Figure 3. FT-IR patterns of PPS-based bag filter materials with different loading units.
3.2 Chemical evolutions of PPS-based bag filter materials
In order to obtain the configuration change of PPS bag filter materials with various loading units in coal-fired power plants, ATR-FTIR was conducted directly and related data were shown in Fig. 3. Besides, main changes in the characteristic peaks of PPS-based bag filter materials with loading units below 200 MW, 200-300 MW and above 300MW were summarized from Fig. 3 and displayed in Table 4, Table S1 and Table S2, respectively.
The characteristic peaks of in-plane stretching vibration of C-C bond in the benzene ring at 1572 cm-1, 1470 cm-1 and 1386 cm-1 and the stretching vibration of C-S bond at 1092 cm-1 are observed for all samples, which are originated from the bulk materials of PPS[7, 32, 33]. The new peaks of the stretching vibration of -SO- at 1036 cm-1and the stretching vibration of -SO2- at 1157 cm-1, and 1321 cm-1 appear for sample 2#-5# compared with pure PPS (Table 4), indicating that the oxidation of C-S bond into sulfoxide (-SO-) and sulfone (-SO2-) in PPS molecule happens at high temperature when the content of SO2 is more than 1500 mg/m3. However, only an extremely weak peak at 1163 cm-1 belonging to -SO2- is detected for sample 1#, showing that the degree of oxidation of sample 1# is lower than that of sample 2#-5#. Besides, the new peak of the stretching vibration of -SO3H at 646 cm-1 emerges and becomes stronger with the addition of content of SO2(from 1# to 5#). The appearance of new peak at 646 cm-1 indicates that the hydrogen in the benzene ring could be replaced by sulfonic acid group through sulfonation[29]. At the same time, the sulfonation becomes obvious with the content of SO2 adds and above phenomenon can be illustrated. Also, the new peaks representing the oxidation (1036 cm-1, 1157 cm-1, and 1321 cm-1) appear earlier than that on behalf of sulfonation (646 cm-1) with the increase of content of SO2, showing that oxidation is easier to take place than sulfonation in actual operating environment. The bond strength of C-S bond is the lowest in the PPS molecule[34], making it easier to be oxidized into sulfoxide (-SO-) and sulfone (-SO2-) at high temperature than converting hydrogen into sulfonic acid group in the benzene ring.
Table 4. Main changes in the characteristic peaks of PPS-based bag filter materials with the loading units below 200 MW.