Techno‐economic analysis and life‐cycle assessment of cellulosic isobutanol and comparison with cellulosic ethanol and n‐butanol

Abstract

This work presents a detailed analysis of the production design and economics of the cellulosic isobutanol conversion processes and compares cellulosic isobutanol with cellulosic ethanol and n-butanol in the areas of fuel properties and engine compatibility, fermentation technology, product purifi cation process design and energy consumption, overall process economics, and life cycle assessment. Techno-economic analysis is used to understand the current stage of isobutanol process development and the impact of key parameters on the overall process economics in a consistent way (i.e. using the same fi nancial assumptions, plant scale, and cost basis). The calculated minimum isobutanol selling price is $3.62/gasoline gallon equivalent ($/GGE) -similar to $3.66/GGE from the n-butanol process and higher than $3.26/GGE from the cellulosic ethanol conversion process. At the conversion stage, the n-butanol process emits the most direct CO 2 , at 26.42 kg CO 2 /GGE. Isobutanol and ethanol plants have relatively similar CO 2 emissions, at 21.91 kg CO 2 /GGE and 21.01 kg CO 2 /GGE, respectively. The consumptive water use of the biorefi neries increases in the following order: ethanol (8.19 gal/ GGE) < isobutanol (8.98 gal/GGE) < n-butanol (10.84 gal/GGE). Field-to-wheel life cycle greenhouse gas (GHG) emissions for the ethanol and n-butanol conversion processes are similar at 4.3 and 4.5 kg CO 2 -eq/GGE, respectively. The life cycle GHG emissions result for the isobutanol conversion process is 5.0 kg CO 2 -eq/GGE, approximately 17% higher than that of ethanol. The life cycle fossil fuel consumption is 39 MJ/GGE for n-butanol, 43 MJ/GGE for ethanol and 51 MJ/GGE for isobutanol. The energy return on investment for each biofuel is also determined and compared: isobutanol (2.2:1) < ethanol (2.7:1) < n-butanol (2.8:1).

The impact of ethanol and iso-butanol blends on gaseous and particulate emissions from two passenger cars equipped with spray-guided and wall-guided direct injection SI (spark ignition) engines

“…The motor octane number of butanol is lower than ethanol. However, both butanol and ethanol improve the octane ratings of gasoline when they are added [15,16].…”

“…Butanol is a higher chain alcohol with a four carbon structure that has different isomers based on the location of the hydroxyl group (1-butanol, n-butanol, 2-butanol, tertiary-butanol, and iso-butanol) [15]. While n-butanol could be an attractive candidate for ethanol replacement because it can be produced via the mature and wellknown ABE (acetoneebutanoleethanol) fermentation process, the dramatic energy demand, high water use, and unfavorable process economics have led research towards iso-butanol [16]. Similar to ethanol, iso-butanol can be produced from biochemical pathways via fermentation using biomass-derived feedstocks, including corn, sugarcane, and cellulosic biomass [16,17].…”

“…While n-butanol could be an attractive candidate for ethanol replacement because it can be produced via the mature and wellknown ABE (acetoneebutanoleethanol) fermentation process, the dramatic energy demand, high water use, and unfavorable process economics have led research towards iso-butanol [16]. Similar to ethanol, iso-butanol can be produced from biochemical pathways via fermentation using biomass-derived feedstocks, including corn, sugarcane, and cellulosic biomass [16,17]. Compared to ethanol, butanol exhibits a higher energy density (33.1 MJ/kg), which is close to that of gasoline.…”

Performance and Regulated/Unregulated Emission Evaluation of a Spark Ignition Engine Fueled with Acetone–Butanol–Ethanol and Gasoline Blends

“…Bio-butanol offers a number of advantages over ethanol, which is currently one of the most widely used alternative fuels [12,13]. Advantages include higher energy density and better miscibility with gasoline, and the fuel is less hydrophilic and corrosive, leading to better fuel economy and capability to blend with gasoline in a higher proportion without modifying the engine [14][15][16].…”

Balance and saving of GHG emissions in thermochemical biorefineries

“…1 shows the GHG saving (cradle-to-grave) of thermochemical and biochemical biorefineries from the literature. The saving for ethanol is the average from references [24,25] (thermochemical biorefinery) and [26][27][28][29][30] (biochemical biorefinery). The values for DME, Fisher-Tropsch diesel (FT) and SNG are taken from references [9,[30][31][32].…”