CO2 Separation Performance Research Articles

A review on facilitated transport membranes based on π-complexation for carbon dioxide separation

The emission of CO2 from human activities is the principal reason for global warming. Membrane separation technology has been extensively regarded as a tremendous potential option for mitigating CO2 emissions when utilizing fossil fuels as a major source of energy. As an important group of CO2 separation membranes, the fixed CO2 carrier-facilitated transport membrane guided by π-complexation reactions is a rising research field and has attracted much attention in the last ten years due to its desirable CO2 separation performance in the dry state and high resistance to oxidation. In this review, facilitated transport theories derived from π-complexation reactions are discussed for an in-depth understanding, rational design and tunable fabrication of facilitated transport membranes. According to the different fixation methods of metal ions (CO2 active carrier), polymer electrolyte membranes and mixed matrix membranes are discussed in detail as two strategies for fabricating CO2-facilitated transport membranes. Future perspectives toward π-complexation reaction-facilitated transport membranes are proposed.

Constructing multi-dimensional transport pathways by mixed-dimensional fillers in membranes for efficient CO2 separation

Mixed matrix membranes (MMMs) with mixed-dimensional fillers can take simultaneously advantages of the different-dimensional materials, and they hold the potential in exhibiting excellent CO2 separation performance. In this study, the mixed-dimensional fillers of NiCo-layered double hydroxide-decorated polypyrrole nanotubes (PNT@NiCo-LDH) were synthesized and incorporated into Pebax MH 1657 (Pebax) matrix to fabricate MMMs for efficient CO2 separation. PNT@NiCo-LDH played a vital role in MMMs. PNT@NiCo-LDH can take the advantages of the tubular structure of PNT, the lamellar structure of LDH, the hollow nanocage structure of NiCo-LDH, constructing 1D/2D/3D CO2 transport pathways in MMMs, respectively. Thus, the construction of multi-dimensional (1D/2D/3D) CO2 transport pathways could synergistically improve CO2 separation performance of MMMs. Besides, the CO2-affinity groups (amino groups and hydroxyl groups) and bimetallic sites (Ni and Co) on PNT@NiCo-LDH effectively accelerated CO2 selective transport in MMMs, increasing CO2/CH4 selectivity. Therefore, the as-prepared MMMs exhibited an excellent CO2 separation performance. The Pebax/PNT@NiCo-LDH-5 MMM showed the optimum CO2 permeability of 513 ± 10 Barrer and CO2/CH4 separation factor of 39 ± 0.5. This work implied that the construction of multi-dimensional CO2 pathways by mixed-dimensional fillers were an effective strategy for efficient CO2 separation in MMMs.

Modeling gas separation in flat sheet membrane modules: Impact of flow channel size variation

Flat sheet membranes offer many advantages over other membrane configurations, (e.g. ease of maintenance and low pressure drops) that make them a strong candidate for post-combustion carbon capture. A performance model for a stacked flat sheet membrane module is reported in this work. The model is based on the reported specifications for the Gen 2 Polaris™ module developed by Membrane Technology & Research (MTR) and predicts performance based on solution of the governing momentum and mass balance equations. The model accounts for variability in flow channel heights within the module that can arise during module manufacturing. The model is first verified against similar membrane models. Simulations are then performed over a wide range of conditions to demonstrate how much performance declines as channel height variability increases. As per the performance metrics, the dimensionless feed flow rate processed per unit membrane area (f-curve) shows the greatest decline. The changes in performance are comparable to those that occur with hollow fiber membrane modules that possess similar fiber size variations. Together, the results of this study indicate that flow channel height variation in flat sheet membrane modules can hurt CO2 separation performance, but the impact is minor except at low CO2 retentate compositions with large channel height variation (e.g. a 10% decline in stage cut performance for a mixture with 94% CO2 in the permeate stream and 30% channel height variation). However, high variation has a significant impact on overall membrane area with a 30% increase at 30% variation.

In-situ growth of ZIF-8 nanoparticles in Pebax-2533 for facile preparation of high CO2-selective mixed matrix membranes

In this work, ZIF-8 nanoparticles were introduced into the Pebax-2533 via a novel “in-situ growth” synthesis approach for easy and fast fabrication of the mixed-matrix-membranes (MMMs) with superior CO2 separation performance. The ZIF-8 nanoparticles were grown and formed in the Pebax solution medium by reacting Zn and imidazole via a one-step procedure (without using any sonication in the preparation procedure). The in-situ prepared ZIF-8 particles in Pebax-2533 have suitable dispersion in the matrix and appropriate polymer-filler interfacial compatibility. As ZIF-8 in-situ synthesized, due to the formation of strong filler/polymer interfacial interactions, the crystallinity and Tg of the membrane severely increased, and FFV simultaneously decreased. The in-situ MMMs revealed promising gas separation performance via a synergistic enhancement in the CO2 permeability and selectivity and proved that they have premiere CO2 selectivity than the ex-situ MMMs. For example, the CO2 permeability, and CO2/N2 and CO2/CH4 selectivities enhanced from 57.5 Barrer, 23.4, and 10.6 for the neat Pebax membrane to 73.3 Barrer (28% enhancement), 82 (250%), 32.6 (208%) for the in-situ Pebax/ZIF-8 MMM containing 8 wt% of nano-filler. In the mixed gas experiments, the gas permeabilities were a little lower than the single gas permeabilities, while the selectivities enhanced due to the competitive sorption between the gas molecules, especially for the in-situ MMMs. The in-situ MMM containing 16 wt% of ZIF-8 also surpassed the upper bound-2019. Furthermore, this study indicated the undeniable potential of the in-situ synthesis approach for the fabrication of high CO2 separation performance membranes with a performance stability in the 24 h permeation test for industrial applications, which is available with a snappier and more convenient manufacturing method than the conventional MMMs.

CuO Modified by 7,7,8,8-Tetracyanoquinodimethane and Its Application to CO2 Separation

7,7,8,8-Tetracyanoquinomethane (TCNQ) was added to polyvinylpyrrolidone (PVP)/CuO composites to modify and prevent agglomeration of the particles, and thus the CuO particles were well dispersed to a small size, thereby increasing CO2 solubility and separation performance. When the separation performance of the PVP/CuO/TCNQ composite membrane was measured for CO2/N2 gases, a CO2 separation of about 174 was measured. This improvement in performance was attributed to the fact that TCNQ was applied to PVP and CuO to prevent agglomeration between particles with surface modification. Due to TCNQ, CuO could be dispersed to a small size in PVP; the bonds between chains in PVP weakened; the interaction between molecules weakened; and the free volume increased, as confirmed by FT-IR, TGA, and UV-Vis spectroscopy.

Interfacial Tailoring of Polyether Sulfone-Modified Silica Mixed Matrix Membranes for CO2 Separation.

In this work, in situ polymerization of modified sol-gel silica in a polyether sulfone matrix is presented to control the interfacial defects in organic-inorganic composite membranes. Polyether sulfone polymer and modified silica are used as organic and inorganic components of mixed matrix membranes (MMM). The membranes were prepared with different loadings (2, 4, 6, and 8 wt.%) of modified and unmodified silica. The synthesized membranes were characterized using Field emission electron scanning microscopy, energy dispersive X-ray, Fourier transform infrared spectroscopy, thermogravimetric analyzer, and differential scanning calorimetry. The performance of the membranes was evaluated using a permeation cell set up at a relatively higher-pressure range (5-30 bar). The membranes appear to display ideal morphology with uniform distribution of particles, defect-free structure, and absence of interfacial defects such as voids and particle accumulations. Additionally, the CO2/CH4 selectivity of the membrane increased with the increase in the modified silica content. Further comparison of the performance indicates that PES/modified silica MMMs show a promising feature of commercially attractive membranes. Therefore, tailoring the interfacial morphology of the membrane results in enhanced properties and improved CO2 separation performance.

Constructing solubility-diffusion domain in pebax by hybrid-phase MOFs for efficient separation of carbon dioxide and methane

A MIL-88B-on-UIO-66 (Abbreviation for UIO@MIL) hybrid-phase MOFs with rod-to-octahedral structure was obtained by the epitaxial growth method, and was added to Pebax matrix to develop a series of Pebax/UIO@MIL MMMs for CO2/CH4 separation. In UIO@MIL hybrid-phase MOF, CO2 solubility domain is formed in the core of UIO@MIL due to the abundant Zr–OH on the surface of UIO-66. MIL-88B has large pores and special rod-like structure that can entangled with the Pebax chain and adjust the spacing of the Pebax chain to form CO2 diffusion domains in MMMs. The results show that Pebax/UIO@MIL-4 membrane has the best CO2 separation performance, the CO2 permeability is 379.07 ± 10.00Barrer, and the CO2/CH4 selectivity is 38.1 ± 1.33. Therefore, hybrid-phase MOFs fillers provide a novel idea for the design of excellent MMMs.

Ultrathin polyamide membrane tailored by mono-(6-ethanediamine-6-deoxy)-β-cyclodextrin for CO2 separation

The fabrication of membranes with high CO2 separation performances is an urgent need for clean energy supply and environmental remediation. In this work, the mono-(6-ethanediamine-6-deoxy)-β-cyclodextrin (MEDβCD) fillers are intentionally constructed to tailor the polyamide membranes (MEDβCD/PA) by interfacial polymerization (IP) for CO2 separation. The unique hollow cone structure of MEDβCD alleviates the vigorous IP process, generating a thinner separation layer with larger chain d-spacing. Additionally, the introduction of CO2-philic groups from MEDβCD can facilitate CO2 molecule transport. The fabricated MEDβCD/PA membrane exhibits remarkable increases in CO2 permeance, CO2/H2, CO2/N2, and CO2/CH4 selectivities, which are 39, 17, 11, and 25 times higher than those of the pure PA membrane, respectively. This work provides a straightforward route to fabricate composite membranes tailored by macrocyclic molecules with cone structures and other cavitands for gas separation.

Application of ionic liquids in the mixed matrix membranes for CO2 separation: An overview

Membrane technology is highly promising in CO2 capture and separation process mainly because of its energy-efficiency and environmental friendliness. Mixed matrix membranes (MMMs) combine the excellent gas separation performance of fillers and the processability of polymer matrix, but it is still a challenge to enhance the gas separation performance for practical application. In this review, ionic liquids (ILs)-based MMMs with modified microstructures and improved separation performance are systematically introduced, which mainly due to the adjustability, the role of wetting agents, as well as the high CO2 affinity of ILs. The development of conventional ILs and functionalized ILs for CO2 separation are first briefly presented, following by the advance of ILs/fillers/polymers blended MMMs, ILs@fillers/polymers MMMs, ILs/fillers/PILs MMMs, and MMMs post-treated with ILs for CO2 separation. Meanwhile, the effects of ILs on the interfacial morphology, membranes microstructures and CO2 separation performance of membranes are emphasized. Finally, the understandings of challenges and perspectives of IL-based MMMs are proposed.

Asymmetric oxygen‐functionalized carbon nanotubes dispersed in polysulfone forCO2separation

AbstractCarbon dioxide separation from flue gases is an important challenge to be faced. Membrane processes are a promising alternative to increase technical and economical constraints once the development of materials with superior characteristics are attained. Integrally asymmetric mixed matrix membranes (MMMs) were prepared by dry/wet phase inversion process of polysulfone (PSF) containing oxygen‐functionalized multiwalled carbon nanotubes (MWNT‐O). Fourier transform infrared (FTIR) spectroscopy confirmed the presence of MWNT‐O in MMMs. Thermal gravimetric analysis (TGA) showed that MMMs are stable up to 150°C. Photomicrographs from scanning electron microscopy (SEM) revealed that MMMs consist of an asymmetric structure with a skin layer supported on a sponge‐like substructure. The pore size of the support of MMMs increased with MWNT‐O content from 0.4 to 0.8 wt.% and the thickness of the dense layer decreased. However, when the content of MWNT‐O increased to 1 wt.%, the pore size decreased, and the dense layer increased. Therefore, MMMs changed CO2separation performance. For 1 wt.% MWNT‐O loading compared to the neat polymer, CO2permeance and CO2/N2selectivity was increased from 1.5 to 2.7 GPU, and from 9.5 to 14.3, respectively.

Controlled Covalent Functionalization of ZIF-90 for Selective CO2 Capture & Separation.

Mixed Matrix Membranes (MMM) with enhanced selectivity and permeability are preferred for gas separations. The porous metal-organic frameworks (MOFs) materials incorporated in them play a crucial part in improving the performance of MMM. In this study, Zeolitic imidazolate frameworks (ZIF-90) are selected to fabricate Polyetherimide (PEI) MMMs owing to their lucrative structural and chemical properties. This work reports new controlled post-synthetic modifications of ZIF-90 (50-PSM-ZIF-90) with ethanolamine to control the diffusion and uptake of CO2. Physical and chemical properties of ZIF-90, such as stability and presence of aldehyde functionality in the imidazolate linker, allow for easy modulation of the ZIF-90 pores and window size to tune the gas transport properties across ZIF-90-based membranes. Effects of these materials were investigated on the performance of MMMs and compared with pure PEI membranes. Performance of the MMMs was evaluated in terms of permeability of different gases and selective separation of CO2 and H2 gas. Results presented that the permeability of all membranes was in the following order, i.e., P(H2) > P(CO2) > P(O2) > P(CH4) > P(C2H6) > P(C3H8) > P(N2), demonstrating that kinetic gas diffusion is the predominant gas transport mode in these membranes. Among all the membranes, permeability of pure PEI membrane was highest for all gases due to the uniform porous morphology. The pure PEI membrane showed highest permeability of H2, which is 486.5 Barrer, followed by 49 Barrer for O2, 29 Barrer for N2, 142 Barrer for CO2, 41 Barrer for CH4, 40 Barrer for C2H6 and 39.6 Barrer for C3H8. Results also confirm the superiority of controlled PSM-ZIF-90-PEI membrane over the pure PEI and ZIF-90-PEI membranes in CO2 and H2 separation performance. The 50-PSM-ZIF-90 PEI membrane exhibited a 20% increase in CO2 separation from methane and a 26% increase over nitrogen compared to the ZIF-90-PEI membrane. The 50-PSM-ZIF-90 PEI membrane showed 15% more H2/O2 separation and 9% more H2/CH4 separation than ZIF-90 PEI membrane. Overall, this study represents the role of controlled PSM in enhancing the property of new materials like ZIF and its application in MMMs fabrication to develop a promising approach for the CO2 capture and separation.

Atomic layer deposition modified PIM-1 membranes for improved CO2 separation: A comparative study on the microstructure-performance relationships

The use of atomic layer deposition (ALD) technology has recently been extended to membrane-based gas separation, whereas how the ALD of metal oxides can tailor the membrane microporosity, and the contribution of the interactions between ALD-grown metal oxide clusters and gas molecules to the resultant gas separation performance, remain largely unclear. Here, a comparative study was performed by individually confining three different metal oxides, including Al2O3, ZnO, and TiO2, to the near-surface region of polymers of intrinsic microporosity (PIM-1) membranes in an attempt to clarify the relationships between microstructural properties and CO2 separation performance. Based on experimental characterizations and density functional theory (DFT) calculations, it is suggested that ALD of metal oxides on PIM-1 membranes can not only effectively narrow the micropore sizes, but also enable enhancement of the solubility of CO2 molecules. Meanwhile, gas permeation results revealed that the CO2 permeation behavior through either Al2O3- or ZnO-modified membranes is diffusion-dominated, while that of the TiO2-modified membranes is sorption-dominated, primarily due to the distinct differences in the loading amount of metal oxides and their interaction strength with the CO2 molecules. As a result, the TiO2-modified membranes achieved a significant increase in the CO2 permeability as the ALD cycle numbers increased together with no sacrifice of CO2/N2 and CO2/CH4 selectivities. This study is expected to lend important insight to the development of ALD-modified membranes for efficient CO2 separation.

Kinetics study and performance evaluation of a hybrid choline-glycine/polyethylene glycol/water absorbent for CO2 separation

Thermodynamic and kinetic properties of absorbents are beneficial in evaluating their CO2 separation performance. In this study, the kinetic properties of CO2 in a hybrid choline-glycine/polyethylene glycol/water absorbent, including the liquid-side mass-transfer coefficient, enhancement factor, and reaction rate constant, were systematically determined through experimental measurements and data processing. Furthermore, an index referred to as “absorbility” was proposed to combine the kinetic properties determined in this study with the thermodynamic properties obtained in our previous study to evaluate the CO2 separation performance. Additionally, the regeneration performance of the hybrid absorbent was also conducted. The results show that the performance of the hybrid absorbent (30 wt% [Cho][Gly] + 10 wt% PEG200 + 60 wt% H2O) is comparable to that of aqueous monoethanolamine, and is thus promising for CO2 separation, considering its low regeneration temperature and low environmental impact.

Constructing Dual-Transport Pathways by Incorporating Beaded Nanofillers in Mixed Matrix Membranes for Efficient CO2 Separation.

Mixed matrix membranes (MMMs) have attracted significant attention in the field of CO2 separation because MMMs have potential to overcome an undesirable "trade-off" effect. In this study, the beaded nanofillers of ZIF-8@aminoclay (ZIF-8@AC) were synthesized using an in situ growth method, and they were doped into a Pebax MH 1657 (Pebax) matrix to fabricate MMMs for efficient CO2 separation. The beaded structure was formed by ZIF-8 particles joined together during the process of AC coating on the ZIF-8 surface. ZIF-8@AC played a vital role in the improvement of gas separation performance. It was mainly attributed to the following reasons: First, the inherent micropores of ZIF-8 constructed the internal pathways for gas transport in the beaded nanofillers, benefiting the improvement of gas permeability. Second, the staggered AC layers constructed the external pathways for gas transport in the beaded nanofillers, increasing the tortuosity of gas transport for larger molecules and favoring the improvement of gas selectivity. Therefore, the internal and external pathways of ZIF-8@AC co-constructed the dual-transport pathways for CO2 transport in MMMs. In addition, the abundant amino groups of the beaded nanofillers provided abounding carriers for CO2, facilitating CO2 transport in the dual-transport pathways. Therefore, the CO2 separation performance of Pebax/ZIF-8@AC-1 MMMs was significantly improved. The CO2 permeability and CO2/CH4 separation factor of Pebax/ZIF-8@AC-1-7 MMM were 620 ± 10 Barrer and 40 ± 0.4, which were 2.3 and 1.6 times those of a pure Pebax membrane, respectively. Furthermore, the CO2/CH4 separation performance of Pebax/ZIF-8@AC-1-7 MMM overcame successfully the "trade-off" effect and approached the 2019 upper bound. It is a novel strategy to design a beaded nanofiller doped into MMMs for carbon capture.

Ultra-selective membrane composed of charge-stabilized fixed carrier and amino acid-based ionic liquid mobile carrier for highly efficient carbon capture

Membrane technology has been extensively studied for CO2 capture applications, especially for flue gas sources. In the past decades, facilitated transport membranes (FTMs) have made breakthroughs overcoming the permeance-selectivity trade-off upper bound restricting traditional CO2 separation membranes, but are still facing challenges towards practical applications, including limited performance, such as insufficient CO2/N2 selectivity to achieve 95 % CO2 dry-base purity by one step separation, and long-term stability. Herein, we designed and fabricated a novel FTM structure containing an ionic liquid (1-ethyl-3-methylimidazolium aminoacetate, [Emim][Gly]) as mobile CO2-carrier and a polymeric amine (polyethyleneimine, PEI) as fixed CO2-carrier. The fixed carrier is confined within a carbon nanotube (CNT) framework of 230 nm thickness via electrostatic forces adjusted by a polyelectrolyte (polystyrene sulfonate, PSS), while the mobile carrier diffuses freely within the CNT framework. After optimization of the membrane recipe and spray-coating fabrication procedure, following our previous work, the resulting CNT-PSS-PEI ∼ IL membranes demonstrated an ultra-high CO2/N2 selectivity up to 1,000 with CO2 permeance up to 2,400 GPU (Gas Permeation Unit, 1 GPU = 3.348 × 10−10 mol·s−1·m−2·Pa−1) under vacuum operation condition. Furthermore, one 100-cm2 flat sheet membrane sample was prepared and exhibited one-stage CO2 enrichment from 15 % to 95 % purity (dry-base) for the first time amongst all reported CO2 separation membranes. The membrane retained a stable performance over 50-h operation period under vacuum condition. The extraordinary CO2 separation performance illustrates the great potential of the CNT-PSS-PEI ∼ IL membranes for flue gas carbon capture application.

Functionalized 3D Covalent Organic Frameworks for High‐Performance CO2 Capture and Separation over N2

AbstractCovalent organic frameworks (COFs) are emerging adsorbent materials for CO2 capture and separation due to their tunable pore size, periodic permutation, and chemical thermal stability. Herein, four functionalized 3D COF‐300s (COF‐300‐X, X = –SO3H, –NO2, –OH, and –NH2) for CO2 adsorption and separation are studied by using density functional theory and grand canonical Monte Carlo simulation. The results show that four functionalized COF‐300s could create a feasible environment for CO2 adsorption with high accessible surface area, suitable pore size, and high porosity. The CO2 adsorption capacity in COF‐300s could be significantly improved by functionalization. In comparison, the best performing COF‐300‐SO3H shows a superior CO2 adsorption capacity of 6.23 mmol g−1 and a high CO2/N2 selectivity of 393 at 298 K and 100 kPa. The adsorption heat and interaction analyses demonstrate that the CO2 affinity in COF‐300s is enhanced by the introduction of polar functional groups, which renders great CO2 adsorption and separation performances. The gas distribution shows that the adsorption sites are concentrated near the functional groups and the distribution of CO2 in COF‐300‐SO3H has a characteristic of multilayer adsorptions. This work highlights COF‐300‐SO3H as an outperforming adsorbent candidate for CO2 capture and separation.

Polyvinyl alcohol membrane incorporated with amine-modified silica nanoparticles and ionic liquid for facilitated transport of CO2

The application of polymeric membranes in post-combustion carbon capture is limited by solution-diffusion. In this work, polyvinyl alcohol (PVA) membranes with facilitated transport of carbon dioxide (CO2) were improved by incorporating the fixed carrier, amine-modified silica nanoparticles (SiO2) and the mobile carrier [bmim][Tf2N] ionic liquid. The BET surface area of diethanolamine (DEA)-modified SiO2 nanoparticles decreased from 150.14 m2/g to 22.68 m2/g, but they improved the surface hydrophilicity of PVA membranes more significantly than the unmodified SiO2 nanoparticles due to the existence of secondary amine groups. Fourier transform infrared spectra confirmed the incorporation of secondary amine and anion of IL that can facilitate CO2 permeation. The thermogravimetric analysis also revealed that the thermal stability of PVA membranes was improved by incorporating inorganic nanoparticles and ionic liquid. The thickness of the dense PVA layer coated on polyethersulfone support increased by incorporating SiO2 and DEA-modified SiO2 nanoparticles, as shown by scanning electron microscope images. The positive effects of SiO2 nanoparticles on the CO2 separation performance of PVA membranes were enhanced by reducing the particle size and increasing particle loading. DEA elevated the enhancement through the Zwitterion mechanism. [bmim][Tf2N] IL also improved the CO2 separation performance of PVA membranes. Hence, the PVA membrane containing 2 wt% of DEA-modified SiO2 nanoparticles (15-20 nm) and 0.4 M of [bmim][Tf2N] IL in ethanol attained a CO2 permeance of 3016 GPU and CO2/N2 selectivity of 62.08.

Synthesis of novel Al2O3 nanoparticle organic hybrid materials for enhancing the CO2-separation performance of prepared Al2O3-NOHMs/Pebax mixed matrix membrane

In this study, a novel liquid-like nanoparticle organic hybrid materials (NOHMs) is synthesized, in which Al2O3 was used as core, called as Al2O3-NOHMs, and it has been used for the first time to improve the performance of mixed matrix membranes (MMMs) for CO2 capture. In addition, the Al2O3-NOHMs with core/corona/canopy structure observed by TEM possess unique enthalpy effect and entropy effect, which can break through the trade-off effect of membrane separation process. According to gas separation permeation tests, the Al2O3-NOHMs/Pebax mixed matrix membranes with 2 wt% Al2O3-NOHMs showed higher CO2 permeability of 137.15 Barrer and CO2/N2 selectivity of 77.8 compared with neat Pebax membranes, and surpassed 2008 Robeson upper bound. Hence, this novel NOHMs is a very promising alternative to prepare MMMs for CO2 capture.

Membrane Fabrication for Carbon Dioxide Separation: A Critical Review

AbstractMembrane fabrication methods, mechanisms, and modification of membranes for CO2 separation are discussed. Various types of membrane materials with high CO2 separation performance are summarized. Rapid prototyping can achieve precise control of the thickness of membranes and freely design the spatial structure of membranes, which provides a new development direction for material application and process combination. Hence, a critical comparison of membrane fabrication using different methods can provide a comprehensive overview on the potential of the rapid prototyping technology in membrane fabrication. This is important to demonstrate the prospects of the membrane technology development for CO2 separation.

Developing hybrid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/titanium dioxide/water absorbent for CO2 separation

The development of novel absorbents is essential for improving CO2 separation technology. In this study, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/titanium dioxide/water ([Hmim][NTf2]/TiO2-H2O) was developed to separate CO2, where the thermodynamic and kinetic experiments were conducted, and Henry’s constant and the liquid-side mass-transfer coefficient were determined accordingly. Furthermore, CO2 separation performance in a bubble tower was validated. A previously proposed index named “absorption ability” (AA) was used to predict and compare the experimental results. Additionally, the cost of biogas upgrading (i.e., CO2 removal for biogas purification) using [Hmim][NTf2]/TiO2-H2O was estimated. The results showed that for the developed [Hmim][NTf2]/TiO2-based technology, the average CO2 mass-transfer rate was increased by 20.0% compared with the current commercialized technology, and the contributions from the thermodynamic and kinetic aspects were 2.5% and 17.5%, respectively. The cost of biogas upgrading was 16.6% lower. In addition, AA successfully predicted the performance of CO2 separation technologies, achieving an average relative deviation of 8.1%.