How does this work?

I was thinking of building a basic potstill for fuel when i thought about how alcohol and acetic acid can just evaporate without residue . I think it is amazing how we can take sugar which is sticky and gets all over the place when concentrated, and turn it into something that can evaporate so cleanly. I would love to learn how this works, like wat difference in the chemical structures make this so. I’d love to take a chemistry class if I could get my brain to work for once.

Hi Row, welcome to Permies.

Generating ethanol is pretty neat, I think. So yeast eat sugar, and poop out ethanol and CO2. Sugar, or glucose is C6H12O6 and is a carbohydrate. If we look at the word carbohydrate, it means carbon-water. If we look at the chemical makeup of glucose, we see 6 carbons, and then 12 hydrogens and 6 oxygens. Water is H20, so in glucose we see twice as many hydrogens (12) as oxygens (6). I should note that glucose isn’t exactly carbon bound to water molecules, but a ring of carbon molecules with various other molecules attached to the six sided ring. Ethanol is C2H5OH, and we see that from glucose, 4 carbons, 6 hydrogens and 5 oxygens are missing. Part of those molecules that were stripped become CO2, and the rest I can’t remember.

This is really an ultra simple layman explanation, as the metabolic process of yeast converting glucose to ethanol isn’t direct and is really quite complicated, and yeast make other compounds in the process, such as pyruvate, first, before converting pyruvate into ethanol. Yeast also excrete other compounds besides ethanol and CO2 in the process, but it’s complicated.

Hope this helps.

James Freyr wrote:  we see that from glucose, 4 carbons, 6 hydrogens and 5 oxygens are missing. Part of those molecules that were stripped become CO2

So is it just a "lighter" molecule and this allows it to become vapor?

Row Morgan wrote:

So is it just a "lighter" molecule and this allows it to become vapor?

Well, sort of, but not completely. Weight of molecules and compounds aren't directly the cause or reason something goes from liquid to vapor. For example, mercury is really quite a heavy molecule, it's adjacent to gold on the periodic table, but mercury will evaporate at room temperature. This is getting into areas of chemistry that I don't know about or really understand.

That is so interesting. It sounds like we could both do some reading on this. Thank you you've definitely inspired me greatly! brains starting to warm up, like an old diesel truck chugachugachuga.

I'm gonna say this will require more than a casual look into chemistry to really understand what is going on.

Chemistry is fascinating, but very complex, and has layers, like onions and ogres.

For fun YouTube videos, check out nile red/ nile blue, dougs lab, and nurd rage. All have really good videos on chemistry.

James Freyr wrote:....Weight of molecules and compounds aren't directly the cause or reason something goes from liquid to vapor. For example, mercury is really quite a heavy molecule, it's adjacent to gold on the periodic table, but mercury will evaporate at room temperature. This is getting into areas of chemistry that I don't know about or really understand.

There's a decent discussion on the issue in a Wiki entry:  https://en.wikipedia.org/wiki/Volatility_(chemistry)

The mercury/gold example is a good one, James!  I'm reasonably sure that basis for ethanol being more volatile (evaporating faster) than water at the same temperature is due to the hydrogen bonding between water molecules that does not occur to the same extent in pure ethanol.  Thus even though water is a 'lighter' molecule based on its mass (molecular weight of ~18) as compared to ethanol (molecular weight of ~ 46), the attractive forces (and possibly other forces) between any two adjacent water molecules promotes the liquid as a whole of not evaporating as fast as ethanol, which has those forces but of smaller magnitude.  (Similar forces are at work when, say, you pour cooking oil onto a pot of water and the droplets disperse.....for a while.  Then you will notice that if the water remains cold, the droplets slowly re-group to form one larger oil-slick on top of the water.  Part of the forces here are 'hydrophobic'....where the oil is resistant to blending with the water.... and 'lipophilic', where the oil molecules have a chemical affinity to be next to other lipid-based molecules.)

As Riley noted, this starts to get into deeper levels of chemistry like atomic forces and affinities, some of which remain theoretical.  One of the most fascinating areas of biological chemistry to me is how two bioactive compounds can differ by only one element....a carbon here or a sulfur there....and the one compound can have astounding activity in an organism whereas the other nearly identical compound can have nearly zero impact on that organisms.  This was seen clearly during the COVID epidemic when, in some cases, only a single amino acid in the long spike protein could render the SARS-CoV2 either more or less virulent or more or less immuno-evasive.  If you imagine a string of pop-beads, the spike protein in SARS-CoV2 is 1,273 pop beads long.  If only one of those beads becomes different than what was originally there...AND...changes the structure or function of the protein as a consequence, big changes can occur at the level of the biology.