Flow Reactor Research Articles

Al-N3 Bridge Site Enabling Interlayer Charge Transfer Boosts the Direct Photosynthesis of Hydrogen Peroxide from Water and Air.

Manipulating the electronic environment of the reactive center to lower the energy barrier of the rate-determining water oxidation step for boosting the direct generation of H2O2 from water, air, and sunlight is fascinating yet remains a grand challenge. Driven by a first-principles screening across a series of metal single atoms in carbon nitride, we report a class of an Al-N3 bridge site enabling interlayer charge transfer in carbon nitride nanotubes (CNNT-Al) for the highly efficient photosynthesis of H2O2 directly from water, oxygen, and sunlight. We demonstrate that the interlayered Al-N3 bridge site in CNNT-Al is able to activate the neighboring surface N atom for promoting the rate-determining step of the two-electron water oxidation to H2O2. It is also able to act as a bridge for enhancing the vertical interlaminar charge transfer due to the hybridization between the 3s and 3p states of the interstitial Al atom and the conduction band of two adjacent carbon nitride layers. Collectively, these factors lead to a highest photocatalytic mass activity of 1410.2 μmol g-1 h-1 (with a photocatalyst concentration of 1 g L-1) for direct photosynthesis of H2O2 out of all CN-based photocatalysts and a 7-fold higher solar-to-chemical conversion efficiency (0.73%) compared to that of the natural photosynthesis of typical plants (∼0.1%). Most importantly, the CNNT-Al-based flow reactor can steadily produce H2O2 for 200 h and be directly used for the on-site degradation of organic dye in water. The CNNT-Al-based flow reactor can also kill a 10 times higher concentration of bacteria in deionized water than that in natural water with 100% efficiency, which makes our design economically appealing for practical water treatment.

Flowing Forward: Continuous Synthesis of and with Ionic Liquids

AbstractHerein, the developments in the field of continuous ionic liquid synthesis and continuous ionic liquid utilization from the last seven years are reviewed. Starting by discussing recent strategies for the preparation of ionic liquids themselves in different flow reactors, the review will further focus on various continuous strategies employing ionic liquids. The application of ionic liquids in continuous processes, particularly as supported catalytic layers, has drawn significant scientific interest in the last decades. These catalyst frameworks provide a versatile tool in many organic transformations, and their application became an attractive strategy in continuous catalytic approaches.

Photoinduced Radical Borylation of Robust Carbon–Heteroatom Bonds

AbstractPhotoinduced borylation has emerged as a valuable strategy for synthesizing arylboronic esters. However, photochemical transformations involving inert bonds such as C(sp2)−F bonds are still challenging. Herein, we report a straightforward and operationally simple method for the activation of various inert carbon–heteroatom bonds, enabling the synthesis of diverse arylboronic esters without the need for transition metals or catalysts. Mechanistic investigations reveal that the deprotonation of DMSO plays a pivotal role in the reaction, and the excited DMSO anion can undergo electron transfer to the aryl substrates activated by anionic sp2–sp3 diboron compounds, i. e., [FB2pin2]−, thereby facilitating the cleavage of carbon–heteroatom bonds. The reaction allows the conversion of diverse Caryl–hetero bonds in batch and flow reactors into the corresponding arylboronic esters. The products can be used in a subsequent Suzuki‐Miyaura cross‐coupling without isolation.

Secondary Organic Aerosol Formation from the Photooxidation of Aromatic Ketone Intermediate Volatile Organic Compounds.

Oxygenated aromatics are substantial secondary organic aerosol (SOA) precursors, such as benzyl alcohol and phenolic compounds. Aromatic ketone intermediate volatile organic compounds (IVOCs), as a subclass of oxygenated aromatics, were found in anthropogenic source emissions and may contribute to SOA formation. However, the SOA yields and formation pathways of aromatic ketone IVOCs remain unknown. In this study, the photooxidations of aromatic ketone IVOCs in the absence and presence of NOx were studied in an oxidation flow reactor, and the particle- and gas-phase oxidation products were measured. The maximum SOA yields of benzophenone and 1,2-diphenylethanone are 0.24 and 0.33-0.35, respectively, relatively high among oxygenated aromatics. The SOA yields in the presence of NOx are 2-3 times higher than those in the absence of NOx in the late stage of oxidation. As the photooxidation proceeds, H/C of SOA slightly increases with O/C, and a greater amount of more-oxidized ring-retaining products exists in the particle phase in the presence of NOx. Based on gas-phase products and possible reaction pathways, functionalization of benzoic acid via the phenolic pathway is favored in the presence of NOx. Thus, our study highlights the significant SOA formation from aromatic ketone IVOCs, especially in the presence of NOx during long-time photooxidation.

Deoxygenation and isomerization activity balance for NiMo/ZSM-23 catalysts as an effect of Mo/(Ni+Mo) ratio in hydroprocessing of fatty acids

Series of Ni-Mo catalysts based on ZSM-23 zeolite were synthesized by incipient wetness impregnation – with a fixed content of Ni (5 wt. %). These catalysts were tested in a hydroprocessing of a mixture of fatty acids (C16-C18) in a flow reactor at a temperature of 300 °C, a pressure of 2.5 MPa and WHSV = 8.4 h-1. The influence of the ratio of metals on the formation of forms of the active component, as well as on the activity, selectivity to iso-alkanes and the stability of catalysts during the hydroprocessing of a mixture of undiluted fatty acids was determined. The ratio of metals was investigated in the range from 0 to 1. The highest deoxygenation activity and highest isoalkanes yield were found for sample with Mo/(Ni+Mo) ratio equal 0.25, in which, according to the XPS, the Mo/(Ni+Mo) ratio on the surface is 0.4.

Small gold nanoparticles for tandem cyclization/reduction and cyclization/hydroalkoxylation reactions

With peculiar structural features at the surface of small metal nanoparticles, some discrete sites can display catalytic behaviour similar to what could be observed with mononuclear metal catalysts in solution. We have studied the transfer of two catalytic tandem reactions from homogeneous to heterogeneous conditions. Tandem cyclisation/reduction of ortho-alkynyl benzaldehyde derivatives was successfully achieved with Au nanoparticles over TiO2 (Au NPs/TiO2) in the presence of Hantzsch ester with 45-98% yields for 15 examples (average yield: 70.4%). Similarly, tandem cyclisation/hydroalkoxylation of ortho-alkynyl benzaldehyde derivatives was successfully achieved with Au NPs/TiO2 in methanol or other alcohols with 62-96% yields for 17 examples (average yield: 84.9%). The application potential of this catalytic system was demonstrated with the total synthesis of a bioactive isochromene derivative featuring one of the developed reactions as the key step and the implementation of the tandem cyclisation/hydroalkoxylation in a continuous flow reactor, scaling up the reaction by a factor of 10 without loss of efficiency.

Investigation of the Cyclohexene Oxidation Mechanism Through the Direct Measurement of Organic Peroxy Radicals.

Monoterpenes, the second most abundant biogenic volatile organic compounds globally, are crucial in forming secondary organic aerosols, making their oxidation mechanisms vital for addressing climate change and air pollution. This study utilized cyclohexene as a surrogate to explore first-generation products from its ozonolysis through laboratory experiments and mechanistic modeling. We employed proton transfer reaction mass spectrometry with NH4+ ion sources (NH4+-CIMS) and a custom-built OH calibration source to quantify organic peroxy radicals (RO2) and closed-shell species. Under near-real atmospheric conditions in a Potential Aerosol Mass-Oxidation Flow Reactor, we identified 30 ozonolysis products, expanding previous data sets of low-oxygen compounds. Combined with simulations based on the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere and relevant literature, our results revealed that OH dominates over ozone in cyclohexene oxidation at typical atmospheric oxidant levels with H-abstraction contributing 30% of initial RO2 radicals. Highly oxidized molecules primarily arise from RO2 autoxidation initiated by ozone, and at least 15% of ozone oxidation products follow the overlooked nonvinyl hydroperoxides pathway. Gaps remain especially in understanding RO2 cross-reactions, and the structural complexity of monoterpenes further complicates research. As emissions decrease and afforestation increases, understanding these mechanisms becomes increasingly critical.

Visible Light Excitation of Poly-(para-Phenylene Ethynylene) Enables Heterogeneous Photocatalytic Oxidations of Amines in Flow.

Heterogeneous visible light photocatalysis is a compelling approach to address sustainability in synthetic photochemistry. However, the use of solid-state photocatalysts remains very unpopular in organic synthesis because of their limited accessibility and the black-box effect associated to the lack of rational between their molecular structure and their photochemical properties. Herein, we disclose the synthesis, characterization, photocatalytic properties and synthetic applications of a simple and readily available solid-state conjugated organic polymer, poly-(para-phenylene ethynylene) 1, which exhibits a strong oxidative power upon irradiation with visible light (E(1*/1•-) = +1.67 V vs SCE). Comparisons with structural analogues highlighted the superior photocatalytic activity of this linear semiconductor, on account of its fully conjugated architecture. The associated excited-state reactivity enabled the transformation of various amines into imines in batch and continuous flow reactors together with straightforward photocatalyst recycling. Mechanistic investigations revealed concomitant photoredox and energy transfer pathways, that led to the formation of the desired products. Ultimately, the inline generation of imines was exploited in telescoped three-component Ugi reactions (3CR) in batch and flow toward biologically relevant α-acylaminoamides.

Visible Light Excitation of Poly‐(para‐Phenylene Ethynylene) Enables Heterogeneous Photocatalytic Oxidations of Amines in Flow.

Heterogeneous visible light photocatalysis is a compelling approach to address sustainability in synthetic photochemistry. However, the use of solid‐state photocatalysts remains very unpopular in organic synthesis because of their limited accessibility and the black‐box effect associated to the lack of rational between their molecular structure and their photochemical properties. Herein, we disclose the synthesis, characterization, photocatalytic properties and synthetic applications of a simple and readily available solid‐state conjugated organic polymer, poly‐(para‐phenylene ethynylene) 1, which exhibits a strong oxidative power upon irradiation with visible light (E(1*/1•–) = +1.67 V vs SCE). Comparisons with structural analogues highlighted the superior photocatalytic activity of this linear semiconductor, on account of its fully conjugated architecture. The associated excited‐state reactivity enabled the transformation of various amines into imines in batch and continuous flow reactors together with straightforward photocatalyst recycling. Mechanistic investigations revealed concomitant photoredox and energy transfer pathways, that led to the formation of the desired products. Ultimately, the inline generation of imines was exploited in telescoped three‐component Ugi reactions (3CR) in batch and flow toward biologically relevant α‐acylaminoamides.

Rate Coefficient and Branching Ratio for the Formation of Criegee Intermediate Syn-/Anti-CH3CHOO from CH3CHI + O2 and the Self-Reaction of Syn-/Anti-CH3CHOO Determined with Simultaneous IR/UV Probes.

A flow reactor coupled with a light-emitting diode at 286 nm, an infrared quantum-cascade laser near 11 μm, and an ultraviolet laser at 335 nm was implemented to probe the precursor CH3CHI2, syn-CH3CHOO, and anti/syn-CH3CHOO, respectively, in the reaction of CH3CHI + O2. The branching between syn- and anti-CH3CHOO was determined to be ≈80:20 from two methods. The concentration temporal profiles of anti-CH3CHOO, derived on comparison of infrared and ultraviolet profiles, yielded the rate coefficient for the self-reaction of anti-CH3CHOO, kself anti = (6 ± 2) × 10-10 cm3 molecule-1 s-1, ∼4 times the corresponding value, kself syn = (1.4 ± 0.3) × 10-10 cm3 molecule-1 s-1, for syn-CH3CHOO; the rate coefficient for the cross-reaction between syn-CH3CHOO and anti-CH3CHOO was estimated to be (2.1 ± 0.6) × 10-10 cm3 molecule-1 s-1. With determined concentrations of syn-CH3CHOO and self-reaction rate coefficients, the rate coefficient for the formation of CH3CHOO from CH3CHI + O2 was determined to be kform = (3.8 ± 0.7) × 10-12 cm3 molecule-1 s-1 at 298 K, ∼45% of previous reports.

One-Dimensional Model for Calculating a Nanoaerosol Flow in a Continuous Reactor in the Presence of Diffusion and Coagulation of Particles

One-Dimensional Model for Calculating a Nanoaerosol Flow in a Continuous Reactor in the Presence of Diffusion and Coagulation of Particles

Performance of the multi-U-style structure based flow field for polymer electrolyte membrane fuel cell

The design of the reactant gas flow field structure in bipolar plates significantly influences the performance of proton exchange membrane fuel cells (PEMFCs). In this study, we introduced four innovative U-shaped flow field designs, namely: In-Out Multi-U, Out-In Multi-U, Distro In-Out Multi-U, and Distro Out-In Multi-U. To investigate the impact of these various flow fields on PEMFC performance, we conducted computational fluid dynamics (CFD) numerical simulations, validated through model experiments. Our results indicate that the Distro Out-In Multi-U flow field offers notable advantages compared to the conventional parallel flow field (CPFF) and conventional serpentine flow field (CSFF). These benefits include reduced inlet and outlet pressures, lower liquid water content, more uniform liquid water distribution, and a more even current density distribution. Furthermore, the Distro Out-In Multi-U design demonstrates improved efficiency, consuming less H2 (91.9%) than the CSFF while achieving a higher net power density output (10.1%). As a result, for the same power output, the Distro Out-In Multi-U utilizes only 83.5% of the H2 consumed by the CSFF. In summary, the U-shaped structured flow field exhibits superior output performance, enhanced energy efficiency, and improved resistance to flooding. These findings suggest that the U-shaped flow field design holds significant potential as a reactive flow field for PEMFCs.

Phase effects in zirconia catalysed glucose conversion to 5-hydroxy methylfurfural.

5-(hydroxymethyl)furfural (HMF) is a key biomass derived platform chemicals used to produce fuel precursors or additives and value-added chemicals,synthesised by the cascade isomerisation of glucose and subsequent dehydration of reactively formed fructose to HMF over Lewis and Bronsted acid catalysts respectively. Zirconia is a promising catalyst for such reactions; however, the impact of acid properties of different zirconia phases is poorly understood. In this work, we unravel the role of the zirconia crystalline phase in glucose isomerisation and fructose dehydration to HMF. The Lewis acidic monoclinic phase of zirconia is revealed to preferentially facilitate glucose isomerisation, while the nanoparticulate tetragonal phase possesses Brønsted acid sites which favour fructose dehydration. Synergy between both zirconia phases facilitates cascade HMF production, with both catalysts investigated as physical mixtures in batch and flow reactor configurations. Usinga physical mixture of only 15 wt% m-ZrO2 with 85 wt% t-ZrO2 in either batch or packed bed reactor configuration is sufficient to reach equilibrium conversion of glucose for subsequent dehydration by the t-ZrO2 component. Under continuous flow, a six-fold increase in HMF production was obtained when operating with a physical mixture of m- and t-ZrO2 compared to that from a single bed of t-ZrO2.

Gaseous emissions from brake wear can form secondary particulate matter

Road traffic is an important source of urban air pollutants. Due to increasingly strict controls of exhaust emissions from road traffic, their contribution to the total emissions has strongly decreased over time in high-income countries. In contrast, non-exhaust emissions from road vehicles are not yet legislated and now make up the major proportion of road traffic emissions in many countries. Brake wear, which occurs due to friction between brake linings and their rotating counterpart, is one of the main non-exhaust sources contributing to particle emissions. Since the focus of brake wear emission has largely been on particulate pollutants, little is currently known about gaseous emissions such as volatile organic compounds from braking and their fate in the atmosphere. This study investigates the oxidative ageing of gaseous brake wear emissions generated with a pin-on-disc tribometer, using an oxidation flow reactor. The results demonstrate, for the first time, that the photooxidation of gaseous brake wear emissions can lead to formation of secondary particulate matter, which could amplify the environmental impact of brake wear emissions.

Investigating the oxidation characteristic of a hydro-processed bio-jet fuel: Experimental and modeling study

A rapid transition from conventional jet fuels to sustainable aviation fuels (SAFs) is imperative in order to reduce carbon emissions. Hydro-processed esters and fatty acids synthetic paraffinic kerosene (HEFA-SPK), as a type of SAF, exhibits broad applications. In this study, a new HEFA-SPK named ZH-HEFA was investigated. The fuel comprises 14% n-alkanes, 85% iso-alkanes and only 1% cycloalkanes by weight, with the majority of alkanes ranging from C9 to C17. Oxidation experiments of the fuel were conducted using an atmospheric pressure flow reactor at temperatures ranging from 550 K to 1075 K under three equivalence ratios (0.5, 1.0 and 1.5). Species mole fraction profiles were measured by an on-line gas chromatographic (GC). For comparison purposes, an experiment was also performed on RP-3, a conventional jet fuel commonly used in China, under the equivalence of 0.5. Compared to RP-3, ZH-HEFA exhibited significantly stronger low temperature reactivity and higher combustion conversion rates while demonstrating considerably lower yields of aromatics at high temperatures. The kinetic simulation of ZH-HEFA was achieved by proposing two surrogates and their corresponding kinetic models. Surrogate S-1 consisted solely of n-dodecane, while S-2 comprised 35% n-dodecane and 65% 2,6,10-trimethyl dodecane by weight. Both surrogate models were validated by the experimental data. S-1 exhibited a closer resemblance to the global oxidation characteristics of ZH-HEFA, whereas S-2 demonstrated improved accuracy in predicting the formation of small hydrocarbon intermediates during the fuel oxidation. Rate of production analysis revealed that the branched alkane component in S-2 possessed more pathways and greater capability than S-1 in generating C3 intermediates, which are important for the generation of aromatics. Furthermore, both models displayed good predictive performance for the auto-ignition properties of HEFA-SPK fuels.-

Kombucha Fermentation in Coffee: Application of Constant Air Flow Reactor

Kombucha Fermentation in Coffee: Application of Constant Air Flow Reactor

Experimental and kinetic study of methanol/ethanol assisted oxidative degradation of ammonia in supercritical water

Ammonia is a refractory intermediate during supercritical water oxidation (SCWO) of nitrogen-containing wastes, and alcohols are usually introduced as auxiliary fuels to accelerate its degradation. The kinetics of methanol/ethanol assisted oxidative degradation of ammonia in supercritical water have been investigated in a flow reactor, covering alcohol-to-ammonia ratios of 0.2–2.0. During SCWO of ammonia-methanol mixtures, ammonia was mostly converted to N2, with N2O as the main by-product. Increasing methanol concentration facilitated effectively the degradation of ammonia. For the cases with ethanol assistance, high concentrations of HCN were detected at the investigated temperature. Increase in ethanol concentration enhanced ammonia conversion, but had a non-monotonic influence on N2 production. A detailed chemical kinetic model was developed by integrating the nitrogen chemistry with methanol/ethanol mechanisms. The model performance was further validated by comparing to the present and literature data. The model reproduced the ammonia conversions at different conditions fairly well, but overpredicted the N2 yield and underpredicted the NO2 and HCN yields slightly. Based on the model, reaction mechanism was inferred and important elementary steps were identified through kinetic analyses. Finally, the influence of process parameters on ammonia degradation rate was numerically explored. This study is expected to facilitate the application of SCWO technology for N-containing wastes treatment.

Influence of design and operational parameters of a Taylor flow reactor on the bioconversion of methane to ectoines

Ectoine is one of the most attractive bioproducts due to its high market price and applications. Methanotrophic bacteria can synthesize ectoine from biogas. In this work, key design and operating parameters were optimised to maximise the bioconversion of methane to ectoine in a novel Taylor Flow bioreactor. This bioreactor configuration is characterized by higher gas-liquid mass transfer coefficients compared to conventional bubble column bioreactors. Thus, the influence of the internal gas recirculation flow rate (1.0 L·min−1, 2.5 L·min−1, 4.0 L·min−1, 5.5 L·min−1) at 60 and 120 min of gas residence time (GRT), the liquid recirculation flow rate (0 L·h−1, 141 L·h−1, 165 L·h−1, 395 L·h−1, 434 L·h−1) and the capillary length (1.50 and 0.75 m) was evaluated using a mixed methanotrophic consortium. Process operation at 120 min of GRT and 5.5 L·min−1 of gas recirculation flow rate enhanced methane bioconversion, resulting in a maximum efficiency of 83.8 ± 2.7 %. The decrease in capillary length from 1.5 to 0.75 m did not enhance methane bioconversion. Intracellular ectoine and hydroxyectoine reached maximum contents of 105.1 ± 8.6 mgEC·gTSS−1 and 33.4 ± 11.7 mgHE·gTSS−1, respectively. Nitratireductor was the dominant genus, while Methylomicrobium and Methylophaga were the main methanotrophic bacteria detected in the consortium. This study confirmed the feasibility of bioconverting novel renewable feedstocks such biogas into high-added value bio-products, boosting the circular and carbon neutral economy in bio-based industries.

Assessment of pillar-array electrodes for electrochemical flow reactors using a novel hydrodynamic electrode performance factor

This work introduces and validates a Hydrodynamic Electrode Performance Factor (HEPF) for flow reactors. Traditional approaches to electrode optimization often rely on separated mass transfer and pressure drop metrics, hindering comparisons. We address this issue by combining electrochemical and hydrodynamic parameters through a new mathematical expression. This formulation draws inspiration from established equations in heat transfer and the widely recognized Chilton-Colburn analogy, aiming to develop a quantification method independent of the experimental arrangement. The HEPF is complementary to the well-established volumetric mass transfer coefficient and to Storck’s energetic effectiveness postulates for electrochemical reactors. Additionally, this study validates the proposed equation experimentally and then applies it to evaluate pillar array electrodes using 2D computational fluid dynamics simulations for laminar flow conditions. Both experimental and simulation approaches are used to analyze the hydrodynamic behaviour of the electrodes, utilizing the Forchheimer and Hagen-Poiseuille numbers. Notably, preliminary turbulence effects are observed at Reynolds numbers as low as 50 to 125. Visualization of velocity streamlines revealed distinct wake formation behind the pillars at these low Reynolds numbers. This study also explores how reactor inlets, outlets, and tubing pressure losses affect electrode performance. Results emphasize the importance of considering pressure drop, which is integral to the new hydrodynamic performance factor. Analysis of pillar array electrodes demonstrates that reducing both interpillar distance and pillar radius leads to improved electrochemical performance

Assessing the Electrode Configuration in a Sandbox System for the Removal of Sulfanilamide: A Pilot Study

Electrochemical oxidation has emerged as an effective and straightforward technology for groundwater remediation. While recent studies have investigated parameters such as current, electrolyte composition, and electrode materials, most have been conducted using small-scale batch or flow reactors, limiting their applicability to real-world conditions. In this study, a pilot-scale sandbox reactor was employed to simulate realistic groundwater conditions and assess the removal of sulfanilamide, a model organic contaminant. Various electrode configurations were systematically evaluated to identify the key operational parameters influencing pollutant removal efficiency, providing insights for practical applications in groundwater treatment. This study proposes three configurations, including a single well with the anode and cathode, a double well with the separated anode and cathode, and an e-barrier with electrodes separately mounted inside a permeable barrier. Single well had the lowest removal efficiency (60%) because cathodic reaction inhibited the anodic oxidation. A double well with a separate anode and cathode can achieve 80% removal efficiency. However, effluent pH can reach up to 13.2, which can adversely impact groundwater. Meanwhile, the e-barrier not only achieved complete removal, but also maintained a neutral pH of 7.0 over 30 days. The e-barriers proved to be the most effective configuration based on their removal efficiency (100%) while yielding an effluent with neutral pH. The energy consumption of the e-barrier was most effective at 1.54 kWh/m3, while the other configurations were 5.40 and 22.18 kWh/m3. E-barriers are deemed a very reasonable configuration, both in terms of removal efficiency and practical application in groundwater.