Speciation Detection Deciphering C₂H₂/Cl-Driven Mercury Escape Mechanisms in PVC Production

Mercury emissions from acetylene hydrochlorination processes in polyvinyl chloride (PVC) production pose severe environmental risks yet remain poorly quantified due to methodological limitations in high-reactivity C₂H₂/HCl atmospheres. We reported an advanced operando mercury speciation platform named PVC-OHM, engineered through systematic optimization of the Ontario Hydro method (OHM), achieving simultaneous real-time detection of elemental mercury (Hg⁰) and divalent mercury (Hg²⁺) with unprecedented sensitivity (0.12 μg/m³) under industrially relevant conditions. Our mechanistic investigation reveals three dominant mercury escape pathways: (1) thermal desorption, wherein localized hotspots accelerate HgCl₂ decomposition and elevate the saturated vapor pressure at carbon-mercury interface (from 0.9 to 20.3 atm), contributed to 80% of total Hg loss; (2) C₂H₂ driven reductive decomposition of HgCl₂ catalyst at carbon-mercury interfaces, responsible for 65-78% of Hg⁰ emissions and (3) excess chlorine adsorption-induced desorption ([HgCl₂/AC] Cl₅, E_ads > 0) accounting for >10% of Hg²⁺ emissions. Quantitative tracking demonstrates alarming mercury loss of per gram catalyst (5 wt % Hg) reached as 3.08 mg Hg⁰ and 9.01 mg Hg²⁺, directly linked to localized thermal gradients (ΔT = 250-300 °C) at reaction hotspots. This work establishes the first experimentally validated framework for mercury fate prediction in carbide-based PVC synthesis, providing actionable strategies for emission control through hotspot mitigation and coordination environment optimization.