Mass balance case studies

However, conducting a complete LCA is very time consuming. Fortunately, simple mass balancing may already indicate most relevant requirements for action. This was illustrated by one case study concerning a pharmaceutical intermediate (Scheme 5.1). Compared to LCA, the system boundaries of mass balancing are relatively narrow. For instance, the case study focuses on the chemical reaction and does not take into account the production of substrates. In this respect, a look at two reduction reactions of the synthetic routes via B and via C is worthwhile (Scheme 5.1). 

Mass balances of four case studies were evaluated. Additionally, an LCA is considered for the last case study. Case study 1 and Case study 2 are academic and include a comparison between alternative synthesis protocols. In the industrial Case study 3 and Case study 4, a comparison of the steps of a scale up was possible. 

In Case study 2, mass balancing is used to compare a biocatalytic (a) and a chemical catalytic (b) enantioselective epoxidation reaction (Scheme 5.3). 

These findings support the general usefulness of efforts to increase yield and solvent recycling rates, as documented in Case study 4 (see also Geisler et al. [9]). However, producing an LCA requires a substantially higher effort for data acquisition as compared to mass balancing. 

The scope to increase resource efficiency during scale up was shown to be large in the case studies assessed here. Therefore, efforts to implement methods such as mass balancing or LCA would pay off soon, since this would help to fully tap optimization potentials concerning ecology and economy. 

In the previous discussion of the one- and two-compartment models we have loaded the system with a single-dose D at time zero, and subsequently we observed its transient response until a steady state was reached. It has been shown that an analysis of the response in the central plasma compartment allows to estimate the transfer constants of the system. Once the transfer constants have been established, it is possible to study the behaviour of the model with different types of input functions. The case when the input is delivered at a constant rate during a certain time interval is of special importance. It applies when a drug is delivered by continuous intravenous infusion. We assume that an amount Z) of a drug is delivered during the time of infusion x at a constant rate (Fig. 39.10). The first part of the mass balance differential equation for this one-compartment open system, for times t between 0 and x, is given by ... 

In this case study, steady-state mass balance models are applied for critical loads calculation for the heavy metals. 

The second case study corresponds to an existing pyrolysis reactor also located at the Orica Botany Site in Sydney, Australia. This example demonstrates the usefulness of simplified mass and energy balances in data reconciliation. Both linear and nonlinear reconciliation techniques are used, as well as the strategy for joint parameter estimation and data reconciliation. Furthermore, the use of sequential processing of information for identifying inconsistencies in the operation of the furnace is discussed. 

In the sorption experiments of Icopini et al. (2004), the measured isotopic contrast between Fe(II)aq and the goethite starting material was -0.8%o after Fe(II) had sorbed to the surface over 24 hours in this case, the isotopic fractionation between sorbed Fe(II) and Fe(II)aq is not the 0.8%o measured difference, but is approximately +2.1%o based on an inferred 8 Fe value for the sorbed component as calculated from Fe mass balance (Fig. 4), as was noted in that study. Measured differences in Fe isotope compositions between ferric oxide/hydroxide and Fe(II)aq during dissimilatory Fe(III) reduction and photosynthetic Fe(II) oxidation have been proposed to reflect fractionation between soluble Fe(II) and Fe(III) species, where the soluble Fe(III) component is postulated to be bound to the cell and is not directly measured (Beard et al. 2003a Croal et al. 2004). In the case of dissimilatory Fe(III) reduction, assuming a static model simply for purposes of illustration, if 50% of the Fe in a pool that is open to... 

In other words, it is used to verify that the specificity of the levels 1-3 method is maintained throughout development. In cases where the orthogonal method shows the primary method to be deficient, the orthogonal method is validated and is used as a secondary method in conjunction with the primary method. Additional new methods may also need to be developed to address specific issues encountered in stress studies, such as when mass balance is not observed. 

The primary endpoint of the toxicokinetic studies is the concentration-time prohle of the substance in plasma/blood and other biological fluids as well as in tissues. The excretion rate over time and the amount of metabolites in urine and bile are further possible primary endpoints of kinetic studies, sometimes providing information on the mass balance of the compound. From the primary data, clearance and half-life can be derived by several methods. From the excretion rate over time and from cumulative urinary excretion data and plasma/blood concentration measured during the sampling period, renal clearance can be calculated. The same is the case for the bUiary excretion. 

A number of field studies have been carried out in which individual nitrogen compounds have been measured simultaneously with NO, to determine whether the individual species add up to the measured NO. In some cases there is indeed an approximate mass balance, whereas in others the sum of the individual species is less than the total measured NOr This discrepancy is often referred to as missing NO. Compounds that may contribute to the shortfall, when it exists, are discussed in Chapters 6.E.3 and 11.A.4. 

Recovery levels for individual organic compounds were, as expected, less than the values predicted by using the membrane solute rejections. Differences in the actual recovery and the theoretical recovery were partially due to adsorption losses. Mass balance analysis still indicated a deficiency in some cases. Rectification of the inconsistencies in these data was complicated by the limited water solubility of compounds chosen for study, the necessity of using a cosolvent in spiking, and, in particular, the limitations of the analytical procedures at these extremely low concentrations. 

Trapping Device Experiments. The system used to collect the organic compounds extracted from the aqueous stream was, in most cases, a series of glass U-tubes held at —76 °C. That temperature represented a practical lowest limit to prevent deposition of solid carbon dioxide. During the course of this program, it became evident that, for many compounds, complete mass balances were not being achieved. The trapping system appeared to be a likely source of such losses because many of the compounds studied had a finite vapor pressure at —76 °C. An effluent C02 stream saturated with these... 

Richardson WL, Smith VE, Wethington R (1983) In Mackay D, Peterson S, Eisenreich SJ, Simmons MS (eds) Dynamic mass balance of PCB and suspended solids in Saginaw Bay - A case study in physical behavior of PCBs in the Great Lakes. 

If one or more chemical reactions are at equilibrium within the system, we can still set up the set of Gibbs-Duhem equations in terms of the components. On the other hand, we can write them in terms of the species present in each phase. In this case the mole numbers of the species are not all independent, but are subject to the condition of mass balance and to the condition that , vtpt must be equal to zero for each independent chemical reaction. When these conditions are substituted into the Gibbs-Duhem equations in terms of species, the resultant equations are the Gibbs-Duhem equations in terms of components. Again, from a study of such sets of equations we can easily determine the number of degrees of freedom and can determine the mathematical relationships between these degrees of freedom. 

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