AROMATIZATION OF PROPYLENE OVER HZSM-5: A DESIGN OF EXPERIMENTS (DOE) APPROACH

Aromatization of propylene was performed in a continuous reactor over HZSM-5 catalysts. A full-factorial design of experiments (DOE) methodology identified the effects of temperature (400°–500°C), Si:Al ratio (50–80), propylene feed concentration (8.9–12.5 mol.%), and catalyst amount (0.2–1.0 g) on propylene conversion as well as the yields of benzene, toluene, p-xylene, o-xylene (BTX), and total BTX. The Si:Al ratio and amount of the HZSM-5 catalyst influenced all of the responses, while temperature affected all the responses except the yield of p-xylene. An increase in feed concentration significantly increased the yields of benzene, toluene, and total BTX. An interaction between propylene feed concentration and catalyst amount influenced the yields of benzene, toluene, and total BTX. This interaction indicated that a higher feed concentration promotes aromatization at higher catalyst concentrations. By contrast, the interaction of Si:Al ratio with propylene feed concentration was found significant for p-xylene and o-xylene yields, but not for benzene and toluene, suggesting that xylenes are synthesized on different sites than those for benzene and toluene. These interaction effects demonstrate how the use of DOE can uncover significant information generally missed using traditional experimental strategies.