Literature unit-level models

We can divide the literature on FCC modeling into two categories kinetic and unit-level models. Kinetic models focus on chemical reactions taking place within the riser or reactor section of the FCC unit, and attempt to quantify the feed as a mixture of chemical entities to describe the rate of reaction from one chemical entity to another. In contrast, unit-level models contain several submodels to take into account the integrated nature of modem FCC units. A basic unit-level model contains submodels for the riser/reactor, regenerator and catalyst transfer sections. 

Table 5.5 Summary of unit-level models reported in the literature. 

Aspen HYSYS Petroleum Refining includes a method to convert limited feed information (distillation curve, density, viscosity, refractive index, etc.) into kinetic lumps for use in the unit-level FCC model. In this section, we present an alternative method based on data and methods available in the public literature. We extend the work by Bollas et al. [52] to infer the kinetic lump composition from limited process data. This method uses techniques to normalize the distillation curve, cut the distillation curve into boiling-point lumps, and infer the composition of the each of these boiling-point lumps. We have developed all of these techniques into spreadsheets using Microsoft Excel. These spreadsheets are available in the DVD accompanying this text... 

Because of the number of unit-level and kinehc models available in the literature and commercially, it is impossible to prescribe a single cahbrahon method that wiU work for ah models and methods. However, there are significant common features in ah of the models to allow for general recommendahons. These recom-mendahons form a simple workflow to manage the large number of parameters that many occur in a many models. 

In terms of analyzing the contemporary literature, it is probably advisable to consider as overly attractive any interaction energies that have not been corrected for basis set superposition error. It is emphasized that overly attractive refers in this context to the correct result with a given theoretical model, not to the experimental value as a reference. Results computed at the SCF level with a counterpoise correction can probably be taken as the most accuracy one is likely to achieve with a particular basis set without correlation. There remains some difference of opinion concerning correlated results, but counterpoise corrections should probably be taken as more valid than those with no such corrections at all. There is also some lingering question as to the precise details of properly correcting BSSE when there are more than two identifiable units involved in the interaction . ... 

The most common methods used for pharmaceutical pK values are based on pH measurements, Eqs. (3-8). Thus, they cannot be interpreted with greater accuracy than 0.02 pKa unit [see the definition in Section 2.1, Eq. (1)]. This level of precision and accmacy should always be the aim in determining pK values for inclusion in the drug sciences literature. Potentiometric titrations [Eqs. (3-4)] are often performed with this level of accmacy, primarily for compounds with either a single ionization step or for multiple ionizations with >4 log units between the pKa values. The careful use of precise pH meters (e.g., the series of Beckman Research models, or the corresponding Radiometer, Orion, or Metrohm instruments) for the determination of pH data means that reproducibility for replicate measurements may be rather better than 0.02. In the author s experience, these instruments may be calibrated with a reproducibility of 0.002 pH imit, which can be maintained (with proper temperature control and exclusion of CO2) for at least 8 h. This does not imply accuracy of 0.002 pH unit, which is not possible according to the current definition of pH. Spectrophotometric [Eq. (5)] and solubility-pH dependence [Eqs. (7-8)] methods are potentially capable of similar accuracy, but often do not give results better than 0.05 pKa unit, due to the inevitable inclusion of additional sources of error from the absorbance or concentration measurements. 

The supply chain configuration concept model at the generic level is shown in Fig. 7.4. These concepts are identified according to the literature review reported in Chap. 3 and represent the most commonly used concepts. From the structural perspective, it defines types of units and types of links used in supply chains. In... 

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