Phase emulsions

Analysis of a method of maximizing the usefiilness of smaH pilot units in achieving similitude is described in Reference 67. The pilot unit should be designed to produce fully developed large bubbles or slugs as rapidly as possible above the inlet. UsuaHy, the basic reaction conditions of feed composition, temperature, pressure, and catalyst activity are kept constant. Constant catalyst activity usuaHy requires use of the same particle size distribution and therefore constant minimum fluidization velocity which is usuaHy much less than the superficial gas velocity. Mass transport from the bubble by diffusion may be less than by convective exchange between the bubble and the surrounding emulsion phase. 

The flow pattern of gas within the emulsion phase surrounding a bubble depends on whether the bubble velocity Ug is less than or greater than minimum fluidization velocity U . For Ubflow lines. For Ub> U , the much different case of Figure 4(B) results. Here a gas element which leaves the bubble eap rises much more slowly than the bubble, and as the bubble passes, it remms to the base of the bubble. Thus, a cloud of captive gas surrounds a bubble as it rises. The ratio of eloud diameter to bubble diameter may be written... 

In addition to this convective cross flow of gas from the bubble into the emulsion phase of the cloud, mass transfer also occurs by diffusion into the emulsion. 

The effectiveness of a fluidized bed as a ehemical reactor depends to a large extent on the amount of convective and diffusive transfer between bubble gas and emulsion phase, since reaction usually occurs only when gas and solids are in contact. Often gas in the bubble cloud complex passes through the reactor in plug flow with little back mixing, while the solids are assumed to be well mixed. Actual reactor models depend greatly on kinetics and fluidization characteristics and become too complex to treat here. 

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

Microspheres were prepared from carboxymethyl chitosan and alginate by emulsion phase separation. The encapsulated bovine serum albumin was... 

The bubbles play the role of the gas phase. The role of the liquid is played by an emulsion phase that consists of solid particles and suspending gas in a configuration similar to that at incipient fluidization. The quasi-phases are in cocurrent flow, with mass transfer between the phases and with a solid-catalyzed reaction occurring only in the emulsion phase. The downward flow of solids that occurs near the walls is not explicitly considered in this simplified model. 

Values for the various parameters in these equations can be estimated from published correlations. See Suggestions for Further Reading. It turns out, however, that bubbling fluidized beds do not perform particularly well as chemical reactors. At or near incipient fluidization, the reactor approximates piston flow. The small catalyst particles give effectiveness factors near 1, and the pressure drop—equal to the weight of the catalyst—is moderate. However, the catalyst particles are essentially quiescent so that heat transfer to the vessel walls is poor. At higher flow rates, the bubbles promote mixing in the emulsion phase and enhance heat transfer, but at the cost of increased axial dispersion. 

The emulsion phase approaches the performance of a CSTR with its inherent lower yield for most reactions. To make matters worse, mass transfer between the emulsion and bubble phases becomes limiting to the point that some of the entering gas completely bypasses the catalytic emulsion phase. The system behaves like the reactor in Example 11.5. 

Hollow and porous polymer capsules of micrometer size have been fabricated by using emulsion polymerization or through interfacial polymerization strategies [79,83-84, 88-90], Micron-size, hollow cross-linked polymer capsules were prepared by suspension polymerization of emulsion droplets with polystyrene dissolved in an aqueous solution of poly(vinyl alcohol) [88], while latex capsules with a multihollow structure were processed by seeded emulsion polymerization [89], Ceramic hollow capsules have also been prepared by emulsion/phase-separation procedures [14,91-96] For example, hollow silica capsules with diameters of 1-100 micrometers were obtained by interfacial reactions conducted in oil/water emulsions [91],... 

The fluidization quality significantly decreased when the reaction involving a decrease in the gas volume was carried out in a fluidized catalyst bed. In the present study, we carried out the hydrogenation of CO2 and used relatively large particles as the catalysts. Since the emulsion phase of the fluidized bed with these particles does not expand, we expected that the bed was not affected by the gas-volume decrease. However, we found that the fluidization quality decreased and the defluidization occurred. We studied the effects of the reduction rate of the gas volume and the maximum gas contraction ratio on the fluidization behavior. 

It is reported [1] that the fluidization quality was drastically decreased when the hydrogenation of CO2 was carried out in a fluidized catalyst bed (FCB). Recently, the phenomena occurring in the bed were directly observed [2] and it was found that the upper part of the emulsion phase was defluidized and this packed particles was lifted up through the column like a moving piston. 

In the case of a FCB, the gas volume decreases when the reaction involving a decrease in the volume is carried out at constant temperature and under constant pressure. If the gas in the emulsion phase cannot be compensated by the gas supply from bubbles, the emulsion phase is condensed and bubbles cannot rise through the emulsion phase. Finally, defluidization in the bed occurs. This part of the packed bed will be lifted up like a moving piston. 

In the case of a FCB with small particles, the emulsion phase expands [5, 6, 7] when the bed is fluidized. This would make the bed sensitive to the decrease in the gas volume in the emulsion phase. If this assumption is true, we can postulate that the fluidization quality is hardly affected by the gas-volume reduction when the particles, which induce a small emulsion phase expansion, are used. The emulsion phase expansion decreases with increasing particle size and density [6]. In the present study, therefore, the particles used were larger and heavier than that generally used in the FCB. We carried out the hydrogenation of CO2 in a... 

By considering the small region in the emulsion phase where the distribution of the gas concentration can be regarded as flat, the equation for a batch reactor can be adapted and the following relationship is finally obtained. 

Fig. 3 shows the emulsion phased expansion measured by the bed collapse method [10] under the reaction conditions. In this case, the value of a was 3.9. The expansion ratio when the bed was fluidized by only H2 shows that the emulsion phase slightly expanded, and that the ratio was not influenced by the temperature. On the other hand, when H2 and CO2 were supplied as fluidizing gases, the expansion ratio decreased with the reaction temperature when... 

Fig. 3. Effect of reaction temperature on the emulsion-phase expansion.

An alkoxylated fatty oil is used in a nonionic composition [1821]. The alkoxylated fatty oil has low solubility in the main emulsion phase. The process is used for breaking emulsions used in wellbore drilling fluids and in oil recovery. 

Phase Inversion The phase inversion of brine/oil/surfactant systems was established routinely by measuring solution conductivity employing a Jenway FWA 1 meter and cell. The process identifies the range over which a large decrease in conductivity occurs as the sytem under test is converted from an oil in water emulsion to a water in oil emulsion. Phase... 

Fernandez, P., Andre, V., Rieger, J. and Kuhnle, A. (2004) Nano-emulsion formation by emulsion phase inversion. Colloids and Surfaces A Physicochemical and Engineering Aspects, 251, 53-58. 

Because of the inadequacies of the aforementioned models, a number of papers in the 1950s and 1960s developed alternative mathematical descriptions of fluidized beds that explicitly divided the reactor contents into two phases, a bubble phase and an emulsion or dense phase. The bubble or lean phase is presumed to be essentially free of solids so that little, if any, reaction occurs in this portion of the bed. Reaction takes place within the dense phase, where virtually all of the solid catalyst particles are found. This phase may also be referred to as a particulate phase, an interstitial phase, or an emulsion phase by various authors. Figure 12.19 is a schematic representation of two phase models of fluidized beds. Some models also define a cloud phase as the region of space surrounding the bubble that acts as a source and a sink for gas exchange with the bubble. 

Design and development of an electro spray bioreactor was reported and its suitability for biodesulfurization applications was demonstrated [261], Mixing oil with water in large bioreactors requires significant energy input for classical impeller-based reactors. The electro spray bioreactor (ESB) was developed from an emulsion phase contactor... 

US5525235 [44] separating a petroleum containing emulsion phase liquid mixture, using wet filters. The liquid mixture contains a fossil fuel, an aqueous phase and a biocatalyst. The first filter is wetted with an agent miscible with the fossil fuel but immiscible with the aqueous phase. The second filter is wetted with a wetting agent miscible with the aqueous phase but immiscible with the fossil fuel. The mixture is then passed sequentially for each filter. The fossil fuel is recovered from the final filtrate and the biocatalyst is retained in the aqueous phase of the final retentate. 

Bubble Dynamics. To adequately describe the jet, the bubble size generated by the jet needs to be studied. A substantial amount of gas leaks from the bubble, to the emulsion phase during bubble formation stage, particularly when the bed is less than minimally fluidized. A model developed on the basis of this mechanism predicted the experimental bubble diameter well when the experimental bubble frequency was used as an input. The experimentally observed bubble frequency is smaller by a factor of 3 to 5 than that calculated from the Davidson and Harrison model (1963), which assumed no net gas interchange between the bubble and the emulsion phase. This discrepancy is due primarily to the extensive bubble coalescence above the jet nozzle and the assumption that no gas leaks from the bubble phase. 

The Davidson and Harrison (1963) model assumed there was no net exchange of gas between the bubble and the emulsion phase. The validity of this assumption was later questioned by Botterill et al. (1966), Rowe and Matsuno (1971), Nguyen and Leung (1972), and Barreto et al. (1983). The predicted bubble volume, if assumed no net gas exchange, was considerably larger than the actual bubble volume experimentally observed. 

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