Karine De Oliveira Vigier and Francois Jerome

Abstract The progressive introduction of biomass in chemical processes has dramatically changed the way how we design a catalytic process. Among different strategies, assisted catalysis is expected to play a pivotal role in the future. In this context, ChCl-derived ionic liquids and deep eutectic solvents has recently emerged as promising solvents to assist a conventional catalyst in the selective conversion of biomass. In particular, their ability to disrupt the hydrogen bond network of bio­polymers, their ability to stabilize polar chemicals and their low miscibility with common low boiling point solvents open a promising route for the conversion of biomass in a more sustainable way. Beside their low price and low ecological footprint, we wish to demonstrate here that these neoteric solvents have processing advantages that no other solvent can provide in the field of biomass.

Keywords Catalysis • Bioinspired ionic liquids • Deep eutectic solvents • Biomass • Carbohydrates

Abbreviations

BMIM 1-butyl 3-methyl imidazolium

ChCl Choline chloride

DMSO Dimethylsulfoxide HMF 5-hydroxymethylfurfural

IL Ionic liquid

K. De Oliveira Vigier • F. Jerome (*)

Institut de Chimie des Milieux et Materiaux de Poitiers (IC2MP) CNRS-University of Poitiers, ENSIP, 1 rue Marcel Dore, 86022 Poitiers, France e-mail: francois. jerome@univ-poitiers. fr

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_3,

© Springer Science+Business Media Dordrecht 2014

3.1 Introduction

The progressive introduction of renewably-sourced raw materials in chemical processes has dramatically changed the way how we design a catalytic reaction and catalysis is now facing to new technological and scientific challenges in this area. Beside the necessity to find innovative ways capable of selectively activating these renewable raw materials, modern catalysis has also to take into account resource management (i. e. carbon, water and metals) to ensure the sustainability of these processes. If during several years catalysis aimed at building new molecules, catalysis has now to integrate the notion of deconstruction (e. g. disassembling of (bio)polymers). Response to all these constraints is however not self-satisfied anymore and catalysis also has to provide chemicals with similar prices and even superior performances than chemicals derived from fossil reserves in order to favour their emergence on the market.

The progressive introduction of biomass, especially renewable polyols such as cellulose, hemicelluloses, monomeric carbohydrates and glycerol, in chemical processes is a clear illustration of this fundamental change that is now operating catalysis. In particular, due to the complex structure and high oxygen content of biomass, catalysis is now facing to new fundamental questions that are currently hampering the industrial emergence of bio-based derivatives such as (1) how to control the regioselectivity of reaction since the presence of numerous hydroxyl groups (and different linkages) can lead to the formation of many side products, (2) how to overcome the low accessibility of biopolymers to catalyst, a major bottleneck in the deconstruction of biomass, (3) how to activate biomass without degrading carbohydrates, (4) what is the effect of water, a contaminant of biomass, on catalyst activity, selectivity, stability, and (5) how to overcome the low solubility of biomass. The specialized literature (academic and industrial) and prospective reports from different institutions and governments estimate that more than 10 years of fundamental researches are still needed to achieve mature industrial processes based on the use of biomass.

Faced with the introduction of biomass in chemical processes, several strategies are under investigation. The first one consists in a direct transfer of actual catalytic technologies based on fossil carbon to renewable carbon. This approach is for instance efficient from vegetable oils and actually explains the large number of publications/patents dedicated to this raw material although it represents less than 5 % of the worldwide production of biomass [1]. Fatty derivatives indeed have structures close to those of hydrocarbons, thus allowing a possible rapid transfer of catalytic technology with minimal cost investments. On the other hand, glycerol, the main co-product of vegetable oils, can be used as a C3 chemical to enter the propene platform [2]. However, this approach can hardly be transposed to ligno — cellulosic biomass (95 % of the worldwide production of biomass!!) mainly because current catalytic systems are not adapted to these oxygenated raw materials that exhibit very complex structures. In this context, a second strategy is under investigation and consists in designing novel catalytic surfaces capable of

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High cost investments-long term vision Use of conventional catalysts

Scheme 3.1 Heterogeneous catalysis applied to biomass processing selectively activating biopolymers [3]. This long term vision is necessary but clearly requires important cost investments. Indeed, as compared to homogeneous catalysis for which all elementary steps of the catalytic cycles are known at a molecular level, it is not the case for heterogeneous catalysis for which the design of novel solid catalysts is still empirical mostly due to the difficulty to have informa­tion on the catalytic sites at an atomistic level. Assisted catalysis is another concept which is now gaining more and more interest in the field of biomass processing. The idea consists in finding innovative ways capable of assisting or driving a conven­tional catalyst in the selective conversion biomass. For instance, physical methods such as ultrasound or ball-milling are already known techniques to help solid catalysts in the conversion of recalcitrant substrates such as cellulose or lignocel — lulose. From 2000, novel and innovative media such as bio-inspired ionic liquids and deep eutectic solvents have emerged in the current literature. These new media have processing advantages (large dissolution of polyols, insolubility with many organic solvents, tunable electrochemical window, tunable acidity, tolerance to water, etc….) that no other solvent can provide. Their abilities to deactivate water, to stabilize or destabilize reaction intermediates, to disrupt hydrogen bond networks now open efficient tools for assisting a catalyst in the selective decon­struction and conversion of structurally complex raw materials such as biopolymers to more value added chemicals (Scheme 3.1).

In this book chapter, we report the most recent advances made in the field of catalytic conversion of biomass assisted by choline-derived solvent. In particular,

their ability to decrease the crystallinity of cellulose, to assist the deconstruction of biopolymers or to promote the conversion of carbohydrates to higher value added chemicals is discussed. Additionally, at the end of the manuscript, we will discuss the contribution of these neoteric solvents for the purification of bio-based chemicals such as biodiesel and furanic esters.