Note: Descriptions are shown in the official language in which they were submitted.
~7793
This invention relates to a process ~or the removal of un- -
reacted vinyl chloride from a slurry or latex resulting from aqueous
processes for the production of polyvinyl chloride. It further re-
lates to a slurry or latex of low vinyl chloride content and to
polyvinyl chloride containing very little or no ~etectible monomer.
This application ;s divided from Canadian application
Serial No. 229,921 filed on June 23, 1975 which is directed to the
process for the removal of vinyl chloride from a slurry or latex
that conta;ns- from about 1000 parts to 15,000 parts by weight of
vinyl chloride per ~illion parts by weight of the slurry or latex
and from 5% to 50% b~ weight of a polymer selected from the group
consisting of polyvinyl chloride and copolymers of vinyl chloride
~ith at least one monomer copolymerizable therew;th that comprises
(a) heating said slurry or latex at a temperature in the
range of 70C to 125C and then
(b) removing vinyl chloride vapor from the slurry or
latex~
When vinyl chloride is polymerized in an aqueous medium by
suspension or emulsion polymerization techniques, there is obtained
a slurry or latex that conta;ns from 5~ to 50% by weight and in
most cases 20% to 45~ by weight of polyvinyl chloride. It also
contains up to 5~ by weight of unreacted vinyl chloride. Most of
the unreacted monomer is usually removed by heating the slurry or
latex under reduced pressure to about 65C. As it is ordinarily
practiced, this stripping procedure reduces the monomer content of
the slurry or latex to about 1000 parts to 15,Q00 parts by weight of
vinyl chloride per million parts by weight of the slurry or latex.
~ .
~l2,77~3
Further processing yields dried products that may contain 500 ppm
or more of monomer.
In view of recently-developed safety standards that require
that the amount of vinyl chlori~e in polyvinyl chloride and in the
atmosphere that workers breathe be maintained at very low levels, it
is necessary that the monomer content of the slurry or latex be suf-
ficiently reduced so th.at th.ese requirements can ~e met.
In accordance with the present invention, it has been found
that the monomer.content of aqueous slurries and latexes of vinyl
chloride homopolymers and copolymers can be substantially reduced
by contacting the.slurry or latex with at least one organic liquid
at a temperature in the range of 25C to 125C and removing the vinyl
chloride from it.
Thus, in accordance with the present invention there is
provided the process for the removal of vinyl chloride 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) contacting the slurry or latex with 0.5% to 20~ by
weight, based on the weight of the slurry or latex, of a compound
selected from the group consisting of vinyl acetate, methylene
chloride, di-tert-butyl-p-cresol, and mixtures thereof r at a temper-
ature in the range of 25C to 125C and then
(b) removing vinyl chloride vapor from the slurry or latex.
l~Z,775~3
Aqueous slurries and latexes of the very low VCM content
described herein are unique and have not been required in convention-
al PVC processes for the preparation of PVC resin in the past. The
recently-discovered potential carcinogenicity of vinyl chloride now
demonstrates the need for slurries or latexes of very low monomer
content from which dried PVC resin of sïgnificantly reduced ~JCM con-
tent to the point of no detectible VCM by gas chromatography can be
produced.
An advantage of slurries and latexes of this invention is
that, upon further dewatering and drying as conventionally practiced
in the PVC industry, such slurries or latexes release significantly
less vinyl chloride into the working areas of such plants.
The aqueous slurries and latexes that are treated by the
process of this invention are prepared by the conventional suspen-
sion or emulsion polymerization processes. In the suspension poly-
merization process, vinyl chloride or a mixture of vinyl chloride
with at least one comonomer is suspended in water by the use of
suspending agents and agitation. The polymerization is started by
means of a free radical generating polymerization initiator, such as
lauroyl peroxide, benzoyl peroxide, diisopropyl peroxydicarbonate,
tertiary butyl peroxypivalate, azobisisobutyronitrile, azobis-2,4-
dimethylvaleronitrile, combinations of dialkyl peroxydicarbonates
and lauroyl peroxide, sulfonyl peroxides and the like. Suspending
agents such as methylcellulose, hydroxymethylcellulose, hydroxy-
ethylcellulose, hydroxypropylmethylcellulose, hydrolyzed polyvinyl
acetate, gelatin, methyl vinyl ether-~aleic anhydride copolymers
and combinations of the above are included in the reaction mixtures~
1~,7793
In the emulsion polymerization proces.s, vinyl chloride
homopolymers and copolymers are preparea by conventional emulsion
polymerization technique5 Free radical initiatorsr such as hydro-
gen peroxide, organic peroxides, persulfates, and redox systems are
used. Surface acti~e ayents, such as alkyl sulfates, alkane sul-
fonates, alkylaryl sulfonates and fatty acid soaps, are employed to
emulsify the vinyl ch.lor~de monomer ana comonomers, if any. An
alternate method of dispersion res-in preparation is described in
~nited States Patent No. 2,981,722 to Enk et al, ~ranted April 25,
lQ 1961.
When copolymers are prepared, vinyl chloride is polymerized
with a copolymerizable monomer to form a product that contains up
to 30~ by weight of tfi.e comonomer. Among the monomers that can be
copolymerized with vinyl chloride are acrylic acid, acrylonitrile,
n-butyl acrylate, diallyl maleate, dibutyl maleate, diethyl fumarate,
dimethyl itaconate, ethyl acrylate, ethylene, isobutylene, maleic
anhydride, methacrylic acid, methacrylonitrile, ~ethyl acrylate,
methyl vinyl ether, 2-ethylhexyl acrylate, propylene, triallyl cyan-
urate, triallyl isocyanurate, trimethylolpropane, trimethacrylate,
2~ vinyl acetate, N-vinyl carbazole, vinylidene chloride, vinyl iso-
butyl ether, N-vinylpyrrolidone, and mixtures thereof.
Further details concerning the production of vinyl chloride
homopolymer and copolymers by suspension and emulsion polymerization
processes are set forth ;n Kirk-Othmer, "Encyclopedia of Chemical
Technology", Second Edition, Volume 21, pages 373-379.
In a prefe~red embodiment of Applicants aforementioned
application Serial No. 229,~21, a slurry or latex that contains from
7793
5% to 50% by weight of a vinyl chloride polymer and from lOQ0 ppm
to 15,000 ppm of vinyl chloriae is heated at a t~mperature in the
range of 70C to 125C, and preferably in the range of 85C to 125C
to remove vinyl chloride from it. The heating may ~e carried out
under atmospheric or subatmospheric pressure. In this way there is
obtained a slurry or latex that contains not more than 50 ppm and
in most cases lQ ppm or less of vinyl chloride. The dried polymer
produced by dewatering the sl-urry or latex has a very low vinyl
chloride content ana can be further processed w-ithout creating health
hazards in the work area.
The processing of vinyl chloride polymers at elevated temper-
atures to reduce their monomer content is contrary to the teachings
of the art, since the art teaches that such heating decomposes these
polymers.
In a preferred embodiment of the present invention, a slurry
or latex that contains from 5% to 50% by weight of a vinyl chloride
polymer and from 1000 ppm to 15,000 ppm of vinyl chloride is contact-
ed with an organic liquid, which is preferably vinyl acetate, before,
during, or following normal residual monomer recovery, and vinyl
chloride is removed from it by the stripping techniques practiced in
the art, preferably at a temperature in the range of 25C to 125C.
Because the treated slurry or latex has a substantially reduced
monomer content, its subsequent processing does not constitute a
health hazard in the operating work areas, and the dried polymer
obtained after dewatering also has a very low monomer content.
The organic liquids that can be used in this process include
esters such as vinyl acetate, vinyl propionate, n-butyl acrylate,
-- 6 --
J793
dibutyl maleate, diethyl fumarate, dimethyl itaconate, ethyl
acrylate, methyl methacrylate, octyl acrylate, ethyl acetate,
di-2-ethylhexylphthalate and di-n-octylphthalate; hydrocarbons
such as pentane, heptane, white oil, cyclohexane, methylcyclopen-
tane, benzene, toluene, xylene, ethylbenzene, styrene, pentene,
hexene, heptene, butadiene, isoprene; alcohols such as methyl
alcohol, ethyl alcohol, isopropyl alcohol, butanol, 2-ethylhexanol
dodecanol, cetyl alcohol, ethylene glycol, propylene glycol, and
butylene glycol; phenols such as phenolr di-tertiary butyl para-
cresol, styrenated phenols, butylated phenols and bisphenol A;ethers such as diethyl ether, methyl vinyl ether and low molecular
weight polyethers; nitrogen-containing compounds such as triethyl-
amine, triethanolamine, aniline, dimethylaniline, morpholine,
pyridine, pyrrole, acetonitrile, acrylonitrile, methacrylonitrile,
acetamide, dimethylacetamide, dimethylformamide, caprolactam, N-
vinylcarbazole and N-vinylpyrrolidone; nitro compoun2s such as
nitromethane, nitroethane and nitrobenzene; halogen-containing
compounds such as methylchloride, methylene chloride, chloroform,
carbon tetrachloride, ethylene dichloride, ethyl chloride, vinyli-
dene chloride, chlorobenzene, and fluorinated methanes and ethanes;carboxylic acids such as formic acid, acetic acid, acrylic acid,
methacrylic acid, lauric acid, stearic acid and oleic acid; alde-
hydes such as propionaldehyde, butyraldehyde and benzaldehyde;
ketones such as acetone, methyl ethyl ketone,-methyl isobutyl
ketone, benzoin, benzophenone, methyl vinyl ketone and cyclohexan-
one; carboxylic acid anhydrides such as maleic anhydride and
phthalic anhydride; acid chlorides such as acetyl chloride~ benzoyl
1~,779~
chloride and phthaloyl chloride; sulfur-containing compounds such
as carbon disulfide, ethyl mercaptan, dodecyl mercaptan, dimethyl
sulfoxide, dimethyl sulfone, tetramethylene sulfone, thioglycolic
acid and thiophene; cyclic ethers such as dioxane, trioxane, furan,
tetrahydrofuran, propylene oxide and butylene oxide; conventional
diester and polymeric plasticizers for PVC such as phthalates,
maleates and adipate diesters, phosphate esters and polyesters;
dimethyl silicones; and liquid stabilizers for PVC such as dialkyl
tin dilaurates including dibutyl tin dilaurate. A single organic
liquid or a mixture of two or more organic liquids can be used.
In general the amount of organic solvent added to the slurry
or latex will be from about 0.5% to about 20~ by weight, based upon
the weight of the slurry or latex, although smaller and larger
amounts can also be used.
Those skillea in the art will understand that when the
organic liquid used is of relatively low boiling point, such as
vinyl acetate or methylene chloride, the liquid is essentially
separated from the resin when the process of this invention is
carried out. On the other hand, when the organic liquid used is
relatively high boiling, such as di-2-ethylhexyl phthalate, the
organic liquid used essentially remains with the resin. This can
be a further advantage of our invention, when the organic liquid
is a conventional additive to vinyl chloride homopolymers and co-
polymers, as when the organic liquid is a commonly known stahilizer,
lubricant, plasticizer, antioxidant, antifoam, antistatic agent,
etc.
The invention of this application and copending Serial No.
7~33
229,921 is further illustrated by the following examples.
Examples 1-15
In each of Examples 1-15 (Table I), an aqueous slurry con-
taining about 30 percent by weight of polyvinyl chloride was heated
and agitated at the temperature and pressure for the time stated
with the vinyl chloride monomer evolved being removed.
Resins A, B and C were prepared using a mixture of lauroyl
peroxide and di-2-ethylhexylperoxydicarbonate as the initiator and
methyl cellulose as the suspension agent. Resin D was prepared
using the ;nitiator used in preparing Resin A, hydroxypropylmethyl-
cellulose as the suspension agent, and trichloroethylene as a chain
transfer agent. Resin E was prepared using the initiator and the
suspension agent used in preparing Resin D.
In Table I, each of the Examples, with the exception of
Example 10, relates to a laboratory treatment in which the samples
of slurry that were treated ranged from about 500-1000 grams.
Example 10 represents a pilot plant run in which ahout 30 gallons
of the slurry was treated. In each Example, except 10 and 15, the
slurry was a commercial slurry produced by conventional low temper-
ature and vacuum treatment to remove unreacted vinyl chloridemonomer (~CM).
In Table I, the VCM concentrations are concentrations of
vinyl chloride monomer in ppm, based upon the weight of the resin.
Comparison of the results obtained shows the advantage of
the present invention.
l~Z7793
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Examples 16 21
In each of Examples 16-21, an aqueous slurry of a copolymer
of vinyl chloride and vinyl acetate (vinyl acetate content about
8-16 percent by weight) was heated and agitated at the temperature
and pressure for the time stated with vinyl chloride monomer evolved
being removed. The slurry contained about 30 percent by weight of
the copolymer.
Resin F was prepared using a mixture of lauroyl peroxide and
di-2-ethylhexylperoxydicarbonate as the initiator and hydroxypropyl-
methylcellulose as the suspension agent. Resin G was prepared using
lauroyl peroxide as the initiator, gelatin as the suspension agent,
and trichloroethylene as a chain transfer agent.
Examples 16-21 were laboratory experiments in which the
amount of slurry treated was between 500 and 1000 grams. In each
of Examples 16-21, the slurry treated was a commercial slurry pro-
duced by conventional low temperature and vacuum treatment to re-
move vinyl chloride.
In Table II, the VCM concentratïons are concentrations of
vinyl chloride in ppm, based upon the weight of the resin.
~xamples 22-28
In each of Examples 22-28, to an aqueous slurry containing
about 30 percent by weight of polyvinyl chloride was added five
percent by weight of vinyl acetate, based upon the initial weight
of the slurry; from the mixture, vinyl chloride was removed by vap-
orization. The temperatures, pressures, vaporization times and
results obtained are set forth in Table II~
In Table III, the VCM concentrations are concentrations of
1~2~7~3
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77~3
vinyl chloride in ppm (weight/weight), based upon the weight of the
resin. Resins H and J were prepared using a mixture of lauroyl
peroxide and di-2 ethylhexylperoxydicarbonate as the initiator and
methylcellulose as the suspension agent. Resin I was prepared
using the initiator used in preparing Resin H, hydroxypropylmethyl-
cellulose as the suspension agent, and trichloroethylene as a chain
transfer agent. In Table III, each of the Examples relates to a
laboratory treatment in which a 500 gram sample of slurry was treat-
ed, with the exception of Example 27 where a 1500 gram sample was
treated.
Examples 29-36
In each of Examples 29-36, an aqueous slurry of a copolymer
of vinyl chloride and vinyl acetate (vinyl acetate content about 8
to 16 percent by weight~ was heated and agitated at the temperature
and pressure for the time stated with vinyl chloride monomer evolved
being removed.
Resin K was prepared using the initiator of Resin H and the
suspension agent of Resin I. Resin L was prepared using lauroyl
peroxide as the initiator, gelatin as the suspension agent, and tri-
chloroethylene as a chain transfer agent. Examples 29-36 were lab-
oratory experiments in which the amount of slurry treated was 500
grams.
In Table IV, the VCM concentrations have the same meaning as
in Table III. In Examples 29-36, the added vinyl acetate was es-
sentially removed from the resin.
- 13 -
~7793
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1~27793
Example 37
About 550 grams of a latex containing about 30 percent by
weight of a homopolymer of vinyl chloride was agitated in a one
liter, three neck flask. The latex had been prepared using the in-
itiator of Resin H and the ammonium salt of oxidized oleic acid as
the suspension agent. The latex contained 5052 ppm s~M, based on
the weight of the resin.
Twenty-five grams of vinyl acetate was added dropwise. A
vacuum of 100 mm Hg was applied for two hours at room temperature.
The latex then contained 888 ppm VCM, based on the weight of the
resin.
After heating for 40 minutes at 55-60C at 250 mm Hg vacuum,
the latex contained 4.2 ppm VCM, based on the weight of the resin.
Example 38
Seven hundred fifty grams of a latex containing about 30
percent by weight of a copolymer prepared from vinyl chloride and
vinyl acetate (vinyl acetate content about one to six percent by
weight) was agitated in a one liter, three neck flask along with 35
grams of di-2-ethylhexylphthalate. The latex contained 264 ppm
2Q VCM, based upon the weight of the copolymer.
The mixture was stirred for 15 minutes under a vacuum of
630 mm Hg. Still under vacuum, the mixture was heated at 75C for
one-half hour. The latex then contained 45 ppm VCM based upon the
weight of the copolymer. Continuing the heating and stirring at the
same temperature and with the same vacuum for a further period of
one-half hour, the latex then contained 9 ppm VCM, based upon the
weight of the copolymer. The bulk of the added di-2-ethylhexyl-
- 16 -
793
phthalate essentially remained with the resin.
Example 39
A slurry (about 30 percent solids by weight) of vinyl
chloride-vinyl acetate copolymer made with lauroyl peroxide as the
initiator and gelatin as the suspending agent and containing tri-
chloroethylene as the chain transfer agent that weighed 344 pounds
was charged to a 50 gallon, glass-lined reactor. The slurry, which
contained about 3000 ppm VCM, based upon the weight of the resin,
was heated to 60C. Then 10.32 lbs. of vinyl acetate was added,
and the reactor was sealed. When the slurry had been heated to
74C with agitation, a vacuum of 250 mm Hg was applied to recover
the VCM. The resulting slurry contained no YCM detectible by gas
chromatography.
Example 40
The resin used was a dried commercial homopolymer of vinyl
chloride prepared by the suspension process using a combination of
lauroyl peroxide and di-2-ethylhexylperoxydicarbonate as the in-
itiator and hydroxypropylmethylcellulose as the suspending agent
that had a VCM content of 145 parts per million (ppm).
The homopolymer was mixed with 400 ml of water in a one liter
flask to form a slurry containing 35 percent by weight of solids.
To the slurry 50 ml of methylene chloride was aaded. The mixture
was steam-stripped to remove all the methylene chloride following
which the resin was separated by filtration and dried at 40C over-
night. The dried resin had a vinyl chloride monomer content not
detected by gas chromatography.
- 17 -
~Z,7793
Example 41
An aqueous slurry containing 65 percent by weight of a com-
mercial vinyl chloride homopolymer was prepared by the suspension
process using the initiator system and the suspending agent of
Example 40. The slurry contained about 9,000 ppm of vinyl chloride
monomer, based upon the weight of the homopolymer.
To 450 grams of the slurry was added 50 ml of methylene
chloride. The mixture was stirred for one-half hour at room temper-
ature, after which a vacuum was applied for a period of two hours by
means of a water aspirator. The slurry was then filtered and dried
overnight at 50C. ~inyl chloride monomer could not ~e detected by
means of gas chromatography.
Exa~ple 42
The procedure of Example 23 was repeated, but in this
example the 25 grams of vinyl acetate added had previously been
mixed with 5 grams of di-tert-butyl-para-cresol. Results similar
to those obtained in Example 23 were obtained with respect to the
VCM concentration (ppm). Those skilled in the art will understand
. that upon further processing the slurry to produce solid resin the
20 di tert-butyl-para-cresol will remain in the resin and serve as an
ant~-oxidant.
Example 43
Two hundred grams of a slurry that contained 35 percent by
weight of polyvinyl chloride and 9000 ppm of vinyl chloride was
heated and agitated at 80C for 3 hours.
Samples which were taken at the end of one, two, and three
hours were dried overnight at 50C. These dried samples contained
- 18 -
..~
~Ll.Z'~ 3
13 ppm, 7 ppm, and less than 5 ppm of vinyl chloride, respectively.
Example_44
An aqueous slurry containing 30 percent by weight of a com-
mercial vinyl chloride homopolymer was prepared by the suspension
polymerization process using a mixture of lauroyl peroxide and di-
2-ethylhexylperoxydicarbonate as the initiator, hydroxypropyl-
methylcellulose as the suspending agent, and trichloroethylene as
a chain transfer agent. The slurry contained 1,212 ppm of vinyl
chloride, based upon the weight of the homopolymer.
A sample of the slurry was heated and agitated at 85C for
four hours in a one liter round bottom flask fitted with an air
condenser. The slurry was then filtered and dried overnight at 50C.
The dried resin had a VCM content of 8 ppm.
Example 45
The procedure of Example 44 was repeated, but at a tempera-
ture of 75C rather than 85C and with a homopolymer prepared with
the initiator system of Example 40 and with hydroxymethylcellulose
as the suspension agent. Samples taken at the end of one, two,
three and four hours, after dry;ng overnight at 50C had VCM con-
tents of 9 ppm, 7 ppm, not detected, and not detected, respectively.
When the slurry was heated and agitated at 85C, samplestaken at the end o~ one and two hours had VC~ contents of 7 and 3
ppm, respectively, after drying at 50C overnight.
Exa~ple 46
An aqueou8 slurry containing about 30 percent by weight of a
commercial vinyl chloride-vinyl acetate copolymer (about 10 percent
by weight vinyl acetate) was prepared by the suspension process
using the initiator and the suspending agent of Example 40.
-- 19 --
~93
When a portion of the slurry was filtered and the resin was dried
overnight at 50C, the dried resin had a VC~ content of 83 ppm.
A 500 gm sample of the slurry was placed in a one-liter,
three-neck, round bottom flask at ambient temperature along with
50 gm of vinyl acetate. After one-half hour of stirring, vacuum
was applied (28 mm of mercury) with continued stirring. Samples
were taken at the end of one and two hours. The dried products
showed no detectible monomer content.
The procedure of the preceding paragraph was repeated, but
this time the slurry was heated to 45C with a vacuum of 100 mm
of mercury after the one-half hour of stirring. Again the final
sample showed no detectible VCM content.
Example 47
A water slurry of a commercial homopolymer of vinyl chloride
prepared using lauroyl peroxide and di-2-ethylhexylperoxydicarbon-
ate as the initiator and methyl cellulose as the suspending agent
was heated and agitated in a three-necked, round bottom flask at
80C while maintaining a vacuum of 400 mm Hg. The vinyl chloride
concentration of the starting slurry was 4663 ppm based on the weight
of the slurry. Samples of the slurry were withdrawn from the flask
after heating as describea above after one, two and three hours,
and these slurry samples had VCM contents o~ 20 pp~, none detected,
and none detected, respectively.
Example 48
To 2000 gm of a polyvinyl chloride dispersion resin latex
(resin content about 40 percent by weic3ht) that had a vinyl chloride
content of 12,955 ppm, based on the weight of the resin, as prepared
by the process of United States Patent No. 2,981,722 to Enk et al,
- 20 -
~1~ 7793
granted April 25, 1961, was added 300 ml of a one percent by weight
aqueous magnesium sulfate solution. The batch was brought to 90C
and maintained and agitated at this temperature for one hour. The
dispersion latex that was obtained had a monomer content of less
than one ppm. The dispersion latex was cooled, filtered and dried
in an oven overnight at 45C. The dried resin had no detectible
VCM content.
E ample 49
To 500 grams of a polyvinyl chloride dispersion latex (resin
content about 40 percent by weight) having a vinyl chloride content
of 5898 ppm as prepared by the process of United States Patent No.
2,981,722 to Enk et al, granted April 25, 1961, was added 250 grams
of water. The batch was brought to 90C and maintained and agitat-
ed for one hour at this temperature. The dispersion latex and the
dried resin prepared from it had no detectible VCM content.
- 21 -
