Practical and thermodynamic constraints on electromicrobially accelerated CO2 mineralization

2023

Preprint

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Electromicrobial production is a process where microorganisms use electricity as a charge and energy source for the production of complex molecules, often from starting compounds as simple as CO2. The aviation industry is in need for sustainable fuel alternatives that can meet their requirements of high-altitude performance while also meeting 21stcentury carbon emissions standards. The electromicrobial production of jet fuel components with CO2-derived carbon provides a unique opportunity to generate jet fuel blends that are compatible with modern engines with net-neutral carbon emissions. In this study, we analyze the pathways necessary to generate single- and multi-branched-chain hydrocarbonsin vivoutilizing both extracellular electron uptake (EEU) and H2-oxidation as methods for electron delivery, the Calvin cycle for CO2-fixation and the ADO decarboxylation pathway. We find the maximum electrical-to-fuel energy conversion efficiencies for single- and multi-branched chain hydrocarbons areand. Utilizing this information, as well as previously collected predictions on straight-chain alkane and terpenoid biosynthesis, we calculate the efficiency of electromicrobial production of jet fuel blends containing straight-chain, branched-chain, and terpenoid components. Increasing the fraction of branched-chain alkanes in the blend from zero to 47% only lowers the electrical energy conversion efficiency fromto.

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“…As seen in previous studies, H2-oxidation is a more efficient method for electron delivery than EEU 4,8,25,26 .…”

Section: Electron Uptake By H2-oxidation Produces 2% Higher Energy Co...supporting

confidence: 60%

“…Below we summarize all of the key equations utilized in this article. For detailed derivations see Salimijazi et al 8 and our subsequent work that builds upon this theory 4,25,26 . All model parameters are shown in Table 1, and all symbols used in this article are shown in Table S1.…”

Section: Electromicrobial Production Of Jet Fuel Componentsmentioning

confidence: 99%

Efficiency Estimates for Electromicrobial Production of Branched-chain Hydrocarbons

2023

Preprint

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“…4 blue bars). As we have discussed in earlier articles 11,21,32 the small difference in efficiency is due to the fact that electrons in EEU-mediated EMP are delivered to the cell at a higher redox potential than NADH, requiring the use of reverse electron transport to raise their energy sufficiently to reduce NADH 11,14,34 (-0.32 V vs. Standard Hydrogen Electrode (SHE) for NADH, while the redox potential of the electronaccepting Mtr complex is ≈ -0.1 V vs. SHE 52 ). In contrast, H2-mediated EMP delivers electrons at a redox potential slightly lower than NADH (-0.42 Volts vs. Standard Hydrogen Electrode for H2 vs. -0.32 V for NAD(P)H) meaning that that direct reduction of NADH is possible.…”

Section: Electron Uptake By H2-oxidation Produces the Higher Energy C...mentioning

confidence: 85%

“…Electrical flow provides the reducing power required for metabolism, and carbon fixation is performed completely enzymatically (e.g., by the Calvin-Bassham-Benson (CBB or Calvin) cycle) or through the assimilation of electrochemically-synthesized C1 compounds, such as formate 15,16 (e.g., by the Formolase pathway 17 ). Theoretical analysis demonstrates that EMP is dramatically more efficient than the use of photosynthesis, both thermodynamically as well as in terms of land use 11,[18][19][20][21] . Further, while photosynthesizing cyanobacteria are promising in principle, they remain very difficult to engineer 22 .…”

Section: Introductionmentioning

confidence: 99%

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Upper Limit Efficiency Estimates for Electromicrobial Production of Drop-In Jet Fuels

2022

Preprint

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Microbes which participate in extracellular electron uptake or H2 oxidation have an extraordinary ability to manufacture organic compounds using electricity as the primary source of metabolic energy. So-called electromicrobial production could be of particular value in the efficient production of hydrocarbon blends for use in aviation. Because of exacting standards for fuel energy density and the costs of new aviation infrastructure, liquid hydrocarbon fuels will be necessary for the foreseeable future, precluding direct electrification. Production of hydrocarbons using electrically-powered microbes employing fatty acid synthesis-based production of alkanes could be an efficient means to produce drop-in replacement jet fuels using renewable energy. Here, we calculate the upper limit electrical-to-energy conversion efficiency for a model jet fuel blend containing 85% straight-chain alkanes and 15% terpenoids. When using the Calvin cycle for carbon-fixation, the energy conversion efficiency is 38.4% when using extracellular electron uptake for electron delivery and 40.6% when using H2-oxidation. The efficiency of production of the jet fuel blend can be raised to 44.9% when using the Formolase formate-assimilation pathway and H2-oxidation, and to 50.1% with the Wood-Ljungdahl pathway. The production efficiency can be further raised by swapping the well-known ADO pathway for alkane termination with for the recently discovered MCH pathway. If these systems were were supplied with electricity with a maximally-efficient silicon solar photovoltaic, even the least efficient would exceed the maximum efficiency of all known forms of photosynthesis.

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Upper limit efficiency estimates for electromicrobial production of drop-in jet fuels

2023

Bioelectrochemistry

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