Catalytic hydrodechlorination of PCDD/Fs from condensed water with Pd/γ-Al2O3.

Abstract

A continuous pyrolysis system equipped with air pollution control devices was developed for remediating soil with elevated PCDD/F concentrations. The quench tower generated condensed water containing 16–44 ng I-TEQ/L of PCDD/Fs, requiring further processing. Activated carbon adsorption at a liquid-to-solid ratio of 3:1 met regulatory discharge limits but involved high material costs. Catalytic hydrodechlorination using Pd/Al2O3 was therefore evaluated. Without a reducing agent, 53.21% mass removal was achieved over 180 minutes; adding 5% methanol as a hydrogen donor raised this to 71.86%. When the condensed water was pre-aerated with molecular hydrogen gas prior to palladium-catalyzed hydrodechlorination, removal efficiency reached 97.34% within the same timeframe, demonstrating the superior performance of molecular hydrogen compared with conventional hydrogen donors in this catalytic dechlorination process.

Mechanism

Molecular hydrogen adsorbed on palladium catalyst sites reductively cleaves carbon-chlorine bonds in PCDD/Fs, enabling efficient dechlorination that surpasses methanol-based hydrogen donor systems.