DE2151482C3 - Process for the selective hydrogenation of polyunsaturated fats, oils, fatty acids or mixtures of these substances - Google Patents

Description

(a) in which the weight ratio between chromium and palladium is about 1 to 3: 1 and the The amount of palladium and chromium (calculated as metals) is about 0.1 to 20% by weight or

(b) which contain about 0.05 to 10% by weight palladium, the remainder Cr ₂ O * as a catalytically active substance and carrier.

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2. The method according to claim 1 (alternative a), characterized in that there are catalysts used, in which the weight ratio between chromium and palladium (as metals calculated) is about 1 to 1.5: 1.

3. The method according to claim 1 or 2 (alternative a), characterized in that there are catalysts used with a support on which the chromium and palladium in amounts of about 0.2 to 10.0 % By weight, preferably from 0.5 to 5.0% by weight (based on the total catalyst) are applied.

4. The method according to one or more of claims 1 to 3 (alternative a), characterized characterized in that catalysts with aluminum oxide, preferably with γ-aluminum oxide, as Carrier used

5. The method according to claim 1 (alternative b), characterized in that catalysts are used which contain about 0.1 to 5.0% by weight, preferably about 0.25 to 2.5% by weight, of palladium , Remainder Cr ₂ O ₃ .

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It is known from DE-AS 1123 423 that Platinum metals are suitable as catalysts for the hydrogenation of fats, oils and fatty acids. It is also off the US-PS 31 23 574 a process for the selective hydrogenation of polyunsaturated oils known, in which supported Pd catalysts are used. This procedure is carried out at around 40 to 200 ° C carried out. In addition to Pd, other metals or metal compounds can also be placed on the carrier substances be applied, e.g. B. Compounds of mercury, silver, bismuth and copper. Chromium compounds are not given.

The catalysts from the group of platinum metals eo are relatively active, but they have the disadvantage that their selectivity leaves much to be desired. at Using polyunsaturated fats, oils and fatty acids the hydrogenation proceeds up to the saturated products, which is undesirable in that it is easy, for example, for making margarine unsaturated products are essential.

For the hydrogenation of polyunsaturated

Fats, oils and fatty acids are also known copper chromite catalysts, which have a better selectivity than the catalysts based on platinum metals (DE-AS 12 28 740), for example, can with Help of the copper chromite catalyst linolenic acid can be selectively hydrogenated to linoleic acid. However, these catalysts have in relation to the catalysts on the basis of the platinum metals very little activity, so that if the hydrogenation does not take too long is to take, it is necessary to carry out the reaction at relatively high temperatures and pressures. However, decomposition reactions already occur here on.

Finally, are used to hydrogenate fats, oils and Fatty acids supported nickel catalysts are known, which in terms of activity and selectivity are roughly in the middle between the catalysts based on the platinum metals and the copper chromite catalysts stand (Ullmann's Encyclopedia of Industrial Chemistry, Vol. 7, page 529 ff [1956]). These catalysts however, have the disadvantage that they are easily poisoned.

A process has now been found, surprisingly, according to which unsaturated fats, oils. Fatty acids or mixtures of these substances with hydrogen in the presence of supported palladium catalysts at temperatures of about 60 to 200 ° C can be selectively hydrogenated; the process is characterized in that chromium-containing supported palladium catalysts are used,

(aj in which the weight ratio between chromium and palladium is about 1 to 3: 1 and the The amount of palladium and chromium (calculated as metals) is about 0.1 to 20% by weight or

(b) which contain about 0.05 to 10% by weight of palladium, the remainder Cr ₂ Oa, as a catalytically active substance and carrier.

The catalysts used correspond to the best known in terms of their selectivity Nickel catalysts, however, have a much higher activity than nickel catalysts and are used in the In contrast to these, not poisoned by sulfur, carbon monoxide and similar catalyst poisons. Farther they are inactivated much less strongly than the known nickel catalysts.

Preference is given to using in the process according to alternative (a) catalysts in which the Weight ratio between chromium and palladium (as Metals calculated) is about 1 to 1.5: 1.

In alternative (a), preference is given to using Catalysts with a support on which the chromium and the palladium in amounts of about 0.2 to 10.0% by weight, particularly preferably in amounts of from 3 to 5% by weight (based on the total catalyst) Are.

The ranges given are the ranges calculated for the corresponding metals. In fact, however, the chromium is also present as Cr ₂ Cb during the hydrogenation, while the palladium is present as the reduced metal during the hydrogenation.

For the catalysts according to alternative (a) it is possible, for example, to use oxidic supports, e.g. B. Magnesium oxide, aluminum oxide, silicon dioxide, titanium dioxide, zirconium dioxide and similar inert oxides. the Carriers must not contain any alkali oxides. Furthermore, the use of physiologically toxic oxides such as

Barium oxide, gallium oxide, indium oxide, thallium oxjci, Tin oxide, lead oxide, vanadium oxide, etc., not possible. Calcium oxide and strontium oxide are also less suitable.

The oxidic carriers can also be in the form of mixed oxides.

Carriers based on silicates and aluminates are also suitable, again based on Physiological harmlessness is to be observed when the catalysts for the hydrogenation of fats and oils for Intended to be used for culinary purposes. Examples of supports based on silicate or aluminate are zeolites and Montmorillonite.

Finally, activated charcoal can also be used as a carrier will.

Preference is given to the alternative (a) catalysts with aluminum oxide, preferably with γ-aluminum oxide, used as a carrier.

According to alternative (b), in which catalysts are used in which the chromium in the form of Cr ₂ O ₃ not only serves as a catalytically active substance but also as a carrier material, the catalysts preferably contain about 0.1 to 5.0 wt . ^%, particularly preferably about 0.25 to 2.5% by weight, palladium. Remainder Cr ₂ O ₃ .

The catalysts used according to the invention can be prepared by any of the processes customary for the preparation of supported catalysts. Particularly useful catalysts are those in which the catalytically active substances have been applied to previously formed supports. Here z. B. soluble chromium and palladium compounds, such as palladium chloride, CrO ₃ or ammonium chromate or bichromate (the alkali chromates or bichromates should not be used in the form of aqueous solutions. This can be applied, for example, by Immersion of the support in the salt solution or by spraying the salts onto the support.Another possibility of applying the catalytically active substances to the already preformed support is to deposit insoluble precipitates on the support from salt solutions of the catalytically active metals in a suspension of the support to attract attention.

It is also possible to use such catalysts that by co-precipitation of the catalytically active substances and the carrier.

By applying the catalytically active substances to the already pre-formed carrier or Catalysts produced by joint precipitation of the catalytically active substances and the support are calcined in the usual way, which occurs at temperatures in the range from about 400 to 450.degree can happen.

The catalysts can be in the form of powders or in the form of shaped bodies, which are produced in the usual way can be used.

The hydrogenation using the catalysts is carried out at temperatures of about 60 to 220 ^° C., preferably at temperatures of about 120 to 200 ^° C., and can be carried out at pressures of about 1 to 30 atm. In the hydrogenation of polyunsaturated oils and fats, pressures of about 1 to 5 atm are preferably used, while pressures of about 5 to 30 atm are preferably used in the hydrogenation of the corresponding fatty acids.

The hydrogenation can be carried out batchwise or continuously. The continuous hydrogenation is because of the associated lower workload and the more consistent product quality more advantageous in large-scale operations than discontinuous hydrogenation, for continuous Hydrogenation can be used, for example, the systems known per se, in which a powdery Catalyst is circulated by methods known per se. The hydrogenation can also be carried out in

ίο in a novel way for fat hydrogenation, by passing the hydrogenation mixture over a fixed bed reactor in which the catalyst is in lumpy form, for example in the form of tablets. In this case, the space velocity is about 0.1 to 3 parts by volume of liquid feed per part by volume of catalyst and hour. The pressure areas correspond essentially to those in the batchwise operation, but with the hydrogenation of For greasing or oiling, the preferred pressure range is between 1 and 10 at. The molar ratio is between Hydrogen and fatty acid are between about 1: 1 and 20: 1, preferably 1: 1 to 10: 1, depending on the iodine number of the starting and end product.

The invention is illustrated by the following examples

example 1

Hydrogenation of soybean oil

In an unpressurized hydrogenation, with stirrer, heater, temperature controller, thermometer was charged with and H ₂ -Emleitungsrohr, 200 g soybean oil containing approximately 25% oleic acid, 50% linoleic acid and about 8% linolenic acid were contained, heated to 125 ° C. 20 g of the pulverulent catalyst prepared according to Example 5 and containing 0.5% Pd and 0.5% Cr (calculated as metals) were added to the oil, and hydrogen was passed in at a rate of 0.75 liters / hour. The decrease in the iodine number as a function of time was determined as a measure of the progress of the reaction. The iodine number of the starting oil was 125. After a short start-up time of about 4 minutes, there was a linear decrease in the iodine number. After 20 minutes the iodine number was 76.5.

For practical purposes, the hydrogenation was carried out up to an iodine number of 71 obtained fat had a melting point of 35 ° C, what corresponds to an extremely favorable relationship between melting point and iodine number

The hydrogenation product contained only traces of linolenic acid.

The experiment was repeated at a temperature of 110 ⁰ C. Here, too, an essentially linear decrease in the iodine number could be observed after a short start-up period. After 30 minutes the iodine number was 97.

Example 2
Draft of soybean oil

1 g of catalyst according to Example 5, corresponding to 10 ppm by weight of palladium, was added to 0.5 kg of soybean oil in an autoclave. Curing was at a pressure of 3 and a temperature of 200 ⁰ C. The iodine number of the soybean oil was 95 after 25 minutes, corresponding to a decrease in iodine number

of 35 units, the determination of the selectivity Su gave a value of 50, the selectivity S "gave a value of 3, the melting point was 3O ⁰ C; the

Determination of the transistors showed a content of 78% transisomers. The selectivities are as follows Are defined;

_ Reaction rate triple unsaturated acid -> double unsaturated acid ³² ~ Reaction rate double unsaturated acid -> single unsaturated acid

_ Reaction rate polyunsaturated acid - * polyunsaturated acid ³¹ ~~ Reaction rate polyunsaturated acid - »saturated acid

Example 3

Continuous hydrogenation in a fixed bed reactor

500 ml of the catalyst prepared according to Example 5 in the form of cylindrical bodies measuring 5 × 5 mm were introduced into a cylindrical pressure reactor with a capacity of about 750 ml Refined soybean oil (iodine number 129) was passed upwards to the top. The reactor was kept at a temperature of 140 ° C. and a pressure of 10 atm. The hydrogen was also passed into the reactor from above, in a molar ratio of 5: 1 (5 MoI H ₂ per mole of fatty acid residue) The end product had an iodine number of 77 and a melting point of 35 ° C. and contained only traces of linolenic acid.

Example 4

Hydrogenation of refined soybean oil with a Pd / Cr ₂ O ₃ catalyst

4 g (2% by weight) of a Pd / Cr ₂ O ₃ catalyst which contained 0.6% Pd were added to 200 g of refined soybean oil. This corresponds to a Pd concentration of 0.012% in the oil. The catalyst was prepared as follows: Chromium oxide was sprayed with palladium chloride solution. The material was calcined after drying at temperatures between 200 and 400 ⁰ C. The soybean oil was heated within 20 minutes at a temperature of 146 ° C and atmospheric pressure

Hydrogenated to an iodine number of 80. The melting point of the hydrogenated product was 33.4 ° C.

B e i s ρ i e! 5

Preparation of a catalyst for the process
according to alternative (a)

Palladium compounds in amounts of 0Ή to 0.5% by weight (calculated as metal) and chromium compounds in amounts of 0.01 to 2% by weight (calculated as metal) were applied to a γ- _{aluminum oxide carrier. For example, PdCl 2 was applied as the compound} , used as a chromium compound CrO ₃ , in the form of a single or in the form of separate solutions. The solution or the solutions were sprayed onto the γ-aluminum oxide carrier, or the carrier was immersed in these solutions. The carrier impregnated with the palladium and chromium compounds was then calcined at about 450 ° C. for 3 to 4 hours.

Example 6

Preparation of a catalyst for the process
according to alternative (b)

The procedure according to Example 5 was repeated with the difference that Cr ₂ O ₃ in the form of a powder or in the form of pressed tablets was _{impregnated with a 10% strength aqueous PdCl 2} solution. The amount of the solution was chosen so that the catalyst contained about 2% by weight of Pd in the calcined state. The calcination was carried out as in Example 5 at about 150 ° C. over a period of 3-4 hours.

Claims (1)

Patent claims: 1. A process for the selective hydrogenation of polyunsaturated fats, oils, fatty acids or mixtures of these substances by treatment with hydrogen in the presence of supported palladium catalysts at temperatures of about 60 to 220 ^° C., characterized in that chromium-containing supported palladium catalysts are used,