Selective mass balance

Table I. Selected mass balance equations (after Wilderer P.A., et al (2001).

As discussed earlier, the admissible compositions may be selected as the lean-phase composition at some particular instant of time, or any other situation which is compatible with stoichiometry and mass-balance bounds such as Eqs. (8.20) and (8.21). Let us aihitrarily select the admissible composition of to be zero. 

The competitive adsorption isotherms were determined experimentally for the separation of chiral epoxide enantiomers at 25 °C by the adsorption-desorption method [37]. A mass balance allows the knowledge of the concentration of each component retained in the particle, q, in equilibrium with the feed concentration, < In fact includes both the adsorbed phase concentration and the concentration in the fluid inside pores. This overall retained concentration is used to be consistent with the models presented for the SMB simulations based on homogeneous particles. The bed porosity was taken as = 0.4 since the total porosity was measured as Ej = 0.67 and the particle porosity of microcrystalline cellulose triacetate is p = 0.45 [38]. This procedure provides one point of the adsorption isotherm for each component (Cp q. The determination of the complete isotherm will require a set of experiments using different feed concentrations. To support the measured isotherms, a dynamic method of frontal chromatography is implemented based on the analysis of the response curves to a step change in feed concentration (adsorption) followed by the desorption of the column with pure eluent. It is well known that often the selectivity factor decreases with the increase of the concentration of chiral species and therefore the linear -i- Langmuir competitive isotherm was used ... 

In the case of NO reduction by propene, the only detectable reaction products were CO2, N2, N2O and H2O. The overall mass balance was found to close within 5% as observed by a combination of GC and mass spectroscopic analyses. Figure 3 shows the effect of varying the catalyst potential on the rate of production of CO2, N2, N2O and on the selectivity towards nitrogen formation, Sn2- As can be seen from this figure, both the CO2 and N2... 

The notions of mass balance, selectivity and conversion (see Figure 1.6) need to be added to the idea of yield when chemists consider a chemical transformation, particularly if this consideration takes place in the context of pollution prevention or green chemistry. ... 

Figure 1.7 Conversion, selectivity and mass balance for a reaction to produce methyl chloride from methanol.

If he selects the still pressure (which for a binary system will determine the vapour-liquid-equilibrium relationship) and one outlet stream flow-rate, then the outlet compositions can be calculated by simultaneous solution of the mass balance and equilibrium relationships (equations). A graphical method for the simultaneous solution is given in Volume 2, Chapter 11. 

However, if he selects an outlet stream composition (say the liquid stream) instead of a flow-rate, then the simultaneous solution of the mass balance and v-l-e relationships would not be necessary. The stream compositions could be calculated by the following step-by-step (sequential) procedure ... 

Transfer rate constants are postulated as shown in Table II, following the approach described by Mackay and Paterson (4). The air-water value selected was lower than is generally used since it appears that a low value is necessary to reconcile observed air and water concentration, and mass balances as discussed in a recent review of PCB behavior in the Great Lakes (Mackay et al. U3)). 

The catalytic tests were carried out in a fixed bed micro-reactor at atmospheric pressure at 540 °C. The feed composition was 2.5 vol.% of propane, 5 vol. % of ammonia and 5 vol.% of oxygen. The weight of catalyst in the reactor was varied in order to keep the number of Fe ions in the reactor constant (9 pmol of Fe atoms). Conversion, selectivity and yields were calculated on the basis of mass balance in dependence on the time of stream. 

Different levels of description of the rate expressions, rw and tp can be selected when using a simple mass balance as expressed in Equation (5.10). Matos and de Sousa (1996) propose a temperature-dependent, however, DO nondependent value for rw ... 

Vaclavek, V., and Loucka, M. (1976). Selection of measurements necessary to achieve multicomponent mass balances in chemical plants. Chem. Eng. Sci. 31,1199-1205. 

For carrier-based ISEs, the selectivity is determined by the composition of the membrane. Eq. (18a.l8) describes the relationship between the ion selectivity and the membrane composition of cation-selective membranes by using charge balance and mass balance considerations [69]. 

Even if HPLC is chosen as the main stability indicating method, CE will be useful as orthogonal technique, especially in cases where the reason of mass balance deviations is unclear. In addition, due to its increased peak capacity and selectivity in comparison to HPLC, the detection of possible enantiomers, stereoisomers, and position isomers, having the same molecular weight and equal/similar spectra as the drug substance may be separated by a secondary CE method. 

Small hospital in a small urban catchment area a local mass balance analysis of micro- and macropoUutant loads can provide useful information about the contribution of the different users. Environmental risk assessment of the expected final effluent and analysis of the characteristics of the local receiving water body will guide selection of the advanced treatment sequence (MBR, ozone, UV). 

All these arguments require a single reactant A on which to base the calculation of selectivity. For more complex situations we can stiU determine how the selectivity varies with conversion in PFTR and CSTR, but calculation of the selectivity requires complete solution of the mass-balance equations. 

For the achievement of mass balances in intrazeolite photooxygenation reaction, >80%, loading levels of 0.1-0.3 adsorbed molecules per zeolite supercage have been successfully used in the past. However, the recent observation by Pace and Clennan, that replacing the solvent hexane with peril uorohexane was very crucial for the efficiency of the reaction, allowed the zeolite medium to be used for preparative scale photooxygenation reactions (500 mg of alkene), without loss of the product selectivity or the reduction of the mass balance. 

Next, the applications have to be validated and placed into standardized forms. Validation should consist of two steps. First, simulated data sets of aerosol properties should be generated from pre-selected source contributions as did Watson in his simulation studies of the chemical mass balance method. These data should be perturbed with the types of uncertainties expected under field conditions. The types of sources and their contributions predicted by the receptor model application should be compared with the known source model values and the extent of perturbation tolerable should be assessed. 

When these CCH conditions were applied to o-iodonitrobenzene (1), cr iodoaniline (2) together with iodoaniline (4) and nitrobenzene (1) were obtained in the yields indicated in Scheme 1 (88% mass balance), which corresponds to a 62% selectivity for the formation of o iodoaniline (3). Under the same conditions, the ECH of o-iodonitrobenzene (2) gave aniline (90% yield) as the sole product. There was complete hydrogenolysis of the C-I bond (no selecti vity). Thus, in basic medium (pH 12.5), CCH method is much more selective than ECH. However, in weakly acidic medium (pH 3, pyridine.HCl buffer), it has been reported that ECH at a RCu cathode in methanol-water 95 5 (v/v) gave o-iodoaniline in a 97% yield (1, 3). 

The CCH and ECH of / -cyanonitrobenzene (7) at pH 12-13 gave the three products shown in Scheme 3 with low selectivities for the formation of p-cyanoaniline (8) respectively of 8-13% (82% mass balance) and 7% (65% mass balance). In neutral medium, the ECH of 7 has been reported to be very efficient, giving only p-cyanoaniline (8) in a quantitative yield (1,3). 

We then perform the kinetic measurements. We select pressures, p, flows, F, temperatures, T, and inlet concentrations XH,...,Xni We select a key component r and measure the exit concentration, Xre, of this component. The exit concentration of all other components may then be determined from a mass balance, the inlet concentrations and... 

Since two independent reactions exist, a mass balance must be written for each of two independent species. We select these as CO and C02. Note that i = 1 refers to CO and i = 2 refers to C02 in the following. 

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