Commercial fluid cracking catalysts

Commercial fluid cracking catalysts are predominantly particles with diameters ranging from 20 to 100 microns and densities of the order of 1.0 to 1.6 g./cc. (based on geometric volume of particles including pores). Gas velocities of 1 to 2.5 ft./second are ordinarily used in the reaction vessels of fluid cracking units. Within this range, the bulk density of the dense-phase fluidized bed is typically 40 to 60% of the bulk density of the packed static bed. 

The stimulus to create new compositions is to meet several major perceived needed improvements to make PILCs effective commercial fluid cracking catalysts (FCC) ... 

Pillared rectorites are expanded clay minerals with a surface area in the 150-220 mVg range, and thermal and hydrothermal stability similar to that of zeolites with the faujasite structure (1-4). After steaming at 760°C/5h (100% steam, 1 atm), these materials retain their pillared structure, and at microactivity test conditions (MAT) they are as active as commercial fluid cracking catalysts (FCC) for gas oil conversion... 

Steam pre-treatment of fluid cracking catalysts has been conventionally employed to represent the deactivation occurring in a commercial FCC unit. Appropriate steam pre-treatment methods have been developed so that the activity and selectivity of the steam pre-treated catalyst is equivalent to a commercially deactivated catalyst (12). However, a unique steaming method may not be suitable for catalysts of varying compositions (12). Two steaming methods designed to simulate deactivation in a commercial unit of the two types of catalysts used in this work were employed. Super-D was treated for 8 hours at 732 C with a steam pressure of 2 atmospheres. The catalysts containing ZSM-5 were treated for 12 hours at 827°C with a steam partial pressure of 0.2 atmosphere. 

DFCC systems appear to have the necessary metals tolerance to process residual oils and the abundant, cheaper, but heavily vanadium-contaminated, Venezuelan and Mexican crudes (66). Therefore, the dual function fluid cracking catalyst (DFCC) concept could lead to the generation of important catalysts for U.S. refineries should Middle East politics cause another sudden escalation in crude oil prices and availability. The concept is practical and easily implementable and it may offer a cost advantage over conventional commercial cracking catalysts (66). 

Porous ceramic or micrometallic filters are very effective for recovering entrained fines from gas streams (228,252). Multiple installations are required because it is necessary to blow back each filter element periodically to dislodge the catalyst cake that builds up on the surface and leads to increased pressure drop. Filters have been used for catalyst recovery in other fluid-catalyst processes where high cost or other considerations justify extraordinary measures to minimize catalyst losses. However, this expedient has not been employed in commercial fluid cracking units because losses are readily controlled to a reasonable level by simpler means. In fact, intentional discard of catalyst is often practiced, in addition to normal losses, in order to maintain catalyst quality at a high level by permitting increased additions of fresh catalyst. 

Vanadium, while not the only contributor to fluid cracking catalyst (FCC) deactivation, frequently dictates the amount of fresh catalyst added to the FCC unit to mmntain activity. Improvements have been made to both zeolites and matrices to minimize the effect of vanadium [1]. Another method of protecting the catalyst from vanadium deactivation is to use traps that prevent the vanadium from contacting the catalyst in the first place. Vanadium traps have frequently shown more promise in laboratory testing than has been realized commercially[2,3]. Sulfur, present in commercial operations, has been known to interfere with previous traps ability to capture vanadium. Recently it has been shown vanadium traps can be designed to perform successfully under commercial conditions. 

A model for the riser reactor of commercial fluid catalytic cracking units (FCCU) and pilot plants is developed This model is for real reactors and feedstocks and for commercial FCC catalysts. It is based on hydrodynamic considerations and on the kinetics of cracking and deactivation. The microkinetic model used has five lumps with eight kinetic constants for cracking and two for the catalyst deactivation. These 10 kinetic constants have to be previously determined in laboratory tests for the feedstock-catalyst considered. The model predicts quite well the product distribution at the riser exit. It allows the study of the effect of several operational parameters and of riser revampings. 

Alumina-promoted fluid catalytic cracking catalysts, commercial viability, 414 Analysis of testing responses definition of sensitivity of result to given variable, 94 problems, 95... 

Commercial production of synthetic silica-alumina catalysts for use in fluid cracking was initiated in 1942. The synthetic catalysts were first manufactured in ground form, but means were later developed for production in MS (micro-spheroidal) form. First shipments of the MS catalyst were made in 1946. The synthetic catalysts contain 10 to 25% alumina. Synthetic silica-magnesia catalyst has also been used commercially in fluid-catalyst units (19,100). Magnesia content is 25 to 35% as MgO (276). 

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