Liquid Volumetric Mass Transfer Coefficient Research Articles

Experimental study on volumetric mass transfer coefficient of CO2 absorption into MEA aqueous solution in a rectangular microchannel reactor

Abstract Monoethanol amine (MEA) aqueous solution is one of the most widely used absorbents for CO2 in industry. The mass transfer behavior of CO2 absorption into MEA aqueous solution in a microreactor was investigated experimentally. Liquid side volumetric mass transfer coefficients (kLa) of CO2 were measured in horizontal microreactor with rectangular cross section. The influences of gas and liquid phase flow rates on kLa for Taylor and annular flow were primarily studied. The concentration of CO2 in liquid phase at the outlet of microreactor was obtained by titration method and then kLa was calculated. Results indicated that: under the same liquid side flow rate, kLa increased gradually up to a stable value with increasing gas phase flow rate; when the gas flow rate was relatively small, kLa decreased with the increase of the liquid flow rate; while the gas flow rate reached a critical flow rate, kLa increased with increasing liquid phase flow rate. Several dimensionless criterions were correlated to predict kLa, and the calculated values coincided well with experimental data.

Effect of internal pressure and gas/liquid interface area on the CO mass transfer coefficient using hollow fibre membranes as a high mass transfer gas diffusing system for microbial syngas fermentation

This study proposed a submerged hollow fibre membrane bioreactor (HFMBR) system capable of achieving high carbon monoxide (CO) mass transfer for applications in microbial synthesis gas conversion systems. Hydrophobic polyvinylidene fluoride (PVDF) membrane fibres were used to fabricate a membrane module, which was used for pressurising CO in water phase. Pressure through the hollow fibre lumen (P) and membrane surface area per unit working volume of the liquid (AS/VL) were used as controllable parameters to determine gas–liquid volumetric mass transfer coefficient (kLa) values. We found a kLa of 135.72h−1 when P was 93.76kPa and AS/VL was fixed at 27.5m−1. A higher kLa of 155.16h−1 was achieved by increasing AS/VL to 62.5m−1 at a lower P of 37.23kPa. Practicality of HFMBR to support microbial growth and organic product formation was assessed by CO/CO2 fermentation using Eubacterium limosum KIST612.

Gas–Liquid Mass Transfer Characteristics in a Gas–Liquid–Solid Bubble Column under Elevated Pressure and Temperature

The volumetric mass transfer coefficient kLa of gases (H2, CO, CO2) and mass transfer coefficient kL on liquid paraffin side were studied using the dynamic absorption method in slurry bubble column reactors under elevated temperature and elevated pressure. Meanwhile, gas-holdup and gas–liquid interfacial area a were obtained. The effects of temperature, pressure, superficial gas velocity and solid concentration on the mass transfer coefficient were discussed. Experimental results show that the gas–liquid volumetric mass transfer coefficient kLa and interfacial area a increased with the increase of pressure, temperature, and superficial gas velocity, and decreased with the slurry concentration. The mass transfer coefficient kL increased with increasing superficial gas velocity and temperature and decreased with higher slurry concentration, while it changed slightly with pressure. According to analysis of experimental data, an empirical correlation is obtained to calculate the values of kLa for H2 (CO, CO2) in the gas–paraffin–quartz system in a bubble column under elevated temperature and elevated pressure.

Taylor flow and mass transfer of CO2 chemical absorption into MEA aqueous solutions in a T-junction microchannel

The mass transfer of CO2 chemical absorption into monoethanol amine (MEA) aqueous solutions under Taylor flow in a T-junction microchannel was investigated experimentally using a high speed camera and two pressure sensors. Overall liquid side volumetric mass transfer coefficient (kLa), specific interfacial area (a), and overall liquid side mass transfer coefficient (kL) were obtained in terms of the image analysis and processing. The influences of operating conditions on overall volumetric mass transfer coefficient were studied systematically. Experimental results show that the bubble length decreases exponentially along the microchannel due to the CO2 reactive absorption. For a given concentration of MEA aqueous solution, both kLa and kL increase significantly with the increase of the ratio of the gas and liquid flow rates until closing to a constant. For different concentrations of MEA aqueous solutions, there exists a turning point in the flow rate ratio of gas and liquid phases. Before this point, lower concentration of MEA aqueous solution lead to higher kLa, while reverse tendency is found after this point. A semi-empirical correlation for predicting CO2 overall volumetric mass transfer coefficient accompanied with fast chemical absorption in the microchannel was proposed based on Higbie’s unsteady-state diffusion theory, and the predicted values agreed well with the experimental data.

Overall gas–liquid mass transfer from Taylor bubbles flowing upwards in a circular capillary

ABSTRACTOverall liquid side volumetric mass transfer coefficient kLa was determined experimentally for cocurrent Taylor flow moving upwards in a glass tube of an internal diameter of 3 mm. Experiments were performed for physical absorption of oxygen in 20% aqueous solution of ethanol. Shadowgraph technique was deployed for precise measurements of bubble lengths and velocities. Experimental values of volumetric mass transfer coefficient kLa were evaluated by use of oxygen sensor and contributions of two possible mass transfer mechanisms: bubble to liquid slug and bubble to liquid film were discussed. Effects of various hydrodynamic parameters such as superficial velocity, length of bubble and slug, and so forth on kLa have also been presented. A correlation has been proposed for the estimation of kLa for a wide range of bubble to slug lengths ratio and superficial velocities of gas and liquids. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

Remotely excited magnetic nanoparticles and gas–liquid mass transfer in Taylor flow regime

Gas–liquid mass transfer from oxygen Taylor bubbles to liquid in tube was studied using dilute colloidal suspensions of magnetic nanoparticles (MNPs) as the liquid phase. The tube was hosted inside the bore of a tubular two-pole three-phase magnet and the MNPs were remotely excited by subjecting them to different types of magnetic fields. The influence of magnetic field on the liquid side volumetric mass transfer coefficient (kLa) was cast as an enhancement factor with respect to the magnetic field free base case. The repercussions of magnetic field frequency, MNP concentration, tube alignment and gas velocity on this enhancement factor were measured experimentally. Experimental results suggested that spinning nanoparticles under transverse rotating magnetic fields (TRMF) improved mixing in the lubricating film that surrounds Taylor bubbles which reflected in a measurable enhancement of kLa. On the contrary, axial stationary magnetic fields (ASMF) pinned MNPs translating in systematically degraded gas–liquid mass transfer rates whereas axial oscillating magnetic field had no detectable effects on the mass transfer coefficient.

Mass Transfer Studies in a Rotating Packed Bed with Novel Rotors: Chemisorption of CO2

In this work, gas–liquid mass transfer characteristics, such as effective interfacial area (ae) and liquid side mass transfer coefficient (kL), were investigated in a rotating packed bed (RPB) contactor with 5 novel rotors equipped with blades in the packing section and 1 conventional rotor without blades and fully filled with the same packing. The chemisorption of CO2 into a NaOH solution was used to evaluate ae and kL within each rotor of the RPB. The experimental results indicate that the rotors with blades can significantly intensify the mass transfer process at all rotational speeds, over a range of gas–liquid ratios. The mass transfer rate achieved within these novel rotors was between 8% and 68% higher in comparison with the conventional rotor. A model based on the Danckwerts surface renewal theory was developed to calculate the liquid side volumetric mass transfer coefficient (kLae) in the rotor. The experimentally obtained values of kLae are in agreement with model predictions within ±15%.

Oxygen mass transfer coefficient in bubble column slurry reactor with ultrafine suspended particles and neural network prediction

AbstractThe gas–liquid volumetric mass transfer coefficient was determined by the dynamic oxygen absorption technique using a polarographic dissolved oxygen probe and the gas–liquid interfacial area was measured using dual‐tip conductivity probes in a bubble column slurry reactor at ambient temperature and normal pressure. The solid particles used were ultrafine hollow glass microspheres with a mean diameter of 8.624 µm. The effects of various axial locations (height–diameter ratio = 1–12), superficial gas velocity (uG = 0.011–0.085 m/s) and solid concentration (εS = 0–30 wt.%) on the gas–liquid volumetric mass transfer coefficient kLaL and liquid‐side mass transfer coefficient kL were discussed in detail in the range of operating variables investigated. Empirical correlations by dimensional analysis were obtained and feed‐forward back propagation neural network models were employed to predict the gas–liquid volumetric mass transfer coefficient and liquid‐side mass transfer coefficient for an air–water–hollow glass microspheres system in a commercial‐scale bubble column slurry reactor. © 2012 Canadian Society for Chemical Engineering

Effects of surface active agents on hydrodynamics and mass transfer characteristics in a split-cylinder airlift bioreactor with packed bed

The effects of three types of surface active agents (containing SDS, HCTBr and Tween 40) with various concentrations (0–5ppm) on the hydrodynamic and oxygen mass transfer characteristics in a split-cylinder airlift bioreactor with and without packing were investigated. It was observed that in the surfactant solutions, surface tension of the liquid decreased and smaller bubbles were produced in comparison with pure water. So, surfactants presence strongly enhanced mixing time and gas hold-up although oxygen mass transfer coefficient and the liquid circulation velocity reduced. Furthermore, the packing installation enhanced the overall gas–liquid volumetric mass transfer coefficient by increasing flow turbulency and Reynolds number compared to an unpacked column. The packing increased gas hold-up and decreased bubbles size and liquid circulation velocity.

Absorption of Carbon Dioxide with Ionic Liquid in a Rotating Packed Bed Contactor: Mass Transfer Study

Using ionic liquids for CO2 capture is of great interest due to their unique characteristics. However, low gas–liquid mass transfer rates in conventional gas–liquid contactors due to the high viscosities of ionic liquids lead to the significant limitation for large-scale application of CO2 capture using ionic liquids. Therefore, there is an urgent demand to develop a novel gas–liquid contactor for the intensification of the mass transfer efficiency in such a system. In this article, CO2 absorption with an ionic liquid in a rotating packed bed (RPB) gas–liquid contactor is first reported. It was found that the RPB markedly enhanced the physical absorption of CO2 in the ionic liquid in a very short contact time, within seconds. Only one cycle gas–liquid contact in the RPB could make the saturation ratio of CO2 in the ionic liquid reach 60%. The effects of various operation conditions on the liquid side volumetric mass transfer coefficient (kLα) were elucidated. Increasing the rotating speed from 1100 to 310...

Effects of surfactants on hydrodynamics and mass transfer in a split‐cylinder airlift reactor

AbstractEffects of various concentrations (0–5 ppm) of anionic (sodium dodecyl sulfate, SDS) and non‐ionic (Tween‐80 and Triton X‐405) surfactants on gas hold‐up and gas–liquid mass transfer in a split‐cylinder airlift reactor are reported for air–water. Surfactants were found to strongly enhance gas hold‐up. Non‐ionic surfactants were more effective in enhancing gas hold‐up compared to the anionic surfactant SDS. An enhanced gas hold‐up and a visually reduced bubble size in the presence of surfactants implied an enhanced gas–liquid interfacial area for mass transfer. Nevertheless, the overall gas–liquid volumetric mass transfer coefficient was reduced in the presence of surfactants, suggesting that surfactants greatly reduced the true liquid film mass transfer coefficient and this reduction outweighed the interfacial area enhancing effect. Presence of surfactants did not substantially affect the induced liquid circulation rate in the airlift vessel.

Limiting Gas Liquid Flows and Mass Transfer in a Novel Rotating Packed Bed (HiGee)

The flooding and mass transfer characteristics of a rotating packed bed (RPB) incorporating the split packing design innovation is studied. The air−water system is used for characterizing the flooding behavior, while mass transfer is studied for the chemisorption of CO2 in aqueous NaOH. Danckwert’s chemical method is used to infer the effective specific interfacial area (ae) for mass transfer. The variation in the liquid side volumetric mass transfer coefficient (kLae) with operating conditions is also measured. Consistently higher values of ae and kLae are observed for counter-rotation of the adjacent packing rings compared to co-rotation. The flooding and mass transfer results are compared with existing literature data on packed columns and conventional HiGee to evaluate the process intensification potential of the novel HiGee. The flooding limits are comparable to conventional HiGee, while the reported ae and kLae values are higher.

Experimental investigation of the liquid volumetric mass transfer coefficient for upward gas-liquid two-phase flow in rectangular microchannels

The gas-liquid two-phase mass transfer process in microchannels is complicated due to the special dynamical characteristics. In this work, a novel method was explored to measure the liquid side volumetric mass transfer coefficient kLa. Pressure transducers were utilized to measure the pressure variation of upward gas-liquid two-phase flow in three vertical rectangular microchannels and the liquid side volumetric mass transfer coefficient kLa was calculated through the Pressure-Volume-Temperature correlation of the gas phase. Carbon dioxide-water, carbon dioxide-ethanol and carbon dioxide-n-propanol were used as working fluids, respectively. The dimensions of the microchannels were 40 µm×240 µm (depth×width), 100 µm×800 µm and 100 µm×2000 µm, respectively. Results showed that the channel diameter and the capillary number influence kLa remarkably and that the maximum value of kLa occurs in the annular flow regime. A new correlation of kLa was proposed based on the Sherwood number, Schmidt number and the capillary number. The predicted values of kLa agreed well with the experimental data.

An experimental study of air–water Taylor flow and mass transfer inside square microchannels

Flow and mass transfer properties under air–water Taylor flow have been investigated in two square microchannels with hydraulic diameters of 400 and 200 μm. Experimental data on Taylor bubble velocity, pressure drop and liquid side volumetric mass transfer coefficient ( k L a ) have been presented. It was shown that the measured Taylor bubble velocity in square microchannels could be well interpreted based upon an approximate measurement of the liquid film profile therein. Then, the obtained two-phase frictional pressure drop values in both microchannels were found to be significantly higher than the predictions of the correlation proposed by Kreutzer et al. [2005b. Inertial and interfacial effects on pressure drop of Taylor flow in capillaries. A.I.Ch.E. Journal 51, 2428–2440] when the liquid slug was very short, which can be explained by the inadequacy of their correlation to describe the excess pressure drop caused by the strong inner circulation in such short liquid slugs. An appropriate modification has been made to this correlation in order to improve its applicability in microchannels. Finally, the experimental ( k L a ) values in the microchannel with hydraulic diameter of 400 μm were found to be in poor agreement with those predicted by the existing correlations proposed for capillaries with diameters of several millimeters. The observed deviation was mainly due to the fact that mass transfer experiments in this microchannel actually corresponded to the case of short film contact time and rather poor mixing between the liquid film and the liquid slug, which was not in accordance with mass transfer assumptions associated with these correlations. A new empirical correlation has been proposed to describe mass transfer data in this microchannel.

Gas–liquid mass transfer in three‐phase inverse fluidized bed reactor with Newtonian and non‐Newtonian fluids

AbstractLiquid‐phase volumetric mass transfer coefficients, kLa were determined in three‐phase inverse fluidized beds of low‐density polyethylene (LDPE) and polypropylene (PP) spheres fluidized by a countercurrent flow of air and Newtonian (water and glycerol solutions) or non‐Newtonian liquids [carboxy methyl cellulose (CMC) solutions]. The effects of liquid and gas velocities, particle size, solid loading and addition of organic additives (glycerol and CMC) on the volumetric mass transfer coefficient, kLa were determined. The superficial liquid velocity had a weak effect on the mass transfer whereas the gas flow rate affected the mass transfer positively. kLa increased with increase in particle diameter and decreased with increase in initial bed height (solid loading). kLa decreased as the concentration of glycerol (viscosity) and CMC increased. Empirical correlations are presented to predict the gas–liquid volumetric mass transfer coefficient in terms of operating variables. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

Simple correlations for bubble columns and draft tube airlift reactors with dilute alcohol solutions

Simple empirical correlations were developed to predict gas holdup, liquid circulation time, downcomer liquid velocity and volumetric mass transfer coefficient in dilute alcohol solutions in bubble columns and draft tube airlift reactors with single orifice sparger. Also, new experiments were conducted with diluted alcohol solutions to n-octanol, expanding the experimental data from C1 up to C8. The proposed empirical correlations include, beside the superficial gas velocity, the alcohol chain length as the only factor to characterize the liquid phase. The suggested correlations have shown good agreement between the calculated and the experimental data.

Flow Pattern, Pressure Drop, and Mass Transfer in a Gas−Liquid Concurrent Two-Phase Flow Microchannel Reactor

Flow pattern, pressure drop, and mass transfer characteristics have been studied for the gas−liquid two-phase flow in a 1.0 mm inner diameter circular microchannel reactor. A mixture of CO2, N2, and polyethylene glycol dimethyl ether was used to represent the gas and liquid phases, respectively. Bubbly, slug, churn, and slug-annular flow patterns were observed in the present work. A flow pattern map using superficial gas and liquid velocities as coordinates has been developed and compared to the existing flow pattern maps for ∼1 mm diameter channels. The data obtained for the pressure drop of the two-phase flow were analyzed and compared with the homogeneous model and the separate flow model to assess their predictive capabilities. The liquid side volumetric mass transfer coefficient increased with an increase of the superficial gas and liquid velocities, and the influences of the superficial gas and liquid velocities on it were demonstrated. The liquid side mass transfer coefficient, which was as high as...

Hydrodynamics and mass transfer characteristics in gas–liquid flow through a rectangular microchannel

Researches on two-phase transfer and reaction processes in microchannnels are important to the design of multiphase microchemical systems. In the present work, hydrodynamics and mass transfer characteristics in cocurrent gas–liquid flow through a horizontal rectangular microchannel with a hydraulic diameter of 667 μ m have been investigated experimentally. Liquid side volumetric mass transfer coefficients were measured by absorbing pure CO 2 into water and a 0.3 M NaHCO 3 / 0.3 M Na 2 CO 3 buffer solution. Interfacial areas were determined by absorbing pure CO 2 into a 1 M NaOH solution. Two-phase flow patterns and pressure drop data were also obtained and analyzed. This paper shows that two-phase frictional pressure drop in the microchannel can be well predicted by the Lockhart–Martinelli method if we use a new correlation of C value in the Chisholm's equation. Liquid side volumetric mass transfer coefficient and interfacial area as high as about 21 s - 1 and 9000 m 2 / m 3 , respectively, can be achieved in the microchannel. Generally, liquid side volumetric mass transfer coefficient increases with the increasing superficial liquid or gas velocity, which can be described satisfactorily by the developed empirical correlations. A comparison of mass transfer performance among different gas–liquid contactors reveals that the gas–liquid microchannel contactor of this study can provide at least one or two orders of magnitude higher liquid side volumetric mass transfer coefficients and interfacial areas than the others.

Mass transfer correlations for multiple-impeller gas–liquid contactors. Analysis of the effect of axial dispersion in gas and liquid phases on “local” [formula omitted] values measured by the dynamic pressure method in individual stages of the vessel

Mixing intensity of the liquid phase, power consumption and volumetric mass transfer coefficients are presented for various single-, double- and triple-impeller configurations. The measurements were carried out in a flat-bottomed vessel of inner diameter 0.29 m. Twenty-eight combinations of various impeller types inducing radial, axial and combined liquid flow were used, viz. a Rushton Turbine (RT), a six Pitched Blade (PB), Techmix 335 (TX) impellers pumping downwards (D) and upwards (U), Lightnin A315 (LTN) and a Narcissus (NS) impeller. Water, 0.5 M Na 2SO 4 solution and solution of commercial thickener (Sokrat 44) were used as a liquid phase, representing coalescent, non-coalescent and viscous batches, respectively. Mixing intensity of the liquid phase was characterized by both exchange flows and homogenization times. The dimensionless mixing time, Nt m , does not depend on Reynolds number but on the direction of liquid flow induced by the impeller. The axial impellers (TXU, TXD, and LTN) provide more effective homogenization than the impellers with combined or radial flow (PBU, PBD, NS and RT). General correlations of gassed to ungassed power ratio (valid for all types of batches used) are presented separately for the bottom and upper stages of the vessel. Volumetric mass transfer coefficient k L a was measured in individual stages of the vessel by the dynamic pressure method (DPM). Analysis of the effect of liquid exchange flow between stages and the effect of axial dispersion in the gas phase on k L a values measured by the DPM has shown that the arithmetic mean of these “local” values depends neither on gas phase axial dispersion nor on the liquid exchange flows and is equal to the arithmetic mean of the true local mass transfer coefficients in individual sections of the vessel. Two types of correlations were used to fit the “local” and the average k L a values with specific total power dissipated, superficial gas velocity, power number (characterizing impeller type) and gassed to ungassed power ratio (characterizing impeller placement in the multiple-impeller configuration, bottom vs. upper stages). General correlations (valid for all impeller configurations) are presented for each type of liquid batch used (coalescent and non-coalescent non-viscous batches and viscous batch). 3RT, RT + 2 PBD and RT + 2 PBU are the most efficient impeller combinations for the mass transfer performance in the triple-impeller vessel. The two latter configurations require a 15% enhancement of agitator frequency to reach an equivalent power dissipation and performance when compared to the 3RT configuration.

Gas–liquid mass transfer in bubble column reactor: Analytical solution and experimental confirmation

Gas–liquid mass transfer behavior in a bubble column is investigated. The used reactor is of 6 m height and has an internal diameter of 0.15 m. The classical ‘gassing out’ dynamic method is used to obtain the dissolved oxygen (DO) concentration profiles. An analytical description of the dissolved oxygen concentration evolution with time following the switch in the inlet gas is presented and allows the evaluation of the gas–liquid volumetric mass transfer coefficient for the different superficial gas velocities used. The comparison between the k L a values determined from this exact solution and those obtained in the same reactor from a more complete and sophisticated model, numerically solved, shows a good agreement.