Agitating – By vibration – Of stirrer
Reexamination Certificate
2000-04-07
2001-11-20
Soohoo, Tony G. (Department: 1723)
Agitating
By vibration
Of stirrer
C366S275000
Reexamination Certificate
active
06318888
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process for introducing mechanical vibrations into vessels through a flexible membrane installed in the vessel wall by means of a push rod and to an arrangement for introducing vibrations produced by a vibration generator into a vessel, the vibrations being designed to be delivered through a linkage as vibration pickup to a flexible membrane installed in the vessel wall.
In many chemical reactions between immiscible phases, it is important to obtain a good mass transfer between the phases. Thus, reactions between liquids and the gases dispersed therein take place at the phase interface. The overall reaction rate depends on the transfer of the gas into the liquid phase. In many cases, this transfer of the gas limits the reaction rate.
There are known processes which accelerate the transfer of a gas into a liquid and hence reduce energy costs or increase the specific volume yield or both. Thus, it has been proposed to increase the reaction rate in a process for hardening unsaturated fats by catalytic hydrogenation with hydrogen by exposing the reaction mixture to high-energy ultrasound. High increases in the reaction rate were measured but unfortunately cannot be attributed to an improvement in mass transport. Instead, detailed investigations have shown that they are based on an increase in the temperature of the reaction mixture through the effect of the high-energy ultrasound waves. Comparative measurements with and without exposure to high-energy ultrasound under isothermal conditions revealed no differences in the overall reaction rate.
Other disadvantages are an obstacle to the application of this proposal for industrial purposes. The acoustic power density used in this process amounts to more than 100 W/I reactor volume and is thus far too high for industrial purposes. Also, ultrasonic waves are very heavily attenuated in gas/liquid dispersions so that ultrasonication is uneconomical for relatively large reactors suitable for industrial purposes.
In an Article in Trans. Instn. Chem. Engnrs. 44 (1966) T91, G. J. Jameson reports on another process for increasing mass transfer in gas/liquid dispersions by sound waves. In this process, a gas/liquid column is made to resonate through low-frequency sound. This process is unsuitable for industrial purposes because very low frequencies would have to be used for relatively large vessels and hence tall liquid/gas columns. These frequencies would have to be below 10 Hz and would have to have amplitudes of more than 0.5 m in order significantly to improve mass transport.
DE 44 36 064 A1 describes a process in which the frequency of the sound acting on the gas/liquid column is substantially equal to one of the resonance frequencies of the phase interface between the gas bubbles and the liquid. The power density of the sound is below the levels sufficient for degassing the liquid. Under these conditions, mass transfer in the gas/liquid mixture is clearly improved and the overall reaction rate in a liquid/gas reaction is greatly increased.
In such a process, the sound waves can be introduced into a reactor or other vessel through the delivery of the vibrations produced by a vibration generator via a linkage to a flexible membrane. This membrane is installed in the wall of the reactor or vessel. However, this is only possible when substantially the same pressure prevails on both sides of the membrane. Accordingly, arrangements in which ambient pressure prevails in the vessel or reactor belong to the prior art. This technique cannot be applied when the difference in pressure between the two sides of the membrane is such that the membrane is significantly moved from its neutral or rest position. Thus, where a pressure of 20 bar prevails in the vessel, a compressive force of about 2 tonnes is applied, for example, to a relatively small membrane area of 100 cm
2
.
BRIEF SUMMARY OF THE INVENTION
The technical problem addressed by the present invention was further to develop the process described at the beginning in such a way that it would be suitable for introducing sound into pressure vessels and pressure reactors. This problem is solved by carrying out the process for introducing mechanical vibrations in such a way that a pressure acting on the membrane and push rod on the vessel side is compensated through the arrangement of the membrane and push rod in chambers with pressures acting in opposite directions, the push rod transmitting the mechanical vibrations acting thereon without play, and by an arrangement in which the vessel is a pressure vessel and the outside of the membrane is arranged in a pressure chamber in which the same pressure as in the vessel prevails, the vibration pickup being connected to the membrane without play via a push rod.
Reactions between various substances and, in particular, the mass transfer between immiscible phases in pressure vessels can be favorably influenced in a simple, readily controllable manner by the process according to the invention. One particular advantage is that the force acting on the membrane and push rod through the pressure prevailing inside the vessel is made independent of the cross-sectional area of the membrane through the provision of the pressure chambers. The cross-sectional area of the sound-transmitting membrane can thus be varied relatively freely which is very useful where the process is applied on an industrial scale.
The push rod which is introduced into the pressure chamber from the surrounding atmosphere to transmit the vibrations transmitted to it by the vibration pickup to the membrane has to be pressure-tight. This can lead to attenuation and hence to impairment of its movability. This is avoided by an embodiment of the arrangement in which the push rod is mounted for pressure compensation at both ends in its direction of movement. This is achieved by providing a flexible seal connected to the push rod in the pressure chamber on the side opposite the membrane and a second flexible seal on the wall of a second pressure chamber at the other end of—and connected to—the push rod, both pressure chambers containing a fluid under substantially the same pressure as prevails in the vessel or reactor. If the two flexible seals have equally large pressure transmission surfaces with respect to the fluid, the end result is equally large compressive forces which act on the push rod from both sides and cancel out each other's effect.
If the vibration pickup is connected to the push rod outside and between the two pressure chambers, the linkage of the vibration pickup advantageously does not have to be guided into the pressure chambers and accordingly does not have to be pressure-insulated. The interconnection of the two pressure chambers by a fluid line ensures in a simple manner that the same fluid pressures prevail in both pressure chambers.
The design of the flexible seals as a cup or roll membrane advantageously provides for extremely flexible and effective sealing which does not interfere with the movability of the push rod. In addition, in an embodiment such as this, the problem of supporting the roll or cup membrane on the side remote from the pressure chamber can be favorably solved by means fixed to the push rod.
The fact that the membrane in the vessel or reactor wall consists of a flexible membrane material which is tightly clamped in the reactor wall at its outer edge and between two metal disks at its center creates particularly favorable conditions for connecting the push rod to the membrane via the metal disks.
Besides the advantages already mentioned, other advantages will become apparent from the following description of one example of embodiment with reference to the accompanying drawings, wherein:
REFERENCES:
patent: 2124983 (1938-07-01), Martin
patent: 2499203 (1950-02-01), Warren
patent: 2552970 (1951-05-01), Horsley et al.
patent: 2693944 (1954-11-01), Fowle
patent: 2702692 (1955-02-01), Kessler
patent: 3313240 (1967-04-01), Bentov
patent: 3517674 (1970-06-01), Allen et al.
patent: 3567185 (1971-03-01),
Bartsch Achim
Fieg Ferdinand
Kuesegen Rainer
Cognis Deutschland GmbH
Drach John E.
Soohoo Tony G.
Trzaska Steven J.
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