Phase changes of benzo(a)pyrene in supercritical water combustion

This paper presents new data on the behavior of benzo(a)pyrene (BaP) during supercritical water (SCW) combustion. It focuses on phase changes of the B aP throughout the transition from subcritical to supercritical regions. A s equence of images illustrates BaP's phase change for the first time. They w ere obtained in situ using a hydrothermal diamond anvil cell coupled with F ourier transform infrared spectrometer as well as optical and infrared micr oscopes. Combustion/reaction at different oxygen concentration (0-49% H2O2) , and pyrolysis experiments were conducted. The results show conclusively t hat (1) BaP is stable at pyrolytic conditions up to 452 degreesC; (2) It ca n disserve in supercritical water at 442-452 degreesC forming partly decomp osed globule. At extended reaction times above 500 degreesC the globule und ergoes carbonization while the dissolved compounds inhibit char formation. No complete dissolution was observed. (3) BaP combustion occurs simultaneou sly with dissolution in a single homogenous phase. At higher oxygen content , the dissolution and complete combustion takes place even in subcritical r egion (353 degrees and 145 MPa). In such a case no melting phase is present . These observations may affect the design and organization of the SCW comb ustion process. (C) 2001 by The Combustion Institute.