NMR studies of cellulose dissolution in ionic liquids

This study examines the properties of ionic liquid and co-solvent mixtures, investigating fundamental aspect of cellulose dissolution in ionic liquids and developes a new technique to study the kinetics of cellulose coagulation. The first system that we studied is the mixture of 1-Ethyl-3-Methylimidazolium Acetate (EMIMAc) and Dimethyl Sulfoxide (DMSO). The motivation behind this study is that the use of DMSO as a co-solvent for cellulose dissolution in ionic liquid makes the cellulose processing more efficient and cost effective. Detailed studies of solutions are carried out to probe the macro- and micro-scopic changes of the ionic liquid properties as well as DMSO in the mixtures. The results suggest that ionic liquid and DMSO mixtures behave almost like an ideal solution. Solutions of 1-Butyl-3-Methylimidazolium Chloride (BMIMCl)-cellulose are investigated across a range of cellulose concentrations and temperatures using NMR- spectroscopy and relaxometry, diffusion and viscosity measurements. Using Bloemberg-Purcell-Pound (BPP) theory, NMR relaxation times T1 and T2 have been expressed in terms of an isotropic correlation time, τc for molecular motion. The derivation of the relation between correlation time and translational diffusion shows that the rotational motion can be best correlated to translational motion in term of hydrodynamic radius and activation energy. Mixtures of ionic liquids and carbohydrates (glucose, cellobiose and cellobiose) are investigated using viscosity and NMR spectroscopy, relaxometry and diffusion measurements. The results give the interaction stoichiometry of ionic liquid:hydroxyl group, 1:1. Analysis of the dynamic properties of the mixtures suggests that in solutions the bulk viscosity, η is best replaced by a microviscosity, ηµ = fµη, where fµ is the microviscosity correction factor. A new method to study the kinetics of cellulose coagulation in water from cellulose/IL/co-solvent using NMR has been successfully developed. Diffusion coefficients of EMIMAc and DMSO are found not to be significantly affected by cellulose and DMSO concentrations within the range studied, which suggests that if we want to change the coagulation rate and therefore the morphology, we would need to change the anti-solvent

Effect of 1-butyl-3-methyl-imidazodium chloride (BMIMCl) pretreatment on structural and glucose yield of the rice husk

Ionic liquid (IL) are of great interest as solvents for production of fuels from lignocellulosic biomass. The aim of this research is to determine the effect of ionic liquid, 1-butyl-3-methylimidazolium (BMIMCl) pretreatment on rice husk (Oryza sativa) based on it structural changes and glucose yield production. The pretreatment was conducted by heating 5% (w/w) rice husk in BMIMCl solution at 80 °C for 48 hours. The structural changes of regenerated rice husk were observed and characterized using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). It was found that the regenerated rice husk was less crystalline and higher amorphous upon BMIMCl treatment. The total sugar yield before and after fermentation by saccharomyces cerevisiae was analysed using dinitrosalicyclic acid (DNS) method. The regenerated rice husk produces higher total sugar yield compared with untreated rice husk

Influence of cellulose on ion diffusivity in 1-ethyl-3-methyl-imidazolium acetate cellulose solutions

International audienceSolutions of microcrystalline cellulose in 1-ethyl-3-methyl-imidazolium acetate have been investigated using pulsedfield gradient 1H NMR. In all cases the geometrically larger cation was found to diffuse faster than the smaller anion. Arrhenius temperature analysis has been applied to the ion diffusivities giving activation energies. The diffusion and published viscosity data for these solutions were shown to follow the Stokes-Einstein relationship, giving hydrodynamic radii of 1.6 A˚ (cation) and 1.8 A˚ (anion). Theories for obstruction, free-volume and hydrodynamic effects on solvent diffusion have been applied. The Mackie-Meares and Maxwell-Fricke obstruction models provided a correct trend only when assuming a certain fraction of ions are bound to the polymer. From this fraction it was shown that the maximum dissolvable cellulose concentration is ˜27% w/w, which is consistent with the highest known prepared concentration of cellulose in this ionic liquid. The Phillies' hydrodynamic model is found to give the best description for the cellulose concentration dependence of the ion diffusivitie

Macroscopic and microscopic study of 1-Ethyl-3-methyl-imidazolium acetate-water mixtures

International audienceMixtures of 1-ethyl-3-methyl-imidazolium acetate ([C2mim][OAc]) and water across the entire composition range, from pure [C2mim][OAc] to pure water, have been investigated using density, viscosity, and NMR spectroscopy, relaxometry, and diffusion measurements. These results have been compared to ideal mixing laws for the microscopic data obtained from the NMR results and macroscopic data through the viscosity and density. It was also found that the mixing of the two fluids is exothermal. The proton spectra indicate though that [C2mim][OAc] and water are interacting without the formation of new compounds. The maximal deviations of experimental data from theoretical mixing rules were all found to occur within the range 0.74 ± 0.06 mol fraction of water, corresponding to approximately three water molecules per [C2mim][OAc] molecul

Diffusion of 1-ethyl-3-methyl-imidazolium acetate in glucose, cellobiose, and cellulose solutions.

Solutions of glucose, cellobiose and microcrystalline cellulose in the ionic liquid 1-ethyl-3-methyl-imidazolium ([C2mim][OAc]) have been examined using pulsed-field gradient (1)H NMR. Diffusion coefficients of the cation and anion across the temperature range 20-70 °C have been determined for a range of concentrations (0-15% w/w) of each carbohydrate in [C2mim][OAc]. These systems behave as an "ideal mixture" of free ions and ions that are associated with the carbohydrate molecules. The molar ratio of carbohydrate OH groups to ionic liquid molecules, α, is the key parameter in determining the diffusion coefficients of the ions. Master curves for the diffusion coefficients of cation, anion and their activation energies are generated upon which all our data collapses when plotted against α. Diffusion coefficients are found to follow an Arrhenius type behavior and the difference in translational activation energy between free and associated ions is determined to be 9.3 ± 0.9 kJ/mol