Effects of silica nanoparticle addition and PDMS coating on membrane performance and stability in the extraction of aromatic amines

Abstract

This study investigates novel strategies to improve membrane performance and stability in the extraction of aromatic amines for chiral amine production. The effects of silica nanoparticle addition and polydimethylsiloxane (PDMS) coating were explored, with a focus on the selective extraction of $\alpha$-methylbenzylamine (MBA) and 1-methyl-3-phenylpropylamine (MPPA) from isopropyl amine (IPA). This work introduces a comparative analysis between open and tight membrane extraction (ME) systems, with and without the ionic liquid (IL) [P_6,6,6,14][N(Tf)₂]. The results reveal that PDMS creates a uniform and dense coating, particularly on PTFE and PVDF supports, while silica nanoparticle coatings were less stable, retaining only 50 % of nanoparticles after ME testing. A PDMS-coated PTFE membrane achieved significantly higher solute fluxes of 1.12 ± 0.01, 1.66 ± 0.02, and 0.36 ± 0.08 g/(m²h) for MBA, MPPA, and IPA, respectively, compared to an IL-wetted PTFE membrane, which was found to have fluxes of 0.60 ± 0.06, 1.01 ± 0.04, and 0.33 ± 0.10 g/(m²h) for the same solutes. A reduction in the pore size of the PTFE support further increased the fluxes to 1.74 ± 0.28, 2.75 ± 0.25, and 0.45 ± 0.08 g/(m²h) for MBA, MPPA, and IPA, respectively, achieving selectivity values of 3.83 ± 0.65 for MBA/IPA and 6.24 ± 0.88 for MPPA/IPA. Although IL impregnation marginally improved selectivity, it caused a significant reduction in solute fluxes. The PDMS coating retained 92.1 % of its mass after 24 h, while the IL retained 87.2 % over the same period. Compared to the tested IL, which presents safety concerns due to its flammability and corrosiveness, PDMS coatings provide a safer and more environmentally friendly alternative, as PDMS is non-toxic and does not bioaccumulate. These findings underscore the superior performance and environmental benefits of novel PDMS-coated membranes in tight ME setups compared to IL-based open ME systems.