A few years ago, Ben Freeman had an energy trader's dream job: as a managing director and head of global oil derivatives trading at Goldman Sachs, he ran one of the largest – if not the largest – oil derivatives books in the world.

But the writing was on the wall. New regulations such as the US Dodd-Frank Act, the Volcker rule and Basel III were threatening to undermine the business model of Wall Street commodity desks. As banks began to retreat from commodities, Freeman saw an opportunity