Theoretical Distillation Model: Exploring a Baseline Distillation Model With Refractometers

Distillation is a time-honored process used to separate components based on differences in their volatilities. In this post, we delve into a theoretical model for distillation, referred to as the Baseline Distillation Model, which serves as a foundational understanding of the behavior of various components during the distillation of a typical fermented wash.

Components in the Wash

A typical wash contains a mixture of ethanol, water, and minor components like methanol, fusel oils, acetaldehyde, ethyl acetate, propylene glycol, and glycerol. Each of these components has its own unique boiling point and refractive index, which influences its behavior during distillation.Here’s a summary of the key components and their typical concentrations:

• Ethanol: ~8% to 12% ABV (Alcohol by Volume)

• Water: ~85% to 95%

• Methanol: 0.1% to 0.5%

• Fusel Oils, Acetaldehyde, Ethyl Acetate, Propylene Glycol, Glycerol: Present in small amounts, typically less than 1% each.

The Baseline Distillation Model

The Baseline Distillation Model is built on theoretical principles, where the concentration of each component is calculated based on known physical properties such as boiling points and refractive indices. The model assumes that as distillation progresses:

• Methanol: Being more volatile than ethanol, methanol is expected to evaporate first, leading to a rapid decrease in its concentration during the heads phase.
• Ethanol: The concentration of ethanol increases as the temperature reaches its boiling point (~78.37°C), peaking during the hearts phase, and then gradually decreases as distillation enters the tails phase.
• Water and Other Components: These remain as the major components throughout the process, with their concentrations adjusting as the more volatile substances evaporate.

Refractive Index as an Indicator

A key feature of the example Baseline Distillation Model is the use of the refractive index to monitor the progress of distillation. The refractive index provides a measure of how light is bent as it passes through the liquid mixture, which varies depending on the concentration of the components.

In this model:

• The refractive index is calculated based on the weighted sum of the refractive indices of all components.
• As ethanol concentration rises, the refractive index increases, reflecting the change in composition.
• Conversely, as water becomes more dominant in the tails phase, the refractive index decreases.

Visualizing the Distillation Process

In the theoretical graph generated by the Baseline Distillation Model (Figure 1):

• Ethanol concentration is shown to rise and peak during the hearts phase.
• Methanol concentration rapidly decreases during the heads phase and stabilizes at a low level.
• Refractive Index follows the changes in ethanol concentration, providing a clear signal of the transition between different phases.

Conclusion

The Baseline Distillation Model provides a theoretical framework for understanding the distillation process. While it simplifies the complex interactions between components, it offers valuable insights into the dynamics of distillation. By modeling refractive index changes, it also highlights the potential of using optical measurements to monitor and optimize distillation in real-time.

This baseline model serves as a foundation for further refinements and comparisons with real-world data, ultimately leading to more accurate and practical distillation models.