(590d) Economic and Environmental Impact of Recovering and Upgrading Lignin Via the ALPHA Process on an Ethanol Biorefinery

Despite its prevalence as one of the world’s most abundant organic polymers, a small minority of lignin is recovered for nonfuel uses. Many challenges face lignin recovery and valorization, including achieving low ash and metal contents and a tight molecular weight distribution. In this study, we investigate economics and environmental impacts of one emerging method to valorize lignin: the Aqueous Lignin Purification with Hot Agents (ALPHA) process. The ALPHA process has been proven capable of fractionating and purifying 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. Through sequential ALPHA reactors with controlled liquid-liquid equilibrium conditions, distinct fractions of lignin can be produced with different molecular weight profiles, while also controlling the distribution of sugars and ash within the separation system. These tailored fractions can be sold as high-quality feedstock for producing polyurethane foam, activated carbon, carbon fiber.

Our analysis considers the recovery of lignin from two lignin-rich waste streams from an ethanol biorefinery: black liquor and lignin cake. The black liquor is subjected to three sequential ALPHA stages with varying ethanol/water solvent concentrations, which produces lignin suitable as a polyurethane foam precursor, activated carbon precursor, and carbon fiber precursor. Two different lignin cake scenarios are analyzed: selling the lignin cake directly as an activated carbon feedstock with no processing and subjecting the lignin cake to one ALPHA stage which produces a refined lignin for both polyurethane foam and activated carbon processes. Using inputs generated at the lab scale, an ASPEN Plus simulation was developed to model a 130,000 dry metric tons lignin/yr plant that valorizes the waste lignin from an ethanol biorefinery. Economic results generated using a 30-year discounted cash flow table show a net present value greater than $100 million for the simulated scenarios. Environmental impacts were calculated using life cycle assessment methodology and the software SimaPro. The fractionated lignin products have GHG emissions and cumulative energy demand equivalent to or lower than the fossil precursor equivalents. Coupling the economic and environmental results show that using the ALPHA process is a promising emerging technology to valorize waste lignin.