Junho Yoon

One pot synthesis of environmentally friendly lignin nanoparticles with compressed liquid carbon dioxide as an antisolvent

Nanoparticles from commercial kraft lignin were developed using a facile, one pot green technology of a compressed CO2 antisolvent. N,N-Dimethylformamide (DMF) was employed as an organic solvent to prepare the lignin solution. The effects of various process parameters: temperature, pressure, solution flow rate and initial solution concentration, on the product yields, morphology, size, size distribution, surface area and textural properties of the particles were investigated by FESEM, HRTEM analyses and BET analyzers, and their formation mechanisms were deduced by the solubility behavior of lignin with liquid CO2 and DMF in the operating system. Moreover, the quality of lignin nanoparticles were elucidated by ATR-FTIR, XPS, XRD, DSC, TG/DTA and UV-vis measurements. This study showed that as the temperature and lignin concentration increased, and the pressure and solution flow rate decreased, the degree of particle aggregation/coalescence and the size increased along with the broader size distribution. In particular, the coalescence of particles was strongly influenced by the operational pressure, and even more significant with the increasing temperature. As a result, uniform, quasi-spherical nanoparticles with a mean particle diameter of 38 nm were obtained at 280.2 K, 15.0 MPa, and 0.06 kg h−1 of the solution flow rate and 5.3 wt% of the initial lignin concentration. Besides, the lignin nanoparticles have a relatively high BET surface area (nearly 92 m2 g−1) which primarily consisted of mesopores, and exhibited higher UV absorbing and dispersion stability, enhanced solubility, and homogeneous thermal degradation activity as compared with the raw lignin. Noteworthily, their biodegradable and biocompatible character may render them a candidate for applications in cosmetics, health and drug delivery systems.

Evaluation of hot compressed water pretreatment and enzymatic saccharification of tulip tree sawdust using severity factors.

Tulip tree sawdust was pretreated using hot compressed water with different pretreatment severities (LogR0, 3.05-5.01) by varying reaction temperatures (180-220°C) and residence time (1-30 min). It is found that the chemical composition and physicochemical properties of the pretreated products can be characterized and correlated with severity. Removal of most of the xylan and other hemicellulosic sugars from the raw material was observed at a severity of 4.5. Thus, the residual solids were recovered with increased cellulose and lignin contents. Nearly complete glucan conversion was achieved after 48 h of hydrolysis with 10 FPU/g of wet residual solid obtained above a severity of 4.8. The characteristics of the pretreated solids according to the pretreatment severity were strongly related with the glucose yield. The removal of structural barriers to the enzyme attack was the dominant factor affecting enzyme accessibility to the substrate.

Impact of bleaching on subcritical water- and Formosolv-pretreated tulip tree to enhance enzyme accessibility.

A novel method was developed for fractionating cellulose microfibrils from forest residue (tulip tree sawdust) to enhance cellulose digestibility, particularly at minimum enzyme loadings. This method involved three main stages: selective hemicellulose solubilization by subcritical water (SCW) pretreatment, delignification of the SCW-pretreated solids using the Formosolv process, and deformylation/bleaching of the cellulose pulp with alkaline hydrogen peroxide solution. This process produced nearly 98% white cellulose microfibrils with 23-fold higher conversion to glucose as compared to the raw substrate after 72 h of enzymatic hydrolysis. This study showed that cellulose swelling had the greatest effect on the enzymatic hydrolysis efficiency of delignified pulp obtained by the Formosolv process.

Hydrolysis kinetics of tulip tree xylan in hot compressed water.

Lignocellulosic biomass, a promising renewable resource, can be converted into numerous valuable chemicals post enzymatic saccharification. However, the efficacy of enzymatic saccharification of lignocellulosic biomass is low; therefore, pretreatment is necessary to improve the efficiency. Here, a kinetic analysis was carried out on xylan hydrolysis, after hot compressed water pretreatment of the lignocellulosic biomass conducted at 180-220°C for 5-30min, and on subsequent xylooligosaccharide hydrolysis. The weight ratio of fast-reacting xylan to slow-reacting xylan was 5.25 in tulip tree. Our kinetic results were applied to three different reaction systems to improve the pretreatment efficiency. We found that semi-continuous reactor is promising. Lower reaction temperatures and shorter space times in semi-continuous reactor are recommended for improving xylan conversion and xylooligosaccharide yield. In the theoretical calculation, 95% of xylooligosaccharide yield and xylan conversion were achieved simultaneously with high selectivity (desired product/undesired product) of 100 or more.