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Show effectively destroys PICs under conditions where the parent waste approaches complete conversion, so the issue of PIC destruction may not be entirely decoupled from the destruction of the waste feed. Specifically, optimizing the process for the feed conversion is likely to also destroy any associated PICs. One strength of the approach being used here is that major organic PICs which m a y pose a serious challenge to the photothermal process will be detected early in the development program and methods for destroying them devised and tested before the process evolves to a larger scale. Quantum Yield Equations 6 and 7 illustrate h o w the quantum yield of a photothermal reaction m a y be found from the photothermal and thermal conversion data and the emission spectrum of radiation source and the high temperature absorption spectrum of the waste. Applying Equation 7 to the emission/absorption data presented in Figures 3 through 6 results in the U V photon absorption rate constant for T C E , D C B z , M C B z , and T C B shown in Figures 15 through 18, respectively. These Figures illustrate that the rate of photon absorption steadily increases with temperature. Combining these data with the respective thermal and photothennal conversion data gives the quantum yield as a function of temperature as shown in Figures 19 through 22. These data show that the quantum yield typically increases at high temperature, indicating that the rate of reactions from the excited state increase with temperature at a faster rate than the rate of photon absorption. Therefore, the increase in the overall process efficiency with temperature is a result of the synergism between the increase in photon absorption and excited state reaction rates. Performance Prediction The last topic to be discussed is the predicted performance of a large scale system. Specifically, the data presented here has been taken with relatively mild levels of radiant intensity, so it is informative to explore the conditions required to reach acceptable levels of conversion in a full scale system. W e begin with the assumption that the photothennal process operate at temperature below that where thennal reactions are likely to occur. This simplifies the model presented in Equation 1 to; fr = exp(-(j)rkabtT) (8) where fr is the fraction remaining, <j)r is the quantum yield, kab is the UV absorption rate constant (s"1), and ty is time (s). Equation 8 is the plug flow reactor performance model for the photothermal process assuming no thennal reactions. This model can now be used to detennine the conditions required to achieve a specific conversion given the fundamental parameters as measured in the laboratory (ca. Equations 6 and 7). Taking T C E as an example, and 10 s as the maximum desirable exposure time, a conversion versus temperature curve may be constructed as shown in Figure 23. This Figure shows that at ambient temperatures, the system gives very low 13 III-19 |
