Abstract:

NH4-βzeolite with hierarchical porous structure was directly prepared in a nearly neutral synthetic systemusing nonionic compound (polyoxyethylene nonyl phenylether) as the mesoporogen and fluoride as a mineralizer. Samples were characterized by powder X-ray diffractometry (PXRD), scanning electron microscopy (SEM), NH3-temprature programmed desorption (NH3-TPD), N2 adsorption/desorption and differential thermogravimetry (DTG). N2 analysis results showed that the synthesized H-(NH4)-βzeolite contained stepwise distributed micro-mesoporous structure. The Barrett-Joyner-Halenda (BJH) method of analyzing the N2 adsorption isothermshowed that the mesopore volume was 0.67 cm3·g-1 and the most probable pore size was about 21.8 nm. This value was higher than that for the conventional H-βzeolite (0.37 cm3·g-1 and 3.8 nm). The large amount of Lewis acid and the moderate amount of Bronsted acid in the H-(NH4)-β zeolite was examined by means of Pyridine-IR spectroscopy. Compared to conventional H-βzeolite, the conversion in the catalytic cracking reaction of mixed C4 hydrocarbons using this H-(NH4)-βzeolite was improved by 15%. Yields for the olefins (ethene and propene) and aromatic hydrocarbons (benzene and toluene) increased by 10%and 3%, respectively.

Key words: NH4-βzeolite, Hierarchical porous structure, C4 alkane mixture, Catalytic cracking, Fluoride mineralizer