Fluidized Bed Membrane Reactor Research Articles

Optimization of Small-Scale Hydrogen Production with Membrane Reactors

In the pathway towards decarbonization, hydrogen can provide valid support in different sectors, such as transportation, iron and steel industries, and domestic heating, concurrently reducing air pollution. Thanks to its versatility, hydrogen can be produced in different ways, among which steam reforming of natural gas is still the most commonly used method. Today, less than 0.7% of global hydrogen production can be considered low-carbon-emission. Among the various solutions under investigation for low-carbon hydrogen production, membrane reactor technology has the potential, especially at a small scale, to efficiently convert biogas into green hydrogen, leading to a substantial process intensification. Fluidized bed membrane reactors for autothermal reforming of biogas have reached industrial maturity. Reliable modelling support is thus necessary to develop their full potential. In this work, a mathematical model of the reactor is used to provide guidelines for their design and operations in off-design conditions. The analysis shows the influence of temperature, pressures, catalyst and steam amounts, and inlet temperature. Moreover, the influence of different membrane lengths, numbers, and pitches is investigated. From the results, guidelines are provided to properly design the geometry to obtain a set recovery factor value and hydrogen production. For a given reactor geometry and fluidization velocity, operating the reactor at 12 bar and the permeate-side pressure of 0.1 bar while increasing reactor temperature from 450 to 500 °C leads to an increase of 33% in hydrogen production and about 40% in HRF. At a reactor temperature of 500 °C, going from 8 to 20 bar inside the reactor doubled hydrogen production with a loss in recovery factor of about 16%. With the reactor at 12 bar, a vacuum pressure of 0.5 bar reduces hydrogen production by 43% and HRF by 45%. With the given catalyst, it is sufficient to have only 20% of solids filled into the reactor being catalytic particles. With the fixed operating conditions, it is worth mentioning that by adding membranes and maintaining the same spacing, it is possible to increase hydrogen production proportionally to the membrane area, maintaining the same HRF.

Membrane reactors for green hydrogen production from biogas and biomethane: A techno-economic assessment

This work investigates the performance of a fluidized-bed membrane reactor for pure hydrogen production. A techno-economic assessment of a plant with the production capacity of 100 kgH2/day was carried out, evaluating the optimum design of the system in terms of reactor size (diameter and number of membranes) and operating pressures. Starting from a biomass source, hydrogen production through autothermal reforming of two different feedstock, biogas and biomethane, is compared.Results in terms of efficiency indicates that biomethane outperforms biogas as feedstock for the system, both from the reactor (97.4% vs 97.0%) and the overall system efficiency (63.7% vs 62.7%) point of views. Nevertheless, looking at the final LCOH, the additional cost of biomethane leads to a higher cost of the hydrogen produced (4.62 €/kgH2@20 bar vs 4.39 €/kgH2@20 bar), indicating that at the current price biogas is the more convenient choice.

Fluidized Bed Membrane Reactor for the Direct Dehydrogenation of Propane: Proof of Concept.

In this work, the fluidized bed membrane reactor (FBMR) technology for the direct dehydrogenation of propane (PDH) was demonstrated at a laboratory scale. Double-skinned PdAg membranes were used to selectively remove H2 during dehydrogenation tests over PtSnK/Al2O3 catalyst under fluidization. The performance of the fluidized bed membrane reactor was experimentally investigated and compared with the conventional fluidized bed reactor (FBR) by varying the superficial gas velocity over the minimum fluidization velocity under fixed operating conditions (i.e., 500 °C, 2 bar and feed composition of 30vol% C3H8-70vol% N2). The results obtained in this work confirmed the potential for improving the PDH performance using the FBMR system. An increase in the initial propane conversion of c.a. 20% was observed, going from 19.5% in the FBR to almost 25% in the FBMR. The hydrogen recovery factor displayed a decrease from 70% to values below 50%, due to the membrane coking under alkene exposure. Despites this, the hydrogen extraction from the reaction environment shifted the thermodynamic equilibrium of the dehydrogenation reaction and achieved an average increase of 43% in propylene yields.

New configuration gas-cooled fluidized bed membrane reactor to reduce the thermodynamic limitations of dimethyl ether production

In this study, a gas-cooled fluidized bed membrane reactor with a new configuration was investigated aiming to reduce thermodynamic limitations in DME production. In this configuration, two Pd-Ag and alumina-silica membranes were used simultaneously for the permeation of hydrogen into the reactor and to remove its containing water, respectively. The heat of the exothermic DME synthesis reactions is removed by heat transfer with sweep and hydrogen gaseous flows. The simulation of the fluidized bed membrane reactor shows that the presence of the membranes increases DME production and carbon monoxide (CO) conversion by about 30.6% and 28.3%, respectively. Enhanced DME production was observed by raising temperature, pressure, and shell and tube side flow rates. Space velocity and H2/CO ratio had an optimum point in DME production. The proposed model can be used for the design of an industrial catalytic membrane reactor for DME production from synthesis gas.

Model-Based Quality, Exergy, and Economic Analysis of Fluidized Bed Membrane Reactors.

In petroleum refineries, naphtha reforming units produce reformate streams and as a by-product, hydrogen (H2). Naphtha reforming units traditionally deployed are designed as packed bed reactors (PBR). However, they are restrained by a high-pressure drop, diffusion limitations in the catalyst, and radial and axial gradients of temperature and concentration. A new design using the fluidized bed reactor (FBR) surpasses the issues of the PBR, whereby the incorporation of the membrane can improve the yield of products by selectively removing hydrogen from the reaction side. In this work, a sequential modular simulation (SMS) approach is adopted to simulate the hydrodynamics of a fluidized bed membrane reactor (FBMR) for catalytic reforming of naphtha in Aspen Plus. The reformer reactor is divided into five sections of plug flow reactors and a continuous stirrer tank reactor with the membrane module to simulate the overall FBMR. Similarly, a fluidized bed reactor (FBR), without membrane permeation phenomenon, is also modelled in the Aspen Plus environment for a comparative study with FBMR. In FBMR, the continuous elimination of permeated hydrogen enhanced the production of aromatics compound in the reformate stream. Moreover, the exergy and economic analyses were carried out for both FBR and FBMR.

Numerical studies of sorption-enhanced glycerol steam reforming in a fluidized bed membrane reactor at low temperature

In order to improve the hydrogen production efficiency by glycerol steam reforming, a membrane-assisted fluidized bed reactor with carbon dioxide sorption is developed to enhance the reforming process. Low-temperature operation in a membrane reactor is necessary considering the thermal stability of membrane. In this work, the sorption-enhanced glycerol steam reforming process in a fluidized bed membrane reactor under the condition of low temperature is numerically investigated, where the hydrotalcite is employed as CO2 sorbents. The impact of operating pressure on the reforming performance is further evaluated. The results demonstrate that the integration of membrane hydrogen separation and CO2 sorption can effectively enhance the low-temperature glycerol reforming performance. The fuel conversion above 95% can be achieved under an elevated pressure.

Comprehensive Modeling of Sorption-Enhanced Steam Reforming of Coke Oven Gas in a Fluidized Bed Membrane Reactor

Integration of membrane hydrogen separation and carbon dioxide capture with fuel steam reforming efficiently promote hydrogen production and feedstock conversion. In this study, catalytic steam reforming of coven oven gas in a sorption-enhanced fluidized bed membrane reactor (MA-SE-SRCOG) was simulated using a reactive three-fluid model under Euler framework. The numerical studies provided insights into details about interactions of multi-scale sub-processes, including hydrogen permeation, carbon dioxide adsorption, catalytic reforming and multiphase flow dynamics, during MA-SE-SRCOG. Concentration polarization caused by hydrogen separation was also examined. Meanwhile, impacts of several operating parameters, such as reaction pressure, steam concentration, membrane position and reactor scale, on the performances of MA-SE-SRCOG were evaluated in terms of CH4 conversion, CO selectivity, hydrogen recovery factor and CO2 fix factor. The simulation results demonstrated that membrane hydr...

Alginate to simulate biofouling in submerged fluidized ceramic membrane reactor: Effect of solution pH and ionic strength

Membrane fouling was investigated experimentally by fluidizing non-adsorbed plastic scouring media on flat-tubular ceramic membrane treating a sodium alginate solution as a representative of polysaccharides in wastewater. Fouling rate increased with set-point permeate flux, but it was remarkably reduced by fluidizing the scouring agent regardless of the flux applied. Higher solution pH resulted in more reduction in membrane fouling due to electrostatic repulsion enhanced between alginate foulant and membrane surface which are both negatively charged. The addition of divalent cations such as Ca2+ and Cu2+ mitigated alginate fouling significantly due to the back transport associated with formation of larger particles away from membrane. However, the addition of monovalent cations accelerated the membrane fouling with less effectiveness of the media fluidization in fluidized bed membrane reactor. Adding monovalent ions was thought to transform rigid, compact and spherocolloidal macromolecular structure of alginate into the intramolecular charge shielding to neutralize functional groups.

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.

Simulation of autothermal hydrogen-producing limestone calcination for calcium looping in turbulent fluidized bed reactors

This paper investigates the performance of combining limestone calcination with catalytic methane reforming and combustion in turbulent fluidized bed membrane reactors. The equilibrium performance of the process was evaluated using Aspen simulation, with a unique correlation to estimate the required gaseous feed composition for autothermal and complete sorbent regeneration at operating temperatures of 800–900 °C. A one-dimensional, isothermal, steady-state kinetic model is then employed to study the performance of the four-in-one (combustion + reforming + calcination + optional membrane separation) integrated process under turbulent fluidization conditions. The simulation results demonstrate the high potential of this novel sorbent regeneration technique for autothermal, rapid and hydrogen-producing limestone calcination. The performance is shown to depend strongly on the sorbent/total gas molar feed ratio, operating temperature, operating pressure and sorbent residence time.

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...

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.

Effect of gas extraction on the hydrodynamics in a fluidized bed membrane reactor at elevated temperatures

AbstractThis study describes experimental explorations on the effects of gas extraction on hydrodynamics in a pilot‐scalegas fluidized bed membrane reactor (FBMR) at high temperatures. Differential pressure signals were measured at different vertical intervals in bed and were then characterized by multiscale resolution and power spectra analysis. The experimental results showed that the relative amplitude of σr (σ/xav) of pressure signal tended todecrease with the increase of gas extraction fraction.At room temperature, 20% gas extraction caused defluidization at an inlet velocity of 2Umf. However, athigh temperatures the gas extraction simultaneously decreased the magnitude of the low‐frequency components and the numbers of the medium‐ to small‐sized structures, mainly due to the decreased number of small‐sized structures and the integration of bubbles. This effect of gas extraction increased with increase of gas extraction fraction and slightly decreased at higher inlet gas velocities. At elevated temperatures, the D6 sub‐signals (0.781~1.562Hz) possessed the highest wavelet energy distribution percentage of the pressure signals, which meant that the medium‐ to small‐sized bubbles dominated the gas‐solid flow dynamics. Gas extraction was observed to enhance the dominance of the D6 scale components..

Structural characteristics of hazardous organic dyes and relationship between membrane fouling and organic removal efficiency in fluidized ceramic membrane reactor

In this study, combined effect of types of anionic dye compounds and solution pHs on organic removal efficiency and membrane fouling on the alumina-based microfiltration (MF) flat-tubular membrane was investigated using a laboratory-scaled, fluidized bed membrane reactor at constant permeate flux operation. For the Congo-Red dye solution at the solution pH of 6, there was no increase in suction pressure with only 10% of organic removal efficiency measured by ultraviolet-visible (UV–Vis) spectrometer during operational period. However, lowering the solution pH to 4.5 accelerated suction pressure increase while higher than 90% organic removal efficiency was achieved. At the solution pH of 4.5, a zwitterion nature characterized by Congo-Red dye compound resulted in more deposit of cake layer on membrane than that formed at higher pH. In the case of Tartrazine and Acid Orange 7 which are categorized as anionic dye compound, the increase in suction pressure with time was much slower than that observed with Congo Red at same solution pH (4.5) and permeate flux (40 L m−2 h−1). Our results suggested that higher fouling rate should be associated closely with higher organic removal efficiency in ceramic MF membrane filtration. Regardless of types of dye compounds tested, granular activated carbon (GAC) fluidized in submerged ceramic membrane reactor was found to be propitious tool to reduce membrane fouling with excellent organic removal due to adsorption functionality and scouring action provided by GAC fluidization on membrane.

Stability of pore-plated membranes for hydrogen production in fluidized-bed membrane reactors

Pd-based membranes prepared by pore-plating technique have been investigated for the first time under fluidization conditions. A palladium thickness around 20 μm was achieved onto an oxidized porous stainless steel support. The stability of the membranes has been assessed for more than 1300 h in gas separation mode (no catalyst) and other additional 200 h to continuous fluidization conditions. Permeances in the order of 5·10−7 mol s−1 m−2 Pa−1 have been obtained for temperatures in a range between 375 and 500 °C. During fluidization, a small decrease in permeance is observed, as consequence of the increased external (bed-to-wall) mass transfer resistances. Moreover, water gas shift (WGS) reaction cases have been carried out in a fluidized bed membrane reactor. It has been confirmed that the selective H2 separation through the membranes resulted in CO conversions beyond the thermodynamic equilibrium (of conventional systems), showing the benefits of membrane reactors in chemical conversions.

A numerical study on concentration polarization in 3D cylindrical fluidized beds with vertically immersed membranes

Concentration polarization is a serious issue for systems in which high-flux, palladium-based, hydrogen perm-selective membranes are used to extract hydrogen, not only for packed-bed reactor systems, but also for fluidized bed membrane reactors. Two-Fluid Model simulations of 3D cylindrical lab-scale fluidized beds with single and multiple vertically immersed cylindrical membranes with state-of-the-art hydrogen permeability were performed to quantify concentration polarization, to study the interaction between concentration polarization zones of multiple vertically immersed membranes and to link these findings to the bed hydrodynamics. Simulations of a fluidized bed consisting of 500 μm particles using a H2/N2 mixture as fluidization gas with a single immersed membrane, show that reduced hydrogen concentrations prevail mostly within 1 cm from the membrane surface, and have disappeared beyond about 2 cm distance from the membrane surface. A 3D simulation was compared to a Cartesian 2D simulation that represents a slice of the 3D system, to assess the accuracy of 2D simulations. The 2D simulation did not fully capture the hydrodynamics and radial mass transfer effects of 3D cylindrical fluidized bed membrane reactors and overestimated the severity of concentration polarization and the formation of densified zones near the membrane surface. In particular, the hydrogen fluxes were determined at 0.217 mol/(m2 s Pa0.5) for the 3D case, and 0.133 mol/(m2 s Pa0.5) for the 2D case. The severity of densified zones is also affected by the particle size, because for smaller particles (250 μm) the emulsion phase density near the membrane surface is higher than for systems with larger particles (500 μm), which results in increased concentration polarization and a reduced extractive hydrogen flux. Therefore, employing relatively large particles of at least 500 μm in fluidized beds with modern high-flux membranes is advised. In fluidized beds with multiple membranes, interaction between concentration polarization zones of each membrane was observed. The interaction becomes more significant at smaller inter-membrane distances, especially below 2 cm, and decreasing the bed diameter decreases the system performance even more due to hydrogen depletion. Vertically immersed membranes also affect the fluidized bed hydrodynamics by reducing bubble size and increasing the number of small bubbles.

Oxidative Coupling of Methane: A Comparison of Different Reactor Configurations

A quantitative comparison of the performance of the most common reactor configurations proposed for the oxidative coupling of methane (OCM) is made on the basis of numerical calculations with phenomenological reactor models. The configurations that are analyzed can be divided into two main categories, namely, packed‐bed reactors (including conventional packed beds with external cooling, packed‐bed membrane reactors, and adiabatic packed beds with post cracking) and fluidized bed reactors (bubbling fluidized bed reactor, circulating fluidized bed reactor, and fluidized bed membrane reactor). The challenges in both configuration types, mainly the heat management in the case of the packed‐bed reactors and the low C2+ yields obtained in fluidized bed reactors, are evaluated and quantified. To ensure a fair comparison, La2O3/CaO is chosen as the OCM catalyst for all the considered cases, mainly in view of the availability of a comprehensive kinetics model. The results show that, with conventional configurations, it is not possible to achieve high C2+ yields that are needed to make the process economically viable. However, the results also indicate that the C2+ yield can be significantly improved by feeding the oxygen distributively along the reactor axial length.

Estimation of concentration polarization in a fluidized bed reactor with Pd-based membranes via CFD approach

A fluidized bed membrane reactor has its great advantage in the industrial application of hydrogen production owing to good mass and heat transfer characteristics compared to a fixed bed membrane reactor. However, the concentration polarization and the densification zone formation caused by membrane permeation will restrict mass and heat transfer as well as hydrogen membrane flux. In this work, a three-dimensional simulation is carried out to investigate the hydrogen separation process in a fluidized bed membrane reactor under the Euler-Euler framework. The effects of membrane arrangements with different eccentric distances and membrane sites including internal and external membranes on concentration polarization and densification zones are discussed. The results reveal that the enhancement of eccentric distances can weaken the concentration polarization, whereas the densification zone scope is enhanced. The arrangement of internal membranes can hinder the concentration polarization and promote the hydrogen separation, while external membranes significantly influence the hydrogen removal at the bottom of the reactor.

Modeling of a Nickel-based Fluidized Bed Membrane Reactor for Steam Methane Reforming Process

Hydrogen being a green fuel is rapidly gaining importance in the energy sector. Steam methane reforming is one of the most industrially important chemical reaction and a key step in the production of high purity hydrogen. Due to inherent deficiencies of conventional reforming reactors, a new concept based on fluidized bed membrane reactor is getting the focus of researchers. In this work, a nickel-based fluidized bed membrane reactor model is developed in the Aspen PLUSand#174; process simulator. A user-defined membrane module is embedded in the Aspen PLUSand#174; through its interface with Microsoftand#174; Excel. Then, a series combination of Gibbs reactors and membrane modules are used to develop a nickel-based fluidized bed membrane reactor. The model developed for nickel-based fluidized bed membrane reactor is compared with palladium-based membrane reactor in terms of methane conversion and hydrogen yield for a given panel of major operating parameters. The simulation results indicated that the model can accurately predict the behavior of a membrane reactor under different operating conditions. In addition, the model can be used to estimate the effective membrane area required for a given rate of hydrogen production.

Analysis of the Hydrodynamic Effects of Gas Permeation in a Pilot-Scale Fluidized Bed Membrane Reactor

This study experimentally investigates the effects of gas extraction/addition, via multiple vertical membrane panels, on the hydrodynamics in different regions of a pilot-scale gas fluidized bed membrane reactor (FBMR), based on differential pressure signals measured at different vertical bed sections at high temperature. In a bed section where membrane panels were installed and activated, the extraction of gas caused the average bubble size to increase, but decreased the number of small- and medium-sized bubbles. This effect of gas extraction penetrated into bed sections above the active membrane panel, but attenuated with increasing distance away from the extraction location. The attenuation rate was much faster in FBMR with lower bed voidage, mainly due to the large decrease of the drag force exerted by gas extraction on fluidizing gas in a denser bed. With the same inlet gas velocity, gas addition favored the growth of bubbles, especially in the upper bed sections compared with operation without gas permeation. The increase of the effective fluidizing velocity was the major reason for the increase of the bubble size during gas addition. These findings preliminarily suggest that membrane units should not be installed in or below fast-reacting zones in a scale-up FBMR, and operation with a lower bed voidage is preferable to avoid the formation of large bubbles enhanced by gas extraction.