Diffusivity tables

In comparison with adsorptive/absorptive techniques for aroma recovery from bioconversions, the disadvantage of pervaporation is the fact that both sorption and diffusion determine the overall selectivity. While the sorption selectivity is very high (equal to that of adsorptive/absorption), the diffusion selectivity favours water owing to the simple fact that water is a smaller molecule than aroma compounds and thus sterically less hindered during diffusion (Table 19.1). The overall (perm)selectivity P=SD) is therefore lower than in strictly sorption controlled processes, although it is still favourable compared with that for evaporation. This shortcoming compares, however, with operational advantages of pervaporation as outlined before. 

Mechanistic investigations by Chapman and co-workers (99) indicated that these reactions occurred via a nonfluorescent singlet exciplex intermediate. While the rate constant for quenching of - -t5 by 2,3-dimethy 1-2-butene is slower than the rate of diffusion (Table 8), the limiting quantum yield for cycloaddition is 1.0. Thus, highly efficient exciplex cycloaddition may account for the absence of exciplex fluorescence, as in the case of t-1 photodimerization. Photochemical [2+2] cycloaddition reactions have also been observed to occur upon irradiation of the cyclic c-1 analogues diphenylcyclobutane (7) and diphenyl-vinylene carbonate (10) with 2,3-dimethyl-2-butene (96) however, the mechanistic aspects of these reactions have not been investigated. 

These compounds identified in meat diffusate (Table I) are only a small percentage of volatile compounds from heated meat or meat systems reviewed and discussed by MacLeod and Seyyedean-Ardibili (54), Bailey (55) and Shahidi et al. (56). 

The rates of diffusion of small molecules in the gels are usually less than in aqueous solutions. When there are no electrical effects, the gel structure mainly increases the path length for diffusion. Table 6.5 shows a few typical values of the diffusivity of some solutes in various gels. In some cases, the diffusivity of the solute molecule in pure water (wt% = 0) is given in Table 6.4. This shows how much the diffusivity decreases due to the gel structure. For example, at 293 K, Table 6.4 shows that the diffusivity of sucrose in water is 0.460 X 10 9 m2/s, while it is 0.107 X 10 9 m2/s in 5.1 wt% gelatin. This indicates a considerable decrease of 77%. 

Only a few Di values have been reported for micellar systems. Most of the data have been determined by using NMR relaxation and fluorescence methods D/ values range between 10 and 10 cm s (Table 2 [44]), intermediate between vesicles and homogeneous solution. Reported values for diffusion coefficients within micelle interiors are very similar to those measured for surface diffusion (Table 2 [45]). 

Gaseous diffusion. Table 14.3 lists gaseous diffusion plants in operation in 1977 and those then under construction, planned, or under consideration. Part 1 of Table 14.3 lists plants in operation at that time. The three large plants of the UJS. Department of Energy (DOE) had a capacity of over 17 million kg separative work units (SWU) per year when supplied with the maximum amount of electric power, 6100 MW, they could then utilize. 

The specific power of 1.80 MWh/kg SWU, with no allowance for process inefficiencies, is equivdent to 0.205 kW/(kg SWU/year). This may be compared with 0.168 for gaseous diffusion (Table 14.9), and 0.31 for the nozzle process (Fig. 14.23). The higher value for the nozzle process may be due to its expanding the heavy stream through the full pressure ratio. 

The Ru-Qt thermometer has the same theoretical advantages as Mt-Qt. The temperature coefficient of fractionation is large and solid-solution is minor. The greatest limitation of this system may be the rate of oxygen diffusion (Table 3). 

C at five different heating rates (0.5, 1, 5, 10, and 15°C/min). The thermal properties of the samples were then measured in x, y, and z directions with a Xenon flash diffusivity apparatus. The thermal conductivity of the samples was calculated from their thermal diffusivity. Table 2 lists the Z-direction thermal conductivity values for each graphitization heating rate and position within the furnace. From these data, it is clear that the thermal conductivity is directly related to the graphitization heating rate. A similar trend was observed in the crystal properties of the foams determined from X-ray diffraction (not shown here for brevity). However, it is not understood why there is a maximum at l°C/min. 

Comparative investigations between the conventional adsorption/desorption method and PFG NMR have been carried out with aromatics in zeolite NaX. It was pointed out in Table 2 that there is still some divergence between the data obtained by both methods on intracrystalline diffusion. Table 3 compares the values for Tjnira and Tjn,ra determined by the NMR methods [143,175,176]. H PFG NMR measurements of these systems are complicated by the rather short transverse nuclear magnetic relaxation times, which range over milliseconds and lead to mean errors up to 50%. However, as with the n-paraffins in NaX, there is no indication of a significant enhancement of Tjn,ra 0 comparison with Tin,ra° " as... 

Both facilitated transport systems and active transport mechanisms can be saturated, and the rates of transport are similar. In addition, both carrier-mediated transport systems have less transport capacity than channel-mediated transport or simple diffusion (Table 5.6). 

Surface diffusion tables 3.11.3.2.1 Thermal diffusion in vacuum 3.11.3.2.1.1 Intrinsic diffusion Table 4. Refractory metals on W. ... 

The decrease of the aggregation of surfactant particles in the comse of reaction is confirmed by light scattering studies. A study using the turbidity spectrum showed (Fig. 2.5) that the decrease of the colloid particle concentration occms in line with the decrease of the colloid particle size. The decrease of the particle size is also confirmed by the data from viscosity-diffusion (Table 2.3). 

Yang et al. (2001) studied PV properties of different zeolite-filled PDMS membranes. They reported that the incorporation of hydrophobic zeolites into PDMS enhances the permeation selectivity toward the VOCs, but decreases the permeation rate in the corresponding membranes. The decrease in the permeation rate results from the cross-linking effect of the zeolite particles and also from the increase in the diffusion path the zeolite particles act as solvent reservoirs in the sorption, but as obstacles for the permeation diffusion. Table 9.5 shows the flux and selectivity of filled and unfilled PDMS membranes in the PV of 1.23% EA-water mixture at 50°C. 

The mobile phases may be characterized by three key factors density, diffusivity and viscosity. Typical values of these properties regarding gases, supercritical fluids and liquids are given in Table 2.1. Let us first consider the densities. These reflect the solubilities of the analytes. The mobile phase in GC does not dissolve the analytes and as a consequence the analytes will have to pass through the column in a gaseous state, and that is the inherent limitation of GC. Nowadays there are GC columns that can withstand up to 600°C, but there are few analytes that are stable at those temperatures. In liquid chromatography (LC) the situation is different because here the mobile phase, by virtue of its density, transports the analytes through the separation column and there is no immediate need for elevated temperatures. However, there is a price to pay for the increase in analyte solubility, and that is a drastically reduced diffusivity (Table 2.1). 

When the kinetics of the final polymerization of higher methacrylates are compared with that of methyl methacrylate, the most Important difference is the size of the molecule and thus its diffusibility. Table 2 presents a summary of the monomers investigated and provides information on the glass transition temperatures measured by DSC, the molar volumes, and the final conversions achieved after 2 hours at temperatures 5K above T. In Figure 8... 

Diffusion. Table 3.1-217 gives only one value for self diffusion of iridium but further information may be obtained from Landolt-Bdrnstein [1.238]. 

Diffusion. Table 3.1-217 gives some values for self diffusion of Ru. 

Ionic Mobility and Diffusivity, Table 1 Ion transport properties at infinite dilution in water at 25 °C and 1 atm [5] ... 

The computer package Microsoft Excel 7.0 was applied for the nonlinear parameter estimation to minimise the squares of the residuals. The higher values (/5> 1) demonstrate that mainly the initial period of the release process slows down and refer to parallel running processes, such as disintegration, diffusion, with a rate close to that of the dissolution. In this case these shape parameter values refer to the parallel running processes such as drug dissolution and diffusion (Table 2). 

The value of the terms fSy (for 0> 5/3) or Q.(xj)fiy (for 4>critical value 0.05 for very exothermic reactions and strong limitations by pore diffusion (Table 4.7.1). For industrial practice the influence of internal heat transfer can be neglected. This can also be demonstrated by an inspection of coke combustion (Example 4.7.1). 

Solubility and diffusivity were also compared for membranes without and with CNT loading. The results shown in Table 8.26 indicate that diffusivity decreased by incorporating CNTs. This is consistent with the incorporation of closed-ended CNTs that behave as impermeable filler. The solubility for N2 increased and as a result there was no change in permeability statistically. Thus, incorporation of CNT lowered the He permeability (Table 8.25) and hindered the diffusion path of N2, lowering its diffusivity (Table 8.26). 

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