UV PHOTON-ASSISTED INCINERATION OF POLYCYCLIC AROMATIC-HYDROCARBONS AT ELEVATED-TEMPERATURES BETWEEN 150 AND 800-DEGREES-C

In this feasibility study we investigated the UV photon-assisted therm al decomposition of the title compounds. UV photons from an appropriat e light source such as a laser or a lamp were combined with heat at mo dest temperatures in an incinerating flow reactor in order to obtain a more efficient decomposition of hydrocarbons. In model experiments we have achieved a destruction enhancement factor of the photon-assisted thermal compared with the pure thermal decomposition process in exces s of 10(3). Comparing pyrene with 1-bromopyrene we were able to demons trate that the efficiency of populating the lowest energy triplet stat e by intersystem crossing from the corresponding singlet state plays a n important role in the photon-assisted thermal destruction in additio n to the importance of the molecular absorption coefficient, The overa ll quantum yield for the photon-assisted thermal decomposition general ly increases slightly with temperature but decreases with increasing p hoton Bur. For some compounds we determined overall quantum yields exc eeding unity thus pointing towards a possible photon-initiated chain r eaction. Levels of destruction in the ppb range seem possible at moder ate temperatures of less than 900 degrees C and gas phase residence ti mes of only a few seconds. (C) 1997 Elsevier Science S.A.