Fluid sprinkling – spraying – and diffusing – Processes – Including mixing or combining with air – gas or steam
Reexamination Certificate
1998-05-05
2001-11-27
Kashnikow, Andres (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Processes
Including mixing or combining with air, gas or steam
C239S430000, C239S433000, C366S340000
Reexamination Certificate
active
06321998
ABSTRACT:
Dispersion is the term used to describe the break-up and finest possible distribution of one substance in another. The finished mixture is known as a dispersion. A dispersion comprises one or dispersed phases in a continuous phase. Thus, in contrast to mixing, the aim is not to achieve mutual interpenetration of the individual phases, but instead to achieve the most uniform possible break-up and distribution of one or more disperse phases in a continuous phase. Typical examples from the chemicals sector of dispersions produced by dispersion are liquid/liquid systems such as emulsions (disperse phase: liquid, continuous phase: liquid), gas/liquid systems such as gas-bubbled liquids and melts (disperse phase: gas, continuous phase: liquid/melt), such as for example during foaming of plastic melts, and mist (disperse phase: liquid, continuous phase: gas) together with liquid/solid systems such as suspensions (disperse phase: solid, continuous phase: liquid), in which the solid phase arises during the dispersion process by precipitation of a dissolved substance as an insoluble precipitate. Dispersion is either a purely physical process of break-up as in the case of producing emulsions for ointments or creams or, as in many industrial applications, is used as the first initiating reaction stage in the performance of chemical reactions in two- or multiphase reaction systems. During the performance of chemical reactions, the nature of the dispersion is substantially determined by kinetics, i.e. by the rate of the underlying reaction. Thus, in the case of rapid chemical reactions, mass transfer between the phases participating in the reaction is decisive to the rate of the chemical reaction. One substantial task of the dispersion stage is accordingly, in order to accelerate mass transfer, to produce the largest possible interfacial area per unit reaction volume, i.e. small disperse particles, such as liquid droplets or gas bubbles, and to minimise the energy input required for this purpose.
The aim of industrial dispersion processes is thus to break up and distribute one or more components uniformly and reproducibly in a continuous phase. The objectives here are, inter alia, the production of dispersions having defined particle sizes for the disperse phase, the smallest possible particles with a correspondingly large interfacial area per unit volume between the disperse and continuous phases together with narrow particle size distributions. The dispersion apparatus used for dispersion should be designed and constructed such that it accomplishes the dispersion task with minimal energy input, i.e. highly efficiently.
Numerous dispersion units are used for dispersion in the prior art. A distinction must be drawn in principle between dynamic and static dispersion apparatus [1], [2], [3]. A dynamic dispersion apparatus is characterised in that both the disperse phase as it forms and the continuous phase pass through or over it and that it is set in motion by input of energy, wherein the kinetic energy of the continuous phase exerts an additional break-up action on the disperse phase. In contrast, in a static dispersion apparatus only the disperse phase as it forms passes through or over the apparatus.
Examples of dynamic dispersion apparatus for liquid/liquid systems are nozzles, nozzles combined with downstream jet dispersers, stirrers and rotor/stator systems [2], those for gas/liquid systems are injectors, ejectors (=jet suction pumps), venturi nozzles and stirrers [1], [3] and those for liquid/solid systems are precipitator nozzles and stirrers.
Examples of static dispersion apparatus for liquid/liquid, gas/liquid and solid/liquid systems are submerged tubes, sieve-plates, perforated plates made from metal, rubber or plastic, optionally also with a pulsating plate, manifold rings and sintered glass or metal plates (preferably for gas/liquid systems [1], [3]).
A disadvantage of using available prior art dynamic dispersion apparatuses is that the disperse phase is broken up in a turbulent shear field, wherein the non-uniform distribution of local energy dissipation rates results in broad particle size distributions for the disperse phase. Moreover, in comparison with static dispersion apparatuses, a high energy input is required to produce dispersions having small average particle dimensions for the disperse phase and a correspondingly large interfacial area per unit volume.
Conventional static dispersion apparatuses are indeed more efficient than dynamically operated apparatuses, i.e. the ratio of the resultant interfacial area per unit volume to the energy input is greater. However, the interfacial area per unit volume and thus reactor output or space-time yield actually achievable with static apparatuses is generally small. Using static apparatuses, particle dimensions for the disperse phase are obtained which are larger than the dimensions of the bores through which the disperse phase is introduced, i.e. usually larger than 1 mm. While sintered plates do indeed allow particles smaller than 1 mm to be produced, they have a tendency to soiling and encrustation and their use is restricted to relatively small throughputs and thus relatively small reactor outputs.
Starting from this prior art, the object underlying the present invention is as follows. The aim is to produce high quality dispersions tailored to the particular application. It is necessary to this end for the disperse phase to consist of particles, the dimensions of which are freely adjustable within broad limits and the size of which is preferably in the range of finely divided particles of smaller than 1 mm. This results in a correspondingly large interfacial area per unit volume. It is furthermore advantageous to be able to establish narrow particle size distributions. The energy input for the production of such dispersions must be lower than when a prior art dispersion apparatus is used. The dispersion apparatus used must furthermore allow relatively large throughputs so rendering industrial implementation feasible.
This object is achieved by a process for the continuous dispersion of at least one fluid A constituting the disperse phase and at least one continuous phase constituting the enclosing phase of a fluid B, in which at least one fluid stream A and at least one fluid stream B are fed into a dispersion apparatus and come into contact therein in a dispersion chamber. The characterising feature of the subject-matter of the invention is that the fluid streams A, B are broken up into spatially separate, flowing fluid filaments in a microstructure dispersion apparatus by a system of microchannels associated therewith, which filaments are discharged into the dispersion chamber at identical flow velocities for the particular fluid in such a manner that on discharge into the dispersion chamber a fluid jet of the disperse phase is in each case immediately adjacent to a fluid jet of the continuous phase and in each case a fluid jet of the disperse phase is enclosed as it is broken up into particles in the adjacent fluid jets of the continuous phase. The fluid filaments may be cylindrical, lamellar or of any other geometric shape.
The process may be performed in such a manner either that a gas is used as fluid A and a liquid as fluid B or that at least two different liquids are used as the fluids. In the first case, the process is thus used for gas bubbling and in the second for production of an emulsion.
One specific embodiment which is of interest is that educts A, B which react together chemically are used as the fluid, such that immediately after dispersion a chemical reaction of the educts A, B proceeds in the dispersion chamber.
Laminar flow conditions for the fluid streams A and B are preferably maintained in the microchannels. Laminar flow conditions thus also prevail for fluid streams A and B immediately after discharge from the microchannels. Dispersion of the disperse phase A into the continuous phase B, which begins on discharg
Bier Wilhelm
Herrmann Erhard
Koglin Bernd
Linder Gerd
Menzel Thomas
Bayer Aktiengesellschaft
Kashnikow Andres
Nguyen Dinh Q.
Norris & McLaughlin & Marcus
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