Volume 21, Issue 3

Controlling unstable and integrating type continuously stirred tank reactors (CSTRs) are more difficult due to the presence of poles in the right half and at the origin of the s-plane respectively. The existence of dead-time needs more efficient control requirements for CSTRs. In this work, a modified indirect fractional-order internal model control proportional-derivative (MIFOIMC-PD) decoupled dual-loop control strategy is suggested for unstable and integrating plants with dead time. The external-loop controller is designed using the MIFOIMC strategy for obtaining adequate servo performance. PD controller is designed such that it stabilizes the plant while disturbances occur. Decoupled nature of the suggested strategy allows this PD controller to be designed without considering the external-loop dynamics. Reference tracking and disturbance elimination capabilities of the suggested method are also quantitatively compared with reported methods. It is established that the suggested MIFOIMC-PD control architecture controls CSTRs more effectively than some lately reported schemes.

In this study, oxidative desulfurization was performed on simulated oil fraction consist of 1000 ppm dibenzothiophene. Cobalt supported on natural zeolite of Kaolin has been used as heterogeneous catalysts. 10% Co/metaKaolin with hydrogen peroxide as oxidant and acetonitrile as extraction solvent have shown excellent performance on desulfurization. Response surface methodology in experimental design and its subset Box–Benken was used to evaluate the performance of the selected catalyst in different operating conditions such as temperature, oxidant to sulfur molar ratio, time and catalyst amount. Also, optimum conditions was obtained are equal to 60 °C, O/S molar ratio (10.8 mol/mol), time (46 min) and catalyst amount 0.04 g with 97.1% sulfur removal. Oxidative desulfurization of model oil containing 1000 ppm of each sulfur component benzothiophene and thiophene was also tested at the optimum conditions, Oxidative desulfurization yield was ordered as DBT > BT > Th. In addition, after four steps consecutive recycle under optimum conditions oxidative desulfurization capacity of 10% Co/metaKaolin catalyst decreased from 97% to 92%, which is still high desulfurization capability. Finally, the performance of 10% Co/metaKaolin catalyst in oxidative desulfurization was evaluated for real oil fractions, gasoline and gasoil that was provided from regional oil refinery with sulfur content of 286 ppm and 7900 ppm, respectively. At the optimum conditions of operating variables desulfurization yield was 58% and 79% of total sulfur removal for gasoline and gasoil respectively with no significant changes in fuels properties.

The skin effect causes about 86% of the energy to be concentrated in the narrow surface layer during the induction heating process, which leads to the uneven temperature distribution during the treatment of flowing liquid by induction heating technology. The concentration of heat caused by the skin effect can be avoided by dispersing the induced heating metal structure in the treated fluid, but in most cases, this will lead to a decrease in heating efficiency. Therefore, the purpose of this study is to compare and design the susceptor structures that can avoid the heating concentration problem caused by the skin effect and have higher efficiency. Hence, in this research four kinds of susceptor structures that are the metal sphere, sheet metal, static mixer, and metal pipe were studied. The results show that the combination of metal sphere susceptor and sheet metal susceptor can result in higher heating efficiency than the metal sphere susceptor alone. Ferromagnetic stainless steel with lower relative permeability is more suitable for making sheet metal susceptor than paramagnetic stainless steel. Adding internal components to the metal pipe susceptor will not change its heating efficiency. The heating efficiency of metal sphere type susceptor, sheet metal susceptor, and static mixer susceptor can be up to 58%, 64%, and 67%, respectively. When 430 metal pipe heater is used, the highest heating efficiency can be obtained, and the highest heating efficiency is 80%.

Despite extensive contributions have been made over the past several decades, there are still ongoing challenges in improving gas dispersion performance in stirred tanks. To that end, a stirred tank equipped with four semi-circular (SC) tube baffles was designed. Hydrodynamics in the stirred tank before and after aeration were studied. The turbulent fluid flow was simulated using the standard k-ε turbulence model. The gas–liquid two-phase flow was simulated by the Eulerian–Eulerian multiphase model and the k - ε dispersed turbulence model. The impeller rotation was modeled with the multiple reference frame (MRF) approach. Firstly, the grid independence test was made. By comparing the distributions of gas holdup in the flat-plate (FP) baffled stirred tank with literature results, the reliability of the numerical model and simulation method was verified. Subsequently, the flow field, gas holdup and power consumption of the SC and FP configurations were studied, respectively. Results show that the former can increase the fluid velocities and promote the gas holdup dispersion. Besides, it is energy-saving and has a higher relative power demand (RPD). The findings obtained here lay a preliminary foundation for the potential application of the SC configuration in the process industry.

Support structures of various materials are used to enhance the performance of catalytic process chemistry. Typically, fixed bed supports contain regular channels enabling high throughput because of the low pressure drop that accompanies high flow rates. However, many fixed bed supports have a low surface-area-to-volume ratio resulting in poor contact between the substrates and catalyst. Three dimensional polymer printing (3dP) can be used to overcome these disadvantages by offering precise control over key design parameters of the fixed bed, including total bed surface area, as well as accommodating system integration features that are compatible with continuous flow chemistry. Additionally, 3dP allows for optimization of the catalytic process based on extrinsic constraints (e.g. operating pressure) and digital design features. These design parameters together with the physicochemical characterization and optimization of catalyst loading can be tuned to prepare customizable reactors based on objectives for substrate conversion and desired throughput. Using a Suzuki (carbon–carbon) cross-coupling reaction catalyzed by palladium, we demonstrate our integrated approach. We discuss key elements of our strategy including the rational design of hydrodynamics, immobilization of the heterogeneous catalyst, and substrate conversion. This hybrid digital-physical approach enables a range of pharmaceutical process chemistries spanning discovery to manufacturing scale.

PAN microtubule hyperfiltration reactor (PMHR) with organic phosphate system containing simulant wastewater section with buffer solution acetic acid and enrichment section with nitric acid solution and organic phosphate C 16 H 35 O 4 P (Di (6-methylheptyl) phosphate) dissolved in benzin, has been studied for the praseodymium (III)[expressed as Pr(III) or Pr 3+ ] recovery in the rare-earth simulant wastewater. Many factors of Pr(III) recovery using PMHR need to explore, including hydrogen ion concentration (or pH), cinit of Pr(III) and different ionic strength of rare-earth simulant mine wastewater, volume ratio of C 16 H 35 O 4 P with benzin and nitric acid solution (O/W), nitric acid concentration, C 16 H 35 O 4 P concentration, different acid solution of enrichment section on Pr(III) recovery with PMHR were investigated. The experimental results show that the best recovery conditions of Pr(III) were obtained as that nitric acid concentration was 4.00 mol/L, C 16 H 35 O 4 P concentration was 0.200 mol/L, and O/W was 0.6 in the enrichment section, and pH value was 4.90 in the wastewater section. Ionic strength of rare-earth simulant mine wastewater had no obvious effect on Pr(III) recovery. When cinit of Pr(III) concentration was 1.67 × 10 −4  mol/L, the recovery percentage of Pr(III) was up to 94.7% in 160 min. The kinetic equations were developed, and diffusion coefficient in the microtubule reactor and thickness of diffusion layer between the wastewater section and the microtubule pipe wall were obtained by linear slope method. They were 4.16 × 10 −6  m 2 /s and 4.65 μm, respectively. PMHR, owing to a large number of C 16 H 35 O 4 P was used in the enrichment section, can renewal the losing carrier of microtubule reactor. As a result, the recovery percentage of Pr(III) was increased, the stability of PMHR system was enhanced, and the life span of the PMHR system was extended.

Flow reactors are widely used to study the formation of various nanoparticles, such as carbon black, soot, nickel, titania, and silica. Such reactors provide well-controlled conditions, making them a favored laboratory tool to investigate the details of particle formation. Here we present NanoParticle Flow Reactor (NanoPFR), a detailed model to simulate nanoparticle synthesis in flow reactors. The model predicts the agglomerate fractal-like morphology and size distribution with a 2-variable sectional population balance model coupled with gas-phase chemistry. The particle formation processes employed in the code are tested using detailed discrete element modeling simulations and then used to predict carbon black formation from ethylene pyrolysis experiments from the literature. The code is a robust flow reactor predictive tool with a strong foundation that can serve as a basis for further development, including the simulation of other nanoparticles formation.

Hot slag modification during its discharging process is considered to be a key technology to improve the recycling rate of metallurgical slag, and hot slag is converted into new value-added materials. In order to prevent the solidification of hot slag surface during modification and facilitate the modifier addition, a slag pot with mechanical stirring was applied and the heat transfer characteristics of hot slag were studied by numerical simulation. By comparison, the heat transfer behavior in a non-agitated slag pot was also studied by considering the natural convection. In addition, to reduce the heat loss of hot slag, a pot cover was installed on the agitated slag pot and its heat transfer characteristics were studied. The results show that the turbulent kinetic energy of hot slag surface can be significantly increased by mechanical stirring. After 20 min, the surface temperature of hot slag in the agitated slag pot is higher than that of the non-agitated slag pot, about 1650 K. After installing a pot cover, the surface temperature of hot slag in the agitated slag pot can be increased by about 17 K after 5 min holding time, and the average surface heat flux on the top surface of slag pot can be reduced by almost 1.75 × 10 5  W/m 2 .

the present paper, the effectiveness factor of porous catalytic particles is evaluated in the absence of boundary conditions symmetry over the external surface by computational fluid dynamic (CFD) techniques. The first-order kinetics of decane oxidation, already evaluated experimentally, is taken as a representative reaction. Our study arises from the fact that, in the open literature, the effectiveness factor is usually calculated considering conditions of symmetry of concentration field around particles. However, depending on the fluid dynamics of the system, such conditions are not always established and, thus, our work aims at studying for the first time the behaviour of particle catalysts with non-uniform concentration fields over the surface. In particular, the effectiveness factor of the particles in a catalytic layer is calculated in the absence of symmetry by changing several parameters (temperature, tortuosity and mean pore diameter of particle) using two different methods, named Sphere-by-Sphere ( SbS ) and Equisized-Volume ( EV ), respectively. The results of these two methods are then compared to the theoretical one obtained in the presence of spherical symmetry. As a main result, we found that, for moderately low values of Thiele modulus (<1.3 ca.), the analytical expression of the effectiveness factor obtained under spherical symmetry can be also applied in non-symmetric conditions. On the contrary, this cannot be done for higher values of Thiele modulus, for which we propose an empirical correlation of the effectiveness factor based on a corrected Thiele modulus. The efficacy of our approach is stated by the fact that pseudo-homogeneous-mode simulations of the heterogeneous system show results that match very well those obtained in heterogeneous mode, with an important reduction of calculation time and memory. The presented methodology can be also applied to n -order kinetics.

The present study aims at increasing the prediction accuracy of simulating gas–solid fluidized bed hydrodynamics. Two simulation packages, Fluent and MFIX, were used to predict the pressure drop, voidage, and solid-phase velocities by solving mass, momentum, and energy balance equations. A 2D multi-fluid Eulerian model with the kinetic theory of granular flow (KTGF) was applied to simulate the process by considering two different drag models. The same comparative criterion of average absolute relative deviation (AARD%) was considered to compare the present simulation with the previous works. Compared to the prior works, the minimum decrease in error (AARD% of 5.91%) was 3.17% related to the estimation of the time-averaged voidage by applying the Gidaspow model, while the maximum reduction in error (ARRD% of 5.88%) was 17.35% attributed to the prediction of pressure drop by employing the Syamlal-O’Brien model, both in Fluent software. However, MFIX software was the best CFD tool in predicting time-averaged voidage by AARD% values less than 9% under all conditions. Furthermore, similar patterns in contours were observed for solid-phase volume fraction and gas/solid phase velocities in both simulation tools, which are compatible with results from the literature without any significant difference.