11 Mini-review Received: 11 July 2013 Revised: 13 August 2013 Accepted article published: 22 August 2013 Published online in Wiley Online Library: 24 September 2013 (wileyonlinelibrary.com) DOI 10.1002/jctb.4201 Recent trends in (ligno)cellulose dissolution using neoteric solvents: switchable, distillable and bio-based ionic liquids Pablo Dom´ ınguez de Mar´ ıa * Abstract Recent years have witnessed the use of different ionic liquids for biomass processing, either at the level of lignocellulose pre-treatment, to fractionate biomass in its main components, separating hemicellulose and lignin from cellulose, or directly in cellulose decrystallization by dissolving it in the ionic liquid and subsequent precipitation by adding anti-solvents. Yet, most of the ILs employed in these strategies (e.g. imidazolium-based solvents) are (still) expensive for such applications, and provide discussable ecological footprints. In an attempt to combine the highly useful generated knowledge with novel neoteric solvents with improved properties, economics, availability and ecology, several new trends have appeared in these areas during recent years. They comprise the use of switchable ILs, based on strong organic bases and CO 2 , the application of distillable ILs, as well as the use of bio-based and low-cost ILs and deep-eutectic-solvents (DES), e.g. choline chloride-based derivatives. Apart from other emerging uses, for all these solvents some preliminary applications in biomass processing involving pretreatments, cellulose dissolution and other applications have been successfully reported. This Minireview contextualizes these recent trends and discusses them with emphasis on future use of them in biorefineries and biomass valorization. c  2013 Society of Chemical Industry Keywords: ionic liquids; lignocellulose; pretreatment; switchable; bio-based (LIGNO)CELLULOSE AND BIO-BASED ECONOMY The depletion of fossil resources, combined with environmental challenges and unstable geopolitical energy-dependence, is stimulating the research on biomass as the future feedstock for chemical industries, to provide an array of platform chemicals and biofuels. 1 – 4 Many (bio)catalytic strategies are being put forth for holistic integration within the so-defined biorefineries. The ultimate goal of these technologies is the entire valorization of lignocellulosic biomass to compensate processing costs by providing a palette of high-added to low-added value products with diminished waste formation. In this scenario cellulose has a core position as it is the most abundant biopolymer over the earth, encompassing a substantial proportion of the lignocellulosic materials (up to c. 50–60 wt%). 1 – 7 Typically, pretreatment methods applied to lignocellulose aim at separating their main components, namely, lignin, hemicellulose, and cellulose, to subsequently manufacture all these fractions separately for value generation. In this respect, lignin may represent a source of aromatics, plastics, as well as other derivatives; 1,8 and from hemicellulose, xylose, furfural and its further chemistry may be applied. 1 Cellulose may deliver a remarkably broad product range, from paper production and other cellulose-based materials, 1,7,9 – 11 to a source of sugars for their use either in fermentations or in the production of platform chemicals, such as 5-hydroxymethylfurfural (HMF), among other relevant and promising examples (Scheme 1). 1 From that perspective, it may be easily inferred that a key step in biorefineries is the set-up of efficient, sustainable and economic methods for cellulose depolymerization to afford glucose of high purity and low cost. 6 Once pretreatment methods have been applied, the focus is on cellulose and related polysaccharides. Cellulose is a crystalline and highly packed polymeric material, which confers high resistance and stability. This converts cellulose into a challenging substrate for its further processing, whatever biological or chemical methods are considered for its depolymerization. 6 When the necessary provision of low-cost glucose for biorefineries is envisaged, either for fermentations or for other (bio)chemical derivatizations (Scheme 1), considerable research efforts have been undertaken in developing efficient and clean cellulose hydrolytic strategies. One approach for the depolymerization of cellulose is the use of cellulases, a group of different enzymes specifically designed by nature for such purposes. Tremendous developments have been reached in this area, representing a promising strategy, especially if further fermentative processes are considered. The mild hydrolytic conditions needed for efficient catalysis with glycosidases, aqueous solutions, room temperature, ambient pressure, mild pHs, etc., prevent the formation of degradation productions (e.g. HMF), which may inhibit the further microbial growth. 1 – 5 Likewise, another widely used strategy is the acid- catalyzed depolymerization of cellulose. A broad number of ∗ Correspondence to: Pablo Dom´ ınguez de Mar´ ıa, Institut f¨ ur Technische und Makromolekulare Chemie (ITMC), RWTH Aachen University. Worringerweg 1. 52074 Aachen, Germany. E-mail: dominguez@itmc.rwth-aachen.de Institut f¨ ur Technische und Makromolekulare Chemie (ITMC), RWTH Aachen University, Worringerweg 1, 52074, Aachen, Germany J Chem Technol Biotechnol 2014; 89: 11–18 www.soci.org c  2013 Society of Chemical Industry