Hardwood and softwood lignins from sulfite liquors: structural characterization and valorization through depolymerization

This work aims to evaluate the structural characteristics and study the oxidative depolymerization of lignins obtained from hardwood and softwood sulfite liquors. Lignins were obtained after ultrafiltration and freeze- drying of the sulfite liquors and characterized based on inorganic content, nitrobenzene oxidation, 13C NMR, and molecular weight determination. The structural characteristics achieved allow evaluating the potential of each lignin through oxidative depolymerization to produce added-value phenolic monomers. Hardwood and softwood lignins were submitted to alkaline oxidation with oxygen and the reaction conditions optimized to obtain a final oxidation mixture with the maximum yield of phenolic monomers. Through oxidation with O2, hardwood lignin generates mostly syringaldehyde while lignin from softwood biomass mainly produces vanillin; moreover, a lower reaction time and the interruption of O2 admission avoid the degradation of the oxidation products in the final mixture for both lignins, more evidenced to hardwood lignin due to its higher reactivity. From the results, it is possible to conclude that a phenolic aldehyde-rich oxidation mixture could be obtained, confirming the viability of lignin as raw material to produce added-value products as vanillin and syringaldehyde.This work was financially supported by LA/P/0045/2020 (ALiCE), UIDB/50020/2020 and UIDP/50020/2020 (LSRE-LCM), funded by national funds through FCT/MCTES (PIDDAC); Base Funding - UIDB/00690/2020 of CIMO - Centro de Investigação de Montanha - funded by national funds through FCT/MCTES (PIDDAC); COST Action LignoCOST (CA17128). Carlos Vega-Aguilar thanks the Costa Rican Science, Technology and Telecommunications Ministry for the PhD. Scholarship MICITT-PINN-CON-2-1-4-17-1-002. Authors are grateful to Company A and Caima - Indústria de Celulose, S.A. (Portugal) for the supply of the samples of sulfite liquorinfo:eu-repo/semantics/publishedVersio

Kinetics of oxidative degradation of lignin-based phenolic compounds in batch reactor

Vanillin, vanillic acid, acetovanillone, syringaldehyde, syringic acid, and acetosyringone are products obtained from lignin oxidation in an alkaline medium. The evaluation of their individual degradation under oxidation conditions mimicking lignin oxidation is an important tool to better understand this reaction and maximize the yield of target value-added products. In this context, the main objective of the present work was to study the kinetics of degradation of the selected ligninbased phenolic compounds. The effect of temperature, initial concentration, and oxygen partial pressure was evaluated, and a simple mathematical model was developed to describe the data from the degradation of the phenolics during oxidation reactions. The results indicate that, for all the evaluated compounds, the reaction order is first order with respect to both the initial phenolic compound concentration and oxygen concentration. A high degradation rate was found for the reactions performed at 413 K, and an activation energy in the range of 53−86 kJ/mol was found for all the studied phenolic compounds. Moreover, syringic acid is the phenolic compound more prone to degradation, while vanillin is the less one.This work is a result of Project “AIProcMat@N2020 - Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020”, with the reference NORTE-01-0145-FEDER-000006, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF); Associate Laboratory LSRE-LCM-UID/EQU/50020/2019 - funded by national funds through FCT/MCTES (PIDDAC) and Foundation for Science and Technology (FCT, Portugal). CIMO (UID/AGR/00690/2019) through FEDER under Program PT2020.info:eu-repo/semantics/publishedVersio