Mackey David <[EMAIL PROTECTED]> wrote:
> Most Ethanal is manufactured from agricultural crops such as sugar
>cane, corn and wheat starch. Ethanol can be produced from trees but the
>production costs are very high and have only been experimental. Brazil uses
>sugar cane to produce most of its ethanol.
Yes, that makes sense to me. I'm puzzled by a number of things in the article
Ed posted. Generally ethanol is produced by aqueous fermentaion of sugars,
then it must be distilled by application of considerable heat, which
severely encroaches on the efficiency of the process, unless one can
arrange for heating by otherwise waste or unused heat such as sunlight or
industrial waste heat. As to "cellulosic biomass", that is protein, and
while it will give off methanol as part of its decomposition under
application of heat (this is where wood alcohol comes from), I haven't
heard before of any means of yielding ethanol from it (chemical synthesis
of ethanol from methanol is not trivial). I'm rather curious about the
mechanism and efficiency of this process. Potentially, one could get
a fair amount of ethanol out of cellulose, just in terms of counting
atoms, but it doesn't look to me that there would be an easy way of
getting a high yield. Of course, the organic waste coming out of the
process might have other uses which could feed back into the process to
increase its energy efficiency, but still I suspect a lot of cellulose
would have to go in relative to the amount of ethanol coming out.
Another item in the post which has me puzzled is this question of CO2
output. I can't see why ethanol should put out only 1% the CO2 of
gasoline. There is a higher ratio of hydrogen to carbon in ethanol,
which I could see giving an improvement, say decreasing CO2 to around
65-70% that of gas, but You're still burning carbon, and you've
got to end up with CO2.
-Pete Vincent
