Thermal Degradation and Thermooxidation of O-Acetyl-(4-O-methyl-D-glucurono)-D-xylan and Related Derivatives

Abstract

Four polysaccharide samples related to (4-O-methyl-D-glucurono)-D-xylan were analyzed by thermogravimetry (TG) and differential scanning calorimetry (DSC) in nitrogen and oxygen environments. The calculated difference in the measured fG-residues run in different environments and obtained at temperatures close to 300 °C by a dynamic experiment indicate the action of oxygen on the formation of gaseous products. The rats constants and activation energies of the degradation process in both environments indicate the increase in stability due to the protection of hydroxyls by acetylation. In an inert environment xylans have one broad multicomponent exotherm, as determined by dynamic DSC measurement. In an oxygen environment two or three independent exotherms are observed. The pretreatment of xylan with trifluoroacetic acid (solvent used for acetylation) and acetylation lowers the exothermic effect of both the thermolysis and thermooxidation. The recycling of the acetylated xylan to Na + -salt form leads to a greater exothermic effect of the degradation in both environments.

An overview on fast pyrolysis of the main constituents in lignocellulosic biomass to valued-added chemicals: Structures, pathways and interactions

“…It is found that many of the OH-groups at C2 and C3 of the xylanpyranosyl units are substituted by O-acetyl groups and the acetyl content varies between 8% and 14% [40][41][42]. Thus, Oacetyl-4-O-methylglucuronoxylan is generally utilized to represent the xylan-based hemicellulose (mainly the xylan content) [27,[43][44][45][46]. The average degree of polymerization (DP) of the hemicellulose is estimated to be much less than that of cellulose, leading to its thermally unstable during pyrolytic process.…”

“…4, such as acetic acid, glycolaldehyde, furfural and 1:4-anhydroxylopyronose [31,43,45,56,91]. The tar fraction from α-D-xylose condensation gave a more complex mixture of volatile products containing large amounts of glycoladhehyde (3.1%) [43].…”

“…5a), and the other is the cleavage of the 1,2 glycosidic bond between the xylan unit and 4-O-methylglucuronic acid unit, followed by the ring-opening reaction and rearrangement of the 4-O-methylglucuronic acid after the elimination of CO 2 and methanol (pathway (12) in Fig. 5b) [43,45,93]. The prevalent mechanism of the formation of acetic acid is involved with the primary elimination reaction of the active O-acetyl groups linked to the main xylan chain on C2 position (pathway (9) in Fig.…”

“…2) in liquid product (around 30%) [18,37,45,55,56,[97][98][99]. The extremely difficult situation for lignin was addressed in understanding the relationship between the formation of diverse aromatic compounds and its 3-D polymerized chemical structure which was highly influenced by the origins, isolation method and analytical technology [16,47].…”

“…Lignin-related cracking compounds distribution of the prominent aromatic compounds and specify their formation mechanism [18,45,47,56,62,[100][101][102][103][104][105][106]. This would help to optimize the thermal cracking process for improving the quality of bio-oil from biomass, and also promote the utilization of lignin as original chemical feestock itself.…”