A systematic study on the physicochemical properties of two protic ionic liquids (ILs) {2-hydroxyethylammonium acetate ([Mea][Ac]) and 2-hydroxyethylammonium hexanoate ([Mea][Hex])} and their mixtures with water was performed. The density and viscosity were assessed across the entire range of aqueous dilutions between 278 and 393 K. The conductivities, water activities, and surface tension of the binary systems in water were also assessed, and the influence of anions was evaluated. Differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), and 1H and 13C nuclear magnetic resonance (NMR) techniques were used to study the systems at different IL compositions. The excess molar volumes (VE) and thermal expansion coefficients were calculated, with negative values for VE across the entire concentration range. Density data were fitted to a polynomial for density prediction, function of temperature, and concentration, with the average deviation percentage not exceeding 0.63%. The viscosities of the binary systems were studied considering six different models and were better predicted by the model of Herráez et al. at IL concentrations higher than 0.25 mole fraction. The systems containing [Hex]- exhibited higher water activities and lower conductivity and surface tension. All studied systems exhibited a glass transition event, which varied according to the IL composition. The FTIR and NMR analysis confirmed the distinct molecular arrangement of [Mea][Ac] and [Mea][Hex] systems.

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The use of lignocellulosic (LC) materials, especially residues, as feedstock in biorefinery applications is a promising alternative to the oil refinery production of fuels, power and chemicals, reducing the global warming potential (GWP) related to these activities. The conversion of LC's carbohydrates into useful sugars is entirely dependent on the efficiency of the pretreatment (PT) step. Ionic liquids (ILs) have been explored as tailored solvents for the solubilization of LC's complex structure during PT, which can overcome the existing hurdles related to PT. This work assesses the impact of PT variables and the IL recycling through freezing concentration (FC) in an IL-based biorefinery. The influence of temperature, solid loading and IL dilution was systematically studied and the mass and energy balances, economic and environmental outcomes calculated. Life cycle analysis (LCA) was employed in a cradle-to-gate approach. Results showed that solid loading and IL dilution, rather than PT temperature, have the major influence on the energy requirements to produce 1 kg of ethanol. IL make up is a critical parameter to minimize the environmental impact and operational costs associated with the process. Product selling price and IL recycling were the most impacting variables concerning profitability. Extra investment for improved IL recycling is advantageous up to 99% of recovery. Product diversification can improve the economic feasibility even if it is associated with increased capital expenditure. The results show the importance of the pretreatment design and solvent recycling from an integrated perspective, thus challenging the criteria defined while assessing these steps alone.

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The use of Lignocellulosic residues (LC) such as conventional food crop remains, for Bioenergy and Biorefinery applications is an attractive way to increase feedstock availability without the investment in additional land area. Moreover, it is noteworthy that biomolecules produced from LC, namely second generation (2G), has a potentially better greenhouse gases (GHG) emissions balance. One of the most economically successful lignocellulosic sources is the sugarcane crop, with a global production of about 1.7 gigatonnes in 2019. Although LC is rich in carbohydrates, 40 – 90 wt%, these sugars are not readily converted due to their molecular structure. Consequently, it must be treated, so that LC’s molecular nature is changed into a more convenient arrangement favoring subsequent conversions. Such process is called pretreatment (PT) and is considered the most important step to obtain an efficient conversion of LC’s constituents. Recently, ionic liquids (ILs) have emerged as an alternative technology for biomass pretreatment. ILs can break the H bonds which stabilize LC’s molecular structure, improving components solubility and/or turning LC’s structure more susceptible to further conversions, such as improving the enzymatic digestibility of pretreated solids.@en

Ionic liquids (ILs) have great potential as solvents and catalysts for pretreatment of lignocellulosic biomass. However, process scale-up necessitates that IL-based pretreatment methods be optimized in terms of cost and sustainability. In this study, low-cost and easily synthesizable ethanolammonium-based ILs were prepared and used in the pretreatment of sugar cane straw (SW). The effects of ILs, IL mixtures, pretreatment temperature, water content, solids loading, ultrasonication, and agitation speed on residual solids enzymatic digestibility and delignification were systematically assessed, and the process was scaled up from a 50 mL static flask to a 1 L impelled reactor. IL mixtures improved enzymatic digestibility at higher solids loading and water addition in the reaction medium under mild temperature conditions (90 °C). Enzymatic hydrolysis of residual solids after bench-scale pretreatment of SW for 3 h at 15% (w/w) solids loading and 20% (w/w) water content in the liquid phase resulted in 98% cellulose digestibility under nonoptimized conditions. This study provides a practical review of IL-based pretreatment methods, discusses the selection of variables for process design and scale-up, and presents empirical results.

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