Pulse Modulated Electrochemical Conversion of Biomass
Authors: Radhakrishnan Rajeswaran , Hall Timothy D. , Inman Maria , Taylor E. J. 
Published: February 2020

Wet and gaseous waste streams are widely geographically distributed, frequently in areas of high population density, affording them unique current and emerging market opportunities. When compared to terrestrial feedstocks, these waste streams are largely aggregated and any derivative biofuels, bioproducts, or biopower are close to end markets. Thus, various public and private entities are actively exploring and deploying novel solutions for waste stream valorization. Potential competition between biofuels, bioproducts, and other beneficial uses will likely be a key element of future markets, and clearly merits further analytical and modeling investigation. In particular, the interest has been expressed by the Department of Energy in the development of cheap, scalable and novel cell-free biomass conversion technology that produces biofuels / bioproducts, with enhanced carbon conversion efficiency. Therefore, Faraday is developing a scalable electrolytic reactor to convert medium chain fatty acids (MCFA) to longer chain hydrocarbon fuels of C10-18 for jet, gasoline, and/or biodiesel fuels.[1] The MCFAs are produced by a biocatalytic fermentation step using non-food biomass such as cellulosic biomass, cellulosic hydrolysates, organic wet wastes, wastewater and wastewater solids, food wastes, industrial wastes, and feedstock blends.

Carboxylic acid produced through biocatalytic routes, have been upgraded to valuable fuel products via three process routes: 1) Kolbe Electrolysis, 2) Secondary Alcohols, and 3) Primary Alcohols.[2] Although, the front end biocatalytic (fermentation) carboxylic acid production routes is the same for all, each upgrading routes have various levels of complexity. They all either require the supply of H2 or require H2 to be produced during processing. Among these both alcohol upgrading routes require external supplies of H2, which could cost anywhere from $3 to $1/kg depending on its manufacturing process.2 Whereas, in Kolbe electrolysis, required H2 will be produced during processing. Additionally, the number of processing steps for Kolbe electrolysis is significantly shorter without the need for the addition of commodity chemicals and only a CO2 product as the only other output. Considering that the CO2 produced could be sequestered and reformed we do not believe this approach would emit a net carbon dioxide content in the atmosphere.2 Therefore, due to no require chemical additions and a scalable electrochemical processing backbone Kolbe electrolysis should be the most economical process to upgrade carboxylic acids from conventional biocatalytic processes if the product selectivity and conversion efficiencies can be improved. Kolbe electrolysis could be easily designed to accommodate various production scales including micro system (<5 tpd dry waste), mobile systems, or large permanent system.

In this SBIR program, Faraday is specifically focusing on efficiently converting MCFA via Kolbe electrolysis with the use of FARADAYIC® pulse modulated waveforms to produce jet/diesel biofuel at industrially feasible scale with improved selectivity. Preliminary results demonstrated that the use of pulse enhanced Kolbe electrolytic conversion method and apparatus, to electrochemically upgrade the MCFA carboxylic acid biocatalysts products to C10 hydrocarbon mixtures was shown to increase by 30% per the change in the intensity peak height of our FTIR analysis, in contrast to conventional direct current (DC) electrolysis. Additionally, we performed a first order techno-economic and life cycle analysis for the electrolytic conversion process as unit operation, which seems to be significantly more energy and conversion efficient than traditional strategies. This work can enable the economic and life cycle analysis to be refined such that realistic scale estimates for centralized and decentralized conversion facilities can be made.

Acknowledgements: Funding for this work is gratefully acknowledged from DOE SBIR Grant Number DE-SC0018796.

[1] http://www.caslab.com/Petroleum-Hydrocarbon-Ranges/

[2] Holzapple, M., SBE Supplement Lignocellulosic Biofuels, "Producing Biofuels via the Carboxylate Platform", March, 2015 52-57, Society for Biological Engineering, AIChE.