DE4118526A1 - Removing residual monomers etc. from aq. polymer dispersions - by passing through the dispersion a stream of inert gas contg. specified vol. of water to gas - Google Patents

Abstract

Process is claimed for removing residual monomers and low-mol wt. impurities (I) from polymers in aq. dispersion by passing through the dispersion a stream of gas produced by means of a distributor device, the novelty is that the gas stream contains 0.01-0.5-1 liq. water per 100-1 gas. The process can be used with aq. dispersions (pref. 40-60 wt. %) of various polymers (based on styrene, olefins, dienes, acrylonitrile, acrylate, vinyl ethers, etc. contg. up to 1500 ppm (I), pref. the dispersion is treated at 70-80 deg.C with a stream of gas (nitrogen, air, etc) contg. water at 10-30 deg.C then worked up e.g. by spray drying. USE/ADVANTAGE - The process enables the removal of (I) from polymer dispersions without the disadvantages of prior art processes (high cost of steam treatment, breakdown of dispersions, coagulation).

Description

The present invention relates to an improved method for Ent Removal of residual monomers and low molecular weight contaminants from in aqueous dispersion by passing a polymer gas flow generated by means of a distributor device.

EP-A 1 87 927 describes a process for removing organic Compounds from polymer slurries described, the Auf Slurries with vigorous stirring and at an elevated temperature with a non-condensable gas are treated.

DE-B 26 35 478 describes a process for removing vinyl chloride known from aqueous dispersions, latices or slurries, in which these dispersions, latices or slurries under reduced pressure be blown through with an inert gas.

According to the teaching of BE 8 65 673, polymer suspensions are used for removal treatment of residual monomers with steam.

Steam treatment is not only very expensive in terms of equipment, it often also leads to an excessive dilution of the polymer suspensions, which results in increased energy consumption during subsequent drying Consequence.

The treatment of aqueous dispersions with an inert gas stream is also problematic in that it often destroys the Dispersions comes, with the distribution of the coagulate Block devices for the inert gas.

The object of the present invention was to provide an improved method for Removal of residual monomers and other contaminants which the described shortcomings are avoided.

Accordingly, a process for removing residual monomers and lower molecular impurities from poly in aqueous dispersion merisaten by passing one by means of a distribution device generated gas flow found, which is characterized in that the Gas flow contains 0.01 to 0.5 l of liquid water per 100 liters of gas.  

The polymers present as aqueous dispersions can be homo- or Copolymers that are manufactured by generally known methods can be.

Examples of monomers are styrene or its core-substituted one Derivatives such as α-methylstyrene and divinylbenzene, ethylene, propylene, vinyl chloride, butadiene, isoprene, chloroprene, acrylonitrile, methacrylonitrile, Alkyl esters of acrylic acid or methacrylic acid such as ethyl acrylate, ethyl hexyl acrylate or methyl methacrylate, vinyl ethers such as vinyl methyl ether or Butanediol divinyl ether into consideration, depending on the type of monomers does not arrive.

Such polymers can usually contain up to 1500 ppm of residual monomers or contain low molecular weight impurities. Low molecular weight Impurities can ent by cycloaddition reaction of monomers are, for example 4-carbethoxycyclohexane from butadiene and ethyl acrylate. The impurities can also be incorporated into the set monomers may be included; for example, styrene can be up to Contain 200 ppm ethylbenzene.

The dispersions of such polymers to be treated can be a solid substance content of 30 to 70, preferably 40 to 60 wt .-%, have.

Dispersions with a suitable solids content are usually obtained the polymerization directly.

The dispersions are treated with the inert gas stream in a more customary manner wise in a stirred tank in which the inert gas is introduced from below can be. The introduction of the inert gas can, for example, with the help of commercially available nozzles, which are usually a diameter can have from 0.5 to 5 mm, the diameter of which is used The amount of gas depends on what the person skilled in the art can easily do according to known formulas can calculate.

The number of nozzles used is not critical and depends on the amount of dispersion to be treated and the type of Treatment boiler, the number of nozzles required by light Experiments can be determined.

Such gases are considered as inert gases, which are included in the process conditions practically do not react with the polymers, e.g. B. Air, nitrogen, carbon dioxide or low-boiling hydrocarbons, air is preferred. Per kg of dispersion expediently 1 to 50 l of inert gas are used.  

0.01 to 0.5 l of fully demineralized water are combined per 100 l of inert gas supplied with the inert gas, the amount of water being measured in this way can that the total volume of the dispersion does not change.

The water supplied can be a temperature of 10 to 90 ° C, preferably 10 to 30 ° C.

The dispersions are usually treated at temperatures of 30 to 95, preferably 70 to 80 ° C. The process can be carried out under normal pressure, but can also be carried out under reduced pressure.

The duration of the inert gas treatment depends on the type and amount of Residual monomers and impurities and can easily in individual cases can be determined experimentally. The duration of treatment is usually 3 to 30 h.

To avoid unwanted foaming, the dispersions additional commercially available defoamers such as organic Silicone compounds or mixtures of higher aliphatic alcohols are added will.

The inventive method can be both continuous and dis done continuously.

After the inert gas treatment has ended, the dispersions can be prepared in the customary manner Be worked up, for example by spray drying.

The concentration of residual monomers and impurities can be determined using Pyrolysis gas chromatography can be determined.

As a rule, the concentration of the volatile accompanying substances can be in the solid polymers according to the inventive method except for one Reduce residual content by less than 10 ppm.

The method according to the invention can cause undesirable effects the removal of accompanying substances, such as coagulation, dilution of the Dispersion and clogging of the gas distribution devices in a simple manner avoid.  

Preparation of the polymer dispersion

template
200 kg of fully demineralized water
0.5 kg mixture of C₁₂-C₁₄ alkyl sulfonates
0.5 kg sodium bicarbonate
0.6 kg of potassium persulfate
30 kg styrene

Inlet 1
150 kg of fully demineralized water
0.2 kg mixture of C₁₂-C₁₄ alkyl sulfonates
30 kg styrene
150 kg butadiene

Inlet 2
120 kg of demineralized water
3 kg of alkyl sulfants
0.4 kg of potassium persulfate

Inlet 3
60 kg styrene
20 kg acrylonitrile
40 kg of ethyl acrylate
18 kg methyl methacrylate

The polymerization was carried out in a conventional closed Polymerization kettle.

After heating the template to 75 ° C, feed 1 was during a Period of 8 hours added continuously. Then was polymerized for a further 3 hours at 75 ° C.

Then feed 2 was added to the reaction mixture and then Feed 3 was added over a period of 2 hours and then post-polymerized for a further 3 hours. Then it was relaxed and the Approach cooled. A dispersion with a solids content was obtained of approx. 40% by weight.

example 1

100 l of the polymer dispersion were stirred at 80 ° C. for 5 hours heated. During this time 3000 l of air and 0.5 l were added per hour Demineralized water via three arranged in a star shape on the bottom of the boiler Nozzles with a diameter of 1.3 mm passed into the dispersion.  

The dispersion was then worked up by spray drying. The Amount of residual monomers and impurities in the poly thus obtained merisat are listed in Table I.

Example 2 (for comparison)

The procedure was as in Example 1, but without simultaneous feeding of water. After 90 minutes, coagulate had deposited on the nozzles, so that two out of three nozzles were clogged.

Example 3

15,000 l of polymer dispersion were placed in a stirrer Container, at the bottom of which a pipe was attached, with 30 holes from 2 mm in diameter for the passage of air was provided on a Temperature heated to 70 ° C and 15 hours at this temperature held. 50,000 liters of air and 60 liters of demineralized water were produced per hour Water introduced through the pipe into the dispersion. Then was the dispersion worked up by spray drying. At the pipe openings no coagulum had settled.

The content of residual monomers and impurities in the polymer is in Table I listed.

Example 4

100 l of polymer dispersions were applied untreated by spray drying is working. The content of residual monomers and impurities is in Table I listed.

Table I

Amount of residual polymers and accompanying substances [ppm]

Claims (1)

Process for removing residual monomers and low molecular weight impurities from polymers in aqueous dispersion by passing a gas stream generated by means of a distributor device, characterized in that the gas stream contains 0.01 to 0.5 l of liquid water per 100 liters of the gas.