James M. Maselli

Vanadium poisoning of cracking catalysts: mechanism of poisoning and design of vanadium tolerant catalyst system

The mechanism of vanadium poisoning of cracking catalysts is described. Experimental results identify the poison precursor as volatile vanadic acid, H3VO4 which is formed under FCC regenerator conditions by the reaction V2O5(s) + 3H2O(v) 2H3VO4(v). The concentration of H3VO4 in a typical regenerator (730 °C, 20% H2O, 2 atm total pressure) is 1–10 ppm. Since H3VO4 is a strong acid analogous to H3PO4, it can destroy the zeolite by hydrolysis of the zeolite SiO2Al2O3 framework. A basic solid with reasonable pore structure should be an effective scavenger. Basic alkaline earth oxides such as MgO or CaO are shown to be effective for vanadium scavenging. Microactivity testing shows excellent activity retention when 20% MgO is blended with cracking catalyst at vanadium loadings of 0.67% and 1.34% V by weight on catalyst. However, the SOx, in the regenerator flue gas can form a sulfate that competes with the formation of the vanadate. The degree of competition will be thermodynamically controlled. Since the formation of the vanadate from the oxide expands the lattice, pore structure effects exist similar to those observed for the reaction of calcium oxide with sulfur oxides.

Preparation and Properties of Fluid Cracking Catalysts for Residual Oil Conversion

Abstract Catalytic cracking of petroleum to produce gasoline began in about 1912. The early pioneering work was carried out by Eugene Houdry [1]. Modern fluid catalytic cracking (FCC) was conceived at Exxon and commercially developed in about 1940 [2] using amorphous catalysts. Fluid catalysts are small spherical particles ranging from 40 to 150 um in diameter with acid sites capable of cracking large petroleum molecules to products boiling in the gasoline range. One advantage of the FCC process is the absence of the diffusion limitations present in conventional gas oil cracking due to the small size of the catalyst particle. Since 1964 virtually all catalysts contain faujasite, a stable, large pore, Y-type zeolite dispersed in a silica/alumina matrix [3]. The catalytic aspects of contemporary FCC processes have been reviewed by Venuto and Habib [4], Gates, Katzer, and Schuit [5], Magee and Blazek [6], and Magee [7]. A more recent update of refinery trends has been made available by Blazek [8].

Effect of support on noble metal catalysts for three-way conversions

Noble metals including small amounts of rhodium (Pt/Rh = 14 approximately 19 weight ratio) supported on silica, alumina and silica-alumina were tested for three-way conversions. Catalysts were evaluated fresh, after in-situ hydrothermal aging at 816/sup 0/C, and after cyclic pulsator aging at 538/sup 0/C approximately 704/sup 0/C. All samples exhibited good three-way conversions when fresh. Overall, the catalysts supported on alumina performed the best based on resistance toward chemical poisons such as Pb, P and S.