Semi-batch Stirred Tank Reactor Research Articles

Two-stage integrated process for bio-methanol production coupled with methane and carbon dioxide sequestration: Kinetic modelling and experimental validation

The study demonstrates a two-stage integrated process for bio-methanol production using Methylosinus trichosporium NCIMB 11131, coupled with sequestration of methane and carbon dioxide. The first stage involved generation of methanotrophic biomass via sequestration of methane; which was used as biocatalyst to reduce carbon dioxide into methanol in the second stage. Maximum biomass titer of 3.39 g L−1 and productivity of 0.60 g L−1 d−1 were achieved in semi-batch stirred tank reactor with methane concentration in the inlet gas mixture of 2.5% v/v and gas flow rate of 0.5 vvm. Methane fixation rate was estimated to be 0.32 g L−1 d−1. Maximum methanol titer of 0.58 g L−1 was achieved at headspace carbon dioxide concentration of 50% v/v and liquid to headspace volume ratio 10:90. Subsequently, a kinetic model was developed to predict and understand the system behaviour in terms of dynamic profile of growth, methanol formation, concentration of dissolved methane or carbon dioxide in the aqueous phase and headspace carbon dioxide concentration, in response to varying process parameters. The model can serve as a tool for estimation of process parameters and aid in overall production optimization.

On the complete similitude of technical precipitation. Part II: Stirred-tank reactors

The particle size distribution (PSD) of precipitated products is often influenced by mixing. This poses a serious challenge if stirred-tank reactors (STRs) are applied, because the complex fluid dynamics in STRs impedes process development and scale-up. Previous research has been limited to investigating the impact of dimensional physical or chemical parameters because their governing Π groups remained unclear. We aim within this work to fill this gap by transferring our recently developed theory of complete similitude to STRs. Hence, we propose that the dimensionless PSD depends solely on the STR’s Reynolds number, Re, the solids formation Damköhler number, Dasf and the feed velocity ratios, ζj if the same materials, educt concentration ratios and geometrically similar reactors are applied. Barium sulfate precipitation experiments in two semi-batch STRs with 0.4 and 10.8 L are conducted to validate this hypothesis. In addition to proving that complete similitude is possible for STRs, the results indicate that Re does not impact the dimensionless PSD for flows dominated by meso or macro mixing. This finding is further supported by a timescale analysis revealing that, contradictory to literature, meso and macro mixing are independent of Re. Furthermore, we demonstrate that complete similitude represents a fundamental framework from which other novel and established scale-up criteria can be derived.

On disclosing the role of mesoporous alumina in the ozonation of sulfamethoxazole: Adsorption vs. Catalysis

Ordered mesoporous alumina (MA) and Fe-doped MA were synthesized by evaporation-induced self-assembly and tested for the ozonation of sulfamethoxazole (SMX). The synthesis methodology produced MA whose surface and structural properties exceeded those of commercial types displaying a BET surface area of 263 m2/g, a pore volume of 0.8 cm3/g and aligned cylindrical pores of c.a. 10 nm. The ozonation of SMX (20 mg/L) was performed in a semibatch stirred tank reactor at: T = 22 °C, [O3]gas = 10 mg/L, Qgas = 42 L/h NTP, [solid] ≈ 1 g/L, t = 120 min. Single ozonation achieved fast and complete SMX removal and mineralized up to 35% of the organics at neutral pH. The addition of MA or Fe-doped MA did not affect the removal rate of SMX, but did achieve a remarkable TOC removal up to 86% at acid pH. However, under the selected operating conditions, ferric species did not improve the removal of organic matter. Then, the adsorption and catalytic contribution of MA was evaluated in specifically-designed experiments. While SMX adsorption was low, its oxidation intermediates did adsorb onto MA surface. Despite the high ability of the materials to decompose ozone, the results revealed that the by-products adsorption is the prevailing process for the TOC removal. After four successive reuses, MA reduced its adsorption performance due to chemisorption of carboxylates. Nevertheless, the worn material was regenerated by direct ozonation in gas phase. In addition, primary transformation products were identified by LC–ESI–TOF–MS and the scavenging effect of the water matrix was assessed using bottled water and a real secondary wastewater.

Modeling of atmospheric and vacuum petroleum residue hydroconversion in a slurry semi-batch reactor: Study of hydrogen consumption

In this work, Arabian light atmospheric residue and Safaniya vacuum residue were hydroconverted in a slurry phase semi-batch stirred tank reactor at 15 MPa for a wide range of temperatures (420–440 °C) and reaction times up to 4 h. Experimental data was used to develop a semi-batch reactor model including vapor-liquid equilibrium, gas-liquid mass transfer and gas phase hydrodynamics. Mass transfer and kinetic parameters were estimated by minimizing not only the total masses of products but also the outlet gas flow dynamics. Mass transfer and hydrogen consumption were compared against former studies using a batch reactor, a continuous stirred tank reactor and work by other authors, reported in the literature. Higher hydrogen consumption was achieved with the semi-batch reactor and no hydrogen mass transfer limitation was observed. Therefore, it was concluded that this setup is more suited and reliable for studying the chemical kinetics of slurry-phase hydroconversion of petroleum residues and permits improved representation of the role of hydrogen compared with current models.

CFD modeling of turbulent reacting flow in a semi-batch stirred-tank reactor

Abstract For the mixing-sensitive reactions, both chemical kinetics and mixing conditions of the reactants determine the distributions of products. The direct quadrature method of moments combining with the interaction by exchange with the mean micro-mixing model (DQMOM-IEM) has been validated for the chemical reacting flows in micro-reactors. Quite encouraging simulation results offer great promise, but the applicability of this method is needed to be explored furthermore, such as in stirred reactors. In this work, the two-environment DQMOM-IEM model was created with C language and used to customize Fluent through the user-defined functions. The mixing effects on the course of parallel competing chemical reactions carried out in a semi-batch single-phase stirred reactor were predicted. The simulation results show that the rising feed velocity enlarges the volume of reaction zone and maximize the yield of the by-product, which also indicates that the feed stream is more difficultly dispersed into the main stream and the zone surrounding feedpipe exit with high turbulent kinetic dissipation rate cannot be efficiently used.

Mole fraction measurement of methane and ethane in aqueous solutions of NaCl and MgCl2 during hydrate growth

In this paper, the mole fraction of methane and ethane in aqueous solutions of NaCl and MgCl2 during hydrate growth in a semi-batch stirred tank reactor is reported. Methane mole fraction measurements in aqueous solutions of NaCl were conducted at molalities of 0.529 and 1.092, temperatures of 275.15–290.15 K, and pressures of 40–68 bar. The same conditions were provided to measure the mole fraction in the aqueous solution of MgCl2 at molalities of 0.325 and 0.670 mol kg−1. We also report the mole fraction of ethane in aqueous solution of NaCl at molalities of 1.901 and 3.020 mol kg−1, temperatures of 273.15–278.15 K, and pressures of 11–24 bar; however, molalities of 0.325 and 0.791 mol kg−1, temperatures of 279.15–283.15 K, and pressures of 14–29 bar were investigated for the C2H6-MgCl2 system. Furthermore, the effects of pressure and salt concentrations on the mole fraction of these gases in aqueous phase in the presence of hydrate were investigated. It was observed the mole fraction of hydrate formers in the aqueous phase are close to solubility of this gases at experimental temperature and corresponding equilibrium pressure. In addition, it was found the mole fraction of methane and ethane in bulk liquid phase remain constant during the hydrate growth period, whereby the fugacity of the aqueous phase was constant throughout this period.

Stoichiometric Approach toward Modeling the Decomposition Kinetics of Gas Hydrates Formed from Mixed Gases

Following a recent study by Giraldo et al. (Giraldo, C.; Maini, B.; Bishnoi, P. R. A simplified approach to modeling the rate of formation of gas hydrates formed from mixtures of gases. Energy Fuels 2013, 27, 1204−1211), in which a new stoichiometry-based approach was taken to model the rate of gas hydrate formation for mixed gases, a new stoichiometric approach has been proposed to describe the kinetics of gas hydrate decomposition from mixed gases. Similar to the model of gas hydrate formation by Giraldo et al., the newly proposed model of gas hydrate decomposition has the advantage that the intrinsic rate constant of gas hydrate decomposition is only required for a single component. To test the model, gas hydrate decomposition experiments were conducted in a semi-batch stirred-tank reactor, equipped with an in situ particle size analyzer, to study the rate of decomposition of gas hydrates formed from mixtures of carbon dioxide and methane. Two gas mixtures of CO2 (1) + CH4 (2), one with x1 = 0.4 and th...

Experimental and Modeling Study of Catalytic Hydrogenation of Glucose to Sorbitol in a Continuously Operating Packed-Bed Reactor

Sorbitol is an alternative sweetener and a platform chemical for a wide variety of compounds. Selective hydrogenation of glucose to sorbitol over a commercial Ru/C catalyst was studied both experimentally and with the aid of detailed mathematical modeling. The experiments were conducted in a laboratory-scale trickle bed and in a semibatch stirred tank reactor. Sorbitol was obtained from the packed-bed reactor as the main product, typically with ∼90% selectivity within the studied temperature range (90–130 °C), while the side product was mannitol. The factors of interest were the temperature- and concentration-dependent reaction kinetics, deactivation, internal diffusion and heat conduction within particles, radial heat conduction and mass dispersion in the selected reactor section, liquid holdup, gas–liquid mass transfer, pressure drop, and axial dispersion. A mass-balance-based axial dispersion model (using temperature-dependent kinetics and deactivation modeled using the final activity concept) was capable of explaining the observed continuous packed-bed behavior rather well. The stirred tank reactor behavior could be described by a mass-balance-based model. Parameter estimation revealed that the main difference between semibatch and continuous operations arose from the more-severe deactivation in the packed bed. Simultaneous solution of heat and mass transfer for the top-most reactor section and for a catalyst particle revealed that heat-transfer limitations were not severe.

A Simplified Approach to Modeling the Rate of Formation of Gas Hydrates Formed from Mixtures of Gases

Experiments were conducted in a semibatch stirred tank reactor, equipped with an in situ particle size analyzer, to study the rate of formation of hydrates from mixtures of carbon dioxide and methane. Two gas mixtures of CO2 (1) + CH4 (2), one with x1 = 0.4 and the other with x1 = 0.6, were used in the current study. The experimental temperature ranged from 274 to 276 K and the experimental pressure ranged from 20 to 27 bar absolute. The range of temperatures was bounded by the freezing point of water and the temperature at which the CO2 vapor pressure curve intersects the methane hydrate curve. Initially, the results were analyzed using the kinetic model of Englezos et al. (Chem. Eng. Sci. 1987, 42, 2659−2666). After a careful re-examination of the model of Englezos et al., it was realized that the mathematical model for gas hydrate formation from gas mixtures could be simplified by directly incorporating the hydrate phase stoichiometry. The new approach has the added advantage that the intrinsic rate co...

Kinetic Studies on Methane Hydrate Formation in the Presence of Kinetic Inhibitor via in Situ Raman Spectroscopy

To fully understand the influence of kinetic inhibitor, poly-N-vinylcaprolactam (PVCap), on methane hydrate formation, gas uptake measurement (macroscopic point of view) and in situ Raman spectroscopic analysis (microscopic point of view) were carried out simultaneously in a semibatch stirred tank reactor at constant temperature (T) and pressure (P). The capturing the behavior of guest molecules (large to small cavity ratio or cage variation) is one of the most important properties of gas hydrate studies. However the real-time properties of the cage variation under constant T and P conditions in an agitation system have not been reported previously. In this study, we measured this property (i.e., the large to small cavity ratio) from the in situ Raman spectra during hydrate formation in an agitation system instead of a static system, which provided valuable information on the time-dependent hydrate kinetic behavior. The study reveals that the presence of PVCap prevents the rate of large cavity encapsulati...

Kinetics of structure II gas hydrate formation for propane and ethane using an in-situ particle size analyzer and a Raman spectrometer

The kinetics of structure II gas hydrates, formed from pure propane and a mixture of propane and ethane, were investigated and intrinsic rate constants were regressed from the experimental data. The experiments were conducted in a semi-batch stirred tank reactor equipped with an in-situ particle size analyzer and connected to an external Raman spectrometer. Experiments were conducted with pure propane at temperatures ranging from 274 to 276 K and pressures ranging from 0.39 to 0.43 MPa. The intrinsic rate constant for ethane in structure II was subsequently regressed from experimental data on the formation of hydrates formed from an equimolar mixture of propane and ethane at 274 K and 0.35 MPa. Raman spectroscopy was used to verify that ethane was present only in the large sII cavity.

Characterization of CO2 hydrate formation and dissociation kinetics in a flow loop

The objective of this work is to investigate CO2 hydrate formation and dissociation kinetics in the aim of designing a circulation loop with heat exchangers for secondary refrigeration applications. The formation of gas hydrates is a crystallization process which requires a supersaturated environment. The majority of the experimental formation data from the literature were obtained in semi-batch stirred tank. It was found that the hydrate growth for CO2 hydrate formation was approximately 1.8 × 10−3 %hydrate.s−1 for a stirring velocity about 450 rpm. The study reveals that for our system, an isothermal circulation loop, the kinetic varied from 4.3 × 10−3 to 8.3 × 10−3 %hydrate s−1, respectively for two protocols with water and water-additives selected for their dispersive and promoter properties. The first results of CO2 hydrate dissociation kinetics with or without additives were equivalent with various systems (semi-batch stirred tank reactor or loop) with approximately 5 × 10−3 %hydrate s−1.

Formation Kinetics of Structure I Clathrates of Methane and Ethane Using an in Situ Particle Size Analyzer

Experimental data on the kinetics of structure I (sI) clathrate formation were obtained for pure methane and pure ethane in a semi-batch stirred-tank reactor that is equipped with an in situ particle size analyzer. The particle size analyzer used is a Lasentec focused beam reflectance measurement (FBRM) probe capable of measuring particle chord lengths between 0.5 and 100 μm. Experiments were conducted at temperatures ranging from 274 to 282 K and with pressures ranging from 0.99 to 7.25 MPa. A novel procedure for cleaning the FBRM probe tip, which eliminated the need to remove the probe between runs, was developed. Experimental data on the pressure, temperature, and particle size distribution were analyzed using the approach of Clarke and Bishnoi (Clarke, M. A.; Bishnoi, P. R. Determination of the intrinsic kinetics of CO2 gas hydrate formation using in situ particle size analysis. Chem. Eng. Sci. 2005, 60, 695−709), with minor modifications, and intrinsic rate constants were obtained for methane and ethane in sI.

Separation of propylene/propane mixtures using Ag +–RTIL solutions. Evaluation and comparison of the performance of gas–liquid contactors

Over the past few years reactive absorption systems have been explored as alternative to traditional distillation columns in the separation of propylene/propane gas mixtures. This work evaluates the performance of two different contactors, a membrane contactor, MC, and a semi-batch stirred tank reactor, STR, in the separation of the gas mixtures based on the absorption of propylene in Ag +–BmimBF 4 reactive media. The experimental study analysed the influence of operation variables such as gas feed composition (30–70%, v/v of C 3H 6), solvent type (aqueous solutions or ionic liquid) and silver salt concentration on the absorption flux of propylene at room temperature. After development of the mass balances to both contactors the characteristic parameters have been determined from the fitting of the experimental data of the absorption flux to the mathematical models. In MC employing low silver concentrations, 0.1 M, the propylene fluxes reached the highest values when the ionic liquid was used as a solvent whereas for higher silver ion concentrations, 0.25 M, the aqueous media attained lower overall resistance to mass transport than the corresponding ionic liquid and consequently higher propylene fluxes. Working with the STR high propylene fluxes were obtained, that were directly proportional to the inlet C 3H 6 partial pressure. Under similar operating conditions and 298 K of temperature the overall mass transfer parameters took the values of K overall a = 5.9 × 10 −4 s −1 for MC and K overall a = 236 × 10 −4 s −1 for STR respectively; although the use of the membrane contactor resulted in a lower value of the mass transport coefficient a considerable decrease of the overall resistance to mass transport (1/ k l H adi E A) can be induced by acting on the design and on the operating conditions due to the favourable influence of the higher absorption capacity of the olefin in the ionic liquid media (high values of H adi) with the enhancement in the absorption rate due to the instantaneous reaction with silver ions, thus further optimization of the process could improve the performance of the MC.

Safety aspects in modelling and operating of batch and semibatch stirred tank chemical reactors

Safety aspects in modelling of batch and semibatch stirred tank reactors as well as a model based safety analysis have been considered. Applicability of two basic types of models – i.e. the perfectly mixed reactor model and the CFD model, both formulated for laboratory scale as well as pilot plant scale reactors – has been discussed. A formulation of the appropriate reactor model, which is adequate to the considered case study has been demonstrated and tested experimentally. Particular attention has been devoted to the formulation of robust CFD models employed to simulate a performance of the stirred tank reactors. It has been found that models for perfectly mixed reactors may have quite wide range of application, while the CFD models should be definitely used in case of fast reactions, high viscosity of the reacting mixture as well as of failure leading to stopping of the impeller. The CFD models are able to predict a dynamic behaviour of reactors at any circumstances, so they can play a significant role in safety analysis carried out for industrial scale reactors, for which experimental safety tests are expensive and dangerous.

CO 2 and CH 4 mole fraction measurements during hydrate growth in a semi-batch stirred tank reactor and its significance to kinetic modeling

A new experimental technique has been developed to measure the mole fraction of the gas hydrate former in the bulk liquid phase, at the onset of hydrate growth and thereafter, in a semi-batch stirred tank reactor. The mole fraction of carbon dioxide and methane in the bulk liquid phase was obtained for the first 11 and 13 min of the growth stage, for the carbon dioxide–water and methane–water systems respectively. Experiments were conducted at temperatures ranging from 275.3 K to 281.4 K and at pressures ranging from 2017 kPa to 4000 kPa for the carbon dioxide–water system, while temperatures ranging from 275.1 K to 279.1 K and pressures ranging from 3858 kPa to 6992 kPa were investigated for the methane–water system. The mole fraction of carbon dioxide in the bulk liquid phase was found to be constant during the growth period, varying on average by 0.6% and 0.3% at 275.4 K and 279.5 K. Similarly, the mole fraction of methane in the bulk liquid phase was found to remain constant during the growth stage, varying on average by 2.0%, 0.8% and 0.2% at 275.1 K, 277.1 K and 279.1 K respectively. The mole fraction of the gas hydrate former in the bulk liquid phase was also found to increase with pressure and decrease with temperature, while remaining greater than its hydrate-liquid water equilibrium value. As a result, an alternate formulation of a hydrate growth model is proposed.

Modeling and Comparison of Continuous and Semi-Continuous Processes for Simulating Decontamination of Liquid Nuclear Wastes by the Coprecipitation of Strontium Ions with Barium Sulphate

In the nuclear industry, large volumes of liquid wastes with a low radioactivity have to be treated. The method which is commonly applied to remove contaminants consists of the use of an insoluble finely divided solid material formed in situ by precipitation in the waste stream. In this study, a new mathematical approach of the adsorption of radioactive strontium on growing barium sulphate precipitate is established and used for the decontamination process modeling in both continuous and semi-continuous stirred tank reactors. The comparison of the two types of reactors is carried out under the same operating conditions by studying the influence of the stirring speed and, respectively, the mean residence time (for continuous stirred tank reactor) and/or process time (for semi-batch stirred tank reactor) on the efficiency of the decontamination process. Simulations have shown that the mean residence time is the critical parameter in controlling decontamination in the continuous reactor, while the stirring speed plays a minor role. Comparison of results indicates that the best configuration to carry out the decontamination process is the semi-batch stirred tank reactor.

Inferential Conversion and Composition Monitoring via Microcalorimetric Measurements in Emulsion Terpolymerization

Online calorimetry was used to estimate the conversion and the cumulative terpolymer composition in free radical emulsion polymerization of styrene/methyl methacrylate (MMA)/methyl acrylate (MA) within batch and semi-batch stirred tank reactors. The model includes the mass and energy balance equations over the reactor and its peripherals. Energy balance equations include the heat of reaction, internal and external heat transfer effects, as well as external heat losses. Experiments were conducted in conjunction with a reactor instrumented with platinum resistance thermal transducers and gravimetric conversion measurement devices. The experiments were conducted at variable operational conditions of feed rate, temperature and monomer feed ratios. The estimated values of conversion and terpolymer composition obtained from calorimetric data were compared with measurements of conversion and cumulative terpolymer composition by gravimetry and NMR techniques. Good agreement was observed between the inferential calorimetric estimation and corresponding process measurements. We established that online calorimetry is suitable for use as a soft sensor for the prediction of the rate of reaction, conversion and terpolymer composition.

Gas Hydrate Growth Model in a Semibatch Stirred Tank Reactor

The gas hydrate growth model of Englezos et al. (Chem. Eng. Sci. 1987, 42, 2647) was modified based on a concentration driving force where the equilibrium concentration at the hydrate surface is determined at the surface pressure and temperature, with the latter varying between the bulk and three-phase equilibrium temperature depending on the rate of heat removal. In order to study hydrate growth kinetics, literature mole consumption rates and hydrate surface area obtained in a semibatch stirred tank reactor were used. The extraction of the intrinsic kinetic rate constant is intimately linked to the estimated hydrate surface area, which is difficult to accurately measure. Theoretical estimation of the surface area using a population balance is also problematic since it does not account for the inherent presence of foreign particles, of unknown quantity and size distribution, serving as nucleation sites. Finally, mole consumption rates in such experimental systems may be controlled by gas−liquid interphase mass transfer, suggesting that accurate interphase mass transfer coefficients are required for proper estimation of the intrinsic kinetic rate constant.

Ionic liquid synthesis in a microstructured reactor for process intensification

Ionic liquids (IL) are the focus of growing interest over the last few years due to their low vapour pressure being beneficial for replacing common organic solvents with high vapour pressure. IL synthesised via alkylation are produced in batch or semi-batch stirred tank reactors. The reaction is highly exothermic and the kinetics was shown to be fast. The heat management during the reactor operation is a crucial point leading to high quality IL product and avoiding thermal runaway. This study reports the use of a microstructured reactor (MSR) system for the production of ethylmethylimidazole ethylsulfate by a solvent-free alkylation reaction. A combination of MSR and two tubular capillary reactors operating at two different cooling temperatures has been proposed. The save and stable operation of this reactor system is proven experimentally rendering the IL of high quality. The specific reactor performance was about 4 kg m −3 s −1 being ca. 3 orders of magnitude higher as compared to more traditional reactors.