Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 23Citation - Scopus: 27Isomerization of Alpha-Pinene Over Acid Treated Natural Zeolite(Taylor and Francis Ltd., 2005) Ünveren, Ercan; Günüz, Gönül; Çakıcıoğlu Özkan, FehimeIn this study, isomerization of α-pinene was studied over several acid-treated natural zeolite catalysts rich in clinoptilolite. Zeolite samples were contacted with HCl at different concentrations at 30°'C or at 60°C for 3 and 24 hours and tested in isomerization reaction of alpha-pinene. The catalysts prepared were characterized by XRD, nitrogen adsorption, and acidity studies. Acidity strength and the distribution of Lewis and Brönsted acid sites of the catalysts were determined, and their catalytic activities in α-pinene isomerization and selectivities to main reaction products, camphene and limonene, were investigated. Acid treatment improved the selectivity of catalyst samples to camphene, decreasing the selectivity to limonene, probably forcing limonene to secondary reactions at high conversions. The kinetics of α-pinene consumption was described by first-order kinetics. Two kinetic models were tested for the reaction mechanism and one model was found to give a good correlation between the theoretical and experimental data. In the models, the key intermediate was the pinylcarbonium ion, which was formed irreversibly from α-pinene. Number and distribution of Lewis and Brönsted acid sites affect the formation of bicyclic and monocyclic products.Article Citation - WoS: 50Citation - Scopus: 54Isomerization of ?-Pinene Over Calcined Natural Zeolites(Elsevier Ltd., 2004) Akpolat, Oğuz; Gündüz, Gönül; Özkan, Fehime; Beşün, NurgünIn this work, isomerization reaction of α-pinene was studied over several heat-treated natural zeolite catalysts, rich in clinoptilolite, from Balýkesir-Bigadic region in Turkey in a batch slurry reactor under nitrogen atmosphere. Zeolite samples were calcined at different temperatures such as 300, 450 and 600°C. All catalysts were tested in the isomerization reaction of α-pinene and were characterised by nitrogen adsorption experiments, IR, and XRD measurements. Acidity strength and the distribution of Lewis and Bronsted acid sites of the samples were determined. Selectivities to main reaction products, camphene and limonene, and reaction kinetics were investigated. Catalytic activity, that is total conversion of α-pinene, of heat-treated samples decreased with increasing calcination temperatures. Selectivity to limonene is dependent on α-pinene conversion at high conversion levels while the selectivity to camphene is not. The formation of heavy products increased with treatment temperature. It was seen that α-pinene consumption could be described by a first-order kinetics.Article Citation - WoS: 39Citation - Scopus: 46Alpha-Pinene Isomerization on Acid-Treated Clays(Elsevier Ltd., 2002) Beşün, Nurgün; Özkan, Fehime; Gündüz, GönülLiquid phase isomerization of α-pinene was studied over a number of differently pre-treated montmorillonite clays. The effects of the acid pre-treatment parameters (acid-to-clay ratio (A/C), water-to-acid ratio (W/A), temperature and pre-treatment time) on the product distribution were investigated. It was observed that the pre-treatment with acid improved the catalytic activity of that catalyst which was activated at 200 °C for 4 h at A/C ratios between 0.2 and 0.4. Alpha-pinene consumption was very small over the catalysts prepared with an A/C ratio of 0.8. Characterization studies that were done by nitrogen and water vapor adsorption experiments and by IR measurements showed that catalysts with high differential pore volumes for pores around 2 nm and homogenous mesopore distributions and with low dealumination degrees were good catalysts for the production of camphene. Catalysts having heterogeneous mesoporosity were found to be the preferable ones for limonene production.