Increasing concerns with climate change and depleting fossil based resources require a shift in the current methods for chemical and fuel production and utilization. The transition to biomass as a sustainable carbon feedstock to replace petroleum represents an important step to address these concerns. Unfortunately, the mature technologies available in the petrochemical industry make it a considerable challenge to establish operations that produce biobased chemicals at a competitive cost. As a result, it becomes critical to establish streamlined operations to reduce the costs associated with the conversions of biobased feedstocks or synthesize higher value products with new or interesting properties not available in the current petrochemical market.

One strategy to convert biomass to commercial products entails the fermentation of cellulosic sugars to intermediates, which are then further diversified using chemical catalysts. In this process, biological catalysis facilitates the selective production of complex platform molecules, which are then efficiently converted to various biorenewable chemicals through chemical catalysis. However, previous attempts to combine chemical and biological processes have led to low conversion rates because of deactivation by residual biogenic impurities and catalyst leaching. In this work, an electrochemical conversion scheme is employed to mitigate deactivation caused by the inherent catalyst poisons present in biological feedstocks and fermentation growth media.

To demonstrate the efficacy of using an electrochemical conversion, muconic acid (MA), a C6 dicarboxylic acid derived from sugar fermentation, was hydrogenated to trans-3-hexenedoic acid (t3HDA) and adipic acid. An initial screening and optimization found that Pb was able to hydrogenate MA to t3HDA in the presence of all possible biogenic impurities at a 94% yield. To diversify the hydrogenation products derived from cis,trans-muconic acid, an electrode screening study was undertaken. Early thermodynamic calculations suggest the potential to synthesize 3-hexenedioic acid isomers as well as adipic acid by fine tuning the reaction kinetics due to the similar theoretical reduction potentials. Electrodes screened were selected with varying degrees of hydrogen binding strength, a potential intermediate for electrocatalytic hydrogenation reactions. Metals that displayed a weak hydrogen binding strength produced t3HDA with large faradaic efficiencies and metals with a stronger hydrogen binding strengths displayed the production of trans,trans-muconic acid and adipic acid with small faradaic efficiencies. Details into the specific electron transfer and reaction mechanisms were found to be influential for product selectivity.

Pb, a common industrial electrode, was selected for further study as a potential cathode to scale the MA hydrogenation. Bulk electrolysis of a concentrated solution of MA displayed similar yields to previous studies (94%), however, with the implementation of an Ar purge to remove all other electroactive species a 100% faradaic efficiency was observed. Because of the high yields and faradaic efficiencies, a technoeconomic analysis for the production of t3HDA was performed. A conservative value for the production of t3HDA at $2.13 kg-1 was obtained. The low cost was a direct result of streamlining the chemical conversion steps, which minimized the cost for additional separation processes and operating units.