Xinhua Qi, Richard L. Smith Jr., and Zhen Fang

Abstract The furan derivative, 5-hydroxymethylfurfural (5-HMF), can replace many petroleum-derived monomers and intermediates presently used in the man­ufacture of plastics and fine chemicals. Ionic liquid solvents provide a sustainable path for 5-HMF production since they can dissolve crude biomass and allow conversion of polysaccharide fractions to 5-HMF with high selectivity. This chapter presents current progress in the synthesis of 5-HMF with ionic liquid solvents and considers conversion of saccharide substrates such as fructose, glucose, inulin and cellulose under catalytic reaction conditions. Challenges for 5-HMF production with ionic liquids are addressed and interesting aspects that still need to be explored for developing practical systems are highlighted.

Keywords Biomass • Ionic liquid • Cellulose • Hydroxymethylfurfural • Glucose • Fructose • Catalysis

9.1 Introduction

Biomass represents a possible sustainable resource for production of fuels and valuable chemicals [1]. However, the overabundance of oxygen within the molec­ular structures of carbohydrates limit the application of biomass as a feedstock for

X. Qi (*)

College of Environmental Science and Engineering, Nankai University, Tianjin, China e-mail: qixinhua@nankai. edu. cn

R. L. Smith Jr.

Graduate School of Environmental Studies, Research Center of Supercritical Fluid Technology, Tohoku University, Sendai, Japan e-mail: smith@scf. che. tohoku. ac. jp

Z. Fang

Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Kunming, China e-mail: zhenfang@xtbg. ac. cn

Z. Fang et al. (eds.), Production of Biofuels and Chemicals with Ionic Liquids, Biofuels and Biorefineries 1, DOI 10.1007/978-94-007-7711-8_9,

© Springer Science+Business Media Dordrecht 2014

substitutes of traditional fossil fuels [2]. Removal of water from carbohydrates by dehydration is one of the main ways for reducing their oxygen content and obtaining commodity compounds [2]. Among the possible compounds that can be derived from dehydration of carbohydrates, 5-hydroxymethylfurfural (5-HMF) is a highly versatile intermediate, since it can be used for furan-based fine chemicals and polymers [3—5] (see Fig. 9.1). In the past few years, water [6—11], organic solvents [9, 12—15] and organic-water mixtures [1, 16—18] have been broadly investigated for the production of 5-HMF from a variety of biomass-derived carbohydrates such as fructose, glucose, and other di-poly-saccharides (Fig. 9.2).

Water is a good solvent for both monosaccharides and the products and it is favored as a reaction solvent from its environmental aspects. However, as a reaction solvent, water leads to the formation of undesired side-products, especially levulinic, formic acids, and humins result from either polymerization of 5-HMF or cross-polymerization of 5-HMF and carbohydrates that is attributed to water’s ionization [20—22]. When water is used as a solvent for conversion of saccharides to

5- HMF, by-product formation leads to 5-HMF yields of below 40 % and the conditions required are harsh [8 , 22—24]. Therefore, it is necessary to prevent rehydration of 5-HMF in the reaction chemistry so that humin formation can be suppressed. Suppression of humin formation can be accomplished by carrying out the reactions in nonaqueous systems. Dimethylsulfoxide (DMSO) was identified early as an efficient solvent for the preparation of 5-HMF from fructose [12,13, 25], since the furanoid form of fructose is favored in DMSO [4]. However, DMSO suffers from difficult product recovery and environmental problems in its use. Acetone is a good alternative solvent for DMSO due to some similarities in its

chemical properties, however, it has to be used with water or DMSO as cosolvent since monosaccharides have only limited solubility in pure acetone [4, 15].

Ionic liquids have favorable properties, such as nonvolatility, high thermal and chemical stability and adjustable solvent power for organic substances [26]. ILs have good attributes as solvent for producing 5-HMF from carbohydrates since they can allow reaction under relatively mild conditions and have the possibility of being used in one-pot reactions with biomass as the feedstock. This chapter provides an overview on research works that have studied the catalytic transformation of 5-HMF from a variety of carbohydrates in ionic liquids.