2.2 Volatility, vapor pressure, and condensation dynamics

Here’s a focused, detailed explanation of volatility, vapor pressure, and condensation dynamics, tailored for essential oil extraction and hydrodistillation courses:

1. Volatility

  • Definition: Volatility is a measure of how readily a substance vaporizes at a given temperature.
  • Relevance in Essential Oils:
    • Essential oils consist of compounds like monoterpenes, sesquiterpenes, aldehydes, and esters, which have different volatilities.
    • Highly volatile compounds vaporize first and are collected early during distillation.
  • Factors Affecting Volatility:
    1. Molecular weight: Lower molecular weight → higher volatility.
    2. Intermolecular forces: Weaker forces → easier to vaporize.
    3. Temperature: Higher temperatures increase kinetic energy → more molecules enter vapor phase.

Example: Linalool (found in lavender) is more volatile than sesquiterpenes like caryophyllene (found in cedarwood), so linalool distills earlier.

2. Vapor Pressure

  • Definition: Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature.
  • Relationship with Distillation:
    • A compound vaporizes when its vapor pressure equals the ambient pressure.
    • In steam distillation, the total vapor pressure is the sum of water and essential oil vapor pressures. This allows the oil to vaporize at temperatures lower than its normal boiling point, protecting heat-sensitive compounds.
  • Key Points:
    • High vapor pressure → more volatile → easier to distill.
    • Low vapor pressure → less volatile → may require longer distillation or higher temperature.

Formula:
[
P_{total} = P_{water} + P_{oil}
]
Where ( P_{total} ) = atmospheric pressure, ( P_{water} ) = vapor pressure of water, ( P_{oil} ) = vapor pressure of oil.

3. Condensation Dynamics

  • Definition: Condensation is the phase change from vapor back to liquid when vapor loses heat.
  • In Essential Oil Extraction:
    • Vapor containing water and oil passes through a condenser.
    • Heat is removed → molecules lose kinetic energy → condense.
    • Due to immiscibility and density differences, oil separates from water in the collection vessel.
  • Factors Affecting Condensation Efficiency:
    1. Cooling rate: Faster cooling → quicker condensation.
    2. Surface area: Larger condenser surface → more efficient heat transfer.
    3. Vapor composition: Mixtures with higher oil content may require careful control to avoid emulsions.
  • Dynamics:
    • Condensation is energy removal-driven, dependent on latent heat of vaporization.
    • Effective condensation ensures high yield and purity of essential oil.

4. Practical Implications for REHD / Steam Distillation

ConceptApplication
VolatilityDetermines which compounds are extracted first; guides fractionated collection.
Vapor PressureAllows extraction at lower temperatures via co-distillation; protects thermolabile compounds.
CondensationEfficient condensers maximize oil recovery and minimize water loss; prevents emulsion formation.

Visual/Infographic Concept for Training

  1. Volatility: Molecules escaping liquid → vapor (size/color indicating volatility).
  2. Vapor Pressure: Diagram showing oil + water vapor pressure combining to reach atmospheric pressure.
  3. Condensation: Vapor entering condenser → liquid droplets forming → oil-water separation.
  4. Include labels showing temperature, pressure, and density differences.

If you want, I can create a clear, visually appealing infographic showing volatility, vapor pressure, and condensation dynamics in essential oil distillation, which would be perfect for REHD training slides.

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