Corrosion behavior analyses of metallic membranes in hydrogen iodide environment for iodine-sulfur thermochemical cycle of hydrogen production

HI decomposition in Iodine-Sulfur (IS) thermochemical process for hydrogen production is one of the critical steps, which suffers from low equilibrium conversion as well as highly corrosive environment. Corrosion-resistant metal membrane reactor is proposed to be a process intensification tool, which can enable efficient HI decomposition by enhancing the equilibrium conversion value. Here we report corrosion resistance studies on tantalum, niobium and palladium membranes, along with their comparative evaluation. Thin layer each of tantalum, palladium and niobium was coated on tubular alumina support of length 250 mm and 10 mm OD using DC sputter deposition technique. Small pieces of the coated tubes were subject to immersion coupon tests in HI-water environment (57 wt% HI in water) at a temperature of 125–130 °C under reflux environment, and simulated HI decomposition environment at 450 °C. The unexposed and exposed cut pieces were analyzed using scanning electron microscope (SEM), energy dispersive X-ray (EDX) and secondary ion mass spectrometer (SIMS). The extent of leaching of metal into liquid HI was quantified using inductively coupled plasma-mass spectrometer (ICP-MS). Findings confirmed that tantalum is the most resistant membrane material in HI environment (liquid and gas) followed by niobium and palladium.     

Synthesis,characterization and corrosion performance evaluation of DDR membrane for H2 separation from HI decomposition reaction

An all silica DDR (deca dodecasil rhombohedral) zeolite membrane with dense, interlocked structure has been developed for separation of H₂ from HI/I₂ mixture of HI decomposition reaction. In this work, the DDR zeolite membrane was synthesized on the seeded clay-alumina substrate within 5 days. The seeds were synthesized by sonication mediated hydrothermal process within short crystallization time which enhanced the nucleation for the membrane growth. The synthesized membranes along with seed crystals were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Field emission scanning electron microscope (FESEM) and energy dispersive X-ray spectroscopy (EDAX). The selectivity of hydrogen with respect to CO₂ and Ar was evaluated by single gas permeation studies at room temperature. The tests for corrosion resistance were carried out upto 120 h with both support and DDR membrane at 130 °C which confirmed the stability of membrane under the harsh HI/I₂ environment.     

Numerical simulations of HI decomposition in packed bed membrane reactors

Numerical simulations to develop an understanding of transport processes inside PBMRs (packed bed membrane reactors) and to evaluate effectiveness of PBMRs in increasing the conversion of HI (hydrogen iodide) decomposition reaction of IS (iodine–sulfur) thermochemical cycle are reported. The computational approach used in the simulations has been validated using the data reported for HI decomposition in a packed bed reactor (PBR). The validated computational approach has been used for parametric studies. Effects of different parameters (temperature, pressure, space velocity, membrane permeability, permselectivity, packed bed porosity and reactor diameter) on HI conversion are reported. The parameters having the maximum impact on the conversion are identified. The findings show that using a PBMR instead of a PBR leads to significant enhancement in conversion and the parameters having high impact on conversion are wall temperature, feed temperature, reactor diameter and packed bed porosity. Based on the findings of parametric studies, ranges of the parameters having maximum impact on conversion are suggested, e.g. the reactor wall temperature is recommended to be in the range of 690–700 K, the bed porosity is recommended to be in the range of 0.2–0.4.     

Module design of silica membrane reactor for hydrogen production via thermochemical IS process

The potential of the silica membrane reactors for use in the decomposition of hydrogen iodide (HI) was investigated by simulation with the aim of producing CO₂-free hydrogen via the thermochemical water-splitting iodine-sulfur process. Simulation model validation was done using the data derived from an experimental membrane reactor. The simulated results showed good agreement with the experimental findings. The important process parameters determining the performance of the membrane reactor used for HI decomposition, namely, reaction temperature, total pressures on both the feed side and the permeate side, and HI feed flow rate were investigated theoritically by means of a simulation. It was found that the conversion of HI decomposition can be improved by up to four times (80%) or greater than the equilibrium conversion (20%) at 400 °C by employing a membrane reactor equipped with a tubular silica membrane. The features to design the membrane reactor module for HI decomposition of the thermochemical iodine-sulfur process were discussed under a wide range of operation conditions by evaluating the relationship between HI conversion and number of membrane tubes.     

Multi-tube tantalum membrane reactor for HIx processing section of IS thermochemical process

HI_x processing section of Iodine-Sulphur (IS) thermochemical cycle dictates the overall efficiency of the cycle, which poses extremely corrosive HI–H₂O–I₂ environment, coupled with a very low equilibrium conversion (~22%) of HI to hydrogen at 450 °C. Here, we report the fabrication, characterization and operation of a 4-tube packed bed catalytic tantalum (Ta) membrane reactor (MR) for enhanced HI decomposition. Gamma coated clay-alumina tubes were used as supports for fabrication of Ta membranes. Clay-alumina base support was fabricated with 92% alumina (~8 μm particle size) and 8% clay (~10 μm particle size), sintered at a temperature of 1400 °C. An intermediate gamma alumina coating was provided with 4% polyvinyl butyral as binder for a 10% solid loading. Composite alumina tubes were coated with thin films of Ta metal of thickness <1 μm using DC magnetron sputter deposition technique. The 4-tube Ta MR assembly was designed and fabricated with integration of Pt-alumina catalyst for carrying out the HI decomposition studies, which offered >80% single-pass conversion of HI to hydrogen at 450 °C. The hydrogen throughput of the reactor was ~30 LPH at a 2 bar trans-membrane pressure, with >99.95% purity. This is the first time a muti-tube MR is reported for HI_x processing section of IS process.     

Introduction and preliminary testing of a 5 m3/h hydrogen production facility by Iodine–Sulfur thermochemical process

The Iodine–Sulfur (IS) or Sulfur–Iodine (SI) thermochemical water-splitting cycle is considered as one of the most promising hydrogen production methods through thermal chemical cycle process with heat. This paper introduces the new built hydrogen production testing facility of IS process made by industrial structural material (IS-5m³ facility). The TC4, Hastelloy C276 and SiC materials were chosen in this pilot-scale testing facility for different modules. The new designed structure of Bunsen reactor, HI decomposer and H₂SO₄ decomposer are described particularly, and the corresponding individual tests are successfully executed to verify the function of each section. Based on testing, a preliminary continuous experimental run was carried out in September of 2021 for about 4 h with the hydrogen production capacity of 80 L/h. The problems such as slight corrosion, lower hydrogen gas yield and shorter operation time faced in this experiment will be modified in the near future. A longer time operation and higher H₂ production rate test will be carried out soon.     

Research and development on membrane IS process for hydrogen production using solar heat

Thermochemical hydrogen production has attracted considerable interest as a clean energy solution to address the challenges of climate change and environmental sustainability. The thermochemical water-splitting iodine-sulfur (IS) process uses heat from nuclear or solar power and thus is a promising next-generation thermochemical hydrogen production method that is independent of fossil fuels and can provide energy security. This paper presents the current state of research and development (R&D) of the IS process based on membrane techniques using solar energy at a medium temperature of 600 °C. Membrane design strategies have the most potential for making the IS process using solar energy highly efficient and economical and are illustrated here in detail. Three aspects of membrane design proposed herein for the IS process have led to a considerable improvement of the total thermal efficiency of the process: membrane reactors, membranes, and reaction catalysts. Experimental studies in the applications of these membrane design techniques to the Bunsen reaction, sulfuric acid decomposition, and hydrogen iodide decomposition are discussed.     

Overview of nuclear hydrogen production research through iodine sulfur process at INET

Thermochemical water-splitting cycle is a promising process to produce hydrogen using solar or nuclear energy. R&D on hydrogen production through iodine sulfur (IS) thermochemical cycle was initiated in 2005 at INET. Fundamental studies on the three reactions of IS cycle, i.e., Bunsen reaction, HI decomposition reaction, sulfuric acid decomposition reaction, and related techniques, such as separation, concentration and purification, were carried through. In Bunsen section, the reaction kinetics and separation characteristics of H₂SO₄ and HIx phases were studied. In HI section, Pt catalysts were loaded on different supporters by various methods and used for HI decomposition; and electro-electrodialysis(EED) was developed for concentration of HI acid. In sulfuric acid section, non-Pt catalysts were developed for SO₃ decomposition. Based on fundamental researches, a closed-loop test apparatus of 10 NL/h H₂ was designed and established. The current status of IS process research is summarized in this paper. In addition, R&D plan of IS process at INET is presented.     

Fe3+-Clinoptilolite/graphene oxide and layered MoS2@Nitrogen doped graphene as novel graphene based nanocomposites for DMFC

Fe³⁺ doped in a natural zeolite (Fe³⁺-Clinoptilolite) hybridized with graphene oxide (GO) was used as an electro-catalyst for methanol oxidation in direct methanol fuel cells (DMFC). Furthermore, thin layered molybdenum disulfide (MoS₂) composited with nitrogen doped graphene (NG) was used for oxygen reduction. Successful synthesis of these nanomaterials was confirmed by X-ray diffraction (XRD), X-ray florescence (XRF), Fourier transform infrared (FTIR), energy-dispersive X-ray (EDX), Raman spectroscopy, Field Emission Scanning Electron Microscopy (FESEM) and transmission electron microscopy (TEM) images. In the following, by using the cyclic voltammetry (CV) technique the electrochemical behaviors of the glassy carbon electrodes modified with the mentioned composites were investigated. The results of methanol oxidation and oxygen reduction showed sufficient electro-catalytic effects as well as significant diffusion currents in presence of the non-precious synthetic materials. Obtained exchange currents (i₀) from Tafel plots showed increasment up to 6.02 × 10^?6 and 1.47 × 10^?5 μA for anode and cathode respectively. Also, thermodynamic potential of the DMFC was estimated about 1.1 V in alkaline media that was very close to reported value for theoretical potential in DMFC.     

HI extraction by H3PO4 in the Sulfur–Iodine thermochemical water splitting cycle: Composition optimization of the HI/H2O/H3PO4/I2 biphasic quaternary system

Iodine excess separation from hydriodic acid (HI) is one of the most challenging steps of the Sulfur–Iodine thermochemical water splitting cycle. One promising method is the extraction of HI by using phosphoric acid (H₃PO₄), with the subsequent separation of gaseous hydriodic acid from water and H₃PO₄ by a distillation step.     

Texture/phase evolution during microwave fabrication of nanocrystalline multicomponent (Cu/Zn/Al)O metal oxides with varying diethylene glycol content applied in hydrogen production

A series of Cu/Zn/Al mixed oxides, as steam methanol reforming catalysts, were synthesized via the microwave assisted combustion synthesis method using diethylene glycol as the organic fuel. The nanocatalysts were analyzed by XRD, FESEM, EDX, BET, H₂-TPR and FTIR techniques to ensure authenticity of the synthesis steps and pursuing the effect of the fuel/nitrate ratio on their physicochemical properties. The results proved the necessity of defining an optimum fuel/nitrate ratio for the combustion synthesis method. Fuel/nitrate ratio affects significantly on crystal growth and crystalline facets size. Proper crystallography of CuO/ZnO/Al₂O₃ (DEG/Nitrate = 3) nanocatalyst along with higher specific surface area and distributed particle size, made it predictable that it could result in higher methanol conversion in the steam methanol reforming process. The catalytic performance studies justified assumptions, since the CZA (DEG/N = 3) presented higher methanol conversion and selectivity toward desired products as well as its high stability.     

Structural transformations of highly porous nickel catalysts during ethanol conversion towards hydrogen

In this work, we report a liquid-phase reduction method to prepare porous non-supported amorphous nickel catalysts with high surface areas (65–250 m²/g). A highly crystalline face center cubic Ni (fcc-Ni) catalyst with 110 m²/g surface area was also prepared by frontal crystallization of the amorphous nickel catalyst. The catalytic activity and stability of these catalysts for ethanol decomposition was investigated at different time on stream (TOS) to understand structural transformations occurring at the early stages of catalyst activation-deactivation. Activity vs. TOS results obtained at 473 K show that on the amorphous catalysts the conversion increases from about 50% to 60–75% reaching a steady value at ～30 h TOS, which remains constant during the observed 96 h of TOS. The fcc-Ni catalyst initially exhibits a higher conversion (～85%), however, it quickly deactivates to a conversion in the similar range as the amorphous catalysts. It is also shown that BET surface areas of amorphous catalysts decreases during hydrogen pretreatment at 473 K due to crystallization, grain growth, and sintering. The structure of amorphous catalysts continuously refines to form a combination of fcc-Ni and hexagonal close-packed nickel (hpc-Ni) phases, as well as nickel carbide (Ni₃C) and carbon layers that stabilize catalytic activity. The structure of the fcc-Ni catalyst remains unchanged during the 96 h TOS experiment indicating that carbon deposition might cause its initial deactivation. At 523 K, the amorphous catalyst shows 100% conversion, which remains constant during 96 h of TOS, while the fcc-Ni crystalline catalyst initially exhibits 95% conversion and then slowly deactivates to ～80% at 96 h TOS. Thus at 523K the stabilized amorphous catalyst does not deactivate under the same TOS compared to the crystalline fcc-Ni catalyst, showing that the active sites on these catalysts are different. The findings of this work suggest that the liquid-phase reduction method can be used to prepare active and stable catalysts for reactions involving decomposition of alcohols and hydrocarbons to produce hydrogen.     

H2 production by low pressure methanol steam reforming in a dense Pd–Ag membrane reactor in co-current flow configuration: Experimental and modeling analysis

The aim of this work is to generate a pure or CO_x-free hydrogen stream by using a dense Pd-based packed bed membrane reactor (PBMR) during methanol steam reforming (MSR) reaction and developing a valid model that can provide a tool for deeper analyses of the reaction parameters in the PBMR. Therefore, in this study, a dense Pd–Ag membrane reactor (MR) is used to carry out MSR at different gas hourly space velocity (GHSV), feed molar ratio and sweep gas factor (SF) and for low reaction pressures (1.5–2.5 bar). For a better analysis, a traditional packed bed reactor (PBR) is operated at the same PBMR conditions. In the PBMR setup, a dense Pd–Ag membrane with a thickness of 50 μm is used and also a commercial Cu/ZnO/Al₂O₃ catalyst is packed in both kinds of reactors. Methanol conversion equal to 100% is experimentally achieved in the PBMR at 280 °C, H₂O/CH₃OH = 3/1 and 2.5 bar, while at the same conditions the PBR reaches 91% methanol conversion. Moreover, 46% CO_x-free hydrogen on total hydrogen produced is collected by using sweep gas in the PBMR permeate side. Furthermore, a 1-dimensional and isothermal model is developed for theoretically analyzing MSR performance in both PBMR and PBR, validated by the combined experimental campaign.     

Hydrogen production by steam methane reforming in a membrane reactor equipped with a Pd composite membrane deposited on a porous stainless steel

With the aim of producing hydrogen at low cost and with a high conversion efficiency, steam methane reforming (SMR) was carried out under moderate operating conditions in a Pd-based composite membrane reactor packed with a commercial Ru/Al₂O₃ catalyst. A Pd-based composite membrane with a thickness of 4–5 μm was prepared on a tubular stainless steel support (diameter of 12.7 mm, length of 450 mm) using electroless plating (ELP). The Pd-based composite membrane had a hydrogen permeance of 2.4 × 10^?3 mol m^?1 s^?1 Pa^?0.5 and an H₂/N₂ selectivity of 618 at a temperature of 823 K and a pressure difference of 10.1 kPa. The SMR test was conducted at 823 K with a steam-to-carbon ratio of 3.0 and gas hourly space velocity of 1000 h^?1; increasing the pressure difference resulted in enhanced methane conversion, which reached 82% at a pressure difference of 912 kPa. To propose a guideline for membrane design, a process simulation was conducted for conversion enhancement as a function of pressure difference using Aspen HYSYS^®. A stability test for SMR was conducted for ～120 h; the methane conversion, hydrogen production rate, and gas composition were monitored. During the SMR test, the carbon monoxide concentration in the total reformed stream was <1%, indicating that a series of water gas shift reactors was not needed in our membrane reactor system.     

Impregnation vs. sol-gel and sol-gel-plasma dispersion of nickel nanoparticles over Al2O3 employed in combined dry reforming and partial oxidation of greenhouse gases to syngas

This paper is focused on the fabrication of Ni/Al₂O₃ nanocatalyst via impregnation, sol-gel and hybrid sol-gel plasma techniques. Physiochemical properties of the samples were characterized by XRD, FESEM, TEM, EDX, BET and FTIR analyses. Also, used nanocatalysts were characterized via TG-DTG, FESEM, EDX and XRD analyses. The catalytic performance of the nanocatalysts was investigated. XRD patterns proved that for sol-gel based samples, amorphous behaviour was intensified and concentration of prone planes to coke deposition was decreased especially in plasma treated one. FESEM images were exhibited that homogenous particle size distribution was obtained for the sample which prepared by sol-gel-plasma method. TEM and EDX analyses reported the promoted nickel dispersion for sol-gel based samples especially in plasma treated sample. Owing to the BET results utmost surface area 297 m²/g was declared for sol-gel-plasma catalyst. Sol-gel-plasma catalyst indicated the higher catalytic activity compared to the others. In addition, conducted stability test during 2880 min asserted that, deactivation was occurred in all samples but sol-gel-plasma catalyst is more stable. After stability test, sol-gel-plasma catalyst roughly preserved its structure while active phase migration was took place for the others. Also, based on EDX and TG-DTG results, more uniform dispersion and lowest amount of coke deposit was found for sol-gel-plasma catalyst.     

Methane steam reforming using a membrane reactor equipped with a Pd-based composite membrane for effective hydrogen production

Herein, a methane steam reforming (MSR) reaction was carried out using a Pd composite membrane reactor packed with a commercial Ru/Al₂O₃ catalyst under mild operating conditions, to produce hydrogen with CO₂ capture. The Pd composite membrane was fabricated on a tubular stainless steel support by the electroless plating (ELP) method. The membrane exhibited a hydrogen permeance of 2.26 × 10^?3 mol m² s^?1 Pa^?0.5, H₂/N₂ selectivity of 145 at 773 K, and pressure difference of 20.3 kPa. The MSR reaction, which was carried out at steam to carbon ratio (S/C) = 3.0, gas hourly space velocity (GHSV) = 1700 h^?1, and 773 K, showed that methane conversion increased with the pressure difference and reached 79.5% at ΔP = 506 kPa. This value was ～1.9 time higher than the equilibrium value at 773 K and 101 kPa. Comparing with the previous studies which introduced sweeping gas for low hydrogen partial pressure in the permeate stream, very high pressure difference (2500–2900 kPa) for increase of hydrogen recovery and very low GHSV (<150) for increase hydraulic retention time (HRT), our result was worthy of notice. The gas composition monitored during the long-term stability test showed that the permeate side was composed of 97.8 vol% H₂, and the retentate side contained 67.8 vol% CO₂ with 22.2 vol% CH₄. When energy was recovered by CH₄ combustion in the retentate streams, pre-combustion carbon capture was accomplished using the Pd-based composite membrane reactor.     

Diffusion barrier coating using a newly developed blowing coating method for a thermally stable Pd membrane deposited on porous stainless-steel support

In this study, we present an intermetallic diffusion barrier coating using a newly developed blowing coating method for a thermally stable Pd-based composite membrane on porous stainless steel (PSS). A tubular PSS sample with 1/2 inch (12.7 mm) in diameter and 450 mm in length was used for the support. The support was welded with a stainless-steel cap and a 450-mm-long stainless-steel tube for each end. Before the diffusion barrier coating, the large-sized entrance pores were gradually blocked with sub-micron (～500 nm) and nano (50–80 nm) yttria stabilized zirconia (YSZ). 8YSZ, i.e., 8wt.% YSZ, was used for the interdiffusion barrier material and dispersed on the surface of the pre-treated PSS using the blowing coating method. The blowing coating method has 4 steps: (i) spraying the 17 wt. % 8YSZ paste on the surface of the PSS tube, (ii) blowing the paste using compressed air, (iii) drying at room temperature, and (iv) heat treatment at 923 K for 2 h in air. Steps (i) and (ii) were repeated 3 times to have a ～240 nm thick 8YSZ layer. A thin palladium layer (～3 μm) was deposited on the pre-treated PSS using electroless plating, and the membrane stability was tested at 673–773 K for ～ 200 h. A hydrogen permeation flux of 9.86 × 10^?2 mol m^?2 s^?1 and an H₂/N₂ selectivity of 595 were obtained at 773 K and a transmembrane pressure difference of 20 kPa. The surface and cross-sectional SEM/EDX analysis confirmed that the 8YSZ layer sufficiently prevented the interdiffusion between Pd and PSS elements, such as Fe, Cr and Ni.     

Flowsheet study of the thermochemical water-splitting iodine–sulfur process for effective hydrogen production

The Japan Atomic Energy Agency (JAEA) is performing research and development on the thermochemical water-splitting iodine–sulfur (IS) process for hydrogen production with the use of heat (temperatures close to 1000 °C) from a nuclear reactor process plant. Such temperatures can be supplied by a High Temperature Gas-cooled Reactor (HTGR) process. JAEA's activity covers the control of the process for continuous hydrogen production, processing procedures for hydrogen iodide (HI) decomposition, and a preliminary screening of corrosion resistant process materials. The present status of the R&D program is reported herein, with particular attention to flowsheet studies of the process using membranes for the HI processing.     

HI decomposition over PtNi/C bimetallic catalysts prepared by electroless plating

The catalytic decomposition of hydrogen iodide (HI) has drawn increasing attention because it is the key reaction for hydrogen production in the Iodine–sulfur (IS) thermochemical water splitting cycle, which is considered one of the most promising alternative methods for massive hydrogen production with high efficiency and without CO₂ emissions. Because it is very difficult for HI to decompose without the catalysts even at 500 °C, some catalysts have to be used to catalyze this reaction. In this study, four kinds of PtNi bimetallic catalysts supported on activated carbon (PtNi/C) were prepared by electroless plating and their catalytic activities were compared for HI decomposition in a fixed bed reactor at 400 and 500 °C under atmospheric pressure. Their differences in structures, surface areas, and morphology were characterized by XRD, BET and TEM, respectively. The used catalysts were also analyzed by TEM characterization in order to investigate the stability of catalysts. The results showed that the PtNi/C bimetallic catalysts are promising catalysts for HI decomposition because of their high activity and good stability, especially at high reaction temperature.     

Energy requirement of HI separation from HI–I2–H2O mixture using electro-electrodialysis and distillation

The separation of HI from HI–I₂–H₂O mixture is an essential subsection of the Iodine–Sulfur (IS) process for thermochemical hydrogen production. The energy requirement of the separation determines, to a large extent, the hydrogen production efficiency of the IS process. In order to examine duty of the separation using electro-electrodialysis (EED) and distillation, a process simulation study was carried out using an analytical model of EED based on ideal membrane properties and properties of the reported EED experiments using a Nafion^® membrane and graphite electrodes. For both of the ideal-membrane case and Nafion-membrane case, effects of the operating parameters on heat duty were estimated, which comprised column pressure, HI molality in the column feed, and the flow rate ratio of the input from Bunsen section to distillate rate. Low column pressure, and high HI molality in the column feed were preferable for the ideal-membrane case; column pressure of 1.0 MPa and optimized HI molality in the column feed were desired for the Nafion-membrane case. The flow rate ratio had little effect on the minimum heat duty in the ideal-membrane case; a value in the vicinity of the lower limit of the flow rate ratio was optimal for the Nafion-membrane case. The difference of the inclination of parameters resulted from the fractional vaporization of the column feed in the ideal-membrane case and weight of the EED cell duty on the total duty due to the membrane voltage drop. The optimization of these parameters was also carried out. The minimum total heat duty of the Nafion-membrane case was 3.07 × 10⁵ J/mol-HI, and that of the ideal-membrane case was 12.5% of this value.