Changing the Molecular Structure of Kraft Lignins—Ozone Treatment at Alkaline Conditions

Abstract

Homogeneous solutions of Kraft lignin can be prepared in alkali. In this environment, ozonean effective and established bleaching agentrapidly converts into a variety of reactive oxygen species, leading to complex oxidation processes. In this study, Kraft lignin was treated with ozone in alkaline solution, and the modified lignin was fractionated into a precipitable, an adsorbable, and a soluble fraction to trace and understand the effects of this treatment. Changing the starting pH showed a distinct effect on the proportion of the obtained fractions. During the oxidation process, several small organic compounds were formed, resulting in a severe drop in pH and a shift in the predominant reactive species. In addition, these fragments were linked quantitatively to specific reaction pathways, which allowed the study of occurring degradation mechanisms. Here, a clear predominance of ring-opening reactions over side chain cleavage was observed. Chemical characterization revealed an increase in carboxyl and a decrease in methoxyl groups in the lignin polymer, thus increasing its solubility at neutral pH.

Novel and Integrated Process for the Valorization of Kraft Lignin to Produce Lignin-Containing Vitrimers

“…Therefore, oxidation of oxygen-pretreated lignin with ozone will result in a further increase in the carboxyl content. The ozonation treatment was carried out at ambient pressure in a glass bubbler with a capacity of 1 L. The details of the ozonation procedure are described in the literature . The glass bubbler was heated to 80 °C in a water bath with constant stirring.…”

“…The ozonation treatment was carried out at ambient pressure in a glass bubbler with a capacity of 1 L. The details of the ozonation procedure are described in the literature. 38 The glass bubbler was heated to 80 °C in a water bath with constant stirring. A flow of ozone was supplied by a “5G Lab Benchtop Ozone Generator” from A2Z Ozone providing an ozone dosage of 5000 mg h –1 (100% capacity, oxygen flow rate 2 LPM).…”

High-Temperature Electrolysis of Kraft Lignin for Selective Vanillin Formation

“…Unfortunately, Kraft lignin is mainly used for thermal energy generation . Several reactions have been reported for the depolymerization of lignin, ,, including thermal, − biochemical, − oxidative, − and reductive conversions. , Overall, the degradation reaction mostly suffers from the use of toxic chemicals, reagent waste, harsh reaction conditions, and/or a broad spectrum of cleavage products. A common method for the oxidative Kraft lignin depolymerization to monoaromatic compounds is the use of nitrobenzene under alkaline conditions.…”

Review on the preparation of fuels and chemicals based on lignin

“…It was found that the in situ formed peracid could be used as the main oxidant. Musl et al 78 treated sulfate lignin in alkaline solution with ozone. During the oxidation process, small molecular organic compounds were produced, resulting in the transfer of main active substances.…”