Development of palygorskite-SO42 −/ZnAl2O4 composites as a novel solid acid catalyst for the esterification of acetic acid with n-butanol

A novel series of palygorskite-SO42 −/ZnAl2O4 (PAL-S/Z) composites were simply synthesized by loading ZnAl2O4 on raw clay minerals of palygorskite (PAL) for acid catalysis of acetic acid and n-butanol. The prepared PAL-S/Z composites were characterized by means of X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and thermogravimetric analysis (TG). The experimental results indicated that the support of PAL played a significant role in the good dispersion of ZnAl2O4 active components and consequently improved the catalytic performance of PAL-S/Z composites. Compared with SO42 −/ZnAl2O4 (S/Z), PAL-S/Z composites showed the higher catalytic activities with above 98% conversion of acetic acid in the esterification of acetic acid with n-butanol. Meanwhile, the structures and the catalytic performance of PAL-S/Z composites were significantly affected by PAL/ZnAl2O4 ratio. The optimal PAL/ZnAl2O4 ratio was 1:1 and PAL-S/Z (1:1) exhibited 98.7% conversion of acetic acid under the optimum synthesis conditions and reaction conditions. Particularly, PAL-S/Z (1:1) showed a better reusability, which could remain above 85% conversion of acetic acid even after being used for seven times in the esterification of acetic acid with n-butanol.