Ionic Liquids for Conversion of Biomass to Sugars or HMF Without Additional Catalysts
05 April 2010
Researchers at Colorado State University have shown that under relatively mild conditions (≤140 °C, 1 atm) and in the absence of added acid catalysts typically employed in biomass conversion, cellulose dissolved in certain ionic liquids (ILs) can convert into water-soluble reducing sugars in high total reducing sugar yield (up to 97%), or directly into the biomass platform chemical 5-hydroxymethyl furfural (HMF) in high conversion (up to 89%) when CrCl2 is added.
The results, they say, are broadly relevant to reactions involving the use of IL-H2O mixtures (as solvents, reactants, or catalysts), including, but not limited to, organic catalysis, electrochemistry, and biomass processing or conversion. A paper describing the work was published 10 March in the ACS journal Energy & Fuels.
The majority (60-90 wt %) of plant biomass is the biopolymer carbohydrates stored in the form of cellulose and hemicelluloses. As cellulosic material is the most abundant renewable biomass resource on earth, it can potentially meet our future energy needs if it can be efficiently converted into sugar molecules (such as glucose) with higher energy densities than the parent biomass. The biomass-derived sugars can be converted into fuels and value-added chemicals by liquid-phase catalytic processing.
Alternatively, lignocellulosic materials can be directly converted into the biomass platform chemical 5-hydroxymethyl furfural (HMF), a versatile intermediate for top-value added chemicals and fuels (e.g., 2,4-dimethylfuran, a biofuel with a 40% higher energy density than ethanol).
—Zhang et al.
Converting cellulosic biomass in ionic liquids is an alternative to enzymatic and chemical hydrolysis under typically heterogeneous conditions, or the hydrolysis in hot-compressed water under hydrothermal (high temperature and pressure) conditions.
However, ionic liquid-water mixtures are currently only viewed as a solvent currently recognized only as solvent (IL for solubilizing cellulose) and reactant (H2O for hydrolysis). As a result, Zhang et al. note, the current cellulosic conversion process still employs additional mineral or organic acids (as catalyst). The process demonstrated by the Colorado State team avoids the use of the additional acid catalysts.
Their study, a combination of experimental methods and ab initio calculations, demonstrated that the significantly increased Kw [dissociation constant of water] by ILs in the IL-water mixture is responsible for the catalysis seen in the current efficient biomass conversion system without added acid catalysts. The finding that the water in ILs under mild conditions can exhibit high Kw values (up to 3 orders of magnitude higher than the pure water under ambient conditions) is significant because such high Kw values are typically achievable by the water under harsh high-temperature or subcritical water conditions, they note.
...this work has demonstrated experimentally the significant [H+] in the aqueous solution of water-stable ILs [R(D)MIM]Cl, which has been attributed to the significantly increased Kw of the water by ILs in the IL-water mixture through the theoretical study using combined quantum mechanical and continuum solvation methods. This intrinsic property of the IL-water mixture has been utilized, in absence of any additional acid catalysts, for the near quantitative conversion of cellulosic biomass into water-soluble reducing sugars.
Not only glucose, but also other reducing sugars can be subsequently converted to HMF (with aid of the catalyst CrCl2). The TRS and HMF yields are highly sensitive to the reaction temperature and time as well as the amount of water added.
—Zhang et al.
Resources
Article Yuetao Zhang, Hongbo Du, Xianghong Qian and Eugene Y.-X. Chen (2010) Ionic Liquid-Water Mixtures: Enhanced Kw for Efficient Cellulosic Biomass Conversion. Energy Fuels, Article ASAP doi: 10.1021/ef1000198
Hydrogen derived from the heat energy of nuclear reactors can produce all needed fuels for the earth at very low costs. This hydrogen can be added to CO2 from the air or from recycled sources to make liquid fuels for existing motor vehicles. Plug-In-Hybrid electric vehicles when they become available can use nuclear electric energy directly. A cube of uranium six meters on a side can supply all of the earth's industrial, automobile and home energy for a year. This is also all of the space needed to store fission products. There is far more than enough room in any US state to store safely all of the fission products of the whole earth. The fission products have a shorter radioactive life than the original uranium that is found all over the earth. Every 70 kg human has about 4000 internal nuclear explosions that produce high energy XRAYS every second. No one who uses a cell phone whilst driving can logically complain about the dangers of nuclear energy. In fact no one who drives or rides in an automobile can logically complain about the miniscule dangers of nuclear energy. The uranium that would fit into a Coke can is more than enough to supply a person with all of his energy needs for over a hundred year life time. This would weigh less than twenty pounds. There is far more than enough uranium in the sea alone to supply the earth at the present rate of energy consumption until the sun explodes in a few billion years ..HG..
Posted by: Henry Gibson | 05 April 2010 at 05:09 PM
HG:
Very few look at future energy supply and CO2 control in an integrated way. There are too many divergent interests to even consider that it could be possible.
Smaller mass produced haulable nuclear integrated power plants, installed close to CO2 sources, could effectively produce enough hydrogen to transform unwanted CO2 into useful fuels and/or chemicals. Will it ever be done? If so, where? Certainly not in USA/Canada.
Posted by: HarveyD | 05 April 2010 at 05:49 PM
Henry, thermochemical H2 processes are a long way from industrial use. Your rambling speculations don't do anything to improve the field, GCC's worth or your own credibility.
Posted by: Engineer-Poet | 06 April 2010 at 04:58 PM
Why don't all you smart guys come back to the subject of the article. I would like to hear some relevant comments on the potentially worthwhile discovery above. Does anyone know the kinetics of the processes discussed above? Ionic conversion is no help if it takes 10x the processing time.
Posted by: Tim Duncan | 12 April 2010 at 05:31 AM
The subject of the article has been dealt with. Ionic liquids may cut the cost of converting cellulose to sugars and increase the yield. Whether this results in anything useful is in question; loss of ionic chromium from the process will result in a rather nasty pollution problem.
Even if it works cheaply and cleanly, the products are still going to need processing (5-HMF) or fermentation and distillation to make motor fuel; both will require energy. The supply of feedstock is also not sufficient to replace petroleum. Possibilities, yes; panacea, no.
Posted by: Engineer-Poet | 13 April 2010 at 08:47 PM