Methanol dehydration to dimethyl ether using modified clinoptilolite

Clinoptilolite, a natural zeolite from the Semnan region in the West of Iran, has been converted to a catalyst for the methanol dehydration to dimethyl ether process. To produce such a catalyst and to create acidic sites on the latter, the ion-exchange process has been used. In addition, to investigate and optimize the effective factors of the catalyst synthesis process, a L9 Taguchi experimental design method has been implemented. The effects of four factors have been considered: the type of ion-exchange solution (2 levels); ion-exchange solution concentration; calcination temperature and calcination time (the last three factors have been studied in 3 levels). The yield of catalyst (conversion×selectivity) has been chosen as the response of the system. The catalytic behaviour of the produced samples was investigated using a fixed bed reactor (T = 350 ºC, P = 1 atm and WHSV = 4.78 h–1). The results of the statistical design showed that the optimum conditions were: calcination time – 3 h, calcination temperature – 500 ºC, ion-exchange solution concentration – 2M, and ion-exchange solution – ammonium chloride. The optimum catalyst was tested using a fixed bed reactor at 330 ºC, 1 atm and WHSV = 3.8 h–1 resulting in 98.1% conversion and 96.5 % selectivity. In order to investigate the catalyst behaviour under industrial operating conditions, the catalyst was tested in a fixed bed reactor at 300 ºC, 16 atm pressure, and WHSV = 52.5 h–1. The results were 67.02 % conversion and 99.74 % selectivity. Key words: clinoptilolite; dimethyl ether; catalyst; zeolite; Taguchi experimental design 1