@article {46426,
	title = {Lignin conversion using catalytic ionic liquids: understanding the role of cations, anions, and hammett acidity functions},
	journal = {Industrial \& Engineering Chemistry Research},
	volume = {58},
	year = {2019},
	month = {NOV },
	pages = {21273-21284},
	type = {Article},
	abstract = {<p>Because it is undisputable that lignin depolymerization is a must to make the biorefinery concept economically feasible, several efforts are put toward it; however, a lot of catalyst designing is required to achieve efficient depolymerization activities. In this work, we show a systematic approach in the synthesis and characterization of ionic liquids (ILs) with varying combinations of cations (imidazole, benzimidazole, phosphonium, and ammonium) and anions (HSO4, PTS (p-toluenesulfonate), Cl, H2PO4, SnCl3, FeCl4, and CuCl3) for the depolymerization of lignin into low-molecular weight aromatic fractions (\&lt;220 g/mol) under mild reaction conditions (120 degrees C, 1 h, ambient pressure). In a methodical approach, effects of various reaction parameters such as temperature (70-170 degrees C), time (15-360 min), pressure (N-2, 0.5-3 MPa), solvents and substrate, and so forth were studied to achieve best activity. Among all the catalysts, IL with the imidazolium cation and HSO4 as the anion showed best activity (78\% yield). Subsequent to depolymerization, three aromatic monomers (5 wt \% pure vanillin) were isolated using flash column chromatography. These aromatic monomers were characterized using gas chromatography (GC), GC-mass spectrometry, and NMR techniques for their purity. Hammett acidity functions (H-0) of ILs were measured using UV-vis photo-spectroscopy, and values are correlated with lignin depolymerization results. Lignin and tetrahydrofuran-soluble products were thoroughly characterized using assorted physicochemical techniques such as NMR (H-1 and C-13), gel permittivity chromatography, thermogravimetric analysis, and so forth. The catalyst was recycled up to six runs and showed similar results in consecutive reactions.</p>
},
	issn = {0888-5885},
	doi = {10.1021/acs.iecr.9b03375},
	author = {Singh, Sandip K. and Dhepe, Paresh L.}
}
