Concentrating evaporators – Superheating and pressure release
Reexamination Certificate
2001-11-27
2004-07-13
Manoharan, Virginia (Department: 1764)
Concentrating evaporators
Superheating and pressure release
C159S043100, C159S047100, C159SDIG001, C202S158000, C202S259000, C202S262000, C528S501000
Reexamination Certificate
active
06761797
ABSTRACT:
The invention relates to an industrial apparatus for carrying out mass transfer processes with high-viscosity liquids, particularly for boiling down and/or devolatilizing polymer melts. The apparatus is essentially based on a vertically disposed vessel, in which the high-viscosity liquid to be treated is divided into a multiplicity of individual streams which under the action of gravity run off into the sump of the vessel.
BACKGROUND OF THE INVENTION
Important mass transfer processes in the case of liquids include boiling down and devolatilization of solutions, dispersions or melts. During the preparation of polymer plastics, in particular, the problem of separating low molecular weight substances, e.g. water or monomers, from the plastic melt is encountered, as such substances adversely affect product quality or, in some cases, are even toxic.
To boil down polymer melts, use is often made, according to the prior art, of thin-film evaporators, as described in the publications DE 3 310 676 A1, DE 4 328 013 A1 and U.S. Pat. No. 3,630,689. The drawbacks of such machines are the relatively high investment costs and especially the wear of rotating parts of such machines.
Also known are strand evaporators, in which the polymer melt is divided, in a vertically disposed vessel, by means of a nozzle plate into a multiplicity of individual strands or filaments which in free fall flow separately and parallel to one another through the vessel from top to bottom and are recombined at the vessel bottom. The polymer melt is therefore separated at the head of the vessel into strands which taper in free form under the influence of gravity and at the bottom of the vessel dip into the melt sump. Such apparatuses are described in the patents U.S. Pat. No. 2,719,776, U.S. Pat. No. 5,024,728 and U.S. Pat. No. 4,934,433. A basic drawback of the apparatuses described is that these are suitable only for those liquids which, after emerging from the nozzle plate, by themselves form long filaments in a similar manner as in a spinning process. A further drawback is that a prolonged dwell time in the devolatilizing chamber can only be achieved with the aid of a very great drop out and consequently great overall height of the apparatus.
In addition, the publication CA 2 168 630 describes a method of preparing polycarbonate, wherein a mixture of monomers and prepolymer is distributed onto a multiplicity of individual wires which are arranged vertically in a reactor and along which the liquid mixture runs off downwards and at the same time polymerizes to completion. The polymerization therefore takes place in a thin liquid strand enveloping the wire; i.e. by means of the vertically mounted wires a defined polymerization zone is established in the reactor. This publication gives no description of the devolatilization of finished polymer solutions.
It is an object of the invention to develop an industrial apparatus for mass transfer processes which ensures a long product dwell time in the gas space while maintaining as narrow as possible a dwell time spectrum and which is also suitable for high-viscosity liquids where the formation of continuous strands or filaments is impaired or prevented by foaming or the formation of bubbles.
SUMMARY OF THE INVENTION
This object is achieved, starting from the apparatus described at the outset comprising a vertically disposed vessel, by wire loops being disposed essentially parallel to the vertical plane at the liquid feeder means in the vessel, at the top ends of which wire loops at least one liquid feeder means each is provided for feeding in a substream which runs off downwards along the wire loop. “Parallel to the vertical plane” in this case means that the plane of the wire loop coincides with the vertical plane, minor deviations being quite permissible all the same. In the case of a high-viscosity, nonfoaming liquid the substream running off via the wire loop forms a liquid lamella and in the case of a foaming liquid forms a thin layer which extends in part or in its entirety across the plane of the wire loop. In both cases, the liquid is delimited and guided by the wire loop. At the top end of the wire loop the liquid is supplied continuously. At the bottom end it drips off again. The effect of the wire loop is that the thin liquid layer or lamella is stabilized and maintained in the flowing state, large phase interface areas being provided for mass transfer.
The invention relates to an apparatus for carrying out mass transfer processes with high-viscosity liquids, particularly for boiling down and/or devolatilizing polymer melts, comprising at least one vertically disposed vessel having a feeder means for the liquid to be treated, an outlet for volatile components and an outlet for the treated liquid, the feeder means being equipped with a distributor element having a multiplicity of orifices for subdividing the high-viscosity liquid to be treated into a multiplicity of individual streams, characterized in that essentially vertically arranged wire loops are disposed in the vicinity of the orifices, along which wire loops the high-viscosity liquid runs off under the action of gravity.
The wire loops can have different geometries, e.g. form squares, rectangles or triangles. The wire loops are preferably bent from steel wire having a thickness of from 0.5 to 6 mm and, depending on the field of application, preferably have a length (height) of from 0.5 to 4 m.
In a preferred apparatus, the distributor element is a perforated plate.
Preferably, according to one variation, the distributor element includes at least one horizontally arranged tube which has orifices for the outflow of the high-viscosity liquid pointing downwards and/or upwards (i.e. counter to the direction of flow of the liquid).
Preferably, for better cleaning, the wire loops in the vicinity of the orifices in the distributor element are disposed detachably.
Particularly advantageous is an apparatus in which the distributor element comprises at least one horizontally arranged tube which has slotted orifices pointing upwards.
Particularly preferably, the distributor tubes have an inner diameter of from 10-100 mm. The slot width of the orifices is particularly preferably 0.2-10 mm, and the slot length, particularly preferably, is 10-100 mm.
More easy to clean is also a further preferred variation of the apparatus, in which the distributor element comprises at least one horizontally arranged tube which has slotted orifices pointing upwards, into which the wire loops are clipped.
Particularly preferred is an apparatus in which two, three or more of the wire loops at a time are combined into a basket-like lattice or wire mesh.
Particular advantages also result if, in a preferred embodiment of the apparatus, two or more adjacent lattices or wire meshes are linked to one another.
To achieve a further increase in stability in a particularly preferred embodiment of the apparatus, the wire loops can be additionally attached to the vessel bottom.
In a preferred embodiment, the wire loops can be heated, particularly by means of electric resistance heating means.
A further preferred variation of the apparatus is characterized in that the distributor elements are formed by heat exchange tubes which are vertically arranged in the vessel, debauch into the vessel and have orifices, the wire loops being attached to the bottom ends of said heat exchange tubes.
The area enclosed by a wire loop is preferably from 0.5 cm to 2500 cm
2
.
Another preferred embodiment of the apparatus is characterized in that the wire loops taper in the direction of flow of the liquid and, in particular, terminate in an acute angle at their bottom ends.
For the purpose of improved heat exchange in a particular embodiment of the apparatus, the vessel is designed to be heatable and/or coolable, and in particular is provided with a jacket for an electric heater or for a heat transfer medium to be passed through.
A further alternative of the invention consists in the wire loops not being fastened to a distributor tube or a distributor plate or to the h
Kohlgrüber Klemens
Weyrich Frank
Manoharan Virginia
Norris McLaughlin & Marcus P.A.
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