Supercritical fluid extraction of Benz(a)anthracene from coal fly ash using modified carbon dioxide and chlorodifluoromethane

Benz(α)anthracene (BaA) was deposited from the vapor phase onto the surface of a carbonaceous fraction of coal fly ash for extraction efficiency studies. Organic modifiers in conjunction with supercritical fluid extraction with CO₂ were studied to attempt to improve the extraction recovery of BaA from the fly ash matrix. The efficiency of supercritical fluid extraction (SFE) of BaA from the ash using methanol-, toluene-, and dichloromethane-modified CO₂, as well as pure CO₂, was investigated. Modified SFE was performed both in the static (non-flowing) mode and the dynamic (continuous flow) mode to learn if either technique improved the recovery of BaA from the fly ash matrix. Comparisons were made to ultrasonic extraction in toluene to determine if SFE is the best technique for extraction of PAH from fly ash. Toluene-modified CO₂ offered the highest extraction efficiency of the modified CO₂ systems studied and gave recoveries comparable to ultrasonic extraction.

Additionally, chlorodifluoromethane (CHCIF₂) was investigated as a replacement for pure CO₂ to see if improved recovery of BaA could be achieved. CHCIF₂ was able to greatly improve the recovery of BaA as compared with SFE using pure CO₂ and gave slightly higher recoveries than both ultrasonic extraction and toluene-modified SFE. The use of toluene-modified CHCIF₂ was also investigated and proved to be the best extraction medium for the removal of BaA from coal fly ash.