One of the unique trademarks of ILs, which results from the possibility to combine a huge number of potential anions and cations, is their broad diversity in terms of structural features as well as physical and chemical properties. Based on the number of IL cations and anions, which have been reported in literature for the dissolution of the polysaccharide, about 300 ILs can be generated that are likely to act as solvents for cellulose [8]. Nevertheless, the vast majority of studies related to the use of ILs for processing of cellulose or cellulosic biomass focused on only three of those, namely BMIMCl, AMIMCl, or EMIMAc (see Sect. 5.3.1). Although most of the derivatization reactions described above have been carried out more or less successfully in these ILs, they possess certain ‘intrinsic restrictions’. With respect to the increasing interest to use novel solvents for cellulose processing in commer­cial scales, it can be concluded that the development of task-specific IL based reaction media for the homogeneous cellulose chemistry bears huge potential and are going to be a focus of future research in this area.

‘Task-specific’ is not an absolute term but related to a particular ‘task’, i. e., homogeneous synthesis of different cellulose derivatives, and a “specific” feature that is enabled or prevented by a particular IL. In general, task-specific reaction media for the chemical modification of cellulose should be characterized by:

1. decreased viscosity

2. tunable hydrophobicity/hydrophobicity

3. efficient solvent recycling

4. the presence of specific chemical functionalities that prevent or catalyze specific derivatization reactions and

5. improved biocompatibility and/or biodegradability. The last two issues have scarcely been considered up to now.

First of all, even those ILs, used thus far for processing of cellulose, can become task-specific reaction media if they are applied consciously according to their specific advantages and disadvantages. This approach is limited to a certain extend and requires fundamental knowledge on the specific properties of ILs, e. g., viscos­ity and specific side reactions of anion and cation, with respect to the restrictions imposed by the particular derivatization reaction in which they are used as cellulose solvent and the subsequent recycling process. As an example, EMIMAc can be the reaction medium of choice for derivatization of cellulose at low temperatures. It is liquid at room temperature and shows lower viscosity then imidazolium chloride based ILs, which is beneficial in order to guarantee efficient mixing and mass distribution. However, it also needs to be considered that the acetate anion might act as catalyst or react with the derivatization reagents yielding unexpected reaction products (see Sect. 5.3.2) [37, 67]. Novel cellulose solvents can be obtained by systematic synthesis of ILs and low-melting organic salts with tailored properties based on the knowledge gained with common ILs, on one hand (Sect. 5.3.4.1). On the other, molecular co-solvents can be used to alter the properties cellulose/IL solutions towards specific applications (Sect. 5.3.4.2).

While research in the area of catalysis of biomass in ionic liquids has been the subject of significant work in recent years, there is still much to do. The potential of these biomass/IL systems has been proven at the laboratory scale, but the use of ILs in biomass processing has not reached its potential as an industrially viable tech­nology yet. One of the main inhibitors of industrial adoption is the cost of ILs. While increased adoption of IL technology will increase production and thus drive costs down, improved IL synthesis and processing methods would be beneficial to any process that relies on ILs.

Separation and recovery of ILs is one of the most important aspects of any biomass processing scheme due to the high cost of ILs and the potential for detrimental effects from ILs remaining in later processing steps. Separation of soluble products such as sugars from ILs and separation of ILs from aqueous solutions have received some attention, although there is still room for significant advances in this area [83—85]. Simply evaporating water from ILs is too energy intensive to be useful in most processes. Until satisfactory separation techniques are developed for recovery of both ILs and biomass products, the use of ILs will not gain wider use in the industrial world.

There are some areas that have been the subject of initial investigation that could use further research. As has been discussed in this chapter, metals and metal salts have been shown to be effective in a number of different catalytic systems. Since ILs provide a unique environment for metal complexes [143], there may still be better catalysts that take advantage of ILs for the catalysis of biomass. Supported metal catalysts could also use further study in the catalysis of biomass as long as the catalysts remain truly heterogeneous throughout the reaction processes. Addition­ally, the use of microwave irradiation to enhance rates and yields of reactions in ILs has received some attention from a limited number of researchers and could use further research.

Enzymatic catalysis of biomass in ionic liquids also has room to expand. Some work has already been done in making lipase-compatible ILs that also dissolve biomass [71], but more work could be done to expand on this idea. Cellulase — compatible ILs would allow biomass to be pretreated and saccharified in a one-pot process without the use of harsh acids or metal catalysts. Cellulase that is tolerant of ILs is already the subject of some research [144]. Because many ILs tend to inhibit enzymatic and microbial activity, there is significant room to develop ways to make ILs and bio-processes compatible.

8.2 Conclusions

ILs present a unique set of challenges as well as a unique set of advantages as solvents for processing biomass. ILs provide lignocellulose solvation, enhanced catalyst activity, recyclability and, in some cases simple separations making them a promising avenue of research and potential candidate as a technology in the next generation of biorefineries. In addition to the basic research needed to find the optimize the IL/catalyst/substrate combination, overcoming the unique challenges of ILs must be thoroughly investigated [145]. When applying the work done with compounds such as monosaccharides and lignin model compounds to lignocellu — lose, care must be taken to select ILs that will work for the process and accommo­date the realities of a more difficult lignocellulosic substrate. Processes designed with ILs will need to take these challenges into account, along with possible health effects and corrosion caused by highly ionic media [146].

Even with the remaining challenges of developing new industrial processes, the promise of homogenous conversion of biomass into fuels, commodity chemicals, and polymers is a strong motivator. While ILs have worked their way into some pilot scale and industrial processes [147], the technology for IL use in biomass processing on an industrial scale may still be somewhat immature. More research aimed at optimizing recent discoveries, developing separations and recycling processes, and discovering new uses for IL/biomass systems has the potential to make IL systems practicable for industrial biomass processing.

Solvent choice is the first issue to be considered since it will determine the whole process. The selected non-aqueous phase liquid (NAPL) should not add pollution, must be non-flammable, and its chemical and thermal properties must fulfil those required with the aim of its recycling [6]. The NAPL must be liquid and not very viscous in a range of temperature between 5 and 40 °C. To make the separation from water after biodegradation step feasible, the considered NAPL should be water-immiscible and should not lead to a stable emulsion.

Several NAPL have been previously used either in a two-phase partitioning bioreactor or as absorbents in gas-liquid contactors (scrubber, airlift, bubble column, etc.). Most of them display very low degradation rates or are refractory towards microorganisms and are described as bio-recalcitrant. However, recalcitrance is not enough for the proposed process, since it means a biodegradation of the considered NAPL after an acclimation time. According to some authors [7], five classes of NAPL are potentially non-biodegradable: HMN (2,2,4,4,6,8,8-Heptamethylnonane) owing to the presence of terminal methyl groups, fluorocarbon FC 40, some polymers like the polyisobutylene which contains many terminal methyl groups, silicone oils, especially polymethylsiloxane, and ionic liquids. However, HMN seems biodegrad­able by some acclimated microbial communities [8]; fluorocarbons are toxic toward humans or the environment [9], while polymer viscosity may induce a too high energy consumption in the TPPB (stirring).

Among the available solvents, only silicone oils and ionic liquids appear there­fore really relevant [1, 10]. Even if silicone oils are interesting NAPL candidates, especially polydimethylsiloxane, for hydrophobic VOCs removal, owing to their biocompatibility, their non-biodegradability [10], and have often been implemented in TPPB [11—13], ionic liquids seem promising.

Ionic liquids have been recognized for about a century, but have only started receiving closer attention in the last two decades. Historically, an ionic liquid is an organic salt with a melting point below 100 °C [14]. They are composed by an association between an organic cation containing one or more hetero-atom(s) (nitro­gen, phosphorus or sulfur) and an inert anion or Lewis acid [15], namely the counter­ion, leading to aneutral compound [16]. Since the first chloroaluminate “molten salt”, many efforts have been made about ionic liquids to lower their melting points (development of RTILS, “Room-Temperature Ionic Liquids”) and to improve their stability towards air and water.

Their low vapor pressure and non-flammability [17, 18] makes them particularly interesting class of solvents for ‘green chemistry’ or absorption. However, based on recent data, these assumptions have been progressively reconsidered [19—23]. In addition, they are generally thermically stable (decomposition temperatures >150-200 °C), chemically or electrochemically inert.

Their interest is not only due to their remarkable physicochemical properties (lipophilicity, viscosity, density, etc.) but also for their recyclability. However, these properties are usually presented as applicable to all ILs are not so “universal” and the large number of possible combinations of a structural point of view suggests that some ILs are not as harmless [24].

So, ILs can be designed for specific applications [2, 18]. Hence, it is possible to fine-tune IL physicochemical properties by means of modifying the substituent groups or the identity of the cation/anion pair [17, 18].

One of the first reviews on ILs (synthesis, applications, etc.) was published in 1999 and related the general methods of synthesis and the first applications of ILs based chloroaluminates [25]. Below are shown the structures of most common ILs (Fig. 12.2).

As they are readily tunable, ILs could be selected as NAPL for TPPB. The physico­chemical characteristics of the ionic liquid (viscosity, hydrophobicity toxicity, etc.), as well as possible biodegradability, vary according to the considered radical.

Temperature plays an important role on the dissolution rate of cellulose. Because a change of the cellulose structure from a highly crystalline to a low crystalline form is not thermodynamically favorable, dissolution process of cellulose generally occurs at relatively high temperature. Under these conditions, cellulose and, in some cases, the ILs, are partly degraded making the long term viability of these systems a serious limitation. In this context, assistance of microwave has been explored to accelerate the dissolution process and promising results have been reported [12]. Once dissolved, cellulose is regenerated by precipitation upon addition of an antisolvent such as ethanol, water or acetone. The regeneration of cellulose from ILs is a very important step and should be closely controlled. Indeed, owing to its amphiphilic nature, cellulose is known for its ability to encapsulate a wide range of organic substrates including ILs. The presence of residual ILs in regenerated cellulose is problematic not only because the anion may lead to a denaturation of enzymes or poisoning of acid sites during the subsequent (bio) catalytic depolymerization of cellulose but also because ILs are relatively expen­sive and the entire amount of ILs need to be recovered in order to design a viable process. Recent studies have shown that regeneration of cellulose from [BMIM]Cl at temperature around 60 °C or assistance of ultrasound allows to recover nearly 99 % of the ILs offering a suitable route to limit the contamination of cellulose.[4]

Lignocellulosic material (typically ca. 1 g) was quickly added to a flask containing dry [amim]Cl (typically ca. 20 g) under nitrogen atmosphere. The mixture was homogenized with vortex mixer until an even dispersion was obtained. Dissolution was performed in a temperature controlled oil bath using a three-necked flask under positive pressure of nitrogen. This was equipped with an overhead mechanical stirrer with steel blade. A positive pressure of nitrogen gas was maintained during the whole dissolution period. Solvation conditions and quantities of materials were varied according each experiment performed, ranging from 48 h at 80 °C to 122 h at 110 °C. Rotary milled Norway spruce powder generally dispersed and gave a clear solution in a short period of time. Wiley milled and sawdust materials remained slightly cloudy even after extensive heating at 100 or 110 °C.

The influence of water content on the production of 5-HMF from biomass has many aspects. Firstly, in the dehydration of fructose in ionic liquids, a small amount of water (5 wt%) present in the ionic liquid mixture has a negligible effect on the fructose conversion and 5-HMF yield, and it reduces the viscosity of the ionic liquid system and is beneficial to mass transfer [20, 36]. However, when the water content increases above about 5 wt%, the fructose and 5-HMF yield decrease significantly, which can be ascribed to the loss of catalytic activity due to the lowering of the dielectric constant of the reaction media by the addition of water [41]. Further, the presence of water in the reaction mixture favors the rehydration of 5-HMF to generate undesired products such as levulinic and formic acids. From one point of view, water should be completely avoided and removed from the production process of 5-HMF. On the other hand, water serves as a necessary reactant in the hydrolysis step in the conversion of oligosaccharides, thus an appropriate amount of water is required in the reaction system, although water has all the disadvantages connected to the dehydration reaction, and polysaccharides are no longer soluble in ionic liquids and precipitate from the ionic liquid solution when the water content exceeds a certain level [94, 95]. Therefore, water content should be carefully controlled in the conversion of polysaccharides in ionic liquids.

Considering that the addition of water can reduce the catalytic activity of the reaction system but increase the stability of glucose, Qi et al. developed an efficient two-step process for converting microcrystalline cellulose into 5-HMF with ionic liquids under mild conditions [95]. In the first step, cellulose was efficiently hydrolyzed by a strong acidic cation exchange resin in 1-ethyl-3-methyl imidazolium chloride ([EMIM][Cl]) with gradual addition of water. The addition of water probably allowed a balance to be achieved between glucose stability and cellulose solubility, since too much water will result in the precipitation of the cellulose substrate. Through the water addition technique, Qi et al. reported glucose yields above 80 % for converting microcrystalline cellulose under mild conditions [95]. Based on the high glucose yield, a second step was applied to produce 5-hydroxymethylfurfural by separating the resin from the reaction mixture and adding CrCl3 as catalyst, which lead to a 5-HMF yield of 73 % based on cellulose substrate. The strategy described should be useful for efficient conversion of cellulose into 5-HMF as well as into other biomass-derived chemicals.

Junli Xu, Qing Zhou, Xinxin Wang, Xingmei Lu, and Suojiang Zhang

Abstract Ionic liquids (ILs) are composed of cations and anions that exist as liquids at relatively low temperatures (<100 °C). They have many attractive properties, such as chemical and thermal stability, low flammability, and immeasurably low vapor pressures. This review provides a summary of the fundamental structural features of ionic liquids, the physical properties, and their applications as solvents for biomass.

Keywords ILs • Properties • Cellulose • Biomass

1.1 Introduction

The energy crisis has caused great pressure on the economic development and environmental sustainability worldwide, resulting in renewable energy, such as, solar, wind, and biomass, receiving significant attention [1]. Especially, as a resource of fuel and chemicals, biomass is developed greatly due to its large potential and universality as an energy resource. Biomass pretreatment is a key procedure for efficient processing. Biomass pretreatment was first conducted with acid or alkali, as well as some organic solvents. Gradually, considering the envi­ronmental and economic influence, ionic liquids (ILs) were introduced for biomass

J. Xu

Beijing Key Laboratory of ILs Clean Process, Key Laboratory of Green Process

and Engineering, State Key Laboratory of Multiphase Complex Systems, Institute of Process

Engineering, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China

College of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China

Q. Zhou • X. Wang • X. Lu (*) • S. Zhang (*)

Beijing Key Laboratory of ILs Clean Process, Key Laboratory of Green Process and Engineering, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China e-mail: xmlu@home. ipe. ac. cn; sjzhang@home. ipe. 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_1,

© Springer Science+Business Media Dordrecht 2014

pretreatment and biomass conversion with ILs was followed since ILs have many unique and excellent properties.

This part aims to briefly introduce the definition of ILs, the structures and classi­fication of ILs, meanwhile, the properties of ILs will be discussed in detail, including melting point, viscosity, density, and thermal stability. Then the history, advantage and current status of ILs applied to cellulose/biomass, the quantities and kinds of ILs are used in dissolution and separation of cellulose from biomass are also summarized.

Homogeneous chemical modification of cellulose provides several advantages over heterogeneous reactions such as: increased reactivity, uniform product composi­tion, and efficient control over the overall degree of substitution (DS) as well as the distribution of functional groups within the anhydroglucose unit (AGU) and along the polymer chain. A variety of specific polysaccharide solvents that can be used not only for dissolution but also for the derivatization of cellulose have been reported in scientific literature [9]. They could be applied for preparing a broad variety of polysaccharide derivatives with potential applications from multi-kiloton food — and construction material industry to highly engineered materials for medical and biotechnological use. Nevertheless, none of the many cellulose solvents that could be utilized in lab-scale synthesis was found to be suitable for commercially attractive synthesis of cellulose derivatives up to now. Production of cellulose derivatives in technical scales is performed exclusively under heterogeneous con­ditions. In this context, ILs received a lot of interest because these versatile novel solvents might overcome the limitations of classical cellulose solvents; such as low dissolution power, inefficient solvent recycling, and incompatibility with derivati — zation reagents. In particular the broad structural diversity of ILs and the possibil­ities to create task-specific solvents by subtle manipulation of the molecular structure bear huge potential. Moreover, ILs have been employed with high effi­ciency in low-molecular chemistry as solvents for a vast number of advanced organic reactions that are still waiting to be transferred to cellulose derivatization [10]. Many cellulose derivatives could be prepared already by using ILs as reaction media for cellulose (Table 5.1). A comprehensive overview of the chemical deriv- atization of cellulose in ILs is provided in the following passages. Most of the synthesis described focused mainly on three particular imidazolium based ILs (Fig. 5.1) or slightly modified analogues. However, some reports on novel IL based reaction media were included as well.

aDS: degree of substitution

bIonic liquids: cations: ADMIM+: 1-allyl-2,3-dimethylimidazolium, AMIM+: 1-allyl-3- methylimidazolium, BDMIM+: 1-butyl-2,3-dimethylimidazolium, BMIM+: 1-butyl-3-methylimi — dazolium, EMIM+: 1-ethyl-3-methylimidazolium, anions: Ac-: acetate, Bz-: benzoate, Cl-: chloride, DEP-:diethylposphate, Pr-: propionate

cValues in braces represent degree of polymerization of the grafted chain

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.

Teresa de Diego, Arturo Manjon, and Jose Luis Iborra

Abstract This chapter focuses on the application of enzyme technology in non-aqueous green solvents as ionic liquids (ILs) to transform biomass, mainly non-edible biomass (e. g. cellulose, lignocellulose, wood, forest residues, etc.), into fermentable monomeric compounds, and low cost vegetable oils or animal fats in biodiesel. This review aims to identify the key parameters that determine the biocompatibility of ionic liquids with enzymes for the rational design of ionic liquid-based formulations in biocatalysis for biofuel production.

Keywords Biofuels • Ionic liquids • Enzymatic-saccharification • Enzymatic- transesterification • Biodiesel • Bioethanol

Abbreviations

T. de Diego • A. Manjon • J. L. Iborra (*)

Department of Biochemistry and Molecular Biology B and Immunology, University of Murcia, P. O. Box 4021, E-30100 Murcia, Spain e-mail: jliborra@um. es

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_11,

© Springer Science+Business Media Dordrecht 2014

[(MeO)2PO2] Dimethylphosphate

[Ac] Acetate

[TFA] Trifluoroacetate

[DMP] Dimethylphosphate

[MeSO4] Methylsulfate

[TfO] Trifluoromethylsulfonate

[NTf2] Bis[(trifluoromethyl)sulfonyl] amide

[SCN] Thiocyanate

[SbF6] Hexafluoroantimonate

Cations

1-Methyl-3-methylimidazolium

1-Ethyl-3-methylimidazolium

1-Butyl-3-methylimidazolium

1-Octyl-3-methylimidazolium

1-Butyl-1-methylpyrrolidinium

Triethyl-3-methylimidazolium

1-Hexadecyl-3-methylimidazolium

1- Octadecyl-methylimidazolium Methyl trioctylammonium Butyl trimethylammonium

Ethyloctadecanoyl oligoethyleneglycol ammonium Ethyloctadecanoyl oligoethyleneglycol ammonium

2- Hydroxy-N, N,N-trimethylethanammonium

11.1 Introduction

Increasing energy demands inevitably lead to an increase in crude oil prices, directly affecting global economic activity [1]. The progressive depletion of con­ventional fossil fuels with increasing energy consumption and gas emissions have led to a move towards alternative, renewable, sustainable, efficient, and cost — effective energy sources with lower emissions. Biomass appears to be the most feasible feedstock for current routes towards the production of biofuels since it is renewable, cheap, has low sulphur content and involves no net release of carbon dioxide, meaning that it has a high potential to become economically feasible at the present time [2].

Bioethanol is a major biofuel on the market worldwide. In 2011, total fuel bioethanol production worldwide was 28.94 billion gallons (109.4 billion litres)

[3] . It is estimated that bioethanol production could reach more than 227.4 billion litres of bioethanol thereby displacing a substantial portion of the fossil fuel currently consumed by the transportation sector [4]. Bioethanol is used to partially replace gasoline to make gasoline-ethanol mixtures, E15 (15 % ethanol and 85 % gasoline) and E85 (85 % ethanol and 15 % gasoline). The current commercial fuel
ethanol is produced mainly from sugarcane and corn, depending on the climatic conditions of the producers’ locations. The feedstock used for fuel ethanol produc­tion is mainly sugarcane in tropical areas such as Brazil and Colombia, while it is predominantly corn in other areas such as the United States, the European Union and China [2].

However, the production of these raw materials is competing for the limited arable land available for food and feed production. Therefore, it is critical to investigate advanced or second generation biofuel production technologies. Bioethanol can also be produced from lignocellulosic materials, which is com­monly called second generation bioethanol [5]. The feedstocks for the second generation bioethanol include agricultural residues, grasses, and forestry and wood residues [6].

Biodiesel which is produced using vegetable oil, plant oil and animal fat is another major biofuel. Nigam and Singh [7] consider biodiesel as a “carbon neutral” fuel, as any carbon dioxide released from its burning was previously captured from the atmosphere during the growth of the vegetative crop that was used for its production. Obviously, biodiesel is an alternative fuel for diesel, and most diesel engines can use 100 % biodiesel. The main feedstock currently used for biodiesel production includes soy bean, canola seed or rapeseed, sunflower and palm oil. There are going research activities into using alternative oils such as waste oils from kitchens and restaurants and microalgal oils for biodiesel production. However, these biofuels represent a tiny portion (<4 %) of the total fuels consumed because it is not feasible to greatly increase biofuel production using the current technologies available [7].