Concentrating evaporators – Film type – Centrifugal
Patent
1981-05-20
1982-11-30
Sever, Frank
Concentrating evaporators
Film type
Centrifugal
159 49, B01D 122
Patent
active
043614620
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method and apparatus for removing volatile matter such as solvents and monomers from highly viscous materials like synthetic polymer compositions by the use of a falling-film evaporator.
BACKGROUND ART
In the continuous process of block or solution polymerization of styrene, the product polymer which is discharged from the polymerization reactor contains a high concentration of volatile matter, i.e., the monomer styrene or the solvent used for polymerization. A high-degree evacuation technique by the use of a vertical falling-film evaporator has been practiced to remove the volatile matter included in such a polymer composition.
In the conventional process employing this technique, the polymer composition is heated through a heater or heat exchanger in advance of the evaporation to offset the latent heat taken away by the evaporation. This method is, however, undesirable in point of polymer quality because the remaining monomer tends to form the polymer of low-molecular weight when exposed to high temperatures of the preheating. When the polymer composition of low temperature is fed to the evaporator, its viscosity increases with the vaporization of the solvent and/or monomer and it becomes liable to partly solidify on account of the temperature drop due to the vaporization, so that smooth revolution of the agitator becomes difficult.
DISCLOSURE OF INVENTION
This invention intends in particular to remove volatile matter such as a solvent and/or monomer from a highly viscous polymer composition by feeding the polymer composition of low temperature into a falling-film evaporator and performing the polymer heating and the evaporation of volatile matter simultaneously, wherein reaction of the monomer and the temperature drop due to vaporization are prevented and the operation is carried out smoothly. For this purpose each agitator blade of the evaporator is provided at the outer end with a heating blade so as to give a wide contact area between the heating blade and the falling film, and thereby the driving power for the agitator is partly converted to friction heat at a low agitator speed to keep the temperature of the falling film. In addition, the friction heat to be applied to the polymer composition is controlled by regulating the heating blade-falling film contact area, i.e., by employing the heating blades of a proper shape and area according to a given amount of the volatile matter to be evaporated, thus eliminating unnecessary, undesirable heating and improving evaporation efficiency.
BRIEF DESCRIPTION OF DRAWING
FIG. 1 is a vertical sectional view of a falling-film evaporator to represent a prefered embodiment of the invention.
FIG. 2 is a cross-sectional view taken on line II--II of FIG. 1.
FIG. 3 is an elevation to illustrate preferred embodiments of the heating blade.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to FIGS. 1 to 3, there is illustrated an embodiment of the invention. FIG. 1 is a vertical sectional view of a falling-film evaporator for carrying out the invention, wherein 1 is a polymer composition inlet; 2 and 3 a distributor and agitator blades, respectively, all attached to a rotary shaft 13; 4 a heating jacket mounted around the evaporator body 5; 6 inlets and outlets for the heat medium; 7 a bottom tank of the evaporator 5; 8 a discharge means fitted within the bottom of the tank 7; 9 a bottom bearing for the rotary shaft 13; 10 a vent fitted into the upper wall of the bottom tank 7; 11 a polymer outlet located at the bottom of the tank 7; 12 a stuffing box; 14 and 15 pulleys; and 16 a driving means. FIG. 2 shows a horizontal cross-section of the agitator blades 3, which are assembled into a body through the rotary shaft 13 and each comprises a twisted blade 17 helically secured around the rotary shaft 13, a heating blade 19 having given widths in the direction of the agitator revolution and keeping a small clearance between its own face and the inner wall of the evaporator body 5, and a squeeze blade 18 bei
REFERENCES:
patent: 2520729 (1950-08-01), Kollsman
patent: 3812897 (1974-05-01), Latinen
Fujii Yuji
Oda Chikao
Hitachi , Ltd.
Sever Frank
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