New Solid Catalyst for Hydrolysis of Cellulose Performs as Well as Sulfuric Acid
08 September 2008
Researchers at the Tokyo Institute of Technology have developed a solid carbon-based catalyst for the hydrolysis of cellulose into glucose, with performance comparable to that of sulfuric acid, but with lower environmental and financial costs. A paper on their work was published online in the Journal of the American Chemical Society on 29 August.
Converting cellulose to sugars (saccharides) is a critical step in most processes for the production of cellulosic ethanol via fermentation. A variety of approaches have been developed to hydrolyze cellulose to saccharides, including catalysis using mineral acids, enzyme-driven reactions, the use of supercritical water, and solid catalysts for hydrogenolysis. The Tokyo Tech team, lead by Professor Michikazu Hara, notes that sulfuric acid catalyzed hydrolysis of cellulose has received considerable attention and has been implemented on relatively large scales.
However, while sulfuric acid is inexpensive and acts as a highly active catalyst for this reaction, its use is wasteful and energy-inefficient, requiring separation, recycling, and treatment of the waste sulfuric acid.
The move toward more environmentally sustainable approaches to chemical processes has stimulated the use of recyclable solid acids as replacements for the unrecyclable liquid acid catalysts such as sulfuric acid. Any solid Brønsted acid catalyst that is as effective as sulfuric acid in hydrolyzing cellulose is potentially applicable for the efficient conversion of cellulose, and particulate catalysts can be readily separated from the water-soluble saccharides following the reaction, allowing for repeated reuse of the catalyst with low energy consumption.
—Suganuma et al. (2008)
The researchers developed a catalyst consisting of amorphous carbon bearing SO3H, OH, and COOH groups. Although the carbon material has a small surface area, and the acid density is only 1/10th that of sulfuric acid, they found that the catalyst was as effective as sulfuric acid in hydrolyzing cellulose.
Furthermore, the apparent activation energy for the hydrolysis of cellulose into glucose using the carbon catalyst is estimated to be 110 kJ mol-1, smaller than that for sulfuric acid under optimal conditions (170 kJ mol-1). The carbon catalyst can be readily separated from the saccharide solution after reaction for reuse in the reaction without loss of activity.
The researchers attributed the catalytic performance of the catalyst to three factors: its ability to adsorb β-1,4 glucan; its large effective surface area in water; and SO3H groups tolerable to hydration in the carbon material.
A report on the development in the Nikkei said that use of the new catalyst could lower the cost of producing cellulosic ethanol by more than 30%.
Resources
Satoshi Suganuma, Kiyotaka Nakajima, Masaaki Kitano, Daizo Yamaguchi, Hideki Kato, Shigenobu Hayashi, and Michikazu Hara (2008) Hydrolysis of Cellulose by Amorphous Carbon Bearing SO3H, COOH, and OH Groups, ASAP J. Am. Chem. Soc., doi: 10.1021/ja803983h
The idea of fixed enzymes has been around for a long time. It might even be possible to eliminate the fermentation process altogether. There are many organic wastes that could be converted to fuel instead of putting them in land fills. The cost of conversion is one problem, but in the long run there is not enough organic cellulose to replace enough of the US energy rerquirements. Nuclear energy can both assist in converting waste cellulose and also provide prime energy in unlimited quantities. ..HG..
Posted by: Henry Gibson | 08 September 2008 at 01:02 PM
@Henry,
Nanosolar has some data about how much land you need to power your cars with various crops, versus photovoltaic. http://www.nanosolar.com/blog3/
From well to wheels (or from photon to newton), solar-powered electric cars are absolutely hugely more efficient, especially when you include the energy costs of refining and distribution of liquid fuels.
That said, even if we just look at ethanol and butanol as transitional energy storage mediums while we retire the existing ICE fleet, we still could use a lot of them, and this is encouraging research. This could be useful for breaking down what's left of algae after you squeeze out the lipids for biodiesesl
Posted by: Healthy Breeze | 08 September 2008 at 01:45 PM
Anything that can reduce the costs (or supply more product for a smaller environmental footprint) is welcome as a better way to do business.
There are many uses for the product including on processing and less efficient plants will need retiring when better options are available.
Posted by: arnold | 08 September 2008 at 03:17 PM
Even if we wouldn't need liquid fuels, transforming cellulose to sugar, and then sugar to animal (or human) feed would be very interesting.
Posted by: Alain | 09 September 2008 at 12:30 AM
Sounds like another very promising technique to produce sustainable and environment-friendly fuel that could be cheaper than fossil-gasoline.
Start with algae or cellulosic refuse. Convert the cellulose to sugar with this technology. Then convert the sugar to ethanol with (yeast or) this genetically-engineered bacteria:
http://www.greencarcongress.com/2008/09/researchers-eng.html#more
Here's a competing ethanol biotechnology by Algenol using algae that produces ethanol directly:
http://news.cnet.com/8301-11128_3-9966867-54.html
http://www.algenolbiofuels.com/
Here's another ethanol biotechnology by Coskata using bacteria that converts carbon monoxide to ethanol:
http://www.coskata.com/
We shouldn't let any such promising alternatives get buried. But besides typical oil industry dirty tricks, there's a high likelihood they will be buried due to deficient process optimization. We cannot afford to let corruption and/or negligence deny us of any such economical and sustainable alternative fuels.
Posted by: Jay Dee | 09 September 2008 at 03:42 PM