Life Cycle Assessments of Ethanol Production via Gas Fermentation: Anticipated Greenhouse Gas Emissions for Cellulosic and Waste Gas Feedstocks Robert M. Handler,* ,† David R. Shonnard, † Evan M. Griffing, ‡ Andrea Lai, § and Ignasi Palou-Rivera § † Sustainable Futures Institute, Department of Chemical Engineering, Michigan Technological University, Houghton, Michigan 49931, United States ‡ Environmental Clarity, 2505 Fauquier Lane, Reston, Virginia 20191, United States § LanzaTech, 8045 Lamon Avenue Suite 400, Skokie, Illinois 60077, United States ABSTRACT: LanzaTech has developed novel microbial bioreactor systems capable of direct gas fermentation to produce ethanol from carbon-containing gases. In this study, a life-cycle assessment method is used to quantify the global warming potential of several scenarios for producing renewable ethanol with the LanzaTech process. Scenarios considering ethanol produced from steel mill waste gases or biomass (corn stover, forest residue, or switchgrass, via gasification) have been considered, using input data from peer-reviewed literature, government reports, life cycle inventory databases, and LanzaTech process engineering estimates. Using standardized life-cycle assessment methods, ethanol produced via LanzaTech fermentation appears to result in greenhouse gas emissions that are at least 60% lower than that of conventional fossil gasoline, with biomass- based ethanol achieving close to 90% emission reductions. Results indicate that the LanzaTech gas fermentation technology can be a viable alternative for producing next-generation biofuels that satisfy United States Renewable Fuels Standard policies concerning fuels with a reduced greenhouse gas emissions footprint. ■ INTRODUCTION The United States continues to depend on petroleum for transportation fuels, which accounted for roughly 28% of the country’s energy-related CO 2 emissions in 2012. 1 Roughly one- third of petroleum fuels used in the United States are imported, warranting a continued focus on domestic energy production as a means to improve domestic economic and energy security. 2 Several solutions are being developed to deal with the environmental, economic, and social challenges caused by continued use of polluting fossil transportation fuels from imported and domestic sources. The most widely adopted emissions reduction strategy is the production of alternative liquid transportation fuels (ethanol and biodiesel, among others) made from renewable feedstocks. These fuels are compatible as blendstock with existing transportation infra- structure as minor components of the final fuel mix, generally 10 or 15% for ethanol, and have benefitted from existing agricultural production systems to generate large quantities of feedstock. Ethanol is the predominant alternative liquid transportation fuel. It has successfully been integrated into the national fuel system and is offered in a range of blend ratios with petroleum gasoline. Corn-based ethanol has been touted as a domestic energy success story, with measurable impacts on environ- mental metrics and rural economies. 3,4 While corn-based ethanol currently comprises the large majority of domestic renewable fuel production, scientists and policy makers continue to develop plans for transitioning to a new array of renewable transportation fuels that improve upon the environ- mental benefits of corn ethanol while reducing concerns about the environmental impact of large-scale biofuels production, such as competition for land and water resources, especially for irrigated crops, the impact on the price of food; and the resulting decline in genetic diversity, among others. 5-8 Biofuels relying on nonfood crops, agricultural residues, or other wastes would alleviate some of these concerns. An increasing portion of the renewable fuels requirement in the United States is due to come from nonstarch sources and qualify as advanced (50% reduction) or cellulosic (60% reduction) biofuels, depending on their level of greenhouse gas (GHG) emissions reductions compared to petroleum sources. 9 These “second-generation” biofuels based on agricultural residues promise to lower GHG emissions associated with liquid transportation fuels, but ongoing life cycle studies will be required to ensure that environmental concerns associated with expansion of conven- tional agriculture are also mitigated. 10 One example of an advanced, second-generation biofuel is that produced by LanzaTech. LanzaTech has developed novel fermentation processes to convert carbon monoxide and hydrogen-containing gases into valuable fuel and chemical products, including ethanol, 2,3-butanediol, acetic acid, isopropanol, acetone, butanol, succinic acid, and isoprene. Process inputs can be low-value or waste gases from industries such as steel manufacturing, oil refining, and chemical production, as well as gases generated by gasification of forestry and agricultural residues, municipal waste, natural gas, and coal. Special Issue: Sustainable Manufacturing Received: September 1, 2015 Revised: December 3, 2015 Accepted: December 7, 2015 Article pubs.acs.org/IECR © XXXX American Chemical Society A DOI: 10.1021/acs.iecr.5b03215 Ind. Eng. Chem. Res. XXXX, XXX, XXX-XXX