Chemists have a peculiar obsession with separating everything - they simply can't stand having things mixed together! They invented distillation to separate liquid mixtures as far back as ancient Egypt and Rome, with archaeological evidence dating back 5,000 years.
But how does this process work? It takes advantage of the fact that each substance has a different boiling point, allowing them to be evaporated one by one and collected separately.
Imagine a party where you want to separate true music lovers from reggaeton fans. DJ Bunsen gradually heats up the atmosphere with varied music, playing well-known anthems that everyone dances to with varying degrees of enthusiasm. But when a certain "perreo" temperature is reached, some people leave the dance floor and head to the bar... There you have it - you've separated one group on the dance floor from another off it. Distillation does the same thing with liquids, carefully raising the temperature until the most volatile liquid reaches its boiling point and begins to evaporate, "leaving the dance floor," while the rest keeps "dancing" in the flask.
[🔥 In the laboratory, the "DJ" is the Bunsen burner or hot plate. The temperature is regulated to evaporate only the most volatile component (e.g., ethanol boils at 78°C vs. water at 100°C).]
Just as good music lovers go to the bar to cool off, we need to cool down the vapor from the liquid we just evaporated. So we pass it through the condenser, a water slide that uses cold water to condense the vapor, collecting it drop by drop in another flask.
[❄️ The "water slide" is a Liebig condenser: an inner tube where vapor flows, surrounded by a jacket of cold water.]
- Don't let the dance floor empty out: believe it or not, there will always be someone who likes reggaeton, so we must monitor the liquid level in the flask.
- Don't let the party drag on too long: After too much time, even the most dedicated dancers might have taken a break at the bar. So when we have enough distillate, it's better to end the party.
- Don't let the temperature get too high: if the "perreo" becomes excessive and borders on obscene, we've probably evaporated more than one substance in the mixture.
- Watch if people at the bar start dancing: if you suddenly see twerking at the bar, the liquids have probably mixed again.
In summary, you need to ensure you don't run out of mixture in the flask. The distillation temperature should remain constant since a sudden change likely means you're evaporating the undesired substance. Observe the characteristics of the distillate - if there's any change in color or appearance, it's better to start over. You must monitor the process time and, of course, stop the process once you've obtained enough distillate.
Fractional Distillation
Unfortunately, not all liquids have boiling points as far apart as reggaeton is from good music. After all, many musical styles resemble others. In such cases, we use the fractionating column. Imagine a building where there's a gradual change in music style as you go up the floors. Young people move from floor to floor, but some always stay where their favorite songs are playing. This way, we achieve a more precise separation. In the case of liquids with very close boiling points, the fractionating column allows multiple evaporations and condensations, ensuring that only the pure substance reaches the final room - the penthouse isn't for everyone.
[🏢 Fractionating columns have internal elements like plates or beads (Raschig rings) that create liquid-vapor equilibrium stages. Each "floor" is equivalent to a simple distillation repeated over and over, achieving purities >99%.]
Vacuum Distillation
When dealing with people who are too sensitive to sound, we must be careful when setting up our distillation party. We'll keep the music at low volume, in the background, so they get distracted with conversation. Eventually, the hustle and bustle will bother those with sensitive ears, and they'll leave. Something similar happens with vacuum distillation, used for thermolabile products - the sensitive ones. To avoid heating the mixture too much and prevent degradation, we lower the pressure, achieving boiling points at much lower temperatures.[🎚️ Reducing ambient pressure (vacuum) decreases the temperature needed to evaporate liquids. Thus, vitamin E (which degrades at 200°C) can be distilled at 50°C if we use 0.001 atm.]
Steam Distillation
But nature always finds ways to complicate separation for chemists, inventing substances that can decompose when they reach their boiling point, yet are too volatile for vacuum distillation to be effective - such is the case with essential oils. So chemists decided to organize a foam party.
Water is heated in a flask to produce steam, which is passed through another container holding the sample with essential oils. It's like when foam starts flowing at the party - some will stay playing, but others will run away pushed by the foam and commotion. That's how water vapor pushes volatile oils toward a third container where they condense. And as you know, water and oil don't mix, so you just need to wait a bit for them to separate on their own to collect your aromatic product.
[💨 Steam distillation takes advantage of Raoult's Law and Dalton's Law of partial pressures. The sum of the partial pressures of water vapor and the volatile compound allows reaching atmospheric pressure at a temperature below the individual boiling point of each component, thus facilitating the volatilization of the oils.]
Did you think chemistry and partying weren't comparable?
Well, you can see how wrong you were. Just as there can be many themes for organizing a party, there are many applications for distillation - liquors, fuels, perfumes, and so on. Everyday products that are often present at any party.