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In Reply to: RE: well, the most elegant source (besides interstellar) is electrolysis of water posted by b.l.zeebub on November 20, 2014 at 07:14:32
and there's the problem -- the structure of xylose contains C-H bonds (which oxidize with the release of some respectable amount of energy, akin to our much-beloved hydrocarbons) -- but there're too many hydroxyl groups in a carbohydrate to get a lot of heat energy out per molecule by combustion -- compared to petroleum products, are mostly hydrocarbon: CH3(CH2)nCH3 e.g., (long-chain aliphatic hydrocarbon).
The good thing, of course, is that xylose is readily renewable (so-called "wood sugar", and, yes, it does grow on trees, so to speak) but pound per pound, not so great really.
In the interest of full and complete disclosure - xylose is an aldopentose; C5H10O5, but it does have that meaningless but compelling "hydrate of carbon" empirical formula that we think of when we think of classical carbohydrates.
all the best,
mrh
Follow Ups:
I wasn't thinking of using xylose to burn but as a source of H2.
Xylose can be used to produce hydrogen very efficiently at low temperatures and normal atmospheric pressure by using enzymes to 'digest' it.
a thermophile of some sort?
I could always actually look it up... but I am with you now.
If the bioreactor could be rigged to deliver adequate hydrogen in real time, that'd be very sweet (no pun intended)!
One of the byproducts would, presumably be CO2, though, I assume.
all the best,
mrh
From wiki:Xylose
In 2014 a low-temperature 50 °C (122 °F), atmospheric-pressure enzyme-driven process to convert xylose into hydrogen with nearly 100% of the theoretical yield was announced. The process employs 13 enzymes, including a novel polyphosphate xylulokinase (XK).[84][85]It is a bio-technological process which mimics digestion in an actual living thing.
Works with any kind of plant material. Seems to be quite simple and elegant really.
There is more in the link to Virginia Tech who came up with it all.Then again it could all be a belated April's Fool thing...
Edits: 11/22/14
It's clever and efficient -- but, like normal biological oxidation of carbohydrate, it produces water and CO2.
... oh, and, when I was in school, the single most abundant carbohydrate in Nature was reputed to be glucose (the monomeric building block of starch and cellulose, as well as an extremely important energy source for all cellular metabolism... and half of that tasty disaccharide sucrose!).
I am not a biofuels guy... but I am a carbohydrate biochemist.
all the best,
mrh
the difference to fossil fuels is that those release CO2 which has been stored and taken out of circulation for millions of years while this process cannot release more CO2 than has been fixed in the plant material over the last year or so depending on the crop used.
And the amount released will be fixed again when growing crops to replace the Hydrogen fuel used.
So logically over time the net CO2 released must be close to zero unless you chop down forests and replace them with deserts which would clearly be insane.
-- and compare it to an alkyl (straight-chain) hydrocarbon.
While I see your point, I am not sure on a molar basis that it's gonna be such a great deal. An improvement no doubt, but still, perhaps, a crutch akin to using natural gas (which is seen by many as a crutch) as an energy source.
Interesting topic, for sure!
all the best,
mrh
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