# 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)
The 1970s and 1980s saw the advent of co-catalyst systems for emission control and the introduction of small pore zeolites. Zeolite Y is still the major active ingredient in FCC catalysts, but it has undergone many modifications since its introduction to meet the changing needs of the refining industry to produce high-quality FCC catalysts for today's market. [PERSON], who initially patented the synthesis of zeolite Y, used precipitated silica, sodium aluminate, and caustic soda as starting materials [168]. This process required a 24 h aging step at lower temperatures before crystallization could begin. Later, researchers at the Davison Division of W. R. Grace and Co. refined the synthesis by incorporating sodium silicate and seed crystals, eliminating the need for the aging step [169]. Several studies have demonstrated the viability of kaolinite as a starting material for synthesizing microspherical zeolitic materials due to its resistance to attrition, thermal and hydrothermal stability, affordability, and availability [163; 170; 171]. A standard method involves mixing metakacolin (derived from kaolinite), raw kaolinite, sodium silicate, and water, which is followed by spray-drying the mixture before calcination to form the desired fluid microspheres. These microspheres are then mixed with an aqueous NaOH solution to form a slurry, which is stirred continuously during hydrothermal treatment to crystallize into faujasite zeolite. Proper monitoring of the crystallization process minimizes the formation of unwanted B zeolite. The resulting composite material may contain more than 15% faujasite zeolite with a Si/Al ratio greater than four. For instance, [PERSON] et al. [172] and [PERSON] et al. [170] have synthesized and patented catalytic cracking catalysts, including  
Figure 15: Schematic representation of the FCC fractionation system process flow. Figure extracted from [PERSON]. [PERSON] et al. (2023) [165]. Reproduced with the permission of Elsevier. crystalline fujaisite, X, and Y zeolites. In the approach proposed by [PERSON], the complete transformation of the material to zeolite Y is neither achieved nor intended. Instead, the clay undergoes calcination above the high-temperature kaolin exotherm to form an incipient mullite phase, rendering only a portion of the alumina active for zeolite synthesis. Initially, synthesis was performed on extrudates containing both high-temperature-calcined kaolin and metakaolin, typically in the presence of caustic in a mineral oil medium, yielding catalysts suitable for moving bed reactors. Subsequent patents reported by [PERSON] et al. [173] expanded this technology to include spray-dried microspheres and aqueous slurries. In these methods, kaolin is spray-dried into microspheres appropriate for FCC, which are then calcined and treated with caustic to form about 25 to 30 wt% zeolite Y throughout the microsphere. Aging the caustic microsphere slurry at approximately 100\({}^{\circ}\)F for 6 to 12 h precedes crystallization at 180\({}^{\circ}\)F. The resulting slurry filtration produces a disilicate mother liquor. NaY zeolite with a Si/Al ratio of 4.53 was synthesized at 22.6% using this procedure. To enhance the yield of faujasite zeolite, they proposed using a defloculating agent in slurries of hydrated kaolin with higher solids content to aid spray drying. The resulting microspheres were separated into two fractions (10/90 by weight) before calcination and alkali treatment, with calcination temperatures for the 10% and 90% fractions being below and above the clay exotherms, respectively. Mixing the two fractions before treating them with a caustic soda solution resulted in Y zeolite with improved attrition resistance and a higher yield of 52% within a shorter crystallization time. In addition to that, [PERSON] et al. demonstrated that omitting the washing step after filtration allows some mother liquor to remain within the microsphere [170]. The material is then flash-dried and undergoes further treatment to reduce matrix surface area and decrease gas and coke production.