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Originally Posted by spadlet
So can bioethanol be produced from anything that we currently consider to be waste, or does it have to be grown as a crop in it's own right? That was the main thing I was trying to work out, as it doesn't seem to me that substances such as waste chip fat can be converted into bioethanol, but then I don't know the organic chemistry behind the conversion techniques.
The other thing I was wondering was, what about the sustainability of producing the reactants and catalysts required for all of these fuel conversions? Nobody ever seems to go into that.
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Spadlet, to make ethanol you need to start with a carbohydrate that can be broken down into simple sugars. Potentially a lot of waste that is made of cellulose, like cardboard, could be used provided we can find a way of efficiently reducing it from a complex carbohydrate to a sugar.
Waste chip fat is an oil rather than a carbohydrate, so you would not get ethanol out of it.
The fuek conversions from the simple building blocks are actually quite easy. You only need yeasts and a distillation process to turn sugar into ethanol. Oils are esterified with either an alcohol, typically methanol, using a base catalyst generating an alkyl ester and glycerine. The alkyl ester is used for biodiesel.