DEACTIVATION OF FIXED-BED NICKEL HYDROGENATION CATALYSTS BY SULFUR

A series of fixed-bed nickel hydrogenation catalysts was tested in the dearomatization of hydrocarbon solvents. The mechanism of catalyst de activation by aromatic sulfur compounds was studied in high-pressure m icro-flow equipment by variation of the experimental conditions and th e sulfur content of the feed. It is concluded that catalyst deactivati on proceeds under mild but realistic conditions through formation of a surface sulfide which blocks the active surface. The rate of the disa ppearance of the active sites is a first-order process with rate const ant 1.0 x 10(-3) (ppm S)(-1) h(-1). Under more severe conditions, more sulfide layers are formed, but bulk Ni3S2 was not observed even after full deactivation of the catalysts. The poisoning of the active sites in the latter case is no longer a first-order process. Consequently, under the circumstances investigated, the sulfur resistance of nickel catalysts is determined by the nickel surface area per unit weight of catalyst.