# Transforming Petrochemical Processes: Cutting-Edge Advances in Kaolin Catalyst Fabrication
## 7 Kaolin in Petrochemical Catalysis: From Fundamentals to Innovations
### Kaolin-Driven Catalysis in Petrochemical Processes
#### 7.4.1 Fluid Catalytic Cracking (FCC)
Initial attempts to use pure zeolite for catalytic cracking of gas oil were unsuccessful because the high surface area and site density of the zeolite, combined with extended catalyst-oil contact times in early FCC units, led to a product stream with high levels of unwanted secondary reaction products, such as coke and light gases. This overcracking rapidly deactivated the pure zeolite catalyst due to coke formation. Indeed, [PERSON] and [PERSON] [178] discovered that diluting the zeolite in a matrix reduced overcracking and coke poisoning, resulting in a zeolite-containing FCC catalyst that significantly outperformed the previously used amorphous silica-alumina or acidified clay catalysts. Before the development of zeolite-containing FCC catalysts, amorphous FCC catalysts had been the dominant materials for twenty years. Early formulations of zeolite FCC catalysts included rare earth exchanged zeolites (either type X or Y), kaolin clay, and a binder, which was often synthetic silica-alumina or peptidized pseudobehmite [179; 180]. The in situ technology developed by [PERSON] [173] was distinctive because it was binderless; particle hardness was achieved through the thermal treatment of spray-dried clay microspheres before zeolitization. No specific component was added to the spray dryer feed to bind the clay particles. While all three binders exhibited catalytic activity, their selectivity in cracking oil molecules differed. Reactions over these matrices were less selective compared to zeolite, producing more coke and gas and less gasoline. During the 1970s, when gasoline selectivity was crucial and FCC feedstocks were more paraffinic, the matrix cracking activity was seen as a drawback [167]. Adjustments in unit design to capitalize on zeolitic cracking and the increasing zeolite content in catalysts highlighted the need for improved attrition resistance, leading to the mid-1970s introduction of silica sol-based binders. These low-surface area binders were essentially inactive in gas oil cracking but produced much harder catalysts. The use of heavier feeds and the need for increased metal tolerance necessitated the reintroduction of active matrix components into FCC catalysts. Modern FCC catalysts must be extremely hard yet sufficiently porous to crack heavy, large oil molecules into smaller fractions suitable for the fuel oil range or small enough to be processed by the zeolite component. Additionally, matrices must mitigate the effects of contaminant metals, like vanadium and nickel, on gas and coke production and act as soda sinks. They should also synergize with zeolite to maximize transportation fuel yields and minimize coke and light gas formation. In FCC catalyst formulations, clay is predominantly added as an inert densifier to enhance the apparent bulk density (ABD) without affecting the catalyst's activity or selectivity. Kaolin is the preferred clay due to its ability to form high-solids pumpable slurries, its low fresh surface area, and its efficient packing properties attributed to its platelet structure. Typically, manufacturers acquire kaolin as a 60 to 65 wt-% slurry, dispersed with agents such as sodium silicate or tetrasodium pyrophosphate, and use it directly without additional processing [167]. Several key parameters of kaolin are critical for FCC catalyst production. The particle size of the kaolin must be small to ensure that the resultant catalyst has good ABD and attrition resistance. Typically, kaolin particles for FCC use have average sizes (measured by sedigraph) of 0.3 to 0.4 microns, with 90% of particles being approximately 1 micron. The content of iron and titania in the kaolin is also crucial. Elevated levels of these elements can cause undesirable secondary reactions, such as increased gas and coke formation and heightened CO combustion in the regenerator. For FCC catalysts, acceptable levels are typically below 3.0 wt-% for titania and between 0.4 and 0.8 wt-% for iron.