in 1975-76. He said that Exxon spent millions studying the feasibility however they scrapped their plans as it cost about $40 per barrel to produce compared to oil at $25. (Last I heard OPEC said they needed $50 per barrel to break even.) The coal process was clean in the sense that it kept the mercury out of the air, as you noted, and also the sulfur could be used for a variety of beneficial pharmaceuticals.
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