John Gräsvik

Evaluation of four ionic liquids for pretreatment of lignocellulosic biomass

BackgroundLignocellulosic biomass is highly recalcitrant and various pretreatment techniques are needed to facilitate its effective enzymatic hydrolysis to produce sugars for further conversion to bio-based chemicals. Ionic liquids (ILs) are of interest in pretreatment because of their potential to dissolve lignocellulosic materials including crystalline cellulose.ResultsFour imidazolium-based ionic liquids (ILs) ([C=C2C1im][MeCO2], [C4C1im][MeCO2], [C4C1im][Cl], and [C4C1im][HSO4]) well known for their capability to dissolve lignocellulosic species were synthesized and then used for pretreatment of substrates prior to enzymatic hydrolysis. In order to achieve a broad evaluation, seven cellulosic, hemicellulosic and lignocellulosic substrates, crystalline as well as amorphous, were selected. The lignocellulosic substrates included hybrid aspen and Norway spruce. The monosaccharides in the enzymatic hydrolysate were determined using high-performance anion-exchange chromatography. The best results, as judged by the saccharification efficiency, were achieved with [C4C1im][Cl] for cellulosic substrates and with the acetate-based ILs for hybrid aspen and Norway spruce. After pretreatment with acetate-based ILs, the conversion to glucose of glucan in recalcitrant softwood lignocellulose reached similar levels as obtained with pure crystalline and amorphous cellulosic substrates. IL pretreatment of lignocellulose resulted in sugar yields comparable with that obtained with acidic pretreatment. Heterogeneous dissolution with [C4C1im][HSO4] gave promising results with aspen, the less recalcitrant of the two types of lignocellulose included in the investigation.ConclusionsThe ability of ILs to dissolve lignocellulosic biomass under gentle conditions and with little or no by-product formation contributes to making them highly interesting alternatives for pretreatment in processes where high product yields are of critical importance.

Mechanistic insights into lignin depolymerisation in acidic ionic liquids

Acidic anions of ionic liquids have been demonstrated as efficient catalysts for the cleavage of the β-O-4 ether linkage prevalent in the lignin superstructure. Through the use of lignin model compounds with varying functionality and by monitoring reaction kinetics, a full mechanistic investigation into the hydrolysis of the β-O-4 linkage in acidic ionic liquid solutions is reported. Hammett acidities are reported for different 1-butyl-3-methylimidazolium hydrogen sulfate [C4C1im][HSO4] ionic liquid systems with varying acid and water concentrations and were correlated to substrate reactivity. Results show that the rate of ether cleavage increases with an increase in acidity and the initial dehydration of the model compound is the rate-determining step of the reaction. The Eyring activation parameters of the reaction in hydrogen sulfate ionic liquids with a variety of cations are reported, indicating a consistent E1 dehydration mechanism. Hydrogen bonding in protic ionic liquids was shown to significantly influence anion–cation interactions, consequently altering the solvation of the protonated starting material and therefore the overall rate of reaction. Comparison of reaction rates in these ionic liquids with results within aqueous or aqueous/organic media indicate that the ionic liquids facilitate more rapid cleavage of the β-O-4 ether linkage even under less acidic conditions. All the reported results give a complete overview of both the mechanistic and solvation effects of acidic ionic liquids on lignin model compounds and provide scope for the appropriate selection and design of ionic liquids for lignin processing.

A quick, simple, robust method to measure the acidity of ionic liquids

Introduced here is a quick, simple, robust method to measure acidity in ionic liquid (IL) systems by the use of the NMR-probe mesityl oxide. Acidity corresponding to a Hammett acidity of -1 to -9 can be measured reliably using this technique, a range that vastly exceeds that of any single UV-vis probe.

Synthesis and Properties of Open Fullerenes Encapsulating Ammonia and Methane

Abstract We describe the synthesis and characterisation of open fullerene (1) and its reduced form (2) in which CH4 and NH3 are encapsulated, respectively. The 1H NMR resonance of endohedral NH3 is broadened by scalar coupling to the quadrupolar 14 n nucleus, which relaxes rapidly. This broadening is absent for small satellite peaks, which are attributed to natural abundance 15N. The influence of the scalar relaxation mechanism on the linewidth of the 1H ammonia resonance is probed by variable temperature NMR. A rotational correlation time of τc=1.5 ps. is determined for endohedral NH3, and of τc=57±5 ps. for the open fullerene, indicating free rotation of the encapsulated molecule. IR spectroscopy of NH3@2 at 5 K identifies three vibrations of NH3 (ν 1, ν 3 and ν 4) redshifted in comparison with free NH3, and temperature dependence of the IR peak intensity indicates the presence of a large number of excited translational/ rotational states. Variable temperature 1H NMR spectra indicate that endohedral CH4 is also able to rotate freely at 223 K, on the NMR timescale. Inelastic neutron scattering (INS) spectra of CH4@1 show both rotational and translational modes of CH4. Energy of the first excited rotational state (J=1) of CH4@1 is significantly lower than that of free CH4.

Methods of Synthesis and Purification of Ionic Liquids

Abstract The synthesis and purification of ionic liquids is reviewed in this chapter. Brief discussions on the classical synthetic routes are included with the focus directed to those ionic liquids with novel moieties and synthetic routes, since the start of the 2000s. The likely impurities found in ionic liquids at each stage of synthesis are examined, the purification methods to remove them discussed, and the possible detection methods outlined.

Microbial mineralization of cellulose in frozen soils

High-latitude soils store ~40% of the global soil carbon and experience winters of up to 6 months or more. The winter soil CO2 efflux importantly contributes to the annual CO2 budget. Microorganisms can metabolize short chain carbon compounds in frozen soils. However, soil organic matter (SOM) is dominated by biopolymers, requiring exoenzymatic hydrolysis prior to mineralization. For winter SOM decomposition to have a substantial influence on soil carbon balances it is crucial whether or not biopolymers can be metabolized in frozen soils. We added 13C-labeled cellulose to frozen (−4 °C) mesocosms of boreal forest soil and followed its decomposition. Here we show that cellulose biopolymers are hydrolyzed under frozen conditions sustaining both CO2 production and microbial growth contributing to slow, but persistent, SOM mineralization. Given the long periods with frozen soils at high latitudes these findings are essential for understanding the contribution from winter to the global carbon balance.High latitude soils can store around 40 % of the Earth’s soil carbon. Here, the authors add 13C-labeled cellulose to frozen mesocosms of boreal forest soils and find that cellulose biopolymers are hydrolysed under frozen conditions and therefore contribute to the slow degradation of soil organic matter.