February 2023 Meeting

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Using Aqueous Renewable Solvents to Valorize Lignin: Conversion to Carbon Fibers, PU Foams, and Activated Carbons

presented by Dr. Thies is the Dow Chemical Professor of Chemical and Biomolecular Engineering at Clemson University.

Dr. Thies received his Bachelor of Chemical Engineering from Georgia Tech. He worked at P&G developing Jif peanut butter and Duncan Hines cake mixes before returning to academia for his Ph.D. at the University of Delaware and continuing on to join the ChBE faculty at Clemson.  Mark was a Humboldt Fellow at TUHH in Hamburg, Germany, a Marie Curie Fellow at NTUA in Athens, Greece, and is also an AIChE Fellow.  

His research interests are focused on materials and energy research where thermodynamics, phase behavior, and equilibrium-based separations play key roles.  Today his emphasis is on developing higher-value applications from poorly defined, oligomeric systems, including both “prehistoric” lignin and lignin from today’s plants and trees.

Dr. Thies is the author of 100+ archival publications, including 4 patents and 5 book chapters, and has directed research funding from PRF, NSF, DOE, ARO, ARL, AFRL, AFOSR, and multiple global companies and small businesses, as well as an NSF ERC on Fibers and Films. Finally, Mark is on the Editorial Advisory Board for the journal Carbon, and organized and chaired the World Conference on Carbon in 2010.

Abstract:

Although lignin is second in abundance only to cellulose, its conversion to higher-value materials, vs. just being burned as fuel, continues to be a significant challenge.  In particular, the impurities inherent in lignin (polysaccharides and metal salts), along with the wide range of functionalities and molecular weights in lignin, can create numerous problems when unpurified and unfractionated lignin is substituted directly into a process or formulation. Furthermore, today it is imperative that lignin-refining strategies also include sustainability as a core principle.

We have discovered that hot renewable organic solvents that form homogeneous solutions with water, including lower molecular weight (MW) alcohols and acetic acid, can be used to simultaneously fractionate and purify lignin, both batchwise and continuously.  The key to this so-called ALPHA (Aqueous Lignin Purification using Hot Agents) process is the formation of two liquid phases in equilibrium, one liquefied lignin and the other solvent, when solid lignin is contacted with a hot, one-phase aqueous solvent. With the lignin partitioning between the two phases, control of both molecular weight and purity becomes possible. 

ALPHA-processed lignins are being investigated for three large and growing markets: (1) high-performance carbon fibers for automotive applications, (2) rigid polyurethane foams for spray insulation for buildings, and (3) activated carbon for food and pharmaceutical use.  Here, we demonstrate how control of molecular weight, and even the concentration of specific impurities, leads to improvements in the properties of the final commercial products.