Gibbs phenol hydrogenation

Table 5.3 shows the enthalpy and Gibbs free energy of formation of species at 289.13 K and 1 atm [3]. On this basis standard AH and AG[J can be determined, as shown in Table 5.4. The hydrogenation of phenol is highly exothermic, while the dehydrogenation of cyclohexanol is moderately endothermic. The conversion...

The study of chemical equilibrium can detect thermodynamic constraints on the achievable conversion and selectivity. In this section we make use of the Gibbs free-energy minimization method available in Aspen Plus [9], We assume that both cyclohexanone and cyclohexanol are products. The curves in Figure 5.2 show the evolution of the phenol equilibrium conversion, yield and selectivity with the ratio hydrogen/phenol at temperatures of 180, 200, 220 °C and a pressure of 3 bar. 

Fig. 25. Plot of proton affinities of substituted pyridines (PA) versus their hydrogen-bonding Gibbs free-energy change (—AGh) for the pyridine-t-phenol complex reaction (75JA854 78JPC1268).

Early studies were carried out at the liquid gas interface [22, 23]. Castro et al. [24] studied the adsorption of / -propyl-phenol from aqueous solutions at the air interface as a function of phenol concentration in the bulk. They showed that the square root of the second-harmonic intensity plotted against bulk phenol concentration followed a Langmuir isotherm with a standard Gibbs energy of adsorption equal to -24.3 kJmol Similar results were obtained for other alkylphenols and alkylanilines. In other work with phenols, the orientation of phenol at the water air interface was determined by studying the phase of the xfl component of the susceptibility. As expected, the OH was oriented toward the water phase [25] so that it could participate in the hydrogen-bonded structure of water. The same conclusion was reached for / -bromophenol and -nitrophenol. 

This suggestion is supported by the fact that the de-rm-butylation of the more weakly intra-molecularly hydrogen-bonded p-rt rt-butylcalix[5]arene is very rapid even in the absence of phenol, while that of the more strongly intramolecularly hydrogen-bonded p-rert-butyl-calix[4]arene is very sluggish Gibbs, C. G. Gutsche, C. D. unpublished observation. 

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