Comment by pfdietz
It was a technical failure, I believe. It was too difficult to hydrolyze cellulose and hemicellulose efficiently into a mixture that would allow enzymatic conversion to ethanol. Enzymes are easily poisoned and the mixture is more complex than what one gets from starch (which is just polymerized glucose.)
There is one success story, in Brazil.
https://pubs.aip.org/physicstoday/article/75/7/22/2848574/Wh...
Conversion of cellulosic biomass into chemicals other than ethanol might be the better route to take, particularly if green hydrogen can be used to boost the yield. Virent (which was bought out by an oil company) has a process for doing this. It would yield even more fuel per unit of biomass than conversion to ethanol, as potentially all the carbon can end up in the fuel. The fuel could also be drop-in replacement for existing hydrocarbon fuels. But there's not much interest in this as long as oil is still being used.
again i recall it wasnt technical, but i dont recall where i heard that (i could be wrong). they might also not have been doing enzymes, it might have been orgsnismal. do you have specific knowledge that this effort failed for technical reasons?