Study of dissolution of cellulose in ionic liquids by computer modeling

Abstract

Computer modeling of the geometry and electronic structure of the solvent and its complexes with water and cellobiose allowed: explaining the decrease in the dissolving power of an ionic liquid in the presence of water using data on the electronic structure of the molecules; determining the overall mechanism of solvation of cellulose by ionic liquids and other organic solvents; calculating the change in the energy in formation of a solvate complex of the elementary cellulose unit with 1-butyl-3-methylimidazolium chloride, which was -20.64 kcal/mole.Renewable fibre-forming polymers in nature have traditionally drawn the special attention of scientists and process engineers. Processing them from solutions is constantly being improved, and the search for new solvents plays an important role here. At the beginning of the last century, cellulose processing technologies were based on use of aqueous inorganic systems [1]. In the last quarter of the 20th century, production of viscose and cuprammonium fibres stopped for environmental considerations, and inorganic solvents were replaced by organic solvents [2]. Using N-methylmorpholine N-oxide (NMMO), it became possible to create a closed process cycle for production of hydrated cellulose fibres. Moreover, the relative instability of NMMO at temperatures above 100°C and some drawbacks of the fibres obtained from these solutions made it necessary to continue the search for promising solvents of cellulose. In 2001, ionic liquids [3] organic compounds whose molecules consist of a cation and an anion were proposed for this purpose. This highly polar solvents are in the liquid state at temperatures from ~50 to ~300°C, and solutions of cellulose in them are easily precipitated by water and produce fibres with good physicomechanical properties [4]. These solvents are still not used on the industrial scale, since they are manufactured in limited quantities and are thus expensive.Modern methods of computer modeling of the molecules of solvents, including ionic liquids [5,6] and polymer solvent solvate complexes [7,8], play an invaluable role in understanding the features of dissolution processes. Theoretical studies make it possible to explain the experimentally obtained characteristics and if there are not enough experimental data, to predict the behavior of a polymer during dissolution.We investigated the structural and energetic features of ionic liquids that determine their dissolving power with respect to cellulose and the characteristics of solvate complexes of cellulose with an ionic liquid. We used 1-butyl-3-methylimidazolium chloride with the following formula as the ionic liquid:where R = C 4 H 9 and anion B = Cl. Cellobiose, for which the characteristics of the geometry and electronic structure are reported in [7], was used as the model of cellulose. Calculation of the optimum geometric parameters (bond length, valence

The Application of Ionic Liquids in Dissolution and Separation of Lignocellulose

“…Their study proved the presence of 1:1 hydrogen bonding between Cl -and carbohydrate hydroxyl proton. Similar conclusions have also been obtained by computer modeling in a later literature (Novoselov et al, 2007). In our recent work, the effects of anionic structure and lithium salts addition on the dissolution of microcrystalline cellulose has also been studied through 1 H NMR, 13 C NMR and solvatochromic UV/vis probe measurements (Xu et al, 2010).…”

Aqueous ionic liquids and deep eutectic solvents for cellulosic biomass pretreatment and saccharification

“…3): a lower IL polarity correlates to a faster hydrolysis. A likely explanation is that favorable cellulose solvation and dissolution require balanced van der Waals forces and hydrophobic interactions, 37 which is only partially reflected in the empirical polarity determined by Reichardt’s dye. Conversely, as shown in Figs.…”

Regenerating cellulose from ionic liquids for an accelerated enzymatic hydrolysis

“…Overall, this process is easier to operate, less energy demanding, and more environmentally friendly than current commercial dissolution processes such as the viscose method (Fink et al, 2001;Heinze and Liebert, 2001) and the N-methyl-morpholine-N-oxide (NMMO) process (Fink et al, 2001). As summarized in recent papers (Liebert and Heinze, 2008;Zhao et al, 2008), cellulose-dissolving ILs usually contain anions of chloride, formate, acetate or alkylphosphonate because they form strong hydrogen-bonds with cellulose and other carbohydrates at elevated temperatures (Remsing et al, 2006;Youngs et al, 2006;Novoselov et al, 2007;Youngs et al, 2007;Remsing et al, 2008), allowing these biomolecules to dissolve. In general, acetate-based ILs are less viscous than the chloride type, and are more thermally stable than formate ones (Fukaya et al, 2008;Zhao et al, 2008).…”