Maybe ten years ago I fiddled with a couple of batches of biofuel (haha) when it was all the rage to go eco friendly - the results were excellent, clean fuel, smell of fish & chips whilst driving, cheapish (the oil was free), good power from the fuel for a 40 year old Landrover.
BUT.....the chemicals put into the brew were less than "green" - caustic soda (by product of the oil refineries) and methanol (methylated spirits) a byproduct of chopping down tress and large amounts of water (5 litres of water to 1 litre of fuel) to wash the caustic from the fuel when the "cooking" was finished.
Mixing the warmed meths and caustic gave off clouds of vapour and required caustic proof cannister breathing apparatus - and maybe a new tin roof to the shed as there is a circle of rust on it. Mixing the meths/caustic into the veg oil was another pleasant experience needing breathing apparatus, PVC aprons, PVC gauntlets, etc. etc.
The sludge (fats turned to soap) leftover from the process was no use to man or beast and i used it to kill weeds, trees, etc. - scorched earth comes to mind as there are still patches of earth where nothing grows. Sieve filters were blocked pretty quickly with bits of fish, batter and chips and this muck has to be removed before you start cooking - you'll never eat at your local fish and chip shop again after seeing the muck that is in the oil. Plus I had to get rid of the muck and we were inundated with stray cats trying to get at the rubbish bins to feed on it.
No doubt the chemistry has moved on in the last ten years.
