Microporous Tube-in-tube Microchannel Reactor Research Articles

CFD modeling on the chemical absorption of CO2 in a microporous tube-in-tube microchannel reactor

In this paper, combining recently developed mesoscale mass transfer model with reaction kinetics, the chemical absorption process of CO2 by MEA solution in a microporous tube-in-tube microchannel reactor (MTMCR) was numerically simulated for the first time. The predicted values by CFD simulations were in agreement with the public experimental data (Na-Na Gao et al., Ind. Eng. Chem. Res., 2011). The distributions of CO2 removal efficiency and volumetric mass transfer coefficient under different gas flow rate, solvent flow rate, solvent temperature, and MEA concentration were analyzed. Among these factors, MEA concentration had a more significant influence on the CO2 chemical absorption. The KGa in the MTMCR was more than 200 times of that in the randomly packed bed under the similar operating conditions. The local mass transfer rate of chemical absorption was one order of magnitude higher than that of physical absorption. This research work could lay a theoretical foundation for the simulation of the complex gas–liquid systems including the chemical absorption by CFD method.

CFD analysis on the intensified mechanism of gas-liquid mass transfer in a microporous tube-in-tube microchannel reactor

A three-dimensional CFD model coupled with a mesoscale mass transfer model was developed to simulate the absorption of CO2 in the microporous tube-in-tube microchannel reactor (MTMCR). The simulation results were validated by experimental data and empirical correlations, with the discrepancies within ±20%. The local breakage and coalescence of the gas-liquid interfaces enhanced mass transfer in the annular microchannel. The higher ReG and ReL means lower ratio between energy for mass transfer and surface, and also, larger contribution of interfacial area to the mass transfer. Additionally, an entrance-effect zone was revealed, and the entrance-effect zone enlarged with the increase in ReG and ReL. The overall mass transfer coefficient and entrance-effect zone enlarged significantly with appropriate decrease in the length of the gas-liquid collision zone. Results of this work could provide a theoretical basis for the further optimization of MTMCR.

CFD analysis of CO2 absorption in a microporous tube-in-tube microchannel reactor with a novel gas-liquid mass transfer model

Due to the greenhouse effect, new technologies of CO2 capture attract wide attention. In this paper, computational fluid dynamics (CFD) was employed to simulate the absorption of CO2 in a microporous tube-in-tube microchannel reactor (MTMCR). Based on the eddy cell model, a novel gas-liquid mass transfer model considering the surface work was proposed and the simulated results of volumetric mass transfer coefficient agreed well with the published experimental data. In the lower turbulence range, the deviations between experimental data and predictions of kla using eddy cell model are over ± 40%. Meanwhile, results from the modified eddy cell model agree well with experimental data within ±10% deviation in a wide range of operating conditions. The novel gas-liquid mass transfer model could benefit for understanding the mass transfer mechanism and improving the mass transfer performance in reactors.

Flow characteristics and micromixing modeling in a microporous tube-in-tube microchannel reactor by CFD

Micromixing performance in reactor is one of the key factors for fast reaction systems, such as fine chemicals, pharmaceutical and crystallization. In this work, a three-dimensional CFD model was developed for analyzing flow characteristics and micromixing efficiency in microporous tube-in-tube microchannel reactor (MTMCR). PDF transport model based on Lagrangian Monte Carlo method and a modified Finite-rate/Eddy dissipation model were used to build micromixing model, respectively. The effects of Reynolds number and flow ratio on micromixing efficiency were studied using Villermaux–Dushman iodide–iodate reaction system. The segregation index XS is used to quantify the micromixing performance. The results showed that XS decreased with the increasing of Re and the decreasing of flow ratio R, and simulated values agreed well with published experimental data. Based on the modified Finite-rate/Eddy dissipation model, the parallel competing reaction system was analyzed by taking into account mixing-controlled and kinetic-controlled factors, which explained how this model worked. Moreover, porous diameter and width of annular channel were optimized to improve the micromixing efficiency of MTMCR, and the optimal values were 20μm and 250μm, respectively.

Removal of nitric oxide in a microporous tube‐in‐tube microchannel reactor by ferrous chelate solution

AbstractNO gas emission has harmfully impacted human health and the environment. Absorption of NO gas into an aqueous solution is considered to be a promising approach for its removal. FeII(EDTA) solution has been demonstrated as an efficient option in the denitrification process. However, its absorption rate is strongly affected by mass transfer limitation of NO into FeII(EDTA) solution in traditional reactors. In this paper, the removal process of NO with FeII(EDTA) solution was studied in a microporous tube‐in‐tube microchannel reactor (MTMCR). The effects of design and operating parameters such as micropore size, annular channel width, liquid flow rate, gas flow rate, gas‐liquid ratio, pH and concentration of absorbent, and absorption temperature on overall volumetric mass transfer coefficient (KLa) and NO removal efficiency were explored. The results indicated that the MTMCR exhibited obvious advantages owing to continuous operation mode and higher NO removal efficiency of over 90 %, as compared to traditional reactors. Both KLa and NO removal efficiency increased with increases of absorbent concentration and liquid flow rate, as well as decreases of absorption temperature, micropore size, and annular channel width. In addition, KLa increased while NO removal efficiency decreased with increasing gas‐liquid ratio and gas flow rate. The obtained results imply a great potential of the MTMCR in the removal of NO from post‐combustion flue gas.

Selective absorption of H2S from a gas mixture with CO2 in a microporous tube-in-tube microchannel reactor

In industrial gas processing, there is an increasing interest in gas absorption processes for the selective removal of H2S from gas streams with a high CO2/H2S ratio. In this work, the selective absorption of H2S from a gas mixture with CO2 into N-methyldiethanolamine (MDEA) in a microporous tube-in-tube microchannel reactor (MTMCR) was studied. A high H2S removal efficiency of 99.85% could be achieved. The effects of various parameters such as MDEA concentration, liquid and gas flow rates, gas–liquid ratio, absorbent temperature, mean micropore size and annular channel width of MTMCR on H2S removal efficiency and selectivity were explored. The results indicated that MDEA concentration, liquid and gas flow rates had significant influence on H2S removal efficiency and selectivity. With the increase of MDEA concentration and liquid flow rate, H2S removal efficiency increased while selectivity decreased. Increasing gas flow rate resulted in H2S removal efficiency decrease and the selectivity increase. The smaller micropore size and annular channel width led to higher H2S removal efficiency and lower selectivity. Furthermore, the micropore size had a bigger effect on H2S selective removal process than the annular channel width. The results obtained imply a great potential for MTMCR applied to the selective absorption of H2S.

Ozonation of Acid Red 14 in the Presence of Inorganic Salts in a Microporous Tube-in-Tube Microchannel Reactor

This study was conducted to investigate the effect of inorganic salts on the mass-transfer coefficient of O3 and decolorization of azo dye (Acid Red 14, AR14) solution through ozonation in a microporous tube-in-tube microchannel reactor (MTMCR). The overall volumetric mass-transfer coefficient (KGa) of O3 in the MTMCR was deduced by material balance. The effects of different salts on the KGa of O3 and decolorization efficiency of the AR14 solution were studied, and results show that both were significantly affected by the inorganic salts. Although the KGa of O3 and the decolorization efficiency of AR14 increased with increasing salt concentration and pH, the effect of NaNO3 was much weaker than that of NaCl, Na2SO4, Na2CO3, and NaHCO3. The enhanced KGa of O3 and decolorization could be due to the generation of species with high oxidizing ability in the presence of the salts.

Erythorbic acid promoted formation of CdS QDs in a tube-in-tube micro-channel reactor

Erythorbic acid assistant synthesis of CdS quantum dots (QDs) was conducted by homogeneous mixing of two continuous liquids in a high-throughput microporous tube-in-tube micro-channel reactor (MTMCR) at room temperature. The effects of the micropore size of the MTMCR, liquid flow rate, mixing time and reactant concentration on the size and size distribution of CdS QDs were investigated. It was found that the size and size distribution of CdS QDs could be tuned in the MTMCR. A combination of erythorbic acid promoted formation technique with the MTMCR may be a promising pathway for controllable mass production of QDs.

Oxidation of ammonium sulfite by oxygen in a microporous tube-in-tube microchannel reactor

Abstract The homogeneous catalytic oxidation of ammonium sulfite in a microporous tube-in-tube microchannel reactor (MTMCR) was studied in this paper. It was found that the oxidation rate of ammonium sulfite in the MTMCR is 360 times higher than that in a packing column and could be further boosted about 4–6 times by the Co 2+ catalyst. The effects of different operating parameters on the oxidation of ammonium sulfite were investigated. Experimental results indicated that the oxidation ratio of ammonium sulfite increased with the increase of the oxygen volumetric flow rate, but decreased with the increase of the liquid volumetric flow rate and sulfite concentration, and a smaller micropore size and annular channel width resulted in a higher oxidation ratio of ammonium sulfite. The oxidation ratio reached 80% under the optimum operating conditions in the catalytic oxidation process. This study reveals that the MTMCR is a potential intensification device for the oxidation process of ammonium sulfite.

Controllable preparation of nano-CaCO3 in a microporous tube-in-tube microchannel reactor

In this work, nano-CaCO3 particles with tunable size have been synthesized via CO2/Ca(OH)2 precipitation reaction in a microporous tube-in-tube microchannel reactor (MTMCR) with a throughput capacity up to 400L/h for CO2 and 76.14L/h for liquid. The overall volumetric mass-transfer coefficient (KLa) of CO2 absorption into Ca(OH)2 slurry in the MTMCR has been deduced and analyzed. To control the particle size, the effect of operating conditions including initial Ca(OH)2 content, gas volumetric flow rate, liquid volumetric flow rate, micropore size, and annular channel width was investigated. The results indicated that the mass transfer in the MTMCR can be greatly enhanced in contrast with a stirred tank reactor, and the particle size can be well controlled by tuning the operating parameters. The nano-CaCO3 particles with an average size of 28nm and a calcite crystal structure were synthesized, indicating that this process is promising for mass production of nanoparticles.

Absorption of carbon dioxide into N-methyldiethanolamine in a high-throughput microchannel reactor

Global warming due to greenhouse effects is on the rise, and many efforts to reduce emissions of CO2 which is a major greenhouse gas from combustion of carbonaceous materials are being made. In this study, chemical absorption of CO2 into N-methyldiethanolamine (MDEA) solution combined with effective activator piperazine (PZ), from a gas mixture containing N2 was carried out in a high-throughput microporous tube-in-tube microchannel reactor (MTMCR). As a novel microreactor, MTMCR greatlyintensifies gas–liquid mass transfer due to its large gas–liquid interfacial area. The effects of different parameters on the overall volume mass transfer coefficient and CO2 removal efficiency were investigated. The results showed that both mass transfer coefficient and CO2 removal efficiency increased with an increase in the liquid flow rate, temperature and concentration of liquid solvent. Also, the gas–liquid mass transfer efficiency increased with a decrease in the size of the micropore and annular channel of MTMCR. The volume mass transfer coefficient and CO2 removal efficiency reached 1.70s−1 and 97%, respectively, at flow rates of 100L/h and 5.32L/h for gas and liquid respectively, with alkanolamine solutions containing 10wt.% MDEA and 4wt.% PZ.

Removal of Carbon Dioxide by Absorption in Microporous Tube-in-Tube Microchannel Reactor

In this article, preliminary experimental results are presented on the absorption of carbon dioxide (CO2) in a novel high-throughput microporous tube-in-tube microchannel reactor (MTMCR), with an aqueous solution of monoethanolamine (MEA) and a mixture of CO2/N2 as the working fluids. The effects of design and operating parameters on the CO2 removal efficiency were investigated. The absorbent concentration was given the priority as a key factor for consideration, with the result that the CO2 removal efficiency increased with increasing concentrationan and could reach 90% or even higher at a high throughput of 440 L/h for gas with an MEA concentration of 30 wt %. With a decrease of the superficial gas velocity or an increase of the superficial liquid velocity, the CO2 removal efficiency increased. Increasing the absorbent temperature yielded better absorption performance. Reducing the most important structural parameters of the MTMCR, such as the micropore size and the annular channel width, led to a higher mass-transfer rate and was beneficial for CO2 removal. This work also investigated the characteristics of the pressure drop of two-phase flows through the MTMCR. The results obtained imply a great potential for MTMCRs applied to the separation of the greenhouse gas CO2 from the exhausted gases.

High‐throughput microporous tube‐in‐tube microreactor as novel gas–liquid contactor: Mass transfer study

AbstractHigh‐throughput microporous tube‐in‐tube microchannel reactor (MTMCR) was first designed and developed as a novel gas–liquid contactor. Experimentally measured kLα in MTMCR is at least one or two orders of magnitude higher than those in the conventional gas–liquid contactors. A high throughput of 500 L/h for gas and 43.31 L/h for liquid is over 60 times higher than that of T‐type microchannel. An increase of the gas or liquid flow rate, as well as a reduction of the micropore size and annular channel width of MTMCR, could greatly intensify the gas–liquid mass transfer. The interfacial area, α, in MTMCR was measured to be as high as 2.2 × 105 m2/m3, which is much higher than those of microchannels (3400–9000 m2/m3) and traditional contactors (50–2050 m2/m3). The artificial neural network model was proposed for predicting α, revealing only an average absolute relative error of <5%. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Liquid antisolvent preparation of amorphous cefuroxime axetil nanoparticles in a tube-in-tube microchannel reactor

This article presents the preparation of nanoparticles of amorphous cefuroxime axetil (CFA) in a microporous tube-in-tube microchannel reactor (MTMCR). The experimental results indicated that CFA particle with a tunable size of 400–1400 nm could be achieved under a high throughput in the range of 1.5–6 L/min. The average particle size decreased with increasing overall volumetric flow rate and decreasing CFA concentration, micropore size, and annular channel width. The produced CFA nanoparticles were characterized by SEM, XRD, FT-IR, DSC and a dissolution test, which indicated that the nanosized CFA was amorphous and exhibited higher dissolution rate compared to the raw CFA. The MTMCR might offer a general and facile pathway for mass production of the nanoparticles of hydrophobic pharmaceuticals thanks to its high throughput capacity and excellent micromixing performance.

High Throughput Methodology for Continuous Preparation of Hydroxyapatite Nanoparticles in a Microporous Tube-in-Tube Microchannel Reactor

A microporous tube-in-tube microchannel reactor (MTMCR) was successfully adopted to prepare hydroxyapatite (HAP) nanoparticles. The rodlike HAP nanoparticles with a mean size of 58 nm, a specific surface area of 49.32 m2/g, and a narrow size distribution were obtained in an MTMCR under a high throughput of 3 L/min. The mean particle size sharply decreased with increasing the continuous phase flow rate, while first decreased and subsequently increased with increasing the dispersed phase flow rate and the reactant concentration. The extension of the mixing distance led to the initial rapid and following slight decrease of the mean particle size. The size of HAP nanoparticles was also strongly dependent on the micropore size on the surface of inner tube. Small micropore size was beneficial for producing small particles. For comparison, HAP nanoparticles were also prepared in a stirred tank reactor (STR) and a T-junction microchannel reactor (TMCR), clearly exhibiting the advantages of the MTMCR over the STR ...

Investigation of Micromixing Efficiency in a Novel High-Throughput Microporous Tube-in-Tube Microchannel Reactor

This article presents a new microporous tube-in-tube microchannel reactor (MTMCR) with high throughput and excellent micromixing performance. In the MTMCR, one liquid from the inner tube is divided into many liquid fragments through the microscale pores in the walls, and then these fragments vertically collide with another flowing annular liquid sheet between the inner and outer tubes, generating cross-flow. The annular microchannel allows a mass of fluid to go through it rapidly without enlarging the channel width, thereby achieving a throughput as high as 9 L/min (typical microreactor throughput = 4―100 mL/min). Furthermore, the micromixing performance is expressed in terms of a segregation index, which can be as low as 0.0007. The micromixing time evaluated by the incorporation model reaches the magnitude of milliseconds. In addition, several factors affecting the micromixing such as reactant concentration, flow rate, volume flow ratio, micropore size, and channel width were investigated. The results indicated that an increase of the flow rate, as well as a reduction of the micropore size and channel width, could greatly intensify the micromixing. Therefore, it can be envisioned that the MTMCR would exhibit great potential for various industrial applications in the future.

Large-scale preparation of barium sulphate nanoparticles in a high-throughput tube-in-tube microchannel reactor

One method for increasing productivity of a microreactor is presented without demanding numbering-up processes by using a newly proposed microporous tube-in-tube microchannel reactor (MTMCR) with a high throughput of 9 L/min. Barium sulphate nanoparticles with an average size of 37 nm and a narrow size distribution were successfully produced in MTMCR. The size of barium sulphate particles was strongly dependent on the flow rate of the reactants in the microchannel and high flow rate was beneficial for producing small particles. Furthermore, it was possible to control the average particle size in the range from 30 to 150 nm by changing the reactant concentrations and the micropore size on the surface of the inner tube. The average particle size decreased by increasing the total flow rate and reactant concentrations or decreasing the micropore size. The dispersed-phase flow rate and mixing distance exhibited little effects on the particle size. The proposed microreactor concept was confirmed to be valid and promising for the industrial production of nanoparticles.