Process of polymerizing vinyl chloride with post-heating of charging passage

A process of preparing a vinyl chloride polymer in a polymerization vessel comprising the steps of: PA0 charging a polymerization initiator through a charging passage communicating with the inside of the polymerization vessel, and PA0 polymerizing vinyl chloride or a vinyl monomer mixture containing vinyl chloride in an aqueous medium, PA0 wherein after said polymerization initiator has been charged into the polymerization vessel, said charging passage is externally heated. This process can prevent scale formation in the charging passage, and produce a vinyl chloride polymer of high quality.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process of preparing a vinyl chloride polymer, 
and more particularly to a process of preparing vinyl chloride polymer, 
that can prepare a vinyl chloride polymer of high quality with a high 
productivity. 
2. Description of the Prior Art 
In preparing vinyl chloride polymers, it may sometimes occur that, after a 
polymerization initiator has been fed into a polymerization vessel through 
charging passage comprising a charging pipe, etc., the polymerization 
initiator sticks on the inner wall of the charging passage, particularly 
at a charging port positioned at the end of the charging passage to remain 
there. The polymerization initiator remaining like this reacts with a 
monomer during the polymerization, resulting in formation of polymer 
scale. Since the polymer scale may grow to clog the charging passage, 
particularly at the charging port, the grown polymer scale must be 
removed. 
As methods of removing the polymerization initiator having stuck and 
remained in the charging passage and of preventing formation of the 
polymer scale, proposed are a method in which the charging passage is 
washed with an organic solvent, a method in which the charging port is 
closed to block the invasion of the monomer from the inside of the 
polymerization vessel, etc. 
However, in the former method, in which the charging passage is washed with 
an organic solvent, a large quantity of organic solvent is required for 
completely removing the polymerization initiator having stuck and remained 
therein, so that the solvent remains in a manufactured polymer to cause a 
lowering of quality, and generation of an ill smell when the polymer is 
molded or formed. Hence, there is a limit on the amount of the organic 
solvent to be used, and thus the washing can not be thoroughly performed. 
As the results, the polymerization initiator remains more or less, 
bringing about the problem that the polymer scale are still formed if the 
polymerization is carried out for a long period of time. In the latter 
method, in which the charging port is closed, there has been the problem 
that the monomer invades into the charging passage from a gap in the 
closed charging port resulting in the formation of polymer scale. 
There has been also proposed a method in which the polymerization initiator 
is charged as an aqueous emulsion in order to reduce the amount of an 
organic solvent to be used. This method can make it avoidable that the 
organic solvent remains in a manufactured polymer, but yet it is difficult 
to prevent the polymerization initiator from sticking and remaining in the 
charging passage, and to prevent the scale formation in the charging 
passage. 
SUMMARY OF THE INVENTION 
Accordingly, an object of this invention is to provide a process of 
preparing a vinyl chloride polymer, that makes it possible to effectively 
prevent the formation of polymer scale with use of no organic solvent but 
also makes it possible to decrease an organic solvent remaining in the 
resulting polymer and obtain a manufactured polymer of high quality. 
As a means for solving the above problems, this invention provides a 
process of preparing a vinyl chloride polymer in a polymerization vessel 
comprising the steps of: 
charging a polymerization initiator through a charging passage 
communicating with the inside of the polymerization vessel, and 
polymerizing vinyl chloride or a vinyl monomer mixture containing vinyl 
chloride in an aqueous medium, 
wherein after said polymerization initiator has been charged into the 
polymerization vessel, said charging passage is externally heated. 
The process of this invention can remove the polymerization initiator 
sticking and remaining on the charging passage more effectively than the 
conventional methods and yet without any use of an organic solvent. Hence, 
the formation of polymer scale can be effectively prevented, requiring no 
operation for removing polymer scale, and thus enabling preparation of 
vinyl chloride polymers with a high productivity. Moreover, the amount of 
the solvent there remaining in the manufactured polymer can be so small 
that vinyl chloride polymers of high quality can be obtained. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
According to the process of this invention, a charging passage used for 
charging of a polymerization initiator is externally heated. The charging 
passage is not required to be the one specially prepared for charging the 
polymerization initiator. For instance, where a charging passage prepared 
for charging a polymerization medium such as water, has been used for 
charging a polymerization initiator, this charging passage used must be 
externally heated. 
In the process of this invention, there is no particular limitation on the 
form of the charging passage to be heated. However, the charging passage 
usually comprises a pipe connected with the polymerization vessel, and it 
has a port at its end (herein, called "charging port") which opens in the 
inside of the polymerization vessel. There is no limitation on the form of 
the charging port. For example, the charging port may be able to be opened 
and closed with a valve. 
As the method of externally heating the charging passage, a heated fluid 
such as water vapor, hot water, or heated solvent or oil may be passed 
through a heating jacket provided on the outer peripheries of the charging 
passage comprising a charging pipe and charging port, or between an outer 
pipe and inner pipe of a pipe of double-pipe structure. When the water 
vapor is used, the water vapor used or generated in other processes in the 
factory can be utilized as the water vapor to be used. 
The charging passage may be heated at the temperature that may cause the 
decomposition of the polymerization initiator used, and, in usual cases, 
preferably at not less than 80.degree. C., and more preferably at not less 
than 1OO.degree. C. Heating at not less than 100.degree. C. enables rapid 
decomposition of the polymerization initiator. 
In this invention, there are no particular limitations on the 
polymerization initiator which may be used and it may include those 
conventionally used in preparing vinyl chloride polymers, as exemplified 
by percabonate compounds such as diisopropyl peroxydicarbonate, 
di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; 
perester compounds such as t-butyl peroxyneodecanate, t-butyl 
peroxypivarate, t-hexyl peroxypivarate, and alpha-cumyl peroxyneodecanate; 
peroxides such as acetylcyclohexylsulfonyl peroxide, 
2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, and 3,5,5trimethylhexanoyl 
peroxide; azo compounds such as azobis-2,4-dimethylvaleronitrile, and 
azobis(4-methoxy-2,4-dimethylvaleronitrile); potassium persulfate, 
ammonium persulfate, and hydrogen peroxide. These can be used either alone 
or in combination. 
In this invention, the above polymerization initiator may be charged as it 
is, or appropriately charged as a solution thereof in an organic solvent 
such as toluene or isoparaffin, or as an aqueous emulsion prepared using a 
dispersant, with its viscosity so modified as to be readily charged, but 
there are no particular limitations. Charging the polymerization initiator 
as the aqueous emulsion has the advantage that the above stated 
disadvantages that the organic solvents entail can be obviated. The above 
dispersant used in preparing the aqueous emulsion may be any of those used 
in the ordinary suspension polymerization or emulsion polymerization of 
vinyl chloride, and may include partially polymerized polyvinyl alcohols, 
cellulose esters, water-soluble starch esters, polyacrylic acid, and 
polyoxyethylene sorbitan monolaurate. There are no particular limitations 
on the concentration of the polymerization initiator in the aqueous 
emulsion and on the viscosity of the aqueous emulsion. However, the 
polymerization initiator may usually be contained in a concentration of 
from about 20 to 90% by weight, and the viscosity of the aqueous emulsion 
may be usually adjusted to 500 cP or less at 25.degree. C. Where the 
polymerization initiator is charged as a solution in an organic solvent, 
the concentration of the polymerization initiator is not particularly 
limited but may be usually about 20 to 90% by weight. 
The process of this invention can be applied to polymerization of any 
conventionally known vinyl chloride or vinyl monomer mixtures containing 
vinyl chloride. The form of polymerization is also not limited, including, 
for example, suspension polymerization and emulsion polymerization. 
The vinyl monomers other than vinyl chloride may include, for example, 
alpha-olefins such as ethylene propylene, 1-butene, 1-pentene, 1-hexene, 
1-heptene, 1-octene 1-nonene, 1-decene, 1-undecene, 1-dodecene, 
1-tridecene and 1-tetradecene, acrylic acid and esters thereof, 
methacrylic acid and esters thereof, maleic acid and esters thereof, vinyl 
compounds such as vinyl acetate, vinyl propionate and alkyl vinyl ethers, 
maleic anhydride, acrylonitrile, styrene, vinylidene chloride, other 
monomers copolymerizable with vinyl chloride, and mixtures of any of 
these. 
In instances in which a dispersant is used in the present polymerization, 
there are no particular limitations on the dispersant to be used, and 
those hitherto commonly used may be used. For example, it may include 
water-soluble cellulose ethers such as methyl cellulose, hydroxyethyl 
cellulose, hydroxypropyl cellulose, and hydroxypropylmethyl cellulose; 
watersoluble starch ethers partially saponified polyvinyl alcohol; acrylic 
acid polymers such as polyacrylic acid; water-soluble polymers such as 
gelatin; oil-soluble emulsifying agents such as sorbitan monolaurate, 
sorbitan trioleate, glycerol tristearate, and ethylene oxide propylene 
oxide block copolymers; and water-soluble emulsifying agents such as 
polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerol oleate, and 
sodium laurate. These can be used either alone or in combination. 
Other conditions in the polymerization according to the process of this 
invention, such as the manner by which the aqueous medium, vinyl chloride 
or other vinyl monomer, and dispersant are charged in the polymerization 
vessel, may be in the same manner as conventionally taken, and require no 
particular limitation. The same applies also to polymerization conditions 
such as charge proportion for these and polymerization temperature. 
It is also optional to further add, if necessary, a polymerization 
regulator, a chain transfer agent, a pH adjustor, a gelation improver, an 
antistatic agent, an anti-scale agent, etc. which are commonly used in 
preparing vinyl chloride polymers. 
In the practice of the process of this invention, an aqueous medium, 
monomer, polymerization initiator and other necessary materials are 
charged into the polymerization vessel. There are no limitations on the 
order of charging of these materials. The polymerization initiator may be 
charged at any time, before and/or in the course of polymerization, as 
required. It may also be charged continuously or intermittently in plural 
portions. It should be appreciated that, according to the process of this 
invention, in any cases, the charging of the polymerization initiator must 
be followed by heating of the charging passage. 
In the process of this invention, the polymerization is carried out at a 
temperature in the range of about 10.degree. to 95.degree. C., depending 
on the desired polymerization degree of the resulting polymer.

EXAMPLES 
This invention will be described below in detail by giving Examples and 
Comparative Examples. 
EXAMPLES 1 
In a polymerization vessel made of stainless steel and having an internal 
volume of 2,000 lit., 980 kg of deionized water, 382 g of partially 
saponified polyvinyl alcohol and 143 g of water-soluble methyl cellulose 
were charged, the inside of the polymerization vessel was evacuated, and 
thereafter 700 kg of vinyl chloride was charged. Next, 280 g of 
di-2-ethylhexyl peroxydicarbonate was fed into the polymerization vessel 
with use of a constant rate pump. Thereafter water vapor (130.degree. C.) 
was passed for three minutes through a heating jacket provided on the 
outside of the pipe having an internal diameter of 1 cm and a length of 3 
m and charging port communicating with the pipe through which the 
polymerization initiator had flowed, thereby the pipe and charging port 
being heated to 110.degree. C. 
With stirring the content of the polymerization vessel, temperature was 
raised to 66.degree. C. to initiate polymerization, which was stopped when 
the inner pressure of the polymerization vessel fell to 6.0 kg/cm.sup.2, 
and the unreacted monomer was recovered, followed by dehydration and 
drying to obtain a vinyl chloride polymer. 
After the polymerization, the charging pipe and charging port for the 
polymerization initiator were taken apart to observe the sticking of 
polymer scale on these parts, which was evaluated on the basis of the 
following criterions, and also the amount of the solvent remaining in the 
resulting polymer was measured according to the following method. Results 
obtained are shown in Table 1. 
Evaluation method for the sticking of scale 
A: No scale stuck. 
B: Scale stuck a little. 
C: Scale stuck in a large quantity, having clogged the charging port. 
Measurement method for the amount of remaining solvents 
Into a vial, 5 g of the resulting polymer was put, and heating was carried 
out at 130.degree. C. for 30 minutes. A gaseous phase portion in the vial 
was analyzed by gas chromatography to indicate by ppm the amount measured 
for the remaining solvent. 
EXAMPLES 2 and 3 
In each Example, the procedure of Example 1 was repeated to carry out 
polymerization 100 times (Example 2) or 500 times (Example 3), and 
thereafter the sticking of polymer scale was observed and the amount of 
the organic solvent remaining in the resulting polymers was measured in 
the same manner as in Example 1. Results obtained are shown in Table 1. 
COMATIVE EXAMPLES 1 and 2 
The procedure of Example 1 was repeated to carry out polymerization, except 
that the charging pipe and charging port were not heated, but washed with 
300 cc of toluene (Comparative Example 1) or 300 cc of n-hexane 
(Comparative Example 2). The sticking of polymer scale was observed and 
the amount of the organic solvent remaining in the resulting polymers was 
measured in the same manner as in Example 1. Results obtained are shown in 
Table 1. 
COMATIVE EXAMPLE 3 
The procedure of Example 1 was repeated to carry out polymerization, except 
that the charging pipe and charge port were not heated, and no washing was 
carried out. The sticking of polymer scale was observed and the amount of 
the solvent remaining in the resulting polymers was measured in the same 
manner as in Example 1. Results obtained are shown in Table 1. 
TABLE 1 
______________________________________ 
Sticking 
Amount of remaining 
of scale 
organic solvent(ppm) 
______________________________________ 
Example: 
1 A .ltoreq.1 
2 A .ltoreq.1 
3 B .ltoreq.1 
Comparative Example: 
1 A 390 
2 B 235 
3 C .ltoreq.1 
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EXAMPLES 4 
In a polymerization vessel made of stainless steel and having an internal 
volume of 2,000 lit., 980 kg of deionized water, 382 g of partially 
saponified polyvinyl alcohol and 143 g of water-soluble methyl cellulose 
were charged, the inside of the polymerization vessel was evacuated, and 
thereafter 700 kg of vinyl chloride was charged. Next, 580 g of an aqueous 
emulsion containing 50% of di-2-ethylhexyl peroxydicarbonate was fed into 
the polymerization vessel with use of a constant rate pump, and thereafter 
water vapor (120.degree. C.) was passed for three minutes through a 
heating jacket provided on the outside of the pipe having an internal 
diameter of 1 cm and a length of 3 m and a charging port communicating 
with the pipe through which the polymerization initiator had flowed, 
thereby the pipe and charging port being heated to 100.degree. C. 
With stirring the content to the polymerization vessel, temperature was 
raised to 60.degree. C. to initiate polymerization, which was stopped when 
the inner pressure of the polymerization vessel fell to 6.0 kg/cm.sup.2, 
and the unreacted monomer was recovered, followed by dehydration and 
drying to obtain a vinyl chloride polymer. 
After the polymerization, the sticking of polymer scale on the charging 
pipe and charging port for the polymerization initiator was evaluated, and 
also the amount of the solvent remaining in the resulting polymer was 
measured in the same manner as in Example 1. Results obtained are shown in 
Table 2. 
EXAMPLES 5 and 6 
In each Example, the procedure of Example 4 was repeated to carry out 
polymerization 100 times (Example 5) or 500 times (Example 6), and 
thereafter the sticking of polymer scale was observed and the amount of 
the organic solvent remaining in the resulting polymers was measured in 
the same manner as in Example 1. Results obtained are shown in Table 2. 
COMATIVE EXAMPLES 4 and 5 
The procedure of Example 4 was repeated to carry out polymerization, except 
that the charging pipe and charging port were not heated, but washed with 
300 cc of toluene (Comparative Example 4) or 300 cc of n-hexane 
(Comparative Example 5). The sticking of polymer scale was observed and 
the amount of the organic solvent remaining in the resulting polymers was 
measured in the same manner as in Example 1. Results obtained are shown in 
Table 2. 
COMATIVE EXAMPLE 6 
The procedure of Example 4 was repeated to carry out polymerization, except 
that the charging pipe and charging port were not heated, and no washing 
was carried out. The sticking of polymer scale was observed and the amount 
of the organic solvent remaining in the resulting polymers was measured in 
the same manner as in Example 1. Results obtained are shown in Table 2. 
TABLE 2 
______________________________________ 
Sticking 
Amount of remaining 
of scaIe 
organic solvent(ppm) 
______________________________________ 
Example: 
4 A .ltoreq.1 
5 A .ltoreq.1 
6 B .ltoreq.1 
Comparative Example: 
4 C 420 
5 C 250 
6 C .ltoreq.1 
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