Optimization of the reactor–regenerator system with catalytic parallel–consecutive reactions

The system with moving deactivating catalyst, composed of a cocurrent tubular reactor and a catalyst regenerator with an additional flux of a fresh catalyst, has been investigated. For the temperature dependent catalyst deactivation, the optimization problem has been formulated in which a maximum of a process profit flux is achieved by a best choice of temperature profile along tubular reactor, best catalyst recycle ratio and best catalyst activity after regeneration. The set of parallel–consecutive reactions, A+B→R and R+B→S, with desired product R has been taken into account. A relatively unknown, powerful discrete algorithm in which a suitably defined Hamiltonian is constant along the optimal path, has been applied for optimization. The optimal solutions have been discussed. In particular, it has been shown that an increase of the unit cost of catalyst regeneration or an increase of the catalyst recycle ratio causes such optimal temperatures in reactor which save the catalyst, as the optimal temperature profiles are then shifted towards lower temperatures. Finally these profiles reach isothermal shape at the level of minimum allowable temperature and then there is no further possibility to control the reactor process by the temperature profile. Thus the catalyst activity after regeneration, as well as an average catalyst activity in the reactor do decrease when the unit catalyst regeneration cost increases. This is a new form of catalyst saving, as the catalyst deactivation rate becomes reduced when an average catalyst activity is allowed to decrease. It is important that this form of catalyst saving appears in the region where any saving of the catalyst by an optimal choice of temperature profile is impossible. It has been also shown that for small values of the catalyst recycle ratio, the catalyst regenerator should be removed from the system. In such a case, the renewal of catalyst takes place due to a fresh catalyst input, exclusively.     

RESIDENCE TIME DISTRIBUTIONS IN A JETLOOP REACTOR

The effect of residence time, jet position, jet size, catalyst mass and temperature on the recycle ratio in a jetloop reactor using a residence time distribution model is reported. The recycle ratio goes through a maximum as residence time changes. The recycle ratio increases as jet size, catalyst mass and temperature are reduced. The optimum position of the jet is between 0 and 5 mm above the top of the central draft tube.     

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 pseudo-dynamic optimization of a dual-stage methanol synthesis reactor in the face of catalyst deactivation

This paper presents an optimization investigation on methanol synthesis reactor in the face of catalyst deactivation using multi-objective genetic algorithms. Catalyst deactivation is a challenging problem in the operation of methanol synthesis reactor and has an important role on productivity of the reactor. Therefore, determination of the optimal temperature profile along the reactor could be a very important effort in order to cope with catalyst deactivation. Our previous studies clarify the benefits of a two-stage reactor over a single stage reactor. In this study, an optimal temperature trajectory is obtained for each stage of the corresponding two-stage reactor. Here, steady state optimization is performed in six different activity levels by maximizing the yield and minimizing the temperature of the first stage of the reactor. Multi-objective genetic algorithms are used to solve this two-objective optimization. The set of optimal solutions obtained for six activity levels represents an optimal temperature trajectory for each stage, which has been extended and proposed as a dynamic optimization. This optimization resulted in an additional 3.6% yield, during the course of 4-year process.     

Incorporation of Flexibility in the Design of a Methanol Synthesis Loop in the Presence of Catalyst Deactivation

This paper presents the incorporation of process flexibility into a methanol synthesis loop operating under catalyst deactivation. A design methodology is discussed with regard to catalyst deactivation, and some limitations are identified. In the current flexibility study the size of the reactor and recycle ratio have been fixed. Attempts to maintain methanol production at the rates observed with fresh catalyst included increased pressure, increased make up gas flow rate, and the injection of carbon dioxide into the make up gas at optimized inlet temperature. In order to provide flexibility and produce a design compatible with increased production rates, the effect of interrelating equipment had to be considered. As a result of catalyst deactivation, an increased flow rate is necessary and the altered process streams entering the preheater disturb the reactor inlet temperature. These issues should be considered in the design stage and may be resolved by the flexible designs presented.     

Maximum catalyst temperature (hot spot) in adiabatic fixed-beds

Conditions are derived under,which the reactor profile of catalyst temperature goes through a maximum at a point other than outlet in an adiabatic reactor. Relatively simple methods are developed for the calculation of this maximum temperature. It is shown that the maximum catalyst temperature an increase with time for a certain time period when the catalyst undergoes deactivation. Conditions under which this can happen are also derived. The maximum temperature always increases with time in the cases of uniform sintering and dependent poisoning provided that a certain condition is met in the latter case, if the initial maximum occurs at a point other than the outlet.     

Dynamic mathematical modeling of a novel dual-type industrial ethylene oxide (EO) reactor

In this paper, the dynamic behavior of a novel dual-type industrial ethylene oxide reactor has been proposed with taking catalyst deactivation into account. The configuration of two catalyst beds instead of one single catalyst bed is developed for conversion of ethylene to ethylene oxide. In the first reactor which is an industrial fixed-bed water-cooled reactor, the feed gas is partly converted to ethylene oxide. This reactor functions at very high yield and at a higher than normal operating temperature. In the second converter, the reaction heat is used to preheat the feed gas to the first reactor and a milder temperature profile is observed. The potential possibilities of a two-stage catalyst bed system are analyzed using a 1D heterogeneous dynamic model to obtain necessary comparative estimates. A differential evolution (DE) algorithm is applied as an effective and robust method to optimize the reactors length ratio. The results obtained from the simulation demonstrate that there is a desirable catalyst temperature profile along the dual-type reactor (DR) compared with the conventional single-type reactor (SR). In this way, the catalysts are exposed to less extreme temperatures and thus, diminishing the catalyst deactivation via sintering. Results from this study provided beneficial information about the effects of reactors configuration on catalyst lifetime and ethylene oxide production rate simultaneously.     

Hydrotreated-LCO oxidation in a transport reactor-hydrocyclon system for a low-emission fuel oil production. II Catalyst deactivation and simulation model

The CuCr/IP (4-PVP) catalyst deactivation was studied using continuous stirred-tank reactor (CSTR) laboratory equipment at different temperatures during the oxidation of a tetralin- and fluorene-doped diesel. The concentration of naphtho-aromatics molecules was followed as a function of time on stream, and the catalyst properties analyzed at the beginning and end of run. A computational program was developed to simulate the operation of a continuous recirculation slurry-hydrocyclon-type reactor. The program uses a Runge Kutta Felberg numerical method to solve the mass and energy balance equations for gas, liquid, and solid. For this calculation, it uses a plug flow recycle reactor model for the riser and a plug flow for the downcomer, in agreement with previous fluid dynamic study. The deactivation results indicate a low catalyst deactivation that can be modeled by using an exponential function of the time on stream. The simulation results show that the most important operating variables affecting activity and selectivity are the gas/liquid ratio, the solid hold-up, and the initial temperature. The study confirms the effect of both fluid dynamics and kinetics model parameters in the diesel quality improvement     

Influence of the solids R.T.D.F. on the conversion in three phase fluidized bed reactors

Three phase fluidized bed reactors (F.B.R.) are used industrially for the hydrodesulfurization of petroleum products (see for instance the H-oil Process) and are suitable for continuous operations since, thanks to the large catalyst size, the solids separation from gas and liquid is easier than in other slurry reactors. The continuous catalyst flow rate in the reactor and its renewal are necessary because of catalyst deactivation.In this paper a theoretical investigation is presented in which the influence of the Residence Time Distribution Function and of the solids mean residence time on the conversion rate in three phase fluidized bed reactor is evaluated.The deactivation equations for the HDS catalyst suggested by Shah, Mhaskar and Paraskos (1976) and by Raiagopalan and Dan Luss (1979) were used.It is shown that, when the deactivation of the catalyst is very rapid or the residence time of the solids rather long, the R.T.D.F. of the solids affects the conversion degree substantially.For instance, in the two extreme conditions of:

• 1.solid-liquid perfectly mixed systems and
• 2.solid-liquid with ideal plug flow at different velocities, and for peculiar values of the parameters involved, the ratio between conversion degrees with the models b) and a) may vary up to 30%.</lt>

     

Thermal sintering studies of an autothermal reforming catalyst

This paper describes a novel approach to life studies on catalysts used in non-isothermal reactors, using a single long-term experiment. Temperature dependence of catalyst aging is determined by comparing the activity reduction of portions of the catalyst from different sections of the reactor, subjected to different temperatures. Time dependence is determined by fitting the drift in catalyst temperatures to a time-dependent reaction rate via a thermodynamic reactor model. Experimentally, a monolithic autothermal reforming catalyst was subjected to thermally accelerated aging under reforming conditions in an adiabatic laboratory mini-flow reactor for 1000 h. Methane was used as the fuel. The axial temperature profile of the catalyst was monitored using thermocouples placed at various locations along the catalyst. A gradual change in temperature profile, with increasing temperatures due to decreasing steam-reforming activity, was observed. The aged monolith was cut up into short pieces centered on the thermocouple locations. The pieces, each aged at a different temperature due to its location, were tested individually for activity. The reduced activities were correlated with the aging temperature to obtain the temperature dependence of thermal sintering rates. A generalized power-law equation (GPLE) model for sintering was fit to the activity data. A plug flow reactor (PFR) model describing the reaction was built and the sintering kinetics were incorporated. The PFR model was used to predict changes in catalyst performance due to sintering under normal operating conditions. Thermal sintering deactivation for this catalyst was found to be within acceptable limits for commercial applications.     

Short Vapour Residence Time Catalytic Pyrolysis of Spruce Sawdust in a Bubbling Fluidized-Bed Reactor with HZSM-5 Catalysts

Catalytic pyrolysis of spruce sawdust was carried out in a bubbling fluidized-bed reactor using HZSM-5 catalysts. The effects of space velocity, catalyst deactivation, catalyst acidity and catalyst regeneration were studied. The use of catalysts decreased the yield of organic liquids compared to non-catalytic yields while the yields of pyrolytic water and gases increased. Decreasing the space velocity enhanced these effects. The rate of catalyst deactivation depended on the acidity of the catalyst, with more acidic catalysts deactivating more rapidly. Using a catalyst with a Si/Al ratio of 140 resulted in the largest changes in bio-oil properties. Periodic regeneration of the catalyst in the fluidized-bed reactor was also demonstrated using varying regeneration times and temperatures. It was shown that compared to BFB reactors, CFB reactor types would offer better operating characteristics for commercial scale catalytic pyrolysis processes in regard to vapour residence times, and catalyst activity and regeneration.     

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.     

Optimization by distributed control of reactors with decaying catalyst Part I: Non-linear catalyst deactivation

The quasi-steady state optimization of a single tubular fixed bed reactor with a slowly decaying catalyst is considered. The optimal choice of temperature T(z, t) distributed in both the space of the reactor and in chronological time is sought so as to maximize the total amount of reaction in a fixed given period of time. A single irreversible reaction is considered with a rate expressible as a product of separate functions of temperature, activity and conversion. The rate of catalyst decay is also a product of separate functions of temperature and activity but independent of conversion. Upper and lower bounds are placed on the permitted temperature. Theoretical characterization of the optimal policy is obtained using Sirazetdinov and Degtyarev's maximum principle derived for first-order partial differential equations and the influence of the ratio of reaction activation energy to catalyst deactivation energy on the derived optimal policy is indicated. Numerical calculations are presented to illustrate the optimal policies.     

A comparison of auto-thermal and conventional methanol synthesis reactor in the presence of catalyst deactivation

This study proposed a one-dimensional dynamic plug flow model to analyze and compare the performance of an auto-thermal and a conversional methanol synthesis reactor in the presence of catalyst deactivation. An auto-thermal two-stage industrial methanol reactor type is a system with two catalyst beds instead of one single catalyst bed. In the first catalyst bed, the synthesis gas is partly converted to methanol in a water-cooled reactor. In the second bed which is a gas-cooled reactor, the reaction heat is used to preheat the feed gas to the first bed. To analyze the effect of important control variables on the rector performance, steady state and dynamic simulations are utilized to investigate effect of operating parameters on the performance of reactors. The simulation results show that there is a favorable profile of temperature along the two-stage auto-thermal reactor type in comparison with conventional single stage reactor type. In this way the catalysts are exposed to less extreme temperatures and, catalyst deactivation via sintering is reduced. Overall, this study resulted in beneficial information about the performance of the reactor over catalyst life-time.     

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

In 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.     

高纯氯化氢对电石法PVC失活低固汞催化剂的原位再生

以电石法乙炔氢氯化失活低固汞催化剂为基础,在等温固定床反应器中模拟实际生产转换器单管装置,对失活催化剂通入高纯无水氯化氢气体,研究在氯化氢气体作用下,失活低固汞催化剂的再生效果,并考察再生温度、再生压力、空速以及再生时间对低固汞催化剂再生后汞含量、碘吸附值、四氯化碳吸附值、载体BET比表面积以及催化性能的影响。结果表明,在再生温度220℃、再生压力100 k Pa、空速500 h~(-1)和再生时间60 h条件下,失活低固汞催化剂再生性能最好,再生后乙炔转化率达到99.8%。     

Coking behavior and catalyst deactivation for catalytic pyrolysis of heavy oil

For the catalytic pyrolysis of heavy oil on catalyst CEP-1, coking behavior was investigated in a confined fluidized bed reactor. Coke content on the spent catalyst decreases with the increase of H/C mol ratio of feeds and catalyst-to-oil weight ratio, while it increases with the enhancement of reaction temperature. An empirical model is proposed to predict the coke content based on feed properties and operating conditions. The predicted coke content is close to the experimental data. The relationship between micro-activity index of catalysts and coke content is studied. A coking deactivation model for pyrolyzing catalysts is established, and then model parameters are determined by the least square regression analysis. According to the deactivation model, the variations of relative activity of catalysts with both residence time of catalysts and catalyst-to-oil weight ratio are predicted.     

微反应器中环戊烯催化氧化制备戊二醛的研究

以C5副产物制备出的环戊烯为原料,在微通道反应器内以钨酸为催化剂,在叔丁醇溶剂体系下经双氧水催化氧化制备戊二醛产品,重点考察了钨酸加入量、反应温度、停留时间以及助剂对实验结果的影响。优化实验条件为：催化剂钨酸的物质的量浓度为0.02mol/L,反应温度40℃,停留时间为4.5h;添加助剂KBr物质的量浓度0.02mol/L,停留时间缩短为2h,环戊烯转化率大于98%,选择性达93%以上。研究表明,应用微通道反应器提高此反应的选择性是由于反应器的独特结构控制了中间产物的生成和转化过程,对于此类中间产物过程复杂的反应通过控制停留时间可以使反应达到理想的效果,完成了在普通反应器中不可实现的难题。     

Reactor design and operation for gas-phase ethylene polymerization using ziegler-natta catalysts

A well-instrumented, semi-batch reactor has been constructed for studying the gas-phase polymerization of ethylene using solid Ziegler—Natta type catalysts. This reactor can be operated over the entire range of temperatures and pressures used in the commercial production of linear low, and high density polyethylenes. Successful operation of the reactor depends on careful control of the reaction temperature which in turn is mainly dependent on the total rate of polymerization. If this rate is too large, then the reaction temperature increases uncontrollably (thermal runaway) until catalyst deactivation occurs when melting polymer encapsulates the catalyst particles. Operating conditions are described which resulted in precise and reproducible kinetic measurements for a δ-TiCl₃ δ 1/3AlCl₃ catalyst (Stauffer AA Type 2.1) with diethylaluminum chloride (DEAC) as the co-catalyst. This system displayed first-order kinetic behavior over the temperature range 20 to 90°C with an activation energy of 32.6 kJ/mol.     

Deactivation of V2O5-WO3-TiO2 SCR catalyst at a biomass-fired combined heat and power plant

The deactivation of a commercial type V₂O₅-WO₃-TiO₂ monolith catalyst under biomass combustion was studied at a full-scale grate-fired power plant burning straw/wood using a slip stream pilot scale reactor. The aerosols in the flue gas consisted of a mixture of potassium chloride and sulphate. Three catalyst elements were exposed at 350 °C, and one element was exposed at 250 °C for comparison. The catalyst activity was measured in the reactor at the exposure temperature by addition of NH₃ and extra NO. The activity, in terms of a first-order rate constant, dropped by 52% after about 1140 h indicating a very fast deactivation compared to coal firing. It was also found that the reactor temperature was not of importance for the deactivation rate. SEM-EDX analysis showed that particle deposition and pore blocking contributed to the deactivation by decreasing the diffusion rate of NO and NH₃ into the catalyst. However, potassium also penetrated into the catalyst wall and the resulting average K/V ratio in the catalyst structure was high enough (about 0.3–0.5) for a significant chemical deactivation. Chemisorption studies carried out in situ showed that the amount of chemisorbed NH₃ on the catalyst decreased as a function of exposure time, which reveals that Brøndsted acid sites had reacted with potassium compounds and thereby rendered inactive. When washed by 0.5 M H₂SO₄ the regenerated catalyst regains a higher activity than that of the fresh catalyst at temperatures higher than 300 °C, but even though reactivation is possible, the deactivation rate appears too high for practical use of the SCR process in straw combustion.