Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Patent
1998-11-24
2000-08-22
Hampton-Hightower, P.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
528312, 528322, 528323, 528332, 528335, 528336, 528499, 528500, C08G 6904, C08G 6928, C08G 6936
Patent
active
061074497
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process and an apparatus for carrying out the process for continuous preparation of polyamides, the monomeric starting material for which is composed of up to 100% of adipic acid/hexamethylenediamine salt and water.
For polymerizing adipic acid/hexamethylenediamine salt (AH salt) or adipic acid and hexamethylenediamine, it is known that an aqueous AH salt solution can be used as starting material and be heated in a pressurized reactor to a temperature in the range of 220 to 280.degree. C. in order to prepare an AH precondensate in which the NH.sub.2 groups of the hexamethylenediamine have reacted with the COOH groups of the adipic acid.
It is known that the aqueous adipic/hexamethylenediamine solution is heated under a pressure which is lower than the vapor pressure of the solution, with simultaneous evaporation of the water, and that the most volatile material driven off, hexamethylenediamine, is collected in a column and reintroduced to the polymerization process (U.S. Pat. No. 2,689,839; U.S. Pat. No. 3,960,820). When the pressure acting on a precondensate of this type is released, small amounts of hexamethylenediamine can escape. To compensate for the excess of acid, which reduces viscosity, an excess of hexamethylenediamine is added (U.S. Pat. No. 3,193,535; DE 2,417,003). Using known processes, water is removed from the polyamide melt, and the melt is post-condensed.
DESCRIPTION OF THE INVENTION
The object of the invention is to use the closed-system method of operating the polymerization reactor under the full pressure which becomes established at the appropriate reaction temperature to achieve complete reaction of the NH.sub.2 groups of the hexamethylenediamine and the COOH groups of the adipic acid.
The first step of the novel process is carried out under pressure at temperatures of from 180 to 280 degrees Celsius and then after this the polyamide is fed to further steps at the start of each of which the water which has evaporated is removed or driven out by an inert gas.
According to the invention, for continuous preparation of polyamides the process is conducted in such a way that nylon-6,6 and a copolyamide of the nylon-6
ylon-6,6 type can be prepared in the treatment steps described.
A polymerization reactor of the type described is used to carry out the following steps:
a) preheating the starting materials,
b) polymerizing the starting materials in a pressure step with no driving-off of water to give a prepolymer and/or precondensate, preferably at a temperature of from 180 to 220 degrees Celsius,
c) removing water from the prepolymer and/or precondensate in a one- to five-stage coiled tube in which a slow and controlled reduction of pressure takes place. The coiled tube was designed so that both relatively highly viscous prepolymer and relatively highly pressurized low-viscosity precondensate can be conveyed or discharged by pressure into the pressure reactor downstream,
d) treating the intermediate product in a second pressure reactor with driving-off of water, where the lactam driven off during the preparation of copolyamide of the nylon-6
ylon-6,6 type is directly reintroduced into the pressure stage in a rectification column,
e) further removal of water from the polymeric melt as described under c) and feeding the polymeric melt to a first postcondensation reactor,
f) a first postcondensation in a vertical reactor at temperatures in the range from about 210 to 285.degree. C., where the process is conducted from top to bottom by forming thin films of melt and driving off the water no longer needed for the remainder of the polymerization process,
g) further postcondensation of the melt in downstream reactors if high viscosities are to be achieved.
The invention will be described in more detail using working examples listed below and a drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawing shows a diagram of the arrangement according to the invention of the steps for the continuous preparation of polyamides.
EXAMPLES
Worki
REFERENCES:
patent: 2361717 (1944-10-01), Taylor
patent: 5646191 (1997-07-01), Wiltzer et al.
patent: 5723569 (1998-03-01), Sato et al.
patent: 5739262 (1998-04-01), Morhenn et al.
patent: 5777067 (1998-07-01), Sato et al.
patent: 5902553 (1999-05-01), Wiltzer et al.
Ebert Baldur
Schuster Mattias
Wiltzer Karlheinz
Hampton-Hightower P.
Polymer Engineering GmbH
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