(251b) Synthesis and Analysis of Biorefinery Systems with Novel Lignin and Stillage Valorization Technologies

Lignocellulosic biomass has three
major constituents i.e. cellulose, hemicellulose, and lignin. To develop
economical and sustainable biorefineries, all three major constituents must be
effectively converted to value-added products. Over the last decades,
significant progress has been made in cellulose and hemicellulose
deconstruction and monomer upgrading technologies to fuels and chemicals. In
contrast, lignin valorization technologies have been limited to heat and power
production in biorefinery. In addition, to further increase the economic value
of lignocellulosic biomass, waste streams (e.g., carbon-rich stillage) can also
be utilized to produce valuable bioproducts instead of biogas for heat and
power generation. However, successful commercialization of lignin and/or
stillage valorization strategies requires targeting narrow range of products
and optimizing the biorefinery configuration to minimize capital and operating
costs.

In this work, we study the configurations and economics of
biorefinery employing lignin and stillage valorization. We generate a
superstructure (see Fig. 1) to represent potential biorefinery configurations,
and then utilize superstructure based process synthesis subject to various
energy related constraints. We develop a mixed-integer nonlinear programming
(MINLP) model that allows us to efficiently synthesize and evaluate various configurations
and assess the impact of various parameters of lignin and stillage
valorizations (e.g., impact of bioproduct selling price, unit conversion cost,
conversion coefficient, and energy requirement on the performance of
biorefinery). The results show that the optimal strategy leading to a minimum
ethanol selling price (MESP) of $3.44/GGE includes γ-valerolactone
deconstruction, glucose and xylose co-fermentation, heat and power generation,
and does not include lignin or stillage valorization. Results indicate that
under certain scenarios, the optimal biorefinery strategies with lignin or
stillage valorization tend to be energy-deficient when the lignin or stillage
fraction is utilized for valorization, and the optimal pretreatment technology
may switch from γ-valerolactone deconstruction
to ammonia fiber expansion. Further studies are performed to establish targets
for researchers working in the areas of  lignin and stillage valorization.
Finally, we discuss how improvements in combinations of selected parameters can
lead to lower cost for a thermal-neural biorefinery.

Fig.
1. The superstructure of corn stover-to-ethanol. Abbreviations – AFEX: ammonia fiber expansion, AHP:
copper-catalyzed alkaline hydrogen peroxide, CB: combustor and boiler, COFER:
co-fermentation, DA: dilute acid, EA: extractive ammonia, GVL: γ-valerolactone, HYD: hydrolysis, LV: lignin valorization,
SEP: separation, SSCF: simultaneous saccharification and co-fermentation, SV:
stillage valorization, TBG: turbogenerator, WWT:
wastewater treatment.

References

Ng RTL, Fasahati P, Huang
K, Maravelias CT. Utilizing Stillage in the Biorefinery: Economic,
Technological, and Energetic Analysis. Applied
Energy, 241, 491-503, 2019.

Sun Z, Fridrich
B, de Santi A, Elangovan S, Barta
K. Bright Side of Lignin Depolymerization: Toward New Platform Chemicals. Chem Rev, 118, 614–78, 2018.