Downstream processing of ethanol After alcoholic fermentation is complete, which primary unit operation is used to recover ethanol from the fermentation broth?

Introduction / Context:
Fermentation produces a dilute ethanol solution mixed with water, cells, and residual solubles. The first major recovery step concentrates ethanol for beverages or fuels.

Given Data / Assumptions:

• Ethanol is volatile relative to water and many broth components.
• We need a process that separates based on volatility, not solids removal alone.

Concept / Approach:
Distillation exploits differences in relative volatility of ethanol and water to concentrate ethanol. While solids removal steps (centrifugation/filtration) may precede or accompany processing, they do not recover ethanol by themselves.

Step-by-Step Solution:

Verification / Alternative check:
Process flow diagrams universally show distillation as the core concentration step, followed by dehydration (e.g., molecular sieves) for fuel-grade ethanol.

Why Other Options Are Wrong:

• Centrifugation/filtration: remove cells or particulates but do not selectively recover ethanol.
• Cell disruption: irrelevant; ethanol is extracellular.
• Spray drying: used for solids (e.g., yeast powder), not ethanol concentration.

Common Pitfalls:
Confusing cell harvest steps with product recovery; overlooking azeotrope behavior which requires dehydration after distillation for anhydrous ethanol.

Final Answer:
Distillation