Blair J. Cox and John G. Ekerdt

Abstract This chapter focuses on a number of developing technologies based on catalytic transformations of biomass in ionic liquids. As an introduction, an overview of biomass and ionic liquids is given. The chapter continues with a description of catalysis of monosaccharides and polysaccharides in ionic liquids, covering saccharification, depolymerization, isomerization, dehydration into 5-hydroxymethylfurfural, and fur­ther processing. The derivatization of mono- and polysaccharides is also discussed. Because fermentation of biomass is an important technology that is widely used and continuing to grow, a section is devoted to the use of ionic liquids in pretreatment of biomass for saccharification and fermentation into ethanol. Extraction and depoly­merization of lignin model compounds and the whole lignin polymer in ionic liquids are discussed both for pretreatment and use of lignin fragments as a source of fuel and chemicals. A discussion of deoxygenation and hydrogenation of lignin fragments is also given, followed by a concluding section outlining the advantages, challenges, and prospects for catalytic processing of biomass in ionic liquids.

Keywords Biomass • Ionic liquid • Cellulose • Saccharides • Lignin • Catalysis • Carbohydrates

B. J. Cox

Department of Chemical Engineering, The University of Texas at Austin, 200 E. Dean Keeton St. Stop C0400, Austin, TX 78712-1589, USA

UT Dallas Venture Development Center, Cyclewood Solutions Inc., Richardson, TX 75080, USA e-mail: blair. cox@cyclewood. com

J. G. Ekerdt (*)

Department of Chemical Engineering, The University of Texas at Austin, 200 E. Dean Keeton St. Stop C0400, Austin, TX 78712-1589, USA e-mail: Ekerdt@che. utexas. edu

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_8,

© Springer Science+Business Media Dordrecht 2014

8.1 Introduction

Biomass is already the single largest source of renewable energy in the United States and has great potential for further utilization as a renewable resource

[1] . Globally, the potential for sustainable biomass derived energy is 100 EJ/a, which is 30 % of the 2003 global energy consumption [2]. The majority of biomass falls into the category of lignocellulosic biomass, so named because it is composed of three biopolymers: cellulose, hemicellulose and lignin. Agricultural lands in the United States can produce nearly 1 billion dry tons of biomass annually while still meeting food, feed, and export demands, while US forest resources can produce an additional 368 million dry tons [1]. Other forms of biomass, such as corn starch (840 million tons in 2010 worldwide [3] and 216 million tons corn annually in the US [4]), or simple sugars such as glucose, fructose, or sucrose may also prove to be important resources.

The utilization of biomass as a source of fuels and chemicals has increased in recent years. Production of ethanol from biomass has seen rapid growth with the US and Brazil leading the world in bio-ethanol production. Corn based ethanol pro­duction in the US has reached 13.9 million gal while Brazil produces 5.6 million gal of ethanol from the fermentation of sugar cane annually [5]. In the US, the Energy Independence and Security Act of 2007 mandated production and blending of ethanol as a biofuel, which has led to the large scale production of corn based ethanol [6]. Based on the availability of resources, other substrates for fermentation can be used as is the case with sugar cane in Brazil [7]. Cellulose is looked to as the next generation of substrates for ethanol production using feed stocks such as switch grass, sugarcane bagasse, or corn stover as a cellulose source [8]. In order for the cellulose to ethanol conversion to work, biomass sources must be pretreated to make the structural carbohydrates accessible to saccharification in preparation for conventional fermentation into ethanol [9]. The pretreatment step has been the subject of considerable research. Steam explosion, ammonia treatment, dilute acid treatment, milling, and even treatment with ionic liquids have been explored as methods for preparing biomass for saccharification [10—14].

While fermentation into ethanol is one option for converting biomass into fuel, other catalytic processes have been investigated and developed for the utilization of biomass. Using algae as a means of production for both bio-oil and carbohydrates has been looked to as a next generation source of biomass products due the algae’s high energy yield per cultivation area and ability to thrive in a wide range of locations [15]. Conversion of biomass into bio-oil has received considerable atten­tion. Both fast pyrolysis and syn-gas processes hold considerable potential for biofuel production [16, 17]. Catalyst development and application of petro­chemical technology is also an important subject in the field of biofuels [18]. Even the less technologically advanced method of burning biomass provides a significant source of energy. Residue from processing of biomass into food or consumer products and biomass harvested specifically for fuel are a significant source of energy and have a high sustainable potential that has not yet been realized

[2] . Further discussion of the current state of the utilization of biomass for the production of ethanol, bio-oil, commodity chemicals, and other products is covered in a number of articles [2, 15, 17, 19, 20].

One of the challenges in utilizing biomass in chemical processing for fuels or other products is that, in most cases, the biomass is insoluble in commonly used solvents. Ionic liquids (ILs) are a class of compounds that are composed completely of anions and cations and melt at temperatures below 100 °C. Recently, it has been found that some ILs are effective for dissolution of many kinds of biomass. Some can even completely dissolve lignocellulose up to 25 % by weight without chemical modification of the biomass occurring [21]. Based on this discovery, the research on the catalytic transformation of biomass in ionic liquids has increased markedly in recent years. The hope of this research is that the unique solvent properties of ionic liquids coupled with the potential of biomass as a renewable resource will lead to advances in the next generation of fuel and chemical production.