A SAPO-5-coated membrane for nanofiltration of tetraalkyl ammonium hydroxide

• A SAPO-5 coated membrane was prepared by a secondary growth method.
• The membrane was applied to nanofiltration of tetraalkyl ammonium hydroxide (TAAH).
• Rejection of TAAH was progressed with the molecular sieving mechanism.
• The membrane could be reused for nanofiltration with backwashing between cycles.

Nanofiltration of tetraalkyl ammonium hydroxide (TAAH) was investigated with a membrane coated with SAPO-5, a silicoaluminophosphate with a 12-member ring channel. The SAPO-5-coated membrane was prepared on an α-alumina support by a secondary growth method. Rejection of TAAH by the SAPO-5-coated membrane increased with the molecular size of the TAAH, because of the molecular sieve mechanism imparted by the SAPO-5 coating. However, the rejection decreased with increasing operational pressure because of concentration polarization near the membrane surface. The SAPO-5-coated membrane could be repeatedly used for nanofiltration, after backwashing with a dilute hydrochloric solution between cycles.