Chunbao (Charles) Xu

Hydrolytic degradation of alkaline lignin in hot-compressed water and ethanol.

Alkaline lignin of a very high molecular weight was successfully degraded into oligomers in a hot-compressed water-ethanol medium with NaOH as the catalyst and phenol as the capping agent at 220-300 degrees C. Under the optimal reaction conditions, i.e., 260 degrees C, 1 h, with the lignin/phenol ratio of 1:1 (w/w), almost complete degradation was achieved, producing <1% solid residue and negligible gas products. The obtained degraded lignin had a number-average molecular weight M(n) and weight-average molecular weight M(w) of 450 and 1000 g/mol respectively, significantly lower than the M(n) and M(w) of 10,000 and 60,000 g/mol of the original lignin. A higher temperature and a longer reaction time favoured phenol combination, but increased the formation of solid residue due to the condensation reactions of the degradation intermediates/products. The degraded lignin products were soluble in organic solvents (such as THF), and were characterized by HPLC/GPC, IR and NMR. A possible mechanism for lignin hydrolytic degradation was also proposed in this study.

Energy recovery from secondary pulp/paper-mill sludge and sewage sludge with supercritical water treatment

Secondary pulp/paper-mill sludge (SPP) and sewage sludges (primary, secondary, and digested sewage sludges) were treated in supercritical water at temperatures ranging between 400 degrees Celsius and 550 degrees Celsius over 20-120 min for energy recovery. Low temperature and short reaction time favored the formation of heavy oil (HO) products, which were mainly composed of a variety of phenol and phenolic compounds, as well as some nitrogen-containing compounds, long-chain alkenes and alcohols, etc., with high gross calorific values (>36 MJ/kg). By contrast, the formation of synthetic gases, a mixture of hydrogen, carbon monoxide, carbon dioxide, methane, and other light hydrocarbons, were not significantly affected by reaction time but greatly enhanced with increasing temperature. The highest gas yield was obtained at 550 degrees Celsius, where 37.7 wt.% of the SPP (on dry basis) was converted into gases, with hydrogen yields as high as 14.5 mol H(2)/kg SPP (on a dry basis). In comparison to sewage sludges, SPP exhibited a greater capability for the production of HO and gases owing to its higher contents of volatiles and alkali metals, indicating a prospective utilization potential for SPP as a source of bio-energy.

Liquefaction of bio-mass in hot-compressed water for the production of phenolic compounds

Direct liquefaction of lignocellulosic wastes (sawdust and cornstalks) and two model bio-mass compounds (pure lignin and pure cellulose as references) has been conducted in hot-compressed water at temperatures from 250 to 350 degrees C in the presence of 2MPa H(2), for the production of phenolic compounds that may be suitable for the production of green phenol-formaldehyde resins. The liquefaction operations at 250 degrees C for 60 min produced the desirable product of phenolic/neutral oil at a yield of about 53, 32, 32 and 17 wt.% for lignin, sawdust, cornstalk and cellulose, respectively. The yield of phenolic/neutral oil for each feedstock was found to decrease with increasing temperature. As evidenced by GC-MS measurements, significant quantities of phenolic compounds such as 2-methoxy-phenol, 4-ethyl-2-methoxy-phenol, and 2,6-dimethoxy-phenol, were present in the resulting phenolic/neutral oils from the two lignocellulosic wastes and pure lignin. The relative concentration of phenolic compounds in the lignin-derived oil was as high as about 80%. As expected, the liquid products from cellulose contained essentially carboxylic acids and neutral compounds. Addition of Ba(OH)(2) and Rb(2)CO(3) catalysts were found to significantly increase both phenolic/neutral oil and gas yields for all feedstocks except for lignin.

Production of polyols via direct hydrolysis of kraft lignin: Effect of process parameters

Kraft lignin (KL) was successfully depolymerized into polyols of moderately high hydroxyl number and yield with moderately low weight-average molecular weight (Mw) via direct hydrolysis using NaOH as a catalyst, without any organic solvent/capping agent. The effects of process parameters including reaction temperature, reaction time, NaOH/lignin ratio (w/w) and substrate concentration were investigated and the polyols/depolymerized lignins (DLs) obtained were characterized with GPC-UV, FTIR-ATR, (1)H NMR, Elemental & TOC analyzer. The best operating conditions appeared to be at 250°C, 1h, and NaOH/lignin ratio ≈0.28 with 20 wt.% substrate concentration, leading to <0.5% solid residues and ∼92% yield of DL (aliphatic-hydroxyl number ≈352 mg KOH/mg and Mw≈3310 g/mole), suitable for replacement of polyols in polyurethane foam synthesis. The overall % carbon recovery under the above best conditions was ∼90%. A higher temperature favored reduced Mw of the polyols while a longer reaction time promoted dehydration/condensation reactions.

Catalytic conversion of glucose to 5-hydroxymethyl furfural using inexpensive co-catalysts and solvents

Efficient conversion of glucose to 5-hydroxymethyl furfural (5-HMF), a platform chemical for fuels and materials, was achieved using CrCl(2) or CrCl(3) as the catalysts with inexpensive co-catalysts and solvents including halide salts in dimethyl sulfoxide (DMSO) and several ionic liquids. 5-HMF (54.8%) yield was achieved with the CrCl(2)/tetraethyl ammonium chloride system at mild reaction conditions (120°C and 1h). The 5-HMF formation reaction was found to be faster in ionic liquids than in the DMSO system. Effects of water in the reaction system, chromium valence and reaction temperature on the conversion of glucose into 5-HMF were discussed in this work.

Liquefaction of cornstalk in hot-compressed phenol–water medium to phenolic feedstock for the synthesis of phenol–formaldehyde resin

Cornstalk powders were effectively liquefied in a hot-compressed phenol-water medium (1:4 wt/wt). The optimum liquefaction temperature was around 350 degrees C, where the liquid yield attained a maximum at about 70 wt%. The addition of sodium carbonate showed negligible effect over the Liquefaction product yields. When liquefied in phenol-water medium, essentially no phenol was combined with the liquid products, and the cornstalk-derived bio-oils were partially degraded monomeric and oligomeric products with a broad molecular distribution. Resol type bio-based phenol formaldehyde resins were readily synthesized from the cornstalk-derived bio-oils catalyzed by sodium hydroxide.

Supercritical water gasification of an aqueous by-product from biomass hydrothermal liquefaction with novel Ru modified Ni catalysts.

Supercritical water gasification (SCWG) of glucose solution (50-200 g/L), a simulated aqueous organic waste (composed of glucose, acetic acid and guaiacol) and a real aqueous organic waste stream generated from a sludge hydrothermal liquefaction process was performed in a bench-scale continuous down-flow tubular reactor with novel 0.1 RuNi/γ-Al(2)O(3) or 0.1 RuNi/activated carbon (AC) catalyst (10 wt.% Ni with a Ru-to-Ni molar ratio of 0.1). 0.1 RuNi/γ-Al(2)O(3) was very effective in catalyzing SCWG of glucose solution and the simulated aqueous organic waste, attaining an H(2) yield of 53.9 mol/kg dried feedstock at 750°C, 24 MPa and a WHSV of 6h(-1). However, the γ-Al(2)O(3)-supported catalyst was not resistant to the attack of alkali and nitrogen compounds in the real waste during the SCWG of the real aqueous organic waste, whereas the AC-based catalyst exhibited higher stability. This research provides a promising approach to the treatment and valorization of aqueous organic waste via SCWG.

Synthesis of lignin-based epoxy resins: optimization of reaction parameters using response surface methodology

Owing to the presence of phenolic groups in the lignin structure, this provides the potential to substitute bisphenol-A in synthesis of epoxy resin. In this work, organosolv lignin (OL) was first depolymerized by reductive depolymerization in supercritical acetone at 350 °C in the presence of Ru/C catalyst and 10 MPa H2. The obtained depolymerized organosolv lignin (DOL), with a low average molecular weight (Mw) and high hydroxyl number, was used to synthesize lignin-based epoxy pre-polymers. A set of experiments was designed by utilizing the central composite design (CCD) to synthesize lignin-based epoxy resin. Three synthesis variables including reaction temperature, reaction time and NaOH/DOL molar ratio were investigated and the synthesized epoxy pre-polymers were characterized by FTIR and potentiometric titration. The mathematical model derived from the CCD was found to be accurate to predict the optimum conditions. At the optimal synthesis conditions, i.e., 8 h at 55 °C with NaOH/DOL molar ratio of 6.3, a high product yield (99%) and high epoxy content of ∼8 were achieved.

Reductive de-polymerization of kraft lignin for chemicals and fuels using formic acid as an in-situ hydrogen source

In this study, formic acid (FA) was employed as an in-situ hydrogen donor for the reductive de-polymerization of kraft lignin (KL). Under the optimum operating conditions, i.e., 300 °C, 1 h, 18.6 wt.% substrate concentration, 50/50 (v/v) water-ethanol medium with FA at a FA-to-lignin mass ratio of 0.7, KL (Mw∼10,000 g/mol) was effectively de-polymerized, producing de-polymerized lignin (DL, Mw 1270 g/mol) at a yield of ∼90 wt.% and <1 wt.% yield of solid residue (SR). The MW of the DL products decreased with increasing reaction temperature, time and FA-to-lignin mass ratio. The sulfur contents of all DL products were remarkably lower than that in the original KL. It was also demonstrated that FA is a more reactive hydrogen source than external hydrogen for reductive de-polymerization of KL.

Characteristics of wastewater and mixed liquor and their role in membrane fouling.

Effects of wastewater and mixed liquor characteristics on membrane fouling in both a submerged anaerobic membrane bioreactor and a thermophilic submerged aerobic membrane bioreactor were studied with four types of industrial wastewaters. Significant differences in particle size distribution, colloidal content, the protein to polysaccharide ratio, and soluble compounds molecular weight distribution were observed among the four types of wastewaters and mixed liquors. Differences in wastewater and mixed liquor characteristics were correlated to the changes in membrane filtration behavior in both systems. The colloidal content in feed and mixed liquor plays a dominant role and is more important than the quantity of total suspended solids in controlling membrane fouling. The ratio of proteins to polysaccharides is more important than the total quantity of soluble organic substances in controlling membrane fouling. A full characterization of feed and mixed liquor may be used as a tool to predict membrane performance.