Researchers at the University of California, Davis have developed a new method for the direct conversion of cellulose into furanics, which can become the basis for new biofuels. The simple, low-cost process delivers furanic compounds in yields not yet achieved, according to Mark Mascal and Edward B. Nikitin in an early view paper published online 1 August in the journal Angewandte Chemie.
Currently, biofuel producers primarily use starch, which is broken down to form sugars that are then fermented to give ethanol. Cellulose, however, is the most common form of photosynthetically fixed carbon. Exploiting that resource for fuels via a fermentation pathway—e.g., cellulosic ethanol—is difficult because the degradation of cellulose into its individual sugar components, which could then be fermented, is a slow and expensive process.
Another problem is that the carbon economy of glucose fermentation is poor. For every 10 g of ethanol produced, you also release 9.6 g CO2.—Mark Mascal
Researchers are thus looking for effective approaches to biomass conversion which avoid fermentation altogether and exploit all of the available carbon present. One of the promising areas of effort in this area is the production and use of furanics—high-energy, furan-based organic liquids. Work at the University of Wisconsin led by Professor James Dumesic (earlier post) showed that fructose could be efficiently converted, via 5-hydroxymethyfurfural (HMF). Researchers at the Pacific Northwest National Laboratory (PNNL) led by Z. Conrad Zhang (earlier post) have converted glucose directly and with high yield to HMF.
Mascal and Nikitin developed a process for the conversion of cellulose directly—i.e., without relying on glucose or fructose—into furanic products in isolated yields of greater than 80% by conversion mainly into 5-(chloromethyl)furfural (CMF), a hydrophobic molecule.
The process entailed adding microcrystalline cellulose to a stirred solution of lithium chloride (5 wt%) in concentrated hydrochloric acid to give a homogeneous mixture, which was introduced into a reaction chamber containing 1,2-dichloroethane. The solvent was heated to reflux and the aqueous slurry was kept at 65°C with continuous mechanical stirring and extracted for 18 h. At this point, a further solution of LiCl in concentrated hydrochloric acid was added to the reaction chamber and extraction continued for another 12 h. The combined organic extracts were distilled to recover the solvent.
The process yielded 71% CMF; 8% 2-(2-hydroxyacetyl)furan; 5% HMF; and 1% levulinic acid. Total, isolated yield of these four simple organics was thus 85%. Applied to glucose, the process delivered the same organics in yields of 71%, 7%, 8% and 3%, respectively. Applied to sucrose, it yielded 76%, 6%, 4% and 5% respectively.
While CMF itself is not a biofuel candidate, it can be combined with ethanol to give ethoxymethylfufural (EMF). CMF can also be catalytically hydrogenated to yield 5-methylfurfural (HMF). Both of these compounds are suitable as fuels. EMF has previously been investigated and found to be of interest in mixtures with diesel by Avantium Technologies, a spin-off of Shell. (Earlier post.)
While future reports will address further optimization, scaleup, and applications of the method to raw biomass, these preliminary results suggest that this simple, efficient approach to cellulose deconstruction has the potential, at the very least, to complement fermentation as a means to produce biomass-derived automotive fuels, and to establish furanics both as a renewable energy source and industrial chemical feedstock of the future.—Mascal and Nikitin (2008)
Mark Mascal and Edward B. Nikitin (2008) Direct, High-Yield Conversion of Cellulose into Biofuel. Angew. Chem. Int. Ed. 2008, 47, 1 – 4 doi: 10.1002/anie.200801594