Extractions of polychlorinated biphenyl (PCB) compounds from surfactant suspension/soil extracts with dechlorination on-line

Polychlorinated biphenyl (PCB) formulation (Aroclor 1242 or 1248)-surfactan t (Brij 97 or Triton CF54) emulsions (0.1-1.0%, v/v) were extracted with su percritical carbon dioxide (scCO(2)). The declinations curve that resulted for each loading of PCB substrate was accurately modelled as a single-expon ential decay, and the half-life [t(1/2), 10.76 min +/-2% (Brij 97) or 10.0 min +/- 14% (Triton CF54)] was independent of the level of loading. When th e extraction was combined with on-line dechlorination, t(1/2) was increased to -17.62 min +/- 6% or 16.46 min +/-5%, respectively The dechlorination r eactor contributed appreciably to the back-pressure of the system so that. under identical scCO(2) head pressures, the flow rate at the exit of the sy stem was reduced from 1500 mL min(-1) (as decompressed gas) to 900 mL min(- 1), When corrected for the difference in flow rates, the declination curves in the absence and presence of the reactor became virtually identical. For a surfactant suspension from a soil that was field-burdened with only 6 pp m PCBs, extended operation (extraction-dechlorination) for 15 h, during whi ch the substrate suspension was replaced every 30 min, caused no loss of th e dechlorination efficiency; however, for 1% (v/v) Aroclor 1242 or 1248 in surfactant suspension, the reactor gradually lost reactivity over 5 h of co ntinued operation. However, the reactivity could be restored virtually comp letely by purging the reactor column with scCO2 for 3 h or washing the colu mn at ambient temperature with 30 mL of methanol-water (7 + 3, v/v). Mass s pectrometry of the reaction products indicated that the principal products included biphenyl and toluene, but methylated benzenes and phenols were als o present.