Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Agitating to form larger particles
Patent
1991-06-27
1993-02-23
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Agitating to form larger particles
264140, 252 891, B29B 908
Patent
active
051887860
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for the continuous granulation of a mixture containing at least one solid and at least one liquid having a tendency to gel.
A granulation process of the type in question is used, for example, in the production of detergents. Hitherto, the granules have been produced as follows: the liquid ingredients were sprayed onto a granulated support produced by spray-drying or were incorporated in a prepared formulation by a granulation process. By contrast, solid ingredients were either made into a slurry and spray-dried or were directly incorporated in powder form.
Since problems consistently arise when liquids or liquid mixtures have a tendency to gel, attempts have always been made to avoid such gelation.
According to patent application P 38 35 918.9 filed in the name of Henkel KGaA on the 21.10.1988, it was surprisingly found that dry and free-flowing granules can be obtained if the liquid tending to gel is first allowed to gel completely and solids, such as for example spray-dried zeolite, bentonite or other predominantly apolar or weakly polar solids, are incorporated thereafter. The sequence can also be reversed.
The problem addressed by the present invention was to provide a process of the type mentioned at the beginning which worked with a gel-like intermediate phase and which could be carried out continuously.
According to the invention, the solution to the problem has been solved by a process of the type mentioned at the beginning which is characterized in that a mixture prepared in a static mixer and containing liquid raw materials with no tendency to gel on their own is used as the liquid with a tendency to gel, the average residence time in the static mixer being shorter than the gel time, in that the liquid is then allowed to gel in a stirred tank, the average residence time in the stirred tank being longer than the gel time, and in that the highly viscous paste obtained is only then granulated together with the solid.
According to the invention, therefore, gelation does not occur in the static mixer or even in the granulation unit, but only in the stirred tank. A stirred tank which the liquid enters continuously and from which the highly viscous paste is continuously discharged is used for gelation. The tank is stirred to prevent the formation both in the tank and within the already gel-like mass of any liquid passages through which the liquid could issue from the tank without the necessary residence time for gelation having been reached. The static mixer consists essentially of a tube-like passage in which individual swirling elements are firmly incorporated. The liquid is thoroughly mixed as it flows through this tubular element.
To ensure that the average residence time in the stirred tank is longer than the gel time, the throughflow rate of the liquid through the stirred tank and also the shape and rotational speed of the stirrer are correspondingly adapted to the contents of the tank. Providing the shape and rotational speed of the stirrer are suitably selected, a long average residence time can be obtained despite a large throughflow volume and a small tank capacity.
In one particularly favorable embodiment, the liquid enters at the bottom of the stirred tank while the gel is discharged from the upper part of the stirred tank.
Since the viscosity of the gel is dependent on temperature, it can be influenced by using a coolable and/or heatable stirred tank.
In another advantageous embodiment, the highly viscous paste, which is not readily pumpable, only has to travel a short distance between the stirred tank and the granulation unit.
To prevent the mixture from caking on the walls near the inlet openings of the granulation unit, at least one of the solids is introduced first during the granulation process. If the gel is subsequently added, caking problems do not arise. The apparent density can be adjusted through the granulation time in the granulation unit.
No particular granulation unit is required for the purposes of the invention. Any commercially available
REFERENCES:
patent: 4059538 (1977-11-01), Green et al.
patent: 4925585 (1990-05-01), Strauss et al.
Wiemer Frank
Wilms Elmar
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
Ortiz Daniel S.
Szoke Ernest G.
Theisen Mary Lynn
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