Improving the physicochemical properties of Y zeolite for catalytic cracking of heavy oil via sequential steam-alkali-acid treatments

In this study, modified Y zeolite with high catalytic activity and long lifetime was successfully prepared using sequential steam-alkali-acid treatments. Different alkali agents (NaOH, Na₂CO₃ and CaCO₃) with various concentrations were used in order to improve the catalytic performance of the synthesized Y zeolite in heavy oil conversion process. The physicochemical properties of the prepared samples were investigated using XRD, FESEM, EDX, solid-state²⁹Si and ²⁷Al NMR, BET, XRF, ICP, FTIR, and NH₃-TPD techniques. In addition, the properties of the deposited coke on the used catalysts were studied by FTIR and TGA-DTA techniques. Al extraction via steam treatment created Si-rich regions in the Y zeolite samples. Then, the Si elements were easily extracted from these Si-rich regions by using alkali treatment. In addition, acid washing with weak EDTA solution resulted in removal of extracted elements from the zeolite structure and pore opening after steam and alkali treatments. Combination of these treatments stimulated mesopores formation and improvement in textural properties for the Y zeolite samples. Structural and textural properties of Y zeolite were found to be preserved after sequential treatments. Catalytic performance of the prepared catalysts was investigated for the heavy oil catalytic cracking process in a fixed bed reactor. Regardless of the type of alkali agent used for sequential treatments, the heavy oil conversion and gasoline selectivity were strongly improved for all the modified catalysts in reference to the parent catalyst. The catalytic activity tests showed that sample treated with 1 M CaCO₃ solution could secure a high heavy oil conversion (70%) and high selectivity towards gasoline and kerosene (45%). Furthermore, modification with CaCO₃ inhibits coke formation significantly and enhanced the catalytic lifetime.