Corn ethanol plants generate high‐purity carbon dioxide (CO₂) while producing ethanol. If that CO₂ could be converted into ethanol by carbon capture and utilization technologies it would be possible to increase ethanol production more than 37% without additional corn grain inputs. Gas fermentation processes use microbes to convert carbon‐containing gases into ethanol and so have the potential to be used with the CO₂ from biorefineries for this purpose. However, as CO₂ utilization technologies for converting thermodynamically stable CO₂ are typically energy intensive, it is necessary to evaluate the related life‐cycle greenhouse gas (GHG) emissions (carbon intensities or CIs) to see whether there are actual emission reduction benefits. In this study, we evaluate the CIs of ethanol produced from high‐purity CO₂ in corn ethanol plants by gas fermentation plus electrochemical reduction. Our analysis shows that the sources of electricity and hydrogen are key drivers of CO₂‐based ethanol's GHG emissions. With wind electricity, the design cases show the potential of near‐zero CI ethanol (1.1 g CO₂e/MJ), but that can increase to up to 331–531 g CO₂e/MJ when today's U.S. Midwest electricity mix is used. To avoid the renewable electricity intermittency issue, we considered a power purchase agreement option using wind electricity 40% of the time and using the regional mix for the rest, which provides a 42% GHG emission reduction from the CI of gasoline. © 2020 The Authors and UChicago Argonne, LLC, Operator of Argonne National Laboratory. Biofuels, Bioproducts and Biorefining published by Society of Chemical Industry and John Wiley & Sons, Ltd.

中文翻译：

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利用玉米乙醇生物炼制厂产生的废CO2进行额外的乙醇生产：生命周期分析

玉米乙醇工厂在生产乙醇的同时会产生高纯度的二氧化碳（CO ₂）。如果可以通过碳捕获和利用技术将CO ₂转化为乙醇，则无需增加玉米籽粒投入，就有可能使乙醇产量增加37％以上。气体发酵过程使用微生物将含碳气体转化为乙醇，因此具有与生物提炼厂的CO ₂一起使用的潜力。然而，作为用于转化热力学稳定的CO _2的CO ₂利用技术通常是高耗能的，因此有必要评估相关的生命周期温室气体（GHG）排放（碳强度或CI），以查看是否有实际的减排收益。在这项研究中，我们评估了通过气体发酵加电化学还原在玉米乙醇工厂中由高纯度CO ₂产生的乙醇的CI值。我们的分析表明，电力和氢气是基于CO ₂的乙醇温室气体排放的主要驱动力。对于风电，设计案例显示了潜在的CI乙醇接近零（1.1 g CO ₂ e / MJ）的潜力，但是最多可以增加到331–531 g CO _2。当使用今天的美国中西部电力结构时，使用e / MJ。为避免可再生电力间歇性问题，我们考虑了一项购电协议选项，其中40％的时间使用风电，其余时间使用区域混合能源，从而使汽油CI的温室气体排放减少了42％。©2020作者和Argonne国家实验室运营商UChicago Argonne，LLC。化学工业协会和John Wiley＆Sons，Ltd.出版的生物燃料，生物产品和生物精炼。