Techno-economic analysis and life cycle assessment of a biorefinery utilizing reductive catalytic fractionation

Reductive catalytic fractionation (RCF) is a promising approach to fractionate lignocellulose and convert lignin to a narrow product slate. To guide research towards commercialization, cost and sustainability must be considered. Here we report a techno-economic analysis (TEA), life cycle assessment (LCA), and air emission analysis of the RCF process, wherein biomass carbohydrates are converted to ethanol and the RCF oil is the lignin-derived product. The base-case process, using a feedstock supply of 2000 dry metric tons per day, methanol as a solvent, and H-2 gas as a hydrogen source, predicts a minimum selling price (MSP) of crude RCF oil of $1.13 per kg when ethanol is sold at$ 2.50 per gallon of gasoline-equivalent ( $0.66 per liter of gasoline-equivalent). We estimate that the RCF process accounts for 57% of biorefinery installed capital costs, 77% of positive life cycle global warming potential (GWP) (excluding carbon uptake), and 43% of positive cumulative energy demand (CED). Of$ 563.7 MM total installed capital costs, the RCF area accounts for $323.5 MM, driven by high-pressure reactors. Solvent recycle and water removal via distillation incur a process heat demand equivalent to 73% of the biomass energy content, and accounts for 35% of total operating costs. In contrast, H-2 cost and catalyst recycle are relatively minor contributors to operating costs and environmental impacts. In the carbohydrate-rich pulps, polysaccharide retention is predicted not to substantially affect the RCF oil MSP. Analysis of cases using different solvents and hemicellulose as an in situ hydrogen donor reveals that reducing reactor pressure and the use of low vapor pressure solvents could reduce both capital costs and environmental impacts. Processes that reduce the energy demand for solvent separation also improve GWP, CED, and air emissions. Additionally, despite requiring natural gas imports, converting lignin as a biorefinery co-product could significantly reduce non-greenhouse gas air emissions compared to burning lignin. Overall, this study suggests that research should prioritize ways to lower RCF operating pressure to reduce capital expenses associated with high-pressure reactors, minimize solvent loading to reduce reactor size and energy required for solvent recovery, implement condensed-phase separations for solvent recovery, and utilize the entirety of RCF oil to maximize value-added product revenues.

Lignin monomer production integrated into the γ-valerolactone sugar platform

Jeremy Luterbacher

We demonstrate an experimental approach for upgrading lignin that has been isolated from corn stover via biomass fractionation using c-valerolactone (GVL) as a solvent. This GVL-based approach can be used in parallel with lignin upgrading to produce soluble carbohydrates at high yields (>= 70%) from biomass without the use of enzymes, ionic liquids, or concentrated acids. The lignin was isolated after an initial hydrolysis step in which corn stover was treated in a high-solids batch reactor at 393 K for 30 min in a solvent mixture consisting of 80 wt% GVL and 20 wt% water. Lignin was isolated by precipitation in water and characterized by 2D HSQC NMR, showing that the extracted lignin was similar to native lignin, which can be attributed to the low acid level and the low extraction temperatures that are achievable using GVL as a solvent. This lignin was upgraded using a two-stage hydrogenolysis process over a Ru/C catalyst. The isolated lignin was first dissolved to form a mixture of 10% lignin, 80% THF, 8.5% H3PO4 and 1.5% H2O, and treated at 423 K under hydrogen. The THF was removed by evaporation and replaced with heptane, forming a biphasic mixture. This mixture was then treated at 523 K in the presence of Ru/C and H-2. The resulting heptane phase contained soluble lignin-derived monomers corresponding to 38% of the carbon in the original lignin. By adding 5% methanol during the second catalytic step, we produced additional monomers containing methyl esters and increased carbon yields to 48%. This increase in yield can be attributed to stabilization of carboxylic acid intermediates by esterification. The yield reported here is comparable to yields obtained with native lignin and is much higher than yields obtained with lignin isolated by other processes. These results suggest that GVL-based biomass fractionation could facilitate the integrated conversion of all three biomass fractions.

Royal Soc Chemistry2015

Production, characterization and upgrading of biomass-derived acetal-stabilized carbohydrates

Ydna Marie Questell-Santiago

Biomass is an attractive source of renewable carbon-based fuels and chemicals. Multiple research efforts are centered around integrated biorefineries, where all fractions of biomass are converted to fuels or chemical products. These efforts are focused around making biorefineries more economically competitive and sustainable. One of the major drawbacks is the incomplete utilization of biomass, specifically, lignocellulosic biomass, which is the largest terrestrial source of renewable carbon. Given the significant differences in the structure and reactivity of its components, the integrated depolymerization and subsequent upgrading of all the fractions involved has been challenging. The depolymerization of lignocellulosic biomass is controlled by the kinetic competition between depolymerization and degradation reactions. Multiple strategies have relied in the modification of reaction conditions to mitigate this limitation, but are either expensive or have not fully overcome this issue. Here, I present the use of protecting group chemistry to reversibly stabilize biomass-derived carbohydrates during depolymerization by acetal formation with formaldehyde (FA). This stabilization technique, altered the kinetic paradigm by limiting sugar dehydration and further degradation. The depolymerization of beech wood using acid organosolv processes in the presence of FA led to recoveries of over 90% sugars with a final concentration of ~5wt%. The produced acetal-stabilized biomass-derived sugars possess versatile properties compared to unmodified sugars, which motivated me to further investigate their reactivity. I found that diformylxylose (acetal-stabilized xylose, DX) produced an intermediate during its acid hydrolysis deprotection that promoted a 1,2-hydride shift that led to the low temperature production of furfural. Generally, this shift is catalyzed by Lewis acids, but its presence did not affect the rate of reaction when DX was used as a starting material. Based on these findings and Operando NMR studies, a tandem hydrolysis-dehydration of DX to furfural, was pro-posed. The benefits of using acetal-stabilized sugars was studied by performing a preliminary techno-economic analysis for the non-enzymatic production of ethanol and the direct upgrading of DX to xylitol. After taking account the solvent savings and the extra recovery steps of FA, a minimum selling price of

4.05 (

2014) of gasoline gallon equivalent was calculated. In the case of xylitol production, a proposed process was constructed around the volatility and unique reactivity of DX. The key advantages included the purification potential of DX by distillation rather than activated carbon adsorption and ion exchange chromatography, which is used for xylose purification, and a rate limiting step that was independent of hydrogen pressure, which minimized hydrogen requirements. The on stream study of the catalyst demonstrated an evolution of the active sites of Pt that led to an enhanced xylitol yield. This phenomenon is attributed to the formation of Pt(OH)2 (detected by X-ray photoelectron spectroscopy), which accelerates the hydrolysis and hydrogenation reactions due to the proximal acid site to Pt0. In overall, I have demonstrated that acetal functionalization of carbohydrates can, not only increase yields by reducing sugar degradation but also reveal new reactivity that can be exploited to create novel catalytic upgrading pathways for the production of bio-based chemicals.

EPFL2019