Internal mass transfer stability

Carulite 300 ) in SCH2O at 400 C, 230-300 bar and a residence time of approximately 25 However, TOC analysis of the liquid effluent indicated that deep oxidation only reached 90%. Neither external nor internal mass transfer was experimentally measurable. Catalyst stability changed during the first two hours of operation as the conversion dropped by approximately 20% and was then stable for another 6 hours at 75% quinoline conversion and 65% TOC removal. 

Maximum stability is attained when saturation of the adsorbed surfactant layer is reached. In the case of high-volume fraction at a specific surfactant concentration, if the adsorbed layer is unsaturated, the emulsion stability decreases. In a low-volume fraction case, if the specific surfactant concentration is too high, emulsion stability is also decreased. Therefore, while an increase in surfactant concentration may increase the stability of the internal phase, the absolute stability of the ELM may be decreased [88]. Carrier Concentration Mass transfer rates can be increased by increasing the carrier concentration [41], however, increasing the carrier concentration usually increases swelling and lowers the emulsion stability [33,108]. Other studies have found limits to the carrier concentration where further increases do not lead to an increase in extraction rates as the mobility of the carrier is stifled due to an increase in viscosity [34,41]. 

The simplest mode of LM operation available is a batch reactor. The LM emulsions containing enzymes or cells are kept agitated in a vessel by using impellers. Periodic samples of external aqueous phase can be taken to monitor the reaction rate it is much more difficult to monitor the conditions in the internal aqueous phase. Impeller speed becomes an important parameter in batch operation, as it determines the size of the emulsion globules and therefore influences the emulsion stability and the mass-transfer resistance (46). 

Abnormal regions C and B also exhibit low-stability emulsions, a feature that is consistent with the fact that the emulsion type, and thus the interface curvature, is opposite to the one favored by the fomtulation effect. Since multiple emulsions are often made in these regions, a closer look is warranted. For instance, a multiple Wi/O/Wi emulsion i.s found in the C" region. W represents the most internal phase, i.e.. the water dnqtlcts that are located inside the oil drops. It may be considered that the principal" or outside" 0/W2 emulsion has the W,/0 inside" emulsion as internal phase. Since the W,/0 inside emulsion matches the expected type from formulation effects, it is certainly stable, whereas the outside emulsion is not. Thus, such a W,/0/W emulsion would quickly decay in a two-layer system, consisting of a W. phase and an oil layer that would actually be a W /0 emulsion, which is expected to be quite stable if the formulation is sufficiently away from optimum. This means that such unstable" multiple emulsions do not necessarily yield a quick and complete phase separation unless the formulation is q>propriate. e.g.. near-optimum. This feature could be useful for applications dealing with controlled release or capture through mass transfer. 

Enhanced diffusion of liquid and vapor moisture Coincidental temperature and mass concentration gradients Internal pressure gradient as an additional mass transfer driving force Stabilized material temperature at or below the liquid boiling point... 

Rohatgi, U.S., Duffey, R.B., 1998. Stability, DNB, and CHF in natural circulation two-phase flow. International Communications in Heat and Mass Transfer 25, 161—174. 

First, a single wire problem will be considered as an introduction. It brings out essential features of the stability problem and is similar in many respects to the more familiar stability problem with a CSTR. A simple and yet realistic case of negligible internal heat transfer and external mass transfer resistances will also be treated. The general problem will then be analyzed in a limited form for the case of unit Lewis number (Le) appearing in Eq. 8.27. This considerably simplifies the problem and yet the result can be extended to a certain extent to the general case of arbitrary Lewis numbers. Readers interested in more details on stability can refer to the book by Aris (1975) and the review by Luss (1977), from which the subsequent sections are derived. 

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