Groundwater at a contaminated site contains the following substances:
• Fine clay particles (average diameter ≈ 1 µm)
• Dissolved benzene (boiling point 80 °C; non-polar)
• Dissolved acetic acid (boiling point 118 °C; polar; forms hydrogen bonds with water)
• Natural yellow dye molecules (non-volatile, highly polar, molar mass ≈ 1200 g mol⁻¹)
Engineers must design an on-site treatment train that produces (1) potable water with contaminant concentrations below detection limits, (2) benzene collected as a recyclable solvent, and (3) a concentrated dye solution suitable for further processing. Minimal chemical additives may be used, and any thermal step must operate below 100 °C to conserve energy.
(a) Rank the four listed substances in order of increasing strength of intermolecular interactions with liquid water. Justify your ranking.
(b) Devise a multi-stage separation scheme that fulfills the treatment objectives under the stated temperature constraint. For each stage, specify the driving physical principle and the form in which each substance exits that stage.
(c) Explain, on the molecular level, why your chosen sequence successfully isolates benzene without significant loss of acetic acid.
(d) Evaluate the energy efficiency of your scheme by identifying which step offers the greatest opportunity for heat recovery and describing how that heat could be reused elsewhere in the process.