of the tube and affect the accuracy of the sizing or metering.

Using the method according to the invention, it is possible to transesterify edible oils without saponification with considerable amounts of glycerides so that transesterified products, which are virtually free of by-products, are obtained.

"Glyceride oils" are used for the purposes of ^a5 Invention is understood to mean both fatty acid glycerides which are solid at ambient temperature and are commonly called "fats", as well as glycerides which are liquid at ambient temperature.

The alkali metal is preferably added to the mixture to be transesterified in an amount equal to or greater than that consumed by the catalyst poisons so that the catalyst poisons in the mixture to be reesterified are balanced by an equivalent amount of alkali metal expressed in terms of grams equivalents. Many substances can be catalyst poisons, e.g. As water, fatty acids and peroxides. However, the property they have in common is their tendency to associate with alkali metal to a substance which is catalytically inert under the reaction conditions or only slightly active. It has been found that in the transesterification of edible oils, water should not be considered a catalyst poison when present in amounts less than 0.05%, more preferably +5 less than 0.01%. Furthermore, alkali soaps must be considered to be catalytically inert at a reaction temperature of less than 180 ° C.

Prior to feeding to the reactor, the mixture of oils and alkali metals should be subjected to vigorous shearing stresses to obtain a microdispersion of catalytic reagent in the oil. It has been observed that when the alkali metals are so vigorously dispersed that they are completely dissolved at the reaction temperature within 1 minute, and preferably within 20 seconds, the reaction can be carried out with optimal amounts of catalytic reagents. A particularly suitable dispersion device is a colloid mill, e.g. As such, as described in the German Patent 11 52 003.

The transesterification reaction may, for. B. in a cascade of vessels provided with agitator; However, it can also be carried out with advantage in a tubular reaction space⁶S will be.

According to the catalyst concentration, the reaction temperature and the kind of the mixture to be treated, the transesterification can be completed in 1 to 10 minutes. After leaving the reaction space, the reaction product of hydrogen which may have formed is dissolved and then freed of soaps and components of the catalyst by vigorous stirring with 5 to 30% by weight of water, after which the aqueous phase is separated from the reaction product.

Fully or partially interesterified products can be prepared by controlling the residence time and the amount of active catalyst used.

The transesterification of an edible oil mixture can, for. B. be determined by means of dilation measurements. For a mix of z. As palm oil and coconut oil is the dilation at 20 ° C, which is represented by D20, a suitable measure for determining the degree of transesterification. Dilatation is determined as described in "Analysis and the characterization of oils, fats and fat products," HA Boekenoogen (1964), p. 143 ff.

The transesterification takes place at a temperature at which the catalyst is formed in situ with sufficient activity, between 100 and 275 ° C. The chosen temperature depends on the type of catalyst and the proportion of the mixture to be esterified, but is above that Melting point of the alkali metal.

Good results are obtained using sodium at a temperature of 100 to 140 ° C, preferably 115 to 135 ° C.

In the transesterification of glyceride oils are advantageously treated esters, of which at least the greater part of the existing catalyst poisons was first removed because the amount of alkali metal required for the transesterification strongly depends on the amount of catalyst poisons present in the oil. On the other hand, the effect of using larger amounts of alkali metal to compensate for substantial amounts of catalyst poisons present results in excessive soap formation, unacceptably high viscosity of the oil / soap mixture, clogging of filters with soap gel, soaping on the inner wall of the reaction equipment and a considerable amount of soap Reduction of the reaction rate. If a crude mixture with z. B. an acid number of 2 to 5 and an amount of water above O, O5 ° / o is transesterified, at least 0.3 weight percent sodium is required, resulting in these undesirable results. Since water and free acids are the major catalyst poisons, it is desirable to carefully neutralize the mixture to be transesterified, desirably lower to an acid number less than 0.3, and preferably lower than 0.03% water.

Although the drying step can be carried out in various ways when a deacidification process is carried out by distillation, as is usual in the edible oil industry, supplementary drying is usually not necessary for the purposes of the invention. Drying may, if desired, be carried out by treating the mixture at elevated temperature with an aerated, inert gas. However, drying is preferably carried out by means of a device which removes the heated mixture of esters at a reduced pressure of e.g. B. 10 to 50 mm Hg

and at an elevated temperature of e.g. B. 100 to 140 ° C, wherein the mixture is sprayed at the top of a chamber of the device in which a vacuum is maintained, for the rapid evaporation of most of the water present. If desired, the operation may be carried out in two or more stages. It has been found that good results can be obtained by means of a two-stage vacuum drying apparatus operating at pressures of 45 and 45, respectively. 10 mm Hg at oil inlet temperature of 125 to 140 ° C works.

The temperature of the medium to be sprayed and the vacuum conditions are chosen so that the product to be transesterified reaches the required moisture content below 0.05% by weight.

Oils which undergo transesterification are preferably deacidified to an acid number of less than 0.3. By "acid number" is meant the number of mg of potassium hydroxide required to neutralize 1 g of the mixture to be transesterified. The acid value is determined by the method described by HA Boekenoogen "Analysis and characterization of oils, fats and fat products", Vol. I (1964), pages 23 to 24. Since this determination is carried out at ambient temperature in a short period of time, the esters are not saponified to give zero acid number in the absence of free acids. The mixture to be transesterified may be deacidified by use of a process for deacidification by distillation in vacuo, but deacidification may also be effected by direct contact with an alkaline solution through which soaps are formed by the difference in specific gravity between the oil and the soap can be separated. Such alkali acidification can be carried out by means of a 0.2 to 8 N sodium hydroxide solution.

The deacidification can be carried out continuously in a centrifugal device, which ensures a short contact time between the oil and the alkali solution. In addition, continuous deacidification may also be carried out by rapidly mixing the product with the alkane solution, then washing the mixture in a packed or packed column. However, deacidification is preferably carried out by passing the acid to be deacidified cocurrently or countercurrently through a packed column filled with the alkaline solution, optionally at an elevated pressure and at a temperature of 80 to 160 ° C Oil represents the dispersed phase. Such deacidification processes are described in Dutch Patent Application Nos. 65 03 471 and 66 03 470.

The method according to the invention will be explained in more detail below with reference to the drawings.

F i g. Figure 1 illustrates a process for the preparation of dispersions of an alkali metal in which the alkali metal is supplied in a liquid state and solidified before being contacted with the liquid.

F i g. Fig. 2 shows a design apparatus for the alkali metal in which the alkali metal is supplied in a solid state.

F i g. Figure 3 is a flow diagram of a continuous interesterification plant to which the method according to the invention is applied.

In F i g. 1, a storage vessel 1 for liquid alkali metal is shown, which is provided with an outer heating jacket 2. The contents of the vessel are heated above the melting point of the alkali metal by means of a heat transfer medium supplied at the inlet 3 and removed at the outlet 4

ίο will. On top of the liquid alkali metal 5 is a layer of paraffin oil 6 which prevents oxidation of the liquid alkali metal.

By means of a gear spinning pump 9, the alkali metal is passed through a valve 8 and a pipe 7 in and through the metering tube 12.

The feet swirling liquid of the Alkaürne. Tails is set by means of the changing device 10, which is connected to both an electric motor 11 and the gear pump 9.

O The sizing pipe 12 is provided with a heat exchanger 13 through which such an amount of coolant of such a temperature is conducted from the inlet 14 to the outlet IS that the alkali metal of that part of the sizing pipe passing through the heat exchanger 13 solidifies. Via the opening at the end of the sizing pipe, alkali metal enters the pipe or conduit 16 through which preheated glyceride oil is pumped from a storage vessel 17 provided with a heater (not shown) via a valve 18 by means of a pump 19.

The mixture of alkali metal and liquid glyceride oil maintained at a temperature above the melting point of the alkali metal is then passed through a colloid mill 2θ in which the alkali metal is dispersed in the liquid. Instead of the supply of alkali metal in the liquid state by means of a circulating pump, as in F i g. 1, the alkali metal can also be supplied in the solid state by means of a device as shown in FIG. 2 is shown.

According to F i g. 2, a cylindrical sizing pipe 21 is connected at 29 by bolt bolts (not shown) and a seal ring 28 to a cylinder head 22. The dimensioning tube 21 is provided with a hydraulically or mechanically actuated piston 23.

The actuating mechanism is not shown. The cylinder head 22, which forms part of the metering tube 21, is provided with an opening 25 through which the solid alkali metal from the interior 24 of the tube can be pressed into the glyceride oil flowing through the tube 26. The tube 26 is connected to the same device, such. As a pump and a colloid mill, provided as in F i g. 1 for the tube 16 is shown.

The cylinder head 22 is also provided with a cooling jacket 27 to prevent melting of the alkali metal in the opening 25.

A continuous transesterification using the method according to the invention will be described below with reference to Figs. 3 described. A transesterified glyceride oil mixture is added

⁶S 31 introduced by a pump 32 and a heat exchanger 33 by being preheated to a temperature of 125 to 140 ° C, in a vacuum drying apparatus 34, in which they

is sprayed by means of a spray head 35. The vacuum dryer 34 is connected at 36 to a vacuum system (not shown), which allows maintaining a pressure of 10 to 50 mm Hg in the dryer. The mixture, the moisture content of which has been reduced in this way below 0.05 percent by weight, is conveyed by a pump 37 to the reaction device 40. Before the product to be transesterified enters the reaction apparatus, the required amount of alkali metal is added at 38 and dispersed in the mixture through a colloid mill 39. The mixture is then passed into the tubular reaction space 40, which is provided with a thermal insulation and a heating coil 41, whereby the temperature is maintained at the required level. The residence time in the reactor can be maintained at a value of 1 to 10 minutes by adjusting the flow of the liquid accordingly. The transesterified product is then mixed in a mixing device 43 with 5 to 30 weight percent water introduced at 42 to extract the formed soaps and catalyst residues by washing. In the centrifugal device 44, the unwanted by-products are removed at 45, while the transesterified product is sprayed by means of a spray head 47 in the dryer 46, which is connected at 48 to a vacuum system. The drying device 46 can be maintained at a pressure of 45 mm Hg, so that the transesterified product is dried to a water content of 1 to 0.1 percent by weight. The cleaned and dried transesterified product is then withdrawn from the spray chamber by a pump 49.

The method according to the invention will be explained in more detail below with reference to examples.

example 1

A mixture of palm oil and coconut oil in a weight ratio of 60:40 was used in a plant as described in FIG. 3, transesterified. Prior to mixing, the oils were neutralized with a 0.8 N aqueous strength sodium hydroxide solution and then dried by spraying them into a vacuum chamber at a pressure of 100 mm Hg at a temperature of 125 ° C.

The oils were then mixed.

The Eigensiäiaiten the crhäiicneii ölmisdiung were as follows:

Water content: 0.008% Acid value: 0.13 Peroxide number: 0.8 Dilatation value at 20 ° C: 240

The oil mist was pumped through the device at 390 kg / h, and sodium was added to the oil mixture by means of the method shown in FIG. 2 in an amount of 0.072 kg / h, ie 0.0184 weight percent added.

The amount of sodium added exceeds the equivalent amount of catalyst poisons by 0.001% based on the total amount of oil.

The sodium was fed from a press fitted with a 40 mmφ piston through a 2 mm diameter hole at a pressure of about 150 kg / cm² pressed.

The extruder was sufficiently isolated to hold all the sodium in a solid state. The squeezed out sodium was then distributed in the mixture of oils by means of a colloid mill fitted with rotors with a diameter of 10 cm, spaced 2 mm apart and running at a speed of 2910 rpm,

versehenο was provided.

After a mean residence time of 4 seconds in this colloid mill, no dispersed sodium particles could be observed with the unaided eye, which probably means that such a fine dispersion was obtained that the surface of the sodium was increased to such an extent that the active catalyst immediately was produced. The obtained mixture was continuously introduced into a tubular reaction space.

The residence time in the reaction space was 1.15 min. The degree of transesterification was measured by the dilation value at 20 ° C {D20). The product leaving the tubular reaction space had a dilation D20 greater than 610,

"5 meaning that the transesterification was completed. The transesterified product was then freed from the catalyst residues by a 10 wt% fresh water wash.

The soap formed during the reaction was removed by a centrifuge, and the transesterified product was dried by spraying in a vacuum chamber.

Example 2

To illustrate that the process according to the invention can be advantageously applied to a continuous transesterification of neutralized oils, 2 mixtures (a and b) of palm oil and coconut oil were prepared in the same weight ratio as used in Example 1. Both mixtures were dried under the same process conditions as described in Example 1, but the mixture a was neutralized only.

The most important properties of the oil blends were:

Water content acid number Feroxycizahi dilatation value at 20 ° C

<p><tgroup cols="2"><tbody><row><entry>0,01%</entry><entry>0,01%</entry></row><row><entry>0,2</entry><entry>2,0</entry></row><row><entry>ö, S</entry><entry> 0,8 </entry></row></tbody></tgroup></p>

240

240

The sodium was continuously added to each oil mixture in the solid state by means of a device as described in FIG. 2 and metered and distributed by means of a colloid mill.

The oil blends were then placed in a tubular reaction space as shown in Figs. 3 is introduced. The transesterification reactions were carried out under the following process conditions:

.

from

Throughput oil t / h sodium in%

6 0.05

6 0.10

Sodium in kg / h

Diameter piston pressing device in cm

Diameter extrusion holes in mm 1,4

Number of ejection holes

Temperature oil mixture ° C

25 1,4 5 120

The residence time in the tubular reaction device was 2 min for both oil mixtures.

10

The oil mixture a was in the in F i g. 3 shown without interruption transesterified for 5 days.

Due to the high soap content of the product in the tubular reactor, the transesterification of the mixture b was stopped once every 2 days to remove impurities from the reaction equipment and the pump filter. During these operations, samples had dilation values ​​in excess of 600, indicating that the products had completely transesterified.

The oil blends were then purified as described in Example 1.

For this 3 sheets of drawings