There was a question in our forum about CBD extraction and methods that could be used. This is what made me do a little research to find the answers to his questions.
I will not discuss what is CBD because there are lots of sources in the Internet but it is good to mention that cannabis plant has more than 20 known cannabinoids and one of them is CBD. According to some authors medical benefits of CBD may be result of synergism with other cannabinoids. So the question is how to remove THC and keep the rest of the components.
But let`s start with the sources of CBD. According to the literature cannabis plants can contain up to 40% CBD. This, of course, varies between different strains. However, one of the best sources of CBD is hemp. Bluebird Botanicals, one of the hemp oil manufacturer, states that they can produce extracts with more than 26% CBD. Another option is to identify cannabis crosses bred for high CBD.
During my research I discovered a paper, Cannabis Oil: chemical evaluation of an upcoming cannabis-based medicine (published on 5 May 2013), which discusses methods for cannabis oil preparation. The authors have focused their attention to THC, however, their methods will be valid for CBD extraction as well.
For their research they have used cannabis plant with 19% THC. They have compared naphtha, petroleum ether, ethanol, olive oil + 20% water and pure olive oil for their extraction. Decarboxylation was done with pre-heating: water bath at low boil (98-100C for 5 min) and oven (145C for 30 min). They have used chromatographic methods to determine the content of the oil extracts that they have prepared.
According to their results the oil extracts contain average THC 5-10% (THC + THCA in total). Surprisingly naphtha extract had 33% THC. Other components of the extracts were the monoterpenes beta-pinene, myrcene, beta- phellandrene, cis-ocimene, terpinolene and terpineol, and the sesquiterpenes beta-caryophyllene, humulene, delta-guaiene, gamma-cadinene, eudesma-3,7(11)- diene and elemene. Naphtha extract and petroleum ether did not contain such variety of terpenes. They have discovered that pure olive oil was the most beneficial solvent and preserved most of the terpenes, especially during extended heating. Ethanol extracts chlorophyll and reduces significantly the cannabinoid content (~50%) so the authors do not recommend alcohol extraction.
Naphtha and petroleum ether are considers harmful and flammable.
Researchers comment that according to their results heating reduces the amount of terpenes in the extract. They pay special attention that hazardous solvents should not be used for preparation of edibles.