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The imperative to decarbonize the energy sector has prompted substantial advancements in clean electricity generation, with hydrogen emerging as a promising low-carbon energy carrier. While hydrogen synthesis from renewable sources is crucial, challenges persist, necessitating innovative approaches for efficient and sustainable production. This study leverages diverse artificial neural network (ANN) models to assess and predict system efficiency based on key operational variables in membrane reactor systems. The multilayered perceptron (MLP) and radial basis function (RBF) methodologies are employed, with the MLP models optimized across twelve training algorithms and eight activation functions, exploring up to three hidden layers with variable neuron counts. The MLP model, utilizing the Levenberg-Marquard training algorithm and Tangent-Sigmoid activation function, achieved a high correlation coefficient (R2) of 0.9975 for training and 0.9962 for testing, and a mean squared error (MSE) of 0.00425 for training and 0.23951 for testing, indicating precise and accurate efficiency predictions. The Log-Sigmoid activation function also performed well, with R² values of 0.9971 (training) and 0.9961 (testing), and MSE values of 0.004086 (training) and 0.17694 (testing). Optimization of the RBF network identified the best performance with a spread parameter of 1 and 35 neurons, although the MLP model demonstrated superior accuracy and reduced computational time. Statistical analysis, encompassing correlation coefficient, mean squared error, Root Mean Squared error, absolute average deviation, absolute average relative deviation, and runtime, confirms the network's consistent and accurate estimation of system efficiency across various input variables. The study highlights that applying tansig and logsig activation functions, configured with neuron counts of 20, 17, 6 and 23, 20, 2 at the first, second and third hidden layers, respectively, offers enhanced accuracy and reliability. The MLP model's high performance underscores its potential to identify optimal conditions for H2 generation based on system efficiency, thereby advancing membrane reactor technology for hydrogen production. [ABSTRACT FROM AUTHOR]

Membrane reactors for the production of hydrogen are interesting devices that allow for the decentralized production of pure hydrogen while reducing the energy cost of the traditional steam reforming process. The performance of these systems is strongly dependent on the permeability and selectivity of the membrane employed for the separation of the produced hydrogen. Several studies have shown that the actual rate of hydrogen permeation is lower than the one that would be expected based on studies of membrane permeability carried out with pure hydrogen. This difference has been attributed to the competitive adsorption of other species, specifically CO, on the membrane surface. Here we show that this phenomenon could also lead to steady state multiplicity and analyze the dynamics of membrane reactors in the presence of competitive adsorption by CO. Emphasis has been placed on the effect of temperature and gas composition on possible multistable behavior. The results have been interpreted in terms of a transition between kinetics- and permeation-controlled regimes, in which the behavior of the reactor is limited, respectively, by the rate of the chemical reactions or the rate of hydrogen permeation. [Display omitted] • Dynamics of membrane reactors in the presence of permeance inhibition were analyzed. • Effect of gas composition and temperature on multistable behavior was investigated. • Relationship between observed multistability and membrane inhibition was assessed. • Multistability due to competition between rate of H 2 production and permeation is observed. [ABSTRACT FROM AUTHOR]

Zeolites have been used as a separation membrane material by taking advantages of their unique adsorption properties and molecular sieving properties based on the micropores. Zeolite membranes are widely used in practical applications, mainly for dehydration of organic solvents. Furthermore, the research and development continue toward large-scale implementation in the energy and carbon neutral field. The high heat and chemical resistance of zeolite membranes are also expected to be utilized as membrane reactors. Zeolite membrane and membrane separation will contribute to the fulfillment of a carbon-neutral society through energy saving in separation, reaction, and CO2 recovery. In this review, the basic structure, the synthesis methods and the applications of zeolite membranes are introduced. The recent research trends of zeolite membrane in the research and applications are also explained. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Ammonia decomposition is a key technology for its use as a hydrogen carrier and in the recovery of H 2 from waste streams containing ammonia. The coupling of the catalytic decomposition of ammonia with an H 2 permeoselective membrane improves the process by mitigating thermodynamic constraints and producing a flux of high-purity hydrogen, not requiring further separation/purification. In this study, we compare the behaviour of an eggshell catalyst 1.3 wt % Ru/Al 2 O 3 catalyst in a packed bed reactor (PBR) and a packed bed membrane reactor (PBMR) using an ultrathin Pd membrane (3.4 μm). Tests were made at 11 bar(a) with a weight hourly space velocity of NH 3 in the 0.560–1.68 Lꞏg−1ꞏh−1 range and temperatures of 350–400 °C, e.g. milder conditions than the conventional ammonia cracking catalysts. Under optimised conditions (0.56 Lꞏg−1ꞏh−1, 400 °C, sweep gas flow 0.55 L min−1), the PBMR shows excellent performance, achieving NH 3 conversion, H 2 productivity and recovery factor of 99%, 47 mmol H2 ·g Ru −1·min−1, and 94.9%, respectively. PBMR increases by ∼50% the conversion rate compared to PBR. Without a sweep gas, PBMR performances are lower, even still higher than in PBR. For the first time, superior or comparable performance was demonstrated compared to similar systems using pure ammonia in terms of conversion, hydrogen recovery, H 2 productivity, and Ru utilisation. These results can be further enhanced with vacuum systems to convert diluted ammonia streams into high-purity hydrogen for small-scale distributed systems and can be extended to other reactions. • An egg-shell Ru/Al 2 O 3 with an ultra-thin Pd membrane achieved 99% NH 3 conversion at 400 °C in PBMR, outperforming PBR. • Ultra-thin Pd membranes and sweep gas allow 94.88% H 2 recovery factor by decomposition of diluted ammonia. • Dilute NH 3 can improve safety and decrease noble metal usage, offering economic and environmental benefits. [ABSTRACT FROM AUTHOR]

This study proposes a combination system consisting of a biogas dry reforming reactor and a solid oxide fuel cell (SOFC). Since biogas dry reforming is an endothermic reaction, this study adopted a membrane reactor operated due to the non-equilibrium state with H2 separation from the reaction space. This study aimed to clarify the performance of the Ni/Cr/Ru catalyst using a biogas dry reforming membrane reactor. Additionally, this study also undertook a comparison of the performance of the Ni/Cr/Ru catalyst with that of the Ni/Cr catalyst. The impact of operation temperature, the molar ratio of CH4:CO2, the differential pressure between the reaction chamber and the sweep chamber, and the introduction of a sweep gas on the performance of the biogas dry reforming membrane reactor using a Pd/Cu membrane and a Ni/Cr/Ru catalyst was examined. The concentration of H2 using the Ni/Cr/Ru catalyst was greater than that using the Ni/Cr catalyst by 2871 ppmV for the molar ratio of CH4:CO2 = 1.5:1 at the reaction temperature of 600 °C and the differential pressure of 0 MPa without a sweep gas in particular. Under this condition, CH4 conversion, H2 yield, and thermal efficiency were 67.4%, 1.77 × 10−2%, and 0.241%, respectively. [ABSTRACT FROM AUTHOR]

Abstract The imperative to decarbonize the energy sector has prompted substantial advancements in clean electricity generation, with hydrogen emerging as a promising low-carbon energy carrier. While hydrogen synthesis from renewable sources is crucial, challenges persist, necessitating innovative approaches for efficient and sustainable production. This study leverages diverse artificial neural network (ANN) models to assess and predict system efficiency based on key operational variables in membrane reactor systems. The multilayered perceptron (MLP) and radial basis function (RBF) methodologies are employed, with the MLP models optimized across twelve training algorithms and eight activation functions, exploring up to three hidden layers with variable neuron counts. The MLP model, utilizing the Levenberg-Marquard training algorithm and Tangent-Sigmoid activation function, achieved a high correlation coefficient (R2) of 0.9975 for training and 0.9962 for testing, and a mean squared error (MSE) of 0.00425 for training and 0.23951 for testing, indicating precise and accurate efficiency predictions. The Log-Sigmoid activation function also performed well, with R² values of 0.9971 (training) and 0.9961 (testing), and MSE values of 0.004086 (training) and 0.17694 (testing). Optimization of the RBF network identified the best performance with a spread parameter of 1 and 35 neurons, although the MLP model demonstrated superior accuracy and reduced computational time. Statistical analysis, encompassing correlation coefficient, mean squared error, Root Mean Squared error, absolute average deviation, absolute average relative deviation, and runtime, confirms the network’s consistent and accurate estimation of system efficiency across various input variables. The study highlights that applying tansig and logsig activation functions, configured with neuron counts of 20, 17, 6 and 23, 20, 2 at the first, second and third hidden layers, respectively, offers enhanced accuracy and reliability. The MLP model’s high performance underscores its potential to identify optimal conditions for H2 generation based on system efficiency, thereby advancing membrane reactor technology for hydrogen production.

This study proposes a combination system consisting of a biogas dry reforming reactor and a solid oxide fuel cell (SOFC). Since biogas dry reforming is an endothermic reaction, this study adopted a membrane reactor operated due to the non-equilibrium state with H2 separation from the reaction space. This study aimed to clarify the performance of the Ni/Cr/Ru catalyst using a biogas dry reforming membrane reactor. Additionally, this study also undertook a comparison of the performance of the Ni/Cr/Ru catalyst with that of the Ni/Cr catalyst. The impact of operation temperature, the molar ratio of CH4:CO2, the differential pressure between the reaction chamber and the sweep chamber, and the introduction of a sweep gas on the performance of the biogas dry reforming membrane reactor using a Pd/Cu membrane and a Ni/Cr/Ru catalyst was examined. The concentration of H2 using the Ni/Cr/Ru catalyst was greater than that using the Ni/Cr catalyst by 2871 ppmV for the molar ratio of CH4:CO2 = 1.5:1 at the reaction temperature of 600 °C and the differential pressure of 0 MPa without a sweep gas in particular. Under this condition, CH4 conversion, H2 yield, and thermal efficiency were 67.4%, 1.77 × 10−2%, and 0.241%, respectively.

Methylcyclohexane (MCH) dehydrogenation is an equilibrium‐limited reaction that requires high temperatures (>300 °C) for complete conversion. However, high‐temperature operation can degrade catalytic activity and produce unwanted side products. Thus, a hybrid zeolite membrane (Z) is prepared on the inner surface of a tubular support and used it as a wall in a membrane reactor (MR) configuration. Pt/C catalysts is packed diluted with quartz sand inside the Z‐coated tube and applied the MR for MCH dehydrogenation at low temperatures (190–250 °C). Z showed a remarkable H2‐permselectivity in the presence of both toluene and MCH, yielding separation factors over 350. The Z‐based MR achieved higher MCH conversion (75.3% ± 0.8% at 220 °C) than the conventional packed‐bed reactor (56.4% ± 0.3%) and the equilibrium state (53.2%), owing to the selective removal of H2 through Z. In summary, the hybrid zeolite MR enhances MCH dehydrogenation at low temperatures by overcoming thermodynamic limitations and improves the catalytic performance and product selectivity of the reaction. [ABSTRACT FROM AUTHOR]

Multi-objective optimization (MOO) of methane reforming process has been performed for hydrogen and oxygen perm-selective membrane reactor (MR) considering three objectives, namely H 2 yield maximization, CO 2 minimization and reactor length minimization. The performance of the MR has been compared with that of the cylindrical reactor (CR) using the same objective functions. Four MOO problems have been formulated and solved in this work. Among these, three problems consist of 2-objectives, while one has 3-objectives. Comparative results and discussions of the two reactors are presented based on the multi-objective pareto curve analysis and the trends of decision variables. The results in this work indicate that MR performs better than CR in all the four multi-objective scenarios. We further optimize the reactor with the above mentioned all the three objectives to produce syngas with different (H 2 / CO) ratios in the product stream. This is especially useful for producing the syngas targeting a specific end application. • Multi-objective optimization (MOO) study of a membrane reactor. • Comparative study of cylindrical and membrane reactors using MOO. • Maximization of H 2 yield, minimization of CO 2 emission & reactor length. • Achieving desired syngas ratio in membrane reactor using MOO. • MR size is observed to be 48.7% smaller than CR for achieving the H 2 yield of 2.69 [ABSTRACT FROM AUTHOR]

Rising levels of carbon dioxide (CO 2) emissions due to human activities exert a substantial adverse effect on the environment. The conversion of CO 2 into methanol (CH 3 OH) through hydrogenation is a promising way to utilize this greenhouse gas, thus maintaining carbon in the cycle. In terms of sustainability, methanol is of particular interest because of its dual utilization potential as a fuel or base material to produce different chemicals. The versatility of the latter allows it to be used directly as a precursor to produce numerous compounds, including dimethyl ether (DME), olefins, formaldehydes, and hydrocarbon fuels. This paper first reviews the latest developments in catalyst design, focusing on the relationship between catalyst structure and performance. In addition, recent advances in understanding the reaction mechanisms, optimizing catalyst architectures, innovating membrane reactors, and reaction conditions have been discussed. This summarizes the strategies for increasing the efficiency of sustainable methanol production with the help of membranes. This study provides an outlook for future research in this field. [Display omitted] • Developing efficient hydrogen conversion is essential for addressing climate change. • Technological improvements in the synthesis of water selective zeolite membranes. • Latest developments in CO 2 hydrogenation using Cu-based catalysts. • Adapting zeolite membranes in catalytic membrane reactors to increase methanol yield. • Challenges and perspectives of CO 2 hydrogenation in the presence of a membrane. [ABSTRACT FROM AUTHOR]

Acidic gases such as H2S and CO2 are generated in the refineries during coal gasification. These pollutant gases need to be treated before releasing to the atmosphere. Conventionally, H2S gas is treated by Claus process in which H2S is converted to elemental S and H2O, in presence of O2 at ∼1,200 K. In the present energy scenarios, hydrogen has got importance as a source of clean fuel for industrial application. The H2S generated in the refineries can be a potential precursor of hydrogen. If this hydrogen can be obtained by thermal decomposition of H2S, that can increase the overall economic value of the H2S containing streams and the produced hydrogen can be used for hydrocracking and hydro-treating in refineries, as well as to synthesize value-added products for chemical industries. However, H2S thermal decomposition is an endothermic and equilibrium limited reaction (equilibrium conversion is only ∼15 % at 1,000 K), requiring a very high temperature (∼1,500 K) to achieve even a conversion of greater than 40 %. Packed Bed Catalytic Membrane Reactor (PBCMR) for thermal decomposition of H2S can be a potential technology augmentation and process intensification to increase this equilibrium conversion. In this work, modeling and experimental studies of H2S thermal decomposition using in-house designed & developed PBCMR have been carried out. The modeling studies were validated with experimental data. Clay-alumina ceramic tubular membrane (L: 250 mm; OD: 12 mm; thickness: 2 mm) was fabricated using extrusion process having an average membrane pore size of ∼1 μm and with a porosity of ∼20 %. Pt (2 %) coated alumina extrudes were used as catalyst to accelerate the reaction kinetics. Experimental studies showed that H2S to hydrogen conversion of ∼90 % is achieved using PBCMR at ∼1,523 K, compared to only ∼40 % conversion in a conventional packed bed tubular reactor (without membrane). Modelling studies were carried out to study the influence of operating parameters such as, reactor wall temperature, feed temperature, pressure and feed velocity. Studies showed that reactor wall temperature is having the most dominant effect on H2S conversion, which is confirmed by experimental findings. The studies offer useful insights into the application of PBCMR technology for management of waste gas stream containing H2S and recovery of hydrogen. [ABSTRACT FROM AUTHOR]

This work aims at investigating the potential of catalytic membrane reactors (CMRs) for ammonia production from renewable hydrogen. To achieve this objective, computer-aided process simulation is deployed using Aspen plus v14 simulation tool. A 1D model is developed to describe the integration of a ruthenium catalyst into a CMR equipped with inorganic membranes that are selective to NH 3 over N 2 and H 2. First, the CMR performance is studied across a broad spectrum of membrane properties and operating conditions. Subsequently, the CMR model is integrated into several Power-to-Ammonia (PtA) process layouts, which are optimized and techno-economically compared against a traditional PEM-based PtA production process, employing condensation for the purification stage. Key findings at the reactor level confirmed that beyond a selectivity threshold towards hydrogen of 10–20, both the degree of conversion and recovery tend to be generally independent of the membrane's selectivity. However, for producing pure ammonia permeate, highly selective membranes (>1000 towards H 2) depending on the pressure drop are found essential making this alternative elusive based on existing membranes. At the PtA level, results in terms of efficiency indicates that the use of membrane reactor increases the system efficiency by around ∼8% with respect to reference case while ∼15% enhancement is achieved with this process when using SOEC technology. When examining the final Levelized Cost of Ammonia (LCOA), incorporating a membrane reactor in conjunction with condensation separation results in a cost that nearly matches the reference case. Future research should focus on replacing the condensation process with a method of purification at lower pressures. This could potentially further improve efficiency and reduce the cost of the membrane reactor compared to the traditional one. • A reactor model for ammonia production using a ruthenium catalyst-based CMR was developed, analyzing a range of membrane properties and operating conditions. • MR shows over 90% higher ammonia conversion compared to conventional reactors. • The MR increased the system efficiency by around 8% with respect to reference cases. • MR process showed a marginal 2% increase in cost over the reference process. [ABSTRACT FROM AUTHOR]

The increasing interest in leveraging green ammonia to mitigate carbon emissions in fertilizer production is paralleled by an expanding acknowledgment of its potential as a fuel for decarbonizing the electricity sector, particularly in high-efficiency gas turbine power plants. Co-firing ammonia with hydrogen presents a promising method for integrating ammonia into existing infrastructures. Within this context, the development of efficient technology for ammonia cracking presents a potential avenue for deploying ammonia in gas turbines. The objective of this study is to conduct a preliminary techno-economic evaluation and uncertainty analysis of two cracking technologies namely a membrane reactor and a conventional FTR (Fired Tubular Reactor) for the co-firing of ammonia with hydrogen in a CCGT (Combined Cycle Gas Turbine) plant. The integration of a membrane reactor during the cracking stage demonstrates a remarkable improvement in the system's thermal efficiency, surpassing traditional approaches by over 25%. Additionally, it brings about an approximate 10% reduction in the levelized cost of hydrogen (LCOH), despite a higher initial capital expenditure (CAPEX). At the CCGT level, the discrepancy in levelized cost of electricity (LCOE) narrows, as it is strongly influenced by the cost of ammonia constituting 80% of the LCOE. Beyond LCOE, the widespread adoption of these systems also faces challenges due to material scarcity. Analysis reveals that revamping just 1 GWe of CCGT assets using membrane reactors would for example necessitate approximately 0.11% of the global palladium supply, and 10% of the global ruthenium production. Considering the limited availability of these resources, coupled with their high demand across multiple sectors and the possibility of external factors such as geopolitical tensions, this strategy seems unfeasible. To tap into this market, future research should prioritize the exploration of alternative membrane materials, such as carbon molecular sieves, and catalysts, like nickel. • Two cracking technologies for NH3–H2 co-firing in CCGT plants have been evaluated. • Membrane reactors reduces H2 cost by 10% and raise efficiency by 25%. • The study indicates the need to explore new materials for this market (e.g. carbon molecular sieve membrane). [ABSTRACT FROM AUTHOR]

H 2 S is a toxic gas released during many industrial processes, especially oil and gas refining. Currently, H 2 S is converted to sulfur using Claus process, but it leads to loss of another valuable product, i.e., hydrogen, in the form of water. Thermal decomposition of H 2 S in a membrane reactor is a promising route for recovering both hydrogen as well as sulfur in an efficient manner. In the present work, the authors report H 2 S decomposition studies with packed-bed membrane reactor (PBMR) using in-house developed clay-alumina ceramic membrane. In order to have a comparative evaluation, these studies were conducted in packed bed reactor (PBR) as well as in single-tube PBMR at different operation parameters. In PBMR, conversion of ∼90% was obtained at 1573 K and 0.5 bar, whereas a conversion of ∼50% was obtained in PBR. CFD simulations for H 2 S decomposition using ceramic PBMR were carried out and validated using experimental results. 3D simulations for parametric optimisation of multi-tube PBMR were also carried out by extrapolation of validated model. This is for the first time, CFD studies on H 2 S decomposition and its validation using ceramic PBMR are being reported in this work. • Enhanced H 2 S decomposition (up to 90%) carried out using alumina membrane reactor. • A comparative evaluation of H 2 S decomposition made in PBR & PBMR. • CFD simulation studies carried out & parameters optimised for scale-up of PBMR. [ABSTRACT FROM AUTHOR]

Nowadays, the studied flowing molten salt heated methane/steam reforming membrane reactors are of roughly the same structure and vastly different sizes, which needs to be further explored with the consideration of reactor design optimization and system economy. This research investigates the effect of catalyst bed thickness, membrane tube configuration and reactor length on reactor performance under a series of operation conditions. The impact of concentrated solar thermal cost and methane cost on the levelized cost of hydrogen are focused to provide reference for the reactor design from an economic perspective. The results show that the catalyst bed thickness of 10 mm and the membrane diameter of 20 mm are appropriate for reactor design. Long membrane tube with big flow rate is more economical than the short one and its advantages in economy will be further reflected with the decreasing CST cost. [Display omitted] • A model of molten salt heated membrane reformer is developed. • The catalyst bed thickness of 10 mm is appropriate for reactor design. • Increasing the membrane diameter beyond 20 mm is not sensible. • Membrane reactors with long pipe and high flow rate are more economical. [ABSTRACT FROM AUTHOR]

The utilization of ammonia for hydrogen storage relies on the implementation of efficient decomposition techniques, and the membrane reactor, which allows simultaneous ammonia decomposition and hydrogen recovery, can be regarded as a promising technology. While Pd-based membranes show the highest performance for hydrogen separation, their applicability for NH3-sensitive applications, such as proton exchange membrane (PEM) fuel cells, demands relatively thick, and therefore expensive, membranes to meet the purity targets for hydrogen. To address this challenge, this study proposes a solution involving the utilization of a downstream hydrogen purification unit to remove residual ammonia, thereby enabling the use of less selective, therefore more cost-effective, membranes. Specifically, a carbon molecular sieve membrane was prepared on a tubular porous alumina support and tested for ammonia decomposition in a membrane reaction setup. Operating at 5 bar and temperatures ranging from 450 to 500 °C, NH3 conversion rates exceeding 90% were achieved, with conversion approaching thermodynamic equilibrium at temperatures above 475 °C. Simultaneously, the carbon membrane facilitated the recovery of hydrogen from ammonia, yielding recoveries of 8.2–9.8%. While the hydrogen produced at the permeate side of the reactor failed to meet the purity requirements for PEM fuel cell applications, the implementation of a downstream hydrogen purification unit comprising a fixed bed of zeolite 13X enabled the production of fuel cell-grade hydrogen. Despite performance far from being comparable with the ones achieved in the literature with Pd-based membranes, this study underscores the viability of carbon membranes for fuel cell-grade hydrogen production, showcasing their competitiveness in the field. [ABSTRACT FROM AUTHOR]

A mathematical model was constructed to estimate the performance of an MFI-membrane reactor used for Fischer–Tropsch synthesis to produce a mixture of liquid hydrocarbons. In order to accurately evaluate the reactor's performance a parametric study was performed. Under certain operational conditions, such as the total initial pressure in the reaction zone (1–4 MPa) and the hydrogen/carbon monoxide ratio (H2/CO: 1 to 2) on the performance of the studied reactor. The selectivity (productivity) of the hydrocarbon products (Si), the quantity of hydrocarbons permiated (θi) and the separation factors of each space (αi) were predicted. With increasing pressure, it is observed that θCO and θ H 2 are decreasing from 0.62 to 0.45 and from 0.55 to 0.49 respectively. However, as the H2/CO ratio rises, this measurement shows a slight increase. Aside from, the separation factors of the majority of the current species are unaffected by the H2/CO ratio increasing, while the separation factors of carbon monoxide and hydrogen are increasing. Similarly the selectivity of water, methane, carbon dioxide and ethane increases with increasing H2/CO ratio. Based on these findings it is revealed that the membrane can enable permeability for all species present in the products mixture with varying separation factors, and that the ability to separate species other than water from the reaction side is essentially non-existent. [ABSTRACT FROM AUTHOR]

Hydrogen is a carbon-free fuel and can be expected to play a significant role in the global clean energy transition. In this study, two proposed small-scale hydrogen production plant configurations were designed and simulated for high-purity hydrogen production at a rate of 25 kg H2 /day. The feasibility and economic viability of the proposed plant configurations were examined. Additionally, the performance and sensitivity analysis were assessed under different operating conditions. Configuration A proposed to use two reactors for ammonia cracking and H 2 separation, respectively. Configuration B considers that the decomposition of ammonia and H 2 separation simultaneously occurs in a single integrated reactor. Despite the configuration B was more energy efficient than configuration A but both configurations are applicable. The total H 2 production cost of configuration A was 6.39 $/kg H2 and that of configuration B was 6.06 $/kg H2. Since the proposed plant configurations generated both hydrogen and nitrogen, the total cost of production was distributed between them. Therefore, the final H 2 and N 2 separation costs of configuration A was 5.05 $/kg H2 and 1.14 $/kg N2 , and configuration B was 4.72 $/kg H2 and 1.08 $/kg N2. The hydrogen production cost from different ammonia synthesis pathways was compared. The technology readiness level (TRL) for hydrogen production from ammonia cracking was assessed and identified at a range of TRL 4–6. It can also be considered that the ammonia synthesis pathway controlled the ammonia prices and subsequently the hydrogen production cost. • Two proposed configurations were designed for H 2 production from blue NH 3. • Techno-economic assessment was performed for small-scale H 2 plants. • The final H 2 cost of proposed configuration A was higher than configuration B. • The H 2 production cost from different NH 3 synthesis pathways was also compared. • The pathway of NH 3 synthesis influenced the prices of NH 3 and H 2. [ABSTRACT FROM AUTHOR]

Copyright of Dokuz Eylul University Muhendislik Faculty of Engineering Journal of Science & Engineering / Dokuz Eylül Üniversitesi Mühendislik Fakültesi Fen ve Mühendislik Dergisi is the property of Dokuz Eylul Universitesi Muhendislik Fakultesi Fen ve Muhendislik Dergisi and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Water-gas shift (WGS) reaction for hydrogen production and CO 2 removal/capture in a catalyst-packed CO 2 -permselective membrane reactor is studied experimentally and simulated with a computational model. The reactor utilizes a tubular dense ceramic-carbonate dual-phase membrane with a commercial high-temperature WGS catalyst. Equations governing CO 2 permeation through the membrane and WGS reaction kinetics on the catalyst were obtained through independent CO 2 permeation experiments and a fixed-bed reaction kinetic study. The simulation results using the validated model are presented to examine the effects of feed gas composition, steam/CO ratio, gas hourly space velocity, temperature, reactor pressure, sweep to feed molar flow rate ratio, and the membrane area to catalyst volume ratio on the performance of the membrane reactor for WGS with CO 2 removal. Under optimized conditions, the catalyst-packed membrane reactor for WGS demonstrates significantly enhanced CO conversion and product H 2 purity by effectively removing/capturing CO 2 from the WGS reaction side. [Display omitted] • A model is established and validated for WGS reaction in a membrane reactor (MR). • Reactor comprises a CO 2 perm-selective membrane and high-temperature WGS catalyst. • The model examines the effects of operational conditions on the MR performance. • MR favors CO conversion, CO 2 capture, and H 2 purity at high pressure/temperature. [ABSTRACT FROM AUTHOR]

The depletion of fossil fuels such as oil, natural gas, and coal, as well as environmental concerns, pave the way for the effective utilization of renewable energy sources. Hydrogen is forecasted as an energy alternative which can be utilized at high conversion causing zero or near-zero emission at the point of use. Methanol is an ideal hydrogen carrier owing to its low cost, high H/C ratio, low reforming temperature, no sulfur content and liquid state at ambient conditions and it can be produced from a variety of feedstocks. This review article provides an overview of the various catalysts employed in steam reforming of methanol (SRM). It delves into the effect of catalyst preparation methods and catalyst composition on the catalytic activity and selectivity for SRM. Thermodynamic analysis, the reaction schemes and kinetics over various catalysts used in SRM were discussed in detail. Various reactors used for SRM, including conventional packed bed, microchannel and membrane reactors were thoroughly reviewed and discussed. • Various hydrogen production methods are presented. • Thermodynamic analysis of SRM is summarized. • Performances of Cu and Pd based catalysts on SRM are reviewed. • Various reactor configurations used in SRM are summarized. • Reaction mechanisms and Kinetic expression for SRM are tabulated. [ABSTRACT FROM AUTHOR]

The site‐specific activation of bioorthogonal prodrugs has provided great opportunities for reducing the severe side effects of chemotherapy. However, the precise control of activation location, sustained drug production at the target site, and high bioorthogonal reaction efficiency in vivo remain great challenges. Here, we propose the construction of tumor cell membrane reactors in vivo to solve the above problems. Specifically, tumor‐targeted liposomes with efficient membrane fusion capabilities are generated to install the bioorthogonal trigger, the amphiphilic tetrazine derivative, on the surface of tumor cells. These predecorated tumor cells act as many living reactors, transforming the tumor into a "drug factory" that in situ activates an externally delivered bioorthogonal prodrug, for example intratumorally injected transcyclooctene‐caged doxorubicin. In contrast to the rapid elimination of cargo that is encapsulated and delivered by liposomes, these reactors permit stable retention of bioorthogonal triggers in tumor for 96 h after a single dose of liposomes via intravenous injection, allowing sustained generation of doxorubicin. Interestingly, an additional supplement of liposomes will compensate for the trigger consumed by the reaction and significantly improve the efficiency of the local reaction. This strategy provides a solution to the efficacy versus safety dilemma of tumor chemotherapy. [ABSTRACT FROM AUTHOR]

Butyric acid, a four-carbon fatty acid, is an important industrial chemical and feedstock. To produce this chemical, a control fermentation was run with a 126.5 g.L−1 glucose concentration in the feed medium. In this medium, the strain produced 44.8 g.L−1 total acid with a productivity of 0.23 g.L−1h−1 and a yield of 0.41 g.g−1. The strain (Clostridium tyrobutyricum ATCC 25755) was also able to utilize glucose and xylose simultaneously with similar fermentation performance. The culture was also used to produce butyric acid from wheat straw hydrolysate (WSH) employing a hot water pretreatment. In a batch system, the strain resulted in a productivity and yield of 0.27 g.L−1h−1 and 0.44 g.g−1, respectively, which was an improvement over the use of glucose or xylose alone or mixtures of both. To improve reactor productivity, a membrane cell recycle bioreactor was used which resulted in a productivity of 1.89 g.L−1h−1. This productivity was 822% of that achieved in the glucose or xylose batch fermentation. Furthermore, a butyric acid recovery method was developed using XAD-4 adsorbent resin. In this system, up to 206.1 g.L−1 of butyric acid was used in the feed and, as a result of the quick adsorption, the residual butyric acid concentration was 29.5 g.L−1. In this experiment, the rate of acid removal of 1059.4 g.L−1h−1 was achieved. [ABSTRACT FROM AUTHOR]

Abstract Methylcyclohexane (MCH) dehydrogenation is an equilibrium‐limited reaction that requires high temperatures (>300 °C) for complete conversion. However, high‐temperature operation can degrade catalytic activity and produce unwanted side products. Thus, a hybrid zeolite membrane (Z) is prepared on the inner surface of a tubular support and used it as a wall in a membrane reactor (MR) configuration. Pt/C catalysts is packed diluted with quartz sand inside the Z‐coated tube and applied the MR for MCH dehydrogenation at low temperatures (190–250 °C). Z showed a remarkable H2‐permselectivity in the presence of both toluene and MCH, yielding separation factors over 350. The Z‐based MR achieved higher MCH conversion (75.3% ± 0.8% at 220 °C) than the conventional packed‐bed reactor (56.4% ± 0.3%) and the equilibrium state (53.2%), owing to the selective removal of H2 through Z. In summary, the hybrid zeolite MR enhances MCH dehydrogenation at low temperatures by overcoming thermodynamic limitations and improves the catalytic performance and product selectivity of the reaction.

The utilization of oxygen transport membranes enables the production of high-purity hydrogen by the thermal decomposition of water below 1000 °C. This process is based on a chemical potential gradient across the membrane, which is usually achieved by introducing a reducing gas. Computational fluid dynamics (CFD) can be used to model reactors based on this concept. In this study, a modelling approach for water splitting is presented in which oxygen transport through the membrane acts as the rate-determining process for the overall reaction. This transport step is implemented in the CFD simulation. Both gas compartments are modelled in the simulations. Hydrogen and methane are used as reducing gases. The model is validated using experimental data from the literature and compared with a simplified perfect mixing modelling approach. Although the main focus of this work is to propose an approach to implement the water splitting in CFD simulations, a simulation study was conducted to exemplify how CFD modelling can be utilized in design optimization. Simplified 2-dimensional and rotational symmetric reactor geometries were compared. This study shows that a parallel overflow of the membrane in an elongated reactor is advantageous, as this reduces the back diffusion of the reaction products, which increases the mean driving force for oxygen transport through the membrane.

The inorganic-carbonate dual-phase membrane represents a class of dense membranes that are fabricated using diverse support materials, ranging from metals to ceramics. This dual-phase membrane consists of a porous metal or ceramic support with an introduced carbonate phase within the support pores. Compared with polymer and zeolite membranes, inorganic-carbonate dual-phase membranes exhibit exceptional CO2 selectivity at elevated temperatures (>500 °C), making them an ideal choice for high-temperature CO2 separation in power plant systems. The present paper provides a comprehensive overview of the separation principle, significant models, and preparation techniques employed in carbonate dual-phase membranes for CO2 separation. The present study aims to discuss key factors that limit the CO2 permeation performance and stability of membranes, while also exploring the potential applications of dual-phase membranes in various fields. The identification of key challenges in the future development of the carbonate dual-phase membrane has been highlighted in this work. The future trajectory of research and development should be directed toward overcoming these challenges, encompassing the synthesis technology of membranes, balance optimization of membrane structure and performance, modification of physical and chemical properties of molten carbonate, and advancement in high-temperature sealing techniques, as well as exploration of diverse membrane reactors based on carbonate dual-phase membranes for prospective applications. [ABSTRACT FROM AUTHOR]

The present paper focus in design studies of a process for pure hydrogen production at decentralized scale. 9000 Nm3/h biogas are proposed as feedstock to the process. The plant includes a biogas-to-biomethane purification unit, a convective reformer equipped with bayonet-type tubes, a Pd-based membrane reactor profiting simultaneous hydrogen extraction and extra hydrogen production via water-gas shift, a combustion chamber and auxiliary units. Three optimization scenarios were considered where the hydrogen production is maximized and reformer and membrane reactors areas are minimized using different weights. All designs are fully thermally integrated aiming self-sustainability in terms of energy. To these ends, the retentate of the membrane reactor and the permeate of the biogas purification unit are both used as fuel to the combustion chamber. Results show the feasibility of operation with an overall thermal efficiency for the process of ca. 77.0–77.5% (based on LHV), comparable with values reported for processes of similar scale. [Display omitted] • A decentralized-scale process plant aiming at H 2 generation from biogas is proposed. • Self-sustainabilty in terms of energy is achieved for the designed hydrogen plant. • Minimization of reactors sizes along with maximization of H 2 production are studied. • Operation with efficiencies of 77% (based on LHV) are feasible. [ABSTRACT FROM AUTHOR]

Ammonia plays a key role in the renewable hydrogen economy nowadays, thus, the efficiency of ammonia decomposition for hydrogen production becomes an important research topic. In this study, a numerical model was built to study the performance of ammonia decomposition using a membrane reactor and Ru/Al 2 O 3 catalyst under various operating conditions such as feed NH 3 temperature and volume flow rate as well as retentate side pressure. The reactor performance was characterized by ammonia conversion, hydrogen recovery, and recovered hydrogen flow rate. Pre-exponential factor and activation energy of ammonia reaction rate were obtained by equilibrium conversion and two-step parametric sweeping. It was found that ammonia conversion can be increased by about 33% compared to a conventional fixed-bed reactor under the same operating conditions. H 2 recovery can be enhanced when the reactant inlet temperature and the pressure difference between the retentate and permeate sides increase. The increase in feed NH 3 flow rate (gas hourly space velocity, GHSV) decreased the ammonia conversion and H 2 recovery. An optimum GHSV that results in a maximum recovered H 2 flow rate can be found. Finally, optimum operation conditions for maximizing the hydrogen recovery and recovered hydrogen flow rate were analyzed using the multi-objective Non-dominated sorting genetic algorithm-II (NSGA-II). It was found that maximum H 2 recovery with a value of 79.7% can be obtained under the conditions of inlet temperature of 336 °C, GHSV of 900 h−1, and retentate side pressure of 9.9875 bar. The maximum recovered hydrogen flow rate with a value of 9.55 × 10 − 14 (mol · s − 1) can be obtained under the conditions of an inlet temperature of 394 °C, GHSV of 1315 h−1, and retentate side pressure of 9.9879 bar. • A novel two-step parametric sweeping is employed to obtain parameters in reaction rate. • Increasing reaction pressure produces more significant enhancement than temperature. • An optimum GHSV for recovered H 2 flow rate is found due to the change in residential time. • Optimum operating conditions for H 2 recovery and recovered H 2 flow are found using NSGA-II. [ABSTRACT FROM AUTHOR]

Ammonia can be used for hydrogen storage as it is relatively easy to transport, and can be generated at the site by decomposition of ammonia. In this work, the authors report studies on ammonia decomposition using packed-bed catalytic membrane reactor (PBCMR) based on Pd–Ag alloy membrane. The studies were carried out at different operating conditions in single tube PBCMR as well as in packed bed catalytic reactor without membrane (PBCR). A conversion of ∼93% was achieved in PBCMR at a temperature of 773 K and 1 bar, as against a conversion of ∼80% in PBCR. A CFD model was also developed and validated using experimental results. The model was further extrapolated to carry out 3D simulations of multi-tube PBCMR for parametric optimisation. This is a first of its kind study wherein a computational approach is used for studies on ammonia decomposition using multi-tube PBCMR. • Fabrication and characterization of Pd–Ag alloy membranes. • Ammonia decomposition using packed-bed catalytic membrane reactor (PBCMR). • CFD model developed and validated using experimental results. • CFD simulations of multi-tube PBCMR for parametric optimisation. [ABSTRACT FROM AUTHOR]

In this work, an experimental module for hydrogen purification based on nickel capillaries was fabricated. The module was tested by varying the temperature and the difference in the partial pressure of hydrogen on the supply and permeate sides of the capillaries. The maximum hydrogen flow obtained using a module based on 7 nickel capillaries with a wall thickness of 50 µm was 37.2 mL/min at a temperature of 900°C and a hydrogen pressure of 0.9 atm. The stability of the hydrogen flow to thermal cycling in a temperature range 600–800°С for 55 h was demonstrated. [ABSTRACT FROM AUTHOR]

The excessive production of carbon dioxide, the greenhouse effect, and the resulting global warming due to the use of fossil fuels have prompted governments, industry, and researchers toward renewable and clean energy sources. Hydrogen has emerged as a novel carbon neutral energy carrier with the highest specific energy content. Production, storage, distribution, and utilization of hydrogen are rapidly increasing. In this context, the use of hydrogen in power plants, fuel cells and internal combustion engines is constantly being developed. However, widespread use of hydrogen requires its sustainable production at low cost and under high purity conditions, which is the subject of further research. Hydrogen separation using membrane reactors is not a new concept; however, it has gained special attention in the last decades and represents a relevant and promising option to potentially overcome the above mentioned problems. This review examines advances in industry and research in hydrogen utilization, hydrogen production using membrane reactors, the nature and physicochemical properties of membranes, and the various configurations of membrane reactors. The effects of membrane reactors on the interplay of temperature, pressure, reactant conversion, hydrogen production, and thermodynamic equilibrium are explained, and the results are compared with those of conventional reactors. Finally, fuel cells, solar collectors, and their integrability into membrane reactors are discussed. [Display omitted] • Membrane reactor technology is an innovative and intensified method for decarbonised H 2 generation. • Membrane reactors configurations are described for simultaneous H 2 production, and purification. • H 2 perm-selective membranes are described for application in catalytic H 2 generation in membrane reactors. [ABSTRACT FROM AUTHOR]

The accessibility of hydrogen stations has been problematic for remote areas, although the demand for fuel-cell electric vehicles has risen. We propose a 50-Nm3/h on-site hydrogen production system using the accessible liquid-fuel infrastructure. The system integrates a pressurized steam reformer and a catalytic membrane reactor to produce high-purity hydrogen. This study focuses on scaling up our membrane reactor for enhanced hydrogen permeation while maintaining acceptable similarity and performance to make the system compact and effective. We compare three scale-up methods, which keep the inlet Reynolds number, gas hour space velocity, and Damköhler-Peclet number constant, respectively. After selecting the third case for its best similarity, we increase the scale to eight and conclude that any scale beyond four is not ideal for our specific membrane reactor. By increasing the scale to four, we reduce the number of reactors for the 50 Nm3/h target by 91% while achieving a hydrogen recovery of 91%. Future studies can refer to the scale-up process that maintains the reactor similarity and high performance in this work for choosing an appropriate scale for membrane reactors. • A single flat membrane reactor (MR) is scaled up for a 50 Nm3/h on-site H 2 station. • Three scale-up strategies are compared, and their performances are evaluated. • Four zones are seen as the MR is scaled up with a constant Damköhler-Peclet number. • In the first zone, the scaled-up MR had similar performance to the original MR. • We reduced the number of MRs by 91% after ensuring their stability and efficiency. [ABSTRACT FROM AUTHOR]

This study explores the optimization of membrane reactor configurations to enhance hydrogen production through CH4 tri-reforming. The investigation employs ceramic membranes for oxygen, vapor, and carbon dioxide distribution within the reactor bed. A differential evolution algorithm is utilized alongside cuckoo search algorithm (CSA) and support vector regression (SVR) to determine optimal values for O2/CH4, H2O/CH4, and CO2/CH4 ratios, membrane thickness, and shell pressure, with hydrogen yield as the objective function. Results demonstrate that the oxygen membrane reactor achieves the highest hydrogen yield, reaching 2.02 and 1.75 for direct methanol synthesis and Fischer–Tropsch processes, respectively, representing a 7.98 % and 10.03 % increase compared to the conventional tri-reforming reactor. Furthermore, CSA and SVR emerge as invaluable tools, facilitating robust optimization and predictive modeling. The CSA efficiently navigates complex solution spaces to identify optimal parameters, while SVR accurately models relationships between input variables and hydrogen yield. Incorporating these methodologies enhances the effectiveness of membrane reactor design and synthesis gas production. This study contributes to advancements in clean energy technologies by providing insights into efficient hydrogen production methods using membrane reactors.

The present study aims to analyze the performance characteristics of the biogas dry reforming process conducted in a membrane reactor using Ni/Cr catalysts and to compare these characteristics with those obtained using pure Ni catalysts. The effect of the pre-set reaction temperature, the molar ratio of CH4:CO2 and the pressure difference between the reaction chamber and the sweep chamber on the characteristics of biogas dry reforming is analyzed. In the present work, the molar ratio of the supplied CH4:CO2 is varied to 1.5:1, 1:1 and 1:1.5. In this case, CH4:CO2 = 1.5:1 simulates a biogas. The pressure difference between the reaction chamber and the sweep chamber is varied to 0 MPa, 0.010 MPa and 0.020 MPa. The reaction temperature is changed to 400 °C, 500 °C and 600 °C. It is revealed that the highest concentration of H2 is achieved using a Ni/Cr catalyst when the molar ratio of CH4:CO2 is 1.5:1 at the differential pressure of 0.010 MPa and the reaction temperature of 600 °C. Under this condition, the H2 yield, H2 selectivity and thermal efficiency are 12.8%, 17.5% and 174%, respectively. The concentration of the H2 produced using a Ni/Cr catalyst is larger than that produced using a Ni catalyst regardless of the pre-set reaction temperature, the molar ratio of CH4:CO2 and the differential pressure.

Co‐hydrogenation of CO2/CO to produce ethanol presents an important way to utilize carbon‐neutralized biomass resources through gasification. By applying a water‐permselective membrane reactor, water, the byproduct of CO2/CO hydrogenation to ethanol, can be removed. Thus, ethanol formation can be promoted thermodynamically. Accordingly, herein, the thermodynamics of ethanol synthesis by CO2, CO, CO2/CO hydrogenation was investigated, as well as the promoting effects of water removal under various temperatures and pressures by Aspen Plus. It is found that, at medium reaction temperature (e.g., 250 °C), medium pressure (e.g., 10–50 bar), and medium CO fraction (e.g., 0.1–0.5) together with 1‐stage water removal, a CO2/CO equilibrium conversion higher than 80 % can be obtained. [ABSTRACT FROM AUTHOR]

Ammonia synthesis via non-thermal plasma presents advantages over the Haber–Bosch process, particularly for small-scale and distributed operations powered by intermittent electricity from renewable energy sources. We designed and characterized a membrane Dielectric-Barrier Discharge (mDBD) reactor for ammonia synthesis from nitrogen and hydrogen. The reactor used a porous alumina membrane as dielectric barrier and as distributor of H2. This arrangement enabled greater residence time for N2 decomposition together with greater H2 availability in the reaction zone, as assessed by a computational thermal-fluid model. We evaluated the reactor's operation with membranes of 0.1, 1.0, and 2.0 µm pore size and porosities between 25 and 51%, and also in conventional DBD mode using a non-porous dielectric. The experimental characterization of the reactor encompassed electrical, optical, and spectroscopic diagnostics, as well as Fourier-Transform Infrared Spectroscopy to analyze gas products, as function of driving voltage. The results show that both, ammonia production and power consumption vary inversely with the product of membrane pore size and porosity. The highest energy yield of 0.25 g-NH3/kWh was obtained with the membrane with 1.0 µm pore size and 35% porosity, whereas the maximum yield under conventional DBD operation was three-times lower. Our findings demonstrate that the use of a membrane dielectric can enhance the performance of DBD-based ammonia synthesis. [ABSTRACT FROM AUTHOR]

MOF-based catalytic membrane reactor (MCMR), which can simultaneously achieve membrane separation and chemical catalytic degradation in an integrated system, is a cutting-edge technology for effective treatment of organic pollutants in water. The coupling of MCMR and advanced oxidation process (AOP) not only significantly improves the pollutant removal efficiency but also inhibits the membrane pollution through self-cleaning effect, thus improving the stability of MCMR. This paper reviews different MCMR systems combined with photocatalysis, Fenton oxidation, and persulfate activation, elucidates the reaction mechanism, discusses key issues to improve system effectiveness, and suggests future challenges and research directions. [ABSTRACT FROM AUTHOR]

The present investigation pertains to a theoretical study of mathematical model for methane steam reforming in membrane reactor, by simulating the operating variables of the reactor for high hydrogen yield and methane conversion. Basically, it deals with the development of the mathematical model of a fluidized bed Auto thermal membrane reactor (without integrated O2 perm-selective membranes), by using the mass balance macroscopically. Model is validated with the available experimental data in the literature and was found that the prediction from the models is in excellent agreement with the experimental values, with a maximum deviation of –12 to +13% and –12 to +1.8% for methane gas conversion and hydrogen yield, respectively. Finally, it investigates the effect of operating variables namely, reactor pressure, temperature, and steam to methane ratio (SMR) and permeates side pressure, on the methane gas conversion and hydrogen. The prediction reveals that the hydrogen yield and methane conversion increases with increase in reactor temperature and pressure whereas decreases with increase in SMR and permeate side pressure. [ABSTRACT FROM AUTHOR]

This article focuses on the separation characteristics and research status of the metal palladium membrane and nickel membrane that are the most representative dense metal H2 separation membranes, the advantages and disadvantages of the two membranes in the high-temperature H2 separation process are compared and analyzed. The concept and research progress of the dense metal membrane reactors for synchronous hydrogen production and separation are also described, this article discusses the problems existing in the industrial application process of the dense metal membrane and prospects the optimization development direction in the future. [ABSTRACT FROM AUTHOR]

The methanol-reforming solid oxide fuel cell (SOFC) emits high concentration of CO2 from the anode outlet. To achieve the goal of clean and low-carbon power generation, a CO2 capture unit is integrated with SOFC. In this work, the CO2 capture unit were set at different places in the conventional SOFC and gas turbine (GT) hybrid system. One was to place the water-gas-shift membrane reactor (WGSMR) at the anode inlet (SOFC-MRpre) and the other at the anode outlet (SOFC-MRpost). The key parameters, including the anode off-gas recycling ratio (RR), steam-to-carbon ratio (S/C), and operating pressure, have been investigated. Besides, the effects of the parameters on the power production, electrical efficiency, system efficiency, and CO2 capture capacity of the two processes were analyzed. It was found that the electrical and system efficiencies reached 53.3% and 41.8% for the SOFC-MRpre process, while 62.0% and 60.4% for the SOFC-MRpost process, respectively. The results show that placing the membrane reactor at the anode outlet can significantly reduce the energy consumption of the vacuum and blower, thus increasing the system efficiency. Besides, near-zero carbon emissions with only a 7.3% energy penalty can be achieved by the SOFC-MRpost process. These results reveal that the SOFC-MRpost process has more advantages than the SOFC-MRpre process. [ABSTRACT FROM AUTHOR]

Hydrogen stations have limited geographic coverage despite the rising demand for fuel cell electric vehicles. An on-site hydrogen production system that utilizes the liquid-fuel infrastructure can improve access to hydrogen in remote areas. The system has a pressurized steam reformer to convert the liquid fuel and a catalytic membrane reactor to produce high-purity hydrogen. This comprehensive computational-fluid-dynamics study aims to enhance the performance of the membrane reactor. We validate our models of a water-gas-shift catalyst reactor, the membrane reactor with high-purity hydrogen, and the same reactor loaded with the catalyst. The flow configuration, inlet, and outlet of the reactor are then changed to enhance the performance. We enlarge the membrane area at constant catalyst volume and observe 97% of the maximum hydrogen permeation at 38.5 cm2. This work is significant because it describes a step-by-step approach to improving the performance of a given reactor for future studies of membrane-reactor design. • The flow configuration of the membrane reactor was varied for its performance. • The widths of the retentate inlet/outlet were optimized for the permeation rate. • We had an even membrane-temperature distribution and an optimum catalyst thickness. • We achieved 97% of the maximum possible permeation for the reactor. • The geometry was optimized at constant volume with a 37% performance improvement. [ABSTRACT FROM AUTHOR]

Hydrogen as an energy vector is going to play an important role in the global energy mix. On the other hand, wastewater management has become a worldwide concern, as urban settlements have been considerably increasing for decades. Consequently, biodigestion to produce biogas (rich in methane) in water treatment plants could be an interesting starting point to obtain a valuable gas that can be converted into hydrogen through steam reforming. The aim of this work was to review the main aspects concerning steam reforming of biogas from wastewater treatment plants. For this purpose, the whole chain, from water treatment to hydrogen production and purification, was considered, paying attention to the main challenges and new technologies for its optimization. Thus, a wide range of possibilities is offered, from direct energy use of syngas to high purification of hydrogen (mainly through pressure swing adsorption or membrane reactors), presenting advantages and disadvantages. In any case, the role of catalysts seems to be essential, and aspects such as hydrogen sulfide and coke deposition control should be addressed. In conclusion, biogas steam reforming applied to wastewater treatment plants is a reality, with serious possibilities for its global implementation at the industrial level, according to techno-economic assessment. [ABSTRACT FROM AUTHOR]

The present study aims to analyze the performance characteristics of the biogas dry reforming process conducted in a membrane reactor using Ni/Cr catalysts and to compare these characteristics with those obtained using pure Ni catalysts. The effect of the pre-set reaction temperature, the molar ratio of CH4:CO2 and the pressure difference between the reaction chamber and the sweep chamber on the characteristics of biogas dry reforming is analyzed. In the present work, the molar ratio of the supplied CH4:CO2 is varied to 1.5:1, 1:1 and 1:1.5. In this case, CH4:CO2 = 1.5:1 simulates a biogas. The pressure difference between the reaction chamber and the sweep chamber is varied to 0 MPa, 0.010 MPa and 0.020 MPa. The reaction temperature is changed to 400 °C, 500 °C and 600 °C. It is revealed that the highest concentration of H2 is achieved using a Ni/Cr catalyst when the molar ratio of CH4:CO2 is 1.5:1 at the differential pressure of 0.010 MPa and the reaction temperature of 600 °C. Under this condition, the H2 yield, H2 selectivity and thermal efficiency are 12.8%, 17.5% and 174%, respectively. The concentration of the H2 produced using a Ni/Cr catalyst is larger than that produced using a Ni catalyst regardless of the pre-set reaction temperature, the molar ratio of CH4:CO2 and the differential pressure. [ABSTRACT FROM AUTHOR]

Butyric acid, a four-carbon fatty acid, is an important industrial chemical and feedstock. To produce this chemical, a control fermentation was run with a 126.5 g.L−1 glucose concentration in the feed medium. In this medium, the strain produced 44.8 g.L−1 total acid with a productivity of 0.23 g.L−1h−1 and a yield of 0.41 g.g−1. The strain (Clostridium tyrobutyricum ATCC 25755) was also able to utilize glucose and xylose simultaneously with similar fermentation performance. The culture was also used to produce butyric acid from wheat straw hydrolysate (WSH) employing a hot water pretreatment. In a batch system, the strain resulted in a productivity and yield of 0.27 g.L−1h−1 and 0.44 g.g−1, respectively, which was an improvement over the use of glucose or xylose alone or mixtures of both. To improve reactor productivity, a membrane cell recycle bioreactor was used which resulted in a productivity of 1.89 g.L−1h−1. This productivity was 822% of that achieved in the glucose or xylose batch fermentation. Furthermore, a butyric acid recovery method was developed using XAD-4 adsorbent resin. In this system, up to 206.1 g.L−1 of butyric acid was used in the feed and, as a result of the quick adsorption, the residual butyric acid concentration was 29.5 g.L−1. In this experiment, the rate of acid removal of 1059.4 g.L−1h−1 was achieved.

Endeavors have recently been concentrated on minimizing the dependency on fossil fuels in order to mitigate the ever-increasing problem of greenhouse gas (GHG) emissions. Hydrogen energy is regarded as an alternative to fossil fuels due to its cleaner emission attributes. Reforming of hydrocarbon fuels is amongst the most popular and widely used methods for hydrogen production. Hydrogen produced from reforming processes requires additional processes to separate from the reformed gases. In some cases, further purification of hydrogen has to be carried out to use the hydrogen in power generation applications. Metallic membranes, especially palladium (Pd)-based ones, have demonstrated sustainable hydrogen separation potential with around 99.99% hydrogen purity. Comprehensive and critical research investigations must be performed to optimize membrane-assisted reforming as well as to maximize the production of hydrogen. The computational fluid dynamic (CFD) can be an excellent tool to analyze and visualize the flow/reaction/permeation mechanisms at a lower cost in contrast with the experiments. In order to provide the necessary background knowledge on membrane reactor modeling, this study reviews, summarizes and analyses the kinetics of different fuel reforming processes, equations to determine hydrogen permeation, and lastly, various geometry and operating condition adopted in the literature associated with membrane-reactor modeling works. It is indicated that hydrogen permeation through Pd-membranes depends highly on the difference in hydrogen pressure. It is found that hydrogen permeation can be improved by employing different pressure configuration, introducing sweep flow on the permeate side of the membrane, reducing retentate side flow rate, and increasing the temperature.