Distillation Arrhenius Coefficients

Statistical evaluation of the peak maximum temperatures of the distillation bitumens results in means with coefficients of variation V = 1.01 % maximum. When using these means in the calculation, the following average values of the Arrhenius coefficients are found ... 

Table 4-80 Arrhenius coefficients and conversion for DSC pyrolysis in 1 bar argon Distillation bitumen...

Table 4-92 Average values of the Arrhenius coefficients and the conversion for the pyrolysis of distillation bitumens in 10 bar methane.

The straight lines for the distillation bitumens and their colloid components in the plot of half life time, versus temperature run almost parallel, because the differences in the Arrhenius coefficients are small (Fig. 4-75). 

Even the corresponding peak temperatures of the blown bitumens show very small variances in the tests in 10 bar methane and also permit the calculation of statistical means. The resulting coefficients of variation are 3.0 % maximum. This is also true for the colloid components, except for the dispersion medium of the two bitumens 85/40 (sample III) and 85/25 (sample IV). Here again a weight loss caused by distillation even occurs under pressure with the consequence of low values for the activation energy and frequency factor. Only the data of the other three samples was included in the statistics. The average values of the Arrhenius coefficients calculated in this manner and the means of the conversion aie shown in Table 4-93. 

Comparison of the means shows that there is a significant difference in the Arrhenius coefficients for distillation and blown bitumens and their colloid components. The conversions only differ for the dispersion medium whereas the bitumens, the petroleum resins, and the asphaltenes do not differ in the conversions, either in 1 bar argon or in 10 bar methane. 

Table 4-103 Arrhenius coefficients of the oxidation of distillation bitumen in 7 bar air. 

The experiments in 10 bar methane show that neither the origin nor the composition affect the results for the distillation bitumens and for their colloid components. No correlation was found for the Arrhenius coefficients with analytical data. The average values of these coefficients for the colloids components showed only small differences, but the conversions show considerable differences. The conversion may be correlated with the H/C ratio in a similar way to the correlation of the H/C ratio with the residues /f600 and / 800 in thermogravimetry (Fig. 4-49). Decreasing H/C ratios, i.e. increasing aromacity, lead to a decrease of the conversions (Fig. 4-80). In this case the data of the blown bitumens also fit the regression line very well. 

The blown bitumens do not exhibit peaks in the evaporation range when the system pressure is inereased to 10 bar, except for the dispersion medium of the bitumens 85/40 and 85/25, which demonstrate only an evaporation loss. The Arrhenius coefficients of the blown bitumen showed greater differences than those of the distillation bitumens. In the plot of half life time, versus the inverse Kelvin temperature, the distillation bitumens and their colloid components follow almost parallel lines, whereas the graphs for the blown bitumens and their colloid components diverge. The plot of versus 1 000/T shows the residence time required to achieve a conversion of fifty percent, at a preset reaction temperature, or which temperature is required to achieve a preset conversion at a preset residence time. This information is valuable in thermal processing, for example in selection of the crack severity of the visbreaking process. 

For the study of the process, a set of partial differential model equations for a flat sheet pervaporation membrane with an integrated heat exchanger (see fig.2) has been developed. The temperature dependence of the permeability coefficient is defined like an Arrhenius function [S. Sommer, 2003] and our new developed model of the pervaporation process is based on the model proposed by [Wijmans and Baker, 1993] (see equation 1). With this model the effect of the heat integration can be studied under different operating conditions and module geometry and material using a turbulent flow in the feed. The model has been developed in gPROMS and coupled with the model of the distillation column described by [J.-U Repke, 2006], for the study of the whole hybrid system pervaporation distillation. 

The experiments were performed in argon at 1 bar pressure and a gas flow rate of 5 cmVmin. Four of the 25 samples (samples 18, 23-25) show only one maximum in the temperature range from 275 °C to 400 °C, and this represents a distillation process. Fourteen samples (samples 2-13, 20-22) possess only one maximum each in the temperature range from 450 °C to 550 °C, which clearly represents a pyrolysis reaction. The remaining six samples (samples 1, 14-17, 19) show two maxima, one each in the distillation range and the pyrolysis range. The coefficients of the Arrhenius equation, activation energy E and frequency (pre-exponential) factor A are presented in Table 4-37 ... 

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