Mass transfer kinetic

Main axis experimental conversions ( ) intrinsic kinetic model (solid line) kinetic model + mass transfer kinetics (dashed line). Secondary axis variation of computed k,o with flow rate. 

Flow Rate Efficiency Flow rates may be slightly lower than in other HPLC methods to maximize resolution and improve mass transfer kinetics. 

Miyabe, K., Cavazzini, A., Gritti, F., Kele, M., Guiochon, G. (2003). Moment analysis of mass-transfer kinetics in Ci8-silica monolithic columns. Anal. Chem. 75, 6975-6986. 

Using three-dimensionally structured adsorbent with a large number of uniform gas channels, the limitations of mass transfer kinetics and fluidization of the conventional beaded sorbents may be removed. Such structured adsorbents have been described in... 

Tonon RV, Baroni AF and Hubinger MD. 2007. Osmotic dehydration of tomato in ternary solutions influence of process variables on mass transfer kinetics and an evaluation of the retention of carotenoids. J Food Eng 82 509-817. 

Lazarides, H.N., Katsanidis, E., and Nickolaidis, A. 1995. Mass transfer kinetics during osmotic preconcentration aiming at minimal solid uptake. J. Food Engineer. 25, 151-166. 

Sacchetti, G., Gianotti, A., and Dalla Rosa, M. 2001. Sucrose-salt combined effects on mass transfer kinetics and product acceptability Study on apple osmotic treatments. J. Food Engineer. 49, 163-173. 

Efficiency the organic modifier can be used to adjust solvent selectivity as normally practiced in reversed-phase chromatography. Lowers mobile-phase viscosity and improves solute mass-transfer kinetics. 

For adsorption limited by mass transfer kinetics, the educt should be significantly less retained than the most strongly adsorbed product. 

W. Piatkowski, D. Antos, F. Gritti and G. Guiochon, Study of the competitive isotherm model and mass transfer kinetics for a BET binary system. J. Chromatogr.A 1003 (2003) 73-89. 

Another approach to preparing a stable reversed phase with fewer residual silanols is the use of polyfunctional silanes of the type R2SiX2. These react to form a polymeric stationary phase that shields the siloxane bonds and restricts access to residual silanols. Polymer phases have higher carbon loads and are typically more retentive than monomeric phases. However, they are more difficult to synthesize reproducibly and may exhibit batch-to-batch variability in their properties. They also exhibit poorer mass transfer kinetics and so provide poorer efficiency than monomeric phases. 

Concerning the structure of dispersed CLAs, the model originally proposed by Sebba [57] of a spherical oil-core droplet surrounded by a thin aqueous film stabilized by the presence of three surfactant layers is, in our opinion, essentially correct. However, there is still little direct evidence for the microstructure of the surfactant interfaces. From an engineering point of view, however, there is now quantitative data on the stability of CLAs which, together with solute mass transfer kinetics, should enable the successful design and operation of a CLA extraction process. 

The apparent dispersion coefficient in Equation 10.8 describes the zone spreading observed in linear chromatography. This phenomenon is mainly governed by axial dispersion in the mobile phase and by nonequilibrium effects (i.e., the consequence of a finite rate of mass transfer kinetics). The band spreading observed in preparative chromatography is far more extensive than it is in linear chromatography. It is predominantly caused by the consequences of the nonlinear thermodynamics, i.e., the concentration dependence of the velocity associated to each concentration. When the mass transfer kinetics is fast, the influence of the apparent axial dispersion is small or moderate and results in a mere correction to the band profile predicted by thermodynamics alone. 

A sample similar to that shown in Figure 11.10 was used as the feed in displacement chromatography separations [36], For these experiments, the authors employed a longer (105 mm) column of the same diameter as the analytical column. Displacement chromatography on 10 mg of a melittin sample was carried out at two temperatures to demonstrate the advantage of higher temperature on mass transfer kinetics in the separation (Figure 11.11). 

Chen YB, Kele M, Sajonz P, Sellergren B, Guiochon G. Influence of thermal annealing on the thermodynamic and mass transfer kinetic properties of D- and L-phenylalanine anilide on imprinted polymeric stationary phases. Anal Chem 1999 71 928-938. 

Both the mass transfer kinetic parameters (diffusion in the phases, D, D j, surface renewal frequency, s) and chemical reaction rate constants (kg, kj) strongly influence enhancement of the absorption rate. The particle size, dp, the dispersed liquid holdup, e and the partition coefficient, H can also strongly alter the absorption rate [42-44,46,48]. Similarly, the distance of the first particle from the gas-liquid interface, 6q is an essential factor. Because the diffusion conditions are much better in the dispersed phase (larger solubility and, in most cases, larger diffusivity, as well) the absorption rate should increase with the decrease of the (5g value. 

In principle, highly specific and tailor-made CSPs for certain (chiral) analytes, guests, are generated. However, the chromatographic performance of such sorbents is usually relatively low, which is associated with slow mass-transfer kinetics due to rather small pore volumes and microcavities within the polymeric network. 

The shape of the front is given by the spreading of the front around the point S. The spreading depends mainly on toxic mass transfer kinetics between gas and solid phases. Thus numerous parameters can be considered air flow rate, size of the toxic molecule, pore sizes of the carbon, carbon grain diameter. With large pores and small grains, the mass transfer from gas to carbon is very fast the spreading... 

Solutions of the combined equations of mass transfer, kinetics and electrochemical transport expressed in terms of the limiting current, i generally are of the form... 

Micro-encapsulation, as obtained by continuous SAS techniques, is a physical process, guided both from thermodynamics and kinetics. The entire process involved is not clear. Mass-transfer kinetics and thermodynamic equilibria related to polymer-particle precipitation from a solution expanded by supercritical CO2 are currently being investigated [9,10], Many empirical observations are now available, suggesting that for a given polymeric solution, both pressure and temperature play an important role in determining the precipitated particles morphology. 

It is interesting that, for reaction mixtures consisting of molecules with dimensions close to the cross-sections of the catalyst pores (as in the case of butyl alcohol dehydration in HZSM-5), the reacting mixture may be envisaged as a liquid with dimensions less than three. This, in turn, introduces additional factors with respect to the unanalyzed peculiarities of mass-transfer kinetics in the catalyst pores. 

Several papers have shown that isotherm nonlinearity is indeed an important factor in MIP HPLC [31-35]. The consequences will be dealt with in the next sections. Mass transfer kinetics, on the other hand, has not yet been sufficiently studied. Its role has been proven in some cases [36] but it is not known how general these observations are and how important the effects are generally. 

Sajonz P et al (1998) Study of the thermodynamics and mass transfer kinetics of two enantiomers on a polymeric imprinted stationary phase. J Chromatogr A 810(1—2) 1—17... 

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