Note: Descriptions are shown in the official language in which they were submitted.
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Process for producing a polymer dispersion based on
polychloroprene and plant for producing a polymer
dispersion based on polychloroprene
The present invention relates to a process and a plant
for producing a polymer dispersion based on
polychloroprene.
It is known from DE 10 2006 060 378 Al that a
polychloroprene (CR) dispersion can be obtained by
polymerization of monomeric chloroprene, where from 50%
to 95% of the chloroprene used is reacted in the
polymerization. In a subsequent steam distillation,
unpolymerized chloroprene (residual monomer) can be
decreased to a proportion of monomeric chloroprene in
the polychloroprene dispersion of about 100 ppm or
50 ppm and less.
According to JP 61-060843 B2, steam distillation of
polychloroprene dispersions has in practice been found
to be uneconomical since lines and apparatuses of the
steam distillation column used very quickly become
blocked by polychloroprene coagulum formed and the
steam distillation column used would have to be
shutdown and cleaned after a short period of operation.
Polymer dispersions based on polychloroprene are used,
for example, for diving goods, moulded foam or as
constituent of contact adhesives. Since monomeric
chloroprene is readily flammable and toxic, there is a
continuing need to reduce the proportion of monomeric
chloroprene (residual monomer) in polychloroprene
dispersions further in order to improve and aid the
handling of products produced on the basis of
polychloroprene dispersions, for example adhesives.
It is an object of the invention to provide a process
and an apparatus for producing a polymer dispersion
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based on polychloroprene, with the aid of which the
proportion of monomeric chloroprene in polychloroprene
dispersions can be reduced without a significant
reduction in the time of operation of the plant
components used having to be accepted.
The object is achieved according to the invention by a
process having the features of Claim 1 and a plant
having the features of Claim 11. Advantageous
embodiments of the invention are defined in the
dependent claims.
In the process of the invention for producing a polymer
dispersion based on polychloroprene, a polymerization
of chloroprene to polychloroprene is carried out in an
emulsion up to a maximum solids content Wsolid of
proportions by weight of wsolid S 50%, in particular wsolid
<_ 40%, preferably Wsolid 35% and particularly
preferably Wsolid <_ 30'-. in a polychloroprene dispersion
present after the polymerization and a removal of
chloroprene from the polychloroprene dispersion is
carried out in a multistage and/or multitray stripper
column to a chloroprene content WCR,Out in proportions by
weight of WCR,out <_ 50 ppm, in particular WCR,Out <_ 30 ppm,
preferably WCR,Out <_ 15 ppm and particularly preferably
WCR,Out <_ 10 ppm in a purified polychloroprene dispersion
present after the removal of chloroprene. A dilution of
the product obtained with aqueous phase and/or water
carried out during and/or after the chemical
polymerization reaction is considered to be part of the
polymerization.
The solid in the polychloroprene dispersion after the
polymerization is made up essentially of
polychloroprene. The determination of the solids
content is carried out in accordance with ISO 124. The
proportion by weight of polychloroprene in the solids
in the polychloroprene dispersion is, in particular,
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>_ 806, preferably >_ 90%. The minimum proportion by
weight WCR,out,min of chloroprene in the purified
polychloroprene dispersion present after removal of
chloroprene is, in particular, WCR,out,min ? 1 ppm,
preferably wcR,out,min ? 0.5 ppm. The minimum proportion by
weight WCR,out,min of chloroprene is particularly
preferably below the detection limit of customary
routine analytical methods, which is generally 0.5 ppm.
The minimum proportion by weight Wsolid,min of solid in
the polychloroprene dispersion present after the
polymerization is, in particular, Wsolid,min ? 10%,
preferably Wsolid,min ? 15% and particularly preferably
wsolid,min ? 20%, in order to make particularly economical
operation of the process of the invention possible.
Compared to conventional continuous and/or
discontinuous polymerizations of chloroprene to
polychloroprene, a significantly lower proportion of
polychloroprene in the polychloroprene dispersion after
the polymerization is deliberately set in the process
of the invention. This can be achieved, for example, by
means of a lower conversion of chloroprene and/or a
larger amount of aqueous phase than is usually
provided, with a dilution of the product obtained with
aqueous phase and/or water carried out during and/or
after the chemical polymerization reaction being
considered to be part of the polymerization. Here, use
is made of the recognition that the lower proportion of
polychloroprene in the polychloroprene dispersion after
the polymerization leads to a significantly lower
solids content in the polychloroprene dispersion, as a
result of which removal of chloroprene in a stripper
column, for example by means of steam, is surprisingly
possible without lines or apparatuses blocked by
polychloroprene coagulum having to be feared. It is
even possible to reduce the chloroprene content of the
purified polychloroprene dispersion significantly
without having to accept a significantly increased risk
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of downtimes of the stripper column. In the process of
the invention, uninterrupted periods of operation of
the stripper column used of more than 3 weeks, in
particular more than 5 weeks and particularly
preferably of more than 6 weeks, can be achieved, while
a maximum period of operation of less than one day was
found at a solids content wsolid of about 550-o. The
polymerization can, in particular, be carried out by
emulsion polymerization in an alkaline aqueous medium,
as described, for example, in "Ullmanns Encyclopedia of
Polymer Science and Technology", Vol. 3, pp. 705-730,
John Wiley, New York 1965, with, as a difference, the
maximum solids content Wsolid in the polychloroprene
dispersion after the polymerization as provided
according to the invention being taken into account and
process conditions suitable for this purpose being
employed.
It is assumed that, owing to the lower solids content
based on the amount of polychloroprene, a comparatively
large amount of aqueous phase is present in the
stripper column and the aqueous phase present prevents
formation of lumps of polychloroprene and caking of the
polychloroprene as a result of coagulum formation in
the stripper column. In the process of the invention,
the solids content of the polychloroprene dispersion
after the polymerization is, in particular based on the
aqueous phase, set so that blockages are avoided and at
the same time a particularly low proportion of
chloroprene can be achieved in the polychloroprene
dispersion leaving the stripper column. The stripper
column is, in particular, operated in such a way that
the steam used condenses at least partly. As a result,
the heat of condensation can firstly be used for
heating and, at the same time, the amount of aqueous
phase can be increased by the amount of the condensate,
so that an unfavourably high solids content within the
stripper column can be avoided. The stripper column
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can, in particular, be formed by a single tower having
a plurality of trays, with each tray defining the
commencement of an individual stage of the stripping
process assigned to the respective tray. In particular,
stripping can be carried out at a pressure of <_ 1 bar
in order to aid vaporization of chloroprene. Although a
comparatively low polychloroprene content is
deliberately set in the polymerization, this measure
has been found to be more economical overall taking
into account the chloroprene removal. As a result of
the improved degassing of chloroprene from the
polychloroprene dispersion and the resulting lower
amount of chloroprene in the finished product, handling
of products produced on the basis of polychloroprene
dispersions, for example adhesives, is improved and
aided. In particular, occupational hygiene is improved
in the further processing of the polychloroprene
dispersion, for example to produce a solid rubber.
Occupational safety in the further processing is
improved, as a result of which lower occupational
safety requirements are even made possible.
The polychloroprene dispersion fed to the stripper
column preferably comprises essentially the entire
aqueous phase of the polychloroprene dispersion present
immediately after the polymerization, with, in
particular, additional aqueous phase and/or water
having been added to the polychloroprene dispersion
before introduction into the stripper column. In
particular, essentially only chloroprene, if anything,
is removed from the organic phase, preferably by
vaporization. Intermediate removal of liquid
constituents such as aqueous phase, emulsifier,
catalyst, stabilizer, activator or stopper can be
avoided. Instead, additional aqueous phase and/or water
can be added to the polychloroprene dispersion in order
to reduce or adjust the solids content wsolid= In
particular, the polychloroprene dispersion present
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after the polymerization is fed continuously and/or
directly to the stripper column.
The polymerization is particularly preferably carried
out continuously or pseudocontinuously, in particular
by means of a cascade of a plurality of batch reactors.
Since a particularly high polychloroprene content is
not desirable after the polymerization because of the
increased solids content in the process of the
invention, it is possible for the first time to provide
a continuous or pseudocontinuous polymerization which
is more economical on an industrial scale than a
plurality of batch reactions. It is also possible to
connect a plurality of individual tank reactors in
series in order to achieve a pseudocontinuous
polymerization which is likewise more economical on an
industrial scale than a plurality of batch reactions.
In a further embodiment, the polymerization is carried
out predominantly by means of a batch reaction in at
least one batch reactor, with the polychloroprene
dispersion present after the polymerization being fed
to a buffer tank before the separation in the stripper
column and the polychloroprene dispersion being fed
essentially continuously to the stripper column from
the buffer tank. This makes continuous operation of the
stripper column possible even when the polymerization
is carried out discontinuously, so that the stripper
column can be operated particularly economically. The
respective polymerization is particularly preferably
carried out offset in time in various batch reactors,
so that the buffer tank can be filled with the product
obtained in a respective batch reaction in
correspondingly shorter time intervals. In particular,
additional aqueous phase is fed to the buffer tank in
order to ensure the desired maximum solids content
wsolid
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In particular, the polychloroprene dispersion fed to
the stripper column has a chloroprene content WCR,in in
proportions by weight of 200 ppm WCR,in <_ 30 000 ppm,
in particular 2000 ppm < WCR, in 20 000 ppm and
particularly preferably 5000 ppm WCR,in <_ 15 000 ppm.
At such a chloroprene content WCR, in of the
polychloroprene dispersion in the feed stream to the
stripper column, blockage of the stripper column can be
avoided with certainty and at the same time a
chloroprene content of wcR,out _< 30 ppm and even WCR,out
<_ 10 ppm in the degassed polychloroprene dispersion
present after the removal of chloroprene can be
achieved.
Degassing of the polychloroprene dispersion present
after the polymerization is preferably carried out
after the polymerization has been carried out and
before the removal of chloroprene. In this way,
components which are already in gaseous form and
volatile components can be removed from the
polychloroprene dispersion without the stripper column
being used for this purpose. This makes it possible to
remove a proportion by weight of about 90% of the
monomeric chloroprene. This reduces the amount of steam
required for the removal of chloroprene in the stripper
column.
The purified polychloroprene dispersion is particularly
preferably concentrated, in particular by means of a
creaming process, after the removal of chloroprene.
This is carried out, for example, as described in DE 10
145 097 with the aid of a coalescing agent or as
described in "Neoprene Latices", John C. Carl, E. I.
DuPont 164, p. 13. The additional concentration makes
it possible for some more chloroprene to be
additionally separated off to a small extent. At the
same time, the solids content of polychloroprene in the
product polychloroprene dispersion remaining after the
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separation phase formed has been separated off is
increased. Subsequent transport quantities and
transport costs for the polychloroprene can be reduced
in this way.
In particular, a vapour, in particular essentially
steam, having an overpressure Ap compared to the
pressure of the polychloroprene dispersion fed in of
3 bar _< Ap <_ 10 bar, in particular 4 bar <_ Ap <_ 9 bar,
preferably 5 bar <_ Ap <_ 8 bar and particularly
preferably 6 bar <_ Ap 7 bar, and/or a temperature at
the bottom of 55 C T <_ 110 C, in particular
60 C <_ T <_ 100 C, preferably 65 C <_ T _< 90 C and
particularly preferably 70 C S T <_ 80 C is fed to the
stripper column. A vapour selected in this way allows
the predominant proportion of chloroprene to be removed
even in a relatively large stripper column having a
plurality of trays. The vapour enables the chloroprene
present to be vaporized down to a few ppm and to be
discharged via the top and be, for example, reused for
a further polymerization of chloroprene to
polychloroprene.
A ratio R of a mass flow of a vapour fed into the
stripper column, in particular essentially steam, to a
mass flow of the polychloroprene dispersion fed to the
stripper column preferably obeys the relationship
0.04 _< R <_ 0.20, in particular 0.06 _< R _< 0.17,
preferably 0.08 5 R <_ 0.14 and particularly preferably
0.09 <_ R 5 0.12. At this vapour to polychloroprene
dispersion ratio R, the chloroprene present in the
polychloroprene dispersion fed in can be removed down
to a few ppm in an energy-efficient way.
The stripper column particularly preferably has a
number N of stages and/or trays such that 5 N 5 35,
in particular 8 _< N S 20, preferably 10 _< N 14 and
particularly preferably 11 <_ N <_ 13. Such a number N,
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for example N = 12, has been found to be particularly
economical, with a larger number N naturally being
technically possible for particularly small chioroprene
contents in the purified polychloroprene dispersion. In
particular, a single tower having N trays, with the
number of trays corresponding to the number of stages,
can be used for the stripper column. At such a number
of stages or trays, a particularly high proportion of
chloroprene can be removed without blockage of the
stripper column occurring. The high purity of the
purified polychloroprene dispersion is at the same time
achieved particularly economically at low cost.
In particular, the stripper column has a stage height h
such that, in particular, 800 mm 5 h <_ 1500 mm,
preferably 1000 mm _< h <_ 1300 mm and particularly
preferably 1100 mm <_ h <_ 1200 mm, and/or a stage and/or
a tray of the stripper column has, based on a circular
cross section, a diameter D such that, in particular,
500 mm <_ D <_ 5000 mm, preferably 1000 mm S D <_ 3000 mm
and particularly preferably 1500 mm <_ D 2000 mm. The
stage height h is defined by the distance between two
adjacent trays. As trays, it is possible to use, in
particular, sieve trays. This dimensioning of the
stripper column gives a good separation performance at
a comparatively low outlay. At the same time, the
stripper column can easily be serviced and cleaned.
The invention further provides a plant for producing a
polymer dispersion based on polychloroprene, in
particular for carrying out the process configured and
developed as described above, having a polymerization
unit for the polymerization of chloroprene to
polychloroprene in an emulsion, where the
polymerization unit is dimensioned as a function of the
formulation used so that a polychloroprene dispersion
present after the polymerization having a maximum
solids content wsolid in proportions by weight of wsolid
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<_ 50 0, in particular Wsoiid _< 40'1, preferably Wsolid <_ 35%
and particularly preferably wsolid <_ 30%, can be obtained
and a multistage and/or multitray stripper column
connected directly or indirectly to the polymerization
unit for the removal of chloroprene from the
polychloroprene dispersion, where the stripper column
is dimensioned, as a function of the polychloroprene
dispersion fed to the stripper column, so that a
purified polychloroprene dispersion present after the
removal of chloroprene having a chloroprene content
WCR,out in proportions by weight of WCR,out _< 50 ppm, in
particular WCR,out <_ 30 ppm, preferably WCR,out <_ 15 ppm
and particularly preferably WCR,Out <_ 10 PPM, can be
obtained.
Owing to the appropriate dimensioning of the
polymerization unit and of the stripper column, the
proportion of monomeric chloroprene in polychloroprene
dispersions can be reduced without a significant
reduction in the operating times of the plant
components used having to be accepted. As a result of
the low solids content of the polychloroprene
dispersion after the polymerization, the monomeric
chloroprene (residual monomer) can be removed from the
polychloroprene dispersion down to a few ppm without
the risk of blockage of the stripper column. The plant
can, in particular, be configured and developed as
explained above for the process of the invention.
The stripper column particularly preferably has, at
least in part, a heat-insulating and/or thermally
insulating cladding. The energy introduced by the
vapour into the stripper column is in this way largely
kept in the stripper column without being given off to
the environment by natural cooling. The amount of
vapour required can be reduced as a result. At the same
time, it can be ensured that even in the case of a
large number of stages and/or trays in the stripper
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column, the vapour has a sufficiently high temperature
to vaporize and carry out chloroprene even in the
uppermost stages or trays. Additional introduction of
vapour at a higher point in the stripper column can be
avoided in this way.
The invention further relates to a joining process for
joining a first part to a second part, wherein an
adhesive which has been produced using a polymer
dispersion based on polychloroprene is employed as
joining means and the polymer dispersion has been
produced by a process as described above and/or by
means of a plant as described above. Owing to the
particularly low residual monomer content of the
polychloroprene dispersion, the adhesive produced from
this polychloroprene dispersion also has a particularly
low chloroprene content. The risk to the environment
and/or the health of a user posed by this adhesive
during joining of parts is significantly reduced.
The invention will hereinafter be illustrated by way of
example with reference to the accompanying drawing by
means of a preferred example. In the figure:
Fig. 1 shows a schematic flow diagram of the plant of
the invention for carrying out the process of the
invention.
The plant 10 shown in Fig. 1 has a polymerization unit
12 which is configured as a cascade of stirred tanks
having six stirred tanks 14 connected in series in
order to carry out a pseudocontinuous polymerization in
the polymerization unit 12. Chloroprene, recycled
chloroprene, solvent such as aqueous phase and/or H2O
are introduced via a feed line 16 into the
polymerization unit. The polymerization unit 12 is
dimensioned on the basis of the formulation used and/or
the process conditions used in such a way that a
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polychloroprene dispersion leaving the polymerization
unit 12 via a polymerization outlet line 24 has a
comparatively low content of polychloroprene solid. For
example, the reaction temperature and/or the number of
stirred tanks 14 is selected appropriately. In addition
or as an alternative, it is possible to set the
conversion of chioroprene and/or the amount of solvent
appropriately.
The polychloroprene dispersion present after the
polymerization is fed via the polymerization outlet
line 24 to a preliminary degassing unit 26 in order to
separate off gaseous and/or volatile constituents of
the polychloroprene dispersion via a degassing line 28
and work them up if appropriate. Worked-up components
which have been separated off via the degassing line 28
can, if appropriate, be returned to the polymerization
unit 12 via the feed line 16. To aid the degassing of
volatile constituents of the polychloroprene
dispersion, steam can be blown into the degassing unit
26 via a steam feed line 30.
The polychloroprene dispersion can be fed by means of a
first pump 32 via a stripper feed line 34 to a stripper
column 36 having, for example, eleven trays in an upper
region of the stripper column 36. In a lower region of
the stripper column 36, steam is blown into the
stripper column 36 via a steam inlet line 38 in order
to separate off the residual monomer of the
polychloroprene dispersion overhead in the form of
monomeric chloroprene via a vapour outlet line 40. The
chioroprene which has been separated off via the vapour
outlet line 40 can be worked up and returned to the
polymerization unit 12 via the feed line 16.
The polychloroprene dispersion which has been purified
in the stripper column 36 and is taken off via a
stripper outlet line 42 has a chloroprene content of
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only a few ppm, with the proportion by weight of
chloroprene in the purified polychloroprene dispersion
being significantly less than 50 ppm, and being able,
in particular, to be 10 ppm or less. The purified
polychloroprene dispersion can be fed by means of a
second pump 44 to a creaming unit 46 where the
polychloroprene in the purified polychloroprene
dispersion is concentrated. In the creaming unit 46,
two separable phases are, for example, produced, and a
concentrated polychloroprene product dispersion can be
discharged via a product outlet line 48. The other
phase can be separated off via a separation phase
outlet line 50 and, if appropriate, worked up and
reused.
