Tuesday, November 13, 2007

Biohydrogen Production by Electrical Stimulation.

I had given-up on the idea that producing hydrogen by fermentation to run all the world's transport is at all feasible. I remain to be convinced that it is, as I stated in an early posting (Feb. 26th, 2006) "Biohydrogen from Sugar - a Preposterous Idea," on the basis that "We would need an area of land more than twice the size of the U.K. to grow enough crops to replace our current demand for liquid petroleum fuels by bio-hydrogen, and hence the concept is utterly preposterous." The other problem is that to fill the huge volume of reactors for fermentation would require 150 cubic kilometers of fresh water, which is more than the total volume available for every man, woman and child in the UK.

However, I was sent a an early press-release of a paper which reports on the greatly enhanced production of hydrogen, in yield and rate, that might be achieved by immobilising hydrogen-producing bacteria onto the surface of an electrode, passing a current and thereby stimulating the proton and electron generating activity of such "exoelectrogenic" bacteria using a small applied voltage. The cell is described in [1], and is impressive, in comparison with simply having hydrogen producing bacteria swirling around in a stirred fermentation vessel. Naturally, there are additional resource demands incurred by this more sophisticated technology, which employs a cathode made of carbon cloth onto which a platinum catalyst is supported. The anode chamber was filled with graphite granules and a graphite rod was inserted into the granules.

Bacteria from a soil or waste-water source were inoculated and enriched on a specific substrate using a phosphate buffer and nutrient medium. High yields of hydrogen were obtained from glucose and also from its commonly encountered fermentation products, e.g. acetic acid, butyric acid, lactic acid, propionic acid and valeric acid, meaning that by a change in applied voltage it might be possible to produce hydrogen from these too, and thus rendering the process of fermentation overall more efficient in respect to hydrogen production.

By looking at some rough numbers, it is possible to gauge the likelihood of the technology being adopted on the large scale, in order to match the amount of oil we currently get through in terms of fuel.

The reactor volume is given as 14 mls (anode chamber) and 28 mls (cathode chamber), making a total of 42 mls, from which 1.1 m^3 of H2 is obtained per day. The cathode has an area of 1 cm^2 and is made of carbon cloth on which 0.5 mg of Pt has been deposited.

To match 60 million tonnes of oil, we need about 6 x 10^9 kg of H2 (6 million tonnes). 1 kg of H2 is 500 moles, and occupies a volume of:

500 moles x 24.5 litres/mole/1000l/m^3 = 12.25 m^3.

Hence, 6 x 10^9 kg of H2 has a volume = 12.25 m^3/kg x 6 x 10^9 kg = 7.35 x 10^10 m^3

The reactor produces 1.1 m^3 of H2 per day x 365 days/year = 401.5 m^3/year.
Therefore we need: 7.35 x 10^10 m^3/year/401.5 m^3 H2/m^3 (reactor volume)/year =
1.83 x 10^8 m^3 reactor volume.

[This is a huge improvement over the 1.5 x 10^11 m^3 for a "free" fermentation process, and implies a factor of 800 less in terms of water required. However, in some of the fermentations, water is a reactant but even so, we still need much less than 1% of the comparable quantity of water to run it].

How much platinum is required? 0.5 mg/cm^2/42 mls of reactor cell volume in total.

1.83 x 10^8 m^3/42 x 10^-6 m^3 x 0.5 mg = 2.18 x 10^3 tonnes of Pt = 2180 tonnes. This is equal to the world output of new platinum for 14 years, and that is just to fit the UK's needs, let alone the rest of the world! Thus we have hit the first resource bottleneck.

We would also need 50g Pt/fuel cell x 33 million cars on UK roads = 1650 tonnes of new Pt for fuel cells in which to "burn" the hydrogen, making 3830 tonnes of Pt required in total, or 25 years worth of the world output of the metal.

How much land would be needed to grow the sugar crop? Let's assume that the technology can be adapted to extract 100% of the hydrogen in a sugar C6H12O6 (including the acids etc. that it produces in a first fermentation) which is pretty optimistic:

C6H12O6 ---> 6CO2 + 6H2 + 6 "O" (in an unspecified chemical form).
MW = 180 12

So, we need 180/12 x 6 x 10^9 kg H2 = 9 x 10^10 kg = 9 x 10^7 tonnes of glucose.

If we assume a yield of 19 tonnes of "sugar" per hectare, and an efficiency of 80% to extract the hydrogen, we need:

100/80% x 9 x 10^7/19 = 59.21 x 10^6 ha of arable land = 59,210 km^2 which is 91% of the total of 65,000 km^2 there is altogether. So, we couldn't grow any other crops for food, and while it represents a considerable improvement over unassisted fermentation of sugar into hydrogen, it is still impractical on the grand scale of our transportation requirement.

How much generating capacity would be needed to run the system, by applying a voltage to the anodes?
The average is 300 mW/m^2 of electrode surface.

1 cm^2 corresponds to 42 mls of reactor volume, and the total reactor volume is 1.83 x 10^8 m^3.

Hence the total electrode area is: 1.83 x 10^8/42 x 10^-6 x 1 cm^2 = 4.36 x 10^12 cm^2, and since 1 m^2 = 10^4 cm^2, this amounts to 4.36 x 10^8 m^2.

Thus, the power needed is: 4.36 x 10^8 m^2 x 300 x 10^-3 W/m^2 = 1.31 x 10^8 W = 131 MW, which is not too bad, about 13% of the output of a typical power plant.

How much graphite is needed?
Anode chamber has a volume of 14 mls. If we assume spherical particles, their volume is:

4/3 x pi x (4.54/2 x 10^-3)^3 = 4.9 x 10^-8 m^3. To find the overall volume they occupy, it is helpful to imagine each one occupying a cube of side 4.54 x 10^-3 m (4.54 mm), for which the volume is:

(4.54 x 10^-3 m)^3 = 9.36 x 10^-8 m^3. The total anode volume is (14/42) x 1.83 x 10^8 m^3 = 6.1 x 10^7 m^3, of which, (4.90 x 10^-8/9.36 x 10^-8) x 6.1 x 10^7 m^3 = 3.19 x 10^7 m^3 is graphite. There is a graphite electrode inserted too, which occupies some of the internal space of the cell, but assuming the volume just determined and a density of graphite of 2.25 tonnes/m^3, this amounts to:

3.19 x 10^7 m^3 x 2.25 tonnes/m^3 = 7.2 x 10^7 tonnes or 72 million tonnes of graphite.

As a means to replace oil for transportation, the technology could not be scaled-up sufficiently for the task, certainly not to fuel the entire world's transport. The above figures only refer to the UK, and should be multiplied by around 20 to meet the needs of ca 600 million road vehicles as there are reckoned to be altogether. This would mean that 3830 tonnes x 600 million/33 million vehicles = 69,636 tonnes of Pt would be required, and yet the metal is recovered at a rate if about 150 tonnes per year, implying it would take 464 years to install the lot, using electrohydrogenolysis with fuel cells. This quantity is actually close to the reckoned world reserve of Pt, and so we all of that would need to be turned-over for this purpose, and none for jewelry, scientific apparatus or catalytic convertors to keep the internal combustion engine powered vehicles running "clean" while they were phased out by the new "hydrogen" technology.

It is an interesting paper, and the authors may be correct in their assertion that the technology might still prove useful for local fertilizer production, say, even if a full-scale transportation system based on hydrogen is never implemented (which it never will be). However, the scale even of this will be likely be very small, for the simple facts of limited resources and the otherwise massive engineering requirements.


Related Reading.
[1] S.Cheng and B.E.Logan, "Sustainable and efficient biohydrogen production via electrohydrogenolysis," PNAS, 2007, Early Edition.

7 comments:

Political Umpire said...

Mr Rhodes,

I just came across your blog when googling the Great War, and saw a post you had written on the subject last year. Just a note to say I found it interesting, though I very much disagree with the 'Lions led by Donkeys' thesis (a phrase certainly never used by Germans to describe the British in WWI; Alan Clark deliberately lied about this). In short the Generals started the war with a small, colonial police force and, over 4 years of bitter experience managed to turn it into the most powerful field army in the world. Whatever else that was, it was not the result of out of touch cavalrymen (which most generals were not). Anyway, if the subject interests you I have done a short series of posts on it for this year's Remembrance Sunday, which you can find at my blog http://cricketandcivilisation.blogspot.com

Regards,
PU

energybalance said...

Hello PU,

thanks for your interest in that earlier article, intended to honour the fallen. I don't dispute your scholarship, but you may be interested in the wikipedia posting: "Lions led by donkeys", which refers to the use of the phrase and similarities to it going back to the Crimean war, and to French soldiers and so on.

Perhaps you could edit that entry, to set the record straight.

Remembrance Sunday is always a moving occasion, especially in recollection of those that didn't make it back, or only partially returned, like my grandfather.

I suppose at least treatment began for Post-traumatic Stress Disorder, originally believed to be due to "percussion of the brain" caused by repetitious explosions, rather than the psychological condition it is now known to be. It was originally re-termed "Percussion injury" I believe, from the original "Shell Shock".

Yes, for the damage inflicted on the Germans, these early battles could be called "victories", but what did they really achieve?

I think Wilfred Owen recorded his experiences of hell better than anyone I have read. My grandfather would never talk about it.

I shall be interested in reading your blog.

Kind regards,

Chris.

Political Umpire said...

Cheers Chris. I have set it out in much more detail on my blog, but really most of the battles were products of necessity, given that the war hadn't gone the way either side had hoped or planned for. The Somme in particular was a year earlier than Haig wanted to fight (he had real - and as it turned out valid - concerns about the equipment, training etc of the hurridly assembled new armies) but they had no choice as the French were about to collapse at Verdun. Britain was then the junior coalition power as far as the land war was concerned and if the French fell (which they came agonising close to doing) the game would be up. As it turned out the Somme failed to break the German line but did achieve the main objective of halting Verdun and thus saving the French. And, interestingly, though the cost was huge, it was not by scale the worst British battle by any means. Just one comparison: the British campaign at Normandy in 1944 - landing at D-Day and breaking out through the Bocage - was at a higher proportionate cost, it is just that fewer divisions were involved and they did, unlike the Somme, break the German line. They had significant advantages Haig did not - attack at the time of their choosing, doing so with aerial superiority and with the massive US war machine behind them.

Anyway, I could go on - and have done over at mine.

Regards,
P-Ump.

sustain_ability said...

Charity Begins At Home
(In the hope of avoiding wars..)

http://www.canada.com/montrealgazette/news/business/story.html?id=12d6d1b0-b82d-4bd2-8c0e-9de295c5512f&k=26043

From the outside, the Éco Terra house looks like any other home you'd find in an upscale new subdivision. It just goes to show how deceiving looks can be.
The recently completed 1,500-square-foot, two-bedroom home represents a glimpse of the future of homebuilding. It uses the latest techniques and technologies to create a comfortable and energy-efficient living environment. How efficient? By the end of one calendar year, the Éco Terra will produce 5,575 kilowatt hours of energy, exactly as much as it consumes. A conventionally built house of similar size would use about 26,000 kilowatt hours of power, according to its builder, Alouette Homes.
The house is one of 12 across the country taking part in Canada Mortgage and Housing Corp.'s EQuilibrium sustainable housing initiative. It is also the first of the 12 to be completed. A second, Abondance Montréal, will have its sales launch tonight in Verdun. A third is being built in Hudson's Alstonvale housing development.
Alouette Homes, a family owned business, has been delivering factory-built houses from its 100,000-square-foot production facility in Ste. Anne de la Rochelle since 1971. It took the Alouette team three weeks to build the Éco Terra's six modules in the factory. That's about two weeks longer than usual, as the design and construction team nitpicked over each construction step. The modules were then transported by flat-bed truck and assembled outside Eastman, 35 kilometres west of Sherbrooke, in a single day.

Among the innovations Alouette brought to the project is a modularized mechanical room, the brains and guts of the home's energy-management system. The other is an integrated roofing module that incorporates a photo-voltaic membrane for capturing solar heat that can then be converted into energy. The steel roof system also includes a thermal collector that takes that heat and redistributes it to the clothes dryer, hot-water tank and the basement's concrete slab floor.

"We think there will be a market with other builders who don't have the expertise for this technology. They can incorporate the modules into their own homes ready to go," said Alouette president Bradley Berneche.

The Éco Terra capitalizes on its rural setting. It has a wall of south-facing windows to make optimal use of passive solar energy and natural light. The mature trees that encircle it offer cooling shade in summer and a windbreak in winter. In all, the Éco Terra has hundreds of monitoring devices that track water consumption, indoor and outdoor temperature, and shifts in the wind and air quality. It is intuitive enough to deploy motorized window awnings to cut the sun's glare at high noon on a summer day.
None of this comes cheaply. The Éco Terra comes with a $475,000 price tag. Part of that is the price one must pay to own a prestige property on a three-acre lot. The energy-efficiency elements add about 30 per cent to the over-all cost, Berneche said.

"We think there is a very small market for a house like this. We might sell two of them in Quebec," he said last Friday during the Éco Terra's unveiling. "We hope to influence the marketplace. Maybe you can't afford to have all of these features, but maybe you can use some of them."
Buyers will have a chance to decide for themselves. The Éco Terra, like the other 11 houses in the EQuilibrium initiative, will be open to the public for the next six months before being sold. The house will then undergo another two years of CMHC monitoring to see how it functions under normal family use.

Cheap and abundant hydro-electric power is both Quebec's blessing and its Achilles' heel, according to Berneche.
"We aren't very serious about reducing energy consumption, but we're going to have get serious".

The same can't be said in Europe, where Alouette makes 30 per cent of its sales. Last year, it shipped 200 homes to Europe, mostly to Britain and France. Those countries are taking the challenges of global warming and sustainability seriously.
Sustain
A cheaper alternative(!?):
http://www.i-domehouse.com/

Dr Johnny said...

It's called trade.

Why are you so idiotic of sticking to the idea that the UK can not use ships to import carbohydrates.

You keep pushing this autistic nonsense based on some hysteric idea of autarky.

And I thought the UK was a nation of mariners. Apparently not.

Import the sugar, dummy.

We can produce 1200EJ from it worldwide - more than 6 times total world oil consumption. And we can produce it sustainably.

So get a grip please.

energybalance said...

"Autistic"? Oh dear, I have touched a nerve haven't I?

The British are traditionally a nation of mariners and engineers too. Do you know anything about engineering "Dr" Johnny? I am well aware of all you refer to, including all issues regarding biomass, gasification and so on.

But do you have any idea of the scale of new technology/engineering required to produce our oil equivalent in terms of sugar/biomass in total, and what sources of energy we might use to fabricate it all?

Oil, gas, coal?

And we would power those ships by what? Oil, as they are now mostly run on?

Traditionally the British ran their ships on coal (apart from those clippers, which we may need again) but that would need to be produced on a large scale from new mines if it is to become our substitute fuel.

"1200 EJ"... And so we in the industrialised world eat the planet... is that what you are saying? As all that sugar will be grown in the southern (developing) nations presumably? And it will be farmed using what sources of energy? Oil?

By the way, how will we make all those fuel cells when there is such a low availablity of platinum? Yes, we could use putative nano-nickel and so on, but we are placing our bets on future technologies all the time, when oil runs inexorably costlier and more difficult to extract.

So, do you think we can switch over to a biomass economy in time, i.e. within 10 years?

Yes, do "Get a grip"?, calm down and learn some manners and I am open to further discussions or debates.

"Hysterical"? You will rarely find a calmer man than me...

energybalance said...

If my critic is right and we can simply buy all that sugar in from elsewhere, how much arable land would it take to grow enough sugar to run the world's transportation on biohydrogen made from it? Roughly 30% of the Earth's surface is land and around one tenth of that is arable. This makes a grand total of 14.9 million square kilometres. We may deduce that to grow sufficient sugar from cane or beet would require 34.4 million km^2 of arable land to substitute for the entire world's oil requirement to fuel transport (clearly not feasible) and more than half of it, or 8.8 million km^2 just to keep the U.S. mobile. Unfeasible though these numbers are per se, they must be further regarded against recent estimates that the Earth can only support about 3 billion people, or half the present human population, in the absence of fertilizers etc. and a system of modern agriculture based on oil and natural gas. It should be noted too, that this population is predicted to rise to around 9 billion by 2050, but how can it, when many producing wells of oil and gas will be running out by then?