Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HOE 78/H 034
This invention re~ates to a process for carrying
out exothermal and endothermal reactions in a container
under commercial conditions b~y indirect cooling or
heating with the aid of a cooling or heating medium,
which is caused to flow through a space formed and
left between the wall of the container and a heat ex-
changing surface area mounted thereon. The invention
also relates to an apparatus for carrying out the
process and to the use of the process ~or admitting
heating energy to, and/or abstracting reaction heat
from, a container as commonly used for the polymeri-
zation of monomers~ especially for the suspension
polymerization of vinyl chloride.
It has been described that tempered vessels can
be used for admitting heat~hen~o and abstracting heat
therefrom and also ~or mixing therein liquids or solid
matter particles which undergo chemical reaction with
each other, the vessels being relatively easy to clean
and to free from encrusted material. These are vessels
which are provided with a jacket permitting them to
be cooled or heated from the outside, and may be
further provided with an agitator permitting the
transfer of heat to be improved by a multiple.
The jacket surrounding the vessel may be comprised
of semicylindrical tubular coils of profiled angle
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structur~swhich are welded to the vessel (cf. "Ullmanns
Encyklopadie der technischen Chemie", 4th edition,
volume 2, 1972, pages 439 and 440).
In industry, it is customary to subject large
batche~ to polymerization, e. g. suspension or mass
polymerization, in an autoclave in which the temperature
is constantly maintained at an optimum value by ab-
straction of the polymerization heat. The heat is more
particularly abstracted through the wall of the auto-
clave which is normally provided with a double-wall
jacket for circulation of a cooling med~um therethrough
(cf. German Patent Specification "Auslegeschrift"
2 038 ~63 and German Patent 2 032 700).
Heating or cooling a large container through its
wall is however not fully satisfactory in ~ew of the
particularly unfavorable ratio o~ wall sur~ace area
to Gontainer volume, which results in a small specific
heat transfer rate per unit time and unit volume. In
addition to this 9 it is necessary for a high capacity
container, especially an autoclave, to be provided with
disproportionately thick walls which additionally impair
the transfer of heat, per unit surface area. Needless
to say, it is poesible for the heat exchanging surface
area to be increased by the provision of accessory
equipment, such as cooling coils, fingers or plates,
which are secured to the inside of the container.
Normally, however, these are technically complicated
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structural parts which adversely affect the stirring and flow
conditions inside the container. Containers in which processes
such as polymerization reactions are effected are naturally very
liable to become encrusted with reaction material and have
therefore often to be cleaned so as to be freed from encrusted
material. To this end, it is always necessary for the above
accessory equipment to be dismantled which is disadvantageous.
Still further containers having accessory equipment mounted
therein inevitably present dead flow zones in the vicinity of
which reaction material is very liable to cake together and
deposit, naturally with adverse effects on the transfer of heat
and the quality of the final reaction product, whenever fragments
of agglomerated material get thereinto.
According to the present invention there is now provided
an apparatus for carrying out exothermal and endothermal reactions
by indirect cooling or heating with the aid of a circulating
cooling or heating medium, the apparatus comprising a container
provided with baffle plates, at least one multiple blade mixer and
a heat exchanging structural component secured to the inside wall
of the container, said heat exchanging structural component being
comprised of a helically wound semicylindrical tubular coil.
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The presen~ invention also preferably provides for the
pressure under which the cooling or heating medium is maintained
in the space formed and left between the wall of the container
and heat exchanging surface area which is secured thereto, to be
continuously controlled and conformed to the pressure prevailing
inside the container. As a result, it is possible, even in the
event of high pressure prevailing inside the container, for the
heat exchanging surface area to present a small wall thickness
opposing little resistance to the transfer of heat.
In the present process, use is made of a container
provided with a heat exchanging surface area increased by up
to 57 % as compared with a smooth-walled container. The contain-
er used in accordance with this invention also permits
establishment of very favorable flow conditions which promote
the transfer of heat through its wall and reliably prevent solid
material from caking and depositing thereon.
The present process is particularly useful for admitting
heating energy or abstracting reaction heat evolved during the
polymerization of monomers, especially during the suspension
polymerization of vinyl chloride.
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Preferred features of the present apparatus provide
a) for the semicylindrical tubular coil to have narrow
wlndlngs;
b) for the heat exchanging structural components to have a
corrugated surface area;
c) for the heat exchanging structural components to be
comprised of channels made from profiled angle structures; and
d) for the heat exchanging structural components to be
welded to the wall of the container.
In the apparatus of the present invention, it is the
wall of the container which provides the necessary mechanical
strength so that the walls of the heat exchanging structural
components can be made thinner than heretofore. This has highly
beneficial effects on the transfer of heat as results from the
following data determined for a container which is to be operated
under a pressure of 17 bars, for example. With respect to the
walls of such container, it is generally accepted that it is
necessary for them to be made the thicker the larger the volume
of the container, e.g. as follows: ;;
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(25 m = 17 mm; 100 m3 = 25 mm; 200 m = 38 mm
thick walls).
This is in contrast with the present apparatus in which
the heat exchanging structural component can be given
a wall thickness of only 3 mm in the three cases.
The present invention will now be described in
more detail with reference to the accompanying drawings,
in which:
Figure 1 graphically illustrates the heat capacity
transferable for containers of different volume, and
Figure 2 is a partially sectioned side elevation
of an exemplary form of apparatus for carrying out the pre-
sent process.
Referring firstly to Figure 1 showing the heat
capacity transferable for containers of different reactor
volume; curve 1 relates to prior art containers and curve 2
relates to an example of the present apparatus.
The apparatus of this invention has no dead flow
zones and is easy to clean by hand or with the aid of
high pressure water without the need to dismantle any struc-
tural component disposed inside the container.
As compared with the prior art polymerization of
monomers, it is possible in accordance with this invention
to use a shorter heating period and maintain the heating ` ~`
medium at the same temperature as in prior art polymeriza-
tion, or to use the same heating period and maintain the
heating medium at lower temperatures than in prior art poly-
merization. This has beneficial effects in the discontinuous
production of polyvinyl-chloride by suspension polymerization.
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Polymeric material is subStantially not liable to cake
together and deposit on the walls of the container,
and the quality of the resulting final product is im-
proved ~reduced number of so-called fisheyes).
With reference now to Figure 2:
A cylindrical container 1 has a plurality of
baffle plates 3 disposed therein. Provided in the lower
portion of the container 1 is a multiple blade mixer 2 of
which the shaft is passed through the bottom portion of
the container 1, Welded to the inside wall of the con-
tainer 1 are heat-exchanging structural components 4
which are comprised of a narrowly wound semi-cylindrical
tubular coil, in the embodiment shown, for circulating
a cooling or heating medium therethrough, the medium
being admitted through an inlet 5 and removed through an
outlet 6.
The following Examples illustrate the invention
and its technically beneficial effects.
EXA~IPLE 1: (Prior art)
24 m3 of water of 20 C was introduced into a
cylindrical container in upright position, designed
for operation under a pressure of 17 bars. The container
had a reactor volume of 25 m3, was provided with a mixer
and had a semi-cylindrical tubular coil welded to its
outside wall (cf. "Ullmanns Encyklop'adie der tech-
nischen Chemie", 4th edition, volume 2, page 439,
Figure 16 D). The mixer was set to work and hot water
of 95 C was circulated through the semi-cylindrical
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tubular coil. The period necessary to heat the water
in the vessel to a temperature of 55 C was determined.
It was 36 minutes. The quant~ty of heat admitted per
unit time was 1.63 x 103 kw.
EXAMPLE 2: (Prior art)
24 m3 of water, which had a temperature of 55 C~
was introduced into the container of Example 1. The
mixer was set to work, water of 20 C was passed through
the semicylindrical tubular coil and 1400 kg/h of
saturated steam (120 C) was introduced into the
container. This permitted the water to be maintained
at a constant temperature of 55 C, The quantity of
heat abstracted per unit time was 0.962 x 103 kw.
EXAMPLE 3: (Invention)
24 m3 of water of 20 C was introduced into a cylin-
drical container in upright position, designed for
operation under a pressure of 17 bars. The container
had a reactor volume of 25 m3, was provided with a
mixer and had a semicylindrical tubular coil 3 mm
thick welded to its inside wall. The mixer was set
to work and hot water of 95 C was circulated through
the semicylindrical tubular coil. The period necessary
to heat the water in the vessel to 55 C was determined.
It was 20 minutes. The quantity of heat admitted per
unit time was 2,97 x 103 kw, i. e. 182 % of the quantity
of heat which could be admitted in prior art Example 1.
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~XAMPLE 4: (Invention)
24 m3 of water, which had a temperature o~ 55 C ,
was introduced into the container of Example 3. The
mixer was set to work, water of 20 C was circulated
through the semicyclindrical tubular coil and 2480 kg/h
of saturated steam (120 C~ was introduced into the con-
tainer. This permitted the water therein to be maintained
at a constant temperatureof 55 C . The quantity of
heat abstracted per unit time was 1.70 x 103 kw, i. e.
177 % of the quantity of heat which could be abstracted
in prior art Example 2.
EXAMPLE 5: (Prior art)
The apparatus of Example 1 was used. The mixer was
set to work and the container was filled with the
following materials:
13 800 kg o~ demineralized water,
3.1 kg of partially saponified polyvinyl acetate,
2.6 kg of hydroxypropylmethyl cellulose,
15 kg of sorbitane monolaurate.
Air was expelled by evacuation and 8300 kg of
vinyl chloride and 5 kg of bis-(2-ethylhexyl)peroxi-
dicarbonate (65 % strength) were added. Hot water
(95 C) was passed through the semicylindrical tubular
coil. The material inside the container was heated to
the reaction temperature of 55 C within 29 minutes.
The reaction temperature was maintained constant by
circulating water of 20 C through the semicylindrical
tubular coil.
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The polymerization was terminated and the pressure
released. The suspension was stripped with steam so as
to be freed from residual vinyl chloride and polyvinyl
chloride was separated from the suspension by centri-
fugation. ~95 kg/h of polrrinyl chloride was obtained.
The polyvinyl chloride so obtained was evaluated
qualitatively a~ follows:
a) K-value = 70; determined in accordance wlth
DIN-specification 53 726, June 1961;
(DIN stands for German Industrial Standard);
b) Bulk density = 470 g/cm3
- c) Fisheye test. To this end, a sheet 0.2 mm thick
was prepared which was rolled for 15 minutes
at 140 C. The number of fisheyes was determined
on altogether five 100 cm sheet specimens. The
avarage number of fisheyes counted was 12. Next, -
the container was cleaned with the use of water -~
maintained under a pressure of 250 bars.
The cleaning water was filtered and found to
contain about 0.5 kg of solid matter particles
which originated from material encrusted on
the wall of the container.
EXAMPLE 6: (Invention)
The four materials specified in Example 5 were
placed in the container of Example 3 with agitation.
Air was expelled by evacuation and the material in
the container was admixed with 8300 kg of vinyl
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chloride and 6.1 kg of bis-(2-ethylhexyl)-peroxidi-
carbonate (65 % strength). Hot water (95 C) was
circulated through the semicyl:indrical tubular coil.
The material inside the contailler was heated to the
reaction temperature of 55 C within 14 minutes. The
reaction temperature was maintained constant by
circulating water of 20 C through the semicylindrical
tubular coil.
The polymerization was terminated and the whole
processed as described in Example 5. 1250 kg/h of
polyvinyl chloride, i. e. 126 % of the quantity
obtained in prior art Example 5 was produced. The
cleaning water was found to contain 0.2 kg of solid
matter particles originating ~rom material encrusted
on the walls of the container.
The polyvinyl chloride so made was evaluated
qualitatiu~y as described in Example 5. The following
results were obtained.
a) K-value = 70
b~ Bulk density = 475 g/cm3
~) 5 fisheyes per 100 cm2 sheet.
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