微通道反应器内"就地"合成沸石膜催化层及其性能

采用简单、新颖的沸石粒子引入方法,将NaX沸石晶种引入不锈钢微反应器的微通道内,并用流动法"就地"直接在微通道内通过沸石生长形成NaX沸石膜层,经铯离子交换处理成为CsNaX催化层,用苯甲醛和氰基乙酸乙酯的Knoevenagel缩合反应评价了该催化层的催化性能.结果表明,微通道内形成的沸石膜层连续,均匀,具有良好的催化功能.微反应器内缩合反应的结果明显优于传统反应器.     

Ceramic microreactors for heterogeneously catalysed gas-phase reactions

The high surface to volume ratio of microchannel components offers many advantages in micro chemical engineering. It is obvious, however, that the reactor material and corrosion phenomena play an important role when applying these components. For chemical reactions at very high temperatures or/and with corrosive reactants involved, microchannel components made of metals or polymers are not suited. Hence, a modular microreactor system made of alumina was developed and fabricated using a rapid prototyping process chain. With exchangeable inserts the system can be adapted to the requirements of various reactions. Two heterogeneously catalysed gas-phase reactions (oxidative coupling of methane, isoprene selective oxidation to citraconic anhydride) were investigated to check the suitability of the system at temperatures of up to 1000 degrees C. Apart from the high thermal and chemical resistance, the lack of any blind activity was found to be another advantage of ceramic components.     

Efficiency of Zn/TiO<Subscript>2</Subscript> catalyst operation in a microchannel reactor in methanol steam reforming

The activity of a Zn/TiO₂ catalyst deposited on metal microchannel plates in methanol steam reforming was studied. The catalyst exhibited maximum activity upon deposition on microchannel plates made of copper foam. In this case, the specific hydrogen production of a microreactor at 450°C was 78.6 l (g Cat)^?1 h^?1. The catalysts deposited on a microchannel plate of nickel foam and on corrugated brass foil exhibited lower activity because of the lower efficiency of heat transfer to the reaction zone. A correlation between the thermal conductivity of the microchannel plate material and the activity of the catalyst was observed in the following order: copper, brass, and nickel. The kinetic parameters of the process of methanol steam reforming in a microreactor were calculated with the use of a plug-flow reactor model. In this case, the calculated formal activation energy of 132 kJ/mol was independent of the microchannel plate material. A comparison of the equilibrium concentrations of reaction products at the reactor outlet, which were calculated from thermodynamic data, with the experimental data demonstrated that methanol steam reforming at a temperature higher than 400°C occurred in the nonequilibrium region. The concentration of carbon monoxide at the microreactor outlet was lower than 1 mol %, which is lower than the equilibrium concentration by one order of magnitude. This effect was attributed to the suppression of the reversed water gas shift reaction on the catalyst.     

Application of a temperature-controllable microreactor to simple and rapid protein identification using MALDI-TOF MS

We have carried out a simultaneous thermal denaturation and trypsin digestion of proteins using a temperature-controllable microreactor. This is a simple and rapid sample preparation technique for use before matrix-assisted laser desorption ionization time-of-flight mass spectrometry. In contrast to a conventional sample preparation method, which involves several chemical treatments, our sample preparation was performed using only trypsin digestion with the thermal denaturation of the target protein. Optimization of the reactor operational parameters for trypsin digestion using a temperature-controllable microreactor was carried out. The entire trypsin digestion procedure took about 11 min, and consisted of 1 min for the thermal denaturation of the sample protein (3 microl, 0.2 microM) at 85 degrees C, and 10 min for digestion of the protein at 37 degrees C. The resulting sequence coverage ranged from 24% to 57%, which was sufficient for practical protein identification.     

Functionalized magnetic micro- and nanoparticles: optimization and application to micro-chip tryptic digestion

The preparation of an easily replaceable protease microreactor for micro-chip application is described. Magnetic particles coated with poly(N-isopropylacrylamide), polystyrene, poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate), poly(glycidyl methacrylate), [(2-amino-ethyl)hydroxymethylen]biphosphonic acid, or alginic acid with immobilized trypsin were utilized for heterogeneous digestion. The properties were optimized, with the constraint of allowing immobilization in a microchannel by a magnetic field gradient. To obtain the highest digestion efficiency, sub-micrometer spheres were organized by an inhomogeneous external magnetic field perpendicularly to the direction of the channel. Kinetic parameters of the enzyme reactor immobilized in micro-chip capillary (micro-chip immobilized magnetic enzyme reactor (IMER)) were determined. The capability of the proteolytic reactor was demonstrated by five model (glyco)proteins ranging in molecular mass from 4.3 to 150 kDa. Digestion efficiency of proteins in various conformations was investigated using SDS-PAGE, HPCE, RP-HPLC, and MS. The compatibility of the micro-chip IMER system with total and limited proteolysis of high-molecular-weight (glyco)proteins was confirmed. It opens the route to automated, high-throughput proteomic micro-chip devices.     

Fabrication of tunable microreactor with enzyme modified magnetic nanoparticles for microfluidic electrochemical detection of glucose

A microfluidic device was designed for amperometric determination of glucose by packing enzyme modified magnetic nanoparticles (MNPs) in its microchannel as an enzyme microreactor. Glucose oxidase was covalently attached to the surface of MNPs and localized in the microchannel by the help of an external magnetic field, leading to a tunable packing length. By changing the length of microreactor from 3 to 10 mm, the performance for glucose detection was optimized. The optimal linear range to glucose was from 25 μM to 15 mM with a detection limit of 11 μM at a length of 6 mm. The inter- and intra-day precisions for determination of 1.0 mM glucose were 0.8% and 1.7%, respectively, and the device-to-device reproducibility was 95.6%. The enzyme reactor remained its 81% activity after three-week storage. Due to the advantages of the device and fracture sampling technique, serum samples could be directly sampled through the fracture to achieve baseline separation from ascorbic acid, and proteins in the samples did not interfere with the detection. This work provided a promising way for pretreatment-free determination of glucose with low cost and excellent performance.     

Effect of the microchannel plate design on the capacity of methanol steam reformers

Methanol steam reforming in microreactors is considered, and the effects of the microreactor geometry (cylindrical and rectangular) and microchannel plate (MCP) design on the hydrogen capacity of the microreactor is analyzed. The MCPs were made from aluminum foil, stainless steel, and foamed nickel by laser engraving, electrochemical etching, and pressing. The amount of catalyst powder (CuO/ZnO = 40: 60 mol/mol) fixed on one MCP was 0.04–2.5 g. The specific hydrogen capacity (U _w) of the cylindrical microreactor is more than 3 times as high as the U _w of the rectangular microreactor and is 6 times as high as the U _w of a conventional fixed-bed catalytic reactor. This gain in hydrogen capacity is due to the more efficient use of the catalyst in the microreactors. The MCP design, which determines the residence time of the reactants in the microreactor, also has a significant effect on the capacity of the microreactor.     

Monitoring of chemical reactions within microreactors using an inverted Raman microscopic spectrometer

An inverted Raman microscope spectrometer has been used to profile the spatial evolution of reactant and product concentrations for a chemical reaction within a microreactor operating under hydrodynamic flow control. The Raman spectrometer was equipped with a laser source at wavelength of 780 nm, confocal optics, a holographic transmission grating, and a charge-coupled device (CCD) detector. The microreactor consisted of a T-shaped channel network etched within a 0.5 mm thick glass bottom plate that was thermally bonded to a 0.5 mm thick glass top plate. The ends of the channel network were connected to reagent reservoirs that were linked to a syringe pump for driving the solutions by hydrodynamic pumping within the channels. The microchannels were 221 micro m wide and 73 micro m deep. The synthesis of ethyl acetate from ethanol and acetic acid was investigated as a model system within the microreactor as Raman scattering bands for each reactant and product species were clearly resolved. Raman spectral intensities of each band were proportional to concentration for each species and hence all concentrations could be quantitatively measured after calibration. By scanning specific Raman bands within a selected area in the microchannel network at given steps in the X-Y plane, spatially resolved concentration profiles were obtained under steady-state flow conditions. Under the flow conditions used, different positions within the concentration profile correspond to different times after contact and mixing of the reagents, thereby enabling one to observe the time dependence of the product formation. Raman microscopy provides a useful complementary technique to UV/VIS absorbance and fluorescence methods for the in situ monitoring and analysis of chemical reaction species having their lowest S(0)-S(1) absorption bands too far in the UV to be of use, due to their probable overlap with the bands from other reactant, product and solvent molecules.     

Hydrogen generation using a CuO/ZnO-ZrO₂ nanocatalyst for autothermal reforming of methanol in a microchannel reactor

In the present work, a microchannel reactor for autothermal reforming of methanol using a synthesized catalyst porous alumina support-CuO/ZnO mixed with ZrO? sol washcoat has been developed and its fine structure and inner surface characterized. Experimentally, CuO/ZnO and alumina support with ZrO? sol washcoat catalyst (catalyst slurries) nanoparticles is the catalytically active component of the microreactor. Catalyst slurries have been dried at 298 K for 5 h and then calcined at 623 K for 2 h to increase the surface area and specific pore structures of the washcoat catalyst. The surface area of BET N? adsorption isotherms for the as-synthesized catalyst and catalyst/ZrO? sol washcoat samples are 62 and 108 ± 2 m2g?1, respectively. The intensities of Cu content from XRD and XPS data indicate that Al?O? with Cu species to form CuAl?O?. The EXAFS data reveals that the Cu species in washcoat samples have Cu-O bonding with a bond distance of 1.88 ± 0.02 ? and the coordination number is 3.46 ± 0.05, respectively. Moreover, a hydrogen production rate of 2.16 L h?1 is obtained and the corresponding methanol conversion is 98% at 543 K using the CuO/ZnO with ZrO? sol washcoat catalyst.     

Microreactor for the Catalytic Partial Oxidation of Methane

Fixed-bed reactors for the partial oxidation of methane to produce synthetic gas still pose hot-spot problems. An alternative reactor, which is known as the shell-and-tube-typed microreactor, has been developed to resolve these problems. The microreactor consists of a 1 cm outside-diameter, 0.8 cm inside-diameter and 11 cm length tube, and a 1.8 cm inside-diameter shell. The tube is made of dense alumina and the shell is made of quartz. Two different methods dip and spray coating were performed to line the tube side with the LaNixOy catalyst. Combustion and reforming reactions take place simultaneously in this reactor. Methane is oxidized in the tube side to produce flue gases (CO2 and H2O) which flow counter-currently and react with the remaining methane in the shell side to yield synthesis gas. The methane conversion using the higher-loading catalyst spray-coated tube reaches 97% at 700℃, whereas that using the lower-loading catalyst dip-coated tube reaches only 7.78% because of poor adhesion between the catalyst film and the alumina support. The turnover frequencies (TOFs) using the catalyst spray-and dip-coated tubes are 5.75×10-5 and 2.24×10-5 mol/gcat·s, respectively. The catalyst spray-coated at 900℃provides better performance than that at 1250℃because sintering reduces the surface-area. The hydrogen to carbon monoxide ratio produced by the spray-coated catalyst is greater than the stoichiometric ratio, which is caused by carbon deposition through methane cracking or the Boudouard reaction.     

Off-line form of the Michaelis-Menten equation for studying the reaction kinetics in a polymer microchip integrated with enzyme microreactor

We firstly transformed the traditional Michaelis-Menten equation into an off-line form which can be used for evaluating the Michaelis-Menten constant after the enzymatic reaction. For experimental estimation of the kinetics of enzymatic reactions, we have developed a facile and effective method by integrating an enzyme microreactor into direct-printing polymer microchips. Strong nonspecific adsorption of proteins was utilized to effectively immobilize enzymes onto the microchannel wall, forming the integrated on-column enzyme microreactor in a microchip. The properties of the integrated enzyme microreactor were evaluated by using the enzymatic reaction of glucose oxidase (GOx) with its substrate glucose as a model system. The reaction product, hydrogen peroxide, was electrochemically (EC) analyzed using a Pt microelectrode. The data for enzyme kinetics using our off-line form of the Michaelis-Menten equation was obtained (K(m) = 2.64 mM), which is much smaller than that reported in solution (K(m) = 6.0 mM). Due to the hydrophobic property and the native mesoscopic structure of the poly(ethylene terephthalate) film, the immobilized enzyme in the microreactor shows good stability and bioactivity under the flowing conditions.     

Deactivation of a Zn/TiO<Subscript>2</Subscript> catalyst in the course of methanol steam reforming in a microchannel reactor

The service life tests of a Zn/TiO₂ catalyst deposited on the microchannel plates of copper foam, nickel foam, and corrugated brass foil in the process of methanol steam reforming demonstrated that the catalyst stability and operation time depend on microchannel plate material. The rate of catalyst deactivation correlated with the thermal conductivity of the microchannel plate material. It was found that catalyst deactivation resulted from the decomposition of zinc titanates, which are active components, and it was accompanied by the appearance of a zinc oxide phase. The best results in the service life tests were obtained with the microchannel plates of copper foam. A microchannel reactor containing 16 copper plates continuously operated at 400°C for 150 h; in this case, the conversion of methanol decreased by 8%. The subsequent microreactor operation for 500 h caused a decrease in the methanol conversion by 26%. It was found that the loss of the catalyst activity was a reversible process, and the activity can be restored by annealing in air.     

Zeolite nanoparticle modified microchip reactor for efficient protein digestion

An enzymatic microreactor has been fabricated based on the poly(methyl methacrylate) (PMMA) microchchip surface-modified with zeolite nanoparticles. By introducing the silanol functional groups, the surface of PMMA microchannel has been successfully modified with silicalite-1 nanoparticle for the first time due to its large external surface area and high dispersibility in solutions. Trypsin can be stably immobilized in the microchannel to form a bioreactor using silica sol-gel matrix. The immobilization of enzyme can be realized with a stable gel network through a silicon-oxygen-silicon bridge via tethering to those silanol groups, which has been investigated by scanning electron microscopy and microchip capillary electrophoresis with laser-induced fluorescence detection. The maximum proteolytic rate constant of the immobilized trypsin is measured to be about 6.6 mM s(-1). Using matrix assisted laser desorption and ionization time-of-flight mass spectrometry, the proposed microreactor provides an efficient digestion of cytochrome c and bovine serum albumin at a fast flow rate of 4.0 microL min(-1), which affords a very short reaction time of less than 5 s.     

Pile-up glass microreactor

We made a 'pile-up' microreactor in which ten levels of microchannel circuits were integrated to form a single glass entity. Solutions were distributed to each layer via cylindrical holes with a diameter much larger than that of the microchannel. Fabrication of the pile-up reactor was completed using only conventional photolithography, wet etching and thermal bonding techniques, and no special facilities or instruments were required. An amide formation reaction between amine in aqueous solution and acid chloride in organic solution was carried out using the pile-up reactor. The yield of the amide formation reaction is dependent on the size of the specific surface area between the two solutions, and the small space inside the microchannels is good for acquiring a large specific surface area without any stirring processes. The maximum throughput for the ten-layered pile-up reactor was ten times larger than that of a single-layered one, yet the reaction yield was still high. Productivity of the pile-up reactor for the reaction was as high as on a gram per hour scale. This value suggests that many conventional plants producing fine chemicals can be replaced by microreactors through the numbering-up technology.     

Assembly-controlled biocompatible interface on a microchip: strategy to highly efficient proteolysis

A biocompatible interface was constructed on a microchip by using the layer-by-layer (LBL) assembly of charged polysaccharides incorporating proteases for highly efficient proteolysis. The controlled assembly of natural polyelectrolytes and the enzyme-adsorption step were monitored by using a quartz-crystal microbalance and atomic force microscopy (AFM). Such a multilayer-assembled membrane provides a biocompatible interconnected network with high enzyme-loading capacity. The maximum digestion rate of the adsorbed trypsin in a microchannel was significantly accelerated to 1600 mM min(-1) microg(-1), compared with the tryptic digestion in solution. Based on the Langmuir isotherm model, the thermodynamic constant of adsorption K was calculated to be 1.6 x 10(5) M(-1) and the maximum adsorption loading Gammamax was 3.6 x 10(-6) mol m(-2), 30 times more than a monolayer of trypsin on the native surface. The tunable interface containing trypsin was employed to construct a microchip reactor for digestion of femtomoles of proteins and the produced peptides were analyzed by MALDI-TOF mass spectroscopy. The efficient on-chip proteolysis was obtained within a few seconds, and the identification of biological samples was feasible.     

A replaceable microreactor for on-line protein digestion in a two-dimensional capillary electrophoresis system with tandem mass spectrometry detection

We describe a two-dimensional capillary electrophoresis system that incorporates a replaceable enzymatic microreactor for on-line protein digestion. In this system, trypsin is immobilized on magnetic beads. At the start of each experiment, old beads are flushed to waste and replaced with a fresh plug of beads, which is captured by a pair of magnets at the distal tip of the first capillary. For analysis, proteins are separated in the first capillary. A fraction is then parked in the reactor to create peptides. Digested peptides are periodically transferred to the second capillary for separation; a fresh protein fraction is simultaneously moved to the reactor for digestion. An electrospray interface is used to introduce peptides into a mass spectrometer for analysis. This procedure is repeated for several dozen fractions under computer control. The system was demonstrated by the separation and digestion of insulin chain b oxidized and β-casein as model proteins.     

溶胶凝胶微流控酶反应器用于蛋白质肽谱分析的研究

The silica-based poly(dimethylsiloxane)(PDMS)microfluidic enzymatic reactor was reported along with itsanalytical features in coupling with MALDI TOF and ESI MS.Microfluidic chip was fabricated using PDMS cast-ing and O_2-plasma techniques,and used for the preparation of enzymatic reactor.Plasma oxidation for PDMS en-abled the channel wall of microfluidics to present a layer of silanol(SiOH)groups.These SiOH groups as anchorsonto the microchannel wall were linked covalently with the hydroxy groups of trypsin-encapsulated sol matrix.As aresult,the leakage of sol-gel matrix from the microchannel was effectively prevented.On-line protein analysis wasperformed with the microfluidic enzymatic reactor by attachment of stainless steel tubing electrode and replaceabletip.The success of trypsin encapsulation was investigated by capillary electrophoresis(CE)detection,and MALDITOF and ESI MS analysis.The lab-made device provided excellent extent of digestion even at the fast flow rate of7.0 μL/min with very short residence time of ca.2 s.In addition,the encapsulated trypsin exhibits increased stabil-ity even after continuous use.These features are the most requisite for high-throughput protein identification.     

Immobilization of enzymes on a microchannel surface through cross-linking polymerization

A novel and facile method for the preparation of an enzyme-immobilized microreactor has been developed in which enzymes are immobilized as an enzyme-polymer membrane formed on the inner wall of the microchannel by a cross-linking polymerization method; the resulting microreactor shows excellent reaction performance and stability against denaturating agents.     

Integrated platform of capillary isoelectric focusing, trypsin immobilized enzyme microreactor and nanoreversed-phase liquid chromatography with mass spectrometry for online protein profiling

An integrated platform with the combination of protein and peptide separation was established via online protein digestion, by which proteins were first separated by CIEF, online digested by a trypsin immobilized enzyme microreactor, trapped and desalted by two parallel trap columns, separated by nanoreversed-phase and finally identified by MS. In such a platform, two hollow fiber membrane interfaces were used. One was applied to supply catholyte and electric contact, and another to supply adjustment buffer to improve the compatibility of protein separation and tryptic digestion. A poly(octadecyl acrylate-co-ethylene dimethacrylate) monolithic column served as the trap column to capture sample and to remove the ampholytes from CIEF. A hybrid silica monolith-based immobilized trypsin microreactor was used for online protein digestion. To evaluate the performance of such a platform, a 4-protein mixture with a loading amount of only 0.29?μg, was analyzed, and sequence coverages for BSA, myoglobin, β-lactoglobulin and ribonuclease A were 8, 26, 10 and 54%, respectively. Furthermore, such an integrated platform was successfully applied for the analysis of proteins extracted from Escherichia coli, and 101 proteins were positively identified. We anticipate that the integrated platform developed herein will provide a promising tool for low-abundance protein identification with the combination of top-down and bottom-up approaches.     

Chemiluminescence biosensor chip based on a microreactor using carrier air flow for determination of uric acid in human serum

A chemiluminescence biosensor on a chip coupled to a microfluidic system and a microreactor is described in this paper. The chemiluminescence biosensor measured 25 x 75 x 6.5 mm in dimension, and was readily produced in an analytical laboratory. The sol-gel method is introduced to co-immobilize horseradish peroxidase (HRP) and luminol in the microreactor, and to immobilize uricase in the enzymatic reactor. The main characteristic of the biosensor was to introduce air as the carrier flow instead of the more common solution carrier for the first time. The uric acid was determined by a chemiluminescent (CL) reaction between the hydrogen peroxide produced from the enzymatic reactor and luminol under the catalysis of HRP in the microreactor. The linear range of the uric acid concentration was 1 to 100 mg L(-1) and the detection limit was 0.1 mg L(-1) (3sigma).