Techno-Economic Analysis of Cellulosic Butanol Production from Corn Stover through Acetone–Butanol–Ethanol Fermentation

Biobutanol has fuel properties comparable to those of gasoline; however, its commercial production through acetone–butanol–ethanol (ABE) fermentation from lignocellulosic biomass is still encumbering due to low product yield, energy extensive recovery method, and butanol toxicity to microbes. Recent development of simultaneous saccharification, vacuum fermentation, and recovery technique has the potential to reduce these problems and improve butanol yield, which has gained significant attention as an emerging alternative way for ABE fermentation. Thus, the main objective of this study was to assess the techno-economic feasibility of commercial-scale ABE fermentation for a 113.4 million L/year (30 million gal/year) butanol production and identify operational targets for process improvement. Commercial dilute sulfuric acid pretreatment and corn stover feedstock were used in this study. Experimental data on the pretreatment of corn stover and the ABE fermentation and recovery were gathered from recent publications. Process modeling and economic analyses were performed using a modeling software, SuperPro Designer. Estimated butanol production costs were $1.8/L and$1.5/L without and with byproduct credits. Butanol recovery was identified to be the most sensitive parameter followed by sugar utilization in the fermentation reactor, feedstock cost, corn stover to sugars conversion rate, and heat recovery. Furthermore, optimizing these sensitive operating parameters could reduce the butanol production cost to $0.6/L, which is competitive with current gasoline prices; however, achieving these targets will require further research and development efforts on the ABE fermentation

Economic and Environmental Trade-Offs of Simultaneous Sugar and Lignin Utilization for Biobased Fuels and Chemicals

Efficient lignin conversion is vital to the production of affordable, low-carbon fuels and chemicals from lignocellulosic biomass. However, lignin conversion remains challenging, and the alternative (combustion) can emit harmful air pollutants. This study explores the economic and environmental trade-offs between lignin combustion and microbial utilization for producing bisabolene as a representative biobased fuel or chemical. Results for switchgrass and clean pine-based biorefineries show that using lignin to increase fuel yields rather than combusting it reduces the capital expenditures for the boiler and turbogenerator if the facilities process more than 1100 bone-dry metric tons (bdt) feedstock/day and 560 bdt/day, respectively. No comparable advantage was observed for lower-lignin sorghum feedstock. Deconstructing lignin to bioavailable intermediates and utilizing those small molecules alongside sugars to boost product yields is economically attractive if the overall lignin-to-product conversion yield exceeds 11–20% by mass. Although lignin-to-fuel/chemical conversion can increase life-cycle greenhouse gas (GHG) emissions, most of the lignin can be diverted to fuel/chemical production while maintaining a >60% life-cycle GHG footprint reduction relative to diesel fuel. The results underscore that lignin utilization can be economically advantageous relative to combustion for higher-lignin feedstocks, but efficient depolymerization and high yields during conversion are both crucial to achieving viability

Greenhouse Gas Footprint, Water-Intensity, and Production Cost of Bio-Based Isopentenol as a Renewable Transportation Fuel

Although ethanol remains the dominant liquid biofuel in the global market, there is a strong interest in high-energy density and low-hygroscopicity compounds that can be incorporated into gasoline at levels beyond the current ethanol blend wall. Isopentenol (3-methyl-3-buten-1-ol) is one of these promising advanced biofuels that is also an important precursor for isoprene (the main component of natural rubber). In this study, we model the production cost, greenhouse gas (GHG) emissions, and water footprint of biologically produced isopentenol, including the current state of the technology and the impact of potential improvements. We find that the minimum selling price of biobased isopentenol, given the current state of technology demonstrated at bench-scale, is $5.14/L-gasoline equivalent, and the GHG footprint exceeds that of gasoline. However, biobased isopentenol could reach a$0.62/L-gasoline equivalent [$2.4/gal-gasoline equivalent (gge), just 5in an optimized future case where yield and other process parameters are pushed to near their theoretical limits. In this future case, isopentenol could achieve a GHG reduction of 90and a carbon abatement cost of$9.3/metric ton CO2e. Reaching these goals will require dramatic improvements in isopentenol yield, near-100% recovery of ionic liquid used in pretreatment, and low-lignin and high-cellulose and -hemicellulose biomass feedstocks

Production Cost and Carbon Footprint of Biomass-Derived Dimethylcyclooctane as a High-Performance Jet Fuel Blendstock

Near-term decarbonization of aviation requires energy-dense, renewable liquid fuels. Biomass-derived 1,4-dimethylcyclooctane (DMCO), a cyclic alkane with a volumetric net heat of combustion up to 9.2% higher than Jet A, has the potential to serve as a low-carbon, high-performance jet fuel blendstock that may enable paraffinic bio-jet fuels to operate without aromatic compounds. DMCO can be produced from bio-derived isoprenol (3-methyl-3-buten-1-ol) through a multistep upgrading process. This study presents detailed process configurations for DMCO production to estimate the minimum selling price and life-cycle greenhouse gas (GHG) footprint considering three different hydrogenation catalysts and two bioconversion pathways. The platinum-based catalyst offers the lowest production cost and GHG footprint of $9.0/L-Jet-Aeq and 61.4 gCO2e/MJ, given the current state of technology. However, when the supply chain and process are optimized, hydrogenation with a Raney nickel catalyst is preferable, resulting in a$1.5/L-Jet-Aeq cost and 18.3 gCO2e/MJ GHG footprint if biomass sorghum is the feedstock. This price point requires dramatic improvements, including 28 metric-ton/ha sorghum yield and 95–98% of the theoretical maximum conversion of biomass-to-sugars, sugars-to-isoprenol, isoprenol-to-isoprene, and isoprene-to-DMCO. Because increased gravimetric energy density of jet fuels translates to reduced aircraft weight, DMCO also has the potential to improve aircraft efficiency, particularly on long-haul flights

In Situ Synthesis of Protic Ionic Liquids for Biomass Pretreatment

Ionic liquids (ILs) have emerged as versatile solvents that are facilitating advances in many industries such as energy storage, separations, and bioprocessing. Despite their great promise, the cost of many ILs remains excessively high, thus limiting their scalability and commercialization. Therefore, the aim of this paper was to develop a simple and integrated process for synthesizing protic ionic liquids (PILs) in situ, while utilizing them directly as pretreatment solvents for biomass deconstruction/biorefining. The in situ method eliminates the major steps associated with increased cost and carbon footprint, thereby yielding an economically advantaged and environmentally efficient process. The PIL hydroxyethylammonium acetate ([Eth][OAc]) was utilized in the pretreatment and enzymatic hydrolysis of sorghum biomass with the in situ method, which demonstrated equivalent sugar yields relative to the presynthesized [Eth][OAc]. Techno-economic analysis demonstrated the economic advantage of the in situ synthesis over other PIL synthesis methods, due to its reduction of production costs up to $2.9/kg, while the life-cycle assessment showed the environmental efficiency of the process, yielding >30% reduction of GHG per kilogram of PIL. Therefore, this method demonstrates an improvement in the sustainability impact for the utilization of PILs for biomass pretreatment and other IL-utilizing processes