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The application of membrane assisted fluidized bed reactors for distributed energy production has generated considerable research interest during the past few years. It is widely accepted that, due to better heat and mass transfer characteristics inside fluidized bed reactors, the reactor efficiency can outperform other reactor configurations such as packed bed units. Although many experimental studies have been performed to demonstrate and monitor the long term performance of membrane assisted fluidized bed reactors, the hydrodynamics of membrane-assisted fluidized bed reactors has thus far only been studied in pseudo-2D geometries. In this work the solids concentration inside a real 3D fluidized bed reactor geometry was measured using a fast X-ray analysis technique. Experiments were conducted in absence and presence of two different membrane modules with different configurations and number of membranes (porous Al2O3 tubes) for two types of particles, viz. 400–600 μm polystyrene (Geldart B type) and 80–200 μm Al2O3 (Geldart A/B type). Results from the experiments with Geldart B type particles revealed that the membrane modules (both the membranes and the spacers) can significantly reduce bubble growth along the fluidized bed resulting in a smaller average bubble diameter, expected to improve the bubble-to-emulsion mass transfer, whereas for the experiments with fine Geldart A/B particles, and at a very high extraction values (40% of the inlet flow), a densified layer with high solids concentration was formed near the membrane, which may impose an additional mass transfer resistance for gas components to reach the surface of the membranes (concentration polarization). The results from this study help designing and optimizing the positioning of the membranes and membrane spacers for optimal performance of fluidized bed membrane reactors., ChemE/Afdelingsbureau, ChemE/Product and Process Engineering, ChemE/Transport Phenomena

Hydrotalcite-based adsorbents have shown great potential for use in sorption-enhanced water-gas-shift applications. A combination of thermogravimetric experiments and breakthrough experiments have been carried out to elucidate the effect of steam on the CO2 cyclic sorption capacity on a K-promoted hydrotalcite-based adsorbent. Different TGA cycles have been designed to study the mass change on sorbents exposed to different sequences of different CO2/H2O/N2 mixtures. Because the complex sorption/desorption and replacement phenomena cannot be explained by TGA experiments only, additional information from breakthrough experiments in a packed bed reactor was used to correlate the observed total mass change in the TGA cycles to the phenomena prevailing on the sorbent. A mechanism has been developed which is able to describe the cyclic working capacity, for both CO2 and H2O under different experimental conditions. It was found that at least four different adsorption sites participate in the sorption/desorption of CO2 and H2O. Two adsorption sites can be regenerated with N2, whereas the other adsorption sites require the presence of H2O or CO2 to be desorbed. Regeneration of the adsorbent with steam leads to a significant increase in the CO2 cyclic working capacity from 0.3 to 0.53 mmol/g compared to a dry regeneration with N2 using the same cycle times.

The PC-SAFT 'pseudo-pure' approach was used for the modeling of CO2 solubilities in various hydrophobic deep eutectic solvents (DESs) for the first time. Only liquid density data were used to obtain the segment number, the temperature-independent segment diameter and the dispersion-energy parameter, as water activities cannot be obtained for hydrophobic substances. VLE data were successfully predicted without the need for any adjustable binary interaction k ij. Thus, solubilities of CO2 in hydrophobic DESs could be approximated with the PC-SAFT model using parameters fitted to liquid densities only.

This work reports the results of an experimental investigation on densified zone formation in a membrane fluidized bed reactor using combined pressure fluctuation and PIV (Particle Image Velocimetry) measurements. A pseudo 2D experimental setup was used, where porous plates on the back plate of column mimicked gas extraction through flat vertically inserted membranes. The maximum in the standard deviation of pressure fluctuations, commonly employed to indicate the transition to turbulent fluidization, shifted to lower fluidization velocities with an increase in the fraction of fluidizing gas being extracted. Flow visualization showed that this result is connected to the onset of stable densified zone formation, which occurred at progressively lower fluidization velocities as the gas extraction fraction was increased. It has also been found that the extent of densified zones quantified using instantaneous particle velocity maps collected by PIV increases with increasing gas extraction rates. This effect became larger for smaller particles. Results have therefore shown that the peak in pressure fluctuations in fluidized beds with gas extraction through flat vertical membranes indicates the onset of densified zones formation rather than turbulent fluidization. Such densified zones can have substantial detrimental effects (such as induced mass transfer limitations, gas bypass etc.) on the reactor performance and can be identified via pressure measurements, as illustrated in this work.

This paper reports an experimental investigation on a novel reactor concept for steam-methane reforming with integrated CO2 capture: the gas switching reforming (GSR). This concept uses a cluster of fluidized bed reactors which are dynamically operated between an oxidation stage (feeding air) and a reduction/reforming stage (feeding a fuel). Both oxygen carrier reduction and methane reforming take place during the reduction stage. This novel reactor configuration offers a simpler design compared with interconnected reactors and facilitates operation under pressurized conditions for improved process efficiency. The performance of the bubbling fluidized bed reforming reactor (GSR) is evaluated and compared with thermodynamic equilibrium. Results showed that thermodynamic equilibrium is achieved under steam-methane reforming conditions. First, a two-stage GSR configuration was tested, where CH4 and steam were fed during the entire reduction stage after the oxygen carrier was fully oxidized during the oxidation stage. In this configuration a large amount of CH4 slippage was observed during the reduction stage. Therefore, a three-stage GSR configuration was proposed to maximize fuel conversion, where the reduction stage is completed with another fuel gas with better reactivity with the oxygen carrier, e.g. PSA-off gases, after a separate reforming stage with CH4 and steam feeds. A high GSR performance was achieved when H2 was used in the reduction stage. A sensitivity analysis of the GSR process performance on the oxygen carrier utilization and target working temperature was carried out and discussed.

Gas Switching Combustion (GSC) is a promising new process concept for energy efficient power production with integrated CO2 capture. In comparison to conventional Chemical Looping Combustion (CLC) carried out in interconnected fluidized beds, the GSC concept will be substantially easier to design and scale up, especially for pressurized conditions. One potential drawback of the GSC concept is the gradual temperature variation over the transient process cycle, which leads to a drop in electric efficiency of the plant. This article investigates heat management strategies to mitigate this issue both through simulations and experiments. Simulation studies of the GSC concept integrated into an IGCC power plant show that heat management using a nitrogen recycle stream can increase plant efficiency by 3 percentage points to 41.6% while maintaining CO2 capture ratios close to 90%. Reactive multiphase flow simulations of the GSC reactor also showed that heat management can eliminate fuel slip problems. In addition, the GSC concept offers the potential to remove the need for a nitrogen recycle stream by implementing a concentrated air injection that extracts heat while only a small percentage of oxygen reacts. Experiments have shown that, similar to nitrogen recycle, this strategy reduces transient temperature variations across the cycle and therefore merits further investigation.

Copper oxide on alumina is often used as oxygen carrier for chemical looping combustion owing to its very high reduction rates at lower temperatures and its very good mechanical and chemical stability at temperatures below 1000 °C. In this work, the redox behaviour of CuO/Al2O3 has been studied in great detail together with the redox behaviour of CuO/SiO2 to identify the main phenomena affecting the observed redox kinetics. Combination of TGA results with detailed characterisation with XRD of the oxygen carriers at different stages during the redox cycling allowed elucidating the causes for the sudden decrease in the reaction rate observed at higher conversions for the CuO/Al2O3 oxygen carriers. The main results of the study can be summarized as: i) oxidation reaction reaches always full conversion independent of the reaction temperature; ii) reduction reaction reaches only full conversion at very high temperatures, showing a significant decrease in the reaction rate at lower temperatures at higher particle conversions; iii) the observed sudden decrease in the reduction rate is related to the spinel reduction of CuAl2O4 and CuAlO2.

Distributed power generation via Micro Combined Heat and Power (m-CHP) systems, has been proven to over-come disadvantages of centralized generation since it can give savings in terms of Primary Energy consumption and energy costs. The FluidCELL FCH JU/FP7 project aims at providing the Proof of Concept of an advanced high performance, cost effective bio-ethanol m-CHP cogeneration Fuel Cell system for decentralized off-grid applications by end of 2017. The main idea of FluidCELL is to develop a new bio-ethanol membrane reformer for pure hydrogen production (3.2 Nm3/h) based on Membrane Reactors in order to intensify the process of hydrogen production through the integration of reforming and purification in one single unit. The novel reactor could be more efficient than the state-of-the-art technology due to an optimal design aimed at circumventing mass and heat transfer resistances. Moreover, the design and optimization of the subcomponents for the BoP could also be improved. Particular attention has to be devoted to the optimized thermal integration that can improve the overall efficiency of the system at >90% and reducing the cost due to low temperature reforming. The main results obtained until now in terms of performance of the catalysts, membranes and the membrane reactors will be presented in this work.

This work reports the preparation and characterization of ultra-thin (~1 µm thick) Pd-Ag supported membranes for hydrogen purification. Ultra-thin membranes with different thicknesses (ranging from 0.46 to 1.29 µm) have been prepared by electroless plating (ELP) technique onto asymmetric tubular porous alumina supports. The membranes have been characterized by single gas and mixed gas permeation experiments at temperatures between 300 and 500 °C obtaining a correlation for the membrane permeation as a function of the activation energy and the membrane thickness. Hydrogen permeation results of the ultra-thin Pd-Ag membranes have been compared with other highly permeable membranes reported in the literature and they show some of the highest H2 permeance values. A 1.29 µm thick membrane has been tested for 1000 h at 400 °C and has shown a stable H2 permeance of 9.0−9.4×10−6 mol m−2 s−1 Pa−1 with a H2/N2 perm-selectivity between 3300 and 2000 at 100 kPa transmembrane pressure difference. The same membrane has been tested with a feed gas mixture of H2/N2/CO with a 15% CO content and H2 binary mixtures containing N2, CH4 and CO2. When tested in a catalyst fluidization environment during 100 h, the 1.29 µm thick membrane showed stable H2 permeance and H2/N2 perm-selectivity.

In order to make a detailed comparison between Pd-Ag and Pd-Ag-Au membranes according to their H2 permeation properties and sulfide resistance Au was deposited by the electroless plating (ELP) technique onto one half of Pd-Ag membranes. Membranes' thicknesses are ranged between 2.45 and 3.13 µm. Permeation tests have been carried out from 400 to 600 °C under single gas conditions. The Pd91.7Ag4.8Au3.5 membrane has shown a H2 permeance of 4.71·10−3 mol s−1 m−2 Pa0.5 at 600 °C, which is one of the highest values ever reported in the literature, where the Pd-Ag-Au membranes have exhibited higher hydrogen permeation rates compared to their respective Pd-Ag membranes above 550 °C. The H2 permeation properties have been determined in terms of the degree of H2S inhibition, up to 17 ppm, and subsequent H2 flux recovery rate. Pd-Ag membranes alloyed with gold resisted 12.5 h of H2S exposure showing recovery rates of 85% and 83% for Pd91.5Ag4.7Au3.8 and Pd90.5Ag4.6Au4.9 membranes, respectively, whereas the hydrogen flux of non-gold membranes decreased below detectable values. H2/N2 ideal perm-selectivity of the Pd-Ag membrane was reduced to 18 after H2S tests (starting from > 1308) while Pd-Ag-Au membranes showed a better resistance to sulfur with H2/N2 selectivity values of 793 and 121 (starting from > 4115 and > 2557 respectively). No evidence of the formation of a crystalline sulfide phase on the Pd-Ag-Au alloy membrane surfaces was found in the XRD patterns after H2S exposure and also XPS characterization did not show important changes in the composition before and after the H2S exposure tests. However, SEM images showed a decrease in the thickness of the Pd-Ag membrane and signs of corrosion and roughening on its surface, while gold-alloyed membranes did not show any damage. Keywords Palladium-silver-gold membrane; Electroless plating; H2 permeation; H2S poisoning; H2 recovery

Oxidative coupling of methane (OCM) has been investigated as an interesting way to obtain higher hydrocarbons from natural gas. The aim of this article is to evaluate the reactor concepts for oxidative coupling of methane, from the 1980s through the current state of the art, giving a general insight into the reactor engineering possibilities and perspectives of application of OCM in large scale reactors. The concepts were classified according to the type of reactor bed, the heat management system, the oxygen feeding policy, the degree of integration with separation units, the relative cost, and the current demonstration on industrial scale.

The solids mass flux distribution and internal solids circulation rates in freely-bubbling gas-solid fluidized beds has been studied in detail in a pseudo-2D column. A non-invasive Particle Image Velocimetry (PIV) combined with Digital Image Analysis (DIA) technique has been further extended to investigate and quantify the gas and solids phase properties simultaneously for different particle types and sizes (all Geldart B type) at different fluidization velocities. It is found that the solids fluxes increase strongly, practically linearly, as a function of the vertical position and depend on the excess gas velocity but not on the particle size, while the most often used phenomenological two-phase fluidized bed models assume the vertical solids fluxes to be constant. To further investigate this important discrepancy, the underlying assumptions of the phenomenological models have been validated, especially concerning the average solids fraction inside the bubbles, the laterally and time-averaged axial bubble fraction profile (or visual bubble flow rate) and the wake parameter (the amount of solids carried along a bubble relative to the bubble volume). To this end, the PIV/DIA technique was further extended and a new method for the determination of the wake parameter is proposed. From the experimental results, it was concluded that i) the average solids fraction inside the bubbles is about 2.5–3% for glass beads and alumina particles and is practically independent of the excess gas velocity and particle size; ii) the measured laterally and time-averaged bubble fractions are considerably lower compared to often used correlations from literature, which would lead to a significant over-prediction of the visual bubble flow rate and iii) the wake parameter depends strongly on the bubble size and with the developed correlation the axial solids mass fluxes as a function of the vertical position can be well described. Finally, the influence of these findings was evaluated by p

This work investigates the full process design of a natural gas combined cycle integrated with a packed-bed reactor system where a hydrogen rich gas is produced with inherent CO2 capture based of the CaO/CaCO3 and Cu/CuO chemical loops. The different stages of this Ca-Cu process were modelled with a dynamic 1D pseudo-homogeneous model, proposing a novel reactor configuration allowing to achieve carbon capture efficiency close to 90%. Process simulations of the whole power plant resulted in electric efficiencies of around 48%LHV and SPECCA of 4.7 MJ/kgCO2.

This work addresses the techno-economic assessment of two chemical looping technologies for H2 production from natural gas fully integrated with CO2 capture. In the first configuration, chemical looping combustion operated with a dual circulating fluidized bed system at atmospheric pressure is used as furnace for the reforming reaction. In the second configuration, a chemical looping reforming system at pressurized conditions is used for the production of the reformed syngas. Both configurations have been designed and compared with reference technologies for H2 production based on conventional fired tubular reforming with and without CO2 capture. The results of the analysis show that both new concepts can achieve higher H2 reforming efficiency than a conventional plant when integrated with CO2 capture (+8-10% higher). The improvement in the performance of the plant is accompanied with an efficiency penalty of 4-6% and the cost of CO2 avoidance varies from 20-85 €/tonCO2.

Thermogravimetric analysis and breakthrough experiments in a packed bed reactor were used to validate a developed adsorption model to describe the cyclic working capacity of CO2 and H2O on a potassium-promoted hydrotalcite, a very promising adsorbent for sorption-enhanced water-gas-shift applications. Four different adsorption sites (two sites for CO2, one site for H2O and one equilibrium site for both species) were required to describe the mass changes observed in the TGA experiments. The TGA experiments were carried out at operating temperatures between 300 and 500 °C, while the total pressure in the reactor was kept at atmospheric pressure. Cyclic working capacities for different sites and the influence of the operating conditions on the cyclic working capacity were studied using the developed model. A higher operating temperature leads to a significant increase in the cyclic working capacity of the sorbent for CO2 attributed to the increase in the desorption kinetics for CO2. The model was successfully validated with experiments in a packed bed reactor at different operating temperatures.

Copper oxide on alumina is often used as oxygen carrier for chemical looping combustion owing to its very high reduction rates at lower temperatures and its very good mechanical and chemical stability at not too high temperatures. In this work, the redox kinetics of CuO/Al2O3 have been studied at elevated pressures and temperatures. All the experiments have been started under the same initial conditions to assure the same starting point. While other studies reported a negative effect of the total pressure on the redox kinetics, this study shows that this negative effect of the pressure is most probably caused by external mass transfer limitations in previous studies. Additionally, as long as external mass transfer limitations are prevented, the total pressure at which the reduction is performed does not affect the redox kinetics nor the morphological and chemical structure of the oxygen carrier. The sudden decrease in the reduction rate at higher particle conversions was not influenced by the operating pressure and was attributed to limitations in the spinel reduction kinetics.

The theoretical approach for the bubble-to-emulsion phase mass exchange in bubbling gas-solid fluidized beds developed by Davidson and Harrison in the early 60’s is still widely applied in phenomenological models, mainly because of lack of more detailed experimental data to improve the description. In this study a novel infrared transmission technique that allows the direct and non-invasive measurement of gas concentration profiles inside bubbles with a high temporal resolution has been used for the validation of the theoretical description for the gas exchange. At first, the experimental technique has been further improved concerning the selective removal of particles raining through the bubbles, as well as the reconstruction of tracer gas concentration profiles throughout the gas bubble. The bubble-to-emulsion phase mass transfer coefficients have been measured by injecting tracer gas bubbles into incipiently fluidized beds and beds at freely-bubbling conditions, for beds consisting of glass beads of different particle size and with different injected bubble diameters. The results show that the Davidson and Harrison approach can reasonably well describe the mass exchange for isolated bubbles injected into a bed at minimum fluidization conditions. However, experiments carried out in a freely bubbling bed have shown that the mass exchange rate is considerably enhanced due to the increased gas through-flow through the bubbles. An empirical correlation (with deviations within only 20%) for the volumetric bubble-to-emulsion phase mass transfer coefficient has been developed based on the bubble size and superficial gas velocity, where it is noted that in this work the convective contribution in the mass exchange is dominant.

Palladium-based membranes for hydrogen separation have been studied by several research groups during the last 40 years. Much effort has been dedicated to improving the hydrogen flux of these membranes employing different alloys, supports, deposition/production techniques, etc. High flux and cheap membranes, yet stable at different operating conditions are required for their exploitation at industrial scale. The integration of membranes in multifunctional reactors (membrane reactors) poses additional demands on the membranes as interactions at different levels between the catalyst and the membrane surface can occur. Particularly, when employing the membranes in fluidized bed reactors, the selective layer should be resistant to or protected against erosion. In this review we will also describe a novel kind of membranes, the pore-filled type membranes prepared by Pacheco Tanaka and coworkers that represent a possible solution to integrate thin selective membranes into membrane reactors while protecting the selective layer. This work is focused on recent advances on metallic supports, materials used as an intermetallic diffusion layer when metallic supports are used and the most recent advances on Pd-based composite membranes. Particular attention is paid to improvements on sulfur resistance of Pd based membranes, resistance to hydrogen embrittlement and stability at high temperature.

This paper addresses the experimental demonstration and model validation of chemical looping reforming in dynamically operated packed-bed reactors for the production of H2 or CH3OH with integrated CO2 capture. This process is a combination of auto-thermal and steam methane reforming and is carried out at high pressure, as typical for reforming processes, and at relatively low to intermediate temperatures (ranging from 600 to 900 °C). The oxidation of the oxygen carrier is performed with air and the hot depleted air stream is fed to a gas turbine, which contributes to reduce the electricity demand. After oxidation, a low-grade fuel is used for the reduction of the oxygen carrier, e.g. off-gas from a PSA unit or non-condensable species from methanol synthesis and, when the bed is completely reduced, natural gas diluted with H2O and CO2 is reformed while the reactor is cooled down. An experimental campaign has been carried out in a 2 kWth packed-bed reactor using 500 g of NiO supported on CaAl2O4 as reforming catalyst and oxygen carrier. This material has demonstrated very high stability over > 400 h of consecutive redox and reforming cycles. Due to the flexibility of the process, dry, wet and steam reforming compositions have been tested during the reforming phase. A 1D reactor model has been validated with the obtained experimental results, including also a detailed thermal model to account for the inevitable heat losses of the system. The experimental and model results are in good agreement in terms of breakthrough curves and temperature profiles. The experimental campaign during reforming also confirmed the possibility to carry out the heat removal phase by means of endothermic methane reforming. The validated reactor model has subsequently been used for the simulation of different configurations in terms of heat management in which the different phases (oxidation, reduction and reforming) are simulated in series. In these analyses, the reactor design and perfor

This paper addresses the techno-economic assessment of two technologies for olefins production from naphtha and natural gas. The first technology is based on conventional naphtha steam cracking for the production of ethylene, propylene and BTX at polymer grade. The unused products are recovered in a boiler to produce electricity for the plant. The plant has been designed to produce 1 MTPY of ethylene. In the second case, ethylene is produced from natural gas through the oxidative coupling of methane (OCM) in which natural gas is fed to the OCM reactor together with oxygen from a cryogenic air separation unit (ASU). The overall reactions are kinetically controlled and the system is designed to work at about 750–850 °C and close to 10 bar. Since the overall reaction system is exothermic, different layouts for the reactor temperature control are evaluated. For the naphtha steam cracking plant, the energy analysis shows an overall conversion efficiency of 67% (with a naphtha-to-olefins conversion of 65.7%) due to the production of different products (including electricity), with a carbon conversion rate of 70%. The main equipment costs associated with naphtha steam cracking are represented by the cracker (about 30%), but the cost of ethylene depends almost entirely on the cost associated with the fuel feedstock. In case of the OCM plant, the overall energy conversion efficiency drops to maximally 30%. In the studied plant design, CO2 capture from the syngas is also considered (downstream of the OCM reactor) and therefore the final carbon/capture efficiency is above 20%. The cost of ethylene from OCM is higher than with the naphtha steam cracking plant and the CAPEX affects the final cost of ethylene significantly, as well as the large amount of electricity required.

Membrane technology applied in the chemical and energy industry has the potential to overcome many drawbacks of conventional technologies such as the need of large volume plants and large CO2 emissions. Recently, it has been reported that this technology might become more competitive when operated at high temperatures. This is mostly associated with the required of heat integration at large scale. However, good membrane stability combined with high permeation rates and high perm-selectivities, has only been achieved at intermediate/low temperatures (< 500 °C). When operated at these lower temperatures in a fully integrated plant, there is often the need of electricity import, which strongly decreases the process efciency and renders the membrane-based technology less competitive compared to conventional technologies. To improve the competitiveness of membrane technology further developments are required, demanding in particular an improvement in the preparation methods, the use of new materials and/or the development of novel reactor confgurations. In this study, a comprehensive review on the latest advancements in membrane technology for H2 separation at high temperature is presented. Special attention is given to the membranes prepared and presented in the literature in the last years for high-temperature applications, as well as the different membrane reactor confgurations that have proposed, tested and evaluated for different reaction systems at elevated temperatures. Since concerns about the need of high temperatures in membrane technology are relatively new, this review is limited to the results reported in the literature during the last fve years.