J. Leglise

Effect of hydrogen sulphide on the reaction of 2,6-dimethylaniline over sulphided hydrotreating catalysts

Abstract The reaction of 2,6-dimethylaniline was studied between 280°C and 320°C at 4 MPa on CoMo and NiMo/Al 2 O 3 hydrotreating catalysts. The formation of dimethylcyclohexanes and dimethylcyclohexenes, of m -xylene and of o -toluidine plus mesidine gave access to three functionalities of the catalysts: hydrogenation, C-N bond cleavage and acidity. The influence of H 2 S on the activity and the selectivity of the catalysts was examined for H 2 S/H 2 molar ratios ranging from 0 to 0.07. The response of hydrogenation and of hydrogenolysis to H 2 S were similar: activity of both functions decreased up to about 1 % H 2 S, and stayed constant beyond that value, while the acidity continuously increased with the H 2 S concentration. From these results, the distribution of active species originating from H 2 and H 2 S is discussed in relation with the reaction mechanism.

Sulphidation of an oxidic CoMo/Al2O3 catalyst under practical conditions: different kinds of sulphur species

The sulphidation of a CoMo/Al2O3 hydrotreating catalyst was studied under pressure and flow conditions close to industrial practice. The sulphiding mixture contained equal amounts of H2S and CH4 diluted in hydrogen under 3.9 MPa total pressure. The oxidic precursor was flushed by the reagent gas at 40 °C for 10 h, then the temperature was raised to 400 °C within 2 h. Mass variation was continuously recorded by means of a suspension magnetic balance, and the gas phase was analysed by mass spectrometry. Sulphur contents were also determined at intermediate temperatures by chemical analyses. Thus, mass variations due to the presence of adsorbed species or to the formation of CoMo sulphides could be distinguished. The rapid gain in mass noted at 40 °C was mostly due to adsorption of H2S over the oxidic solid, since it increased with H2S partial pressure. At this stage, however, a small amount of the reactive oxygen was already exchanged for sulphur. Upon raising the temperature, the mass decreased due to a combination of desorption and sulphiding steps. Above 140 °C, H2S consumption was evidenced, together with water production, and the rate of sulphiding increased with the H2S partial pressure. At 300 °C, the mass variation was close to that expected for complete transformation into Co9S8 and MoS2. Above 350 °C, the mass further increased due to the replacement of adsorbed water by H2S. At 400 °C, an important excess mass was observed at all H2S partial pressures. Thus, the adsorption sites on the metal sulphides are essentially saturated by H2S species under practical conditions.

Promotion and inhibition by hydrogen sulfide of thiophene hydrodesulfurisation over a sulfide catalyst

The reaction of thiophene has been studied between 300 and 400 °C and 0.1 MPa over a sulfided CoMo–Al2O3 catalyst with various amounts of H2S; besides the usual inhibiting effect, it has been found that low levels of H2S promoted the reaction above 380 °C.

Alkyl Polysulfides as Presulfiding Agents of a CoMo/Al2O3 Catalyst: Effect on Catalytic Properties

Abstract Presulfiding a CoMo/Al2O3 catalyst with t-nonyl or t-dodecyl pentasulfides improved both activities for thiophene hydrodesulfurization and cyclohexene hydrogenation.