CNN: The old kings of ethanol are struggling for survival but a new crop of companies are poised to ascend to the throne and hope to offer a superior product. Tight credit and slim profit margins in the traditional corn ethanol business are felling the sector’s once-mighty big boys. Pacific Ethanol (PEIX), where Bill Gates had a big stake, has seen its shares fall to a paltry 25 cents from over $40 in 2006. Verasun, formerly the second biggest ethanol producer in the country, is currently …