Mixing two immiscible fluids of differing density

#Certain chemical processes involve the interaction of two liquids or fluids of different densities and limited mutual solubility. When these liquids are mixed to form a two-phase system and are then catalytically reacted under strongly exothermic or endothermic conditions, it becomes desirable and even necessary to achieve an intermixing between the two liquids before they are subjected to reaction conditions. With liquids of differing density, it is particularly difficult to achieve a distribution of one liquid in the other, or vice versa, on a uniform basis, even transitorily, because of the inherent physical tendency of such liquids to assume different flow rates, even with all other variables being substantially constant.

#For example, the hydration of acrylonitrile to acrylamide is a highly exothermic reaction. The problem of controlling reaction temperature is particularly, and perhaps even uniquely, difficult when using a reactor feed of relatively high acrylonitrile concentration due to the relatively low system heat capacity per mole of reactant acrylonitrile. This results in the necessity of conducting the reaction between acrylonitrile and water when using a concentrated acrylonitrile feed in a reaction zone from which the heat of reaction can be continuously removed to avoid undesirably high temperatures where side reactions may occur.

#As those skilled in the art will appreciate, if the heat of reaction is continuously removed from a fixed-bed catalytic reaction zone, the zone or zonal elements must have a relatively small cross-sectional area with a coolant circulated around the outside of the zone or zonal elements. If large cross sectional areas are used for the zone or zonal elements, some areas of the reaction zone are too far from the cooling surface and hence tend to experience undesirably large temperatures. In addition, a small cross sectional area tends to maximize the interfacial area between the reaction zone and the cooling media, which allows removing the heat of reaction efficiently with a relatively small temperature difference between reaction zone and cooling media. In common, normal practice using a tubular reaction zone with a fixed catalytic bed in the zones, it is common to employ tubes having inside diameters in the range of from about 0.4 to 2.6 inches with a circular cross section.

#FIG. 1 diagramatically illustrates problems associated with the use of a prior art fluid intermixing technique for purposes of achieving equal distribution between two fluids of differing density being charged to a tubular reactor having a plurality of reaction tubes;

#FIG. 2 is a view similar to FIG. 1 but showing a different form of prior art fluid mixing technique;

#FIG. 3 is a view similar to FIG. 1 but showing another form of prior art fluid mixing technique;

#The difficulties of achieving a substantially equal distribution of two liquids of differing density over a predetermined zone, such as a zone 20 immediately preceding the entrances 21 of each of a plurality of tubes 22 in a tubular reactor 23, the tubes 22 being contained within a shell 24, are illustrated in FIGS. 1-3. Thus, in FIG. 1, a more dense liquid fluid 26 and a less dense fluid 27 are both charged into the mouth 25 of a tube 28 equipped with a plurality of longitudinally spaced (relative to tube 28) nozzles 29, the tube 28 extending transversely across zone 20. Even when the fluids 26 and 27 are charged at equal pressures and temperatures, the less dense fluid 26 tends to leave tube 28 through nozzles 29 before the more dense liquid 26; that is, the residence time of less dense fluid 27 is less than the residence time of more dense liquid 26 in tube 28. Thus, more dense liquid 26 tends to separate from less dense fluid 27, so that terminal nozzles 29 of tube 28 are richer in liquid 26 than fluid 27, and vice versa for initial nozzles 29. Hence, a tube distribution arrangement of FIG. 1 is unsatisfactory for solving the problems faced on this present invention.

#In FIG. 3, a less dense fluid 27 is fed into chamber 33 through pipe 34 just below zone 20 and comes into contact with a more dense liquid fluid 26 upwardly flowing in chamber 33 from an input pipe 35. As the arrows in chamber 33 suggest, the fluids 26 and 27 tend to mix only to a limited or incomplete extent, since more of the less dense fluid 27 enters the entrances 21 of tubes 22 nearest pipe 34 than otherwise, and fluids 26 and 27 tend to pass through zone 20 without achieving a desired uniform distribution, so that individual tubes 22 contain differing compositions of fluids 26 and 27. Hence, this distribution arrangement of FIG. 3 is unsatisfactory for solving the problems faced in this present invention.

#What is required in a distribution system for achieving equal distribution of such fluids 26 and 27 (as respects intermixing and flow characteristics) to each of the plurality of tubes 22 in accord with the present invention is the establishment, in a zone 20 in a bottom chamber 33, of a uniform, mixed dispersion of fluid 27 in liquid fluid 26 flowing preferably upwardly in a manner such that the overall velocity profile across any transverse section of zone 20 in bottom chamber 22 is substantially flat and uniform (see FIGS. 1-3). The mixing should be sufficient to produce a composition which, in any unit volume 36 thereof, as shown in FIG. 4 across a transverse section of zone 20 in chamber 33 immediately below tube entrances 21, is substantially the same. It is sufficient for the size of a unit volume 36 to be about the same as that across the tube entrances 21, although the size of such a unit volume can be substantially smaller, because it is not necessary to achieve a higher degree of mixing to obtain uniform distribution to tubes 22 for purposes of the present invention.