Properties of Zeolite-based Composite Catalysts and Their Application to Catalytic Naphtha-cracking Process

A catalytic naphtha-cracking process using fixed-bed-type reactor for on-purpose propylene production has been developed in Chiyoda Corporation. Composite catalysts, consisting of MFI-type zeolites containing Fe, Ga and Al species and silicon-oxide binder, were employed for naphtha cracking. The Fe-Ga-Al-MFI zeolites as matrix component, containing each heteroatom at adequate ratio in zeolite framework, exhibited both acid strength suitable for cracking and dehydrogenation activity to alkenes, resulting in high selectivity to light olefins by suppressing aromatics formation in naphtha cracking. Moreover, the unique acidity of zeolite species was maintained in the molded form for industrial use as well as enhancement of its mechanical strength, due to the combination with silicon-oxide as a binder. The zeolite-based composite thus converted light hydrocarbons into propylene selectively and kept catalytic performance stably for long time, being applicable to fixed-bed operation, due to its high resistance to coke formation. Furthermore, the present catalytic cracking saves thermal energy required in reaction unit because cracking reactions proceed in the absence of steam at much lower temperatures than conventional thermal cracking process, which makes it possible to reduce total amount of naphtha feedstock by ca. 15%, compared to existing naphtha crackers. In the present paper, excellent properties of the developed zeolite-based catalysts and catalytic cracking of naphtha over the present zeolites are described from the viewpoints of catalytic chemistry and process engineering.