Continuous Flow Reactor Research Articles

Hydrogen Peroxide Producing Titania-Silica Supraparticles as Tailorable Photocatalysts for Flow Chemistry Reactions in Microfluidic Reactors

Hydrogen Peroxide Producing Titania-Silica Supraparticles as Tailorable Photocatalysts for Flow Chemistry Reactions in Microfluidic Reactors

Organocatalytic Packed-Bed Reactors for the Enantioselective Flow Synthesis of Quaternary Isotetronic Acids by Direct Aldol Reactions of Pyruvates

The utilization of the homogeneous (S)-2-pyrrolidine-tetrazole organocatalyst (Ley catalyst) in the self-condensation of ethyl pyruvate and cross-aldol reactions of ethyl pyruvate donor with non-enolizable pyruvate acceptors, namely the sterically hindered ethyl 3-methyl-2-oxobutyrate or the highly electrophilic methyl 3,3,3-trifluoropyruvate, is described as the key enantioselective step toward the synthesis of the corresponding biologically relevant isotetronic acids featuring a quaternary carbon functionalized with ester and alkyl groups. The transition from homogeneous to heterogeneous flow conditions is also investigated, detailing the fabrication and operation of packed-bed reactors filled with a silica-supported version of the pyrrolidine-tetrazole catalyst (SBA-15 as the matrix).

Continuous flow solvent-free and catalyst-free mechanochemical production of rhodamine B dyes and their derivatives.

In this communication, we have described a simple and efficient, catalyst free and solvent-free protocol for the continuous flow synthesis of rhodamine B dyes developed from 3-diethyl amino phenol and phthalic anhydride. Nearly 95% conversion was achieved within 12 min using a jacketed single screw reactor. This method is further used for the synthesis of six derivatives with 70-84% yield, which can be compared to 85% yield from a 1-hour long batch synthesis involving a catalyst.

Heterogeneously catalyzed lignin depolymerisation in continuous flow: Assessing feedstock pretreatment and catalyst deactivation

Due to the large-scale production of lignin, continuous flow reactors are preferred for its further valorization through depolymerization. However, there is limited literature on their use in lignin depolymerization, especially concerning feedstock pretreatments and catalyst deactivation. Therefore, in this study, the impact of a batch solvolysis pretreatment on the mild reductive catalytic depolymerization of Soda lignin, with and without a Pd catalyst, is evaluated and catalyst deactivation is systematically assessed. The Pd catalyst substantially enhances Mw reductions, e.g., without feedstock pretreatment, it increases the Mw reduction from approximately 70 % to 90 % at low time-on-streams (T.O.S.). It also yields products with more functionalities from the untreated feedstock, i.e., at low T.O.S., the phenolic and aliphatic OH content increases from 4.21 to 4.89 mmol/g and 2.30 to 3.72 mmol/g, respectively. The differences are less pronounced with the pretreated feedstock due to condensation of the lignin structure. Furthermore, the high space–time that can be achieved at a short residence time negates the need for a pretreatment. Regarding deactivation, no significant Pd leaching or poisoning by S or Na was observed. The Pd nanoparticles grew from about 8 nm to 20 nm (pretreated feed) and 17 nm (untreated feed), which is likely due to the phase change from PdO to metallic Pd rather than deactivation through sintering. The support material changed from γ-Al2O3 to boehmite, leading to the loss of acid sites and morphological changes. While some indications for small amounts of coke deposits were observed, they could not be differentiated from interstitial water within the boehmite structure. Thus, the main cause for deactivation of the Pd catalyst was identified to be the hydrothermal instability of the alumina support.

Photo-induced transformation of α-diazocarbonyl compounds into mono-substituted alpha-halogen derivatives.

Herein, the hydrogen halogenation reaction of diazo compounds with three new halogenating agents under photoinduced conditions is reported. This method realized hydrofluorination, hydrochlorination, and hydrobromination (56 cases in total, with the highest preparative yield of 94%) without requiring heating, transition metal catalysts or photocatalysts and exhibits a broad substrate scope. Notably, gram-scale synthesis using a continuous flow reactor was performed.

Enhanced photocatalytic hydrogen production efficiency using urea-derived carbon nitride in a continuous flow reactor

In this study, we conducted a comprehensive comparison of the photocatalytic properties and the reactivity towards the hydrogen evolution reaction (HER) of carbon nitride (GCN) in batch and flow photo-reactors.

Integrating continuous flow reaction and work-up: chiral amine resolution, separation and purification using a novel coalescing filter system.

To maximize the benefits of a continuous flow reaction, a continuous work-up is also needed. Herein, we present a process design and novel equipment for a continuous amine resolution reaction, integrated with liquid-liquid (L-L) extraction, back-extraction into a different solvent, and crystallisation purification for product isolation. The reaction, in iso-propyl acetate, flows through a heated fixed-bed reactor with solid supported Candida antarctica lipase which catalyses the resolution of (rac)-1-phenylethylamine to give the (R)-amide in 50% conversion and 96% enantiomeric excess (ee). This is separated from the unreacted (S)-amine co-product by mixing with an acidic aqueous stream and separating the phases using our recently reported coalescence filter separator. The aqueous stream is neutralised by mixing with base and back-extracted into methyl-THF solvent before separating the phases using a membrane separator. Finally, a solid amine salt is isolated by filtration, achieved by mixing the free base with an organic acid to cause crystallisation to give the (S)-1-phenylethylamine in 43% yield and >99% ee from racemate. The work illustrates how typical reactions, work-up and purification steps that involve multiple phases can be telescoped together using both new and commercially available laboratory equipment. This continuous system uses mild reaction conditions, green solvents and minimises their use for reduced waste.

Sustainable fertiliser mesh, ‘4D’-precision engineered by flow chemistry: minimising agrochemical pollution

Flow synthesis of a chitosan-coated fertilliser 'necklace' arrangement (3D), woven into a mesh-like structure (4D). This hierarchical localised fertiliser is evaluated for efficiency and leaching behaviour of P, Ca and K nutrients.

Self-Optimising Continuous-Flow Hydrothermal Reactor for Nanoparticle Synthesis

Self-Optimising Continuous-Flow Hydrothermal Reactor for Nanoparticle Synthesis

Evaluating the performance and stability of microalgal-bacterial granular sludge in municipal wastewater treatment plants.

The microalgal-bacterial granular sludge (MBGS) process shows potential for carbon-neutral wastewater treatment, yet its application in wastewater treatment plants remains underexplored. This study attempted to use a continuous-flow raceway reactor to treat real municipal wastewater using the MBGS process. The results showed that the removal efficiencies of organics peaked on the fifth day, while declining trends were observed for nitrogen and phosphorus removal. Microbial community and functional gene analyses indicated that the removal of organics, nitrogen, and phosphorus might be heavily influenced by Proteobacteria, suggesting that fluctuations in their abundance significantly impacted the performance of MBGS. Bacteroidota and Actinobacteria played a vital role in cellulose decomposition via the cbhA gene. Moreover, energy shortages caused by light attenuation due to wastewater turbidity and environmental fluctuations disrupted the microbial balance, shifting metabolic activity towards carbon pathways. Key challenges for the broader application of the MBGS process include managing wastewater turbidity and ensuring process stability. These findings highlight the need for pretreatment measures and robust operational strategies to mitigate environmental fluctuations and maintain system performance.

Continuous flow synthesis of metal nanowires: protocols, engineering aspects of scale-up and applications.

This review comprehensively covers the translation from batch to continuous flow synthesis of metal nanowires (i.e., silver, copper, gold, and platinum nanowires) and their diverse applications across various sectors. Metal nanowires have attracted significant attention owing to their versatility and feasibility for large-scale synthesis. The efficacy of flow chemistry in nanomaterial synthesis has been extensively demonstrated over the past few decades. Continuous flow synthesis offers scalability, high throughput screening, and robust and reproducible synthesis procedures, making it a promising technology. Silver nanowires, widely used in flexible electronics, transparent conductive films, and sensors, have benefited from advancements in continuous flow synthesis aimed at achieving high aspect ratios and uniform diameters, though challenges in preventing agglomeration during large-scale production remain. Copper nanowires, considered as a cost-effective alternative to silver nanowires for conductive materials, have benefited from continuous flow synthesis methods that minimize oxidation and enhance stability, yet scaling up these processes requires precise control of reducing environments and copper ion concentration. A critical evaluation of various metal nanowire ink formulations is conducted, aiming to identify formulations that exhibit superior properties with lower metal solid content. This study delves into the intricacies of continuous flow synthesis methods for metal nanowires, emphasizing the exploration of engineering considerations essential for the design of continuous flow reactors. Furthermore, challenges associated with large-scale synthesis are addressed, highlighting the process-related issues.

Photocatalytic degradation of tetracycline antibiotics and elimination of N-nitrosodimethylamine formation potential by BiOCl/ZnIn2S4 heterostructure under visible-light irradiation.

Photocatalysis is an effective method for removing tetracycline antibiotics, which are important precursors to the potential carcinogen N-nitrosodimethylamine (NDMA). Herein, a BiOCl/ZnIn2S4 heterojunction was successfully synthesized using a simple hydrothermal method. This heterojunction was applied for the first time to degrade various tetracycline antibiotics and reduce NDMA formation potential (NDMA-FP) under visible-light irradiation. Characterization of surface morphology, crystal structure, chemical composition and photoelectrochemical properties revealed that the BiOCl/ZnIn2S4 heterojunction significantly improved light absorption, charge transport and carrier separation efficiency, thereby enhancing photocatalytic performance. The BiOCl/ZnIn2S4 catalyst achieved high degradation efficiencies of 88.0%, 90.7%, 88.7% and 91.7% for tetracycline, minocycline, chlortetracycline and doxycycline, respectively, within 60min of visible-light irradiation. Additionally, it exhibited the lowest NDMA-FP values of 1.5%, 3%, 0.9% and 1.4%, respectively. Radical trapping studies and EPR experiments identified •O2- and •OH radicals as the primary reactive species involved in the photocatalytic process. Analysis of the degradation intermediates and structure-activity relationships indicated that the variations in NDMA-FP were closely associated with the number of dimethylamine groups in the antibiotics and the stability of the resulting carbocations. Notably, the BiOCl/ZnIn2S4 catalyst presented satisfactory stability and positive tetracycline degradation in real antibiotic wastewater. Incorporating BiOCl/ZnIn2S4-loaded nonwoven fabric into a continuous-flow reactor efficiently degraded tetracycline in real wastewater under visible light. This work provides new insights on developing Z-scheme photocatalysts for the simultaneous degradation of various antibiotics and highlights their potential as commercially viable photocatalytic system.

Continuous flow synthesis of N,N-dimethyltryptamine (DMT) analogues with therapeutic potential.

Herein, we describe the continuous flow synthesis and in-line extraction of N,N-dimethyltryptamine (DMT) and several of its analogues using a Fischer indole reaction, along with a larger gram scale synthesis (4.75 g) of the model compound. These products could then be quickly transformed into their respective fumarate salts, making them easier to handle and stable for long time storage using a straightforward batch procedure. Additionally, the commercially available drug rizatriptan benzoate could be synthesised with high purity using this setup. The presented method employs relatively green solvents both for the synthesis and purification of the target products.

A color-coordinated approach to the flow synthesis of silver nanoparticles with custom morphologies.

In an effort to meet the high demand for silver nanostructures in both research and consumer applications, we devise a simple and readily scaleable photochemical method through which silver nanostructures of varying morphologies, sizes, and optical properties can be synthesized using batch and flow photochemical strategies. For the latter we build upon the application of a wrapped-lamp photochemical flow system recently developed by our group to enable sequential irradiation with several wavelengths of LEDs in series in an approach that we describe as "plasmon pushing". We find that this strategy can accelerate the conversion of silver nanoparticle seeds to decahedral and triangular nanostructures, and that with it we have control over the tuning of the size and optical properties of triangular nanostructures in the red and near-IR regions. Moreover, through sequential flow irradiation, we gain a better understanding of the formation pathways and relative stability of decahedral and triangular silver nanostructures.

The scale-up of microwave flow syntheses by recirculation: the chlorine-free preparation of walkyl phenyl-H-phosphinates

The MW flow esterification of phenyl-H-phosphinic acids with alcohols at ca. 150 °C in the presence of 5% of [bmim][PF6] afforded target alkyl phenyl-H-phosphinates with productivity of ca. 6–9 g h−1 by applying a recirculating mode of operation.

Magnetic framework composites via continuous flow syntheses for CO2 capture

Magnetic framework composites via continuous flow syntheses for CO2 capture

Enzyme‐Nanozyme Cascade Flow Reactor Synergy with Deep Learning for Differentiation and Point‐of‐Care Testing of Multiple Organophosphorus Pesticides

AbstractCombining nanotechnology with biocatalysts, the construction of a cascade continuous flow reactor is a cutting‐edge strategy to enhance the stability and efficiency of catalysis. In this study, C60@MOF‐545‐Fe nanozyme is synthesized by utilizing fullerene (C60) as a guest encapsulated inside a metal‐organic framework (MOF‐545‐Fe), the unique host‐guest interaction optimizes the oxidase (OXD)‐ and peroxidase (POD)‐like activities, based on which a cascading catalytic strategy is proposed without external energy input. Simultaneously, C60@MOF‐545‐Fe offers the potential to effectively flow at the nanoscale through its unique nanostructure cavity and spatially confined environment. Therefore, the AChE/C60@MOF‐545‐Fe enzyme‐nanozyme continuous flow reactor is constructed by combining C60@MOF‐545‐Fe with acetylcholinesterase (AChE) through supramolecular interactions. Notably, the reactor not only achieves the simultaneous detection of glyphosate, omethoate, and paraoxon but also efficiently differentiates these three organophosphorus pesticides (OPs) by applying the differences in the responses of the three array channels. Subsequently, a portable platform is developed utilizing the YOLO v5‐OPs model based on deep learning, enabling the direct output fitting equation through terminals to achieve rapid point‐of‐care testing (POCT) of OPs. This work not only provides a promising strategy for hazard detection systems but also opens up new avenues for the design of technologies based on flow reactors.

Continuous flow synthesis of di‐tert‐butyl peroxide in microreactors and kinetic study

AbstractDi‐tert‐butyl peroxide (DTBP) is a widely used organic peroxide. Its synthesis using tert‐butyl alcohol (TBA) and H2O2 via traditional batch processes has suffered from low space–time yield, uncontrollable product distribution, and safety issues. An efficient continuous‐flow microreaction system was proposed to enhance DTBP synthesis. Optimal reaction conditions were determined: a molar ratio of 1.5 (H2SO4/TBA) and 0.5 (H2O2/TBA), a reaction temperature of 50°C, and concentrations of 75 wt% H2SO4, 85 wt% TBA, and 50 wt% H2O2. A kinetic model was established, indicating that reducing local H2O2 concentration is key to increasing space‐time yield. Consequently, a novel two‐stage H2O2 feeding strategy was proposed, which improved the DTBP selectivity from 94.7% to 97.6% compared to the single‐stage feeding process. The maximum TBA conversion reached upto 98.7% within only 410 s, with a DTBP yield of 96.3%. With proper design and optimization, this microreaction system could be further applied to continuously synthesize other dialkyl peroxides.

Heterocoupling Two Similar Benzyl Radicals by Dual Photoredox/Cobalt Catalysis.

Transition-metal-regulated radical cross coupling enables the selective bonding of two distinct transient radicals, whereas the catalytic method for sorting two almost identical transient radicals, especially similar benzyl radicals, is still rare. Herein, we show that leveraging dual photoredox/cobalt catalysis can selectively couple two similar benzyl radicals. Using easily accessible methylarenes and phenylacetates (benzyl N-hydroxyphthalimide (NHPI) esters) as benzyl radical sources, a range of unsymmetrical 1,2-diarylethane classes via the 1°-1°, 1°-2°, 1°-3°, 2°-2°, 2°-3° and 3°-3° couplings were obtained with broad functional group tolerance. Besides the photochemical continuous flow synthesis, the one-pot procedure that directly uses phenylacetic acids and NHPI as the starting materials to avoid the pre-preparation of benzyl NHPI esters for the gram-scale synthesis is also feasible and affords good yields, showcasing the synthetic utility of our protocol.

High‐speed continuous flow calorimetry in a nonadiabatic environment

AbstractMany rapid and strongly exothermic reactions have transitioned to continuous flow reactors for safety considerations. However, data from batch calorimeters often fall short in guiding these processes due to substantial differences in transfer characteristics, and the adiabatic components of calorimeters significantly escalate equipment costs and dimensions. Inspired by the human body's thermoregulatory mechanism, we developed the Dynamic Tracking Reference Continuous Calorimeter (DTRCC). This novel device enables rapid and precise calorimetry in continuous‐flow reactions under nonadiabatic conditions and variable external temperatures. The measurement time can be reduced to 110 s with a low difference of 0.5%. The DTRCC proves versatile across various reaction types, including nitrification and photoreaction. It can also determine solutions' heat capacity and reactions' selectivity according to calorimetry. Implementing the DTRCC provides crucial data that enhance the design and optimization of continuous flow reactors, significantly boosting chemical process safety and efficiency.