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Modelling and Optimization of Chemical Reactors

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A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Chemical Processes and Systems".

Deadline for manuscript submissions: closed (15 October 2023) | Viewed by 37279

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Prof. Dr. Maria Cristina Annesini

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Dipartimento di Ingegneria Chimica Materiali Ambiente, Sapienza Università di Roma, Via Eudossiana 18, 00184 Roma, Italy
Interests: membrane process modeling; chemical reactors; membrane reactors; bioreactors; hydrogen production processes; transport phenomena; separation processes
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Dr. Maria Anna Murmura

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Dipartimento di Ingegneria Chimica Materiali Ambiente, Sapienza Università di Roma, Via Eudossiana 18, 00184 Roma, Italy
Interests: hydrogen production from renewable sources; membrane reactors; transport phenomena; micromixing
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear colleagues,

The development of accurate models describing reaction and separation processes is an essential component of chemical engineering. The modelling of chemical reactors entails the description of mass, momentum, and energy transport equations, often at the same time. In addition, reactors with complex geometrical configurations are increasingly being applied in the fields, for instance, of thermochemical cycles and micro reactors. For the case of micro devices, in addition, the transport phenomena that are negligible on larger scales may become relevant.

The challenge related to the modelling of reacting systems is represented mainly by the need to obtain an accurate description, while avoiding an unnecessarily high degree of complexity. The increasing ease of solutions of complex systems of equations through sophisticated CFD modelling software, along with powerful computers, has led to a tendency to develop very complete descriptions of reactors, regardless of the utility of this approach. While it is true that the solution of these problems has become fairly easy, it is also true that the results of such calculations are often difficult to interpret and analyze. In addition, the accuracy of such models is limited to that with which the numerous empirical model parameters have been determined.

The scope of this Special Issue is to present insightful models of chemical reactors and proposed procedures for their optimization. The models may describe the chemical or biological reactors of any scale.

Prof. Dr. Maria Cristina Annesini
Dr. Maria Anna Murmura
Guest Editors

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Keywords

CFD
model
chemical reactors
biological reactors
micro reactors
mass transport
energy transport
momentum transport

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Published Papers (11 papers)

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Research

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12 pages, 2462 KiB

Open AccessArticle

Theoretical and Experimental Demonstration of Advantages of Microwave Peat Processing in Comparison with Thermal Exposure during Pyrolysis

by Tatiana Krapivnitckaia, Svetlana Ananicheva, Alisa Alyeva, Andrey Denisenko, Mikhail Glyavin, Nikolay Peskov, Alexander Vikharev, Anastasiia Sachkova, Sergey Zelentsov and Nikolay Shulaev

Processes 2024, 12(1), 92; https://doi.org/10.3390/pr12010092 - 30 Dec 2023

Cited by 2 | Viewed by 993

Abstract

A series of theoretical and experimental studies was carried out with the aim of a direct comparison of the thermal and microwave destruction of peat during pyrolysis. Different heating mechanisms in these processes were investigated in the framework of simulations conducted using a commercial 3D software package, CST Studio Suite, to define their specific features. Based on these simulations, identical reactors were constructed exploiting an electric element and a microwave complex as a heat source, and an experimental technique was developed that allows these processes to be correctly compared under similar conditions. Using these reactors based on different heat sources, comparative experiments on peat pyrolysis were performed, and the results of the theoretical analysis were confirmed. As a result, the advantages of microwave exposure were demonstrated to achieve a more uniform and deep fragmentation of peat, increase the reaction rate and reduce the processing time, with high energy efficiency accompanying this method. As part of the experiments, the yield of pyrolysis products was analyzed. During the microwave destruction of peat, a high gas output (up to 27%) was obtained, which allows for a further increase in the efficiency of this processing method when burning these gases. The conducted elemental analysis showed an increase in the percentage of carbon from about 50% to 78% after microwave processing, which can become a raw material for obtaining effective environmentally friendly sorbents. The prospects for creating industrial microwave complexes for processing organic materials are discussed. Full article

(This article belongs to the Special Issue Modelling and Optimization of Chemical Reactors)

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11 pages, 2030 KiB

Open AccessArticle

Experimental Complex for Peat Fragmentation by Low-Temperature Microwave Pyrolysis

by Tatiana Krapivnitckaia, Svetlana Ananicheva, Alisa Alyeva, Andrey Denisenko, Mikhail Glyavin, Nikolai Peskov, Dmitriy Sobolev and Sergey Zelentsov

Processes 2023, 11(7), 1924; https://doi.org/10.3390/pr11071924 - 26 Jun 2023

Cited by 1 | Viewed by 1055

Abstract

The design of a technological complex for microwave processing of organic materials is proposed. The electrodynamic system of an oversized microwave reactor for low-temperature pyrolysis has been developed. The constructive elements of the complex that allow its continuous failure-free operation in conditions of high radiation intensity are described. Based on the prototype of the elaborated reactor, model experiments on microwave pyrolysis of peat were carried out. The elemental composition of the solid fraction was analyzed during the conducted experiments. The possibility of the efficiency enhancement of the proposed processing method and potential applications of the novel technology are discussed. Full article

(This article belongs to the Special Issue Modelling and Optimization of Chemical Reactors)

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15 pages, 854 KiB

Open AccessArticle

A Model for the Flow Distribution in Dual Cell Density Monoliths

by Consuelo Reinao and Iván Cornejo

Processes 2023, 11(3), 827; https://doi.org/10.3390/pr11030827 - 10 Mar 2023

Cited by 5 | Viewed by 2376

Abstract

Monoliths are promising as catalytic structured supports due to their many operational advantages. Compared to pellets, monoliths offer low backpressure and good heat distribution, even at high flow rates. There is interest in the industry for improving temperature control in highly exothermic systems, [...] Read more.

C O_{2}

for e-fuels synthesis. In this context, novel substrate shapes, such as non-homogeneous cell density monoliths, show good potential; however, to date, they have only been sparsely described. This work focuses on a dual cell density substrate and uses a computational model of a straight-channel monolith with two concentric regions to analyze its flow distribution. The central (core) and peripheral (ring) regions of the substrate differ in cell density in order to obtain a non-homogeneous cross-section. The model is validated against classical data in the literature and theoretical equations. Then, the flow fraction passing through each region of the substrate is registered. Several flow rates, core sizes and combinations of apparent permeabilities are tested. According to the results, the flow distribution depends only on the monolith geometrical features and not on the flow rate. A model for this phenomenon is proposed. The model accurately predicted the flow fraction passing through each region of the monolith for all the cases analyzed. Full article

(This article belongs to the Special Issue Modelling and Optimization of Chemical Reactors)

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20 pages, 6053 KiB

Open AccessFeature PaperArticle

Effects of Fuel Input on Pulsation Reactor Behavior—An Experimental Study

by Jakub Dostál, Stefan Heidinger, Christian Klaus, Simon Unz and Michael Beckmann

Processes 2023, 11(2), 444; https://doi.org/10.3390/pr11020444 - 1 Feb 2023

Cited by 1 | Viewed by 1730

Abstract

Material treatment in pulsation reactors (PR) brings the possibility of synthesizing powdery products with advantageous properties, such as nanoparticle sizes and high specific surface areas, at an industrial scale. The extraordinary material properties can be ascribed to special process parameters in a PR, primarily the periodically varying conditions and the consequently enhanced heat and mass transfer between the medium and the particles of the material. Understanding the connections between the PR operation parameters, such as fuel and air intake or PR geometry, and the resulting process parameters (temperature distribution, flow velocity and pressure field, and frequency of the pulsations) is essential to enabling a controllable treatment process. Despite the long history of pulsation reactor technology, many connections and dependencies remain unclear. Thus, the influence of the fuel (and air) supply on the pulsation reactor behavior is experimentally examined in this study. The investigated PR characteristics and process parameters are primarily those that have an impact on the heat and mass transfer, i.e., the temperature distribution, flow velocity, and pressure field, and frequency of the pulsations. In addition to these, the harmonic distortion of the oscillations and the heat losses are evaluated. Full article

(This article belongs to the Special Issue Modelling and Optimization of Chemical Reactors)

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15 pages, 654 KiB

Open AccessArticle

Mathematical Modeling and Robust Multi-Objective Optimization of the Two-Dimensional Benzene Alkylation Reactor with Dry Gas

by Menglin Yang, Feifei Shen, Zhencheng Ye and Wenli Du

Processes 2022, 10(11), 2271; https://doi.org/10.3390/pr10112271 - 3 Nov 2022

Viewed by 1895

Abstract

The benzene alkylation reactor using the dry gas is the most significant equipment in the ethylbenzene manufacturing process. In this paper, a two-dimensional homogeneous model is developed for steady state simulation of the industrial multi-stage catalytic reactor for ethylbenzene. The model validation on a practical benzene alkylation reactor shows the model is accurate and can calculate the hot spot temperatures. The composition of dry gas from upstream process varies with the operating conditions, which can cause unexpected hot spots in the reactor and catalyst deactivation. Considering the uncertainty in dry gas composition, a robust multi-objective optimization framework is proposed: first, the back-off in constraints is introduced to the multi-objective optimization problem to hedge against the worst case; then the optimal operating point can be selected using the multi-criteria decision-making. The reactor optimization objectives are maximizing selectivity of ethylene and conversion of ethylbenzene, and the distribution ratios of dry gas are defined as decision variables. Results of robust multi-objective optimization show the selectivity and conversion at the optimal operating point are 90.88% (decreased by 0.24% compared to the practical condition) and 99.94% (increased by 0.72%). Importantly, the proportion of violations of the hot spot constraints decreases from 13.7% of the traditional method to 3.8% by applying the proposed robust multi-objective optimization method. Full article

(This article belongs to the Special Issue Modelling and Optimization of Chemical Reactors)

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14 pages, 20359 KiB

Open AccessFeature PaperArticle

Model-Based Prediction of Perceived Light Flashing in Recirculated Inclined Wavy-Bottomed Photobioreactors

by Giuseppe Olivieri, Monica Moroni, Marcel Janssen, Luca Piersanti, Daniela Mezza and Marco Bravi

Processes 2021, 9(7), 1158; https://doi.org/10.3390/pr9071158 - 2 Jul 2021

Cited by 1 | Viewed by 1883

Abstract

Microalgae biomass production rate in short light-path photobioreactors potentially can be improved by mixing-induced flashing light regimes. A cascade photobioreactor features a thin liquid layer flowing down a sloping, wavy-bottomed surface where liquid flow exhibits peculiar local recirculation hydrodynamics, potentially conducive to an ordered flashing light regime. This article presents a model-based analysis of the frequency distribution of perceived irradiance in said wavy-bottomed photobioreactor. The model combines a Lagrangian description of the motion of individual cells, in turn derived from the hydrodynamic parameters of the photobioreactor extracted from an experimentally validated Computational Fluid Dynamic model, with a simplified description of the irradiance field across the culture thickness, down to the spectral analysis of perceived irradiance. The main finding of the work is that the wavy bottomed photobioreactor provides a ‘robust’ spectral excitation to the circulating microalgae up to 3 Hz frequency, while in flat panels and bubble columns excitation decays evenly at a 24 db/octave rate. This analysis paves the way to improving the light flashing performance of the wavy-bottomed photobioreactor with respect to geometry (cavity size and installation inclination) and operation (flow rate). Full article

(This article belongs to the Special Issue Modelling and Optimization of Chemical Reactors)

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22 pages, 3208 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Modelling and Multi-Objective Optimization of the Sulphur Dioxide Oxidation Process

by Mohammad Reza Zaker, Clémence Fauteux-Lefebvre and Jules Thibault

Processes 2021, 9(6), 1072; https://doi.org/10.3390/pr9061072 - 20 Jun 2021

Cited by 3 | Viewed by 11167

Abstract

Sulphuric acid (H₂SO₄) is one of the most produced chemicals in the world. The critical step of the sulphuric acid production is the oxidation of sulphur dioxide (SO₂) to sulphur trioxide (SO₃) which takes place in a multi catalytic bed reactor. In this study, a representative kinetic rate equation was rigorously selected to develop a mathematical model to perform the multi-objective optimization (MOO) of the reactor. The objectives of the MOO were the SO₂ conversion, SO₃ productivity, and catalyst weight, whereas the decisions variables were the inlet temperature and the length of each catalytic bed. MOO studies were performed for various design scenarios involving a variable number of catalytic beds and different reactor configurations. The MOO process was mainly comprised of two steps: (1) the determination of Pareto domain via the determination a large number of non-dominated solutions, and (2) the ranking of the Pareto-optimal solutions based on preferences of a decision maker. Results show that a reactor comprised of four catalytic beds with an intermediate absorption column provides higher SO₂ conversion, marginally superior to four catalytic beds without an intermediate SO₃ absorption column. Both scenarios are close to the ideal optimum, where the reactor temperature would be adjusted to always be at the maximum reaction rate. Results clearly highlight the compromise existing between conversion, productivity and catalyst weight. Full article

(This article belongs to the Special Issue Modelling and Optimization of Chemical Reactors)

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13 pages, 1013 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

In Situ Bio-Methanation Modelling of a Randomly Packed Gas Stirred Tank Reactor (GSTR)

by Leone Mazzeo, Antonella Signorini, Giuseppe Lembo, Irene Bavasso, Luca Di Palma and Vincenzo Piemonte

Processes 2021, 9(5), 846; https://doi.org/10.3390/pr9050846 - 12 May 2021

Cited by 5 | Viewed by 2694

Abstract

In situ Bio-Methanation (BM) is a recently developed biogas upgrading technique which finds application also in the Power to Gas (P2G) field. In this study a novel configuration of BM digester, the randomly packed Gas Stirred Tank Reactor (GSTR), was modelled. A 49 L reactor, in thermophilic conditions (55 °C) and at atmospheric pressure, was filled up with random packing on which the microbial populations could adhere. The feedstock used was Second Cheese Whey (SCW), liquid waste of cheese factories, rich in lactose (38 g/L), and its flowrate was chosen to obtain a Hydraulic Retention Time (HRT) of 30 days. The process was analyzed for different hydrogen inlet flowrates of 10 mL/min and 50 mL/min. The produced biogas was also recirculated in the reactor in order to transfer, into the liquid phase, as much hydrogen as possible. The model parameters were estimated by means of stationary state information of the reactor working without hydrogen injection, while a dynamical fitting was necessary to evaluate the value of the hydrogen mass transfer coefficient during BM. The model well described the reactor behavior and, by means of a dimensionless analysis in which the numbers of Stanton (St) and β were defined, it was found out that the mass transfer coefficient is the limiting step of the process. Full article

(This article belongs to the Special Issue Modelling and Optimization of Chemical Reactors)

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10 pages, 4392 KiB

Open AccessArticle

New Method to Evaluate the Crosslinking Degree of Resin Finishing Agent with Cellulose Using Kjeldahl Method and Arrhenius Formula

by Jiangfei Lou, Jinfang Zhang, Shengxiang Xu, Dan Wang and Xuerong Fan

Processes 2021, 9(5), 767; https://doi.org/10.3390/pr9050767 - 27 Apr 2021

Cited by 7 | Viewed by 3389

Abstract

In anti-wrinkle finishing, the crosslinking degree of fabric is mainly determined by wrinkle recovery angle, stiffness, and viscosity, these indicators can only reflect the finishing effect from a macro perspective, which cannot reflect whether the crosslinking is sufficient, and it is difficult to quantify the crosslinking degree. In this paper, we combined the Kjeldahl method with the Arrhenius formula and proposed a method to analyze the crosslinking degree of dimethyloldihydroxyethyleneurea (two-dimensional (2D) resin) with cotton cellulose during delayed-cure finishing for the first time. The nitrogen content of completed fabrics during storage was measured by the Kjeldahl method, and the reaction rate equation of the 2D resin and cellulose under normal temperature conditions was calculated. The results show that the nitrogen content is more suitable to indicate the crosslinking degree, and the apparent activation energy was 28.271 kJ/mol and the pre-finger factor was 0.622, which indicated that the 2D resin was prone to cross-linking with cotton fabrics during storage. During long-term storage, the relative errors between the calculated and measured values of the nitrogen content were within ±5%, and the accuracy was higher than the traditional evaluation method. The stability of 2D resins during the storage of delayed-curing finishing was also analyzed through this method. Full article

(This article belongs to the Special Issue Modelling and Optimization of Chemical Reactors)

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18 pages, 2148 KiB

Open AccessFeature PaperArticle

The Impact of Local Hydrodynamics on High-Rate Activated Sludge Flocculation in Laboratory and Full-Scale Reactors

by Sophie Balemans, Siegfried E. Vlaeminck, Elena Torfs, Leonie Hartog, Laura Zaharova, Usman Rehman and Ingmar Nopens

Processes 2020, 8(2), 131; https://doi.org/10.3390/pr8020131 - 21 Jan 2020

Cited by 4 | Viewed by 4185

Abstract

High rate activated sludge (HRAS) processes have a high potential for carbon and energy recovery from sewage, yet they suffer frequently from poor settleability due to flocculation issues. The process of flocculation is generally optimized using jar tests. However, detailed jar hydrodynamics are often unknown, and average quantities are used, which can significantly differ from the local conditions. The presented work combined experimental and numerical data to investigate the impact of local hydrodynamics on HRAS flocculation for two different jar test configurations (i.e., radial vs. axial impellers at different impeller velocities) and compared the hydrodynamics in these jar tests to those in a representative section of a full scale reactor using computational fluid dynamics (CFD). The analysis showed that the flocculation performance was highly influenced by the impeller type and its speed. The axial impeller appeared to be more appropriate for floc formation over a range of impeller speeds as it produced a more homogeneous distribution of local velocity gradients compared to the radial impeller. In contrast, the radial impeller generated larger volumes (%) of high velocity gradients in which floc breakage may occur. Comparison to local velocity gradients in a full scale system showed that also here, high velocity gradients occurred in the region around the impeller, which might significantly hamper the HRAS flocculation process. As such, this study showed that a model based approach was necessary to translate lab scale results to full scale. These new insights can help improve future experimental setups and reactor design for improved HRAS flocculation. Full article

(This article belongs to the Special Issue Modelling and Optimization of Chemical Reactors)

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Review

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24 pages, 1573 KiB

Open AccessFeature PaperReview

Methodologies for the Design of Solar Receiver/Reactors for Thermochemical Hydrogen Production

by M.A. Murmura and M.C. Annesini

Processes 2020, 8(3), 308; https://doi.org/10.3390/pr8030308 - 7 Mar 2020

Cited by 8 | Viewed by 4195

Abstract

Thermochemical hydrogen production is of great interest due to the potential for significantly reducing the dependence on fossil fuels as energy carriers. In a solar plant, the solar receiver is the unit in which solar energy is absorbed by a fluid and/or solid particles and converted into thermal energy. When the solar energy is used to drive a reaction, the receiver is also a reactor. The wide variety of thermochemical processes, and therefore of operating conditions, along with the technical requirements of coupling the receiver with the concentrating system have led to the development of numerous reactor configurations. The scope of this work is to identify general guidelines for the design of solar reactors/receivers. To do so, an overview is initially presented of solar receiver/reactor designs proposed in the literature for different applications. The main challenges of modeling these systems are then outlined. Finally, selected examples are discussed in greater detail to highlight the methodology through which the design of solar reactors can be optimized. It is found that the parameters most commonly employed to describe the performance of such a reactor are (i) energy conversion efficiency, (ii) energy losses associated with process irreversibilities, and (iii) thermo-mechanical stresses. The general choice of reactor design depends mainly on the type of reaction. The optimization procedure can then be carried out by acting on (i) the receiver shape and dimensions, (ii) the mode of reactant feed, and (iii) the particle morphology, in the case of solid reactants. Full article

(This article belongs to the Special Issue Modelling and Optimization of Chemical Reactors)

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