Electrochemical generation of hydroxide and hydrogen peroxide for hydrolysis of sulfuryl fluoride fumigant

Authors: WENG, CINDY - Stanford University; NAPIER, CADE - Stanford University; CEDRIC, KATTE - Stanford University; Walse, Spencer; MITCH, WILLIAM - Stanford University

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2024
Publication Date: 6/30/2024
Citation: Weng, C., Napier, C., Cedric, K., Walse, S.S., Mitch, W.A. 2024. Electrochemical generation of hydroxide and hydrogen peroxide for hydrolysis of sulfuryl fluoride fumigant. Journal of Agricultural and Food Chemistry. 72(27):15133-15141. https://doi.org/10.1021/acs.jafc.4c00864.
DOI: https://doi.org/10.1021/acs.jafc.4c00864

Interpretive Summary: Sulfuryl fluoride has emerged as a valuable postharvest alternative to methyl bromide, since the use of the later was restricted to quarantine purposes via the Montreal Protocol's regulation of substances that deplete stratospheric ozone. Sulfuryl fluoride is the primary means for disinfesting homes, structures, pallets, and museum pieces from wood boring and clothes feeding insects. Sulfuryl fluoride also significantly contributes to global food security, as it is used to control beetle and moth insects that destroy an estimated 30% of stored foods. Although the overall contribution of sulfuryl fluoride to global warming is negligible relative to carbon dioxide and methane, a molecule of sulfuryl fluoride has roughly 4000-fold more Global Warming Potential (GWP) than a molecule of carbon dioxide. In the context of limiting the amount of sulfuryl fluoride that is vented to atmosphere following such a treatment, which will aid in retaining this critical pest control tool, we explored a novel electrochemical approach that converts sulfuryl fluoride into non-volatile salts. During evaluation of technical aspects at the laboratory-scale, we found that the conversion was highly efficient and that the efficiency did not decline with the continued accumulation of salt. These promising results reinforce the need to scale this technology for further technical evaluation as well as an economic assessment.

Technical Abstract: The post-harvest fumigant, sulfuryl fluoride (SO2F2), is >1000-fold more potent of a greenhouse gas than carbon dioxide and methane. Pilot studies have shown that SO2F2 fumes vented from fumigation chambers can be captured and hydrolyzed by hydroxide (OH-) and hydrogen peroxide (H2O2) at pH ~12 in a scrubber, producing SO42- and F- as waste salts. To reduce the costs and challenges associated with purchasing and mixing these reagents onsite, this study evaluates the electrochemical generation of OH- and H2O2 within spent scrubbing solution, taking advantage of the waste SO42- and F- as free sources of electrolyte. The study used a gas diffusion electrode constructed from carbon paper coated with carbon black as a catalyst selective for the reduction of O2 to H2O2. Under galvanostatic conditions, the study evaluated the effect of electrochemical conditions, including applied cathodic current density and electrolyte strength. Within an electrolyte containing 200 mM SO42- and 400 mM F-, comparable to the waste salts generated by a SO2F2 scrubbing event, the system produced 250 mM H2O2 at pH 12.6 within 4 h with a Faradaic efficiency of 98.8% for O2 reduction to H2O2. In a scrubbing-water sample from a lab-scale fumigation, the system generated ~200 mM H2O2 at pH 13.5 within 4 h with a Faradaic efficiency of 75.6%. A comparison of the costs to purchase NaOH and H2O2 against the electricity costs for electrochemical treatment indicated that the electrochemical approach could be 38–71% lower, depending on the local cost of electricity.