23.
Catalytic desulphurization of benzothiophene (BTH) in a water/toluene emulsion, a model system for heavy oil emulsions, was achieved at 340°C using a water-soluble phosphomolybdic acid (PMA), a precursor for dispersed Mo catalyst. This process is based on the activation of H
2O to generate H
2 in situ via the water gas shift reaction (WGSR) for hydrodesulphurization (HDS). At 340°C with an initial CO loading of 4.14 MPa, essentially complete sulphur removal was obtained. Kinetic expressions for the WGSR and HDS of BTH with in situ generated H
2 and externally supplied H
2 were developed and verified experimentally. The kinetic analysis indicates that WGSR is rate-determining and desulphurization with in situ generated H
2 is a relatively fast step. Apparently, in situ H
2 is about seven times more active than externally supplied H
2 for the hydrogenation of BTH. A mechanism for desulphurization involving initial hydrogenation of BTH to dihydrobenzothiophene (DHBTH) followed by hydrogenolysis to give ethylbenzene (EB) and H
2S is proposed.
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