I imagine your talking about just making really good oil out of a high cbd strain. To the best of my knowledge a butane blast into water is the best way, and it is highly dependent on the quality of trim you start with. I am currently trying to find time to study this and other processes more, I wonder if other oils similar in solubility build up more in worse trim, and how much "purging" matters. Experimentation would help.
If by chance you were wanting to separate the cbd from the thc and other "turpines" (admittedly, this another word I need to get around to defining) i wouldn't know much on the subject yet. Browsing around this forum I ran into a thread where the subject was mentioned. Someone who seemed to know what they were talking about responded:
To get pure CBD or THC you would need to do an extraction and then use chromatography to separate the extracts.
I have also not encountered much about this "chromatography" process.
I knew rene was using this forum for a while, but i had no idea there was so much knowledge here, if I find he time I would love to do some more reading on these and may other subjects