|Main product and byproducts from the acid catalyzed hydrolysis of cellulose. Click to enlarge. Credit: Angewandte Chemie.|
Researchers at the Max Planck Institute for Coal Research (MPI für Kohlenforschung) at Mülheim, Germany, have combined ionic liquids and solid catalysts in a new mild pre-treatment process for cellulosic biomass.
With this process, cellulose undergoes selective depolymerization, yielding cellulose oligomers (cellooligomers) and subsequently sugars without any substantial formation of side products. Even wood, a lignocellulosic material, is hydrolyzed using this methodology.
More conventional pre-treatment options for freeing sugars from cellulose for subsequent processing into fuels or chemicals can use high temperatures and pressures, or aggressive acid baths.
Ferdi Schüth and his colleagues Roberto Rinaldi and Regina Palkovits dissolved cellulose in an ionic liquid (1-butyl-3-methylimidazolium chloride). To this they added water, and then the commercially available resin. Depolymerization of the cellulose was carried out at 373 K (100°C) for 5 hours.
Schüth suggests stopping the process at the oligomer stage, because sugars are soluble in ionic liquids, and therefore hard to separate. The oligomers can be separated from the ionic liquids by adding water. Schüth suggests that these cellulose oligomers could then be treated with enzymes to produce fuels or chemical feedstocks.
The solid resins can be filtered out from the reaction mixture and recycled as catalysts. Scale-up would require an energy-efficient mechanism for separating the ionic liquid solvent from the added water.
It’s been known for half a decade that ionic liquids can dissolve cellulose—even from solid wood; while researchers have also tried using solid acid resins to break down cellulose, but only in water and without much success. Schüth suggests that cultural boundaries between research communities may explain why nobody has connected the two process before.—“Cracking Wood Gently”