Low-cost, micron-sized particles still pose a barrier to their use in thin-film composite mixed-matrix membranes (TFC-MMMs) owing to their poor interfacial contact with the polymer matrix. Also, the particles are too large to be fabricated into the submicron-thick membranes. Herein, we report high-performing, TFC-MMMs based on a CO2-philic comb copolymer, poly (tetrahydrofurfuryl methacrylate)–co–poly (poly (oxyethylene methacrylate)) (PTO), and an irregular, micron-sized, CO2-selective metal-organic framework (MOF), UTSA-16. The PTO comb copolymer matrix exhibited excellent film-forming ability, adhesion properties and showed a good gas separating performance. The PTO comb copolymer also enhanced the dispersibility of UTSA-16 in an environment-friendly solvent mixture (i.e., ethanol/water), which did not adversely damage the underlying porous polymeric support. Despite the micron-scale particle size of UTSA-16, PTO copolymer completely covered the surface of UTSA-16 via strong interactions without any deep pore infiltration and exhibited excellent interfacial contact properties. Consequently, defect-free TFC-MMMs with a polymer thickness of 300 nm were successfully prepared on the porous support. The TFC-MMM with 10% filler loading exhibited excellent CO2 permeance and selectivity, i.e., CO2 permeance of 1070 GPU, CO2/N2 selectivity of 41.0, CO2/CH4 selectivity of 17.2, outperforming the TFC-MMMs prepared with commercially available Pebax. All PTO-based MMMs, with the exception of the low content of UTSA-16 (5%), exceeded the gas separation performance required for post-combustion CO2 capture process.
|Journal||Journal of Membrane Science|
|Publication status||Published - 2023 Mar 5|
Bibliographical noteFunding Information:
This work was supported by National Research Foundation of Korea ( NRF ) grants funded by the Korean government ( MSIT ) ( 2020K1A4A7A02095371 , 2017R1D1A1B06028030 ), and by the Norwegian Research Council ( NRC , grant number 267873 ).
The TFC-MMMs were prepared via a facile, scalable solution casting process using a bar-coating method. First, a PTMSP gutter layer was coated onto a polysulfone support. 1.5 wt% PTMSP solution in cyclohexane was cast onto the support membrane using an RK control coater (Model 101, Control RK Print-Coat Instruments Ltd., UK) and then dried at 25 °C. Separately, a tailored amount of UTSA-16 was added to the PTO copolymer solution in an EtOH/DI water mixture (9:1 v/v) under vigorous stirring for 72 h. The total concentration of the solution was fixed at 5 wt % to control the thickness of the selective layer. The weight ratio of UTSA-16 was varied as 5 wt%, 10 wt%, 15 wt%, 20 wt%, and 30 wt%. The MMM solution was then coated onto the PTMSP-coated polysulfone support by using an RK control coater at the speed rate of 1.5 m/min and dried at 40 °C for 24 h. The prepared MMMs were denoted as PTO-UX, where PTO, U and X represented PTHFMA-co-POEM, UTSA-16 and the weight ratio of UTSA-16, respectively. Pebax-based MMMs were also fabricated for comparison with the PTO copolymers. Pebax was dissolved in EtOH/DI water (7:3 v/v) at 70 °C and mixed with UTSA-16 filler at 50 °C to prevent the gelation of the polymer. Except for the dissolution and mixing conditions, all other processes in the fabrication of PTO-U MMMs were kept identical.We first compared the permeability in barrer (1 barrer = 1 × 10−10 cm3 (STP) cm cm−2 s−1 cmHg−1) and selectivity of MMMs to explain the effect of UTSA-16 filler on the gas separation performance. The thickness of MMM on the porous support was fixed at approximately 1 μm to eliminate the effect of layer thickness on the selectivity loss. The permeability data of the membranes was calculated by the product of the measured permeance times the thickness of the dense selective layer. The average thickness of the layer was obtained from 10 different points on the membrane from SEM images. As shown in Fig. 6a and b, both CO2 permeability and selectivity gradually increased with the addition of UTSA-16 to the PTO comb copolymer matrix. The PTO/UTSA-16 with 20% of loading showed the highest CO2 permeability of 298 barrer with a high CO2/N2 selectivity of 47.4, and CO2/CH4 selectivity of 27.5. The addition of UTSA-16 to the PTO comb copolymer increased the CO2 permeability by about 60%. Gas permeated more easily through the pores of the UTSA-16 filler than through the PTO comb copolymer matrix. In particular, the N2 permeability with negligible solubility compared to diffusivity increased with UTSA-16 loading due to the larger surface area and higher porosity of the filler. It indicates that the incorporation of UTSA-16 microparticles contributed to the increase in gas diffusivity. Notably, both CO2/N2 and CO2/CH4 selectivities increased with the incorporation of UTSA-16. Especially, the CO2/CH4 selectivity increased significantly compared to the CO2/N2 selectivity. This is due to the size-sieving effect of UTSA-16 in which the permeation of CH4 having a larger kinetic diameter than N2 is inhibited. In addition, the strong interaction of the K+ active site of UTSA-16 with CO2 could enhance the CO2 solubility selectivity. Collectively, it was confirmed that UTSA-16 plays an important role in enhancing the gas separation performances in both permeability and selectivity. However, both the permeability and selectivity of the PTO/UTSA-16 MMM decreased when an excess was added such as 30 wt%, which is due to the aggregation of UTSA-16 clusters as shown in Fig. S5b. Agglomerated UTSA-16 could not act as an effective transport channel for CO2 gas and the pores of the filler were not sufficiently activated, thus reducing the CO2 permeability at high filler loading.This work was supported by National Research Foundation of Korea (NRF) grants funded by the Korean government (MSIT) (2020K1A4A7A02095371, 2017R1D1A1B06028030), and by the Norwegian Research Council (NRC, grant number 267873).
© 2022 Elsevier B.V.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physical and Theoretical Chemistry
- Filtration and Separation