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Modelling of methane dry reforming over Ni/Al2O3 catalyst in a fixed-bed catalytic reactor
Abstract
The dry reforming of CH4 in a fixed-bed catalytic reactor for the production
of hydrogen at different temperatures over supported Ni catalyst has been
studied. In the simulation of the reactor, a one-dimensional heterogeneous model is
applied. Temperature and concentration gradients are accounted for in the axial
direction only. The reactor model for the dry reforming of methane used the
Richardson and Paripatyadar kinetics and the Snoeck et al. kinetics for the cokedeposition
and gasification reactions. The effect of using different temperatures on
the performance of the reactor was analyzed. The amounts of each species consumed
or/and produced were calculated and compared with the experimental
determined ones. It was shown that the Richardson and Paripatyadar–Snoeck et al.
kinetics gave a good fit and accurately predicted the experimental observed profiles
from the fixed bed reactor, and thus the degree of conversion of CH4 and CO2.
... Total mass and momentum balances for this zone are described by Equations (15) and (16), respectively. The boundary conditions for these ODEs are also listed in Table 2. Equations (17)- (20) describe the boundary conditions in the reactor's inlet (z = 0), while Equations (21) and (22) the boundary conditions in the reactor's outlet (z = 1). The ODEs that comprise the mathematical model for the retentate zone of the MR are listed in Table 2. Equation (13) represents the partial mass balance for each species and Equation (14) describes the energy balance for the retentate zone. ...
... The kinetic model implemented in the simulations was the same as that reported by [22]. Those authors determined the kinetics for five relevant reactions over a Ni/Al 2 O 3 catalyst in the temperature range of 450-650 • C and for a total pressure of 1 bar. ...
... The results obtained experimentally by [22] were compared with simulated results to validate the kinetic model. The fixed-bed dimensions, catalyst parameters and experimental conditions used by those authors to determine the kinetic model are shown in Table 4. Table 4. Fixed-bed reactor dimensions, catalyst parameters and experimental conditions [22]. ...
Biogas is a valuable renewable energy source that can help mitigate greenhouse emissions. The dry reforming of methane (DRM) offers an alternative hydrogen production route with the advantage of using two main greenhouse gases, CO2 and CH4. However, its real application is limited mainly due to catalyst deactivation by coke formation and the reverse water gas shift (RWGS) reaction that can occur in parallel. Additionally, the typical dry reforming temperature range is 700–950 °C, often leading to catalyst sintering. A low-temperature DRM process could be in principle achieved using a membrane reactor (MR) to shift the dry reforming equilibrium forward and inhibit the RWGS reaction. In this work, biogas reforming was investigated through the simulation of MRs with thin (3.4 µm) and thick (50 µm) Pd-Ag membranes. The effects of the feed temperature (from 450 to 550 °C), pressure (in the range of 2–20 bar), and biogas composition (CH4/CO2 molar ratios from 1/1 to 7/3) were studied for the thin membrane through the calculation and comparison of several process indicators, namely CH4 and CO2 conversions, H2 yield, H2/CO ratio and H2 recovery. Estimation of the CO-inhibiting effect on the H2 molar flux through the membrane was assessed for a thick membrane. Simulations for a thin Pd-Ag MR show that (i) CO2 and CH4 conversions and H2 yield increase with the feed temperature; (ii) H2 yield and average rate of coke formation increase for higher pressures; and (iii) increasing CH4/CO2 feed molar ratio leads to higher H2/CO ratios, but lower H2 yields. Moreover, simulations for a thick Pd-Ag MR showed that the average H2 molar flux decreases due to the CO inhibiting effect (ca. 15%) in the temperature range considered. In conclusion, this work showed that for the considered simulation conditions, the use of an MR leads to the inhibition of the RWGS reaction and improves H2 yield, but coke formation and CO inhibition on H2 permeation may pose limitations on its practical feasibility, for which proper strategies must be explored.
... The packed bed's schematic diagram is shown in Figure 1a, and it comes from the experimental apparatus of Benguerba et al. [40]. Atmospheric pressure mixed gas with a molar ratio of CH4:CO2:N2 = 1:1:8 controlled the device's inlet. ...
... In the DRM process at equilibrium, the temperature affected the reactant conversion favorably within a given temperature range. Additionally, the obtained simulation conversions were close to Benguerba's numerical data and experimental results [40]. Although the CH 4 conversions in this study were slightly lower than the experimental data, the CO 2 conversions were very close to the experiment. ...
... Thermal methane cracking occurs as the temperature rises above 400 • C for most catalysts [18,[51][52][53]. Numerous studies have demonstrated that carbon deposition on the catalyst is a necessary part of the DRM process and the primary cause of catalyst deactivation [18,40,54]. In the DRM process, the methane decomposition (3), Boudouard reaction (4), and carbon gasification (5) are the primary contributors to coke formation. ...
Replacing the conventionally used steam reforming of methane (SRM) with a process that has a smaller carbon footprint, such as dry reforming of methane (DRM), has been found to greatly improve the industry’s utilization of greenhouse gases (GHGs). In this study, we numerically modeled a DRM process in lab-scale packed and fluidized beds using the Eulerian–Lagrangian approach. The simulation results agree well with the available experimental data. Based on these validated models, we investigated the effects of temperature, inlet composition, and contact spatial time on DRM in packed beds. The impacts of the side effects on the DRM process were also examined, particularly the role the methane decomposition reaction plays in coke formation at high temperatures. It was found that the coking amount reached thermodynamic equilibrium after 900 K. Additionally, the conversion rate in the fluidized bed was found to be slightly greater than that in the packed bed under the initial fluidization regime, and less coking was observed in the fluidized bed. The simulation results show that the adopted CFD approach was reliable for modeling complex flow and reaction phenomena at different scales and regimes.
... The highly endothermic DRM process is popular owing to its ability to convert two principal greenhouse gases-CO2 and methane (CH4)-to syngas with a low H2/CO ratio. 4 Syngas has been widely adopted as a building block for generating low-carbon fuels, including methanol, dimethyl ether, and synthetic natural gas. Syngas can also be produced by steam methane reforming, such as the Fischer-Tropsch method: ...
... Fluids 10.1063/5.0140307 4 challenges involve combining two or more of the following processes: photochemistry, 7 electrochemistry, 8 chemical catalysis, and other engineering solutions. Several studies have identified possible mechanisms for reducing CO2 to CO. 4 Numerous efforts have been made toward developing catalysts resistant to carbon formation for use under favorable thermodynamic conditions. ...
... Fluids 10.1063/5.0140307 4 challenges involve combining two or more of the following processes: photochemistry, 7 electrochemistry, 8 chemical catalysis, and other engineering solutions. Several studies have identified possible mechanisms for reducing CO2 to CO. 4 Numerous efforts have been made toward developing catalysts resistant to carbon formation for use under favorable thermodynamic conditions. The work by Wei and Iglesia 9 describes the reaction mechanisms involved in CH4 conversion over nickel catalysts using CO2, but Ni-based catalysts are more prone to carbon deposition. ...
In the present study, the dry reforming of methane (DRM) has been simulated in fluidized-bed reactors using the multiphase particle-in-cell model. The model was meticulously built to investigate the effect of a wide range of superficial gas velocities covering particulate, aggregative, and lean-phase flow regimes on bed hydrodynamics, conversion, and yields of product gases. Constant values for catalyst loading, CH 4 :CO 2 :N 2 ratio (1:1:1.3), and catalyst and gas properties were maintained in all simulations. The simulation results obtained are in good agreement with the experimental data reported in the literature. The results show that under different gas velocities, conversion is relatively indiscernible in the particulate regime. In contrast, for the inhomogeneous phases, the turbulent fluidized bed had the best reactor performance with high CH 4 and CO 2 conversion rates, good CO + H 2 productivity, and high CO/H 2 molar ratio. This is due to the vigorous turbulent flow and relatively high gas-solid contact. Due to gas bypassing and backmixing triggered by bubbling, the bubbling fluidized bed generally had the worst performance and below that of the fast-fluidized bed. The present study demonstrates that the performance of DRM reactions in fluidized-bed reactors is strongly related to the hydrodynamics. Moreover, it shows the significance of gas velocity on DRM conversion, yield, and overall reactor performance.
... As shown in the literature, the problem is due to the high temperature of the DMR process, which leads to coking as well as sintering of the support and active material. This issue is covered in several articles (Alipour et al., 2014;Aramouni et al., 2018;Bawadi et al., 2017;Benguerba et al., 2015;Borowiecki, 2006;Chein and Fung, 2019;Dębek et al., 2014;Richardson and Paripatayadar, 1990;Snoeck et al., 2002;Zambrano et al., 2019;Zhang et al., 2018), which present the state of the art in the field of catalysts dedicated to the DMR process. The above-mentioned investigations show that the nickel catalyst supported on Al 2 O 3 carrier is the most widely used for the DMR process due to low cost and quite high specific surface area of the support. ...
... As shown in the literature (Alipour et al., 2014;Bawadi et al., 2017;Benguerba et al., 2015;Borowiecki, 2006;Dębek et al., 2014), carrying out the DMR process at high temperatures may lead to coking and deactivation of the catalyst. With this in mind the activity of the catalyst was monitored in each measurement series (for each temperature) in such a way that the first measurement in the series was repeated at its end. ...
... The reaction kinetics of DMR can be represented by a system of the following chemical reactions (Benguerba et al., 2015;Zambrano et al., 2019): ...
In memory of Professor Jerzy Bałdyga-our colleague, friend and teacher This paper presents the results of investigations into dry methane reforming (DMR). The process was aimed at obtaining synthesis gas required for the production of dimethyl ether (DME). The effect of temperature, pressure and inlet gas composition on the process was determined in the experimental part of this work. The tests were carried out in a laboratory tubular reactor over a Ni/CaO-Al 2 O 3 catalyst. The obtained experimental results were used to verify literature kinetic data and to develop a mathematical model of the DMR process.
... And the periodic boundary conditions (Succi, 2001) are applied to the bottom and top boundaries. In the present work, Ni=Al 2 O 3 is selected as the model catalyst, which is extensively used in DRM (Alipour et al., 2014;Benguerba et al., 2015Benguerba et al., , 2017Pizzolitto et al., 2019). Five reactions and reaction rates are shown in Table 1. ...
... And Table 2 shows the reaction fluxes of all components caused by the above reactions. More detailed reaction rates can refer to Benguerba et al. (2015). ...
... For the sake of simplicity, in this section, a dimensionless reaction flux J Ã which involved the mass transport and reaction Table 1 The definition of five reactions and reaction rates referred to Benguerba et al. (2015). ...
... Additionally, discernible structural hydroxyl bands (OH − ) were observable around 3570 and 3435 cm −1 for HAP S and at 3435 and 3643 cm −1 for HAP C [38], indicating weaker interactions in the latter case, leading to higher transmittance. Furthermore, peaks associated with B-type carbonate groups (CO 3 2− ) incorporated into the HAP structure were detected at 1416, 1456, and 2345 cm −1 for HAP S and at 874, 1449, and 2514 cm −1 for HAP C [39,40]. These carbonate-related peaks were attributed to the thermal treatment of HAP, likely due to contamination with CO 3 2− ions from atmospheric CO 2 [39]. ...
... These carbonate-related peaks were attributed to the thermal treatment of HAP, likely due to contamination with CO 3 2− ions from atmospheric CO 2 [39]. These findings suggest structural modifications in the HAP supports, aligning with prior research that attributes variations in phase and crystallinity to multiple influencing factors [40]. For 10% Ni over HAP S (Figure 4b), the incorporation of this active phase did not significantly alter the vibrational modes of the HAP support. ...
Catalyst deactivation, mainly due to coke deposition, presents a significant challenge in the process of dry reforming of methane (DRM). This study focused on coke-resistant catalysts for DRM, particularly nickel-based catalysts supported on hydroxyapatite (HAP). A novel HAP formulation (HAPS) with a Ca/P ratio of 1.54, below the stochiometric ratio studied in previous studies, was compared with commercial HAP (HAPC), and both were impregnated with 10 wt% nickel. The synthesis of HAPS involved low temperature (60 °C), moderate stirring, and a pH of 11, using a custom setup. Dry-reforming reactions were conducted under severe conditions (T = 800 °C) to assess the resistivity of both supports over 120 h. Our findings indicated sustained high conversion rates, reaching 93% for CH4 and 98% for CO2 with HAPS, despite an increase in gas hourly space velocity. Characterisation, including X-ray diffraction, thermogravimetric analysis, and transmission electron microscopy, revealed coke formation using HAPC, leading to initial deactivation, in contrast with the custom support. This discrepancy may be attributed to the distinct physical and chemical properties of the catalysts, their reaction mechanisms, and the deactivation precursors. Overall, the performance of nickel-based catalysts significantly hinges on support–catalyst interactions, in addition to thermal stability.
... Moreover, two artificial numerical algorithms are developed specifically for constructing hierarchical pore structures for porous pellet and open-cell foam, respectively. Based on Benguerba et al. [25], five reactions associated with DRM shown in Table 1 are used in the study, where R 3 , R 4 and R 5 are related to coking. The impacts of various hierarchical pore structure parameters on the catalyst performance and coke resistance are investigated. ...
... In order to investigate how the hierarchical structure of the catalyst affects its performance, we maintain the constant reaction operating conditions for DRM (T = 923:15 K, P = 1 bar, F CH 4 =F CO 2 = 1:1). These conditions align with Benguerba et al. [25]. ...
Dry reforming of methane (DRM) is one of the feasible strategies for carbon capture and utilization. However, DRM has a high tendency toward coking, which is restricted to industrial applications. The primary cause of coking in DRM is the limitation of mass transfer inside porous catalysts. To overcome this limitation, optimizing the pore structure of the porous catalyst becomes crucial. Hierarchical pore structure has received considerable attention in recent years due to its superior mass transfer performance. Therefore, this chapter focuses on the structure-performance relationship of hierarchical porous catalysts in DRM. Specifically, two types of porous catalysts, namely porous pellet and open-cell foam, are examined. The impacts of various hierarchical pore structure parameters on the catalytic activity and coke resistance are investigated. The findings offer a theoretical foundation and technical guidance for the design of porous catalysts with hierarchical pore structures.
... As shown in Figure 4a, the solar radiation distributions on the receiving surface were well-matched for all three deflection angles (30 • , 45 • , and 60 • ). The results of the methane dry reforming kinetic model calculations were compared with those of the experimental study [51]. As shown in Figure 4b, the absolute error did not exceed 5.5% in the conversions of CH 4 and CO 2 , so the kinetic model of this study can be considered feasible and accurate. ...
... Verifications of (a) optical model of dish concentrator, (b) and of chemical reaction[50,51]. ...
In this work, the solar-thermal-chemical integrated design for a methane dry reforming reactor with cavity-type solar absorption was numerically performed. Combined with a multiphysical reactor model, the gradient optimization algorithm was used to find optimal radiation flux distribution with fixed total incident solar energy for maximizing overall hydrogen yield, defined as the ratio of molar flow of exported hydrogen to imported methane, which can be applied for guiding the optical property design of solar adsorption surface. The comprehensive performances of the reactor under the conditions of original solar flux and optimal solar flux were analyzed and compared. The results show that for the inlet volume flow rate of 8–14 L·min−1, the hydrogen production rate was increased by up to 5.10%, the energy storage efficiency was increased by up to 5.55%, and the methane conversion rate was increased by up to 6.01%. Finally, the local absorptivities of the solar-absorptive coating on the cavity walls were optimized and determined using a genetic algorithm, which could realize the predicted optimal radiation flux distribution.
... As shown in Table 1, five reactions are considered in this work, including dry reforming of methane (DRM), reversed water-gas-shift (RWGS), and three coke formation reactions. More detailed definitions of kinetic parameters refer to Benguerba et al. (2015). ...
... In this artificial algorithm, four structure parameters are used to control the geometry, which are porosity (e), the fine pore diameter (d 1 ), the hierarchical pore size ratio (the ratio of the coarse pore diameter to the fine pore diameter, d 2 =d 1 ), the hierarchical pore volume ratio (the ratio of the coarse pore volume to the fine pore volume, V 2 =V 1 ). It should be noted that whend 2 =d 1 = 1 and Table 1 Five reactions and reaction rates referred from Benguerba et al. (2015). ...
Dry reforming of methane (DRM) is one of the feasible strategies for carbon capture and utilization. However, the DRM process has a high tendency toward carbon deposition, which is restricted to industrial applications. In order to further improve coke formation resistance, open-cell foam with hierarchical pore structure was investigated. An artificial algorithm was adopted to construct a hierarchical pore structure in open-cell foam. Based on a 3-D lattice Boltzmann model, this work explored the effect of two hierarchical pore structure parameters on the fluid flow and coke formation characteristics in open-cell foam, which are hierarchical pore volume ratio (V2/V1 ) and hierarchical pore size ratio (d2/d1 ). The results indicated that increasing V2/V1 and d2/d1 can significantly promote permeability. Under the restriction of V2/V1 =4, from d2/d1 =1 to 4, the coke formation rate decreases by approximately 57.49%. These findings provide a theoretical basis and technical guidance for designing and developing open-cell foam reactors.
... However, the remaining visible bands are not totally the same for both catalysts. The 20Mo10Ni catalyst spectrum exhibits a broad band at 945e950 cm À1 corresponding to the hydrated surface of molybdenum oxide species [41] which can be attributed to NiMoO x phase. This phase is more difficult to reduce or is present in larger proportions in this catalyst than in the 20Mo2Ni catalyst prior to the reduction. ...
... The reaction scheme of DRM is complex (Table 1) [40]. Benguerba et al. [13,41] After testing many combinations of these reactions, only three reactions (the first three chemical reactions given in Table 1) were found to be kinetically significant, giving the best fit of the experimental results. ...
An investigation of methane dry reforming over Mo–Ni based catalysts is carried out in a fixed bed catalytic reactor at different temperatures. Two Mo–Ni catalysts supported on alumina are prepared with 20%Mo–10%Ni and 20%Mo–2%Ni, respectively, in which the nickel is used for its highly resistance at high temperature during dry reforming of methane (DRM) reaction. Experimental results shows that an increase in temperature favours the CH4 conversion and determined a higher H2/CO ratio. A small amount of deposited coke is observed because of the abundant presence of CO2 in the reaction medium and only for 2% Ni catalysts.
A kinetic model is proposed for the DRM with Mo–Ni based catalysts, in which the reaction mechanism routes and the operating conditions such as the reaction temperature and the CH4/CO2 molar ratio are accounted for. The results of the mathematical model allow a consistent description of the experimental data, in terms of gas outlet composition. The absence of the methane decomposition reaction, responsible of carbon deposition that is known to lead to catalyst deactivation, is the main result that is adequately predicted by the model.
... Currently, the most adopted synthetic route for hydrogen production is reforming gaseous fuels such as methane, ethane, and higher hydrocarbons [14]. However, dry methane reforming (DRM) is considered one of the most promising technologies because it consumes two major greenhouse gases (CH 4 and CO 2 ) while producing syngas, which is a mixture of hydrogen (H 2 ) and carbon monoxide (CO) [15][16][17]. (See In order to remove the undesirable CO from the syngas while reducing H 2 loss, various approaches can be used, such as the preferential oxidation of CO and water-gas shift [18]. The water-gas shift reaction (WGS) has received much attention as a fundamental step in converting carbon monoxide (CO) into hydrogen, which may be used in the Fischer-Tropsch reaction to produce high-value chemicals and other alternative liquid hydrocarbons or to feed fuel cells [19,20]. ...
The global push toward a hydrogen economy fuels hydrogen production from various sources. A crucial step in enriching hydrogen and reducing CO in syngas derived from carbon-based hydrogen production is the water-gas shift reaction (WGSR). Given the equilibrium-limited nature of WGSR, low temperatures are necessary to reduce carbon monoxide concentrations to the desired level. Traditionally, iron-chromium (Fe/Cr) and copper-zinc (Cu/Zn) catalysts have been widely used at high and low temperatures, respectively. Numerous studies have focused on developing optimal WGS catalysts with the desired characteristics and efficiency. This review extensively discusses various catalysts for different stages of WGSR, including low, medium, high-temperature, and sour WGS catalysts. However, understanding the contrast between the redox and associative mechanisms and the nature of intermediates in the WGS pathway remains unclear. A detailed study of the WGSR pathway is imperative to develop highly active and stable catalysts. Various experimental kinetic values and models have also been reported to elucidate the WGSR mechanism at different temperatures. The primary deactivation sources of WGS catalysts have been discussed to highlight recent advances to improve catalyst performance. The contribution of computational methods such as Density Functional Theory (DFT) to developing WGS catalysts is also explored. Furthermore, the review addresses the challenges encountered in the WGSR, and recommendations and conclusions are drawn to guide future research efforts.
... As reported in the literature, high temperatures may cause the catalyst support and the active metal to be sintered [55,56], which will lead to the collapse of pore structure and consequently reduce the effective surface area, resulting in the decreasing of active sites and thus the decreasing of the catalyst activity. High temperatures promote the CH 4 decomposition [57,58] as well, which results in a large amount of coke formation. The coke deposits on the pore surface, causing the loss of active sites and deactivating the catalyst. ...
CO2 methanation suffers from the problem of temperature runaway phenomenon due to its exothermic nature. To mitigate this issue, optimizing catalyst structure becomes crucial. This work established numerical models to investigate the CO2 methanation reaction and heat/mass transfer process in the reactor with porous pellet and monolithic catalysts. Results show that the reactor with porous pellets has the lowest carbon conversion per unit pressure drop due to its large total pressure drop. In contrast, the reactor with monolith exhibits a much larger carbon conversion per unit pressure drop but a smaller absolute carbon conversion. Based on this, an improved "CHESS" monolith structure was proposed and improved, which not only maintains a high absolute carbon conversion (62.6%) but also enhances the heat transfer process in CO2 methanation. Moreover, compared with the reactor with porous pellets, the maximum temperature in the improved "CHESS" monolith was decreased by around 11.09%.
... Both data sets were generated by Barracuda software version 21.0 software. 52 Table 2 details the CFD data generation setup for data set 1, and Table 3 shows the operating conditions and geometries of data set 2 that validated the experimental and simulation works of Benguerba et al. 53 ...
... As the literature reported, high temperatures may cause the catalyst support and the active metal to be sintered [61,62], which will lead to the collapse of pore structure and consequently reduce the surface area, resulting in the decreasing of active sites and thus the decreasing of the catalyst activity. High temperatures promote the CH 4 decomposition [63,64] as well, which results in a large amount of coke formation. The coke deposits on the pore surface inside the catalyst, causing the loss of active sites and deactivating the catalyst. ...
The extraction of petroleum and natural gas is often accompanied by a large number of associated gases, especially the high CO2 content reservoirs facing the emission of a large amount of CO2. CO2 methanation is recognized as one of the suitable candidates for CO2 utilization to reduce the emission of CO2. Because of the highly exothermic nature of the reaction, however, it is very important to enhance the heat transfer process inside the reactor and inhibit the formation of hot spots. In the fixed bed reactor, the heat transfer in the radial direction is greatly limited compared with that in the axial direction. Thus, this work adopted the radial flow reactor to evaluate the CO 2 methanation process by the means of a numerical model based on OpenFOAM. Four types of radial flow reactor configurations, namely centrifugal Z-type, centrifugal P-type, centripetal Z-type, and centripetal P-type, were compared. The fluid flow, heat transfer, and reaction performances for these reactors were discussed under consistent operating conditions. Results show that the centrifugal P-type structure has the most uniform flow field. In terms of heat transfer and reaction performance, the centripetal Z-type structure is the best among the four radial flow reactor configurations. These findings provide a theoretical basis and technical guidance for designing and developing radial flow reactors.
... Thus, CH 4 and CO 2 emissions could potentially be reduced to some extent [3][4][5][6]. Alternatively, synthesis gas is a crucial feedstock for producing chemicals and fuels via Fischer-Tropsch synthesis, methanol, and dimethyl ether [7,8]. ...
... Thus, CH 4 and CO 2 emissions could potentially be reduced to some extent [3][4][5][6]. Alternatively, synthesis gas is a crucial feedstock for producing chemicals and fuels via Fischer-Tropsch synthesis, methanol, and dimethyl ether [7,8]. ...
This study investigated the performance of supported Ni catalysts in the utilization of greenhouse gases like CO2 and CH4 via dry reforming. The support SBA-15 was impregnated first with Sc at different loadings (0.5, 1, and 3 wt.%) and then with Ni (5 wt.%). The catalysts were first tested up to 8 h on stream with stoichiometric feed as well as methane in excess. The as-prepared catalysts were characterized using BET, XRD, TPR, CO2-TPD, XPS, TGA, and TEM.
This is in accordance with the surface area measurement, XRD, and TEM data. The Ni added to Sc-SBA-15 appeared to interact with both the support and Sc as the intensity and reduction temperature of the Sc promoted catalysts increased relatively to the unpromoted sample depending on Sc content.
The catalyst with 0.5 wt.% Sc loading led to the highest conversion and the lowest relative activity loss. The CH4 and CO2 conversions, on average, were 78 and 86 %, respectively, at the end of the runs at 750 °C. The final H2/CO ratio was 0.99, which is a good value compared to many literature catalysts. This catalyst also showed relatively constant CH4 and CO2 conversions over 80 h on stream. Increasing the Sc loading above 0.5 wt.% was not beneficial in terms of activity.
... Mokheimer et al. (2015) developed a two-dimensional pseudohomogeneous model of a steam-methane reformer, studied its performance under different operating conditions (temperature, pressure, feed flow rate, and feed composition), and drew comparisons between reactor results and equilibrium calculations. To evaluate the use of dry reforming and coking kinetics presented by Richardson and Paripatyadar (1990), and by Snoeck et al. (1997bSnoeck et al. ( , 2002, Benguerba et al. (2015) compared experimental results with simulated data from a one-dimensional heterogeneous model, finding that these kinetics worked well for a nickel-alumina catalyst. In a later study, Benguerba et al. (2017) used a three-dimensional pseudohomogeneous model to compare the performance of fixed bed and membrane enhanced reactors for dry reforming, finding that membrane reactor may be used without increasing catalyst deactivation. ...
The reforming of methane is an important industrial process, and reactor modeling and simulation is frequently employed as a design and analysis tool in understanding this process. While much research work is devoted to catalyst formulations, reaction mechanisms, and reactor designs, this review aims to summarize the literature concerning the simulation of methane reforming. Applications in industrial practice are highlighted, and the three main approaches to representing the reactions are briefly discussed. An overview of simulation studies focusing on methane reforming is presented. The three central methods for fixed-bed reactor modeling are discussed. Various approaches and modern examples are discussed, presenting their modeling methods and key findings. The overall objective of this paper is to provide a dedicated review of simulation work done for methane reforming and provide a reference for understanding this field and identifying possible new paths.
... These data have been derived from experimental studies conducted at different feed conditions, operating conditions, and catalysts. In the current study, the kinetic parameters for SMR and WGS reactions (eqs 7 and 8) were adopted from Xu and Froment 27 and Oliveria et al., 28 and those for the DR reaction (eq 9) were taken from Richardson et al. 29 and Benguerba et al. 30 The selection of kinetic data was based on the comparison of model predictions with the experimental data of Olah et al. 3 The selected kinetic parameters for the bi-reforming process from the literature are listed in Table 3. Note that these kinetic parameters are not for a single-step BR reaction but rather a combination of the literature data available for SMR and DR. ...
... All these aspects make these expressions inadequate for a robust reactor modelling and design, where is desired a model that describes the catalytic sequence of the dry reforming of methane reaction with a physicochemical and statistical basis. [41][42][43] Where, r CH 4 (mol.g -1 .s ...
The dry reforming of methane is a promising technology for the abatement of CH4 and CO2. Solid solution Ni–La oxide catalysts are characterized by their long–term stability (100h) when tested at full conversion. The kinetics of dry reforming over this type of catalysts has been studied using both power law and Langmuir–Hinshelwood based approaches. However, these studies typically deal with fitting the net CH4 rate hence disregarding competing and parallel surface processes and the different possible configurations of the active surface. In this work, we synthesized a solid solution Ni–La oxide catalyst and tested six Langmuir–Hinshelwood mechanisms considering both single and dual active sites for assessing the kinetics of dry reforming and the competing reverse water gas shift reaction and investigated the performance of the derived kinetic models. In doing this, it was found that: (1) all the net rates were better fitted by a single–site model that considered that the first C–H bond cleavage in methane occurred over a metal−oxygen pair site; (2) this model predicted the existence of a nearly saturated nickel surface with chemisorbed oxygen adatoms derived from the dissociation of CO2; (3) the dissociation of CO2 can either be an inhibitory or an irrelevant step, and it can also modify the apparent activation energy for CH4 activation. These findings contribute to a better understanding of the dry reforming reaction's kinetics and provide a robust kinetic model for the design and scale–up of the process.
... For the DRM, the most used catalysts are usually based on Ni thanks to their high activity and efficiency and low cost [7]. However, the problem with these catalysts is their easy deactivation because of the coke deposition and metal sintering which causes plugging of the reactor. ...
Lantanium and Cerium supported Nickel catalysts with Ni-loading close to 15 %wt were synthesized using sol-gel methods in order to design efficient catalysts for the dry reforming of methane to produce syngas (H2 + CO). The catalytic test was performed after calcining the as-prepared samples at 700 °C and subsequent in situ reduction was performed under hydrogen flow at 600 °C. The resulting catalysts were characterized by X-ray diffraction (XRD), Temperature Programmed Reduction (TPR), transmission electron microscopy (TEM) and N2 adsorption-desorption isotherm measurements. The investigation of the catalytic performances of Ni–CeO2 and Ni–La2O3 catalysts prepared by sol gel method (SG), for a duration of 12 h, under a reaction CH4/CO2 shows that, for the same synthesis method, the efficiency varies with according to the support nature. Indeed, conversions and yields are higher in the presence of the lanthanum than with the cerium support (XCO2 = 18% and YCo = 15% for Ni–La compared of XCO2 = 8% and YCo = 6% for Ni–Ce. Comparing the catalysts stability, we can notice that it is 100% (no deactivation) in the presence of Ni–La2O3 catalyst compared to Ni–CeO2, which showed a high deactivation (78% after 12 h of reaction). This difference in stability is probably related to the perovskite structure and to the strong interactions between the active phase and the support, reinforced by the basicity of lanthanum support which inhibits carbon deposition during the CH4/CO2 reaction.
... El RSM es una vía conveniente para convertir gases de efecto invernadero (CH 4 + CO 2 ) en gas de síntesis el cual puede ser utilizado en la producción de hidrocarburos líquidos, formaldehidos y policarbonatos [1]. Este proceso altamente endotérmico presenta sus mejores rendimientos a temperaturas comprendidas entre 700 y 1000°C. ...
En este trabajo se estudia la producción de gas de síntesis (CO+H2) mediante reformado seco de biogás (RSM) utilizando un catalizador Ni/Ce-Al2O3. Los experimentos realizados ayudaron a determinar las condiciones necesarias de operación de la planta experimental para que el proceso sea controlado por la cinética de reacción.
This study explored how CH4/CO2 feed ratio, temperature, and pressure affect the conversion of carbon dioxide and methane and the H2/CO ratio of syngas using simulations for six catalysts: Rh/La2O3, Rh/La2O3-SiO2, Ru/La2O3, Ni-Co/Al-Mg-O, LaNiO3, and Ce-La-Ni-O2. Simulations with DWSIM© were conducted at CH4/CO2 feed ratios of 1–2, pressures of 1–5 bar, and temperatures of 550–750 °C. The effects showed that increasing the temperature by as much as 750 °C boosted the H2/CO ratio and improved CO2 and CH4 conversions because of the endothermic nature of the reactions. Higher pressure reduced conversion rates and H2/CO ratios across all catalysts, with a notable similarity between 2 and 5 bar, indicating thermodynamic limits. A higher feed ratio of CH4/CO2 decreased CH4 conversion while increasing the H2/CO ratio at the expense of reduced H2 yield. As the pressure decreases, the Ru/La2O3 and Rh/La2O3-SiO2 catalysts exhibited higher activity because of the kinetic factor. The current research focuses on the possibility of using dry reforming of biogas to synthesize syngas with suitable H2/CO ratios for different uses. The observations suggest that future studies should include techno-economic analysis to determine the least expensive catalysts that will ensure the dry reforming process yields the right composition of syngas.
The dry reforming of methane (DRM) was conducted using a Ni-SiO2 catalysts. It was evaluated the catalyst’s stability within the temperature range of 973–1033 K under low spatial time conditions (kinetic regime) in the reactor. The catalyst deactivated more rapidly at high temperatures, contrary to the prediction based on chemical equilibrium calculations. To understand this behavior, it was investigated the impact of reactor operating conditions by simulating the reactor using a pseudo-homogeneous model and comparing the results with the chemical equilibrium prediction. The simulations revealed that, at high spatial times (W/FCH4), the reactions considered for the DRM process closely approach equilibrium. In contrast, at low spatial times, the reactive system deviates from chemical equilibrium, with the water gas shift and disproportionation of CO being the most favored. This results in increased coke production, which leads to faster catalyst deactivation. The effect is attributed to the kinetic inhibition of CO2 adsorption, hindering the activation of this molecule at high spatial time. The spatial time in the reactor, whether high or low, strongly depends on the intrinsic catalytic activity of the catalyst. Thus, when studying catalytic solids, the operating conditions of the reactor should be taken into account to avoid erroneous interpretations of the experimental data when evaluating their performance (for example, catalyst selectivity or resistance against deactivation by coke).
Dry-Reforming-of-Methane(DRM) presents an attractive process for the conversion of CO2 and CH4 to syngas. Catalyst deactivation by carbon formation is a major challenge hindering DRM scale-up. A novel bimetallic Ni/Cu catalyst developed previously in our lab demonstrated significant carbon resistance and superior stability compared to conventional Ni catalysts. This paper presents the kinetics of the bimetallic catalyst. A unique approach utilizing carbon formation rates obtained from Density-Function-Theory(DFT) results is presented to scale monometallic Ni catalyst kinetics. The developed kinetics model incorporated within a 1-D pseudohomogeneous reactor-bed model was validated with thermodynamics and experimental results. The experimental results were obtained at 923-K temperature, flowrates (30 mL/min-250 mL/min), catalyst-loading (<10 mg), and bed-dilution (<500 mg). Additionally, the catalysts were characterized to identify crystal phase, surface area, pore-volume, and composition using XRD, BET-BJH, and ICP analysis, respectively. The developed kinetics model and the associated characterization dataset could be used for future scalability/reproducibility assessments.
A solar thermochemical reactor with better thermal management is proposed to improve the performance for dry reforming of methane. Conical cavity is introduced in the thermochemical reactor to adjust incident solar radiation distribution. Preheating area is adopted to recover sensible heat from gas outlet. Multiphysical model is presented for analyzing the overall performance of the reactor under different inlet flow rates. Also, local ideal reaction temperature required for maximizing local hydrogen production is analyzed according to the reaction kinetics. It is shown that better synergy between real temperature distribution and ideal temperature requirement can be achieved in this new reactor. Compared with conventional reactor, the present reactor exhibits the better performance in terms of reactant conversion, energy storage efficiency and hydrogen yield. Particularly, hydrogen yield is increased by 4.31%–17.12% at inlet flow rates between 6 and 12 L min⁻¹.
Thermodynamically limited reactions in membrane reactors for hydrogen generation require a high hydrogen concentration gradient for separation, which imposes an energy requirement that reduces the process energy efficiency. To decrease the required separation energy, chemical hydrogen separation by CO2 is proposed by combining solar-driven dry reforming of methane (DRM) in a hydrogen permeable membrane (HPM) reactor with either reverse water gas shift (RWGS) or methanation. This system has the benefit of using solar renewable energy as well as reducing CO2 emissions. The performances of the proposed membrane reactor configurations for in situ hydrogen consumption are compared to DRM and super-dry reforming of methane (SDRM) in a fixed-bed reactor. The thermodynamic, kinetic, and environmental performances are analyzed and compared from 300 °C to 1000 °C. 2.01 mol CO2 can be reduced to CO per mole CH4 consumed at 1000 °C by coupling DRM with RWGS in a membrane reactor, resulting in a CO2 reduction rate of 1064 kg m⁻² yr⁻¹. Alternatively, the minimum energy consumption per mole CO2 converted is 0.79 MJ at 860 °C. This study demonstrates the feasibility of DRM enhanced by chemical hydrogen separation in HPM reactors to convert CO2 into fuels and store solar thermal energy as chemical energy.
Dry reforming of methane (DRM) over Ni-based supported catalysts has been widely studied due to Ni's low cost and high activity. Despite their excellent performance, side reactions such as methane decomposition and Boudouard reaction can cause severe coke formation leading to catalyst deactivation. Our recent work reported that both yolk-shell morphology and Pt-Ni interaction in single-atom-alloy (SAA) structures could maintain the DRM activity. However, the effect of morphology and Pt-Ni interaction could not be elucidated. In this work, we studied the reaction kinetics of DRM by proposing a detailed elementary reaction mechanism with 12 surface species and 17 elementary steps over the Ptx[email protected]2 and Pt0.25-NiCe/SiO2WI catalysts. Due to the different DRM activity over the wet-impregnated and yolk-shell structures, we examined multiple reaction models to explain the effect of morphology and Pt-Ni interaction on the DRM activity. Our results show that the reverse Boudouard reaction and dissociative adsorption of CO2 and CH4 are the rate-limiting steps. The desorption of CO* and H* is also critical to products yield and selectivity. Compared with Pt0.25-NiCe/SiO2WI catalyst, the C* removal followed by the fast CO* desorption is more favored on Pt0.25[email protected]2 SAA, suggesting the reverse Boudouard reaction prevents the catalyst deactivation by coking. The high O* and low H* coverages are observed on Pt0.25[email protected]2 SAA due to the confined yolk-shell morphology and enhanced Pt-Ni interaction in SAA structures, respectively. Both these effects can lead to facile C* removal in the Pt0.25[email protected]2 SAA catalyst leading to a stable DRM activity.
Efficient solar-driven production of fuels and electricity is significant for achieving a decarbonized society. However, the existing systems still suffer from drawbacks including limited photovoltaic (PV) efficiency under high temperatures and large irreversibility in solar-to-thermal conversion. In this research, a novel system involving the integration of PV modules and membrane reactor via spectral splitting technology is proposed to cogenerate fuels and electricity with improved efficiency. The sunlight with suitable wavelengths for the PV power generation is directed on the PV module, and the residual part is concentrated on a membrane reactor for solar fuels production via dry reforming of methane (DRM). Instead of generating waste heat in PV system, the thermal energy from sunlight can be utilized by thermochemical reactions and stored in solar fuels, leading to a decline of the PV temperature and enhanced PV efficiency. Based on membrane reactors, the equilibrium of DRM shifts forward for achieving a high methane conversion at a relatively low temperature. This system can deliver 75% of energy efficiency, 34% of solar-to-electric efficiency, and 71% of exergy efficiency. Additionally, the carbon dioxide reduction rate (CDRR) could reach 514.5 kg m⁻² year⁻¹. Our findings provide insights into high-efficient solar energy utilization involving membrane reactors.
Thermochemical energy storage performance of methane reforming with carbon dioxide in cavity reactor under concentrated sun simulator has been experimentally and numerically studied. Novel catalyst bed with Ni/Al2O3 particles and perforated quartz encapsulation is proposed to perform high bed temperature for greenhouse effect, and then chemical energy storage efficiency and total energy utilization efficiency of experimental system can respectively reach as high as 41.1% and 80.3%. As concentrated heat flux increases or reactant flow rate decreases, methane conversion rises with bed temperature increasing, while chemical energy storage efficiency first rises and then falls for larger heat loss. As inlet mole fraction of methane increases, chemical energy storage efficiency firstly increases and then drops. Numerical model of cavity reactor under concentrated heat flux is established and validated. In catalyst bed, maximum reaction rate occurs near focal point, while reverse reaction occurs near its side. With the improvement of porosity in catalyst bed, methane conversion and thermochemical storage efficiency firstly increase and then decrease, while they gradually increase with heat conductivity of bed rising. In addition, optimal concentrated heat flux, flow rate, mole fraction of methane (0.5) and bed porosity (0.6) are derived for maximum chemical energy storage efficiency.
In this chapter we analyze the digestion of biomass wastes and the processing, upgrading, and valorization of the major products, biogas and digestate, toward the production of chemicals and fertilizers. The mechanisms, thermodynamics, and kinetics of the various stages involved are studied, from the anaerobic digestion to the biogas clean-up, upgrading, and its use in synthesis as well as the digestate conditioning and nutrient recovery out of it.
The process design and life cycle assessment (LCA) of various methanol production processes, including the conventional natural gas reforming process and alternative CO2 utilization-based pathways, are performed in this work. Three main technologies are considered for the CO2 conversion to methanol: direct CO2 hydrogenation, dry reforming and tri-reforming of methane. For each pathway, a process simulation that includes the CO2 capture from typical flue gas of a cement kiln, the methanol synthesis and purification steps, is performed using the Aspen engineering suite. In addition, for each process, several heat integration measures are considered to maximize thermal efficiency. According to the simulation results, the thermal efficiency of the direct CO2 hydrogenation process (47.8 % LHV) is higher than the dry reforming (40.6 % LHV) while it is lower than the conventional (68.4 % LHV) and tri-reforming (57.9 % LHV) processes. The LCA results showed that the direct CO2 hydrogenation pathway is an environmentally friendly option, only when the electricity GHG intensity is lower than 0.17 kg CO2 equivalent per kWh of electricity. As a result, in the context of Canada, the CO2 hydrogenation options can be recommended only for the provinces where low-carbon electricity is available, such as Quebec, British Columbia, Manitoba and Ontario.
In the present study, the reformed exhaust gas recirculation (REGR) technique was employed on the marine engine fueled with LNG (i.e., marine LNG engine) for the reduction of emissions. A specially designed exhaust gas reformer was integrated with the marine LNG engine and then the performance of the closed-loop system of the reformer and engine was investigated, aiming at exploring the emissions reduction potential of the REGR technique for the marine LNG engine. The results showed that the NOx emission of the marine LNG engine with REGR was lower than that of the prototype engine by 60–70% and meanwhile can meet the Tier III emissions regulations. For the marine LNG engine with REGR, high rate of natural gas supplied to the reformer (RRNG) increased the concentrations of H2 and CO in the reformate. This advanced the flame speed of in-cylinder mixtures and led to a high peak pressure and heat release rate, resulting a 20–26% increase in NOx emission and a 10–12% decrease in the unburned hydrocarbon emission. Because of the variation in thermal efficiency of the reformer and engine, the fuel consumption rate of the closed-loop system showed a different trend with the increase of RRNG at different loads.
CO2 is a major greenhouse gas emitted at the global scale from burning fossil fuels. Converting CO2 to chemicals such as syngas is a promising way to reduce CO2 emissions from stationary sources. In this work, we explore technologies for the thermochemical conversion of CO2 to syngas using both rigorous and reduced order reactor models. Specifically, we study the CO2 utilization potentials of primary reforming such as dry reforming (DR), steam methane reforming (SMR) and partial oxidation (POX), and combined reforming such as combined dry and steam methane reforming (CDSMR), auto-thermal reforming (ATR), combined partial oxidation and dry reforming (PODR) and tri-reforming (TR). Through detailed simulation and analysis, we show the importance of considering rigorous models for accurate prediction. We also develop algebraic surrogate models for reactor outlets as functions of reactor design and operating conditions. The replacement of the high-fidelity models with their simpler algebraic surrogates provides an efficient way for superstructure-based reactor synthesis. Using a mixed-integer nonlinear optimization (MINLP)-based reactor synthesis model, the reactors are further optimized for maximizing CO2 utilization and syngas selectivity. PODR has been found to have the highest potential for converting CO2 for the range of syngas ratios (H2/CO) between 1 and 1.7, achieving almost 100% CO2 conversion with a syngas selectivity ranging 80–93%. We further improve the conversion and syngas selectivity by distributing the feeds to multiple reformers. A combination of DR, CDSMR and TR achieves the best CO2 conversion for syngas ratios up to 2.4. For higher syngas ratios, a combination of SMR, TR and RWGS are found to be optimal. These are non-intuitive results that need further attention.
In this work, a novel loop is designed for simultaneous production of pure hydrogen and synthesis gas (syngas) from a domestic refinery purge gas. The purge gases are the combination of flare gas (consist mainly of methane) and high-temperature flue gas (containing CO2 and steam). The proposed loop including three main parts: 1) flare gas desulfurization unit; 2) CO2 and steam recovery unit and, 3) a membrane reformer for combined dry-steam reforming of methane, heating with high-temperature flue gas. The hazardous hot gases convert to valuable products instead of discharging to the atmosphere.
A steady-state one-dimensional model is used to predict the loop performance. The results show that 55.5% of methane conversion can be achieved from the purge gases consisting of 797 kmol/h flare gas and 17,200 kmol/h flue gas. The proposed process can produce 338 kmol/h of pure hydrogen and 1,209 kmol/h of syngas. In addition, the effects of purge gas properties and process modifications on the loop performance were investigated.
The method presented in this work is a promising alternative to reduce purge gas released to the atmosphere from industrial plants. This can result in a significant reduction in CO2 emissions that causes global warming.
In this study, the cracking phenomenon of methane taking place in a cylindrical cavity of 16 cm in diameter and 40 cm in length under the heat of concentrated solar radiation without any catalyst is analysed. Three cases have been chosen; in all cases the primary phase contains methane and hydrogen gases. In the first case, we consider two phases; the secondary phase is a homogeneous carbon black powder with 50 nm of diameter; in the second case we have three phases where the two secondary phases are a particles powder with two diameters 20 and 80 nm and finally, a third case of five phases with a powder of four different diameters 20, 40, 60 and 80 nm. The low Reynolds K-ε turbulence model was applied. A calculation code "ANSYS FLUENT" is used to simulate the cracking phenomena where an Eulerian – Eulerian model is applied. The choice of several diameters greatly increases the calculation time but it approaches more of the physical reality of the radiation by these particles during the cracking. Results have shown that increasing the number of diameters gives higher cracking rates; the case of the powder of 4 different diameters gives the highest cracking rate. A parametric study as a function of the inlet velocity, carbon particle diameters and the intensity of solar radiation is realized. For the cracking heat, provided by the choice of the two concentrators of 5 and 16 MW/m² used in this simulation, the CH4 inlet velocity is a decisive parameter for the cracking rate. Any increase in the inlet velocity requires more heat and this leads to a decrease in the cracking rate. For a velocity not exceeding 0.177 m/s (i.e. 0.3 L/min), both solar concentrations give the same amount of hydrogen produced. These quantities of hydrogen obtained reach maximum values for an inlet flow rate of CH4 between 0.58 L/min (i.e. 0.34 m/s) and 0.62 L/min (i.e. 0.3655 m/s) for both reactors. The results are interpreted and compared with experimental work.
Steam methane reforming has been extensively used in producing syngas, but the H2/CO ratio of the syngas produced by the method is too large to feed to subsequent processes such as the Fischer-Tropsch process. The dry methane reforming process produces a syngas with a small H2/CO ratio. Combining these two processes makes it possible to adjust the H2/CO ratio to provide a syngas with a proper ratio for subsequent processes. Dry reforming is well known to suffer a severe coke generation problem. If the two reactions occur simultaneously in one reactor, the coke generation problem can be greatly reduced by the presence of water in the reactor. However, this setup needs a catalyst suitable for both reactions in terms of both stability and performance, and no commercialized catalyst has been reported to do this job. We propose a novel spatially patterned catalytic reactor in which two different catalysts, one suitable for steam reforming and the other suitable for dry reforming, are spatially layered. The catalysts and inert material are spatially layered, and the temperature of each catalyst layer can be maintained within in the range of temperatures suitable for the corresponding reaction of the layer. The proposed method is shown to be able to provide syngas with a desired ratio while mitigating the coke generation problem. The optimization problem, which minimizes the length of the reactor, is formulated to provide an optimum temperature profile for the reactor. The two catalyst and inert layers are arranged along the length of the reactor to realize the temperature profile. The optimization results show that the amount of catalysts, capital and energy costs are greatly reduced compared to the conventional combined reforming process. The proposed reactor is also shown to maintain stable operation with large changes in feed flow rate and H2/CO ratio by adjusting the fuel flow rate to maintain the reactor outlet temperature.
Due to the utilization of concentrated solar energy, a more complex high-temperature thermal environment will be formed inside the solar thermochemical reactor, thereby resulting in complicated behaviors of chemical reactions. This paper numerically investigates the carbon deposition behaviors inside a Ni/Al2O3-based catalyst porous-filled STR for DRM process under various operational conditions. The reaction kinetics for DRM including four side reactions are programmed via UDFs. The simulation results indicate that the optimal structural parameters of porous media for high-value syngas products with less carbon deposition are φ = 0.8 and dp = 2 mm, while the optimal feed ratio is CH4/CO2 = 1. Besides, the operating condition at vin = 100 ml/min and Plamp = 0.7 kW has the advantage of obtaining higher conversion rate while reducing the carbon deposition rate to some extent.
In this work, the vacuum co-impregnation of glucose and nickel precursor followed by the carbonization in an inert gas was developed as a new method for the preparation of the directly reduced Ni-based catalysts (Ni–C/Al2O3), which can be directly applied for CO2 reforming of CH4 (CRM) without any reduction. The materials were characterized by XRD, TEM, and N2 adsorption-desorption at low temperature. The results showed that H2 and CH4 derived from the decomposition of the glucose acted as the reducing agents for synthesizing metallic Ni from Ni precursors, and the reduction content of nickel was strongly dependent on the amount the glucose. The introduction of carbon derived from decomposition of glucose decreased the interaction between Ni and Al2O3 and then resulting in bigger Ni particle. Under the same CRM reaction conditions, the as-prepared Ni-0.35C/Al2O3 catalyst without further reduction showed highest catalytic activity and stability. The use of the directly reduced Ni-based catalyst without further high-temperature reduction is promising for the development of a more efficient CRM process.
The steam reforming process converts hydrocarbons into mixtures of hydrogen, carbon monoxide, carbon dioxide, and methane
(1) (2) (3)
The expression reforming is misleading since it is used also for the well-knowm process for improvement of the octane number of gasoline [1]. In the gas industry, reforming has generally been used for “the changing by heat treatment of a hydrocarbon with high heating value into a gaseous mixture of lower heating value” [2].
La1−xSrxNi0.4Co0.6O3 and La0.8Sr0.2Ni1−yCoyO3 solid solutions with perovskite-type structure were synthesized by the sol–gel resin method and used as catalytic precursors in the dry reforming of methane with CO2 to syngas, between 873 and 1073K at atmospheric pressure under continuous flow of reactant gases with CH4/CO2=1 ratio. These quaternary oxides were characterized by X-ray diffraction (XRD), BET specific surface area and temperature-programmed reduction (TPR) techniques.XRD analyses of the more intense diffraction peaks and cell parameter measurements showed formation of La-Sr-Ni-Co-O solid solutions with La0.9Sr0.1CoO3 and/or La0.9Sr0.1NiO3 as the main crystallographic phases present on the solids depending on the degree of substitution. TPR analyses showed that Sr doping decreases the temperature of reduction via formation of intermediary species producing Ni0, Co0 with particle sizes in the range of nanometers over the SrO and La2O3 phases. These metallic nano particles highly dispersed in the solid matrix are responsible for the high activity shown during the reaction and avoid carbon formation. The presence of Sr in doping quantities also promotes the secondary reactions of carbon formation and water–gas shift in a very small extension during the dry reforming reaction.
Carbon dioxide reforming of methane over different semi-cokes (Hongce lignite, Shenmu bituminous coal and Jincheng anthracite) is being investigated at atmospheric pressure, temperature of 800–1000 °C, CH4/CO2 ratios of 3:1–1:3 and gas–solid contact times of 0.11–1.76 min using a fixed-bed reactor. The semi-cokes still shows stable catalyst activity after 480 min of reaction. The results show that the catalyst activity of the semi-cokes was lower with increasing coal rank. The order of the catalyst activity is Hongce lignite semi-cokes > Shenmu bituminous coal semi-cokes > Jincheng anthracite semi-cokes. This is somewhat related to the content of the functional groups of the semi-cokes. The analysis for the surface structure of the semi-cokes before and after the reforming reaction shows that the CO and –NH2, etc., functional groups on the surface of the semi-cokes participated in the reforming reaction, the coal rank and the BET are the main factors which influenced the catalyst performance, and the functional groups on the surface of the semi-cokes and the types and amounts of alkaline metals have a certain type of influence on the activity of the reforming reaction.
A rigorous kinetic model for the formation of filamentous carbon on a nickel catalyst by methane cracking is derived. The experimental study was performed in an electrobalance unit. The temperature ranged from 773 to 823 K and the partial pressure of methane ranged from 1.5 to 10 bar. The mode of experimentation ensured that the rate of growth of the carbon filaments was always based upon the same number of filaments. A kinetic model is selected in which the abstraction of the first hydrogen atom from molecularly adsorbed methane is the rate-determining step. Based on the results of the parameter estimation, an energy diagram for the methane cracking is constructed.
Kinetic studies of COâ reforming of methane over a highly active Ni/La/α-AlâOâ catalyst were performed in an atmospheric microcatalytic fixed-bed reactor. The reaction temperature was varied between 700 and 900 C, while partial pressures of COâ and CHâ ranged from 16 to 40 kPa. From these measurements kinetic parameters were determined; the activation energy amounted to 90 kJ/mol. The rate of COâ reforming was described by applying a Langmuir-Hinshelwood rate equation. The developed kinetics was interpreted with a two-phase model of a fluidized bed. The predictions for a bubbling-bed reactor operated with an undiluted feed (CHâ:COâ = 1:1) at 800 C showed that, on an industrial scale, significantly longer contact times (H{sub mf} = 7.8 m, m{sub cat}/V{sub STP} = 31.8 g·s·ml) are necessary for achieving thermodynamic equilibrium (X{sub CHâ} = 88.2%, X{sub COâ} = 93.6%). The performance of the reactor was strongly influenced by the interphase gas exchange: the highest space time yields were obtained for small particles (D{sub p} = 80 μm).
The catalytic activity of Ni on a series of catalysts supported on the synthesized KH zeolite for the CO2 reforming of methane has been investigated. The KH zeolite supports were previously synthesized via silatrane and alumatrane precursors using the sol–gel process and hydrothermal microwave treatment. Eight percent Ni was impregnated onto the synthesized KH zeolites, which have different morphologies: called dog-bone, flower, and disordered shapes. The prepared Ni/KH zeolites were tested for their catalytic activity at 700°C, at atmospheric pressure, and at a CH4/CO2 ratio of 1. The results showed that Ni supported on dog-bone and flower-shaped KH zeolites provided better activity than that of disordered KH zeolite due to higher CH4 and CO2 conversions, a higher H2 production, and a smaller amount of coke formation on the catalyst surface. Furthermore, the stability of the Ni/KH zeolite was greatly superior to that of Ni supported on alumina and clinoptiolite catalysts after 65h on stream.
The kinetics of CO2reforming of CH4were studied over Pt supported on TiO2, ZrO2, Cr2O3, and SiO2, and the catalysts were characterized using chemisorption, X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), temperature-programmed hydrogenation (TPH), and temperature-programmed surface reaction. Although the Pt/SiO2and Pt/Cr2O3catalysts deactivated significantly within 5 and 15 h onstream, respectively, the Pt/ZrO2and Pt/TiO2catalysts exhibited much higher stability even after 80 to 100 h onstream. TPH results with used catalysts showed that both Pt/ZrO2and Pt/TiO2have suppressed carbon deposition under reaction conditions. H2and CO chemisorption as well as DRIFTS provided evidence of metal–support interactions in the Pt/TiO2catalyst and indicated that large ensembles of Pt atoms, active for carbon deposition, are deactivated or destroyed by the presence of mobile TiOxspecies. Activities for CO formation and CH4consumption on a turnover frequency basis were five times greater on Pt/TiO2compared with the other catalysts, suggesting that active sites for reforming are created in the Pt–TiOxinterfacial region. The kinetic behavior was explained well by a kinetic model recently proposed for supported Ni.
Dry reforming of methane has been investigated on two series of catalysts either prepared by co-precipitation: n(NixMgy)/Al, NixMgy and NixAly or prepared by impregnation: Ni/MgO (mol% Ni=5, 10). The catalysts, calcined at 600–900°C, were characterized by different techniques: BET, H2-TPR, TPO, XRD, IR, and TEM-EDX analysis. The surface BET (30–182m2g−1) decreased with increasing the temperature of calcination, after reduction and in the presence of Mg element. The XRD analysis showed, for n(NixMgy)/Al catalysts, the presence of NiAl2O4 and NiO–MgO solid solutions. The catalyst reducibility decreased with increasing the temperature of pretreatment. The n(NixMgy)/Al catalysts were active for dry reforming of methane with a good resistance to coke formation. The bimetallic catalyst Ni0.05Mg0.95 (calcined at 750°C and tested at 800°C) presents a poor activity. In contrast, the 5% Ni/MgO catalyst, having the same composition but prepared by impregnation, presents a high activity for the same calcination and reaction conditions. For all the catalysts the activity decreased with increasing the temperature of calcination and a previous H2-reduction of the catalyst improves the performances. The TPO profiles and TEM-EDX analysis showed mainly four types of coke: CHx species, surface carbon, nickel carbide and carbon nanotubes.
This paper reports a study about the behaviour of different Pt-based catalysts supported on Al2O3, Na–Al2O3, K–Al2O3 and ZrO2 in methane reforming with CO2. Results indicate that Pt/Na (0.3 wt%)-Al2O3 and Pt/ZrO2 catalysts show both a good activity and selectivity with a very high catalytic stability at 1073 K. The Pt/K (0.3 wt%)-Al2O3 catalyst showed a good performance but a slightly lower conversion level than Pt/Na (0.3 wt%)-Al2O3. On the other hand, the Pt/Al2O3 catalyst displayed an important decrease of the methane conversion through the reaction time at 1073 K and hence, a lower catalytic stability due mainly to the carbon deposition. It can be concluded that either Na or K addition to Pt/Al2O3 enhances the catalytic stability since they provide basic sites, which favour the dissociation reaction of CO2 into CO and O. The O species can react with the carbon deposited on the Pt, thus cleaning the metallic phase of the doped catalysts.
The relation between coke formation and the deactivation of supported Pt catalysts during CO2 reforming of methane at temperatures above 1070 K such as used in the commercial process was studied. Temperature-programmed oxidation and temperature-programmed reaction with CO2 were applied to Pt catalysts (Pt/Al2O3 and Pt/ZrO2) which were exposed to CH4/CO2 (reforming reaction conditions) or CH4/He (facile coke formation) to identify the carbon species. The activity decrease for Pt/Al2O3 was rather slow and minor at high temperature (≥1070 K), while it was fast and almost complete during a comparative experiment at low temperature (875 K). Coke deposited on the supported Pt particles was oxidized by CO2, but coke on the Al2O3 support was not removed at 1070 K. At this temperature the decay in activity with time on stream corresponded solely to the amount of coke accumulated on Pt particles. This indicates the main reaction between CO2 and CH4 on all Pt atoms without significant participation of the support. The activity is concluded to decrease gradually due to coverage of Pt by coke induced by CH4 decomposition (initial phase of deactivation observed at high temperature). After a while only the perimeter of Pt particles remains as site of activity. There, the activity is speculated to be stable because of the higher reactivity of CO2 at the metal–support boundary. Gradually, the coke on the support (Al2O3) increases to an extent that it blocks the reaction also at that location. In contrast to the situation with Pt/Al2O3, coke was not observed on Pt/ZrO2 even after exposure to reforming gas (CH4/CO2) for 12 h. The combination of three factors is concluded to cause the high catalytic stability of Pt/ZrO2 in CO2/methane reforming: (i) coke on Pt (supported on ZrO2) is more reactive toward CO2 than coke on Pt (supported on Al2O3) under reforming reaction conditions/ (ii) methane decomposition is slower on Pt/ZrO2 than on Pt/Al2O3; and (iii) coke is hardly formed on the ZrO2 support.
A rigorous kinetic model was derived for the formation on a nickel catalyst of filamentous carbon by the Boudouard reaction and for the gasification of filamentous carbon by carbon dioxide, by hydrogen, and by steam. The experimental study was performed in an electrobalance unit. Carbon formation and gasification experiments were performed at temperatures ranging from 773 to 848 K. The partial pressures of the various components were chosen in the ranges encountered in industrial steam reformers. The influence of the carbon formation reaction on the subsequent gasification process was also investigated. The mode of experimentation ensured that the rates of growth or gasification of the carbon filaments were always based on the same number of carbon filaments. The same reaction mechanism was derived from the study both of methane cracking and the Boudouard reaction and of the reverse reactions, gasification by hydrogen and carbon dioxide. Using the results of the parameter estimation, energy diagrams were constructed for the Boudouard reaction and for gasification by carbon dioxide and by hydrogen.
Dry reforming of methane was studied over the systems on the base of Ni3Al and Ni3Al + 5%Mo in the temperature range 600–900 °C. The materials have been prepared by self-propagating high temperature synthesis and characterized by XRD (in situ and ex situ), DTA–TG, SEM + EDX, HRTEM + EDS and XPS. The formation of Mo2C phase was observed at moderate Mo content (5–10 wt.%), which corresponds to a much improved catalytic activity and stability under the severe carbon dioxide reforming conditions. The structure and morphology of different types of carbon deposits obtained on Ni3Al and Ni3Al + 5%Mo catalysts were investigated. The results indicated that the addition a low amount of Mo to Ni3Al led to a decrease in carbon deposition. It is shown that Ni3Al + 5%Mo is promising catalyst for dry reforming of methane with carbon dioxide.
The deposition of carbon on catalysts during the partial oxidation of methane to synthesis gas has been investigated and it has been found that the relative rate of carbon deposition follows the order Ni>Pd>Rh>Ir. Methane decomposition was found to be the principal route for carbon formation over a supported nickel catalyst, and electron micrographs showed that both whisker and encapsulate forms of carbon are present on the catalyst. Negligible carbon deposition occurred on iridium catalysts, even after 200 h.
Rhodium supported on γ-Al2O3 was an effective catalyst for reforming methane with carbon dioxide at low ratios of CO2/CH4. Unlike other metals tested, no carbon deposited on the catalyst in the temperature range 600–800°C. Kinetic experiments on a 0.5 wt.-% Rh/Al2O3 catalyst gave rate equations for the reforming and shift reactions. A model was constructed for conversion in a pellet by incorporating both the reverse reaction and the effect of external and internal diffusion. This model, when tested with the data from a pellet string reactor, gave very good agreement with conversions and product distributions. External diffusion was negligible but internal effectiveness factors were about 0.3 or more. The model was expanded to a large-scale packed bed with appropriate heat transfer parameters. Adjustable factors were determined by matching measured temperature profiles from pilot unit experiments. The catalyst later performed successfully in a solar receiver/reactor and shows potential for conventional processing.
A detailed description is given of the formation and the gasification of filamentous carbon. The diffusion of carbon through nickel originates from a concentration gradient, which implies a different solubility at the nickel–gas and the nickel–carbon interface. A thermodynamic basis for the different solubilities is provided. The segregation of carbon, taking place at the gas side of the nickel particle, is added as one of the steps in the global mechanism of carbon filament formation and gasification. The segregation process may be described in a way similar to that of gas adsorption. The coupling of the surface reactions, the segregation process, and the diffusion of carbon through the nickel particle leads to a detailed model of the process of carbon filament formation, which forms the basis for the kinetic modeling of carbon formation and gasification reactions. Experimental results for the methane cracking revealed that the number of carbon filaments that is able to nucleate strongly depends upon the affinity for carbon formation.
Catalytic steam reforming Catalysis science and technology
- Rostrup-Nielsen
- Jr
Rostrup-Nielsen JR (1983) Catalytic steam reforming. In: Anderson JR, Boudart M (eds) Catalysis science and technology, vol 5. Springer, Berlin, pp 1–118
Reforming of CH 4 with CO 2 on Pt-supported catalysts: effect of the support on the catalytic behaviour
- A D Ballarini
- S R De Miguel
- E L Jablonski
- O A Scelza
- A A Castro
Ballarini AD, de Miguel SR, Jablonski EL, Scelza OA, Castro AA (2005) Reforming of CH 4 with
CO 2 on Pt-supported catalysts: effect of the support on the catalytic behaviour. Catal Today
107-108:481-486