Alkylation of benzene with α-olefins over zirconia supported 12-silicotungstic acid

Abstract

Liquid phase alkylation of benzene to linear alkyl benzene (LAB) with α-olefins has been investigated with 12-silicotungstic acid supported on zirconia (STA/ZrO₂) as the catalyst. Among the catalysts, 15 wt.% STA/ZrO₂ calcined at 750 °C was found to be most active than others in the alkylation reaction. The total amount of acid sites of different STA loaded catalysts were estimated by TPD of NH₃ and 15 wt.% STA/ZrO₂ calcined at 750 °C was found to have the highest acidity and more active in the reaction. The optimization of reaction conditions of alkylation of benzene with 1-dodecene was performed with 15 wt.% STA/ZrO₂ calcined at 750 °C by varying catalyst concentration (1–5 wt.% of reaction mixture); temperature, 373–423 K and benzene:1-dodecene (1-dd) molar ratio, 5–15 in a Parr autoclave under N₂ pressure. Under the optimized reaction conditions, conversion of 1-dodecene (50.8%) gave high selectivity to 2-phenyl dodecane (47.1%) and the remaining 3-, 4-, 5- and 6-phenyldodecanes in 4 h. The reaction was found to be heterogeneously catalyzed and no contribution from homogeneous (leached) STA into the reaction medium.

Introduction

Linear alkyl benzenes (LABs) are important intermediates for synthetic detergents and these are traditionally manufactured in presence of aluminum trichloride or hydrofluoric acid catalysts. Because of the hazardous nature of conventional systems, there is a need to develop solid acid catalysts to replace the existing production methods. Solid acid catalysts such as zeolites [1], [2], [3], [4], [5], [6], [7], clays [8], [9], heteropoly acids [10], [11], [12], [13], [14], fluorided silica-alumina [15], ionic liquids [16], [17], [18], H-ZSM-5, H-ZSM-12, H-Y [19], [20], [21], La-doped Y zeolite [22] and high silica mordenite (HSM) [23] have been widely investigated for the above transformations. Immobilized AlCl₃ over MCM-41 has been used for benzene alkylation with 1-olefins [24]. Already UOP/Petresa has industrialized a process with aluminum–magnesium silicate catalyst for alkylation of benzene with α-olefins [25], [26]. A new catalytic distillation technology for benzene alkylation with α-olefins with suspended catalytic distillation (SCD) column has been developed [27]. Recently, supported tungstophosphoric acid catalyst was used for synthesizing LAB with high activities and with high selectivities to 2-LAB [28], [29].

The present work deals with the alkylation of benzene with 1-dodecene using zirconia supported silicotungstic acid as the catalyst. The reaction was carried out with an aim to maximize 1-dodecene conversion together with the selectivity to 2-phenyldodecane as compared to other isomers like 3-, 4-, (5 + 6)-linear alkyl benzene. The influence of STA loading and catalyst calcination temperature on 1-dodecene conversion was studied. The catalyst with highest activity was used to study various reaction parameters such as temperature, molar ratio and catalyst weight. The catalyst regeneration and heterogeneity of reaction were also examined in the above reaction.