PTQ Q4 2024 Issue

catalyst, the presence of a catalyst promotes the decom- position of TBPS into sulphur-containing and non-sulphur- containing species. Even under the mildest testing condi- tions (T=150°C and LHSV=4 L/L/h), approximately 50% of the TBPS is decomposed into a range of products. The relatively weak S-S bonds can easily break, resulting in the formation of tert-butyl mercaptan species. In both subplots, it is evident that TBPS is progressively decomposed as the temperature increases, reaching complete conversion above approximately 230°C. Furthermore, H₂S is the primary by-product of TPBS decomposition at temperatures above 200°C, with a maxi- mum yield of 54-57% observed around 230°C. The slightly higher maximum H₂S content vs the theoretical 54% can be explained by the fluctuations that may be attributed to intrinsic variations in sample analysis and deviations from the assumptions described in the Experimental section. The influence of temperature and LHSV on the product distribu - tion follows the expected behaviour. For instance, at a given temperature, the fraction of unconverted TBPS is higher at the highest LHSV (shortest contact time). Similarly, the trends observed in the evolution of prod- ucts shift to higher temperatures in reactors operating at LHSV=4 compared to those at LHSV=2. The plot for LHSV=4 demonstrates that C₄ mercaptans and isobutene act as intermediate reaction products in a series of reac- tions involving TBPS as the reactant and H₂S and isobu - tane as the final products. Notably, the maximum yield of C₄ mercaptans is achieved at a lower temperature than isobutene, suggesting that C 4 mercaptans likely serve as intermediates in the formation of isobutene. Additionally, isobutane is only formed once a substantial concentration of isobutene is present in the system, indicating that isobu- tane is formed through the hydrogenation of isobutene. It is important to note that the observed species evolution is partially observed at LHSV=2; however, starting the test at

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Temperature [T] (˚C)

Mean (HS yield (wt%)) (Nominal H pressure (barg)=60) Mean (i-C= yield (wt%)) (Nominal H pressure (barg)=60) Mean i-C yield (wt%)) (Nominal H pressure (barg)=60) Mean (HS yield (wt%)) (Nominal H pressure (barg)=120) Mean (i-C yield (wt%)) (Nominal H pressure (barg)=120) Mean (iC= yield (wt%)) (Nominal H pressure (barg)=120)

lower temperatures would be necessary to obtain a similar profile as the one shown at LHSV=4. The thermal decomposition of TBPS investigated in Run01 without catalyst present showed that at temper- atures below 200°C, TBPS remained mostly unconverted or decomposed into non-volatile sulphur components. The presence of a NiMo catalyst facilitated the decomposition of TBPS, resulting in the formation of sulphur-containing and non-sulphur-containing species. Higher temperatures led to increased decomposi- tion rates, with H 2 S being the primary by-product. The Figure 5 Key components yields resulting from the thermal decomposition of TBPS without catalyst at PH2 = 60 bar (Run02, blue) and PH2 = 120 bar (Run03, red)

Nominal LHSV

Mean (i-C yield (wt%)) (Nominal LHSV=2) Mean (i-C= yield (wt%)) (Nominal LHSV=2) Mean (HS yield (wt%)) (Nominal LHSV=2) Mean (SZ54 yield (wt%)) (Nominal LHSV=2) Mean (C mercaptans yield (wt%)) (Nominal LHSV=2) Mean (i-C yield (wt%)) (Nominal LHSV=4) Mean (i-C= yield (wt%)) (Nominal LHSV=4) Mean (HS yield (wt%)) (Nominal LHSV=4) Mean (SZ54 yield (wt%)) (Nominal LHSV=4) Mean (C mercaptans yield (wt%)) (Nominal LHSV=4)

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Temperature (˚C)

Figure 6 Product yields resulting from the decomposition of TBPS over NiMo catalysts (Run 01)

PTQ Q4 2024