Pathways for Glycerol-to-Fuels
13 September 2006
The rapid increase in global biodiesel production is resulting in a worldwide surplus of glycerol, which is generated as a by-product of transesterification. Once considered a valuable co-product, crude glycerol is rapidly becoming a waste product with an attached disposal cost.
A growing body of research is focusing on developing new glycerol platform chemistry and product families to take advantage of a substance that is increasingly abundant and cheap. At the 232nd National Meeting of the ACS in San Francisco, researchers described various approaches to utilizing glycerol (C3H8O3) as a feedstock for different fuel outcomes: a low-temperature catalytic approach to using glycerol as a source for fuel and chemicals; the steam reformation of glycerol to produce hydrogen; and glycerol as a feedstock for microbial hydrogen production.
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| Various glycerol pathways. Click to enlarge. Source: Soares, Simonetti and Dumesic. |
Low-temperature catalytic processing. Dante Simonetti from the University of Wisconsin described work that puts glycerol through a two-step process involving low-temperature catalytic conversion to a syngas (H2 and CO) and subsequent Fischer-Tropsch or methanol synthesis.
The group found that gas mixtures of H2 and CO can be produced at high rates and selectivities from glycerol over platinum-based bi-metallic catalysts at temperatures (e.g., 500 K to 620 K) that are significantly lower compared to conventional gasification of biomass.
The two-step process can also serve as an energy-efficient alternative to processes used to convert starch-based materials to fuel-grade ethanol, because glycerol can be produced in high concentration (e.g., 30 wt%) by fermentation of glucose. Accordingly, this process opens new pathways to more effectively utilize renewable biomass resources to provide liquid fuels and chemical intermediates.
The University of Wisconsin Group, led by Prof. James Dumesic, have also developed a low-temperature aqueous phase reforming process that can use glycerol as a feedstock. Dumesic is one of the co-founders of Virent. (Earlier post.)
Steam reforming of gylcerol to produce hydrogen. Several papers tackled the issue of hydrogen generation via the steam reforming of glycerol, with the focus being the discovery of the optimum catalyst and process.
A team from Spain presented experimental results indicating the catalysts they tested are all able to convert the glycerol completely with values very close to the theoretical results predicted by thermodynamic equilibrium.
The experiments were carried out in a fixed-bed catalytic reactor at 773 K and 873 K with nickel catalysts supported on g-alumina and modified by different contents of MgO, ZrO2, CeO2 or La2O3. The feed composition was increased from 1 to 10% of glycerol in water which is a similar content to that obtained in the first phase glycerol separation from biodiesel.
The team found that the addition of promoters significantly improves hydrogen selectivity and avoids the formation of undesirable by-products if compared with non-promoted catalysts. The best performer was a promoted catalyst with 5 wt.%.
Although the focus of a paper from Mississippi State was the steam reforming of sugar, the researchers found that the process was problematic, due to caramalization resulting from the process temperature. The team is in parallel investigating glycerol in its experimental process, which apparently works fine, although no results were presented.
A separate paper from the Mississippi State team described a thermodynamic analysis of the steam reforming of glycerol to produce hydrogen.
The group analyzed the steam reforming process of glycerol over the following variable ranges: pressure 1 atm, temperature 600-1000 K and water-to-glycerol feed ratio 1:1-9:1. The study revealed that the best conditions for producing hydrogen is at a temperature >900 K and a molar ratio of water to glycerol of 9:1. These conditions minimize methane production and inhibit carbon formation.
Microbial hydrogen production. A team from Brookhaven National Laboratory is investigating the processes under which Thermatoga neapolitana, an anaerobic, thermophilic bacterium, efficiently processes glucose feedstock—in this case, glycerol—to produce hydrogen.
One surprising finding was that T. neapolitana produced hydrogen most efficiently in a moderately low-oxygen—but not oxygen-free—environment. Previously, hydrogen production by bacteria has only been reported under anaerobic conditions.
The ability to operate with some oxygen in the production lines would make this process more economically feasible. The team is further studying the mechanistic aspects of the hydrogen production system, and is beginning to work on scaling up the process to a larger 14-liter reactor.
Resources:
“Glycerol as a Source for Fuels and Chemicals by Low-Temperature Catalytic Processing”; Ricardo R. Soares, Dante A. Simonetti, James A. Dumesic; Angewandte Chemie International Edition Volume 45, Issue 24, Date: June 12, 2006, Pages: 3982-3985
Glycerol as a source for fuels and chemicals by low-temperature catalytic processing (FUEL 121)
Hydrogen production from residual glycerol obtained from biomass transesterification (FUEL 122)
A thermodynamic analysis of hydrogen production by steam reforming of glycerol (FUEL 154)
Microorganisms mediated hydrogen from biomass: Scale-up issues for farm-based economical production (PETR 100)
YES! One man's waste is another's treasure. Just put all of the processes close enough together to create an ECOsystem like E3 biofuels does, and we will "get there".
Posted by: John Schreiber | 13 September 2006 at 07:50 AM
Glycerol becoming plentiful and cheap? Great, just what we need: another source for would be terrorists to create explosives.
Posted by: Patrick | 13 September 2006 at 08:23 AM
Great, just what we need: another source for would be terrorists to create explosives.
I am sure inability to obtain glycerol was never a serious constraint on terrorist activity.
Posted by: Paul Dietz | 13 September 2006 at 08:30 AM
Taking the glycerol out of vegetable oil to make biodiesel is stupid.
The process itself is just a total waste of energy and it also throws away a lot of calorific fuel value present in the glycerol.
Diesel engines should run on straight vegetable oil (mines does), not this biodiesel nonsense.
Posted by: clett | 13 September 2006 at 08:38 AM
what are the characteristics of SVO at colder temps? Seems like gelling would be an issue.
Posted by: tripp | 13 September 2006 at 08:40 AM
Glycerol makes a great defrosting agent for roads and sidewalks. It is sticky but gentler for boots, grass and cars than the salt used now. I'm not sure what it will do to the rivers, needs to be looked at.
EM, in Canada.
Posted by: EM | 13 September 2006 at 09:26 AM
Most SVO in unrefined form has a cloud point between 24-32C (75-90F) and needs to be used in conjunction with a fuel heater to avoid clogging the fuel filter or being just plain unpumpable in gel form. There are a bazillion websites that describe the conversion kits. Do a yahoo or google search for "SVO as fuel".
Posted by: Sid Hoffman | 13 September 2006 at 10:48 AM
To me the most important part of the article is this: The two-step process can also serve as an energy-efficient alternative to processes used to convert starch-based materials to fuel-grade ethanol, because glycerol can be produced in high concentration (e.g., 30 wt%) by fermentation of glucose. Accordingly, this process opens new pathways to more effectively utilize renewable biomass resources to provide liquid fuels and chemical intermediates.
Glycerol fermentation as a replacement for the inefficient and energy intensive ethanol fermentation. Add to that the ability to produce the same hydrocarbon fuels that are in widespread use today.
Posted by: An Engineer | 13 September 2006 at 12:37 PM
SVO technology has been around for a long time but never caught on because of low temperature gelling problems and high PM emissions. Biodiesel is preferable, at least for general consumer applications.
Note that at present, the acreage that can be made available for biofuel feedstock production in the Western world will not yield more than 5-10% of the total volume of automotive fuels required.
In Europe, the EU has mandated that gradually increasing fractions of renewable compounds be blended into all fuels for on-road vehicles. Among other things, this means that biodiesel and mineral diesel are produced at the same location, permitting the glycerol waste stream of transesterification to be used on site. Converting the glycerol waste stream from transesterification to syngas appears to be the most promising route, as it involves neither large quanities of water nor fickle bacteria. Syngas is readily routed around a facility and easily combusted. A typical refinery will consume several percent of the total energy content of its feedstocks to sustain its operations.
In terms of aggregate CO2 emissions, it makes no difference where in the well-to-wheels value chain you substitute renewables for fossil fuels. In terms of operating profit, every BTU derived from a refinery waste stream is doubly valuable: it reduces the amount of saleable commodity that must be sacrificed and, it eliminates the cost of traditional waste disposal.
Afaik, traditional and biodiesel refineries are not typically co-located in the US. If so, I imagine it would be a little harder to leverage the energy contained in the glycerol waste stream as described above.
Posted by: Rafael Seidl | 13 September 2006 at 03:18 PM
Note that at present, the acreage that can be made available for biofuel feedstock production in the Western world will not yield more than 5-10% of the total volume of automotive fuels required.
Proving once again what a dump idea food->fuel is. Waste->fuel on the other hand is an excellent idea, and is estimated to be capable of providing a third of US oil needs. Imagine how well it would do in Europe.
In terms of aggregate CO2 emissions, it makes no difference where in the well-to-wheels value chain you substitute renewables for fossil fuels. In terms of operating profit, every BTU derived from a refinery waste stream is doubly valuable: it reduces the amount of saleable commodity that must be sacrificed and, it eliminates the cost of traditional waste disposal.
You are kidding, right? There is a huge difference with CO2 emissions from renewable fuels:
1. Before the CO2 was fixed by a plant, it was CO2 in the air, hence the term carbon neutral.
2. Leaving the waste to rot in a landfill will convert most of it into CO2 or CH4 anyway. Remember, CH4 is 20X worse as a GHG.
As for all the concerns about WVO: I bet you use less fossil energy driving on WVO (starting and stopping on fossil diesel) than when you factor in all the energy (catalyst, methanol, losses, etc.) needed to produce biodiesel.
Posted by: An Engineer | 13 September 2006 at 03:39 PM
An Engineer -
perhaps I did not articulate my point clearly enough: In terms of aggregate CO2 emissions, it does not matter if you combust a renewable compound at the refinery or if you do it in the vehicle fleet - either way, an equivalent amount of fossil fuel is NOT burnt. By traditional waste disposal, I meant transporting the glycerol waste to a separate incineration facility for electricity generation, NOT a landfill.
As for fuel from waste, the organized collection of waste grease from restaurants has been common practice in e.g. Austria for a long time. Separately, the same businesses also collect spent vehicle fluids, chiefly engine oil. Both are sold to the refinery (we only have one) as recycled feedstocks after filtering. Ever gallon of fuel contains some processed WVO but no-one has to retrofit their vehicle to benefit from it.
However, the volume impact from these recycling streams is nowhere near as large as you suggest it could be. There simply isn't that much of this type of waste out there. More aggressive waste-to-fuel processes such as TDP have not yet been implemented in Europe.
Posted by: Rafael Seidl | 13 September 2006 at 05:00 PM
I have a question here. Why do people make biodiesel in the first place? Why dont they burn the SVO?
Posted by: rexis | 13 September 2006 at 06:16 PM
rexis:
As noted by Sid above, SVO has a much higher gel point, which means cold weather problems. And engines/fuel tanks need modifications in order to run it. Biodiesel is less viscous (thus easily pumpable) and requires no modifications in most modern engines.
Therefore, biodiesel is better.
Posted by: Cervus | 13 September 2006 at 06:22 PM
Its made into biodiesel solely for the gel point? Is there other issue?
This has been an issue here in Malaysia, where we are going to mandate our Palm oil diesel(aka Envodiesel, a diesel blend with 5% mix of non esterified distilled palm oil) soon around 2007/08. But the car makers disagree to give warrenty to whatever that burn vegetable oil as it might cause unknown consequences to the fuel injectors.
I believed that India is working toward blending jatropha oil into their diesel too.
But if we can directly burn SVO, why not? Skip out whole lots of process. Imagin, just spend a little more work in the engine(so that it can burn vege oil) and you skipped a whole lots of works in the fuel making(no more biodiesel plant, straight from oil press to your tank).
Posted by: rexis | 13 September 2006 at 08:47 PM
Just burn the stuff.
Posted by: Robert Schwartz | 13 September 2006 at 09:52 PM
I'm not denying at all that the problems of using SVO directly are that it gels at low temperatures (so a heated tank is required) and engine manufacturers like to have very precisely and reproducibly formulated fuels (ie following a continent-wide specification so that it makes the engine fuel systems easy to develop.)
However I am arguing that the very modest adaptations to the fuel tank and injection system are outweighed by the benefits of using the glycerol energy as part of the largely unrefined SVO.
An alternative, and simple, strategy to improve the gelling point and lubricity of SVO is to use an arctic marine algae, or engineer an existing algae to produce shorter chain (eg C10) more highly unsaturated oils (more double bonds = much lower gelling point).
Posted by: clett | 14 September 2006 at 03:13 AM
I run A 20% biodiesel blend in my car instead of straight vegetable oil because of the fuel pump and injectors. The PD engines that volkswagen produces right now can't take the higher viscosity of preheated SVO compared to DINO or BIO diesel.
Posted by: coal_burner | 14 September 2006 at 08:25 AM
However I am arguing that the very modest adaptations to the fuel tank and injection system are outweighed by the benefits of using the glycerol energy as part of the largely unrefined SVO.
It's not clear that the much higher viscosity of SVO is compatible with modern common rail and other high pressure injection systems. The very high pressures (2000 atm) and resulting very fine fuel droplets decrease PM formation and increase efficiency (more carbon ends up as CO2 and less as PM).
Posted by: dt | 14 September 2006 at 10:54 AM
Sorry Rafael,
I did not read your post as thoroughly as I should have. You are right, where the renewable fuel is used is of little importance.
Yes, grease is a small part of the overall waste we produce (probably <2%). Hence this does not change the overall picture much. If you read the USDA/DOE report you will notice that they are relying mostly on agricultural and forestry waste. Much of the forestry waste is currently burned to reduce fire risk - so we are already getting the CO2 (and other pollutants) without any benefit (beyond reduced fire risk). So, using the waste to replace fossil fuel is a great step forward!
One solution is to burn the forestry wastes to provide heat during winter (forests are often located in cold climates). What do you use for heating in EU?
Posted by: An Engineer | 14 September 2006 at 03:42 PM
An Engineer -
much of Europe is heated with natural gas, some produced domestically (UK, Netherlands, Italy, Germany), the rest imported from Russia. Sweden, Finland and to a lesser extent countries such as Germany, Switzerland and Austria also use wood pellets. Sometimes these are used for electricity generation, freeing up natural gas to be burnt cleanly in people's homes. In France, space heting is electric as there is a surplus of nuclear energy.
District heating is also popular where available (e.g. certain neighborhoods of Malmo Sweden and Vienna Austria). A small number of these facilities have been expended to district cooling in summer (via absorption chillers).
Posted by: Rafael Seidl | 15 September 2006 at 11:45 AM