Highly effective fractionation chemistry to overcome the recalcitrance of softwood lignocellulose.

The efficient fractionation and thus production of individual biomass components are pivotal processes in the biorefinery concept. However, the recalcitrant nature of lignocellulose biomass, especially in the case of softwood, is one of the main obstacles to the wider application of biomass-based chemicals and materials. In this study, the use of aqueous acidic systems in the presence of thiourea was studied for the fractionation of softwood in mild conditions. Despite relatively low temperature (100 °C) and treatment times (30-90 min), notable high lignin removal efficiency (approximately 90 %) was obtained. Chemical characterization and the isolation of minor fraction of cationic, water-soluble lignin indicated that the fractionation proceed via nucleophilic addition of thiourea to lignin, resulting in dissolution of lignin in acidic water in relatively mild conditions. Besides high fractionation efficiency, both fiber and lignin fractions were obtained with bright color, significantly elevating their usability in material applications.

High-purity lignin fractions and nanospheres rich in phenolic hydroxyl and carboxyl groups isolated with alkaline deep eutectic solvent from wheat straw.

A combined pretreatment based on alkaline deep eutectic solvent (DES) of K2CO3 and glycerol and sequential acid fractionation was developed to extract reactive lignin from wheat straw biomass. This process exhibited excellent purification performance in lignin isolation, and the lignin fractionated at low pH displayed high reactivity, having hydroxyl and carboxyl groups up to 9.60 and 2.52 mmol/g, respectively. Silica was selectively separated and removed during the precipitation stage, avoiding the "silica interference". Moreover, DES-lignin nanospheres created by self-assembly using lignin fractions obtained by acid precipitation possessed a high zeta potential, large particle size and high content of hydrophilic groups. Overall, the findings related to the dissociation mechanism and fractionation of reactive lignin during alkaline DES pretreatment and the acid sequence precipitation are crucial for facilitating lignin valorization in high-added value products.

Aqueous phase reforming of birch and pine hemicellulose hydrolysates.

The current work focuses on studying the aqueous phase reforming (APR) of pine and birch hydrolysate obtained from waste wood by using organic acids available from biorefineries. Processing of representative synthetic mixtures was utilized in the work in order to support data interpretation related to the influence of different chemical compound and processing parameters on the APR of the actual hydrolysates. It was shown, that hydrogenation of the hydrolysates prior to APR was not feasible in the presence of formic acid, which ruled out one potential processing route. However, it was successfully demonstrated that birch and pine hydrolysates could be directly processed obtaining close to full conversion. The best results were obtained with tailored bimetallic Pd-Pt/sibunit catalyst in a trickle bed reactor system in the temperature range 175 °C-225 °C.

Comparison of Lignin Fractions Isolated from Wheat Straw Using Alkaline and Acidic Deep Eutectic Solvents.

This study aims to examine the characteristics of two solid lignin fractions isolated from wheat straw using alkaline and acidic deep eutectic solvents (DESs). The chemical properties and morphological characteristics of the two lignin fractions were evaluated by measuring their purity, elemental composition, molecular weight and particle size distributions, and microstructure. Their chemical structure was evaluated using DRIFT (diffuse reflectance infrared Fourier transform) spectroscopy, GPC (gel permeation chromatography), TGA (thermogravimetric analysis), 13C NMR (nuclear magnetic resonance), 31P NMR, and HSQC NMR. Our findings showed that the lignin isolated using alkaline DESs was less pure and had a smaller particle size, higher molecular weight, and thermal stability compared to the lignin isolated using acidic DESs. Their lignin structure was also determined to be different due to varying selective fractures on the linkages of lignin. These results suggest that the DES treatments could selectively extract lignin from wheat straw with different yields, compositions, morphologies, and structures, which could then provide a theoretical basis for the selection of DESs for specially appointed lignin extraction.

Formic acid aided hot water extraction of hemicellulose from European silver birch (Betula pendula) sawdust.

Hemicellulose has been extracted from birch (Betula pendula) sawdust by formic acid aided hot water extraction. The maximum amount of hemicellulose extracted was about 70mol% of the total hemicellulose content at 170°C, measured as the combined yield of xylose and furfural. Lower temperatures (130 and 140°C) favored hemicellulose hydrolysis rather than cellulose hydrolysis, even though the total hemicellulose yield was less than at 170°C. It was found that formic acid greatly increased the hydrolysis of hemicellulose to xylose and furfural at the experimental temperatures. The amount of lignin in the extract remained below the detection limit of the analysis (3g/L) in all cases. Formic acid aided hot water extraction is a promising technique for extracting hemicellulose from woody biomass, while leaving a solid residue with low hemicellulose content, which can be delignified to culminate in the three main isolated lignocellulosic fractions: cellulose, hemicellulose, and lignin.

Phosphonated nanocelluloses from sequential oxidative-reductive treatment-Physicochemical characteristics and thermal properties.

Nanocellulosic materials with good thermal stability are highly desirable for applications, such as reinforcement and filler agents in composites. In the present work, phosphonated cellulose was utilized to obtain nanocelluloses with good thermal stability and potential intumescent properties. Phosphonated cellulose was synthetized from birch pulp via sequential periodate oxidation and reductive amination using a bisphosphonate group-containing amine, sodium alendronate, as a phosphonating reagent. After high-pressure homogenization, bisphosphonate cellulose nanofibres or nanocrystals were obtained, depending on the initial oxidation degree. Nanofibres had a typical diameter of 3.8nm and length of several micrometers, whereas nanocrystals exhibited a width of about 6nm and an average length of 103-129nm. All nanocelluloses exhibited cellulose I crystalline structures and high transparency in water solutions. Phosphonated nanocelluloses exhibited good thermal stability and a greater amount of residual char was formed at 700°C compared to birch pulp and mechanically produced, non-chemically modified NFC.

Acid-catalysed xylose dehydration into furfural in the presence of kraft lignin.

In this study, the effects of kraft lignin (Indulin AT) on acid-catalysed xylose dehydration into furfural were studied in formic and sulphuric acids. The study was done using D-optimal design. Three variables in both acids were included in the design: time (20-80 min), temperature (160-180°C) and initial lignin concentration (0-20 g/l). The dependent variables were xylose conversion, furfural yield, furfural selectivity and pH change. The results showed that the xylose conversion and furfural yield decreased in sulphuric acid, while in formic acid the changes were minor. Additionally, it was showed that lignin has an acid-neutralising capacity, and the added lignin increased the pH of reactant solutions in both acids. The pH rise was considerably lower in formic acid than in sulphuric acid. However, the higher pH did not explain all the changes in conversion and yield, and thus lignin evidently inhibits the formation of furfural.

Hydrolysis of organosolv wheat pulp in formic acid at high temperature for glucose production.

Organosolv methods can be used to delignify lignocellulosic crop residues for pulp production or to pretreat them prior to enzymatic hydrolysis for bioethanol production. In this study, organic solvent was used as an acidic hydrolysis catalyst to produce glucose. Hydrolysis experiments were carried out in 5-20% formic acid at 180-220 °C. Wheat straw pulp delignified with a formicodeli™ method was used as a raw material. It was found that glucose yields from pulp are significantly higher than yields from microcrystalline cellulose, a model component for cellulose hydrolysis. The results indicate that cellulose hydrolysis of real fibers takes place more selectively to glucose than hydrolysis of microcrystalline cellulose particles does. The effect of the particle size on pulp hydrolysis was investigated, the crystallinity of hydrolyzed pulp was measured by XRD analysis, and the product distribution and its influence on the process was discussed.