| OCR Text |
Show The PIC data for the photothermal and thermal oxidation of T C B are shown in Figures 10 and 14, respectively. Carbon balances (including the measure of carbon monoxide and carbon dioxide) were conducted at 675°C, the temperature of maximum thermal PIC yield. These showed that 1 2 7 % (photothermal) and 136% (thermal) of the carbon was recovered at this temperature, indicating that all major organic products were identified. Figures 10 and 14 illustrate that under both conditions T C B produces a complex mixture of organic products, albeit at relatively low yields. Reviewing this data shows that as the molecular weight of the PICs increases, the photothermal yield of a particular product decreases and the temperature required for its destruction is reduced as compared to the thermal product. For example, the lightest organic product observed was 1,2-dichlorobenzene, which reached a maximum photothermal yield of 0.124% at 600°C, as compared to 0.153% at 675°C thermally. As an example of a product of intermediate molecular weight consider the data for trichloronaphthalene. In this case the maximum photothermal yield is 0.282% at 550°C as compared to 0.453% at 675°C from the thermal exposure. Finally, the highest molecular weight products found from the thermal exposures included three tetrachlorodibenzofuran isomers. Furthermore, detailed analysis suggests that the first of these may be the toxic 2,3,7,8 isomer. Examination of the photothermal data shows that none of these products were formed with yields above 0.1%. The PIC data presented in Figures 9 and 13 for the products from MCBz illustrate an even greater contrast between the photothermal and thennal products. Extensive carbon balances (including the measure of carbon monoxide and carbon dioxide) were conducted throughout the temperature range studied. For the thennal process the carbon recovery varied from 1 0 0 % at 300°C, to 1 3 1 % at 675°C, to 1 1 3 % at 710°C. For the photothermal tests, carbon recovery ranged from 124% at 300°C, to 1 3 3 % at 500°C, to 1 0 4 % at 700°C. These recoveries again illustrate that all major organic products have been accounted for. In this case, the thermal oxidation produced a far more complex mixture of PICs than did the photothermal process. However, the overall trend in the PIC production is consistent with the data from the T C B tests. Specifically, the photothermal process tends to produce products of lower molecular weight and simpler structure, and that it is capable of destroying these products at lower temperatures than the comparable thermal process. The data being gathered on PICs as part of the current development project is not as exhaustive as previously done largely because such analysis are very time consuming. Furthermore, data taken to-date suggests that at high levels of photothermal conversion, PICs may not present a significant problem. Consequently, quantitative data is being obtained only for PICs with relatively large yields (i.e., > 1 % ) . However, raw data is being collected and stored so that detailed analysis may be conducted later if circumstances warrant it. Therefore, the PIC data from these tests, which include the detoxification of T C E and D C B z , are not as highly detailed as that 11 III-19 |
