Phenol distribution coefficient temperature

Figure 6. Phenol distribution coefficient as a function of temperature at constant density.

The distribution coefficients of phenol obtained for the aqueous system as a function of pressure and temperature using pure supercritical carbon dioxide are shown in Figure 2. The values increase proportionately with pressure for each isotherm, but decrease overall at higher temperatures. At 298 K, reproduction of the distribution coefficients yielded an average standard deviation of 1.5 %. At 323 K the data axe somewhat more scattered due to fluctuations in the temperature caused by control. Figure 3 shows the effect of various concentrations of benzene and methanol used as entrainers in supercritical carbon dioxide at 17.3 and 27.6 MPa at 298 K. Methanol, a commonly used entrainer in studies concerning solid organics, was found to have little effect on the distribution of phenol in the aqueous system. The presence of a small amount of benzene, however, did increase the distribution coefficient up to 50 % over those obtained with pure carbon dioxide. 

Phenol was successfully extracted from water using pure supercritical carbon dioxide at pressures up to 31 MPa for two isotherms 298 and 323 K. The distribution coefficient increased with increasing pressure, but decreased with increasing temperature. This is expected since increasing the temperature severely drops the carbon dioxide density and hence the solubility of the phenol in it. Increased volatility at the higher temperature is not sufficient to off-set the density effect, since phenol has a low vapor pressure. Benzene was foimd to be a suitable entrainer since its solubility in water is very small and it enhances the distribution of phenol into the supercritical phase. The presence of methanol was found to have no effect. Since methanol is polar and completely soluble in water, it favors the aqueous phase and therefore does not change the characteristics of the supercritical phase. Others have found that the distribution of short chain alcohols between water and supercritical carbon dioxide highly favors the aqueous phase (ifl). 

FIGURE 15.2-5 Equilibrium distribution coefficients vs. temperature for extraction of phenol and catechol from dilute aqueous solution into a solvent mixture of 25% w/w TOPO in DIBK. Stoichiometric ratio 2.5 mol TOPO/mol solme.M... 

The various phenols in the untreated gas liquor may total anything from 0.5 to 1.5 gm./l. for coke-oven operation to as high as 12 gm./l. for low-temperature carbonization, with phenol itself usually accounting for the majority of the total. Phenol has the poorest distribution coefficient (2 to 2.5 for light oil as solvent) and is the most difficult to extract. Removal of total phenols is usually carried out to the extent of 95 to 99 per cent for coke-oven gas liquors. 

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