Test Results Show Biobutanol Performs Similarly to Unleaded Gasoline
20 April 2007
|1-butanol is less volatile than ethanol, and butanol-gasoline blends are less volatile than ethanol blends. Adding a fraction of butanol to an ethanol blend brings down the volatility. Click to enlarge. Source: BP|
New fuel testing results on bio-derived 1-butanol presented by DuPont and BP at the SAE World Congress indicate that biobutanol has proven to perform similarly to unleaded gasoline on key parameters, based on ongoing laboratory-based engine testing and limited fleet testing.
According to BP Biofuels program manager Frank Gerry, biobutanol formulations meet key characteristics of a “good” fuel, including high energy density, controlled volatility, sufficient octane and low levels of impurities.
He described early testing data that indicate that biobutanol fuel blends at a nominal 10 vol% level perform very similarly to unleaded gasoline fuel. Additionally, the energy density of biobutanol is closer to unleaded gasoline.
Butanol does not phase-separate in the presence of water, unlike ethanol. With a lower oxygen content than ethanol, higher volumetric concentrations of butanol could be blended into gasoline while still adhering to oxygen limits. Fuel testing also has proven that biobutanol does not phase separate in the presence of water, and has no negative impact on elastomer swelling.
Combined with ethanol in gasoline blends, butanol can bring down the vapor pressure of the fuel.
|1 Blend values of alcohol octane numbers and vapor pressure.|
2 Summer / Winter specifications.
|Sp. Gravity 60/60 F||0.794||0.814||0.720 - 0.775|
|Heating Value [MJ/l]||21.1 - 21.7||26.9 - 27.0||32.2 - 32.9|
|RON||106 - 1301||941||95|
|MON||89 - 1031||80 - 811||85|
|[email protected] 5% / 10% [psi]||311 / 201||6.41 / 6.41||< 7.8 / 152|
|Oxygen [%wt]||34.7||21.6||< 2.7|
15% biobutanol + E85 anyone ???
Posted by: Lucas | 20 April 2007 at 02:17 PM
Didn't we know this already?
Posted by: Brad | 20 April 2007 at 02:18 PM
what about production costs?
Posted by: rick | 20 April 2007 at 02:24 PM
Interesting. While ethanol is a good idea, butanol sounds even more promising. BTW, what materials could be used for making butanol?
Posted by: Mark R. W. Jr. | 20 April 2007 at 03:35 PM
Posted by: Lucas | 20 April 2007 at 03:47 PM
Butanol would be made from cellulose via advance ABE fermentation (hence bio-butanol instead of made-from-petroleum butanol). Many are trying to engineer ABE fermentation to only produce one product (in this case Butanol, and no Ethanol or Acetone, Hydrogen though is a given bi-product) thus simplifying the system and making it energy positive.
Posted by: ben | 20 April 2007 at 04:07 PM
Butanol is a potential substitute for bulk gasoline because of its comparable energy density, octane number and suitability for pipeline systems. Ethanol is a good octane improver and it helps reduce emissions. Both alcohols can be produced from glucose using the appropriate strains of micro-organisms. Biobutanol can therefore be made from the same sugary or starchy feedstocks used to produce ethanol today.
The main difference is that industrial-scale technology for ethanol is already in use today. Yields for current butanol fermentation systems are typically lower and some of the by-products (e.g. butyric acid) require post-processing. Others, e.g. hydrogen, are valuable in their own right.
As for alcohols from cellulose, a big hurdle is making the pre-processing affordable. Also, cellulose breaks down a mixture of glucose and xylose, which complicates the process engineering and operations.
Still, I expect scalable solutions for these technological problems will be found in the next few years, provided the price of crude oil stays high enough. A good quality fuel might consist of a blend of fossil-based gasoline, quite a bit of bio-butanol and a little bio-ethanol.
Posted by: Rafael Seidl | 20 April 2007 at 05:47 PM
The lower octane of butanol is a real problem, why burn butanol (more expensive) at 25% efficiency when you can burn methanol at 43% efficiency and ethanol at 41% efficiency, and I expect a higher emissions problem.
The greater energy content of butanol, is a minor matter, liquid fuels are so concentrated in energy already that the question is of $/mile, emissions per mile, and non-Middle East source. The plastic methanol fuel tank is a vastly simpler, cheaper more economic proposition than the 5,000-10,000 psi H2 fuel tank or Natural Gas fuel tank, or even the LPG fuel tank.
And producing fuels by fermentation methods is not only inefficient, but throws away most of the biomass carbon, which is the real advantage of biomass to liquid fuel, get all of the carbon into the fuel, this means Fischer-Tropsch not fermentation.
I would say butanol would be good for aircraft where fuel weight is an important concern or remote communities where fuel must be flown in or trucked great distances.
Posted by: Warren Heath | 20 April 2007 at 07:25 PM
Warren - you cannot possibly be quoting combustion efficiency - what do those percentages represent?
Posted by: Angelo | 20 April 2007 at 07:36 PM
Angelo, the EPA has tested a VW 90hp TDI diesel converted to burn neat methanol and ethanol (spark ignition & port fuel injection). The numbers are the peak brake thermal efficiency of the engines @ 57.5 hp/2150 rpm for the ethanol version, and 54 hp/2200 rpm for the methanol engine. The methanol engine also has a maximum hp of 112 hp @ 4000 rpm & 37.5% eff. vs the diesel of 106 hp @ 4010 rpm & 35% eff. The most interesting feature is the much larger high efficiency island of the methanol engine vs. the diesel. Whereas the diesel has a peak efficiency of 41% at 2200 rpm & 64 hp, at a typical 60 mph driving speed for the VW sedan, the engine would need to supply 13.5 hp which would be max 32% engine efficiency for the diesel, while the methanol version would be 40% efficient or 25% better than the diesel.
Running the methanol engine in a series hybrid, you could vary the engine output from 13.5 hp to 89 hp, and still achieve 40-43% engine brake thermal efficiency, throughout. This is important because the optimal way to run a series hybrid generator engine is to supply the maximum amount of energy directly to the PEM DC Bus bypassing the battery, where ~15% charging losses will occur.
Posted by: Warren Heath | 20 April 2007 at 08:36 PM
Warren, your comments regarding ethanol and methanol are important as they are better fuels than their petroleum counterparts, However I think that the butanol 25% efficiency numbers are suspect. Certain benefits in terms of thermal efficiency, and flame travel/propagation are related to the latent heat of vaporization of the lesser alcohols. You are correct that gasification will be the likely method of production.
Posted by: John Schreiber | 20 April 2007 at 09:14 PM
What your argument ignores is that, regardless of the efficiency of methanol in converted diesel engines, biobutanol can be shipped through the present pipeline infrastructure and run at much higher concentrations in gasoline-powered vehicles presently on the road. With butanol there is no need to replace the entire vehicle fleet with methanol-capable engines. Regardless of higher methanol efficiency, you cannot ignore those facts butanol has in its favor.
Pure efficiency is not the sole consideration.
Posted by: Cervus | 20 April 2007 at 09:19 PM
drivers do care about range on a full tank, though perhaps more so than they should. The bigger issue is that fuel logistics and storage costs scale with volume rather than mass, so lower density fuels tend to increase the per-mile cost of operating a vehicle.
Methanol has long been advocated as an alternative fuel and, it would be fairly cheap to produce compared to ethanol let alone butanol. Evidently, its drawbacks (highly hygroscopic, low energy density, colorless flame, formaldehyde emissisons, neurotoxicity etc.) outweigh its advantages or we'd all be driving around with it already.
Wrt F-T/MTG: synthetic alkanes are very attractive fuels but these processes are fairly inefficient (55-65%) in their own right. Fermentation is generally the preferred route because it is substantially cheaper - though subsidies and import tariffs are skewing the market.
I'd also be careful about drawing general conclusions regarding diesel engines based on a single conversion effort based on VW's antiquated 90hp 1.9L TDi. Modern designs feature much larger islands of high efficiency in their engine map than that particular one did.
Posted by: Rafael Seidl | 21 April 2007 at 06:34 AM
As I understand it biobutanol burns very much like gasoline. Since a thermal efficiency around 38% is commonly achieved with gasoline, I think Bio Butanol would achieve something in the neighborhood of 36%, not 25%. So a 15% lower efficiency than ethanol but a 25% higher energy content than ethanol. Result, higher mileage with biobutanol. And the fuel works well in cold environments, does not require significant engine modifications, and can be transported in the existing pipelines.
Posted by: Van | 21 April 2007 at 07:07 AM
John, the 25% efficiency of the Butanol is for the article discussion of a 5-10% mix with gasoline, so presumably the oft quoted 25% efficiency of gasoline engine. I would imagine that neat butanol can be burned in a diesel at ~40% peak efficiency.
Posted by: Warren Heath | 21 April 2007 at 08:22 AM
Cervus, methanol can easily be shipped in existing pipelines, the only problem being it will clean all the crud out of the pipeline on the first run, then it should be no problem, and spills are not an environmental hazard unlike with petroleum products. It can, like ethanol be burned as M15 or M85, but this will reduce engine efficiency compared to an optimized NEAT alcohol engine.
Posted by: Warren Heath | 21 April 2007 at 08:23 AM
Rafael, it amazes me that anyone could complain about energy density of methanol, when we are talking about extraordinarily difficult storage and transport of H2, or CNG, or even LNG. Put in a bigger, cheapo plastic fuel tank. Burnt in a series hybrid, with an optimized engine, you'll still get at least double the range of a typical gasoline vehicle, on the same size fuel tank.
Actually, fermentation methods of converting biomass to alcohol are substantially more expensive and less efficient than combustion methods. And since biomass is inherently an inefficient way to produce energy, the goal is to use it to fix carbon out of the atmosphere for liquid fuels that will be carbon neutral.
Posted by: Warren Heath | 21 April 2007 at 08:27 AM
As for the toxicity of methanol (not actually methanol but the formic acid that it is converted to in the body after 10-24 hrs), it is a simple matter to add a few parts per billion of a bitterant and a simple colorant would make accidental ingestion a non-event, and the fact is that methanol poisoning deaths would not even minutely approach deaths due to gasoline fires & carcinogenic fumes, never mind toxic automobile exhaust or prescriptiondrug overdose deaths. A colorless flame is desirable – it means you’re not producing pollutants – just like H2 & Natural Gas burns. Add a colorant if it really bothers you. Formaldehyde emissions are easily treatable in a catalytic converter. The hydroscopicity of methanol (like ethanol) is a minor problem , and both ethanol & methanol have long been successfully used as a fuel. China has prioritized methanol as a fuel, and is building 80 coal to methanol plants. It amazes me how people bring up these mickey mouse problems when talking about alcohol fuels, but when it comes H2 or any compressed gas fuel, they conveniently ignore the vastly more serious difficulties they create.
Posted by: Warren Heath | 21 April 2007 at 09:40 AM
The fact remains that we have many millions of gasoline-powered vehicles on the road right now that can easily use biobutanol as a total substitute for gasoline. Can't do that with methanol, sorry.
Posted by: Cervus | 21 April 2007 at 09:43 AM
All this is old news to me.
Posted by: ai_vin | 21 April 2007 at 10:21 AM
I believe some clarification is needed.
High-percentage ethanol and methanol blends have high flame speed, high octane rating, and good ignitability even at very high EGR rates. These properties allows for near diesel-like efficiency over broad range of throttling and RPM, but only on heavily modified high-compression engine (currently under intensive research).
This SAE paper presents results of high methanol and ethanol blends in modified turbocharged diesel engine with whopping 19.5 compression ratio with port fuel injection and spark ignition, and very high EGR ratio of 30-45%:
Take a look at figures 2, 3, and 5. E85 allows around 38% thermal efficiency from half to full throttle from 1200 to 3000 RPM, and M85 – about 40% thermal efficiency from one third to nearly full throttle from 1200 to 3500 RPM. Gasoline (and butanol) could not nearly match such high thermal efficiency numbers at such broad engine operation conditions.
Posted by: Andrey | 21 April 2007 at 08:54 PM
Doesn't butanol smell really funky? And butyric acid? Holy crap. You don't want any of that around.
Posted by: George | 21 April 2007 at 09:53 PM
Well butanol smells like musky rotten wood, I would not say its that nasty an odor. Butyric acid though... well you ever wonder what makes vomit smell like it does?
Posted by: Ben | 21 April 2007 at 11:05 PM
Cervus, I'm all for biobutanol, if it can compete favorably with methanol & ethanol & electricity. Anything to get us off of Middle East Oil.
Wasting precious funds on stupid, pork barrel, destructive, immoral crap, like corn ethanol, we can do without. If butanol can be produced at a reasonably competitive cost, must not be made from food sources like corn, must not be made from biomass needed for soil rejuvenation or with irrigation (at least in areas where water is not plentiful), and must not be made on good food production land and should be made carbon neutral.
Methanol production can easily meet all the above goals. I would expect methanol to be a preferable fuel for small high efficiency generators for series Hybrid EV’s and for Direct Methanol Fuel Cell generators for Series HEV’s. This is the future, and ramping up methanol production along with the series Hybrid EV’s would make good sense.
Posted by: Warren Heath | 22 April 2007 at 08:00 AM
I very much hope we do NOT see coal-to-alcohols, for a host of reasons:
We've frittered away the 30 years we had to fix this problem before it hit us in earnest; we have no time for either half-measures or silly mistakes. We especially have no time for interest-group politics masquerading as science.
- Once built, those plants will have a constituency to continue the status quo for the life of the plants. That could be 50 years.
- Phase-out of the plants might force the taxpayer to eat loan guarantees.
- All of this is to provide energy for a vehicle fleet with an average age of about 8.5 years; half of this year's production will be out of service before these plants start up.
Posted by: Engineer-Poet | 22 April 2007 at 10:32 AM