Rafał Bogel-Łukasik

Ionic liquid-mediated formation of 5-hydroxymethylfurfural-a promising biomass-derived building block.

The reduction of fossil fuels dependence in a framework of shifts in oil prices and geopolitical instability1 is one of the major interests of the current world. It can be achieved by using lignocellulosic biomass. However, there is also growing concern about its overall sustainability, especially regarding land use change, intensified use of agricultural inputs, and possible limitations on food security. Furthermore, the global energy demand is projected to grow over 50% by 2030. This will have an additional impact on the climate and, hence, on our planet. The recent United Nations Framework Convention on Climate Change in Copenhagen, Denmark, has ratified the Kyoto Protocol and is intended to reduce global emissions by at least 20% by 2020 and by 50%-60% by 2050 relative to the emission level in 2006.2 To achieve these ambitious goals in the near future, the next generation of chemicals and fuels from the biorefinery of lignocellulosic biomass has to be used sustainably, since the competition for raw materials between the food and energy industries prevents further (significant) increase of the current first-generation biofuels already on the market. Biomass, especially that which exists in the form of nonedible lignocellulosic materials such as grasses, woods (hard and soft), and crop residues (corn stover, wheat straw, sugar cane, bagasse, etc.), serves as renewable feedstock and could be considered as an alternative source of the chemicals and energy currently derived from petroleum. There are a number of technological breakthroughs necessary to reach a mature and cost-effective commercial technology for biomass utilization. Cost reductions in biological and chemical conversion are to be found in the improvement of individual process steps, far-reaching integration, the development of new efficient methods of carbohydrate conversions by alternative solvents or by robust microbial cell fermentation and by integration of all residues (e.g., spent lignins) and wastewaters into a one-pot process. Lignocellulosic biomass is composed of cellulose, hemicellulose, and lignin. The compositions of these materials vary, and their structures are very complex. Biomass requires many hydrolytic technologies and biological as well as chemical pretreatments to be reduced in size and have its physical structure opened.3 Various methods such as acid hydrolysis, hydrothermal or alkaline treatments, organosolv, solid (super)acids, ionic liquids, or subcritical or supercritical fluids can be employed.4 Carbohydrates constitute up to 75% of the annual production of biomass, estimated at 170 × 109 tons.5 Carbohydrates are an abundant, diverse, and reusable source of carbon. They find many industrial applications in such diverse areas as the chemistry, fermentation, petroleum production, food, paper, and pharmaceutical industries.6 Unfortunately, the * Fax: +351217163636. Telephone: +351210924600ext 4224. E-mail: rafal.lukasik@lneg.pt. † Universidade Nova de Lisboa. ‡ Laboratório Nacional de Energia e Geologia. Małgorzata Ewa Zakrzewska received her two M.Sc. B.Sc. degrees in Environmental Protection Technology and in Biotechnology from the Gdańsk University of Technology, Poland. Currently, at REQUIMTE, Universidade Nova de Lisboa, she has been gaining experience in highpressure work under the supervision of Doctor Rafał Bogel-Łukasik and Professor Manuel Nunes da Ponte. Her research is focused on the application of supercritical CO2 in reaction and extraction. Chem. Rev. 2011, 111, 397–417 397

Pre-treatment of lignocellulosic biomass using ionic liquids: wheat straw fractionation.

This work is devoted to study pre-treatment methodologies of wheat straw with 1-ethyl-3-methylimidazolium acetate ([emim][CH3COO]) and subsequent fractionation to cellulose, hemicellulose and lignin. The method developed and described here allows the separation into high purity carbohydrate and lignin fractions and permits an efficient IL recovery. A versatility of the established method was confirmed by the IL reuse. The fractionation of completely dissolved biomass led to cellulose-rich and hemicellulose-rich fractions. A high purity lignin was also achieved. To verify the potential further applicability of the obtained carbohydrate-rich fractions, and to evaluate the pre-treatment efficiency, the cellulose fraction resulting from the treatment with [emim][CH3COO] was subjected to enzymatic hydrolysis. Results showed a very high digestibility of the cellulose samples and confirmed a high glucose yield for the optimized pre-treatment methodology.

Ionic liquids as a tool for lignocellulosic biomass fractionation

Lignocellulosic biomass composes a diversity of feedstock raw materials representing an abundant and renewable carbon source. In majority lignocellulose is constituted by carbohydrate macromolecules, namely cellulose and hemicellulose, and by lignin, a polyphenilpropanoid macromolecule. Between these biomacromolecules, there are several covalent and non-covalent interactions defining an intricate, complex and rigid structure of lignocellulose. The deconstruction of the lignocellulosic biomass makes these fractions susceptible for easier transformation to large number of commodities including energy, chemicals and material within the concept of biorefinery. Generally, the biomass pre-treatment depends on the final goal in the biomass processing. The recalcitrance of lignocellulose materials is the main limitation of its processing once the inherent costs are excessively high for the conventional pre-treatments. Furthermore, none of the currently known processes is highly selective and efficient for the satisfactory and versatile use, thus, new methodologies are still studied broadly. The ionic liquid technology on biomass processing is relatively recent and first studies were focused on the lignocellulosic biomass dissolution in different ionic liquids (ILs). The dissolution in IL drives to the structural changes in the regenerated biomass by reduction of cellulose crystallinity and lignin content contrasting to the original biomass. These findings provided ILs as tools to perform biomass pre-treatment and the advantageous use of their specific properties over the conventional pre-treatment processes. This review shows the critical outlook on the study of biomass dissolution and changes occurred in the biomass during this process as well as on the influence of several crucial parameters that govern the dissolution and further pre-treatment process. The review of currently known methods of biomass fractionation in IL and aqueous-IL mixtures is also discussed here and perspectives regarding these topics are given as well.

Current Pretreatment Technologies for the Development of Cellulosic Ethanol and Biorefineries.

Lignocellulosic materials, such as forest, agriculture, and agroindustrial residues, are among the most important resources for biorefineries to provide fuels, chemicals, and materials in such a way to substitute for, at least in part, the role of petrochemistry in modern society. Most of these sustainable biorefinery products can be produced from plant polysaccharides (glucans, hemicelluloses, starch, and pectic materials) and lignin. In this scenario, cellulosic ethanol has been considered for decades as one of the most promising alternatives to mitigate fossil fuel dependence and carbon dioxide accumulation in the atmosphere. However, a pretreatment method is required to overcome the physical and chemical barriers that exist in the lignin-carbohydrate composite and to render most, if not all, of the plant cell wall components easily available for conversion into valuable products, including the fuel ethanol. Hence, pretreatment is a key step for an economically viable biorefinery. Successful pretreatment method must lead to partial or total separation of the lignocellulosic components, increasing the accessibility of holocellulose to enzymatic hydrolysis with the least inhibitory compounds being released for subsequent steps of enzymatic hydrolysis and fermentation. Each pretreatment technology has a different specificity against both carbohydrates and lignin and may or may not be efficient for different types of biomasses. Furthermore, it is also desirable to develop pretreatment methods with chemicals that are greener and effluent streams that have a lower impact on the environment. This paper provides an overview of the most important pretreatment methods available, including those that are based on the use of green solvents (supercritical fluids and ionic liquids).

Acidic Ionic Liquids as Sustainable Approach of Cellulose and Lignocellulosic Biomass Conversion without Additional Catalysts

The use of ionic liquids (ILs) for biomass processing has attracted considerable attention recently as it provides distinct features for pre-treated biomass and fractionated materials in comparison to conventional processes. Process intensification through integration of dissolution, fractionation, hydrolysis and/or conversion in one pot should be accomplished to maximise economic and technological feasibility. The possibility of using alternative ILs capable not only of dissolving and deconstructing selectively biomass but also of catalysing reactions simultaneously are a potential solution of this problem. In this Review a critical overview of the state of the art and perspectives of the hydrolysis and conversion of cellulose and lignocellulosic biomass using acidic ILs using no additional catalyst are provided. The efficiency of the process is mainly considered with regard to the hydrolysis and conversion yields obtained and the selectivity of each reaction. The process conditions can be easily tuned to obtain sugars and/or platform chemicals, such as furans and organic acids. On the other hand, product recovery from the IL and its purity are the main challenges for the acceptance of this technology as a feasible alternative to conventional processes.

Novel pre-treatment and fractionation method for lignocellulosic biomass using ionic liquids

An efficient lignocellulosic biomass pre-treatment is a crucial step for the valorization of these kind of raw materials. Lignocellulosic biomass is a potentially valuable resource for transformation into biofuels and bio-based products. The use of ionic liquids as media for the biomass pre-treatment is an alternative method that follows the green chemistry concept. This work proposes a new methodology for wheat straw pre-treatment with the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([emim][OAc]), which allowed the production of cellulose, hemicellulose and lignin-rich fractions in a rapid and simple three-step fractionation process. Various temperatures (80–140 °C) and processing times (2–18 h) of the pre-treatment were studied. The quantitative and qualitative analysis of each lignocellulosic biomass fraction was determined by FTIR measurements. The glucan content in recovered cellulose-rich fractions was investigated by enzymatic hydrolysis. The cellulose recovery dependence on the pre-treatment conditions was ascertained through regression analysis. The optimal result for the recovery of the cellulose-rich fraction was obtained at 140 °C during 6 h achieving 37.1% (w/w) of the initial biomass loading. For the same conditions, optimal results were also produced regarding the amount of glucan present (81.1% w/wbiomass) in cellulose-rich fractions, the carbohydrate enrichment in the hemicellulose fraction (96% wt) and the purity of lignin (97% wt). The recovery of IL was performed after each pre-treatment and the obtained yields were up to 86% (w/w). The recovered ILs were analyzed by 13C and 1H NMR. The presence of value-added phenolic compounds in the recovered ILs was analyzed by capillary electrophoresis. Vanillin and its derivatives, as well as other lignin-based products, were identified.

Pretreatment and fractionation of wheat straw using various ionic liquids.

Pretreatment of lignocellulosic biomass with ionic liquids (ILs) is a promising and challenging process for an alternative method of biomass processing. The present work emphasizes the examination of wheat straw pretreatment using ILs, namely, 1-butyl-3-methylimidazolium hydrogensulfate ([bmim][HSO4]), 1-butyl-3-methylimidazolium thiocyanate ([bmim][SCN]), and 1-butyl-3-methylimidazolium dicyanamide ([bmim][N(CN)2]). Only [bmim][HSO4] was found to achieve a macroscopic complete dissolution of wheat straw during pretreatment. The fractionation process demonstrated to be dependent on the IL used. Using [bmim][SCN], a high-purity lignin-rich material was obtained. In contrast, [bmim][N(CN)2] was a good solvent to produce high-purity carbohydrate-rich fractions. When [bmim][HSO4] was used, a different behavior was observed, exhibiting similarities to an acid hydrolysis pretreatment, and no hemicellulose-rich material was recovered during fractionation. A capillary electrophoresis (CE) technique allowed for a better understanding of this phenomenon. Hydrolysis of carbohydrates was confirmed, although an extended degradation of monosaccharides to furfural and hydroxymethylfurfural (HMF) was observed.

The CO2-assisted autohydrolysis of wheat straw

The CO2-assisted autohydrolysis was used for wheat straw treatments at temperatures ranging from 180 to 210 °C and an initial CO2 pressure of 60 bar. The study was performed using three different mixture loadings, such as 250 g of H2O/25 g of wheat straw, 150 g of H2O/15 g of wheat straw and 75 g of H2O/7.5 g of wheat straw. The in situ formed carbonic acid was found to result in a higher dissolution of xylose as well as XOS (xylo-oligosaccharides) in comparison to CO2-free pre-treatments under the same conditions (temperature and LSR). The effect of CO2 concentration was also investigated to address the issue of CO2 involved in the reaction that allows to significantly increase the XOS content. At 210 °C with a mixture loading of 75 g of H2O/7.5 g of wheat straw, XOS were present in the liquor at a concentration of 15.75 g L−1. However, with more severe conditions more degradation products (mainly furfural) were detected (in the liquor and the recovered gas phase from depressurization after the reaction). Glucan was mainly retained in the solid phase (containing up to 64%) together with Klason lignin (maximum dissolution of 18%). The dissolved XOS in the liquid phase are proposed to be used in other applications, either directly, such as prebiotic ingredients, or indirectly, after post-hydrolysis to biofuel production through C5 sugars’ fermentation.

A new outlook on solubility of carbohydrates and sugar alcohols in ionic liquids

Ionic liquids are innovative media characterised by an easy tunability of physical and chemical properties with the potential for broad usefulness in a wide spectrum of chemical applications. One example of such an application is a complex biorefinery concept leading to the exploitation of the biomass for the production of energy (heat, power, fuel) and value added products. Until now ionic liquids have proven their feasibility to dissolve selectively biomass as a whole as well as individual carbohydrates. This work demonstrates the solubility of carbohydrates and value added products—sugar alcohols—which can be obtained from biomass through the biorefinery concept. The novelty of our investigation includes either solubility studies of sugar alcohols or an involvement of unexplored ionic liquids yet. In this research, a variety of ionic liquids constituted by imidazolium, pyridinium and phosphonium cations was applied. Furthermore, anions of ionic liquids, attractive from a point of view of a broad application, such as: 2-(2-methoxyethoxy)ethylsulfate, hydrogen sulfate, thiocyanate, tricyanomethanide, tetrachloroferrate, perfluorobutane sulfonate and tosylate were investigated. In this work, it was discovered that solubility of carbohydrates and sugar alcohols can exceed even 75 wt% at an easily achievable temperature depending on the choice of the ionic liquid.

Phase equilibrium-driven selective hydrogenation of limonene in high-pressure carbon dioxide

Pressure-tuning of selectivity in the hydrogenation of limonene in carbon dioxide was found in biphasic systems, close but below the critical conditions of the reaction mixture, where hydrogen solubility in the liquid is highly dependent on pressure. The subtle effects of pressure on the two-phase region in CO2 + H2 + a liquid reagent mixtures are essential factors in determining hydrogenation rates and selectivities in high-pressure carbon dioxide.