The effect of aluminum on efficiency of mordenite catalyst for conversion of methanol to olefins

Abstract

Hydrogen mordenite catalysts with silicon to aluminum ratios of 11, 39, 73 and 120 were used in this study. Three methods for preparing the hydrogen mordenite catalysts were compared. A 3-cycle alternation of ammonium exchange and calcinations method provided the catalyst with maximum hydrogen content. To obtain the catalysts having precisely required silicon to aluminum ratios the conditions for zeolite dealumination by acid leaching were systematically studies. It was found that the silicon to aluminum ratios depend strongly on acid concentration, temperature and duration of acid treatment. The catalysts were characterized using XRD, 27Al-NMR, NH3-TPD and AAS techniques. The catalysts were tested for their activities in methanol conversion to olefins. Various parameters including time on stream, temperatures (300-500°C) and Si/Al ratios affect the methanol conversion and product selectivity. For example, using a feed of 20% methanol in nitrogen at a gas hourly space velocity (GHSV) of 2000 h-1, the methanol conversion on mordenite catalyst (silicon to aluminum = 120) at 500 °C is 100%, and only little coke formation content leads to higher selectivity to light olefins and less coke deposition on the catalysts. The catalyst lifetime can be extended by reducing of number of acid sites which importantly affects the degree of coke formation.