JPS6037125B2 - Method for removing vinyl chloride from polymer-containing slurries or latexes - Google Patents

Abstract

The invention relates to a novel process for the production of polyvinyl chloride having a low vinyl chloride monomer content, the latter being removed from a slurry or latex which result from polymerization of vinyl chloride in aqueous media. In the novel process vinyl chloride is removed from a slurry or latex that contains from about 1000 parts to 15,000 parts by weight of vinyl chloride per million parts by weight of the slurry or latex and from 5% to 50% by weight of a polymer selected from the group consisting of polyvinyl chloride and copolymers of vinyl chloride with at least one monomer copolymerizable therewith that comprises a) heating said slurry or latex at a temperature in the range of 70.degree.C. to 125.degree.C.or contacting the slurry or latex with at least one organic liquid at a temperature in the range of 25.degree.C. to 125.degree.C.and b) removing vinyl chloride vapor from the slurry or latex. The resultant aqueous slurry or latex and final polymer product has reduced carcinogenicity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing polyvinyl chloride having a low vinyl chloride content by removing unreacted monomers from a slurry or latex produced by an aqueous process for producing polyvinyl chloride. It is related to.

The invention further relates to slurries or latexes with low vinyl chloride content and polyvinyl chloride containing very low or undetectable monomers. When vinyl chloride is polymerized by suspension or emulsion polymerization in an aqueous medium, it contains 5% to 50% by weight, in most cases 20% to 45% by weight, of polyvinyl chloride. Slurry or latex can be obtained.

It also contains up to 5% by weight of unreacted vinyl chloride. Most of the unreacted monomer is typically removed by heating the slurry or latex to about 65 qo under reduced pressure. As is commonly done,
This stripping step reduces the monomer content of the slurry or latex to about 1000 to 15,00 parts vinyl chloride by weight per 100 parts by weight of slurry or latex. Further processing provides a dry product containing 50 PM or more of monomer. In view of recently published safety standards requiring extremely low levels of vinyl chloride in polyvinyl chloride and in the atmosphere that workers breathe, the monomer content of the slurry or latex must be It is necessary to reduce the amount sufficiently to meet the requirements.

According to the invention, the monomer content in the aqueous slurry or latex of vinyl chloride homopolymer or copolymer is
It has been discovered that vinyl chloride can be substantially reduced by contacting a slurry or latex with at least one particular organic liquid under reduced pressure at temperatures ranging from 25°C to 12,500°C and removing vinyl chloride therefrom. It was done.

The aqueous slurries and latexes with extremely low vinyl chloride monomer content described here are unique and have not been previously required in conventional polyvinyl chloride processes for the production of polyvinyl chloride resins. .

The recently discovered carcinogenic potential of vinyl chloride now provides dry polyvinyl chloride resins with significantly reduced vinyl chloride monomer content to the extent that they are undetectable by gas chromatography. identified a need for slurries or latexes with very low monomer content that can be used. An advantage of the slurries and latexes of the present invention is that, when further dewatered and dried as is commonly done in the polyvinyl chloride industry, such slurries or latexes release very little vinyl chloride into the working areas of such plants. It is simply a matter of doing.

Aqueous slurries and latexes treated by the method of the invention can be prepared by conventional suspension or emulsion polymerization methods.

In the suspension polymerization process, vinyl chloride or a mixture of vinyl chloride and at least one comonomer is suspended in water by use of a suspending agent and by suspension. Polymerization can be carried out, for example, with lauroyl peroxide, penzoyl peroxide, diisopropyloxydicarbonate, tert-butyl peroxypivalate, azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, dialkyl peroxydicarbonate and peroxide. Initiated by the use of free radical generating initiators such as mixtures of lauroyl, sulfonyl peroxides, etc. For example, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxyphropylmethylcellulose, polyvinyl acetate hydrolyzate, gelatin, methyl Suspending agents such as vinyl ether monohydric maleic acid copolymers and mixtures of those listed above are included in the reaction mixture.In the emulsion polymerization process, vinyl chloride homopolymers or copolymers are usually Manufactured by emulsion polymerization method.

Use free radical initiators such as hydrogen peroxide, organic peroxides, persulfates, and redox systems; surfactants such as alkyl sulfates, alkanesulfonates, alkylarylsulfonates and fatty acid soaps. The vinyl chloride monomer and comonomer (if used) are emulsified using a solvent.Another method for the preparation of dispersion resins is described in U.S. Patent No. 2,981,7 to E. Blood) et al.
I have been entrusted with No. 22. In producing the copolymer, pinyl chloride is polymerized with copolymerizable monomers to give a product containing up to 30% comonomer by weight.

Can be copolymerized with vinyl chloride. Among the monomers, acrylic acid, acrylonitrile, n-butyl acrylate, diallyl maleate, dibutyl maleate, jetyl fumarate, dimethyl itaconate, ethyl acrylate, ethylene, isobutylene, maleic anhydride, methacrylic acid, Methacrylonitrile, methyl acrylate, methyl vinyl ether, 2-ethylhexyl acrylate, propylene, triallyl cyanurate, triallyl isocyanurate, trimethylolbropane, trimethacrylate, vinyl acetate, N-pinylcarbazole, pinylidene chloride , vinyl isobutyl ether, N-vinylpyrrolidone, and mixtures thereof. Further details on the preparation of pinyl chloride homopolymers and copolymers by suspension and emulsion polymerization methods are given in Kirkoo Osmer, Official Dictionary of Chemical Technology, 2nd Edition, Volume 21, pages 373-379. ing.

In a preferred embodiment of the invention, 5% to 50% by weight
% vinyl chloride polymer and 100 pm to 15,0 pm
A slurry or latex containing 0.00 ppm vinyl chloride is treated with an organic liquid, preferably vinyl acetate, at 25° C. under reduced pressure between 28 and 630 ppm of vinyl chloride, before, during or after conventional residual monomer recovery operations. The vinyl chloride is then removed by stripping methods known in the art. The treated latex or slurry has a substantially reduced monomer content so that its subsequent processing does not pose a hygiene hazard in the working area and the dry polymer obtained after dewatering also has a very low monomer content. Organic liquids that can be used in this method are vinyl acetate, di-tert-butyl-para-cresol-methylene chloride, and mixtures of two or more thereof.

Generally, the amount of organic liquid added to a slurry or latex is based on the weight of the slurry or latex.
About 0.5% to 20% by weight, but smaller or larger amounts can be used.

Those skilled in the art will appreciate that when carrying out the process of the invention, when the organic liquid used is of a relatively low boiling point, such as vinyl acetate or methylene chloride, for example:
One would expect that the liquid would essentially separate from the resin.

In contrast, di-tertiary butyl paracresol has a relatively high boiling point and therefore essentially remains in the resin and serves as an antioxidant. The invention is further illustrated by the following examples.

Examples 1 to 15 (Reference Example) In each of Examples 1 to 15 (Table 1), an aqueous slurry containing about 30% by weight of polyvinyl chloride was prepared by removing the generated vinyl chloride monomer. At the same time, the samples were heated and heated at the temperatures and pressures listed in the table.

Resins A, B and C were prepared using a mixture of lauroyl peroxide and di-2-ethylhexyl peroxydicarbonate as the initiator and methylcellulose as the suspending agent. Resin D was prepared using the initiator used in Resin A, hydroxypropyl methylcellulose as the suspending agent, and trichloroethylene as the chain transfer agent. Resin E was prepared using the initiator and suspending agent used in Resin D. In Table 1, each example except Example 10 relates to a laboratory scale process in which samples of slurry were treated over a range of about 500 to 1000 hours.

Example 10 shows interim test results that processed approximately 30 gallons of slurry. In each example except 10 and 15, the slurry contained unreacted vinyl chloride monomer (V
It was a commercially available slurry prepared by conventional low temperature and vacuum treatment to remove CM).

In Table 1, vinyl chloride monomer concentration is the vinyl chloride monomer concentration expressed in ppm relative to the weight of the resin.

A comparison of the results obtained shows the advantages of the invention.

Table 1 Examples 16 to 21 (Reference Examples) In each of Examples 16 to 21, an aqueous slurry of a copolymer of vinyl chloride and pinyl acetate (vinyl acetate content about 8 to 16% by weight) was generated. While removing the vinyl chloride monomer, heating and heating were carried out at the temperature, pressure and time indicated in the table.

The slurry contained approximately 30% copolymer by weight. Resin F contains lauroyl peroxide and di-2- as an initiator.
A mixture of ethylhexyl peroxydicarbonate,
It was prepared using hydroxypropyl methylcellulose as a suspending agent.

Resin G was prepared using lauroyl peroxide as the initiator, gelatin as the suspending agent, and trichlorethylene as the chain transfer agent. Examples 16-21 were laboratory experiments in which the amount of slurry treated was 500 to 1000 mm.

In each of Examples 16-21, the treated slurry was a commercially available slurry that was subjected to conventional low temperature and vacuum processing to remove vinyl chloride. In Table 2, the vinyl chloride monomer concentration is the vinyl chloride concentration in ppm relative to the weight of the resin.

Example Matsu~28 (Example of the present invention) In each of Examples 22 to 28, approximately 30 by weight
To an aqueous slurry containing 5% polyvinyl chloride, 5% by weight of pinyl acetate, based on the initial weight of the slurry, was added and the vinyl chloride was removed from the mixture by evaporation.

The temperature, pressure, evaporation time and the results obtained are shown in Table 3. Table 2 Table 3 * Altitude Difference of Mercury Manometer In Table 3, the vinyl chloride monomer concentration is the concentration of vinyl chloride in ppm (wt/wt) relative to the weight of the resin.

Resins Day and J were prepared using a mixture of lauroyl peroxide and di-2-ethylhexyl peroxydicarbonate as the initiator and hydroxymethylcellulose as the suspending agent. Resin 1 was prepared using the initiator used in Resin Day, hydroxymethylcellulose as the suspending agent, and chloroethylene as the chain transfer agent. In Table 3, each example relates to a laboratory process processing a 500-day chiller sample, except for Example 27, which processed a 1500-day sample. Example 29~
36 (Example of the present invention) In each of Examples 29 to 36, vinyl chloride and vinyl acetate (vinyl acetate content of about 8 to 16% by weight) were used.
) was heated and boiled at the temperature and pressure indicated in the table for the indicated time while removing the vinyl chloride monomer generated.

Resin K was prepared using Resin Day's initiator and Resin 1's suspending agent.

Resin L was prepared using lauroyl peroxide as the initiator, gelatin as the suspending agent and trichlorethylene as the chain transfer agent. Examples 29 to 36 are 500 night sura. In a laboratory-scale experiment to treat lye. In Table 4, the vinyl chloride monomer concentration has the same meaning as in Table 3.

In Examples 29-36, the added vinyl acetate was essentially removed from the resin. Table 4 * Altitude difference example of mercury pressure gauge 37 (Example of the present invention) Approximately 550 g of latex containing about 30% by weight of vinyl chloride homopolymer was placed in a 1 liter Mitsuro flask.

This latex was prepared using an oxidized ammonium salt of oleic acid as an initiator and suspending agent on the resin day. This latex contained 505 pm vinyl chloride monomer based on the weight of resin. 2
Vinyl acetate was added dropwise for 5 minutes.

A vacuum of 10 mV was applied for 2 hours at room temperature. Thus, the latex has a weight of 888pp based on the weight of the resin.
It contained m vinyl chloride monomer. After processing for 40 minutes at 55-600°C in a vacuum of 25 days, the latex has a 4. pm of vinyl chloride monomer.

Example 38 (Reference Example) 750 parts of a latex containing about 30% by weight of a copolymer of vinyl chloride and vinyl acetate (vinyl acetate content is about 1 to 6% by weight) was mixed with 35 parts of a phthalic acid di-2 - with ethylhexyl, 1 liter of:
I worshiped a candle in my flask.

This latex was 264p based on the weight of the copolymer.
pm of vinyl chloride monomer. This mixture was placed under vacuum for 15 minutes on 63rd day.

While maintaining the vacuum, the mixture was heated at 75qo for 1 hour and 30 minutes.
It was heated for a minute. The latex thus contained 45 ppm vinyl chloride monomer based on the weight of the copolymer. When the heating and heating were continued for another hour and a half at the same temperature and pressure, the vinyl chloride monomer content of the latex was 1.5 pm based on the weight of the copolymer. Most of the added di-2-ethylhexyl phthalate remained with the resin.
Example 39 (Example of the Invention) A slurry of vinyl chloride-vinyl acetate copolymer prepared using lauroyl peroxide as an initiator, gelatin as a suspending agent, and trichloroethylene as a chain transfer agent (approximately 30% by weight) % solids) 34
Four pounds of this slurry, containing about 300 pm 4 of vinyl chloride monomer based on the weight of resin, was charged to a 50 gallon glass lined reactor and heated to 6000 ℃.

10.32 pounds of vinyl acetate was then added and the reactor was sealed. When the slurry was heated to 7,400 ℃ while stirring, the pinyl chloride monomer was recovered by vacuuming for 25 days. The content of vinyl chloride monomer in the resulting slurry was undetectable by gas chromatography. Example 40 (Inventive Example) The resin used was prepared by a suspension polymerization method using a mixture of lauroyl peroxide and di-2-ethylhexylberoxydicarbonate as an initiator and hydroxypropylmethylcellulose as a suspending agent. It was a commercially available dry simulated vinyl chloride homopolymer having a pinyl chloride monomer content of 145 parts per 100 parts (ppm).

This homopolymer was added in a 1 liter flask at 400
of water to form a slurry containing 35 parts by weight of solids.

50' of methylene chloride was added into this slurry. After steam distilling the mixture to remove all methylene chloride, the resin was separated by filtration and dried overnight at 40°C. The dried resin had an undetectable vinyl chloride monomer content by gas chromatography. Example 41 (Inventive Example) An aqueous slurry containing 65% vinyl chloride homopolymer by weight was prepared by a suspension polymerization method using the initiator system and suspending agent of Example 40.

This slurry contained about 900 pm of pinyl chloride monomer based on the weight of the homopolymer. To 450 g of this slurry was added 50 g of methylene chloride. The mixture was allowed to stand at room temperature for 1 hour and 30 minutes and then vacuum was applied for 2 hours using a water aspirator. Next, this slurry was heated in an oven and then dried overnight at 50 qo. Vinyl chloride monomer could not be detected by gas chromatography. Example 42 (Example of the Invention) The method of Example 23 was repeated, except that in this example, the added 25% vinyl acetate had been premixed with 5% di-tert-butyl-para-cresol. Ta.

The same results as those obtained in Example 23 were obtained for vinyl chloride monomer concentration (ppm). Those skilled in the art will appreciate that when this slurry is further processed to produce a solid resin, the di-tert-butyl-para-cresol remains dissolved in the resin and acts as an antioxidant. Probably. Example 43 (Reference Example) A slurry containing 35% by weight of polyvinyl chloride and 900 pm of vinyl chloride was heated and boiled at 80 qo for 3 hours.

Samples taken every 1, 2 and 3 hours were dried at 50°C overnight.

These dry samples contained 13 ppm and 7 ppm, respectively.
and contained less than 5 ppm of vinyl chloride.
Z Example 44 (Reference Example) Suspension polymerization using a mixture of lauroyl peroxide and di-2-ethylhexylberoxydicarbonate as an initiator, hydroxypropyl methylcellulose as a suspending agent, and trichlorethylene as a chain transfer agent. Depending on the method, 3 by weight
An aqueous slurry containing 0% vinyl chloride monomer was prepared.

This slurry has 121 parts by weight based on the weight of the homopolymer.
It contained m vinyl chloride. A sample of this slurry was placed in a 1 liter round bottom flask equipped with an air condenser.
The mixture was heated and stirred at 8,500 ℃ for 1 hour. The slurry was then filtered and dried overnight at 5,000 °C. The dried resin had a vinyl chloride monomer content of 8 ppm. Example 45 (Reference Example) Example 44 except using a temperature of 7500 instead of 8500 and using a homopolymer prepared with the initiator system of Example 40 and hydroxymethylcellulose as the suspending agent. The method was repeated.

Samples taken after 1 hour, 2 hours, 3 hours, and 4 hours were dried overnight at 5000°C to give vinyl chloride monomer levels of 9 ppm, 7 ppm, undetectable, and undetectable, respectively.

When this slurry was heated and stirred at 8500 °C, samples taken after 1 and 2 hours showed vinyl chloride monomer content of 7 and 3 ppm, respectively, after overnight drying at 50 qo.

Example 46 (Inventive Example) Approximately 30% by weight vinyl chloride-vinyl acetate copolymer (vinyl acetate content approximately 10% by weight) was prepared by a suspension polymerization method using the initiator and suspending agent of Example 40. An aqueous slurry was prepared containing:

A portion of this slurry was oven-dried and the resin dried at 5,000 ℃ overnight, and the dried resin had a vinyl chloride monomer content of 8 pm. A 500-year sample of this slurry was placed at room temperature with a 50-year sample of vinyl acetate into a 1 liter three-liter flask.

After 1 hour of rope pounding, a vacuum was applied while continuing rope pounding (28 ropes per day and evening). Samples were taken after 1 and 2 hours.

None of the dried products had undetectable abundance. The above method was repeated, except that in this case 1
After a period of 30 minutes of coagulation, the slurry was heated to 4:0 with a vacuum of 10 days. The final sample again showed no detectable vinyl chloride monomer content. Example 47 (
Reference example) Three mouthfuls of an aqueous slurry of a commercially available homopolymer of pinyl chloride prepared using a mixture of lauroyl peroxide and di-2-ethylhexyl peroxydicarbonate as an initiator and methylcellulose as a suspending agent. In a bottom flask, the mixture was heated and ignited at 8 psi while maintaining a vacuum of 400 ml.

The vinyl chloride concentration of the starting slurry was 4663 ppm based on the weight of the slurry. Samples of the slurry were removed from the flask after 1 hour, 2 hours and 3 hours at the above temperature. Each of these slurry samples had a 2 yield pm, undetectable vinyl chloride monomer concentration. Example 48 (Reference Example) 12,955 ppm by weight of resin prepared by the method of U.S. Pat. No. 2,981,722 to Enk et al., granted April 25, 1961.
To 2000 g of a polyvinyl chloride dispersion resin latex having a vinyl chloride content of about 40% by weight, 300 g of a 1% by weight aqueous magnesium sulfate solution was added.

This batch was heated to 90°C and kept at that temperature for 1 hour. The dispersed latex obtained had a monomer content lower than 1 ppm. The dispersed latex was cooled, filtered, and dried overnight at 45°C.
The dried resin had no detectable pinyl chloride monomer content. Example 49 (Reference Example) A polyvinyl chloride dispersion latex having a vinyl chloride content of 5898 ppm (approximately 40 ppm by weight) prepared by the method of U.S. Pat. % resin content) 50
I added 250 yen of water to 0.00 yen.

Claims (1)

Claims: 1. About 1000 to 15,000 parts by weight of vinyl chloride and 5% to 50% by weight of polyvinyl chloride and vinyl chloride, per million parts by weight of slurry or latex. A method for removing vinyl chloride from a slurry or latex containing a polymer selected from the group consisting of a copolymer with at least one copolymerizable monomer, comprising: a. 5 to 20% vinyl acetate, di-tertiary
adding butyl-para-cresol, methylene chloride, or a mixture thereof, b maintaining the slurry or latex at a temperature of 25°C to 125°C under a vacuum of 28 mmHg to 630 mmHg, and c removing the vinyl chloride from the slurry or latex. A method characterized in that vinyl chloride gas is removed until the content becomes 50 ppm or less.