Richard Franklin Wormsbecher

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.

Effect of Ionic Radius of Rare Earth on USY Zeolite in Fluid Catalytic Cracking: Fundamentals and Commercial Application

The ultrastable Y zeolite (USY) in fluid cracking catalyst is commonly stabilized by ion-exchange with rare earth (RE) cations. The RE-exchange provides hydrothermal stability to the zeolite by improving surface area retention, as well as inhibiting dealumination, resulting in greater preservation of acid sites. Though La and Ce are commonly used in fluid catalytic cracking (FCC) catalysts, we have observed that the stability of REUSY catalysts improves as the ionic radius of the RE cation decreases. In this paper, we compare the activity and selectivity of REUSY catalysts, stabilized with La and heavy (Ho, Er, and Yb) rare earth cations, the latter having a smaller ionic radius, due to the well-known phenomenon of lanthanide contraction. The experimental data show that a significant improvement in catalytic activity is achieved when RE elements having a smaller ionic radius are used to make the REUSY catalyst. Yttrium is even more effective than the heavier lanthanides in stabilizing Y-zeolite, leading to higher cracking activity and gasoline selectivity under a variety of deactivation conditions. These benefits of yttrium exchange does not only result from a larger resistance to dealumination, but also to an increase of the catalyst intrinsic cracking activity, which may be explained by changes in the adsorption of hydrocarbons at the active sites. Examples of commercial applications of yttrium-based FCC catalysts are given.

Penta-co-ordinated aluminium in zeolites and aluminosilicates

Solid state 27Al n.m.r. spectroscopy of various aluminosilicates (zeolites, clays, amorphous SiO2–Al2O3) shows that upon thermal or hydrothermal treatment a line appears at ∼30 p.p.m.; the position of this line suggests that penta-co-ordinated Al is present in all these aluminosilicates.

The Structural Elements of Faujasite and their Impact on Cracking Selectivity

The location of alumina in the dealuminated faujasite framework is described. The selectivities of dealuminated and rare earth exchanged faujasite, including selectivities for octane, coke, hydrogen transfer, and isomerization, are shown to depend on the relative amounts of paired and isolated sites present. Pentacoordinated and octahedral nonframework alumina do not contribute to selectivities in cracking. Selectivity and activity is controlled by the framework aluminum sites.

Impact of Zeolite Structure on Entropic-Enthalpic Contributions to Alkane Monomolecular Cracking: An IR Operando Study

The monomolecular cracking rates of propane and n-butane over MFI, CHA, FER and TON zeolites were determined simultaneously with the coverage of active sites at reaction condition using IR operando spectroscopy. This allowed direct determination of adsorption thermodynamics and intrinsic rate parameters. The results show that the zeolite confinement mediates enthalpy-entropy trade-offs only at the adsorbed state, leaving the true activation energy insensitive to the zeolite or alkane structure while the activation entropy was found to increase with the confinement. Hence, relative cracking rates of alkanes within zeolite pores are mostly governed by activation entropy.