OCR Text |
Show and chemical stability of the chlorobenzenes and compare them with similar properties for related compounds. The actual data base on reactions involving chlorinated aromatics is very sparse. We are forced to make estimates. In some cases the methodology is fairly well established. In others, particularly wh~re small distinctions may have important consequences the situation is less satisfactory. This is the reason for the rate measurements on the hydrogen atom induced decompositions. Since for incineration we are frequently interested in relative incinerability, we must consider the rate constants in the context of other molecules likely to be present in the system. This is the reason for their inclusion in the tables given below. a. Unimolecular Decomposition: The predominant mechanism for the unimolecular decomposition of chlorinated aromatics involve the breaking of the C-CI bond. Although no direct measurements have ever been made. Our capability for predicting the rate expressions for such process is very good inasmuch as the thermochemistry is well known or can be estimated, there exist measurement of a closely related system, iodobenzene7, and the reverse combination reaction is fast and has negligible activation energy. On this basis we estimate the rate expression for the breaking of a C-CI bond in chI oro benzene to be k(C-CI) = 1 x 1015 Exp(-95000/RT) /s In contrast, for the breaking a C-H bond in benzene the appropriate rate expression is k(C-H) = 2 x 1015 Exp(-110000/RT) /s From a more practical point of view, assuming a typical 1 sec residence time, one can calculate the temperature requirements for 4 nines destruction. For chlorobenzene this comes out to 1484 K or 2210 F for chlorobenzene and 1602 K or 2430 F for benzene. Benzene is more thermally stable. Nevertheless the 7 |