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

Abstract

AbstractMicrobes which participate in extracellular electron uptake or H2oxidation 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 iswhen using extracellular electron uptake for electron delivery andwhen using H2-oxidation. The efficiency of production of the jet fuel blend can be raised towhen using the Formolase formate-assimilation pathway and H2-oxidation, and towith 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.