Residence Time Distribution Studies Research Articles

Mass transfer and RTD studies in 3D printed serpentine and wavy serpentine millireactor

This study investigates the performance of serpentine and wavy serpentine millireactors. Millireactors, with their microscale features, offer advantages such as heightened surface-to-volume ratio, improved heat transfer coefficients, and reduced mass transfer pathways. The serpentine and wavy serpentine millireactors, characterized by their channel structures, demonstrate superior energy efficiency, reaction speed, and scalability compared to conventional reactors. The focus of this research is on understanding the mass transfer rates and residence time distribution (RTD) in these millireactors, crucial for optimizing their design and operation. The residence time distribution studies providing insights into the mixing characteristics and overall flow behavior. The (RTD) data was fitted to different models. Mass transfer studies examine the movement of acetic acid between aqueous and organic phases, with the volumetric mass transfer coefficient (KLa) as a key parameter. Results from the serpentine millireactor indicate a partially mixed flow behavior with a dispersion number of 0.611, while the wavy serpentine millireactor exhibits a dispersion number of 0.130, indicating improved mixing efficiency. The mass transfer studies yield KLa values in the range of 0.31–1.42 min−1 and 0.49–2.71 min−1 for serpentine and wavy serpentine millireactors, respectively. Efficiency assessments reveal 72.31% and 83.21% for serpentine and wavy serpentine millireactors, respectively. The study concludes that the use of serpentine and wavy serpentine millireactors represents an effective method for process intensification, offering valuable insights for chemical engineering and process optimization applications. The results contribute to advancing the millireactor technology and its potential in continuous flow chemical manufacturing.

Effect of superimposing oscillatory flow in a milli‐channel with static internals—A numerical study

AbstractSuperimposition of oscillatory flow over the axial flow is expected to further enhance the mixing phenomenon based on the limited reported literature. A detailed study on the physics of such superimposed flows will be useful to widen the scope of application of static mixers with superimposed oscillatory flow in continuous modes of operation for several purposes. The flow behaviour of a water–vinyl acetate system in a milli‐channel with static internals is studied under the laminar flow regime using computational fluid dynamics (CFD) as a tool. A CFD model is developed and validated with reported literature on a Kenics static mixer. The effect of oscillatory flow superimposed over the axial flow in a milli‐channel is studied for Ren = 5 and Reo = 20–65. Residence time distribution (RTD) studies have been carried out and compared numerically for two different geometries, (1) tube without an internal and (2) tube with internals, for two different velocities, (1) net axial velocity and (2) superimposed oscillatory velocity. Results of these RTD studies indicate a sharp distribution in the channel with static internals having superimposed oscillatory flow followed by the channel with static internals with net axial velocity and then a tube without an internal. It is also found that Péclet number (Pe) for static internals with oscillatory flow > net axial flow > tube without an internal (736 > 641 > 315). Further, velocity magnitude, pressure, and Q‐criterion are discussed in detail to understand fluid flow behaviour in the milli‐channel. From this research, it is understood that superimposing oscillatory flow along with static internals resulted in enhanced mixing when compared with a tube with no internal.

Study of Hydrodynamics and Residence Time Distribution in a Trickle Bed Reactor

This study focuses on investigating the hydrodynamics using computational fluid dynamics (CFD) simulation and residence time distribution (RTD) within a trickle bed reactor (TBR). CFD simulation was performed on a packed column filled with structured packing of glass beads, while the experiments for RTD studies were conducted in a TBR filled with random packing of Raschig rings. The geometry of TBR and size of packing during CFD simulation was kept close to that of the experimental setup. CFD simulation results were obtained which predicted the flow of fluid through the TBR at different vertical planes along the column. The fluctuations of liquid velocity at various positions inside the reactor were predicted by the CFD model. RTD studies were performed for both pulse input and step input using a non-reactive tracer such as sodium hydroxide. The flowrate of water was varied from 0.6 LPH to 6 LPH for pulse input, while for step input the ratio of water to tracer flowrates was kept at 1:1, 1:2 and 2:1. This study allows us to understand how hydrodynamics and residence time distribution may have an effect on the performance of TBR.

Statistical data treatment for residence time distribution studies in pharmaceutical manufacturing

Residence time distribution (RTD) method has been widely used in the pharmaceutical manufacturing for understanding powder dynamics within unit operations and continuous integrated manufacturing lines. The dynamics thus captured is then used to develop predictive models for unit operations and important RTD-based applications ensuring product quality assurance. Despite thorough efforts in tracer selection, data acquisition, and calibration model development to obtain tracer concentration profiles for RTD studies, there can exist significant noise in these profiles. This noise can make it challenging to identify the underlying signal and get a representative RTD of the system under study. Such concerns have previously indicated the importance of noise handling for RTD measurements in literature. However, the literature does not provide sufficient information on noise handling or data treatment strategies for RTD studies. To this end, we investigate the impact of varying levels of noise using different tracers on measurement of RTD profile and its applications. We quantify the impact of different denoising methods (time and frequency averaging methods). Through this investigation, we see that Savitsky Golay filtering turns out to a good method for denoising RTD profiles despite varying noise levels. The investigation is performed such that the key features of the RTD profile (which are important for RTD based applications) are preserved. Subsequently, we also investigate the impact of denoising on RTD-based applications such as out-of-specification (OOS) analysis and RTD modeling. The results show that the degree of noise levels considered in this work do not significantly impact the RTD-based applications.

Numerical simulations of the effect on twisted spacer filaments on biofouling and scaling in the feed channel of reverse osmosis membrane modules

Overcoming biofouling and scaling in membrane-based separation processes is significant as it affects the permeate quality. In the present study, the effect of biofouling (on membrane only, spacer only, membrane as well as spacer) and scaling on the velocity field, pressure variation, solute residence time distribution and water flux in the reverse osmosis feed channel consisting of twisted spacer filaments is presented using numerical simulations. The twisted spacer filaments caused fluid mixing, which enhanced membrane performance. The biofouling on spacer filaments and/or membrane surfaces and scaling resulted in a narrower effective area for fluid flow, thus causing fluid acceleration and higher pressure drop. The study of solute residence time distribution for biofouling revealed that the breakthrough time decreased with residence time due to fluid acceleration. The observations of solute tracer movement revealed that the solute advection pattern broadened when the feed time for the solute tracer was increased. An irregular and heterogeneous pattern of solute tracer movement was observed in the reverse osmosis feed channel with biofouling which enhanced the flow dispersion and acceleration. The effect of feed temperature on the biofouling pattern was also observed. Biofouling reduced with temperature because the increased feed temperature improved biomass mobility. The water flux in the computational domain containing spacer with scaling was higher compared to the computational domain containing spacer with biofouling because biofouling reduced the membrane porosity, diffusion coefficient and increased flow resistance. The present study concludes that the twisted spacer can effectively reduce biofouling and scaling with improved water flux in reverse osmosis membrane modules.

Experimental determination and mathematical modelling of residence time distributions by using pieces of urban art

Residence time distribution (RTD) has a very high impact on the performance of a chemical reactor. The development of new reactor and catalyst structures has increased the importance of deep knowledge in theories of RTDs and good experimental practice in measuring RTDs in real systems. Therefore, RTD studies are included in chemical engineering education all over the world. This work demonstrates how RTDs can be measured by using urban pieces of art. Impulse experiments with an inert tracer (NaCl) were conducted in a marvelous modern artwork, ‘Flow of time’ in Turku/Åbo. The results were successfully interpreted with the classical laminar flow model. The application of the methodology in historical university cities is suggested.

Investigation of aqueous phase dynamics in a uranium stripping unit using radioactive tracer

Mixer-setters units are widely used in uranium purification processes. For efficient operations of mixer-settler units, it is essential to measure the hydrodynamics parameters of the different phases involved. The residence time distribution (RTD) measurement is commonly used method to estimate the hydrodynamics parameters of process reactors. In the present study, RTD of the aqueous phase was measured in different stages mixer-settler unit (mixers, settlers and mixer-settler units) used for stripping operation using Iodine-131 as a radiotracer. For the RTD measurements, radiotracer was injected as an impulse in aqueous phase feed line and its movement was monitored at different locations in the stripping unit using NaI(Tl) detectors. The mean residence times (MRTs) of the aqueous phase were estimated from measured RTD curves. For quantification of the degree of mixing, suitable flow models were proposed based on design and nature of the measured RTD curves and subsequently used for simulation. Based on the results of the RTD study, the mixing of aqueous phase was characterized and design of the stripping unit and its sub-units were validated. The optimum conditions were identified for efficient for the operation of the stripping unit.

Hydrodynamics of wall-bounded turbulent flows through screens: a numerical study

The hydrodynamic performance of turbulent flows in circular pipes equipped with screen-type static mixers is numerically assessed in this study. A three-dimensional computational fluid dynamics model is used to study the effect of changing the operating conditions and reactor configuration on the flow field. The accuracy of the numerical results is validated by comparing pressure drop predictions to empirical correlations where a maximum relative error of 13.3% is recorded. The macro-mixing performance of screen type static mixers is also assessed using residence time distributions. The study shows that the flow through screens is three-dimensional by nature with secondary flows being prominent near the pipe walls. Moreover, the presence of the screen has a major impact on the turbulent velocity profile both up- and down-stream. The flow field and velocity gradients are interpreted using strain rate and vorticity. These parameters also show that the flow through screens is highly dispersive where 39.3% of the reactor volume has an extensional efficiency value greater than 0.6. This explains their good performance in processing multiphase flows and gives an insight on how to design systems that maximize this dispersive effect in their volume. The residence time distribution study shows that the presence of screens renders the flow closer to plug flow with the effect being more pronounced using finer mesh screens operating at high flow velocities.

Hydrodynamics modeling and electrochemical performance of a lab-scale single-channel cell through residence time distribution and kinetic studies

Hydrodynamics modeling and electrochemical performance of a lab-scale single-channel cell through residence time distribution and kinetic studies

Continuous flow synthesis of Butyl Levulinate using a microreactor –RTD and kinetic studies

Levulinic acid (LA) is produced abundantly from biomass processing, it serves as an eminent precursor for the synthesis of a variety of levulinate esters used as fuel additives. One such additive is Butyl Levulinate (BL) which possess excellent fuel blending properties. With the advent of process intensification techniques like microreactors higher conversions of value added chemicals and API's (Active Pharmaceutical Ingredients) can be achieved in lesser time. In the present work a Residence Time Distribution (RTD) study was performed on a microreactor to probe into non-idealities existing within the system. The microreactor system was then used to study the synthesis of Butyl Levulinate by varying the catalyst loading and residence time. In the microreactor 89.19% conversion of levulinic acid was obtained at 35% (mole) catalyst loading and 2 ​min space time, the mole ratio and temperature were fixed at 1:8 (LA:butanol) and 60 ​°C. Whereas, under similar conditions in a batch reactor LA conversion of 40.54% was achieved after 50 ​min.

Intensification of Sonocrystallization of CaSO4 in Continuous Operation Using a Tube Sonicator

Residence time distribution (RTD) studies based on the pulse input method have been performed to analyze the behavior of a continuous-flow tube sonicator with subsequent application for sonocrystal...

The remediation of textile wastewater using solid Bauxite Residue waste as a potential Fenton catalyst in the fluidized bed Fenton process

Abstract The synergistic relationship between the reactor and the catalysts has gained immense popularity in the field of Chemical Engineering due to their wide application. Catalytic processes have evolved over the decades from expensive commercial catalysts to low-cost solid waste catalysts for the sustainable development and reduction of their impacts on the environment. This alternative use of solid waste can greatly decrease the cost of wastewater treatment and addresses solid wastes issues. Bauxite Residue (BR) is one such waste from alumina-based industries with excellent catalytic properties. The fluid dynamics of fluidized bed technology improves profoundly the hydrodynamics and mass transfer of the heterogeneous Fenton process. This paper presents the preparation of the catalyst with minimum processing effort. It was characterized and factors affecting the degradation efficiency of synthetic dye wastewater were investigated. The optimum conditions for the eosin yellow dye were observed at a pH of five, oxidant concentration of 30 mM, catalyst dosage of 4 g/L. The removal efficiency at these optimum conditions was observed to be 91%. The residence time distribution (RTD) study was aimed to determine the behavior of the reactor using the mean residence time, variance, and dispersion number for the fluidized bed reactor.

Residence time distribution studies on recycle reactor with recirculation

Abstract Residence time distribution (RTD) experiments provide very important information about the performance of reactors. In the present work, RTD experiments were performed with varying recycle and recirculation rates to see their effect on mean residence time (MRT), flow bypassing and stagnant volume in the reactor. A computer program was developed to solve the model equations using fourth-order Runge–Kutta method. A low bypass flow (<5%) was observed from the experimental RTD curves obtained at different operating conditions. A change in the MRT from 1.2 to 1.8 h was observed at different recycle and recirculation rates. At maximum recycle and maximum recirculation, in the study ranges, a 37% stagnant volume (with exchange) was predicted. In the absence of recycle and recirculation, a 53% stagnant volume (with exchange) was predicted corresponding to the best fit of the experimental RTD data.

Residence time distribution study in a pilot-scale liquid phase catalytic exchange (LPCE) column packed with a mixture of hydrophobic and hydrophilic catalysts

Residence time distribution (RTD) measurements were carried out in a packed bed column designed for exchange of hydrogen isotopes. The main objective of the study was to characterize the liquid phase mixing under various processes and operating conditions. The packed bed was composed of a mixture of two different types of catalytic packing materials, i.e., a hydrophobic material and a hydrophilic material. Technitium-99m (99mTc) as sodium pertechnetate was used as a radiotracer for RTD measurements. From the measured RTD curves, mean residence times (MRTs), liquid holdup and degree of mixing of liquid phase were evaluated. An axial dispersion model exchange with stagnant zones was used to simulate the measured RTD curves. The results of model simulation showed that volume fraction of hydrophobic to hydrophilic packing and gas/liquid superficial velocities affect the liquid holdup, bed pressure drop and liquid phase dispersion/mixing characteristics. The results of the present study will help to screen packing, optimize the volume of the packing fractions, design and construct the catalyst and optimize the operating conditions for scale up of the isotope exchange process.

Cu-catalyzed aerobic oxidation of diphenyl sulfide to diphenyl sulfoxide within a segmented flow regime: Modeling of a consecutive reaction network and reactor characterization

A continuous flow homogeneous Cu-catalyzed aerobic oxidation of diphenyl sulfide to diphenyl sulfoxide was investigated. The protocol utilized copper sulfate pentahydrate as catalyst, pyridine as ligand, molecular oxygen as oxidant, 2,2,6,6-tetramethyl-1-piperidinyl oxidanyl (TEMPO) as co-oxidant, and methanol as solvent. The continuous flow reactor system was characterized through a residence time distribution (RTD) study, showing that the flow reactor could be modeled as a plug flow reactor. The hydrodynamics of the system were simulated using computational fluid dynamics (CFD). The liquid slug length, bubble length and bubble frequency from the simulation closely corresponded to the experimentally-observed values. The volumetric mass transfer coefficient (kLa) was estimated by applying Higbie’s penetration model for micro-scale diffusion. A reaction profiling approach was applied within continuous flow to generate experimental data to fit a consecutive reaction network for the monooxidation of diphenyl sulfide to the diphenyl sulfoxide and then the subsequent overoxidation to the diphenyl sulfone. The reaction network comprised of four kinetic parameters (A1, Ea1, A2 and Ea2). Three out of four of the fitting parameters could be estimated with less than 7% uncertainty and the fitted model closely correspond to the experimental data, with R2 = 0.994. The fit-for-purpose model was then used to explore the experimental design space in silico. The models were successfully validated in a scale-out experiment which was operated over 4 h collection time to give 72% conversion and 65% sulfoxide yield, corresponding to a selectivity of 91% and a throughput of 0.61 g·h−1.

Residence time distribution studies and modeling of rotating biological contactor reactor for decolorization of Congo red from synthetic dye wastewater

A continuous study in a rotating biological contactor (RBC) reactor was carried out using polyurethane foam (PU) surface-immobilized live fungal biomass of Neurospora crassa with wheat bran adsorbent/substrate for the removal of Congo red (CR) color from aqueous solutions. Residence time distribution studies were conducted at various flow rates of water (1–6.5 mL min–1) using pulse input of tracer to explore the performance of mixing and type of flow behavior inside the reactor. It was found that the value of dispersion number at various flow rates of water such as 1, 3, and 6.5 mL min–1 was 4.36, 7.89, and 13.65, respectively, which indicates that the RBC reactor can be modeled as a mixed flow reactor. A model for a single stage RBC reactor for the decolorization of CR from synthetic dye wastewater has been developed using the principles of conservation of mass. Using the developed mathematical model and experimental data, the model parameters such as maximum specific growth rate of the attached active biomass (μmax), Monod kinetic constant (Ks ), rate constant for pseudo-second-order biosorption (K2 ), and effluent dye concentration at equilibrium (Se ) were estimated. The system of non-linear first-order ordinary differential mass balance equation was solved by the fourth-order Runge–Kutta method and the model parameters were evaluated using the Solver tool in Excel. The predicted and experimental values of effluent dye concentrations are then compared. The predicted values of effluent concentrations found from the theoretical model developed fitted well to the experimental data, suggests that the proposed model is valid for CR dye decolorization. The results reveal that the live fungal biomass of N. crassa with wheat bran is a suitable dual adsorbent for decolorization of CR from synthetic effluents using RBC reactor and it can be used effectively in wastewater treatment.

Kinetic and residence time distribution modeling of tubular electrochemical reactor: analysis of results using Taguchi method

Abstract Decolorization of dye waste water is performed using a tubular electrochemical reactor. Stainless steel and oxide coated on titanium mesh acts as the cathode and anode respectively. Experiments were conducted in batch with recirculation mode. The effect of operating parameters such as current density, initial dye concentration, flow rate and supporting electrolyte concentration on decolorization of Acid red dye has been studied and the results were analysed using Taguchi method. A residence time distribution (RTD) study has been conducted in a tubular electrochemical reactor and an axial dispersion model has been developed to determine percentage decolorization. The model results are compared with experimental results and it was found that the model satisfactorily matches with the experimental results with high correlation coefficient.

Investigation of flow dynamic characteristics of inverse fluidized bed biofilm reactor for degrading pharmaceutical based biomedical wastewater

The paper investigates the flow dynamic behaviour of inverse fluidized bed biofilm reactor (IFBBR) for the treatment of pharmaceutical based biomedical wastewater. The residence time distribution (RTD) study has been employed as a tool to investigate the flow dynamic behaviour of wastewater within the reactor. The biofilm reactor is operated using Pseudomonas fluorescens for various ratios of settled bed volume to reactor working volume (Vb/Vr) with different superficial air velocities and examined their impact on flow dynamics. The outcomes of this study demonstrate the presence of dead volume and short circuiting in the reactor were reduced for the optimized (Vb/Vr) ratio of 0.20 and optimum superficial air velocity (Ug)m of 0.220 m/s. The potential of IFBBR was experimentally validated by analysing the chemical oxygen demand (COD) removal efficiency, total dissolved solids (TDS) and total suspended solids (TSS) emanating from the wastewater. Findings of this study reveals that maximum COD reduction of about 92% was achieved when the reactor was operated with (Vb/Vr)m of 0.20 with superficial air velocity, Ugm of 0.220 m/s showing the optimal operating parameters for IFBBR which has good mixing and less back mixing condition inside the reactor.

Optimization and Residence Time Distribution Study of Waste Cooking Oil Transesterification in a Continuous Stirred Tank Reactor

Waste cooking oil (WCO) transesterification using a catalyst of Dodecylbenzenesulfonic acid was investigated using a continuous stirred tank reactor. A techniques of surface response plus the design of centered composite were used for the optimizing the factors effecting on the process. The optimum conditions in this research were concluded as (catalyst amount: 1 wt. %; reaction time: 20 min; methanol/oil flow ratio: 4; reactor temperature: 60°C). The biodiesel obtained at the optimum conditions in the process was obtained at yield of 98.5%. The distribution of residence time was found experimentally and a dead zone of (110 cm3) was estimated in the CSTR using the compartment model. The physic-chemical properties for the biodiesel were found in agreement with the ASTM standard (D-6751-2) and the conventional diesel properties. The specific gravity value of biodiesel (0.87) was greater than that one of the diesel fuel (0.834). The calorific value was slightly lower than that one prescribed in the ASTM D-6751 specifications. The kinematic viscosity proved to be within the accepted limits of the. The flash point was found greater than the value specified in the ASTM and that for mineral diesel, which means safer. Acid value of 0.4 mg KOH/g was found accepted according to the biodiesel standard ASTM D-6751-2. Cetane value was found greater than that for mineral diesel.

RTD Modeling of a Non-Ideal Coiled-Tube Reactor Through Experimental Investigation for Pulse Input Using Methylene Blue Dye

This paper focuses on the grasp of a deep understanding of flow behavior in a coiled tube reactor through Residence Time Distribution (RTD) studies. The reactors, in general, are classified ideally: mixed and plug-flow patterns. Unfortunately, in the real world, it has been observed that they show very different behavior from that expected. Thus, the characterization of the nonideal coiled tube reactor is needed to carry out. The calculations were carried out in the Matlab for distribution of residence time of the coiled tube reactor that is used in the Chemical Reaction Engineering Laboratory at MIET College. Pulse input tests were used significantly to analyzed the flow behavior using methylene blue (MB) tracer. A significant disparity in RTD curves in the presence of the secondary flow was examined and data were recorded. Finally, a suitable mathematical model was selected from the Tank in Series (TIS) and Axial Dispersion Models (ADMs) based on residual error and was used to validate these outcomes. The deconvoluted of the signal was used to get Cin for the verification of the pulse input behavior. The results were compared with the experimental data that concluded the modeling of the reactor is in good agreement.