I have recently starting distilling my own essential oils using a still that I built out of an old diesel barrel. Before the first run with the still, I cleaned the inside using soap and water. I distilled until I created 5 gallons of hydrosol. The issue is that it seems that the oil and water are emulsified (hope that is the right term, I don't have a background in chemistry). There appears to be a thin film of oil on the surface, rather than the "globs" I would expect. Another reason I believe this is an emulsion is that no matter how much I skim off the top, that film is always present, making me think that the oil is thoroughly mixed in the solution.I have done some research and it seems to be that there may be a surfactant present that is causing this.

Is there a way that I can test for the presence of a surfactant?

Does it sound like my issue is the presence of a surfactant or something entirely different?

Could the soap I used to clean it be the surfactant?


Update in Response to Answer:

The end goal is to use a few drops of the oil to enhance the smell of a facial product (beard oil), so the end product has to be safe for skin.

I don't have a diagram at the moment, but here is a smaller still that is basically the same as my setup, just much smaller. I am using a propane heat source to control the temperature.

To be honest, I don't know the expected structure of the oils. This is my first attempt at anything like this (I'm a software engineer that recently acquired an interest in chemistry!).

Thanks for the help!

  • $\begingroup$ These types of problems can be tough to solve. Please provide additional details as requested if you can so we can better help you! $\endgroup$ – J. Ari Mar 10 '17 at 18:37
  • $\begingroup$ What is your starting material? Are you sure that isn't already an emulsion? $\endgroup$ – J. Ari Mar 10 '17 at 20:05
  • $\begingroup$ The starting material is water and leaves and branches of "Artemisia tridentata", more commonly known as sagebrush. There isn't too much literature that I have been able to find on obtaining essential oil from this plant but I have found a few papers where it was done successfully $\endgroup$ – jteezy14 Mar 10 '17 at 20:15
  • $\begingroup$ The original mixture was approximately five pounds of plant material and 10 gallons of water. I ran the distillation process until 5 gallons came out of the distiller. It just occurred to me, is it possible that all of the oil came out early in the process and the last four or so gallons were just water, which diluted it? $\endgroup$ – jteezy14 Mar 10 '17 at 20:38
  • $\begingroup$ I see, since you are condensing mainly water vapors, (and probably your boiler temperature is around 100 C), your main condensate is water and watery oils (in unscientific terms)!! No wonder the resulting oil is kind of miscible with water. Assuming the oils have higher boiling point than water, my suggestion is to minimize the water and push the reboiler temperature above 100. Test is once, be careful not to burn your feed though. $\endgroup$ – Kinformationist Mar 10 '17 at 20:42

There are multiple issues that need to be addressed before one can give a definite answer to this question. Let's start by what we are certain about:

1- The soap is not the issue (unless you haven't rinsed the barrel thoroughly with water). The remnant soap would be so dilute that should not cause any problem.

2- Since the film keeps forming there seems to be an equilibrium issue for your oil to separate. If you look into partition coefficients of the oils you should be able to estimate how much will remain in the water. Anyway, the less water you have, the more oil you can collect. (concentration factor pushes the oil out to keep the equilibrium) One idea is to add less water to your feed.

3- THEORETICALLY one way to enhance oil extraction is to use a nonpolar solvent. HOWEVER, I STRONGLY ADVISE AGAINST ACTUALLY TRYING IT AT HOME due to the flammable nature of most nonpolar solvents and health issues related to it. If you can find a nonpolar benign solvent (that is a big IF), mix it with your final water oil mixture, and then decant the water from the bottom and then distill the solvent out to get the oil as a residue.

4- Depending on the chemical structure of the oil, some of it will always remain in water. If they are not highly hydrophobic, it might be difficult to separate them from water anyway without using an assistant solvent.


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