Interaction parameters reforming

The greatest barrier in the application of the Multicomponent Fowler-Guggenheim or Bragg-Williams Lattice gas model to, a practical situation like Pet-reforming, is the absence of experimental interaction parameters. In the simulations of the earlier sections, representative values were used. In general, for an n component system, we need to fix n(n+l) / 2 interaction parameters of the symmetric W matrix (91 for a 13 component Model ). Mobil has used successfully a 13 lump KINPTR model(5), which essentially uses a Hougen-Watson Langmuir-Hinshelwood approach. This results in a psuedo-monomolecular set of reactions, which is amenable to matrix analysis. 

The last step before building the reformer flowsheet is to verify the interaction parameters (Figure 5.45). If we had chosen a correlation-based approach (Grayson-Streed, etc.), we do not have to examine the interaction parameters. Since we choose an equation of state approach, we must make sure that the binary interaction parameters for the equation-of state are meaningful. In Aspen HYSYS, the interaction parameters for defined components (such as methane. 

The frequent breaking and reforming of the labile intermolecular interactions stabilizing the reversed micelles maintain in thermodynamic equilibrium a more or less wide spectrum of aggregates differing in size and/or shape whose relative populations are controlled by some internal (nature and shape of the polar group and of the apolar molecular moiety of the amphiphile, nature of the apolar solvent) and external parameters (concentration of the amphiphile, temperature, pressure) [11], The tendency of the surfactants to form reversed micelles is, obviously, more pronounced in less polar solvents. 

The direct detection of a complex from an equilibrium mixture is certainly the most obvious evidence of specific molecular interactions between components. Electrophoresis of an equilibrium mixture is an easily performed experiment, enabling the determination of complex formation parameters. When the dissociation kinetics of the complex is slow, the complex gives rise to a new peak in the electropherogram, in addition to the peaks of the free component molecules. Since the separation of the free components prevents the reformation of the complex inside the capillary, the complex peak should decrease in size during electrophoresis. The extent of this decrease depends on dissociation kinetics and separation time. In view of that fact, short analysis times, as obtained in CE, are required to detect less stable complexes, which would hardly be detected using previous formats of electrophoresis with longer separation times. 

All these factors are functions of the concentration of the chemical species, temperature and pressure of the system. At constant diffu-sionai resistance, the increase in the rate of chemical reaction decreases the effectiveness factor while al a constant intrinsic rate of reaction, the increase of the diffusional resistances decreases the effectiveness factor. Elnashaie et al. (1989a) showed that the effect of the diffusional resistances and the intrinsic rate of reactions are not sufficient to explain the behaviour of the effectiveness factor for reversible reactions and that the effect of the equilibrium constant should be introduced. They found that the effectiveness factor increases with the increase of the equilibrium constants and hence the behaviour of the effectiveness factor should be explained by the interaction of the effective diffusivities, intrinsic rates of reaction as well as the equilibrium constants. The equations of the dusty gas model for the steam reforming of methane in the porous catalyst pellet, are solved accurately using the global orthogonal collocation technique given in Appendix B. Kinetics and other physico-chemical parameters for the steam reforming case are summarized in Appendix A. 

The model was applied in order to investigate the influence of various parameters on the performance of FBMR with oxygen addition. Although the results showed that autothermal operation can be achieved by using approximately 0.3 O2/CH4 feed ratio, the interaction between the different parameters is quite complex. For instance, in methane reformers an important parameter is the steam/carbon ratio. However, when feeding oxygen, the steam becomes also a product of the oxidation reaction and this makes the prediction of the reactor behaviour a bit more complicated. Furthermore, an important conclusion of the work is that oxygen addition reduces the coke formation and consequently the catalyst deactivation. 

For simplicity, the factors X -x are standardized and therefore the lower and upper values are defined as — 1 and 1, respectively. The repHcation experiments are carried out using the mean value for each factor. The main effects, the two-factor and the three-factor interactions, can easily be calculated. The experimental results are presented for the superheated steam temperature at the inlet of the reformer as a function of different parameter combinations in Table 22.6. 

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