COMPARATIVE-STUDY OF ACTIVITY AND SELECTIVITY OF TRANSITION-METAL SULFIDES IN PARALLEL HYDRODECHLORINATION OF DICHLOROBENZENE AND HYDRODESULFURIZATION OF METHYLTHIOPHENE

Carbon-supported sulfides of V, Cr, Mn, Fe, Co, Ni, Mo, Ru, Rh, Pd, W, Ir, and Pt were compared in parallel hydrodechlorination (HDC) of o-d ichlorobenzene and hydrodesulfurization (I-IDS) of 3-methylthiophene a t 300 degrees C and 1 MPa in a flow reactor. The reference catalyst wa s a commercial hydrotreating Ni-Mo/Al2O3 sulfide catalyst. The work wa s related to disposal of chlorinated organic wastes contaminated by su lfur and to HDC in organic technology. The kinetics were described by means of a parallel consecutive scheme of pseudo first-order reactions . Pt-group metal sulfides exhibited the highest HDS activity but their ranking did not fully correlate with literature results on HDS in the absence of HDC, the maximum activity being at Pd and Pt in the second and third rows, respectively. The Pd sulfide was by far the best HDC catalyst showing about two times higher activity than the reference Ni -Mo sample. The ranking of the sulfides in HDC corresponded with publi shed reports on comparative studies on HDC over metals. The selectivit y to intermediate chlorobenzene was the highest on Pd and the lowest o n Ni-Mo, with maximum conversions to chlorobenzene during the reaction of 64 and 15%, respectively. HDC was faster than HDS over the convent ional Ni-Mo system but the behavior of other sulfides was very heterog eneous. The Ni sample was very selective to HDC (HDC conversion of 90% at HDS conversion of 10%), the Pt and Ir sulfides were very selective to HDS (HDC conversion of 10% at HDS conversion of 90%), and the rate s of HDC and HDS were about the same over the Mo sulfide. The features of the parallel HDC/HDS were discussed in the relation to performance of metal sulfides in other hydrotreating reactions: HDS in the absenc e of chlorine compounds, hydrodearomatization, and hydrodenitrogenatio n. (C) 1997 Academic Press.