SK277890B6 - Method of one-stage elimination of solvent from solution of elastomer polymer - Google Patents

Abstract

One-stage elimination of solvent from solution of elastomer polymer, which is selected from butadiene and isopren homopolymers and vinylaromate copolymers and conjugated diene in which is fraction of conjugated diene hydrogenate mainly of block copolymers styrene-butadiene and styrene-isopren, with contents at least 20 per cent of this elastomere polymer, means, that to filling hoper of endless threading machine is led solution of elastomer polymer, heated on 150 to 200 degrees of Celsius at which by lowering of press in filling zone is eliminated 80 to 95 per cent of solvent. Solution of elastomer polymer is by degassing of solution anti current to motion of polymer, pusched forward at which is again heated on temperature 150 - 200 degrees of Celsius and surplus of solvent is eliminated by next degassing of solution stepping forward, at which is casually between different ventilating zones injected mass of water moving between 0,5 to 2 per cent of weight of polymer for accelerating of solvent elimination, and then the paste of elastomer polymer deprived of solvent is led into nozzle and pelletized.

Description

Technical field

The invention relates to a method of removing solvent from a polymer solution, in particular to a method of removing solvent from an elastomeric polymer solution having a different polymer content of at least 20% by weight.

BACKGROUND OF THE INVENTION

Treatment of polymer solutions to remove solvent and obtain polymer granules usually has two steps. In the first step, most of the solvent is removed to form a relatively viscous solution, which is fed to a degassing apparatus comprising one or two endless worms and a plurality of openings arranged on the circumference of the worm to escape the evaporated solvent.

The first stage can be carried out either in the reactor or equally finally in the screw. In both cases, the problems that arise are associated not only with flow control between the systems used in both stages, but also with the transfer of the polymer solution between the two systems, especially when highly viscous elastomeric polymer solutions are processed.

In two-stage systems, poor thermal stability of the resulting polymer is also observed with respect to many dead zones formed on the screw (s) and a long polymer retention time in the extruder.

In addition, when solutions of rubber-type elastomeric polymers are treated in conventional underwater granulation plants, rubber crosslinking is observed at the nozzle site. This is due to the high temperature resulting from the pressure drop before the nozzle during granulation of this type.

There is also a need to process these elastomeric polymer solutions to achieve a low volatile compound content; however, in conventional two-stage processes, this means a reduction of the residual content to about 0.5 wt. due to the small size of the screw used in the second stage.

Accordingly, it is desirable to find a process for removing the solvent from a solution of elastomeric polymers of rubber or non-rubber nature in one step, to obtain a residual volatile compound content of less than 0.1% by weight.

According to the present invention, the term elastomeric polymer means a polymer of which at least 15 wt. it is composed of an elastomer and the remainder is made of a thermoplastic resin.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION The present invention provides a process for the single-step removal of a solvent from an elastomeric polymer solution selected from butadiene and isoprene homopolymers and vinylaromate and conjugated diene copolymers in which the conjugated diene fraction is hydrogenated or the like, especially styrene-butadiene block styrene butene. contains at least 20% of this elastomeric polymer, wherein a feed solution of an elastomeric polymer heated to a temperature of 150 to 200 ° C, at a pressure higher than the solvent vapor pressure, is introduced into the feed hopper of the endless screw; up to 95% of the solvent is removed, with degassing of the upstream polymer solution, the elastomeric polymer solution is advanced, re-heated to 150 to 200 ° C, the remainder of the solvent is removed by further degassing of the forward solution, if any. suitable a quantity of water ranging between 0.5 and 2% by weight of the polymer is injected between the different ventilation zones to accelerate solvent removal, whereby the solvent-free elastomeric polymer paste is fed into the nozzle and cut.

The process according to the invention is carried out by passing the elastomeric polymer solution into a feed hopper of an endless screw. A residual volatile compound content of less than 0.1 wt.

The elastomeric polymers that are treated according to the invention may be of rubber or thermoplastic nature. For this purpose it is possible to process butadiene and isoprene polymers or, in most cases, rubber copolymers consisting of vinylaromatic monomers and conjugated dienes, such as styrene-butadiene copolymers or isoprene-styrene copolymers in which the proportion of monomeric conjugated diene is at least 15% by weight. When the process according to the invention is applied to the elastomer by thermoplastic polymers, these are in most cases block copolymers of conjugated diene having a high styrene content. It will be understood that the inventive process also applies to elastomeric vinylaromate / conjugated diene block copolymers in which the conjugated diene fraction is partially or fully hydrogenated.

These polymers are made by solution polymerization of the corresponding parent monomers. The polymers or copolymers are in the form of a solution in a polymerization solvent, in most cases in paraffinic, cycloparaffinic or aromatic hydrocarbons. Examples of suitable solvents are, in particular, cyclohexane, pentane, hexane, cyclopentane (sic), isooctane, benzene, toluene or mixtures of hexane with cyclohexane. The polymer content of the solution is generally 20 to 60 wt.

It has been found that it is possible to carry out solvent removal to a residual solvent content of equal to or less than 0.1% when processing the polymer solution in one step.

It has also been found that it is necessary to remove most of the solvent, i. 80 to 95%, through a ventilation opening located behind the rear of the charging hopper.

Unexpectedly, it has been found that by such a process, not only the polymer paste continues to move freely with the endless screw, but the solvent is easily removed since its passage to the back of the screw is not impeded at all.

This back ventilation is achieved by preheating the solutions to 150 to 200 ° C and reducing the pressure in the feed zone of the endless screw. This pressure reduction is controlled by a control valve located in the feed line of the endless screw.

The effect of this solvent removal is to substantially reduce the temperature of the polymer solution.

The Applicant has found that in order to obtain good solvent removal efficiency in the following ventilation zones, it is necessary to reheat the polymer solution to 150 to 200 ° C, the heat input being formed either by heating the screw cylinder to 180 to 250 ° C or equipping the screw with components. that induce shear forces, or a combination of different means.

It has been found that if the polymer solution is not reheated to a sufficient temperature, a residual content of the order of 0.1% cannot be achieved.

The residual solvent is gradually removed in the individual ventilation zones along with the progressive movement of the polymer paste in the worms.

These zones are usually under a pressure that is lower than or equal to atmospheric pressure. The vacuum rises with the progress of the polymer solution in the screw and varies from atmospheric pressure to about 500 Pa at the end of the screw. These degassing zones are usually 3 to 5 depending on the amount of solvent removed.

Water supplies may be formed between the individual degassing zones to aid in solvent removal. The amount of water introduced into the polymer paste is usually 0.5 to 2% by weight, based on the weight of the polymer.

As mentioned, there is a different pressure in the degassing zones, and sealing elements are typically used between the degassing zones of the screw to prevent suction. They usually consist of left-hand threads. A component of this type is also located downstream of the water supply points, since at the same time it allows perfect mixing.

It has also unexpectedly been found that granulation conditions are very important. In the usual underwater granulates, the pressure drop is too high and crosslinking is observed, which is very unpleasant.

It has been found that using a type of granulator that allows the nozzle to be installed just behind the endless screw, it is possible to reduce dead zones and reduce the pressure drop so that the temperature of the product remains below the crosslinking temperature of the polymer. Likewise, it is not necessary to cut the polymer under water, which constitutes an undoubted advantage of the process according to the invention.

It was also found that good removal of volatile components is necessary that the rotation speed of the screw was 100 and 300 rpm ¹ (sic). Usually, the speed of 150 to 250 rpm ^{the first}

The process according to the invention successfully removes large amounts of solvent from elastomeric polymer solutions in one step, but does not block or clog the screw.

It is to be understood that the invention relates in particular to the treatment of elastomeric polymer solutions, but can also be applied to any type of polymer which is in the form of a solution in a solvent.

Overview of the figures in the drawing

The method of the invention is described in connection with the accompanying drawing, illustrating an extruder for removing solvent from a polymer solution containing at least 20% polymer.

The polymer solution is fed to a feed hopper 10 of an extruder 12 comprising a double endless screw 14.

The extruder pressure and feed rate are controlled by a control valve 16.

The extruder comprises a rear ventilation zone 18 to remove most of the solvent. The polymer paste is advanced by means of an endless screw 14. To remove residual solvent, a plurality of ventilation zones 20 are arranged in the extruder 12. Between the ventilation zones, liquid introduction means 22, typically water, may be provided to facilitate removal of the solvent.

The solvent-free polymer paste passes through the nozzle 24 and is cut into granules in the granulator 26.

The following non-limiting examples illustrate the invention.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

After solution polymerization of butadiene and styrene, a cyclohexane solution containing a 38% starch styrene-butadiene copolymer containing 40% styrene is obtained.

This solution is fed at a temperature of 170 ° C at a rate of 75 kg / h to the double hopper feed hopper (type WP ZSK-57). The pressure is controlled by a valve located in the feed line. This extruder has one ventilation zone located behind the rear of the feed hopper and three ventilation zones located upstream of the feed hopper. The nozzle and the granulator are arranged immediately behind the endless screw.

The following operating conditions are used: Vacuum in ventilation zones:

rear zone 80 kPa

1. anterior zone of 80 kPa

2. Front zone 8 kPa

3. Front zone 1 kPa Rotation speed: 230 min ^-1

Before the last two ventilation zones, a water injection of 1%, based on the weight of the polymer, is made.

The solvent is obtained in an amount of 92% in the rear zone, 3% in the first and second anterior zones (sic) and 2% in the final zone. The final volatile content is 0.1 wt.

The pressure before congratulation is 1.5 MPa and the temperature of the material before granulation is 195 ° C.

The polymer is perfectly granulated without the need for underwater cutting.

Example 2

After solution polymerization of butadiene and styrene, a cyclohexane solution containing 38% styrene-butadiene block copolymer containing 75% styrene is obtained.

This solution is fed at a temperature of 165 ° C at a rate of 80 kg / h into the feeding hopper of a twin screw extruder (type WP ZSK-57). The pressure is controlled by a valve located in the feed line. This extruder has one ventilation zone located behind the rear of the feed hopper and three ventilation zones located upstream of the feed hopper. The nozzle and the granulator are arranged immediately behind the endless screw.

The following operating conditions are used: Vacuum in ventilation zones:

rear zone 80 kPa

1. anterior zone of 80 kPa

2. Front zone 8 kPa

3. Front zone 700 Pa Rotation speed: 270 min ^-1

Before the last two ventilation zones, a water injection of 1% based on the weight of the polymer is made.

The solvent is obtained in an amount of 89% in the rear zone, 3% and 6% in the first and second front zones and 2% in the final zone. The final volatile content is 0.1 wt.

The pre-granulation pressure is 1.5 MPa and the pre-granulation temperature is 192 C. The polymer is perfectly granulated without the need for underwater cutting.

Example 3

After solution polymerization of isoprene and styrene, a cyclohexane solution containing 38% styrene-isoprene block copolymer containing 15% styrene is obtained.

This solution is fed at a temperature of 160 ° C at a rate of 50 kg / h into the feeding hopper of a twin screw extruder (type WP ZSK-57). The pressure is controlled by a valve located in the feed line. This extruder has one ventilation zone located behind the rear of the feed hopper and three ventilation zones located upstream of the feed hopper. The nozzle and the granulator are arranged immediately behind the endless screw.

The following operating conditions are used: Vacuum in ventilation zones:

rear zone 80 kPa

1. Front zone 60 kPa

2. Front zone 6 kPa

3. Front zone 900 Pa Rotation speed: 220 min ^-1

Water is injected in front of the last two ventilation zones in an amount of 1% of water, based on the weight of the polymer.

The solvent is obtained in an amount of 89% in the rear zone, 4% and 6% in the first and second anterior zone (sic) and 1% in the final zone. The final volatile content is 0.1 wt.

The pressure before granulation is 800 kPa and the temperature of the material before granulation is 180 ° C.

The polymer is perfectly granulated without the need for underwater cutting.

Claims (4)

A process for the single-step removal of a solvent from an elastomeric polymer solution selected from butadiene and isoprene homopolymers and vinylaromate and conjugated diene copolymers wherein the conjugated diene traction is hydrogenated, in particular styrene-butadiene block copolymers and at least 20% styrene-isoprene, An elastomeric polymer, characterized in that a feed solution of an elastomeric polymer, heated at a temperature of 150 to 200 ° C, at a pressure higher than the boiling pressure of the solvent, is fed to the feed hopper of the endless screw and the pressure in the feed zone is reduced. 80-95% of the solvent, wherein degassing of the upstream polymer solution moves the elastomeric polymer solution forward, then reheats to 150-200 ° C, removing the remainder of the solvent by further degassing the forward solution, where appropriate between rôzn An amount of water between 0.5 and 2% by weight of polymer is injected through the ventilation zones to accelerate solvent removal, then the elastomeric polymer paste is discharged into the nozzle and cut. Method according to claim 1, characterized in that the polymer solution, which is free from 80 to 95% of the solvent, is subjected to repeated heating by heating the screw roller to a temperature between 180 to 250 ° C and / or introducing the shear-inducing components. force, into the screw. The method according to any one of claims 1 or 2, characterized in that the absolute screw pressure gradually decreases from atmospheric pressure up to 500 Pa as the polymer solution progresses. 4. The process of any of claims 1 to 3, characterized in that the combination screw rotates at a speed between 100 and 300 minutes ^1, preferably from 150 to 250 rpm for ^{the first}