Abstract
The liquid-phase esterification of acetic acid with n-butanol has been studied over tungsten oxide supported on alumina, silica and silica–alumina containing two different W loadings. They were prepared by the impregnation of precipitated supports and characterized using X-ray diffraction, N2 adsorption, SEM-EDX and NH3-TPD techniques. The effects of esterification conditions including the reaction time and temperature, the acid-to-alcohol mole ratio, the amount of catalyst and the catalyst reusability as well as the effect of reactant pre-adsorption on the reaction conversion were investigated. The best catalytic performance was obtained with WO3 supported on silica-alumina with a silica-to-alumina mole ratio of 0.4 (10W-Si(0.4)Al sample). The activity of the different catalysts ranged as follows (the conversion of acetic acid at 120min reaction time in parenthesis): 10W-Si(0.4)Al (95.5)>10W-Al (86.2)>10W-Si(1.0)Al (82.1)>10W-Si(2.5)Al (79.8)>5W-Al (77.5)>10W-Si (75.9)>5W-Si (70.6). The catalytic activity correlated well with the total number of acid sites determined by NH3-TPD. In all cases the reaction was completely selective to n-butyl acetate. Reactant pre-adsorption experiments suggested that the reaction follows the Langmuir–Hinshelwood mechanism. A good reusability of the 10W-Si(0.4)Al catalyst after three reaction cycles was observed.
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