90 80 100
100
80
i-C yield (wt%) (Nominal LHSV=2) i-C = yield (wt%) (Nominal LHSV=2) H S yield (wt%) (Nominal LHSV=2) SZ54 yield (wt%) (Nominal LHSV=2) i-C yield (wt%) (Nominal LHSV=4) i-C = yield (wt%) (Nominal LHSV=4) H S yield (wt%) (Nominal LHSV=4) SZ54 yield (wt%) (Nominal LHSV=4) C mercaptans yield (wt%) (Nominal LHSV=2) C mercaptans yield (wt%) (Nominal LHSV=4)
0 30 20 10 40 50 60 70
60
Mean (i-C yield (wt%)) Mean (H S yield (wt%)) Mean (SZ54 yield (wt%)) Mean (C mercaptans yield (wt%))
40
20
0
140 150
160
250 220 230 240 200 210 170 180 190
160
180
200
220
240
Temperature (˚C)
Temperature [T] (˚C)
the assumptions described in the Experimental section. Between 200°C and 210°C, noticeable amounts of H₂S and isobutene are produced in the absence of a catalyst, indi- cating partial decomposition of TBPS. Beyond this temper - ature range, the decomposition rate of TBPS significantly increases, as evidenced by the rapid changes in the yields of H₂S, isobutene, and unconverted TBPS. This observation aligns with findings reported in the literature, where the exclusive formation of H₂S and isobutene as decomposition products has been reported. 4 Figure 3 Product yields resulting from the thermal decom- position of TBPS without catalyst (Run01)
The thermal decomposition of TBPS was also investi - gated in Run02 and Run03 in the absence of catalyst, with identical testing protocols except for the partial pressure of H₂. The results from Run02, presented in Figure 4 in the absence of catalyst, exhibited concentration profiles that followed similar trends to those observed in Run01 with- out catalyst. However, TBPS started to decompose at a lower temperature of around 170°C, likely due to the lower space velocity employed in the experiment. At this temper- ature, clear formation of H₂S and isobutene was observed, consistent with the findings of Heller and Roberts,² who reported a decomposition temperature of approximately 160°C for TBPS. The results of the thermal decomposition in Run03 were similar to those of Run02. Figure 5 compares the yields of three key components (H₂S, isobutene, and isobutane) between the two runs. Differences mainly manifested in the H₂S and isobutene yields. At a higher partial pressure of hydrogen (120 bar in Run03), the formation rate of H₂S appeared slightly higher compared to the test using 60 bar of H₂. Additionally, at any given temperature, the content of isobutene was consistently lower, while the content of isobutane was higher when the partial pressure of H 2 was increased. This indicates that the hydrogenation reaction of isobutane is favoured at higher partial pressures of H₂, aligning with the expected behaviour as hydrogenation reactions typically exhibit positive reaction rate orders with respect to the hydrogen partial pressure. The decomposition of TBPS over NiMo catalysts was inves - tigated in Run01, designed to simulate the sulphiding in naphtha hydrotreating. The resulting product distribution of sulphur species and non-sulphur species vs temperature is presented in Figure 6 . The results are grouped by LHSV, with LHSV=2 displayed on the left in blue and LHSV=4 on the right in red. The data represents the mean values obtained from duplicate reactors operating under the same reaction conditions. Unlike the behaviour observed in the reactors without a Decomposition of TBPS over NiMo used in naphtha hydrotreating Figure 4 Product yields resulting from the thermal decom- position of TBPS without catalyst (Run02)
68
PTQ Q4 2024
www.digitalrefining.com
Powered by FlippingBook