JPS6037127B2 - Method for removing vinyl chloride from polyvinyl chloride dispersions, latexes and slurries - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for purifying polyvinyl chloride.

More particularly, the present invention relates to a method for removing residual vinyl chloride from polyvinyl chloride dispersions, latexes and slurries. When vinyl chloride is polymerized in an aqueous medium by suspension polymerization or emulsion polymerization, 5-5% by weight
and obtain a dispersion, latex or slurry containing in most cases 15-4% by weight of polyvinyl chloride.

It also contains up to 5% by weight of residual vinyl chloride. Most of the unreacted monomer is usually removed by heating the dispersion, latex or slurry under reduced pressure to about 660°C. As commonly practiced, this stripping operation reduces the monomer stock from approximately 100 pm to 20,000 pm.
pm. Further processing yields a dry product containing 50 pm or more of monomer. In light of recently published safety standards that require maintaining very low levels of vinyl chloride in polyvinyl chloride and in the atmosphere that workers breathe, it is important to reduce the monomer content of dispersions, latexes, or slurries. It is necessary to lower the temperature sufficiently to meet these conditions.
A number of operations have been proposed for removing residual monomer from polyvinyl chloride dispersions, latexes and slurries.

However, it has been found that none of them are completely satisfactory. Operations that involve heating them to temperatures above 6 inches or subjecting them to high shear conditions are effective in reducing vinyl chloride cargo weight to low levels, but the stability of the dispersion or latex This has an adverse effect on the oxidation properties and on the functional performance of the dried product. In addition, the foaming that occurs at high temperatures creates serious processing problems.
Other operations, such as sparging with inert gas or stripping at low temperatures, either do not reduce the monomer content to the desired very low levels or are too slow to be carried out industrially. In accordance with the present invention, an improved method for removing residual monomer from polyvinyl chloride dispersions, latexes and slurries has been developed.

This method rapidly reduces the vinyl chloride content of the dispersion, latex or slurry without affecting its stability and other properties or properties of the dried polymer. Unlike many previously known monomer removal operations, the method of the present invention uses dispersions, latexes, or slurries.
It destabilizes the polypynylic chloride without altering its particle size distribution, and has no adverse effect on the oxidation properties of the dispersion, latex or slurry, or on the handling and drying characteristic of wet polymer cakes. I don't call. In the process of the invention, a dispersion, latex or slurry containing 5-50% by weight of polyvinyl chloride and 100-20,00 parts of pinyl chloride per million parts by weight of the dispersion, latex or slurry is used. Maintain pressure below atmospheric while sparging with ammonia.

Following this process, the dispersion, latex or slurry
is further processed to yield a solid product containing less than 1 ppm, and often less than 1 ppm, of vinyl chloride. Monomer and ammonia are suitably removed using a vacuum system. They can be collected and recycled if desired. During the removal of vinyl chloride by the process of the invention, the dispersion, latex or slurry is heated to a temperature between about 2000 C and the temperature at which its properties are adversely affected or the water therein becomes key. Maintain a pressure of 100-600 mm (absolute), preferably 125-50 mm (absolute).

Sparging may be performed by any operation that provides maximum contact between the polyvinyl chloride particles and ammonia.

It is preferably carried out by passing the ammonia through one or more diffusers directed below the surface of the dispersant, latex or slurry. The amount of ammonia used and the rate at which it is added is such that rapid removal of vinyl chloride is achieved without causing foaming or handling problems.

They depend on factors such as the amount of dispersion, latex or slurry being purified, its vinyl chloride content, and the processing conditions used. The optimum amount of ammonia and optimum sparging rate for each dispersion, latex or slurry and each combination of processing conditions can be readily determined by performing some preliminary experiments. In a preferred embodiment of the present invention, the method of the present invention has a size of about 0.01-54, and preferably 0.05-54.
Used to remove vinyl chloride from dispersions and latexes containing vinyl chloride particles in the range of 2. These dispersions and latexes make them 650
It cannot be subjected to operations involving heating to zero temperatures. Because such treatments have an adverse effect on their stability, physical properties and furnace suitability as well as on the properties of the dried polymers. In addition, foaming that occurs at high temperatures creates serious processing problems. These dispersions and latexes are preferably maintained at a temperature of 40-60 pm and a pressure of 100-50 pm (absolute) while sparging them. 45% dispersion or latex
Particularly advantageous results have been obtained when a temperature of -55 qo and a pressure of 125 -40 kw (absolute) are maintained during the sparging with ammonia. The rate at which vinyl chloride is removed from polyvinyl chloride dispersions and latexes is 2-8% by weight, preferably about 4% by weight, and about 50-1% by weight.
Polar, water-soluble organic compounds, such as acetonitrile, having a boiling point of 500°C, and preferably 75-100°C.

Improvements can be made by adding roacetonitrile, formamide, dimethylformamide, diisopropylamine, 1-chlorobutene-2 and butyl bromide. The most effective of these additives are acetonitrile and dimethylformamide. In another preferred embodiment of the invention, the method is used to remove pinyl chloride from an aqueous slurry containing polyvinyl chloride particles ranging in size from about 5 to 200 W.

The slurries are preferably maintained at a temperature between about 600C - their boiling point and a pressure of 100 - 60C (absolute) while sparging them. As used herein, the term "polyvinyl chloride" refers to high molecular weight homopolymers of pinyl chloride and the copolymerization of vinyl chloride with essentially water-unsaturated ethylenically unsaturated monomers copolymerizable therewith. high molecular weight copolymers produced.

Suitable comonomers include vinyl acetate, pinyl propionate, pinyl butyrate, pinyl stearate, vinyl benzoate,
Included are ethylene, propylene, ethyl acrylate, acrylic acid, acrylamide, acrylonitrile, methacrylonitrile, vinylidene chloride, dialkyl fumarate and dialkyl maleate, vinyl ethers, and the like. When using one or more of these monomers,
The monomer content is at least 70%, and preferably 8
Contains 0-90% vinyl chloride. To remove residual vinyl chloride, polyvinyl chloride dispersions, latexes or slurries treated by the process of the invention may be prepared by well-known suspension or emulsion polymerization techniques. In suspension polymerization, monomers are suspended in water using a suspending agent and stirring. Polymerization can be carried out, for example, with lauroyl peroxide, pensoyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, tertiary butyl peroxypivalate, azopisisobutyronitrile, azobis-2,4
-dimethylvaleronitrile and mixtures thereof.
Suspending agents that can be used include methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydrolyzed polyvinyl acetate, gelatin, methyl vinyl ether-maleic anhydride copolymer, and the like.
In emulsion polymerization methods, the polymerization initiator may be hydrogen peroxide, organic peroxides, persulfates or redox-based.
For example, alkyl sulfates, alkanesulfonates,
Surfactants such as alkylaryl sulfonates and fatty acid soaps are used as emulsifiers in these methods. A preferred method of making these polymers is 19
No. 2, US Pat. No. 1,722, issued to Enk et al. on April 25, 1961. Reaction mixtures prepared by these methods are typically heated to about 60-65°C under vacuum to remove the majority of unreacted monomer from them. The resulting stripped dispersion, latex or slurry generally contains 5-50%, preferably 15-4% by weight polyvinyl chloride and about 1000% polyvinyl chloride as particles ranging in size from about 0.01 to 20 mosquitoes.
Contains 120,00 pm of vinyl chloride. Following removal of vinyl chloride from them by the method of the invention,
The dispersion, latex or slurry may be dewatered, for example on a rotating drum filter, and then dried, or alternatively it may be spray dried. The polyvinyl chloride produced by this method has a vinyl chloride content of less than 1 ppm, often less than 1 ppm. It can be further processed without causing health problems. The invention is further illustrated by the following examples.

In these examples, and throughout this application, the terms "parts per million" and "ppm" mean parts by weight of vinyl chloride per million parts of polymer. Reference Example 1-6 A A series of polyvinyl chloride latexes and dispersions were produced by the following operations.

An aqueous dispersion containing vinyl chloride, a mixture of lauroyl peroxide and di-2-ethylhexyl peroxydicarbonate as an initiator, ammonium oleate as an emulsifier, and methylcellulose as a suspending agent is homogenized and then was polymerized to form a latex or dispersion containing 30-33% polyvinyl chloride in the form of particles ranging in size from 0.05-5 mm.

The latex or dispersion is heated under vacuum to a temperature below 65°C to reduce its vinyl chloride content to 10,000 parts per 100 parts.
Reduced to below 00 Ikari Kaku. The latex or dispersion in a B2 Tough flask was maintained at subatmospheric pressure for 1000 minutes and sparged with gas at a rate of 0.22 $/hour (6.23 x 10-3).

Samples were taken periodically and analyzed to determine their monomer content. The conditions used, the sparging gas used and the results obtained are shown in Table 1. Vinyl chloride and sparging gas were recovered from the exhaust gas and recycled.

The treated latex or dispersion was milled and dehydrated.
Each dried product contained less than 1 oppm of vinyl chloride. C. For comparison purposes, the latex or dispersion in two flasks was sparged with gas for 1000 hours each or subjected to subatmospheric pressure for a period ranging from 2 to 4 hours.

Samples were taken periodically and analyzed to determine the amount of monomer present. The conditions used and the results obtained are shown in Table 1. Examples 1-3 A small amount of acetonitrile was added to each 1000 ml of latex prepared by the method described in paragraph A of Reference Examples 1-6 and containing 7680 ppm of vinyl chloride.

The resulting mixture is then heated at a rate of 0.22 dos per hour while maintaining them at subatmospheric pressure.
sparged with ammonia at a rate of . Samples were taken periodically and analyzed to determine the amount of vinyl chloride removed. The conditions used and the results obtained are shown in Table B. Table 1 Table n Reference Examples 7 and 8 The aqueous slurry of polyvinyl chloride is a mixture of lauroyl peroxide and di-2-ethylhexyl peroxydicarbonate as an initiator, hydroxypropyl methyl cellulose as a suspending agent, and trichloro as a chain transfer agent. It was produced by polymerizing vinyl chloride using ethylene.

Every 1000 liters of slurry in two flasks was maintained at 75 quarts, 400 liters (absolute) while sparging them with air.

For comparison purposes, a portion of the slurry was either sparged with air at atmospheric pressure or subjected to subatmospheric pressure without sparging. The conditions used and the results obtained are shown in Table m.

Table M Reference Example 9 The influence of the molecular weight of the polymer on the efficiency of removal of vinyl chloride from the slurry was determined while keeping them at 7500 and the pressure 360 degrees centigrade (absolute) per hour. mt3 (5.60
× 10−2) by sparging a series of slurries with nitrogen.

The results obtained are shown in Table W. In this table the molecular weights of the polymers are defined by their relative viscosities. The data in Tables N and W show that pinyl chloride was most easily removed from the slurry containing the highest molecular weight polypinyl chloride.

Reference Examples 10 and 11 An aqueous slurry containing 3% by weight of vinyl chloride/vinyl acetate copolymer containing about 12% vinyl acetate. t3 (5.60×10-
Sparged with nitrogen at a rate of 3).

The conditions used and the results taken are shown in Table V. Table V Reference Example 12 A slurry containing 35% by weight of a vinyl chloride/vinyl acetate copolymer containing about 1% by weight of vinyl acetate was fed at a rate of about 100 m/min. While stirring and sparging with vinyl acetate, the mixture was kept at 90° C. and pressure paper (absolute).

Claims (1)

[Scope of Claims] 1. 1000-20,000 parts by weight of vinyl chloride per 1 million parts by weight of a dispersion, latex or slurry;
Vinyl chloride from an aqueous dispersion, latex or slurry comprising polyvinyl chloride and 5-50% by weight of a vinyl chloride polymer selected from the group consisting of polyvinyl chloride and at least one monomer copolymerizable therewith and a copolymer. a dispersion, latex or slurry at atmospheric pressure while sparging the dispersion, latex or slurry with ammonia until the dispersion, latex or slurry contains not more than 10 parts by weight of vinyl chloride per million parts by weight of the vinyl chloride polymer as described above. A method characterized by keeping it under pressure. 2. Before sparging the dispersion, latex or slurry with ammonia at subatmospheric pressure,
adding 8% by weight of a polar, water-soluble organic compound selected from the group consisting of acetonitrile, chloroacetonitrile, formamide, dimethylformamide, diisopropylamine, 1-chlorobutene-2 and butyl bromide to the dispersion, latex or slurry; A method according to claim 1.