An industrial plant must remove phenol from an aqueous waste stream (25 °C

CHEMISTRY · Multi-part · A Level · Chemistry · Chromatography · Chromatography

Problem

An industrial plant must remove phenol from an aqueous waste stream (25 °C, pH 7) prior to discharge. Three candidate organic solvents are being evaluated for a liquid–liquid extraction process. Relevant data are summarized in the table.

Property	Toluene	Methyl tert-butyl ether (MTBE)	Chloroform
Dielectric constant (ε)	2.4	6.0	4.8
Distribution coefficient for phenol, $K_D\,(\text{phenol})$ (defined as $[\text{phenol}]_{\text{org}} / [\text{phenol}]_{\text{aq}}$ )	12	18	40
Normal boiling point (°C)	111	55	61
Qualitative toxicity rating*	Moderate	Low	High

*Relative occupational toxicity based on permissible exposure limits. Answer the following questions. (a) Rank the three solvents in order of expected single-stage extraction efficiency for phenol removal from highest to lowest, citing the appropriate quantitative parameter. (b) Identify and discuss two operational advantages and two potential disadvantages of using chloroform relative to MTBE in this extraction application, referencing data from the table. (c) Recommend one solvent for large-scale use, providing a justified argument that balances extraction efficiency, solvent recovery (via distillation), and worker safety considerations.

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