Presence Of Catalyst Deactivation Research Articles

Model of an industrial multitubular reactor for methanol to formaldehyde oxidation in the presence of catalyst deactivation

In the present work, a first-principles model of methanol partial oxidation to formaldehyde in an industrial reactor was developed and the reaction kinetic and deactivation parameters estimated, taking advantage of the temperature profile established by the exothermic reaction. The catalyst deactivation was assigned primarily to hot-spot regions in the oxidation reactor. The exposure to high temperatures enhances solid-state reactions that produce volatile compounds and a consequential loss of catalyst active compounds that migrate downstream from the hot-spot. This phenomenon was modelled implementing a new method where, instead of time, the deactivation was integrated as a function of the total consumed reagent until the instant of interest. This approach allowed computing the activity of the catalyst at any instant without needing to solve the model for the whole operating history until the pertinent instant; for simulating industrial reactors, where the operating conditions are changing frequently, this feature is quite relevant.

Dynamic Optimization of Lurgi Type Methanol Reactor Using Hybrid GA-GPS Algorithm: The Optimal Shell Temperature Trajectory and Carbon Dioxide Utilization

At present, methanol is mostly produced from syngas, derived from natural gas through steam methane reforming (SMR). In a typical methanol production plant, unreacted syngas is recycled for mixing with natural gas and both used as fuel in the reformer furnace resulting in carbon dioxide (CO2) emissions from the flue gases emitted into the atmosphere. However, CO2 can be captured and utilized as feedstock within the methanol synthesis process to enhance the productivity and efficiency. To do so, dynamic optimization approaches to derive the ideal operating conditions for a Lurgi type methanol reactor in the presence of catalyst deactivation are proposed to determine the optimal use of recycle ratio of CO2 and shell coolant temperature without violating any process constraints. In this context, this study proposes a new approach based on a hybrid algorithm combining genetic algorithm (GA) and generalized pattern search (GPS) derivative-free methodologies to provide a sufficiently good solution to this dynam...

Membrane/sorption-enhanced methanol synthesis process: Dynamic simulation and optimization

In this study, a dynamic mathematical model of a Membrane-Gas-Flowing Solids-Fixed Bed Reactor (Membrane-GFSFBR) with in-situ water adsorption in the presence of catalyst deactivation is proposed for methanol synthesis. The novel reactor consists of water adsorbent and hydrogen-permselective Pd-Ag membrane. In this configuration feed gas and flowing adsorbents are both fed into the outer tube of the reactor. Contact of gas and fine solids particles inside packed bed results in selective adsorption of water from methanol synthesis which leads to higher methanol production rate. Afterwards, the high pressure product is recycled to the inner tube of the reactor and hydrogen permeates to the outer tube which shifts the reaction towards more methanol production. Dynamic simulation result reveals that simultaneous application of water adsorbent and hydrogen permeation in methanol synthesis process contributes to a significant enhancement in methanol production. The notable advantage of Membrane-GFSFBR is the continuous adsorbent regeneration during the process. Moreover, a theoretical investigation has been performed to evaluate the optimal operating conditions and to maximize the methanol production in Membrane-GFSFBR using differential evolution (DE) algorithm as a robust method. The obtained optimization result shows there are optimum values of inlet temperatures of gas phase, flowing solids phase, and shell side under which the highest methanol production can be achieved.

Dynamic optimal analysis of a novel cascade membrane methanol reactor by using genetic algorithm (GA) method

The potential of a novel cascade membrane methanol reactor (CMMR) in the presence of catalyst deactivation has been investigated by Rahimpour and Bayat [Int J Energy Res 34(15):1356–1371, 2010]. In the present paper, this novel configuration is optimized using genetic algorithm strategy, dynamically. In the first approach, optimum inlet molar flow rate, the inlet pressure of the tube and shell side for both reactors, the temperatures of feed (cooling gas) and cooling saturated water have been obtained within their practical ranges. In the second approach, a stepwise trajectory has been followed in order to determine the optimal profiles for saturated water and gas temperatures in three steps during operation. The objective of each optimization case is to maximize the methanol production rate. Here, genetic algorithms have been used as powerful methods for optimization of complex problems. The optimization results represent 19.67 and 25.63 % enhancement in the methanol production for first and second optimization approaches, respectively.

The aromatic enhancement in the axial‐flow spherical packed‐bed membrane naphtha reformers in the presence of catalyst deactivation

AbstractBecause of some disadvantages of conventional tubular reactors (CTRs), the concept of spherical membrane reactors is proposed as an alternative. In this study, it is suggested to apply hydrogen perm‐selective membrane in the axial‐flow spherical packed‐bed naphtha reformers. The axial flow spherical packed‐bed membrane reactor (AF‐SPBMR) consists of two concentric spheres. The inner sphere is supposed to be a composite wall coated by a thin Pd‐Ag membrane layer. Set of coupled partial differential equations are developed for the AF‐SPBMR model considering the catalyst deactivation, which are solved by using orthogonal collocation method. Differential evolution optimization technique identifies some decision variables which can manipulate the input parameters to obtain the desired results. In addition to lower pressure drop, the enhancement of aromatics yield by the membrane layer in AF‐SPBMR adds additional superiority to the spherical reactor performance in comparison with CTR. © 2011 American Institute of Chemical Engineers AIChE J, 2011

Methanol synthesis in a novel axial-flow, spherical packed bed reactor in the presence of catalyst deactivation

Since in the foreseeable future liquid hydrocarbon fuels will play a significant role in the transportation sector, methanol might be used potentially as a cleaner and more reliable fuel than the petrochemical-based fuels in the future. Consequently, enhancement of methanol production technology attracts increasing attention and, therefore, several studies for developing new methanol synthesis reactors have been conducted worldwide. The purpose of this research is to reduce the pressure drop and recompression costs through the conventional single-stage methanol reactor. To reach this goal, a novel axial-flow spherical packed bed reactor (AF-SPBR) for methanol synthesis in the presence of catalyst deactivation is developed. In this configuration, the reactor is loaded with the same amount of catalyst in the conventional single-stage methanol reactor. The reactants are flowing axially through the reactor. The dynamic simulation of the spherical reactors has been studied in the presence of long-term catalyst deactivation for four reactor configurations and the results are compared with the achieved results of the conventional tubular packed bed reactor (CR). The results show that the three and four stages reactor setups can improve the methanol production rate by 4.4% and 7.7% for steady state condition. By utilizing the spherical reactors, some drawbacks of the conventional methanol synthesis reactors such as high pressure drop, would be solved. This research shows how this new configuration can be useful and beneficial in the methanol synthesis process.

Modeling of an axial flow, spherical packed-bed reactor for naphtha reforming process in the presence of the catalyst deactivation

Improving the octane number of the aromatics’ compounds has always been an important matter in refineries and lots of investigations have been made concerning this issue. In this study, an axial -flow spherical packed-bed reactor (AF-SPBR) is considered for naphtha reforming process in the presence of catalyst deactivation. Model equations are solved by the orthogonal collocation method. The AF-SPBR results are compared with the plant data of a conventional tubular packed-bed reactor (TR). The effects of some important parameters such as pressure and temperature on aromatic and hydrogen production rates and catalyst activity have been investigated. Higher production rates of aromatics can successfully be achieved in this novel reactor. Moreover, results show the capability of flow augmentation in the proposed configuration in comparison with the TR. This study shows the superiority of AF-SPBR configuration to the conventional types.

Dynamic optimization of a multi-stage spherical, radial flow reactor for the naphtha reforming process in the presence of catalyst deactivation using differential evolution (DE) method

In the present research, differential evolution (DE) method has been used to optimize the operating conditions of a radial flow spherical reactor containing the naphtha reforming reactions. In this reactor configuration, the space between the two concentric spheres is filled by catalyst. The dynamic behavior of the reactor has been taken into account in the optimization process. The achieved mass and energy balance equations in the model are solved by orthogonal collocation method. The goal of this optimization is to maximize the hydrogen and aromatic production which leads to the maximum consumption of the paraffins and naphthenes. In order to reach this end, the inlet temperature of the gas at the entrance of each reactor, the total pressure of the process, as well as the catalyst distribution in each reactor have been optimized using the differential evolution (DE) method. The results of the optimization of the spherical reactor have been compared with the non-optimized spherical reactor. The comparison shows acceptable enhancement in the performance of the reactor.

Comparison of two different flow types on CO removal along a two-stage hydrogen permselective membrane reactor for methanol synthesis

Carbon monoxide (CO) is a gaseous pollutant with adverse effects on human health and the environment. Industrial chemical processes contribute significantly to CO accumulation in the atmosphere. One of the most important processes for controlling carbon monoxide emissions is the conversion of CO to methanol by catalytic hydrogenation. In this study, the effects of two different flow types on the rate of CO removal along a two-stage hydrogen permselective membrane reactor have been investigated. In the first configuration, fresh synthesis gas flows in the tube side of the membrane reactor co-currently with reacting material in the shell side, so that more hydrogen is provided in the first sections of the reactor. In the second configuration, fresh synthesis gas flows in the tube side of the membrane reactor counter-currently with reacting material in the shell side, so that more hydrogen is provided in the last sections of the reactor. For this membrane system, a one-dimensional dynamic plug flow model in the presence of catalyst deactivation was developed. Comparison between co-current and counter-current configurations shows that the reactor operates with higher conversion of CO and hydrogen permeation rate in the counter-current mode whereas; longer catalyst life is achieved in the co-current configuration. Enhancement of CO removal in the counter-current mode versus the co-current configuration results in an ultimate reduction in CO emissions into the atmosphere.

A novel dynamic radial-flow, spherical-bed reactor concept for naphtha reforming in the presence of catalyst deactivation

In this work a novel radial-flow, spherical packed bed reactor (RF-SPBR) for naphtha reforming in the presence of catalyst deactivation, has been proposed. In this reactor configuration, the space between the two concentric spheres is filled by catalyst. The reactants are flowing through the outer surface to the inner sphere. The dynamic simulation of spherical reactors has been studied in the presence of long-term catalyst deactivation. Model equations were solved by the orthogonal collocation method. Further, the performance of the spherical reactors was compared with conventional axial-flow, tubular packed bed reactors (AF-TPBR). The theoretical investigations on the effect of the important parameters, pressure and temperature, on aromatic and hydrogen production and catalyst activity have been investigated. This spherical reactor configuration solves some drawbacks of conventional naphtha reforming reactors such as pressure drop. This work shows how spherical reactor can be useful for catalytic naphtha reforming.

Dynamic optimization of a novel radial-flow, spherical-bed methanol synthesis reactor in the presence of catalyst deactivation using Differential Evolution (DE) algorithm

In this work, a novel radial-flow spherical-bed methanol synthesis reactor has been optimized using Differential Evolution (DE) algorithm. This reactor's configuration visualizes the concentration and temperature distribution inside a radial-flow packed bed with a novel design for improving reactor performance with lower pressure drop. The dynamic simulation of spherical multi-stage reactors has been studied in the presence of long-term catalyst deactivation. A theoretical investigation has been performed in order to evaluate the optimal operating conditions and enhancement of methanol production in radial-flow spherical-bed methanol synthesis reactor. The simulation results have been shown that there are optimum values of the reactor inlet temperatures, profiles of temperatures along the reactors and reactor radius ratio to maximize the overall methanol production. The optimization methods have enhanced additional yield throughout 4 years of catalyst lifetime, respectively.

Enhancement of methanol production in a novel fluidized-bed hydrogen-permselective membrane reactor in the presence of catalyst deactivation

In this study, a dynamic model for a novel bubbling fluidized-bed membrane dual-type methanol reactor has been developed in the presence of long-term catalyst deactivation. The proposed model has been used to compare the performance of a novel fluidized-bed membrane dual-type methanol reactor (FMDMR) with membrane dual-type methanol reactor (MDMR) and conventional dual-type methanol reactor (CDMR). In this new concept, the feed synthesis gas is preheated in the tubes of the gas-cooled reactor and flowing in a counter-current mode with reacting gas mixture in the shell side. Due to the hydrogen partial pressure driving force, hydrogen can penetrate from feed synthesis gas into the reaction side through the membrane. The outlet synthesis gas from this reactor is fed to tubes of the water-cooled packed-bed reactor and the chemical reaction is initiated by the catalyst. The methanol-containing gas leaving this reactor is directed into the shell of the gas-cooled reactor and the reactions are completed in this fluidized-bed side. This reactor configuration solves some observed drawbacks of new conventional dual-type methanol reactor such as pressure drop, internal mass transfer limitations, radial gradient of concentration and temperature in gas-cooled reactor. The proposed dynamic model has been validated against measured daily process data of a methanol plant recorded for a period of four years and a good agreement has been achieved. The simulation results show there is a favorable profile of temperature and activity along the fluidized-bed membrane dual-type reactor relative to membrane and conventional dual-type reactor systems. Therefore, the performance of methanol reactor system improves when membrane assisted fluidized-bed concept is used for conventional dual-type reactor system.

Enhancement of hydrogen production in a novel fluidized-bed membrane reactor for naphtha reforming

In this work, a novel fluidized-bed membrane reactor (FBMR) for naphtha reforming in the presence of catalyst deactivation has been proposed. In this reactor configuration, a fluidized-bed reactor with perm-selective Pd–Ag (23 wt% Ag) wall to hydrogen has been used. The reactants are flowing through the tube side which is a fluidized-bed membrane reactor while hydrogen is flowing through the shell side which contains carrier gas. Hydrogen penetrates from fluidized-bed side into the carrier gas due to the hydrogen partial pressure driving force. Hydrogen permeation through membrane leads to shift the reaction toward the product according to the thermodynamic equilibrium. This membrane-assisted fluidized-bed reactor configuration solves some drawbacks of conventional naphtha reforming reactors such as pressure drop, internal mass transfer limitations and radial gradient of concentration and temperature. In FBMR the hydrogen which is produced in shell side is a valuable gas and can be used for different purposes. The two-phase theory of fluidization is used to model and simulate the FBMR. Industrial packed bed reactor (PBR) for naphtha reforming is used as a basis for comparison. This comparison shows enhancement in the yield of aromatic production in FBMR for naphtha reforming. Although using FBMR reduces hydrogen mole fraction in reaction side and enhances catalyst deactivation due to coking, but this effect can be compensated using advantages of FBMR such as suitable hydrogen to hydrocarbon molar ratio, lowering deactivation rate due to lower temperature, control of permeation rate by adjusting shell side pressure and shifting the equilibrium reactions. The impacts of hydrogen to hydrocarbon molar ratio, pressure, membrane thickness, flow rate and temperature have been investigated in this work.

Dynamic optimization of membrane dual-type methanol reactor in the presence of catalyst deactivation using genetic algorithm

This paper presents a study on optimization of a membrane dual-type methanol reactor in the presence of catalyst deactivation. A theoretical investigation has been performed in order to evaluate the optimal operating conditions and enhancement of methanol production in a membrane dual-type methanol reactor. A mathematical heterogeneous model has been used to simulate and compare the membrane dual-type methanol reactor with conventional methanol reactor. An auto-thermal dual-type methanol reactor is a shell and tube heat exchanger reactor which the first reactor is cooled with cooling water and the second one is cooled with synthesis gas. In a membrane dual-type reactor the wall of the tubes in the gas-cooled reactor is covered with a pd–Ag membrane, which is only hydrogen-permselective. The simulation results have been shown that there are optimum values of reacting gas and coolants temperatures to maximize the overall methanol production. Here, genetic algorithms have been used as powerful methods for optimization of complex problems. In this study, the optimization of the reactor has been investigated in two approaches. In the first approach, the optimal temperature profile along the reactor has been studied and then a stepwise approach has been followed to determine the optimal profiles for saturated water and gas temperatures in three steps during the time of operations to maximize the methanol production rate. The optimization methods have enhanced 5.14% and 5.95% additional yield throughout 4 years of catalyst lifetime for first and second optimization approaches, respectively.

A Novel Radial‐Flow, Spherical‐Bed Reactor Concept for Methanol Synthesis in the Presence of Catalyst Deactivation

AbstractA radial‐flow, spherical‐bed reactor concept for methanol synthesis in the presence of catalyst deactivation, has been proposed. This reactor configuration visualizes the concentration and temperature distribution inside a radial‐flow packed bed with a novel design for improving reactor performance with lower pressure drop. The dynamic simulation of spherical multi‐stage reactors has been studied in the presence of long‐term catalyst deactivation. Model equations were solved by the orthogonal collocation method. The performance of the spherical multi‐stage reactors was compared with a conventional single‐type tubular reactor. The results show that for this case study and with similar reactor specifications and operating conditions, the two‐stage spherical reactor is better than other alternatives such as single‐stage spherical, three‐stage spherical and conventional tubular reactors. By increasing the number of stages of a spherical reactor, one increases the quality of production and decreases the quantity of production.

A membrane catalytic bed concept for naphtha reforming in the presence of catalyst deactivation

In this work, theoretical investigation has been used to evaluate the performance, optimal operating conditions and increasing the aromatic production in a Pd–Ad membrane reactor for catalytic naphtha reforming. A reactor configuration has been used with perm-selective Pd–Ag (23 wt% Ag) wall to hydrogen. The reactants are flowing through the tube side and hydrogen is flowing through the shell side. Hydrogen penetrates from reaction side into the carrier gas due to the hydrogen partial pressure driving force. Hydrogen permeation through membrane leads to shift the reaction towards the product side according to the thermodynamic equilibrium. In this study the theoretical investigation on the effects of pressure, membrane thickness, temperature, H 2/HC ratio and flow rate has been investigated. The changes of aromatic production, H 2/HC mole ratio, temperature, catalyst activity and comparison of equilibrium conversion and reactor model have been shown in this research. Also changing in parameters such as temperature, catalyst activity, components mole fractions and the production or consumption rates of species in industrial case have been demonstrated. This work shows how membrane reactor can be useful for catalytic naphtha reforming by enhancement of aromatic production, increase of catalyst activity and hydrogen separation.

Application of hydrogen-permselective Pd-based membrane in an industrial single-type methanol reactor in the presence of catalyst deactivation

This work presents application of palladium-based membranes in a conventional single-type methanol reactor. A novel reactor configuration with hydrogen-permselective Pd and Pd–Ag membrane are proposed. In this configuration the reacting synthesis gas is fed to the shell side of reactor while the high pressure product is routed from recycle stream through tubes of the reactor in a co-current mode with reacting gas. The reacting gas is cooled simultaneously with recycle gas in tube and saturated water in outer shell. The permselective palladium layer on inner tube allows hydrogen to penetrate from the tube side to the reaction side. In this work, the results of two types of novel membrane reactors are compared with a conventional methanol synthesis reactor at identical process conditions. Also the effect of key parameters such as membrane thickness, reaction and tube side pressure, ratio of tube side flow rate to reaction side flow rate on performance of reactor are investigated. The steady-state and quasi-steady-state simulations results show that there are favorable profiles of temperature and methanol mole fraction along the reactor in proposed reactor relative to conventional reactor system. Therefore using this novel configuration in industrial single-type methanol reactor improves methanol production rate.

Dynamic Simulation and Optimization of a Dual‐Type Methanol Reactor Using Genetic Algorithms

AbstractIn this investigation, a dynamic simulation and optimization for an auto‐thermal dual‐type methanol synthesis reactor was developed in the presence of catalyst deactivation. Theoretical investigation was performed in order to evaluate the performance, optimal operating conditions, and enhancement of methanol production in an auto‐thermal dual‐type methanol reactor. The proposed reactor model was used to simulate, optimize, and compare the performance of a dual‐type methanol reactor with a conventional methanol reactor. An auto‐thermal dual‐type methanol reactor is a shell‐and‐tube heat exchanger reactor in which the first reactor is cooled with cooling water and the second one is cooled with synthesis gas. The proposed model was validated against daily process data measured of a methanol plant recorded for a period of 4 years. Good agreement was achieved. The optimization was achieve by use of genetic algorithms in two steps and the results show there is a favorable profile of methanol production rate along the dual‐type reactor relative to the conventional‐type reactor. Initially, the optimal ratio of reactor lengths and temperature profiles along the reactor were obtained. Then, the approach was followed to get an optimal temperature profile at three periods of operation to maximize production rate. These optimization approaches increased by 4.7 % and 5.8 % additional yield, respectively, throughout 4 years, as catalyst lifetime. Therefore, the performance of the methanol reactor system improves using optimized dual‐type methanol reactor.

On the dynamical instability of packed-bed reactors in the presence of catalyst deactivation

Due to the thermal instability of the packed-bed reactor running an exothermic reaction, unsteady-state operation (for example a fluctuating inflow temperature) can result in a variety of thermal responses. These include the amplification of input temperature perturbations and high-temperature pre-extinction waves. Catalyst deactivation adds further dynamical features to these scenarios. We explore them numerically, using a first-order exothermic reaction and a pseudo-homogeneous (single phase) model of the PBR together with a first-order deactivation model of the catalyst. At low deactivation rate, moving hot spots are found, as well as a non-uniform activity profile of the catalyst. At high deactivation rate, however, high-temperature waves (so-called pre-extinction waves) are followed by the complete extinction of the reactor. The amplification of input temperature perturbations is generally enhanced by the presence of catalyst deactivation. Finally, a power-law model is derived numerically that predicts the resonance frequency for amplification as a function of operating parameters.

Differential Flow Instability in Packed-bed Reactors in the Presence of Catalyst Deactivation

Differential Flow Instability in Packed-bed Reactors in the Presence of Catalyst Deactivation