Solvent resistant integrally skinned asymmetric polyimide nanofiltration membrane based on thermal treatment for the efficient separation and concentration of spiramycin

The isolation of spiramycin (SPM), a macrolide antibiotic with potent activity against gram-positive bacteria and intracellular pathogens, is critical for pharmaceutical applications and antimicrobial research. As emerging antibiotic resistance underscores the need for effective therapeutics, efficient extraction and purification of SPM from fermentation broths remain essential to ensure its availability for clinical use, industrial production, and structural derivatization. Compared with the traditional separation processes, membrane process has attracted extensive attention owing to its low cost, high separation efficiency, and energy savings in the traditional medicine industry. A novel soluble polyimide (PI) material with flexible branches and imide rings was synthesized based on molecular structure design. Using the homemade polymer material, a novel recyclable, acid-alkali resistant and solvent resistant PI nanofiltration (NF) membrane was fabricated for SPM extraction. The membrane exhibited optimal performance at 20 wt% solid content, and the effects of pressure, flow rate, concentration, and temperature on its separation performance were investigated. The rejection rate of SPM was >91 % and the permeance of butyl acetate reached 21 L/(m 2 . h), respectively. The permeances of rose Bengal in methanol, acetone, and isopropyl alcohol were 38, 48, and 10 L/(m 2 . h), with separation performances of 92.0 %, 92.3 %, and 92.4 %, respectively. Moreover, the enhanced stability with a permeance of 21 L/(m 2 . h) and rejection of >91 % for SPM was maintained after five days of long-term practical operation. The obtained PI NF membrane is prospective for improving traditional antibiotic extraction and advancing nanofiltration membrane in the pharmaceutical system.