Aminosilane-functionalized ZIF-8/PEBA mixed matrix membrane for gas separation application

Mixed matrix membranes (MMMs) are hybrid membranes, which have been intensively studied and expected to overcome the drawbacks of both polymeric and inorganic counterparts. In fact, MMMs are still facing great challenges, mostly due to the poor compatibility and adhesion between the fillers and polymer matrix, which considerably reduce MMMs separation performance. To address that issue, the work in this thesis focus on modification methods in order to improve the interfacial adhesion between polymer/fillers in the MMMs and consequently enhance the gas separation efficiency of the MMMs.In the first part of experiment, a non-porous nano-size filler, nanodiamond (ND) was introduced into Pebax copolymer to fabricate the MMM. While being promising filler, the non-porous structure and susceptible to agglomeration of ND are still the issues in gas separation membrane. This chapter proposes an efficient approach as grafting polyethyleneimine (PEI) onto the surface of ND before embedding into the polymer matrix to fabricate the MMMs for CO2/N2 separation. The presence of PEI layer on ND surface significantly improved the interfacial adhesion and dispersion of ND in the Pebax matrix, which were clearly indicated by SEM and FIB-SEM observation. The improvement of interfacial interaction led to the increment in CO2/N2 selectivity compared to the pristine polymer membranes and the non-PEI MMMs as well. The CO2/N2 selectivity of the Pebax/oxND-PEI 0.5 wt.% increased 25% compared to the neat polymer and 43.66% compared to the Pebax/oxND. This chapter has contributed to a simple but effective method to improve the dispersion of the non-porous nanofiller, as well as enhance the gas separation performance of the MMMs.The next chapter studied the effects of different morphologies of filler on the dispersion, interfacial interaction and gas separation performance of the MMMs. Three types of filler morphologies: conventional polyhedral (P-ZIF), nanorod (R-ZIF) and leaf-shaped nanosheet (L-ZIF) were introduced and investigated. The change in morphology can alter the interfacial interaction between polymer and fillers due to the different aspect ratio and surface structure. The L-ZIF and R-ZIF showed better compatibility with the 6FDA-durene polymer matrix compared to the polyhedral ZIF. L-ZIF improved the gas selectivity of CO2/N2 (30.3%), CO2/CH4 (40%) compared to the neat polymer, while the R-ZIF enhance the CO2 permeability (41%) with comparable gas selectivity to the neat polymer. This chapter's results suggested that the nanorod and nanosheet morphologies are more effective in enhancing the interfacial adhesion between polymer/filler and contributed to the guidance in filler morphology selection to achieve improved gas separation performance.In the following chapter, ZIF nanorod (R-ZIF) was further investigated as the filler and was coated with two types of ILs before incorporated in the the 6FDA-durene matrix. In the previous chapter, while showing compatibility with the 6FDA-durene matrix at low filler loading (10 wt.%), R-ZIF still formed aggregates in the membrane at high loading (20 wt.%) which decrease the gas separation performance of the MMMs. The ionic liquid decoration improved the interfacial interaction between R-ZIF and the polymer matrix leading to the enhancement in gas separation performance of the PR/IL MMMs which was intensively investigated by conventional SEM, FTIR, single and mix gas tests. The most significant improvements were the increment of 50% in CO2/CH4 selectivity, while maintaining the CO2 permeability of the 10 wt.% R-ZIF/IL MMM. The improvement in gas separation efficiency of the IL-incorporated MMMs compared to the non-IL MMMs was still observed even at high loading of filler (20 wt.%). The contribution in this part is to confirm that IL-decoration is an effective approach to enhance the interfacial issues and improve the gas separation efficiency of the MMMs.In the last experiment section, micron size polyhedral shape ZIF (P-ZIF) was coated with 3 different ILs and dispersed in 6FDA-durene matrix to prepare the MMMs. As investigated in previous experiment section, P-ZIF exhibited the worst interfacial interaction with the polymer matrix among 3 different morphologies. Thus, it is more challenging to obtain excellent filler/polymer contact between micron-sized P-ZIF and polymer matrix and achieve improvement in gas separation efficiency. Acting as the interfacial binder, IL layer has effectively reduced the non-selective interfacial voids in the MMM and enhanced the polymer/P-ZIF adhesion. The vol.% of interfacial voids of the pristine PZ MMM has been reduced from 1.17% to 0.35%, 0.33% and 0.49% with the PZ/IL1, PZ/IL2 and PZ/IL3 MMM, respectively, leading to a significant improvement in gas separation performance, particularly with the CO2/CH4 separation performance surpassing the 2008 upper bound. Additionally, the PZ/IL MMMs also showed enhancement in gas separation performance for the CO2 - CH4 mix gas (50:50) compared to the non-IL MMMs and the neat polymer membrane. The contribution of this chapter is that it further evidenced the effectiveness of using IL as a interfacial binder to minimize the interfacial defects in MMMs as well as enhance the gas separation performance in both ideal and real conditions.

Mixed matrix membranes with highly dispersed MOF nanoparticles for improved gas separation

A novel analytical method for prediction of gas permeation properties in ternary mixed matrix membranes: Considering an adsorption zone around the particles

Energy-efficient separation of gases has attracted intensive attentions both in research and in industry.nThe separation of gases by membranes is more effective and energy saving with lower productionnand equipment cost than some traditional gas separation methods, such as adsorption or distillation.nHowever, most of the polymeric membranes suffer from the trade-off between mass transport ratesnand separation efficiency. Polymeric membranes show high gas permeation flux but low selectivity,nand vice versa. To overcome such weakness, mixed matrix membranes (MMMs) can providenpromising potentials in high performance gas separation, by combining high separation properties ofnthe inorganic filler with low cost and flexible of the polymers. For filler selection, metal-organicnframeworks (MOFs) are promising adsorbents for gas storage and separation due to their high surfacenarea and porosity, adjustable pore sizes and controllable surface functionality.This thesis is focused on developing novel MOFs-based MMMs for gas separation with highnpermeability and selectivity, as well as good thermal and chemical stability. The studies includenfabrication and optimization of MOFs-based MMMs, designing MMMs with good filler/polymerninteraction and good interfacial morphology, as well as evaluating the permeation and selectivitynperformance of all the prepared membranes. It aims to establish the guidance for the MOF/polymernpair selection and interface manipulation in the fabrication of MMMs to greatly increase thenmembrane permeability and selectivity.In the first part of the experimental chapters, novel MMM with dispersed MOF into polyimide matrixnwere fabricated and the derived membranes are employed for gas separation. MMMs werensynthesized from 2,2-bis(3,4-anhydrodicarboxyphenyl) hexafluoropropane (6FDA) and 4,4(-diaminodiphenyl ether (oxydianiline, ODA) into which were incorporated Cd-6F MOF filler. Cd-6Fnwas synthesized by using 4,4p-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) as the organicnlinker which is also one of the monomers in the 6FDA-ODA synthesis. A specific interfacialninteraction between MOF crystals and polymer chains was innovatively targeted with this specificnMOF/polymer pair by controlling the in-situ 6FDA-ODA polymerization procedure with thenexistence of MOF particles. The enhanced adhesion between filler particles and polymer phase wasnachieved and the improved interfacial interaction between MOF and polymeric matrix was confirmednby FTIR, NMR and XPS. Moreover, it was found that the MOF/polymer interfacial morphologynstrongly affects the gas permeability and selectivity of the membrane. The MMM prepared by in-situnpolymerization displays excellent interfaces between micron-ized Cd-6F crystals and polymernmatrix as well as increased permeability and selectivity compared to pure 6FDA-ODA polymericmembrane. The interaction between MOF crystals and polymeric matrix can be controlled for theninterfacial voids elimination and optimal membrane transport properties.The second part of the experimental chapters focuses on MMMs with MOF/CNT composite. NovelnMMM filler CNT-MIL was synthesized by in-situ growth of NH2-MIL-101(Al) on the externalnsurface of carbon nanotubes (CNT) and applied to fabricate MMMs for CO2/CH4 separation. Extranamino groups and active sites were introduced to the surface of CNT. Compared to pure polymericnmembrane, MMMs containing synthesized MOF/CNT composite displayed significantly increasednCO2 permeance (up to 150%) and selectivity (up to 37.5%). The separation performance of derivednMMMs clearly transcends the 1991 upper bound and being on the 2008 upper bound for polymericnmembrane performance. MMMs for efficient C3H6/C3H8 separation were fabricated by embeddingnZIF-8/CNT composite into 6FDA-durene polymer matrix. The volume of filler and voids in thenpolymeric matrix as well as the distribution of the fillers and their contact with the polymeric matrixnwere quantitatively evaluated by using the tomographic focused ion beam scanning electronnmicroscopy (FIB-SEM). The dispersion of ZIF-8 in 6FDA-durene polymer was enhanced by growthnof ZIF-8 on the CNT surfaces. Meanwhile, good adhesion between the synthesized MOF/CNT fillersnand polymer matrix was observed, only 0.086% voids volume fraction is determined, even at a highnfiller loading. The improved ZIF-8 dispersion and filler/polymer interface lead to the efficient C3H6separation in MMMs. MMMs containing synthesized MOF/CNT composite displayed significantlynincreased C3H6 permeability (up to 105%) and selectivity (up to 96%) compare to pure 6FDA-durenenmembrane.The third part of the experimental chapters focuses on elimination of interfacial voids bynincorporating ionic liquid (IL) as the MOFs/polymer interfacial binder into MMM. Thin layer of ILnhas been fabricated on CuBTC fillers for MMMs fabrication. With the aid of ionic liquid, theninterfacial voids of the CuBTC-IL MMM was significantly reduced due to the favourable MOF/ILnand IL/polymer adhesion, thus improving CO2 selectivity compare to pure polymer membrane andnMMMs with untreated CuBTC. The performance of 10% CuBTC-IL/6FDA-durene MMM clearlyntranscends the 2008 upper bound for polymer membrane. The strategy of IL decoration method cannprovide an effective way to eliminate interfacial voids and enhance CO2 selectivity and can be appliednin large sized fillers with better gas separation properties.n

Gas sorption has been an underutilized technique for characterizing organic–inorganic hybrid (mixed matrix) membranes. Sorption in these membranes, which are composed of rigid inorganic domains, such as zeolites, dispersed in a polymer matrix, should be approximately additive. Sorption in the neat polymers and zeolites were first measured to demonstrate that sorption in mixed matrix membranes is approximately additive in the absence of other effects. Sorption in mixed matrix membranes was demonstrated to be additive. This extends to cases where sorption in one or both phases of the mixed matrix membrane is affected by an outside contaminant. For example, zeolite 4A is extremely hydrophilic and easily affected by contaminants from processing or from the test gases. Zeolite 4A encapsulated within a polymer matrix can still be affected by these same components, and this causes sorption lower than predicted based on that in unaffected polymers and sieves. This sorption analysis has proven to be very important in understanding the permeabilities and selectivities of mixed matrix membranes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4053–4059, 2007

Spherical MgO nanoparticles and Flake-like clay minerals modified with polyaniline (PAni) are applied in Matrimid in order to fabricate mixed matrix membranes (MMMs) having improved gas separation performance. The CO2 permeability, CO2/CH4 selectivity and CO2-induced plasticization pressure of MMMs are assessed at 4-30 bar feed pressure. The chemical structure, morphology and thermal properties of MMMs are analyzed by Fourier transform infrared equipped with attenuated total reflection (FTIR-ATR), X-ray diffraction, field emission scanning electron microscopy (FESEM) and differential scanning calorimetry/thermogravimetric analyses. Crater-like morphology is seen for MMMs by FESEM tests Physical interaction of Matrimid with MgO and PAni, confirmed by FTIR-ATR, helps better distribution of both the fillers in the polymer matrix. Mechanistical analysis of gas sorption and diffusion terms reveals that PAni/clay (PC) enhances gas permeability by controlling diffusivity paths, while MgO nanoparticles improves both gas solubility and diffusivity. The permeability tests reveal that the sample PC5M5 with 5 wt% PC and 5 wt% MgO, has the best gas separation properties. High pressure tests reveal that this sample can enhance plasticization pressure and CO2 permeability as well by 76% and 200%, respectively; resulting in 425% enhancement in MMMs capacity in natural gas sweetening.

Construction of Ag@ZIF-8/PVDF mixed-matrix ultrafiltration membranes with high separation performance for dye from high-salinity wastewater by microemulsion coupling with blending

Mixed matrix membranes comprising of polysulfone and microporous Bio-MOF-1: Preparation and gas separation properties

The Lifshitz-van der Waals acid-base theory assisted fabrication of MFI-containing mixed matrix membranes for gas separations

Deep eutectic solvent functionalized mesoporous silica SBA-15 based mixed matrix polymeric membranes for mitigation of CO2 (Extended Version)

Sealing Tröger base/ZIF-8 mixed matrix membranes defects for improved gas separation performance

In-situ glass transition of ZIF-62 based mixed matrix membranes for enhancing H2 fast separation

The fabrication of mixed matrix membranes (MMMs) has been regarded as an effective and economic approach to enhance the gas permeability and selectivity properties of conventional polymeric membranes for gas separation applications. However, the poor compatibility between polymeric matrix and inorganic filler in MMMs could lead to the generation of interfacial defects resulting in reduced gas selectivity. In this work, with the aim of studying the effect of particle size and pore structure of the filler on the performance of the resultant MMMs, nano/micro sized spherical mesoporous silicas with 2D/3D pore structure (MCM-41 and MCM-48) were synthesized and selected as fillers for the preparation of polydimethylsiloxane (PDMS)-based MMMs. The separation properties of the membranes prepared were characterized by permeability measurements for nitrogen and organic vapors (C3H6 and n-C4H10). Compared with microsized particles, nanosized fillers have better dispersion in the polymer matrix which could minimize the formation of non-selective microvoids around the particles, leading to higher vapor/N2 ideal selectivities of the MMMs, even at the high loading (15 wt%). Moreover, due to the conventional random packing orientation of the particles in the polymer, vapor permeation was severely hindered in the MMMs fabricated from mesoporous silica with 2D pore channels. The interface morphologies and gas diffusion paths in the MMMs have also been proposed. With an optimum loading of nanosized MCM-48 (3D pore structure), the vapor permeabilities and vapor/N2 ideal selectivities of the MMMs were shown to increase simultaneously, compared with the neat polymer membrane.

In this paper, a novel comprehensive permeation model for mixed matrix membranes (MMMs) is introduced. This model shows the importance of understanding and developing a more reliable model for the permeation behavior of MMMs containing porous filler nanoparticles. A new method is established to provide a more precise/large‐scale three‐dimensional MMMs geometry. The required number of spherical porous fillers in random/nonuniform positions in the polymer matrix is calculated. Interfacial equilibrium constant (K) at the polymer/filler interfaces was adjusted as the concentration ratio of the diffusing penetrants (C2 and C1) at the interface, respectively. In this case, the K values are changed by varying the intended gaseous concentration due to their permeation through the MMM. Hence, its effect on penetrants effective diffusion coefficient was examined. Then, the obtained results were evaluated with similar experimental data, which showed much consistency. Therefore, the accurate calculation method for MMMs permeability was governed for the entire range of the operating pressures in MMMs. The results showed that the permeability of MMMs increases with increasing filler particle size. On the other hand, variations that occur in the MMM permeability at various particle size were much more distinct at higher loadings. Moreover, some well‐known analytical permeation models were used to compare and validate the model's permeability results. It can be concluded that this model provides a method for more precise and realistic design of MMMs as well as to better construe the large number of related experimental data. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Carbon dioxide (CO2) generally exists as the main impurity in natural gas, whose main component is methane. The presence of CO2 reduces the energy content of natural gas and also causes the corrosion of pipelines. To prevent such problems, natural gas must contain a small concentration of CO2 (less than 2% by weight). Membrane technology is an attractive separation method that has been widely studied due to its advantages such as high efficiency, low operating costs, and low energy requirements. However, in the last decade, Mixed Matrix Membranes (MMMs) have attracted the attention of many researchers due to their suitable capabilities in separating polar from non-polar gases. In this research, a new MMMs was obtained by adding imidazole zeolite nanoparticle (ZIF-8) to the poly methyl pentene (PMP) polymer matrix. The polymer part of this membrane can provide high permeability and suitable mechanical and thermal stability. In addition, ZIF-8 particles enhance CO2 separation by offering high CO2 adsorption capacity and molecular sieving, improving selectivity. The gas permeability test was performed on pure and mixed matrix membranes at 30 ℃ and pressures of 2, 6 and 10 bar. In addition, the fabricated membranes were evaluated by FESEM, FTIR-ATR, BET, DMA and TGA tests. The results indicated that in the MMMs containing 30 wt% of nanoparticles in the polymer, the permeability of CO2 gas improved by more than 180% and reached about 278.95 barrer, compared to the pure polymer membrane at a pressure of 10 bar. Moreover, the selectivity of CO₂/CH₄ and CO₂/H₂ increased by 142% and 155%, respectively, primarily due to the preferential sorption of CO₂ over H₂ and CH₄ facilitated by ZIF-8 particles.