Pretreatment to Retrieve Xylose and Xylooligosaccharides by HCl Gas Directly from Biomass.

In this study, anhydrous hydrogen chloride gas was employed to selectively hydrolyze hemicellulose from aspen wood flour utilizing a gas-solid system. Selectivity toward hemicellulose was achieved by adjusting the acid concentration inside wood flour to 36% during gas hydrolysis, so only hemicellulose and disordered cellulose would be degraded during hydrolysis. Process parameters included the moisture content of the aspen wood flour (20%, 40%, and 60%) and reaction times from 30 min to 24 h. The optimal reaction conditions for the production of xylose and xylooligosaccharides was achieved with 40% moisture content and 6 h reaction time. Under these parameters, it was possible to retrieve 84% of the available xylan from aspen wood flour with only 1% glucan degradation.

Production of Water-Soluble Carbohydrates from Aspen Wood Flour with Hydrogen Chloride Gas.

The aim of this study was to optimize the reaction conditions for concentrated acid hydrolysis of aspen wood flour by employing anhydrous hydrogen chloride gas to produce fermentable sugars. Gas hydrolysis with HCl was conducted both with and without temperature control during hydrolysis under a relatively low pressure of 0.1 MPa. Process parameters for HCl gas hydrolysis included the moisture content of aspen wood flour (0.7-50%) and reaction time under pressure (30 min to 24 h). In addition, liquid-phase hydrolysis with concentrated hydrochloric acid was conducted in concentrations of 32-42% and 15 min to 24 h reaction times for comparison with the gas-phase process. The highest yields (>90%) for water-soluble carbohydrates from aspen wood flour were achieved with temperature-controlled gas hydrolysis using 50% moisture content and 2 h total reaction time, which is in line with the previous research and comparable to hydrolysis with concentrated (42%) hydrochloric acid.

Optimization of Dry-Jet Wet Spinning of Regenerated Cellulose Fibers Using [mTBDH][OAc] as a Solvent.

Superbase-based ionic liquids (ILs) have demonstrated excellent dissolution capability for cellulose, and employing the dry-jet wet spinning process, high-tenacity regenerated textile fibers have been made. Among a range of superbase-based ILs, [mTBDH][OAc] exhibited not only good spinnability but also exceptional recyclability, making it highly suitable for a closed-loop production of regenerated cellulose fibers. To further optimize the spinning process, we investigated the influence of the cellulosic raw materials and the IL with residual water on spinnability and fiber properties. In addition, single-filament spinning and multifilament spinning using spinnerets with different hole densities were investigated to reveal the upscaling challenges of the dry-jet wet spinning process. The air gap conditions, for example, temperature and moisture concentration were simulated using COMSOL multiphysics. The results indicate that the presence of a small amount of water (3 wt%) in the IL has a positive effect on spinnability, while the mechanical properties of the fibers remain unchanged.

Degradation of cellulose polymorphs into glucose by HCl gas with simultaneous suppression of oxidative discoloration.

As cellulose is the main polysaccharide in biomass, its degradation into glucose is a major undertaking in research concerning biofuels and bio-based platform chemicals. Here, we show that pressurized HCl gas is able to efficiently hydrolyze fibers of different crystalline forms (polymorphs) of cellulose when the water content of the fibers is increased to 30-50 wt%. Simultaneously, the harmful formation of strongly chromophoric humins can be suppressed by a simple addition of chlorite into the reaction system. 50-70 % glucose yields were obtained from cellulose I and II polymorphs while >90 % monosaccharide conversion was acquired from cellulose IIIII after a mild post-hydrolysis step. Purification of the products is relatively unproblematic from a gas-solid mixture, and a gaseous catalyst is easier to recycle than the aqueous counterpart. The results lay down a basis for future practical solutions in cellulose hydrolysis where side reactions are controlled, conversion rates are efficient, and the recovery of products and reagents is effortless.

Filament spinning of unbleached birch kraft pulps: Effect of pulping intensity on the processability and the fiber properties.

Man-made lignocellulosic fibres were successfully prepared from unbleached birch kraft pulps by using the Ioncell-F technology. Pulps with different lignin content were produced by tailored kraft pulping with varying intensity. The degree of polymerization of the pulps was adjusted by acid-catalyzed hydrolysis and electron beam treatment. All substrates were completely soluble in 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc) and the respective solutions were spinnable to yield fibres with good to excellent mechanical properties despite the use of only mildly refined wood pulp. The tensile properties decreased gradually as the lignin concentration in the fibres increased. Changes in the chemical composition also affected the structure and morphology of the fibres. Both the molecular orientation and the crystallinity decreased while the presence of lignin enhanced the water accessibility. The effects of the crystallite size and lignin content on monolayer water adsorption are discussed.

Assessing the reactivity of cellulose by oxidation with 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxo-piperidinium cation under mild conditions.

The accessibility and reactivity of cellulose are key parameters in its conversion into various products. Several indirect measures, such as water retention value (WRV), fiber saturation point (FSP) and specific surface area (SSA), are often used to characterize cellulosic samples for their reactivity. In this paper, we report on using oxidation with 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxo-piperidinium cation (4-AcNH-TEMPO+) as a probe reaction for the reactivity of cellulose in mild conditions (pH 9, room temperature). 4-AcNH-TEMPO+ is able to selectively convert hydroxymethyl groups into carboxylate groups. The time dependence of the conversion was monitored by iodometric quantification of the residual 4-AcNH-TEMPO+. Soluble substrates, such as 1-propanol and maltose, were quantitatively oxidized in ca. 1min while 3-16% of cellulose was oxidized in ca. 15min depending on its origin. Extrapolation of the slow residual oxidation to zero time allowed quantification of the easily reactive or accessible cellulose. The 4-AcNH-TEMPO+ reactivity was correlated with several pulp characteristics, including WRV, FSP, SSA, chemical composition, crystallinity, the pulping process and the drying history.

Correction: Cellulose regeneration and spinnability from ionic liquids.

Correction for 'Cellulose regeneration and spinnability from ionic liquids' by Lauri K. J. Hauru et al., Soft Matter, 2016, 12, 1487-1495.

Cellulose regeneration and spinnability from ionic liquids.

Ionic liquid solutions of cellulose or dopes can be spun into Lyocell-type textile fibers by dry-jet wet spinning. An extruded dope is drawn over an air gap into water, where the water hydrates the ionic liquid and cellulose is regenerated. Spinnability studies have concentrated on the deformation and failure modes in the air gap and thus the rheology of the unhydrated spinning dope. Herein, a breach in the bath, another failure mode, is discussed. Dopes are prepared from the good spinning solvents NMMO·H2O and [DBNH]OAc and the poor spinning solvents [emim]OAc and [TMGH]OAc. The diffusion constants for water diffusing inwards and for ionic liquid diffusing outwards the emerging filament are measured offline. The resiliences and strengths of cellulose-ionic liquid solutions with different hydration stoichiometries are measured by means of rheometry. By calculating the diffusion dynamics, the resilience distribution of the forming filament is simulated. Gel strength distribution accounts for the tendency of [emim]OAc dopes to undergo a telescope-type breach, whereas the gelatinous solution state of [TMGH]OAc dopes accounts for their poor spinnability.

Cellulose degradation in alkaline media upon acidic pretreatment and stabilisation.

The present study reports on a revised kinetic model for alkaline degradation of cellulose accounting for primary peeling/stopping reactions as well as for alkaline hydrolysis followed by secondary peeling. Oxalic acid pretreated cotton linters was utilised as the model substrate for the prehydrolysis-soda anthraquinone process. The main emphasis was investigating the effect of end-group stabilising additives such as sodium borohydride (BH), anthraquinone (AQ), and anthraquinone-2-sulphonic acid sodium salt (AQS) on the rates of the yield loss reactions. BH and AQS ensured a cellulose yield gain of 13% and 11%, respectively, compared to the reference. Both stabilisation agents decreased the content of the reducing end groups in the samples, while in the case of AQS stabilisation a 25% increase in carboxyl group content compared to the reference was also observed. As expected, the addition of end group stabilisers resulted in a significant decrease in the peeling-to-stopping rate constants ratio.

Degradation kinetics of the main carbohydrates in birch wood during hot water extraction in a batch reactor at elevated temperatures.

Hot water extraction of wood at elevated temperatures may be a suitable method to produce hemicellulose-lean pulps and to recover xylan-derived products from the water extract. In this study, water extractions of birch wood were conducted at temperatures between 180 and 240 °C in a batch reactor. Xylan was extensively removed, whereas cellulose was partly degraded only at temperatures above 180 °C. Under severe extraction conditions, acetic acid content in the water extract was higher than the corresponding amount of acetyl groups in wood. In addition to oligo- and monosaccharides, considerable amounts of furfural and 5-hydroxymethylfurfural (HMF) were recovered from the extracts. After reaching a maximum, the furfural yield remained constant with increasing extraction time. This maximum slightly decreased with increasing extraction temperature, suggesting the preferential formation of secondary degradation products from xylose. Kinetic models fitting experimental data are proposed to explain degradation and conversion reactions of xylan and glucan.