A polymerization autoclave for the suspension polymerization of vinyl compounds in the aqueous phase having a volume of from 50 to 200 m.sup.3, an impeller agitator driven from below at the bottom of the autoclave and two cylindrical displacement bodies acting as flow interrupters, secured downwardly from the autoclave dome, where the autoclave has a height-to-diameter ratio of from 2.4 to 3 with a critically dimensioned agitator and critically dimensioned flow interrupter fittings. By the use of this invention in the case large-scale autoclaves, the heat of polymerization can be removed merely by wall-cooling. The autoclave according to the invention are very economical, as shown by, for example, a spatial capacity of 0.3 to 0.4 metric tons of polyvinyl chloride per m.sup.3 autoclave volume.

BACKGROUND OF THE INVENTION 
The invention relates to a large-scale autoclave for the polymerization of 
vinyl compounds in aqueous suspension. According to present usage, a 
large-scale autoclave is understood as meaning an autoclave having a 
volume of more than 50 m.sup.3 (13,200 gallons). 
The polymerization of vinyl compounds in aqueous suspension is carried out 
by dispersing the monomeric vinyl compounds, which are optionally present 
under pressure in the liquid phase, by intensive agitation in the 
continuous aqueous phase, the dispersed phase being stabilized by the 
presence of a protective colloid. Polymerization is started by 
monomer-soluble initiators that decompose at an elevated temperature to 
form free-radicals and the resulting heat of polymerization must be 
removed. 
Especially in the case of polymerization of vinyl chloride according to the 
suspension process, the trend is to use relatively large polymerization 
units. Thus, for example, a large-scale autoclave having a volume of 200 
m.sup.3 has been described (Hydrocarbon Processing, Nov. 1976, pages 177 
ff.). The use of large polymerization units has economic as well as 
technical advantages. One of the economic advantages is the low investment 
cost since only one set of autoclave auxiliary equipment, for example, 
vents, fixtures, lines, controls, etc., is needed in contrast to the case 
of a relatively large number of smaller units. Likewise, the smaller 
number of operating personnel required is also of economic advantage. One 
of the technical advantages is the improved consistency of the quality of 
the products and another is, for example, the lower speck-content of the 
polymers. 
Because of the relatively unfavorable surface-to-volume ratio, the removal 
of the heat of polymerization in the case of large-scale autoclaves is 
less efficient. It has generally been observed that the removal of the 
heat of polymerization through the autoclave wall alone is not sufficient, 
especially if production conditions are to be economical, that is high 
polymerization rates and high spatial capacity, with a high monomer:water 
ratio. 
The use of a reflux condenser may be helpful in this case. In the case of 
polymerization batches that form a large amount of foam, however, the 
condenser becomes coated very rapidly and becomes ineffective as a result. 
If the danger of insufficient heat removal is to be avoided in this case, 
the condenser must be cleaned frequently during the course of repeated 
polymerizations. The condensate flowing back into the autoclave can also 
lead to problems (Chemtech. May 73, page 308). Finally, when operating a 
completely full autoclave, the use of a reflux condenser is not possible. 
The final paragraph of page 2 of German published application DE-OS No. 
2,032,700 indicates that, in large-scale autoclaves, wall-cooling alone is 
not sufficient to remove the heat of polymerization. It is also stated 
that agitation in narrow autoclaves is not sufficiently effective in all 
parts of the autoclave. 
OBJECTS OF THE INVENTION 
An object of the present invention is to provide a large-scale autoclave 
which permits all the heat of polymerization to be removed via the shell, 
while nevertheless preserving economical operating conditions. 
Another object of the present invention is to provide a polymerization 
autoclave for the suspension polymerization of vinyl compounds in the 
aqueous phase to form homopolymers and copolymers said autoclave having a 
substantially cylindrical wall with a slightly dished dome and bottom and 
having a volume of from 50 to 200 m.sup.3, a impeller agitator mounted on 
a shaft extending from the bottom of said autoclave and driven from below 
and two cylindrical displacement bodies suspended from said dome and 
acting as flow interrupters, consisting in that said autoclave has a 
height-to-diameter ratio of from 2.4 to 3 and satisfies the following 
ratios: 
d/D=0.45 to 0.55 
h/d=0.15 to 0.18 
h/H=0.025 to 0.045 
l/H=0.30 to 0.65 
d'/l=0.08 to 0.10 
d"/d'=0.8 to 1.2 
h'/h=1.5 to 2.5 
wherein 
H=the height of said autoclave 
D=the diameter of said autoclave 
d=the diameter of the impeller agitator 
h'=the distance from the top of the impeller blade at the impeller shaft to 
the bottom of said autoclave 
h=the height of the impeller blade 
l=the length of the said displacement body 
d'=the diameter of said displacement body 
d"=the distance of said displacement body from the cylindrical wall of said 
autoclave 
These and other objects of the invention will become more apparent as the 
description thereof proceeds.

DESCRIPTION OF THE INVENTION 
The subject of the invention is a polymerization autoclave for the 
suspension polymerization of vinyl compounds in the aqueous phase, which 
autoclave is substantially cylindrical and which has a volume of from 50 
to 200 m.sup.3, preferably from 70 to 125 m.sup.3, an impeller agitator 
driven from below and two cylindrical displacement bodies that act as flow 
interrupters and are secured from the dome of the autoclave, characterized 
in that the autoclave has a H/D ratio of from 2.4 to 3, preferably from 
2.5 to 2.7, and in addition, satisfies the following conditions: 
d/D=0.45 to 0.55, preferably 0.5 to 0.53 
h/d=0.15 to 0.18, preferably 0.16 to 0.17 
h/H=0.025 to 0.045, preferably 0.03 to 0.04 
l/H=0.30 to 0.65, preferably 0.35 to 0.45 
d'/l=0.08 to 0.10, preferably 0.085 to 0.095 
d"/d'=0.8 to 1.2, preferably 0.9 to 1.1 
h'/h=1.5 to 2.5, preferably 1.7 to 2.0 
in which 
H=the height of the autoclave 
D=the diameter of the autoclave 
d=the diameter of the impeller agitator 
h'=the distance from the top of the impeller blade at the impeller shaft to 
the bottom of the autoclave 
h=the height of the impeller blade 
l=the length of the displacement body 
d'=the diameter of the displacement body 
d"=the distance of the displacement body from the autoclave wall 
More particularly, the present invention is directed to a polymerization 
autoclave for the suspension polymerization of vinyl compounds in the 
aqueous phase to form homopolymers and copolymers said autoclave having a 
substantially cylindrical wall with a slightly dished dome and bottom and 
having a volume of from 50 to 200 m.sup.3, a impeller agitator mounted on 
a shaft extending from the bottom of said autoclave and driven from below 
and two cylindrical displacement bodies suspended from said dome and 
acting as flow interrupters, consisting in that said autoclave has a 
height-to-diameter ratio of from 2.4 to 3 and satisfies the following 
ratios: 
d/D=0.45 to 0.55 
h/d=0.15 to 0.18 
h/H=0.025 to 0.045 
l/H=0.30 to 0.65 
d'/l =0.08 to 0.10 
d"/d'=0.8 to 1.2 
h'/h=1.5 to 2.5 
wherein 
H=the height of said autoclave D=the diameter of said autoclave d=the 
diameter of the impeller agitator h'=the distance from the top of the 
impeller blade at the impeller shaft to the bottom of said autoclave 
h=the height of the impeller blade 
l=the length of said displacement body 
d'=the diameter of said displacement body 
d"=the distance of said displacement body from the cylindrical wall of said 
autoclave. 
Surprisingly, it has now been found that, even at a H/D ratio of the 
autoclave of over 2.4 to 3.0, it is possible to obtain, with the same 
spatial capacity, (metric tons of monomer/m.sup.3 autoclave space) a vinyl 
polymer of the same quality as in the case of H/D ratios of from 1 to 2.2, 
which have previously been considered more favorable, and in the case of 
the invention the heat of polymerization can be removed completely via the 
shell. Because of the autoclave fittings according to the invention it is 
possible to achieve a sufficient agitation effect even in the parts of 
large-scale autoclaves which are some distance from the agitator. 
In order to illustrate the invention, a large-scale autoclave according to 
the invention is described in more detail below, with reference to FIGS. 1 
and 2. 
The autoclave 1 has a jacket, not shown, a substantially cylindrical wall 
2, a slightly dished dome 3 with a central opening 4 and a slightly dished 
bottom 5. An impeller agitator consisting of impeller blades 6 mounted on 
an impeller shaft 7 extends from the bottom of the autoclave 1. Two 
cylindrical displacement bodies 8 are suspended from the dome 3 and act as 
flow interrupters. The drawings also give the various dimensions H, D, d, 
h', l, d' and d". 
An autoclave meeting the critical dimensions of the present invention has, 
for example, a volume of 78 m.sup.3 and a H/D ratio of 2.59. The relative 
dimensions of the agitating members are as follows: 
d/D=0.52 
h/d=0.167 
h/H=0.034 
l/H=0.38 
d'/l=0.09, 
d"/d'=1.0 
h'/h=2.0 
the letters having the meanings already mentioned. The autoclave according 
to the invention has, of course, the customary rounded or convex base and 
top curvature. 
The relative dimensions according to the invention of the agitating members 
are crucial. Outside the given ranges, the polymerization conditions 
become rapidly unfavorable. 
If, for example, the displacement bodies are lengthened to beyond the given 
range, or if additional displacement bodies of this type are provided, the 
mixing in the autoclave is impaired, the upper parts of the suspension 
being moved to a lesser extent. This then results in undesirable large 
polymer particles (coarse grained), which constitutes reduced quality. In 
a particularly unfavorable case, lumps and polymer bridges may even be 
formed. It is possible to avoid these phenomena to a limited extent by 
reducing the monomer:water ratio but this is economically disadvantageous. 
Conversely, if the displacement bodies are shortened, the effect of the 
flow interrupters is reduced. Agitation is then carried out rather by 
rotation of the material, i.e. agitation is less effective and there is a 
danger that the area of turbulent flow will tend to become laminar. The 
result of this in practice is that there is a great difference between the 
power consumption of the agitator at the beginning of polymerization and 
at the end of polymerization: it increases very steeply towards the end of 
polymerization. If the width of the impeller blade is too small, agitation 
is insufficient in this case too, even at high speeds, and the result of 
this is that the monomer:water ratio must be lower to achieve the same 
product quality. Otherwise, agglomerates would be formed in this case as 
well, which could increase to form polymer bridges. On the other hand, a 
relatively wide impeller blade would also yield unfavorable ratios. 
By using the large-scale autoclave according to the invention for 
polymerization, it is possible to effect polymerization with a high 
spatial capacity. A high spatial capacity means a large monomer input i.e. 
a high monomer:water ratio. Normal ratios are 0.5 to 0.75 in the 
polymerization of, for example, vinyl chloride. 
According, the spatial capacity is between 0.3 and 0.4 metric ton (t) to 
polyvinyl chloride/m.sup.3 autoclave volume. The following Example 1 shows 
that, despite the high H/D ratio, polymerization can be effected at a 
spatial capacity of 0.4 t of vinyl chloride/m.sup.3 autoclave volume. 
Polymerization in large-scale autoclaves can be employed especially in the 
homopolymerization of vinyl chloride under suspension polymerization 
conditions. In addition to homopolymerization, however, copolymers may 
also be produced using ethylenically unsaturated copolymerizable monomers 
in which the copolymers portion derived from the vinyl chloride is over 
60% by weight. Copolymerization monomers are, for example, monomers, such 
as styrene, substituted styrenes, acryl monomers and substituted acryl 
monomers, vinyl esters with alkanoic acids having from 1 to 18 carbon 
atoms, vinyl halides having from 1 to 3 halogen atoms and unsaturated 
carboxylic acids, such as maleic acid and fumaric acid. 
The following examples are illustrative of the practice of the invention 
without being limitative in any respect. 
EXAMPLE 1 
An autoclave was employed having a volume of 78 m.sup.3 and an H/D ratio of 
2.59, the relative dimensions of the agitating members being: 
d/D=0.52 
h'/d=0.167 
h/H=0.034 
l/H=0.38 
d'/l=0.09, 
d"/d'=1.2 
h'/h=2.0 
The following mixture was charged into the autoclave and polymerized: 
28,600 kg of water 
31,000 kg of vinyl chloride 
18.9 kg of hydroxyethyl cellulose 
4.5 kg of aminooethyl-hydroxypropyl cellulose 
3.5 kg of sorbitan monostearate 
6.0 kg of sulfuric acid 
0.06 kg of sodium nitrite 
15.7 kg of dicetyl peroxydicarbonate 
During polymerization, 850 l/h of water were metered in. The polymerization 
time was 9.0 hours. The agitator was employed at 117 rev/min. The 
polymerization temperature was maintained at 54.degree. C. The product had 
a bulk density of 0.662 g cm.sup.-3 and a compacted bulk density of 0.746 
g cm.sup.-3, the parameters of the particle size distribution according to 
Rosin-Rammler were d'=0.17 mm and n=6.2. The characteristic data thus 
correspond exactly to the values obtained when an analogous mixture is 
processed in a 25 m.sup.3 autoclave having an H/D ratio of 1.77. 
EXAMPLE 2 
In an autoclave as in Example 1, the following polymerization mixture was 
processed: 
37,000 kg of water 
25,000 kg of vinyl chloride 
7.5 kg of methyl-hydroxypropyl cellulose 
2.385 kg of di(2-ethylhexyl) peroxydicarbonate 
4.762 kg of t-butyl peroxypivalate 
The polymerization temperature was maintained at 71.degree. C. During 
polymerization, 900 l/h of water were metered in. The polymerization time 
was 4.5 h and the rate of stirring was 117 rpm. 
This example demonstrates that, using the autoclave according to the 
invention, polymerization times can be achieved which are equivalent to 
those achieved when using a reflux condenser. 
The preceding specific embodiments are illustrative of the practice of the 
invention. It is to be understood however, that other expedients known to 
those skilled in the art or disclosed herein, may be employed without 
departing from the spirit of the invention or the scope of the appended 
claims.