Electroless Pd membrane deposition on alumina modified porous Hastelloy substrate with EDTA-free bath

This study demonstrates palladium membranes can be electrolessly plated on aluminum oxide-modified porous Hastelloy with hydrazine using an EDTA-free bath. The plating bath temperature affected the membrane surface morphology, with the palladium grain size increasing with increasing temperature. A 7.5 μm thick membrane plating was obtained at room temperature. Helium leak testing confirmed that the membrane was free of defects. Hydrogen permeation test showed that the membrane had a hydrogen permeation flux of 3.3 × 10⁻¹ mol m⁻² s⁻¹ at a temperature of 823 K and at a pressure difference of 100 kPa. There was no measurable interdiffusion between the membrane film and the porous Hastalloy substrate at 823 K. This room temperature membrane plating method provides several advantages such as very high selectivity, stability, favorable energy efficiency and simplicity.     

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.     

Novel micro-channel methane reformer assisted combustion reaction for hydrogen production

A metal catalyst-containing, 80 ml, micro-channel reactor (MCR) with a section dedicated to combustion reaction was investigated for the potential application of on-board methane steam reforming (MSR) to hydrogen production. The metal catalyst was introduced into the MCR as a shape of a thin plate that was diffusion-bonded with the other micro-channel plates. The combustion reaction was performed on the other side of the MCR for direct provision of the necessary heat for the endothermic MSR and for miniaturizing the system volume. In the MCR, both the methane conversion and the hydrogen production rate are extremely high compared with those of the equilibrium under atmospheric pressure. The required heat of reaction is successfully provided by the combustion of either hydrogen or the methane mixture on the other side of the MCR without the need for any heating cartridges. This novel micro-channel reformer is suitable for application as a compact fuel processor due to its production of hydrogen-rich syn-gas, small volume, simple catalyst loading and use of an active and easily stackable catalyst.     

The property of hydrogen separation from CO2 mixture using Pd-based membranes for carbon capture and storage (CCS)

This study investigates the module configuration for upscaling CO₂ capture capacity to a bench-scale in hydrogen selective Pd-based composite membranes. In order to confirm effective upscaling, four plate-type membranes of two inch diameter were stacked in a newly designed plate-and-frame type module, reaching a total membrane surface area of 6.64 × 10⁻³ m² (66.4 cm²). A pure gas test carried out using H₂ and He confirmed that there were no effects of module configuration in gas permeation behavior, indicating that the upscale of the separation capacity by numbering-up of membranes using our module design was successful. The CO₂ enrichment test was conducted using a 40%CO₂ + 60%H₂ mixture (i.e. a similar composition for the coal gasifier after both the shift reaction and H₂O removal), under high feed pressure and flow rate, i.e. 600–2100 kPa and 0.48–0.72 N m³ h⁻¹. The mixture gas test confirmed that the bench-scale membrane module could enrich 40% of the CO₂ at a feed flow rate of 0.48 N m³ h⁻¹ up to 93% with a hydrogen recovery ratio of >90% at 673 K and a total feed pressure of 2100 kPa, i.e. ∼4 times CO₂ enrichment capacity of one membrane.     

Development of a hydrogen purifier with Pd-based composite membrane

A hydrogen purifier equipped with Pd-Cu-Ni/PNS membranes has been developed to purify low-grade hydrogen and supply it to processes requiring high-purity hydrogen. The purifier does not include any purge system to flush out hydrogen from the membrane module to prevent membrane embrittlement because there is no α-β phase transition below the critical point of the Pd-H system, making the purifier simple. The hydrogen purifier was tested with three different grades of hydrogen, 90, 99 and 99.9%, to determine the effects of the grade of feed hydrogen on the hydrogen permeation behavior. A lower grade required a lower recovery ratio of the purifier to obtain a given relative hydrogen permeation flux. It was confirmed that the purifier can provide high-purity hydrogen to a gas chromatograph (GC) for carrier and make-up gases. A 75-day durability test provided evidence that the hydrogen purifier could be useful for extended periods as needed for commercial processes.     

Pd–Cu alloy membrane deposited on CeO2 modified porous nickel support for hydrogen separation

In this study, the hydrogen permeation behavior of a Pd₉₃–Cu₇ alloy membrane deposited on ceria-modified porous nickel support (PNS) was evaluated. PNS, which has an average pore size of 600 nm, was modified by alumina sol. Alumina sol was prepared using precursors that had a mean particle size of 300 nm. Alumina-modified PNS was further treated with ceria sol modification to produce a smoother surface morphology and narrow surface pores. A 7 μm thick Pd₉₃–Cu₇ alloy membrane was made on an alumina-modified PNS and a ceria-finished membrane was fabricated by magnetron sputtering followed by Cu-reflow at 700 °C for 2 h. SEM analysis showed that the membrane deposited on a ceria-finished PNS contained more clear grain boundaries than the membrane deposited on the alumina-modified PNS. The membrane was mounted in a stainless steel permeation cell with a gold-plated stainless steel O-ring. Permeation tests were then conducted using pure hydrogen and helium at temperatures ranging from 673 to 773 K and feed side pressures ranging from 100 to 400 kPa. These tests showed that the membrane had a hydrogen permeation flux of 2.8 × 10⁻¹ mol m⁻² s⁻¹ with H₂/He selectivity of >50,000 at a temperature of 773 K and pressure difference of 400 kPa.     

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.     

Pd-Cu alloy membrane deposited on alumina modified porous nickel support (PNS) for hydrogen separation at high pressure

This study reports on the hydrogen permeation properties of Pd-Cu alloy membranes at high pressures. A 7 μm thick Pd-Cu alloy membrane was prepared on an alumina-modified porous nickel support (PNS) by our developed magnetron sputtering and Cu-reflow method at 700 °C for 2 hours. The membrane was mounted in a stainless steel permeation cell with a gold-plated stainless steel O-ring. Helium leak testing confirmed that the membrane and membrane module were free of defects. Permeation tests were then conducted using hydrogen at temperatures in the range from 678 to 816 K with a transmembrane pressure difference of 1–20 bars, which showed that the membrane had a hydrogen permeation flux of 1.06 mol m⁻² s⁻¹ at a temperature of 816 K and a pressure difference of 20 bars. EDX analysis was carried out after hydrogen permeation test at 816 K and showed that there was no intermetallic diffusion between the Pd-Cu layer and PNS because the alumina layer inhibited it effectively.