Researchers argue that the optimal use of biomass as a renewable resource is for production of select chemicals, not power, heat or fuels
11 November 2011
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| Total US oil consumption compared to potential and currently harvested nonfood biomass divided into its main uses. The area of each circle is proportional to the consumed amount. Vennestrøm et al. Click to enlarge. |
In an essay presented in the journal Angewandte Chemie, Esben Taarning and co-workers from the catalyst company Haldor Topsøe and the Lindoe Offshore Renewables Center (Denmark) argue that the most efficient use of biomass—which, although renewable is still a limited resource—is for the production of select chemicals, thereby effectively replacing petroleum.
Biomass differs from the other renewable resources, they note, since the energy it contains is stored as chemical bonds. This enables biomass to be used for several purposes apart from electricity and heat generation, such as the production of liquid fuels and chemicals. While to date most of the biomass used by industry has been burned to generate energy, in the long-term neither that use, nor the use of biomass to produce fuels, are optimal, the authors argue.
It is also not the most sensible solution to convert biomass into fuels. In the first place, the amount of biomass available does not meet the demand for fuels; in the second, the chemical characteristics of fuels and biomass are too different, so the processes would be too complex and uneconomical.
In contrast, it really makes sense to use biomass as the feedstock for chemical industry. The available biomass should suffice to replace the fossil feedstocks used in the production of chemicals. The chemical characteristics of biomass and many bulk chemicals are also very similar, so the processes should be more economical than those for the conversion into fuels.
—Esben Taarning
Means of transportation should be gradually switched to batteries or fuel cells, says Taarning.
To explore the best utilization of biomass, the team used the effective H/C ratio: the ratio between hydrogen and carbon atoms in the molecule adjusted for heteroatoms.
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| Effective H/C ratio map of current and future bulk chemicals as well as feedstocks with a qualitative indication of the degree of processing. Horizontally they are arranged according to their degree of processing, with the target chemicals at center. Vertically, the molecules are arranged according to their effective H/C ratio. Chemical reactions resulting in a horizontal shift include isomerization reactions; (de)hydrations; and condensation or fragmentation reactions; while redox reactions imply a vertical shift. B = benzene, BDO = 1,4-butanediol, EG = ethylene glycol, EO = ethylene oxide, GVL = g-valerolactone, PE = polyethylene, PG = propylene glycol, PP = polypropylene, T = toluene, X = xylenes. Vennestrøm et al. Click to enlarge. |
Transportation fuels have an effective H/C ratio in the range of 1 to 2.3...which is close to the ratio of crude oil. This ratio implies a high energy density, and it is thus ideal for liquid fuel purposes. Commodity chemicals, on the other hand, span a much wider H/C ratio, which is more comparable to that of biomass. A wide gap in the effective H/C ratio between a resource and a target chemical implies that a lengthy process is needed for its conversion.
Sugars, for example, have a similar effective H/C ratio to many functionalized high-value chemicals and should therefore be a more ideal feedstock than fossil resources in some cases. By utilizing biomass as feedstock for the production of chemicals instead of fuels, the necessity for deoxygenation, which is one of the biggest challenges when making fuels from biomass, is partially or completely avoided. Oxygen-rich chemicals such as ethylene glycol, acetic acid, and acrylic acid are examples of chemicals that could be obtained more efficiently from biomass than is possible from fossil resources.
Since oxidation reactions typically involve product loss owing to overoxidation, it would be desirable if these reactions could be avoided, or at least their use minimized, when producing chemicals; an objective which seems simpler to achieve when starting from lignocellulosic biomass. Olefins, on the other hand, have an H/C ratio far from that of biomass, which implies that biomass is a poor starting point. It seems that the vast amounts of olefins produced by the chemical industry today will not be easy to directly replace by biomass-based olefins, and the ideal solution is to develop alternative materials with an effective H/C ratio in the range of 0 to 1, thereby indirectly replacing olefins.
—Vennestrøm et al.
Switching to broad use of biomass for chemicals will require divergence from the established value chains, the authors say. Instead of using brute force to convert these raw materials into specific platform chemicals that were originally selected because of their easy accessibility when starting from fossil resources, it would be better to use the interesting chemical characteristics already available in the biomass resources themselves and to optimize the use of favorable catalytic reaction pathways.
Because the development costs will be high and the first processes inefficient, it makes sense to initially concentrate on high-value products, thereby allowing for faster widespread adoption.
Through the clever selection of target chemicals it is possible to significantly increase the value added.
—Esben Taarning
Also, many primary products and by-products of the current biofuel industry could be interesting platform chemicals in themselves they note: for example, ethanol as a starting material for the production of acetic acid, ethylene, and ethylene glycol, or glycerol for conversion into acrylic acid, a polymer precursor.
The shift from a fossil-based chemical industry to one based on biomass poses many challenges, but the possibilities are also great: to develop a more sustainable chemical industry utilizing a more versatile feedstock supply and producing products with superior properties.
—Esben Taarning
Resources
P. N. R. Vennestrøm, C. M. Osmundsen, C. H. Christensen, and Esben Taarning (2011) Beyond Petrochemicals: The Renewable Chemicals Industry. Angewandte Chemie International Edition 50, No. 45, 10502–10509 DOI: 10.1002/anie.201102117
Finally, somebody came up with a common sense approach/solution.
We cannot feed 2+ B gas guzzlers with bio-mass while feeding 10++ B people. Common sense would suggest that we should switch from ICE to electrified vehicles and keep bio-mass for airplanes fuel, essential chemicals and food.
Posted by: HarveyD | 11 November 2011 at 09:19 AM
clearly we cannot especially considering that some critical fertilizer like Phosphorus might be in short supply sooner than we think
Posted by: Treehugger | 11 November 2011 at 09:57 AM
Tree trimmings and grass clippings can probably produce enough material to satisfy our current appetite for plastics. If that's not enough there's garbage, straw, seed husks and grain hulls....
It was obvious to anyone with a calculator that biomass was not going to replace petroleum as a source of fuel; there just isn't enough of it. Once you've broken out of that conceptual box, the conclusions in this report look very likely. I'm glad to see someone did the homework to check the details.
Posted by: Engineer-Poet | 11 November 2011 at 03:34 PM
Suggestion that hydrogen would be better solution than biomass (cellulose) ethanol for light transportation little suspicious. My preference still not changed - PHEV with flexfuel range extender. PHEV or EREV electric range will be gradually increased with battery cost and energy density increase reducing ethanol or other fuel share and range extender complexity and cost. Fuel Cell will never compete economically with electricity and moreover will never be feasible as range extender due to the high infrastructure investment cost.
Analytically more complex situation is with heavy transport since electricity still not viable solution for heavy road trucks. More emphasis should be made on railroad transportation and electrification. Heavy road transport could be switched to the natural gas or DME. Decisions should be based on natural gas availability. But on other hand, heavy road transport is easy for making changes since big government/corporate decisions could be implemented without any market risk.
Posted by: Darius | 12 November 2011 at 05:43 AM
EVs might reduce oil consumption 0.1% in 10 years and bio synthetic fuels could reduce it 10% in the same time frame. Always good to keep the reality in perspective.
Posted by: SJC | 12 November 2011 at 06:50 AM
Biosynthetic fuels are uncompetitive without subsidies, and with governments going broke around the world those subsidies will not continue.
The easy way to 20% savings in 10 years (or less) is universal HyBoost and progressive taxes on fuel and vehicle weight.
Posted by: Engineer-Poet | 12 November 2011 at 07:59 AM
Darius....most heavy cargo could be more effectively handled with high speed e-trains. Electrified tractors could take over at each end. Very high speed e-trains could replace many national passenger/cargo flights and further reduce liquid fuel consumption. Neither of the above will happen without pro-active political support or interference. Governments have to make it happen with appropriate taxes and subsidies.
E-P.... you may be correct in both cases. The 20% savings in 10 years could be further increased with improved electrified road vehicles and electrified trains.
Posted by: HarveyD | 12 November 2011 at 08:59 AM
Synthetic fuels are competitive at today's oil prices. If we want to reduce oil imports, we need to do something that is effective and not just wishful thinking.
Posted by: SJC | 12 November 2011 at 01:33 PM
They said synthetic fuels were competitive in the late 1970's, too. They turned out to be very uncompetitive when recession cut demand and oil prices, and just about every effort went broke and left the American taxpayer to pay off the loan guarantees.
Unless you're going to pair such efforts with an oil import tariff to keep the synfuels in the market no matter what happens elsewhere, they're economically DOA.
Posted by: Engineer-Poet | 12 November 2011 at 03:45 PM
So have an oil import fee and make fuel.
Posted by: SJC | 12 November 2011 at 05:15 PM
Sell that to the Tea Party on the one hand, and OWS complaining about unemployment on the other. Good luck.
Posted by: Engineer-Poet | 12 November 2011 at 07:06 PM
A democracy needs to be free from the control of special interests.
Posted by: SJC | 13 November 2011 at 06:45 AM
And we need honest politicians
and no more greedy people
and more silly love songs.
Posted by: ToppaTom | 14 November 2011 at 08:54 PM
The days of burning liquid fuels and coal for energy-heating-cooking and/or for ground transportation may be over soon, as are coal and wood kitchen stoves and domestic furnaces.
As always, many will fight this change as many others were fought before and they will loose. Resistance is futile.
The Oil age is progressively coming to an end. By 2050 it will be reserved for commercial/military flights and chemicals.
Coal may be transformed into NG (etc) and used till the end of the current century or so.
Posted by: HarveyD | 15 November 2011 at 08:32 AM