Pyrolysis experiments of n-hexane were performed and the product distribution and fuel consumption were measured as a function of temperature. The experimental temperatures ranged from 550-675 degrees C, with a pressure of approximately 1 atm, and residence times of approximately 5 s. N-Hexane was used as a model compound to represent the linear alkanes that might be found in practical hydrocarbon fuels. Under these conditions, high fuel conversion was observed at the higher temperatures and a wide range of products were formed. The experimental observations were compared to predictions from a plug-flow model using a reaction mechanism consisting of 205 species and 1403 reactions. The hydrogen abstraction and isomerization rate coefficients in this model were based on CBS-QB3 calculations. The only model modification was adjustment of the A-factor of the initiation rates to match conversion at one temperature. This model was able to successfully predict the observed trends in both product selectivities as well as fuel conversion over the temperature range. The mechanism was also used to capture the trends previously observed in n-butane pyrolysis under similar experimental conditions. Significant differences in the sensitivity coefficients for the hexane and butane systems are discussed in terms of the competition between beta-scission and isomerization of the initial radicals formed. The kinetic model predicts that n-hexane will be completely converted within 0.1 s in the higher temperature environment ( approximately 800 degrees C) of the anode channel of a solid-oxide fuel cell (SOFC). This result clearly illustrates the need to explicitly account for gas-phase reactions in SOFC models for those cases where hydrocarbons, especially those larger than methane, are fed directly to an SOFC.
Global consumption of protein is projected to double by the middle of the 21st century1. However, protein production is one of the most energy intensive and environmentally damaging parts of the food supply system today. Electromicrobial production technologies that combine renewable electricity and CO2-fixing microbial metabolism could dramatically increase the energy efficiency of commodity chemical production2–5. Here we present a molecular-scale model that sets an upper limit on the performance of any organism performing electromicrobial protein production. We show that engineered microbes that fix CO2 and N2 using reducing equivalents produced by H2-oxidation or extracellular electron uptake could produce amino acids with energy inputs as low as 64 MJ kg-1. This work provides a roadmap for development of engineered microbes that could significantly expand access to proteins produced with a low environmental footprint.
This report is being disseminated by the Department of Energy. As such, the document was prepared in compliance with Section 515 of the Treasury and General Government Appropriations Act for Fiscal Year 2001 (Public Law 106-554) and information quality guidelines issued by the Department of Energy. Though this report does not constitute "influential" information, as that term is defined in DOE's information quality guidelines or the Office of Management and Budget's Information Quality Bulletin for Peer Review (Bulletin), the study was reviewed internally prior to publication.
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