Method for removing residual monomers

A method for removing residual vinyl chloride monomers from an aqueous slurry is disclosed. The method preferably utilizes a tower having a plurality of vertically spaced plates, which define a plurality of chambers, each chamber defined between adjacent plates. The tower features a plate in one of the chambers having a diameter of 1.05 to 5 times larger than the diameter of the plates in chambers above and below the chamber having the large plate. The method is based upon introducing the slurry to a particular location in the tower depending upon the porosity of the polyvinyl chloride in the slurry.

BACKGROUND OF THE INVENTION 
1.Field of the Invention 
The present invention relates to an apparatus for removing unreacted 
residual monomers primarily comprising vinyl chloride monomer (hereinafter 
referred to as VC) contained in a mixture of polyvinyl chloride 
(hereinafter referred to as PVC) and an aqueous medium (hereinafter 
referred to as PVC slurry), in the manufacture of vinyl chloride resins 
(hereinafter referred to as PVC). The present invention also relates to a 
method for removing the unreacted residual monomers using such an 
apparatus. 
More particularly, the present invention relates to an apparatus for 
removing residual monomers having a wide range of capability of compliance 
such that one apparatus for removing the residual monomers can achieve a 
uniformly high deal efficiency to PVC slurries which are largely different 
in PVC characteristics or properties and in readiness of releasing 
monomers, and produce a high resin quality at an excellent operating 
performance. The present invention also relates to a method for removing 
the residual monomers using such an apparatus. 
2.Description of the Related Art 
PVC is a resin having excellent chemical and physical characteristics, and 
therefore, it is used in a wide variety of fields. Generally, PVC is 
manufactured by suspension polymerization, emulsion polymerization, or 
bulk polymerization. Among these methods, suspension polymerization and 
emulsion polymerization are commonly employed since they provide 
advantages such that heat of reaction can be easily removed, that the 
final product of PVC containing a reduced amount of impurities can be 
manufactured, and that PVC after polymerization is particulate and thus a 
granulating step is unnecessary. Suspension polymerization and emulsion 
polymerization are generally carried out by placing VC, an aqueous medium, 
a dispersant, a polymerization initiator, etc. in a reactor equipped with 
a stirrer, and polymerizing VC while keeping it at a predetermined 
temperature. It is a general practice that the polymerization reaction is 
not continued until the VC is converted to PVC by 100%, but the 
polymerization is terminated at a conversion from 80 to 95% which provides 
an optimum manufacturing efficiency. Therefore, the PVC slurry after 
termination of polymerization reaction contains a considerable amount of 
unreacted residual monomers. 
Since these residual monomers are harmful to humans, care must be taken to 
prevent the residual monomers from migrating into PVC particles or 
transferring into waste water or air. Accordingly, residual monomers must 
be removed and recovered from the PVC slurry as much as possible. 
According to conventional methods of removing residual monomers, an aqueous 
medium is mechanically separated from the PVC slurry obtained by 
polymerization, and then the aqueous medium and residual monomers which 
remain in PVC in small amounts are removed by hot air-drying, etc. to 
obtain PVC powder as an end product. 
These methods cannot effectively remove residual monomers from waste water, 
and in addition, allow residual monomers to migrate into the gas exhausted 
from a dryer. Moreover, it sometimes occurs that residual monomers are not 
removed to a sufficient level from the end product, PVC powder. Thus, 
conventional methods are not satisfactory in terms of safety, hygiene, and 
preservation of the environment. 
As a method to efficiently remove and recover unreacted residual monomers 
from a slurry after termination of the polymerization, Japanese Patent 
Application Laid-open (kokai) Nos. 54-8693 and 56-22305 have proposed a 
method which employs an apparatus including a hollow cylindrical tower 
which has a plurality of plates having a number of through perforations, 
disposed one on another with a space therebetween inside the tower, a port 
for jetting steam into the tower at the bottom of the tower, and a slurry 
introducing port and a gas discharging port at the top of the tower. In 
that apparatus, PVC slurry is treated as follows. First, the slurry is 
introduced from a sole PVC slurry introducing port provided at 
substantially the top of the hollow cylindrical apparatus. The PVC slurry 
flows along treating passages formed on the plates which have a number of 
through perforations, are substantially concentrically disposed, and have 
partition walls thereon so that a treating passage of many U-turns is 
formed. While the slurry flows through the passage, it is exposed to steam 
jet which comes up from the bottom through the perforations in the plates. 
Therefore, as the slurry flows down the plates one by one, residual 
monomers contained in the slurry are evaporated to separate. The PVC 
slurry thus treated is discharged from a sole PVC slurry discharging port 
which is provided substantially at the bottom section of the apparatus. 
Presently, various kinds of improvements have been achieved on the quality 
of PVC as its application has been diversified. As a result, the problems 
at the time of removing residual monomers concerning the releasability of 
residual monomers which depends on the internal structure of PVC 
particles, degradation of PVC when exposed to heat, and bubbling 
properties of slurries in the apparatus for separating residual monomers 
are diversified. In particular, PVC which has been improved to have 
greater amounts of voids in its particles in order for an increased amount 
of plasticizing agent to be absorbed contains a large amount of residual 
monomers which are left in PVC particles after polymerization reaction. 
Therefore, if a PVC slurry including such PVC is treated with a 
conventional apparatus for removing residual monomers, the slurry is 
excessively bubbled with evaporated residual monomers when it contacts 
with steam, causing the following drawbacks: 
1. PVC slurry flows over the partition walls and is discharged without 
passing through predetermined passages for treatment. Thus, a PVC slurry 
from which residual monomers have not sufficiently been removed migrates 
into a PVC slurry which has normally passed through the passage, 
contaminating the PVC end product with PVC particles containing residual 
monomers at a high concentration. 
2. PVC particles blown up by the bubbles tend to adhere to the inner walls 
of the apparatus. The adhered particles deteriorate after being exposed to 
steam at a high temperature for a long time to produce colored particles, 
which migrate into the PVC end product, reducing its value. 
These drawbacks may be overcome by introducing a reduced amount of PVC 
slurry in conventional methods so that the slurry will not flow over the 
partition walls. However, this approach results in a decrease in amounts 
of PVC treated per hour in the process of residual monomer treatment to 
eventually reduce the production of the PVC end product per hour. 
In the case where the PVC readily releases residual monomers, the contact 
time of the PVC with steam may be shorter than that required for a PVC 
from which residual monomers are difficult to remove. However, if the 
apparatus for removing residual monomers is designed to meet conditions 
suitable for the treatment of slurries containing PVC from which residual 
monomers are difficult to remove, use of such an apparatus for treating a 
PVC slurry containing PVC which easily release residual monomers causes 
such an undesirable result that the PVC undergoes excessive heat 
degradation to deteriorate the quality of the PVC end product. This is 
because the PVC slurry contacts with steam for an unnecessarily prolonged 
period even after residual monomers was sufficiently removed. On the other 
hand, if the apparatus for removing residual monomers has been designed to 
meet conditions suitable for the treatment of slurries containing PVC from 
which residual monomers are easily removed, and if a slurry containing PVC 
from which residual monomers are difficult to remove is treated with such 
an apparatus, residual monomers cannot be completely removed, allowing the 
PVC slurry to pass through the residual monomer removing process while 
retaining residual monomers at a high concentration. Thus, conventional 
apparatuses for removing residual monomers cannot satisfy either the case 
where PVC slurries containing PVC from which residual monomers are easily 
removed are treated and the case where PVC slurries containing PVC from 
which residual monomers are difficult to be removed are treated. 
SUMMARY OF THE INVENTION 
As a result of diligent studies carried out by the present inventors to 
solve the above problem, an apparatus for removing residual monomers which 
is capable of smoothly complying with a wide variety of PVC slurries 
having different characteristics, and a method using such apparatus have 
been developed to achieve the present invention. 
Specifically, as a result of the research conducted on the bubbling of a 
PVC slurry when residual monomers are removed therefrom, the following 
facts have been found. First, the bubbles generated from a PVC slurry when 
it is treated with steam on the plates are the ones generated from the 
residual monomers liberated from the inside of PVC particles and the 
aqueous medium. Second, the bubbling makes the PVC slurry flowing on the 
plates overflow beyond the partition walls dividing the passages for 
treatment. Third, a 5-minute contact of the slurry with steam removes not 
less than 70% of the residual monomers existing inside the PVC particles, 
from which it is presumed that the bubbling phenomenon takes place most 
vigorously on a plate serving as the floor of the chamber to which the PVC 
slurry is first introduced. From these facts, it has been found that when 
the diameter of the plate which serves as the floor of the chamber having 
at least one PVC slurry introducing port was increased so as to have a 
diameter greater than that of other plates, the height of the PVC slurry 
on the plate is substantially reduced, and thus, bubbles of a bubbling 
slurry are prevented from overflowing beyond the partition walls, and, 
according to this approach, the amount of the PVC slurry to be treated is 
not necessary to be reduced. In addition, in view of the fact that PVC 
slurries containing PVC from which residual monomers are more easily 
removed tend to more vigorously boil up, the following have been carried 
out. First, a PVC slurry introducing port is provided in at least two 
separate chambers of the tower. Then, when a PVC slurry which requires a 
prolonged time for evaporating and separating VC is treated, the slurry is 
introduced from a slurry introducing port provided in a chamber remote as 
much as possible from that having a slurry discharging port to secure the 
residence time. On the other hand, when a PVC slurry from which VC is 
evaporated and separated in a short time is treated, the residence time 
necessary and sufficient to evaporate and separating VC can be afforded by 
introducing the slurry from a slurry introducing port provided in a 
chamber relatively close to that having a slurry discharging port while 
avoiding the PVC slurry from contacting with steam for an excessively 
prolonged period not to cause an excessive heat degradation of PVC. 
The term "porosity" as used hereinafter means a volume of microvoids in PVC 
(ml/g). 
The invention claimed in the present application is summarized as follows: 
a hollow cylindrical tower; 
a plurality of plates provided one on another with a space therebetween in 
a vertical direction in the tower, each having many perforations; 
a plurality of chambers each formed on one of the plates which serves as a 
floor of the chamber; 
a slurry introducing port provided in at least two of the chambers; 
a flow-down section provided between two adjacent plates to allow a slurry 
to sequentially flow down from a plate of a higher chamber to a plate of a 
lower chamber; 
a steam introducing port provided at a bottom of the tower; and 
a slurry-discharging port provided in a chamber lower than the chamber 
having the slurry introducing port, wherein the plate in one of the 
chambers provided with the slurry introducing port has a diameter 1.05 to 
5 times as large as that of the plates located in the chambers immediately 
above and below the plate of the chamber provided with the slurry 
introducing port, respectively. 
In another aspect of the present invention, there is provided an apparatus 
described above, further comprising hot water jetting means located in the 
proximity of at least one of plates, with being faced to the lower face of 
the plate. 
Preferably, the diameter of each perforation is from 0.5 to 5.0 mm. 
Preferably, the proportion of an area of the perforations in each plate to 
an area of the plate is from 0.001 to 10%. 
In a further aspect of the present invention, there is provided a method 
for removing residual monomers using the above apparatus, which method 
comprises the steps of: 
introducing a polyvinyl chloride-containing slurry from the slurry 
introducing port; 
blowing steam from a steam introducing port provided at a bottom of the 
tower; 
allowing the slurry to contact with steam while the slurry flows downward 
through the plates; 
thereby separating residual monomers from the slurry; and at the same time 
discharging a gas containing the separated residual monomers from the top 
of the tower, and discharging the slurry from which residual monomers were 
removed from the slurry-discharging port; 
wherein the step of introducing the polyvinyl chloride-containing slurry is 
carried out in accordance with the following (1), (2), or (3): 
(1) supplying the slurry from the slurry introducing port provided in a 
chamber above the chamber having a plate with a greater diameter, in the 
case where the residual monomers are difficult to remove from the slurry, 
(2) supplying the slurry from the slurry introducing port provided in the 
chamber having a plate with a greater diameter or from the slurry 
introducing port provided in a chamber lower than the chamber having a 
plate with a greater diameter, in the case where the residual monomers are 
easily removed from the slurry, 
(3) supplying the slurry from the slurry introducing port provided in the 
chamber having a plate with a greater diameter, in the case where the 
slurry has a high bubbling property. 
Particularly, when the porosity of the polyvinyl chloride in the slurry is 
not less than 0.300 ml/g, the slurry is introduced to the chamber having a 
plate with a greater greater diameter or to a chamber located lower than 
that chamber. 
Also, when the porosity of the polyvinyl chloride in the slurry is not less 
than 0.350 ml/g, the slurry is introduced to the chamber having a plate 
with a greater diameter, 
Also, when the porosity of the polyvinyl chloride in the slurry is less 
than 0.300 ml/g, the slurry is introduced to a chamber located above the 
chamber having a plate with a greater diameter.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The apparatus for removing residual monomers of the present invention can 
select optimal conditions according to respective PVCs to be treated so 
that when a PVC slurry from which residual monomers are difficult to 
remove is treated, the residence time is prolonged, and in contrast, when 
a PVC slurry from which residual monomers can be easily removed is 
treated, the residence time is reduced. Thus, there is substantially no 
need to change the amount of the PVC slurry to be treated depending on the 
readiness of releasing residual monomers. Therefore, residual monomers can 
be very efficiently removed with the apparatus of the invention. 
Moreover, according to the present invention, it is possible to flexibly 
control the conditions for removing residual monomers for PVCs having a 
variety of characteristic and properties which were not complied with by a 
single conventional apparatus. For example, residual monomers can 
efficiently removed with one apparatus depending on bubbling properties of 
slurries, readiness of releasing monomers, and susceptivity of the PVC to 
heat degradation. 
In this invention, the term PVC is used to refer to homopolymers of VC, 
copolymers of VC and a monomer which is polymerizable with VC, polymers 
obtained by graft polymerization of VC to an olefin polymer, and polymers 
which are composed of two or more of these polymers. In order to 
efficiently remove residual monomers according to the present invention, 
polymers preferably contain 50% by weight or more of VC as a structural 
unit of the polymer. Such polymers may be obtained either by suspension 
polymerization or emulsion polymerization. 
Specific examples of the polymerizable monomers which are polymerizable 
with VC include carboxylic esters of a vinyl alcohol, such as vinyl 
acetate; vinyl ethers such as alkylvinyl ethers; unsaturated carboxylic 
esters such as acrylates and methacrylates; vinylidene halides such as 
vinylidene chloride and vinylidene fluoride; unsaturated nitriles such as 
acrylonitrile; and olefins such as ethylene and propylene. 
In the present invention, the term PVC slurry is used to refer to a slurry 
containing PVC and an aqueous medium. A PVC slurry after termination of 
polymerization reaction contains unreacted residual monomers in addition 
to PVC and an aqueous medium. In the manufacture of PVC, a dispersant such 
as polyvinyl alcohol and hydroxypropyl methylcellulose, and if desired, a 
buffer, particle size regulator for PVC, agent for suppressing scale 
adhesion, defoamer, etc. are used. PVC slurries may therefore contain a 
necessary amounts of these additives. 
It is preferred that the concentration of the PVC contained in a PVC slurry 
(hereinafter referred to as the slurry concentration) which is treated by 
the method of the present invention be from 5 to 45% by weight, and more 
preferably from 10 to 40% by weight. If the slurry concentration is too 
high, the fluidity of the PVC slurry in the apparatus for removing 
residual monomers becomes poor. On the other hand, if the slurry 
concentration is too low, substantial amount of the PVC which is treated 
significantly decreases. 
Generally speaking, the PVC slurry which is subjected to the treatment of 
the present invention may be one that is transferred to a PVC slurry tank 
after the polymerization reaction has been terminated, and after or before 
the inside pressure of the reactor has dropped to atmospheric pressure. 
Alternatively, a PVC slurry for which polymerization reaction is 
terminated when conversion has reached an arbitrary point in the course of 
polymerization may also be used after being transferred to a PVC slurry 
tank. The PVC slurry is supplied from the slurry tank to the apparatus for 
removing residual monomers of the present invention using a transferring 
means such as a pump at a predetermined flow rate. 
The method for removing residual monomers from a PVC slurry using the 
apparatus of the present invention will be described with reference to 
FIGS. 1 to 3. However, the present invention is not limited to the 
specific embodiments described herein. 
FIG. 1 is a schematic drawing of an apparatus for removing residual 
monomers according to an embodiment of the present invention. This 
apparatus includes a hollow cylindrical tower 4, a plurality of plates 31 
to 37 which are disposed in the vertical direction in the tower 4, each 
having many perforations, a plurality of chambers 8 and 25 to 30 each 
formed on one of the plates 31 to 37 which serves as a floor of the 
chamber, slurry introducing ports 19 to 24 provided in at least two of the 
chambers, flow-down sections 13 to 18 provided between two adjacent plates 
to allow a slurry to sequentially flow down from a plate of a higher 
chamber to a plate of a lower chamber, a steam introducing port 10 
provided at a bottom of the tower 4, a slurry discharging port 12 provided 
in a chamber lower than the chamber 29 having the slurry introducing port, 
and hot water jetting means 46 to 51 each provided immediately below the 
plates 31 to 36. The plate of chamber 26, one of the chambers provided 
with a slurry introducing port, has a diameter 1.05 to 5 times as large as 
that of the plates located in chambers 25 and 27 located immediately above 
and below chamber 26. In the top chamber 8 of the tower 4 is provided a 
deaerating port 11 which is connected to a condenser 7. Each of the plates 
31 to 37 has a number of perforations 43 as shown in FIG. 2. On each 
plate, partition walls 38 to 42 are provided so that the slurry flowed 
down forms a passage of many U-turns (or a zig-zag passage) which is 
defined by the partition walls and inside wall of the tower. Numeral 45 
indicates a division plate. The slurry introducing ports 19 to 24 are 
connected to a slurry supply line having valves 19A to 24A. The slurry 
supply line is also connected to a slurry tank 1 via valves 52, 53, a heat 
exchanger 3, and a pump 2. 
The apparatus of the present invention can be manufactured with ease by 
assembling plate chambers (compartments) as unit each having plates 31 to 
37. Alternatively, if a conventional apparatus is retrofitted, the 
apparatus can be manufactured by replacing a plate of the conventional 
apparatus with a plate 33 having a larger diameter which was fabricated 
separately in advance. 
In the apparatus shown in FIG. 1, the PVC slurry which was obtained by 
suspension polymerization or emulsion polymerization and temporarily 
stored in a PVC slurry tank 1 is introduced to a heat exchanger 3 by a 
pump 2. The slurry is heated to a predetermined temperature in the heat 
exchanger 3 and is thereafter introduced into the apparatus through any 
one of the PVC slurry introducing ports 19 to 24. 
The flow rate of the PVC slurry which is introduced into the inside of the 
tower body 4 of the apparatus for removing residual monomers is from 0.1 
to 300 m.sup.3 /h, and preferably from 1 to 100 m.sup.3 /h, per m.sup.2 of 
the area of the plate 31 shown in FIG. 2. The flow rate is preferably 
adjusted by the amount of liquid forwarded by the pump 2. 
The PVC slurry to be introduced into the tower 4 is preferably pre-heated 
at 50.degree.-100.degree. C. with the heat-exchanger 3. When the slurry is 
pre-heated, the efficiency of removal of residual monomers is enhanced. 
The inner diameter of the plates provided in the tower 4 is from 200 to 
10,000 mm with the plate having a smallest inner diameter, and 1.05 to 5 
times, preferably 1.2 to 5 times as large as that of the plate having the 
smallest diameter with the plate having a largest inner plate. 
The inner peripheral shape and size of the chambers each having a plate as 
a floor therefor may be the same or different from each other in any 
cross-section parallel to the plate. 
The height of the tower 4 is from 2 to 20 times, and more preferably from 5 
to 15 times as large as the diameter of the plate having the smallest 
diameter. 
The apparatus for removing residual monomers according to the present 
invention has a slurry introducing port in at least 2 chambers. Moreover, 
the diameter of the plate which serves as a floor for a chamber having a 
slurry introducing port is generally from 1.05 to 5 times, and preferably 
1.2 to 5 times as large as the diameter of the plates provided in the 
chambers immediately above and below the plate of the chamber having the 
slurry introducing port, respectively. 
The readiness of a PVC slurry to release monomers depends on the structure 
of PVC particles in the PVC slurry. When PVC particles have a large 
porosity, contact between the PVC particle and steam is good. Accordingly, 
residual monomers tend to be easily removed. In addition, a slurry, after 
polymerization, containing such PVC particles tends to bubble. On the 
other hand, PVC having a small porosity does not readily release residual 
monomers. Thus, in the present invention, when polyvinyl chloride 
particles in a slurry have a porosity of not less than 0.300 ml/g, the 
slurry is preferably introduced into a chamber having a plate with a 
larger diameter or into a chamber located lower than that chamber. When 
polyvinyl chloride particles in a slurry have a porosity of not less than 
0.350 ml/g, the slurry is preferably introduced into a chamber having a 
plate with a larger diameter. Moreover, when polyvinyl chloride particles 
in a slurry have a porosity of less than 0.300 ml/g, the slurry is 
preferably introduced into a chamber located upper than a chamber having a 
plate with a larger diameter. 
In an apparatus for removing residual monomers, the number of plates is a 
decisive factor for determining the time in which a PVC slurry stays in 
the apparatus, i.e., the contact period of the PVC slurry with steam. In 
the apparatus of the present invention, the number of plates is determined 
so that the PVC slurry which requires the longest time for releasing 
residual monomers among a plurality of PVC slurries to be treated has a 
residence time at least necessary to cause a complete removal of residual 
monomers from the slurry can be secured. The introducing port from which 
the PVC slurry is actually introduced may be selected depending on the 
readiness of the slurry to release monomers and the residence time 
required. 
The residence time in the apparatus can be determined based on the 
readiness of the slurry to release monomers as well as the concentration 
of the residual monomers in the PVC slurry to be introduced and the preset 
concentration of residual monomers contained in a discharged PVC slurry, 
etc. 
A method for controlling the residence time in accordance with the 
readiness of the slurry to release monomers will be described with 
reference to FIG. 1. When a PVC slurry which does not readily release 
residual monomers is treated, for instance, the PVC slurry is introduced 
from the slurry introducing port 19. Introduced PVC slurry passes through 
a treatment passage formed by plate 31, partition walls 38 to 42 on the 
plate 31, and the inner wall of the tower to a flow-down section 13, and 
then introduced onto a plate 32 in the lower neighboring chamber. 
The slurry thus introduced onto the plate 32 successively passes through a 
treatment passage on the plate 32 and flows down onto the plate in a 
chamber below. Thus, the slurry passes through the treatment passages on 
plates 31 to 37, and is finally discharged to outside the apparatus 
through the PVC slurry discharging port 12. On the other hand, when a PVC 
slurry from which residual monomers are easily removed is treated, for 
instance, the PVC slurry is introduced from the PVC introducing port 23 
onto a plate 35. 
The slurry is allowed to pass through the treatment passages on plates 36 
and 37 in turn and treated. Moreover, when a PVC slurry which bubbles 
vigorously is treated, for instance, the PVC slurry is introduced from the 
PVC introducing port 21 which is arranged in the chamber 26 provided with 
a plate having a diameter greater than that of the plates 32 and 34 
provided in the chambers immediately above and below the chamber 26, 
respectively, on the plate 33, and treated in the same way as mentioned 
above. Thus, by selecting the position of the plate on which a PVC slurry 
is introduced, according to the characteristics of the PVC slurry to be 
treated, the contact time of the PVC slurry with steam can be controlled 
to a time necessary and sufficient for removing residual monomers, and 
heat degradation of PVC due to excessive contact with steam can be 
avoided. When a PVC slurry which easily bubbles is treated, it is 
preferred that the slurry be introduced from the PVC introducing port 21 
which is arranged in chamber 26 provided, as its floor, with plate 33 
having a diameter 1.05 to 5 times, and preferably 1.2 to 5 times as large 
as that of the plate having the smallest diameter. If the diameter of a 
plate is great, the depth of the PVC slurry flowing through the passage on 
the plate becomes shallow. Therefore, the residence time of the steam 
which passes through the PVC slurry on the plate decreases, and bubbling 
of the slurry on that plate can be suppressed. As a result, the PVC slurry 
is prevented from overflowing beyond partition walls, and migration of a 
PVC slurry from which residual monomers is not sufficiently removed into a 
PVC product can be avoided. In addition, stabilized removal of residual 
monomers and operation of the apparatus becomes possible. If the diameter 
of the plate is less than 1.05 times as large as that of the plate having 
the smallest diameter, effect on suppression of bubbling is limited. On 
the other hand, if the diameter of the plate is greater than 5 times as 
large as that of the plate having the smallest diameter, the amount of the 
steam per unit area blown to the plate chamber through perforations is too 
small and results in insufficient stirring of the PVC slurry. This will 
cause precipitation of PVC particles, which sometimes makes operation of 
the apparatus difficult. In addition, construction costs of the apparatus 
will increase. 
The readiness of the PVC slurry to release residual monomers depends on the 
porosity of the PVC in the slurry. Therefore, the port for introducing the 
slurry can be selected based on the determined value of the porosity of 
the PVC. That is, in the case where the porosity is not less than 0.300 
ml/g, the slurry is introduced from the slurry introducing port located in 
chamber 26 (which is provided with a plate having a greater diameter) or 
any one of the chambers 28, 29, and 30 which are located below the chamber 
26. In the case where the porosity is not less than 0.350 ml/g or the 
slurry tends to bubble, the slurry is introduced into the chamber 26 
(which is provided with a plate having a greater diameter). Moreover, in 
the case where the porosity is less than 0.300 ml/g, the slurry is 
introduced into the chamber 25 which is located above the chamber 26. 
Although only one slurry discharging port 12 is provided in the apparatus 
shown in FIG. 1, a plurality of slurry discharging ports may be provided 
in any chambers below the port from which the slurry is introduced. If a 
plurality of slurry discharging ports are provided, it is possible to 
select the port(s) from which the slurry is discharged. Thus, the chamber 
in which the plate having a greater diameter is located in the apparatus 
for removing residual monomers is no specifically limited. This is because 
the residence time can be controlled by selecting the discharging port. 
When a demonomer treatment is performed, if the temperature of the PVC 
slurry is high, the efficiency of removing residual monomers enhances. 
However, if the temperature is too high, coloring or heat degradation of 
PVC particles are caused to deteriorate quality. Accordingly, the 
temperature of the PVC slurry must be adjusted properly. The temperature 
of the slurry flowing on plates is generally from 50.degree. to 
150.degree. C., preferably from 70.degree. to 120.degree. C. and more 
preferably from 80.degree. to 110.degree. C. The temperature of the PVC 
slurry on plates can be controlled by the temperature and amounts of the 
steam which is jetted from below. 
The pressure inside the tower 4 is preferably maintained in the range from 
0.2 to 3 kg/cm.sup.2 (abs). 
If the balance of the temperature and pressure in the apparatus for 
removing residual monomers is lost due to disturbance, the flow of the PVC 
slurry on the plates tends to pulse. As its cause, it can be mentioned 
that the amount of heat exchanged by the heat exchanger is varied 
primarily by the fluctuation of the amount of the PVC slurry discharged 
from a PVC slurry discharging port, and thus the temperature of the PVC 
slurry introduced from the PVC slurry introducing port is varied. In such 
a case, if all the plates have the same size, the pulsating motion 
generated is transmitted down to a lower plate, which results in an 
unstable operation. In contrast, with the apparatus for removing residual 
monomers according to the present invention, when the PVC slurry is 
introduced to the plate having a diameter greater than that of other 
plates, a removal treatment of residual monomers begins to proceed under 
mild conditions with a smaller amount of steam jet compared to other 
plates. Thus, a pulsating motion which has already been started is 
mitigated on that plate with a greater diameter to cut off transmission of 
the pulsating motion onto lower plates. Moreover, with the apparatus for 
removing residual monomers according to the present invention, the flow of 
the PVC slurry is very stable. Therefore, even the amount of the PVC 
slurry which is discharged is also stabilized. Thus, the apparatus of the 
present invention has a remarkable effect in solving or singinifactly 
reducing the cause of the pulsating itself. 
In a treatment for removing residual monomers, bubbling of slurry is not 
necessarily suppressed at all during the treatment even in a PVC slurry 
which does not readily release residual monomers, or in other words, which 
needs a number of plates for flowing the slurry thereon. 
Especially when the balance of temperature and pressure was lost in the 
apparatus for removing residual monomers, bubbling sometimes causes the 
operation of the apparatus to become unstable. If all the plates have the 
same size, bubbling continues to no small number of lower plates, and PVC 
particles lifted up by bubbles or foams tend to adhere onto the walls of 
the chambers. Therefore, even when a water jet was applied to remove the 
adhered PVC from the walls, the separated PVC sometimes migrates as 
colored particles into the PVC discharged from the apparatus for removing 
residual. With the apparatus for removing residual monomers according to 
the present invention, any bubbling regardless of its degree can be 
efficiently mitigated at the plate having a greater diameter. Thus, when a 
PVC slurry which does not boil up significantly and which is generally 
difficult to release residual monomers is treated with the apparatus of 
the present invention, bubbling is substantially killed in the course of 
passing the plates. As a result, colored PVC is scarcely detected in the 
PVC discharged from the apparatus. 
The apparatus for removing residual monomers according to the present 
invention, based on its specific structure and shape as described above, 
produces excellent effects of stilling the pulse of a PVC slurry to make a 
stable operation possible at a very high level and controlling the number 
of colored PVC particles contained in the PVC, which has undergone the 
treatment, at a high and stable level, which effects could never be 
obtained with conventional apparatuses. 
In order to treat a slurry which does not bubble at all or bubble only 
slightly, the plate to which the slurry is introduced preferably has a 
smaller diameter. If the diameter is reduced, the amount of steam jetted 
per unit area of the plate is increased. In addition, the slurry depth on 
the plate becomes deep. As a result, the contact time of the PVC slurry 
with steam on the plate can be sufficiently secured to enhance the 
efficiency of removing residual monomers. Since the concentration of 
residual monomers in a PVC slurry decreases as the slurry flows down 
through the flow-down section in the apparatus, bubbling occurs less 
vigorously on lower plates than upper plates even though the slurry depth 
on lower plates become deep. 
Referring to FIG. 1, a PVC slurry with a high bubbling property is 
introduced into the apparatus through a slurry introducing port 21. The 
PVC slurry thus introduced flows through the treatment passage formed with 
partition walls on plate 33 which has a number of through perforations. 
The slurry flows down the flow-down section 15 onto the lower plate. In 
this case, although the amount of the slurry introduced onto plate 33 is 
the same as other plates, the amount of slurry which is introduced into 
the apparatus per unit area of the plate 33 can be decreased since the 
diameter of the plate 33 is large. As a result, even with PVC slurries 
which bubble vigorously, demonomer treatment can be efficiently performed 
while suppressing bubbling. 
In the present specification, the plates provided in an apparatus for 
removing residual monomers and each having a number of through 
perforations therein and a plurality of vertical partition walls on one 
surface thereof are called "plate structures". 
The perforations in the plates are provided for that the PVC slurry is 
subjected to a treatment for removing residual monomers by the steam 
jetted through the perforations when the slurry flows on the plates. The 
size of each perforation, steam pressure, and the amount of the steam 
introduced must be set so that the PVC slurry is not be allowed to flow 
down through the perforations, the perforations are not blocked, and the 
steam jetted from below passes continuously and uniformly through the 
perforations. 
The diameter of each perforation provided in the plates is not more than 5 
mm, preferably from 0.5 to 2 mm, and more preferably from 0.7 to 1.5 mm. 
The opening ratio of each plate (total area of perforations/area of plate) 
is from 0.001 to 10%, preferably from 0.04 to 4%, and more preferably from 
0.2 to 2%. If the opening ratio is too small, PVC particles in a PVC 
slurry flowing on the plates are not sufficiently stirred by the steam 
jetted through the perforations, causing the PVC particles to precipitate 
to reduce the efficiency of removing residual monomers. Moreover, the 
fluidity of the PVC slurry also decreases. On the other hand, if the 
opening ratio is too large, a phemenon that the PVC slurry drips from the 
perforations (this phenomenon is hereinafter referred to as the slurry 
leaking) occurs, or a large amount of steam is wasted in order to prevent 
the slurry leaking from the perforations. 
The partition walls are provided for securing a treatment passages through 
which a PVC slurry can flow on the plates. Because of the presence of the 
partition walls, the PVC slurry can flow on each plate for a certain 
period of time, during which the slurry is treated with steam to remove 
residual monomers therefrom. The plate structure shown in FIGS. 2 and 3 
has partition walls 38 to 42 arranged in an alternate relationship on 
plate 31. 
The residence time of a PVC slurry in an apparatus for removing residual 
monomers is the time during which the PVC slurry passes through the 
passages for treatment formed on a predetermined number of plates. 
Accordingly, if the PVC slurry is desired to be introduced in an increased 
amount when each plate has a fixed diameter, it is sufficient to increase 
the height of the division plate 45 which divides each treatment passage 
from an entrance to each flow-down section in the apparatus. By 
controlling the height of division plates, the liquid depth of the PVC 
slurry on that plate can be adjusted. The treatment passages are defined 
by the manner of installation of the partition walls. The pattern of the 
passages is preferably the type of hair-pin curve as shown in FIG. 2. 
Other types of selectable examples include spiral, wheel, and star 
(radial). 
There are no specific limitations on the plate structure of the present 
invention in the aspect of the number of partition walls and the width of 
the passages. However, if the number of partition walls is excessively 
increased and the height of the passages is made too high, the liquid 
depth of the PVC slurry becomes too deep, allowing unpreferable flooding 
of the slurry over the partition walls. 
The apparatus of the present invention has a steam introducing port 10 in 
the bottom chamber 9 of the tower. The steam which is introduced from the 
port 10 is blown through perforations in plates 37 to 31 onto the PVC 
which flows on each of those plates. The amount of the steam introduced is 
preferably from 1 to 100 kg/h, and more preferably from 5 to 50 kg/h per 1 
m.sup.3 of PVC slurry. If the amount is too small, PVC particles in the 
PVC slurry precipitates, and thus, residual monomers in the PVC slurry 
cannot be removed efficiently. On the other hand, if the amount of the 
steam introduced is too large, the PVC slurry violently splashes, making 
stable treatment for removing residual monomers difficult. In addition, 
the efficiency of removing residual monomers from a PVC slurry is not 
improved compared with a large amount of steam introduced, leading to a 
very poor treatment efficiency. 
The apparatus of the present invention preferably has at least one hot 
water jetting device at a position just under a plate. The hot water 
jetting devices 46 to 51 are fabricated by processing a pipe having a 
number of nozzle holes to a predetermined shape to form jet nozzles . The 
jet nozzles are preferably disposed such that the hot water is jetted to a 
direction crossing the vertical line at an angle of 10.degree. to 
60.degree.. In the apparatus in FIG. 1, the hot water jetting devices 46 
to 51 are placed right beneath the plates 31 to 36, respectively. Hot 
water is jetted from each device at predetermined time intervals to wash 
the lower surface of the plate and the inside wall of the tower. 
The shape of the pipe which constitutes the hot water jetting devices 46 to 
51 is generally like Greek letter omega (.OMEGA.) or phi (.PHI.), spirals, 
stars, or hair-pins. The shape like multiple layered rings in which rings 
are layered so that every other rings are cocentrically disposed may also 
be used. Each of the hot water jetting devices 46 to 51 is arranged in 
parallel to and directly below each plate. However, if the outermost parts 
of the hot water jetting devices 46 to 51 come too close to the inner 
circumferential walls of the tower, PVC particles and other materials 
which have been washed off may block clearances. Therefore, it is 
preferable that the hot water jetting devices be placed so that the 
outermost parts of each device is 20 mm or more apart from the surface of 
the inner walls of the tower. 
The shape of the jet nozzle holes provided in the hot water jetting devices 
46 to 51 may be circular, oval, slit-like, etc. The shape is selected 
depending on the purpose of use. If a circular or oval shape is employed, 
the diameter or the major axis is generally selected in a range from 1 to 
8 mm, whereas if a slit-like shape is employed, the maximum length of the 
slit is generally in a range from 1 to 8 mm. 
The PVC slurry from which residual monomers was sufficiently removed in the 
apparatus for removing residual monomers is introduced into a heat 
exchanger 3 by a pump 5. The slurry is cooled down in the heat exchanger 3 
and then temporarily stored in a PVC slurry tank 6. Subsequently, the 
slurry is dewatered and is then supplied to a drying apparatus (not 
illustrated). The method of supplying the PVC slurry which has undergone a 
treatment for removing residual monomers and subsequent process steps are 
not particularly limited. 
The monomer gas which was separated in the apparatus for removing residual 
monomers can be condensed in a condenser 7 after the gas has passed 
through the deaerating port 11. If the condensed water contains a great 
amount of vinyl chloride monomers, the condensed water may be treated 
again by returning it to the apparatus for removing residual monomers. 
EXAMPLES 
The present invention will next be described below with reference to 
Examples and Comparative Examples, which should not be construed as 
limiting the invention. In the following Examples and Comparative 
Examples, evaluation was made as follows. 
(1) Concentration of residual monomers 
A PVC slurry was sampled immediately after it was discharged from the 
slurry discharging port, and dewatered. Using a Gas Chromatograph 9A 
(tradename) manufactured by Shimadzu Corporation, the concentration of 
residual vinyl chloride monomers in PVC particles was determined based on 
a "head space" method. The determination was performed in accordance with 
ASTM D4443. The detection section employed a FID. 
Generally, the concentration of residual vinyl chloride monomers in end PVC 
products is controlled so as not to become in excess of 1 ppm. After the 
slurry was discharged from the removal apparatus, small amounts of 
residual monomers can further be removed through the subsequent steps such 
as a drying step. It is preferred that the concentration of residual vinyl 
chloride monomers be controlled to be not more than 10 ppm at the stage 
where the PVC was discharged from the apparatus for removing residual 
monomers. 
(2) Method for determining the yellowing factor (heat degradation factor) 
PVC slurries before and after a treatment for removing residual monomers 
were dewatered, respectively. They were dried at 40.degree. C. for 24 
hours. Subsequently, PVC plates having the following composition were 
prepared under the below-described rolling conditions. The yellowing 
factor of the PVC plates were measured in accordance with JIS K7105. The 
greater the value, the more significant the yellowing (heat degradation) 
factor. 
______________________________________ 
Composition 
PVC 100 parts 
Tri-basic lead sulfate 
3 
Di-basic lead sulfate 1 
Calcium stearate 1 
Stearic acid 0.5 
Rolling conditions: 
Roll type 8 inch rolls 
Roll temperature 170.degree. C. 
Rolling time 15 min. 
Thickness of rolled sheet 
0.32 mm 
______________________________________ 
It is generally well known that the PVC with a low polymerization degree 
has undergone more severe heat degradation than the PVC with a high 
polymerization degree during polymerization since the former PVC has been 
prepared at a relatively high polymerization temperature compared to the 
latter PVC and that the former PVC contains many unstable structures from 
which heat degradation starts. It is also noted that PVC with a lower 
polymerization degree has a smaller porosity, and therefore residual 
monomers are difficult to separate from such a PVC. Therefore, a PVC with 
a low polymerization degree must requires a longer contact time of slurry 
with steam at the time for removing residual monomers compared to the 
contact time required by a PVC with a high polymerization degree. Because 
of this reason, PVCs with a low polymerization degree generally have a 
yellowing factor greater than that of PVCs with a high polymerization 
degree. In the process of removing residual monomers, if the yellowing 
factor of a PVC with a polymerization degree of 1300 can be suppressed not 
more than 5 and that of a PVC with a polymerization degree of 700 can be 
suppressed not more than 10, the quality of the final products will not 
depreciate its commercial values. 
(3) Number of colored PVC particles 
A part of the PVC slurry discharged from the PVC slurry discharging port 12 
was sampled. The sample was dried to obtain 100 g of a PVC resin, which 
was spread on a white kent paper. While mixing the whole sample resin with 
a spatula, the colored PVC particles were visually identified and picked 
up. The number of the colored PVC particles was counted. 
(4) Bubbling conditions on plates 
On the two plates identified by A and B below, bubbling conditions were 
observed and evaluated based on the following criteria. 
Plate A: The plate which serves as a floor of the chamber having a slurry 
introducing port through which a slurry is introduced into the apparatus 
from outside. 
Plate B: The third plate below the plate A mentioned above (plate A is not 
counted). 
Evaluation 
A: Only slight bubbling or no bubbling is observed. The fluidity of the PVC 
slurry is excellent. 
B: Low bubbling. The fluidity of the PVC slurry is good. 
C: High bubbling, but the PVC slurry does not overflow beyond the partition 
walls. 
D: Bubbles sometimes overflow beyond the partition walls. 
(5) Porosity of PVC 
Method of measurement: Mercury penetration method 
Device: Porosimeter Model-70 (manufactured by Carlo-elba) 
Pressure: Max 2,000 kg/cm.sup.2 
Six measurements were averaged. 
Example 1 
(1) Apparatus used for removing residual monomers 
The apparatus for removing residual monomers used in Example 1 had the 
structure as shown in FIGS. 1 to 3. More detailed particulars were as 
follows: 
A) Number of plates: 7 
B) Space between adjacent two plates: 1,400 mm 
C) Specification of plate structure: 
a) Plate structures No. 1, 2, 3, 4, 6, and 7 counted from the bottom: 
Diameter of plates: 1,300 mm 
Diameter of each perforation: 1.3 mm 
Opening ratio (%): 0.3% (total area of perforations/area of plate) 
Height of partition walls: 500 mm 
Height of division walls: 450 mm 
Width of the passages for treatment: 200 mm 
b) Plate structure No. 5 counted from the bottom: 
Diameter of plate: 2,000 mm 
Diameter of each perforation: 1.3 mm 
Opening ratio (%): 0.3% (total area of perforations/area of plate) 
Height of partition walls: 290 mm 
Height of division wall: 250 mm 
Width of the passage for treatment: 200 mm 
D) PVC slurry introducing port: 
Location: Chambers No. 3, 4, 5, 6, 7, and 8 counted from the bottom. 
Number: One for each chamber, a total of 6 ports. 
E) PVC slurry discharging port: 
Location: Chamber No. 2 counted from the bottom. 
Number: One. 
F) Hot water jetting device: 
Location: At the position 15 cm below the lower surface of each of plate 
Nos. 2, 3, 4, 5, 6, and 7 counted from the bottom. 
Number: One at each location, a total of 6 devices. 
Diameter: 800 mm 
Jet nozzle: Circular nozzles each having a diameter of 4 mm. Some nozzles 
were inclined 4.degree. from a vertical direction, and the other ones were 
inclined 30.degree. from a vertical direction. 
Each of them was arranged to wash the inside walls of the chamber and the 
lower surface of the immadiate upper plate. 
Shape: A ring shape, made of a pipe having a diameter of 50A. 
Manner of jetting: Hot water was jetted in an amount of 0.5 m.sup.3 /h for 
5 seconds at intervals of 10 minutes. 
(2) Used PVC slurry: 
PVC: A homopolymer having an average polymerization degree of 1,300. 
Slurry concentration: 30% by weight 
Concentration of residual vinyl chloride monomers: 30,000 ppm 
Porosity of PVC: 0.322 ml/g 
(3) Steam introduced from the steam introducing port 10: 
Temperature: 110.degree. C. 
Flow rate: 600 kg/h 
(4) Operation for removing residual monomers: 
A PVC slurry after termination of polymerization reaction was quickly 
transferred to a slurry tank 1, and further to a heat exchanger 3 with a 
pump at a rate of 20 m.sup.3 /h, where the slurry was heated. The heated 
slurry was introduced from a PVC slurry introducing port 22 provided in 
No. 5 chamber counted from the bottom of the apparatus for removing 
residual monomers, i.e., chamber 27. The slurry flew through passages 
partitioned with partition walls on Nos. 4, 3, 2, and 1 plates counted 
from the bottom., i.e., plates 34, 35, 36, and 37, during which the slurry 
was treated to release residual monomers with the steam mentioned before 
jetted through perforations in each plate. The PVC slurry which flows on 
the plates was heated to 100.degree. C. by the steam, allowed to flow down 
via flow-down sections, and was discharged through a PVC slurry 
discharging port 12 to outside the residual monomer removing apparatus. 
Subsequently, the PVC slurry was transferred by a pump 5, cooled down to 
50.degree. C. in the heat exchanger, and was stored in a PVC slurry tank 
6. The polyvinyl chloride monomer which was removed from the PVC slurry 
when the slurry contacted with steam on the plates was separated into 
vinyl chloride monomer and condensed water in a condenser 7, and then 
forwarded to a step for liquefying vinyl chloride monomers to recover the 
monomer. 
The results are shown in Table 1. The concentration of residual vinyl 
chloride monomer in the PVC discharged from the apparatus for removing 
residual monomers was 250 ppb, the yellowing factor of the molded PVC 
product was 2.21, and the number of colored PVC particles was 0. The 
apparatus was smoothly operated. Bubbles on plates A and B stayed at a low 
level. Especially on plate B, almost no bubbling was observed, and fluid 
state of the slurry was remarkably excellent. 
Example 2 
The procedure of Example 1 was repeated except that the following changes 
were effected on the conditions (2) and (4) above. 
(2) Used PVC slurry 
PVC: A homopolymer having an average polymerization degree of 700. 
Slurry concentration: 30% by weight 
Concentration of residual vinyl chloride monomers: 25,000 ppm 
Porosity of PVC: 0.231 ml/g 
(4) Operation for removing residual monomers: 
A PVC slurry was introduced into the apparatus for removing residual 
monomers from a PVC slurry introducing port 19 provided in No. 8 chamber 
counted from the bottom of the apparatus. 
The results are shown in Table 1. The concentration of residual vinyl 
chloride monomer in the PVC discharged from the apparatus for removing 
residual monomers was 350 ppb, the yellowing factor of the molded PVC 
product was 8.62, and the number of colored PVC particles was 0. The 
apparatus was smoothly operated. Bubbles on plates A and B stayed at a low 
level. Especially on plate B, almost no bubbling was observed, and fluid 
state of the slurry was remarkably excellent. 
Example 3 
The procedure of Example 1 was repeated except that the following changes 
were effected on the conditions (2) and (4) above. 
(2) Used PVC slurry 
PVC: A homopolymer having an average polymerization degree of 1,300. 
Slurry concentration: 30% by weight 
Concentration of residual vinyl chloride monomers: 30,000 ppm 
Porosity of PVC: 0.409 ml/g 
(4) Operation for removing residual monomers 
A PVC slurry was introduced into the apparatus for removing residual 
monomers from a PVC slurry introducing port 21 provided in No. 6 chamber 
counted from the bottom of the apparatus. 
The results are shown in Table 1. The concentration of residual vinyl 
chloride monomer in the PVC discharged from the apparatus for removing 
residual monomers was 200 ppb, the yellowing factor of the molded PVC 
products was 2.72, and the number of colored PVC particles was 0. The 
apparatus was smoothly operated. Bubbles on plates A and B stayed at a low 
level. Especially on plate B, almost no bubbling was observed, and 
fluidity of the slurry was remarkably excellent. 
Comparative Example 1 
In Comparative Example 1, an apparatus was used which was provided with 
plates all of which have the same size, in contrast to the apparatus for 
removing residual monomers shown in FIGS. 1 to 3, and only one slurry 
introducing port, and has the following specifications: 
A) Number of plates: 7 
B) Space between adjacent two plates: 1,400 mm 
C) Specification of plate structure: 
a) Specification of all plate structures: 
Diameter of plate: 1,300 mm 
Diameter of each perforation: 1.3 mm 
Opening ratio (%): 0.3% (total area of perforations/area of plate) 
Height of partition walls: 500 mm 
Height of division walls: 450 mm 
Width of the passages for treatment: 200 mm 
D) PVC slurry introducing port: 
Location: Chamber No. 8 counted from the bottom. Number: One. 
E) PVC slurry discharging port: 
Location: Chamber No. 2 counted from the bottom. Number: One. 
F) Hot water jetting device: 
Location: At the position 15 cm below the lower surface of each of plate 
Nos. 2, 3, 4, 5, 6, and 7 counted from the bottom. 
Number: One at each location, a total of 6 devices. 
Diameter: 800 mm 
Jet nozzle: Circular nozzles each having a diameter of 4 mm. Some nozzles 
were inclined 45.degree. from a vertical direction, and the other ones 
were inclined 30.degree. from a vertical direction. 
Each of them was arranged to wash the inside walls of the chamber and the 
lower surface of the immadiate upper plate. 
Shape: A ring shape, made of a pipe having a diameter of 50A. 
Manner of jetting: Hot water was jetted in an amount of 0.5 m.sup.3 /h for 
5 seconds at intervals of 10 minutes. 
(2) Used PVC slurry 
The same slurry as in Example 1 was used. 
(3) Steam introduced from the steam introducing port disposed at the bottom 
chamber of the tower 
Temperature: 110.degree. C. 
Flow rate: 600 kg/h 
(4) Operation for removing residual monomers 
The procedure for removing residual monomers described in Example 1 was 
repeated except that a PVC slurry was introduced into the apparatus for 
removing residual monomers from a PVC slurry introducing port provided in 
No. 8 chamber counted from the bottom of the apparatus. 
The results are shown in Table 1. The concentration of residual vinyl 
chloride monomer in the PVC discharged from the removal apparatus was 100 
ppb and the yellowing factor of the molded PVC product was 7.52. Since the 
contact time of the slurry with steam was excessively long compared to 
that in Example 1 in which the same PVC slurry was treated, heat 
degradation of molded PVC product was large, and therefore, commercial 
values was decreased. Bubbles on plate A marked a high level. On plate B, 
bubbling was also observed. The number of colored PVC particles was 5. 
This number indicates that although the hot water jetting device was 
operated, PVC particles which were lifted up by the bubbles and adhered to 
the inner walls of the apparatus could not sufficiently be removed by the 
water jet. Occurrence of the colored PVC is considered to be attributed to 
the bubbling. 
Comparative Example 2 
The procedure of Comparative Example 1 was repeated except that the PVC 
slurry was replaced by that employed in Example 2. 
The results are shown in Table 1. Bubbles on plate A marked a slightly high 
level. On plate B, bubbling was also observed. The number of colored PVC 
particles was 4. Occurrence of the colored PVC is considered to be 
attributed to the bubbling as in Comparative Example 1. 
Comparative Example 3 
The procedure of Comparative Example 1 was repeated except that the PVC 
slurry was replaced by that employed in Example 3. 
The results are shown in Table 1. Vigorous bubbling was observed on plate 
A. The PVC slurry overflew beyond the partition walls. Operation of the 
apparatus became unstable. Since some PVC slurry which did not properly 
contact with steam was included, the concentration of residual polyvinyl 
chloride monomer contained in the PVC discharged from the apparatus showed 
a value as high as 80,000 ppd. Twenty five particles of colored PVC were 
found to be included. It is considered that the PVC particles which were 
lifted up by the bubbles and adhered to the inner walls of the apparatus 
could not sufficiently be removed by the water jet. On plate B, fluid 
state of the slurry flow remained unstable though the height of bubbles 
slightly decreased. 
Comparative Example 4 
In Comparative Example 4, an apparatus was used which had a smaller number 
of plates than the structure of the apparatus for removing residual 
monomers shown in FIGS. 1 to 3, with the diameter of the uppermost plate 
being greater than that of others, had only one slurry introducing port in 
the uppermost chamber, and had the following specifications: 
A) Number of plates: 5 
B) Space between adjacent two plates: 1,400 mm 
C) Specification of plate structures: 
a) Plate structures No. 1, 2, 3, and 4 counted from the bottom: 
Inner diameter: 1,300 mm 
Diameter of each perforation: 1.3 mm 
Opening ratio (%): 0.3% (total area of perforations/area of plate) 
Height of partition walls: 500 mm 
Height of division walls: 450 mm 
Width of the passage for treatment: 200 mm 
b) Plate structure No. 5 counted from the bottom: 
Diameter of the plate: 2,000 mm 
Diameter of each perforation: 1.3 mm 
Opening ratio (%): 0.3% (total area of perforations/area of plate) 
Height of partition walls: 290 mm 
Height of division walls: 250 mm 
Width of the passage for treatment: 200 mm 
D) PVC slurry introducing port: 
Location: Chamber No. 6 counted from the bottom. Number: One. 
E) PVC slurry discharging port: 
Location: Chamber No. 2 counted from the bottom. Number: One. 
F) Hot water jetting device: 
Location: At the position 15 cm below the lower surface of each of plate 
Nos. 2, 3, 4, and 5 counted from the bottom. 
Number: One at each location, a total of 4 devices. 
Diameter: 800 mm 
Jet nozzle: Circular nozzles each having a diameter of 4 mm. Some nozzles 
were inclined 45.degree. from a vertical direction, and the other ones 
were inclined 30.degree. from a vertical direction. 
Each of them was arranged to wash the inside walls of the chamber and the 
lower surface of the immadiate upper plate. 
Shape: A ring shape, made of a pipe having a diameter of 50A. 
Manner of jetting: Hot water was jetted in an amount of 0.5 m.sup.3 /h for 
5 seconds at intervals of 10 minutes. 
(2) Used PVC slurry 
The same slurry as in Example 2 was used. 
(3) Steam introduced from the steam introducing port section of the 
apparatus for removing residual monomers 
Temperature: 110.degree. C. 
Flow rate: 600 kg/h 
The results are shown in Table 1. The concentration of residual vinyl 
chloride monomer in the PVC discharged from the removal apparatus was 
80,000 ppd and the yellowing factor of the molded PVC product was 2.98. 
Since the contact time of slurry with steam was in sufficient, in other 
words, the treating capacity of the apparatus was insufficient compared to 
Example 2 in which the same PVC slurry was treated, the concentration of 
residual monomers in the discharged PVC showed a high value. The PVC 
polymer having a polymerization degree of 700 is very difficult to release 
residual monomers. Therefore, only small amounts of residual monomers can 
be removed on a plate having a great diameter which provides mild 
conditions for the treatment and contributes to mitigate bubbling. 
Accordingly, the PVC slurry is transferred to lower stages while retaining 
a high concentration of residual monomers. As a result, bubbling was 
observed in lower stages. Presumably for this reason, 6 particles of 
colored PVC were included. 
According to the apparatus for removing residual monomers of the present 
invention, the following effects can be obtained: 
(1) Since, according to the present invention, conditions for removing 
residual monomers can be flexibly and suitably selected to comply with 
PVCs which are diversified in characteristics and properties, it became 
possible to control the bubbling property of the slurry, readiness of 
releasing residual monomers, heat degradation degree of PVC, and operation 
efficiency of the apparatus for removing residual monomers to a best 
condition as a whole. 
(2) Since treatment conditions can be selected in accordance with the 
characteristics of the individual PVC after polymerization, inherent 
properties of PVC are not deteriorated compared to the case where a PVC 
slurry is treated with a conventional method for removing residual 
monomers. 
(3) Colored PVC can be significantly reduced. 
(4) Since pulsing and bubbling of a PVC slurry are mitigated and 
tranquilized on a plate having a great diameter, unstable slurry flow 
comes not to be transmitted to the plates in a lower section. As a result, 
a stable operation control at an extremely high level as a whole apparatus 
for removing residual monomers becomes possible. 
(5) Such many factors as overflow of a PVC slurry beyond partition walls, 
blocking of a condenser, and inclusion of colored particles, which are 
caused by bubbling of the slurry; as well as transmission of pulsing due 
to unbalance of pressure and temperature in the apparatus for removing 
residual monomers, all of which adversely affect to the quality of PVC and 
maintenance of apparatus are eliminated or reduced. Therefore, supply of 
PVC with more a stable quality more stably becomes possible. Moreover, the 
steps required for the maintenance of the apparatus and loss of time 
accompanied therewith are improved to enhance the productivity. 
TABLE 1 
__________________________________________________________________________ 
Examples Comparative Examples 
1 2 3 1 2 3 4 
__________________________________________________________________________ 
Slurryl used* 
a! b! c! a! b! c! d! 
Porosity of PVC (ml/g) 
0.322 
0.231 
0.409 
0.322 
0.231 
0.409 0.231 
Bubbling status 
Plate A B B B B B D B 
Plate B A A A B B C B 
Operating condition 
very 
very 
very 
stable 
stable 
unstable 
stable 
stable 
stable 
stable 
VC concentration in PVC in 
250 350 200 100 350 80,000 
80,000 
the discharging section (ppb) 
Yellowing factor (.DELTA.YI) 
2.21 
8.62 
2.72 
7.52 
8.82 
9.64 2.98 
Colored PVC 0 0 0 5 4 25 6 
(/PVC 100 g) 
__________________________________________________________________________ 
*Slurry used: 
a! = PVC: A homopolymer with a polymerization degree of 1,300; Slurry 
concentration: 30 wt %; Concentration of residual monomers: 30,000 ppm; 
Porosity of PVC: 0.322 ml/g. 
a! = PVC: A homopolymer with a polymerization degree of 700; Slurry 
concentration: 30 wt %; Concentration of residual monomers: 25,000 ppm; 
Porosity of PVC: 0.231 ml/g. 
a! = PVC: A homopolymer with a polymerization degree of 1,300; Slurry 
concentration: 30 wt %; Concentration of residual monomers: 30,000 ppm; 
Porosity of PVC: 0.409 ml/g.