Tunable and functional deep eutectic solvents for lignocellulose valorization

Stabilization of reactive intermediates is an enabling concept in biomass fractionation and depolymerization. Deep eutectic solvents (DES) are intriguing green reaction media for biomass processing; however undesired lignin condensation is a typical drawback for most acid-based DES fractionation processes. Here we describe ternary DES systems composed of choline chloride and oxalic acid, additionally incorporating ethylene glycol (or other diols) that provide the desired ‘stabilization’ function for efficient lignocellulose fractionation, preserving the quality of all lignocellulose constituents. The obtained ethylene-glycol protected lignin displays high β-O-4 content (up to 53 per 100 aromatic units) and can be readily depolymerized to distinct monophenolic products. The cellulose residues, free from condensed lignin particles, deliver up to 95.9 ± 2.12% glucose yield upon enzymatic digestion. The DES can be recovered with high yield and purity and re-used with good efficiency. Notably, we have shown that the reactivity of the β-O-4 linkage in model compounds can be steered towards either cleavage or stabilization, depending on DES composition, demonstrating the advantage of the modular DES composition.

The Effect of Heat Flux to the Fire-Technical and Chemical Properties of Spruce Wood (Picea abies L.)

The paper assesses the influence of the heat flux on spruce wood (Picea abies L.) behavior. The heat flux was performed at 15, 20, 25, and 30 kW∙m−2. The fire-technical properties, such as the mass burning rate, charring thickness, charring rate, as well as the chemical composition (contents of the extractives, lignin, cellulose, holocellulose), of wood were determined. The highest burning rate of spruce wood of 0.32 %·s−1 was reached at the heat flux of 30 kW∙m−2. The charring rate ranged from 1.004 mm·min−1 (15 kW∙m−2) to 2.016 mm.min−1 (30 kW∙m−2). The proposed model of the charring process of spruce wood in time and appropriate thickness as a selected parameter is applicable in validation of the results of computer fire models in the design of fire protection of wooden buildings. The decrease in the holocellulose content mostly caused by the degradation of hemicelluloses was observed during thermal loading. The biggest decrease in hemicelluloses (24.94%) was recorded in samples loaded at 30 kW∙m−2. The contents of cellulose increased due to the structural changes (carbonization and crosslinking), the content of lignin increased as well due to its higher thermal stability compared to saccharides, as well as the resulting lignin condensation.

QUICK NON-DESTRUCTIVE ANALYSIS OF CONDENSED LIGNIN BY FTIR. PART 2. PULP SAMPLES FROM ACID SULFITE COOKING

"In our previous work, we demonstrated how lignin condensation and precipitation taking place in kraft pulping can be detected and even quantified by Fourier Transform Infrared (FTIR) spectroscopy. Because lignin reactions in acid sulfite pulping are very different from those occurring during kraft cooking, a new analysis method is proposed to rapidly analyze the condensed lignin in acid sulfite pulp. This kind of analysis is useful for sulfite pulp mills to detect the elevated risk of black cook. This paper presents and discusses the novel method using FTIR spectroscopy to rapidly analyze lignin condensation in softwood pulp samples from acid sulfite processes. Several softwood pulp samples from acid sulfite pulping at varying levels of condensation were included in this research. According to the results, FTIR spectroscopy allows indirect quantification of lignin condensation in a difficult matrix of wood constituents, such as in incompletely delignified acid sulfite pulp."

Evaluation of chemical additives in hydrothermal pre-treatment of wood for the integrated production of monosugars and hydrolysis lignins for PLA-based biocomposites

The use of chemical additives (1- and 2-naphthol, formaldehyde) in hydrothermal pre-treatments of pine, birch, and willow wood was evaluated to minimize lignin condensation reactions and consequently improve the saccharification of the pre-treated materials. The residual hydrolysis lignins were then tested in the preparation of polylactic acid (PLA)-based composites. The results showed that addition of 2-naphthol to the hydrothermal pre-treatment increased the saccharification of pine wood by twofold compared to water-only experiments, but the sugar yield was only 50% of the carbohydrate content in the pre-treated pine. The use of 2-naphthol and formaldehyde also improved somewhat the saccharification of bark-containing willow wood, while the use of 1-naphthol had no effect on the saccharification of any of the pre-treated materials. In birch and willow (without bark), almost complete saccharification could be achieved even without additives. Analyses of hydrolysis lignins from birch revealed structural changes caused by the additives, which were consistent with a reduction of condensation reactions. Selected lignins were successfully used at 20% loading in PLA/lignin composites; however, variation in mechanical properties among composites prepared with different lignins was only minor. In general, the use of lignin decreased the strength and ductility of PLA but increased the stiffness. Based on these results, the use of additives may only be beneficial in the pre-treatment of pine or other softwoods to improve the sugar yields.

Effect of black liquor replacement in wheat straw soda-AQ cooking and lignin structure of pulps

The effects of black liquor replacement cooking (BLRC) on wheat straw soda-anthraquinone (AQ) pulps and their lignin structures were investigated by using different black liquor replacement ratios (BLRR) and alkaline nitrobenzene oxidation and ozonation. The residual AQ, alkali, and dissolved lignin, as well as carbohydrates in the wheat straw black liquor, greatly influence wheat straw soda-AQ cooking. The influence could be controlled by different BLRR. The BLRC with around 60% BLRR resulted in superior delignification selectivity. The residual AQ and dissolved carbohydrates in the black liquor are beneficial to delignification selectivity, while the dissolved and degraded lignin can slow the delignification rate. No obvious differences were found in the lignin condensation and β-O-4 structure degradation by the BLRC at different BLRR compared to control soda-AQ cooking. The BLRC technology has potential application because it reduces chemical charge and chemical recovery load and results in higher yield and quality of pulp.