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.