Paraffin activity coefficient

Figure 3. Solvent selectivity as a function of activity coefficient of paraffin...

The costs of separating paraffin-olefin mixtures by extractive distillation are greatly affected by the solvent selectivity, the paraffin activity coefficient, and the solvent volatility they depend mostly upon solvent characteristics. For a solvent to be effective to separate key components A and B, the solvent must have a high value of y A/y B while it must also have a low y°V Further, the solvent vapor pressure should be lower, but not several orders of magnitude lower, than that of the less volatile hydrocarbon. 

The value of k was obtained by curve-fitting experimental infinite dilution activity coefficients of paraffins, olefins, and aromatics in several polar solvents. The value of k for each hydrocarbon group is given in Table IV. The values for Ai are taken from plots (28). The method for calculating r4 is also available (28). 

A solution is ideal if it satisfies the ideal-solution law. No real solution is rigorously ideal, but solutions of similar substances approach ideal-solution behavior as the similarity increases. Solutions of xylene isomers, for example, deviate from ideal-solution law by about 1% at the maximiun. Close members of the same homologous series are often assumed to be ideal. It is not unusual to calculate mixtures of paraffin hydrocarbons with the ideal-solution equation. Ideal-solution law is the basis for ideal K values often used in industry. However, ideal-solution law is of great value in another way, and that is to provide a basis for introducing a correction factor, known as the activity coefficient. 

Treybal (1963, p. 108) has illustrated ways of estimating i2 by estimating the different activity coefficients y2i, yi2> yii Mtd 722- the system consists of alkyl benzene (i = 1), paraffin (i = 2), ethylene glycol or furfrual (solvent) and n-heptane (feed phase). The solubility-parameter-based approach using relation (4.1.34f) may also be employed. 

Stepanova (1970) worked at pressures up to 150 kg/cm and at f°C = 0,20, 40 and 60°C. Henry s law constants were given, and it was stated that activity coefficients deviated less from unity the higher the bp of the paraffinic hydrocarbon. 

This example has shown how the procedures developed in earlier chapters can be used effectively for modeling. The reaction system has seventeen participants olefin, paraffin, aldehyde, alcohol, H2, CO, HCo(CO)3Ph, HCo(CO)2Ph, and nine intermediates. "Brute force" modeling would require one rate equation for each, four of which could be replaced by stoichiometric constraints (in addition to the constraints 11.2 to 11.4, the brute-force model can use that of conservation of cobalt). Such a model would have 22 rate coefficients (arrowheads in network 11.1, not counting those to and from co-reactants and co-products), whose values and activation energies would have to be determined. This has been reduced to two rate equations and nine simple algebraic relationships (stoichiometric constraints, yield ration equations, and equations for the A coefficients) with eight coefficients. Most impressive here is the reduction from thirteen to two rate equations because these may be differential equations. 

On the basis of the simplified (in the mathematical meaning) equation of Fig. 33, we can identify a calculation logic all lumping coefficients can be broken down into a product of two terms describing the respective free enthalpies of the reactive paraffins and activated complexes involved.22 These two terms are calculated irrespective of the number of carbon atoms and the number of branches. The calculation is performed using recursive series and is therefore extremely fast (approximately two minutes for a C30 network limited to eight branches) this is discussed in Paragraph VI.B.2 below. 

The properties of fluids under supercritical conditions are considered ideal for extracting substances from exhausted activated carbons. Two supercritical fluids are of particular interest, carbon dioxide and water. Carbon dioxide has a low critical temperature of 304 K and a moderate critical pressure of 73 bar, while water has a critical temperature of 647 K and a critical pressure of 220 bar. The character of water at supercritical conditions changes from one that supports only ionic species at ambient conditions to one that dissolves paraffins, aromatics, gases and salts [65]. These supercritical fluids exhibit densities similar to those of liquids (high solvent strengths) and diffusion coefficients similar to those of gases (excellent transport characteristics), enabling them to effectively dissolve and/or desorb contaminants from the carbon surface and to easily enter/exit even the smallest pores and carry away any... 

An attempt to correlate the kinetic parameters of the pyrolysis reaction with analytical data was only partly successful. A fairly high coefficient of correlation r was found for the relation of the activation energy E with the concentration of paraffin bonded carbon (CP) in the samples ... 

The reaction kinetic constants activation energy E and frequency factor A, can only be correlated with the concentration of paraffinic carbon, CP (from structural group analysis) with the concentration of dispersion medium (fiom colloid analysis) and with the H/C ratio (from elemental analysis). These functions show correlation coefficients of an acceptable magnitude. Examination of the correlation of the concentration of maltenes revealed a similar tendency but with very low coefficients of correlation. It is well known that the dispersion medium contains the highest concentration of chemical bonds, which can be cracked under the chosen reaction conditions [4-20]. In the pyrolysis experiments from distillation residues, about 92 % of the dispersion medium was converted, whereas conversion of the petroleum resins was only 83 %, despite the fact that the kinetic coefficients are of nearly the same magnitude for the two components. 

When rubber swelled in benzene (49), or when paraffin (50 was absorbed by cured rubber and by rubber gum, the positive temperature coefficients of the sorption velocity suggested that in these and other organic solids vapours are sorbed by processes of activated diffusion. The occurrence of activated diffusion has already been established for gas-rubber (52), cellulose, -bakelite and similar systems (Chap. IX). In liquids also, diffusion constants (53) may be expressed by the equation D = although the values of E are usually smaller. 

The possibility that the spreading coefficient of PDMS oils is modified by the addition of hydrophobic particles had been explored by Povich [209]. Here the initial spreading coefficient for PDMS was shown to slightly decrease upon the addition of hydrophobed silica (despite the effectiveness of this silica in promoting the antifoam behavior of the oil). Povich [209] attributed this to adsorption of oil-soluble surface-active impurities on the silica. Hydrophobed silica has also been shown to be without significant effect on the spreading behavior of a liquid paraffin [43,71]. 

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