Catalysis 2022 issue

temperature reached by the heat wave from the exothermic reaction during in-situ sulfidation. These represent ‘worst-case’ and ‘perfect start-up’ procedures, respectively. The shaded area in between these lines represents the activity that can realistically be expected from the LT-TGTU catalyst. The graph for the alumina based LT-TGTU cata - lysts shows that after perfect in-situ sulphidation an operation temper- ature of above 230°C is required to prevent slip of sulphur compounds already at start of run. The data suggests that a worst-case start-up makes it virtually impossible to operate at full conversion. In prac - tice, the activity will fall in between in the shaded area, but in any event leaves limited room for the inevita- ble catalyst deactivation over time. Although the first generation of TiO 2 -CoMo catalyst readily outper- forms an alumina based catalyst under similar sulphidation condi- tions, the possibility to operate at start of run in the T in < 230°C range still depends largely on the suc- cess of the sulphidation treatment, as indicated by the grey area in Figure 2 . The new TiO 2 -CoMo catalysts show a completely different picture. At inlet temperatures above 210°C, both catalysts sulphided at 240°C or 300°C perform equally well and no slip in unconverted sulphur com- pounds was observed. This means that if the heatwave during in-situ start-up is lower than expected, because of not having the optimal conditions in the reactor, the cata- lyst will still be sulphided almost to its full potential, with no significant effect on catalyst activity. From the data in Figure 2 , it can be concluded that TiO 2 -CoMo shows a remarkable high activity towards sulphidation under mild conditions. This result raises the obvious ques - tion whether it would be feasible to successfully start-up a TGTU cat - alyst by simply exposing the pris- tine catalyst to Claus tail gas. After all, this would avoid the complex procedure and the chances of mis- haps and permanent loss of catalyst activity. Figure 3 presents the performance of the TiO 2 -CoMo catalysts at T in =

1.50

Al0-CoMo ∆T = 240˚C Al0-CoMo ∆T = 300˚C

Gen 1 TiO/CoMo ∆T = 300˚C TiO-CoMo ∆T = 240˚C TiO-CoMo ∆T = 300˚C Gen1 TiO/CoMo ∆T = 240˚C

1.00

0.50

0.00

190

200

210

220

230

240

250

T (˚C) in

Figure 2 Total sulphur compounds measured in the reactor outlet as function of reactor inlet temperature plotted for ‘worst-case’ (triangle) and ‘perfect’ (square) start-up. The shaded areas indicate the possible catalyst performance for alumina (red) and titania (blue & grey) supported CoMo TGTU catalysts after start-up under in-situ sulphidation conditions. The concentration of sulphur compounds was measured dry and free of elemental sulphur. The total sulphur load in the input gas was 2.0 mol%

increased SO 2 emissions by COS and CS 2 slip to the incinerator to sulphur fouling of the quench water and increased amine degradation by S 8 and SO 2 slip. Experimental All catalyst tests reported were performed in the test laboratories at Euro Support Manufacturing Czechia s.r.o. in a dedicated glass bench-scale test reactor of 30 mm I.D. loaded with 70 mL shaped cat - alyst. The reactor is controlled on inlet temperature and the temper- ature profile in the reactor is moni - tored by a ten-point thermocouple. The glass reactor and preheater are inert for hydrogenation and shift reaction under the applied condi- tions. The test unit is fully auto - mated and can operate autonomous without interruption. The input gas composition is con - trolled by mass flow controllers. Water is added through a HPLC pump and evaporated in the pre- heater. Both input and output gas compositions are analysed by an online gas chromatograph. Prior to analysis, any elemental sulphur vapour is removed and the gas is dried.

In-situ sulphiding conditions: H 2 S = 1.5 mol%, H 2 = 6.0 mol%, H 2 O = 6.7 mol%. GHSV = 450 h-1 STP. Claus tail gas composition: H 2 S = 1.0 mol%, SO 2 = 0.5 mol%, CO = 1.1 mol%, H 2 = 1.5 mol%, COS and CS 2 = 250 ppm, CO 2 = 16.7 mol% and H 2 O = 22 mol%. GHSV = 1500 h-1 STP. Results and discussion Figure 2 displays the total concen- tration of sulphur compounds (SO 2 , CS 2 , COS, methyl mercaptan, and elemental sulphur, excluding H 2 S) found in the reactor outlet of the TGTU catalyst as function of the reactor inlet temperature and max- imum reached in-situ sulphida- tion temperature. This represents the total sulphur load that was not converted to H 2 S. The largest abso - lute contribution to the slip is in the form of elemental sulphur. In Figure 2 , the performance of Euro Support’s new titania based catalyst is compared to alumina based LT-TGTU and the first gen - eration TiO 2 /CoMo TGTU catalysts. Performance is plotted for two con - ditions where the ΔT 240°C and ΔT 300°C indicate the maximum

36 Catalysis 2022