Ana Rita C. Morais

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).

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.

Integrated conversion of agroindustrial residue with high pressure CO2 within the biorefinery concept

Sustainable production of energy and other added-value products from biomass-derived polysaccharides is a key challenge of an efficient biorefinery facility. Most technologies for biomass processing are energy demanding and use significant amounts of chemicals and catalysts. The need to develop a process which is devoid of all these shortcomings associated with conventional processes is emphasized. A new approach is demonstrated for an integrated wheat straw biorefinery using a green technology, high-pressure CO2–H2O, to produce oligosaccharides from hemicellulose fraction and to enhance the cellulose digestibility for the enzymatic hydrolysis. Over the range of reaction conditions (130, 215, 225 °C and 0 to 54 bar of CO2), CO2 adds value to the process by in situ formation of carbonic acid that leads to higher dissolution of hemicellulose into xylo-oligosaccharides and xylose and to the use of less energy in comparison with water-only technologies. Without an additional chemical catalyst, high-pressure CO2–H2O outperformed hydrothermal reactions and gave much higher total sugars yield for wheat straw (as high as 84% in comparison with 67.4% with auto-hydrolysis at a 10 °C higher temperature). Apart from the results obtained for valorisation of hemicellulose fraction, both chemical and physical effects of CO2 coupled to enzymatic hydrolysis resulted in a glucan conversion to glucose yield of 82%, which consists of 26% improvement over those obtained during auto-hydrolysis. The influence of the high pressure reaction on the processed solid was examined by spectroscopic methods (namely Scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy). The obtained results suggest that the high pressure CO2-based method is a very promising alternative technology allowing integrated biomass processing within the biorefinery concept.

Recognition and Realisation Rules in Acquiring School Science ‐‐ the contribution of pedagogy and social background of students

This study investigates the difficulties students encounter in problem solving in the area of sciences. Contrary to usual approaches of a fundamental psychological basis, the research takes into account the sociological processes of learning and transmission in both the family and the school. The aim of the study is to see the extent to which the students have recognition and realisation rules in the micro‐context of problem solving (specific coding orientation) and to find out the reasons which may underlie their difficulties. Thus the data obtained are related to social class, race and gender and also to pedagogic practices (differing in power and control relations) and school science achievement in high level cognitive competencies. They are also related to childrens cognitive level. The results show a strong relation between social class and specific coding orientation to problem solving. The relation is also strong for race and weaker for gender. Specific coding orientation is also strongly related ...

Lignin transformations for high value applications: towards targeted modifications using green chemistry

Lignin represents a considerable source of renewable and bio-based carbon. Pulping processes enable lignin, together with all components of the lignocellulosic biomass, to enter valorizable streams. A current key objective is to further valorize this versatile aromatic biopolymer, and for that, to go beyond its mere energy use. Despite the emergence of numerous proposals for value-added products coming from lignin, most of them remain at the research stage. The main challenges arise from the complexity and heterogeneity of the lignin structure and resulting molecular properties, the variability of the biomass source, pre-treatment processes, and the growing environment. Keeping in mind that future integrated biorefineries must take into account environmental concerns, lignin processing in accordance with green chemistry principles should first be favoured. From this very perspective, this work proposes to review the most promising current routes towards fractionation and/or depolymerization of lignin. Those should represent sustainable treatment technologies potentially leading to a broad spectrum of marketable lignin-based molecules and products. First, lignin fractionation by selective precipitation using pH as well as green solvents, or by using membrane technologies, will be addressed. Then lignin depolymerization will be discussed at length, notably from a catalytic point of view and by hydrogenolysis; the knowledge about the fundamental chemistry stemming from the use of model compounds will be described. Substitution of organic solvents with environmentally harmless supercritical fluids or with negligible vapour pressure ionic liquids is of great interest to modify lignin, and is finally reviewed. Lastly, challenges for integrated biorefineries and for launching new lignin-based compounds and products will be discussed.

A green and efficient approach to selective conversion of xylose and biomass hemicellulose into furfural in aqueous media using high-pressure CO2 as a sustainable catalyst

This work introduces a novel approach to produce furfural from lignocellulosic biomass without the use of mineral acids or heterogeneous catalysts. The proposed concept consists of two reaction stages. The first one consists of an extraction of hemicellulose from wheat straw using high-pressure CO2 and H2O to produce a water-soluble fraction containing pentoses in oligomeric and monomeric forms. The second step involves the conversion of this fraction into furfural in a system consisting of water, tetrahydrofuran (THF), methyl isobutyl ketone (MIBK) and high-pressure CO2 at elevated temperatures with MIBK as the water immiscible extracting solvent. At 200 °C and 50 bar of initial CO2 pressure, the high-pressure CO2 and H2O assisted process of hemicellulose extraction resulted in 81 mol% conversion of hemicellulose into xylose and arabinose (mainly as oligomers). Prior to the use of the produced hemicellulose hydrolysate in dehydration reactions to obtain furfural, a series of preliminary trials with xylose, as a model compound, were performed. The biphasic system with water/THF/MIBK under the reaction conditions with 50 bar of initial CO2 pressure, at 180 °C, 60 min favoured the production of furfural and allowed to obtain furfural at a yield and selectivity of 56.6 mol% and 62.3 mol%, respectively. Under the same conditions, hemicellulose hydrolysate dehydration yielded 43 mol% of furfural with a selectivity of 44 mol%.

Pre-treatment and extraction techniques for recovery of added value compounds from wastes throughout the agri-food chain

The enormous quantity of food wastes discarded annually forces a look into alternatives for this interesting feedstock. Thus, food bio-waste valorisation is one of the current imperatives of society. This review is the most comprehensive overview of currently existing technologies and processes in this field. It tackles classical and innovative physical, physico-chemical and chemical methods of food waste pre-treatment and extraction for the recovery of added value compounds and detection by modern technologies and is an outcome of the COST Action EUBIS, TD1203 Food Waste Valorisation for Sustainable Chemicals, Materials and Fuels.

Green metrics evaluation of isoprene production by microalgae and bacteria

Isoprene is a key intermediate compound for the production of synthetic rubber and adhesives and is also used as a building block in the chemical industry. Traditionally, isoprene is obtained from crude oil during the refinery process. Nevertheless, plants and animals are also able to synthesize this important compound. This work compares two renewable approaches for isoprene production: by photosynthetic organisms (autotrophic microalgae/cyanobacteria) and by heterotrophic organisms (bacteria). These are two alternative pathways for the conventional isoprene production obtained from the petrochemical-based refinery process, which were assessed in this work using green metrics. Their performance was evaluated in terms of: material efficiency, energy efficiency, economic evaluation and land use. A 10-tonne scale was chosen to perform the green metrics evaluation for both biological processes leading to isoprene. For each process, a comparison was made between a scenario considering the highest isoprene produced reported in the literature and a scenario considering the maximum theoretical stoichiometric isoprene productivity.

Highly efficient and selective CO2-adjunctive dehydration of xylose to furfural in aqueous media with THF

The selective dehydration of xylose into furfural using high-pressure CO2 as an effective and more sustainable catalyst in an H2O/THF system is reported for the first time. The conversion of D-xylose into furfural above 83 mol% with a furfural yield of 70 mol% and a selectivity of 84% was achieved with only 50 bar of CO2 pressure within 1 hour at 180 °C.