Membrane Microreactor Research Articles

Performance of tube-in-tube membrane microreactor in E2/EE2 degradation via UV/H2O2/TiO2 process

The tube-in-tube membrane microreactor is an advanced system designed for the continuous removal of contaminants of emerging concerns (CECs) from urban and industrial wastewater. Despite its high removal efficiency, critical questions remain regarding the impact of various operational parameter: (i) flow rate of contaminants, (ii) oxidant dosage, (iii) concentration of the H2O2 stock solution, and (iv) pH of the H2O2 stock solution. This study addresses these questions, with particular focus on the previously unexplored effects of H2O2 concentration and pH. We investigated the degradation of estrogens 17β-Estradiol (E2) and 17α-Ethinylestradiol (EE2) using a UV/H2O2/TiO2 process using a membrane tube-in-tube reactor assembled with an inner glass fiber microfiltration membrane, coated with the catalyst TiO2-P25, and an outer quartz tube. Synthetic contaminated solution [E2/EE2]inlet = 500μgL-1 was fed in the reactor annulus and the H2O2 stock solution with different pHs (2, 3, 4, 5, 6.8, 8) and concentrations ([H2O2]stock solution = 3000, 6000, 9000 and 12000mgL-1) was fed through the membrane pores (radial permeation) or injected upstream the reactor inlet with different dosages ([H2O2]inlet = 0, 5, 10, 15, 20mgL-1) by means of a syringe pump. Experiments were performed under UVC irradiation and dark conditions. The highest observed removal rate was, approximately, 2.9µM/min for both estrogens, achieved after 7min of reactor operation, highlighting the reactor’s potential for effective CEC degradation under optimized conditions.

In Situ Performance Monitoring of Electrochemical Oxygen and Hydrogen Peroxide Sensors in an Additively Manufactured Modular Microreactor.

Miniaturized and microstructured reactors in process engineering are essential for a more decentralized, flexible, sustainable, and resilient chemical production. Modern, additive manufacturing methods for metals enable complex reactor-geometries, increased functionality, and faster design iterations, a clear advantage over classical subtractive machining and polymer-based approaches. Integrated microsensors allow online, in situ process monitoring to optimize processes like the direct synthesis of hydrogen peroxide. We developed a modular tube-in-tube membrane reactor fabricated from stainless steel via 3D printing by laser powder bed fusion of metals (PBF-LB/M). The reactor concept enables the spatially separated dosage and resaturation of two gaseous reactants across a membrane into a liquid process medium. Uniquely, we integrated platinum-based electrochemical sensors for the online detection of analytes to reveal the dynamics inside the reactor. An advanced chronoamperometric protocol combined the simultaneous concentration measurement of hydrogen peroxide and oxygen with monitoring of the sensor performance and self-calibration in long-term use. We demonstrated the highly linear and sensitive monitoring of hydrogen peroxide and dissolved oxygen entering the liquid phase through the membrane. Our measurements delivered important real-time insights into the dynamics of the concentrations in the reactor, highlighting the power of electrochemical sensors applied in process engineering. We demonstrated the stable continuous measurement over 1 week and estimated the sensor lifetime for months in the acidic process medium. Our approach combines electrochemical sensors for process monitoring with advanced, additively manufactured stainless steel membrane microreactors, supporting the power of sensor-equipped microreactors as contributors to the paradigm change in process engineering and toward a greener chemistry.

MnO2@CS modified catalytic membrane for simultaneous organics removal and membrane fouling mitigation via peroxymonosulfate activation

The integration of advanced oxidation process and ultrafiltration membrane has been regarded as an effective method to improve pollutants removal and mitigate membrane fouling simultaneously in the field of wastewater treatment. Hence, a novel catalytic membrane microreactor, referred to as MnO2@CS-UF, was synthesized via coupling MnO2 modified carbon spheres (MnO2@CS) with membrane. The mesoporous structure of MnO2@CS guaranteed adequate water transfer channels and also contributed to more exposure of active sites. With MnO2@CS uniformly dispersed, the MnO2@CS-UF membrane showed increased hydrophilicity, higher permeability and superior peroxymonosulfate (PMS)-activation capability. With synergistic effect of pore interception and catalytic degradation, MnO2@CS-UF showed excellent organic pollutants removal (MB removal of about 100 % in 5 min), and had a prominent mitigation effect on membrane fouling caused by model NOM. In addition, MnO2@CS-UF/PMS system showed excellent catalytic filtration performance in the treatment of actual secondary effluent (SE). MnO2@CS-UF/PMS system could effectively remove fluorescent organics, and the removal rates of I-V region were 36.3 %, 72.3 %, 67.7 %, 73.5 % and 71.4 %, respectively. The permeance decline of MnO2@CS-UF was also effectively alleviated, with irreversible and reversible resistances reduced by 61.0 % and 23.2 % than UF membranes, individually. High-valent manganese-oxo species and singlet oxygen played a leading role in contaminants elimination, whereas radical oxidation acted as auxiliary contributors. Standard blocking became the dominant fouling pattern for MnO2@CS-UF/PMS, demonstrating that the MnO2@CS catalytic layer ensured the synthesis of vast active substances, prevented foulant adhesion on pore walls and alleviated the growth of cake layer. These results illustrated that the integration of MnO2@CS catalytic degradation and membrane filtration was feasible to improve the permeate quality and mitigate membrane fouling in wastewater reclamation.

Multi-channel ceramic catalytic membrane microreactors for highly efficient heterogeneous catalysis

Multi-channel ceramic catalytic membrane microreactors are highly efficient reactors, combining reaction and separation in a single unit. However, the synthesis of multi-channel ceramic catalytic membranes with well-distributed active components keeps a great challenge. Here, we report a flow-induced layer-by-layer assembly of zeolitic imidazolate framework-67 (ZIF-67) followed by pyrolysis that generates highly active and well-distributed Co@N-doped carbon (Co@CN) catalytic materials inside the ceramic membrane (CM) pores, which creates abundant microreactors with enhanced mass transfer efficiency. The pyrolysis temperature, concentration of Co2+, and number of solution cycles are determined as pivotal factors on the microstructures and catalytic performance of the catalytic membranes. The catalytic membrane, Co@CM-550-0.06-2, exhibits outstanding performance in the reduction of p-nitrophenol to p-aminophenol, achieving full conversion within 25 min and maintaining stability over 5 h of continuous operation. The developed multi-channel ceramic catalytic membrane microreactors can be readily scaled up, and have great application potentials in heterogeneous catalysis.

A flow-through catalytic membrane micro-reactor for hydrogen production by methanol steam reforming

A flow-through catalytic membrane micro-reactor (CMR) with Cu/ZnO/Al2O3 nanoparticles immobilized in porous membrane pores has been developed for hydrogen production by methanol steam reforming (MSR). The characteristics for CMR demonstrated Cu/ZnO/Al2O3 nanoparticles with almost 200 nm were successfully in situ immobilized in membrane pores. During MSR for hydrogen production in CMR by flow-through mode, hydrogen yield of 500 mmol h−1 g−1 and selectivity of 100% can be achieved under the condition of temperature being 360℃, molar ratio of water to methanol of 8.8 and weight hourly space velocity (WHSV) of 9.28 h−1. Compared with the commercial fixed bed reactor, the hydrogen productivity in CMR is one order of magnitude higher, owing to MSR confined in the space of membrane pore with micro-scale. The methanol conversion rate of over 95% can be expected, if five sheets of CMR with thickness of 5 mm were assembled in series.

Computational Studies on Microreactors for the Decomposition of Formic Acid for Hydrogen Production Using Heterogeneous Catalysts.

Sustainable alternatives to conventional fuels have emerged recently, focusing on a hydrogen-based economy. The idea of using hydrogen (H2) as an energy carrier is very promising due to its zero-emission properties. The present study investigates the formic acid (FA) decomposition for H2 generation using a commercial 5 wt.% Pd/C catalyst. Three different 2D microreactor configurations (packed bed, single membrane, and double membrane) were studied using computational fluid dynamics (CFD). Parameters such as temperature, porosity, concentration, and flow rate of reactant were investigated. The packed bed configuration resulted in high conversions, but due to catalyst poisoning by carbon monoxide (CO), the catalytic activity decreased with time. For the single and double membrane microreactors, the same trends were observed, but the double membrane microreactor showed superior performance compared with the other configurations. Conversions higher than 80% were achieved, and even though deactivation decreased the conversion after 1 h of reaction, the selective removal of CO from the system with the use of membranes lead to an increase in the conversion afterwards. These results prove that the incorporation of membranes in the system for the separation of CO is improving the efficiency of the microreactor.

Ni-Cu bimetallic catalytic membranes for continuous nitrophenol conversion

Bimetallic nanocatalysts are of great interest due to their greater activity, selectivity, and chemical and electrochemical stability, compared to their monometallic counterparts. Bimetallic nanocatalysts formed from abundant and inexpensive elements provide greater opportunities for applications over noble metal catalysts. In this study, inexpensive Ni-Cu bimetallic catalytic membrane microreactors (CMMRs) were synthesized in a simple two-step process to catalytically degrade the environmental pollutant, 4-nitrophenol (4-NP), and produce the valuable feedstock, 4-aminophenol (4-AP). Ni-Cu nanoparticles were either produced by a replacement reduction reaction or a co-reduction reaction, producing either bimodal or integrated nanostructures, respectively, as demonstrated by transmission electron microscopy (TEM), while the electronic reconfiguration between bimetallic systems was verified by X-ray photoelectron spectroscopy (XPS). Compared to 4-NP batch conversion, flow-through reactions demonstrated enhanced mass transfer contributing to 2-fold higher conversion (>99%), 30-fold higher processing capacity (0.95 mol∙m−2∙h−1) and co-reduced Ni-Cu CMMRs boasted a reaction rate constant of 725.03 min−1.4-NP conversion on the Ni-Cu catalysts in the presence of NaBH4 followed the Langmuir-Hinshelwood (L-H) mechanism, and the conversion efficiency was highly dependent on flow rate, representing an optimization trade-off critical for CMMR applications. The polydopamine-assisted fabrication and the tortuous membrane pore structure contributed to the CMMRs’ stability with <5% metal loss during operation. The enhanced activity was attributed to the synergistic electronic effects of the Ni-Cu bimetallic structure, the metal-polydopamine interactions, and the catalysts’ unique structure and high surface area.

Ultrafiltration Pd-immobilized catalytic membrane microreactors continuously reduce nitrophenol: A study of catalytic activity and simultaneous separation

Catalytic membrane microreactors (CMMRs) are an exciting new technology that combine catalysis with membranes by seeding the high internal surface area of membranes with catalysts. This enables the continuous purification and production of organic compounds with high catalytic activity, while maintaining nanocatalyst size and stability. This study reports a simple two-step batch reaction approach for synthesizing stable Pd-immobilized catalytic membranes to transform 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in a flow-through CMMR system. The product (4-AP) is an essential intermediate for the polymer and solvent chemical industry. Pd-immobilized membranes exhibited strong catalytic activity for 4-NP reduction in the presence of NaBH4, with 4-fold higher reduction (79.7%) and 2-fold higher reduction rate (1.08 mol m−2h−1) as compared to control membranes without catalysts. The catalytic mechanisms were elucidated, such that the catalytic reduction processes were conducted via a sequential hydrogenation reaction where Pd nanocatalysts facilitated H* transfer from BH4- to 4-NP. Ultimately, the 4-AP product was gradually desorbed from the catalytic sites, achieving continuous reduction with high reduction efficiency. Furthermore, by combing ultrafiltration and catalysis, Pd-immobilized membranes showed >99% of 4-NP conversion and >90% of 1 MDa PEO rejection, demonstrating a great potential to be applied in high-efficient wastewater treatment processes.

Carbonized wood impregnated with bimetallic nanoparticles as a monolithic continuous-flow microreactor for the reduction of 4-nitrophenol.

Porous monolithic microreactors show great promise in catalytic applications, but are usually based on non-renewable materials. Herein, we demonstrate a Ni/Au nanoparticle-decorated carbonized wood (Ni/Au-CW) monolithic membrane microreactor for the efficient reduction of 4-nitrophenol. The hierarchical porous wood structure supports uniformly distributed heterobimetallic Ni/Au nanoparticles. As a consequence of these two factors, both mass diffusion and electron transfer are enhanced, resulting in a superior reduction efficiency of 99.5% as the liquor flows through the optimised Ni/Au-CW membrane. The reaction mechanism was investigated by electron paramagnetic resonance spectroscopy and density functional theory calculations. The proposed attraction-repulsion mechanism facilitated by the bimetallic nanoparticles has been ascribed to the different electronegativities of Ni and Au. The Ni/Au-CW membrane exhibits excellent catalytic performance and could be applicable to other catalytic transformations.

Recent progress for hydrogen production from ammonia and hydrous hydrazine decomposition: A review on heterogeneous catalysts

In response to the growing trend of greenhouse gas emissions from the production and use of conventional fuels, COx free hydrogen generation is introduced as an alternative and efficient energy carrier. Due to hydrogen’s storage challenges, is more efficient to be produced on-site by other chemical compounds for fuel cell applications. This work outlines the production of hydrogen (H2) from ammonia (NH3) and hydrous hydrazine (N2H4·H2O) catalytic decomposition. Both substances are giving nitrogen (N2) as a by-product, which is not toxic. Moreover, heterogeneous catalysts that were studied through the years are presented. Lastly, a reactoristic view of the ammonia decomposition is provided with different reactors such as catalytic membrane reactors (CMRs), fixed-bed reactors (FBRs) and micro-reactors (MRs) for the evaluation of their performance.

Natural Wood-Based Catalytic Membrane Microreactors for Continuous Hydrogen Generation.

The development of controlled processes for continuous hydrogen generation from solid-state storage chemicals such as ammonia borane is central to integrating renewable hydrogen into a clean energy mix. However, to date, most reported platforms operate in batch mode, posing a challenge for controllable hydrogen release, catalyst reusability, and large-scale operation. To address these issues, we developed flow-through wood-based catalytic microreactors, characterized by inherent natural oriented microchannels. The prepared structured catalysts utilize silver-promoted palladium nanoparticles supported on metal-organic framework (MOF)-coated wood microreactors as the active phase. Catalytic tests demonstrate their highly controllable hydrogen production in continuous mode, and by adjusting the ammonia borane flow and wood species, we reach stable productivities of up to 10.4 cmH23 min-1 cmcat-3. The modular design of the structured catalysts proves readily scalable. Our versatile approach is applicable for other metals and MOF combinations, thus comprising a sustainable and scalable platform for catalytic dehydrogenations and applications in the energy-water nexus.

Catalytic membrane micro-reactor with nano Cu/ZIF-8 assembly in membrane pores by flowing synthesis combining partial ion-exchange

A catalytic membrane micro-reactor (CMMR) is fabricated, with nano Cu/ZIF-8 particles immobilized in the pores of the microfiltration membrane for flow-through catalysis. Nano ZIF-8 is firstly assembled in polyethersulfone (PES) membrane pores by flowing synthesis and then Cu nanoparticles (NPs) are synthesized in-situ in ZIF-8 by the partial ion-exchange reaction. Cu/ZIF-8 nanoparticles are distributed evenly throughout the whole direction of membrane thickness while Cu NPs are dispersed well in ZIF-8. The 4-nitrophenol (4-NP) reduction is used to test the performance of the CMMR. The 4-NP reduction rate being 99.3% is achieved when the membrane flux is 2293 L m −2 h −1 . The CMMR has good stability for over 210 min and presents a surprisingly high apparent reaction rate constant ( K app , 837.43 min −1 ) at room temperature with the loading of ZIF-8 being 85 mg g −1 (PES) and Cu loading cycle number being 1. Compared with batch catalysis by powder catalysts, the K app is increased by 4 orders of magnitude via flow-through catalysis mode using CMMR. The nanoscale configuration of ZIF-8 and Cu NPs assembled inside pores of the membrane enhances remarkably the catalytic activity owing to the enhanced contact and mass transfer in the confined space of membrane pores. A catalytic membrane micro-reactor (CMMR) with nano Cu/ZIF-8 immobilizing in membrane pores was fabricated by flowing synthesis combining partial ion-exchange. This structure provides excellent activities due to the synergistic effect of membrane pores, ZIF-8, and nano Cu. Cu/ZIF-8 catalytic membrane micro-reactor fabricated by flowing synthesis method Cu/ZIF-8 assembled throughout membrane thickness with high loading and dispersity Synergistic effect between membrane pores, ZIF-8 and nano Cu enhances 4-NP reduction Reduction rate of 4-NP over 99.3% achieved with stability over 210 min Apparent reaction rate constant improved by 4 orders of magnitude via flow-through catalysis

Catalyst-modified perovskite hollow fiber membrane for oxidative coupling of methane

The catalytic oxidative coupling of methane (OCM) to C2 hydrocarbons (C2H6 and C2H4) represents one of the most effective ways to convert natural gas to more useful products, which can be performed effectively using La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) perovskite hollow fiber membrane microreactor. In this work, the effects of adding a thin BaCe0.8Gd0.2O3−δ (BCG) catalyst film onto the inner LSCF fiber surface as the OCM catalyst and a porous Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) perovskite layer onto the outer LSCF surface to improve the oxygen permeation were evaluated. Between 700 °C and 1000 °C, methane conversion increased in the order of uncoated, BCG and BSCF-coated, and BCG-coated LSCF hollow fiber while C2-selectivity and C2-yield increased in the order of BCG and BSCF-coated, uncoated, and BCG-coated LSCF hollow fiber. Oxygen permeation flux at the same temperature range, on the other hand, was enhanced in the order of uncoated, BCG-coated, and BCG and BSCF-coated LSCF hollow fiber. This finding demonstrates the complex interplay between oxygen permeation and OCM performance. The BCG and BSCF-coated hollow fiber was also subjected to thermal cycles between 850 °C and 900 °C for up to 175 hours during which the fiber showed minor degradation in oxygen permeation fluxes and relatively stable OCM performance.

RETRACTED ARTICLE: Catalytic Membrane Micro-Reactors for Fuel and Biofuel Processing: A Mini Review

RETRACTED ARTICLE: Catalytic Membrane Micro-Reactors for Fuel and Biofuel Processing: A Mini Review

CFD Study of the Numbering up of Membrane Microreactors for CO2 Capture

Carbon dioxide (CO2) is one of the major atmospheric greenhouse gases (GHG). The continuous increase of CO2 concentration and its long atmospheric lifetime may cause long-term negative effects on the climate. It is important to develop technologies to capture and minimize those emissions into the atmosphere. The objective of this work is to design and study theoretically and experimentally a numbering-up/scale-out membrane microreactor in order to be used as a capture system. The main aim of the work is to obtain an even flow distribution at each plate of the reactor. Nearly uniform flow distribution was achieved at each layer of the numbering-up microreactor according to the carried-out CFD models. The maximum difference between the average velocities was less than 6% for both gas and liquid flows. To obtain better flow distribution into the microreactor, the radius of the inlet/outlet tube was optimized. Results from CFD and experimental simulations do not match, and slightly maldistribution in achieved in the experimental system due to phase breakthrough and imperfections on the fabrication of the plates. Moreover, comparing the single channel microreactor to the scale-out microreactor, the latter showed poorer performance on CO2 removal while expecting the reactors to have similar performance. By installing inserts with different channel widths, the experimental results were identical to the original case.

Cu-Ag Bimetallic Core-shell Nanoparticles in Pores of a Membrane Microreactor for Enhanced Synergistic Catalysis.

A bimetallic catalytic membrane microreactor (CMMR) with bimetallic nanoparticles in membrane pores has been fabricated via flowing synthesis. The bimetallic nanoparticle is successfully immobilized in membrane pores along its thickness direction. Enhanced synergistic catalysis can be expected in this CMMR. As a concept-of-proof, Cu-Ag core-shell nanoparticles have been fabricated and immobilized in membrane pores for p-nitrophenol (p-NP) hydrogenation. Transmission electron microscopy (TEM) for the characterization of the bimetallic core-shell nanostructure and X-ray photoelectron spectroscopy (XPS) for the characterization of the electron transfer behavior between Cu-Ag bimetal have been performed. The Ag shell on the core of Cu can improve the utilization of Ag atoms, and electron transfer between bimetallic components can promote the formation of high electron density active sites as well as active hydrogen with strong reducing properties on the Ag surface. The dispersed membrane pore can prevent nanoparticle aggregation, and the contact between the reaction fluid and catalyst is enhanced. The enhanced mass transfer can be achieved by the plug-flow mode during the process of hydrogenation catalysis. The p-NP conversion rate being over 95% can be obtained under the condition of a membrane flux of 1.59 mL·cm-2·min-1. This Cu-Ag/PES CMMR has good stability and has a potential application in industry.

Synergistic enhanced catalysis of micro-reactor with nano MnO2/ZIF-8 immobilized in membrane pores by flowing synthesis

A catalytic membrane micro-reactor (CMMR) with nano MnO2/ZIF-8 immobilized in membrane pores has been fabricated by flowing synthesis and formaldehyde degradation was used to test its catalytic performance. The CMMR with deep-permeation nano structure (DPNS) has good stability, uniform nano MnO2/ZIF-8 dispersion and higher loading capacity. The MnO2 coated on the surface of nano ZIF-8 with the size in the range of 100–150 nm was obtained. The contact between formaldehyde and MnO2 is enhanced by the effect of even disperse of membrane pores. The enhanced mass transfer can be achieved in the micro-scale pores of the membrane by the confined space effect. A higher amount of MnO2 loading and higher formaldehyde absorption rate can be achieved by the effect of ZIF-8 in membrane pores. The formaldehyde degradation rate was increased from 82.6% to 94.0%, if the MnO2 loading capacity was increased from 98 mg g−1 to 344 mg g−1.

Design of a novel dual function membrane microreactor for liquid–liquid–liquid phase transfer catalysed reaction: selective synthesis of 1-naphthyl glycidyl ether

Where, Ar-aryl group, Q+X−-phase transfer catalyst, Ar–O−Q+-catalyst complex with Ar–O−, R+–X−-haloalkane, Ar–O–R-product.

HI-Light: A Glass-Waveguide-Based "Shell-and-Tube" Photothermal Reactor Platform for Converting CO2 to Fuels.

SummaryIn this work, we introduce HI-Light, a surface-engineered glass-waveguide-based “shell-and-tube” type photothermal reactor which is both scalable in diameter and length. We examine the effect of temperature, light irradiation, and residence time on its photo-thermocatalytic performance for CO2 hydrogenation to form CO, with a cubic phase defect-laden indium oxide, In2O3-x(OH)y, catalyst. We demonstrate the light enhancement effect under a variety of reaction conditions. Notably, the light-on performance for the cubic nanocrystal photocatalyst exhibits a CO evolution rate at 15.40 mmol gcat−1 hr−1 at 300°C and atmospheric pressure. This is 20 times higher conversion rate per unit catalyst mass per unit time beyond previously reported In2O3-x(OH)y catalyst in the cubic form under comparable operation conditions and more than 5 times higher than that of its rhombohedral polymorph. This result underscores that improvement in photo-thermocatalytic reactor design enables uniform light distribution and better reactant/catalyst mixing, thus significantly improving catalyst utilization.

Enhanced Catalytic Performance of a Membrane Microreactor by Immobilizing ZIF-8-Derived Nano-Ag via Ion Exchange

A catalytic membrane microreactor (CMMR) was fabricated by immobilizing ZIF-8-derived nano-Ag in membrane pores via ion exchange. ZIF-8 was first in situ assembled in polyethersulfone (PES) membran...