Zhongshun Yuan

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.

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.

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.

Hydrolytic depolymerization of hydrolysis lignin: Effects of catalysts and solvents.

Hydrolytic depolymerization of hydrolysis lignin (HL) in water and water-ethanol co-solvent was investigated at 250°C for 1h with 20% (w/v) HL substrate concentration with or without catalyst (H2SO4 or NaOH). The obtained depolymerized HLs (DHLs) were characterized with GPC-UV, FTIR, GC-MS, (1)H NMR and elemental analyzer. In view of the utilization of depolymerized HL (DHL) for the preparation of rigid polyurethane foams/resins un-catalyzed depolymerization of HL employing water-ethanol mixture appeared to be a viable route with high yield of DHL ∼70.5wt.% (SR yield of ∼9.8wt.%) and with Mw as low as ∼1000g/mole with suitable aliphatic (227.1mgKOH/g) and phenolic (215mgKOH/g) hydroxyl numbers. The overall % carbon recovery under the selected best route was ∼87%. Acid catalyzed depolymerization of HL in water and water-ethanol mixture lead to slightly increased Mw. Alkaline hydrolysis helped in reducing Mw in water and opposite trend was observed in water-ethanol mixture.

Hydrolytic liquefaction of hydrolysis lignin for the preparation of bio-based rigid polyurethane foam

Hydrolysis lignin (HL) was liquefied to a low average molecular weight (Mw) intermediate by employing a 50/50 (v/v) water–ethanol mixture. The effects of process parameters including the reaction temperature, the reaction time and the HL concentration were investigated and the liquefied hydrolysis lignin (LHL) products obtained were characterized by GPC, FTIR and 1H NMR. The best operating conditions appeared to be at 250 °C, 1 h with 20% (w/v) HL concentration, leading to ∼70 wt% yield of LHL (Mw ∼ 1000 g mol−1 and OHTotal ∼ 442 mg KOH g−1). The solid form LHL was derivatized into liquid polyols via oxypropylation with 50–70 wt% bio-content, which was subsequently utilized for the preparation of bio-based rigid polyurethane (BRPU) foams. All the foams were characterized in terms of their physical, mechanical and thermal properties & morphology. BRPU foams exhibit superior compression modulus and strengths to a reference foam prepared from commercial sucrose polyols provided by Huntsman Co. At a fixed formulation, i.e., a fixed percentage of physical blowing agent, BRPU foams showed the following sequence in terms of their compression modulus: sucrose polyol reference foam (2695.0 kPa) < LHL50PO50 (9202.0 kPa) < LHL60PO40 (19 847.0 kPa) < LHL70PO30 (21 288.0 kPa). All BRPU foams were thermally stable up to approximately 200 °C and thermal conductivity was low (0.030 ± 0.001 W m−1 K−1), making them suitable candidates for insulation material.

Recent advancements in catalytic conversion of glycerol into propylene glycol: A review

ABSTRACT The renewability of bio-glycerol has made it an attractive platform for the production of diverse compounds. Selective hydrogenolysis of glycerol to propylene glycol (PG) is one of the most promising routes for glycerol valorization, since this compound is an important chemical intermediate in a number of applications. In this article, advancements in the catalytic conversion of glycerol into propylene glycol are reviewed, which include advances in process development, effects of preparation and activation methods on catalytic activity and stability, and the performance of various types of catalysts. The feasibility of using bio-hydrogen and the challenges of utilizing crude glycerol for glycerol hydrogenolysis are also discussed.

Synthesis and thermomechanical property study of Novolac phenol-hydroxymethyl furfural (PHMF) resin

Phenol-5-hydroxymethyl furfural resins were synthesized by reacting phenol with 5-hydroxymethyl furfural (HMF) generated in situ from glucose at 120 °C in the presence of CrCl2/CrCl3 and tetraethylammonium chloride (TEAC) catalysts. The phenol–HMF (PHMF) resin was found to have a relative weight average molecular weight of 700–900 g mol−1. The resins have a structure similar to Novolac phenol–formaldehyde (PF) resin, suggesting that the PHMF resins synthesized using renewable resources may be a promising formaldehyde-free alternative to conventional Novolac PF resins. The PHMF resin was utilized as polymer matrix in fibreglass reinforced plastic (FRP) composites and demonstrated to have similar or better tensile strength than the FRP with conventional PF resin.

Investigation of aqueous phase recycling for improving bio-crude oil yield in hydrothermal liquefaction of algae

In this study, the aqueous phase obtained from catalytic/non-catalytic hydrothermal liquefaction (HTL) of Chlorella vulgaris was recycled as the reaction medium with an aim to reduce water consumption and increase bio-crude oil yield. Although both Na2CO3 and HCOOH catalysts have been proven to be effective for promoting biomass conversion, the bio-crude oil yield obtained from HTL with Na2CO3 (11.5wt%) was lower than that obtained from the non-catalytic HTL in pure water at 275°C for 50min. While, the HCOOH led to almost the same bio-crude yield from HTL (29.4wt%). Interestingly, bio-crude oil yield obtained from non-catalytic or catalytic HTL in recycled aqueous phase was much higher than that obtained from HTL in pure water. Recycling aqueous phase obtained from catalytic HTL experiments resulted in a sharp increase in the bio-crude oil yield by 32.6wt% (Na2CO3-HTL) and 16.1wt% (HCOOH-HTL), respectively.