Continuous Flow Stirred Tank Reactor Research Articles

Innovative reactor technology for selective oxidation of toxic organic pollutants in wastewater by ozone

Ozonation can be a suitable technique for the pre-treatment of wastewater containing low concentrations of toxic or non-biodegradable compounds that cannot be treated with satisfactory results when only the traditional, less expensive biological techniques are applied. In this case, the oxidation process has to be made as efficient as possible, in order to reduce the coats of ozone addition and use. An efficient oxidation process with ozone can be obtained by focusing the oxidation with ozone selectively on the direct oxidation of toxic pollutants and to minimize ozone losses due to the decay of ozone in water. Supported by data of the rate constants of the reactions involved, a mathematical model was developed. It quantifies the ozone consumption by the process, and the share of ozone consumption by undesired side reactions, in several different reactor systems. Results obtained with this model indicate that a plug flow reactor (PFR) will be the most efficient design for the oxidation reactor. As an alternative, the cascaded tank reactor system (CTR), in which the ozone feed may be realized with less practical problems, might be considered. The traditional continuous flow stirred tank reactor (CFSTR) is shown to be the least efficient system.

Agar-plated bacteria found in the activated sludge of lab-scale SBR and CFSTR systems

We identified and compared the predominant agar-plated bacteria in the activated sludge of two popular wastewater treatment systems, the sequencing batch reactor (SBR) and the continuous-flow stirred tank reactor (CFSTR). All tests had the same feed composition except for the buffer intensity. It was found that Corynebacterium sp. seemed to prefer growing under lower buffer condition, and Arthrobacter sp. grew dominantly in the system with higher buffer intensity. Gram-negative bacteria appeared more sensitive to an environment with unstable organic loading, such as in the SBR system. On the contrary, the SBR system was more selective to the Gram-positive genera with a special rod-coccus-cycle characteristic, such as Arthrobacter, Corynebacterium, or Brevibacterium.

The hydraulically integrated serial turbidostat algal reactor (HISTAR) for microalgal production

A hydraulically integrated serial turbidostat algal reactor (HISTAR) for the mass production of microalgae was designed, constructed and preliminarily evaluated. The 9266-l experimental system consists of two enclosed turbidostats hydraulically linked to a series of six open continuous-flow, stirred-tank reactors (CFSTRs). The system was monitored and controlled using GENESIS process control software. A production study was preformed using Isochrysis sp. (C-iso) to assess system stability and production potential under commercial-like conditions. The study was performed at the following target system parameters: system dilution rate of 0.49 per day, pH 7.6, nitrogen=10 mg l −1, phosphorus=2 mg l −1, and artificial illumination (photosynthetic photon flux density) from 1000 W metal halide lamps=800 μmol s −1 m −2. At steady state conditions, daily harvested algal paste was 1454 g (wet), mean areal system productivity=47.8±3.04 g m −2 per day (17.1±1.09 g C m −2 per day) and mean CFSTR6 density=105.5±6.71 mg l −1.

Chemical Kinetics in Dispersed-Phase Reactors

Many chemical engineering processes occur under conditions when a dispersed phase undergoes fragmentation (breakup) and/or aggregation (coalescence). It is of considerable interest to model a chemical process that occurs at the interface and therefore depends on the evolving size distribution of the dispersed phase. We apply distribution kinetics to represent the evolution of the dispersed-phase size distribution for simultaneous fragmentation and coalescence. The continuous phase with dissolved reactant enters and exits a continuous-flow stirred-tank reactor. When the dispersed phase contained within the vessel satisfies a similarity solution, several rate expressions, including one for interphase mass transfer, that depend on mass moments of the size distribution allow analytical or simple numerical solutions. The solutions demonstrate how chemical reaction mass balances can be combined with distribution dynamics to extend chemical reaction engineering analysis.

Experimental and modeling study of the oxidation of benzene

AbstractThis paper describes an experimental and modeling study of the oxidation of benzene. The low‐temperature oxidation was studied in a continuous flow stirred tank reactor with carbon‐containing products analyzed by gas chromatography. The following experimental conditions were used: 923 K, 1 atm, fuel equivalence ratios from 1.9 to 3.6, concentrations of benzene from 4 to 4.5%, and residence times ranging from 1 to 10 s corresponding to benzene conversion yields from 6 to 45%. The ignition delays of benzene–oxygen–argon mixtures with fuel equivalence ratios from 1 to 3 were measured behind shock waves. Reflected shock waves permitted to obtain temperatures from 1230 to 1970 K and pressures from 6.5 to 9.5 atm.A detailed mechanism has been proposed and allows us to reproduce satisfactorily our experimental results, as well as some data of the literature obtained in other conditions, such as in a plug flow reactor or in a laminar premixed flame. The main reaction paths have been determined for the four series of measurements by sensitivity and flux analyses. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 503–524, 2003

Using sucrose as a substrate in an anaerobic hydrogen-producing reactor

This study investigated the performance of a Continuous Flow Stirred Tank Reactor (CSTR) reactor producing hydrogen using sucrose as a substrate. The hydraulic retention time (HRT) effect was also investigated. The hydrogen gas production increased from 4.9 to 26.9 L–H 2/l per day with a HRT decrease from 13.3 to 3 h, but decreased to 20.8 L–H 2/l per day with a HRT decrease to 2 h. The digestion gas contained 35∼47.2% hydrogen and the hydrogen percentage increased with a HRT decrease from 13.3 to 3 h, but decreased markedly at 2 h. Under steady state conditions, the hydrogen production rate (HPR) ranged from 1.42 to 4.52 mol-H 2/mol sucrose and the specific hydrogen production rate ranged from 78 to 841 mmol H 2/g VSS-day.

Mechanism of the oscillatory decomposition of the dithionite ion in a flow reactor.

A simple mechanism consisting of three protonation equilibria and seven redox reactions between sulfur species can describe the large amplitude-sustained temporal pH-oscillations observed during acid-induced decomposition of the dithionite ion in a continuous-flow stirred tank reactor (CSTR) in the temperature range 25-60 degrees C.

Testing Antimicrobials Against Biofilm Bacteria

Standard laboratory methods are needed to assess the efficacy of antimicrobial agents that are applied to biofilm bacteria. Existing standard suspension tests and dried surface tests show much greater efficacy than antimicrobial agents applied to biofilms. The greater resistance of biofilm bacteria to antimicrobial agents can be attributed to a number of interacting factors, including reaction and diffusion processes that limit an agent's accessibility to bacteria, phenotypic changes in biofilm bacteria caused by stress, and adaptation of the bacteria. Because biofilm systems are so diverse, a variety of new biofilm tests with features that differ in important ways from existing tests will ultimately be required. For example, the biofilm test apparatus may include a pump and a continuous-flow stirred tank reactor. This report provides an overview of biofilm testing and suggests a strategy for creating standard test methods.

Determination of glutamic acid by an oscillating chemical reaction using the analyte pulse perturbation technique

An analytical method for the determination of glutamic acid by the sequential perturbation caused by different amounts of glutamic acid on the oscillating chemical system involving the Cu(II)-catalyzed oscillating reaction between hydrogen peroxide and sodium thiocyanate in an alkaline medium is proposed. The method relies on the linear relationship between the changes in the oscillation amplitude of the chemical system and the concentration of glutamic acid. The reaction is implemented in a continuous-flow stirred-tank reactor, and changes in the oscillation amplitude on each perturbation are proportional to the glutamic acid concentration. The use of the analyte pulse perturbation (APP) technique permits sequential determinations on the same oscillating system owing to the expeditiousness with which the steady state is regained after each perturbation. The dynamic range lies between 2.5×10 −6 and 3.2×10 −4 M of glutamic acid, with the regression coefficient is 0.9987. The precision is excellent (less than 0.68% as relative standard deviation (R.S.D.)). Some aspects of the potential mechanism of action of glutamic acid on the oscillating system are discussed.

Experimental and Model Studies of Oscillations, Photoinduced Transitions, and Steady States in the Ru(bpy)32+-Catalyzed Belousov−Zhabotinsky Reaction under Different Solute Compositions

Experiments of the Ru(bpy)32+-catalyzed Belousov−Zhabotinsky (BZ) reaction exhibited several types of oscillations, photoinduced transitions, and steady states in a continuous-flow stirred tank reactor (CSTR) system under a wide range of oxidative and reductive solute conditions. An improved Oregonator-class model of the photosensitive BZ reaction has reproduced the experimental behavior quantitatively as well as other photoinduced behavior reported so far.

Periodic and Bursting pH Oscillations in an Enzyme Model Reaction

Oscillatory behaviour in the pH value was observed during the oxidation of sulfite by hydrogen peroxide mediated by hemin in a continuous-flow stirred tank reactor. The dynamics of this reaction was studied for a variety of flow rates of the reactants. As the flow rates increase, the oscillations evolve from relaxation oscillations to more complex shapes, displaying, among others, bursting behaviour. A reaction mechanism is proposed that involves the autocatalytic oxidation of HSO

Formulation of a soil–pesticide transport model based on a compartmental approach

A semianalytical soil–pesticide transport model is formulated based on a compartmental approach to determine spatial and temporal variations of pesticide residues across a soil profile. The compartmental model is implemented by drawing an analogy between a series of continuous-flow stirred tank reactors and a soil horizon that consists of multiple perfectly mixed compartments. The analogy is strengthened by exploiting a relation between the compartment series and the conventional convective–dispersive equation (CDE) for vertical transport in the soil. Consequently, the number of compartments in the model formulation is not free, but dictated as a function of transport parameters. The model formulation allows consideration of arbitrary boundary value specifications and also, for some cases, spatially varying initial concentration profiles. Sorption kinetics is represented via a two-site model that involves a linear sorption isotherm and a first-order irreversible sorption or a radial diffusive penetrating model. For these three cases, analysis of the compartmental model allows the resultant concentration profiles to be expressed in terms of the Poisson distribution. When a nonlinear kinetic sorption model is used to simulate the sorption processes, an analytical solution is not found and a numerical approach is required.

Synchronization of glycolytic oscillations in a yeast cell population.

The mechanism of active phase synchronization in a suspension of oscillatory yeast cells has remained a puzzle for almost half a century. The difficulty of the problem stems from the fact that the synchronization phenomenon involves the entire metabolic network of glycolysis and fermentation, and consequently it cannot be addressed at the level of a single enzyme or a single chemical species. In this paper it is shown how this system in a CSTR (continuous flow stirred tank reactor) can be modelled quantitatively as a population of Stuart-Landau oscillators interacting by exchange of metabolites through the extracellular medium, thus reducing the complexity of the problem without sacrificing the biochemical realism. The parameters of the model can be derived by a systematic expansion from any full-scale model of the yeast cell kinetics with a supercritical Hopf bifurcation. Some parameter values can also be obtained directly from analysis of perturbation experiments. In the mean-field limit, equations for the study of populations having a distribution of frequencies are used to simulate the effect of the inherent variations between cells.

PH oscillations in the hemin–hydrogen peroxide–sulfite reaction

Oscillatory behaviour in the pH value has been observed during the oxidation of sulfite by hydrogen peroxide mediated by hemin, a well known enzyme model compound, in a continuous-flow stirred tank reactor. The dynamics of this reaction has been studied for a variety of flow rates of the reactants. As the flow rates increase, the oscillations evolve from relaxation oscillations to more complex shapes, displaying, among others, bursting behaviour. A reaction mechanism is proposed that involves the autocatalytic oxidation of HSO3- by H2O2, while slow equilibria between different pH-dependent forms of hemin account for the feedback loop which gives rise to oscillatory dynamics. It is shown in experiments that no participation of CO2 is required for oscillations to occur.

Effects of Mixing on Parallel Chemical Reactions in a Continuous-Flow Stirred-Tank Reactor

Effects of turbulent mixing on the course of two fast parallel chemical reactions (neutralization of sodium hydroxide and hydrolysis of ethyl chloroacetate) carried out in a continuous-flow stirred-tank reactor are experimentally investigated and theoretically interpreted. Mixing effects are modelled using mechanistic models (E-model) and a closure method based on CFD.

Treatment of solutions with binary solutes using an admicellar enhanced CSTR: background solute effect

This study presents an admicellar enhanced continuous-flow stirred tank reactor (CSTR). Solutions containing single and binary aliphatic alcohols are introduced into this reactor for breakthrough experiments. Two phenomena occur during experiments with binary solutes: (a) a competitive effect caused by background solutes with relatively high hydrophobicity; (b) a co-solvent effect attributable to background solutes with relatively low hydrophobicity. The competition phenomenon and the corresponding mechanism involved are well demonstrated by directly monitoring the pre-adsolubilized solutes drawn out back to the solution while adsolubilizing other solutes with higher hydrophobicity. On the other hand, adsolubilization kinetics hindered by the background solute, which acts as a co-solvent, significantly alters the slopes of breakthrough curves of the target solute treated in the reactor.

Changes in product formation and bacterial community by dilution rate on carbohydrate fermentation by methanogenic microflora in continuous flow stirred tank reactor.

Changes in product formation during carbohydrate fermentation by anaerobic microflora in a continuous flow stirred tank reactor were investigated with respect to the dilution rate in the reactor. In the fermentation by methanogenic microflora, stable methane fermentation, producing methane and carbon dioxide, was observed at relatively low dilution rates (less than 0.33 d(-1) on glucose and 0.20 d(-1) on cellulose). Decomposition of cellulose in the medium was a rate-limiting step in the reaction, because glucose was easily consumed at all applied dilution rates (0.07-4.81 d(-1)). Intermediate metabolites of methane fermentation, such as lactate, ethanol, acetate, butyrate, formate, hydrogen, and carbon dioxide, were accumulated as dilution rate increased. Maximum yield of hydrogen was obtained at 4.81 d(-1) of dilution rate (0.1 mol/mol glucose on glucose or 0.7 mol/mol hexose on cellulose). Lactate was the major product on glucose (1.2 mol/mol glucose), whereas ethanol was predominant on cellulose (0.7 mol/mol hexose). An analysis by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified bacterial 16S rDNA of the microflora indicated that changes in the microbial community took place at various dilution rates, and these changes appeared to correspond to the changes in product distributions. Sequence analyses of the DGGE fragments revealed the probable major population of the microflora. A band closely related to the microorganisms of thermophilic anaerobic bacteria was detected with strong intensity on both glucose and cellulose. Differences in the production yield of hydrogen could have been caused by different populations of microorganisms in each microflora. In the case of cellulose, increasing the dilution rate brought about an accumulation of microorganisms related to Clostridia species that have cellulolytic activity, this being in accordance with the notion of cellulose decomposition being the rate-limiting reaction.

Large Amplitude pH Oscillations in the Hydrogen Peroxide−Dithionite Reaction in a Flow Reactor

The kinetics of the reaction between S2O4 2- and H2O2 is found to be very complex both in a closed reactor and in a continuous-flow stirred tank reactor (CSTR) in an unbuffered aqueous solution. The main products of the oxidation are SO4 2- and S2O6 2- in excess H2O2. The reaction is accompanied by acidification of the initially alkaline mixture. The measured pH-time traces show multiple inflection points in a closed reactor, suggesting that the reaction takes place in several distinct steps. Transient formation of SO 3 2- /HSO3 - buffer system is observed in the early stage of the reaction. Next, the sulfite ions are oxidized further to sulfate ions in an autocatalytic reaction. Simultaneously a small amount of dithionate ions is also formed. The pH exhibits very large amplitude relaxation oscillations in a CSTR in a narrow range of input concentrations, flow rate, and temperature. A simple empirical rate law model consisting of three redox reactions and three protonation equilibria is proposed. Numerical simulations based on this model agree well with the experimental results. The key to the pH-regulated oscillation is the H + -autocatalysis that results from the more rapid oxidation of the protonated than of the unprotonated sulfite intermediate.

Kinetics of Supercritical Water Oxidation of Methanol Studied in a CSTR by Means of Raman Spectroscopy

A newly devised continuous flow stirred tank reactor (CSTR) was employed for the study of kinetics of supercritical water oxidation (SCWO) of methanol near the critical point (390−430 °C, 24.7 MPa), where the reaction progress was analyzed by means of Raman spectroscopy. The production of CH2O, CO, and CO2 through the oxidation reaction was directly detected. Methanol conversion as a function of residence time could be analyzed on the basis of a simple first-order CSTR reaction model including phenomenological induction time. The overall reaction rate thus obtained was well-reproduced through simulation by a detailed chemical kinetics model, which supports the belief that the radical chain reaction mechanism is responsible for methanol SCWO even near the critical point.

Experimentally Coupled Thermokinetic Oscillators: Phase Death and Rhythmogenesis

We present an experimental investigation of two coupled thermokinetic oscillators. The system is the exothermic iron-(III)-nitrate catalyzed oxidation of ethanol with hydrogen peroxide to ethanal and acetic acid. The coupling of two continuous flow stirred tank reactors (CSTRs) is performed in four different ways: via coupling of the cooling circuits, via exchange of reaction mass, and via combinations of both in equal and opposite directions. The experiments are modeled by a set of ordinary differential equations, which we have used in previous studies of the uncoupled free running system in a single CSTR. The model calculations predict three different kinds of qualitative behavior before and after the coupling. First, the qualitative behavior can remain unchanged, i.e., one gets steady states when steady states are coupled or one gets periodic oscillations when periodic oscillations are coupled. Second, oscillations can emerge when stationary states are coupled (rhythmogenesis). Third, oscillations are...