Separation of phenol and formaldehyde from industrial wastes. Modelling of the phenol extraction equilibrium

BACKGROUND: The manufacture of phenolic resins causes the generation of hazardous wastes composed of high concentrations of phenol and formaldehyde together with low molecular weight polymers in lower concentrations. The separation of phenol, mainly from synthetic aqueous solutions, has been successfully achieved by means of solvent extraction, 8 - 17 but few references tackle the treatment of industrial wastes because of their complex behaviour. This work aims at the experimental and theoretical analysis of the recovery of phenol from industrial aqueous wastes using CYANEX 923 as organic extractant. RESULTS: Aqueous condensates containing phenol in the concentration range 40–280 g L^?1, and formaldehyde in the range 30–110 g L^?1, were contacted with CYANEX 923 to analyse the influence of feed pH and of concentration of the selective extractant on the extraction equilibrium. Concerning the pH of the feed phase, it was observed that for values higher than 8.0 a decrease in the distribution ratio of phenol between the organic and the aqueous phases took place. Additionally, caustic conditions promoted formaldehyde degradation reactions in the feed phase. Phenol recovery from the loaded organic extractant was obtained by stripping with NaOH solutions. Best results were obtained working with a CYANEX 923 concentration 0.6 mol L^?1. CONCLUSION: Analysis of the experimental data established the optimum conditions of the selective extraction of phenol from industrial condensates. A mathematical model based on the extraction reaction of 2 moles of phenol per mole of Cyanex 923 described successfully the experimental results. The equilibrium parameter was estimated from the fitting of experimental data to the mathematical model obtaining a value of K = 750.9 (mol L^?1)^?2. Copyright © 2010 Society of Chemical Industry