Here’s a pretty impressive picture, and a fun project. If your oil is thin enough (I.E., high terpene extract) you can put it through a membrane with no solvent at all. This is probably the best result I have got for membrane purified oil. These samples are pure oil, not solvent solutions.
Left is feed (garbage quality HTE). Middle is a looser membrane. Right is a tighter membrane. Note it was either treated with the loose or tight membrane. It didn’t use both in series.
Anyone with a few 100 gallons of dark HTE they need prettified?