Gas-phase mass-transfer measurements in a falling-film microreactor

The industrial-scale performance of gas–liquid reactors is difficult to control when very rapid or highly exothermic reactions are involved. Microstructured reactors offer new opportunities for these reactions by enabling precise heat management and accurate control of operating conditions.The present study examines experimentally the gas-phase mass-transfer characteristics of a reactor tool for the characterization of gas–liquid reactions: a falling-film microreactor. A well-known chemical test system, the absorption of sulfur dioxide SO₂ by sodium hydroxide NaOH is employed to determine the characteristics. The measurements of inlet and outlet concentrations in the gas phase enable the mass-transfer coefficient to be determined.The mass-transfer characteristics, in terms of dimensionless Sherwood number Sh_G, are then related to the hydrodynamic characteristics of the gas phase, through the Reynolds number Re_G, and the physico-chemical properties of the reactional system, through the Schmidt number Sc_G. A strong dependence of dimensionless Sherwood number on gas-phase Reynolds number is observed, probably resulting from the specific features of the geometry of the gas-phase inlet.     

Temperature and conversion patterns in a network of catalytic reactors for methanol synthesis with different switch strategies

A network of connected catalytic reactors with periodically switched inlet and outlet sections is numerically studied for reversible exothermic reactions. The methanol synthesis is selected as representative process example and two different switch strategies are compared with the objective of overcoming the conversion limits imposed by thermodynamic equilibrium. The first strategy, which is the most considered in literature, consists of periodically switching the feed to the second reactor of the current reactor sequence while the second strategy is implemented by periodically switching the feed to the last reactor of the current sequence. Periodic regimes corresponding to single square-like temperature waves travelling over the catalytic bed and characterized by comparable methanol conversion values are detected for both the considered strategies. These regimes exhibit, however, a significantly larger domain of existence for the second strategy. Moreover, the second strategy gives rise to other periodic regimes corresponding to spatiotemporal temperature patterns characterized by different spatial and temporal periodicity. These patterns arise in the form of temperature wave trains and ensure methanol conversion values significantly larger than those found under periodic regimes characterized by single temperature waves.     

Automated measurements of gas‐liquid mass transfer in micropacked bed reactors

Gas‐liquid mass transfer in micropacked bed reactors is characterized with an automated platform integrated with in‐line Fourier transform infrared spectroscopy. This setup enables screening of a multidimensional parameter space underlying absorption with chemical reaction. Volumetric gas‐liquid mass‐transfer coefficients (k_La) are determined for the model reaction of CO₂ absorption in a methyl diethanolamine/water solution. Parametric studies are conducted varying gas and liquid superficial velocities, packed bed dimensions and packing particle sizes. The results show that k_La values are in the range of 0.12～0.39 s^?1, which is about one‐to‐two orders of magnitude larger than those of conventional trickle beds. An empirical correlation predicts k_La in micropacked bed reactors in good agreement with experimental data. © 2017 American Institute of Chemical Engineers AIChE J, 64: 564–570, 2018     

Study of an Annular Photoreactor with Tangential Inlet and Outlet: I. Fluid Dynamics

Photochemical reactors tend to exhibit turbulent flow even with low Reynolds numbers. The k‐? model is not always appropriate in this situation. An annular photoreactor was designed with tangential inlet and outlet tubes to investigate this. The fluid flow was characterized by residence time distribution (RTD) experiments, which were reproduced by computational fluid dynamics considering four relevant turbulence models: the k‐?, the k‐ω, the shear stress transport, and the Reynolds stress models. Inlet effects induced helical flow throughout the reactor, switching to plug flow depending on the flow rate and the turbulence model. The k‐ω model properly deals with viscous effects and reproduces the experimental RTD curves with correlation coefficients greater than 0.9566, against 0.8705 from the k‐? model.     

Simulation of nonequimolecular polycondensation in continuous flow-stirred tank reactors

Conversion and molecular weight distribution are computed and compared for uncatalyzed and catalyzed nonequimolecular polycondensation in continuous flow-stirred tank reactors (CSTRs) using two different kinetic schemes proposed by Flory and Lin, respectively. The contrast between the two schemes is also remarkable as found in the batch reactors. The polydispersity indices in the CSTRs are substantially larger than those obtained in the batch reactors. Also, the molecular weight distribution splits into two curves for odd and even homologues regardless of the two different schemes. An extremely long rersidence time is needed to obtain the higher conversion accompanying a large polydispersity index as compared to the batch reactors. The polydispersity can be expressed in CSTR as x?_w/x?_n = 2 Σn²N_n(R+1?2P)/(1+R)²[A]₀.     

Development of the Eco-Cascade- cell reactor

The development of multicompartment rotating cylinder electrode reactors for the removal of metal from aqueous solutions is described. Such reactors approximate to a cascade of continuously stirred tank reactors and the results illustrate that, for electrodeposition of copper powder from acid sulphate solutions, high overall conversions (about 98%) may be realised, with low exit metal concentrations (about 1 mg dm^–3) and reasonable current efficiencies (65–87%).Nomenclature A electroactive surface area (cm²) - C _in inlet concentration of metal (mg dm^–3) - C _out outlet concentration of metal (mg dm^–3) - C _reactor reactor concentration of metal (mg dm^–3) - f _R fractional conversion - (f _R)n overall fractional conversion - F Faraday=96 500 (C mol^–1) - I _L limiting current (A) - k _l mass transfer coefficient (cms^–1) - m weight of metal (g) - M molecular weight of metal - n number of reactor elements in the cascade - N volumetric flow rate (cm³ s^–1) - z electron change - dm/dt rate of removal of metal (gs^–1) This paper was presented, in part, at the Electrochemical Reaction Engineering Symposium, Southampton University, April (1979).     

Process kinetics of UASB reactors treating non‐inhibitory substrate

The degradation of a non‐inhibitory substrate (sucrose) in upflow anaerobic sludge bed (UASB) reactors with different superficial flow velocites (u_s) was performed to generate experimental data. Additionally, a kinetic model accounting for the mass fraction of methanogens (f) and granule size distribution in UASB reactors is also proposed. At the volumetric loadings of 2.65–21.16 g COD dm^?3 day^?1, both the COD removal efficiency and granule size of the UASB reactors increase with increasing u_s. The f values determined experimentally increase from 0.13–0.24 to 0.27–0.43 if the volumetric loading is increased from 2.65 to 5.29 g COD dm^?3 day^?1. With a further increase in volumetric loading, the f values decline because of the accumulation of volatile fatty acids (VFAs). The predicted residual concentrations of VFAs and COD are in fairly good agreement with the experimental data. From the calculated effectiveness‐factor values, the influence of mass transfer resistance of the substrate sucrose on the overall substrate removal rate should not be neglected. From parametric sensitivity analyses together with the simulated concentration profiles, methanogenesis is the rate‐limiting step. Copyright © 2003 Society of Chemical Industry     

Optimal design of n membrane reactors in series using michaelis-menten kinetics

Exact analytical expressions are derived for the optimal design (minimum overall reaction volume) of N perfectly mixed membrane reactors in series carrying out an enzyme catalysed reaction with Michaelis-Menten kinetics. These equations enable the direct calculation of the smallest total reactor volume (holding time) needed for a given overall conversion degree, as well as the individual reactor volume and conversion degrees. Results are compared with the ones obtained with a series of N CSTRs and with a plug flow reactor. The theoretical superiority of membrane reactors versus CSTRs is demonstrated.     

Fluid Flow Characteristics of String Reactors Packed with Spherical Particles

A hydrodynamic investigation of three geometries of string pellet reactors filled with spheres was conducted. Two geometries were circular spiral channels, while the third was a straight horizontal square channel. Stimulus‐response experiments provided data for residence time distribution analysis from which Pe numbers and liquid holdup were deduced. Flow regimes and transitions were determined from visual observations through the transparent tube wall. For the whole range of the experimental conditions applied in this work and for all reactors, the ratio of gas to liquid velocities, V_g/V_l, is a controlling parameter for Pe number, holdup, and pressure drop.     

Micellization of Anionic Sulfonate Gemini Surfactants and Their Interactions With Anionic Polyacrylamide

Anionic sulfonate gemini surfactants 8‐s‐8(SO₃)₂ and 12‐s‐12(SO₃)₂ (s = 3, 6) were synthesized, and their micellization in aqueous solution at 25.0 °C and pH 9 was investigated. The results show that the critical micelle concentrations (CMC) of 8‐s‐8(SO₃)₂ are more than 2 orders of magnitude larger than those of 12‐s‐12(SO₃)₂, but the spacer length has a relatively small impact on the CMC. Moreover, the interactions of n‐s‐n(SO₃)₂ (n = 8, 12; s = 3, 6) with anionic polyacrylamide (PAM) at 25.0 °C and pH 9 were investigated using surface tensiometry, rheolgy, and scanning electron microscopy (SEM). The results indicate that the surface tension and rheological properties of PAM depend on the concentration of n‐s‐n(SO₃)₂. Below the critical aggregation concentration of C₁, surface tension is sharply reduced, the surface tension of n‐s‐n(SO₃)₂/PAM is lower than n‐s‐n(SO₃)₂ alone, but viscosity is almost unchanged with increasing C_{n‐s‐n(SO3)2}. Above C₁, surface tension reduces very slowly until the saturated concentration of C₂ is reached. Above C₂, surface tension rapidly reduces until C_M is attained, suggesting free n‐s‐n(SO₃)₂ micelles begin to form. In the region of C₁–C_M, the viscosity significantly increases. Above C_M, surface tension is basically unchanged and these curves coincide with those of the single surfactant system. Moreover, the viscosity is almost constant. The SEM images indicate that fibrous aggregates are formed below C₁, then transformed into multilayer fibrous aggregates above C₁, and further into fiber‐braided‐structured and spider‐web‐structured aggregates above C_M. The variation of viscosity is closely associated with the transformation of aggregates.     

Modeling of porous radiant burners with large extinction coefficients

A comparative study of numerical and analytical results for a porous radiant burner (PRB) is presented. It is shown that the analytical method captures all the features of the system and can be used for quantitative applications. Two solutions are found, one is located close to the inlet of the burner and the second one is close to the outlet. The effects of the molar flow rate, the interphase heat transfer coefficient (h_s) and the location of the flame in the matrix, on the radiation efficiency (RE) of the burner are studied. Local maxima in the RE vs. h_s curves indicate that intermediate values of h_s will be the optimum choice. Other trends are also analyzed and some recommendations are made.     

Investigations of fluid dynamics in mechanically stirred aerated slurry reactors

The fluid dynamics of stirred aerated slurry reactors with A-310® propeller, 4-blade 45° pitch turbine and 6-blade Rushton disc turbine were studied over a wide range of gas flow rates. With respect to power consumption, gas hold-up, and fluid dynamically limiting cases, viz., suspension and flooding, the Rushton disc turbine was found to be the best in stirred aerated slurry reactors. The influence of particle density, shape and mass fraction and of liquid properties on gassed critical stirrer speed, N_jsg, and of gassed power input per unit volume, P_jsg, on particle suspension and gas dispersion, were investigated. Empircal correlations in combination with that of Zwietering were established for scale-up design in three-phase slurry reactors.     

Monoliths as suitable catalysts for reverse‐flow combustors: Modeling and experimental validation

The performance of a bench‐scale monolithic reverse‐flow reactor (RFR) for methane combustion has been experimentally studied in this work. The influence of the different operating parameters, such as total gas flow rate (2.5 × 10^?4–5 × 10^?4 m³ s^?1 (STP)), methane inlet concentration (1000–5500 ppm), and switching time (300–900 s) on the reactor performance (outlet conversion and stability), has been experimentally determined. The validation of a heterogeneous one‐dimensional dynamic model for monolithic beds with the obtained experimental data allows the use of this model to simulate the behavior of industrial‐scale reactors. In the second part of the work, a systematic comparison of particulate and monolithic RFRs is carried out through design curves. Reactor length for 99% outlet conversion and the corresponding pressure drop is determined for varying operating conditions (surface velocity and inlet methane concentration). © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Sensitivity analysis on a sequencing batch reactor model I. Effect of kinetic parameters

A structured model for sequencing batch reactors, which was developed earlier and tested successfully against a number of experimental data sets, is used in this study to investigate the sensitivity of model predictions to some of the system kinetic parameters for a wide range of parameter values. The results obtained reveal the relative importance of the various parameters. The parameter K_s has insignificant effects on the effluent COD concentration; although its effect on the intermediate COD concentration is appreciable. The parameters α₁, μ_m, K_p, K_x, K_h and B_h have been shown to affect considerably both the intermediate and effluent COD concentrations. Since the effluent COD concentration is one of the prime state variables in the design of wastewater treatment reactors, special attention should be given to these parameters when such a model is used for design and control purposes. ©1997 SCI     

Numerical Calculations of Spray Roasting Reactors of the Steel Industry with Special Emphasis on Fe2O3‐Particle Formation

This work presents numerical calculations for the lay‐out of spray roasting reactors for the steel industry. In these reactors, a pickling liquor based on water and HCl containing FeCl₂ is regenerated in a combustor leading to the formation of Fe₂O₃ particles. For the lay‐out of these reactors, detailed knowledge of the flow and temperature field, the associated gas phase reactions, and especially, of the formation of the Fe₂O₃ particles is required. An extended particle formation model is presented which is based on earlier work. Finally, results for an industrial spray roasting reactor are given showing the potential of the numerical tools developed for the improvement of the technical lay‐out of such thermal reactors.     

Mixing performance comparison of milliscale continuous high‐shear mixers

Mixing performance of two continuous flow millilitre‐scale reactors (volumes 9.5 mL and 2.5 mL) equipped with rotor‐stator mixers was studied. Cumulative residence time distributions (RTD) were determined experimentally using a step response method. Distributions were measured for both reactors by varying impeller speed and feed flow rate. The mixing effect was determined by measured RTDs. Computational fluid dynamics (CFD) were used to verify that the residence time distribution in the measurement outlet agreed with the outlet flow. The mixing power of both reactors was determined using a calorimetric method. The reactor inlet flow rate was found to affect mixing performance at 1–13 s residence times but the effect of impeller speed could not be noted. Both milliscale reactors are close to an ideal continuous stirred‐tank reactor (CSTR) at the studied impeller speed and flow rate ranges. The specific interfacial area was found to depend on the reactor inlet flow rate at constant impeller speed for the case of copper solvent extraction.

     

Approximate design of loop reactors

A loop reactor (LR) is an N-unit system composed of a loop with gradually shifted inlet/outlet ports. This system was shown in our previous study [Sheintuch M., Nekhamkina O., 2005. The asymptotes of loop reactors. A.I.Ch.E. Journal 51, 224-234] to admit an asymptotic model for a loop of a fixed length with N→∞. Both the finite-unit and the asymptotic model exhibit a quasi-frozen or a frozen rotating pulse (FP) solution, respectively, within a certain domain of parameters that becomes narrower as feed concentration declines.In the present paper we derive approximate solutions of the ignited pulse properties in an LR as a function of the external forcing (switching) rate. Analysis of these solutions enable us to determine the maximal temperature in the system, as well as the boundaries of the FP domain. For the optimal solution we determine the maximal temperature and conversion dependencies on the reactor length and on N. The approximate solutions are verified by comparison with direct simulations of the asymptotic model and a good agreement was found. The obtained results can be successfully used for prediction of the finite unit LR.     

Organic–inorganic composite materials as photoinitiator for controlling/living polymerization

Titanium dioxide (TiO₂)/graphitic carbon nitride (g‐C₃N₄) composites were first used as photoinitiator for photochemically mediated controlled/living polymerization of methyl methacrylate. The polymerization was successfully carried out in polyethylene glycol at room temperature with FeCl₃·6H₂O/N,N,N ′,N ′,N ″‐pentamethyldiethylenetriamine as complex catalyst and ethyl 2‐bromoisobutyrate as initiator in this case. A pseudo‐first‐order dependence of the monomer concentration on the polymerization time was observed. TiO₂/g‐C₃N₄ was verified to be an efficient photoinitiator. The polymerization was controlled to produce poly(methyl methacrylate) with narrow molecular weight distribution and controlled number average molecular weight (M_n,GPC). The M_n,GPC matched well with the theoretical values when using both UV and sunlight irradiation as light source. The effects of reaction conditions on the polymerization were investigated. The polymerization could be started and stopped through periodically switching on/off the light. The living nature was further supported by the chain extension experiments. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42891.     

Tomography images to analyze the deformation of the cavern in the continuous‐flow mixing of non‐Newtonian fluids

Tomography, an efficient nonintrusive technique, was employed to visualize the flow in continuous‐flow mixing and to measure the cavern volume (V_c) in batch mixing. This study has demonstrated an efficient method for flow visualization in the continuous‐flow mixing of opaque fluids using two‐dimensional (2‐D) and 3‐D tomograms. The main objective of this study was to explore the effects of four inlet‐outlet configurations, fluid rheology (0.5–1.5% xanthan gum concentration), high‐velocity jet (0.317–1.660 m s^?1), and feed flow rate (5.3 × 10^?5?2.36 × 10^?4 m³ s^?1) on the deformation of the cavern. Dynamic tests were also performed to estimate the fully mixed volume (V_{fully mixed}) for the RT, A310, and 3AM impellers in a continuous‐flow mixing system, and it was found that V_{fully mixed} was greater than V_c. Incorporating the findings of this study into the design criteria will minimize the extent of nonideal flows in the continuous‐flow mixing of complex fluids and eventually improve the quality of end‐products. © 2013 American Institute of Chemical Engineers AIChE J, 60: 315–331, 2014     

Determination of the Initiating Capability of Detonators Containing TKX‐50, MAD‐X1, PETNC,DAAF, RDX,HMX or PETN as a Base Charge,by Underwater Explosion Test

A comprehensive investigation to determine the initiation power of detonators containing as a base charge the novel explosives: dihydroxylammonium 5,5′‐bis(tetrazolate‐1N‐oxide) – TKX‐50, dihydroxylammonium 5,5′‐bis(3‐nitro‐1,2,4‐triazolate‐1N‐oxide) – MAD‐X1, pentaerythritol tetranitrocarbamate – PETNC and 3,3′‐diamino‐4,4′‐azoxyfurazan – DAAF in comparison with RDX, HMX and PETN was undertaken. In order to estimate the initiation power of the detonators, the underwater initiating capability test was used. The total energy as a sum of the primary shock wave energy and the bubble gas energy was determined for each of these explosives, by measuring the overpressure of the shock waves generated in water. Moreover, the complete synthesis for novel explosives is presented. The thermal behavior of the explosives was investigated using DSC (differential scanning calorimetry). The gas phase absolute molar enthalpies at 298 K and 10⁵ Pa were calculated theoretically using the modified complete basis set method (CBS‐4M; M referring to the use of minimal population localization) with the Gaussian 09 software. Gas phase standard molar enthalpies of formation (ΔH_f°_(g)) at 298 K were computed using the atomization energy method. Standard molar enthalpies of formation (▵H_(s)°) were calculated using ΔH_f°_(g) and the standard molar enthalpies of sublimation by applying Trouton’s rule. The Chapman‐Jouguet (CJ) characteristics based on calculated ▵H_(s)° values were computed using the EXPLO5 V6.01 thermochemical computer code. For the calculations the theoretical maximum densities and densities obtained during the experiments presented in this work were used.