Formic-Acid-Induced using Recyclable-Ionic Liquids as Catalysts for Lignin Conversion into Aromatic Co-Products
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ORIGINAL PAPER
Formic‑Acid‑Induced using Recyclable‑Ionic Liquids as Catalysts for Lignin Conversion into Aromatic Co‑Products Sandip K. Singh1,2 · Paresh L. Dhepe1,2 Received: 23 November 2018 / Accepted: 18 November 2019 © Springer Nature B.V. 2019
Abstract Lignin has been widely named as a sustainable and renewable bioresource of energy, fuels, chemicals and materials, particularly phenolic chemicals production on Earth. These bio-derived compounds are in great potential need of biorefinery to valorize complete plant biomass. Lignin depolymerization showed a great promise approach to convert into low molecular aromatic products. In this report, high molecular weight (54,000 Da) lignin depolymerization into maximum yields (87%), (≥ 95 ± 6% mass balance) using a formic acid along with dual (–SO3H) functionalized imidazole-based recyclable (4 times) Brønsted acidic ionic liquids (BAILs) as catalysts have been investigated in H 2O–CH3OH (1:5, v/v) at 120 °C for 1 h. The structural correlations between the lignin and aromatic products were studied by bulk (CHNS, GPC, etc.) and molecular (UV–Vis, FT-IR, NMR (1D/2D) levels experimental techniques. Additionally, the identification of aromatic products was carried out by applying HPLC, GC and GC–MS techniques. Graphic Abstract Addition of a formic acid into Brønsted acidic ionic liquids improved the catalytic efficiency significantly for lignin depolymerization into 87% low molecular weight aromatic products.
Lignin
Aromatic products
Keywords Lignin · Formic acid · Dual functionalized ionic liquids · Depolymerization · Bulk and molecular levels analysis
Statement of Novelty
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12649-019-00896-3) contains supplementary material, which is available to authorized users. * Sandip K. Singh [email protected] Extended author information available on the last page of the article
Use of ionic liquids in catalytic amount for lignin conversion is an economic feasible and environmental benign pathway. In the last few decades, conversion of lignin content of plant biomass is under important consideration and would be valuable within integrated biorefineries. Importantly, the conversion chemistry of lignin into smaller fractions is a challenging task due to developmental and environmental
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factors. In this study, formic acid with a dual-functionalized –SO3H imidazolium based ionic liquids demonstrated for lignin conversion into low molecular weight aromatic products. Experimental 2D (HSQC) NMR study showed that the β–O–4 bond decreased ca. 64% in products compared to real lignin which affirmed the lignin depolymerization. This study provided the novel use of formic acid in a catalytic amount to enhance the catalytic activity of ionic liquids. However, in bulk (as a solvent) quantity, it reduced the yield of aromatic products or enhanced the condensation process of generated aromatic products.
Introduction Fossil hydrocarbons are primary source
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