Jocelyn A. Kowalski

Quantitative characterization of mixing processes in rotary calciners

Experiments were conducted to determine the effects of rotational speed, feed rate, and angle of inclination on the mean residence time, hold-up, and axial dispersion coefficient of cylindrical zeolite catalytic pellets in a rotary calciner (kiln). Nonintrusive sampling and analysis techniques were employed to measure the residence time distribution (RTD) of tracer pellets (injected at the feed entrance) both along and at the exit of the calciner. A single-parameter continuum model was applied to the residence time distribution (RTD) data to compute the dispersion coefficient as a function of distance. It was observed that the mean residence time is strongly dependent on axial velocity, hence, inversely related to rotational speed and angle of inclination, and is not a function of feed rate up to 10% fill. Material holdup was observed to be directly related to feed rate, inversely related to rotational speed, and slightly inversely proportional to angle of inclination. The dispersion coefficient was found to be strongly dependent on rotational speed and angle of inclination, but weakly dependent on flow rate.

Mixing dynamics in catalyst impregnation in double-cone blenders

Abstract The mixing of solids was studied in a 10 in. diameter acrylic scaled-down model of a commercial double-cone blender as a method of investigating catalyst impregnation variables. Layers of labeled and unlabeled particles were assembled in specific horizontal and vertical geometries and a Computed Tomography scanner was used to non-destructively image the particle bed in 10 mm slices at 50 mm intervals after different numbers of rotations through the mixing process. Experiments were performed with both 1/16 in. diameter pellets and nominally 100 μm diameter spherical particles in order to study the effect of particle to vessel diameter ratio. These studies showed that for both material sizes (1) axial mixing (perpendicular to the axis of rotation) was essentially complete within 10 to 20 rotations and that the surface was refreshed after a single rotation; (2) radial mixing (along the axis of rotation) was found to be significantly poorer; (3) filling the vessel 80% rather than 50% full resulted in segregation and therefore very poor mixing. All of these results were quantitatively confirmed in experiments in which vacuuming and image analysis were used to quantify the concentration of particles of a given color throughout the granular bed. These results suggest that, in coating operations—such as catalyst impregnation—the liquid spray distribution must reflect the volume distribution of the solid along the rotation axis in order to avoid uneven distribution of the liquid solution caused by slow axial mixing of the granular bed.

Cracking process and ZSM-5 catalyst produced therefor

A process for converting feedstock hydrocarbon compounds to product hydrocarbon compounds having a lower molecular weight than the feedstock hydrocarbon compounds comprises contacting said feedstock at conversion conditions with a catalyst composition comprising a large-pore molecular sieve material and an additive catalyst composition comprising crystalline material having the structure of ZSM-5 and a silica/alumina mole ratio of less than 30, said crystalline material having, as-synthesized, the following formula on an anhydrous basis: (x)M2O: (0.2 to 1.4)R2O:Al2O3: (y)SiO2 wherein x is a number greater than 0.1, M is alkali or alkaline earth metal, R is n-propylamine, and y is a number less than 30, and said additive catalyst composition having an alpha value greater than 30.