Palladium Membrane Research Articles

Electroless Plating of Palladium Membranes on Porous Substrates for Hydrogen Separation and the Effects of Process Factors on Plating Rate and Efficiency: A Review

The electroless plating of palladium and palladium alloy membranes is fast becoming an important and enabling technology. This is more so when juxtaposed with the rising demand for high purity hydrogen for applications particularly in proton exchange membrane fuel cells (PEMFC). The effect of process factors such as sensitization and activation during surface modification, concentration of the reducing agent, plating temperature, time, pH, additives, air aeration on plating efficiency, quality of the palladium film and deposit morphology is reviewed with the aim of identifying areas requiring further investigation. The paper also reviews how these process factors could be optimised for better plating efficiency and overall membrane quality. The concentration of the reducing agent has been identified as the limiting factor on plating efficiency albeit other process factors separately impact on the plating efficiency. Furthermore, bulk precipitation caused by concentration of the reducing agent has been identified as a major problem during electroless plating with hydrazine based plating baths. To ameliorate this problem, a multi step addition of the hydrazine reducer in separate portions has been recommended.

Development of Palladium-Alloy Membranes for Hydrogen Separation and Purification

This paper summarizes RD 2) preparing and characterizing thin Pd composite membranes; 3) development of Pd-Ru membranes by electroless plating for enhanced stability at higher temperatures; 4) production of palladium membranes for application in hydrogen separation and hydrogen production by fluidized bed membrane reactors.

Periodically Ordered Mesoporous Palladium Membranes with High Intrinsic Electrocatalytic Activity for Formic Acid Oxidation

Periodically Ordered Mesoporous Palladium Membranes with High Intrinsic Electrocatalytic Activity for Formic Acid Oxidation

Study of the plasma and heating effect on hydrogen permeation through Pd0.60-Cu0.40 membrane in a micro-channel plate reactor

The diffusion of hydrogen through palladium and palladium-copper alloys membrane have been provided the highest hydrogen selectivity and permeance. In this study the composite Pd0.60-Cu0.40 wt% membrane foil with thickness 20 μm was measured in the micro-channel plate reactor (MPR) with gap length 4.5 mm. The hydrogen permeation flux was measured at atmospheric feeding pressure for 100% H2 concentration in the temperatures range of 423–573 K under heating only and plasma-heating experiments. The plasma firing high voltage source ranges of 10–18 kV are tested. The hydrogen permeation flux and hydrogen permeability have been calculated according to Fick's and Sieverts combining laws with power exponent n-value 0.5. It was found that the maximum hydrogen flux, hydrogen permeability and Permeation rate percent of the heating only experiment at MPR heating temperature of 573 K and flow rate 0.1 l/min. In the plasma heating experiment, it was observed that the maximum hydrogen flux, hydrogen permeability, and permeation rate percent at MPR heating temperature of 573 K and plasma firing voltage of 14 kV. Also, the hydrogen permeation rate percent decreased due to the hydrogen reverse reaction even though the plasma firing voltage increased to 16 kV and 18 kV. The results also reveal that the activation energy and Pre-exponential constant factor decreased with increasing the feeding H2 flow rate while the linear regression R2 decreased with increasing H2 feeding flow rate that in the heating only experiment, in contrast, the plasma-heating experiment showed non-linearity values. A comparison between both experiments showed the hydrogen permeation flux of the plasma-heating experiment is higher than that obtained from the heating only experiment, additionally; the plasma effect increased at low hydrogen flow rates. In contrast, the energy efficiency of heating only experiment was higher than that obtained from the plasma-heating experiment due to the total energy consumption of plasma experiment is high.

Multiphase Methods in Organic Electrosynthesis.

With water providing a highly favored solution environment for industrial processes (and in biological processes), it is interesting to develop water-based electrolysis processes for the synthesis and conversion of organic and biomass-based molecules. Molecules with low solubility in aqueous media can be dispersed/solubilized (i) by physical dispersion tools (e.g., milling, power ultrasound, or high-shear ultraturrax processing), (ii) in some cases by pressurization/supersaturation (e.g., for gases), (iii) by adding cosolvents or "carriers" such as chremophor EL, or (iv) by adding surfactants to generate micelles, microemulsions, and/or stabilized biphasic conditions. This Account examines and compares methodologies to bring the dispersed or multiphase system into contact with an electrode. Both the microscopic process based on individual particle impact and the overall electro-organic transformation are of interest. Distinct mechanistic cases for multiphase redox processes are considered. Most traditional electro-organic transformations are performed in homogeneous solution with reagents, products, electrolyte, and possibly mediators or redox catalysts all in the same (usually organic) solution phase. This may lead to challenges in the product separation step and in the reuse of solvents and electrolytes. When aqueous electrolyte media are used, reagents and products (or even the electrolyte) may be present as microdroplets or nanoparticles. Redox transformations then occur during interfacial "collisions" under multiphase conditions or within a reaction layer when a redox mediator is present. Benefits of this approach can be (i) the use of a highly conducting aqueous electrolyte, (ii) simple separation of products and reuse of the electrolyte, (iii) phase-transfer conditions in redox catalysis, (iv) new reaction pathways, and (v) improved sustainability. In some cases, a surface phase or phase boundary processes can lead to interesting changes in reaction pathways. Controlling the reaction zone within the multiphase redox system poses a challenge, and methods based on microchannel flow reactors have been developed to provide a higher degree of control. However, detrimental effects in microchannel systems are also observed, in particular for limited current densities (which can be very low in microchannel multiphase flow) or in the development of technical solutions for scale-up of multiphase redox transformations. This Account describes physical approaches (and reactor designs) to bring multiphase redox systems into effective contact with the electrode surface as well as cases of important electro-organic multiphase transformations. Mechanistic cases considered are "impacts" by microdroplets or particles at the electrode, effects of dissolved intermediates or redox mediators, and effects of dissolved redox catalysts. These mechanistic cases are discussed for important multiphase transformations for gaseous, liquid, and solid dispersed phases. Processes based on mesoporous membranes and hydrogen-permeable palladium membranes are discussed.

Exergoeconomic analysis of an HCCI engine polygeneration process

A polygeneration system producing hydrogen, electricity, process steam, and heating water is modeled and studied by conducting an exergoeconomic analysis. This system includes a homogeneous charge compression ignition (HCCI) engine burning a rich methane-air mixture, a water-gas shift reactor (WGSR) and a palladium membrane for hydrogen separation. Different cost-apportioning methods were considered in the present work in order to assess their suitability for the studied system. Furthermore, a global sensitivity analysis was used to identify the relevant system parameters as well as to quantify the influence that the input data uncertainty causes on the costs of the system products. It is shown that these costs are sensitive to the investment costs of only few system components and that the highest exergy destruction rates and costs occur in the engine. With the predicted cost of hydrogen ranging from 3.23 to 3.99 €/kg at EGR ratios of up to 25%, the studied process is promising.

Analysis of combined heat and mass transfer in membrane-assisted thermally coupled reactors containing naphtha reforming and m-xylene hydrodealkylation

In this work, the performance of catalytic naphtha reforming in the thermally coupled membrane reactors has been investigated. It is suggested that the hydrodealkylation of m-xylene be placed in the tube side and the catalytic reforming in the shell side of the proposed reactor. The interior reactor wall has been made of palladium membrane, which permits the hydrogen to penetrate from the shell side with higher partial pressure to the tube with lower partial pressure. Thermal coupling of hydrodealkylation of m-xylene with naphtha reforming, as well as the removal of a part of the hydrogen as a by-product from the reforming side leads to an increase in reformate production. Simulation results indicate that the aromatic production rate in this configuration increases by 16.43% relative to the membrane reactors and by 23.52% relative to the conventional reactors. The effect of parameters including the membrane thickness, inlet temperatures of naphtha and HDA feeds, the molar flow rate of the hydrodealkylation side, the hydrogen to hydrocarbon molar ratio and also, the catalyst deactivation on the performance of the system has been studied. Finally, in order to improve the performance of thermally coupled membrane reactors, the effective parameters in the proposed configuration have been optimized by the genetic algorithm. The yield of aromatic was enhanced by about 14% by this optimization. Also, the conversion of m-xylene in each bed was improved in optimized thermally coupled membrane reactors.

The ITER Tokamak Exhaust Processing System Permeator and Palladium Membrane Reactor Design

The tokamak exhaust processing (TEP) system performs chemical separations on ITER fuel cycle process streams. TEP recovers hydrogen isotopes (Q2) from impurities such as argon, nitrogen, tritiated water (Q2O), tritiated ammonia (NQ3), and tritiated hydrocarbons such as methane (CQ4). TEP sends the hydrogen isotopes for subsequent processing to the isotope separation system or the storage and delivery system. At the same time, an impurity gas stream of extremely low tritium content (less than 8.88 TBq of tritium per day) is produced and sent to the detritiation system (DS). To accomplish the separation, the major hydrogen processing subsystems within TEP are hydrogen-like processing (HLP) and air-like processing/water-like processing (ALP/WLP). (Hydrogen-like gases are Q2, He, and Ne; air-like gases are Ar, O2, N2, O2, and CQ4; and water-like gases are Q2O and NQ3). The main processing equipment used for the HLP is a series of palladium-silver permeators (PMs) with ALP/WLP using a series of Palladium Membrane Reactors (PMRs). Aspen Dynamics is the primary tool for verifying system performance of the TEP design. Aspen Dynamics is a commercial, equation-based simulation package for chemical processing. The software enables the user to develop a process model from predefined unit-operation models or construct its own unique unit-operations model. Verification of the TEP simulation model to experimental data was achieved during the TEP conceptual design. The designs for the TEP HLP and ALP/WLP subsystems are examined for the updated gas inputs in terms of compositions and flow rates. The TEP simulation is used to predict tritium output of the TEP processing subsystems This paper describes how the Aspen model of the equipment was improved and used to size the equipment (PMs and PMRs) to process the various gas streams and maintain the discharge to DS to below the limit.

Efficient Hydrogen Production from Coke Oven Gas by Sorption-Enhanced Steam Reforming in a Membrane-Assisted Fluidized Bed Reactor

High-purity hydrogen was produced by catalytic steam reforming of coke oven gas (COG) in a fluidized bed membrane reactor (FBMR), assisted by calcined dolomite and a tubular palladium membrane. Thi...

Kinetic and thermodynamic analyses of mid/low-temperature ammonia decomposition in solar-driven hydrogen permeation membrane reactor

It is a promising method for hydrogen generation without carbon emitting by ammonia decomposition in a catalytic palladium membrane reactor driven by solar energy, which could also store and convert solar energy into chemical energy. In this study, kinetic and thermodynamic analyses of mid/low-temperature solar thermochemical ammonia decomposition for hydrogen generation in membrane reactor are conducted. Hydrogen permeation membrane reactor can separate the product and shift the reaction equilibrium forward for high conversion rate in a single step. The variation of conversion rate and thermodynamic efficiency with different characteristic parameters, such as reaction temperature (100–300 °C), tube length, and separation pressure (0.01–0.25 bar), are studied and analyzed. A near-complete conversion of ammonia decomposition is theoretically researched. The first-law thermodynamic efficiency, net solar-to-fuel efficiency, and exergy efficiency can reach as high as 86.86%, 40.08%, and 72.07%, respectively. The results of this study show the feasibility of integrating ammonia decomposition for hydrogen generation with mid/low-temperature solar thermal technologies.

Techno-Economic Assessment in a Fluidized Bed Membrane Reactor for Small-Scale H2 Production: Effect of Membrane Support Thickness.

This paper investigates the influence of the support material and its thickness on the hydrogen flux in Palladium membranes in the presence of sweep gas in fluidized bed membrane reactors. The analysis is performed considering both ceramic and metallic supports with different properties. In general, ceramic supports are cheaper but suffer sealing problems, while metallic ones are more expensive but with much less sealing problems. Firstly, a preliminary analysis is performed to assess the impact of the support in the permeation flux, which shows that the membrane permeance can be halved when the H2 diffusion through the support is considered. The most relevant parameter which affects the permeation is the porosity over tortuosity ratio of the porous support. Afterward, the different supports are compared from an economic point of view when applied to a membrane reactor designed for 100 kg/day of hydrogen, using biogas as feedstock. The stainless steel supports have lower impact on the hydrogen permeation so the required membrane surface area is 2.6 m2 compared to 3.6 m2 of the best ceramic support. This ends up as 5.6 €/kg H2@20bar and 6.6 €/kg H2@700bar for the best stainless steel support, which is 3% lower than the price calculated for the best ceramic support.

Optimization of a novel multifunctional reactor containing m-xylene hydrodealkylation and naphtha reforming

In the present study, efforts have been made to improve the performance of the naphtha reforming process. To this end, the conventional reactors in the naphtha reforming process have been replaced with the new multifunctional reactors. These proposed reactors consist of hydrodealkylation and reforming sides separated by a solid wall and also permeation side that is separated from the reforming side by a palladium membrane wall. The naphtha reforming exchanges the heat with the hydrodealkylation of m-xylene, while this process exchanges the hydrogen gas with the permeation side. This new configuration will lead to an improvement in the production yield of aromatic in the catalytic reforming. According to the simulation results, the production rate of aromatic in this new suggestion increases by about 11% in comparison to the conventional process. The effects of design parameters such as the inlet temperatures of naphtha and hydrodealkylation feeds, the inlet molar flow rate of the hydrodealkylation side and, also the membrane thickness on the system performance have been studied. At the end of the work, the genetic algorithm optimization has been used to determine the best values of varies adjustable parameters in this system.

Synthesis and gas transport parameters of membranes modified by star­shaped nanocrystalline palladium

Methods have been developed to modify the surface of Pd-23%Ag alloy films in order to increase the rate of hydrogen transfer with appearance of palladium coatings of the “nanostar” and “nanopore” types. The gas transport parameters of the membranes which surface is activated using the developed methods were investigated. The modification of surface of Pd-Ag films synthesized by star-like palladium nanocrystallites allows achieving a hydrogen flux density of up to 0.75 mmol / (s × m2) - that is 1.7 times more than in case of modification modified by “nanopore” type coating of sufficiently thin palladium membranes (< 10 µm) under low temperature (<100 °C) and pressure (<0.6 MPa).

Palladium Membrane Coated with Zeolitic Armor Anchored by Diffusion-Piling To Enhance Performance

Herein, an innovative technique of diffusion-piling is proposed to nondestructively arm an ultrathin Pd membrane with a zeolite membrane. The effects of arming the Pd film with this zeolitic armor on the performances of H2 permeation and sulfur tolerance were evaluated, and the anchoring mechanism of the zeolite membrane onto the Pd film was discussed. For anchoring zeolite membrane onto the Pd film, coating an Al layer on the Pd film followed by a suitable thermal treatment to diffuse Al atoms into the Pd film are essential. Although the armed Pd film was covered with a zeolite membrane, its H2 permeation flux surprisingly increases under the applied conditions. In the test of H2S tolerance, after 250 min, the H2 permeance of the armed Pd membrane decreased by 61%, which is 25% higher than that of the bare Pd membrane. In particular, it is stable in the following test of 28 h, showing superior resistance to H2S poisoning.

Hydrogen permeation enhancement in a Pd membrane tube system under various vacuum degrees

Hydrogen purification using palladium (Pd) membrane technology has been seen as a potential solution for producing pure hydrogen form hydrogen-rich gas. Compared to traditional practices of operating the permeate side of the membrane at atmospheric pressure, in this study, a vacuum is applied. The effects of various vacuum degrees applied to the permeate side of the Pd membrane are investigated and compared to the results under normal operation without a vacuum. The feed gas used for experiments consists of a mixture of hydrogen (70 vol%) and nitrogen (30 vol%). Three membrane operating temperatures (320, 350, and 380 °C), four pressure differences (2, 3, 4, and 5 atm) across the membrane, and four vacuum degrees (−15, −30, −45, and −53 kPa) applied to the permeate side are considered. For the three operating temperatures, the best improvements in the performance of hydrogen permeation are at 320 and 350 °C when a −53 kPa vacuum is applied, resulting in 79.4% and 79.1% improvements, respectively, compared to normal operations. Increasing temperatures leads to an increase in H2 permeation both with and without a vacuum; however, best performances of H2 permeation are observed in cases without a vacuum.

Coating the porous Al2O3 substrate with a natural mineral of Nontronite-15A for fabrication of hydrogen-permeable palladium membranes

Substrate surface modification is a key pretreatment during fabrication of composite palladium membranes for hydrogen purification in hydrogen energy applications. The suspension of a natural porous material, Nontronite-15A mineral, without any organic additives was employed in dip-coating of the porous Al2O3 substrate. The Nontronite-15A mineral was characterized by SEM, XRD, TG−DSC and granulometry analysis. The surface and cross-section of the coated porous Al2O3 tubes were observed by SEM, and their pore size distribution and nitrogen flux were also measured. Palladium membranes were fabricated over the coated Al2O3 tubes by a suction-assisted electroless plating. The optimal loading amount of the Nontronite-15A mineral is just to fill in and level up the surface cavities of the Al2O3 substrate rather than to form an extra continuous layer. A thin and selective palladium membrane was successfully obtained, and its permeation performances were tested. The kinetic analyses on the hydrogen flux indicate that the hydrogen permeation behavior exhibits typical characteristics for most of the palladium membranes. During the stability test at 450 °C for 192 h, no membrane damage was detected, and the hydrogen flux increased slightly.

Synthesis and Gas-Transport Parameters of Membranes Modified by Star-Shaped Palladium Nanocrystallites

Methods for modifying the surface of Pd–23%Ag alloy films and synthesizing nanostar- and nanopore-type palladium coatings, which enhance the hydrogen transport rate, were developed. The gas-transport parameters of membranes with their surfaces activated this way were examined. Pd–Ag films with surfaces modified by star-shaped palladium nanocrystallites demonstrate hydrogen flow densities as high as 0.75 mmol/(s m2) under low temperatures (<100°С) and pressures (<0.6 MPa) if the palladium membranes are sufficiently thin (<10 μm). The flow density provided by nanopore-type coatings is 1.7 times lower.

Efficient Electrocatalytic Hydrogenation with a Palladium Membrane Reactor.

We report here the benefits of using a palladium membrane reactor to drive hydrogenation chemistry with electricity while bypassing the formation of gaseous H2. This technique uses a palladium membrane to physically separate the electrochemical and hydrogenation chemistry. As a result, hydrogenation can be performed electrochemically with protons but in any organic solvent.In this article, we outline a series of experiments showing how hydrogenation in the palladium membrane reactor proceeds at faster reaction rates and with much higher voltage efficiency than hydrogenation at an electrode. Moreover, the organic reaction chemistry in the membrane reactor can be performed in organic solvents and without contamination by electrolytes. The physical separation of the hydrogenation compartment from the electrolysis compartment therefore broadens the scope of electrolytically-driven reactions that are available, and simplifies reagent handling and purification.

Process analysis of hydrogen production from biomass gasification in fluidized bed reactor with different separation systems

Gasification is one of the most effective and studied methods for producing energy and fuels from biomass as different biomass feedstock can be handled, with the generation of syngas consisting of H2, CO, and CH4, which can be used for several applications. In this study, the gasification of hazelnut shells (biomass) within a circulating bubbling fluidized bed gasifier was analyzed for the first time through a quasi-equilibrium approach developed in the Aspen Plus environment and used to validate and improve an existing bubbling fluidized bed gasifier model. The gasification unit was integrated with a water-gas shift (WGS) reactor to increase the hydrogen content in the outlet stream and with a pressure swing adsorption (PSA) unit for hydrogen separation. The amount of dry H2 obtained out of the gasifier was 31.3 mol%, and this value increased to 47.5 mol% after the WGS reaction. The simulation results were compared and validated against experimental data reported in the literature. The process model was then modified by replacing the PSA unit with a palladium membrane separation module. The final results of the present work allowed comparison of the effects of the two conditioning systems, PSA and palladium membrane, indicating a comparative increase in the hydrogen recovery ratio of 28.9% with the palladium membrane relative to the PSA configuration.

Diffusion of hydrogen in China Reduced Activation Ferritic-martensitic steels at low temperatures

Reduced Activation Ferritic/Martensitic (RAFM) steels have been considered as the most promising candidate structural materials for a fusion reactor. In this paper, the hydrogen diffusion behavior of two types of RAFM steels, called China Low Activation Martensitic (CLAM) steel and China Low-activation Ferritic (CLF-1) steel, have been studied by electrochemical technique over the temperature range of 293–323 K. Before hydrogen permeation, both sides of the CLAM and CLF-1 steels were coated with a thin layer of uniform and dense palladium (Pd) membrane by electro-plating method. The results showed that the diffusion coefficients of hydrogen through CLAM and CLF-1 steels were submitted to the relationships of D(cm2/s) = 3.04 × 10−6exp[-4.72(kJ⋅mol-1)/RT] and D(cm2/s) = 1.82 × 10-5exp[-10.07(kJ⋅mol-1)/RT], which were far higher than that of some other austenitic stainless steels, such as 316 S.S. This indicates that if the RAFM steels as the structural material for fusion reactor are free from hydrogen environment, the hydrogen isotopes will escape from them quickly under low temperatures, which is conducive to keeping the mechanical properties of RAFMs.