Boosted selectivity toward high glycerol tertiary butyl ethers by microwave-assisted sulfonic acid-functionalization of SBA-15 and beta zeolite

We report for the first time the post-synthesis sulfonic acid-functionalization of commercial beta zeolite in one step, by conventional heating as well as with microwaves, and the introduction of higher amounts of sulfonic acid groups in SBA-15 with microwaves. In beta zeolite, dealumination occurred due to the acidic medium used during sulfonation that favored the generation of new silanols groups, which in turn reacted with the organosulfonating agent resulting in the incorporation of the sulfonic acid groups. Microwave-assisted sulfonated catalysts showed higher selectivity toward di- and triethers of glycerol (83–91%) than those sulfonated by conventional heating and much more than a commercial acid macroporous resin type Amberlyst (35%) after 4 h of reaction. It is remarkable the high selectivity to the bulkier triether achieved with functionalized beta samples (32–36%) demonstrating that microporosity is not a barrier for the formation of triether when having appropriate amount and strength of Brønsted acidity.