Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Organic polymerization
Reexamination Certificate
1995-08-24
2001-08-07
Wu, David W. (Department: 1713)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Organic polymerization
C526S344000, C528S500000, C095S264000, C096S201000
Reexamination Certificate
active
06270729
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for the intensive degassing of polyvinyl chloride-containing dispersions, essentially comprising a polymerization reactor (
1
), a cooling device (
2
), and a vacuum unit (
3
), where the polymerization reactor (
1
) contains a steam inlet (
4
) in the lower half, and the polymerization reactor (
1
), the cooling device (
2
) and the vacuum unit (
3
) are connected to one another via a connector (
5
).
The present invention furthermore relates to the use of the novel apparatus for the intensive degassing of PVC dispersions, and to a process for this purpose.
2. Description of the Prior Art
DE-A 25 31 111 describes a process for the removal of residual vinyl chloride (VC) from vinyl chloride polymer in aqueous dispersion (both suspension and emulsion), where the aqueous dispersion of the polymer is brought to a temperature at least the same as the freezing range of the polymer and is subjected to entrainment by an inert fluid. In particular, DE-A 25 31 111 uses steam as the inert fluid, which, after leaving the aqueous dispersion, is condensed in a condenser, on which a vacuum pump is arranged directly. The disadvantage of this process are the residual VC values in the degassed suspensions (in contrast to emulsions, which naturally can be degassed more easily owing to their particle size). According to the table in DE-A 25 31 111, the residual VC contents before drying are not less than 25 ppm. The value given for Example 5 corresponds to the residual VC content after drying, since the same conditions as in Example 1 were observed apart from a shorter (!) degassing time.
EP-A 359 432 describes an apparatus for degassing liquid mixtures essentially comprising polystyrene and volatile constituents such as monomers, in which a heat exchanger and a vacuum unit are connected directly to the vessel containing the polymer mixture to be degassed. The residual monomer contents achieved are less than 300 ppm, but are not below 177 ppm.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved apparatus for the intensive degassing of PVC-containing dispersions, in particular suspensions and emulsions, in the polymerization reactor which allows residual VC values of less than 25 ppm, in particular less than 10 ppm, to be obtained before drying of dispersions, in particular of suspensions, thus avoiding further, subsequent treatment for removal of residual VC without impairing the product quality. Furthermore, the removal of residual VC should be achieved using as little steam as possible.
We have found that this object is achieved by an apparatus for the intensive degassing of polyvinyl chloride-containing dispersions, essentially comprising a polymerization reactor (
1
), a cooling device (
2
), and a vacuum unit (
3
), where the polymerization reactor (
1
) contains a steam inlet (
4
) in the lower half, and the polymerization reactor (
1
), the cooling device (
2
) and the vacuum unit (
3
) are connected to one another via a connector (
5
).
The invention furthermore provides the use of the novel apparatus and a process for the intensive degassing of PVC-containing dispersions.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Polymerization reactors (
1
) which can be employed according to experience hitherto are all reactors which are suitable for polymerization of vinyl chloride. The invention provides that a steam inlet is provided in the lower half of the polymerization reactor. In general, the inlet used is a commercially available inlet, usually installed in a manner known per se. The steam is preferably introduced in such a way that it is homogeneously distributed in the polymerization reactor (
1
) and in the dispersion. The distribution of the steam can, if necessary, be supported by stirring.
The cooling device (
2
) employed can be a commercially available reflux condenser, preferably a tube-bundle condenser, in which the cooling surface area can be changed by introducing inert gas. The dimensions of the cooling surface of the cooling device depend essentially on the residual VC content, the amount of steam introduced and the amount of dispersion. The cooling surface of the cooling device is expediently designed in such a way that some of the steam can condense on the cooling surface in order always to keep the dispersion in a predetermined temperature range under reflux conditions.
The vacuum unit (
3
) employed can be a conventional vacuum pump with compressor, where the performance of the compressor usually depends essentially on the dimensions of the polymerization reactor, the reduced pressure desired and the residual VC content desired. The range of suitable vacuum units is customary to the person skilled in this area, so that further details are superfluous.
According to observations hitherto, the shape of the connector (
5
) has no effect on the success of the process. However, preference is given to cylindrical shape having a length:diameter ratio in the range from 10:1 to 1:1, preferably from 7:1 to 3:1. Furthermore, the dimensions of the connector (
5
) are usually selected so that the ratio between the volumes of the polymerization reactor (
1
) and the connector (
5
) are in the range from 100:1 to 10:1, preferably from 50:1 to 2:1. The connector can also contain internals, which allow any foam produced in the polymerization reactor to be kept away from the cooling device and the vacuum unit.
REFERENCES:
patent: 4077135 (1978-03-01), Tzschoppe et al.
patent: 4130527 (1978-12-01), Miller et al.
patent: 4158092 (1979-06-01), Botsch et al.
patent: 4171427 (1979-10-01), Ohorodnik et al.
patent: 4197399 (1980-04-01), Noel et al.
patent: 1 248 943 (1967-08-01), None
patent: 25 31 111 (1976-02-01), None
Elzer Gunter
Perner Thomas
Cheung William K.
Keil & Weinkauf
Solvin (Societe Anonyme)
Wu David W.
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