Good question about biodiesel for which I am completely ill-prepared to evaluate.

But when has that ever stopped me?

I'm thinking of all the carbohydrates of various kinds that go into landfills and sewage treatment plants. The trick is getting useful work out of that trash and crap. I know that India has some really nice small-community biodigesters that produce low-quality methane suitable for cooking. Low quality because it has CO2 and CO because of the processing method and no scrubber system, last I heard. I thought about this 30 years ago when I was a hippy goat and chicken and Cannabis farmer. Scrubber could be implemented by bubbling the mixed gas through aqueous NaOH or KOH producing Na2CO3 or K2CO3 + H2O and I think its exothermic. You get the NaOH or KOH the old-fashined way, get the fireplace ashes and pour water into them dissolving the 'potash' = potassium --> KOH. But I still wouldn't want to use it to fuel a car. Don't want any loose salts getting into the intake system, thank you.

But for longer chained hydrocarbons you have to have some method of rearranging simple carbons into complex carbons and that takes energy input. So I think you do it the old-fashioned way and just be patient.

Grind-up high-carbon trash with doo-doo to form a thick slurry and pump that melange into old saltmines. let that goo cook for a couple of decades in the natural heat of the mine and it's own anerobic exothermic reactions. The worst that could happen is that it would form methane and crack the salt mine, leaking an evil ooze out into the strata several thousand feet underground. That's essentially what forms around salt domes anyway. What would be extremely cool would be if instead of cracking the mine and causing subterranean environmental hell, it formed long-chain hydrocarbons. In that way the world takes stuff it doesn't want and can't use and can't hide and turns it into something interesting.