Studies On The Alkylation Of Benzene With Long Chain Alkene Over Modified WO₃/ZrO₂

The alkylation of benzene with long chain alkenes is performed in the manufacture of linear alkylbenzene (LAB), an important intermediate used in the production of biodegradable surfactant. Nowadays, LAB is industrially produced by the alkylation technology with HF or AlCl₃ as catalysts, which has caused a series of problems such as environment pollution, equipment corrosion and products separation. So, it is very important to develop the solid acid, which is friendly to environment and easily regenerated. WO₃/ZrO₂ has strong acidity. As solid acid catalyst, WO₃/ZrO₂ has many advantages over liquid acid catalyst. It is non-corrosive, environmentally benign and easily to separate. At the same time, it has stable nature in oxidizing and reducing environments, even at high reaction temperature. But because of its intensive acidity, it easily cause alkenes to polymerize and coke on surface of catalyst. Therefore, it is much significant to use alkali or alkaline earth metals to modify WO₃/ZrO₂ so as to prepare more proper catalyst in the alkylation of benzene with long chain alkenes. In this thesis, a series of WO₃/ZrO₂ modified by alkali or alkaline earth metals, such as K, Na, Ca, Mg, Sr, were firstly prepared via impregnation. The structural and acidic features of samples have been characterized by means of X-ray powder (XRD), NH₃-temperature-programmed desorption (NH₃-TPD), IR spectra of adsorbed pyridine(FT-IR), N₂ adsorption (BET). Their catalytic activities were measured by alkylation of benzene with 1-dodecene as model reaction in a slurry reactor under atmospheric pressure and fixed bed reactor. Results showed that ZrO₂ in the WO₃/ZrO₂ samples mainly existed in tetragonal phase. WO3 phase on the WO₃/ZrO₂ surface can be observed when W loading exceeded 12.5wt%. In alkali or alkaline earth metals doped on WO₃/ZrO₂ samples, tetragonal ZrO₂ content decreased, and monoclinic ZrO₂ content increased. NH₃-TPD and FT-IR results show that tungstated zirconia doped by alkali or alkaline earth metals decreased acid strength and the total amounts of acid sites. At the same time, it decreases Lewis (L) acid site. The catalyst preparation conditions have great effects on the activity in reaction of benzene with 1-dodecene. With the increase of W loading and calcination temperaure, the activity of WO3/ZrO2 increased firstly and then decreased. WO3/ZrO2 with W loading of 10.0wt%, calcined in 800oC had maximum activity. In comparison to WO3/ZrO2, WO3/ZrO2 doped with 0.01wt% alkali or 0.05wt% alkaline earth metals can improve the activity and stability of the catalysts. The stability of WO3/ZrO2 with 0.05wt% Sr was studied in fixed bed reactor. Reaction conditions are as follow: reaction temperature 85oC, benzene/1-dodecene mole ratio 12.5, VSHV 1 h-1. The results showed that the doped WO3/ZrO2 solid acid catalysts with suitable K or Sr content exhibits much higher catalytic activity, and stability than WO3/ZrO2 in the alkylation of benzene with 1-dodecene at reaction temperature of 85°C, with the 1-dodecene conversion of nearly 99%, 2-LAB selectivity of 45.7% and more than 110h stability. In addition, WO3/ZrO2 catalyst was studied in the alkylation of benzene with 1-hexene. Result showed that with the increase of W loading and calcination temperaure, the activity of WO3/ZrO2 increased firstly and then decreased. WO3/ZrO2 with W loading of 10.0wt%, calcined in 800oC had maximum activity. In comparison to WO3/ZrO2, WO3/ZrO2 doped by 0.01wt% K or 0.05wt% Sr improved the activity and stability of the catalysts.