Diesels used to contain quite a bit of sulfur, but I'm not sure about recent ones -- I think they're a lot cleaner. Bunker or other heavy oils used mainly in furnaces or in ships can still contain some significant amount of sulfur.

The problem with ethanol is that engines made primarily for gasoline usually get miserable mpg on E85 because to run it efficiently, one would need a higher compression engine. On the other hand, butanol may be a lot closer to gasoline in many respects. What they had on the butanol website sounds almost too good to be true, but I didn't see any obvious red flag, or a BS alert, and their FAQ appeared to be honest, too.