Design and Engineering of Microreactor and Smart-Scaled Flow Processes

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

Deadline for manuscript submissions: closed (30 November 2013) | Viewed by 149809

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Faculty of Engineering, Computer and Mathematical Sciences, School of Chemical Engineering, University of Adelaide, Adelaide, SA 5005, Australia
Interests: micro process technology; flow chemistry; process intensification; green processing; sustainability (life cycle assessment, cost analysis)
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Dear Colleagues,

Microreactors are small devices with sub-millimeter internals which have superb mass and heat transfer. Initially, they were used for reactions with very high demands on the latter, e.g. very exothermic reactions, gas-liquid reactions with interfacial transport issues, reactions with very fast kinetics which demands even faster mixing, and more. In this way, the processing window was opened widely and, also due to the minute volumes only present in the reaction zone, safe processing under otherwise hazardous conditions was enabled. This includes processing of reactions which are prone to thermal runaway and in the explosive regime. Scale-up of promising reactions and products which was hindered with conventional technology is now possible using the new equipment. This has widened the process development possibilities in chemical industry.

In the last years, micro process technology was not only used for the very problematic synthetic issues which formerly had a dead-end position in industry’s process development. Rather, the scope of chemical reactions to be processed in microreactors was considerably widened by exploring new process conditions with regard to temperature, pressure, concentration, solvents, and more. This is commonly referred to as flow chemistry. This allowed to reduce the processing time-scale for many reactions to the minute range or even below which fits well to the residence times of microreactors. In addition, the process integration of several reactions in one flow to a multi-step synthesis has opened a new door in molecular diversity as well as system and process complexity. The same holds for the combination of reactions and separations in micro-flow. To achieve throughputs relevant for industrial production, smart scale-out to milli-flow units has established and supplemented the num­bering-up concept (parallelization of microchannels/-reactors operated under equal conditions).

New innovations and enabling technologies need anyhow evaluation and benchmarking with conventional technology on the full-system level. Yet, microreactor technology has in the last years deepened so much into process intensification on a holistic scale that the focus increasingly is given towards the process dimension—to process design and automation, real-case applications, cost analysis, life-cycle assessment, and more. The impact on cost competitiveness and sustainability becomes well assessed.

Facing this very recent scientific achievement, the special issue “Design and Engineering of Microreactor and Smart-Scaled Flow Processes” of the journal Processes aims to cover recent advances in the development of microreactor and smart-scaled flow processes towards the process level — in the sense as given above.

Prof. Dr. Volker Hessel
Guest Editor

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Keywords

  • microreactors
  • micro process technology
  • milli process technology
  • flow chemistry
  • process intensification
  • green engineering
  • life cycle assessment
  • cost analysis
  • continuous processing
  • novel process windows
  • process design
  • process control/-automation


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Published Papers (14 papers)

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Editorial

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608 KiB  
Editorial
Special Issue: Design and Engineering of Microreactor and Smart-Scaled Flow Processes
by Volker Hessel
Processes 2015, 3(1), 19-22; https://doi.org/10.3390/pr3010019 - 26 Dec 2014
Cited by 1 | Viewed by 5194
Abstract
Reaction-oriented research in flow chemistry and microreactor has been extensively focused upon in special journal issues and books. On a process level, this resembled the “drop-in” (retrofit) concept with the microreactor replacing a conventional (batch) reactor. Meanwhile, with the introduction of the mobile, [...] Read more.
Reaction-oriented research in flow chemistry and microreactor has been extensively focused upon in special journal issues and books. On a process level, this resembled the “drop-in” (retrofit) concept with the microreactor replacing a conventional (batch) reactor. Meanwhile, with the introduction of the mobile, compact, modular container technology, the focus is more on the process side, including also providing an end-to-end vision of intensified process design. Exactly this is the focus of the current special issue “Design and Engineering of Microreactor and Smart-Scaled Flow Processes” of the journal “Processes”. This special issue comprises three review papers, five research articles and two communications. [...] Full article

Research

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29622 KiB  
Article
Ag/SiO2- and Ag/Co3O4-Based Monolithic Flow Microreactors for Hydrogenation of Dyes: Their Activity and Stability
by Yasemin Hakat, Trupti V. Kotbagi and Martin G. Bakker
Processes 2015, 3(1), 98-112; https://doi.org/10.3390/pr3010098 - 16 Feb 2015
Cited by 5 | Viewed by 6087
Abstract
Silver nanoparticles supported on hierarchically porous silica and cobalt oxide monoliths have previously been shown to be catalytically active for the hydrogenation of common organic dyes in batch studies. This work presents a detailed investigation of the activity and stability of these monoliths [...] Read more.
Silver nanoparticles supported on hierarchically porous silica and cobalt oxide monoliths have previously been shown to be catalytically active for the hydrogenation of common organic dyes in batch studies. This work presents a detailed investigation of the activity and stability of these monoliths during the hydrogenation of eosin-Y in a continuous flow microreactor. The silver-containing monoliths showed excellent catalytic activity that reached a plateau after a period of approximately 6 h. From SEM particle size distribution studies of the catalysts before and after water and hexane were flowed through them, it was determined that under reaction conditions, silver was removed both by washing off of particles and by dissolution of silver. Full article
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1328 KiB  
Article
Stability Analysis of Reactive Multiphase Slug Flows in Microchannels
by Alejandro A. Munera Parra, Nicolai Antweiler, Rachit Nagpal and David W. Agar
Processes 2014, 2(2), 371-391; https://doi.org/10.3390/pr2020371 - 6 May 2014
Cited by 5 | Viewed by 7477
Abstract
Conducting multiphase reactions in micro-reactors is a promising strategy for intensifying chemical and biochemical processes. A major unresolved challenge is to exploit the considerable benefits offered by micro-scale operation for industrial scale throughputs by numbering-up whilst retaining the underlying advantageous flow characteristics of [...] Read more.
Conducting multiphase reactions in micro-reactors is a promising strategy for intensifying chemical and biochemical processes. A major unresolved challenge is to exploit the considerable benefits offered by micro-scale operation for industrial scale throughputs by numbering-up whilst retaining the underlying advantageous flow characteristics of the single channel system in multiple parallel channels. Fabrication and installation tolerances in the individual micro-channels result in different pressure losses and, thus, a fluid maldistribution. In this work, an additional source of maldistribution, namely the flow multiplicities, which can arise in a multiphase reactive or extractive flow in otherwise identical micro-channels, was investigated. A detailed experimental and theoretical analysis of the flow stability with and without reaction for both gas-liquid and liquid-liquid slug flow has been developed. The model has been validated using the extraction of acetic acid from n-heptane with the ionic liquid 1-Ethyl-3-methylimidazolium ethyl sulfate. The results clearly demonstrate that the coupling between flow structure, the extent of reaction/extraction and pressure drop can result in multiple operating states, thus, necessitating an active measurement and control concept to ensure uniform behavior and optimal performance. Full article
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1584 KiB  
Article
Green Process Engineering as the Key to Future Processes
by Dipesh Patel, Suela Kellici and Basudeb Saha
Processes 2014, 2(1), 311-332; https://doi.org/10.3390/pr2010311 - 19 Mar 2014
Cited by 23 | Viewed by 13686
Abstract
Growing concern for the environment, increasing stringent standards for the release of chemicals into the environment and economic competiveness have led to more environmentally friendly approaches that have resulted in greater pollution prevention via waste reduction and efficiency maximisation. Green process engineering (GPE) [...] Read more.
Growing concern for the environment, increasing stringent standards for the release of chemicals into the environment and economic competiveness have led to more environmentally friendly approaches that have resulted in greater pollution prevention via waste reduction and efficiency maximisation. Green process engineering (GPE) is an important tool that could make significant contributions in the drive toward making hazardous and wasteful processes more sustainable for the benefit of the economy, environment and society. This article highlights the guidelines that could be used by scientists and engineers for designing new materials, products, processes and systems. Few examples of current and future applications of GPE, particularly in the areas of biofuels, supercritical fluids, multi-functional reactors and catalytic processes, have been presented. Full article
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951 KiB  
Article
Selection of Technical Reactor Equipment for Modular, Continuous Small-Scale Plants
by Nicolai Krasberg, Lukas Hohmann, Thomas Bieringer, Christian Bramsiepe and Norbert Kockmann
Processes 2014, 2(1), 265-292; https://doi.org/10.3390/pr2010265 - 10 Mar 2014
Cited by 44 | Viewed by 9441
Abstract
Fast process development, flexible production and the utilization of advanced process conditions are the main goals of modular and continuous small-scale plants (MCSPs). A configurable layout of the modules and the use of predefined equipment enable a quick and reliable conceptual process development [...] Read more.
Fast process development, flexible production and the utilization of advanced process conditions are the main goals of modular and continuous small-scale plants (MCSPs). A configurable layout of the modules and the use of predefined equipment enable a quick and reliable conceptual process development and scale-up of continuous processes. Therefore, a computer-assisted selection methodology was developed and is presented, which allows the quick selection of plug flow reactor equipment for homogeneous liquid phase reactions. It identifies a favorable technical apparatus and the configuration in the early stages of process development. This can lead to the effective planning and guiding of scale-up experiments and closes the gap between lab and process development. Full article
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1048 KiB  
Article
Ecological and Economic Assessment of Micro-/Milli-Continuous Campaign Manufacturing: The Case of Writing Ink
by Laura Grundemann and Stephan Scholl
Processes 2014, 2(1), 238-264; https://doi.org/10.3390/pr2010238 - 6 Mar 2014
Cited by 6 | Viewed by 7855
Abstract
Many products from the fine chemicals and pharmaceuticals industries are currently manufactured batch-wise in multi-product plants. However, this processing scheme suffers from severe drawbacks, such as a high specific energy demand, cleaning costs and high staff requirements. Transferring batch into continuous campaign productions [...] Read more.
Many products from the fine chemicals and pharmaceuticals industries are currently manufactured batch-wise in multi-product plants. However, this processing scheme suffers from severe drawbacks, such as a high specific energy demand, cleaning costs and high staff requirements. Transferring batch into continuous campaign productions may overcome these drawbacks. Using the case of writing ink, such a continuous manufacturing scheme was developed employing micro- and milli-structured components in order to intensify certain unit operations. In this paper, an ecological and economic assessment of both production concepts considering all lifecycle stages is presented. The aim of our work is to highlight the advantages and disadvantages of the two multi-product plants and to derive recommendations for the most efficient design and operation of a continuous campaign manufacturing plant. The results show that lower environmental impacts are related to continuous processing, which is due to the option for energy integration in this case. Furthermore, in the economic assessment, continuous processing proved to be economically viable. In this case, reduced staff requirements based on a highly automated manufacturing plant are the key to lower personnel costs. In general, the results emphasize the importance of such micro-/milli-continuous multi-product plants for the future manufacturing of newly developed products in the mentioned industries. Full article
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459 KiB  
Article
Absorption and Chemisorption of Small Levitated Single Bubbles in Aqueous Solutions
by Alexander Tollkötter and Norbert Kockmann
Processes 2014, 2(1), 200-215; https://doi.org/10.3390/pr2010200 - 24 Feb 2014
Cited by 7 | Viewed by 7555
Abstract
The absorption and chemisorption of small bubbles with N2 or CO2 were investigated experimentally in aqueous and alkaline solutions. Different bubble sizes were studied ranging from 0.1 to 2.5 mm in alkaline concentrations of 0.1 mM to 1 M NaOH. The [...] Read more.
The absorption and chemisorption of small bubbles with N2 or CO2 were investigated experimentally in aqueous and alkaline solutions. Different bubble sizes were studied ranging from 0.1 to 2.5 mm in alkaline concentrations of 0.1 mM to 1 M NaOH. The experiments were conducted in a device consisting of a converging microchannel with a down flowing liquid. Levitation positions of single bubbles were optically characterized. A correlation was developed for the drag force coefficient, CD, including wall effects based on the force equilibrium. A linear decrease of bubble diameters was identified with and without chemical reaction, which is referred to as a rigid bubble surface area. Measured Sherwood numbers agree well with the literature values for the investigated Reynolds number range. Full article
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361 KiB  
Communication
Microflow Photochemistry—Photodecarboxylations in Microformats
by Michael Oelgemöller, Sonia Gallagher and Kevin McCarthy
Processes 2014, 2(1), 158-166; https://doi.org/10.3390/pr2010158 - 29 Jan 2014
Cited by 9 | Viewed by 12275
Abstract
This article summarizes selected examples of intra- and intermolecular photodecarboxylations involving phthalimides in a commercially available dwell device. Compared to batch conditions in a larger chamber reactor, the investigated transformations in the microreactor furnished higher conversions and yields after significantly shorter reaction times. [...] Read more.
This article summarizes selected examples of intra- and intermolecular photodecarboxylations involving phthalimides in a commercially available dwell device. Compared to batch conditions in a larger chamber reactor, the investigated transformations in the microreactor furnished higher conversions and yields after significantly shorter reaction times. The product qualities were commonly higher under flow conditions thus avoiding the need for further purifications. Full article
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1036 KiB  
Article
Enhanced Performance of Oxidation of Rosalva (9-decen-1-ol) to Costenal (9-decenal) on Porous Silicon-Supported Silver Catalyst in a Microstructured Reactor
by Enhong Cao, Ioannis Zuburtikudis, Noor Al-Rifai, Mark Roydhouse and Asterios Gavriilidis
Processes 2014, 2(1), 141-157; https://doi.org/10.3390/pr2010141 - 29 Jan 2014
Cited by 6 | Viewed by 8958
Abstract
The use of metal-assisted HF chemical etching as a convenient technique to produce a few microns thick porous layer in silicon microchannels was demonstrated. Gas phase selective oxidation of rosalva to its aldehyde (costenal) was performed in glass/silicon microstructured reactors at temperatures of [...] Read more.
The use of metal-assisted HF chemical etching as a convenient technique to produce a few microns thick porous layer in silicon microchannels was demonstrated. Gas phase selective oxidation of rosalva to its aldehyde (costenal) was performed in glass/silicon microstructured reactors at temperatures of 375–475 °C on silver catalyst which was deposited on both porous and flat silicon surface by sputter-coating. The effects of temperature (375–475 °C), rosalva concentration (1.17%–3.43%), O2 to rosalva ratio (0.5–20) and residence time on the reaction were investigated. The reactivity of rosalva on the porous silicon supported silver was 5.7–6.4 times higher than on the thin film silver catalyst at 450 °C. Furthermore, activation energy for the porous silicon supported silver was lower. Isothermal conditions in the microreactors allowed high conversion and selectivity to be achieved in a wide range of temperature and oxygen concentration. At typical reaction conditions (1.75% rosalva, O2/rosalva = 3, residence time 18 ms and 450 °C), conversion of 97% and selectivity of 95% to costenal was achieved, corresponding to a turnover frequency of 268 h−1. Full article
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904 KiB  
Communication
Scale-up of the Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization Using Continuous Flow Processing
by Nenad Micic, Alan Young, Julien Rosselgong and Christian H. Hornung
Processes 2014, 2(1), 58-70; https://doi.org/10.3390/pr2010058 - 8 Jan 2014
Cited by 27 | Viewed by 12670
Abstract
A controlled radical polymerization process using the Reversible Addition-Fragmentation Chain Transfer (RAFT) approach was scaled up by a factor of 100 from a small laboratory scale of 5 mL to a preparative scale of 500 mL, using batch and continuous flow processing. The [...] Read more.
A controlled radical polymerization process using the Reversible Addition-Fragmentation Chain Transfer (RAFT) approach was scaled up by a factor of 100 from a small laboratory scale of 5 mL to a preparative scale of 500 mL, using batch and continuous flow processing. The batch polymerizations were carried out in a series of different glass vessels, using either magnetic or overhead stirring, and different modes of heating: Microwave irradiation or conductive heating in an oil bath. The continuous process was conducted in a prototype tubular flow reactor, consisting of 6 mm ID stainless steel tubing, fitted with static mixers. Both reactor types were tested for polymerizations of the acid functional monomers acrylic acid and 2-acrylamido-2-methylpropane-1-sulfonic acid in water at 80 °C with reaction times of 30 to 40 min. By monitoring the temperature during the exothermic polymerization process, it was observed that the type and size of reactor had a significant influence on the temperature profile of the reaction. Full article
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609 KiB  
Article
Rapid Determination of Optimal Conditions in a Continuous Flow Reactor Using Process Analytical Technology
by Michael F. Roberto, Thomas I. Dearing, Charles W. Branham, Olav Bleie and Brian J. Marquardt
Processes 2014, 2(1), 24-33; https://doi.org/10.3390/pr2010024 - 27 Dec 2013
Cited by 6 | Viewed by 8996
Abstract
Continuous flow reactors (CFRs) are an emerging technology that offer several advantages over traditional batch synthesis methods, including more efficient mixing schemes, rapid heat transfer, and increased user safety. Of particular interest to the specialty chemical and pharmaceutical manufacturing industries is the significantly [...] Read more.
Continuous flow reactors (CFRs) are an emerging technology that offer several advantages over traditional batch synthesis methods, including more efficient mixing schemes, rapid heat transfer, and increased user safety. Of particular interest to the specialty chemical and pharmaceutical manufacturing industries is the significantly improved reliability and product reproducibility over time. CFR reproducibility can be attributed to the reactors achieving and maintaining a steady state once all physical and chemical conditions have stabilized. This work describes the implementation of a smart CFR with univariate physical and multivariate chemical monitoring that allows for rapid determination of steady state, requiring less than one minute. Additionally, the use of process analytical technology further enabled a significant reduction in the time and cost associated with offline validation methods. The technology implemented for this study is chemistry and hardware agnostic, making this approach a viable means of optimizing the conditions of any CFR. Full article
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Review

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9147 KiB  
Review
Energy Considerations for Plasma-Assisted N-Fixation Reactions
by Aikaterini Anastasopoulou, Qi Wang, Volker Hessel and Juergen Lang
Processes 2014, 2(4), 694-710; https://doi.org/10.3390/pr2040694 - 26 Sep 2014
Cited by 35 | Viewed by 13587
Abstract
In a time of increasing concerns about the immense energy consumption and poor environmental performance of contemporary processes in the chemical industry, there is great need to develop novel sustainable technologies that enhance energy efficiency. There is abundant chemical literature on process innovations [...] Read more.
In a time of increasing concerns about the immense energy consumption and poor environmental performance of contemporary processes in the chemical industry, there is great need to develop novel sustainable technologies that enhance energy efficiency. There is abundant chemical literature on process innovations (laboratory-scale) around the plasma reactor itself, which, naturally, is the essential part to be intensified to achieve a satisfactory process. In essence, a plasma process needs attention beyond reaction engineering towards the process integration side and also with strong electrical engineering focus. In this mini-review, we have detailed our future focus on the process and energy intensification of plasma-based N-fixation. Three focal points are mainly stressed throughout the review: (I) the integration of renewable energy; (II) the power supply system of plasma reactors and (III) process design of industrial plasma-assisted nitrogen fixation. These different enabling strategies will be set in a holistic and synergetic picture so as to improve process performance. Full article
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2866 KiB  
Review
Microreactors for Gold Nanoparticles Synthesis: From Faraday to Flow
by Md. Taifur Rahman and Evgeny V. Rebrov
Processes 2014, 2(2), 466-493; https://doi.org/10.3390/pr2020466 - 5 Jun 2014
Cited by 56 | Viewed by 21263
Abstract
The seminal work of Michael Faraday in 1850s transmuted the “Alchemy of gold” into a fascinating scientific endeavor over the millennia, particularly in the past half century. Gold nanoparticles (GNPs) arguably hold the central position of nanosciences due to their intriguing size-and-shape dependent [...] Read more.
The seminal work of Michael Faraday in 1850s transmuted the “Alchemy of gold” into a fascinating scientific endeavor over the millennia, particularly in the past half century. Gold nanoparticles (GNPs) arguably hold the central position of nanosciences due to their intriguing size-and-shape dependent physicochemical properties, non-toxicity, and ease of functionalization and potential for wide range of applications. The core chemistry involved in the syntheses is essentially not very different from what Michael Faraday resorted to: transforming ions into metallic gold using mild reducing agents. However, the process of such reduction and outcome (shapes and sizes) are intricately dependent on basic operational parameters such as sequence of addition and efficiency of mixing of the reagents. Hence, irreproducibility in synthesis and maintaining batch-to-batch quality are major obstacles in this seemingly straightforward process, which poses challenges in scaling-up. Microreactors, by the virtue of excellent control over reagent mixing in space and time within narrow channel networks, opened a new horizon of possibilities to tackle such problems to produce GNPs in more reliable, reproducible and scalable ways. In this review, we will delineate the state-of-the-art of GNPs synthesis using microreactors and will discuss in length how such “flask-to-chip” paradigm shift may revolutionize the very concept of nanosyntheses. Full article
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4357 KiB  
Review
Microreactor-Assisted Solution Deposition for Compound Semiconductor Thin Films
by Chang-Ho Choi, Brian K. Paul and Chih-Hung Chang
Processes 2014, 2(2), 441-465; https://doi.org/10.3390/pr2020441 - 27 May 2014
Cited by 9 | Viewed by 12500
Abstract
State-of-the-art techniques for the fabrication of compound semiconductors are mostly vacuum-based physical vapor or chemical vapor deposition processes. These vacuum-based techniques typically operate at high temperatures and normally require higher capital costs. Solution-based techniques offer opportunities to fabricate compound semiconductors at lower temperatures [...] Read more.
State-of-the-art techniques for the fabrication of compound semiconductors are mostly vacuum-based physical vapor or chemical vapor deposition processes. These vacuum-based techniques typically operate at high temperatures and normally require higher capital costs. Solution-based techniques offer opportunities to fabricate compound semiconductors at lower temperatures and lower capital costs. Among many solution-based deposition processes, chemical bath deposition is an attractive technique for depositing semiconductor films, owing to its low temperature, low cost and large area deposition capability. Chemical bath deposition processes are mainly performed using batch reactors, where all reactants are fed into the reactor simultaneously and products are removed after the processing is finished. Consequently, reaction selectivity is difficult, which can lead to unwanted secondary reactions. Microreactor-assisted solution deposition processes can overcome this limitation by producing short-life molecular intermediates used for heterogeneous thin film synthesis and quenching the reaction prior to homogeneous reactions. In this paper, we present progress in the synthesis and deposition of semiconductor thin films with a focus on CdS using microreactor-assisted solution deposition and provide an overview of its prospect for scale-up. Full article
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