(508f) Modeling of Lignin–Ethanol–Water Ternary Phase Behavior Using PC-SAFT

Among renewable feedstocks, lignin can play an important role as a precursor for materials applications, such as carbon fibers, PU foams, and activated carbons. Unfortunately, the lignins available today (whether agricultural-based or from the Kraft process) are too polydisperse and too impure to be used for high-value applications.

Thies and co-workers¹ have developed a process for simultaneously solvating, fractionating, and purifying the lignin polymer recovered from biomass by-product streams of lignocellulosic biorefineries and pulp-and-paper mills. Aqueous Lignin Purification with Hot Agents (ALPHA) involves combining solid lignin with hot organic–water solvent mixtures to form two liquid phases: a highly solvated, polymer-rich phase with high MW lignins and a solvent-rich phase with low MW lignins. Ultraclean lignins (key metals <100 ppm) of both high and low MW can be obtained through ALPHA.

Understanding these liquid–liquid equilibria (LLE) is critical for operating and integrating ALPHA into today’s biorefineries. Previous work² has measured the pseudoternary LLE of lignin–organic–water systems at elevated temperatures. This work represents the first attempt to model such systems with Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), in order to predict the phase behavior over a wide range of possible ALPHA operating conditions. Ethanol has been picked as the organic component due to its high availability in biorefineries and recent encouraging phase-behavior results. The PC-SAFT pure component parameters of ethanol and water were obtained from previous studies, while for lignin, our strategy is to treat lignin as a generic polymer, adding multiple associating sites assigned based on the structure of common lignin monomers.

PC-SAFT predictions are being used for the techno-economic analysis of the ALPHA process.

References:

1. Thies, M. C. et al. Solvent and Recovery process for lignin. U.S. Pat. No. US10053482B2 Aug 2018.

2. Ding, J. et al. Liquid–liquid equilibrium compositions and global phase behavior for the lignin–acetic acid–water system at 70 and 95 °C. Fluid Phase Equilibria 2018, 461, 8-14.