Solubility and fractionation of Indulin AT kraft l...
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Werner Marcelo Goldmann, Juha Ahola, Marja Mikola, Juha Tanskanen, Solubility and fractionation of Indulin AT kraft lignin in ethanol-water media, Separation and Purification Technology, Volume 209, 2019, Pages 826-832, ISSN 1383-5866, https://doi.org/10.1016/j.seppur.2018.06.054
Solubility and fractionation of Indulin AT kraft lignin in ethanol-water media
Goldmann, Werner Marcelo1; Ahola, Juha1; Mikola, Marja1;
Tanskanen, Juha1
1Chemical Process Engineering, Faculty of Technology, University of Oulu, P.O. Box 4300, Oulu 90014, Finland
Lignin solubility is a varying property, as depending on the type of lignin and its origin, its solubility in different solvents will differ. This is due to the highly heterogeneous nature of lignin. Solubilizing lignin could improve its potential valorization by making it more conducive to chemical reactions. Solvent fractionation could be utilized as the first step in lignin refining to adjust some of its properties before further processing. It is known that kraft lignin is completely soluble in alkaline solvents such as aqueous NaOH. The purpose of this study was to assess the solubility of Indulin AT lignin in aqueous ethanol solvents and to determine the useful properties of the resulting fractions: namely, molar mass distribution and phenolic hydroxyl groups. The highest concentration of lignin was achieved in 60 wt% ethanol solution with 235.89 g/L at a solid-to-liquid ratio of 300 gLignin/LSolvent. The original lignin had a mass average molar mass of 4.7 kDa. When only water was utilized, the average molar mass of the dissolved fraction was between 1 and 2 kDa and the molecular size distribution was mostly between 0.1 and 1 kDa. When using pure ethanol, the molecular size distribution ranged from 0.1 kDa to 10 kDa, with a mass average molar mass between 1 and 1.3 kDa. With an ethanol content in the solvent higher than 90 wt%, the bigger molar mass molecules (>10 kDa) could be separated as the insoluble fraction. Additionally, the polydispersity of both fractions decreased with an ethanol concentration above 80 wt%. The hydroxyl group content of the insoluble fraction was higher when fractionating with less than 20 wt% ethanol, whereas with 20 wt% ethanol and higher, the soluble fraction retained most of the phenolic hydroxyls. Fractionating lignin prior to use or further processing may be potentially beneficial if the lower molar mass molecules can be used as they are, leaving only the higher molar mass molecules to be further processed or burned for energy.
Separation and purification technology
10.1016/j.seppur.2018.06.054
https://oadoi.org/10.1016/j.seppur.2018.06.054
Hydroxyl
Lignin
Molar mass Phenolic
The financial support of the Academy of Finland (grant number 286633) and TEKES funded project PheRes (Dnr 1357/31/2015) are gratefully acknowledged.
© 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/.