Process and device for the standardized continuous production of

Details Process and device for the standardized continuous production of Process and device for the standardized continuous production of

1998-11-13

2000-10-24

Hampton-Hightower, P.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

528322, 528323, 528332, 528335, 528336, C08G 6916, C08G 6904, C08G 6928

Patent

active

061369470

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a process and a device for carrying out a process for the continuous production of, in particular, polyamide 6, polyamide 6.6 and copolyamides from .epsilon.-caprolactam and/or a salt of adipic acid with hexamethylenediamine or adipic acid and hexamethylenediamine. It is known that the production of polyamide 6, polyamide 6.6 and copolyamides should be carried out in sequences specially adapted in each case to the requirements of the product and with an arrangement of apparatus tailored to an optimal process sequence.
The polymerization of .epsilon.-caprolactam involves hydrolysis, polyaddition and polycondensation reactions whose most advantageous reaction rates occur in each case under other conditions. The hydrolysis of .epsilon.-caprolactam to .epsilon.-amino-caproic acid is the first and slowest reaction of the polymerization process. Expediently, the hydrolysis is carried out at high temperatures and with high water contents of the reaction mixture in the first process stage, in order to utilize the maximum possible hydrolysis rate. This process has to be carried out in a pressure stage. A low-viscosity product is formed. In this pressure stage, a viscosity limit is usually imposed by the added amount of water. In order to achieve the viscosity required for the processing of the polymer, the water added in excess to the pressure stage is expelled in one or more subsequent process stages operated at atmospheric pressure.
The desired viscosity is established by adding chain terminators at the beginning of the polymerization process and by a specific temperature program in the individual reaction steps (East German patent 133 681).
For the polymerization of a salt of adipic acid with hexamethylenediamine or adipic acid and hexamethylenediamine, it is known that an aqueous AH salt solution, which is heated in a pressure reactor to a temperature in the range of 220-280.degree. C., is used as a starting material, with the aim of preparing an AH salt precondensate in which the NH.sub.2 groups of the hexamethylenediamine are virtually all reacted with the COOH groups of adipic acid. It is also known that the aqueous hexamethylenediamine/adipic acid salt solution is heated under pressure with simultaneous evaporation of the water, and the expelled diamine is retained in a column and is recycled to the polymerization process. When such a precondensate is let down to atmospheric pressure, hexamethylenediamine can scarcely escape and no viscosity-reducing excess of acid is obtained. Dewatering and post-condensation of the polyamide 6.6 melt is carried out in principle as for the production of polyamide 6. The dewatering stage should however be adjusted and dimensioned for substantially more extensive dewatering (U.S. Pat. No. 2,689,839; German Offenlegungschrift 2,401,474). Known processes for the production of copolyamides from aqueous AH salt solution and .epsilon.-caprolactam assume that the production will be carried out in barometric reactors, so-called precondensation tubes. In these processes, however, only a maximum of 8% of AH salt can be added to the .epsilon.-caprolactam. A procedure using a high water content, owing to the aqueous AH salt solution which as a rule has a solids content of from 50 to 65% by weight, is difficult to control and, with additions greater than 8% of AH salt solution, leads to considerable quality fluctuations through nonuniform evaporation of water and, in spite of a rectification column on the precondensation tube, different amounts of hexamethylenediamine are discharged. Precondensate formed in a pressure stage and comprising a hexamethylenediamine/adipic acid salt solution is therefore mixed with molten caprolactam in a downstream, barometrically operated reactor, and a copolyamide is obtained as the polymerization progresses. However, this process permits the addition of .epsilon.-caprolactam to the aqueous AH salt solution only in amounts of up to 50% (German Offenlegungschrift 3,912,768).
The disadvantage of this pro

REFERENCES:
patent: 4246395 (1981-01-01), Martimer
patent: 5646191 (1997-07-01), Wiltzer et al.
patent: 5902553 (1999-05-01), Wiltzer et al.

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