(24e) Techno-Economic Analysis and Life Cycle Assessment of Lignin Fractionation and Valorization Via the ALPHA Process: Upgrading to Value-Added Products

This study investigated the environmental and economic sustainability of the Aqueous Lignin Purification with Hot Agents (ALPHA) process. The ALPHA process has been recently investigated for the fractionation and purification of raw, bulk lignins recovered from cellulosic ethanol biorefineries or Kraft pulp mills. The ALPHA process exploits the novel liquid-liquid equilibrium that exists between lignin and hot, one-phase solutions of aqueous renewable solvents to simultaneously purify and fractionate raw bulk lignin. In particular, both the purity and molecular weight (MW) of a given lignin fraction can be controlled. Here, ALPHA is proposed for the isolation of lignin from a corn stover-to-ethanol plant into purified low, medium, and high MW fractions for producing polyurethane foam, activated carbon, and carbon fiber, respectively. Two aqueous renewable solvents were analyzed: acetic acid and ethanol.

Our analysis shows positive economic and environmental results for producing lignins of controlled molecular weight and purity via ALPHA. Solvent choice was found to have a significant impact on production of fractionated lignin using ALPHA, with a minimum selling price of $838/tonne for using acetic acid vs. $463/tonne with ethanol. Converting lignins processed with ethanol–water solutions into high-value products such as activated carbon, carbon fibers, and polyurethane foam yields $151 million/year in profit, which over 30 years results in a total net present value (NPV) of $533 million using a discounted cash flow analysis. The NPV is most sensitive to lignin yield, solvent choice, and the lignin substitution percentage for polyol in PU foam. A life cycle assessment was conducted to determine the “gate-to-gate” greenhouse gas emissions and energy consumption of the lignin-based products compared to fossil-based equivalents using SimaPro. A value allocation scenario was conducted and determined that products generated using the ALPHA process with ethanol have similar or lower greenhouse gas emissions than the same products from fossil feedstocks.