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 U.S. patent, which suggests the use of powdery and therefore easily metered alkali metal alcoholates, the manner of metering 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, were dispergicrl. 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 Natriunihydroxyd, are generally introduced in the form of an aqueous solution, which, however, result in 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 less than 0.05%, in the presence of an alkali metal dispersion at elevated temperature, is characterized in that the transesterification is carried out with an alkali metal dispersion, which by directly pressing solid alkali metal in a liquid glyceride oil from 100 to 275 ° C and dispersing the molten metal has been prepared 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 a liquid state, but 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 the 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 get from holes of fine bore than holes hole is dispersed.

When the alkali metal is supplied in the solid state, the tube may be pre-filled by melting solid alkali metal in the tube and then, before squeezing, cooling the tube to a temperature below the melting point of the alkali metal.

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

17 92 oil 1

two or more distribution tubes are preferred wherein the alkali metal is continuously introduced into the liquid glyceride oil from one or more tubes while the remaining agitation or 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 ester mixtures 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.

When using the process 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.

By "glyceride oils" is meant for the purposes of the invention, 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 transesterified are balanced by an equivalent amount of alkali metal expressed in grams equivalents. Many substances can be catalyst poisons, e.g. As water, fatty acids and peroxides. However, the property they share is their tendency to associate with alkali metal to a substance which is catalytically inert under the reaction conditions or which is only slightly active. It has been found that in the transesterification of edible oils water should not be considered as a catalyst poison when it is present in amounts below 0.05%, especially below 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 Umesteriingsrcaktion z. B. in a cascade of vessels provided with agitator; However, it can also be carried out with advantage in a tubular Rcaklionsraum.

According to the catalyst concentration, the reaction concentration and the kind of the mixture to be treated, the transesterification can be completed in 1 to 10 minutes. After leaving the reaction chamber, the reaction product of hydrogen which may have formed is freed and then freed of soaps and components of the catalyst by vigorous stirring with 5 to 30 weight percent 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 degree of transesterification of an edible oil mixture may, 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.

Transesterification occurs at a temperature at which the catalyst is formed in situ with sufficient activity, between 100 and 275⁰C. The temperature chosen depends on the type of catalyst and the proportion of the mixture to be esterified, but is above the 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, esters are conveniently treated, of which at least the majority of the catalyst poisons present were first removed, because the amount of alkali metal required for transesterification is highly dependent 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. is transesterified at an acid number of 2 to 5 and a water level above 0.05%, at least 0.3 weight percent sodium is required, resulting in these undesirable results. Since water and free acids are the main catalyst poisons, it is desirable to carefully neutralize the mixture to be transesterified, desirably lower to an acid number of less than 0.3 and preferably to a level of less than 0.03%.

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 optionally be carried out by treating the mixture at elevated temperature with a dry, 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

17 92 oil 1

and at an elevated temperature of e.g. 100 to 140 ° C., the mixture being sprayed at the top of a chamber of the apparatus in which a vacuum is maintained for the rapid evaporation of most of the water present The operation may, if desired, be carried out in two or more stages. It has been found that good results are obtained by means of a two-stage vacuum drying apparatus

F i g. Fig. 3 is a flow chart 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 Heizrnantel 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

enough.

Oils which undergo transesterification are preferably deacidified to an acid content of less than 0.3. By "acid number" is meant the number ao of mg of potassium hydroxide required to neutralize 1 g of the mixture to be reprecipitated. The acid number is determined by the method described by HA Boekenoogen

can be used when pressing 45 or i₀ becomes. On the top of the liquid alkali metal 5 H) mm Hg at oil inlet temperature of 125 to is a layer of paraffin oil 6, which operates a 140 C. Oxidation of the liquid alkali metal prevented.

The temperature of the medium to be sprayed by means of a gear spinning pump 9 is the

and the vacuum conditions are chosen. Alkali metal via a valve 8 and a tube 7 in and that the product to be transesterified passed the required 15 through the metering tube 12. Moisture content below 0.05% by weight The flow rate of the liquid alkali metal.

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

The metering tube 12 is provided with a heat exchanger 13 through which such an amount of refrigerant of such a temperature is conducted from the inlet 14 to the outlet 15 that the alkali metal of that part of the metering tube, the

1 through the heat exchanger 13, solidifies, products ", Vol. 1 (1% 4), pp. 23 to 24, is described. Over the opening at the end of the dimensioning tube

Since this determination is carried out at ambient temperature in the tube or line 16 for a short period of time, the preheated glyceride oil from a La ester is not saponified, so that an acid number of zero is 17, which is heated by a heater. 3) is provided, via a valve 18 by means of a mixture to be transesterified, may be pumped by use of a pump 19.

A method of deacidification by distillation The mixture of alkali metal and liquid

Deacidification may be deacidified in vacuo, the deacidification may be carried out at a temperature above but also by direct contact with an alkaline melting point of the alkali metals, through which tires formed thereon are passed through a colloid mill 20 in which which is dispersed by the difference in the specific alkali metal 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 is a cylindrical sizing pipe 21 at 29 by bolts (not shown) and a sealing ring 28 with a cylinder

Continuous deacidification also performed by 45 derkopf 22 connected. The metering tube 21 will be that the product is rapidly mixed with the alka- with a hydraulically or mechanically operated solution, then the mixture is placed in a piston 23.

Column packed or packed column The actuating mechanism is not shown

washes. The deacidification is, however, preferably the cylinder head 22, which forms part of the design.

carried out by representing the oil to be deacidified oil tube 21 is seen with an opening 25 verim DC or in countercurrent by one, through which the solid alkali metal leads from the packed column, with the alkaline solution nenraum 24 of the tube is filled by means of the piston 23 in the, optionally at an elevated pressure through the tube 26 flowing glyceride oil are pressed and a temperature of 80 to 160 ° C, which can. The tube 26 is the dispersed with the same Einrichöl the dispersed phase. Such a discharge, such as. Example, a pump and a colloid mill, acidification processes are provided in the Dutch Pa, as shown in F i g. 1 for the tube 16 shown tentanmeldungen No. 65 03 471 and 66 03 470 loading.

wrote. The cylinder head 22 is also available with a cooling

The process according to the invention is provided at night 27, in order to explain in more detail a melting of the alkali metal with reference to the drawings ^6o in the opening 25 to prevent.

Fig. 1 illustrates a method for producing a continuous transesterification using

The method according to the invention is described below with reference to FIG. 3 to describe.

A glyceride oil mixture to be transesterified is introduced at 31 by a pump 32 and conveyed via a heat exchanger 33 by preheating to a temperature of 125 to 140 ° C in a vacuum drying apparatus 34 in which they

Weight 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, a con-

The preparation of dispersions of an alkali metal, wherein the alkali metal is supplied in a liquid state and solidified before it is brought into contact with the liquid.

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

17 92 oil 1

Water content: O, OO8 ° / o Acid value: 0.13 Peroxide number: 0.8 Dilatation value at 20 ° C:

240

is sprayed by means of a spray head 35. The vacuum drying apparatus 34 is connected at 36 to a vacuum system (not shown), which allows maintaining a pressure of K) to 50 mm Hg in the drying apparatus. The mixture whose moisture content has been reduced below 0.05% by weight in this manner is conveyed by a pump 37 to the reaction apparatus 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 fed into the tubular enclosure 40 ', which is provided with a thermal insulation and a heating coil 4t, thereby allowing the temperature to be maintained at the required level. The residence time in the reactor can be kept at a value of 1 to 10 minutes by adjusting the flow of liquid accordingly. The reacted product is then mixed in a mixer 43 with 5 to 30 weight percent water introduced at 42 to extract the soaps and catalyst residues produced 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 properties of the resulting oil mixture were as follows:

a hole with a diameter of 2 mm with 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 dispersed in the mixture of oils by means of a colloid mill equipped with 10 cm diameter rotors spaced 2 mm apart and circulating at a speed of 2910 rpm.

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 meant that 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 means of the dilatation value at 20 ° C (D20) The product leaving the tubular reaction space had a dilatation D20 of more than 610, which means that the transesterification was completed The transesterified product was then washed by a 10 Weight percent fresh water freed from the catalyst residues.

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 used advantageously on a continuous transesterification of neutralized oils, 2 mixtures (a and b) were prepared before palm oil and coconut oil in the same weight ratio as used in Example 1 posed. Both mixtures were under the same process conditions, as in Beispie! ■ were dried, but it was only lent the mixture a neutralized.

The most important properties of the oil blend egg were:

Water content Acid number Peroxide number Dilatation value at 20 ° C

<p><tgroup cols="2"><tbody><row><entry>0,01Vo</entry><entry>0,010/₀</entry></row><row><entry>0,2</entry><entry>2,0</entry></row><row><entry>0,8</entry><entry>0,8</entry></row></tbody></tgroup></p>

240

55 240

The oil mixture was pumped through the 390 kg'h device and sodium was added to the oil mixture by means of the F i g. 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 passed through a press fitted with a 40 mmφ flask. The sodium was continuously solidified in each solid state oil mixture by means of a device as shown in Figs. 2 and metered and distributed by a colloid mill.

The oil mixtures were then placed in a tubular reaction space, as in F i g. 3 is shown introduced. The transesterification reactions were carried out under the following process conditions:

Throughput oil t / h sodium in%

6 0.05

0.10

Sodium in kg / h 3

Diameter piston press

Arrangement in cm 25

diameter

Squeezing holes in mm 1,4 Number of

Squeezing holes 5

temperature

oil mixture ° C 120

25

1,4

120

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

The oil mixture a was transesterified in the plant shown in Fig. 3 without interruption for 5 days.

Due to the high soap content of the product in the tubular reactor, the transesterification of the mixture b was once every 2 days to remove impurities from the reaction device and the pump filters. During these procedures, samples had dilation values ​​in excess of 600. which showed that the products were completely transesterified.

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

For this 3 sheets of drawings