Oxidative steam reforming of ethanol over a Pt/Al2O3 catalyst in a Pd-based membrane reactor

In this study, the ability of a Pd-Ag membrane reactor of producing ultrapure hydrogen via oxidative steam reforming of ethanol has been evaluated. A self supported Pd-Ag tube of wall thickness 60 μm has been filled with a commercial Pt-based catalyst and assembled into a membrane module in a finger-like configuration. In order to evaluate the hydrogen yield behavior under different operating conditions, experimental tests have been performed at temperatures of 400 and 450 °C and pressures of 150 and 200 kPa. The oxidative steam reforming of ethanol has been carried out by feeding the membrane reactor with a gas stream containing a dilute water-ethanol mixture and air. Different water/ethanol feed flow rates (5, 10, 15 g h⁻¹), several water/ethanol (4, 10, 13) and oxygen/ethanol (0.3, 0.5, 0.7) feed molar ratios have been tested. The results pointed out that the highest hydrogen yield (moles of permeated hydrogen per mole of ethanol fed) corresponding to almost 4.1 has been attained at 450 °C and 200 kPa of lumen pressure by using a water/ethanol/oxygen feed molar ratio of 10/1/0.5.The results of these tests have been compared with those reported for the ethanol steam reforming in a Pd-Ag membrane reactor filled with the same Pt-based catalyst. This comparison has shown a positive effect on the hydrogen yield of small oxygen addition in the feed stream.     

Simulation of steam reforming of biogas in an industrial reformer for hydrogen production

The paper aims to investigate the steam reforming of biogas in an industrial-scale reformer for hydrogen production. A non-isothermal one dimensional reactor model has been constituted by using mass, momentum and energy balances. The model equations have been solved using MATLAB software. The developed model has been validated with the available modeling studies on industrial steam reforming of methane as well as with the those on lab-scale steam reforming of biogas. It demonstrates excellent agreement with them. Effect of change in biogas compositions on the performance of industrial steam reformer has been investigated in terms of methane conversion, yields of hydrogen and carbon monoxide, product gas compositions, reactor temperature and total pressure. For this, compositions of biogas (CH₄/CO₂ = 40/60 to 80/20), S/C ratio, reformer feed temperature and heat flux have been varied. Preferable feed conditions to the reformer are total molar feed rate of 21 kmol/h, steam to methane ratio of 4.0, temperature of 973 K and pressure of 25 bar. Under these conditions, industrial reformer fed with biogas, provides methane conversion (93.08–85.65%) and hydrogen yield (1.02–2.28), that are close to thermodynamic equilibrium condition.     

In-situ CO2 capture in a pilot-scale fluidized-bed membrane reformer for ultra-pure hydrogen production

A novel pilot fluidized-bed membrane reformer (FBMR) with permselective palladium membranes was operated with a limestone sorbent to remove CO₂in-situ, thereby shifting the thermodynamic equilibrium to enhance pure hydrogen production. The reactor was fed with methane to fluidize a mixture of calcium oxide (CaO)/limestone (CaCO₃) and a Ni-alumina catalyst. Experimental tests investigated the influence of limestone loading, total membrane area and natural gas feed rates. Hydrogen-permeate to feed methane molar ratios in excess of 1.9 were measured. This value could increase further if additional membrane area were installed or by purifying the reformer off-gas given its high hydrogen content, especially during the carbonation stages. A maximum of 0.19 mol of CO₂ were adsorbed per mole of CaO during carbonation. For the conditions studied, the maximum carbon capture efficiency was 87%. The reformer operated for up to 30 min without releasing CO₂ and for up to 240 min with some degree of CO₂ capture. It was demonstrated that CO₂ adsorption can significantly improve the productivity of the reforming process. In-situ CO₂ capture enhanced the production of hydrogen whose purity exceeded 99.99%.     

Methane membrane steam reforming: Heat duty assessment

Membrane reactors are an innovative technology with huge application potentialities for equilibrium limited endothermic reactions. Assembling a membrane selective to a reaction product avoids the equilibrium conditions to be achieved, supporting the reactions at lower operating temperatures. Taking as an example the natural gas steam reforming, a methane conversion around 98% can be reached imposing an operating temperature of 823 K, much lower than that of the traditional process. In the present paper, a stringent analysis of heat power requirement needed to carry out the natural gas steam reforming process by applying a membrane reactor is made. The simulations allows to understand how the main operating parameters (inlet temperature, inlet methane flow-rate, steam to carbon ratio, ratio between sweeping steam and inlet methane, operating reaction pressure) influence the total heat power required by the process, divided among power contributions for the reaction heat duty, reactant steam and permeation steam generation and preheating. Moreover, the specific thermal energy per mole of pure H₂ is computed and assessed. Optimizing the operating conditions set, a specific thermal energy per mole of pure hydrogen of 92.3 kWh kmol⁻¹ is obtained corresponding to a total thermal power of 687.4 kW required to convert, in a single membrane reactor, a methane flow-rate of 2 kmol h⁻¹ (GHSV = 9.590 h⁻¹) with a conversion around 98%.     

Noncatalytic gasification of isooctane in supercritical water: A Strategy for high-yield hydrogen production

Continuous supercritical water gasification of isooctane, a model gasoline compound, is investigated using an updraft gasification system. A new reactor material, Haynes^® 230^® alloy, is employed to run gasification reactions at high temperature and pressure (763 ± 2 °C; 25 MPa). A large-volume reactor is used (170 mL) to enable the gasification to be run at a long residence time, up to 120 s. Various gasification experiments are performed by changing the residence time (60-120 s), the isooctane concentration (6.3-14.7 wt%), and the oxidant concentration (equivalent oxidant ratio 0-0.3). The total gas yield and the hydrogen gas yield increase with increasing residence time. At 106 s and an isooctane concentration of 6.3 wt%, a very high hydrogen gas yield of 12.4 mol/mol isooctane, which is 50% of the theoretical maximum hydrogen gas yield and 92% of the equilibrium hydrogen gas yield under the given conditions, is achieved. Under these conditions, supercritical water partial oxidation does not increase the hydrogen gas yield significantly. The produced gases are hydrogen (68 mol%), carbon dioxide (20 mol%), methane (9.8 mol%), carbon monoxide (1.3 mol%), and ethane (0.9 mol%). The carbon gasification efficiency is in the range 75-91%, depending on the oxidant concentration. A comparison of supercritical water gasification with other conventional methods, including steam reforming, autothermal reforming, and partial oxidation, is also presented.     

Application of aspen plus to renewable hydrogen production from glycerol by steam reforming

Steam reforming is the most favored method for the production of hydrogen. Hydrogen is mostly manufactured by using steam reforming of natural gas. Due to the negative environmental impact and energy politics, alternative hydrogen production methods are being explored. Glycerol is one of the bio-based alternative feedstock for hydrogen production. This study is aimed to simulate hydrogen production from glycerol by using Aspen Plus. First of all, the convenient reactor type was determined. RPlug reactor exhibited the highest performance for the hydrogen production. A thermodynamic model was determined according to the formation of byproduct. The reaction temperature, water/glycerol molar feed ratio as reaction parameters and reactor pressure were investigated on the conversion of glycerol and yield of hydrogen. Optimum reaction parameters are determined as 500 °C of reaction temperature, 9:1 of water to glycerol ratio and 1 atm of pressure. Reactor design was also examined. Optimum reactor diameter and reactor length values were determined as 5 m and 50 m, respectively. Hydrogen purification was studied and 99.9% purity of H₂was obtained at 25 bar and 40 °C. The obtained results were shown that Aspen Plus has been successfully applied to investigate the effects of reaction parameters and reactor sizing for hydrogen production from glycerol steam reforming.     

Hydrogen production from supercritical water reforming of glycerol in an empty Inconel 625 reactor

Glycerol reforming was investigated under supercritical water conditions (450–575 °C, 250 bar). A feed containing 5 wt.% of glycerol was continuously fed to an empty Inconel 625 reactor. The products of the reaction were separated into gas and liquid phases in a condenser. At a feed rate of 2.15 g/min, the glycerol conversion significantly increased from 0.05 to 0.97 when increasing operating temperature from 450 to 575 °C. Although lowering the feed rate (i.e. increasing the residence time) could considerably improve the conversion, carbon formation became a problem especially at high operating temperatures (550–575 °C). The major gaseous products were hydrogen (approximately 60 mol%), carbon monoxide, carbon dioxide and methane with some traces of ethane, ethylene, propane, and propylene. Various liquid products were detected including acetaldehyde, acetol, methanol, acetic acid, propionaldehyde, allyl alcohol, acetone, acrolein, ethanol, ethylene glycol, and acrylic acid but the major liquid components were acetaldehyde and acetol. With a feed glycerol concentration of 2.5 wt.% and operating temperature of 525 °C, glycerol conversion of 0.91 and H₂ yield of 2.86 can be obtained without carbon formation. Finally, it was demonstrated that higher H₂ yield with much lower carbon formation was observed in supercritical water reforming (250 bar) compared to conventional steam reforming at 1 bar under similar temperatures.     

Steam reforming of propane in a fluidized bed membrane reactor for hydrogen production

Steam reforming of propane was carried out in a fluidized bed membrane reactor to investigate a feedstock other than natural gas for production of pure hydrogen. Close to equilibrium conditions were achieved inside the reactor with fluidized catalyst due to the very fast steam reforming reactions. Use of hydrogen permselective Pd₇₇Ag₂₃ membrane panels to extract pure hydrogen shifted the reaction towards complete conversion of the hydrocarbons, including methane, the key intermediate product. Irreversible propane steam reforming is limited by the reversibility of the steam reforming of this methane. To assess the performance improvement due to pure hydrogen withdrawal, experiments were conducted with one and six membrane panels installed along the height of the reactor. The results indicate that a compact reformer can be achieved for pure hydrogen production for a light hydrocarbon feedstock like propane, at moderate operating temperatures of 475–550 °C, with increased hydrogen yield.     

H2 production by low pressure methane steam reforming in a Pd–Ag membrane reactor over a Ni-based catalyst: Experimental and modeling

Nowadays, there is a growing interest towards pure hydrogen production for proton exchange membrane fuel cell applications. Methane steam reforming reaction is one of the most important industrial chemical processes for hydrogen production. This reaction is usually carried out in fixed bed reactors at 30–40 bar and at temperatures above 850 °C. In this work, a dense Pd–Ag membrane reactor packed with a Ni-based catalyst was used to carry out the methane steam reforming reaction between 400 and 500 °C and at relatively low pressure (1.0–3.0 bar) with the aim of obtaining higher methane conversion and hydrogen yield than a fixed bed reactor, operated at the same conditions. Furthermore, the Pd–Ag membrane reactor is able to produce a pure, or at least, a CO and CO₂ free hydrogen stream. A 50% methane conversion was experimentally achieved in the membrane reactor at 450 °C and 3.0 bar whereas, at the same conditions, the fixed bed reactor reached a 6% methane conversion. Moreover, 70% of high-purity hydrogen on total hydrogen produced was collected with the sweep-gas in the permeate stream of the membrane reactor. From a modeling point of view, the mathematical model realized for the simulation of both the membrane and fixed bed reactors was satisfactorily validated with the experimental results obtained in this work.     

Efficient H2 production via membrane-assisted ethanol steam reforming over Ir/CeO2 catalyst

Ethanol steam reforming in membrane reactors is a promising route for decentralized H₂ production from biomass because H₂ yield can be greatly enhanced due to the equilibrium shift triggered by instantaneous H₂ extraction. Here a highly active Ir/CeO₂ catalyst has been combined with ca. 4 μm thin Pd membranes employing a 6:1 steam/ethanol feed between 673 K and 873 K at reforming pressures up to 1.8 MPa. The H₂ yield reached 94.5% at 873 K and 1300 kPa due to the separation of 91.8% H₂ whereas H₂ yield was limited to 28.9% without membrane. At lower temperatures and pressures sweep gas was needed at the membranes' permeate side for efficient H₂ generation since the H₂ partial pressure remains equilibrium-limited on the reaction side. Furthermore, the H₂ yield improved from 63.0% to 84.7% at 773 K, 1500 kPa and sweep-to-feed flow ratio 0.5 when the distance between membrane and reactor wall was shortened by ca. 30%. Thus, external H₂ diffusion towards the membrane has a large impact on membrane reactor performance pointing towards microstructured membrane reactors as optimum devices for sustainable H₂ production from biomass.     

Methane steam reforming in a Pd-Ag membrane reformer: An experimental study on reaction pressure influence at middle temperature

In this experimental work, methane steam reforming (MSR) reaction is performed in a dense Pd-Ag membrane reactor and the influence of pressure on methane conversion, CO_x-free hydrogen recovery and CO_x-free hydrogen production is investigated. The reaction is conducted at 450 °C by supplying nitrogen as a sweep gas in co-current flow configuration with respect to the reactants. Three experimental campaigns are realized in the MR packed with Ni-ZrO catalyst, which showed better performances than Ni-Al₂O₃ used in a previous paper dealing with the same MR system. The first one is directed to keep constant the total pressure in both retentate and permeate sides of the membrane reactor. In the second case study, the total retentate pressure is kept constant at 9.0 bar, while the total permeate pressure is varied between 5.0 and 9.0 bar. As the best result of this work, at 450 °C and 4.0 bar of total pressure difference between retentate and permeate sides, around 65% methane conversion and 1.2 l/h of CO_x-free hydrogen are reached, further recovering 80% CO_x-free hydrogen over the total hydrogen produced during the reaction. Moreover, a study on the influence of hydrogen-rich gas mixtures on the hydrogen permeation through the Pd-Ag membrane is also performed and discussed.     

Methanol steam reforming reaction in a Pd–Ag membrane reactor for CO-free hydrogen production

A dense tubular Pd–Ag membrane reactor was used to carry out the methanol steam reforming reaction for producing a CO-free hydrogen stream. A Cu/Zn/Mg-based catalyst was packed in the lumen side of the membrane reactor and the experimental tests were performed at a reaction temperature of 300 °C and at a H₂O/methanol feed molar ratio of 3/1. The effects of the different flow configurations, as well as the sweep factor and the reaction pressure were analysed. Experimental results in terms of CO-free hydrogen recovery, hydrogen yield, CO-free hydrogen yield and hydrogen selectivity are presented. Moreover, a comparison between the performances of the membrane reactor and a traditional reactor working at the same operative conditions is proposed and discussed.     

Economic assessment of membrane-assisted autothermal reforming for cost effective hydrogen production with CO2 capture

A recent techno-economic study (Spallina et al., Energy Conversion and Management 120: p. 257–273) showed that the membrane assisted chemical looping reforming (MA-CLR) technology can produce H₂ with integrated CO₂ capture at costs below that of conventional steam methane reforming. A key technical challenge related to MA-CLR is the achievement of reliable solids circulation between the air and fuel reactors at large scale under the high (>50 bar) operating pressures required for optimal performance. This work therefore presents process modelling and economic assessments of a simplified alternative; membrane assisted autothermal reforming (MA-ATR), that inherently avoids this technical challenge. The novelty of MA-ATR lies in replacing the MA-CLR air reactor with an air separation unit (ASU), thus avoiding the need for oxygen carrier circulation. The economic assessment found that H₂ production from MA-ATR is only 1.5% more expensive than MA-CLR in the base case. The calculated cost of hydrogen (compressed to 150 bar) in the base case was 1.55 €/kg with a natural gas price of €6/GJ and an electricity price of €60/MWh. Both concepts show continued performance improvements with an increase in reactor pressure and temperature, while an optimum cost is achieved at about 2 bar H₂ permeate pressure. Sensitivities to other variables such as financing costs, membrane costs, fuel and electricity prices are similar between MA-ATR and MA-CLR. Natural gas prices represent the most important sensitivity, while the sensitivity to membrane costs is relatively small at high reactor pressures. MA-ATR therefore appears to be a promising alternative to achieve competitive H₂ production with CO₂ capture if technical challenges significantly delay scale-up and deployment of MA-CLR technology. The key technical demonstration required before further MA-ATR scale-up is membrane longevity under the high reactor pressures and temperatures required to minimize the cost of hydrogen.     

CO-free hydrogen production by steam reforming of acetic acid carried out in a Pd–Ag membrane reactor: The effect of co-current and counter-current mode

In this experimental work, a dense tubular Pd–Ag membrane reactor is used for carrying out the acetic acid steam reforming reaction for producing a CO-free hydrogen stream. The influence of the different flow configurations, as well as the sweep factor and the reaction pressure is analysed. A Ni-based commercial catalyst was packed in the lumen side of the membrane reactor and the experimental tests were performed at a reaction temperature of 400 °C and at a H₂O/acetic acid feed molar ratio of 10/1. Results in terms of CO-free hydrogen recovery, hydrogen yield and products selectivities are proposed. Moreover, a comparison between the performances of the membrane reactor and a traditional reactor working at the same operative conditions is illustrated and discussed.     

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.     

Thermodynamic analysis of hydrogen production via glycerol steam reforming with CO2 adsorption

Thermodynamic equilibrium for glycerol steam reforming to hydrogen with carbon dioxide capture was investigated using Gibbs free energy minimization method. Potential advantage of using CaO as CO₂ adsorbent is to generate hydrogen-rich gas without a water gas shift (WGS) reactor for proton exchange membrane fuel cell (PEMFC) application. The optimal operation conditions are at 900 K, the water-to-glycerol molar ratio of 4, the CaO-to-glycerol molar ratio of 10 and atmospheric pressure. Under the optimal conditions, complete glycerol conversion and 96.80% H₂ and 0.73% CO concentration could be achieved with no coke. In addition, reaction conditions for coke-free and coke-formed regions are also discussed in glycerol steam reforming with or without CO₂ separation. Glycerol steam reforming with CO₂ adsorption has the higher energy efficiency than that without adsorption under the same reaction conditions.     

Methanol steam reforming over PdZn/ZnAl2O4/Al2O3 in a catalytic membrane reactor: An experimental and modelling study

A catalytic membrane reactor equipped with Pd–Ag metallic membranes and loaded with PdZn/ZnAl₂O₄/Al₂O₃ catalytic pellets was tested for the methanol steam reforming reaction (S/C = 1) aimed at producing a pure hydrogen stream for PEM fuel cell feeding. The catalyst was prepared in two steps. First, commercial γ-Al₂O₃ pellets were impregnated with ZnCl₂ and calcined at 700 °C to obtain a ZnAl₂O₄ shell, and subsequently impregnated with PdCl₂ and reduced at 600 °C to obtain PdZn alloy nanoparticles. The catalyst was tested both in a conventional packed bed reactor and in a catalytic membrane reactor. A 3D CFD non-isothermal model with mass transfer limitations was developed and validated with experimental data. The reactions of methanol steam reforming, reverse water-gas shift and methanation were modeled under different pressure, temperature and feed load values. The model was used to study and simulate the CMR under different operation conditions.     

Simulation and optimization of hydrogen production by steam reforming of natural gas for refining and petrochemical demands in Lebanon

Steam reforming of natural gas produces the majority of the world's hydrogen (H₂) and it is considered as a cost-effective method from a product yield and energy consumption point of view. In this work, we present a simulation and an optimization study of an industrial natural gas steam reforming process by using Aspen HYSYS and MATLAB software. All the parameters were optimized to successfully run a complete process including the hydrogen production zone units (reformer reactor, high temperature gas shift reactor HTS and low temperature gas shift reactor LTS) and the purification zone units (absorber and methanator). Optimum production of hydrogen (87,404 MT/year) was obtained by fixing the temperatures in the reformer and the gas shift reactors (HTS & LTS) at 900 °C, 500 °C and 200 °C respectively while maintaining a pressure of 7 atm, and a steam to carbon ratio (S/C) of 4. Moreover, ~99% of the undesired CO₂ and CO gases were removed in the purification zone and a reduction of energy consumption of 77.5% was reached in the heating and cooling units of the process.     

Combined generation and separation of hydrogen in an electrochemical water gas shift reactor (EWGSR)

Hydrogen rich gas, originating from fossil fuel reforming processes or biomass gasification, contains a significant amount of CO. Typically, the yield of H₂ is increased with subsequent water gas shift units, converting CO to CO₂ and additional H₂. This study describes a new reactor concept enabling the water gas shift reaction and the separation of the generated hydrogen in one process step by using electrical energy. This electrochemical water gas shift reactor applies a H₃PO₄-doped Poly(2,5-benzimidazole) membrane as electrolyte and carbon supported Pt or PtRu as anode catalyst. The reactor operation was investigated at 130 °C and 150 °C with a H₂ free anode feed stream of humidified CO and N₂. The experimental results show the feasibility of the reactor concept, as H₂ was generated at the cathode according to Faradays Law. Anodic PtRu led to lower power demands than Pt. The operation at the two temperatures showed that 130 °C results in a lower electrical power demand while generating an equal amount of H₂. The feasibility of the reactor was assessed using exergy efficiency analysis.     

Hydrogen production by reforming of liquid hydrocarbons in a membrane reactor for portable power generation—Experimental studies

One of the most promising technologies for lightweight, compact, portable power generation is proton exchange membrane (PEM) fuel cells. PEM fuel cells, however, require a source of pure hydrogen. Steam reforming of hydrocarbons in an integrated membrane reactor has potential to provide pure hydrogen in a compact system. Continuous separation of product hydrogen from the reforming gas mixture is expected to increase the yield of hydrogen significantly as predicted by model simulations. In the laboratory-scale experimental studies reported here steam reforming of liquid hydrocarbon fuels, butane, methanol and Clearlite^® was conducted to produce pure hydrogen in a single step membrane reformer using commercially available Pd–Ag foil membranes and reforming/WGS catalysts. All of the experimental results demonstrated increase in hydrocarbon conversion due to hydrogen separation when compared with the hydrocarbon conversion without any hydrogen separation. Increase in hydrogen recovery was also shown to result in corresponding increase in hydrocarbon conversion in these studies demonstrating the basic concept. The experiments also provided insight into the effect of individual variables such as pressure, temperature, gas space velocity, and steam to carbon ratio. Steam reforming of butane was found to be limited by reaction kinetics for the experimental conditions used: catalysts used, average gas space velocity, and the reactor characteristics of surface area to volume ratio. Steam reforming of methanol in the presence of only WGS catalyst on the other hand indicated that the membrane reactor performance was limited by membrane permeation, especially at lower temperatures and lower feed pressures due to slower reconstitution of CO and H₂ into methane thus maintaining high hydrogen partial pressures in the reacting gas mixture. The limited amount of data collected with steam reforming of Clearlite^® indicated very good match between theoretical predictions and experimental results indicating that the underlying assumption of the simple model of conversion of hydrocarbons to CO and H₂ followed by equilibrium reconstitution to methane appears to be reasonable one.