Mixer phase ratio

Aldehyde linearity is high (ca. 90%). Sufficient N-methyl-pyrrolidone (NMP ca. 40%w) and some water (1 -2%w) are applied to achieve a one-phase system in the reactors. After reaction, water is added in a mixer (phase ratio 1 1 v/v), followed by efficient phase separation in a settler, with virtually all catalyst in the NMP/water layer. The crude product layer is subjected to a multi-stage water extraction to remove residual NMP and catalyst, and a final treatment over a silica-bed to reduce Rh leach levels from 0.2 ppmw to 0.02 ppmw. The recycle catalyst layer (in NMP/water) is dried in two steps, to evaporate water and achieve the low water concentrations required for one-phase reaction, and then recycled to the reactors. Water is recycled, from evaporators, via water extraction, to the mixer. The flexibility of this process with respect to alkene carbon number seems excellent good performance has been found for Cs-C aUcenes [61]. 

The exhaustive U, Pu extraction step is best achieved in pulsed columns rather than in mixer settlers in order to keep the contact time lower at the very high radiation level. This operation is expected to produce as its main product a HAW raffinate that is virtually free of Pu (and Np, U) a scrub appears therefore superfluous and would dilute only the HAW. In order to attain still a good extraction efficiency within a few stages, A/O phase ratios < 3 should be avoided. This ratio corresponds to a TBP saturation by heavy metals of about 18%. Considerable amounts of Zr are therefore co-extracted, being however present essentially as inactive isotope. Either a complexing or a reductive stripping is advisable in order to keep the aqueous flow small and the acidity sufficiently high to avoid hydrolysis of Zr. 

Advances in development resulted in the Oldshue-Rushton and Kiihni extractors [43, 45]. The Kiihni extractor has shrouded turbine impellers for agitation to promote radial discharge characteristies (Fig. 2.19). The stator discs are made from perforated plates and the residence time can be varied by changing the distance and the hole diameter of these plates. These extractors can be used in the dispersion or mixer-settler mode. Therefore, they can be adapted to extreme phase ratios and reach high... 

Sizing of the mixer is based upon providing sufficient agitation and sufficient residence time to allow equilibrium to be approached, and thus will depend upon the flows to be processed as well as the physical properties of the two liquids. Since some extractions actually involve a chemical reaction, the time of contact can be very important. If, for reasons of improved mass transfer, it is desired to disperse the high flow phase, it may be necessary to recycle some of the low flow phase to keep an appropriate phase ratio in the mixer different than the feed flow ratio. 

Stirred tanks mixer settler (including Lurgi) superficial hquid velocity, 0.00015 to 0.004 m/s area per unit volume 400 to 10,000 mVm. Product of the density difference with the interfacial tension (Mg/m, mN/m) >4 and number of theoretical stages needed >3. Usually about one theoretical stage per unit. Rarely build more than 5 stages can handle high phase ratios. 

Here we will pay attention to the gas-liquid reactors. The reaction takes place usually in the liquid phase. Three main types of contact may be distinguished following the phase ratio (1) gas bubbles dispersed in liquid, (2) liquid drops dispersed in gas, and (3) gas and liquid in film contact. In the first category we may cite gas-liquid bubble columns, plate or packed absorption columns, agitated tanks, agitated columns, static mixer columns, pump-type reactors. As examples in the second class we may name spray columns or liquid injection systems. The third category can be used with very exothermic reactions or viscous liquids. 

High phase ratio 1. Perforated plate column 2. Mixer-settler ... 

Drop size too large shear insufficient/rpm too low/faulty selection of impeller/ power too low/baffles missing/surface wettability wrong for the dispersed phase/order of feeding phases into mixer wrong (discontinuous phase sent first)/phase ratio incorrect/impeller not in the continuous phase at startup/sur-face tension higher than expected. 

Under equilibrium extraction condition the solvent mixer was loaded in a two stage continuous counter current mode as determined by McCabe Thiele plot using O/A phase ratio of 1 1 (Fig. 5). The raffinate contains only 11 ppm of cobalt along with 30.3 g/L Ni. The loaded organic... 

Static mixing of immiscible Hquids can provide exceUent enhancement of the interphase area for increasing mass-transfer rate. The drop size distribution is relatively narrow compared to agitated tanks. Three forces are known to influence the formation of drops in a static mixer shear stress, surface tension, and viscous stress in the dispersed phase. Dimensional analysis shows that the drop size of the dispersed phase is controUed by the Weber number. The average drop size, in a Kenics mixer is a function of Weber number We = df /a, and the ratio of dispersed to continuous-phase viscosities (Eig. 32). 

TPEs from blends of rubber and plastics constitute an important category of TPEs. These can be prepared either by the melt mixing of plastics and rubbers in an internal mixer or by solvent casting from a suitable solvent. The commonly used plastics and rubbers include polypropylene (PP), polyethylene (PE), polystyrene (PS), nylon, ethylene propylene diene monomer rubber (EPDM), natural rubber (NR), butyl rubber, nitrile rubber, etc. TPEs from blends of rubbers and plastics have certain typical advantages over the other TPEs. In this case, the required properties can easily be achieved by the proper selection of rubbers and plastics and by the proper change in their ratios. The overall performance of the resultant TPEs can be improved by changing the phase structure and crystallinity of plastics and also by the proper incorporation of suitable fillers, crosslinkers, and interfacial agents. 

Additional experiments in a loop reactor where a significant mass transport limitation was observed allowed us to investigate the interplay between hydrodynamics and mass transport rates as a function of mixer geometry, the ratio of the volume hold-up of the phases and the flow rate of the catalyst phase. From further kinetic studies on the influence of substrate and catalyst concentrations on the overall reaction rate, the Hatta number was estimated to be 0.3-3, based on film theory. 

The types of equipment used, which range from stirred tanks and mixer-settlers to centrifugal contactors and various types of columns, affect both capital and operating costs [9]. In the decision to build a plant, the choice of the most suitable contactor for the specific situation is most important. In some systems, because of the chemistry and mass transfer rates involved, several alternative designs of contacting equipment are available. In the selection of a contactor, one must consider the capacity and stage requirements solvent type and residence time phase flow ratio physical properties direction of mass transfer phase dispersion and coalescence holdup kinetics equilibrium presence of solids overall performance and maintenance as a function of contactor complexity. This may appear very complicated, but with some experience, the choice is relatively simple. 

Vessels for the separation of two immiscible liquids usually are made horizontal and operate full, although some low rate operations are handled conveniently in vertical vessels with an overflow weir for the lighter phase. The latter mode also is used for particularly large flows at near atmospheric pressures, as in the mixer-settler equipment of Figure 3.19. With the usual L/D ratio of three or more, the travel distance of droplets to the separated phase is appreciably shorter in horizontal vessels. 

A stand-alone mixer requires the mass transfer/reaction to be completed within the mixer. If the gas flow rate matches the stoichiometry of the liquid phase, all the gas should be dissolved and reacted at the end of the mixer. This generally involves very high volumetric ratios between gas and liquid. If there is excess gas, there will be some gas at the mixer outlet, which needs to be separated. 

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