Asymmetric polybenzimidazole membranes with thin selective skin layer containing ZIF-8 for H2/CO2 separation at pre-combustion capture conditions

Wrinkled metal-organic framework thin films with tunable Turing patterns for pliable integration

Flexible integration spurs diverse applications in metal-organic frameworks (MOFs). However, current configurations suffer from the trade-off between MOF loadings and mechanical compliance. We report a wrinkled configuration of MOF thin films. We established an interfacial synthesis confined and controlled by a polymer topcoat and achieved multiple Turing motifs in the wrinkled thin films. These films have complete MOF surface coverage and exhibit strain tolerance up to 53.2%. The enhanced mechanical properties allow film transfer onto various substrates. We obtained membranes with large H2/CO2 selectivity (41.2) and high H2 permeance (8.46 × 103 gas permeation units), showcasing negligible defects after transfer. We also achieved soft humidity sensors on delicate electrodes by avoiding exposure to harsh MOF synthesis conditions. These results highlight the potential of wrinkled MOF thin films for plug-and-play integration.

Field-Scale Testing of a High-Efficiency Membrane Reactor (MR)-Adsorptive Reactor (AR) Process for H2 Generation and Pre-Combustion CO2 Capture

The study objective was to field-validate the technical feasibility of a membrane- and adsorption-enhanced water gas shift reaction process employing a carbon molecular sieve membrane (CMSM)-based membrane reactor (MR) followed by an adsorptive reactor (AR) for pre-combustion CO2 capture. The project was carried out in two different phases. In Phase I, the field-scale experimental MR-AR system was designed and constructed, the membranes, and adsorbents were prepared, and the unit was tested with simulated syngas to validate functionality. In Phase II, the unit was installed at the test site, field-tested using real syngas, and a technoeconomic analysis (TEA) of the technology was completed. All project milestones were met. Specifically, (i) high-performance CMSMs were prepared meeting the target H2 permeance (>1 m3/(m2.hbar) and H2/CO selectivity of >80 at temperatures of up to 300 °C and pressures of up to 25 bar with a <10% performance decline over the testing period; (ii) pelletized adsorbents were prepared for use in relevant conditions (250 °C < T < 450 °C, pressures up to 25 bar) with a working capacity of >2.5 wt.% and an attrition rate of <0.2; (iii) TEA showed that the MR-AR technology met the CO2 capture goals of 95% CO2 purity at a cost of electricity (COE) 30% less than baseline approaches.

Polymeric composite membranes in carbon dioxide capture process: a review

Carbon dioxide (CO₂) emission to the atmosphere is the prime cause of certain environmental issues like global warming and climate change, in the present day scenario. Capturing CO₂ from various stationary industrial emission sources is one of the initial steps to control the aforementioned problems. For this concern, a variety of resources, such as liquid absorbents, solid adsorbents, and membranes, have been utilized for CO₂ capturing from various emission sources. Focused on membrane-based CO₂ capture, polymeric membranes with composite structure (polymeric composite membrane) offer a better performance in CO₂ capturing process than other membranes, due to the composite structure it offers higher gas flux and less material usage, thus facile to use high performed expensive material for membrane fabrication and achieved good efficacy in CO₂ capture. This compressive review delivers the utilization of different polymeric composite membranes in CO₂ capturing applications. Further, the types of polymeric materials used and the different physicochemical modifications of those membrane materials and their CO₂ capturing ability are briefly discussed in the text. In conclusion, the current status and possible perspective ways to improve the CO₂ capture process in industrial CO₂ gas separation applications are described in this review.

Pre-combustion gas separation by ZIF-8-polybenzimidazole mixed matrix membranes in the form of hollow fibres-long-term experimental study

Polybenzimidazole (PBI) is a promising and suitable membrane polymer for the separation of the H₂/CO₂ pre-combustion gas mixture due to its high performance in terms of chemical and thermal stability and intrinsic H₂/CO₂ selectivity. However, there is a lack of long-term separation studies with this polymer, particularly when it is conformed as hollow fibre membrane. This work reports the continuous measurement of the H₂/CO₂ separation properties of PBI hollow fibres, prepared as mixed matrix membranes with metal-organic framework (MOF) ZIF-8 as filler. To enhance the scope of the experimental approach, ZIF-8 was synthesized from the transformation of ZIF-L upon up-scaling the MOF synthesis into a 1 kg batch. The effects of membrane healing with poly(dimethylsiloxane), to avoid cracks and non-selective gaps, and operation conditions (use of sweep gas or not) were also examined at 200°C during approximately 51 days. In these conditions, for all the membrane samples studied, the H₂ permeance was in the 22-47 GPU range corresponding to 22-32 H₂/CO₂ selectivity values. Finally, this work continues our previous report on this type of application (Etxeberria-Benavides et al. 2020 Sep. Purif. Technol. 237, 116347 (doi:10.1016/j.seppur.2019.116347)) with important novelties dealing with the use of ZIF-8 for the mixed matrix membrane coming from a green methodology, the long-term gas separation testing for more than 50 days and the study on the membrane operation under more realistic conditions (e.g. without the use of sweep gas).

Green Preparation of Thin Films of Polybenzimidazole on Flat and Hollow Fiber Supports: Application to Hydrogen Separation

This work shows the preparation of thin films, with thickness from 70 nm to 1 μm, of meta-polybenzimidazole (m-PBI) on polyimide P84 supports. Ethanolic solutions of m-PBI were used to coat flat and hollow fiber supports of asymmetric P84 with m-PBI in a process where the coating and drying was performed at room temperature. A solution of NaOH in EtOH allowed the dissolution of the m-PBI powder, providing the perfect coating solution to build thin films of m-PBI without damaging the polymeric support. It also meant a green alternative, avoiding the use of toxic solvents, such as dimethylacetamide. The resulting membranes have been tested for the separation of H₂ mixtures at high temperature at different setups to allow checking their reproducibility. With 100 nm thickness the membranes showed their best gas separation performance. For flat membranes at 180 °C and 3 bar feed pressure a H₂ permeance of 48.5 GPU was obtained, with respective H₂ /CO₂ and H₂ /N₂ selectivities of 33.3 and 55.8. Besides, the hollow fibers under a feed pressure of 6 bar and tested at the same temperature showed near 90 GPU of H₂ with a H₂ /CO₂ selectivity of 13.5 in the one-fiber module and over 39 GPU of H₂ with a H₂ /CO₂ selectivity of 20.2 in the five-fiber module. Finally, the stability of the membranes was proved for 22 days at 180 °C.

Metal-Organic Frameworks Corset with a Thermosetting Polymer for Improved Molecular-Sieving Property of Mixed-Matrix Membranes

Metal-organic frameworks (MOFs) are promising materials for gas separation membranes. However, the framework flexibility affects their molecular-sieving properties. Herein, we restrict the flexibility of zeolitic imidazolate framework-7 (ZIF-7) by controlling its phase transition in mixed-matrix membranes (MMMs), relying on the so-called "space-confinement effect" of a novel thermosetting polymer, poly 2,2'-(p-oxydiphenyl)-5,5'-bibenzimidazole (OPBI) polymer. Compared with the pure OPBI membrane, the optimized membranes containing 30 wt % ZIF-7 with a narrow-pore (np) phase (ZIF-7-II) exhibited a significant improvement in H₂/CO₂ separation, e.g., the H₂/CO₂ ideal selectivity increased ∼2.8 times, surpassing the state-of-the-art upper bound of polymeric membranes and exhibited excellent stability at increased pressure and temperature (8 bar, 180 °C).

Ultrathin permselective membranes: the latent way for efficient gas separation

Membrane gas separation has attracted the attention of chemical engineers for the selective separation of gases. Among the different types of membranes used, ultrathin membranes are recognized to break the trade-off between selectivity and permeance to provide ultimate separation. Such success has been associated with the ultrathin nature of the selective layer as well as their defect-free structure. These membrane features can be obtained from specific membrane preparation procedures used, in which the intrinsic properties of different nanostructured materials (e.g., polymers, zeolites, covalent-organic frameworks, metal-organic frameworks, and graphene and its derivatives) also play a crucial role. It is likely that such a concept of membranes will be explored in the coming years. Therefore, the goal of this review study is to give the latest insights into the use of ultrathin selective barriers, highlighting and describing the primary membrane preparation protocols applied, such as atomic layer deposition, in situ crystal formation, interfacial polymerization, Langmuir-Blodgett technique, facile filtration process, and gutter layer formation, to mention just a few. For this, the most recent approaches are addressed, with particular emphasis on the most relevant results in separating gas molecules. A brief overview of the fundamentals for the application of the techniques is given. Finally, by reviewing the ongoing development works, the concluding remarks and future trends are also provided.

Pebax® 1041 supported membranes with carbon nanotubes prepared via phase inversion for CO2/N2 separation

This work shows the preparation of Pebax® 1041 films from solutions in DMAc and water-DMAc emulsions as alternatives to those prepared by extrusion that can be found in the literature. These membranes were tested in post-combustion CO2 capture, in the separation of a 15/85 (v/v) CO2/N2 mixture. Self-supported membranes of Pebax® 1041 were prepared by solvent evaporation and phase inversion. The characterization of these films defined the intrinsic properties of this polymer in terms of chemical structure, crystallinity, thermal stability and gas separation performance (a CO2 permeability of 30 Barrer with a CO2/N2 selectivity of 21 at 35 °C and 3 bar feed pressure). Supported Pebax® 1041 membranes were also developed to decrease the Pebax® thickness (in the 1.5-10 μm range), resulting in a higher permeance. These membranes were prepared by a phase inversion process consisting of the precipitation of a Pebax® 1041/DMAc solution in water and dispersing it to form a stable emulsion that was drop-cast on PSF asymmetric supports. Once dried, the polymer formed a dense continuous layer. The phase inversion methodology is "greener" than solvent evaporation since dimethylacetamide is not released as toxic vapour during membrane preparation. The amount drop-cast led to a different selective layer thickness, which was enhanced by the dispersion of MWCNTs in the polymer emulsion. The properties of the Pebax® selective layer were studied by thermogravimetry and by measuring the contact angle of the membrane surface, and the optimal CO2/N2 selectivity (22.6) was obtained with a CO2 permeance of 3.0 GPU.

Trends in Solid Adsorbent Materials Development for CO2 Capture

A recent report from the United Nations has warned about the excessive CO₂ emissions and the necessity of making efforts to keep the increase in global temperature below 2 °C. Current CO₂ capture technologies are inadequate for reaching that goal, and effective mitigation strategies must be pursued. In this work, we summarize trends in materials development for CO₂ adsorption with focus on recent studies. We put adsorbent materials into four main groups: (I) carbon-based materials, (II) silica/alumina/zeolites, (III) porous crystalline solids, and (IV) metal oxides. Trends in computational investigations along with experimental findings are covered to find promising candidates in light of practical challenges imposed by process economics.

Thin supported MOF based mixed matrix membranes of Pebax® 1657 for biogas upgrade

Thin mixed matrix membranes with a 2–3 μm thick Pebax® 1657 layer on a porous asymmetric polyimide P84® and dense polytrimethylsilylpropyne for biogas upgrade.

Performance of Mixed Matrix Membranes Containing Porous Two-Dimensional (2D) and Three-Dimensional (3D) Fillers for CO₂ Separation: A Review

Application of conventional polymeric membranes in CO₂ separation processes are limited by the existing trade-off between permeability and selectivity represented by the renowned upper bound. Addition of porous nanofillers in polymeric membranes is a promising approach to transcend the upper bound, owing to their superior separation capabilities. Porous nanofillers entice increased attention over nonporous counterparts due to their inherent CO₂ uptake capacities and secondary transport pathways when added to polymer matrices. Infinite possibilities of tuning the porous architecture of these nanofillers also facilitate simultaneous enhancement of permeability, selectivity and stability features of the membrane conveniently heading in the direction towards industrial realization. This review focuses on presenting a complete synopsis of inherent capacities of several porous nanofillers, like metal organic frameworks (MOFs), Zeolites, and porous organic frameworks (POFs) and the effects on their addition to polymeric membranes. Gas permeation performances of select hybrids with these three-dimensional (3D) fillers and porous nanosheets have been summarized and discussed with respect to each type. Consequently, the benefits and shortcomings of each class of materials have been outlined and future research directions concerning the hybrids with 3D fillers have been suggested.