Structure–Activity Relationships Governing Light Olefin Production during Direct Catalytic Cracking of Hydrocarbon Gas Condensate and Arabian Crude Oils over Nano-ZSM-5 FCC Catalysts

Abstract The direct catalytic cracking of crude oil represents a promising strategy for increasing the production of high-value light olefins while enhancing carbon utilization in integrated crude-to-chemicals processes. In this work, the structure–activity relationships governing light olefin production over fluid catalytic cracking (FCC) catalysts containing nano- and microcrystalline ZSM-5 were systematically investigated using hydrocarbon gas condensate and Arabian crude oils as feedstocks. Nano-ZSM-5 catalysts with different silica-to-alumina ratios were synthesized and incorporated into FCC formulations to evaluate the combined effects of catalyst architecture, acidity, molecular diffusion, feedstock composition, reactor hydrodynamics, and hydrothermal stability on catalytic performance. The catalysts were comprehensively characterized by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), nitrogen physisorption (BET surface area and BJH pore-size distribution), and ammonia temperature-programmed desorption (NH3-TPD) to establish correlations between physicochemical properties and catalytic behavior. The nanocrystalline catalyst possessing an intermediate silica-to-alumina ratio (FCC33) exhibited the highest catalytic performance, producing a propylene yield of 21 wt %, a total light olefin yield of 42 wt %, and the lowest coke formation during hydrocarbon gas condensate cracking. The enhanced performance was attributed to the synergistic interaction between optimized Brønsted acidity, increased external surface accessibility, improved pore connectivity, and shortened intracrystalline diffusion pathways, which promoted rapid β-scission while suppressing hydrogen-transfer reactions and coke precursor formation. Catalytic evaluation using Micro-Activity Test (MAT), Advanced Cracking Evaluation (ACE), and micro-downer unit (MDU) reactors demonstrated that reactor hydrodynamics significantly influence product selectivity, with the MDU providing the closest approximation to industrial FCC operation through its dilute catalyst phase, near plug-flow behavior, and extremely short catalyst–oil contact times. Feedstock composition strongly affected conversion and coke formation, with increasing crude oil aromaticity leading to lower cracking reactivity and higher coke yields. However, the optimized catalyst maintained high light olefin selectivity across the investigated feedstocks owing to its balanced acidity and enhanced molecular transport. Following severe hydrothermal aging at 810 °C for 6 h, the catalyst retained 87% conversion after 100 consecutive reaction–regeneration cycles, demonstrating excellent hydrothermal stability and regeneration durability under FCC-relevant conditions. These results establish that light olefin production during direct catalytic cracking of crude oils is governed by the coupled effects of the catalyst architecture, acidity, diffusion, feedstock composition, reactor hydrodynamics, and catalyst stability. The mechanistic insights developed in this work provide a rational basis for the design of next-generation FCC catalysts for high-severity crude-to-chemical applications.