Metal-ion pillared clays as hydrocracking catalysts (II): effect of contact time on products from coal extracts and petroleum distillation residues

摘要

Novel catalysts have been prepared, based on montmorillonite (a natural clay) and laponite (a synthetic clay) pillared with tin, chromium and aluminium pillars as well as layered double hydroxides based on polyoxo-vanadate and -molybdate as previously described. These novel catalysts were compared initially with a standard Ni/Mo catalyst supported on alumina and a dispersed catalyst, Mo(CO)_6 in hydrocracking a coal extract for a short contact time of 10 mm at 440 deg C in a microbomb reactor with tetralin solvent and hydrogen at a pressure of 190 bar. In the present work, the best of the novel catalysts, chromium montmorillonite calcined at 500 deg C and tin laponite, have been compared with the supported catalyst and a dispersed catalyst (Mo(CO)_6) in the repeated hydrocracking of fresh coal extract over three sequential periods of 1 h. Also, the chromium montmorillonite calcined at 500 deg C has been used in the hydrocracking of primary coal extracts, prepared in the flowing solvent liquefaction rig from Pittsburgh #8 and Illinois #6 coals, for reaction times of 10 mm and 2 h. Further, the chromium montmorillonite calcined at 500 deg C and tin laponite, have been compared with the supported catalyst and in the absence of a catalyst, in the hydrocracking of a petroleum distillation residue with 10 mm and 2 h reaction times. Results were compared by size exclusion chromatography in NMP solvent and by UV-fluorescence and evaluated by the extent of the shift of the SEC profile to small molecules and by the shift of the synchronous UV-fluorescence profiles to shorter wavelengths. The performances of both catalysts at short, long or repeated reaction times are seen to be better than that of the conventional NiMo catalyst for the hydrocracking of coal-derived materials and a petroleum residue. Trials on a longer time scale are necessary in the next level of evaluation.