Improvements in Life Cycle Energy Efficiency and Greenhouse Gas Emissions of Corn‐Ethanol

Abstract

SummaryCorn-ethanol production is expanding rapidly with the adoption of improved technologies to increase energy efficiency and profitability in crop production, ethanol conversion, and coproduct use. Life cycle assessment can evaluate the impact of these changes on environmental performance metrics. To this end, we analyzed the life cycles of corn-ethanol systems accounting for the majority of U.S. capacity to estimate greenhouse gas (GHG) emissions and energy efficiencies on the basis of updated values for crop management and yields, biorefinery operation, and coproduct utilization. Directeffect GHG emissions were estimated to be equivalent to a 48% to 59% reduction compared to gasoline, a twofold to threefold greater reduction than reported in previous studies. Ethanol-to-petroleum output/input ratios ranged from 10:1 to 13:1 but could be increased to 19:1 if farmers adopted high-yield progressive crop and soil management practices. An advanced closed-loop biorefinery with anaerobic digestion reduced GHG emissions by 67% and increased the net energy ratio to 2.2, from 1.5 to 1.8 for the most common systems. Such improved technologies have the potential to move corn-ethanol closer to the hypothetical performance of cellulosic biofuels. Likewise, the larger GHG reductions estimated in this study allow a greater buffer for inclusion of indirect-effect land-use change emissions while still meeting regulatory GHG reduction targets. These results suggest that corn-ethanol systems have substantially greater potential to mitigate GHG emissions and reduce dependence on imported petroleum for transportation fuels than reported previously.

Climate impacts of energy technologies depend on emissions timing

“…However, using the ICI and CCI we observe that by 2040 the climate impact of algae biodiesel surpasses that of corn ethanol, owing to CH 4 leakage in biogas production from algae co-products, which partially offsets the energy requirements of algae production and processing [2]. Although these offsets make biodigestors attractive, with applications in corn ethanol production [25] and other biofuels, resulting CH 4 emissions may make this process less advantageous over time. An alternative catalytic hydrothermal gasification process may achieve much lower CH 4 emissions (Supplementary Fig.…”

Biofuels: policies and impacts

“…Hill et al (2006) show that among current food-based biofuels, soybean biodiesel has much higher GHG reduction potential than corn grain ethanol. However, Liska et al (2009) argue that the GHG reduction potential of corn could be significantly improved to the levels of sugar beets or soybeans through enhanced yield and crop management, biorefinery operation, and co-product utilization. Cui et al (2010) construct an open economy general equilibrium model to investigate the effects of government energy policy on the US economy, with an emphasis on the corn-based ethanol.…”

From Tiny Microalgae to Huge Biorefi neries

“…Biorefinery scenarios evaluated in this study are: (i) a natural gas (NG) dry mill corn grain ethanol plant with dry distillers grain (DDGS) as a co-product for the corn grain-only harvests [23][24][25], (ii) a co-located dry mill corn grain and cellulosic ethanol plant with combined heat and power (CHP) and DDGS co-product, where corn stover is primarily used to displace dry mill ethanol plant natural gas requirements [25,26], (iii) and a standalone cellulosic (switchgrass or corn stover) ethanol plant (sequential hydrolysis and fermentation) with CHP capability and electricity export [22, [27][28][29]. Chemical and enzyme production costs and related GHG emissions for corn grain and cellulosic conversion to ethanol were also incorporated [28].…”