Continuous synthesis method of polyamide and vertical multi-stage reactor

Abstract

The invention provides a continuous synthesis method of polyamide in a manner of parallel flowing of gas and liquid phases with step-by-step reduction on pressure of the gas phase, so that escape of alarge quantity of diamine and water in the early-stage of the reaction can be avoided, and complete reaction of polyamide salt is guaranteed. In the later period of the reaction, the gas phase pressure is low, so that water in the reaction system can be removed easily and increase of molecular weight of the polyamide is promoted; wherein the polymerization degree of a product can reach 20-60, thus relieving or eliminating the requirement on following pressure-reducing apparatuses. The invention further provides a reactor for carrying out the method, which has the advantages of improving reliability of the reaction process, reducing damage on energy and reducing equipment cost and repair cost.

Description

technical field [0001] The present invention relates to a continuous polymerization method for producing polyamide and an apparatus capable of performing the polymerization method. More precisely, the present invention relates to a continuous polyamide synthesis method and a vertical multi-stage reactor. Background technique [0002] Processes for the continuous production of polyamide materials such as Nylon 66 are known in the prior art, and a traditional production process involves the use of 3-5 different reaction vessels connected in series. The production of polyamide materials by these methods needs to be completed through multiple reaction steps. These steps are usually carried out in tubular reactors or stirred tanks, mainly including processes such as evaporation concentration, high-pressure pre-condensation, flash evaporation, atmospheric final polycondensation and vacuum polycondensation. And these steps are performed separately from each other in space. Page 5...

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Problems solved by technology

The above-mentioned process is the mainstream of the continuous polymerization process of nylon 66 at present, and has the following disadvantages: 1. The process is lengthy, and the construction investment and operation costs are high; 2. The high-pressure precondensation stage uses a tubular reactor, and the entire reaction process maintains a high pressure, which is not conducive to The evaporation of the reaction product water limits the growth of the polyamide molecular weight in terms of chemical balance; 3. It takes a long reaction time for the flash pressure to drop from more than 15 atm to normal pressure, and the viscosity of the material in the process is large, and the condensation water It is not easy to evaporate, which restricts the increase of the molecular weight of polyamide; 4. During the flash evaporation process, the polyamide entrained with the evaporation of condensation water and the fluctuation of the reaction liquid level are likely to cause scarring on the reactor wall, and subsequent cleaning is troublesome

However, in order to ensure that the liquid phase flows from the top of the tower to the bottom of the tower, the gas phase is in contact with the liquid phase retrogradely from the top of the tower, and the pressure of the whole tower gradually increases from top to bottom, resulting in the following defects: 1. The pressure at the inlet of the liquid phase is relatively small , a large amount of water evaporates, and the heat load will increase sharply in order to maintain the temperature required for the reaction; 2. The lower pressure in the upper part of the reactor will cause a large amount of diamine to evaporate, which will affect the condensation reaction; 3. The rapid liquid phase in the upper part of the reactor There is a risk of unreacted polyamide salt precipitation in concentration; 4. The polyamide product flows out of the tower kettle at a relatively high pressure, and it is still necessary to configure a decompression device with a long residence time to enter the subsequent normal pressure or vacuum polycondensation reactor react

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