Organic compounds -- part of the class 532-570 series – Organic compounds – Fatty compounds having an acid moiety which contains the...
Reexamination Certificate
2000-10-22
2003-01-28
Carr, Deborah D. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Fatty compounds having an acid moiety which contains the...
C554S132000
Reexamination Certificate
active
06512131
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the priority benefit of European patent application EP 99 121 608.6 filed on October 29, 1999.
FIELD OF INVENTION
The present invention relates to a process and apparatus for carrying out a multi-phase reaction using the counter current principle of a liquid and a gaseous phase.
BACKGROUND
In chemistry, one is frequently confronted with the problem of carrying out multi-phase reactions in the form of separation processes, in particular chemical reactions in multi-phase systems. Decisive in these reactions is the phase transfer velocity of the components of the respective phases to be separated or reacted. The velocity of the reaction, as is generally known, can substantially be increased by enlarging the contact surfaces of the respective phases. Such enlargement can be achieved by intensively mixing the phases. Moreover, it is known that multi-phase reactions proceed particularly efficiently and rapidly, especially, if the process is continuously carried out in the counter current flow. However, when using the counter current principle, serious problems are encountered as will later be described so that the co-current principle is employed as well.
A special problem of multi-phase reaction is constituted by gas-liquid or gas-solid-phase reactions, particularly in the cases where gaseous components in a carrier gas are reacted with emulsified or suspended components in liquid phases. In view of the extremely great differences of the mass density of gases, on one side, and liquids, or solids, on the other side (at normal pressure, a ratio of about 1:1000 and more is found), giant gas volumes have to be brought into contact with relatively small, sometimes solid-containing, liquid volumes.
In gas-liquid multi-phase reactions, liquid mixtures are often brought into the reaction. The flow behavior of such mixtures, particularly when present in the form of emulsions, is extremely complicated. Surface phenomena, for instance, might lead to partial breaking of the emulsion. Different flow velocity reducing properties, such as, for example, differences of the viscosities of the liquids and/or differences in the adhesion of the liquids on the reactor surfaces might cause disturbances when carrying out the gas-liquid multi-phase reactions.
The complexity of gas-liquid multi-phase reactions and of the physical and chemical behavior of the respective components, particularly in the case of a heterogeneously combined liquid phase, is so high that forecasting the flow behavior thereof in reactors is practically impossible. It should for instance be noted that even in the case of two immiscible liquid phases, two types of emulsions might occur, namely phase
1
in phase
2
and phase
2
in phase
1
. Flow behavior, viscosity, adhesion and other physical and chemical properties of the two emulsion types can show considerable differences so that in the case of chemical reaction, the flow behavior of the liquid phase in the reactor might change.
Known methods for increasing the efficiency and the velocity of reactions with or within phase mixtures are often employed. One method includes spraying the liquids (solutions, emulsions and suspensions) into the reaction gas. Another method (preferred in the present invention) includes carrying out of the reactions in tube reactors having built-in packings for enlarging the reaction surfaces.
When carrying out gas-liquid multi-phase reactions in tube reactors according to the counter-current principle, a running-down liquid in the form of a free falling liquid film, the so-called falling film, and an ascending gas phase flowing upwardly constitute the common practice. In that kind of reactor, the gas phase of both non-packed and packed reactors always constitutes a continuous phase and moves in good approximation in the form of a plug flow through the reactor. A significant fundamental problem is encountered in such reactors, particularly in the case of high flow velocities of one or of both phases, and thus, particularly, also in the case of a very large difference in volume flow rate of gas phase and liquid phase.
In the case of ozonolysis of unsaturated fatty acids as later discussed, for example, the velocity of the gas flow has to be adjusted to rates considerably exceeding the velocity of the liquid phase. The counter current flow of the gas quantities in opposite direction to the liquid decreases by friction forces the flow velocity of the liquid. As generally known, this might lead, particularly in the case of reactors having internals or built-in packings, to the generation of a self-generating flow barrier for the liquids in the reactor preventing disturbance-free operation of the reactor (the reactor “floods”). The limit of the respective gas or liquid velocity at which this phenomenon of flooding occurs, is also referred to as the flooding point. A stationary counter current process above the flooding point is not possible. Since it is necessary to operate below velocities at which flooding occurs, in many reactions, particularly in the case of ozonolysis, the possible reactor flow rates are too low.
In view of the above reasons, a reactor with co-current contact is frequently employed. In a co-current process with parallel flow, both the gaseous phase (carrier gas and gaseous reactive component) and the liquid phase flow in the same direction. In the case of stoichiometric use of the reactants and in view of the great density difference, a considerably larger volume flow for the gas as compared to the liquid, and hence a considerably higher flow velocity of the gas, has to be established. Friction forces cause an increase in the flow resistance at the interface between gas and liquid. Thereby it is possible to employ such built-in packings which increase the flow resistance thus reducing the flow velocity and enlarging the surface that would not be passed through by gas and liquids flow in a counter current process.
It is, however, a disadvantage of the co-current principle that considering the high flow velocity, the period of dwell of the gas and hence of the gaseous reactants in the reactor is relatively short. In co-current reactors, furthermore, an unfavorable distribution of temperature and concentration along the length of the reactor can be observed. When entering the reactor, both the liquid and the gas phase have high concentrations of the reactants. During the course of the process, however, the concentrations in both phases substantially decrease. In the case of exothermic reactions, for instance, this results in a high heat development, and thus a high material turnover at the entry of the components into the reactor, and in little heat development and thus in little turnover at the reactor exit. In order to nevertheless obtain a complete turnover, a plurality of co-current reactors are e.g. provided in cross flow arrangement to approximate the counter current principle.
In a counter current process, however, the turnover of the product is inherently uniformly distributed along the reactor length. By this kind of process technique, it is much easier to obtain complete turnover of the reactants. Likewise process control of exothermic reactions can be carried out in a considerably easier manner. One example of a gas-liquid multi-phase reaction known for a long time and carried out on an industrial scale where the above mentioned problems come up, is the above-referenced ozonolysis of unsaturated organic compounds with ozone in oxygen or air and subsequent oxidative cleavage of the ozonides generated in ozonolysis with oxygen or air. The oxidative cleavage of oleic acid by means of ozone and oxygen represents an industrially very significant application of this technique. Oleic acid is first reacted to the oleic acid ozonide in the presence of pelargonic acid and water with an ozone/oxygen mixture, or an ozone/air mixture. The reaction is carried out in a reaction column including, if need be, built-in packings. The resulting ozonide is subsequently cleaved, or fur
Best Bernd
Brunner Karlheinz
Frische Rainer
Kilian Dirk
Seemann Joachim
Carr Deborah D.
Dr. Frische GmbH
Quarles & Brady LLP
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