Friday, February 09, 2007

What Chance for Bio-Butanol?

Much discussion on biofuels circles around bioethanol, as I mentioned most recently in the posting "U.S. May Need to Import Corn", since this is provides a better crop-fuel yield than say, biodiesel and certainly biohydrogen. However, there is a new kid on the block and that is biobutanol. Converting sugars to butanol by fermentation is not new at all, and the ABE process dates back to 1916, when Chaim Weizmann, a student of Louis Pasteur, developed a means for thus making a mixture, of acetone, butanol and ethanol, from which the acetone was used to make cordite - an explosive used extensively in the First World War. However, for every pound of acetone, two pounds of butanol were produced, and it was not until the 1920's and 30's that butanol became widely used in the manufacture of paints for cars and of synthetic rubber to the extent that the acetone was a mere by-product. Weizmann was to become the first President of Israel, and the Weizmann Institute, internationally renowned for its scientific research, is named after him.
The essential science behind biobutanol production is that for producing biohydrogen, as I discussed some while ago, noting that it is a fantasy to suppose that sufficient H2 could be so produced to replace the current levels of fuel used in the U.K. to power its transportation infrastructure. However, the ideal reaction in this regard, namely producing a maximum yield of hydrogen, also produces butyric acid, in a first step, which may then be reduced to butanol, if an appropriate co-bacterium is present to do so. (When the intention is to maximise the yield of H2, a second competing reaction, which produces double the amount of H2 plus acetic acid as the organic counter-product is the most desirable of the two). A batch-process has now been developed which uses Clostridium tyrobutyricum to produce the butyric acid and then Clostridium acetobutylicum to turn this into butanol. Look up the trademarks "Butyl-Fuel" and "Freedom Fuel" and you will find various information about this patented process. I may be missing something, and perhaps the process is more complex that a simple conversion of sugar into butanol plus H2, but the 2.5 gallons per bushel yield claimed, seems to me to imply a yield of 117%, since I would reckon a maximum of 2.14 gallons from the 35 pounds of sugar contained in one bushel of corn. A second figure they give is that a yield of 42% of butanol is obtained based on glucose, which is about 100% yield on the reaction overall. As I say, I may be missing something (patents never disclose all the details do they?), but I am not aware of 100% yield ever being obtained from a fermentation process - e.g. for ethanol somewhere in the range 55% - 77% is typical.
It was intially further confusing to me in that the output is reckoned in U.S. gallons (Avoirdupois) e.g. 3.785 litres, as opposed to U.K. (Imperial) gallons which are equal to 4.56 litres.
Similarly, it is quoted that 2.5 gallons of ethanol can be obtained per bushel of corn (containing 35 pounds of sugar) can be obtained. Let's check that one...

C6H12O6 (mono-saccharide e.g. glucose)--> 2 CH3CH2OH (ethanol) + 2CO2.

(92/180) x (35 pounds/2.2 pounds/kg) = 8.13 kg of ethanol. The specific gravity of ethanol is 0.789 kg/litre and so we have 8.13/0.789 = 10.30 liters of it, for yield of 100%. Dividing by 3.785 litres/gallon (U.S.) we get 2.723 gallons, and so the yield is 2.5/2.723 x 100 = 92%, which seems very high!

If anyone can add anything here to clear up why the quoted yields of butanol or ethanol should be so large, or if I have made a mistake I should like to know what it is!

Anyway, let's accept that we can get 100% yield from glucose (or other sugars), and work the potential butanol production for the U.K. in terms of sugar crops (since we don't grow corn on a scale of proportion as the U.S. does - our traditional crop is wheat, but sugar beet grows well in the climate here). The processes of fermenting sugar to butanol can be represented:

C6H12O6 --> CH3CH2CH2COOH + 2CO2 + 2H2; then

CH3CH2CH2COOH (butyric acid) --> CH3CH2CH2CH2OH (butanol).

If both steps were to go to 100% completion then we expect a yield of (74/180) the ratio of the molecular weights of butanol and glucose, multiplied by the quantity of glucose used. 74/180 gives 41.1%, close to the 42% claimed. So let's (with an element of dubiousness) assume this is the yield than is to be expected.

One tonne of glucose would yield 0.411 tonnes (411 kg). Since it is reckoned that a crop of sugar beet can yield about 19 tonnes per hectare, each hectare would produce 19 x 0.411 = 7.81 tonnes of butanol. The density of butanol is 0.808 kg/litre and so this would occupy a volume of 7.81/0.808 = 9,666 litres/ha.

From the relative enthalpies of combustion of butanol and gasoline we may deduce that the energy punch of ethanol is 92% that of gasoline. However, as with ethanol, an engine can be tuned to burn the fuel at higher efficiency, and so to keep the business simple, lets assume we can compare the two fuels 1:1.

Hence we need to replace 57 million tonnes of oil equivalent in terms of current fuel by butanol. As I have pointed out before, standard internal combustion engines only get about 14% of the total energy that the fuel contains out as miles on the road, and hybrid e.g. Prius vehicles can achieve 42%, so we might deduce that that figure could be cut to a third, making a "mere" 19 million tonnes of butanol we would need to replace with biobutanol. So the crop to provide this would have to be grown on 19 x 10*6/7.81 = 2.433 x 10*6 hectares of land, which is 243,278 km*2, or about the same area as the total U.K. mainland. If we used all our arable land, which is just 65,000 km*2 we could supply 26.7% or about a quarter. (With standard gas-guzzling engines it would be about 9%, or less than one tenth). N.B. the latter figures only apply if we grow no food at all and convert all agriculture over to biobutanol production.

There is a butanol farm in Norfolk which will supply 70 million litres of butanol by 2010, which sounds a lot, and it is, but then we use an awful lot of fuel! Indeed, this would need to be grown on 70 x 10*6/9,666 = 7,242 hectares of land = 72.4 km*2 of arable land. So, how much would it produce as a proportional substitute for the current requirement? Well, the current requirement amounts to: 57 x 10*6 x 1000/0.808 = 70.5 billion litres. Hence 70 million/70.5 billion x 100 = 0.1%. If Prius hybrid engines were universally installed, that rises to a mere 0.3% of the total. Even if blended 5:95 in existing fuels, it amounts to 2% (or 6%) of the total, and a blend of this dilution would make so difference whatsoever to curbing CO2 emissions or ensuring security of fuel supplies. Forget it! Localise communities and cut vehicle use, and grow food instead. Other means must be found to provide for what remaining transport requirement we have following re-localisation, mainly in the form of synthetic oil from coal-liquefaction and electricity-driven transport systems operating over relatively small areas. The only biofuel worth bothering with is bioethanol, and only then on a small scale. If wheat-grass and other agricultural waste can be converted into ethanol, that is a bonus since it avoids any compromise of food production. If there are to be serious amounts of fuel available, post peak-oil, they will necessarily stem from coal, and for that to happen, "many" coal-liquefaction plants must be built from scratch!

14 comments:

Stafford "Doc" Williamson said...

I have been enjoying several of your recent entries on Energy Balance. You are obviously well educated and well informed.

I, too, have heard a lot recently about biobutanol, especially the DuPont/BP alliance to produce it in Britain from sugar beets. That crop density seems potentially very promising relative to corn or grain on any given area of land, but I think there may be some voodoo numbers that no one is talking about, or not so much in public, that may make this a more viable aviation fuel than current information seems to indicate. Sir Richard Branson seems to be a backer, and cheerleader for (bio)butanol, particularly with reference to his transportation businesses.

But I do think too, that your strict chemical formula calculations on yields are misguided slightly. The "modern" biobutanol process is not the ABE process, and based on the claims of yields, I suspect that there are more sugars involved than your assumptions about "sugar" content in either corn or beets. Part of the "advantages" of these "new" fermenation microorganisms is that they can digest "other" sugars, and it is also possible that they are 'squeezing' extra yields from post-processing of the sludge.

I am somewhat more optimistic than you, apparently, that biodiesel, and other "bio" sources will be significant contributors to solving the fuel crises we need to be facing today to avoid disasters tomorrow. I am not totally opposed to gasification of coal projects, but I think they need to focus on trying to produce a "net green" effect by funneling (literally) carbon dioxide emissions from their combustion process directly into algae cultivation to take advantage of the photosynthetic effect of producing more biomass. Yes, it would be a huge undertaking to create biomass production sufficient to replace the disappearing rain forests, and we have to deal with that separately, but it is possible to feed carbon dioxide to certain species of algae that will double in weight and volume in just a couple of days.

That is not to say, either, that the planet can get along swimmingly without also directing some attention to the significant decline in phytoplankton, but if we must release the carbon that has been, in effect, sequestered by prehistoric biosynthesis, then we better be producing a lot of green that keeps the atmosphere clean at the same time.

Respectfully submitted
Stafford "Doc" Williamson
www.winfotech.com

energybalance said...

Thanks you for your interest in my articles here and for your comments. In the absence of a clear explanation for the 2.5 gallons of butanol/bushel of corn, I used the other figure cited in the patent, reckoned as a 42% yield based on glucose. The chemistry has to add-up, and I think much of the over-optimism about renewable resources generally among some environmentalists, is that they haven't done the math on the basic chemistry. That has to add-up, otherwise it is "Voodoo" or not science anyway. So, if someone can show me some figures that prove I'm wrong I should like them to do so. Believe me, I should like to be wrong, but according to my calculations (which I show in detail), and those by other writers, I am not, and we simply cannot continue to run the worlds's existing fleet of vehicles on biofuels. If we had 10% the number of road vehicles and planes, then some considerable impact might be so made. Either way, communities will necessarily begin to localise, and that needs to be planned for, otherwise things could get quite nasty! I did not say that the modern biobutanol process was the same as the old ABE process. I merely mentioned that for historical completeness. The new patented methid apparently turns almost all the sugar into butyric acid and thence to butanol. I am with you on the issue of CO2, but some of the proposed methods for sequestering it are highly energy intensive and might consume up to 40% of the energy output from say a power station fired by coal to do this - hence we would need more or more efficient power stations in that proportion. Coal liquefaction has much to offer and is probably the only way of maintaining subtantial stocks of hydrcarbons both for use as a fuel and as a chemical feedstock for industrty. It is often forgotten that it is not only fuel that we rely on oil to provide! I find the idea of using CO2 to force biomass to grow and that way to both sequester the gas and produce more biomass for biofuel production very interesting. Some of the new technologies for digesting cellulose could prove very useful in enhancing the yield/hectare of these materials, or indeed in providing new substances. Maybe we will end up with a mix of biodiesel, bio-alcohols, and hydrocarbons from coal. However, some definite strategy must be implemented very soon. Undoubtedly, we can't continue on down the car/oil route, and a balance of alternative fuels (including electricity) and cutting demand through localisation will be central to the whole issue of surviving the post-(plentiful)oil era. It is worrying that the phytoplankton is in decline, since that absorbs (through photosynthesis) about 50% of the CO2 emitted from all sources. Is it known why that should be - warmer currents, more acidic waters? Thanks for your comments. Chris Rhodes.

Anonymous said...

Hi, I think there some factual errors in your post. Googling aropund myself I found:
1. sugar beet yiled per hectar is abour 40-70 metric tons with a sugar content of 17-22 %.
2. The US mainland is in the order of 7.8 million km^2. Not sure how much is good for growing beet and such but it is more than 63K Km^2 for sure.
...emm, maybe you should review some of those facts and start those calculations over. I am still working on those details myself...that's how I found your blog.

energybalance said...

Hello anonymous!

Right, my figures referred to the U.K., not the U.S. Over here we have about 65,000 km^2 of arable land (from 165,000 km^2 in farm holdings and around 250,000 km^2 total area of the U.K. maniland), and I worked to a sugar yield of 19 tonnes/hectare, which is close to the upper-limit of your values, i.e. 22% of 70 tonnes = 15.4 tonnes of sugar. I think maybe you need to complete your calculations, then we can compare them usefully. If anything, I am being optimistic and any revision is likely to be downwards! What I do know is that the biobutanol output is not going to be (much?) greater than ethanol, and I have already worked-out that we would need somewhere close to the entire area of the U.K. mainland to grow enough sugar beet to prouduce the equivalent of our oil-based transportation fuel. Please get back to me. I will post something about a comparison between different biofuels and coal liquefaction, as I think it is the latter that will come to our aid, post peak oil, if anything will.

Doc said...

Chris,

I found some info on breaking down "other" and fermenting them, xylose in particular. I am not privy to the details of the BP/duPont process, but that could be a factor.

I haven't heard any satisfactory explanation as to why ocean phytoplankton are in decline. It seems logical to me that warmer water and more carbon dioxide would lead to more of them, but I have seen a couple of "nature" programs on television of late that warn of shortages (in realtion to whales which feed on them, I seem to recall).

Incidentally, having just re-read my prior post here, I seem to have neglected to mention that after you feed the algae the carbon dioxide from the (coal fired) power stations, you can not only harvest it as cattle feed or fertilizer, you can also process the lipids in the algae into more biodiesel, which, in itself displaces the use of other fossil based sources of diesel, so that is why you get an overall much "greener" use of coal than in prior incarnations of electric generating techniques.

Stafford "Doc" Williamson
p.s. Please do drop by my web site at winfotech.com/energy/ for a lot more discussions on biodiesel, biofuels and biobutanol (along with a wild and wooly mix of politics and entertainment too).

energybalance said...

Hi Doc,

good to hear from you again. Yes, I have also heard about making biodiesel from algae, and I like that idea of combining the two technologies to convert CO2 from coal into algae to make the whole process greener!

If the algae to fuel technology can be pulled-off on a large scale it could provide much of our fuel, and since maybe 50% of the algae is protein/carbohydrate there is the option of turning it into food. All in all there is much to recommend this way if thinking, to my mind!

I have posted some articles about algae and there is a link to the "oilgae" site which does the job in far greater detail. From reading it, I think there is much that need to be ironed-out, but along with "cellulosic" methods, this could be the way forward.

Meanwhile, I'll take a look at your web-site.

All the best,

Chris.

Anonymous said...

Whilst these items are somewhat dated It might be worth while stating the obvious.

Pure MonoSaccharides C6 can also be derived from reduction/refraction of Ligno-Cellulose and therefore the proposed yields per hectare can be reconsidered.

I wonder whether you have considered the variant of C5 as this can also be used here.

With regards to using Macro-Algae (or indeed Micr-Algae) as a feed source you open interesting discussions. Applied Biofuels Limited in Israel is currently working on the Farmed MacroAlgae that has nearly 90% pure Cellulose C6 developed in Hybridisation and this grows in shallow lagoons at the rate of 25 to 30 times to prodcution equivalent of Sugar Cane per year! As this grows in saline/brackish polluted water the benefits are immense and it does not beed prime agricultural land.

energybalance said...

As you say, this is quite an old article now, and alternative technologies for providing the "sugar" from cellulose/lignocellulose now look promising.

That said, to derive fuel on the grand scale to effectively replace oil at 20-odd billion barrels a year as are currently refined into petrol and diesel is going to take a lot of land-space nonetheless.

Indeed, we appear to concur about the potential role of algae, for the reasons you say about less pressure on prime land and on freshwater. I am aware of the Israel-company who seem to be at the forefront of algal fuel production.

Regards,

Chris Rhodes

Anonymous said...

Can someone please explain me how to make Butanol from sugarcane or ethanol in easy way or easy steps.
I would be very thankful
Thanks
Fas
fas.butt@yahoo.com

Anonymous said...

When you cite references to Butanol the natural and most obvious statements are in relation to the issues which you record. However using the general mass equation (molecular mass) is confusing.

The real issue is the function of Carbon, and in that the reference to 2 molecules of ethanol per molecule of the C6 Mono-Saccharide is as equally valid as obtaining 1 molecule of butanol from the same (equivalent) molecule of a C6 Mono-Sachharide. The Carbon numbers balance. However you have actually missed the point that not all plants are strictly numerically multiples of C6 Mono-Saccharides, they are polymerised versions of these Saccarides with a lower H-OH radical attached to their chemical chain and it is this that has to be rectified in the formative (pre-treatment) processing.

Yes you are correct with the use of sugar beet (USA Corn-Syrup, and Sugar Cane) in Saccharides are the C6 H12 O6 but a proportion of the end result also arises from the C5H10O5. There is also the issue that the more effective route to obtain ethanol is actually to convert the C6H12O6 to Acetic Acid first and your yield of Ethanol will increase significantly.

This route by Acetic Acid to Butanol is also equally inviting and simpler procedure to make Butanol. Your thoughts again.

The other comment about yields. Your statements show that you doubt any yields higher than say 60%! This would be the case in a closed batch process but now we have a continuous processing route this stop-start issue is not around. I suggest that from the results we have seen from the eminent papers written ex of various UK and USA and Netherlands and Swedish Universities that 85 to over 90% and more is the realism in continuous procedures. Thus when you add together the fact that by Hydrolysis (to reduce the source PolySaccherides down to the MonoSaccharides) and then convert these to Acetic Acid before making either Ethanol or Butanol (and occasionally Propanol!) then yields in the area you have questioned are realistic.

Returning to Algae is of course again the flavour of the year. The two routes that follow Lipids (in MicroAlgae) and Plantella (in MacroAlgae) each have their followers. I like them both for they do not compete against either. Lipids and MicroAlgae need a shallow interface with the sun and hence the use of Photo-Bioreactors and the developments therein in the USA and elsewhere are impressive. How far off it will be before manufacturing "realistic" quantities of oils is not here to be known but the recent EU predictions of 2030 seem reachable. It will be cost which will decide. As to MacroAlgae everyone seems to be missing the issue for there are two distinct pathways. The first is to harvest these grown at sea and thence we come across the analogy of the Food v Fuel debate in a much wider forum. MacroAlgae grown in the Oceans is a feed source material for much of the sea life (fauna) and messing around with these will have serious effect. However in the background there are the major developments in Israel Chile Peru and Africa where Macro-Algae are being grown in shallow lagoons established in desert locations and from which yields of these Macro-algae that can be tailored to replicate C6-PolySaccharides at 95+% fractions or in the converse as C5-PolySaccharides in the 87+% fractions (where this is the internal matrix of the plant, remembering that these do not need Lignin for stability as in the land-based alternatives) and so as the yields previously reported were shown to be over 20 times that per hectare compared to Sugar Cane and can be grown in salt-laden lagoons barely 250 mm deep. As reported in Israel and Peru the potential is phenomenal. Using non-arable lands (deserts etc) or sequestering CO2 at power stations to make such fuels is the way forward and is likely in 4 years!

Are you updating this site?

Anonymous said...

When you cite references to Butanol the natural and most obvious statements are in relation to the issues which you record. However using the general mass equation (molecular mass) is confusing.

The real issue is the function of Carbon, and in that the reference to 2 molecules of ethanol per molecule of the C6 Mono-Saccharide is as equally valid as obtaining 1 molecule of butanol from the same (equivalent) molecule of a C6 Mono-Sachharide. The Carbon numbers balance. However you have actually missed the point that not all plants are strictly numerically multiples of C6 Mono-Saccharides, they are polymerised versions of these Saccarides with a lower H-OH radical attached to their chemical chain and it is this that has to be rectified in the formative (pre-treatment) processing.

Yes you are correct with the use of sugar beet (USA Corn-Syrup, and Sugar Cane) in Saccharides are the C6 H12 O6 but a proportion of the end result also arises from the C5H10O5. There is also the issue that the more effective route to obtain ethanol is actually to convert the C6H12O6 to Acetic Acid first and your yield of Ethanol will increase significantly.

This route by Acetic Acid to Butanol is also equally inviting and simpler procedure to make Butanol. Your thoughts again.

The other comment about yields. Your statements show that you doubt any yields higher than say 60%! This would be the case in a closed batch process but now we have a continuous processing route this stop-start issue is not around. I suggest that from the results we have seen from the eminent papers written ex of various UK and USA and Netherlands and Swedish Universities that 85 to over 90% and more is the realism in continuous procedures. Thus when you add together the fact that by Hydrolysis (to reduce the source PolySaccherides down to the MonoSaccharides) and then convert these to Acetic Acid before making either Ethanol or Butanol (and occasionally Propanol!) then yields in the area you have questioned are realistic.

Returning to Algae is of course again the flavour of the year. The two routes that follow Lipids (in MicroAlgae) and Plantella (in MacroAlgae) each have their followers. I like them both for they do not compete against either. Lipids and MicroAlgae need a shallow interface with the sun and hence the use of Photo-Bioreactors and the developments therein in the USA and elsewhere are impressive. How far off it will be before manufacturing "realistic" quantities of oils is not here to be known but the recent EU predictions of 2030 seem reachable. It will be cost which will decide. As to MacroAlgae everyone seems to be missing the issue for there are two distinct pathways. The first is to harvest these grown at sea and thence we come across the analogy of the Food v Fuel debate in a much wider forum. MacroAlgae grown in the Oceans is a feed source material for much of the sea life (fauna) and messing around with these will have serious effect. However in the background there are the major developments in Israel Chile Peru and Africa where Macro-Algae are being grown in shallow lagoons established in desert locations and from which yields of these Macro-algae that can be tailored to replicate C6-PolySaccharides at 95+% fractions or in the converse as C5-PolySaccharides in the 87+% fractions (where this is the internal matrix of the plant, remembering that these do not need Lignin for stability as in the land-based alternatives) and so as the yields previously reported were shown to be over 20 times that per hectare compared to Sugar Cane and can be grown in salt-laden lagoons barely 250 mm deep. As reported in Israel and Peru the potential is phenomenal. Using non-arable lands (deserts etc) or sequestering CO2 at power stations to make such fuels is the way forward and is likely in 4 years!

Are you updating this site?

Anonymous said...

When you cite references to Butanol the natural and most obvious statements are in relation to the issues which you record. However using the general mass equation (molecular mass) is confusing.

The real issue is the function of Carbon, and in that the reference to 2 molecules of ethanol per molecule of the C6 Mono-Saccharide is as equally valid as obtaining 1 molecule of butanol from the same (equivalent) molecule of a C6 Mono-Sachharide. The Carbon numbers balance. However you have actually missed the point that not all plants are strictly numerically multiples of C6 Mono-Saccharides, they are polymerised versions of these Saccarides with a lower H-OH radical attached to their chemical chain and it is this that has to be rectified in the formative (pre-treatment) processing.

Yes you are correct with the use of sugar beet (USA Corn-Syrup, and Sugar Cane) in Saccharides are the C6 H12 O6 but a proportion of the end result also arises from the C5H10O5. There is also the issue that the more effective route to obtain ethanol is actually to convert the C6H12O6 to Acetic Acid first and your yield of Ethanol will increase significantly.

This route by Acetic Acid to Butanol is also equally inviting and simpler procedure to make Butanol. Your thoughts again.

The other comment about yields. Your statements show that you doubt any yields higher than say 60%! This would be the case in a closed batch process but now we have a continuous processing route this stop-start issue is not around. I suggest that from the results we have seen from the eminent papers written ex of various UK and USA and Netherlands and Swedish Universities that 85 to over 90% and more is the realism in continuous procedures. Thus when you add together the fact that by Hydrolysis (to reduce the source PolySaccherides down to the MonoSaccharides) and then convert these to Acetic Acid before making either Ethanol or Butanol (and occasionally Propanol!) then yields in the area you have questioned are realistic.

Returning to Algae is of course again the flavour of the year. The two routes that follow Lipids (in MicroAlgae) and Plantella (in MacroAlgae) each have their followers. I like them both for they do not compete against either. Lipids and MicroAlgae need a shallow interface with the sun and hence the use of Photo-Bioreactors and the developments therein in the USA and elsewhere are impressive. How far off it will be before manufacturing "realistic" quantities of oils is not here to be known but the recent EU predictions of 2030 seem reachable. It will be cost which will decide. As to MacroAlgae everyone seems to be missing the issue for there are two distinct pathways. The first is to harvest these grown at sea and thence we come across the analogy of the Food v Fuel debate in a much wider forum. MacroAlgae grown in the Oceans is a feed source material for much of the sea life (fauna) and messing around with these will have serious effect. However in the background there are the major developments in Israel Chile Peru and Africa where Macro-Algae are being grown in shallow lagoons established in desert locations and from which yields of these Macro-algae that can be tailored to replicate C6-PolySaccharides at 95+% fractions or in the converse as C5-PolySaccharides in the 87+% fractions (where this is the internal matrix of the plant, remembering that these do not need Lignin for stability as in the land-based alternatives) and so as the yields previously reported were shown to be over 20 times that per hectare compared to Sugar Cane and can be grown in salt-laden lagoons barely 250 mm deep. As reported in Israel and Peru the potential is phenomenal. Using non-arable lands (deserts etc) or sequestering CO2 at power stations to make such fuels is the way forward and is likely in 4 years!

Are you updating this site?

Anonymous said...

Dear Chris Rodes: Isn't Butanol a more favoured material (FUEL) for mixing with petro-Disel up to 40% blend?

Another thought, and one which is very obvious, if you make Ethanol at 95% and mix it with Butanol at 15% tou would have the ideal fuel for cars. Completely Renewable and totally acceptable for Bio-Fuelled Driven cars and Hybrids.

If I recollect here this is waht they are doig in Holland and Malta with their proposed continuous production plants.

Chris Rhodes said...

This is an old (7 years old) article now. Yes, you are probably correct about the fuel blends, but my main point was that the amount of the fuel that can realistically be produced is limited compared to the amount of liquid fuels we get through, as refined from crude oil.