Para-polybenzimidazole Membranes for HCl Electrolysis at High (T < 160 oC) Temperatures

Abstract

Chlorine (Cl2) is a fundamental feedstock material for the chemical industry, and chlorine-derived products contribute more than $46 billion to the US economy annually. Chlorine plays a major role in many applications such as clean drinking water, pharmaceuticals, and crop protection chemicals. Most chlorine is produced from electrolysis of brine1. Chlorine can also be produced from hydrochloric acid by electrolysis. There are two primary techniques to recycle HCl to Cl2 via electrolysis--a diaphragm cell, which has the advantage of generating H2 as the product, and Proton Exchange Membrane (PEM) electrolyzer, which has the benefit of a higher conversion rate and lower energy consumption2,3. PEM electrolyzers are limited by the Nafion membrane separator, which requires hydration to conduct protons efficiently and is limited to temperatures of ≤ 120 °C. para-Polybenzimidazole (PBI; brand name Celtec-P) membranes are known as high temperature (T ≤ 230 °C) polymer separators that do not require hydration to maintain efficient proton conductivity and can operate in strong acid conditions4–6.In this work, we demonstrate a completely anhydrous HCl electrolysis system using a Celtec-P membrane that operates at temperatures up to 160 °C and has apparent conversion efficiencies up to 93% at 1.8V. We also discuss the results of an experimentally validated computational fluid dynamics (CFD) model and how this model can be used to elucidate and overcome potential electrolyzer limitations. Reference Pamphlet 1 Chlorine Basic, 8th ed., p. 62, The Chlorine Institute, (2014). Industrial Solutions HCl Electrolysis Chlorine Recovery for Greater Sustainability. Thyssenkrupp AG. Accessed December 20, 2021. https://ucpcdn.thyssenkrupp.com/_legacy/UCPthyssenkruppBAISUhdeChlorineEngineers/assets.files/products/hydrochloric_acid_recycling/thyssenkrupp_hcl_electrolysis_brochure_web_1.pdf.“Industrial Technologies Program: Advance Chlor-Alkali Technology.” Office of Energy Efficiency and Renewable Energy,U.S. Department of Energy, January 2006. https://www1.eere.energy.gov/manufacturing/industries_technologies/imf/pdfs/1797_advanced_chlor-alkali.pdf.T. R. Garrick et al., J. Electrochem. Soc., 164, F1591–F1595 (2017).L. Xiao et al., Chem. Mater., 17, 5328–5333 (2005).J. A. Mader and B. C. Benicewicz, Macromolecules, 43, 6706–6715 (2010).