Low-temperature synthesis of three-pore system hierarchical ZSM-5 zeolite for converting palm oil to high octane green gasoline

Abstract

Microporous zeolite commonly suffers from a slow diffusion rate due to its restricted micropore channel, especially for bulky molecules. In this case, hierarchical zeolite has emerged as an essential functional material because of its excellence in alleviating the diffusion issue and improving the catalytic performances. In this research, hierarchical ZSM-5 zeolite with a three-interconnected-pore system (3 PS, micro-meso-macro) has been synthesized at a low temperature (90 °C) in the presence of CaCO3 nanoparticles. The low-temperature condition leads to the formation of the highly crystalline ZSM-5 particles with intercrystalline mesopores having a pore size distribution ranging from 3 to 6 nm. Moreover, the resulting zeolites also exhibit void spaces in a macroscale (20 nm–80 nm) created from the removal of CaCO3 nanoparticles. Moreover, the catalytic tests on the catalytic cracking of palm oil demonstrate the superior activity of the trimodal porous ZSM-5 in producing high octane gasoline compared to the ZSM-5 with two pore system (2 PS), and one-pore system (1 PS). A three-interconnected-pore system enhances the accessibility of reactant molecules to and the product molecules out of the active sites within the ZSM-5 crystals. As a result, the 3 PS catalyst produces a remarkable gasoline yield (25–26%) with exceptional aromatic content (>90%) and a research octane number (RON) of 114 with a less amount of cokes deposited during the reaction. Ultimately, the 3 PS catalyst also possesses the highest stability as it can maintain the catalytic performance up to the third cycle.