DE1445974C - Process for the preparation of pyridine - Google Patents

Description

The invention relates to a specific process for the production of pyridine by converting formaldehyde, Acetaldehyde and. Ammonia at elevated temperature in the presence of a catalyst, wherein the formation of other pyridine bases, such as 2-, 3- and 4-picoline, as by-products is reduced.

Various catalytic processes for the chemical synthesis of pyridine bases are already known. So pyridine and 3-PicoIin can by catalytic reaction of formaldehyde, acetaldehyde and ammonia iηjder _v ^ vapor phase at elevated temperature ■ door manufactured. However, no satisfactory process μΓ selective production of pyridine with high yield while reducing the formation of picolihenes as by-products has been known or proposed.

From the British patent 790 994 it is known that pyridine and 3-picoline are produced by reaction of formaldehyde, acetaldehyde and ammonia over a silica-aluminum oxide catalyst "(15% Al ₂ O ;,), which is an oxide of a 3- or tetravalent metal, can be produced in the vapor phase in a temperature range of 400 to 500 "C. British Patent 816 973 also describes that pyridine and 3-picoline are produced by the conversion of formaldehyde, acetaldehyde and ammonia in the presence of methanol and a catalyst, as is used in the production of 2- and 4-picoline from acetylene and ammonia is common, can be produced. In this reaction, the proportion of acetaldehyde to be used should not be more than 2 moles per mole of formaldehyde. The pyridine yield is unsatisfactory in all of these known processes because of the formation of the by-product 3-picoline. '

In contrast, the process according to the invention represents an improved process for the production of Pyridine, with the formation of other pyridine bases, such as 2-picoline, 3-picoline and 4-picoline, as by-products is decreased.

The inventive method consists in that the gaseous reaction mixture contains 2 to 5 moles of acetaldehyde per mole of formaldehyde and the reaction takes place in a temperature range of 400 to 550 ° C. ' _v ! _: . , ".;'' Γ. .- '..,.'

When carrying out the process according to the invention, any catalyst and any reaction condition can be used which are customary in the production of pyridine bases by catalytic reaction in the vapor phase using aldehydes and ammonia as starting materials, although the exact molar ratio of acetaldehyde is used Formaldehyde must be complied with, which is the most important feature of the invention. <,:> r. ^r

A gaseous mixture of formaldehyde, Acetaldehyde and ammonia are continuously introduced into a reaction vessel which is equipped with a The catalyst is filled and kept at an elevated temperature.

Various types of catalysts such as fixed bed, fluidized bed and fluidized bed catalysts can be used in the reaction vessel. As already mentioned above, any conventional catalyst can be used for this reaction. Examples are silica, alumina, silica-alumina and silica-magnesia, with silica-alumina being the most suitable. The C jehalt of alumina in the alumina catalyst is Kieselcrde-IIf variable within a range ^grolien:; also a content .of GewichtsprozentrTpnerde particularly 5 to 25 is favorable. It is also advantageous to combine a suitable co-catalyst with the main catalyst listed above. The metals of the IL, III., IV. And VIII. Group of the Periodic Table and the oxides of these metals are suitable as cocatalysts. In practice, at least one of the metals Zn, Cd, Th, Co and their oxides is used as a cocatalyst. The amount of cocatalyst can be 0.1 to 15 percent by weight, based on the total weight of the catalyst. ■ '-' ■:. '■

The addition of the co-catalyst to the main catalyst, z. B. silica-alumina, can be done in the usual way, for example by common Precipitating or soaking. A catalyst according to the invention can, for. B. by the following procedure Be prepared:. To a silica gel freshly prepared from sodium silicate by adding an acid an aqueous solution of an aluminum salt and a cadmium or zinc salt in the form of nitrate, Sulphate or chloride was added and the mixture was then stirred with alkali, e.g. B. an aqueous ammonia solution added to aluminum and cadmium or zinc together in the form of the hydroxide on the Precipitate silica: the mass is then washed with water to remove the water-soluble substances, shaped, dried and fired. The catalyst prepared in this way remains under the inventive Conditions its activity for a few tens of hours. The regeneration of the used catalyst can be easily done by directing hot air onto the catalyst bed and so carbon and organic substances deposited on the surface of the catalyst burn away.

The gaseous reactants, ie formaldehyde, acetaldehyde and ammonia, can be mixed with one another. Formaldehyde gas and acetaldehyde gas can also be mixed and gaseous ammonia can then be added to this mixture. Mixing of the reaction participants should, if possible, take place before introduction into the reaction zone. The gas mixture is preferably preheated to a temperature close to the reaction temperature. In any case, the aldehydes and ammonia should only be mixed together or brought into contact, after both have been preheated separately to at least 250 ⁰ C. If \ aldehydes and ammonia are reacted at a temperature below 250 ° C into contact, so Adducts that clog the reaction vessel and thereby prevent it from flowing through the reaction vessel, the reaction gas form. The temperature in the reaction zone should, in the range of 400 to 550 ⁰ C, are preferably from 430 to 480 ⁰ C.

The contact time of the gaseous reaction mixture can be in the range from 0.1 to 7 seconds (throughput 36,000-514 h " ¹ ).

In general, the reaction is carried out under normal or atmospheric pressure, it can if required, however, you can also work a little above i or below one atmosphere with one push.

The gas flowing out of the reaction vessel after the reaction has ended can be used to obtain the desired pyridine bases are treated in the usual way. So z. B. the derived gaseous Reaction product condenses, the oily

Layer separated, dried over a desiccant, such as solid alkali hydroxide, and then fractionally distilled to obtain pyridine in the pure state.

Not only formaldehyde as such, but also any other substance, such as an aqueous formaldehyde solution, paraformaldehyde, trioxane, methylal, methyl-hemiformal or a mixture of two or more of these substances are used, which are among those to be applied Reaction conditions can develop formaldehyde. Similarly, acetaldehyde cannot be the only one as such, but also any other substance such as paraldehyde or a mixture of acetaldehyde and Paraldehyde can be used, which develop acetaldehyde under the given reaction conditions. It should therefore be pointed out that the terms "formaldehyde" and "acetaldehyde" in the description and in the claims not only on the corresponding aldehydes, but also on the refer to the substances listed above from which these aldehydes can be formed.

The ammonia content in the reaction mixture is variable within a wide range that it can 0.5 to 10 moles, preferably 1 to 1.5 moles per mole of total aldehyde.

As already mentioned above, the essential feature of the manufacturing process is the particular molar ratio of acetaldehyde to formaldehyde in the reaction mixture, for the invention aims only at the production of pyridine and is based on the observation that the molar ratio from acetaldehyde to formaldehyde the yield of pyridine as well as the reduction in the formation of By-products or picolines decisively influenced, as can be seen from the following examples is.

In the examples, the yields of pyridine and picolines were based on the aldehydes used contained carbon and it was assumed that no other bases were formed. More precisely, the yield of pyridine was calculated on the assumption that if all of the η the carbon contained in the aldehydes used: for the formation of pyridine and not for the formation of Would serve picolines, the yield of pyridine would theoretically be 100%. The same assumption was made made for every picoline.

Example 1

An aqueous solution that is 37% aqueous Formaldehyde solution and acetaldehyde in a molar ratio of 2.5 moles of acetaldehyde per mole of formaldehyde

ίο contained was at a rate of 3.2 g evaporated per minute and preheated to a temperature of about 250 ° C. On the other hand became a stream of ammonia gas at a rate of 0.81 per minute at normal temperature and Generated normal pressure and preheated to a temperature of about 250 ° C. The two gas flows were mixed and passed through a catalyst layer containing 350 ml of an 82% silica, 15% alumina and 3% zinc oxide existing silica-alumina catalyst contained. The temperature of the catalyst layer was maintained at about 435 ° C. during the reaction. The gas mixture flowing out of the reaction vessel, which consisted of the reaction product and unreacted material, was cooled and condensed. The condensed liquid was mixed with solid sodium hydroxide Deposition of the dry, crude pyridine bases added (greenish-gray, oily products). The raw ones Pyridine bases were carefully fractionally distilled and there were pyridine, 2-picoline and a mixture of 3- and 4-picoline separated. The yield and degree of purity of the pyridine bases thus obtained were as follows:

Pyridine, yield 38.2% (purity 98%);
2-picoline, yield 6.5% (purity 98%);

Mixture of 3- and 4-picoline, yield 12.5% (composition: 3-picoline 66%, 4-picoline 34%).

Example 2
40

It was made in the same way as in Example 1

described, carried out a series of experiments, but some reaction conditions were changed, as the following table shows. The table also contains the results of these tests.

approach
No. Type and molar ratio of the reactant formaldehyde lMol acetaldehyde 1.4 moles ammonia 1.9 moles catalyst 1 formaldehyde lMol acetaldehyde 2.0 moles ammonia 2.5 moles SiO ₂ : Al ₂ O ₃ ZnO 2 formaldehyde lMol acetaldehyde 2.3 moles ammonia 2.8 moles SiO ₂ : Al ₂ O ₃ ZnO 3 formaldehyde lMol acetaldehyde 2.5 moles ammonia 2.1 moles SiO ₃ : Al ₂ O ₃ ZnO 4th formaldehyde lMol acetaldehyde 2.5 moles ammonia 3MoI SiO ₂ : Al ₂ O ₃ ZnO 5 formaldehyde lMol acetaldehyde 2.8 moles ammonia 3.3 moles SiO ₂ : Al ₂ O ₃ ZnO 6th formaldehyde lMol acetaldehyde 3.5 moles ammonia 4MoI SiO ₂ : Al ₂ O ₃ ZnO 7th formaldehyde lMol acetaldehyde 5.0 moles ammonia 5.5 moles SiO ₂ : Al ₂ O ₃ ZnO 8th formaldehyde lMol acetaldehyde 7.0 moles ammonia 7.5 moles SiO ₂ : Al ₂ O ₃ ZnO 9 formaldehyde lMol acetaldehyde 2.5 moles ammonia 3MoI SiO ₂ : Al ₂ O ₃ ZnO 10 Trioxane lMol paraldehyde 2.5 moles ammonia 9MoI SiO ₂ : Al ₂ O ₃ CdO 11th SiO ₂ : Al ₂ O ₃ ZnO

approach
No. Throughput
h- ¹ Reaction temperature
⁰ C Pyridine yield
% 2-picoline
% Picoline yield
3-picoline
% 4-picoline
% 1 627 450 21.5 2.5 13.2 1.6 2 735 440 30.4 5.0. 11.3 2.8 3 788 440 35.4 5.7 9.5 3.4 4th 740 435 38.2 6.5 8.3 4.2 5 590 440 38.6 6.3 8.2 4.2 6th 627 440 34.7 7.5 7.0 6.8 7th 718 440 30.6 11.9 5.8 8.5 8th 910 440 26.6 13.1 1.7 12.2 9 870 440 18.0 16.8 0.8 14.6 10 590 450 38.0 6.2 8.1 4.8 11th 875 440 38.4 6.3 8.2 4.1

Claims (2)

Claims: 2 ^ 1. A process for the preparation of pyridine by reacting formaldehyde, acetaldehyde and ammonia at elevated temperature in the presence of a catalyst, characterized in that the gaseous reaction mixture contains 2 to 5 moles of acetaldehyde per mole of formaldehyde and the reaction takes place in a temperature range from 400 to 550 ⁰ C takes place. 2. The method according to claim 1, characterized in that the gaseous reaction mixture Contains 2.2 to 3.5 moles of acetaldehyde per mole of formaldehyde.