Method for continuously polymerizing nylon from bi-component monomer serving as raw material

Abstract

The invention discloses a method for continuously polymerizing nylon from a bi-component monomer serving as a raw material. The method comprises the following steps of: reacting and rectifying a nylon salt aqueous solution serving as a raw material in a pre-condensing tower in which a liquid phase is a continuous phase, a gas phase is a dispersed phase and falling liquid and rising bubbles keep flat push flow respectively under a low pressure to generate a prepolymer of which the polymerization degree 5-50 (preferably 20-40) and a terminal carboxyl group, a terminal amino group and the like are of equal molar amounts; and pre-heating the pre-polymer to generate a polymer of which the polymerization degree reaches process indexes in the pre-condensing tower. In the pre-condensing tower, a film falling or strip falling method is adopted, so that evaporation of condensed water is accelerated, the reaction temperature is lowered, reaction time is shortened, and gel is reduced; and a kettle wall is coated with a falling liquid film, so that kettle wall scars are avoided. The method has the advantages of short flow, large mono-line scale, saving in investment, low running cost, good product quality, long continuous running period, environment friendliness and suitability for continually polymerizing nylon 66, nylon 56 and other nylon made of bi-component monomers serving as raw materials.

Description

technical field [0001] The invention relates to the field of polymer production, in particular to a method for continuous polymerization of nylon using two-component monomers as raw materials. Background technique [0002] The scientific name of nylon is polyamide, which is an important class of engineering plastics and synthetic fiber raw materials. The raw materials for nylon production are diverse and there are many varieties. The main types of nylon and their polymerization raw materials are shown in Table 1 below: [0003] Table 1 [0004] [0005] Nylon can be divided into two categories according to its different polymerization raw materials. One type of raw material is a single-component monomer containing both amine and carboxyl groups in the molecule, such as cyclic lactam or chain amino acid. The largest variety is caprolactam. The raw material is nylon 6; another type of raw material is dibasic acid and diamine two-component monomer, and the largest variety ...

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Problems solved by technology

[0008] The above three processes basically cover the current mainstream of nylon 66 continuous polymerization devices in the world. They have common shortcomings: 1. They all use nylon brine solution as raw material and follow the rules of concentration—high pressure precondensation—flash evaporation—normal (reduced) compression Polymerization route, long process, high construction investment and operating costs; 2. High-pressure precondensation links use tubular reactors, the temperature of the melt in the boundary layer of the tube wall is tens of degrees higher than that of the main area, and the residence time is longer than that of the main area Several times to dozens of times, the molecular weight distribution is wider; the tube diameter of the tubular reactor is restricted by heat transfer, and the single-line production capacity is small; It is not easy to evaporate, which restricts the growth of molecular chains. It takes a higher reaction temperature and a longer reaction time to reach the degree of polymerization specified in the process, resulting in more gels and affecting the quality of the polymer; 4. Condensed water from the liquid phase The entrained mist splashed to the reactor wall and the fluctuation of the reactor liquid level during the middle steaming are easy to cause scarring on the reactor wall, and it is necessary to stop production regularly to remove the scars or configure an online standby station to switch in turn, which is troublesome; 5. Every 1 ton of production The polymer discharges 2.5~3kg of hexamethylenediamine, which increases the consumption of raw materials and affects the environment

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