Investigation of the catalytic activities of heterogeneous catalysts prepared by using modified natural zeolite-clinoptilolite in α-pinene isomerization reaction

In this study, the catalytic properties of acid-treated and Fe3+-loaded clinoptilolites, which was taken from Bigadic (Balıkesir,Turkey), were investigated in the liquid-phase isomerization of α-pinene. In the isomerization reaction of α-pinene, main products were camphene and limonene while tricyclene, terpinolene, p-cymene, α- and γ- terpinene were also formed. Camphene is used in the production of fragrance materials, acrylates, terpene-phenol resins and other derivatives. Camphene is also an important intermediate for the synthesis of camphor which finds use in fragrance and pharmaceutical industry. In the first step of this study, clinoptilolite was dealuminated with aqueous solutions of HCl at different concentrations under reflux in different time and temperature. Catalytic activities of prepared catalysts were tested in the isomerization reaction of α-pinene. Formation of camphene increases with increasing of the reaction time and temperature. However, there is no linear increasing with increasing acid concentration. Highest amount of camphene is obtained with 0.1 M HCl acid treated-clinoptilolite at 150°C for 8 hours. After determining the optimum conditions, the effect of the α-pinene/catalyst ratio on product distribution was tested. The increment in the percentage of the camphene formation was observed with increasing ratio of α-pinene/catalyst. Acid treatment improved the selectivity to camphene while decrasing the selectivity to limonene, probably forcing limonene to secondary reactions at high conversions. Fe3+-loaded clinoptilolite catalysts are successfully used in many production process in chemical industry. Therefore, in the second step of the study, natural zeolite was treated for 12 hours with acetylaceton solutions of Fe3+ ion at different concentrations. Iron contents on the exchanged zeolites increased gradually with the increment of Fe3+ concentration in the ion-exchange reaction mixture. Synthesized catalysts are tested by changing the parameters such as temperature, time and α-pinene/catalyst ratio to obtain highest camphene yield. As a result of tests, maximum camphene formation was obtained with % 5 Fe3+-loaded zeolite at 150°C for 8 hours. Zeolite samples used in this study characterized with using the BET, XRD, TGA, FT-IR, piridine adsorption and UV-Vis methods.