Optimisation of reaction temperature during carboxylation of single and mixed model bio-derived phenolics as effective route for CO2 utilisation
This study investigates the temperature-dependent carboxylation of single and mixed biomass-derived phenolic sodium salts with CO₂ via the Kolbe–Schmitt reaction. Reactions were performed at T = 175–225 °C, t = 2 h, and pCO₂ = 30 bar. Five model phenolics; phenol, 2-cresol, guaiacol, catechol, and s...
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| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Elsevier
2025-06-01
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| Series: | Carbon Capture Science & Technology |
| Subjects: | |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S2772656825000818 |
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| Summary: | This study investigates the temperature-dependent carboxylation of single and mixed biomass-derived phenolic sodium salts with CO₂ via the Kolbe–Schmitt reaction. Reactions were performed at T = 175–225 °C, t = 2 h, and pCO₂ = 30 bar. Five model phenolics; phenol, 2-cresol, guaiacol, catechol, and syringol were examined individually and in mixtures. Characterisation via high-performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) analysis showed that 2-hydroxybenzoic and dicarboxylic acids were favoured at higher temperatures, while 4-hydroxybenzoic acids prevailed at 175 °C. In mixtures, dicarboxylic acid yields increased significantly, reaching 41.9 % for 2,3-dihydroxyterephthalic acid and 20.5 % for 2-hydroxyisophthalic acid. These dicarboxylic acids possess up to 10-fold higher market value than their monocarboxylic counterparts. Syringic acid synthesis via Kolbe–Schmitt is reported here for the first time, with yields rising to 33.0 % in mixtures versus <2.0 % molar yield when reacted individually. The study also presents the first detailed mechanistic explanation of Brønsted acid–base interactions and temperature-driven selectivity in phenolic salt carboxylation. While previous research suggested that producing phenolics solely from lignin was not viable, this work demonstrates that CO₂ incorporation not only enhances product value but also narrows product distribution and enables broader industrial applicability - ultimately opening new opportunities for potential large-scale, economically viable CO₂ utilisation. |
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| ISSN: | 2772-6568 |