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Abstract: Lignin is a three-dimensional, amorphous, polyphenolic and aromatic-rich material, and is a primary recalcitrant molecule in lignocellulosic biomass. Unlocking valuable chemicals and fuel molecules from lignin requires the cleavage of typical inter-unit linkages like β-O-4, α-O-4 and 4-O-5 in a selective manner. In this presentation, I’ll discuss about two strategies, viz. fast pyrolysis and catalytic hydrogenolysis, to selectively convert lignin to simple phenols, alkyl guaiacol and guaiacyl alcohols. In order to understand the fast pyrolysis kinetics of lignin, a Pyroprobe® reactor coupled with Fourier transform infrared (Py-FTIR) spectrometer was employed. The time evolution of pyrolysate functional groups from lignin and its mass loss at different temperatures showed that the kinetics of lignin fast pyrolysis is diffusion-limited. In order to derive simple phenols from lignin, microwave-assisted pyrolysis was conducted using different activated carbons and at different lignin-to-activated carbon mass ratios. The activated carbon played a dual role of microwave absorber and catalyst. Maximum bio-oil yield of 66 wt.% with >90% selectivity to phenol and cresols was obtained using higher amount of activated carbon.
In the second part, the development of novel Pd-metal oxides (Al, Zr, Mo, and W)-supported activated bio-char (AC) for depolymerization of lignin to C9 substituted guaiacols via hydrogenolysis will be discussed. High selectivity to alkyl guaiacols was observed with Pd-Al/AC, while the presence of W and Mo inhibited the hydrogenation of the aliphatic Ca=Cβ bond. At the optimum condition, high selectivity to 4-propyl guaiacol (38%) was observed with Pd-Al/AC. The addition of transition metals to Pd altered the chemoselective hydrogenation (Cα=Cβ) and dehydroxylation (Cγ-OH) of C9 monomeric guaiacols. Based on quantum chemical calculations, the hydrogenation of Cα=Cβ is shown to be catalyzed by the Pd0 active site, while the dehydroxylation of Cγ-OH is catalyzed by the transition metal. Better dehydroxylation activity of the catalyst is attributed to higher Lewis acidity and electropositive nature of the metals. More interesting results on the effect of hydrogenolysis operating conditions on lignin conversion and product selectivities, and surface catalytic mechanism will be discussed during the presentation.
Keywords: Lignin, fast pyrolysis, kinetics, microwave-assisted pyrolysis, hydrogenolysis, phenols.
Biography: Dr. R. Vinu is currently an Associate Professor in Chemical Engineering department at IIT Madras, Chennai. He obtained Ph.D. in Chemical Engineering from Indian Institute of Science, Bangalore, in 2010 and B.Tech. in Chemical Engineering from A.C. College of Technology, Anna University in 2006. Prior to joining IIT Madras in 2012, he was a postdoctoral researcher in the department of Chemical and Biological Engineering at Northwestern University, USA, where he was involved in a US-DoE’s National Advanced Biofuels Consortium project on kinetic modeling of biomass pyrolysis.
At IIT Madras, he leads an active research group that focuses on thermochemical conversion of a variety of feedstocks such as biomass, waste plastics, algae, refuse derived fuels (RDF), municipal solid wastes (MSW) and coals to liquid fuels and chemicals. He is also an expert in microwave-assisted pyrolysis and co-pyrolysis technology to produce high quality fuel oils from different feedstocks.
He has published over 80 research articles in reputed journals, 7 book chapters, an edited book and 2 patents. He is the recipient of several awards including (a) Young Engineer Award of the Institute of Engineers India (IEI) in 2019, (b) Young Scientist Awards of the Institute of Chemical Technology Mumbai in 2019, Indian National Science Academy (INSA) and National Academy of Sciences India (NASI) in 2018, (b) Institute Research and Development Award-Early Career level from IIT Madras in 2018, (c) Young Associate of the Indian Academy of Sciences-Bangalore in 2017, and (d) Young Faculty Recognition Award from IIT Madras in 2015. He also serves as the Editor of Advanced Powder Technology, and serves in the editorial board of Journal of Analytical and Applied Pyrolysis.