Solventless extraction/stripping of phenol using trioctylphosphine oxide impregnated hollow fiber membranes – Experimental & modeling analysis

Abstract

Abstract Trioctylphosphine oxide (TOPO) was impregnated in polypropylene hollow fiber membranes by soaking the membranes first with TOPO containing dichloromethane, and subsequent evaporation of dichloromethane from the membranes. The resulting extractant impregnated hollow fiber membranes (EIHFM) recorded a 60% increase in weight from 0.48 g to 0.77 g. Further evidence of TOPO impregnation was obtained by visualizing TOPO deposition within the membrane walls through scanning electron microscopy. Extraction of 200–2700 mg/L phenol by the EIHFMs was characterized by high uptake rate and capacity, and equilibrium was attained within 1–3 h of contact. Stripping using 0.2 M sodium hydroxide was effective and EIHFM performance remained stable during 10 repeated cycles of extraction and stripping. The mass transfer kinetics of phenol was examined using pseudo-first-order, pseudo-second-order and intraparticle diffusion models, while the distribution equilibrium was modeled using Langmuir, Freundlich, Temkin and Redlich–Peterson isotherms. A kinetics model was also developed based on steady state resistance-in-series approach. The overall mass transfer coefficient was determined and diffusion through the boundary layer was found to be the rate limiting step. The effects of feed phenol concentrations and flow rates on extraction performance of the EIHFMs were simulated, and excellent correlation was obtained between the experimental and the simulated results. These results indicate that the TOPO-based EIHFMs can be used for an effective, sustainable and a relatively solventless extraction of phenol.