Hydrogen Production Via Mediated Electrolysis of Biomass from Distillery Whisky Waste Streams

Abstract

Fuel-flexible hydrogen generation methods, such as electrochemical conversion of waste biomass, offer a route to sustainable production of hydrogen (in addition to steam or water electrolysis using renewable electricity [1]) whilst valorising feedstocks that are often overlooked. [2] In this research, the authors explore the potential of a novel, two-stage electrolysis process to convert biomass-containing solid and liquid distillery waste products into hydrogen, using a phosphomolybdic acid (H3[PMo12O40] or PMA) catalyst, at lower operating voltages (<0.95 V) than proton exchange membrane (PEM) water electrolysers (1.5 – 1.6 V). [3]Firstly, an overview of the processes, energy usage and waste stream generation at the Isle of Raasay Distillery (Hebrides, Scotland) will be provided, before results from the characterization of whisky waste products are introduced. This provides a detailed compositional analysis of both solid (draff/spent barley) and liquid (pot ale and spent lees) wastes, as well as residual alcohol analysis of the liquid wastes, and their potential for conversion to hydrogen.Subsequently, the concept of thermal digestion of each waste-type, using the Keggin-type polyoxometalate PMA catalyst to abstract protons and electrons from biomass, will be outlined. Finally, details of electrolysis of the PMA-biomass solutions using a PEM flow cell will be provided, including electrochemical data (AC impedance spectroscopy, linear sweep voltammetry and potentiostatic operation) in order to determine the optimal operating conditions for the process, in addition to the respective yield of hydrogen from each biomass source. Prospects for upscaling the process will also be discussed. References Götz, M., Lefebvre, J., Mörs, F., McDaniel Koch, A., Graf, F., Bajohr, S. Reimert, R. and Kolb, T., Renew. Energ., 85, 1371 – 1390 (2016).Liu, W., Cui, Y., Du, X., Zhang, Z., Chao, Z. and Deng, Y., Energy Environ. Sci., 9, 467 – 472 (2016).Oh, H., Choi, Y., Shin, C., Nguyen, T. V. T., Han, Y., Kim, H., Kim, Y. H., Lee, J-W., Jang, J-W. and Ryu, J., ACS Catal. 10, 2060 – 2068 (2020).