Optimizing carboxylated nanocellulose preparation: A kinetic and mechanistic study on the enhancement of TEMPO-mediated oxidation via swelling treatment.

This study explored the application of swelling pretreatment as a solution to the high cost and contamination associated with the process of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation for nanocellulose preparation. The results demonstrated that swelling significantly expanded the fibers while preserving the degree of polymerization (DP) of cellulose (approximately 95 %). The native crystal structure and hydrogen bonding of cellulose were disrupted after swelling, leading to a reduction in crystallinity and crystallite size, and the decrease of bonding energy and content of intermolecular O6-H⋯O3'. The TEMPO-mediated oxidation processes of cellulose fibers with or without swelling were successfully fitted using a consecutive first-order reaction kinetic model. The fitting results indicated that swelling significantly reduced the activation energy of TEMPO-mediated oxidation and enhanced the reaction rate. Among three swelling systems, the NaOH/thiourea/water system exhibited the optimal promotion effect. Consequently, the swelling treatment enables a significant reduction of 30 % in the catalyst dose for the TEMPO-mediated oxidation while preserving a competitive reaction rate, yield, and product performance. Lower catalyst dosage helps to reduce cost and environmental impact, facilitating the industrial application of the TEMPO-mediated oxidation process.

Oxidation of p-toluenesulfonic acid fractionated hybrid Pennisetum by different methods for carboxylated nanocellulose preparation: The evaluation of efficiency and sustainability.

An innovative two-step process with p-toluenesulfonic acid (p-TsOH) and oxidation treatment was proposed for the efficient preparation of carboxylated nanocellulose from hybrid Pennisetum. Approximately 90 % of lignin was dissolved by p-TsOH acid under the optimal condition (80 °C, 20 min). Near-complete delignification (down to 0.5 %) and introduction of carboxylate groups (up to 1.48 mmol/g) could be achieved simultaneously during cellulose oxidation treatments without the requirement for bleaching. However, different oxidation methods expressed different efficiency and sustainability. 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) oxidation has higher selectivity for the carboxylation reaction but with detriment to the aquatic environment. Fenton oxidation is more energy-consuming due to the lower carboxylate contents of products (maximum 188 µmol/g), with the carboxylic groups present as carboxylic acids, but competitive in terms of environmental sustainability, especially when renewable energy sources are available. The nanocelluloses obtained by the two oxidation methods differ in morphology and have different application prospects.

Fast hydrothermal co-liquefaction of corn stover and cow manure for biocrude and hydrochar production.

Fast Hydrothermal liquefaction (HTL) has emerged as a versatile means of converting wet biomass into bio-crude oil. This study was aimed to explore a fast hydrothermal co-liquefaction (co-HTL) platform to valorize corn stover and cow manure by evaluating several reaction parameters (i.e., residence time, reaction temperature, and feedstocks mass ratio). The highest yield (over 24 wt%) of bio-crude oil was achieved under the moderate condition (400 °C, 16 min, and the mass ratio of 1:1). The Higher heating value (HHV) of bio-crude oil was around 34 MJ/kg. Up to 43% of selectivity toward phenols in bio-crude oil was gained from fast co-HTL maintained for 30 min. The properties of hydrochar were comprehensively characterized by CHNS elemental analysis, SEM, EDX, and FTIR. The highest HHV of hydrochar was 27.31 MJ/kg, suggesting the high potential as a solid fuel. CO2 as the dominant gaseous fraction were identified and quantified by GC.