Volume Mass Transfer Coefficient Research Articles

Flow characteristics and mass transfer performance of phosphoric acid extraction in a T-type central plug-in microreactor

In recent years, the demand for phosphoric acid, a key raw material for lithium iron phosphate batteries, has surged. However, current phosphoric acid extraction equipment faces challenges such as low mass transfer efficiency and difficulty in phase separation, leading to reduced production efficiency, bulky equipment, and scaling issues. To address these problems, this study introduces a T-type central plug-in microreactor (TCPM) designed to enhance mass transfer efficiency and facilitate rapid phase separation. The extraction of phosphoric acid from the water phase to the organic phase (volume ratio of tributyl phosphate to kerosene is 4:1) was chosen as the experimental system. We investigated the effects of various parameters on liquid-liquid flow and mass transfer characteristics in the TCPM. Visualization techniques identified slug and parallel flow as the primary liquid-liquid flow patterns within the TCPM. Notably, the central plug-in promotes the formation of parallel flow, improving phase separation compared to conventional T-type microreactors. The volume mass transfer coefficient of the TCPM ranges from 0.023 to 0.074 s-1, and the optimal phosphoric acid extraction efficiency and volume mass transfer coefficient can reach up to 90.5% and 0.074 s-1, respectively, outperforming conventional T-type microreactors. Predictive model for extraction efficiency was developed, showing deviations within 10%. These findings demonstrate the TCPM's potential as an efficient phosphoric acid extraction device with rapid phase separation, holding significant promise for liquid-liquid extraction applications.

Revealing the effect of water on the CO2-ionic liquid system in microchannels: Physical properties, hydrodynamics and mass transfer behavior

Microchannels and ionic liquids as media of process intensification have stimulated researchers’ attention. Herein, the effect of water on the physical properties, hydrodynamics, and mass transfer behavior of CO2-ionic liquid systems in microchannels was unraveled. The introduced water resulted in a significant reduction in viscosity, an increase in bubble size, a shift of the transition line between bubble and Taylor flow towards a low-speed region, and a transformation of bubble morphology from bullet-shaped to ideal bubbles. As a result, bubble length and gas–liquid contact area increased. However, the added water weakened the hydrogen-bond network structure of [BMIM]BF4 in solutions, accelerated saturation of the liquid film, and reduced the mass transfer rate (kL). The predominant drop in kL caused a reduction in the liquid-phase volume mass transfer coefficient (kLa), even though the gas–liquid contact area (a) increased. Additionally, correlations for predicting bubble length and liquid-phase volume mass transfer coefficients were proposed.

Characterization of liquid-liquid two-phase flow patterns and mass transfer coefficients in Human-shaped microchannels

Based on the principle of splitting and recombining, this study designed and fabricated millimeter-scale Human-shaped microchannels. The research focused on investigating the flow patterns and mass transfer characteristics of liquid-liquid two-phase flow within the Human-shaped microchannels. The experiment utilized a water and n-butanol system to investigate the flow behavior of liquid-liquid two-phase in the channel with a flow rate ratio of 1. When the total volumetric flow rate increases from 120 µl/min to 2400 µl/min, the flow pattern experiences slug flow, slug-droplet flow, parallel flow and non-steady flow patterns respectively. The study investigated the impact of factors including total flow rate, feed method, angle, curvature, channel width, phase ration extraction efficiency and mass transfer coefficients. The Human-shaped channel exhibited superior mass transfer performance compared to conventional microchannels due to its advantageous configuration. The higher the included angle is, the stabler the flow pattern within the channel, resulting in a better mass transfer performance. Furthermore, the absence of curvature is more favorable for achieving higher mass transfer efficiency. In the experiments, the overall volume mass transfer coefficient ranged from 0.007 to 0.1742 s−1. This study can provide insights for the development and structural optimization of microchannels based on the split-recombine principle.

Gas-liquid flow and mass transfer characteristics in improved heart-shaped structure microreactor

The gas-liquid two-phase flow and mass transfer characteristics in heart-shaped structure microreactor were visually investigated in an Advanced Flow Reactor (AFR). Three various flow patterns were observed in the experiment: Taylor-bubble flow, Taylor-flow, and unstable broken flow. The experiment observed that the bubbles only broke steadily under the action of the first heart-shaped unit obstacle; while in the latter heart-shaped units, the larger bubbles would break resulting in the unstable broken flow. The efficiency of CO2 absorption increases as the gas-liquid two-phase flow rate ratio decreases and the solution concentration rises. The volume mass transfer coefficient increases with the increase of the gas-liquid two-phase flow rate ratio and the solution concentration. The absorption efficiency and mass transfer coefficient in channel 2 with two rows of heart-shaped units is greater than channel 1 with one row of heart-shaped units. Additionally, there exists an optimal performance ratio for reactor under the appropriate gas-liquid flow rate ratio.

Liquid–liquid mass transfer and pressure drop behavior in micro‐packed beds with different shaped packings

AbstractIn this work, the liquid–liquid two‐phase pressure drop and mass transfer characteristics in micro‐packed beds with different shaped packing are investigated. The experimental results show that the liquid–liquid mass transfer performance of micro‐packed bed is significantly affected by both apparent flow rates and phase ratio. By changing the characteristic size of the micro‐packed bed, the experimental results show that the average volume mass transfer coefficient has no obvious correlation with the length of the bed, which indicates that the flow and dispersion behavior along the length of the micro‐packed bed is basically stable. By considering dispersion strengthening, vortex strengthening and size effect, a semi‐empirical model for predicting liquid–liquid mass transfer performance in a micro‐packed bed is established for the first time. The model is in good agreement with the experimental results and has strong applicability to various shaped packings. In addition, by considering the contribution of inertia force, viscous force and interfacial tension to energy dissipation, a semi‐empirical model of liquid–liquid two‐phase pressure drop in a micro‐packed bed is established. The pressure drop prediction model can also be applied to different shaped packings.

Carbon dioxide absorption and anti-clogging performance of a novel millimeter-scale channel absorber

This study proposes a novel millimeter-scale channel absorber for the first time, which involves carbon dioxide (CO2) absorption in the channel to achieve efficient CO2 absorption while avoiding clogging. CO2 absorption experiments were conducted on such a channel absorber with an inner diameter of 2.3 mm to study its CO2 mass transfer and absorption characteristics. Al2O3 particles were introduced as solid impurities to evaluate its anti-clogging performance. The experimental results showed that a stable Taylor flow could be formed in the channel in appropriate gas and liquid flowrate ranges. The liquid-side volume mass transfer coefficient (KLa) reached 0.34 s−1 using a 6% DEA solution as the absorbent, which was approximately one order of magnitude higher than that of the conventional packed towers. When Al2O3 to a maximum extent of 2 wt% was added into the absorbents, no clogging was observed, and the values of KLa even increased. Due to the excellent CO2 absorption mass transfer and anti-clogging performance, millimeter channel absorbers have promising industrial applications for CO2 absorption. Therefore, means and application scenario for applying millimeter-scale channel absorber in the industrial CO2 absorption have been proposed.

Investigation of surfactant effect on ozone bubble motion and mass transfer characteristics

The low solubility and low mass transfer efficiency of ozone (O3) in water are important reasons for limiting the application of ozone oxidation technology and advanced ozone oxidation technology. Low-dose surfactants were introduced to affect the behavior of ozone bubbles, influencing the ozone mass transfer efficiency. The motion of ozone bubbles in three different types of surfactant solutions (polyoxyethylene lauryl ether (Brij35), sodium dodecylsulfate (SDS), and cetyltrimethylammonium bromide (CTAB)) was observed. The decrease in surface tension led to a decrease in bubble size, a tendency to spherical shape, an increase in gas content and residence time, a decrease in lateral displacement of a single bubble, and a more stable trajectory. The effect of surfactants on ozone mass transfer was further investigated. The addition of surfactant was found to increase the gas-liquid interface area but decrease the liquid phase mass transfer coefficient, and the extent of the two opposite effects varied for different surfactants. The analysis combined with the removal of pollutant p-Nitrophenol (PNP) showed that the addition of the nonionic surfactant Brij35 and the anionic surfactant SDS inhibited ozone mass transfer, while low concentrations of the cationic surfactant CTAB enhanced ozone mass transfer. When the CTAB concentration was 3 mg L−1, the ozone volume mass transfer coefficient reached a maximum of 0.2902 min−1.

Performance analysis of heat and mass transfer, thermodynamic and economic of high gravity direct contact evaporation system

Based on the problem of low heat and mass transfer efficiency and low heat utilization rate in the process of efficient utilization and treatment of low-grade waste heat, the high gravity direct contact evaporation (HG-DCE) system driven by industrial waste heat is proposed. The heat and mass transfer properties in HG-DCE process were studied by simulated with hot water and air at room temperature, and the thermodynamic and economic properties were further analyzed in detail. Results showed that the evaporation intensity of the HG-DCE system could reach 1523 kg/(m3·h), and the volume heat and mass transfer coefficients could reach 270.77 kW/(m3·°C) and 12.23 kg/(m3·s), respectively. According to the established analysis models of entropy generation and exergy loss, the rule of irreversibility of system was obtained, and the highest exergy efficiency was higher than 90.0 % at the gas-liquid mass ratio of 1:1. Simultaneously, the evaporation heat of system accounted for 40.0 % of the supplied heating enthalpy, and the evaporation cost about 0.094 $/kg could be easily achieved. The perfect performance and advantages of HG-DCE system were further confirmed, which provided a new method for using low grade heat for seawater desalination and wastewater treatment.

Poroelastic response of inclined wellbore geometry in anisotropic dual-medium/media

Shale gas formations are typically characterized by anisotropic and fracture properties. Existing shale wellbore stability models have only considered the anisotropy of shale rocks and have ignored the effect of fractures. However, the mechanism of wellbore instability under the combined effects of shale anisotropy and dual-media (DM) remains unknown. Therefore, based on anisotropic poroelasticity, the DM theory, and the assumption of generalized plane strain, this study established a pseudo-3D hydraulic-mechanical coupling finite element model considering the DM and anisotropy of shale in wellbores. The effects of elastic anisotropy, fracture volume fraction, fracture permeability, mass transfer coefficient, and fluid pressure on wellbore stress were analyzed parametrically. The results showed that an anisotropic single-medium predicts that the wellbore will fail when the formation is drilled, whereas an anisotropic DM predicts periodic wellbore instability. The poroelastic effect of the matrix pore pressure is much greater than that of the fracture pore pressure. The matrix elastic anisotropy parameters control the distribution of mechanical parameters throughout the DM, further affecting the poroelastic response of the entire DM. When the drilling direction was mostly parallel to the bedding plane, the anisotropy of the matrix and fracture system of the elastic parameters were larger, and the wellbore was more stable. A larger fracture permeability leads to a larger fracture volume fraction and mass transfer coefficient, the matrix pore pressure and fracture pore pressure increase, and the instability of the wellbore also increases.

Micro-interface enhanced mass transfer sodium carbonate absorption carbon dioxide reaction

Micro-interface intensified reactor (MIR) can be applied in series/parallel in the absorption of CO2 in industrial gases by Na2CO3 due to the ability to produce large numbers of stable microbubbles. This work focuses on the variation pattern of mass transfer characteristics parameters of the reaction gas in Na2CO3 solution under the influence of different solution properties and operating parameters in the reaction of CO2 absorption by Na2CO3. The mass transfer characteristics parameters include bubble Sauter mean diameter, gas holdup, interfacial area, liquid side mass transfer coefficient, and liquid side volume mass transfer coefficient kLa. The solution properties and operating parameters include Na2CO3 concentration (0.05–2.0 mol·L−1), superficial gas velocity (0.00221–0.01989 m·s−1), superficial liquid velocity (0.00332–0.02984 m·s−1), and ionic strength (1.42456–1.59588 mol·kg−1). And volumetric mass transfer coefficients kLa and superficial reaction rates r of the MIR and the bubble column reactor are compared in the reaction of sodium carbonate absorption of carbon dioxide, and the former shows a greater improvement under different solution properties and operating parameters. The enhanced role of MIR in mass transfer in non-homogeneous reactions is verified and the feasibility of industrial practical applications of MIR is demonstrated.

CO2 capture in a miniaturized annular rotating device with countercurrent flow

Microdevices are becoming a hot technology for process intensification of CO2 capture. However, most microdevices are limited to a small handling capacity, low volume gas to liquid ratio, and cocurrent flow mode. In this context, we proposed a miniaturized annular rotating device (m-ARD), which has a high handling capacity, can be employed for high volume ratios of gas to liquid, and utilizes a countercurrent flow mode. Variables were investigated to determine the flow characteristic, absorption efficiency of CO2, and volume mass transfer coefficient. The gas hold-up and specific surface area in the m-ARD were up to 43.8 % and 1000 m2/m3, and low pressure drop was observed. Notably, the optimal volume gas to liquid phase ratio, absorption efficiency of CO2, and overall volumetric mass transfer coefficient were close to 200 %, 100 %, and 0.53 s−1, respectively. Furthermore, two dimensionless equations were built to predict the volumetric mass transfer coefficient and gas hold-up. In addition, the contributions of the specific surface area and mass transfer coefficient for enhancing CO2 absorption were discussed, respectively. This work provides a prospective device for enhancing CO2 capture and other gas–liquid separation and reaction processes.

Functionalized cross-linking mechanism of biochar “adsorption-reaction microunit” on the promotion of new ammonia-based CO2 capture

Ammonia-based CO2 capture technology has crucial impacts on power plants carbon emission reduction, which has become one of the most concerning issues. However, there are limitations faced by traditional capture technology in the absorption rate, ammonia escape and regeneration energy consumption. The functionalized biochar (with a specific surface area of up to 2835.36 m2/g, micropores volume of 77.4 %) was used to enhance the mass transfer process of new ammonia-based (ammonia-ethanol mixed absorbent) CO2 capture by the bubbling absorption experiment system, combined with Monte Carlo simulations, which explored the adsorption and release characteristics of CO2/NH3 molecules in biochar with different pore sizes. The results show that the CO2 absorption flux added biochar RH-900 is 59.67 L·min, increased by 16.16 % compared with pure absorbent. And the volume mass transfer coefficient is 1.226 × 10-4mol/m2·s·Pa, increased by 15.3 % compared with the SiO2. The addition of RH-900 also promotes the CO2 load capacity of the carbonated solution up to 0.5255 mol/L, enhancing the CO2 absorption capacity and CO2 capture efficiency significantly. The ultra-micropores adsorb CO2, while the surface of larger pores distributes and achieves the adequate fixation of NH3. Besides, the mesopores and macropores provide space where the CO2 is transported and diffused, and the free ammonia concentration is maintained. The study provides an innovative thought for improving the ammonia-based CO2 capture method and significantly reducing of harmful carbon emissions by biomass energy-carbon capture and storage (BECCS) technology.

Intensification and kinetic study of trifluoromethylbenzen nitration with mixed acid in the microreactor

Microreactors are becoming an important tool for rapid exothermic chemical reaction process intensification and continuous flow chemistry. This work focuses on the process intensification and kinetics of the trifluoromethylbenzen nitration in microreactors. The reaction of trifluoromethylbenzene with mixed acid is a typical liquid-liquid heterogeneous reaction, so the mass transfer is the rate-determining step. Two strategies of microreaction systems were established to enhance mass transfer, respectively. Firstly, a scheme for intensifying the nitration reaction process in a capillary microreactor was proposed. The results showed that the conversion was low and could not achieve the expected results. Finally, a Heart-type micromixer with barriers was used to improve the mixing and mass transfer performance. The effects of molar ratio, temperature, sulfuric acid concentration, flow rate, and residence time on the conversion were investigated. The results showed that the residence time was significantly reduced from 4 hours in the batch reactor to 30 s in the Heart-type micromixer. The volume mass transfer coefficient and space-time yield were up to 0.031 s−1 and 16053.55 g·cm−3·h−1, respectively. Meanwhile, to better understand and control the nitration reaction process, the kinetics of the nitration of trifluoromethylbenzene was reported for the first time in a capillary microreactor, and all kinetic data were obtained.

Fast deoxygenation in a miniaturized annular centrifugal device

Corrosion of steel devices and pipelines by dissolved oxygen (DO) is of major concern in many industries. Miniaturization of devices is becoming increasingly important significant for process intensification and distributed production. In this context, we attempted to realize efficient deoxygenation of water using a miniaturized annular centrifugal device (MACD) based on the centrifugal force and microscale effect. The influence of different operational variables on the deoxygenation performance was studied. It was found that the optimal volume mass transfer coefficient and deoxygenation efficiency are 1.01 s−1 and 97.8 %, respectively. The gas-liquid flow patterns in the mixing cavity, liquid film thickness distribution and residence time of water in the separation cavity of the MACD were investigated. The mechanism of fast deoxygenation and phase separation in MACD is explained. Additionally, a dimensionless correlation was obtained to calculate the volume mass transfer coefficient, and the predicted values were in good agreement with the experimental data. The deoxygenation performance of the MACD was also compared to those of other similar rotating deoxygenation devices, proving that MACD has the advantages of efficient deoxygenation performance, fast phase separation, and low energy consumption.

Solvent extraction with a three-dimensional reticulated hollow-strut SiC foam microchannel reactor

• A novel 3-D reticulated microchannel reactor based on the hollow-strut SiC foam for rare earths extraction. • High extraction efficiency and excellent mass transfer performance at high flow rate. • The structure-performance relationship of the foam was studied by extraction experiments combined with numerical simulations. Recently, there has been considerable interest in the use of microchannel reactors for hydrometallurgy of rare earths (REs). Here, a novel integrated microchannel reactor based on the hollow-strut SiC foam material is presented and demonstrated to extract Ce 3+ and Pr 3+ using 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (P507) as the extractant. The typical three-dimensional reticulated structure of the hollow-strut SiC foam was characterized by scanning electron microscopy and X-ray micro computed tomography. Since the reactor’s structure plays a key role in fluid mixing and mass diffusion during the extraction process, the structure-performance relationship of the foam was studied by extraction experiments combined with numerical simulations. Using the foam with the optimal structure, the influence of the flow rate Q 0 of the two liquid phases on the extraction efficiency η and overall volume mass transfer coefficient K L a was discussed. For both RE ions, with increasing Q 0 , η decreases while K L a increases. For the total flow rate of the two phases of 4 ml⋅min −1 , the η values of Pr 3+ and Ce 3+ reached 98.7% and 97.0%, respectively. For the total flow rate of 36 ml⋅min −1 which was much higher than that of many other microchannel reactors reported in the literatures, the η values of Pr 3+ and Ce 3+ still reached 92.2% and 86.9%, respectively, and the K L a values of Pr 3+ and Ce 3+ were 0.198 and 0.161 s −1 , respectively, similar to the high values reported for other microchannel reactors studied in previous work. These findings indicate that the hollow-strut SiC foam microchannel reactor is suitable for use in REs extraction.

Liquid-liquid flow and mass transfer characteristics in a miniaturized annular centrifugal device

• A MACD with efficient mass transfer, fast phase separation and low energy consumption is proposed. • The dimensionless correlation of maximum throughput is obtained. • Operation region and controlled mechanism of liquid–liquid phase separation are obtained. • the maximum η and k L a are up to 99.8 % and 0.31 s −1 , respectively. • The mean energy dissipation rate is lower than that of similar rotating equipment. Miniaturization of chemical equipment is becoming an important topic in process intensification and microscale flow chemistry. In this context, we developed a miniaturized annular centrifugal device (MACD) based on the microscale effect and centrifugal force. Various parameters were investigated to determine the maximum throughput of the single-phase, operating region of liquid–liquid phase separation, mass transfer performance, and mean energy dissipation rate. Detailed investigations of the controlled mechanism of the liquid–liquid flow process showed that a very fast phase separation can be achieved. The extraction efficiency and volume mass transfer coefficient were up to 99.8 % and 0.31 s −1 , respectively. The mean energy dissipation rate ranged from 0.8 × 10 4 to 3.9 × 10 4 W/m 3 , which is lower than that of the similar rotating equipment. In addition, dimensionless correlations were obtained to predict the maximum throughput of the single-phase, the operating region of liquid–liquid phase separation, and the volume mass transfer coefficient. This study is the first time to propose a MACD with fast phase separation, efficient mass transfer, and low energy consumption, and provides a highly promising liquid–liquid process intensification tool.

Broken and Intact Cell Model for supercritical carbon dioxide extraction of tea Camellia sinensis (L) seed oil

The model of broken and intact cells was used to fit the experimental data, and it was proved to be able to describe the extraction process of tea seed oil. The extraction rate, observed through the overall extraction curves (OEC), resulted in being faster the higher the pressure whereas the temperature had less influence on the extraction kinetics. The volume mass transfer coefficients in the fluid phase (kfa0) and solid phase (ksas) were used as fitting parameters. The maximum average deviation between measured and calculated oil yield was 4.1%. Mass transfer coefficients in the fluid phase and solid phase varied between 2.40·10−2–2.75·10−2 s−1 and 4.32·10−5–6.90·10−5 s−1, respectively. The outcomes of work showed the highest extraction yield (50.03 ± 0.68% w/w) obtained at 300 bar and 40 °C. Tea seed oil extracted using SC-CO2 presented higher antioxidant capacity and lower UV indices than oil extracted with n-hexane.

Chaotic mixing and mass transfer characteristics of fractal impellers in gas-liquid stirred tank

Gas-liquid mixing characteristics in fractal impeller stirred tank were experimentally investigated by measuring multi-scale entropy (MSE), relative power demand (RPD), local gas holdup, bubble size, and mass transfer coefficient (KLa). Results showed that fractal impeller could enhance 21.69% of MSE and 11.94% of RPD on the basis of pitched-blade impeller. Fractal impeller can enhance the local gas holdup, decrease the bubble size, reduce the dispersion coefficient (σ) and improve the gas-liquid dispersion performance. Meanwhile, the regression based on d32− for pitched-blade impeller and fractal impeller were obtained. In addition, fractal impeller can also increase 11.07% of volume mass transfer coefficient (KLa) compared with pitched-blade impeller in the gas-liquid mixing process. The results can provide theoretical guidance for the optimal design of gas-liquid stirred tank.

Updating Packed Fractionating Columns Using Mathematical Model of Multicomponent Mixture Separation

The scientific-engineering problem of mathematical modeling and calculation of separation of hydrocarbon mixtures in industrial columns with random and regular packings is solved. Multicomponent transfer is calculated using matrix of volume mass transfer coefficients and reverse-mixing (longitudinal mixing) of vapor and liquid streams is calculated using Peclet number with a reverse-mixing coefficient. The problem of development of variants of upgradation of oil-gas-condensate mixture stabilizing column in a refinery is discussed. The calculated concentration profiles of key components of the mixture are given. The required packing bed thickness is determined. The column operating conditions in the mixture load and composition range are stabilized after upgradation of the column with a new packing. Also solved is the problem of designing two industrial columns in the technological scheme of separation of benzene from stable condensate. The calculations enabled determination of the operating and design characteristics of the column using random Inzhekhim-2012 metallic packings. The results of materials balance calculation are presented and are compared with the column operation data.

Multilevel cross flow rotating packed bed to enhance gas film control mass transfer process

Using lye to absorb SO2 as the experimental system, the effect of the packing stator, packing distribution and packing axial height on the gas volume mass transfer coefficient kyae in multilevel cross flow rotating packed bed (MC-RPB) was studied. Further explored the mechanism and enhanced characteristics of MC-RPB to enhance gas film control mass transfer. The results show that the kyae increases with the increase of β, q, u; Compared with model II, kyae increased by about 0.6∼1 times in model I, indicating that in the gas film control system, the filler stator can enhance gas disturbance and effectively strengthen the gas film mass transfer process; When the packing distribution is changed, the kyae increases by 0.2 to 0.4 times in model V compared with model IV, indicating that the end effect zone of MC-RPB is located in the area where the gas just enters the packing layer; When the axial height of the packing layer is changed, the kyae of model IV is 0.1∼0.4 times smaller than that of model III, which further proves that MC-RPB can effectively enhance the gas film mass transfer process.