Decontamination of sensitive equipment materials contaminated
by
organophosphorus (OP) compounds by a two-stage process was evaluated.
The process involved extraction of OP from contaminated materials
with methanol (first stage), followed by decomposition of OP by heterogeneous
catalytic methanolysis (second stage). In a series of tests diazinon,
malathion, paraoxon, parathion, and other organophosphorus pesticides
were spiked onto sensitive equipment materials and extracted with
methanol after a presented contact time. After extraction, the lowest
quantity of residue was found for diazinon, while parathion was the
most persistent. High-impact polystyrene (HI-PS) retained 10-fold
or more mass of OP than other tested materials. The surface of the
HI-PS was deteriorated after contacting with OP due to a plasticizing
effect. A longer contact time with HI-PS and lower polarity factor
of OP resulted in higher residual amounts of OP after extraction.
In the second stage of the process, diazinon and paraoxon were decomposed
by methanolysis in presence of palladium- and ytterbium-based solid-supported
catalysts, respectively. Complete destruction of diazinon was achieved
within 30 s, while 60 min was required to destroy paraoxon.
Sensitive equipment materials were decontaminated from organophosphorus compounds paraoxon or parathion by immersion into a catalytic reactive solution and by spraying with the same solution. Immersion of contaminated material samples into methanol-based catalytic solutions resulted in an effective decontamination. Greater than 99% decontamination was observed for paraoxon on high-impact polystyrene (HI-PS) over 15 min of reaction time. Under the same process conditions, the decontamination from parathion did not exceed 95%. The catalytic decompositions of paraoxon and parathion followed firstorder reaction kinetics with rate constants of 5.4 × 10 −3 and 1.3 × 10 −3 s −1 , respectively. These values were by an order of a magnitude lower than the respective rate constants reported for homogeneous reactions in a methanol solution. Decontamination by spraying the catalyst on the contaminated surface revealed that multiple applications would be required to overcome a rapid evaporation of methanol from the surface and an associated loss of catalytic activity.
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