RU2471816C1 - Method of producing polyamide-6 - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention relates to a method of producing polyamide-6 by emulsion polymerisation of caprolactam. The method involves preparation of a reaction mass from caprolactam, an initiator and polyethylsiloxane liquid, heating, preliminary ageing, main ageing, cooling and separating the formed granules, the initiator used being 1,6-hexamethylene diamine in amount of 2-4% of the weight of the starting caprolactam; the reaction mass is heated to 210-215°C, and preliminary ageing is carried out for 1-1.5 hours.

EFFECT: high quality of the end product and low power consumption.

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Description

The invention relates to the chemical industry, and in particular to a method for producing polyamide-6 by emulsion polymerization.

State of the art

The production of fiber-forming polyamide-6 is carried out (Clare G. Synthetic polyamide fibers / G. Clare, E. Fritzsche, F. Grebe; edited by Z. A. Rogovin; M .: Mir. - 1966 - P.683) at present by means of polycondensation of caprolactam in a melt in devices of ideal displacement.

Obtaining polyamide-6 includes the following operations.

Caprolactam from storage tanks (where it is stored under a nitrogen pad at a temperature of T = 95 ° C) is pumped through a candle filter to either the agitator tank or the intermediate tank. The initiator (1-3.5%), the molecular weight regulator (0.5%), and light and heat stabilizers are loaded there. Mixing time about forty minutes. Stirring is carried out in an inert gas medium, in which nitrogen with an oxygen content of not more than 0.0005% is used.

After that, the reaction mixture is fed through a filter into a horizontal tank, which is designed to mix batches of the reaction mixture and its homogenization. Nitrogen is also supplied to the horizontal tank. From a horizontal tank, the reaction mixture is supplied by submersible pumps to the metering device of continuous polymerization apparatuses.

Then the reaction mixture is sent to a continuous polymerization apparatus.

Next, the reaction mass enters the polyamidation step. Depending on the assortment of the obtained polyamide-6, various schemes of semi-continuous technological schemes are used.

According to a semi-continuous technological scheme, the polymer melt from the continuous polymerization apparatus enters the high pressure head unit and is fed to the injection head, where it is forced through the die, forming melt jets that enter the bath with softened water, where they cool and solidify. The temperature of the water supplied to the bath is 20–25 ° C, and the outlet temperature is 25–35 ° C.

The frozen vein is fed into a chipper, where it is chopped into granules washed with water in a two-section hopper. The hopper is filled simultaneously with granules and water. After this, the granules are pumped to the extractor to remove low molecular weight compounds by repeatedly extracting the granules with hot water. Water temperature not lower than 110 ° C. The extraction time is 4-5 hours.

After extraction, the granules contain a large amount of water, which is removed by drying with heated nitrogen at a temperature of 120-140 ° C. Drying is carried out to a residual moisture content in granules of not more than 0.05%. The drying time is 10-14 hours.

After extraction and drying, the granules have a relative viscosity of 2.6-3.0, low molecular weight compounds of 0.5-1.5%.

However, this method is characterized by very high resource and energy costs.

A known method of producing polyamide-6 (RF Patent 2393176; published on 06.27.2010), which is the closest to the invention in terms of essential features. The method includes the following operations:

1. Preparation of the reaction mass. The monomer, the initiator, which is water, and a polyethylsiloxane liquid are charged into the reactor;

2. Heating the reaction mass to 90-100 ° C. It continues until the entire volume of the reaction mass warms up;

3. Preliminary exposure at a temperature of 90-100 ° C for 3-4 hours so that the required number of end groups are formed in the reaction mass. This time is called the induction period.

4. Subsequent heating of the reaction mass to 210-215 ° C and the inclusion of a mixing device.

5. The main exposure at a temperature of 210-215 ° C for 18-22 hours with stirring.

6. Cooling with stirring.

7. Coagulation of the polymer with the formation of granules.

8. Separation of polymer granules from polyethylsiloxane liquid in a centrifuge.

However, the method has the following disadvantages:

- The low quality of polyamide-6 due to the impossibility of guaranteed production with fiber-forming properties. This is due to the fact that due to the hydrophobicity of the polyethylsiloxane liquid during heating, water evaporates, is in the gas phase and does not work as an initiator. So, the polymerization degree of polyamide does not exceed 50;

- Significant energy consumption due to a long induction period - 3-4 hours.

SUMMARY OF THE INVENTION

An inventive task is to find a method for producing polyamide-6 by emulsion polymerization of caprolactam, which includes preparation of the reaction mixture from caprolactam, initiator and polyethylsiloxane liquid, its heating, preliminary exposure, basic exposure, cooling and separation of the formed granules, which would improve the quality of the target product and reduce energy consumption .

The problem is solved by the method of producing polyamide-6 by emulsion polymerization of caprolactam, including the preparation of the reaction mass from caprolactam, initiator and polyethylsiloxane liquid, its heating, preliminary exposure, basic exposure, cooling and separation of the formed granules, in which 1,6-hexamethylene diamine is used as initiator in an amount of 2-4% by weight of the initial caprolactam, the reaction mass is heated to 210-215 ° C, and preliminary exposure is carried out for 1-1.5 hours

The invention allows to obtain the following advantages:

- improving the quality of polyamide-6 due to the guaranteed receipt of a polymer with fiber-forming properties, the degree of polymerization of 75-90;

- reduction in energy consumption due to a decrease in the induction period by 50-60% (up to 1-1.5 hours).

Information confirming the reproducibility of the invention

To implement the method using:

- as a monomer - caprolactam - GOST 7850-86;

- as immersion liquid - polyethylsiloxane liquid GOST 13004-77;

- 1,6-hexamethylenediamine (AG salt) - TU-6-03-418-80.

The method is carried out by sequentially carrying out the following stages:

1. Preparation of the reaction mass. Caprolactam, 2-4% of the taken caprolactam of 1,6-hexamethylenediamine (AG salt) and polyethylsiloxane liquid with a 1: 4 module are loaded into the reactor;

2. Heating the reaction mass to 210-215 ° C. It continues until the entire volume of the reaction mass warms up;

3. Pre-exposure at a temperature of 210-215 ° C for 1-1.5 hours so that the required number of end groups are formed in the reaction mass. This time is called the induction period;

4. The main exposure at a temperature of 210-215 ° C with stirring for 20-22 hours;

5. Cooling with stirring;

6. Coagulation of the polymer with the formation of granules;

7. Separation of polymer granules from polyethylsiloxane fluid in a centrifuge.

The fiber-forming ability of the obtained polyamide-6 was judged by the degree of polymerization of the prepolymer, calculated according to the well-known formula (P = 100 (η _rel -1)) using the value of relative viscosity, determined in accordance with GOST 18249-72.

The properties of polyamide-6 obtained in various modes of the claimed method are shown in the table.

Properties of polyamide-6 obtained in various modes of the claimed method Table No. p / p t, ° C of the reaction mass Excerpt The concentration of salt AH,% wt. Degree of polymerization induction period, h main h one 210 one twenty 2 83 2 215 1,5 22 3 85 3 210 one twenty four 80 four 215 1,5 22 2 90 5 210 one twenty 3 86 6 215 1,5 22 four 75 7 210 one twenty 2 88 8 215 1,5 22 3 86 9 210 one twenty four 78

Claims (1)

A method of producing polyamide-6 by emulsion polymerization of caprolactam, comprising preparing the reaction mixture from caprolactam, initiator and polyethylsiloxane liquid, heating it, pre-exposure, basic exposure, cooling and separation of the granules formed, characterized in that 1,6-hexamethylene diamine is used as an initiator the amount of 2-4% by weight of the original caprolactam, the reaction mass is heated to 210-215 ° C, and preliminary exposure is carried out for 1-1.5 hours