Process for producing polyamide

Details Process for producing polyamide Process for producing polyamide

2001-01-19

2002-12-03

Hampton-Hightower, P. (Department: 1711)

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

Synthetic resins

From carboxylic acid or derivative thereof

C528S312000, C528S322000, C528S332000, C528S335000, C528S336000, C528S339000, C528S340000

Reexamination Certificate

active

06489435

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing polyamide. More specifically, the present invention relates to a process for producing polyamide, comprising a step of preparing a substantially amidation-free slurry liquid comprising a xylylenediamine-rich diamine component and a dicarboxylic acid component in a batch-wise regulation tank. The slurry liquid is fed to a batch-wise or continuous polymerization reactor as a starting material to produce polyamide.
2. Description of the Prior Art
In the production of polyamide from a diamine component and a dicarboxylic acid component, an accurate molar balance between the diamine component and the dicarboxylic acid component is quite important for achieving an intended polymerization degree. To produce polyamide having an intended molar balance, special care is usually taken in accurately controlling the charge amounts of the diamine component and the dicarboxylic acid component as well as in preventing the diamine component from escaping from the reaction mixture. Although a batch-wise polymerization is clearly advantageous over a continuous polymerization with respect to the easy control of the molar balance, the production of polyamide by a continuous polymerization is also under consideration due to its low heat history and industrial advantages.
The charge amounts of the constitutional components of polyamide can be accurately controlled by adjusting pH when a nylon salt or its aqueous solution is used as the starting material to be fed to a polymerization reactor. However, there arises a problem attributable to the use of the nylon salt or its aqueous solution as the starting material.
In batch-wise polymerization using an aqueous solution of nylon salt, the polycondensation is conducted in the same reactor by heating a 50% aqueous solution of nylon salt under pressure, allowing the polycondensation to proceed in homogeneous phase while preventing the diamine component from escaping, and gradually releasing water vapor from the reactor after fixation of the diamine component to finally reach ordinary pressure or reduced pressure, thereby completing the polycondensation.
Known continuous polymerization is usually carried out by two or three stages according to the intended polymerization degree. In the first stage, an aqueous solution of nylon salt is fed to a reactor and subjected to polymerization therein to produce prepolymer. In the second stage, the prepolymer is separated from water and is further polymerized to reach the intended polymerization degree. Since the continuous polymerization is industrially advantageous as compared with the batch-wise polymerization, various techniques for the continuous polymerization using an aqueous solution of nylon salt as the starting material is disclosed in Japanese Patent Publication Nos. 44-22510, 49-20640, 56-46487, 5-52333, etc. However, the proposed methods requires a highly pressure-resistant vessel to prevent water used as the solvent from escaping in the initial stage of polymerization. In the final stage of polymerization, a large amount of water used as the solvent and the condensation water should be removed, and such removal requires means for avoiding various disadvantages such as foaming, solidification of polymer due to evaporation latent heat of water, etc. In addition, the removal of a large amount of water requires a high heat-energy consumption. Thus, the conventional continuous process using an aqueous solution of nylon salt involves various technical and economical problems.
Japanese Patent Publication No. 44-3838 proposes a continuous polymerization using a nylon salt as the starting material. However, the proposed process is not efficient because additional steps for isolation and purification of nylon salt are required.
U.S. Pat. No. 5,674,974 discloses a continuous polymerization using no nylon salt or no aqueous solution of nylon salt as the starting material. In the proposed process, a molten dicarboxylic acid component or a molten dicarboxylic acid-rich component is fed to a multistage reactor, and a vapor or liquid diamine component is fed at the second and subsequent stages while controlling the molar balance of the dicarboxylic acid component and the diamine component by a feedback control system utilizing near infrared spectroscopy. However, unlike the use of nylon salt or its aqueous solution, the process where the monomer components are separately and continuously fed into a continuous polymerization reactor is less accurate in the charge amounts, and it is difficult to achieve, by a flow controller, a molar balance sufficiently accurate for controlling the polymerization degree of polyamide. Therefore, the proposed process requires to detect and adjust the molar balance throughout the polymerization step.
In stead of using nylon salt or its aqueous solution, the best alternative for controlling the molar balance between charged polyamide-constituting components is a method where the amounts of the diamine component and the dicarboxylic acid component are separately measured in batch-wise manner by a mass measuring device such as a load cell, and then each component is fed into the reactior. For example, known is a method in which a molten dicarboxylic acid component is fed to a reactor after measuring its amount by a mass measuring device, and then a diamine component is fed to the reaction system while measuring its amount by a mass measuring device, thereby controlling the molar balance of the dicarboxylic acid component and the diamine component. As disclosed in Japanese Patent Application Laid-Open No. 58-111829, this method is suitably applicable to produce polyamide by a polymerization under ordinary pressure without using nylon salt as the starting material. However, since the mixing of the diamine component with the dicarboxylic acid component is carried out at a temperature higher than the melting point of the dicarboxylic acid component, the amidation proceeds remarkably. In addition, when the mixture is finally subjected to a continuous polymerization, the variation in polymerization degree detrimentally occurs due to the different residence times in transferring the mixture from a batch-wise regulation tank to a continuous polymerization reactor. Therefore, the mixture (reaction product) of the dicarboxylic acid component and the diamine component prepared by this method cannot be a stable starting material for the polymerization.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for producing polyamide without using nylon salt or its aqueous solution as the starting material to be fed to a polymerization reactor, in which a molar-balanced mixture of a diamine component and a dicarboxylic acid component being substantially free from amidation reaction is prepared by using a batch-wise mass measuring method capable of accurately controlling the molar balance between the diamine component and the dicarboxylic acid component (hereinafter may be referred to as “molar balance”), and the resultant mixture is fed to a batch-wise or continuous polymerization reactor where polyamide is suitably produced.
As a result of extensive studies, the inventors have found that a mixture of a diamine component comprising 80 mol % or more of xylylenediamine and a dicarboxylic acid component provides an extremely stable, uniform slurry free from amidation when prepared in the absence of a solvent at a temperature within a specific range and at a specific water content.
Thus, in an aspect of the present invention, there is provided a process for producing polyamide by polymerization of a diamine component comprising 80 mol % or more of xylylenediamine and a dicarboxylic acid component, comprising the steps of (1) feeding the diamine component to a batch-wise regulation tank after accurately measuring the mass of the diamine component; (2) adding the dicarboxylic acid component to the liquid diamine component in the batch-wise regulation tank in an amount so as to

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