SU688506A1 - Method of preparing polycaproamide - Google Patents

Description

(54) METHOD FOR OBTAINING POLYCAPROAMIDE

kind of dosed initiator, resulting in inhomogeneity in the resulting product.

The purpose of the invention is to increase the output per unit time per unit volume of the reactor, reduce energy consumption, increase the conversion rate and improve the quality of the final product.

The goal is achieved by heating up to a temperature of 1O-200 ° C due to the heat of polymerization released in the second stage of polymerization, and then to a temperature of 270-280 ° C for a time period of 0.1-0.5% of the polymerization reaction time. after which the first polymerization stage is carried out, at which the caprolactam ring hydrolytically splits, within 8-30% of the polymerization reaction time with a water content of 2-4%, after which the second polymerization stage is carried out at a constant water content of 0.1 - 0.4 weight. %

A suitable apparatus for carrying out the process consists of a prereactor and a main reactor, the prereactor equipped with a stirrer having a tubular coil, the outlet of which is within the prereactor within the unpolymerized melt. The prereactor is connected through the melt supply line to the main reactor, which contains a nozzle for discharging the released vapor and, if viewed from top to bottom, a distribution device that increases the surface area of the unpolymerized melt, a reaction zone without inserts, a heat exchanger and integrated flow control devices. In the heating jacket of the main reactor, at the height of the heat exchanger, there is a tubular coil fitted with an inlet pipe connected to a coil in the heating jacket of the prereactor.

The proposed method is illustrated in the drawing.

The mixture of e-caprolactam, initiator and stabilizer is introduced at a temperature of 80 ° C into the device in the form of a reactor divided into prereactor 1 and the main reactor 2. The mixture passes primarily through the tubular coil 3 built into the heating jacket 4 of the main reactor 2, and here it is preheated to 190 ° C. The coil 3 is connected to another coil 5 in the heating jacket 6 of the prereactor 1, so that the preheated mixture rushes through the coil 5 and the outlet 7 inside the unpolymerized melt, inside the prereactor 1.

At the same time, in less than 0.5% of the total residence time of the polymer melt in the reactor during turbulent flow in the tubes, the temperature is brought to 270-280 ° C.

The 5N 3 tubular coils are not clogged, since the initial reaction and thus the polymerization of the mixture is still very weak. In prereactor 1, having a nominal volume of 1 m, under optimal conditions, the hydrolytic splitting of the cycle takes place with constant stirring. For this purpose, in the prereactor l, the stirrer 8 is provided. Technological

the process requires the supply of a matting agent in the form of a suspension of TiO2, then mixing is particularly appropriate. A mixture with a water content of 3% is under pressure inside the prereactor from 1 to

4 hours at a temperature of 270-280 ° С. The process can take place in prereactor 1 and in the absence of pressure, the vapors being sent to the reflux condenser, from where the remaining water and caprolactam should be introduced into prereactor 1. After the hydrolytic cycle splitting, the fully unpolymerized melt is fed through a control valve 9 in the pipeline for melting inside the main reactor 2 The control valve 9 is controlled depending on the level of the melt inside the main reactor 2. Instead of the control valve 9, you can also use a metering pump with adjustable speed. The main reactor 2 with a nominal volume of 5.3 m has a discharge pipe for released vapors, a switchgear 10, a reaction zone without inserts, a heat exchanger 11 and inserts 12

for flow direction.

The unpolymerized melt is distributed by arranging lO across the surface of the polymer melt in the inner cavity of the main reactor 2. The distribution device 10 simultaneously performs the function of increasing the specific surface area of the unpolymerized melt in order to achieve more favorable evaporation conditions of the water contained therein.

Due to the relaxation of the unpolymerized melt in the cavity without the pressure of the main reactor 2, the water immediately evaporates.

At the same time, a part of the caprolactam and low oligomers that are not converted due to the equilibrium reaction also evaporate. These vapors are discharged through a vent to a reflux condenser 13, where the condensation of e-caprolactam and oligomers is carried out. The steam is first condensed in the sump 14. In the upper part of the inner cavity of the main reactor 2 at a temperature of 270-

280 ° C polycondensation of the unpolymerized melt takes place for almost 6 hours. The heat liberated in this case causes an increase in the temperature of the melt. Following this, the melt passes through the heat exchanger 11, where the melt is cooled

to a temperature close to the cure point.

The heat obtained here is used for the preheating of the initial mixture from 80 to 190 ° C, therefore the tubular coil 3 is built into the heating jacket 4 of the main reactor 2 at the height of the heat exchanger 11. The circulation of the coolant is carried out according to the principle of natural circulation. It can also be created by force with a pump not shown. Polyaddition as the last phase of the reaction takes place in the lower part of the main reactor 2, where to achieve uniform flow conditions without backmixing, means (inserts) 12 are installed to control the flow movement.

This phase of the reaction lasts up to 8 hours. The polymer melt leaves the main reactor 2 through outlet 15.

The invention has the advantage that polyamide-6 can be obtained with a uniformly high degree of polymerization during short-term residence in the reactor. Reducing the duration of the polymerization reaction is achieved due to the short heating time of the initial mixture and regulation of the polymerization using the amount of water and temperature. Hydrolytic cleavage of the e-caprolactam cycle, as the first phase of the reaction, at the optimum water content of the initial mixture with the quickest form of OOM, leads to a maximum conversion of the e-caprolactam, as a result of which an optimal concentration of the terminal carboxyl groups is achieved, having a catalytic effect on the reaction.

The effect of water content on the equilibrium of polymers and monomers has the opposite effect, since high water content shifts the equilibrium towards the monomers and thus the reaction in the other two phases is forced to occur with a low water content. It was found that, compared to reactors of the same capacity, it was possible to increase the specific productivity per unit volume by approximately 35% and to reduce the energy consumption by approximately 15%.

Claims (1)

Invention Formula The method of producing polycaproamide by preheating the reaction mixture consisting of "e-caprolactam, water and stabilizer, and hydrolytic polymerization in two stages, characterized in that, in order to increase the yield per unit time per unit volume of the reactor, reduce energy consumption, increase the degree of conversion and improvement of the quality of the final product, heating is carried out to a temperature of 180-200 ° C due to the heat of polymerization released in the second stage of polymerization, and then to temperatures of 270-280 ° C for a period of time of 0.1-0.5% of the time of the polymerization reaction, after which the first stage of polymerization is carried out, during which the hydrol1 occurs: caprolactam rings, for 8-30% of the time of the polymerization reaction with a water content of 2-4%, after which the second polymerization stage is carried out with a constant water content of 0.1-0.4 weight. %