Method for producing polyamide-6

Abstract

The invention relates to the field of the chemical industry, and more particularly to a method for producing polyamide-6. The technical result of the invention is an increase in the yield and relative viscosity of high-molecular-weight polyamide-6. A method for producing high-viscosity polyamide-6 includes obtaining a prepolymer by the two-stage hydrolytic polymerization of caprolactam in the presence of an initiator, more specifically water in an amount of 1.0-1.3 wt%, and then producing a granulate of polyamide-6 from the molten prepolymer, and carrying out solid-phase post-polyamidation of the granulate in a flow of inert gas, more specifically nitrogen at a temperature of 175-180°С, and continuous combined solid-phase drying and demonomerization of the resulting equilibrium granulate of polyamide-6 in a flow of inert gas, more specifically nitrogen at a temperature of 150-160°С. In the first stage of hydrolytic polymerization, polymerization is carried out at a temperature of 210-220°С for 9-10 hours, and in the second stage of hydrolytic polymerization, polymerization is carried out at a temperature of 210-220°С for 9-14 hours.

Description

[0001] Method for producing polyamide-6

[0002] AREA OF TECHNOLOGY

[0003] The invention relates to the field of chemical industry, namely, to a method for producing polyamide-6.

[0004] LEVEL OF TECHNOLOGY

[0005] A method for producing fiber-forming polycaproamide is known (RU Patent 2196785. Published 20.01.2003. Application: 2001115082 / 04, 06.06.2001), which includes hydrolytic polymerization of caprolactam by obtaining a melt of prepolymerizate with subsequent dehydration of the melt of the reaction mass.

[0006] Significant disadvantages of this method are the high concentration of initiator (3.0% by weight) and the low degree of polymerization of caprolactam.

[0007] A method for producing fiber-forming polycaproamide is also known (RU 2145329, published 10.02.2000), in which a reaction mixture consisting of caprolactam and water is heated in glass ampoules to a temperature of 210-225°C and held for a certain time until the polymer state is close to equilibrium. The ampoules are then cooled until the contents of the ampoules become solid, after which the ampoules with the solid polymer are heated to a temperature of 170-190°C and held until the end of polymerization. The total duration of the polymerization process in the melt and solid phase is 28-32 hours. Then the ampoules with the polymer are cooled, the polymer is removed, crushed into granules and prepared for molding. This preparation is carried out by heating the polycaproamide granulate to a temperature of 135-140°C. At the same time, water and low molecular weight compounds are removed.Water and low-molecular compounds are removed from the drying zone by a stream of inert gas, which passes from the dryer through a monomer trap, a water seal and is released into the atmosphere. Drying is carried out for 10 hours. Upon completion of drying, the apparatus is cooled, the polymer with a low-molecular compound content of 1.3 to 1.4 wt.% and a relative viscosity of 2.59-2.73 is unloaded and sent for molding.

[0008] However, this method has the following disadvantages:

[0009] - impossibility of regulating the molecular weight of polycaproamide during the technological process, which allows forming only textile yarns. To obtain the target product with a higher molecular weight of the polymer, suitable for forming technical yarns. The polycaproamide obtained in this way must be subjected to additional processing, namely, additional polycondensation in the solid phase at a temperature of 180 ° C for 12-18 hours, which leads to additional energy costs. The use of a known technique in the form of reducing the initial amount of water leads to a significant increase in the duration of the technological process; - low quality of polycaproamide granulate in terms of granulometric composition, since it is obtained only by grinding a polymer block, since this method can only obtain a polymer in a block.

[0010] In addition, a method is known for continuously producing polyamides (RU214408, published 10.01.2000) from a mixture of at least one lactam and water under polyamide-forming conditions, wherein at the first stage the said mixture is heated at a pressure at which the reaction mixture is single-phase and liquid, and at the second stage it is subjected to an adiabatic pressure release and further polymerization, characterized in that at the first stage a mixture containing 0.5 - 7 wt.% water is used, the said mixture is heated to 220 - 310 °C and polymerized until a conversion of at least 85% is achieved, after which at the second stage after an adiabatic pressure release at 215 - 300 °C the polymerization is continued.

[0011] The disadvantage of this method is the low yield of the product and the impossibility of obtaining a high molecular weight polymer.

[0012] The closest, i.e. the prototype, is the method for producing fiber-forming polycaproamide (Patent of the Russian Federation 2196786, published 10.02.2003). In this method, the reaction mixture consisting of caprolactam and water is heated in glass ampoules to a temperature of 210-214°C and maintained for a certain time, necessary for the reaction mass to reach a degree of conversion of caprolactam into polymer close to the equilibrium one. Then the synthesis product is maintained at the same temperature until the end of the polycondensation reaction. The total duration of the synthesis is 24-28 hours. Upon completion of the synthesis, the polymer melt is poured out of the apparatus in the form of a vein, which is cooled and chopped into granules. Polyamide-6 granules are loaded into a dryer with a false bottom. The dryer is heated to 140°C under constant vacuum. Drying is carried out for 10 hours. After drying is complete, the apparatus is cooled and the polymer granules are unloaded.

[0013] The significant disadvantages of this method are:

[0014] - high concentration of initiator (3.0% by weight),

[0015] - the complexity of the hardware design due to vacuuming at the drying stage as a result of the evaporation of a large amount of moisture,

[0016] - low relative viscosity of polyamide-6 - 2.09-2.58.

[0017] DISCLOSURE OF INVENTION

[0018] The objective of the claimed invention is to develop a method for producing a highly viscous and high molecular weight polymer of polyamide-6.

[0019] The technical result of the invention is an increase in the yield and relative viscosity of high-molecular polyamide-6. The said technical result is achieved due to the fact that the method for producing high-viscosity polyamide-6 includes obtaining a prepolymer during two-stage hydrolytic polymerization of caprolactam in the presence of an initiator - water in an amount of 1.0-1.3 wt.%, followed by obtaining polyamide-6 granulate from the prepolymer melt, solid-phase prepolyamidation of the polyamide-6 granulate in a flow of inert gas - nitrogen at a temperature of 175-180°C and continuous combined drying-demonomerization in the solid phase of the obtained equilibrium polyamide-6 granulate in a flow of inert gas - nitrogen at a temperature of 150-160°C. In this case, at the first stage of hydrolytic polymerization, polymerization is carried out at a temperature of 210-220°C for 9-10 hours, and at the second stage of hydrolytic polymerization, polymerization is carried out at a temperature of 210-220°C for 9-14 hours.

[0020] IMPLEMENTATION OF THE INVENTION

[0021] The claimed method for producing high-viscosity polyamide-6 is carried out as follows. First, a process of continuous two-stage hydrolytic polymerization of caprolactam is carried out in a polymerizer apparatus, wherein at the first stage the process of hydrolytic polymerization of caprolactam is carried out in the presence of an initiator - water in an amount of 1.0-1.3 wt. % at a temperature of 210-220 ° C for 9-10 hours with the production of a prepolymer, and at the second stage of hydrolytic polymerization the polymerization is carried out at a temperature of 210-220 ° C for 9-14 hours. As a result of the two-stage hydrolytic polymerization, an equilibrium prepolymer with a degree of polymerization of 94-95% is obtained.Then the prepolymer melt is cooled and granules of polyamide-6 are obtained with subsequent solid-phase pre-polyamidation of the polyamide-6 granulate in a flow of inert gas - nitrogen at a temperature of 175-180°C and continuous combined drying-demonomerization in the solid phase of the obtained equilibrium polyamide-6 granulate in a flow of inert gas - nitrogen at a temperature of 150-160°C.

[0022] Example 1

[0023] In the polymerization apparatus are added 99 wt. % caprolactam and 1 wt. %, then a two-stage hydrolytic polymerization of caprolactam is carried out, in the first stage the mixture is heated to 210 ° C and maintained at this temperature for 9 hours, as a result of which hydrolytic polymerization of caprolactam occurs with obtaining a prepolymer. Then the second stage of hydrolytic polymerization is carried out, in which the obtained prepolymer is maintained at 210 ° C for 9 hours, as a result of which a prepolymer with a degree of polymerization of 94-95% is obtained. Then the prepolymer melt is cooled and granules of polyamide-6 are obtained. Then the polyamide-6 granules were placed in a reactor and the process of solid-phase prepolyamidation of the polyamide-6 granulate was carried out in a stream of inert gas - nitrogen at a temperature of 175 ° C, as a result of which an equilibrium granulate of polyamide-6 with a molecular weight (MM) of 28,000 was obtained.Then the polyamide-6 granules were placed in a drying apparatus and combined drying-demonomerization in the solid phase of the obtained equilibrium polyamide-6 granulate was carried out in a flow of inert gas - nitrogen at a temperature of 150 ° C, as a result of which the viscosity of polyamide-6 increases and granules of high-viscosity polyamide-6 are obtained. As a result (see Table 1), polyamide-6 is obtained (based on the concentration of caprolactam in the polyamide-6 granulate (CL)) with a low content of low-molecular compounds (LMW) in the polyamide-6 granulate, high relative viscosity (g|. О tn) and high yield of polyamide-6.

[0024] Example 2

[0025] Example 2 is similar to Example 1, except that 98.9 wt. % caprolactam and 1.1 wt. % are added to the polymerizer apparatus, the hydrolytic polymerization in the first stage is carried out at a temperature of 215 °C and maintained at this temperature for 9.5 hours, and the second stage of hydrolytic polymerization is carried out at 215 °C for 12 hours. The process of solid-phase prepolyamidation of polyamide-6 granulate is carried out at a temperature of 177 °C, and the combined drying-demonomerization in the solid phase is carried out at a temperature of 155 °C. As a result (see Table 1), polyamide-6 is obtained (based on the concentration of caprolactam in the polyamide-6 granulate (CL)) with a low content of low molecular weight compounds (LMWC) in the polyamide-6 granulate, a high relative viscosity (g| О tn) and high yield of polyamide-6.

[0026] Example 3

[0027] Example 3 is similar to example 1, except that 98.7 wt. % caprolactam and 1.3 wt. % are added to the polymerizer apparatus, the hydrolytic polymerization in the first stage is carried out at a temperature of 220°C and maintained at this temperature for 10 hours, and the second stage of hydrolytic polymerization is carried out at 220°C for 12 hours. The process of solid-phase prepolyamidation of polyamide-6 granulate is carried out at a temperature of 180°C, and the combined drying-demonomerization in the solid phase is carried out at a temperature of 160°C. As a result (see Table 1), polyamide-6 is obtained (based on the concentration of caprolactam in the polyamide-6 granulate (CL)) with a low content of low molecular weight compounds (LMWC) in the polyamide-6 granulate, a high relative viscosity (Pot) and a high yield of polyamide-6.

[0028] The invention has been disclosed above with reference to a specific embodiment thereof. Other embodiments of the invention may be obvious to specialists, without changing its essence as disclosed in the present description. Accordingly, the invention should be considered limited in scope only by the following claims.

Claims

CLAUSES OF THE INVENTION 1. A method for producing high-viscosity polyamide-6, including obtaining a prepolymer by two-stage hydrolytic polymerization of caprolactam in the presence of an initiator - water in an amount of 1.0-1.3 wt.%, followed by obtaining polyamide-6 granulate from the prepolymer melt, solid-phase prepolyamidation of the polyamide-6 granulate in a stream of inert gas - nitrogen at a temperature of 175-180 ° C and continuous combined drying-demonomerization in the solid phase of the obtained equilibrium polyamide-6 granulate in a stream of inert gas - nitrogen at a temperature of 150-160 ° C, wherein in the first stage of hydrolytic polymerization, polymerization is carried out at a temperature of 210-220 ° C for 9-10 hours, and in the second stage of hydrolytic polymerization, polymerization is carried out at a temperature of 210-220 ° C within 9-14 hours.

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