Adiabatic Reactor Research Articles

Mathematical Modelling and Simulation of a Trickle-Bed Reactor for Hydrotreating of Petroleum Feedstock

Abstract In this work, a model for a trickle-bed reactor for catalytic hydrotreating (HDT) of oil fractions is developed and simulations are performed to investigate its behavior. The model considers dynamic, one-dimensional plug-flow to describe a heterogeneous, adiabatic trickle-bed reactor. It takes into consideration the main reactions present in the HDT process: hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrodearomatization (HDA) with a reconstructed petroleum feedstock using a practical approach of generation of pseudo-components by dividing the boiling point curves of the feedstock. The model is solved using the method of lines with a finite difference scheme for discretization in the axial direction and simulations are performed for an industrial hydrotreating unit to evaluate the behavior of the system under different conditions and assumptions e. g. related to the linear gas velocity. A study of the dynamics is carried out to investigate the behavior of the system with a change in the sulfur compound concentration of the feed. In addition, a sensitivity analysis of the most relevant model parameters is performed.

A saturated feedforward/cascade controller for passive continuous reacting systems using entropy production shaping

A control scheme is proposed for adiabatic continuous chemical reactors using thermodynamic properties. This control scheme is inspired by the general advantages of cascade control and Passivity-based Control, using the internal entropy production as a storage function, leading to a transparent physical interpretation. The inner loop shapes the entropy production function (the potential that generates the dynamics) to guarantee stability, while the outer loop regulates process variables such as temperature, pressure, or conversion. The resulting control scheme is equivalent to a feedforward/PI control with control saturations, subject to the available potential and the bounds of the manipulated variable. The controller parameters are given by the physical properties of the system and only a single proportional parameter needs to be tuned to regulate a process variable to its desired value.

Dissipative boundary PI controller for an adiabatic plug-flow reactor with mass recycle

Abstract In this contribution we propose dissipation conditions using the second law of thermodynamics for a class of first order hyperbolic thermodynamic systems. The entropy function is used as a storage function and the internal entropy production as the dissipation function. The supply rate is found to be proportional to the difference of the entropy at the boundaries, and the time derivative of the entropy balance allows to define a PI controller with variable parameters designed using a cascade structure, which is applied to an adiabatic plug flow reactor with mass recycle, using the recycle rate as the manipulated variable. Finally, the controller is tested with numerical simulations tracking a desired yield.

A Novel Reactor Configuration for Industrial Methanol Production From the Synthesis Gas

In this work, the methanol synthesis on a commercial industrial catalyst in a novel cylindrical radial flow packed-bed reactor is investigated. The adiabatic and nonadiabatic cylindrical radial flow reactors were proposed and modeled in this research. The proposed configuration has been compared with conventional reactor for methanol production. It leads to higher methanol production and lower pressure drop, with the same catalyst consumption. Furthermore, the results show that the nonadiabatic radial flow packed-bed reactor has a higher methanol content compared with the adiabatic one. The improvement in methanol production was studied by optimizing the essential parameters such as inlet temperatures of the feed and cooling water as well as the number of cooling tubes. The nonlinearity and complexity of the reactor models make the traditional optimization methods ineffective and improbable. Therefore, the process was optimized by genetic algorithm (GA) method, which is one of the most powerful methods. The optimum values for the number of cooling tubes, feed and cooling water temperatures were 308, 507.6 K, and 522.43 K, respectively. The optimization results showed that a new reactor design could be proposed to reduce the cost of methanol synthesis.

Adiabatic magnesium hydride system for hydrogen storage based on thermochemical heat storage: Numerical analysis of the dehydrogenation

With hydrogen becoming more and more important as storage and carrier for renewable energy, there is an increasing need for flexible and efficient storage technologies. However, existing technologies, such as liquefaction or compression, often require a significant share of the hydrogens lower heating value. High-temperature metal hydrides (HT-MHs), such as magnesium hydride, are a promising alternative. Due to high operation temperatures, their application is challenging. A novel adiabatic hydrogen storage reactor based on the combination of a HT-MH with a thermochemical energy storage system (TCSS), such as Mg(OH)2/MgO + H2O, can be a solution. In this work, the previously published numerical simulations for hydrogen absorption are extended to the desorption process. A two-dimensional model for the hydrogen release was set up. The performance of the storage reactor is strongly dependent on the thermodynamic equilibrium of the reactions involved and less dependent on the reaction kinetics. Dehydrogenation is possible within 132 min, which is in the vicinity of the hydrogenation time. To enhance the dehydrogenation process, the water vapor pressure can be adjusted aiming for higher temperatures during the MgO hydration. Hydrogen can either be provided at constant pressure or constant mass flow rate.

Incorporation of hydrogen by-product from NaOCH3 production for methanol synthesis via CO2 hydrogenation: Process analysis and economic evaluation

A major problem regarding the production of methanol via the CO2 hydrogenation is the source of hydrogen that is still expensive and not economically sustainable. Utilization of hydrogen available as a by-product from other processes may resolve such issue. In this work; therefore, we evaluate the potentiality of incorporating the hydrogen by-product from the NaOCH3 production for the synthesis of methanol via hydrogenation of CO2, a greenhouse gas released from industry. Due to the limited availability of hydrogen from NaOCH3 production, a detailed analysis of kinetic in the reactor systems including, 1) the adiabatic fixed bed, 2) the isothermal multi-tube, and 3) the adiabatic fixed-bed reactors with an intercooler, are simulated using Aspen Plus in order to select the most appropriate reactor system that maximizes the conversion of hydrogen and CO2. The adiabatic fixed bed reactor appears the most appropriate since it consumes the highest amount of CO2, and shows the highest Profitability Index when compared to other reactor systems. In addition, methanol produced from this proposed process can provide a 16.4% reduction in the methanol feedstock required for the upstream process of NaOCH3 production.An analysis using Aspen Economic is also performed in this work which reveals that the saving cost generated from the recycle of methanol to the upstream process is almost comparable to the costs of construction and operation of the process of methanol synthesis. According to our useful sensitivity analysis, a methanol price as well as hydrogen and CO2 feed rates directly influenced the feasibility of the proposed process. The obtained result indicates that this proposed process is potentially feasible when 1) the price of methanol increases, and 2) the availability of hydrogen increases due to the increased NaOCH3 production capacity over than 1.5 times of the current scale.

Dehydration of Methylbutenes to Isoprene. Part 3: Comparative Mathematical Analysis of Methylbutene Dehydrogenation in Axial and Radial Reactors

A mathematical model of the process of dehydrogenation of methylbutenes to isoprene was used for comparative analysis of energetic efficiency of two versions of modernization: (1) a system of consecutively connected two axial reactors with a fixed catalyst beds, and (2) adiabatic radial reactor with fixed catalyst bed. The purpose was to determine the dependence of yield (Y) and selectivity (S) to the target product on the heat energyQsupplied with vapor. In the two-reactor system, the best parameters (Y= 53.1 % andS= 82.9 %) were achieved atQ= 9.0 MJ/kg and contact time t = 0.8 s. At the same time, in the radial reactor the best performance (Y= 42.0 % andS= 86.1 %) was observed atQ= 7.8 MJ/kg andt= 0.8 s. Hence, the radial reactor consumes less heat energy (by 13.0 %) than the radial reactor for methylbutene dehydrogenation.

Modeling of fixed bed reactor for coal tar hydrogenation via the kinetic lumping approach

Hydrogenation technology is an indispensable chemical upgrading process for converting the heavy feedstock into favorable lighter products. In this work, a new kinetic model containing four hydrocarbon lumps (feedstock, diesel, gasoline, cracking gas) was developed to describe the coal tar hydrogenation process, the Levenberg–Marquardt’s optimization algorithm was used to determine the kinetic parameters by minimizing the sum of square errors between experimental and calculated data, the predictions from model validation showed a good agreement with experimental values. Subsequently, an adiabatic reactor model based on proposed lumped kinetic model was constructed to further investigate the performance of hydrogenation fixed-bed units, the mass balance and energy balance within the phases in the reactor were taken into accounts in the form of ordinary differential equation. An application of the reactor model was performed for simulating the actual bench-scale plant of coal tar hydrogenation, the simulated results on the products yields and temperatures distribution along with the reactor are shown to be good consistent with the experimental data.

Mathematical modeling and simulation of an industrial adiabatic trickle-bed reactor for upgrading heavy crude oil by hydrotreatment process

The mathematical modeling of a trickle-bed reactor at particle and catalytic bed levels for the hydrodesulfurization and hydrodemetallization of heavy crude oil was carried out. The kinetic model parameters were estimated from experimental data. Thermodynamic and transport properties were calculated based on existing correlations and equations of state. Simulations of isothermal small scale and large scale adiabatic reactor were carried out and concentration and temperature profiles were obtained. It was demonstrated that temperature affects the catalyst utilization as the effectiveness factor is diminished at higher temperatures. Effectiveness factors undergo changes as reaction mixtures passes through catalytic bed describing different profiles for HDM and HDS.

Model-Based Catalyst Selection for the Oxidative Coupling of Methane in an Adiabatic Fixed-Bed Reactor

Adiabatic operation of catalytic fixed-bed reactors for oxidative coupling of methane (OCM) has been simulated using a detailed microkinetic and reactor model. For several catalysts (1%wt Sr/La2O3,...

System analysis of the ethylbenzene dehydrogenation reactor as a control object

Catalytic dehydrogenation of ethylbenzene charge in a two-stage continuous-action adiabatic reactor is the main stage of the styrene production process. The analysis of this technological process existing automated control systems revealed the following main drawback, that these systems require great efforts from production personnel to ensure a change of the reactor temperature regime in the stages of the reactor in accordance with styrene concentration drop, which is caused by deactivation catalytic layer deactivation. Therefore, the synthesis of the target product concentration at the reactor outlet predictive control system is actual task in the field of technical cybernetics. This article presents the system analysis results of the dehydrogenation reactor as a control object. The main research result is a method choice for controlling of the chemical transformations temperature regime in the reactor, using that, it is possible to increase the energy efficiency and productivity of this device. The general and specific tasks of the control system synthesis are formulated on the basis of the system analysis, the information and functional synthesis of the temperature regime ACS is produced, the information and functional schemes of the reactor unit process equipment control subsystems are developed. As an operating system ACS is selected, which realizes of steam-ethylbenzene mixture temperature change at the reaction zones entrances of the 1st and 2nd reactor sections in accordance with the program control algorithm on the basis of predicting models, describing the heat exchange processes occurring inside the reactor stages as well as the dynamics of changes in such parameters as the concentration of coke deposits, catalyst activity, the basic and by- products concentration of chemical reactions.

B-spline Wavelet Method for Solving Fredholm Hammerstein Integral Equation Arising from Chemical Reactor Theory

AbstractMathematical model for an adiabatic tubular chemical reactor which processes an irreversible exothermic chemical reaction has been considered. For steady state solution for an adiabatic tubular chemical reactor, the model can be reduced to ordinary differential equation with a parameter in the boundary conditions. Again the ordinary differential equation has been converted into a Hammerstein integral equation which can be solved numerically. B-spline wavelet method has been developed to approximate the solution of Hammerstein integral equation. This method reduces the integral equation to a system of algebraic equations. The numerical results obtained by the present method have been compared with the available results.

Catalyst ignition and extinction: A microkinetics-based bifurcation study of adiabatic reactors for oxidative coupling of methane

Understanding ignition and extinction behavior is of crucial importance for oxidative coupling of methane (OCM). Therefore, for the first time the bifurcation behavior of OCM has been investigated while considering both homogeneous gas phase reactions and heterogeneous reactions using a detailed microkinetic model. Three different adiabatic reactor models are considered: a plug flow reactor (PFR), a continuously stirred tank reactor (CSTR) and a lumped thermal reactor (LTR) model. The latter represents the limiting case with zero backmixing (cf. PFR behavior) for species and perfect thermal backmixing (cf. CSTR behavior). For homogeneous processes this reactor type could for example be realized by adding a high thermal conductivity inert to the reactor tubes, for catalytic processes a high thermal conductivity catalyst could be used.The bifurcation behavior in these reactor types is compared with a focus on methane conversion, C2 yields and their dependence on operating conditions such as inlet composition, inlet temperature and space time. Steady state multiplicity is observed for adiabatic CSTR and LTR models. This multiplicity of steady states is not observed for isothermal reactor models, indicating that it is caused solely by thermal backmixing and is not related to chemical feedback features such as autocatalysis. The start-up procedures or initial conditions determine the actual steady state that is obtained. Among the three investigated reactor types, a LTR shows the highest product yields and the lowest extinction temperatures, which allows autothermal operation at a much lower inlet temperature compared to a PFR and CSTR. For OCM without catalyst, autothermal operation on the ignited branch at ambient inlet temperatures and reasonable space times is only possible by using methane-to-oxygen ratios below 3 leading to low selectivities. For catalytic OCM compared to OCM without catalyst, the range for autothermal operation is much broader and it is much easier to find feasible operating conditions allowing autothermal operation at ambient inlet temperatures.By operating a LTR on the ignited branch at ambient inlet temperature of 300 K, methane-to-oxygen ratio CH4:O2 = 6, space time V/FCH4,0 = 0.02 s, bulk density of Sn-Li/MgO = 1000 kgcat/m3 and pressure P = 1 bar, overall C2 selectivities (i.e. sum of ethane, ethylene and acetylene selectivity) of 80% can be obtained at methane conversions as high as 30%.

Feasibility of CaO/CuO/NiO sorption-enhanced steam methane reforming integrated with solid-oxide fuel cell for near-zero-CO2 emissions cogeneration system

In this article, a process for sorption-enhanced steam methane reforming in an adiabatic fixed-bed reactor coupled with a solid oxide fuel cell (SOFC) is evaluated using a 1D numerical reactor model combined with a simplified fuel cell simulation. A novel material comprising CaO/CuO/Al2O3(NiO) pellets is considered. Three operating stages are considered in the proposed system, namely (i) CaO carbonation/reforming, (ii) Cu and Ni oxidation, and (iii) CaCO3 calcination/CuO and NiO reduction. The operating conditions that enable cyclic operation of these stages and the strategy needed to switch between each stage are evaluated. Under the adopted control strategy, methane conversion was about 95%, whilst H2 yield and purity were around 3.2 molH2 molCH4−1 and 90%, respectively. Moreover, a concentrated CO2 stream ready for storage was obtained. By using a portion of the produced H2 to make the process self-sufficient from an energy standpoint, an equivalent H2 yield and a reforming efficiency of about 2.8 molH2 molCH4−1 and 84% were achieved, respectively. With respect to SOFC integration, net power and thermal energy generation of around 11 kW and 6 kW, respectively, can be achieved. With respect to the chemical energy of the inlet methane, the net electrical and thermal efficiencies of the considered process are 56% and 30%, respectively, i.e., the overall efficiency of the entire system is 86%. The proposed cogeneration system showed better thermodynamic, environmental and economic performances than those of conventional systems, with an investment pay-back period of 2.2 years in the worst-case scenario. The levelised cost of electricity, of heat and total power were about 0.096 € kW h−1, 0.19 € kW h−1, and 0.065 € kW h−1, respectively, while the CO2 emissions were avoided at no cost.

Development of Two Novel Processes for Hydrogenation of CO2 to Methanol over Cu/ZnO/Al2O3 Catalyst to Improve the Performance of Conventional Dual Type Methanol Synthesis Reactor

Conventional methanol synthesis process (CR configuration) consists of water-cooled and gas-cooled reactors in which methanol and water are condensed inside the gas-cooled reactor which deactivates the catalyst. In this study, two novel configurations (AW and ACW configurations) are represented to address this problem in which the gas-cooled reactor is replaced with adiabatic reactor. Moreover, a condenser is applied between adiabatic and water-cooled reactors in ACW configuration. Results show that temperature increases somewhat along the adiabatic reactor that prevents gas condensate formation. Besides, the adiabatic reactor maximum temperature is less than that of first reactor in CR configuration which prevents copper based catalyst thermal sintering. Moreover, a high cross section-to-length ratio of the adiabatic reactor leads to negligible pressure drop along the reactor and improvement in CO2 conversion to methanol that has positive environmental effects. Also, water mole fraction decreases along the reactors of AW and ACW configurations to prevent the deactivation of catalyst active sites. Eventually, methanol production rates by AW and ACW configurations are improved around 25.5% and 43.1% in comparison with CR configuration. So, novel AW and ACW configurations provide many benefits including improvement in catalyst activity and durability, CO2 conversion, and the methanol production rate.

Coupling exothermic and endothermic reactions—Application to combined aniline production/methyl‐cyclohexane dehydrogenation

AbstractThe scope of this study is to emphasize the possibility and benefits of direct coupling of exothermic and endothermic reactions. Simultaneous production of aniline by exothermic nitrobenzene hydrogenation and endothermic dehydrogenation of methyl‐cyclohexane to toluene is investigated. Instead of multitubular reactor, the reaction is carried out in an adiabatic reactor eliminating the requirement of complex setup of the hydrogenation reactor. Additionally, large amount of hydrogen needed to avoid reaction runaway is no longer needed. Nonlinear analysis of reactor–separation–recycle shows difficulty in controlling integrated plants where unreacted reactant is recycled. Details of the plant design, obtained by Aspen Plus simulation, are given. The new integrated system is feasible with the benefits of simple reactor and reduce hydrogen requirement. Economic analysis shows that the total annual cost of coupled system is reduced by 20%. The results obtained here are also applicable to other chemical processes of practical relevance.

Production process of di-amyl ether and its use as an additive in the formulation of aviation fuels

This work deals with the production of a high added value ether used as additive in aviation fuel. The ether was synthesized from the iso-amylenes present in the C5, the five-carbon isomer cuts in petroleum distillates and the iso-amyl alcohol found in the fusel oil of the alcohol industry. Qualitative analyses like mass spectrometry and nuclear proton magnetic resonance spectroscopy confirmed the formation and structure of the proposed semi-renewable ether, the high molecular weight di-amyl ether (DAE). Optimization of the reaction parameters resulted in a conversion of the 48%, molar fraction, iso-amylenes when using an adiabatic profile reactor. By using this ether production and purification process, the final product showed 98% w/w of purity. The synthesized di-amyl ether presented physicochemical properties similar to the commercial aviation kerosene. The physicochemical properties evaluation performed in the mixtures of di-amyl ether in aviation kerosene showed relevant improvements, such as reduction of the freezing point and increase of the oxidation reaction rate. The results showed this novel fuel has great potential to be used in gas propulsion turbines in commercial flights and is also strategic for military aircraft.

Numerical Analysis of Hydrogen Sulphide Conversion to Hydrogen during Its Pyrolysis and Partial Oxidation

Production of hydrogen during pyrolysis and partial oxidation of hydrogen sulphide is analyzed on the basis of a detailed kinetic model of H2S oxidation. It is shown that the H2 yield in the case of H2S pyrolysis in an adiabatic flow reactor with a residence time of ≈1 s is rather small. Even for the initial temperature of the mixture T0 = 1400 K, the molar fraction of H2 is only 12%, though the equilibrium value is reached within the reactor in this case. At T0 φb and low values of T0 is essentially nonequilibrium; as a result, the H2 concentration at the exit from a finite-length reactor can be higher than its equilibrium value, e.g., the relative yield of H2 can exceed the equilibrium value by 30–40% at T0 = 800 K and φ = 6–10. The reasons responsible for reaching a “superequilibrium” concentration of H2 at the flow reactor exit are determined.

A detailed reaction mechanism for oxidative coupling of methane over Mn/Na2WO4/SiO2 catalyst for non-isothermal conditions

Direct production of ethylene from natural gas or other methane sources has proven to be challenging from catalytic, process design and economic perspectives, with no reports of a commercially viable process to date. Understanding of the underlying non-ideal homogeneous and heterogeneous reactions involved could lead to success, enabling utilization of vast natural gas resources as a replacement for petrochemicals. In this regards, an improved reaction mechanism and computational model, validated experimentally, for oxidative coupling of methane (OCM) over a Mn/Na2WO4/SiO2 catalyst is developed, taking into account the non-isothermal behavior exhibited by the gas and surface reactions. The reaction mechanism involves detailed gas-phase and surface elementary steps to describe the OCM chemistry and employing a reduced model for computational efficiency. The model uses laboratory-scale packed-bed reactor experiments for kinetic mechanism development. The modeling and simulation is particularly focused on a one-dimensional packed-bed reactor. The kinetic model is validated over a wide range of experimental conditions. The model-predicted results and their comparisons with the experimental data are presented wide temperature ranges and methane-to-oxygen feed ratios under adiabatic reactor conditions. The kinetic model is first of its kind in which non-isothermal OCM kinetic behavior is captured using detailed gas-phase and heterogeneous reaction kinetics.

Bifurcation analysis of methane oxidative coupling without catalyst

We present a detailed bifurcation analysis of methane oxidative coupling in the gas phase using a global kinetic model for the various oxidation, reforming and dehydrogenation reactions. The kinetic model satisfies the thermodynamic constraints and is validated with literature data as well as new data obtained under near isothermal conditions. It is used to determine the methane conversion and C2-products selectivity under various feed and operating conditions in large scale ideal adiabatic reactors. It is found that at higher CH4/O2 ratios (e.g. >4), ignition and extinction points exist only at either high feed temperatures and/or space times, which may not be of practical interest. Autothermal operation on the ignited branch with feed at near ambient conditions (∼300K and 1 bar) is feasible for practical range of space times (1 ms–1 s) only for low CH4/O2 ratios (e.g. 1.7–2.5), which includes the flammability range. Further, the best ethylene yields are obtained on the ignited branch close to the extinction point while best C2 yields may be obtained at higher space times or feed temperatures. Feeds with a high CH4/O2 ratio lead to higher selectivity of C2H4 but lower methane conversion and require higher inlet temperatures. The ratio C2H4/C2H2 decreases as the methane conversion increases or CH4/O2 ratio decreases. While oxidation (exothermic) chemistry dominates on the ignited branch near the extinction point, the dehydrogenation and reforming (endothermic) chemistries dominate as the space time or feed temperature is increased. It is shown that the highest yield of intermediate products and largest region of autothermal operation is obtained for an ideal reactor with perfect thermal back-mixing and zero species back-mixing (lumped thermal reactor model).