Adiabatic Packed Bed Reactor Research Articles

Modelling of a continuous sorption-enhanced methanation process in an adiabatic packed-bed reactor system

The present study investigates a sorption-enhanced methanation process and successive solid regeneration stages using a dual-function catalyst containing nickel as a catalyst and zeolite 13X for water removal. An adiabatic packed bed, modelled by a dynamical and heterogeneous model, has been considered, and a five-stage sequence describes the sorption-enhanced methanation and successive solid regeneration. First, methanation occurs with in-situ water removal; then, the catalyst drying using a pressure and temperature swing approach implemented by blowdown, purge, cooling, and pressurisation stages. In adiabatic operation, heat management is crucial; on the other hand, the heat produced can be efficiently used to dry the zeolite. Process intensification is pursued by addressing the effect of gas inlet temperature, pressure, and GHSV on system performance. Achieving an average purity of 99 % of the methane for pressures greater than 2 bar is possible for long-time operation, with productivity averaging 0.8 mol/(kgads min) at the highest gas hourly space velocity investigated.

One-dimensional modeling of heterogeneous catalytic chemical looping steam methane reforming in an adiabatic packed bed reactor.

Hydrogen production via chemical looping steam methane reforming (CL-SMR) is among the most promising current technologies. This work presents the development in gPROMS Model Builder 4.1.0® of a 1D model of an adiabatic packed bed reactor used for chemical looping reforming (CLR). The catalyst used for this process was 18wt. % NiO with the support of Al2O3. A brief thermodynamic analysis using Chemical Equilibrium Application (CEA) was carried out to identify the optimum operating conditions. The model was simulated for 10 complete CL-SMR cycles. The effects of variations in temperature, pressure, gas mass velocity, nickel oxide concentration, reactor length, and particle diameter were studied to investigate the performance of the CL-SMR process under these variations. A parametric analysis was carried out for different ranges of conditions: temperatures from 600 to 1,000K, pressure from 1 to 5 bar, gas mass velocity between 0.5 and 0.9kg·m-2 s-1, nickel oxide concentration values between 0.1 and 1mol·m-3, particle diameters between 0.7 and 1mm, and fuel reactor (FR) lengths between 0.5 and 1.5m. At the optimum temperature (950K), pressure (1bar), and steam-to-carbon molar ratio (3/1), with an increase in particle diameter from 0.7 to 1mm, an 18% decrease in methane conversion and a 9.5% increase in hydrogen yield were observed. Similarly, with an increase in FR length from 0.5m to 1.5m, a delay in the temperature drop was observed.

Effect of preheat temperature, pressure, and residence time on methanation performance

The present work studies the effect of reagent preheat temperature on methanation while maintaining the initial temperature of the catalytic bed constant. An adiabatic packed bed reactor was used with 193 g of commercial 10% Ni/Al2O3 catalyst. The tested preheat temperatures were 25 °C, 100 °C, 180 °C, and 280 °C, while the initial catalytic bed temperature was 280 °C. Two tests were performed in which the effect of preheat temperature was evaluated: the first comparing gas hourly space velocities (GHSVs) of 935 h−1 and 1559 h−1, and the second comparing gauge pressures of 0 bar, 1 bar, and 4 bar. Similar behavior was observed for the temperature inside the reactor and final CO2 conversion for preheating temperatures of 100 °C, 180 °C, and 280 °C at a gauge pressure of 0 bar. However, at this pressure, conversion was considerably reduced for the preheat temperature of 25 °C, due to a large part of the catalytic bed serving to preheat the reactants to the minimum reaction temperature. This effect can be partially attenuated by decreasing the GHSV, due to the increased residence time. Finally, increased pressure significantly improved the final CO2 conversion for all preheating temperatures (Tin), and attenuates the effect of Tin. These results show that certain operating conditions do not require as high a reactant preheat temperature for methanation, which offers energy savings in certain processes such as power-to-gas (P2G), where the hydrogen is produced from electrolysis and can leave the process at a lower temperature than that required for methanation.

Kinetics and Reactor Design Principles of Volatile Fatty Acid Ketonization for Sustainable Aviation Fuel Production

Ketonization of wet waste-derived carboxylic acids (volatile fatty acids, VFAs) constitutes the first step of a process to catalytically upgrade VFAs to an alkane sustainable aviation fuel blendstock. VFA ketonization has been demonstrated at near-theoretical yields at the lab scale, and robust operation of industrial-scale ketonization reactors is essential for the commercialization of VFA upgrading to sustainable aviation fuel. We present a ketonization kinetic study of hexanoic acid, a VFA model compound, over commercial ZrO2 and use the kinetic parameters derived from the study in an adiabatic packed-bed reactor simulation of hexanoic acid ketonization running to near-complete (98%) conversion. A key findings from the kinetic study is that ketonization rate is positive order in acid pressure at low (<10 kPa) pressures and transitions to zero order at higher pressures, conforming to a Langmuir–Hinshelwood surface coupling mechanism. Rates are inhibited by ketonization coproduct water but not by ketones themselves or coproduct CO2. Reactor simulations using these kinetics show that rate inhibition by water controls reactor size and that size requirements can be lessened by employing designs that allow for the removal of water from the partially converted acid stream.

Economic Potential of Bio-Ethylene Production via Oxidative Coupling of Methane in Biogas from Anaerobic Digestion of Industrial Effluents

Brazil’s large biofuels industry generates significant amounts of effluents, e.g., vinasse from bioethanol, that can effectively be used as substrate for production of biogas via Anaerobic Digestion (AD). The Oxidative Coupling of Methane (OCM) is the heterogeneous catalytic oxidation of methane into ethylene, which is a main building block for the chemical industry. This work investigates the potential and competitiveness of bio-ethylene production via OCM using biogas produced by biological anaerobiosis of vinasse as a feedstock. The proposed process can add incentive to treat of vinasse via AD and replace fossil ethylene, thus potentially reducing emissions of Greenhouse Gases (GHG). A process model is developed in Aspen Plus v10 software and used to design an economic Biogas-based Oxidative Coupling of Methane (Bio-OCM) process that consumes biogas and oxygen as educts and produces ethylene, ethane, and light off-gases as products. Operating conditions in the reaction section are optimized and a reaction product yield of 16.12% is reached by applying two adiabatic Packed Bed Reactors (PBRs) in series. For the downstream CO2 removal section, a standalone amine-absorption process is simulated and compared to a hybrid membrane-absorption process on an economic basis. For the distillation section, two different configurations with and without Recycle Split Vapor (RSV) are simulated and compared. The bio-ethylene production cost for a Bio-OCM plant to be installed in Brazil is estimated considering a wide range of prices for educts, utility, side products, and equipment within a Monte Carlo simulation. The resulting average production cost of bio-ethylene is 0.53 ±0.73 USD kgC2H4-1. The production cost is highly sensitive to the sales price assigned to a light off-gas side-product stream containing mostly the un-reacted methane. A sales price close to that of Brazilian pipeline natural gas has been assumed based on the characteristics of this stream. The Monte Carlo simulation shows that a bio-ethylene production cost below or equal to 0.70 USD kgC2H4-1 is achieved with a 55.2% confidence, whereas market values for fossil ethylene typically lie between 0.70USD kgC2H4-1–1.50USD kgC2H4-1. Technical and economic challenges for the industrial implementation of the proposed Bio-OCM process are identified and relevant opportunities for further research and improvement are discussed.

Productivity Enhancement for the Oxidative Coupling of Methane in Adiabatic Layered-Bed Reactors

Ethylene production via oxidative coupling of methane (OCM) in adiabatic packed-bed reactors is a promising route within the context of natural gas valorization. However, the high exothermicity of OCM imposes low inlet temperatures and, hence, low space-time yields. Layered-bed reactors are proposed in the present work as a potential alternative to mitigate this issue. In this modeling investigation, a first layer of active Sr/La2O3 catalyst is followed by a second layer of more selective NaMnW/SiO2 catalyst. Optimized bed compositions and operating conditions are shown to lead to up to a 10 times higher space-time yield compared to a single-catalyst bed. The achieved values of ca. 15 molC2+ s–1 mr–3 are comparable to conventional values from steam cracking of ethane, suggesting layered-bed adiabatic configurations as a promising way forward for intensified ethylene production via OCM.

Comparison of intensified reactor systems for one–step conversion of CO2–containing syngas to DME

Comparison is drawn among two intensified reactor systems proposed for meeting precise temperature regulation requirement of the direct conversion of syngas to dimethyl ether (DME). In the first (microchannel) system, reaction channels washcoated with physical mixture of catalysts for methanol synthesis (Cu–ZnO/Al2O3) and dehydration (HZSM–5) are accompanied by cooling channels. Decoupled catalytic reaction and cooling functions are conducted in interconnected adiabatic packed–bed reactors and microchannel heat exchangers, respectively, in the second (cascade) system. Both systems are compared under identical inlet conditions, catalyst types and residence times via computational modeling coupled with realistic constraints. Upon syngas (CO2/COx (COx:CO+CO2)=0.2 and H2/COx=2.0) feeding at 493 K, 50 bar and residence time of 1.05 kgcat.s/mol, conversions of CO and CO2, and DME yield are found as 27.4, 6.6 and 18.8%, respectively, for the microchannel, and 23.3, 4.6 and 13.8%, respectively, for the cascade system. At a pilot–scale gasifier syngas throughput of 0.77 mol/s, volumes of the microchannel and cascade systems, the latter being composed of five reactors and four heat exchangers, are computed as 104.5 and 56.2 liters, respectively. Productivity (molDME/m3.s) of the microchannel system (0.15) remains below that of the cascade (0.20), which, however, suffers from notable pressure drop.

Modeling of sorption enhanced steam methane reforming in an adiabatic packed bed reactor using various CO2 sorbents

A 1-D heterogeneous model of sorption-enhanced steam methane reforming (SE-SMR) process in a packed bed reactor consisting of nickel catalyst well mixed with CO2 sorbent particles is investigated for three types of common sorbents. The performance of SE-SMR process is studied under low medium pressure conditions (3 – 11 bar) to find the optimum operating conditions. Optimal CaO sorption corresponding to 82% CH4 conversion and 85% H2 purity is found at 900 K, 3 bar, 3.5 kgm−2s−1 and S/C of 3.0. In contrast, lithium zirconate (LZC) and hydrotalcite (HTC) sorbents exhibited best sorptions under the operating conditions of 773 K, 5 bar and S/C of 3 with CH4 conversion of 91.3% and 55.2%, and H2 purity of 94.1% and 77.8% respectively. In these conditions, the CH4 conversion increased by 114%, 111% and 67% compared to the conventional SMR for the processes enhanced by HTC, LZC and CaO sorption respectively.

Simultaneous Mass, Heat and Momentum Transfer in an Adiabatic Packed Bed Reactor

Process modeling or computer simulation is one of the most important studies which gives the engineer a whole description about certain processes including all the mathematical relationships that are relating the process variables.&#x0D; Transport phenomena on fixed bed reactor was studied because of their importance and their effects on the catalyst performance in all chemical reactions.&#x0D; Simultaneous mass , heat and pressure drop were studied and all the process variables such as temperature, rate of reaction , pressure along length of the reactor were calculated and the data obtained from the mathematical package showed that with the increase the reaction temperature the process production , rate of reaction and pressure drop will increase.

Dynamic simulation of manufacture of styrene by the catalytic dehydrogenation of ethyl benzene

Styrene is an important chemical compound derived from benzene. It is produced conventionally by the catalytic dehydrogenation of ethylbenzene in the presence of iron oxide catalyst. The reaction is reversible endothermic and is carried out in a series of adiabatic packed bed reactors. The present study deals with the dynamic simulation of the process of styrene manufacture using the Honeywell UniSim design suite. The control parameters of various controllers in the process have been derived using the auto-tune feature of the software. Various scenarios of servo problems were studied. The dynamic behaviour of the process parameters during various scenarios in the operating chemical plant is also studied. The results are very much useful for conducting the hazard analysis of the plant and thereby designing the trip systems of the plant.

Small-scale production of hydrogen via auto-thermal reforming in an adiabatic packed bed reactor: Parametric study and reactor's optimization through response surface methodology

In this work, a two-dimensional (2-D) heterogeneous reactor model for ATR process is presented. In order to authenticate the developed reactor model outputs, literature results as well as thermodynamic findings produced by employing chemical equilibrium with applications (CEA) software were compared with the model predictions and an excellent agreement was evidenced that corroborates the model's accurate predictive capability. Response surface methodology combined with central composite design was used to investigate the significance of operational parameters on the performance of the ATR process and Parametric optimization was performed to find the optimal operating conditions. Further insights into the ATR process were obtained by studying the effect of temperature, pressure, S/C, oxygen to carbon ratio (O/C) and gas mass flow velocity (Gs) on CH4 conversion, H2 yield (wt. % of CH4) and H2 purity. It was concluded that 973 K, 1.5 bar, S/C of 3.0, O/C of 0.45 and Gs of 0.15 kg/m2s resulted in CH4 conversion and H2 purity up to 97.6% and 71.8%, respectively.

Modelling of one-dimensional heterogeneous catalytic steam methane reforming over various catalysts in an adiabatic packed bed reactor

Kinetic data relevant to steam methane reforming (SMR) are often applied to catalysts and conditions for which they have not been derived. In this work, kinetic rates for the two SMR and water gas shift reactions were derived for 12 commonly used reforming catalysts based on conversion data obtained from the literature. Subsequently, these rates were tested in dynamic operation, steady-state, and equilibrium using a 1-D reactor model developed in-house with gPROMS model builder. Modelling outputs were further validated independently at equilibrium using the software chemical equilibrium with applications (CEA), and the literature. The effect of variables such as temperature, pressure, steam to carbon ratio (S/C), and gas mass flux (Gs) on the performance of the SMR process was then studied in terms of fuel and steam conversion (%), H2 purity (%), H2 yield (wt. % of CH4) and selectivity of the carbon-based products. A comparative study was then performed for the 12 catalysts. Some catalysts showed better activity owing to their fast kinetics when they are tested in mild industrial conditions, while others performed better in more severe industrial conditions, substantiating that the choice of a catalyst ought to depend on the operating conditions.

Reactor engineering calculations with a detailed reaction mechanism for the oxidative coupling of methane

Abstract The oxidative coupling of methane (OCM) is a potential option for conversion of excess natural gas to higher value products or useful feedstocks. The preferred or ideal OCM stoichiometry is: 2CH4 + O2 → C2H4 + 2H2O, but real OCM produces a variety of species. Using a detailed mechanism from the literature for OCM over a La2O3/CeO2 catalyst that combines coupled elementary gas phase and surface reactions, a reactor engineering study has been done. Adiabatic packed bed reactor (PBR, modeled as plug flow) and continuous stirred tank reactor (CSTR, perfect mixing) simulations using this mechanism are presented. Each reactor simulation used the same total number of catalyst sites. Process variables included CH4/O2 feed ratio (7, 11), feed temperature (843–1243 K), and feed rate. All runs were conducted at 1.01E5 Pa pressure. The results show the CSTR produces high conversions at much lower feed temperatures than those required by the PBR. Once full PBR “light off” occurs, however, its CH4 conversions exceed CSTR. The simulations reveal OCM over this catalyst at these conditions gives a mixture of synthesis gas (CO, H2) and C2Hx (primarily C2H4 plus small quantities of C2H6 and C2H2). The CSTR favors the production of synthesis gas, while the PBR favors C2Hx. Within the suite of CSTR cases, C2Hx is favored at the lowest feed temperature and highest CH4/O2 feed ratio.

Modelling of H2 production via sorption enhanced steam methane reforming at reduced pressures for small scale applications

The production of H2 via sorption enhanced steam reforming (SE-SMR) of CH4 using 18 wt % Ni/Al2O3 catalyst and CaO as a CO2-sorbent was simulated for an adiabatic packed bed reactor at the reduced pressures typical of small and medium scale gas producers and H2 end users. To investigate the behaviour of reactor model along the axial direction, the mass, energy and momentum balance equations were incorporated in the gPROMS modelbuilder®. The effect of operating conditions such as temperature, pressure, steam to carbon ration (S/C) and gas mass flow velocity (Gs) was studied under the low-pressure conditions (2–7 bar). Independent equilibrium based software, chemical equilibrium with application (CEA), was used to compare the simulation results with the equilibrium data. A good agreement was obtained in terms of CH4 conversion, H2 yield (wt. % of CH4 feed), purity of H2 and CO2 capture for the lowest (Gs) representing conditions close to equilibrium under a range of operating temperatures pressures, feed steam to carbon ratio. At Gs of 3.5 kg m−2s−1, 3 bar, 923 K and S/C of 3, CH4 conversion and H2 purity were up to 89% and 86% respectively compared to 44% and 63% in the conventional reforming process.

Modelling of H2 production in a packed bed reactor via sorption enhanced steam methane reforming process

The sorption enhanced steam reforming (SE-SMR) of methane over the surface of 18 wt. % Ni/Al2O3 catalyst and using CaO as a CO2-sorbent is simulated for an adiabatic packed bed reactor. The developed model accounts for all the aspects of mass and energy transfer, in both gas and solid phase along the axial direction of the reactor. The process was studied under temperature and pressure conditions used in industrial SMR operations. The simulation results were compared with equilibrium calculations and modelling data from literature. A good agreement was obtained in terms of CH4 conversion, hydrogen yield (wt. % of CH4 feed), purity of H2 and CO2 capture under the different operation conditions such as temperature, pressure, steam to carbon ratio (S/C) and gas mass flux. A pressure of 30 bar, 923 K and S/C of 3 can result in CH4 conversion and H2 purity up to 65% and 85% respectively compared to 24% and 49% in the conventional process.

Pseudo-transient models for multiscale, multiresolution simulation and optimization of intensified reaction/separation/recycle processes: Framework and a dimethyl ether production case study

Including detailed models of processing equipment in the process flowsheet model is required in the case of “non-standard” unit operations, including, e.g., intensified equipment and unconventional reactor designs. We provide a unified multiscale framework for including such models in equation-oriented process flowsheet modeling, simulation and optimization. Relying on the reaction/separation/recycle process prototype, we propose a multiresolution paradigm, whereby detailed, distributed-parameter representations of reacting systems and rigorous models of (intensified) separation units are embedded in process flowsheet models. We develop an equation-oriented modeling approach based on a pseudo-transient reformulation of the balance equations, enabling the reliable and robust simulation of the process flowsheet. We also describe a companion design optimization routine. We illustrate these concepts with an extensive case study on dimethyl ether production using an intensified process featuring a dividing-wall distillation column and an adiabatic packed bed reactor with intermediate quenching.

Kinetics study and modelling of steam methane reforming process over a NiO/Al2O3 catalyst in an adiabatic packed bed reactor

Kinetic rate data for steam methane reforming (SMR) coupled with water gas shift (WGS) over an 18 wt. % NiO/α-Al2O3 catalyst are presented in the temperature range of 300–700 °C at 1 bar. The experiments were performed in a plug flow reactor under the conditions of diffusion limitations and away from the equilibrium conditions. The kinetic model was implemented in a one-dimensional heterogeneous mathematical model of catalytic packed bed reactor, developed on gPROMS model builder 4.1.0®. The mathematical model of SMR process was simulated, and the model was validated by comparing the results with the experimental values. The simulation results were in excellent agreement with the experimental results. The effect of various operating parameters such as temperature, pressure and steam to carbon ratio on fuel and water conversion (%), H2 yield (wt. % of CH4) and H2 purity was modelled and compared with the equilibrium values.

Temperature rise during stationary and dynamic regeneration of a diesel particulate filter

The development of a safe regeneration procedure which circumvents large temperature excursions during the exothermic regeneration is the current major technological challenge in the operation of diesel particulate filters. The cause of this local hot zone formation is still an open question. The maximum temperature attained under stationary (constant) feed conditions regeneration is not sufficiently high to cause the local melting. The counterintuitive temperature rise in an adiabatic packed-bed reactor following a sudden decrease in the feed temperature suggests that a high transient temperature in a diesel particulate filter (DPF) could be the response to a transient change of the operating conditions, such as a shift from normal driving mode to idle. Here, we review recent experimental measurements by a high speed infrared camera of the transient spatial and temporal temperature rise during stationary and dynamic regeneration of a soot layer deposited on a single layer Cordierite DPF. The experiments confirmed that the response to a simultaneous step change of the feed conditions (temperature, flow rate and oxygen concentration) leads to a transient temperature that exceeds the highest attained under stationary operation with either the initial or final operation conditions. The amplitude of the temperature excursion during step changes of the three feed conditions depended in a complex way on the location at which ignition occurred, when the step change was done and whether the step change was conducted after or before a moving front was established. A surprising finding was that the temperature rise following a simultaneous change of the three input variables was rather close to the sum of the three responses to a step change of only one of the three feed conditions.

Transversal moving-front patterns: Criteria and simulations for two-bed and cylindrical shell packed-bed reactors

We show that a moving-front solution in a cylindrical shell packed-bed catalyzing a first-order activated reaction may bifurcate into transversal patterns when Pe C / Pe T < Δ T ad / Δ T m , i.e. when the ratio of the mass to heat Pe numbers is smaller than the ratio of the adiabatic to maximal temperature rises. This coincides with the previous condition of transversal patterns to emerge in stationary fronts [ Pe C / Pe T < 1 [Viswanathan, G., Bindal, A., Khinast, J., Luss, D., 2005. Stationary transversal hot zones in adiabatic packed-bed reactors. A.I.Ch.E. Journal 51, 3028–3038]] and extends the bifurcations condition to the case of moving fronts. The novel condition cannot be satisfied in a downstream propagating front ( Δ T m / Δ T ad > 1 ) , but for an upstream propagating front (toward the cold reactor inlet) Δ T m / Δ T ad < 1 and the symmetry breaking can be obtained within a feasible domain of operating conditions ( Pe C / Pe T > 1 ). It was also assumed that the axial and the transversal Pe numbers vary consistently, i.e. κ C = Pe C ⊥ / Pe C = κ T = Pe T ⊥ / Pe T . A similar condition was also obtained using a simplified model composed of two 1-D beds with heat and mass exchange between them. Bifurcation diagram showing domains of transversal patterns is constructed using a learning two-bed model. These predictions are verified by direct numerical simulations of the continuous 2-D cylindrical shell model showing various types of moving transversal patterns within a feasible domain of the state parameters with Pe C > Pe T . In the case of varying ratio ( κ C ≠ κ T ) the pattern domain can be significantly extended toward larger Pe C / Pe T .

Coupling exothermic and endothermic reactions in adiabatic reactors

The steady state and the dynamic behavior of coupling exothermic and endothermic reactions in directly coupled adiabatic packed bed reactors (DCAR) are analyzed using one-dimensional pseudo-homogeneous plug flow model. Two different configurations of DCAR (simultaneous DCAR—SIMDCAR and sequential DCAR—SEQDCAR) are investigated. In SIMDCAR, the catalyst bed favors both exothermic and endothermic reactions and both reactions occur simultaneously. SEQDCAR has alternating layers of catalyst beds for exothermic and endothermic reactions and hence the exothermic and endothermic reactions occur in a sequential fashion. The performance of both reactors, in terms of conversion achieved and manifested hot spot behavior, is compared with that of the co-current heat exchanger type reactor. Various possible operational regimes in SIMDCAR have been classified and the conditions for the existence of hot spots or cold spots in SIMDCAR are obtained analytically for the first order reactions with equal activation energies. The reactor behavior for the reactions with non-equal activation energies is also presented. The preliminary criteria for the selection of suitable reactor type and the general bounds on the reaction parameters to obtain the desired conversion for endothermic reaction with minimal temperature rise are proposed. The dynamic behavior of these reactors is important for control applications and we have reported some of the transient behavior.