|
Grex > Science > #79: Hydrogen from sugar water, or Log Cabin in the fuel tank | |
|
| Author |
Message |
russ
|
|
Hydrogen from sugar water, or Log Cabin in the fuel tank
| 
Aug 31 01:25 UTC 2002 |
Slashdot reports (no URL, sorry) the invention of a scheme to
convert glucose and water (sugar syrup) to CO2 and hydrogen.
The reaction appears to be:
C6H12O2 + 6 H2O -> 6 CO2 + 12 H2
This is touted as a way to generate hydrogen to run a fuel cell.
I do not know if the reaction is self-sustaining or endothermic.
I observe that cellulose is a polymer composed of linked glucose
molecules, and that it can be hydrolyzed to monomers in solution.
Evaporate part of the water, and you have... glucose syrup.
Anything which contains lots of cellulose is a potential input to
such a process. Scrap paper, lawn and garden waste, and even
vegetable peelings could feed a glucose generator which is used
to make hydrogen.
|
| 12 responses total. |
rcurl
|
|
response 1 of 12:
|
Aug 31 03:19 UTC 2002 |
Easy to write reaction - hard to accomplish reaction. Even simpler
is
2 H2O --> 2 H2 + O2
No need for the farm.....
|
russ
|
|
response 2 of 12:
|
Aug 31 20:34 UTC 2002 |
The sugar-water solution contains net energy; the water for the
dissociation reaction does not.
You can also get sugars directly from plant sources, holding forth
the possibility of feeding a fuel cell from biomass with minimal
processing.
|
rcurl
|
|
response 3 of 12:
|
Sep 1 05:17 UTC 2002 |
The real point is that sugar is a reducing agent (it will burn), and
hence can assist in the reduction of water to hydrogen. Both reactions
#0 and #1 are endothermic, with the respective heats of reactions of
+30 kj/mole H2 and +242 kj/mole H2.
The commerical production of hydrogen is primarily via the "water gas
shift reaction" (ultimately), which is
CO + H2O --> CO2 + H2
for which the heat of reaction is -41.4 kj/mole H2 - much more favorable
(thermally) than rxn #0.
The fundamental question is where you are going to buy your reducing
agent, although it is likely to be a carbon compound. Chemicals as complex
and expensive as sugars are poor choices, when there is plenty of much
cheaper reducers in natural gas (which is currently used to make the CO to
make the H2), and coal (the previous favorite after conversion to coke).
I suppose the objective of studying potential reactions like #0 is to make
a portable hydrogen generator (although such has been used experimentally
in real automobiles for decades - with wood as the source of the reducer).
Glucose is pretty poor compared to hydrocarbons for this purpose.
(Of course, solid glucose could be burned directly in a diesel engine,
saving the expense of the conversion.)
|
russ
|
|
response 4 of 12:
|
Sep 1 17:47 UTC 2002 |
The idea of confectioner's sugar going into a diesel engine (a la
Rudolph Diesel's original idea of coal dust) is very entertaining,
if not terribly practical. Carmelized injectors, anyone?
The point about natural gas being a much cheaper reducing agent is
a good one, but it isn't the whole story:
1.) You can't put natural gas on board a vehicle easily,
2.) Natural gas isn't usually produced by plants, and
3.) It won't necessarily be cheaper if fossil carbon is taxed.
In theory at least, glucose could be produced by hydrolysis of the
cellulose in crop stalks and leaves, lawn clippings, waste paper and
even domestic garbage. This could then be evaporated to a non-toxic
liquid fuel which can be handled at room temperature. It's even
amenable to use with current internal-combustion engines, because
the heat required to drive the reaction could be supplied by the
engine exhaust.
Whether or not it'll ever hit production, it's pretty slick.
|
rcurl
|
|
response 5 of 12:
|
Sep 1 18:10 UTC 2002 |
I see the proposal as one of thousands made annually in the process of
seeking research funding. Most of these are totally impractical, but
in fact one doesn't know exactly how impractical or, more important,
whether something will come out of the research that will be practical
(and perhaps practical in a form not envisaged in the proposal). For
example, it is *possible* that a sugar based battery could work.
In regard to the use of sugar in a diesel engine - don't snicker. Some
*original* diesel engines burned coal, although materials of construction were
a problem. These have apparently been overcome and a 6.4 MWe coal-fueled
diesel engine demonstration electric power plant is under construction.
It is expected that ultimately 48% power efficiency will be attainable,
far exceeding any steam-based coal-fueled power plant. See
http://www.lanl.gov/projects/cctc/factsheets/disel/ccddemo.html
Running the power plant on sugar would be a piece of cake.
|
russ
|
|
response 6 of 12:
|
Sep 2 02:00 UTC 2002 |
I wasn't snickering at the idea of coal dust (because I know it had
already been done, though it wasn't as easy to do with the technology
of the day as fuel oil), I was pooh-poohing the idea of powdered sugar
in a diesel. Heat it up a little bit, and it melts; let it cool off,
it freezes. It would be a nightmare for the fuel-system designer no
matter how you tried to handle it. Handling sugar as a dust suspension
for blowing into a furnace, a la coal-fired boilers, would be okay...
unless and until it got wet, then you'd be back to sticky gunk again.
Proton-exchange membrane fuel cells are what, 80% efficient? If the
reformer is 75% efficient that nets out at 60%, far better than 48%.
Given the recent work with methanol fuel cells, I don't doubt that a
sugar fuel cell could be done; what's sugar but a complex alcohol?
On the other hand, I expect the technology to get started in a niche
where cost is not as important as energy density and convenience
(like cell phones). The inconvenience and warranty issues of syrup
spills vs. the clean evaporation of methanol make me bet on methanol
over glucose for hand-held devices even if thermal reformers aren't
required. If glucose reformers get a toehold it'll be from the other
end, as bulky but cheap devices for powering larger things (vehicles,
off-grid power systems) perhaps from biomass. If biomass is the
fuel it might be grown for the purpose or derived from waste products
such as spoiled grain or sawdust.
|
rcurl
|
|
response 7 of 12:
|
Sep 2 03:12 UTC 2002 |
Ah, but they are pushing 48% efficiency NOW with diesel electric (and a
very well known electric end of that). That 60% is still pie in the sky.
But more power to them in time.....
|
russ
|
|
response 8 of 12:
|
Sep 6 23:08 UTC 2002 |
I checked that web site, and the projected efficiency for the
first phase coal-slurry engine is only 41%; they expect to be
able to achieve 48%, but it won't be with the first iteration.
Rane, I believe you are guilty of misrepresentation.
|
rcurl
|
|
response 9 of 12:
|
Sep 7 00:12 UTC 2002 |
I said "pushing 48%" so as not to misrepresent the current stage (which
isn't even running at full capacity with coal yet). What's to argue
about, anyway? Coal-Diesel-Electric works, Sugar-Fuel-Cells is still
in the concept stage.
|
russ
|
|
response 10 of 12:
|
Sep 7 14:52 UTC 2002 |
Hydrogen-fuel cells are production items. Methane-reformer-fuel cells
are production items (or at least Plug Power had plenty of demo units).
What's a different type of reformer? The concept was proven ages ago.
|
tsty
|
|
response 11 of 12:
|
Oct 27 00:27 UTC 2002 |
http://www.uaf.edu/ddc/cleancoal/homenew.htm
|
polytarp
|
|
response 12 of 12:
|
Jan 20 23:27 UTC 2003 |
RESP 3: WOW, I UNDERSTOOD ALMOST ALL OF YOU, AND EVEN HOW TO CALCULATE MUCH
OF YOU1
|