Table 1 Effect of iron on dry hydrogenation of coal Conversion to Conversion to liquid and gas asphaltene Charge (% dmmf coal) (% dmmf coal) Coal 12.7 Not determined Coal+S 22.8 Not determined Coal+Fe 33.2 14.3 Coal+S+Fe 93.0 47.3
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Table 2 Results of variation of iron concentration Added catalytic Conversion to ingredients oil and gas (% dmmf coal) (% dmmf coal) Conversion to asphaltene (% dmmf coal) 0.5% Fe + 4.5% S 87.0 48.1 1 .O% Fe + 4.5% S 94.5 42.5 1.86% Fe + 4.5% S 94.9 23.4
hydrated oxide, by precipitation with ammonium hydroxide4g7 and elemental sulphur (4.5 wt%) was added, for hydrogenation at 400Β°C under 21.6 MPa reaction pressure for 3 h in an autoclave (2dm3). Untreated coal was used in one of the control runs while in the other two, 4.5 wt% elemental sulphur and 1.86 wt% Fe were added separately. The results are given in Table 1.
The experimental data show that although elemental sulphur increased the conversion by lo%, the effect of iron alone under the influence of H2S produced from the coal was greater. The combined effect of adding iron and sulphur was, however, very marked in this reaction environment which was suitable for the formation of iron sulphide.
In another set of experiments, the same dry coal (72 g) was hydrogenated at 450Β°C under 24.5 MPa reaction pressure in presence of a tar oil fraction, as a vehicle oil, for 90 min in an autoclave (1 dm3). In this case, the amount of elemental sulphur was kept constant but that of iron, applied as described above, was varied. It can be seen (Table 2) that the reaction was increasingly favoured by increasing concentration of iron.
From the above evidence it is concluded that probably pyrrhotite, i.e. non-stoichiometric iron sulphide, and not hydrogen sulphide alone, is the catalyst. Hydrogen sulphide may, however, have some individual catalytic role in addition to that of iron sulphide". The source of iron may be that present in coal mineral matter, or externally added oxide or pyrite. The optimum composition of the pyrrhotite however depends on the partial pressure ratio of hydrogen sulphide and hydrogen, and other thermodynamic conditions.