Synthesis of long-term acid-stable zeolite membranes and their potential application to esterification reactions

The effect of synthetic parameters upon pervaporation (PV) separation properties of aluminum-rich ZSM-5 zeolite membranes which were prepared not only using both hydroxide and fluoride anions as mineralizing agents but also using an SDA (structure-directing agent)-free precursor gel was studied in detail. Under the optimized conditions, ZSM-5 membranes obtained were demonstrated to be fairly efficient for the dehydration of a range of organic aqueous solutions. Furthermore, durable tests for acid stability showed that ZSM-5 membranes displayed a reasonably strong acid resistance. Comparative study in terms of acid stability against acetic acid aqueous solution was carried out between MOR- and MFI-type zeolite membranes, both of which were separately fabricated in a mixed-mineralizer system of hydroxide and fluoride ions. To highlight the stabilizing effect of fluoride anions against acid attack, non-fluoride-containing MOR (mordenite) zeolite membrane was complementarily synthesized to compare acid-resistant behavior with fluoride-derived MOR membrane. Finally, the products synthesized were characterized by a variety of techniques such as powder XRD (X-ray diffraction), FE-SEM (field emission-scanning electron microscopy) and ICP-AES (inductively coupled plasma-atomic emission spectrometer) analyses.