Esterification of terephthalic acid with methanol over mesoporous Al-MCM-41 molecular sieves

Esterification of terephthalic acid with methanol was carried out over Al-MCM-41 (Si/Al = 25, 50, 75 and 100) molecular sieves in the vapour phase (with respect to methanol) at 200, 250, 300 and 350 °C, and under autogenous pressure conditions at 200 °C. The vapour phase reaction showed 90% conversion at 300 °C over Al-MCM-41 (100) with 100% selectivity to dimethyl terephthalate (DMT). Under the autogenous pressure, the reaction yielded about 95% DMT over Al-MCM-41 (100). The catalytic role of Al-MCM-41 was established by comparing activity with Si-MCM-41. The effects of various reaction parameters such as temperature, terephthalic acid loading, methanol flow rate, and catalyst weight on conversion were studied and the results discussed.

Graphical abstractAl-MCM-41 molecular sieves with different Si/Al ratios were synthesised and characterised. Esterification of terephthalic acid with methanol was carried out in the vapour phase (with respect to methanol) at 200, 250, 300 and 350 °C, and under autogenous pressure conditions at 200 °C using the above synthesised materials. The reaction was shown to occur by leaching of terephthalic acid by methanol and subsequent adsorption on Bronsted acid sites following Eley–Rideal mechanism. Mono methyl terephthalate was not observed and hence esterification of one carbonyl group might not be influenced by other. Liquid phase reaction under autogenous condition gave higher conversion than vapour phase reaction. The requirement of more acidic sites was established by running the reaction over Al-MCM-41 and Si-MCM-41. Figure optionsDownload full-size imageDownload as PowerPoint slide