La-modified SBA-15/H2O2 systems for the microwave assisted oxidation of organosolv beech wood lignin

Abstract

In this manuscript, the in uence of organosolv beech wood lignin (LOB) on its oxidative conversion to high added-value phenolic aldehydes is discussed. Environmental friendly and low-cost H 2 O 2 was used as the oxygen atom donor. e catalyst was prepared by immobilizing Lanthanum compounds onto the periodic mesoporous channels of siliceous SBA-15. e activity of the La/SBA-15 was investigated towards oxidation of LOB in the presence of hydrogen peroxide as oxidant with microwave irradiation. Considering the characteristics of LOB, an unexpected low syringaldehyde concentration at 10min of reaction time (1.47 g/L, corresponding to 15.66% yield) was obtained; the other major product was vanillin at 25min (0.78 g/L, i.e., 9.94% yield). e high reactivity of syringyl nuclei may be pointed out as the main reason for the faster production and degradation of syringaldehyde in oxidation. Other low molecular weight phenolic products were found: vanillic acid, syringic acid and minor quantities of aceto-derivatives. e pro le of products concentration with the reaction time of catalytic oxidation with microwave irradiation are shown and discussed with reference to the investigated lignin features. e mechanism of the microwave catalytic oxidation for LOB under alkaline conditions was proposed.

Chitosan–Quercetin Bioconjugate as Multi‐Functional Component of Antioxidants and Dual‐Responsive Hydrogel Networks

“…The hypothesized mechanism involves the generation of hydroxyl radicals by the reaction between H 2 O 2 and NaOH, with the subsequent oxidation of Q and the formation of Q alkoxyl radical which, due to their high reactivity, form Q oligomers . The addition of CHIT carried out to the production of macro‐radicals, and underwent radical coupling with either Q or Q oligomers, allowing the fabrication of CHITQ conjugates …”

“…The synthesis of CHITQ was performed according to the literature with some modifications. [28,29] In a 50-mL glass flask, 150 mg of Q was dissolved in 15 mL of NaOH solution 0.33 mol L −1 and then 1.0 mL of 3.5% H 2 O 2 was added and the mixture stirred in the dark at room temperature for 2 h. Then, 20 mL of CHIT (medium molecular weight, 75-85% deacetylated) solution (25 mg mL −1 in 1% CH 3 COOH by vol) was added under stirring. After 24 h, the solution was introduced into dialysis tubes and dipped into a glass vessel at 20 °C for 48 h with eight changes of water.…”

“…The conjugation of Q to CHIT backbone was performed by a modified free-radical grafting procedure, involving the employment of H 2 O 2 in alkaline medium as initiator system (Figure 1). Macromol The hypothesized mechanism involves the generation of hydroxyl radicals by the reaction between H 2 O 2 and NaOH, [29] with the subsequent oxidation of Q and the formation of Q alkoxyl radical which, due to their high reactivity, form Q oligomers. [38] The addition of CHIT carried out to the production of macro-radicals, [39] and underwent radical coupling with either Q or Q oligomers, allowing the fabrication of CHITQ conjugates.…”

Promising Techniques for Depolymerization of Lignin into Value‐added Chemicals

“…Interestingly, we found the laws from statistical data that the product distribution is greatly influenced by alkalinity of solution and reactor material. As shown in Figure , lignin oxidation by H 2 O 2 in non‐caustic solution and stainless steel reactor leads to formation of small molecular fatty acids (Figure , top left),, while that in caustic solution and Teflon/glass results in aromatics (Figure , bottom right) ,, . Thus, we speculate that the formation of small molecular fatty acids is attributed to the stronger oxidability probably caused by non‐caustic and stainless steel conditions.…”

Low-Power Microwave Radiation-assisted Depolymerization of Ethanol Organosolv Lignin in Ethanol/Formic Acid Mixtures

“…Environmentally friendly processes have attracted increasing attention (Gu et al 2012). Liquefaction is a good method to degrade lignin, and solvent selection is crucial to improve the economics of the process (Xiao et al 2011;Xie et al 2015).…”