H2 Purification Research Articles

Facilitated transport membranes for H2 purification from coal-derived syngas: A techno-economic analysis

A single-stage membrane process has been designed for using facilitated transport membranes (FTMs) to decarbonize the coal-derived syngas from an integrated gasification combined cycle (IGCC) power plant. The necessary process model and costing method have also been developed to assess the technical feasibility and process economics. In order to account for the carrier saturation phenomenon associated with FTMs, a homogeneous reactive diffusion model is integrated into the process model. The techno-economic study reveals that the mitigated carrier saturation upon bulk CO2 removal can lead to appreciable increases in the CO2 permeance and CO2/H2 selectivity, which can be utilized to achieve 95% CO2 purity and 95% H2 recovery with a CO2/H2 selectivity of 50 at the complete carrier saturation. FTMs with different facilitated transport characteristics can also be arranged in a hybrid membrane configuration to render a H2 recovery of 99% and a cost of electricity of $118.5/MWh, which is 12.5% lower than that of the benchmark Selexol process.

Miscible blend polyethersulfone/polyimide asymmetric membrane crosslinked with 1,3-diaminopropane for hydrogen separation

Abstract Efficient purification technology is crucial to fully utilize hydrogen (H2) as the next generation fuel source. Polyimide (PI) membranes have been intensively applied for H2 purification but its current separation performance of neat PI membranes is insufficient to fulfill industrial demand. This study employs blending and crosslinking modification simultaneously to enhance the separation efficiency of a membrane. Polyethersulfone (PES) and Co-PI (P84) blend asymmetric membranes have been prepared via dry–wet phase inversion with three different ratios. Pure H2 and carbon dioxide (CO2) gas permeation are conducted on the polymer blends to find the best formulation for membrane composition for effective H2 purification. Next, the membrane with the best blending ratio is chemically modified using 1,3-diaminopropane (PDA) with variable reaction time. Physical and chemical characterization of all membranes was evaluated using field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR). Upon 15 min modification, the polymer membrane achieved an improvement on H2/CO2 selectivity by 88.9%. Moreover, similar membrane has demonstrated the best performance as it has surpassed Robeson’s upper bound curve for H2/CO2 gas pair performance. Therefore, this finding is significant towards the development of H2-selective membranes with improved performance.

Nanoporous Titanium‐Oxo Molecular Cluster for CO2 Selective Adsorption

Metal–organic frameworks (MOFs), a new family of porous materials, have received great attention over the past several decades as potential materials for gas separation and storage, and drug delivery. However, the widespread use of these materials has been seriously hampered by their susceptibility to moisture, which impacts their sorption properties. Here, we explored the sorption properties of a titanium‐oxo cluster that can maintain sorption properties in a humid environment for CO2 capture and H2 purification using Monte Carlo (MC) simulations and density functional theory (DFT). The CO2, N2, CH4, and H2 gas‐sorption properties of the titanium‐oxo cluster were investigated using by comparing sorption site and binding energies, demonstrating that the titanium‐oxo cluster can be utilized as a CO2 separator and H2 purification. The comparison between MC and DFT calculations reveals that atomistic MC simulation is particularly useful in the investigation of the sorption behavior of such a complex material.

AuCu/TiO2 Catalysts prepared using electron beam irradiation for the preferential oxidation of carbon monoxide in hydrogen-rich mixtures

The major part of the world production of hydrogen (H2) is originated from a combination of methane steam reforming and water-gas shift reaction resulting in an H2-rich mixture known as reformate gas, which contains about 1% vol (10,000 ppm) of carbon monoxide (CO). The preferential oxidation reaction of CO in H2-rich mixtures (CO-PROX) has been considered a very promising process for H2 purification, reducing CO for values below 50 ppm allowing its use in PEMFC Fuel Cells. Au nanoparticles supported on TiO2 (Au/TiO2) catalysts have been shown good activity and selectivity for CO-PROX reaction in the temperature range between 20-80 ºC; however, the catalytic activity strongly depends on the preparation method. Also, the addition of Cu to the Au/TiO2 catalyst could increase the activity and selectivity for CO-PROX reaction. In this work, AuCu/TiO2 catalysts with composition 0.5%Au0.5%Cu/TiO2 were prepared in a single step using electron beam irradiation, where the Au3+ and Cu2+ ions were dissolved in water/2-propanol solution, the TiO2 support was dispersed and the obtained mixture was irradiated under stirring at room temperature using different dose rates (8 – 64 kGy s-1) and total doses (144 – 576 kGy). The catalysts were characterized by energy dispersive X-ray analysis, X-ray diffraction transmission electron microscopy, temperature-programmed reduction and tested for CO-PROX reaction. The best result was obtained with a catalyst prepared with a dose rate of 64 kGy s-1 and a total dose of 576 kGy showed a CO conversion of 45% and a CO2 selectivity of 30% at 150 oC.

Cage-Like Porous Materials with Simultaneous High C2 H2 Storage and Excellent C2 H2 /CO2 Separation Performance.

Adsorption-based separation is an important technology for C2 H2 purification due to the environmentally friendly and energy-efficient advantage. In addition to the high selectivity of C2 H2 /CO2 , the high uptake of C2 H2 also plays an important role in the separation progress. However, the trade-off between adsorption capacity and separation performance is still in a dilemma. Herein, we report a series of cage-like porous materials named FJI-H8-R (R=Me, Et, n Pr and i Pr) which all have high C2 H2 uptakes at 1 bar and 298 K. Dynamic breakthrough studies show that they all exhibit excellent C2 H2 /CO2 separation performance. Particularly, FJI-H8-Me possesses a long breakthrough time up to 90 min g-1 . Additionally, Grand Canonical Monte Carlo (GCMC) simulation reveals that the suitable pore space and geometry contribute much to the excellent separation performance.

Novel hollow fiber membrane reactor for high purity H2 generation from thermal catalytic NH3 decomposition

Although storage of H2 in various liquid chemicals makes it very attractive for practical applications, production and purification of H2 from decomposition of these chemicals under relatively mild conditions is still challenging. In this work, we reported production of high-purity H2 from NH3 decomposition using a combined packed bed/membrane reactor loaded with Ru-based catalyst. Three types of membranes (modified MFI zeolite membrane, carbon molecular sieve membrane, and Pd/Ag membrane) were employed and compared for H2 production and purification from NH3 decomposition. All these membrane reactors exhibited high NH3 conversion of >99% with H2 recovery of >90% under pressurized NH3 feed of 7 bar. Nevertheless, H2 purity varied because of the different separation performance of these membranes. High H2 purity of >99.999% with <10 ppb NH3 concentration in permeate was achieved using high-quality Pd/Ag membrane reactor. These results suggest a feasible and highly energy efficient option for producing high-purity H2 from NH3 decomposition.

Strain-controlled DHP-graphene for ultrahigh-performance hydrogen purification

External strain induced membrane separation is an efficient strategy to achieve controllable gas purification. Herein, the potential of a new type of graphene consisting of decagonal, hexagonal, and pentagonal rings (DHPG) was investigated for H2 purification under 0–10% tensile strains by using density functional theory (DFT) and non-equilibrium molecular dynamic (NEMD) simulations. The results showed that, with the increase in strain, the H2 diffusion energy barrier decreased while the diffusion rate and permeance increased. The H2 permeance met the industrial standard when the strain reached 6%, at which the selectivities of H2 over CO2, CO, N2, and CH4 were 3.78 × 1030, 1.46 × 1031, 3.61 × 1032, and 1.91 × 1072, respectively, at 300 K. The NEMD results showed that H2 permeance in DHPG increased with the increase in external pressure applied, while CO2, CO, N2, and CH4 were impeded by the membrane. The results of this work highlighted DHPG as a promising strain-controlled membrane for H2 purification.

A Review of Hydrogen Purification Technologies for Fuel Cell Vehicles

Nowadays, we face a series of global challenges, including the growing depletion of fossil energy, environmental pollution, and global warming. The replacement of coal, petroleum, and natural gas by secondary energy resources is vital for sustainable development. Hydrogen (H2) energy is considered the ultimate energy in the 21st century because of its diverse sources, cleanliness, low carbon emission, flexibility, and high efficiency. H2 fuel cell vehicles are commonly the end-point application of H2 energy. Owing to their zero carbon emission, they are gradually replacing traditional vehicles powered by fossil fuel. As the H2 fuel cell vehicle industry rapidly develops, H2 fuel supply, especially H2 quality, attracts increasing attention. Compared with H2 for industrial use, the H2 purity requirements for fuel cells are not high. Still, the impurity content is strictly controlled since even a low amount of some impurities may irreversibly damage fuel cells’ performance and running life. This paper reviews different versions of current standards concerning H2 for fuel cell vehicles in China and abroad. Furthermore, we analyze the causes and developing trends for the changes in these standards in detail. On the other hand, according to characteristics of H2 for fuel cell vehicles, standard H2 purification technologies, such as pressure swing adsorption (PSA), membrane separation and metal hydride separation, were analyzed, and the latest research progress was reviewed.

Adsorption for efficient low carbon hydrogen production: part 2\u2014Cyclic experiments and model predictions

Hydrogen as clean energy carrier is expected to play a key role in future low-carbon energy systems. In this paper, we demonstrate a new technology for coupling fossil-fuel based hydrogen production with carbon capture and storage (CCS): the integration of CO2 capture and H2 purification in a single vacuum pressure swing adsorption (VPSA) cycle. An eight step VPSA cycle is tested in a two-column lab-pilot for a ternary CO2–H2–CH4 stream representative of shifted steam methane reformer (SMR) syngas, while using commercial zeolite 13X as adsorbent. The cycle can co-purify CO2 and H2, thus reaching H2 purities up to 99.96%, CO2 purities up to 98.9%, CO2 recoveries up to 94.3% and H2 recoveries up to 81%. The key decision variables for adjusting the separation performance to reach the required targets are the heavy purge (HP) duration, the feed duration, the evacuation pressure and the flow rate of the light purge (LP). In contrast to that, the separation performance is rather insensitive towards small changes in feed composition and in HP inlet composition. Comparing the experimental results with simulation results shows that the model for describing multi-component adsorption is critical in determining the predictive capabilities of the column model. Here, the real adsorbed solution theory (RAST) is necessary to describe all experiments well, whereas neither extended isotherms nor the ideal adsorbed solution theory (IAST) can reproduce all effects observed experimentally.

Carbon molecular sieve membranes for hydrogen purification from a steam methane reforming process

Asymmetric carbon molecular sieve (CMS) membranes prepared from cellulose hollow fiber precursors were investigated for H2/CO2 separation in this work. The prepared carbon membrane shows excellent separation performance with H2 permeance of 111 GPU and an H2/CO2 selectivity of 36.9 at 10 bar and 110 °C dry mixed gas. This membrane demonstrates high stability under a humidified gas condition at 90 °C and the pressure of up to 14 bar. A two-stage carbon membrane system was evaluated to be techno-economically feasible to produce high-purity H2 (>99.5 vol%) by HYSYS simulation, and the minimum specific H2 purification cost of 0.012 $/Nm3 H2 produced was achieved under the optimal operating condition. Sensitivity analysis on the H2 loss and H2 purity indicates that such membrane is still less cost-effective to achieve ultrapure hydrogen (e.g., >99.8 vol%) unless the higher operating temperatures for carbon membrane systems are applied.

Adsorption for efficient low carbon hydrogen production: part 1\u2014adsorption equilibrium and breakthrough studies for H2/CO2/CH4 on zeolite 13X

Reforming of fossil fuels coupled with carbon capture and storage has the potential to produce low-carbon H2 at large scale and low cost. Adsorption is a potentially promising technology for two key separation tasks in this process: H2 purification and CO2 capture. In this work, we present equilibrium adsorption data of H2 and CH4 on zeolite 13X, in addition to the already established CO2 isotherms. Further, we carry out binary (CO2–CH4) and ternary (H2–CO2–CH4) breakthrough experiments at various pressures and temperatures to estimate transport parameters, assess the predictive capacity of our 1D column model, and compare different multi-component adsorption models. CO2 adsorbs strongly on zeolite 13X, CH4 adsorbs less, and H2 adsorbs very little. Thus, H2 breaks through first, CH4 second (first in the binary breakthrough experiments) and CO2 last. Linear driving force (LDF) mass transfer coefficients are estimated based on a single breakthrough experiment and mass transfer is found to be fast for H2, slower for CH4, and slowest for CO2. The LDF parameters can be used in a predictive manner for breakthrough experiments at varying pressures, temperatures, flows, and, though with lower accuracy, even compositions. Heat transfer inside the column is described well with a literature correlation, thus yielding an excellent agreement between simulated and measured column temperatures. Ideal and real adsorbed solution theories (IAST and RAST, respectively) both model the observed breakthrough composition profiles well, whereas extended isotherms are inferior for predicting the competitive behavior between CH4 and CO2 adsorption. This study provides the groundwork necessary for full cyclic experiments and their simulation.

Intensification and optimization of continuous hydrogen production by dark fermentation in a new design liquid/gas hollow fiber membrane bioreactor

A liquid/gas membrane bioreactor (L/G MBR) was developed to intensify the dark fermentation process. A hollow fiber membrane module was used to combine biohydrogen production, in situ liquid–gas separation and hydrogen producing bacteria retention in a single unit. The L/G MBR was seeded once and did not require further microbial input, as consistent average hydrogen yield of 0.97 ± 0.09 mol-H2/added mol-glucose and hydrogen production rate of 106.5 ± 10.6 mL-H2/L-medium/h were reached over a year. Different biogas extraction strategies showed that efficient in situ H2 extraction is possible without sweeping gas in the lumen of the fibers, thus facilitating H2 purification in an industrial setting. Modelling predicted an optimal hydrogen yield of 1.2 mol/mol-glucose added for a glucose concentration in the feed of 13.1 g/L, close to experimental hydraulic retention time of 8–10 h with an organic loading rate of 1.4 g-glucose/L-medium/h. No washout of hydrogen-producing bacteria was observed at low HRT (2 h), suggesting the possibility of further hydrogen production rate enhancement using an optimized organic loading rate. Acetate and butyrate were the main metabolites identified. Clostridium and Enterobacter dominated in the liquid outlet. The relative abundance of Clostridium pasteurianum increased with glucose concentration in the bioreactor, as opposed to Clostridium beijerinckii which was more abundant at low glucose concentration. The original hollow fiber L/G MBR configuration enabled the testing and selection of fermentation strategies that greatly simplified the implementation of the dark fermentation process by addressing its key operational bottlenecks. Indeed, the L/G membrane surface served as a support and reservoir for the hydrogen producing bacteria across a wide range of HRT conditions.

High loading and high-selectivity H2 purification using SBC@ZIF based thin film composite hollow fiber membranes

Membrane-based separation systems have been widely explored for hydrogen production and purification in the development of next-generation fuels. In this work, we propose a thin film composite hollow fiber membrane (TFCHFM) for H2 purification, incorporating poly(styrene-co-butadiene) copolymers (SBC, 4% butadiene, for flexibility and ease of processing) and ZIF-8 nanoparticles. The TFC was supported on a PEI-based hollow fiber substrate. SBC containing a flexible butadiene segment showed enhanced compatibility through π-π interactions. The morphology of ZIF-8 was altered from a cubic shape to a smaller spherical shape by altering the molar ratio of NH4+/Zn2+. The gas separation mechanism of the ZIF-8 based TFC membrane was predicted by the Maxwell model. In the binary gas permeation test (5 vol% H2), the H2 permeance and H2/CH4 selectivity of TFCHFMs were 6.85 GPU and 152.20, respectively, with 50 wt% ZIF-8 loading. We believe that the high loading weight (50 wt% ZIF-8) and H2/CH4 selectivity presented here are unprecedented for ZIF-8 based TFC membranes reported in the literature.

Hydrogen Purification through a Highly Stable Dual-Phase Oxygen-Permeable Membrane.

Using oxygen permeable membranes (OPMs) to upgrade low‐purity hydrogen is a promising concept for high‐purity H2 production. At high temperatures, water dissociates into hydrogen and oxygen. The oxygen permeates through OPM and oxidizes hydrogen in a waste stream on the other side of the membrane. Pure hydrogen can be obtained on the water‐splitting side after condensation. However, the existing Co‐ and Fe‐based OPMs are chemically instable as a result of the over‐reduction of Co and Fe ions under reducing atmospheres. Herein, a dual‐phase membrane Ce0.9Pr0.1O2−δ‐Pr0.1Sr0.9Mg0.1Ti0.9O3−δ (CPO‐PSM‐Ti) with excellent chemical stability and mixed oxygen ionic‐electronic conductivity under reducing atmospheres was developed for H2 purification. An acceptable H2 production rate of 0.52 mL min−1 cm−2 is achieved at 940 °C. No obvious degradation during 180 h of operation indicates the robust stability of CPO‐PSM‐Ti membrane. The proven mixed conductivity and excellent stability of CPO‐PSM‐Ti give prospective advantages over existing OPMs for upgrading low‐purity hydrogen.

Hydrogen Purification through a Highly Stable Dual‐Phase Oxygen‐Permeable Membrane

AbstractUsing oxygen permeable membranes (OPMs) to upgrade low‐purity hydrogen is a promising concept for high‐purity H2 production. At high temperatures, water dissociates into hydrogen and oxygen. The oxygen permeates through OPM and oxidizes hydrogen in a waste stream on the other side of the membrane. Pure hydrogen can be obtained on the water‐splitting side after condensation. However, the existing Co‐ and Fe‐based OPMs are chemically instable as a result of the over‐reduction of Co and Fe ions under reducing atmospheres. Herein, a dual‐phase membrane Ce0.9Pr0.1O2−δ‐Pr0.1Sr0.9Mg0.1Ti0.9O3−δ (CPO‐PSM‐Ti) with excellent chemical stability and mixed oxygen ionic‐electronic conductivity under reducing atmospheres was developed for H2 purification. An acceptable H2 production rate of 0.52 mL min−1 cm−2 is achieved at 940 °C. No obvious degradation during 180 h of operation indicates the robust stability of CPO‐PSM‐Ti membrane. The proven mixed conductivity and excellent stability of CPO‐PSM‐Ti give prospective advantages over existing OPMs for upgrading low‐purity hydrogen.

Thermodynamic analysis of chemical looping coupling process for coproducing syngas and hydrogen with in situ CO2 utilization

This study proposed a novel chemical looping coupling system for coproducing syngas and hydrogen with in situ CO2 utilization. It integrates chemical looping combustion, chemical looping reforming, CO2-H2O co-splitting, hydrogen production and air oxidation using CH4 as fuel and iron oxide as oxygen carrier. In this process, syngas and H2 purification, in addition to CO2 capture and storage are no longer necessary. It not only produces high-purity hydrogen and syngas without pollutants and greenhouse gas emissions, but realizes the sufficient utilization of feed and oxygen carriers. A detailed thermodynamic analysis of the proposed chemical looping coupling process was conducted by Aspen Plus. The effects of key parameters, such as feed ratio, temperature, and pressure in each reactor on the process performance were investigated in terms of the utilization of CH4, the yield and purity of syngas and hydrogen, and the oxygen carrier coupling. In addition, the energy balance was analyzed for the coupling system with heat exchanger network. Based on the established process model, we concluded that the preferable feed ratios in combustion, reforming, co-splitting, steam and air reactors were 4, 1, 0.4, 1.1 and 1.5, respectively. The preferable temperatures in the five reactors mentioned above were 900, 900, 850, 500 and 500 °C in sequence, and the preferable pressure was 1 atm in each reactor. Under these conditions, high-purity hydrogen (100%) and syngas (99% and 93% purity) with ideal H2/CO ratio (~2) could be obtained. The energy efficiency and exergy efficiency of this coupling system reached up to 90.54% and 72.04%, respectively.

An Innovative 500 W Alkaline Water Electrolyser System for the Production of Ultra-Pure Hydrogen and Oxygen Gases

This paper communicates on an innovative, laboratory size alkaline water electrolyser (AWE) system, capable of efficiently producing ultra-pure hydrogen and oxygen gases. The system is composed of a zero-gap, bipolar-electrode stack, equipped with a polymer-based membrane, along with two drying columns for effective purification of H2 and O2 gaseous products. An optimal electrochemical efficiency of the electrolyser stack is provided through the employment of catalytically activated, extended surface-area nickel foam electrodes. Laboratory electrochemical examinations of the electrolyser included a series of galvanostatic AWE and alternating current (a.c.) impedance (single cell) experiments. Complementary examinations covered catalyst’s surface topography analysis by combined SEM (Scanning Electron Microscopy) and EDX (Energy Dispersive X-ray Spectroscopy) techniques along with chromatographic evaluation of the purity of hydrogen and oxygen products.

Adsorption in the context of clean hydrogen production: process intensification by integrating H2 purification and CO2 capture - A modeling and experimental study of multi-component adsorption

Coupling fossil-based H2 production with carbon capture and storage can produce H2 with low associated CO2 emissions, which is urgently needed to decarbonize industry, the energy sector, and the transportation sector. Vacuum pressure swing adsorption (VPSA) allows for the integration of two key separation tasks in this process, H2 purification and CO2 capture. In this work, we compare experimental and simulation results of a cyclic VPSA process. Our focus is the evaluation of different approaches for modeling multi-component adsorption. In particular, we use a three process Langmuir model for CO2 adsorption and Langmuir model for H2 and CH4 adsorption. We assess the different options for energetic site matching. The results indicate that energetic site matching of H2 and CO2 is of little importance. In contrast to that, only two models with a different energetic site matching for CO2 and CH4 result in a reasonable prediction of the experimental results, i.e. uncorrelated (UC) and uncorrelated unselective B (UCUS B). Both extended Sips isotherms and the use of the real adsorbed solution theory (RAST), however, result in a better prediction of the experimental results.

Hydrogen separation and purification with MOF-based materials

This review provides a comprehensive understanding of the fundamental theories and strategies for MOF-based H2 separation and purification, including hydrogen isotope separation with representative examples.

Stability Investigation of Polyposs-Imide Membranes for H2 Purification and Their Application in the Steel Industry

In the present work, the high-temperature and long-term hydrothermal stability of novel polyPOSS-imide membranes for high-temperature hydrogen separation is investigated. The polyPOSS-imide membranes are found to exhibit an appropriate stability up to 300 °C. Above this temperature the membrane selectivity rapidly decreases, which is seemingly related to changes in the molecular structure coupled to silanol condensation forming siloxane groups. Surprisingly, the exposure of the membrane to temperatures of up to 300 °C even increases the H2 permeance together with the selective feature of the polyPOSS-imide layer. Subsequently, the long-term hydrothermal stability of the polyPOSS-imide membranes was investigated over a period of close to 1000 hours at 250 °C exposing the membrane to 10 mol% steam in the feed. An increase in H2/CH4 selectivity was observed upon water addition, and even though a minor drop was observed over time during the hydrothermal operation, the selectivity exceeds the initial selectivity obtained in the dry feed atmosphere. After the removal of steam from the feed the performance returns to its original state prior to the exposure to any steam showing an appropriate steam stability of the polyPOSS-imide membranes. A conceptual process design and assessment was performed for application of these membranes involving a combination of carbon reuse and electrification of the steel making process with co-production of hydrogen. The results indicate a CO2 avoidance of 14%. The CO2 reduction achieved using renewable electricity in the proposed scheme is a factor 2.76 higher compared to a situation where the same renewable electricity would be fed in the electricity grid.