Alcohol is not really a high energy fuel.

Even the pure alcohol can be disappointing for people used to camping with propane or white gas. Sort of the 'Sterno syndrome', a dozen people shivering in the cold for an hour waiting for the food to get warm. Sterno, jellied alcohol, and Sterno burners were/are notoriously slow and inefficient. Liquid alcohol stoves are not that bad but they are still a bit slower than many of us are used to.

91% rubbing alcohol will work but it soots up more than with the pure stuff and burns cooler so it takes longer to do the same amount of work so you wait even longer and need to carry more of it.

That said if 91% is all you have it will work.

Best deal on alcohol is from industrial suppliers who package it as a solvent.