It is refined using the same process that is used to refine corn or really any plant into a oil. That is all I know. You will have to do research about it to fined out. You could start by looking up:
The Rebirth of Industrial Hemp: Processing and Bio-refineries
http://nocohempexpo.com/2016/04/rebirth-industrial-hemp-processing-bio-refineries/
As Trump seeks ethanol deal, oil industry resists
https://www.chron.com/business/energy/amp/As-Trump-seeks-ethanol-deal-oil-industry-resists-12831488.php
As Trump seeks ethanol deal, oil industry resists
https://www.reuters.com/article/us-usa-biofuels-studies/oil-and-corn-tout-dueling-studies-on-future-of-u-s-biofuel-program-idUSKCN1GK1JY
Wisconsin farmers interested in growing industrial hemp ...
http://www.miamiherald.com/news/business/article208699649.html
State farmers showing strong interest in growing industrial ...
http://host.madison.com/wsj/business/state-farmers-showing-strong-interest-in-growing-industrial-hemp/article_a96e1ca6-e290-5948-91b0-4005792a0298.html
I am sure their is more, but as the people on the front line's you need to know. I haven't read the details on what the information has just did a DuckDuckGo search and found these.