Abstract
Pseudo-hydroxide extraction of sodium hydroxide from aqueous solution using four alkyl phenols of nearly identical molecular weight in 1-octanol at 25°C was examined to understand the effect of alkyl substituents. The order of extraction strength among the four alkyl phenols tested was 4-tert-octylphenol > 3,5-di-tert-butylphenol > 2,4-di-tert-butylphenol > 2,6-di-tert-butyl-4-methylphenol. A good correlation with phenol pKa was observed, indicating that extraction strength is determined by phenol acidity, as modified by steric effects in proximity to the phenol -OH group. The effective partition ratios (Peff) of two phenols from 1M NaOH solution were determined, showing that the phenols remain predominantly in the 1-octanol phase even when converted to their sodium salts. However, the hydrophobicity of the tested phenols may not be sufficient for process purposes. The equilibrium constants for the governing extraction equilibria were determined by modeling the data using the program SXLSQI, supporting the cation-exchange extraction mechanism. The proposed mechanism consists of two simple sets of equilibria for a. Ion -pair extraction to give Na+OH- ion pairs and corresponding free ions in 1-octanol the phase and b. Cation exchange by monomeric phenol molecules (HAs) to form monomeric organic-phase Na+A- ion pairs and corresponding organic-phase ions.
| Original language | English |
|---|---|
| Pages (from-to) | 387-405 |
| Number of pages | 19 |
| Journal | Solvent Extraction and Ion Exchange |
| Volume | 24 |
| Issue number | 3 |
| DOIs | |
| State | Published - 2006 |
Funding
This research was sponsored by the Environmental Management Science Program, Office of Science, U.S. Department of Energy, under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC. Support for H.-A.K. under the Postdoctoral Fellowship Program of Korea Science & Engineering Foundation (KOSEF) is gratefully acknowledged; the participation of H.-A.K. was made possible by an appointment to the Oak Ridge National Laboratory Postgraduate Program administered by the Oak Ridge Associated Universities. The authors thank Peter V. Bonnesen and Nancy L. Engle for providing compounds and Lætitia H. Delmau and Tamara J. Haverlock for providing assistance with experiments and data manipulation. Thanks are also extended to Dr. Reza T. Dabestani for assistance with UV-Vis measurements.
Keywords
- Alkyl phenols
- Alkyl substituents
- Equilibria
- Equilibrium modeling
- Pseudo-hydroxide extraction
- SXLSQI
- Sodium hydroxide