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

Abstract

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.

Selective Hydrolysis of Cellulose and Polysaccharides into Sugars by Catalytic Hydrothermal Method Using Sulfonated Activated-carbon

“…However, control of reactions and effective heat recovery are difficult to achieve in such short residence times. Therefore, saccharification of lignocellulosic materials has never been commercially implemented 20) . Mildly hydrothermal conditions and less short reaction times are desirable for industrial applications of the hydrolysis of cellulose into glucose.…”

Controlled Depolymerization of Cellulose Fibres Isolated from Lignocellulosic Biomass Wastes

“…The schematic reaction mechanism of the depolymerization process is as shown in Figure 2. In this reaction, ion-exchange process occurred between the ionic liquid and acid catalyst resin, resulting in the release of H 3 O + species which cleavaged the β-glycosidic bonds in the cellulose chains to produce cello-oligomers and other side products such as reducing sugar, glucose, and xylose [5]. Figure 3 shows the mean DPw of cello-oligomers derived from cellulose fibres of various lignocellulosic biomass wastes at different reaction times (5-120 min).…”

“…Cellulose is the most abundant organic compound on earth, and utilization of cellulose fibres derived from LBW does not compete with food supply [3]. Nevertheless, the presence of extensive intra-and intermolecular hydrogen bond networks, the basicity of glycosidic bonds, and high crystallinity of cellulose have posed great challenges for breaking down cellulose fibres through both chemical or biological processes [4,5].…”

“…This has led to intense research into the conversion of biomass in ionic liquids. Besides, ionic liquids can be easily recovered and recycled by evaporating water or alcoholic residues using vacuum distillation and then purified by passing it through a neutral alumina column [5,13]. All these unique properties of ionic liquid have led to their uses as the preferred solvent for the depolymerization of cellulose.…”

“…Amberlyst acid resins are highly stable in acidic anion ionic liquid as compared to other basic anion ionic liquids such as 1-butyl-3-methylimidazolium acetate, which leads to rapid decomposition of the catalyst [15]. During the depolymerization of cellulose in ionic liquid, H 3 O + ions are being progressively released from Amberlyst 15 into ionic liquid within the first hour of contact between cellulose solution and solid catalyst, resulting in an induction period for the formation of glucose [5]. This shows that the depolymerization of cellulose solubilized in ionic liquid in the presence of Amberlyst 15 could afford control of the hydrolysis process during the early stage of cello-oligomer production.…”