Inlet Gas Composition Research Articles

Integrating Experimental and Numerical Data for Improved Steam Reforming Simulation with Deep Learning

Abstract In this paper, a data-driven methane steam reforming simulation is developed and used to predict the post-reaction mixture composition. Until today, methane steam reforming remains a predominant hydrogen production method, yet modeling its complex reactions remains a significant challenge due to the intricate interplay of process variables. Here, we show an artificial neural network simulator that can effectively model these reactions, offering precise predictions based on parameters like temperature, inlet gas composition, methane flow, and nickel catalyst mass. Our approach to data curation integrates experimental, interpolated, and theoretically calculated values and refining the model by assessing the relative importance of each data category. Various neural network structures were tested before ultimately identifying an optimal architecture with a 5-6-8-6-4 network structure. The network underwent 6000 epochs of training, leading to a model that demonstrates excellent agreement with experimental observations, as evidenced by the mean squared error of 0.000217 and the Pearson correlation coefficient of 0.965. Moreover, all process trajectories predicted by the network are characterized by a smooth course and are within a physical range of values. Therefore, this work overcomes a common challenge in chemical process simulation using neural networks and also sets a possible direction for future research in this field.

Optimal Dynamic Regimes for CO Oxidation Discovered by Reinforcement Learning.

Metal nanoparticles are widely used as heterogeneous catalysts to activate adsorbed molecules and reduce the energy barrier of the reaction. Reaction product yield depends on the interplay between elementary processes: adsorption, activation, desorption, and reaction. These processes, in turn, depend on the inlet gas composition, temperature, and pressure. At a steady state, the active surface sites may be inaccessible due to adsorbed reagents. Periodic regime may thus improve the yield, but the appropriate period and waveform are not known in advance. Dynamic control should account for surface and atmospheric modifications and adjust reaction parameters according to the current state of the system and its history. In this work, we applied a reinforcement learning algorithm to control CO oxidation on a palladium catalyst. The policy gradient algorithm was trained in the theoretical environment, parametrized from experimental data. The algorithm learned to maximize the CO2 formation rate based on CO and O2 partial pressures for several successive time steps. Within a unified approach, we found optimal stationary, periodic, and nonperiodic regimes for different problem formulations and gained insight into why the dynamic regime can be preferential. In general, this work contributes to the task of popularizing the reinforcement learning approach in the field of catalytic science.

Efficient H2O/CO2 co-electrolysis with NixCu1-x alloy nanocatalysts modified perovskite-type titanate cathodes

Syngas, a mixture of H2 and CO with adjustable compositional ratios, can be directly produced via H2O/CO2 co-electrolysis in solid oxide electrolysis cells (SOECs). In this study, We have developed a strategy to enhance the catalytic activity of titanate perovskite cathodes by constructing active metal-oxide interfaces through the in-situ growth of NixCu1-x alloy nanocatalysts (x = 0, 0.25, 0.5, 0.75 and 1) on LST matrix. The evenly distribution of NixCu1-x alloy nanoparticles (∼30 nm) on the LST substrate has been confirmed through a serious of characterization techniques, including XRD, XPS, SEM and TEM. Specifically, the LSTNi0.75Cu0.25 cathode demonstrated an optimal synergistic effect, achieving high efficiency in the co-electrolysis of H2O/CO2 to syngas. Under an applied voltage of 1.6 V at 800 °C, the syngas production rate reaches 5.43H2 and 3.48 CO ml min−1 cm−2 with ∼96 % Faradaic efficiency. Furthermore, the composition of the produced syngas can be finely tuned in a broad range from 0.8 to 3.5 b y simply adjusting the inlet gas composition (H2O/CO2 ratio) and the operating temperature. The LSTNi0.75Cu0.25 cathode, when subjected to continuous H2O/CO2 co-electrolysis for 100 h, exhibited remarkable stability, attributing to the robust and active nature of the metal-oxide interfaces.

Syngas Production from CO2 and H2O via Solid-Oxide Electrolyzer Cells: Fundamentals, Materials, Degradation, Operating Conditions, and Applications.

Highly efficient coelectrolysis of CO2/H2O into syngas (a mixture of CO/H2), and subsequent syngas conversion to fuels and value-added chemicals, is one of the most promising alternatives to reach the corner of zero carbon strategy and renewable electricity storage. This research reviews the current state-of-the-art advancements in the coelectrolysis of CO2/H2O in solid oxide electrolyzer cells (SOECs) to produce the important syngas intermediate. The overviews of the latest research on the operating principles and thermodynamic and kinetic models are included for both oxygen-ion- and proton-conducting SOECs. The advanced materials that have recently been developed for both types of SOECs are summarized. It later elucidates the necessity and possibility of regulating the syngas ratios (H2:CO) via changing the operating conditions, including temperature, inlet gas composition, flow rate, applied voltage or current, and pressure. In addition, the sustainability and widespread application of SOEC technology for the conversion of syngas is highlighted. Finally, the challenges and the future research directions in this field are addressed. This review will appeal to scientists working on renewable-energy-conversion technologies, CO2 utilization, and SOEC applications. The implementation of the technologies introduced in this review offers solutions to climate change and renewable-power-storage problems.

Tuning the A‐site Element in LaCo0.8Fe0.2O3 Perovskite‐based Catalyst for High Temperature N2O Decomposition in Nitric Acid Plant

AbstractThe effect of La‐deficiency and Ce/Sr‐substitution in the benchmark LaCo0.8Fe0.2O3 has been investigated for the decomposition of N2O between 500 and 900 °C. Real inlet gas composition and space velocity reveal that La‐deficiency and Ce/Sr‐substitution can improve the thermal stability of catalyst, while La1‐xSrxCo0.8Fe0.2O3 with x≥0.1 was highlighted as a promising formula due to the strongest resistance to deactivation and suppressed undesired NOx decomposition at high space velocity. This phenomenon is mainly ascribed to the incorporation of Sr2+ into the perovskite lattice during the reaction consequently stabilizing the Co3+ species and creating the oxygen vacancies in La1‐xSrxCoO3‐δ. On the contrary, the loss of activity on Ce‐substituted LaCo0.8Fe0.2O3 has been preferentially related to the cobalt exsolution to extra framework of perovskite making the catalytic cycle with Co3+ unfavorable. All these bulk and surface changes are accompanied with opposite evolution of apparent activation energy and pre‐exponential factor which can be discussed based on a redox mechanism.

A SiC membrane resistance recovery methodology based on dynamically dust cake layer analysis

Filter cake-induced resistance is a significant contributor to energy consumption in dust filtration processes. This can be optimized by adjusting inlet gas composition, membrane characteristics, and back-flushing parameters. In this study, calcium carbonate (CaCO3) dust with varying hygroscopicity was utilized to investigate the evolution mechanism of the filter cake on SiC membranes under different humidity conditions. The interacting force between particles and between the cake and membrane were analyzed to elucidate the fragmentation mechanism of the cake. It was observed that particles at higher relative humidity (increased RH from 40 % to 85 %) tend to form a more loosely packed cake (hydrophilic filter cake porosity and hydrophobic filter cake porosity increased from 70.8 % to 80.5 % and from 61.4 % to 69 %, respectively) with greater fragility (reduced cohesive force). This characteristic is advantageous for efficient backflushing operations. The strong adhesion between the filter cake and membrane hindered the recovery of the initial filtration resistance. For SiC membrane, the optimized back-flushing parameter is reservoir pressures of 0.2 and 0.15 MPa and pluse-jet intervals of 40 min to hydrophilic and hydrophobic dusts, respectively.

Experimental study and comprehensive kinetic modeling of the direct dimethyl ether synthesis on Cu/ZnO/ZrO2 and H-FER-20

In the direct dimethyl ether (DME) synthesis, the combination of Cu/ZnO/ZrO2 (CZZ) and H-FER-20 (FER) has shown high selectivity and productivity for a broad range of CO2/COX ratio. Aiming to understand the behavior of the studied catalyst system under distinct operating conditions, we developed a new 9-parameter kinetic model. The parameters were estimated based on 815 steady-state experiments carried out at several values of pressure (30–54 bar), temperature (190–250 ℃), space-velocity (0.79–4.34 s−1) and inlet gas composition. This broad database was used in the development and validation of a new 9-parameter kinetic model for the direct DME synthesis. The model adequately simulates experiments in several process conditions, with 95% of the simulated points presenting a deviation lower than 20% with respect to the experimental results for outlet DME molar percentage. In addition, it correctly predicts the trends with respect to variations in H2 inlet fraction, which is of high relevance for processes using fluctuating renewable power sources for H2 production. In comparison to state-of-the-art models with more parameters, the new model is significantly more accurate. It benefits from the broad range of validity and elevated number of experimental points, which makes it a reliable model that can be applied for process optimization and scale-up.

Sulfur Impurities in COx Feed Gases of Solid Oxide Cells: Effect on Degradation and Removal Strategies

High-temperature solid oxide cells (SOC) offer unrivaled Faradaic and energetic efficiencies for carbon dioxide electrolysis. However, it is yet unclear which contaminant level in carbon monoxide and carbon dioxide feed gases are tolerable to achieve low degradation rates in commercial applications. In the present work, electrolyte-supported cells (ESC) with Ni/Gadolinia-doped ceria (Ni/CGO) fuel electrodes were exposed to CO/CO2 gas mixtures at open circuit voltage and in electrolysis operation. The resistance evolution over time was monitored by means of electrochemical impedance spectroscopy. With this approach it is shown that a severe reversible degradation over time periods of up to 72 h occurs. X-ray photoemission spectroscopy (XPS) and high-resolution secondary ion mass spectrometry (SIMS) imaging techniques were used to show that this degradation effect is related to sulfur impurities on the Ni surface. Inlet gas composition variations were carried out to show that sulfur impurities most likely in the low ppb level are present in both industrial CO and CO2 feed gases. The efficacy of different gas cleaning units at room temperature was investigated to identify a suitable desulfurization solution. The results demonstrate the importance of feed gas purity for the commercialization of high-temperature CO2 electrolysis.

Numerical simulation of granular silicon growth and silicon fines formation process in polysilicon fluidized bed

Operating conditions strongly affect the yield and quality of polysilicon in a polysilicon fluidized bed. In this study, a new model of polysilicon fluidized bed was established using the Euler–Euler model coupled with population balance model (PBM), which was combined with fluid flow, heat, and mass transfer models, while considering the scavenging effect of silicon fines. The effects of different operating conditions on the deposition and formation rates of silicon fines were investigated. Results show that the model can correctly describe the particle growth process in the fluidized bed of polysilicon. The silicon fines and the interphase velocity difference show “N”- and “M”-shaped distributions along the axial direction, respectively. The particle temperature and concentration near the wall are higher than those in the central region. The decomposition of silane in the bottom region of the bed is dominated by heterogeneous deposition. The scavenging of silicon fines occurs in the dilute-phase region. The effects of operating conditions, i.e. inlet gas temperature, silane composition, and gas velocity, on the reactor performance were also explored comprehensively. Increasing the inlet gas composition and velocity enhances the formation rates of solid silicon and fines. Increasing the inlet gas temperature promotes the growth of solid silicon and inhibits the formation of silicon fines. High fluidization ratio, low inlet silane concentration, and high inlet gas temperature enhance the selectivity of silicon growth.

Biogas upgrading through calcium looping: Experimental validation and study of CO2 capture

The calcium looping technology is one of the most promising technologies for capturing and storing CO2. This technology has been evaluated with a variety of sorbents and conditions in previous works, but the inlet CO2-ladden gas has typically been a flue gas from combustion, which typically has a composition of 10–20% CO2 and 80–90% N2. On the other side, the performance of the calcium looping process for CO2 capture of other gases (i.e., biogas or gases resulting from hydrothermal carbonization) remains largely unstudied. In this work, this knowledge gap is assessed through evaluating the performance of the calcium looping process for biogas (synthesized as 40% CO2, 60% CH4) in terms of carbonation conversion. This experimental study investigates the impact of: (1) using an inlet gas composition representative for biogas instead of combustion flue gas; (2) different biogas compositions; (3) the carbonation temperature; (4) the cooling-down and heating-up of the sorbent material between the reactor and ambient temperatures within cycles; (5) the atmosphere composition during calcination; and (6) the solids particle size. The main result obtained is that the overall CO2-capture performance of calcium looping improves when using biogas as inlet CO2-ladden gas, in comparison with combustion flue gas. One main contribution to this improved performance is shown to be the presence of secondary reactions (i.e., dry reforming, methanation). The impact of the CH4 to CO2 ratio tested is not remarkable, showing that the potentialities of the process in this aspect can be adapted to several biogas producing feedstocks.

Reaction mechanism for atmospheric pressure plasma treatment of cysteine in solution

Mechanisms for the cold atmospheric plasma (CAP) treatment of cells in solution are needed for more optimum design of plasma devices for wound healing, cancer treatment, and bacterial inactivation. However, the complexity of organic molecules on cell membranes makes understanding mechanisms that result in modifications (i.e. oxidation) of such compounds difficult. As a surrogate to these systems, a reaction mechanism for the oxidation of cysteine in CAP activated water was developed and implemented in a 0-dimensional (plug-flow) global plasma chemistry model with the capability of addressing plasma-liquid interactions. Reaction rate coefficients for organic reactions in water were estimated based on available data in the literature or by analogy to gas-phase reactions. The mechanism was validated by comparison to experimental mass-spectrometry data for COST-jets sustained in He/O2, He/H2O and He/N2/O2 mixtures treating cysteine in water. Results from the model were used to determine the consequences of changing COST-jet operating parameters, such as distance from the substrate and inlet gas composition, on cysteine oxidation product formation. Results indicate that operating parameters can be adjusted to select for desired cysteine oxidation products, including nitrosylated products.

A numerical study on turquoise hydrogen production by catalytic decomposition of methane

Catalytic decomposition of methane (CDM) is a novel technology for turquoise hydrogen production with solid carbon as the by-product instead of CO2. A computational fluid dynamics model was developed to simulate the CDM process in a 3D fixed bed reactor, accounting for the impact of carbon deposition on catalytic activity. The model was validated with experimental data and demonstrated its capability to predict hydrogen concentration and catalyst deactivation time under varying operating temperatures and methane flow rates. The catalyst lifespan was characterized by the maximum carbon yield (i.e., gC/gcat), which is a crucial indicator for determining the cost of hydrogen generation. Parametric studies were performed to analyse the effect of inlet gas composition and operating pressure on CDM performance. Various CH4/H2 ratios were simulated to improve the methane conversion efficiency, generating a higher amount of hydrogen while increasing the maximum carbon yield up to 49.5 gC/gcat. Additionally, higher operating pressure resulted in higher methane decomposition rates, which reflects the nature of the chemical kinetics.

The influence of sulfur impurities in industrial COx gases on solid oxide electrolysis cell (SOEC) degradation

High-temperature solid oxide cells (SOC) offer unrivaled Faradaic and energetic efficiencies during carbon dioxide electrolysis. However, it is still unclear which gas quality and impurity level is required for low degradation rates in their commercial application. Here, it is shown that the polarization resistance of electrolyte-supported cells (ESC) with Ni/Gadolinia-doped ceria (Ni/CGO) degrades strongly over time periods of up to 72 h when operated in CO/CO2 gas mixtures. X-ray photoemission spectroscopy (XPS) and high-resolution secondary ion mass spectrometry (SIMS) imaging techniques were used to show that this degradation effect is related to sulfur impurities in the feed gas and their poisoning of the Ni surface. Variation of the inlet gas composition showed that impurities are present in both CO and CO2. The degradation was significantly less pronounced for Ni/CGO fuel electrodes compared to Ni/Yttria-stabilized zirconia (YSZ) and also when hydrogen was introduced into the feed gas. Generic natural gas cleaning desulfurization units were not able to remove the impurities from the feed gases. After initial electrode deactivation, stable cell performance was obtained for >900 h. The results clearly underline the importance of feed gas purity and the necessity for advanced cleaning units for the commercialization of high-temperature CO2 electrolysis.

Parametric analysis of a high-temperature solar-driven propane steam reformer for hydrogen production in a porous bed catalytic reactor

In this study, a solar-driven porous bed catalytic reactor (PBCR) is investigated with the aim of propane reforming and hydrogen production using a clean energy source. The process consists of two major parts: a PBCR equipped with internal heating tubes and a parabolic dish collector (PDC) with its cylindrical cavity receiver (CCR) to supply the thermal energy required for the reforming process. A proper heat transfer fluid (HTF) is thermally charged in the CCR and discharged in the PBCR. In addition to the reforming reaction, the reversible water–gas shift (WGS) reaction takes place in the PBCR. In the reverse WGS, hydrogen produced in the previous stage is consumed and undesired carbon monoxide is generated. This unfavorable condition should be controlled to restrict the production of undesirable byproducts. In the present study, two CCR and PBCR parts are modeled/simulated using the CFD approach, and then validated using available experimental data. After model validation, the impacts of critical parameters such as inlet gas temperature, pressure and composition, bed porosity, PDC aperture diameter, and HTF circulation rate within the system on the performance of the entire system are assessed. Propane conversion, hydrogen yield, and carbon monoxide selectivity (CMS) are chosen as the system's performance indicators. At optimal conditions, for an inlet pressure of 100 Pa and temperature of 300 K, inlet propane mass fraction of 0.05, bed porosity of 0.3, PDC aperture diameter of 3 m, and HTF circulation rate of 0.05 kg/s, the time average propane conversion, hydrogen yield, and CMS during a typical day and a part of nighttime are obtained at about 62.93 %, 10.326, and 1.0122 %, respectively.

Thermochemical syngas generation via solid looping process: An experimental demonstration using Fe-based material

Chemical looping is investigated for the production of syngas via reforming or reverse water gas shift in a packed bed reactor using 500 g of Fe on Al2O3 was demonstrated. Oxidation, reduction of the OC and subsequent catalytic reactions of reforming or reverse water gas shift were examined in a temperature range of 600–900 °C and a pressure range of 1–3 bara at high flowrate. Different inlet gas compositions were explored for the considered gas–solid and catalytic reaction stages. Oxidation with air successfully heated the reactor. CH4 resulted ineffective at reducing the Fe-based oxygen carrier while H2 and CO-rich stream were able to achieve full reduction to FeO of the material. In terms of catalytic activity, the maximum conversion of CH4 achieved during the reforming was limited to 62.8 % at 900 °C and 1 bara.Thermally integrated chemical looping reverse water gas shift was studied as option for CCU in combination with green H2 to produce renewable fuels. A H2/CO value of 2 could be achieved by feeding H2/CO2 of 2. The pressure did not substantially affect the conversion and the bed did not present carbon deposition.The ability of a Fe-based packed bed chemical looping reactor to recover after the carbon deposition was also explored. It was found that using a mixture of CH4 and CO2 achieved 92% recovery of the original capacity.

High-throughput screening of metal–organic frameworks for hydrogen purification

In industry, the separation/purification of hydrogen from methane impurity is of significant importance, especially under the background of carbon dioxide mitigation towards carbon neutrality. Adsorption separation is an effective route for this application regarding energy cost and separation efficiency, for which the selection of adsorbents is the key. This work proposes a computer-aided high-throughput screening strategy for the selection of metal–organic frameworks (MOFs) for CH4/H2 separation, striving to accelerate the practice of discovering better adsorbents for this particular application. Firstly, a prescreening was conducted on 12,020 computation-ready three-dimensional MOFs based on intuitive structure and chemical analysis, shortlisting 5,096 candidates. Secondly, a molecular simulation-assisted structure–property relationship analysis was performed based on small sampled MOFs, from which two structure criteria were derived for high-performing MOFs. Based on the criteria, a screening procedure was then carried out, narrowing the candidate MOFs down to 2,408. The rigorous molecular simulation was again applied to assess the separation performance metrics of these MOFs, covering adsorption selectivity, working capacity, adsorbent performance score, regenerability and separation potential. By analysing the simulated performance indicators, top-performing MOFs were identified and a more detailed analysis of the structure-performance relationship was carried out. Additionally, the impact of several practical factors, covering humidity, operation temperature and inlet gas composition, on the performance of the selected adsorbents in practice was explored. It was observed that the robustness of MOFs at humidity depends on their hydrophilicity and preferential adsorption sites. Meanwhile, operation temperature can be manipulated to accommodate flexible production scenarios.

Toluene Decomposition in Plasma–Catalytic Systems with Nickel Catalysts on CaO-Al2O3 Carrier

The decomposition of toluene as a tar imitator in a gas composition similar to the gas after biomass pyrolysis was studied in a plasma–catalytic system. Nickel catalysts and the plasma from gliding arc discharge under atmospheric pressure were used. The effect of the catalyst bed, discharge power, initial toluene, and hydrogen concentration on C7H8 decomposition, calorific value, and unit energy consumption were studied. The gas flow rate was 1000 NL/h, while the inlet gas composition (molar ratio) was CO (0.13), CO2 (0.15), H2 (0.28–0.38), and N2 (0.34–0.44). The study was conducted using an initial toluene concentration in the range of 2000–4500 ppm and a discharge power of 1500–2000 W. In plasma–catalytic systems, the following catalysts were compared: NiO/Al2O3, NiO/(CaO-Al2O3), and Ni/(CaO-Al2O3). The decomposition of toluene increased with its initial concentration. An increase in hydrogen concentration resulted in higher activity of the Ni/(CaO-Al2O3) catalysts. The gas composition did not change by more than 10% during the process. Trace amounts of C2 hydrocarbons were observed. The conversion of C7H8 was up to 85% when NiO/(CaO-Al2O3) was used. The products of the toluene decomposition reactions were not adsorbed onto its surface. The calorific value was not changed during the process and was higher than required for turbines and engines in every system studied.

Combined theoretical and experimental kinetic approach for methane conversion on model supported Pd/La0.7MnO3 NGV catalyst: Sensitivity to inlet gas composition and consequence on the Pd-support interface

New insights into reaction mechanism for catalytic methane combustion are provided in broad operating conditions on Pd/La0.7MnO3 as model natural gas vehicle catalyst. Under lean and dry conditions, a dual mechanism is suggested with active sites combining reactive oxygen species from La0.7MnO3 and palladium instead of single site reaction mechanism. Aging in wet atmosphere has no consequence on the kinetic behavior. On the other hand, in wet atmosphere near the stoichiometry, strong accumulation of hydroxyl groups on the support would suppress the metal-support interface. Accordingly, methane combustion would take place only on Pd particles.

Topology optimization of the catalyst distribution of planar methane steam reformers

Wall-coated nickel-based methane steam reformers are extensively used in hydrogen production. In such devices, nickel-based catalyst is coated on the walls and heat is supplied for the reforming process. Due to the existence of endothermic and exothermic characteristics, big temperature differences appear in the reformers, which is likely to cause serious mechanical degradation of the catalyst. This study conducts a topology optimization of the catalyst distribution to reduce the maximum temperature differences of the reformers. Nine cases with different inlet gas compositions and heating fluxes are optimized. For comparison, methane conversion rates are constrained to have the same values as the corresponding reference cases. Results show that optimized catalysts discretely distribute on the wall with different lengths. The narrow catalysts distribute upstream, while the wide catalysts distribute downstream. The optimized results not only largely reduce the maximum temperature differences (24%–82%) and improve temperature uniformity (40%–85%), but also maintain high methane conversion rates. The proposed approach could help to design the catalyst distribution of reformers. • Topology optimization of the catalyst distribution of wall-coating reformers. • Nine cases with different operating conditions are optimized. • The temperature uniformity has been improved 24%–82%. • The CH 4 conversion rates are same as those of references cases. • Discrete catalyst layer only contains two materials with the same porosity.

Chemical looping reforming for syngas generation at real process conditions in packed bed reactors: An experimental demonstration

Chemical looping reforming (CLR) is a promising technology for syngas production combining autothermal operation with integrated CO2 capture. At large scale, reformer outlet pressure during syngas production is an important factor for the overall plant’s process efficiency and defines the energy requirements for downstream processing. Packed bed reactors are widely used and established in industry for high pressure operating conditions due to their robust and, compared to other reactor types, simpler engineering. In this paper, CLR in packed bed reactors (CLR-PB) is demonstrated under a pressure range of 1 – 5 bar in a lab scale reactor, using NiO/CaAl2O4 as the oxygen carrier (OC). Oxidation, reduction and dry reforming processes were examined in a wide range of temperature (400 – 900 °C), pressure (1 – 5 bar), flowrate (10 – 40 NLPM) and different inlet gas compositions, providing an important foreground for the optimal operating conditions for each process.Furthermore, a full CLR-PB pseudo-continuous cycle has been successfully demonstrated for the first time in a lab reactor setup. During the full cycle operation, CH4 conversion > 99% has been achieved, while the temperature and concentration profiles provided identical results for consecutive cycles verifying the continuity and the feasibility of the process. These results constitute the basis for the scale-up of the process, where heat losses would be minimized and the energy efficiency of the process would be significantly higher.