Structure-Oriented Lumping

Quann, R.J. and S.B. Jaffe, Structure Oriented Lumping Describing the Chemistry of Complex Hydrocarbon Mixtures., Ind. and Eng. Chem., (accepted), 1992. 

Quann, R. J., and Jaffe, S. B., Structure oriented lumping Describing the chemistry of complex hydrocarbon mixtures, Ind. Eng. Chem. Res. 31, 2483 (1992). 

FIGURE 8.24 Molecular groups identified for use in structure oriented lumping. 

In recent years more detailed models were developed. Liguras and Allen [1989] described the conversion of Vacuum Gas Oil in terms of a relatively large number of pseudo-components, most of which are lumps in their own way. Klein et al. [1991] generated these pseudo-components from analytical characteristics using Monte-Carlo simulation. Instead, Quann and Jaffe [1992, 1996] and Christensen et al. [1999] in their Structure Oriented Lumping (SOL) expressed the chemical transformations by accounting for typical structures of the various types of molecules, without completely eliminating lumps and because of that, rate parameters that still depend upon the feedstock composition. 

Figure 3. Structure vectors and 22 structural increments defined in the structure-oriented-lumping (SOL) approach.

The optimization of the refinery performance for individual crude oil feedstocks requires the development of simulation and prediction models of the individual refinery processes. Such a model is Quann and Jaffe s Structure-Oriented Lumping. Individual hydrocarbon molecules are represented by this model, as vectors of incremental structural features that can describe the composition, reactions and properties of petroleum mixtures. The approach allows for the molecular modeling of all refinery processes. 

Structure-oriented lumping (SOL) is a leading example of the pathway-based models. Quann and JafFe [20,21,22] have developed a unique method for tracking molecules in the feed oil. The method tracks different compositional and structural attributes of a molecule (number of aromatic rings, number of nitrogen substituents, sulfur substituents, etc.) in a vector format Figure 4.6 shows typical vectors for some sample molecules. 

During the past 20 years, academic and industrial researchers developed composition-based kinetic models with hundreds or even thousands of lumps and pure compounds. The QSRC (quantitative stracture-reactivity correlation) and LFER (linear free energy relationship) lumping techniques are discussed in Chapter 20 by Professor Klein and Chapter 9 by Professor Mochida. The structure-oriented liunping (SOL) approach of Quann and Jaffe yields models rigorous enough for use in closed-loop real-time optimizers (CLRTO), which automatically adjust setpoints for commercial process units several times each day. ... 

One should, however, note that the two philosophies are not entirely the same. In Ref. 76, and in related works we argued that the lumps emerge from a more primordial discrete dynamical substratum, where the lumps have a specific internal structure. In the approach of Menger et al. (at least as far as we can see) they figure as the not-further-resolvable building blocks of spacetime if one approaches the so-called Planck regime discussed above, namely, from the continuum side. In other words, the former approach is more bottom-up-oriented while the latter one is more top-down. Such not-further-resovable scales of spacetime (where the ordinary continuum picture ends) was, of course, also speculated by quite a few other people, most notably Wheeler. 

If one has a randomly oriented sample, all angles between the applied field and the principal axes are populated. The P-NMR spectrum is thus the sum of spectra for all possible orientations. Rather than a featureless lump, the so-called powder spectrum has several distinctive features On and O33 define the outermost edges, and (T22 leads to a peak. The principal values of the chemical-shift tensor can be estimated directly from the spectrum, as shown in Fig. 2 the directions of the principal axes in the molecular system can only be found by studying a single crystal of known structure. Note the values given in Fig. 2A for (7, and <733—the powder spectrum spans some 190 ppm. Principal tensor components for the phosphate moiety in a variety of compounds have been compiled (Seelig, 1978). 

---