The opportunity of membrane technology for hydrogen purification in the power to hydrogen (P2H) roadmap: a review

Palladium Membrane Applications in Hydrogen Energy and Hydrogen-Related Processes

In recent years, increased attention has been paid to environmental issues and, in connection with this, to the development of hydrogen energy. In turn, this requires the large-scale production of ultra pure hydrogen. Currently, most hydrogen is obtained by converting natural gas and coal. In this regard, the issue of the deep purification of hydrogen for use in fuel cells is very relevant. The deep purification of hydrogen is also necessary for some other areas, including microelectronics. Only palladium membranes can provide the required degree of purification. In addition, the use of membrane catalysis is very relevant for the widely demanded processes of hydrogenation and dehydrogenation, for which reactors with palladium membranes are used. This process is also successfully used for the single-stage production of high-purity hydrogen. Polymeric palladium-containing membranes are also used to purify hydrogen and to remove various pollutants from water, including organochlorine products, nitrates, and a number of other substances.

Diamine-Crosslinked and Blended Polyimide Membranes: An Emerging Strategy in Enhancing H2/CO2 Separation

The increasing demand for high-purity hydrogen (H2) as renewable energy sources is driving advancements in membrane technology, which is essential for achieving efficient gas separation. Polyimide (PI) membranes have become an emerging option for H2/CO2 separation due to its excellent thermal stability and stability under harsh conditions. However, the neat PI membrane suffers performance loss due to CO2 plasticization effect and an encountered trade-off limit between permeability and selectivity. Therefore, membrane modification by crosslinking and blending emerged as a recent strategy to enhance the membrane's performance and properties. This paper provides: (1) An overview of the possible method to do the modification in PI membranes, including the advantages and challenges of the membrane modification types; (2) As blending and crosslinking is the most popular modification for the PI membrane, their roles in enhancing membrane properties for improved H2/CO2 separation are discussed; (3) The critical parameters of the blending and crosslinking processes are also clarified for the optimal purification process; (4) The future outlook for H2/CO2 separation using membrane technology is discussed, aiming to provide commercialization strategy for optimal H2/CO2 separation. Thus, this review could provide guidelines for the readers to implement changes that significantly enhance the membrane's features for high-purity H2 production.

Bimetallic PdPt nanoparticle-incorporated PEDOT:PSS/guar gum-blended membranes for enhanced CO2 separation

To address the escalating demand for efficient CO2 separation technologies, we introduce novel membranes utilizing natural polymer guar gum (GG), conjugate polymer (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)) PEDOT:PSS, and bimetallic PdPt nanoparticles. Bimetallic PdPt nanoparticles were synthesized using the wet chemical method and characterized using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques. The morphologies, chemical bonds, functional groups, and mechanical properties of the fabricated membranes were characterized using various techniques. Through meticulous fabrication and characterization, the binary blended membranes demonstrated enhanced homogeneity and smoothness in their structure, attributed to the interaction between the polymers, and superior CO2 permeability due to the amphiphilic nature of the PEDOT:PSS polymer. Gas separation experiments performed using H2, N2, and CO2 gases confirmed that the 20% PEDOT:PSS/GG blended membranes showed the best performance with sufficient mechanical properties. Moreover, the results demonstrated an increase of 172% in CO2 permeability and 138% in CO2/H2 selectivity, respectively. Furthermore, integrating bimetallic PdPt nanoparticles provided an additional 197% increase in CO2/H2 selectivity, owing to the unique catalytic activities of noble metal nanoparticles. The study not only underscores the transformative potential of polymer blending and noble metal engineering, but also highlights the significance of using natural polymers for sustainable environmental solutions.

Bimetallic PdPt Nanoparticles Decorated PES Membranes for Enhanced H2 Separation

Hydrogen separation has significant importance in diverse applications ranging from clean energy production to gas purification. Membrane technology stands out as a low-cost and efficient method to address the purpose. The development of efficient gas-sensitive materials can further bolster the membrane's performance. In this pursuit, bimetallic PdPt nanoparticles were synthesized using a wet chemical approach and were strategically decorated onto poly(ether sulfone) (PES) membranes. The fibrous morphology of the PES membranes provided an ideal platform for the decoration of nanoparticles, promising enhanced gas transport properties. Prior to the attachment of nanoparticles, the membranes were pretreated under UV light to enhance their surface properties and facilitate improved adhesion. The synthesized bimetallic nanoparticles were characterized by using transmission electron microscopy and X-ray photoelectron spectroscopy for their morphological and elemental analysis. Furthermore, the engineered membranes were characterized using various techniques, such as Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and field emission scanning electron microscopy (FESEM) with rigorous scrutiny to ensure a comprehensive understanding of their structural, chemical, and morphological properties. The membranes were examined for their separation performance using pure H2, N2, and CO2 gases, and the results revealed a 30% increment in H2 permeability and 40 and 42% increments in H2/CO2 and H2/N2 selectivity, respectively. These findings confirmed the critical role of tailored material design and synthesis strategies in advancing membrane technologies for H2 separation applications.

Perspectives and State of the Art of Membrane Separation Technology as a Key Element in the Development of Hydrogen Economy

Due to the objectives established by the European Union and other countries, hydrogen production will be a key technology in the coming decades. There are several starting materials and procedures for its production. All methods have advantages and disadvantages, and the improvements in their performance and decreases in operational costs will be decisive in determining which of them is implemented. For all cases, including for the storage and transport of hydrogen, membranes determine the performance of the process, as well as the operational costs. The present contribution summarizes the most recent membrane technologies for the main methods of hydrogen production, including the challenges to overcome in each case.

Energy Application of Graphene Based Membrane: Hydrogen Separation

Hydrogen gas (H2 ) is a viable energy carrier that has the potential to replace the traditional fossil fuels and contribute to achieving zero net emissions, making it an attractive option for a hydrogen-based society. However, current H2 purification technologies are often limited by high energy consumption, and as a result, there is a growing demand for alternative techniques that offer higher H2 purity and energy efficiency. Membrane separation has emerged as a promising approach for obtaining high-purity H2 gas with low energy consumption. Nevertheless, despite years of development, commercial polymeric membranes have limited performance, prompting researchers to explore alternative materials. In this context, carbon-based membranes, specifically graphene-based nanomaterials, have gained significant attention as potential membrane materials due to their unique properties. In this review, we provide a comprehensive overview of carbon-based membranes for H2 gas separation, fabrication of the membrane, and its characterization, including their advantages and limitations. We also explore the current technological challenges and suggest insights into future research directions, highlighting potential ways to improve graphene-based membranes performance for H2 separations.

Monolayer Fullerene Membranes for Hydrogen Separation

Hydrogen separation membranes are a critical component in the emerging hydrogen economy, offering an energy-efficient solution for the purification and production of hydrogen gas. Inspired by the recent discovery of monolayer covalent fullerene networks, here we show from concentration-gradient-driven molecular dynamics that quasi-square-latticed monolayer fullerene membranes provide the best pore size match, a unique funnel-shaped pore, and entropic selectivity. The integration of these attributes renders these membranes promising for separating H2 from larger gases such as CO2 and O2. The ultrathin membranes exhibit excellent hydrogen permeance as well as high selectivity for H2/CO2 and H2/O2 separations, surpassing the 2008 Robeson upper bounds by a large margin. The present work points toward a promising direction of using monolayer fullerene networks as membranes for high-permeance, selective hydrogen separation for processes such as water splitting.

Metal-Induced Aminosilica Rigidity Improves Highly Permeable Microporous Membranes via Different Types of Pendant Precursors

In this study, nickel-doped aminosilica membranes containing pendant groups were prepared with 3-aminopropyltriethoxysilane (APTES), trimethoxy[3-(methylamino)propyl]silane (MAPTS), 3 N,N-dimethyl aminopropyltrimethoxysilane (DAPTMS), N-[3-(trimethoxysilylpropyl]ethylene diamine (TMSPED), and 1-[3-(trimethoxysilyl)propyl] urea (TMSPU). Differences in the structures of terminal amine ligands significantly contributed to the formation of a coordinated structural assembly. Ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and N₂ adsorption isotherms revealed that short and rigid pendant amino groups successfully coordinated with nickel to produce subnanopores in the membranes, while an ion-exchange interaction was suggested for longer and sterically hindered aminosilica precursors. Moreover, the basicity of amine precursors affected the affinity of ligands for the development of a coordinated network. A pristine aminosilica membrane showed low levels of H₂ permeance that range from 0.1 to 0.5 × 10^-6 mol m^-2 s^-1 Pa^-1 with a H₂/N₂ permeance ratio that ranges from 15 to 100. On the contrary, nickel coordination increased the H₂ permeance to 0.1-3.0 × 10^-6 mol m^-2 s^-1 Pa^-1 with H₂/N₂ permeance ratios that range from 10 to 68, which indicates the formation of a microporous structure and enlargement of pore sizes. The strong level of coordination affinity between nickel ions and amine groups induced rearrangement of the flexible pendant chain into a more rigid structure.

Modelling Sorption and Transport of Gases in Polymeric Membranes across Different Scales: A Review

Professor Giulio C. Sarti has provided outstanding contributions to the modelling of fluid sorption and transport in polymeric materials, with a special eye on industrial applications such as membrane separation, due to his Chemical Engineering background. He was the co-creator of innovative theories such as the Non-Equilibrium Theory for Glassy Polymers (NET-GP), a flexible tool to estimate the solubility of pure and mixed fluids in a wide range of polymers, and of the Standard Transport Model (STM) for estimating membrane permeability and selectivity. In this review, inspired by his rigorous and original approach to representing membrane fundamentals, we provide an overview of the most significant and up-to-date modeling tools available to estimate the main properties governing polymeric membranes in fluid separation, namely solubility and diffusivity. The paper is not meant to be comprehensive, but it focuses on those contributions that are most relevant or that show the potential to be relevant in the future. We do not restrict our view to the field of macroscopic modelling, which was the main playground of professor Sarti, but also devote our attention to Molecular and Multiscale Hierarchical Modeling. This work proposes a critical evaluation of the different approaches considered, along with their limitations and potentiality.

Tailor-Made Modification of Commercial Ceramic Membranes for Environmental and Energy-Oriented Gas Separation Applications

Ceramic membranes have been considered as potential candidates for several gas separation processes of industrial interest, due to their increased thermal and chemical stability compared to polymeric ones. In the present study, commercial Hybrid Silica (HybSi^®) membranes have been evaluated and modified accordingly, to enhance their gas separation performance for targeted applications, including CO₂ removal from flue gas and H₂ recovery from hydrogen-containing natural gas streams. The developed membranes have been characterized before and after modification by relative permeability, single gas permeation, and equimolar separation tests of the respective gas mixtures. The modification procedures, involving in situ chemical vapor deposition and superficial functionalization, aim for precise control of the membranes’ pore size and surface chemistry. High performance membranes have been successfully developed, presenting an increase in H₂/CH₄ permselectivity from 12.8 to 45.6 at 250 °C. Ultimately, the modified HybSi^® membrane exhibits a promising separation performance at 250 °C, and 5 bar feed pressure, obtaining above 92% H₂ purity in the product stream combined with a notable H₂ recovery of 65%, which can be further improved if a vacuum is applied on the permeate side, leading to 94.3% H₂ purity and 69% H₂ recovery.

Gas Permeability, Fractional Free Volume and Molecular Kinetic Diameters: The Effect of Thermal Rearrangement on ortho-hydroxy Polyamide Membranes Loaded with a Porous Polymer Network

Mixed-matrix membranes (MMMs) consisting of an ortho-hydroxy polyamide (HPA) matrix, and variable loads of a porous polymer network (PPN) were thermally treated to induce the transformation of HPA to polybenzoxazole (β-TR-PBO). Two different HPAs were synthesized to be used as a matrix, 6FCl-APAF and tBTpCl-APAF, while the PPN used as a filler was prepared by reacting triptycene and trifluoroacetophenone. The permeability of He, H2, N2, O2, CH4 and CO2 gases through these MMMs are analyzed as a function of the fraction of free volume (FFV) of the membrane and the kinetic diameter of the gas, allowing for the evaluation of the free volume. Thermal rearrangement entails an increase in the FFV. Both before and after thermal rearrangement, the free volume increases with the PPN content very similarly for both polymeric matrices. It is shown that there is a portion of free volume that is inaccessible to permeation (occluded volume), probably due to it being trapped within the filler. In fact, permeability and selectivity change below what could be expected according to densities, when the fraction of occluded volume increases. A higher filler load increases the percentage of inaccessible or trapped free volume, probably due to the increasing agglomeration of the filler. On the other hand, the phenomenon is slightly affected by thermal rearrangement. The fraction of trapped free volume seems to be lower for membranes in which the tBTpCl-APAF is used as a matrix than for those with a 6FCl-APAF matrix, possibly because tBTpCl-APAF could approach the PPN better. The application of an effective medium theory for permeability allowed us to extrapolate for a 100% filler, giving the same value for both thermally rearranged and non-rearranged MMMs. The pure filler could also be extrapolated by assuming the same tendency as in the Robeson's plots for MMMs with low filler content.

Recent Advances in Catalysts and Membranes for MCH Dehydrogenation: A Mini Review

Methylcyclohexane (MCH), one of the liquid organic hydrogen carriers (LOHCs), offers a convenient way to store, transport, and supply hydrogen. Some features of MCH such as its liquid state at ambient temperature and pressure, large hydrogen storage capacity, its well-known catalytic endothermic dehydrogenation reaction and ease at which its dehydrogenated counterpart (toluene) can be hydrogenated back to MCH and make it one of the serious contenders for the development of hydrogen storage and transportation system of the future. In addition to advances on catalysts for MCH dehydrogenation and inorganic membrane for selective and efficient separation of hydrogen, there are increasing research interests on catalytic membrane reactors (CMR) that combine a catalyst and hydrogen separation membrane together in a compact system for improved efficiency because of the shift of the equilibrium dehydrogenation reaction forwarded by the continuous removal of hydrogen from the reaction mixture. Development of efficient CMRs can serve as an important step toward commercially viable hydrogen production systems. The recently demonstrated commercial MCH-TOL based hydrogen storage plant, international transportation network and compact hydrogen producing plants by Chiyoda and some other companies serves as initial successful steps toward the development of full-fledged operation of manufacturing, transportation and storage of zero carbon emission hydrogen in the future. There have been initiatives by industries in the development of compact on-board dehydrogenation plants to fuel hydrogen-powered locomotives. This review mainly focuses on recent advances in different technical aspects of catalytic dehydrogenation of MCH and some significant achievements in the commercial development of MCH-TOL based hydrogen storage, transportation and supply systems, along with the challenges and future prospects.

PEEK-WC-Based Mixed Matrix Membranes Containing Polyimine Cages for Gas Separation

Membrane-based processes are taking a more and more prominent position in the search for sustainable and energy-efficient gas separation applications. It is known that the separation performance of pure polymers may significantly be improved by the dispersion of suitable filler materials in the polymer matrix, to produce so-called mixed matrix membranes. In the present work, four different organic cages were dispersed in the poly(ether ether ketone) with cardo group, PEEK-WC. The m-xylyl imine and furanyl imine-based fillers yielded mechanically robust and selective films after silicone coating. Instead, poor dispersion of p-xylyl imine and diphenyl imine cages did not allow the formation of selective films. The H2, He, O2, N2, CH4, and CO2 pure gas permeability of the neat polymer and the MMMs were measured, and the effect of filler was compared with the maximum limits expected for infinitely permeable and impermeable fillers, according to the Maxwell model. Time lag measurements allowed the calculation of the diffusion coefficient and demonstrated that 20 wt % of furanyl imine cage strongly increased the diffusion coefficient of the bulkier gases and decreased the diffusion selectivity, whereas the m-xylyl imine cage slightly increased the diffusion coefficient and improved the size-selectivity. The performance and properties of the membranes were discussed in relation to their composition and morphology.

Ultrafast H2-selective nanoporous multilayer graphene membrane prepared by confined thermal annealing

H₂ selective dense pores are generated in a graphene oxide (GO) layer by thermal-decomposition of oxygen-functional groups under high pressure. The nanoporous GO membrane shows H₂/CO₂ selectivity of 12.1 and H₂ permeability of 10360 Barrer.