Reaction Engineering Model Research Articles

Longevity Aspects of Potable Water Disinfected by Ionic Silver: Kinetic Experiments and Modeling

In the International Space Station (ISS), Russian and European cosmonauts drink water disinfected by dissolved silver. For this to be effective, the concentration of silver should remain above a certain threshold from the moment of its initial disposition in storage tanks on earth until its final consumption in ISS. Unfortunately, during water tanks transportation to ISS and during storage in ISS, silver concentration has been reported to decrease intensively beyond any reason. This work examines the effect of different materials used in ISS water storage and distribution systems on the reduction of silver concentration. An experimental campaign has been organized where passivated stainless steel (SS), passivated and electropolished SS and titanium alloy coupons (official ISS grades) are exposed to simulated ISS potable water at different silver concentrations, different surface to volume ratios, and at stagnant or flow conditions. The evolution of silver concentration remaining in the bulk water is recorded with respect to the exposure time. A reaction engineering model for the Ag loss to the coupons is developed. The model is fitted to the experimental data in order to derive the reaction rate expression and the corresponding parameters. For passivated SS and electropolished SS the silver deposition rate depends on the initial silver concentration in water but is rather unaffected by the progress of silver deposition on the surface. On the other hand, for Ti alloy, while silver deposition rate still depends on initial silver concentration, it decreases continuously as silver deposition on the surface advances, implying that Ti alloy surface becomes gradually saturated and so prevents further silver deposition. Such a model can be useful for material selection and design of water storage and distribution facilities for ISS.

Treatment of Solvent-Contaminated Water Using Vortex-Based Cavitation: Influence of Operating Pressure Drop, Temperature, Aeration, and Reactor Scale

Hydrodynamic cavitation is being increasingly pursued for the development of an intensified and compact wastewater-treatment process. Experimental data on the degradation of water contaminated with three commonly used solvents (acetone; ethyl acetate, EA; and isopropyl alcohol, IPA) using vortex-based cavitation devices are presented. The influence of operating flow or pressure drop across cavitation devices (150 to 300 kPa), operating temperatures (20 to 45 °C), concentrations of pollutant (1000 to 50 000 ppm), and scales of the cavitation reactor (with a scaling-up factor of 4, maintaining the geometric similarity) has been reported. A new reaction-engineering model based on the number of passes through the cavitation device was developed to interpret degradation behavior. The model provides a convenient way to estimate the per-pass degradation factor from batch experiments and allows its extension to continuous processes and to more-sophisticated models for estimating the generation of hydroxyl radicals. The model showed excellent agreement with experimental data. The per-pass degradation factor exhibited a maxima with respect to pressure drop (200–250 kPa) across cavitation devices. Aeration was found to improve degradation performance up to 1 vvm ([L/min]gas/Lliquid]). The initial concentrations of acetone (1000 to 50 000 ppm) and IPA (1000 to 22 000 ppm) were found to have a negligible effect on degradation performance. The per-pass degradation factor for EA was 1.5 and 4 times that of acetone and IPA, respectively. The effect of two scales (nominal capacities of the small- and large-scale devices used were 0.3 and 1.2 m3/h, respectively) was investigated for the first time, and it was found that the per-pass degradation factor decreased with scale. The presented model and experimental data provide new insights into the application of hydrodynamic cavitation for wastewater treatment and provide a basis for further work on the scaling-up of hydrodynamic cavitation devices. The results will be useful to researchers as well as practicing engineers interested in harnessing hydrodynamic cavitation for water treatment.

Reaction Engineering for Continuous Production of Silver Nanoparticles

AbstractA scalable process for the production of silver nanoparticles that allows for complete conversion of the limiting reactant is analyzed in detail. The kinetics of silver nanoparticle synthesis using citrate reduction are investigated and used for development of a reaction engineering model to facilitate the reactor design. The effect of temperature, pH, concentration and mixing (axial dispersion) on the rates of nucleation and growth are analyzed quantitatively. An approach that considers reaction kinetics coupled with quality of dispersion is developed for reactor design as well as selection of reactor configurations for the synthesis of specific particle sizes. The developed approach has been applied for continuous production of 10‐L suspension silver nanoparticles with very narrow particle size distribution.

Modeling G-L-L-S Reactor: A Case of Hydrogenation of Nitrobenzene

Gas–liquid–liquid–solid (GLLS) reaction systems are often encountered in manufacturing of fine and specialty chemicals. More often than not, such reaction systems involve multiple reactions, and selectivity toward the desired component always poses challenges. An adequate understanding of various parameters affecting GLLS reactor performance is essential to develop strategies for realizing desired selectivity. In this work, a comprehensive reaction engineering model for simulating four phase hydrogenation reactions has been developed. A generalized mixing cell based framework for a reaction system with four interacting phases (gas [G], aqueous [L], organic [L], and solid catalyst [S]) was developed. The model is written in a general way so as to specify one of the liquid phases as a continuous phase, and the other three phases are dispersed into it. In each cell, vapor space is included. The model includes the possibility of evaporation of solvent and internal condensation (in vapor space). The model can ...

Speeding up CFD simulation of fluidized bed reactor for MTO by coupling CRE model

The methanol to olefins (MTO) process opens an economical and important route to produce light olefins. The design of MTO reactor borrows ideas from the reaction–regeneration configuration of the modern fluid catalytic cracking (FCC) units. However, their hydrodynamic behaviors are quite different in the sense that the fluidized bed for MTO reactions operates in different flow regime from that of FCC, calling for new modeling for scale-up. In addition, the coke deposited on catalysts greatly affects the MTO reaction while its generation is very slow. It normally takes tens of minutes or even hours for catalysts to reach the desired level of coke content. Time-dependent computational fluid dynamics (CFD) simulation of such a long process poses a big challenge to reactive multiphase flow modeling. To speed up it, we try to integrate the classic chemical reaction engineering (CRE) model with CFD. In particular, the continuous stirred tank reactor (CSTR) model is established to estimate the steady state distribution of coke content, which is then set as the initial distribution for CFD simulation to shorten the time to reach the steady state of reactive flows. Comparison with experimental data shows good agreement and also great speed-up ratio compared to traditional CFD simulation.

Reforming of Methane in a Multistage Microstructured Reactor

AbstractThe concept of a multistage microstructured (MM) reactor was tested in the bench‐scale rig for combined steam and CO2 reforming of methane (RM). In this reactor type, the RM reaction is carried out in a series of adiabatic catalytic reaction steps with heat supply through fin‐plate heat exchangers placed between the stages. The RM reaction was performed over a rhodium‐based catalyst in the form of pellets. The experimental results were described with a reaction engineering model that can be used as the basis for model‐supported scale‐up. This paper describes an intermediate step in the development of the integrated reactor for thermal integration of oxidative coupling of methane and RM. Conversion and yield near thermodynamic equilibrium were achieved. Experiments confirmed the advantages of the MM reactor over wall‐coated microreactors.

Development of a Continuous Plug Flow Process for Preparation of a Key Intermediate for Brivanib Alaninate

A thermal runaway potential was identified for the conversion of a tertiary alcohol to a hydroxypyrrolotriazine intermediate in the synthesis of brivanib alaninate. A continuous process was developed to mitigate the potential thermal runaway and allow for safer scale-up. This paper describes the hazard analysis, process development, reactor development, reaction engineering model development, and scale-up of the continuous process. The process includes three separate and stable feed streams that are mixed in distinct order using in-line static mixers. Heat exchangers are arranged and connected to facilitate a “plug flow” reactor scheme allowing sufficient residence time for reaction completion. The process has been scaled-up to the pilot plant and to manufacturing.

Evaluation of Multipoint Dosing Strategy in a Miniaturized Tubular Reactor: Nitration of Salicylic Acid

AbstractA 2D non‐isothermal reaction engineering model for a tubular reactor was developed for a complex reaction network of salicylic acid nitration. The influence of different operating and design parameters was studied to minimize the amount of secondary nitration products and limit the maximum temperature inside the reactor. Critical temperature effects were observed for larger reaction tubes, whereas close to isothermal conditions were perceived in smaller tubes. With single‐point dosing of both reactants, complete conversion can be achieved but formation of secondary nitration products cannot be avoided. For a given number of dosing points, a suitable combination of the operating parameters allowed to achieve complete conversion and better yield of the desired product.

Kinetic modeling of liquid phase autoxidation of cumene

A new kinetic model for the liquid phase autoxidation of cumene has been developed utilizing the existing knowledge about the traditional free-radical mechanism involving the initiation of the free-radicals, the chain propagation and transfer and the various modes of radical termination. Unlike previous work, in the re-organized reaction network an important cross-termination step replaces an often used but less likely one and a new derivation of the rate model has been provided. A base set of rate parameters for the elementary steps within this reaction network were chosen, many of them were same or very similar to those published in the literature, with a few critical ones re-estimated for correct match with directly observed kinetic data reported in the literature on cumene oxidation in bench scale reactors. Embedding this kinetic sub-model within a simple reaction engineering model for a single air-sparged continuous cumene oxidator, the liquid oxidate composition at the reactor exit could be predicted that compared closely with some limited published data from an industrial reactor. It is hoped that the kinetic model presented here would be a useful tool in the analysis and design of other autoxidation reactors as well with minor adaptations.

Chemical Reaction Engineering Analysis of the Blowout Process for Bromine Manufacture from Seawater

A chemical reaction engineering model has been constructed to describe the extraction and recovery of bromine from a once-through seawater flow. The process uses a closed-loop circulation flow of air. This strips out free bromine from pre-chlorinated seawater in a packed column. Bromine liberated into the gas reacts with injected sulfur dioxide around a circulation loop to form liquid droplets containing product hydrobromic acid captured by mist elimination. Excesses of chlorine and sulfur dioxide compete for bromine and can reduce the recovery efficiency. Pseudo-homogeneous gas-phase kinetics accounts for simultaneous absorption and gas−liquid reaction of liberated bromine, excess chlorine, and injected sulfur dioxide. Re-circulating sulfur dioxide subsequently absorbs and reacts simultaneously with bromine and chlorine stripping. Parameter values are deduced for typical bromine recovery of 70%. The model can be used for optimizing the excesses of chlorine and sulfur dioxide.

VPO Transient Oxidation Kinetics

Transient and steady state reactor data for the partial oxidation of butane to maleic anhydride were collected in a fluid bed over DuPont commercial vanadium pyrophosphate catalyst (VPO) principally under butane rich, oxygen deficient operating conditions. Under moderate reducing conditions, oxygen becomes the determining factor for maleic anhydride productivity and selectivity. As the oxygen becomes depleted, minor changes in butane conversion impacts the selectivity substantially. However, when VPO catalyst is pre-exposed to oxygen for a substantial period of time (as practiced in Circulating Fluidized Bed technology), selectivity may be improved and maleic anhydride yields four times the steady state operation values are achieved. As the butane-to-oxygen ratio rises above 1, carbon deposits onto the surface of the catalyst, resulting in lower activity and selectivity. Based on a detailed reaction engineering model, the re-oxidation rate of the adsorbed carbon is 1st order with respect to the carbon adsorption sites and ½ order in oxygen. The re-oxidation rate of the reduced catalyst appears to be 1st order in sites and oxygen.

Comprehensive Modeling of Gas Fluidized-Bed Reactors Allowing for Transients, Multiple Flow Regimes and Selective Removal of Species

A multiphase reaction engineering model is being developed to investigate the dynamic and steady state behaviour of fluidized-bed catalytic reactors. It accounts for transients, axial and radial dispersion, temperature and pressure profiles, interphase mass and heat transfer, different hydrodynamic flow regimes, catalyst deactivation, reactions with changes in molar flows and various energy options. The model is general enough that it can treat catalytic systems, subject to mass and energy transfer resistances within the phases, as well as permeating membranes. It is able to handle multiple phases and regions (low-density phase, high-density phase, freeboard region and permselective membranes). The model reduces as special cases to a number of simpler fluidized bed reactor models previously reported in the literature, allowing evaluation of the influence of different simplifying assumptions. As a case study, the model is shown to simulate oxy-chlorination fluidized-bed reactors for the production of ethylene dichloride from ethylene, extending a recent paper by Abba et al. (Chem. Eng. Sci., (2002) 57, 4797-4807).

A computational model for predicting particle size distribution and performance of fluidized bed polypropylene reactor

Gas phase polymerization of propylene is one of the most widely accepted and commercially used processes for manufacturing of polypropylene. The present work describes a comprehensive mathematical model for simulating fluidized bed polypropylene reactors. Unlike previously published models, the present model simultaneously predicts both polymer properties as well as particle size distribution. A generalized framework of a dynamic model based on mixing cell approach and detailed polymerization kinetics coupled with population balance model for particle size distribution (PSD) is developed. Need for coupling the reaction engineering model with population balance models is demonstrated. The coupled model was then used to understand influence of operating parameters on polymer properties and particle size distribution. The model is also used to understand the effects of multiple active sites and reaction kinetics on macroscopic variables. The developed framework is useful for simulating multi-monomer, multi-site Ziegler-Natta type olefin fluidized bed polymerization reactors.

Catalyst performance for noble metal catalysed alcohol oxidation: reaction-engineering modelling and experiments

A reaction-engineering model is presented, which describes catalyst performance as a function of the catalyst activity profile, the reaction kinetics, and the degree of catalyst deactivation. With this model, the catalyst activity profile can be optimised for Pt catalysed methyl α- d-glucopyranoside (slowly-reactive) and glucose (highly-reactive) oxidations. This is done by comparing modelling results with experimentally obtained data for catalysts of different activity distributions. Experiments in a semi-batch stirred reactor showed that for methyl α- d-glucopyranoside (MGP) oxidation at oxygen partial pressures below 40 kPa, egg shell catalytic activity distribution gives a higher rate of oxidation than a uniform distribution. It was also observed that with increase in oxygen concentration from 10 to 40 kPa, the rate of deactivation due to catalyst over-oxidation increased dramatically. For glucose oxidation, both catalyst activity distributions give the same oxidation rate for all investigated oxygen partial pressures (5–100 kPa). The developed model adequately describes the observed experimental results of both reactions. It was found that the active metal particle size has a significant influence on the catalyst deactivation for MGP oxidation; the uniform catalyst with higher dispersion shows a higher deactivation rate than the egg shell catalyst. For modelling glucose oxidation, the effect of catalyst particle-to-bubble adhesion and higher diffusivity or partition coefficient for oxygen have to be taken into account.

Two-Dimensional Reaction Engineering Model of the Riser Section of a Fluid Catalytic Cracking Unit

A two-dimensional model that predicts conversion and yield patterns in the riser section of a fluid catalytic cracking unit has been developed. The riser hydrodynamics have been described by the two-dimensional model of Malcus and Pugsley (Circulating Fluidized Bed Technology VII; Grace, J. R., et al., Eds.; Canadian Society of Chemical Engineering: Ottawa, Ontario, Canada, 2002). The hydrodynamic model has been modified to make it predictive by incorporating the slip factor for calculation of the cross-sectionally averaged voidage. The model has been coupled with the four-lump kinetic model of Gianetto et al. (Ind. Eng. Chem. Res. 1994, 33, 3053) to predict how riser operating conditions affect profiles of conversion, yield, temperature, and pressure in the riser. The model was validated against industrial riser data from three literature sources and found to agree within 10−20%. A parametric study of the influence of the liquid feed droplet diameter and feed penetration into the riser was also undertaken. Increasing the droplet size from 50 to 500 μm decreased the gas oil conversion by 4 wt %, while gasoline and light gas yields were both reduced by 1.9 wt %. Increasing the feed penetration distance from the riser wall tended to decrease the gas oil conversion.

Reaction Engineering Model for Supercritical Water Oxidation of Phenol Catalyzed by Activated Carbon

Supercritical water oxidation is an efficient technology for the ultimate destruction of organic waste materials. We previously reported that the addition of activated carbon catalyst promoted the oxidation of phenol in supercritical water and that yield of tarry materials was remarkably suppressed at 400 °C and 25 MPa. In this study, reaction kinetics of the carbon-catalyzed phenol oxidation in supercritical water was studied, and especially, the influence of mass-transfer limitation inside and outside of the catalyst particles was investigated. Experimental results indicated that mass-transfer limitation between bulk fluid and the catalyst surface was negligible whereas mass transfer within the pores of the activated carbon catalyst limited the overall reaction rate. This was in agreement with the result of the calculation of Mears' and Weisz-Prater's criteria. We then developed model equations considering the influence of mass transfer to investigate the intrinsic reaction rate and to describe the temporal change of reaction kinetics. In the model, three reactions were taken into account: homogeneous phenol oxidation, heterogeneous phenol oxidation on the catalyst surface, and combustion of carbon catalyst. The parameter values were determined by curve fitting with the experimental data. By this model, temporal changes of the mass-transfer effect and the reaction rate profile in the packed bed were determined.

Novel Circulating Fluidized-Bed Membrane Reformer for the Efficient Production of Ultraclean Fuels from Hydrocarbons

An integrated novel fluidized-bed membrane steam reformer for the efficient production of hydrogen is proposed and investigated. It consists of two connected subsystems, viz., a circulating fluidized-bed membrane reformer and a reactor−regenerator for dry reforming. The steam-reforming part is an extension of the previous successful work regarding a bubbling fluidized-bed membrane reformer. The fast fluidization regime is more efficient and productive than the bubbling regime. Hydrogen-permeable membranes to remove hydrogen are used together with a CO2 acceptor to remove carbon dioxide and enhance the performance. An in situ supply of heat through oxidative steam reforming is also suggested. The deactivated catalyst is regenerated and recirculated back to the reformer. The CO2-rich stream from the efficient fast fluidized membrane steam reformer is used in a reactor−regenerator dry reforming subsystem, and additional syngas is produced. A reliable reaction engineering model is utilized to investigate this novel configuration. A comparison between the predicted performance of the fast fluidized-bed reformer and the industrial data for a fixed bed as well as the pilot-plant data of the bubbling fluidized-bed configurations investigated earlier shows that the fast fluidized bed is more efficient and productive.

A Chemical Reaction Engineering and Transport Model of Kraft Char Bed Burning

A numerical model for carbon burning in the char bed of a kraft recovery boiler was developed that predicts the rate of char burning and the char bed temperature locally within the furnace. The model describes the char bed chemistry, accounting rigorously for chemical element and energy balances. Char burning rates are based on established kinetic rate data, and diffusion of reactant gases within the bed is taken into account. The chemical model is coupled to the gas field and furnace thermal environment above the bed to account for convective mass and heat transfer from the gases immediately above the bed and for radiant heat transfer from the furnace cavity. This model predicts, within 7% on average, the experimentally measured char burning rates reported by others in laboratory char bed studies, as well as predicting their reported char bed surface temperatures with an average error of 18 °C. It also predicts quantitatively the effects of gas composition and velocity on those rates with an average error of 7%.

Dynamic modelling of a bubble column for particle formation via a gas–liquid reaction

This paper presents a dynamic model of a bubble column reactor with particle formation, accomplished by adopting a hybrid CFD-reaction engineering approach. CFD is employed for estimating the hydrodynamics and is based on the two-phase Eulerian–Eulerian viewpoint. The reaction engineering model links the penetration theory to a population balance that includes particle formation and growth with the aim of predicting the average particle size. The model is then applied to the precipitation of CaCO 3 via CO 2 absorption into Ca(OH) 2aq in a draft tube bubble column and draws insight into the phenomena underlying the crystal size evolution.

Butane partial oxidation in an externally fluidized bed-membrane reactor

An externally fluidized bed-membrane reactor (EFBMR) for partial oxidation reactions is described. This novel reactor concept combines the advantages of fixed bed and fluid bed reactors. Catalyst is loaded inside a porous membrane tube into which the hydrocarbon is fed. An oxygen rich gas fluidizes a powder on the shell side. Oxygen crosses the membrane wall and reacts. Butane partial oxidation to maleic anhydride was adopted as the model reaction and the kinetic parameters were derived based on a full scale commercial pilot plant. A detailed reaction engineering model of the EFBMR showed that hot spots are minimized and the reactor is inherently safer because the flammability potential is lower. Maleic yields are potentially 50% higher in an EFBMR compared to a conventional fixed bed reactor and the reactant concentration operating range is much wider.