Volumetric Liquid-side Mass Transfer Coefficient Research Articles

Heat and mass transfer of a novel CO2 desorption process integrated with highly turbulent catalytic heat exchanger

This was the first work that pioneered the development a novel catalytic CO2 desorption process using an agitated jacket vessel with a coil heat exchanger (JVC) into a bench-scale pilot plant for post-combustion carbon capture technology. The key parameters of heat and mass transport e.g., overall heat transfer coefficient, overall volumetric liquid-side mass transfer coefficient and the enhancement factor for catalyst effect, were experimentally investigated by varying the operating conditions, including temperature, stirring speed, and heating methods. The proposed investigations revealed that the utilization of the JVC was a promising technology for improving heat transfer and mass transfer performance in the desorption process due to the high turbulence flow and more favorable thermal distributions achieved by the JVC. In comparison to the conventional process with a fixed catalyst bed, the JVC demonstrated a remarkable approximately 30 % catalytic enhancement and a substantial 50 % reduction in catalyst demand. Additionally, other potential benefits and challenges of further practical operations were discussed in this paper. This research carried significant potential to contribute to the advancement of knowledge and offer valuable insights into the practicability of the catalytic desorption process for further commercial application in carbon capture. The integration of catalyst and JVC could potentially motivate the utilization of catalyst towards commercial-scale applications.

Enhanced carbon dioxide absorption using alcohol solvents in a microreactor: Comparison with MEA + water mixture

BackgroundCarbon dioxide absorption using solvents is a critical process in mitigating greenhouse gas emissions. The monoethanolamine (MEA) + water (30 wt.%) mixture is the most commonly used solvent, but alternative solvents with better performance are desired. MethodsThis study investigated the effects of temperature, solvent flow rate, and gas flow rate on carbon dioxide absorption and liquid-side volumetric mass transfer coefficient in a microreactor using various solvents. The performance of the tested solvents was compared to the MEA + water (30 wt.%) mixture. Significant findingsEthylene glycol achieved the highest absorption (91.57%) at 15 °C, with a solvent flow rate of 0.05 l.min−1 and a gas flow rate of 1 l.min−1. The maximum klav value of 18.2 s−1 was reached at 15 °C, with a solvent flow rate of 0.01 l.min−1 and a gas flow rate of 1 l.min−1. This value was 1.3 times higher than that of the MEA + water (30 wt.%) mixture under similar conditions, indicating the potential to replace glycolytic solvents with amine-based solvents in carbon dioxide absorption applications.

Analysis of Reaction Kinetics of the Ozonation of Phenolic Compounds and Assessment of the Role of Mass Transfer in the Overall Rate

The ozonation technique for biorefractory phenolic wastewater is preferred as a clean technology. However, its effectiveness and successful implementation on the commercial scale is crucial. The understanding of the rate-determining step and reliable reaction kinetics is the essence to the design and scale-up of ozonation reactors. In the case of phenolic wastewater, it is found that both mass transfer and chemical reaction contribute to the overall reaction rates. However, the mass transfer resistance is often significant in studies that determine the ozonation rate constant. This has resulted in discrepancies in the reported values of the intrinsic reaction kinetic parameters, and such apparent rate constants cannot be useful for suitable reactor design. The aim of this work is to analyze past works on the reaction kinetics of the ozonation of phenol, chlorophenols, and nitrophenols and determine the role of mass transfer steps in the overall reaction rate. The value of the volumetric liquid-side mass transfer coefficient (kLa) is estimated from the overall observed rates using the theory of mass transfer with chemical reaction, and these are found to be appropriate for the reactor geometry used in the respective works. In this way, our appraisal of the literature has provided key insights, which are yet unfamiliar, and renders useful the large body of data published in the literature, which otherwise remains unutilized.

Influence of Liquid Properties and Design Parameters on Mass Transfer in Gas–Liquid Flow through a Miniaturized Reactor

This paper presents the results of oxygen absorption from air in various liquid media within a rectangular milli-channel equipped with exchangeable staggered herringbone-like mixing inserts. We have determined the volumetric liquid-side mass transfer coefficient kLa using three different liquid substances (water, ethanol, and polypropylene glycol) in a range of superficial liquid velocities of 0.047–0.210 m s–1 and superficial gas velocities of 0.012–0.210 m s–1. From this data, we derived an empirical kLa-correlation. Overall, kLa values ranging from 0.036–0.515 s–1 were obtained, and the correlation predicts kLa with a coefficient of determination of R2 = 0.93. We have also examined the influences of changing the static mixer design parameters on the mass transfer performance and evaluated the mixer efficiency by taking the power consumption into account. Depending on liquid properties, the right choice of a mixer design leads to a significant improvement in mass transfer and/or efficiency.

Mass transfer modeling for viscous fluids in a disk-distributor rotating packed bed

Rotating packed beds (RPBs) achieved notable application progress in high-viscosity processes. Mass transfer modeling for viscous fluids, laying the foundation for application research, was a significant and urgent challenge in RPBs. In our previous works, a disk-distributor RPB (DRPB) for facilitating high-viscosity processes was put forward by replacing the conventional nozzle distributor with a disk distributor. The basic flow parameters of viscous fluids in the DRPB have been obtained, involving liquid holdup, wetting efficiency, flow patterns, and liquid element characteristics. In the present study, a liquid-side volumetric mass transfer coefficient model for viscous fluids (143–15259 mPa·s) was further developed based on penetration and surface renewal theories. Via comprehensive analyses of the abovementioned flow characteristics, key model parameters were determined, including the specific area of liquid and the volume fraction of different flow patterns in packing. The experiments of devolatilization from viscous solutions were implemented to examine the mass transfer model. The deviation between the model-predicted and experimental acetone removal efficiencies was within + 15 % and −10 %, proving the reasonability of the mass transfer model.

Determination of volumetric mass transfer coefficients of structured packings at two different column diameters

Considerable work has been done on method standardization for experimental characterization of column packings used in absorption processes. A detailed framework for determination of packing hydraulics as well as gas- and liquid-side volumetric mass transfer coefficients (kGa and kLa) has been established. Packing characterization experiments in large diameter columns result in high equipment and operating costs. Accurate extrapolation of packing properties from experiments in smaller diameter columns would therefore be highly desirable. However, diameter influence is currently not completely understood, making further work necessary. In this work, experiments for the determination of kGa and kLa values were carried out and evaluated independently in two plants (inner diameters 422 and 150 mm). Results from measurements conducted with three metal packings RSP 250Y, RMP N 250X and RMP N 250Y are in good agreement with existing literature data. kGa was found to be dependent on column diameter with larger diameters leading to increased kGa values. The overall effect (approx. 15 %) is consistent with previous works, suggesting the possibility of deriving appropriate scaling factors once the findings are validated by a larger sample size. No clear dependence of kLa values on diameter was found with deviations significantly smaller than for kGa measurements.

Oxygen Transfer Effects in a Two-Phase System of an Aqueous Phase and Liquid Perfluorochemical Subjected to Continuous Wave-Assisted Agitation in Disposable Bioreactor

Systems of two immiscible liquid phases—aqueous phase (i.e., distilled water (dH2O) or phosphate-buffered saline (PBS)) and liquid perfluorochemical (i.e., perfluorodecalin (PFD))—were subjected to wave-assisted agitation, i.e., oscillatory rocked, in a disposable bag-like container in a ReadyToProcess WAVETM25 bioreactor, to recognize oxygen transfer effects and effectivity of the surface aeration. According to the DoE methodology, values of the volumetric liquid-side mass transfer (kLa) coefficient for dH2O, PBS, dH2O-PFD, and PBS-PFD systems were determined for the whole range of operating parameters of the WAVE 25 bioreactor. A significantly higher maximal value of kLa was found for waving dH2O than for dH2O-PFD (i.e., 0.00460 s−1 vs. 0.00331 s−1, respectively) compared to more equal maximal values of kLa reached for PBS and PBS-PFD (0.00355 s−1 vs. 0.00341 s−1, respectively). The interface development factor (f) depended on the interfacial area a, and the enhancement factor (EPFD), depending on kLa, was introduced to quantitatively identify the mass transfer effects in the systems of waving two immiscible liquids. The phase of PFD was identified as the reservoir of oxygen. Dimensional correlations were proposed for the prediction of the kLa coefficient, in addition to the f and EPFD factors. The presented correlations, and the set of kLa values, can be directly applied to predict oxygen transfer effects reached under continuous oscillatory rocked systems containing aqueous phase and liquid perfluorochemical.

Mass transfer intensification mechanism of Al2O3 sphere packing in a rotating packed bed

In this work, the gas–liquid mass transfer performance of rotating packed bed (RPB) with Al2O3 sphere packing, in term of volumetric liquid-side mass transfer coefficient (kLae), was investigated by CO2-NaOH chemical absorption system. The adsorption performance of Al2O3 spheres was also evaluated by an ink adsorption method. Results showed that the kLae values of RPB with Al2O3 sphere packing were higher than those of RPB with nonporous sphere packing, and over one magnitude order higher than those of trickle bed reactor (TBR) with Al2O3 sphere packing. The ink adsorption, film diffusion and pore diffusion rates of Al2O3 spheres have been greatly improved under the high gravity field, and it has been found that the surface tension was the main driving force of ink adsorption. Moreover, the adsorption kinetics was investigated and the experimental data fitted well with the pseudo-first-order adsorption kinetics model.

Mass Transfer Correlation and Optimization of Carbon Dioxide Capture in a Microchannel Contactor: A Case of CO2-Rich Gas

This work focused on the application of a microchannel contactor for CO2 capture using water as absorbent, especially for the application of CO2-rich gas. The influence of operating conditions (temperature, volumetric flow rate of gas and liquid, and CO2 concentration) on the absorption efficiency and the overall liquid-side volumetric mass transfer coefficient was presented in terms of the main effects and interactions based on the factorial design of experiments. It was found that 70.9% of CO2 capture was achieved under the operating conditions as follows; temperature of 50 °C, CO2 inlet fraction of 53.7%, total gas volumetric flow rate of 150 mL min−1, and adsorbent volumetric flow rate of 1 mL min−1. Outstanding performance of CO2 capture was demonstrated with the overall liquid-side volumetric mass transfer coefficient of 0.26 s−1. Further enhancing the system by using 2.2 M of monoethanolamine in water (1:1 molar ratio of MEA-to-CO2) boosted the absorption efficiency up to 88%.

Hydrodynamics and gas-liquid mass transfer in a cross-flow T-junction microchannel: Comparison of two operation modes

Hydrodynamics and gas-liquid mass transfer of CO2-monoethanolamine (MEA) aqueous solution were investigated experimentally in a cross-flow T-junction microchannel. Two operation modes were compared, namely OM-1 (gas entering the branch channel, liquid flowing into the main channel) and the opposite feed mode OM-2 (gas entering the main channel, liquid flowing into the branch channel). The effects of gas and liquid rates and MEA concentrations in the two operation modes were studied in terms of bubble and liquid slug lengths, specific interfacial area, liquid-side mass transfer coefficient (kL), liquid-side volumetric mass transfer coefficient (kLa) and pressure drop (Δp). The results show that the variations of kLa and Δp with the total rate of two phases present a turning point in both two operation modes. Before the turning point, the gas rate is the key factor increasing the kLa and Δp, after that, the liquid rate would predominate. Notably, kL is more likely to be affected by the liquid rate. Comparing with OM-2, more dispersed gas-liquid distribution in OM-1 can be observed, which enhances the mass transfer but simultaneously increases the pressure drop. However, OM-2 is beneficial to a narrower residence time distribution in the liquid phase and better mass transfer performance under a strict energy requirement. This work could provide guidance for the operation of a cross-flow T-junction microreactor based on specific product requirements and energy consumption restrictions.

Experimental determination of gas holdup and volumetric mass transfer coefficient in a jet bubbling reactor

The hydrodynamics and mass transfer characteristics of a lab-scale jet bubbling reactor (JBR) including the gas holdup, volumetric mass transfer coefficient and specific interfacial area were assessed experimentally investigating the influence of temperature, pH and superficial gas velocity. The reactor diameter and height were 11 and 30 cm, respectively. It was equipped with a single sparger, operating at atmospheric pressure, 20 and 40 °C, and two pH values of 3 and 6. The height of the liquid was 23 cm, while the superficial gas velocity changed within 0.010–0.040 m·s −1 range. Experiments were conducted with pure oxygen as the gas phase and saturated lime solution as the liquid phase. The liquid-side volumetric mass transfer coefficient was determined under unsteady-state oxygen absorption in a saturated lime solution. The gas holdup was calculated based on the liquid height change, while the specific interfacial area was obtained by a physical method based on the bubble size distribution (BSD) in different superficial gas velocities. The results indicated that at the same temperature but different pH, the gas holdup variation was negligible, while the liquid-side volumetric mass transfer coefficient at the pH value of 6 was higher than that at the pH = 3. At a constant pH but different temperatures, the gas holdup and the liquid-side volumetric mass transfer coefficients at 40 °C were higher than that of the same at 20 °C. A reasonable and appropriate estimation of the liquid-side volumetric mass transfer coefficient ( k l a ) in a pilot-scale JBR was provided which can be applied to the design and scale-up of JBRs. • k l a is determined experimentally for O 2 absorption into Ca(OH) 2 solution in the JBR. • k l a is calculated for SO 2 absorption into Ca(OH) 2 solution in the JBR. • Specific surface area, is experimentally obtained by a physical method based on BSD. • Effects of temperature, solution pH, and superficial gas velocity are studied on k L a . • Gas holdup as a hydrodynamic parameter is investigated for the JBR.

An effective hybrid solvent of MEA/DEEA for CO2 absorption and its mass transfer performance in microreactor

The gas-liquid two-phase flow and the mass transfer characteristics for CO2 absorption into the binary amine mixture of monoethanolamine (MEA) and N,N-diethylethanolamine (DEEA) aqueous solution were investigated in T-junction microchannel reactor with a square cross-section. The effects of gas-liquid flow rate and absorbent concentration on bubble length, velocity and mass transfer coefficient were studied. Three flow regimes including slug-bubbly flow, slug flow and slug-annular flow were observed under experimental condition, and the gas-liquid two-phase flow pattern map was depicted. It is found that the transitions between three flow regimes depend primarily on the competition of forces exerted on bubble in the T-junction. The kinetics of CO2 absorption into blended amine aqueous solutions was analyzed to understand the mass transfer enhancement mechanism of new hybrid solvent. Furthermore, the liquid-side overall mass transfer coefficient kL and the liquid-side overall volumetric mass transfer coefficient kLa were determined through processing experimental images recorded by a high-speed camera. The results show that kLa is in the range of (3.04–20.07) s−1 in this work, which is 2–3 orders of magnitude higher than that in the conventional equipment. The dimensionless Damköhler number (Da) and Peclet number (Pe) are introduced to correlate the liquid-side volumetric mass transfer coefficient, new correlation shows good prediction accuracy with the average deviation of 3.64%.

Wetting Behavior of the Stainless Steel Wire Mesh with Al2O3 Coatings and Mass Transfer Intensification in a Rotating Packed Bed

An Al2O3-coated stainless steel wire mesh packing was prepared, aiming to serve as the monolithic catalyst support applied in a rotating packed bed (RPB) reactor. Before the application, the wetting behavior and gas–liquid mass transfer performance of Al2O3-coated wire mesh packing were investigated in this work. The results showed that the Al2O3-coated stainless steel fiber had on average 18.8% longer liquid spreading length compared with the uncoated stainless steel fiber. The gas–liquid effective interfacial area (ae) and the volumetric liquid-side mass transfer coefficient (kLae) of the RPB with Al2O3-coated wire mesh packing were on average 25.9 and 45.7% higher than those with uncoated wire mesh packing, respectively. The Al2O3-coated wire mesh packing has great prospects for the catalytic reactions in the RPB reactor by providing double functions of mass transfer intensification and the monolithic catalyst support.

Carbon dioxide desorption from aqueous solutions of monoethanolamine and diethanolamine in a microchannel reactor

In this study, the process of carbon dioxide (CO2) desorption from two saturated solutions of monoethanolamine (MEA) and diethanolamine (DEA) was performed in a microchannel made of stainless-steel grade 316 with a circular cross-section (diameter: 800 μm, length: 35 cm). The operating variables in this study were temperature (55, 75 and 95 °C), rich solvent flow rate (0.3, 0.9 and 1.5 ml/min), and inlet solvent concentration (10, 20 and 30 wt% of the amine). The mass transfer efficiency was determined based on the desorption percentage, volumetric liquid-side mass transfer coefficient (kLaV), volumetric overall mass transfer flux (NCO2aV), and energy consumption per unit mass CO2 (R). The results showed that the use of a microchannel significantly increased the mass transfer rate and decreased energy consumption per removed CO2. The results also showed that the amount of kLaV for the two solvents of MEA and DEA was 1.91 and 3.48 1/s, respectively. Moreover, the R-value for the two solvents of MEA and DEA was 1.3 and 1.63 MJ/kg CO2, respectively, which is at least three times lower than that of other mass transfer devices.

Mass transfer in a rotating packed bed reactor with a mesh-pin rotor: Modeling and experimental studies

A rotating packed bed (RPB) reactor with full stainless steel wire mesh packing loaded in the rotor has excellent mass transfer performance. However, it has the blockage problem when applied to the reactions with solid generated on the surface of the packing. In this work, a mesh-pin rotor (MPR), combining an inner wire mesh packing zone (IMZ) and an outer resin pin zone (OPZ), was designed with the purpose of anti-blockage for the first time, expecting to possess the high mass transfer performance of wire mesh packing and self-cleaning performance of cylindrical pins. With the assistance of liquid holdup measurement by X-Ray CT scan technology, a mass transfer model was proposed for the RPB reactor with MPR and the liquid-side volumetric mass transfer coefficient (kLae) was measured by using an oxygen-water desorption system. The predicted results by the model showed good agreement with the experimental results within a deviation of ±20%, displaying potential application prospects.

High-throughput CO2 capture for biogas purification using monoethanolamine in a microtube contactor

Abstract The utilization of biogas is somewhat limited by its composition especially CO2. The CO2 content in biogas can be substantially reduced via chemical absorption. In this work, the absorption performance of CO2 removal from biogas using aqueous monoethanolamine (MEA) in a T-type microchannel (0.5 × 0.5 × 60 mm3) was experimentally investigated. The effects of operating parameters including MEA-to-CO2 molar ratio, temperature, pressure, and flow rate of MEA solution were studied in terms of main and interaction effects via statistical analysis. Temperature and MEA-to-CO2 molar ratio showed relatively strong influence on both %absorption and the liquid-side volumetric mass transfer coefficient. A positive confounding effect between these two parameters was also present. Hence, high temperature and high molar ratio resulted in high performance CO2 removal from biogas. Methane purity of 90% was obtained with the molar ratio of 1.8 at 50 °C. The kLa of 517 s−1 was achieved at the MEA-to-CO2 molar ratio of 5:1, 50 °C, 2 bar, and 3 mL/min of the MEA solution. In addition, the absorption flux of CO2 in MEA solution, overall mass transfer coefficient, and kinetic rate constant were evaluated to interpret the experimental results.

Impact of operating parameters on values of a volumetric mass transfer coefficient in a single-use bioreactor with wave-induced agitation

The knowledge of a volumetric liquid-side mass transfer coefficient (kLa) characterizing the oxygen transfer in bioreactor working at defined operating parameters, is a fundamental principle for establishing the aeration strategy for aerobic bioprocesses. The design of experiments (DoE) methodology has been applied for distinguishing relevant from irrelevant operating parameters, and for prediction of characteristics of oxygen mass transfer effects, in the whole range of values of operating parameters accessible in setup of ReadyToProcess WAVE™ 25 (WAVE 25; GE Healthcare) bioreactor equipped with 2dm3 disposable culture bag. Due to DoE-aided analysis, rocking speed (ω), rocking angle (α) and volumetric flow of gas phase through the culture bag (QG) have been indicated as the operating parameters robustly impacting on the value of the kLa coefficient. All relevant operational parameters, i.e. ω, α and QG, exerted monotonically increasing influence on kLa. Otherwise, the influence of volume of liquid poured into culture bag (VL) and oxygen partial pressure in applied gas phase (p1) on kLa proved to be negligible. Two original correlations have been proposed to generalize the experimental results and to estimate the kLa coefficient values possible to be reached in the WAVE 25: the dimensional correlation defining the kLa coefficient, as well as the dimensionless correlation that defines Sherwood number and integrating the originally-defined Reynolds number for the liquid phase that is subjected to wave-induced mixing. The validity of results predicted by both correlations has been verified by acceptable level of the relative errors.

Feasibility studies of micromixing and mass-transfer in an ultrasonic assisted rotating packed bed reactor

Ultrasonic is well-known to be helpful for the improvement of chemical reactions due to its acoustic cavitation. This work reports for the first time the use of ultrasonic to enhance micromixing and mass-transfer in a rotating packed bed (RPB) reactor. The ultrasonic probes were installed as stators on the cover of the RPB reactor. Comparisons of micromixing efficiency, effective interfacial area, and volumetric liquid-side mass-transfer coefficient in the RPB reactor with and without ultrasonic were investigated systematically. A discussion for the micromixing and mass-transfer improvement in the RPB reactor was given. Feasibility studies indicated that the relative segregation index decreasing, the relative effective interfacial area increasing, and the relative volumetric liquid-side mass-transfer coefficient increasing are 13.8%, 3.7%, and 5.5%, respectively.

Polytetrafluoroethylene Wire Mesh Packing in a Rotating Packed Bed: Mass-Transfer Studies

Polytetrafluoroethylene (PTFE) material, which is well-known for its excellent anticorrosion properties, was used as wire mesh packing in a rotating packed bed (RPB). The effective interfacial area (ae) and the volumetric liquid-side mass-transfer coefficient (kLae) of the RPB with PTFE packing was studied experimentally by a NaOH–CO2 chemical absorption system and an oxygen–water physical desorption system, respectively. Experimental results showed that both ae and kLae increased with decreasing fiber diameter and pore size. As for material, mass-transfer performance of the PTFE packing was lower than that of the stainless steel wire mesh packing but is applicable in some high-corrosion and -viscosity environments. Moreover, correlations for ae and kLae were proposed.

Process intensification characteristics of a microreactor absorber for enhanced CO2 capture

Gas separation processes, including post-combustion carbon capture (PCCC) by chemical absorption using liquid solvents can be substantially enhanced using high performance micro-structured surfaces to enhance the surface area available for reaction. The present paper studies the hydrodynamics and mass transfer performance of gas–liquid absorption of CO2 into aqueous diethanolamine in a micro-structured reactor. The system was designed to comprise 15 straight parallel channels in a cross flow inlet configuration. The hydraulic diameter of each channel was 456μm. The performance of the reactor was studied with respect to the absorption efficiency, mass transfer coefficient, acid gas loading ratio, and pressure drop. A flow pattern map was developed using available regime transition criteria. Parametric studies varying the gas and liquid flow rates, as well as their respective concentrations at the reactor inlet, were conducted. The two-phase pressure drop was compared against the predictions of a piecewise model and a reasonably good agreement was obtained. Absorption efficiencies close to 100% were observed under certain operating conditions. The presently achieved values of liquid-side volumetric mass transfer coefficients were between 1–3 orders of magnitude higher than those reported for most conventional gas–liquid absorption systems, which can be attributed to the inherent high specific interfacial area provided through micro-structured surfaces. The results reported here indicate the substantial levels of process intensification that can be achieved using microreactors.