DE19856590A1 - Emulsion polymerization of olefinically saturated monomers comprises heating reaction mixture by addition of heated water or steam to reduce formation wall coatings and coagulate - Google Patents

Abstract

A process for the emulsion polymerization of olefinically saturated monomers comprises heating the reaction mixture by the addition of heated water or steam. A process to reduce the wall coating and coagulate formation during the radically initiated polymerization of olefinically unsaturated monomers in aqueous emulsions at a polymerization temperature of 35-120 deg C comprises heating the reaction mixture to at least the polymerization temperature by the addition of heated water and/or steam.

Description

The invention relates to a method for reducing wall wall lay and coagulate in the polymerization reactor at the emulsion poly merization.

It is known to use aqueous polymer dispersions in a stirred tank reactor ren by polymerization of monomer emulsions at 35 to 120 ° C. to produce, the emulsions in stirred polymerization reactor with the help of heat exchangers in the reactor on the poly merization temperature heated or maintained at this. As a heat exchanger serve z. B. reactor jackets, such as stirring boiler reactors with raised floors, or for heat exchange Stinurte reactor internals such as coils, etc. It is also knows that in the metallic reactor in the emulsion polymer Coagulation and deposits on the reactor wall and the reactor form pure structures. These rubbers are undesirable because they are effective heat transfer between the heat exchange surface heat exchangers in the stirred tank wall or inside half of the reactor internals and the reaction mixture in the reactor prevent. Because the rubbers are also irregular form, is a calculated heat exchange at the metallic Heat exchange surfaces very difficult. This is all the more critical because the heat exchange surfaces in the polymerization reactor not only for heating, but also for the necessary cooling of the reactor mixture in exothermic polymerization reactions must serve. Also, the reactor is cleaned more often walls and the reak, which usually has a very large surface area built-in gates, e.g. B. coils, which is often tedious is and optimal use of a polymerization reactor does not make possible.

The present invention was based on the object of a method to find that enables the formation of coagulum and of wall coverings in the polymerization reactors at Emul to reduce ion polymerization of monomers.

It has now been found that this can be achieved by direct heating of the reaction mixture using metal mical heat exchange surfaces in the polymerization reactor leaves and the heating of the batches in the polymerization reactor  hot water and / or with steam, e.g. B. by the reak can be initiated.

The invention thus relates to a method for reduction of wall covering and coagulate in a particularly metallic bottom Polymerization reactor for the radical initiated Polymerisa tion of olefinically unsaturated monomers in aqueous emulsion while heating to a polymerization temperature in the range of 35 to 120 ° C, which is characterized in that a direct heating the reaction mixture via metallic heat avoids exchange surfaces in the polymerization reactor and the heating zen of the reaction mixture in the polymerization reactor using water heated to 35 to 120 ° C and / or by introducing Water vapor.

Carrying out the polymerization in an aqueous monomer Emulsion in a polymerization reactor has been described many times ben, and it will refer to the relevant specialist literature referred, as to the corresponding description in Houben- Weyl, Methods of Organic Chemistry, Volume E 20, Stuttgart 1987. The emulsion polymerization is preferably carried out in the so-called Zu running process in which part of the reaction mixture in the reactor is submitted to which the main part of the reaction mixture then with monomers and initiators or redox initiator components gradually added. This is a standard procedure of Has become emulsion polymerization and often in polymer lite literature, in particular the patent literature. At which he Execution of such a method according to the invention is avoided a direct heating of the polymerization batch during the Po polymerization reaction using heat exchangers in the reactor, such as heated reactor jackets, heated double-bottom reactors or heated reactor internals, such as coils. Instead it will the polymerization approach or the template in the polymerization reactor by introducing water vapor and / or adding hot heated water, including depending on the desired polymerization temperature accordingly at a temperature between 35 and 120 ° C heated water should be understood. It is beyond to what extent using the method according to the invention measures the formation of wall covering within the polymer risk reactor and can be reduced by coagulum.

Preferred metallic polymerization reactors are stirred tanks reactors. Examples of heat exchangers in polymerization reactor are double reactor walls and / or reactor bottoms as well as in the reactor built-in plates and / or pipes in which a heat is exchanged. It should be emphasized that too in the process according to the invention heat exchanger in the polymer  tion reactor can be used because their presence for the cooling and thus the control of some exothermic polymers tion reactions may be required. In the ver Should drive or built-in heat build-up in the reactor only do not use shear to heat the reaction mixture Det, because by polymerization on the hot metal surface surfaces of the heated heat exchange surfaces and coagulum is formed.

The heated water is added in a conventional manner, e.g. B. by running in. If water vapor is introduced, he this preferably follows through the reactor floor.

The following examples and comparative examples are intended to further illustrate but not limit the present invention. Unless otherwise stated, parts and percentages are given on the weight.

The viscosities specified were determined in accordance with DIN 53019.

LD values represent the light transmission of a 0.01% by weight Dispersion sample with a layer thickness of 25 mm compared with pure water.

The stated solids contents were determined gravimetrically after Ein Allow the dispersion in question to dry.

Comparative Example 1

In a stirrer connected to the reflux condenser and inlet vessels a mixture of 7.76 parts water, 3.86 parts egg a 20% aqueous solution of ethoxylated p-nonylphenol (Degree of ethoxylation 25), 1.22 parts of a 35% aqueous solution solution of sulfated, ethoxylated p-nonylphenol (ethoxylie grade 25), 0.155 parts of methoxymethyl cellulose, 0.155 parts Sodium bicarbonate, 0.043 parts of buten-2-ol (70%) and 0.1 part Feed B submitted. Feed B consisted of 1,795 parts of water and 0.135 parts sodium peroxydisulfate. The template was under scramble then heated to 80 ° C in the stirred kettle over the kettle wall, then feed A was added uniformly over a period of 4 hours.

Feed A consisted of 17.7 parts of water, 3.86 parts of a 20% aqueous solution of ethoxylated p-nonylphenol, 1.22 parts of a 35% aqueous solution of sulfated ethoxylated p-nonylphenol, 0.11 parts of acrylic acid, 25. 74 parts of vinyl propionate and 17.2 parts of tert-butyl acrylate. At the same time, the remaining amount of feed B was metered in uniformly over the course of 4.5 hours. During the feeds and up to 1 hour after the reaction temperature was kept at 80 to 85 ° C. in the stirred tank with the aid of the reactor jacket. It was then cooled to 35 ° C. and, with stirring, feed C consisting of 0.064 parts of water, 0.018 parts of a 40% strength aqueous paraffin sulfonate solution (C ₁₅ H ₃₁ SO ₃ Na) and 0.028 parts of tert-butyl hydroperoxide ( 80%), and feed D, consisting of 0.1 part of water and 0.02 part of sodium formaldehyde sulfoxylate, are added. Then the mixture was stirred for half an hour at normal pressure and for a further hour at a reduced pressure of 0.1 bar. Then 0.325 parts of concentrated aqueous ammonia were added. A 55% aqueous copolymer dispersion with a pH of 7.5, an LD of 60% and a viscosity of 1000 mPa.s was obtained, which gave a clear, glossy film on glass. The content of coagulum and the occurrence of wall covering in the stirred tank reactor are given in Table 1.

Comparative Example 2

• a) Preparation of the starting copolymer dispersion (I):
  A mixture of 13.1 g of a 30% aqueous hydrogen peroxide solution, 13.8 g of a 45% aqueous solution of a commercially available sodium salt of a branched C ₁₂ alkyldiphenyl ether disulfonate, 36 g of n-butyl acrylate and 407 g of water were added at 27 ° C with 25% of a feed B, which consists of 3.9 g of ascorbic acid, 0.1 g of iron (II) sulfate and 560 g of water. After 15 minutes, starting simultaneously, within 90 minutes the remaining amount of feed B and within 60 minutes feed A were metered in continuously, the heat of reaction being removed so that the reaction temperature reached 60 ° C. Feed A consisted of a mixture of 367 g of n-butyl acrylate, 367 g of methyl methacrylate, 15 g of methacrylic acid, 16.5 g of a 45% aqueous solution of a commercially available sodium salt of a branched C ₁₂ alkyl diphenyl ether disulfonate. An aqueous dispersion of a copolymer (I) having an average particle diameter of 30 nm was obtained.
• b) Preparation of the final polymer dispersion (II):
  33.3 g of the starting dispersion (I) prepared according to a) and 2.5 g of a 20% aqueous solution of a commercially available sodium salt of a branched C ₁₂ -alkyldiphenyl ether disulphonate were heated to 85 ° C. in a stirred tank reactor with the aid of the boiler and at this temperature was suddenly mixed with 3% of a feed C and then with 20% of a feed D and the mixture was then stirred at 80 ° C. for 15 minutes. Subsequently, the remaining amounts of the feeds C and D were simultaneously added continuously, starting at the temperature of 85 ° C., to the reaction mixture as follows:
  Feed C: 8% within 1 hour, then 89% within 2.5 hours;
  Inlet D: 80% within 4 hours (% numbers are based on the total amount of the corresponding inlets C and D).
  After feed D had ended, polymerization was continued in the stirred tank reactor for 1 hour.
  Feed C consisted of 375 g of ethyl acrylate, 100 g of methyl methacrylate, 10 g of acrylic acid, 10 g of 2-hydroxyethyl acrylate, 22.5 g of a 20% aqueous solution of a commercially available sodium salt of a branched C ₁₂ alkyl diphenyl ether disulfonate, 50 g of a 20% strength aqueous mixture of ethoxylated C ₁₆ -C ₁₈ fatty alcohols (degree of ethoxylation: 18) and 104.17 g of water.
  Feed D: 2.5 g of sodium peroxydisulfate and 100 g of water.
  The content of coagulate in the resulting polymer dispersion and the occurrence of wall covering in the polymerization reactor are given in Table 1.

Comparative Example 3

In a stirred tank equipped with a reflux condenser, 2 inlet vessels, Pilot agitator thermometer and gas inlet and outlet out 30 parts of a 35% aqueous solution were Copolymer of 60% styrene and 40% acrylic acid (pH 9.0) submitted and after purging the reactor with nitrogen, the reactor heated to 85 ° C over the reactor wall. Then 54 g of one 1.5% sodium peroxydisulfate solution added and then 70 parts of a monomer at 85 ° C. with stirring for 2 hours mixture of 80% n-butyl acrylate and 20% styrene. At the same time 126 g of a 1.5% aqueous solution of sodium peroxydisulfate added. After the feeds had ended, postpolymerization was carried out at 85 ° C. for 1 hour siert. Then the reaction mixture cooled to room temperature. It resulted in a final polymer dispersion with a solids content  of 49.9%, a pH of 7, 8 and a viscosity of 180 mPa.s.

The content of the resulting polymer dispersion in coagulum and the occurrence of wall covering in the stirred tank reactor is in the table specified.

Examples 1 to 3

The procedure was as in Comparative Examples 1 to 3, polymerizing in 1 m ³ and 10 m ³ steel reactors, respectively. In contrast to the comparative examples, the polymerization approach was not heated with the help of heat exchangers in the reactor, but with the help of steam introduced through the reactor floor or with water heated to 70, 80 and 90 ° C. The reduction in the coagulum content and the reactor wall covering achieved is shown in Table 1.

Table 1

Coagulate and polymer wall covering of the polymerization reactor

Claims (2)

1. A method for reducing wall covering and coagulate in the free-radically initiated polymerization of olefinically unsaturated monomers in aqueous emulsion with heating to a polymerization temperature in the range from 35 to 120 ° C in a polymerization reactor, characterized in that the heating of the reaction mixture in the polymerization reactor to at least the polymerization temperature by adding heated water and / or by introducing steam. 2. The method according to claim 1, characterized in that one heating by introducing water vapor through the reak door floor.