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The cleavage of intermolecular linkages in lignin is a crucial yet complicated factor to properly deconvolute during the pyrolysis of lignin; thus, four typical β-O-4 lignin dimer compounds with different substituents on C α and C β position (including C α O, C α OH and C β CH 2 OH groups) were synthesized. The results showed that a C β CH 2 OH group greatly inhibited the generation of volatile products, and promoted the generation of char. When the C α O group existed alone, the volatility of model compounds reached a maximum of ∼94 mass-%. At low temperatures (<300 °C), the cleavage of intermolecular linkages dominated, followed by secondary pyrolysis of primary products to various gases ( e.g. , CO 2 , CH 4 , CO). Guaiacol and 2-methoxy-benzaldehyde, two typical products, displayed yields that reflected the degree of cleavage of the C β O and C α C β bonds. It was confirmed that oxidation of the C α OH group to C α O facilitated cleavage of the C α C β bond and favored formation of 2-methoxy-benzaldehyde. In addition, new dimers that were intermediates during the pyrolysis process were formed via intermolecular elimination reactions that further affected products distribution and selectivity. [ABSTRACT FROM AUTHOR]

Vanillin and acetovanillone are typical primary pyrolysis products of β O 4 lignin dimers, but the thermal reactions have not yet been elucidated. Data on their thermal reactivity and secondary pyrolysis pathway was studied via in-situ FTIR within a tube furnace reactor system. The result showed that pyrolysis breakdown products spanned four categories: gas, char, monomers, and polymers and secondary reaction products were polymers and char from re-polymerization and carbonization. In general, vanillin showed higher reactivity than acetovanillone. The removal of the CHO group in vanillin was first observed at 400 °C, to present a thermal reaction similar with guaiacol at higher temperatures. The reactivity of the COCH 3 group in acetovanillone was low during the pyrolysis process in which radical-induced rearrangement of the aryl OCH 3 group into the aryl CH 3 group initially occurred as the major side-chain-conversion reaction. Finally, side-chain-conversion also included aryl demethylation or demethoxylation, tautomerism of COCH 3 , and cyclization between aryl OCH 3 and OH group but at low reaction degrees. [ABSTRACT FROM AUTHOR]

A process for the production of high-value-added phenolics following hydrothermal depolymerization of black liquor lignins after acidification without catalysis was successfully deployed and is described herein. A high yield of liquid products up to 33.3 mg/mL (based on raw black liquor) was recovered at 290 °C, 30 min, and pH 6; meanwhile, only 12.6 mg/mL solid residue was obtained. GC–MS analyses of the liquid products confirmed value-added aromatic monomers, among which the yields of phenol, guaiacol, and 2,6-dimethoxy-phenol were high (∼60% of the identified compounds). FT–IR of the solid residues indicated that the black liquor lignin was depolymerized through cleavage of ether bonds and decarboxylation. The results suggest that black liquor may be a new resource for aromatic products. [ABSTRACT FROM AUTHOR]

Abstract: The pyrolysis process of chromated copper arsenate-treated wood impregnated with phosphoric acid (2–6wt.%) has been investigated using a Kugelrohr short-path distillation apparatus. The presence of phosphoric acid is shown to change the overall pyrolysis kinetics and yields of products resulting in a decrease in the amount of volatile products and an increase in the char formation. The yield of levoglucosan was found to decrease in the presence of relatively higher concentrations of phosphoric acid, while the yield of levoglucosenone increased. The pyrolysis of chromated copper arsenate-treated wood in the presence of phosphoric acid gave rise to 22% (on water-free tar basis) levoglucosenone. Such data demonstrates the potential for a new pathway toward the rational utilization of chromated copper arsenate-treated wood waste. [Copyright &y& Elsevier]

Abstract: The influence of several inorganic compounds (K2Cr2O7, CrO3 and CuSO4) on the pyrolysis of southern pine wood has been investigated. The wood powder was pre-treated with various inorganic compound solutions prior to the pyrolysis and the distribution and yields of the pyrolysis products were obtained by gas chromatography and quantitative 31P nuclear magnetic resonance (NMR) analyses. Our experiments showed that K2Cr2O7 and CuSO4 salts promoted the formation of levoglucosan (LG). In particular, the former providing higher LG yields up to 26.7%. The CrO3 treatment induced the production of low tar and high char yields, with a very low yield of LG and high yield of levoglucosenone (LGO). The underlying reasoning behind these findings may be due to an acidic catalysis mechanism, which promotes cellulose depolymerization and dehydration processes. Due to acid-catalyzed lignin condensation reactions, the yield of lignin degradation products from the pyrolysis of pre-treated wood was found to dramatically decrease in comparison to untreated wood. [Copyright &y& Elsevier]