Modification of acid hydrolysis lignin for value-added applications by micronization followed by hydrothermal alkaline treatment

Abstract

Technical hydrolysis lignin (THL) was micronized by grinding in a rotary-jet mill to obtain a fraction of approximately 5 mm. Both initial and milled THLs were liquefied by thermal alkaline treatment at 220°C for 2 h. Upgraded THLs that were nonmilled (L1) and milled (L2) were desalted by treatment with cation-exchanged resin and were dried. Micronization affected the course of hydrothermal alkaline treatment and the structure and composition of the obtained lignin. Thus, L2 contained much less concomitant polysaccharides and extrac-tives than L1 and was more condensed. The molecular weights of L1 and L2 were 1100 and 1000 Da, respectively, as determined by size-exclusion chromatography. Structural characterization carried out by employing tandem electrospray ionization-mass spectrometry and 1D and 2D nuclear magnetic resonance spectroscopy revealed that small amounts of b-O-4 (~6 mol.%), b-5, and b-b structures still remained in L1 and L2. Overall, upgraded lignins are oligomers (trimers-pentamers) with highly degraded propane chains and possess polyconjugated condensed aromatic structures. Upgraded THL seems to be a promising raw material for polymeric formulations.

Atmospheric pressure ionization mass spectrometry as a tool for structural characterization of lignin

“…The majority of the mass spectra were obtained in the m/z range up to m/z 1000 19–23,26,37 or m/z 1500, 19,24,28,38,39 often with the main goal being to evaluate lignin degradation products 40–42 . However, the MW was mostly left undetermined, 19–24,26,28,37–39 although some studies mentioned the mass range in Daltons in addition to the m/z range, thus recognizing the formation of multiply charged species typical for ESI 15,24,27 . The mass range reported after a presumed deconvolution reached up to 2400, 4500 and 7000 Da 15,24,28 .…”

Hydrothermal Decomposition of a Lignin Dimer under Neutral and Basic Conditions: A Mechanism Study

“…Despite the usefulness of dilute inorganic acids in biomass pretreatment to remove lignin, acidic conditions are only rarely used for hydrothermal decomposition or solvolysis of lignin for biochemicals and fuel. , This is because that repolymerization or condensation of lignin and decomposition products is well known , and is a very serious problem in lignin hydrothermal treatments, which typically require higher temperatures and longer reaction times than used in delignification of biomass . Lignin depolymerization has been intensively studied under various basic conditions in various solvent or solvent mixtures including water − and water–alcohol mixture ,, as base has been found to suppress char formation and enhance the production of liquid products. , It has been observed that the optimal yield of low–molecular-weight lignin oils were obtained for low concentration of bases such 0.5% NaOH and 1.0 M K 2 CO 3 . Surprisingly, there are very few studies on β-O-4 cleavage using model compounds under basic conditions. ,− No β-O-4 cleavage mechanisms and decomposition paths have been found in these literatures.…”

Biomass pretreatments capable of enabling lignin valorization in a biorefinery process

“…Despite recently successful investigations into novel methods of valorizing biorefinery lignin by conversion into precursors for different chemical and material applications, the published results remain at the laboratory scale [27][28][29][30][31]. In order to advance lignin-valorizing technologies, a comprehensive understanding of biorefinery lignin streams must be further established.…”