Abstract

Abstract. Emissions of the potent greenhouse gas perfluorocyclobutane (c-C4F8, PFC-318, octafluorocyclobutane) into the global atmosphere inferred from atmospheric measurements have been increasing sharply since the early 2000s. We find that these inferred emissions are highly correlated with the production of hydrochlorofluorocarbon-22 (HCFC-22, CHClF2) for feedstock (FS) uses, because almost all HCFC-22 FS is pyrolyzed to produce (poly)tetrafluoroethylene ((P)TFE) and hexafluoropropylene (HFP), a process in which c-C4F8 is a known by-product, causing a significant fraction of global c-C4F8 emissions. We find a global emission factor of ∼0.003 kg c-C4F8 per kilogram of HCFC-22 FS pyrolyzed. Mitigation of these c-C4F8 emissions, e.g., through process optimization, abatement, or different manufacturing processes, such as refined methods of electrochemical fluorination and waste recycling, could reduce the climate impact of this industry. While it has been shown that c-C4F8 emissions from developing countries dominate global emissions, more atmospheric measurements and/or detailed process statistics are needed to quantify c-C4F8 emissions at country to facility levels.

Highlights

  • Perfluorocyclobutane (c-C4F8, PFC-318, octafluorocyclobutane, CAS 115-25-3) is a potent greenhouse gas (GHG) with a global warming potential of 10 200 on a 100-year timescale (GWP100) based on a lifetime estimate of 3200 years (Forster et al, 2021)

  • These reports from developed countries account only for a small fraction of global emissions of c-C4F8 inferred from atmospheric measurements (Mühle et al, 2019), similar to the emissions gaps observed for other synthetic GHGs (e.g., Montzka et al, 2018; Mühle et al, 2010; Stanley et al, 2020)

  • For 2016, these limited regional measurements allowed Mühle et al (2019) to allocate ∼ 56 % of global c-C4F8 emissions to specific regions with significant emissions from eastern China (∼ 32 %), Russia (∼ 12 %), and India (∼ 7 %). Spatial patterns of these regional c-C4F8 emissions were roughly consistent with locations of facilities that produce polytetrafluoroethylene (PTFE, a polymer widely used for its non-stick and water repellent properties, chemical, thermal, light, and electrical resistance, high flexibility and low friction), related fluoropolymers, and the necessary precursor monomers tetrafluoroethylene (TFE) and hexafluoropropylene (HFP), which are produced via the pyrolysis of hydrochlorofluorocarbon22 (HCFC-22, CHClF2). c-C4F8, essentially the dimer of TFE, is one of several by-products/intermediates of this process (Chinoy and Sunavala, 1987; Broyer et al, 1988; Gangal and Brothers, 2015; Harnisch, 1999; Ebnesajjad, 2015)

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Summary

Introduction

Perfluorocyclobutane (c-C4F8, PFC-318, octafluorocyclobutane, CAS 115-25-3) is a potent greenhouse gas (GHG) with a global warming potential of 10 200 on a 100-year timescale (GWP100) based on a lifetime estimate of 3200 years (Forster et al, 2021). Emissions of c-C4F8 from developed countries are reported under the United Nations Framework Convention on Climate Change (UNFCCC) These reports from developed countries account only for a small fraction of global emissions of c-C4F8 inferred from atmospheric measurements (Mühle et al, 2019), similar to the emissions gaps observed for other synthetic GHGs (e.g., Montzka et al, 2018; Mühle et al, 2010; Stanley et al, 2020). Murphy et al (1997) demonstrated that co-feeding several percent of cC4F8 to the HCFC-22 feed could reduce additional c-C4F8 formation to less than 0.5 % of the combined TFE and HFP yield, increasing combined TFE and HFP yield to more than 96 % They stated that perfect process control may be impractical.

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