Bin Ru

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.

Pyrolysis mechanism study of minimally damaged hemicellulose polymers isolated from agricultural waste straw samples

The pyrolysis mechanism of hemicellulose has been investigated using two minimally damaged hemicellulose polymers isolated from two agricultural straw samples. The obtained hemicelluloses have been characterized by multiple methods, and the results showed that they were mainly composed of l-arabino-4-O-methyl-d-glucurono-d-xylan. Their O-acetyl groups and high degrees of polymerization and branching were well preserved. Their pyrolyses were subsequently investigated by TG-FTIR and Py-GC/MS. The evolutions of four typical volatile components and the distributions of eight product species were scrutinized. A DG-DAEM kinetic model was applied to quantify the contributions of two major pyrolytic routes for devolatilization during hemicellulose pyrolysis. A mean activation energy of 150kJ/mol for the formation of volatiles was derived. The thermal stability of each bond in four typical fragments of hemicellulose was assessed by DFT study, and the deduced decomposition pathways were in agreement with experimental analysis.

Effects of torrefaction on hemicellulose structural characteristics and pyrolysis behaviors

The effects of torrefaction on hemicellulose characteristics and its pyrolysis behaviors were studied in detail. The oxygen content decreased significantly after torrefaction, leading to the increase of high heating value. Two-dimensional perturbation correlation analysis based on diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was performed to characterize the structural evolutions. It was found the dehydration of hydroxyls and the dissociation of branches were the main reactions at low torrefaction temperature. When the temperature further increased, the depolymerization of hemicellulose and the fragmentation of monosaccharide residues occurred. The distributed activation energy model with double Gaussian functions based on reaction-order model was used to investigate the pyrolysis kinetics. The results showed that torrefaction enhanced the activation energy for degradation reactions while lowered that for condensation reactions, and increased the devolatilization contribution of condensation reactions. Besides, torrefaction decreased the yields of typical pyrolytic products, such as acids, furans, alicyclic ketones and so on.

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.