Niklas Meine

Which Controls the Depolymerization of Cellulose in Ionic Liquids: The Solid Acid Catalyst or Cellulose?

Cellulose is a renewable and widely available feedstock. It is a biopolymer that is typically found in wood, straw, grass, municipal solid waste, and crop residues. Its use as raw material for biofuel production opens up the possibility of sustainable biorefinery schemes that do not compete with food supply. Tapping into this feedstock for the production of biofuels and chemicals requires--as the first-step--its depolymerization or its hydrolysis into intermediates that are more susceptible to chemical and/or biological transformations. We have shown earlier that solid acids selectively catalyze the depolymerization of cellulose solubilized in 1-butyl-3-methylimidazolium chloride (BMIMCl) at 100 degrees C. Here, we address the factors responsible for the control of this reaction. Both cellulose and solid acid catalysts have distinct and important roles in the process. Describing the depolymerization of cellulose by the equivalent number of scissions occurring in the cellulosic chains allows a direct correlation between the product yields and the extent of the polymer breakdown. The effect of the acid strength on the depolymerization of cellulose is discussed in detail. Practical aspects of the reaction, concerning the homogeneous nature of the catalysis in spite of the use of a solid acid catalyst, are thoroughly addressed. The effect of impurities present in the imidazolium-based ionic liquids on the reaction performance, the suitability of different ionic liquids as solvents, and the recyclability of Amberlyst 15DRY and BMIMCl are also presented.

Mechanocatalytic depolymerization of cellulose combined with hydrogenolysis as a highly efficient pathway to sugar alcohols

Cellulose is both insoluble in water and resistant against hydrolysis. These features pose major problems for its conversion into platform chemicals. Herein, we demonstrate that mechanocatalytic, solid-state depolymerization combined with hydrogenolysis, in the presence of Ru/C in water, provides a highly efficient pathway for the production of sugar alcohols. This novel approach leads to yields of hexitols up to 94% at 150 °C in an overall process time of 4 h.

Fractionation of ‘water-soluble lignocellulose’ into C5/C6 sugars and sulfur-free lignins

Recently, we demonstrated the mechanocatalytic depolymerization of lignocellulosic substrates as a powerful methodology that fully converts lignocellulosic substrates into ‘water-soluble lignocellulose’. We now show that the saccharification of the aqueous solution of depolymerized beechwood, pinewood and sugarcane bagasse (at 140 °C for 1 h) produces a high yield of sugars (e.g. 88–92% glucose, 3.5–8% glucose dimers and 93–98% xylose relative to the glucan and xylan fractions, respectively) and leads to precipitation of sulfur-free lignins. Noteworthy, the formation of furfurals is suppressed because the ‘water-soluble lignocelluloses’ undergo hydrolysis at relatively low temperatures. At 140 °C, 5-hydroxymethylfurfural and furfural are formed in yields not exceeding 1.4 and 5.7%, respectively. The separation of the carbohydrate fraction (as C5 and C6 sugars) from the lignin fraction is thus feasible by simple filtration.

Deciphering ‘water-soluble lignocellulose’ obtained by mechanocatalysis: new insights into the chemical processes leading to deep depolymerization

Correction for ‘Deciphering ‘water-soluble lignocellulose’ obtained by mechanocatalysis: new insights into the chemical processes leading to deep depolymerization’ by Mats Kaldstrom et al., Green Chem., 2014, 16, 3528–3538.