Application Of Microreactors Research Articles

Preparation of New Amphiphilic Liquid-Crystal Diblock Copolymers Bearing Side-on Cholesteryl Mesogen and Their Self-aggregation

Amphiphilic block copolymers bearing rigid hydrophobic liquid crystal mesogen have recently attracted broad interests since they could spontaneously self-assemble into functional objects at the micron and/or nanometer scales, and these soft matters bearing high-order hierarchical structures have potential applications in micro-reactors, advanced catalysts, biosensors, drug delivery, biotechnology and so forth. In this work, we designed and successfully prepared a new series of amphiphilic liquid crystal poly(glyceryl methacrylate)-b-poly(6-cholesteryloxyhexyl methacrylate) (PGMA-b-PMA6Chol) with hydrophobic PMA6Chol block bearing end-on cholesteryl mesogen through sequential controlled reversible addition- fragmentation chain transfer polymerization (RAFT) and successive removal of ketal protection groups. Then, their structures and comonomer composition were examined by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). Liquid crystal phase structures and their transition as well as thermal stability of the prepared LC copolymers were characterized by differential scanning calorimeter (DSC), polarized optical microscope (POM), 2D small angle X-ray scat- tering (2D-SAXS) and thermogravimetric analytic instrument (TGA). Moreover, self-aggregation of these amphiphilic LC block copolymers in mixed solution was investigated by means of UV spectrometer, and the aggregate sizes and morpholo- gies were examined by scanning electron microscopy (SEM) and dynamic light scattering (DLS), respectively. As a result, it was revealed that the LC to isotropic phase transition temperature (TLC-I) of as-synthesized LC block copolymers increased with an increase in rigid LC block content, and the presence of bishydroxyl groups of hydrophilic PGMA strongly influenced the self-assembly and LC phase of rigid hydrophobic block in bulk state. In mixed solvent, the synthesized amphiphilic LC copolymers were found to preferably self-aggregate into core-shell spherical objects with average sizes spanning a range from 0.7 to 2.0 μm when the hydrophobic LC block content was less than 93%, in contrast, the LC copolymer with 93 wt% LC block tended to form open hollow spherical aggregates, showing interesting thermal responsive particle sizes in aqueous solution.

γ-Fe2O3 nanoparticle surface controls PtFe nanoparticle growth and catalytic properties

We report a novel method for synthesis of alloy PtFe nanoparticles (NPs) of different compositions using γ-Fe2O3 NPs as an iron source. We show here other growth mechanisms than conventional nucleation on a NP surface leading to core-shell NP or seeded NP growth. Depending on reaction conditions, different compositions of PtFe NPs can be obtained. PtFe NPs may coexist with γ-Fe2O3 NPs in the reaction product. This mixture obtained in situ allows much higher catalytic activity in hydrogenation of methyl-3-buten-2-ol than that of only PtFe nanoparticles or merely mixed PtFe and γ-Fe2O3 NPs. The presence of both PtFe and γ-Fe2O3 NPs allows formation of dense and stable NP arrays which hold promise for catalytic applications in microreactors or other reactor designs where a catalytic film is favoured.

From petal effect to lotus effect: a facile solution immersion process for the fabrication of super-hydrophobic surfaces with controlled adhesion

In this paper, a convenient approach based on the reaction between an alkyl thiol and hierarchical structured Cu(OH)2 substrates is reported for the fabrication of super-hydrophobic surfaces with controlled adhesion. This reaction can etch the Cu(OH)2 microstructures and simultaneously introduce a coating with low surface energy. By simply controlling the reaction time or the chain length of the thiol, super-hydrophobic surfaces with controlled adhesion can be achieved, and the adhesive force between the surface and the water droplet can be adjusted from extreme low (∼14 μN) to very high (∼65 μN). The tunable effect of the adhesion is ascribed to the different wetting states for the droplet on the surface that results from the change of the morphology and microstructure scale after the thiolate reaction. Noticeably, the as-prepared surfaces are acid/alkali-resisting; the acidic and basic water droplets have similar contact angles and adhesive forces to that of the neutral water droplet. Moreover, we demonstrate a proof of water droplet transportation for application in droplet-based microreactors via our surfaces. We believe that the results reported here would be helpful for the further understanding of the effect of wetting states on the surface adhesion and the fabrication principle for a super-hydrophobic surface with controlled adhesion.

Controlled Fabrication of Uniform Hollow Bowl‐Shaped Microspheres Based on Polyphosphazene Material

AbstractMicro or nanoparticles with hollow interiors are receiving immense attention owing to their unique hollow structure and wide application potential. A novel hollow bowl‐shaped microsphere based on a polyphosphazene material is successfully fabricated for the first time by a facile solvent‐treatment process. Based on SEM and TEM observations, the obtained particle is proven to be uniform with a shell thickness of about 120 nm, and a tentative formation mechanism is suggested. By combination of the unique bowl‐shaped structure, uniform microsize, and the superior properties of the hybrid polyphosphazene material, the products are envisioned to have promising applications in microreactors to fabricate functional composite particles, in catalysis, or the biomedical domain.

Amphiphilic diblock copolymer modification of carbon nanotubes in CO2-expanded liquids

Poly(4-vinylpyridine)-block-polystyrene (P4VP-b-PS) is an ideal amphiphilic diblock copolymer for potential applications in emulsion polymerization, colloid stabilization and microreactors, and the self-assembly ability also helps P4VP-b-PS to find wide applications in nanolithography, catalysis, molecular templating, and drug delivery. In this work, the non-covalent functionalization of single-walled carbon nanotubes (SWCNTs) with P4VP-b-PS in CO2-expanded liquids (CXLs) is reported. It is found that P4VP-b-PS stabilized SWCNTs showed better dispersion in organic solvent. Raman spectra indicated that there exist interactions between SWCNTs and P4VP-b-PS chains. Furthermore, the structure and morphology of P4VP-b-PS/SWCNTs composite were examined, focusing on P4VP-b-PS concentration and the pressure of CXLs. It is found that the P4VP-b-PS wrapping patterns undergo a remarkable morphological evolution from dotted coating crystals to compact kebabs, and then to helical patternings by facile pressure tuning in the high polymer concentration series. In other words, the CXLs method enables superior control of the P4VP-b-PS crystallization patternings on SWCNTs. What is more, the CXL-assisted P4VP-b-PS crystal growth mechanism on SWCNT is investigated. The crystal growth exhibited a pressure-switchable mechanism, i.e., the dominating mechanism switches from “soft epitaxy” (kebabs) at pressures below the threshold pressure to “normal epitaxy” (helicals) at higher pressure above the threshold value. We believe these studies would reveal great potential for P4VP-b-PS in building up functional structures in CXLs that are responsive to environmental stimuli.

Catalysis for Lignocellulosic Biomass Processing: Methodological Aspects

Increasing value of lignocellulosic biomass through catalytic approaches is an area, which recently attracted a lot of attention. Due to specific features of such catalysis, different from more traditional heterogeneous catalysis in transformations of petrochemicals, the authors considered important to address various methodological issues, such as product analysis, catalytic measurements, influence of mass transfer, development of kinetic expressions, reactions intensification by application of microreactors and technology development in general. Potential pitfalls, challenges and research opportunities are highlighted.

Biodiesel synthesis in microreactors

As a renewable and environmentally friendly fuel, biodiesel has been widely produced and its demand will continue to grow globally. Innovative technologies and process integration are needed to produce biodiesel in an energy effi cient way. The application of microreactors on biodiesel production, may provide a solution for this purpose, for short residence times, high production effi ciency and low operating cost and energy consumption in biodiesel production via transesterifi cation. This review provides an overview on the current status of research on biodiesel synthesis in microreactors, including the types of microreactors used in biodiesel production, the main factors infl uencing biodiesel synthesis in microreactors, the types of catalysts used, and application of the microfl uidic technique in the purifi cation of biodiesel. Some issues to be considered for commercialization of this technique are discussed.

Thin-walled B–C–N ternary microtubes: from synthesis to electrical, cathodoluminescence and field-emission properties

Microtubes with nanoscale sidewalls, benefiting from their large internal space, can find wide potential applications in microreactors, microfluidic devices, drug delivery systems, etc. We report on the synthesis of thin-walled B–C–N ternary microtubes based on a modified vapor–liquid–solid (VLS) and template self-sacrificing process. The BCN microtubes have unique structures with diameters in the microscale range and wall-thicknesses in the nanoscale range. In situ electrical measurements indicate that the BCN microtubes have a semiconducting behavior with enhanced conductivity. The electrical properties of the microtubes can be tailored by successful C doping. A strong broad UV band is observed from the microtubes, which can be assigned to the impurity and/or defect-related emission (IDRE). Field-emission measurements show that after C doping, the resultant BCN microtubes have greatly improved field-emission characteristics compared with pure BN microtubes.

In situ surface reaction induced adhesion force change for mobility control, droplet sorting and bio-detection

Water droplet mobility can be reversibly controlled based on surface grafted stimuli-responsive polymer brushes by in situ liquid–solid interface chemical reactions. By regulating the pH of a droplet in situ, the real-time dynamic tuning of the chain conformation between the swollen state (hydrophilic) and collapsed state (hydrophobic) can be realized, and the hydrophobic PFOTS background results in the in situ droplets mobility control. Droplet sorting can also be realized by smart stimuli-responsive surfaces due to the different pHs of the droplets. Based on a similar mechanism, protein detection between antibodies and antigens can be realized by immobilizing biotin ligands on a hydrophobic PFTEOS background using probing liquids with or without streptavidin. These methods possess potential applications in microfluidics, micro-reactors and bio-detection.

The Application of a Multi-Channel Microreactor for the Chemical Conversion of Lactate Esters

The Application of a Multi-Channel Microreactor for the Chemical Conversion of Lactate Esters

Window of opportunity – potential of increase in profitability using modular compact plants and micro-reactor based flow processing

Recently, much focus has been given to a new type of chemical production plant, with the aim of a much faster time-to-market (“50% idea”) and better cash-flow revenue. The main enabling technology is to have the plants pre-manufactured and assembled by a modular construction and to use innovative, smart-scale processing and apparatus technology, in order to achieve a compact overall plant footprint. Focal points in such technology are on the one hand, flow processing, with micro process technology as a cutting-edge cornerstone, and on the other hand, the container framework. Yet, other process-intensified technologies are suitable as well such as milli-flow or upgraded batch technologies. Finally, process robustness and short-time applicability make the decision. In this paper, for the first time, a CAPEX and OPEX analysis of the new plant technology is done, at the example of the Evotrainer production platform. This platform is pre-manufactured in serial and provides all the utilities needed around the reactor and e.g., separator to be tailored and inserted. The unit-operational modularization, with respective definition of interfaces, was developed further to a so-called functional modularization, where different cabinets with pre-defined functions and equipment are proposed. Three virtual microreactor applications were used and stand as model-based scenarios for market applications in bulk chemistry, fine chemistry and pharmacy. It is shown, in many facets, that the Evotrainer infrastructure based plants indeed have a faster payback and higher earnings as compared to conventional technology, particularly when serving high-priced markets such as pharmaceutical applications. Further, the combination with novel chemical routes or novel processing (Novel Process Windows) is advantageous. Micro process technology is one of the key enablers and was taken here, since the dataset of such technology was readily available to the authors due to past research efforts and there is some general belief in the combination to the so-called “Future Factories”. Yet, it stands also for any other process intensification technology which can achieve the same performance level and which is able to satisfy the needs of a producing industry.

Lab-on-a-Chip Systems for Microchemical Applications

Lab-on-a-chip microchemical systems were fabricated from PDMS, polyimide (PI) film and functional polymers by different lithographic techniques to look for microreactor applications in the areas of organic syntheses. In detail, efficient gas-liquid reactions in dual-channel microreactor, continuous recovery and recirculation of catalystimmobilized magnetic particles in microfluidic system, and a flexible film microreactor will be discussed.

Superoleophobic Surfaces with Controllable Oil Adhesion and Their Application in Oil Transportation

Controlling liquid adhesion is a fundamental issue in many applications for special wettable surfaces. Compared to superhydrophobic surfaces of different water adhesion, superoleophobic surfaces of controllable oil adhesion are much more practical, as it leads to non-wetting for both water and oil. However, previously the investigation for oil adhesion ability on superoleophobic surfaces in oil/air/solid system has been extremely rare. In this work, we describe a convenient approach to fabricate superoleophobic surfaces through perfluorothiolate reaction on Cu(OH)2 nanostructure surfaces and investigate their possible application in oil droplet transportation. The prepared surfaces exhibit controllable oil adhesive force depending on surface nanostructures or external preloads on the oil droplet. A model of the penetrating Cassie state is used to help analyze the unique phenomena on oil adhesion. Moreover, we provide a proof of demonstrate of oil transportation for application in oil-based microreactors via our surfaces. Our results give a useful attempt in understanding the fabrication principle of preparing superoleophobic surfaces with controllable oil adhesion.

Application of Microreactors in the Dehydrogenation of Isobutane

Microreactors with chromia/alumina catalyst were investigated in isobutane dehydrogenation. Chromia was deposited in the reactor by atomic layer deposition (ALD). Conversion increased with chromium content in the reactor and isobutene selectivity was higher than with conventional powder catalyst. Thermal reactions were negligible making microreactors attractive for measuring kinetic data.

Kinetic study and modeling of the Rh-catalyzed hydrosilylation of acetophenone in a batch reactor and in a microreactor

The Rh-catalyzed hydrosilylation of acetophenone in the presence of [Rh(CO)2(μ-Cl)]2 and [Rh(COD)Cl]2 complexes, as well as with an in situ addition of nitrogen-containing derivatives of mono- and bicyclic terpenes was investigated in a flow microreactor and in a batch reactor. Kinetic modeling, reaction equilibrium analysis and multi-criteria optimization of the process were applied to compare the performances of the reactors. In general, the highest catalytic activity was reached in the presence of [Rh(COD)Cl]2 and [Rh(CO)2(μ-Cl)]2 without the addition of amines. The best reaction selectivity towards 1-phenylethanol silyl ether with the [Rh(CO)2(μ-Cl)]2 complex was observed in the microreactor. The addition of (R)-(−)-cis-MyrtNH2 and (R)-(+)-BornylNH2 amines, as well as an increase of the amine-to-rhodium molar ratio significantly decreased the conversion and selectivity in both reactors. In this connection, the [Rh(COD)Cl]2 complex demonstrated a better catalytic performance in all cases. The application of the flow microreactor promoted another elementary reaction pathway due to micromixing effects.

Tunable wettability of carbon nanotube/poly ( ɛ-caprolactone) hybrid films

We have realized a stable superhydrophobic surface, a thermally tunable superhydrophobic surface, and a thermally tunable hydrophobic surface by combining the crystalline/amorphous phase transition of the poly( ɛ-caprolactone) (PCL) with the optimized surface roughness of the carbon nanotube/PCL hybrid films. The water droplet mobilities and wettabilities were reversibly thermally switched on the tunable superhydrophobic and the hydrophobic surfaces, respectively. These responsive surfaces have potential applications in microfluidic devices and microreactors and for liquid transportation.

Functionalization of PNIPAAm microgels using magnetic graphene and their application in microreactors as switch materials

Aqueous-dispersed graphene/Fe3O4 hybrids are prepared using a two-step method. Functional microgels composed of the poly(N-isopropylacrylamide) (PNIPAAm) and the as-prepared graphene/Fe3O4 hybrids are synthesized in a microfluidic reactor for the first time. The microgel exhibits a good response to an external magnet and near-infrared (NIR) laser irradiation, indicating that it could be used as a light-driven and magnetic controlled switch for applications in microreactors.

Novel polymer–polyphenol beads for encapsulation and microreactor applications

Novel structures with controllable morphology made from natural materials hold promise for several applications in pharmaceuticals, foods and biotechnology field. In this paper, we utilized the strong interactions between epigallocatechin gallate (EGCG), a polyphenol obtained from green tea, and water soluble cellulose ethers like methyl cellulose (MCE) and hydroxyl propyl methylcellulose (HPMC) to fabricate novel beads with controllable core–shell morphology. The novel polymer–polyphenol beads were prepared by simply adding polymer solution dropwise into an aqueous solution of polyphenol. Effect of process variables like concentration and viscosity grades of polymer, reaction time and concentration of EGCG on bead formation was evaluated. Spherical milky white beads with average diameters ranging from 600–2500 µm were obtained that retained shape after freeze drying. Internal structure of beads was studied using automated light microscopy and cold stage scanning electron microscopy (Cryo-SEM). Percent loading of EGCG in the beads was above 25% w/w in all the cases. The release study in simulated intestinal fluid revealed burst release of EGCG (20% in first 5 minutes) followed by sustained release with more than 90% release at the end of 300 minutes. The antioxidant power of EGCG in the beads was effectively maintained in the alkaline conditions with 5–6 fold activity as compared to free EGCG. Further, the temperature triggered release characteristic of beads was explored by encapsulating eucalyptus oil and studying the release of oil using hot stage microscopy. Enzyme immobilisation application of beads was demonstrated by immobilising α-amylase onto the beads and studying its enzyme activity after several washings.

Control of the thickness of mesoporous titania films for application in multiphase catalytic microreactors

A new method of sol–gel polymer template synthesis of mesoporous catalytic thin films has been proposed which allows controlling the chemical nature of the film, the porosity, thickness and loading with an active species. The mesoporous films with a long-order structure can be obtained in a narrow range of surfactant-to-metal precursor molar ratios from 0.006 to 0.009. The catalytic film thickness was varied from 300 to 1000 nm while providing a uniform catalyst distribution with a desired catalyst loading (1 wt. % Au nanoparticles) throughout the film. The films were characterized by TEM, SEM, ethanol adsorption and contact angle measurements. The calcination of the as-synthesized films at 573 K reduced Ti 4+ sites to Ti 3+. A 300 nm thick Au-containing film showed an initial TOF of 1.4 s −1 and a selectivity towards unsaturated alcohols as high as 90% in the hydrogenation of citral. Thicker films demonstrated a high selectivity towards the saturated aldehyde (above 55%) and a lower intrinsic catalytic activity (initial TOF of 0.7–0.9 s −1) in the absence of internal diffusion limitations.

Tailoring Anisotropic Wetting Properties on Submicrometer-Scale Periodic Grooved Surfaces

The use of simple plasma treatments and polymer deposition to tailor the anisotropic wetting properties of one-dimensional (1D) submicrometer-scale grooved surfaces, fabricated using interferometric lithography in photoresist polymer films, is reported. Strongly anisotropic wetting phenomena are observed for as-prepared 1D grooved surfaces for both positive and negative photoresists. Low-pressure plasma treatments with different gas compositions (e.g., CHF(3), CF(4), O(2)) are employed to tailor the anisotropic wetting properties from strongly anisotropic and hydrophobic to hydrophobic with very high contact angle and superhydrophilic with a smaller degree of wetting anisotropy and without changing the structural anisotropy. The change of the surface wetting properties for these 1D patterned surfaces is attributed to a change in surface chemical composition, monitored using XPS. In addition, the initial anisotropic wetting properties on 1D patterned samples could be modified by coating plasma treated samples with a thin layer of polymer. We also demonstrated that the wetting properties of 1D grooved surfaces in a Si substrate could be tuned with similar plasma treatments. The ability to tailor anisotropic wetting on 1D patterned surfaces will find many applications in microfluidic devices, lab-on-a-chip systems, microreactors, and self-cleaning surfaces.