Hydrocarbon partial pressure effect

Pressure effects are, in general, not significant in the range of commercial pyrolysis interests. For hydrocarbon partial pressures of 0.2 to 2.0 x 105 Pa, few differences are seen. When pressures are increased to the range of 50 to 100 x 105 Pa, however, the global rate constants sometimes double. 

Residence Time. The influence of residence time on yields is similar to that of hydrocarbon partial pressure, but smaller. In principle, unsaturated components increase slightly with shorter residence time, depending on the cracking severity. At the same time, saturated components and pyrolysis fuel oil (PFO) decrease. The quality of pyrolysis fuel oil also is influenced by residence time. For constant P E, the ratio of carbon to hydrogen in PFO becomes smaller with decreasing residence time, which has a positive effect on coking tendency besides other parameters. 

The effects of hydrocarbon partial pressure and residence time distribution are easily incorporated into the reaction model, when the reaction kinetics are mathematically described. Figures 3 and 4 show the examples of simulated results by use of the model. They clearly show that the effect of hydrocarbon partial pressure on the product distribution is larger than generally recognized and low pressure is preferable to obtain high liquid yield and that residence time distribution should be controlled as narrow as possible to reduce coke precursor(Ql) in the residual component. 

Figure 3. Effect of Hydrocarbon Partial Pressure on Product.

A negative partial pressure effect was observed in the oxidation of all the hydrocarbons. The potential decreases by about 70 mv per decade increase of pressure at constant current density. At constant potential, 8 log i/0 pH = 0.5. The usual Arrhenius temperature dependence was observed with an apparent activation energy of 22 kcal mole at the reversible potential, calculated by extrapolation from the Tafel region. Radiotracer studies showed that adsorption isotherm is Langmuirian, and that high coverages are obtained in the potential and concentration range studied. 

The two commercial coil designs just discussed have identical pyrolysis selectivity despite their differences in geometrical and process characteristics. The axial gas temperature and partial pressure profiles constitute the major differences. The effect of axial temperature and axial partial pressure profiles on pyrolysis reactor selectivity are taken into account in the definitions of average residence time and hydrocarbon partial pressure. Therefore, when pyrolysis coils of different geometries and thus different temperature and partial pressure profiles are com-... 

The effect of increased pressure drop per unit length has been demonstrated in the pyrolysis selectivity experiment described above. This experiment showed that the shorter residence time coil, i.e. Coil 1, because of the higher pressure drop, and therefore higher average hydrocarbon partial pressure, achieved the same selectivity as the larger diameter, longer residence time, lower partial pressure coil. 

For the steam, to a stripper to be effective, the oil must enter the stripper close to its bubble point. If the feed is sub-cooled, the stripping steam cannot reduce the hydrocarbon partial pressure enough to promote vaporization of the oil. This renders the steam ineffective. The concept is easily understood if we remember that the heat of vaporization for stripping comes from the oil itself and not from the steam. 

Estimating draw tray temperatures for vacuum operations is much more difficult than in atmospheric towers because of the greater relative effect of calculated internal reflux on hydrocarbon partial pressure. As good a rule as any is to assume a hydrocarbon partial pressure equal to 30 to 50 percent of the total pressure at any tray. Plot the assumed profile for the trayed section of the tower. 

NaCl, interact with the sulphur and vanadium oxides emitted from the combustion of technical grade hydrocarbons and die salt spray to form Na2S04 and NaV03- These conosive agents function in two modes, either the acidic mode in which for example, the sulphate has a high SO3 thermodynamic activity, of in the basic mode when the SO3 partial pressure is low in the combustion products. The mechanism of coiTosion is similar to the hot coiTosion of materials by gases widr the added effects due to the penetration of tire oxide coating by tire molten salt. 

Fig. 8. Effect of the partial pressure of carbon monoxide on normal to isoaldehyde ratio and conversion to propane. Reprinted with permission from Hydrocarbon Process, p. 112 (1970). Copyright by Gulf Publishing Company.

The main aim of the present work has been to study the effects of the direct factors (which determine the coking rate in steam reforming) on the length of the induction period of coking and various ways of catalyst pretreatment (without or with the initiation of coking at a relatively high partial pressure of hydrocarbon) on the steady-state rate of coking,... 

Moreover, the condensation side-reaction rate b much more heavily influenced by the hydrocarbon content of the reaction mixture than the rate of the primary reactions, which are substantially of the first order with respect to the reactants. A decrease in the partial pressure of the hydrocarbons, by dilution with steam, for example, reduces the overall reaction rate, but also helps to enhance the selectivity of pyrolysb substantially in favor of the light olefins desirecL Apart from thb specifically kinetic role, steam exerts a number of other beneficial effects ... 

In practice, industrial processes operate in the presence of catalysts, at above 600 C with a large adduct of steam, whose effect is to reduce the partial pressure of the hydrocarbons and also to slow down the formation of coke. Depending on the extent of this coking, the process may require operation in cles, with a frequency proportional to the amount of coke deposited. Table 6.1 gives typic examples of operating conditions and results obtained with several catalysts. 

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