Continuous Flow Research Articles

Modular Cascade of Flow Reactors: Continuous Flow Synthesis of Water-Insoluble Diazo Dyes in Aqueous System.

Continuous flow synthesis is pivotal in dye production to address batch-to-batch variations. However, synthesizing water-insoluble dyes in an aqueous system poses a challenge that can lead to clogging. This study successfully achieved the safe and efficient synthesis of azo dyes by selecting and optimizing flow reactor modules for different reaction types in the two-step reaction and implementing cascade cooperation. Integrating continuous flow microreactor with continuous stirred tank reactor (CSTR) enabled the continuous flow synthesis of Sudan Yellow 3G without introducing water-soluble functional groups or using organic solvents to enhance solubility. Optimizing conditions (acidity/alkalinity, temperature, residence time) within the initial modular continuous flow reactor resulted in a remarkable 99.5% isolated yield, 98.6% purity, and a production rate of 2.90 g · h-1. Scaling-up based on different reactor module characteristics further increased the production rate to 74.4 g·h-1 while maintaining high yield and purity. The construction of this small 3D-printing modular cascaded reactor and process scaling-up provide technical support for continuous flow synthesis of water-insoluble dyes, particularly high-market-share azo dyes. Moreover, this versatile methodology proves applicable to continuous flow processes involving various homogeneous and heterogeneous reaction cascades.

Advances in the Synthesis of Bioorthogonal Reagents: s-Tetrazines, 1,2,4-Triazines, Cyclooctynes, Heterocycloheptynes, and trans-Cyclooctenes.

Aligned with the increasing importance of bioorthogonal chemistry has been an increasing demand for more potent, affordable, multifunctional, and programmable bioorthogonal reagents. More advanced synthetic chemistry techniques, including transition-metal-catalyzed cross-coupling reactions, C-H activation, photoinduced chemistry, and continuous flow chemistry, have been employed in synthesizing novel bioorthogonal reagents for universal purposes. We discuss herein recent developments regarding the synthesis of popular bioorthogonal reagents, with a focus on s-tetrazines, 1,2,4-triazines, trans-cyclooctenes, cyclooctynes, hetero-cycloheptynes, and -trans-cycloheptenes. This review aims to summarize and discuss the most representative synthetic approaches of these reagents and their derivatives that are useful in bioorthogonal chemistry. The preparation of these molecules and their derivatives utilizes both classical approaches as well as the latest organic chemistry methodologies.

Capillarity Constructed Open Siphon for Sustainable Drainage.

Siphon is an effective method to transfer liquid from a higher to a lower level, which has many applications in hygienic design, clinical apparatus, and hydraulic engineering. Traditional operation requires energy to overcome gravity and establish flow in a closed system. Achieving sustainable high flux siphon drainage without energy input remains a challenge due to viscous dissipation. Here, an unexpected open siphon behavior on the South American pitcher plant Heliamphora minor consisting of trichomes covered pitcher and a wedge-shaped sheath is examined. Exploiting the concept of Digital Twin, a new biomimetic research method by transforming the biological sample to a virtual 3D model is proposed and unveiled that maintained connection of wicking on sub-millimeter long trichomes due to asymmetric pressure distribution and ascending in wedge sheath under unbalanced pressure forms continuous surface flow. Exploring this mechanism, a biomimetic siphon device achieving continuous high flux exposed to ambient air is constructed. Besides, particles floating on the meniscus in the outside wedge move under a curvature gradient as water ascends, which implies a biological nutrient capture method and new dust collection manner in the drainage system. Applying the underlying principle enhances the siphon efficiency of floor drains and has the potential for other liquid transfer device design improvements.

Accessing Cyclobutane Polymers: Overcoming Synthetic Challenges via Efficient Continuous Flow [2 + 2] Photopolymerization.

We report an improved and efficient method to prepare well-defined, structurally complex truxinate cyclobutane polymers via a thioxanthone sensitized solution state [2 + 2] photopolymerization. Monomers with varying electron density and structure polymerize in good to excellent yields to afford a library of 42 polyesters. Monomers with internal olefin separation distances of greater than 5 Å undergo polymerization via intermolecular [2 + 2] photocycloaddition readily, as opposed to the intramolecular [2 + 2] photocycloaddition observed in monomers with olefins in closer proximity. Use of a continuous flow reactor decreases reaction time, increases polymer molecular weight, and decreases dispersity compared to batch reactions. Furthermore, under continuous flow, polymerization is readily scalable beyond what is possible with batch reactions. This advancement ushers truxinate cyclobutane-based polyesters, which have been historically limited to a few examples and only research scale quantities, to the forefront of development as new materials for potential use across industry sectors.

Enantioselective Synthesis in Continuous Flow: Polymer-Supported Isothiourea-Catalyzed Enantioselective Michael Addition–Cyclization with α-Azol-2-ylacetophenones

Enantioselective Synthesis in Continuous Flow: Polymer-Supported Isothiourea-Catalyzed Enantioselective Michael Addition–Cyclization with α-Azol-2-ylacetophenones

Efficient synthesis of high vinyl polybutadiene based on continuous flow microchannel reactor

AbstractThe traditional batch synthesis of liquid rubber faces issues such as low monomer polymerization concentration, poor uniformity of the reaction system, and inadequate heat dissipation, resulting in an unsatisfactory synthesis efficiency. This study presents a method for the rapid and efficient synthesis of high vinyl 1,2‐polybutadiene liquid rubber using butadiene as the monomer and n‐butyllithium as the initiator. By applying continuous flow microchannel reactors, the limitation of traditional synthesis method can be overcome. The addition of a modifier in the raw material promotes the formation of high vinyl structure. The preparation of liquid rubber requires the addition of a large amount of metal lithium initiator. However, for aerospace sealants, there is a requirement for low metal ion content. To address this, we employed different methods to reduce the metal ion content in the liquid rubber and increase its purity. Ultimately, we achieved the synthesis of high‐purity polybutadiene liquid rubber with 1,2‐vinyl content exceeding 88%, narrow molecular weight distribution, and tunable molecular weights. This research will provide technical guidance for the industrial application of polybutadiene synthesis in continuous flow microchannel reactors.

Millistructured Coiled Flow Inverter for Biphasic Continuous Flow 5‐Chloromethylfurfural Synthesis

AbstractSyntheses of alternative platform chemicals, such as 5‐chloromethylfurfural (CMF), from bio‐based starting materials are often associated with complicated kinetic schemes and mass transfer processes. Millistructured flow reactor concepts can help to elucidate kinetic schemes and determine rate constants which are of crucial importance for the design of respective technical processes. For the first time, the influence of proton concentration on the rate constants involved in the biphasic synthesis of CMF is systematically investigated. Results are discussed in terms of green chemistry metrics.

Fresh cement as a frictional non-Brownian suspension

Cement is an essential construction material due to its ability to flow before later setting, however the rheological properties must be tightly controlled. Despite this, much understanding remains empirical. Using a combination of continuous and oscillatory shear flow, we compare fresh Portland cement suspensions to previous measurements on model non-Brownian suspensions to gain a micro-physical understanding. Comparing steady and small-amplitude oscillatory shear, we reveal two distinct jamming concentrations, ϕμ and ϕrcp, where the respective yield stresses diverge. As in model suspensions, the steady-shear jamming point is notably below the oscillatory jamming point, ϕμ<ϕrcp, suggesting that it is tied to frictional particle contacts. These results indicate that recently established models for the rheology of frictional, adhesive non-Brownian suspensions can be applied to fresh cement pastes, offering a new framework to understand the role of additives and fillers. Such micro-physical understanding can guide formulation changes to improve performance and reduce environmental impact.

Novel high-pressure/high-temperature reactor cell for in situ and operando x-ray absorption spectroscopy studies of heterogeneous catalysts at synchrotron facilities.

This paper presents the development of a novel high-pressure/high-temperature reactor cell dedicated to the characterization of catalysts using synchrotron x-ray absorption spectroscopy under operando conditions. The design of the vitreous carbon reactor allows its use as a plug-flow reactor, monitoring catalyst samples in a powder form with a continuous gas flow at high-temperature (up to 1000 °C) and under high pressure (up to 1000bar) conditions, depending on the gas environment. The high-pressure/high-temperature reactor cell incorporates an automated gas distribution system and offers the capability to operate in both transmission and fluorescence detection modes. The operando x-ray absorption spectroscopy results obtained on a bimetallic InCo catalyst during CO2 hydrogenation reaction at 300 °C and 50bar are presented, replicating the conditions of a conventional microreactor. The complete setup is available for users and permanently installed on the Collaborating Research Groups French Absorption spectroscopy beamline in Material and Environmental (CRG-FAME) sciences and French Absorption spectroscopy beamline in Material and Environmental sciences at ultra-high dilution (FAME-UHD) beamlines (BM30 and BM16) at the European Synchrotron Radiation Facility in Grenoble, France.

The convergence of Digital Twins and Distributed Ledger Technologies: A systematic literature review and an architectural proposal

In recent years, the emerging Digital Twin (DT) technology is playing a key role in fostering the transition towards the Industry 4.0. DTs, representing virtual replicas of physical objects, products or processes established thanks to a bidirectional continuous flow of information between the physical and the virtual world, are currently adopted in multiple domains such as manufacturing, aerospace, automotive, energy, construction, smart cities and smart mobility, etc.. DTs live together with the physical system they replicate, receiving the same data and often triggering specific control actions that directly impact on the real system status. When dealing with DTs of complex Cyber-Physical Systems (CPSs), the data sources may be heterogeneous and untrustworthy, which requires the DT to be able to address security issues related to data in transit from/to the physical twin and data at rest. A possible way to address these data security issues consists in adopting Distributed Ledger Technologies (DLTs) which provide several security guarantees on data through cryptographic hashing techniques. In this work, we present a three-fold contribution: (i) we discuss the results of a Systematic Literature Review (SLR) on the state-of-the-art of the research related to the integration between DLT and Digital Twins, aimed at clarifying relevant aspects such as, among others, what is the favourite DLT choice in existing proposals or what is the type of DT-related information to store on-chain; (ii) leveraging the SLR results and other related research, we propose an architectural framework for the integration of DT and DLTs (more specifically, blockchains); (iii) we validate the proposed architecture by means of two proof-of-concept implementations leveraging different technological stacks and taking into account two different operational scenarios. Finally, we conduct a requirements coverage analysis and compare the PoCs through a coverage matrix.

Sulfide-rich sediments remediation by slow-release calcium nitrate with low risk: experiments in a continuous flow reactor

Sulfide-rich sediments remediation by slow-release calcium nitrate with low risk: experiments in a continuous flow reactor

Activation of peroxymonosulfate by CoS2 loaded air-laid cloth for rapid degradation of organic pollutants in a shallow continuous flow reactor

Activation of peroxymonosulfate by heterogeneous catalyst is an efficient process for organic pollutants removal. However, it is difficult for solid-liquid separation of the heterogeneous catalysts in slurry-like batch reaction. In this work, CoS2 particles were deposited onto an air-laid cloth (denoted as CoS2-ALC) and were used as a catalyst for activation of peroxymonosulfate (PMS). Unlike traditional slurry-like batch reaction forms, a shallow continuous flow reactor was designed for the installation of a CoS2-ALC, thereby improving the activation efficiency of persulfate and rapid solid-liquid separation. The degradation kinetics constant for carbamazepine (CBZ) by the CoS2-ALC/PMS process was 0.0748 min−1, which is 374, 149.6, 150 times higher than that the CoS2-ALC adsorption process, PMS/ALC oxidation process and PMS alone process, respectively. The significantly enhanced degradation efficiency was due to the S in CoS2 promoting the cycling of Co2+/Co3+, thereby enhancing the generation of free radical. Parameters such as CoS2 deposition amount, PMS concentration, water flow rate, water flow height, water flow direction, solution pH, humic acid and anions that affecting the degradation efficiencies were studied. In addition, the degradation by-products of CBZ as well as their toxicity were detected, and a possible degradation pathway were proposed. Finally, expanded outdoor experiments and cycling experiment demonstrated that the CoS2-ALC/PMS process is potentially useful in practical settings of wastewater treatment.

Oxidation of Alcohols and Aldehydes with Peracetic Acid and a Mn(II)/Pyridin‐2‐Carboxylato Catalyst: Substrate and Continuous Flow Studies

A homogeneous catalyst system, consisting of Mn(OAc)2 and 2‑picolinic acid was studied for alcohol oxidation using peracetic acid as the oxidant. Catalyst loadings as low as 0.01 mol% could be utilized and the system compared well to other peroxide based methods. The utilization of continuous flow allowed the fast, exothermic reactions to be carried out in a safe and scalable manner.

High-Resolution Mapping of Urban Residential Building Stock Using Multisource Geographic Data

The rapid pace of urbanization and the increasing concentration of populations in urban areas have generated a substantial demand for architectural structures, resulting in a significant increase in building stock and continuous material flows that interact with the environment. This study emphasizes the importance of high-spatial-resolution mapping of residential building stock for effective urban-construction resource management, planning, and waste management. Focusing on Xi’an as a case study, the research develops a comprehensive framework for mapping urban residential building stock by integrating diverse data dimensions, including temporal, spatial, network, and multi-attribute aspects. The findings indicate that between 1990 and 2020, approximately 4758 residential communities were established in central Xi’an. The analysis of seven key residential construction materials revealed that the building stock escalated from 1.53 million tons to 731.12 million tons, with a steady spatial expansion of material distribution. The study attributes this growth to factors such as population increase, economic advancement, and policy initiatives, which, in turn, have driven the demand for residential building materials and reinforced the interdependence between urban expansion and residential construction development. Remarkably, from 1990 to 2020, the population surged by 2.1-fold, the economy by 66-fold, and the stock of residential building materials by 477-fold, indicating that the growth rate of material stock consistently outpaced that of both population and economic growth. Over the past three decades, the rapid expansion of residential buildings has led to the encroachment of urban ecological spaces by concrete structures. The methodology proposed in this study for quantifying building material offers valuable insights for policymakers and urban and environmental planners to foster responsible resource consumption and supports component-level circularity in the built environment.

A prospective multicenter feasibility study of a miniaturized implantable continuous flow ventricular assist device in smaller children with heart failure.

There is no FDA-approved left ventricular assist device (LVAD) for smaller children permitting routine hospital discharge. Smaller children supported with LVADs typically remain hospitalized for months awaiting heart transplant-a major burden for families and a challenge for hospitals. We describe the initial outcomes of the Jarvik 2015, a miniaturized implantable continuous flow LVAD, in the NHLBI-funded Pumps for Kids, Infants, and Neonates (PumpKIN) study, for bridge-to-heart transplant. Children weighing 8 to 30 kg with severe systolic heart failure and failing optimal medical therapy were recruited at 7 centers in the United States. Patients with severe right heart failure and single-ventricle congenital heart disease were excluded. The primary feasibility endpoint was survival to 30 days without severe stroke or non-operational device failure. Of 7 children implanted, the median age was 2.2 (range 0.7, 7.1) years, median weight 10 (8.2 to 20.7) kilograms; 86% had dilated cardiomyopathy; 29% were INTERMACS profile 1. The median duration of Jarvik 2015 support was 149 (range 5 to 188) days where all 7 children survived including 5 to heart transplant, 1 to recovery, and 1 to conversion to a paracorporeal device. One patient experienced an ischemic stroke on day 53 of device support in the setting of myocardial recovery. One patient required ECMO support for intractable ventricular arrhythmias and was eventually transplanted from paracorporeal biventricular VAD support. The median pump speed was 1600 RPM with power ranging from 1-4 Watts. The median plasma free hemoglobin was 19, 30, 19 and 30 mg/dL at 7, 30, 90 and 180 days or time of explant, respectively. All patients reached the primary feasibility endpoint. Patient-reported outcomes with the device were favorable with respect to participation in a full range of activities. Due to financial issues with the manufacturer, the study was suspended after consent of the eighth patient. The Jarvik 2015 LVAD appears to hold important promise as an implantable continuous flow device for smaller children that may support hospital discharge. The FDA has approved the device to proceed to a 22-subject pivotal trial. Whether this device will survive to commercialization remains unclear because of the financial challenges faced by industry seeking to develop pediatric medical devices. (Supported by NIH/NHLBI HHS Contract N268201200001I, clinicaltrials.gov 02954497).

Transient Performance Analysis of Centrifugal Left Ventricular Assist Devices Coupled with Windkessel Model: Les Study On Continuous and Pulsatile Flow Operation.

Computational Fluid Dynamics (CFD) simulations are widely used to develop and analyze blood-contacting medical devices such as Left Ventricular Assist Devices (LVADs). This work presents an analysis of the transient behavior of two centrifugal LVADs with different designs: HeartWare VAD and HeartMate3. A scale-resolving methodology is followed through Large Eddy Simulations, which allows for the visualization of turbulent structures. The 3D LVAD models are coupled to a 0D 2-element Windkessel model, which accounts for the vascular resistance and compliance of the arterial system downstream of the device. Furthermore, both continuous- and pulsatile-flow operation modes are analyzed. For the pulsatile conditions, the artificial pulse of HeartMate3 is imposed, leading to a larger variation of performance variables in HeartWare VAD than in HeartMate3. Moreover, CFD results of pulsatile-flow simulations are compared to those obtained by accessing the quasi-steady maps of the pumps. The quasi-steady approach is a predictive tool used to provide a preliminary approximation of the pulsatile evolution of flow rate, pressure head, and power, by only imposing a speed pulse and vascular parameters. This preliminary quasi-steady solution can be useful for deciding the characteristics of the pulsatile speed law before running a transient CFD simulation, as the former entails a significant reduction in computational cost in comparison to the latter.

Numerical Simulation of Water Film Flow and Breakup on Anti-Icing Surface

The flow and morphological characteristics of liquid water on the icing and anti-icing surfaces of aircraft are closely related to the icing characteristics and anti-icing surface temperature distribution. To predict the flow and breakup characteristics of a water film, a 3D model of continuous water film flow and a model of water film breakup into rivulets on an anti-icing surface were constructed based on the icing model, and the corresponding methods for solving the models were developed. Using the NACA0012 airfoil as a simulation object, the changing characteristics of height and velocity for a continuous water film with time and the morphological characteristics of rivulets formed from the breakup of a continuous water film were simulated numerically. The results indicate that, with an increase in inflow velocity, the time required for the water film to completely cover the surface and reach stability decreases. Downstream in the water droplet impact zone, the calculated values of continuous water film height align well with experiments, as well as the stream height at the continuous water film rupture location with the experimental values. With the reasonable contact angle, the calculation error of the stream width is within 10%.

Artificial intelligence (AI) inspired an innovative approach for real-time flow measurements – water distributions at outlets, in Punjab province Pakistan

Abstract Accurate water metering is essential for effective water management, especially for measured and equitable distribution of canal flows, most imperative in Pakistan. The inflows distributed through outlets must adhere to pre-designated levels, defined by Punjab Irrigation Department from head to tail. With recent channels lining, the outlets’ sanctioned flow is found changed requiring adjustments. Furthermore, there is a lack of reliable mechanisms for continuous flow regulations, resulting in unmanaged distributions. The focus of the reported work was on precise and real-time discharge monitoring at outlets using a newly developed device utilizing artificial intelligence. During validation training, a strong agreement was observed, and all evaluation parameters supported the device accuracy for measurements. In detailed studies of canal operations, the sanctioned discharges of individual outlets along selected distributaries were found significantly inequitable. Out of 162 outlets, 42 were suspended for being unmanaged, with tail users receiving ≤50% of their fair intakes. Additionally, there were instances of massive irrational supplies exceeding 200% of allocated discharges. The developed device has the potential to accurately measure real-time discharges for managed distributions. Conclusively, the challenging task of fair and equity-based discharge allocations, in conjunction with the Warabandi system, necessitates the reevaluation of the allocated flow quantity at each outlet.

Continuous flow synthesis of hierarchical low silica X zeolite

Zeolites, renowned for their versatile applications in catalysis, adsorption, and ion exchange, have long been synthesized using conventional batch processes. However, the inherent limitations of these methods, such as resource-intensive conditions and inconsistent product quality, underscore the need for a sustainable and efficient approach. In this study, a continuous flow synthesis process was established for the synthesis of industrially important low silica X (LSX) zeolite using a tubular reactor. The synthesis gel was subjected to aging for 5 days at room temperature to facilitate nucleation and crystal growth combined with the fast-heating rate in a tubular reactor at 363 K & 1.1 atm., which in turn produces LSX after 40 min. The synthesized product was confirmed by the XRD, FE-SEM, EDS, XRF, TEM, and N2 adsorption-desorption; the data was compared with the LSX sample synthesized by batch process. The result implies that LSX prepared by continuous flow has a pure phase of LSX with the hierarchical structure, which provides better adsorption capacity of CO2 at 298 K up to 20 bar. Due to continuous flow synthesis, the crystallization time was reduced and faster kinetics which may be helpful for scale-up the process for LSX synthesis.

WLI, XPS and SEM/FIB/EDS Surface Characterization of an Electrically Fluted Bearing Raceway

Electrical bearing currents may disturb the performance of the bearings via electro-corrosion if they surpass a limit of ca. 0.1 to 0.3 A/mm2. A continuous current flow, or, after a longer time span, an alternating current or a repeating impulse-like current, damages the raceway surface, leading in many cases to a fluting pattern on the raceway. Increased bearing vibration, audible noise, and decreased bearing lubrication as a result may demand a replacement of the bearings. Here, an electrically corroded axial ball bearing (type 51208) with fluting patterns is investigated. The bearing was lubricated with grease lubrication and was exposed to 4 A DC current flow. It is shown that the electric current flow causes higher concentrations of iron oxides and iron carbides on the bearing raceway surface together with increased surface roughness, leading to a mixed lubrication also at elevated bearing speeds up to 1500 rpm. The “electrically insulating” iron oxide layer and the “mechanically hard” iron carbide layer on the bearing steel are analysed by WLI, XPS, SEM, and EDS. White Light Interferometry (WLI) is used to provide an accurate measurement of the surface topography and roughness. X-ray Photoelectron Spectroscopy (XPS) measurements are conducted to analyze the chemical surface composition and oxidation states. Scanning Electron Microscopy (SEM) is applied for high-resolution imaging of the surface morphology, while the Focused Ion Beam (FIB) is used to cut a trench into the bearing surface to inspect the surface layers. With the Energy Dispersive X-ray spectrometry (EDS), the presence of composing elements is identified, determining their relative concentrations. The electrically-caused iron oxide and iron carbide may develop periodically along the raceway due to the perpendicular vibrations of the rolling ball on the raceway, leading gradually to the fluting pattern. Still, a simulation of this vibration-induced fluting-generation process from the start with the first surface craters—of the molten local contact spots—to the final fluting pattern is missing.