Haizhou Lin

Pyrolysis behaviors of four lignin polymers isolated from the same pine wood

Four lignin polymers, alkali lignin (AL), klason lignin (KL), organosolv lignin (OL), and milled wood lignin (MWL), were isolated from the same pine wood. Structural characterization by FTIR and (13)C NMR indicated that the four lignins have different structural features. Their pyrolysis behaviors were analyzed by TG-FTIR and Py-GC/MS. Thermally unstable ether bonds and side branches were well-preserved in AL and MWL, but were broken in OL and KL. Pyrolysis of AL and KL produce more phenols at low temperature by the breakage of ether bonds. AL and KL show lower activation energies in the main degradation stage, quantified by a distribution activation energy model with two linearly combined Gaussian functions. The evolution behaviors of typical gaseous products, CH4, CO2, and CO, were analyzed, and insights about the correlation between chemical structure and pyrolysis behavior were obtained.

Degradation mechanism of monosaccharides and xylan under pyrolytic conditions with theoretic modeling on the energy profiles

Xylan and three monosaccharides (mannose, galactose, and arabinose) were selected as model compounds to investigate the mechanism of hemicellulose pyrolysis. The evolution of several typical pyrolysis products were observed by thermogravimetric analysis coupled to Fourier transform infrared spectroscopy. Monosaccharides underwent similar pyrolysis routes involving ring opening and secondary decomposition. Breakage of the O-acetyl groups and 4-O-methylglucuronic acid units in xylan branches resulted in its different pyrolysis behavior for the formation of acetic acid, CO2, and CO. The detailed reaction pathways of the monosaccharides were studied using density functional theory calculations. Furfural formation was more favorable than the formation of 1-hydroxy-2-propanone and 4-hydroxydihydrofuran-2(3H)-one during xylose degradation. However, in the pyrolysis of mannose and galactose, formation of 5-hydroxymethyl-2-furaldehyde was preferred because of the high energy barrier of the dissociation of the hydroxymethyl group. Meanwhile, the breakage of O-acetyl groups leading to acetic acid formation easily occurred because of its lower energy barrier.

Conversion of carbohydrates into 5-hydroxymethylfurfural in an advanced single-phase reaction system consisting of water and 1,2-dimethoxyethane

5-Hydroxymethylfurfural (HMF) is a bio-based platform chemical that may be converted into various chemicals and fuels. In the present study, we developed an advanced low-boiling single-phase reaction system for producing HMF from glucose. It consists of water and 1,2-dimethoxyethane (DMOE) and uses AlCl3 as catalyst. Our results show that introduction of DMOE can substantially enhance HMF production because of the polar aprotic solvent effect provided by DMOE. Under optimal conditions, a high HMF yield (58.56%) was obtained. GC-MS of the liquid-phase products revealed that HMF and furans comprised 80% and ∼90% of the detected products. Formation of liquid-phase products, including furans, oxygenated aliphatics, cyclopenten-1-ones, and pyrans is discussed. Further study of the humins formed during glucose conversion showed the effective inhibition of humin formation by DMOE. The structure of humins was characterized by FTIR spectroscopy. Finally, HMF production from disaccharides (sucrose, maltose and cellobiose) and polysaccharide (cellulose) using the water–DMOE system resulted in good yields, demonstrating that our single-phase water–DMOE solvent system has good potential use in HMF production from glucose and complex carbohydrates.

Pyrolysis Mechanism of Hemicellulose Monosaccharides in Different Catalytic Processes

The pyrolysis behaviors of four different hemicellulose monosaccharides, namely, two pentoses(xylose and arabinose) and two hexoses(mannose and galactose) catalyzed by HZSM-5 were investigated. The effects of two different processes by which the catalyst comes into contact with the substrate, namely, mixed with monosaccharide( in-bed) or layered above monosaccharide(in situ), were compared. Evolution characteristics of typical pyrolytic products(H2O, CO2, acids, furans and aromatics) were achieved by thermogravimetry-Fourier transform infrared spectroscopy. The in-bed catalytic process significantly lowered the pyrolytic temperature and increased the production of furans and acids at a low temperature by enhancing dehydration, retro-aldol fragmentation and Grob fragmentation. During the in situ catalytic process, volatiles generated from monosaccharides passed through a catalyst bed and underwent further dehydration, decarboxylation, and decarbonylation, significantly lowering the yields of acids and furans. The yield of aromatics was enhanced, and the corresponding volatilization temperature was lowered, especially under the in-bed catalytic conditions. Pentoses entered into the zeolite pores more easily than hexoses did because of their smaller molecular size; thus, the in-bed catalytic process drastically affected pentose pyrolysis.

Conversion of C5 carbohydrates into furfural catalyzed by a Lewis acidic ionic liquid in renewable γ-valerolactone

For the purpose of building a green reaction system to produce furfural (FF), the conversion of two important pentoses from hemicellulose, namely xylose and arabinose, was investigated in an aqueous reaction system including a Lewis acidic ionic liquid as a catalyst and renewable γ-valerolactone (GVL) as a co-solvent. The results showed that the introduction of GVL greatly improved the reactivity of pentose and inhibited the secondary decomposition reaction of FF compared to a pure-water reaction system. NMR analysis suggested that the composition of pentose conformers was greatly altered towards a reactive distribution. The highest FF yields were 79.76% (from xylose) and 58.70% (from arabinose), which were obtained at 140 °C. The influence of reaction parameters on pentose conversion was also studied. A comparison between different reaction conditions suggested that arabinose had less reactivity than xylose, leading to its lower conversion rate and FF yield. Furthermore, xylan and real biomass materials were tested in the proposed reaction system, and decent FF yields of up to 69.66% (from xylan) and 47.96% (from corn stalk) were obtained.

Influence of a Lewis acid and a Brønsted acid on the conversion of microcrystalline cellulose into 5-hydroxymethylfurfural in a single-phase reaction system of water and 1,2-dimethoxyethane

5-Hydroxymethylfurfural (HMF) is a typical dehydration product of C6 carbohydrates, and it can be converted into a series of chemicals and liquid fuels. In this study, an advanced low-boiling single-phase reaction system consisting of water and 1,2-dimethoxyethane (DMOE) was proposed for the production of HMF from microcrystalline cellulose (MCC). AlCl3 and H3PO4 were selected as the Lewis acidic catalyst and Bronsted acidic catalyst, respectively, and the influence of these two catalysts on the conversion behavior of MCC was studied. The results showed that MCC could be selectively converted into HMF or levulinic acid (LA) by altering the solvent composition. As for the composition of the catalyst, high AlCl3 content favored the generation of HMF, whereas high H3PO4 content could decrease the HMF yield and promote the formation of glucose and fructose. The highest HMF yield of 49.42% was obtained at an AlCl3–H3PO4 ratio of 1 : 0.8. GC-MS analysis suggested that much MCC was transformed into furans and cyclopentenones in the presence of AlCl3, while anhydrosugars tended to be generated with a high H3PO4 proportion in the catalyst. Besides, FTIR analysis of the insoluble humin formed during MCC conversion indicated that AlCl3 could also facilitate the depolymerization of MCC.