DE2850719A1 - Nickel catalyst protection against oxidn. - by sorption of fat from soln. on internal surface to maintain hydrogenation activity during transport and storage - Google Patents

Abstract

Protection of Ni catalyst (I) against oxidn. by atmos. O2 is achieved by chemi- and physisorption of an at least monomol. layer of fat from a soln. on the internal surface of (I), without completely filling the pores. An unsatd. soln. of the fat in a solvent is prepd. at a temp. T1, pref. above the m.pt. of the fat (mixt.), then the powdered catalyst is stirred into the soln., the suspension is cooled by 10-50 K and the solvent is pumped away. If the surface requirement is ca. 75 x 10-20 m2/fat mol., a 10-20 mol. layer with a thickness of (1-2) x 10-8 m is formed. The catalyst is pelleted under a pressure of 3-7 MPa, using a solid additive, which passes into the gaseous state below the operating temp. of the reactor in which the catalyst is used, or a hard fat. Catalyst retains its full hydrogenation activity during transport and storage. It is useful in hydrogenation, e.g. of fats.

Description

Method of making a gene the

Oxidation by atmospheric oxygen-protected nickel catalyst subject of the invention is the production of an anti-oxidation by atmospheric oxygen protected nickel catalyst.

Powdered substances are often characterized by a very reactive surface the end. This is especially true when they are microporous within the macroscopic grains Have structure. The same goes for porous bodies made from such powders sinter metallurgical processes are established. In many cases the aim is the reactive state of such porous powders or bodies to get them for to use chemical or electrochemical reactions. This is especially true for those substances that are used as catalysts in chemical processes should.

But also finely distributed metal powder with a large inner surface are worth mentioning here, especially if you think of them as negative electrode materials wants to use in galvanic cells. Since the production of such substances mostly takes place in a reducing atmosphere, they burn when they come into contact with the oxygen in the air or with other gas components present in the air spontaneously with strong heat development. This makes handling between production and use very difficult, because they are always with the exclusion of atmospheric oxygen, moisture or carbon dioxide must be done.

Those in fat chemistry are particularly sensitive in this regard hydrogenation catalysts used. For example, it is obtained catalytically very active, finely divided nickel by converting nickel formate in reducing or decomposed in an inert atmosphere. This creates a nickel powder with a large inner Surface that contains disposable hydrogen and, when exposed to air, creates an appearance of fire burns.

A second way of making a highly active nickel catalyst consists in following a proposal from RANDE? an aluminum-nickel alloy Treated with alkaline lye and thereby dissolve the aluminum.

This creates an extremely disordered, hydrogen-containing one Nickel metal powder, the so-called Raney nickel, which is especially useful when dry is strongly pyrophoric.

A third type of highly active catalyst is produced by that a basic nickel carbonate is used in a highly porous support body such as kieselguhr impregnated and this reduced under hydrogen at approx. 4000C. Also this one in particular Suitable catalyst for fat hydrogenation is highly pyrophoric and must be used its catalytic use must be protected from the ingress of oxygen.

Because of the great technical importance of highly active catalysts Processes were developed to make such catalysts insensitive to atmospheric oxygen and to be able to handle them more easily between production and use, but also to take away the inherent danger during shipping.

For example, it is known to use Raney nickel catalysts isothermal oxidation with atmospheric oxygen or by gentle oxidation in liquid Phase with e.g.

Passivate H202. With this preservation by a thin oxide layer the metallic character of the nickel is retained. The oxide surface is through Exposure to hydrogen before use as a hydrogenation catalyst increases again to reduce. The disadvantage of this method is a certain delay in setting the hydrogenation activity. This method is also used with most other metal catalysts applicable.

A second method is to rub the catalyst surface with a to cover higher-quality alcohol with a high boiling point. This is also used to achieve a certain protection against oxidation with delayed start-up behavior.

In the case of nickel catalysts made from nickel formate and in the case of supported catalysts the catalyst is often embedded in fat. To do this, hot liquid becomes Grease initially placed and the catalyst stirred in, without coming into contact with atmospheric oxygen get. The catalyst-containing Fat is rolled out when it cools and stored in a shed. The advantage of this process is that the catalyst is fully effective immediately and does not interfere with the embedding fat in the hydrogenation product. The disadvantage is that the multiple amount of fat, based on the weight of the catalyst, adheres to this and interferes with shipping.

The invention is therefore based on the object of the nickel catalyst to be preserved in such a way that it is protected against atmospheric oxygen with the covering agent is loaded as little as possible and its hydrogenation activity is still in full Dimensions are retained during transport and storage.

The object is achieved according to the invention in that chemical and physisorption from a solution creates a layer of fat on the inner surface of the Catalyst material is applied, which the catalyst in at least 1-molecular Layer covered, but the pore volume is not completely fulfilled.

Such a layer of fat produced by chemisorption and physisorption can protect the catalytic converter from oxidation by atmospheric oxygen over the long term. Obviously one is dealing with a process that is analogous to isothermal surface adsorption of nitrogen.

It has proven to be particularly beneficial if the fat layer does Pore volume not completely fulfilled, but preferably 10-20 molecular layers thick is. The production of such a layer comprises the following steps: First step is the production of an unsaturated solution of the fat or fat mixture in one Solvent at a temperature T1, which is advantageously above the melting temperature of the fat mixture lies.

The powdery catalyst is introduced into this solution with stirring. The suspension is then allowed to cool by 10 to 500K compared to T1 and finally pumped the solvent off.

After performing these steps, the fat is on the inner surface of the catalyst chemisorbed or physisorbed; when evaporating the Solvent crystallizes the fat on the chemisorbed fat layer as a nucleating agent inside the catalyst powder. This has the surprising effect that a free-flowing catalyst powder remains, which is filled into plastic bags Can be stored for a long time and is easy to put in the hydrogenation reactor, e.g. for fat hydrogenation can be introduced.

For a more detailed explanation, the method should be based on the specific example of a Nickel catalyst on kieselguhr are explained. Such catalysts show with a BET surface area of 120-160 m2 / g has a high hydrogenation activity on. To carry out the process, a hard tallow with a melting point is dissolved from 53-540C in cyclohexane. This solution is carried at about 50 ° C. with stirring the catalyst to be protected. As a guide it may be considered that one per kg Catalyst fat mixture of the finished catalyst requires around 600 ml of C6H12. Under With stirring, the mixture is cooled to 280 ° C. and the cyclohexane is removed by pumping off. The catalyst remains as a powder, which is expediently passed through a sieve happened with a mesh size of 0.8 mm. This catalyst powder is very free-flowing, so that it can be used in a tablet press with 3 - 7 MPa without special precautions Compression pressure at 400C into tablets can be processed under these conditions the preserved catalyst about 1.25 to 1.5 kg of fat per kg of nickel metal.

Assuming a surface area of the fat molecule of 75 x 10 20m2, the fat layer comprises about 15 molecular layers.

The advantage of the tableted catalyst is that it is in Bags can be stored for any length of time, but also after the container has been opened the high concentration of nickel in the tablet reduces oxidation compared to the powder further complicated.

One carries the tabletted catalyst in the 100C hot fat of a A hydrogenation reactor, it disintegrates very quickly within 10 seconds. The catalyst distributed homogeneously suspended in the fat and enables rapid hydrogenation of the material presented.

You can accelerate the disintegration of the tablet by that the powdery catalyst is only gaseous decomposition products prior to aer tabletting forming organic or inorganic substance - comparable to an effervescent powder - added, which is solid during the tableting and storage of the catalyst, in hot fat evaporates spontaneously. Suitable for this are: ammonium carbonate, deer horn salt or agents such as those used as blowing agents in the foam industry will.

To improve the compression properties of the catalyst powder can This is mixed with a portion of fat powder, which can be obtained, for example, by grinding Hard tallow (melting point 53 - 540C) at the temperature of solid carbonic acid.

Claims (7)

Claims 1. A method for producing an anti-oxidation Nickel catalyst protected by atmospheric oxygen, characterized in that by chemisorption and physisorption from a solution a layer of fat on the inner one Surface of the catalyst material is applied, which the catalyst in at least 1-molecular layer, but not completely fulfilling the pore volume. 2. The method according to claim 1, characterized in that an unsaturated Solution of the fat is dissolved in a solvent at the temperature T1, the is preferably above the melting temperature of the fat or fat mixture, that the powdery catalyst is introduced into the solution with stirring, that the suspension is cooled by 10-50 ° K compared to T1 and that the solvent is pumped out on it. 3. The method according to claims 1 and 2, characterized in that that-with a space requirement of approx. 75 x 10 20m2 per rescue molecule the Fel layer on the Area unit the inner surface of the catalyst measured according to Brunauer, Emmett and Teller (BET surface area) comprises 10-20 molecular layers and is 10 8 m to 2 × 10 8 m thick. 4. The method according to claims 1 to 3, characterized in that that the oxidation-protected catalyst powder with a pressure of 3 to 7 MPa is compressed into tablets. 5. The method according to claim 4, characterized in that the oxidation-protected Catalyst powder mixed with the powder of a solid substance before tableting is below the operating temperature of the reactor in which the catalyst is used, passes into the gaseous state. 6. The method according to claims 1 to 5, characterized in that that the melting point of the fat mixture to be dissolved is in the range of 50 - 600C, that cyclohexane is used as the solvent and that it disintegrates in gas Powder ammonium carbonate or staghorn salt is used. 7. The method according to claim 4, characterized in that the protected Catalyst powder before pressing into tablets with the powder of a hard fat is mixed.