Friday, October 7, 2022 | 11:00 AM - 12:00 PM
Uncas A. Whitaker Hall, Whitaker Auditorium, Room 100
6760 Forest Park Pkwy, St. Louis, MO 63105, USA
Mark C. Thies, Dow Chemical Professor
Department of Chemical and Biomolecular Engineering
Creating Liquid–Liquid Equilibrium between Lignin and Aqueous Renewable Solvents: Facilitating Conversion to Carbon Fibers, PU Foams, and Activated Carbons
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.
In a different thrust, we are also studying very old (i.e., “prehistoric”) lignin. Here we seek to elucidate the relationship between oligomeric compositions of pyrene, and the propensity of these unique, carbon-rich materials to form liquid crystalline materials. Pure pyrene trimer (MW = 598 Da), isolated via supercritical extraction, forms 100% mesophase at only 290 °C. The extent to which this desirable, liquid-crystalline state will continue to exist in well-defined mixtures of monomer through tetramer is under investigation.
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