Catalytic Oligomerization of ethylene over nano-sized HZSM-5

Abstract

The nano-sized HZSM-5 zeolites with different Si/Al ratios were pretreated, characterized, and tested in ethylene oligomerization performed in a fixed-bed reactor under relatively mild conditions. The effects of catalyst acidity and reaction temperature on the activity, selectivity and stability were investigated, and a possible reaction route of ethylene over acidic sites of nano-sized HZSM-5 catalyst was proposed. In comparison with micro-sized HZSM-5 zeolite, nano-sized HZSM-5 zeolites exhibited higher activity and better resistance to deactivation. Under optimal conditions (T = 275–300 °C, P = 3.0 MPa, WHSV = 1.0 h−1), The average ethylene conversion was 62.5% over the nano-sized HZSM-5 with an Si/Al ratio of 80, while the selectivity to C4+ olefins and α-olefins was 64.3% and 13.3%, respectively. Furthermore, the products of ethylene oligomerization were a complex hydrocarbon mixture due to the acid-catalyzed secondary reactions, for which the distribution of even and odd numbered carbon atoms formed a continuous volcanic shape mainly centered on C6–C10. Furthermore, these tests demonstrate that the activity and selectivity of ethylene oligomerization depend on the operating conditions and the acidity of the catalysts. These results indicate that the Brønsted acid sites may be mainly responsible for secondary reactions and deactivation of the catalyst, whereas the Lewis acid sites may be more advantageous for ethylene oligomerization.