THERMAL-TREATMENT OF 1,2,3,4-TETRACHLORODIBENZO-P-DIOXIN BY REACTION WITH CA-BASED SORBENTS AT 23-300 DEGREES-C

The fate of combustion-generated polychlorinated dibenzo-p-dioxins (PC DDs) and polychlorinated dibenzofurans (PCDFs) captured in sorbent-bas ed, air pollution control devices remains uncertain. This process was simulated by passing vapor-phase 1,2,3,4-tetrachlorinated dibenzo-p-di oxin (TCDD) to a fixed-bed reactor laden with, typically, 1 g of calci um (Ca)-based sorbent The sorbent bed, reactor rinsate, evaporation ch amber, and gas impingers were analyzed separately to balance and accou nt for the TCDD input. Tests at 160-300 degrees C demonstrated 50 to 1 00% conversion of TCDD to higher molecular weight, chlorinated product s with both aromatic and aliphatic components. The unlikeliness of con ventional semivolatile GC/MS analyses to detect these higher molecular weight products may offer an alternative explanation for research stu dies citing destruction or volatilization of chlorinated organics in t he presence of Ca-based sorbents. The applicability of this reaction t o other halogenated organics, such as polychlorinated biphenyls, may p rovide a method for contaminated soil treatment. More extensive experi mental and analytical work is necessary to fully understand the reacti on mechansim, the full range and stability of potential reaction produ cts, and the ecological and human health implications. Alteration of t he structural symmetry and size of the TCDD molecule (and related halo genated organics) will likely cause significant reductions in toxicity .