DE1255661B - Continuous process for the production of pyridine and 3-picoline - Google Patents

Description

Continuous process for the production of pyridine and 3-picoline The invention relates to a continuous process for the production of pyridine and 3-picoline by passing a gaseous mixture of ammonia with a vaporized one Mixture of acetaldehyde and an aqueous formaldehyde solution over a 400 Common catalyst heated to 550 "C.

Surprisingly, it has been found that the yield of such a process Can improve significantly if the aqueous formaldehyde solution is used before mixing with the acetaldehyde about the equimolar amount of methanol is added.

When the method according to the invention is carried out, a mixture is thus obtained made from methanol and aqueous formaldehyde solution. This mixture becomes Acetaldehyde added. The methanol-formaldehyde-acetaldehyde solution is evaporated, mixed with ammonia gas, and the resulting mixture is through a suitable Reactor containing a conventional catalyst passed. The temperature of the reactor is maintained between about 400 and 5500 ° C, preferably between about 450 and 500 ° C.

But there are also better yields outside of this temperature range than achieved by the known method which works without the addition of methanol.

Various types of reactors can be used, preferably like those for fluidized bed catalysts similar to those commonly used used in the cracking processes in the petroleum industry. Such reactors are tubular and have suitable connections at the entrance and exit. she are equipped with means to maintain the fluidized bed of the catalyst as well as with any suitable heating devices.

In a preferred embodiment of the method according to the invention about 1.5 moles of acetaldehyde, about 1 mole of formaldehyde, about 1 mole of methanol and about 2.4 moles of ammonia reacted.

All or some of the acetaldehyde can be replaced by acetylene.

The method according to the invention is carried out below Example shown in which the specified parts are parts by weight.

EXAMPLE To 67 parts of an aqueous formaldehyde solution containing 45010 formaldehyde 32 parts of methanol are added. There is considerable heat during the addition developed. Therefore, the methanol is slowly added in small proportions while the mixture is kept stirring during the addition. To the one made above 62 parts of acetaldehyde are added to formaldehyde hemiacetal solution. The received Acetaldehyde-formaldehyde hemiacetal solution, hereinafter referred to as AFH, is evaporated and mixed with ammonia to form a gaseous mixture of 4.5 parts AFH and 1 part ammonia. The vapor mixture is passed through a reactor in the manner of a fluidized bed reactor with a catalyst layer of silica-alumina (13 01, clay). The temperature of the reactor is kept at about 5000 ° C. As the vapors of ammonia and AFH pass through the reactor, a reaction takes place instead, whereby pyridine and 3-picoline are formed. The fumes of the unreacted Reactants and the reaction products are when they exit from the Reactor condenses and the condensate collected in a suitable collecting vessel. The condensate obtained contains about 72% water. The water can be added of sodium hydroxide in flake form. Make the raw, dry bases about 47 parts. The crude, dry bases are fractionated to give pyridine and 3-picoline to be won.

The pyridine recovered is about 35 ° 10 and the 3-picoline is about 270% based on the sum of the quantities of formaldehyde and methanol used.

The 3-picoline has a purity of more than 9501, from which it can be seen that little, if any, 4-picoline is formed.

Instead of acetaldehyde, acetylene (which is a dehydrated acetaldehyde is) can be used.

If acetylene is used in the method according to the example, then a gaseous mixture of Formaldehyde hemiacetal, acetylene and Ammonia is produced and the mixture obtained is passed through the reactor.

Instead of the silica-alumina catalyst, a large number other catalysts can be used. Among the catalysts that are in use of the method according to the invention were found to be appropriate, are the Catalysts that are used in the production of 2-picoline and 4-picoline from acetylene and ammonia have been found useful. Such catalysts are besides that Silica-alumina catalyst of the example: alumina, silicic acid, silicic acid-magnesia, Fuller's earth, pumice stone, zinc chloride, zinc fluoride, cadmium chromate, cadmium chloride, Zinc phosphate.

The molecular equivalents of the reactants used in the example acetaldehyde equals 1.5 moles, formaldehyde hemiacetal 1 mole (or 1 mole formaldehyde and 1 mol of methanol), ammonia 2.4 mol. However, it does not need the special molar Amounts of the example to be used.

The proportions of the reactants can vary widely. An excess of ammonia is generally used, although this is not necessary is. It has been found that when 3-picoline does not do so by substantial amounts is contaminated by 4-picoline, the reaction mixture is preferably to be prepared should not contain more than 2 moles of acetaldehyde per mole of formaldehyde hemiacetal; advantageously the mixture should be 1 to 1/2 mole (or less) acetaldehyde (or Acetylene) per mole of formaldehyde hemiacetal.

If it is also appropriate, the formaldehyde hemiacetal by reaction of 1 mole of formaldehyde with 1 mole of methanol, this is not necessary. Instead, a small excess of either formaldehyde or methanol can be used can be used and the resulting mixture instead of the 1 molar mixture of the example be used.

The reaction mechanism of the process of the invention is not clarified. It is quite unexpected that through the interaction of ammonia and Acetaldehyde with a mixture of methanol and formaldehyde significantly better yields compared to those in the reaction of ammonia and acetaldehyde with formaldehyde or obtained with methanol.

Claims (3)

Claims: 1. Continuous process for the production of Pyridine and 3-picoline by passing a gaseous mixture of ammonia with them an evaporated mixture of acetaldehyde and an aqueous formaldehyde solution over a conventional catalyst heated to 400 to 550 "C, characterized by, that the aqueous formaldehyde solution before mixing with the acetaldehyde about the equimolar amount of methanol is added. 2. The method according to claim 1, characterized in that about 1.5 Moles of acetaldehyde, about 1 mole of formaldehyde, about 1 mole of methanol and about 2.4 moles of ammonia implemented. 3. The method according to claim 1 or 2, characterized in that the acetaldehyde is completely or partially replaced by acetylene. Documents considered: British Patent No. 742 643.