Volumetric Liquid-phase Mass Transfer Research Articles

Effects of channel wall wettability on gas–liquid dynamics mass transfer under Taylor flow in a serpentine microchannel

The wall wettability of microchannels plays an important role in the gas–liquid mass transfer dynamics under Taylor flow. In this study, we regulated the contact angle of the wall surface through surface chemical grafting polymerization under controlled experimental conditions. The dynamic changes of CO2 bubbles flowing along the microchannel were captured by a high-speed video camera mounted on a stereo microscope, whilst a unit cell model was employed to theoretically investigate the gas–liquid mass transfer dynamics. We quantitatively characterized the effects of wall wettability, specifically the contact angle, on the formation mechanism of gas bubbles and mass transfer process experimentally. The results revealed that the gas bubble velocity, the overall volumetric liquid phase mass transfer coefficients (kLa), and the specific interfacial area (a) all increased with the increase of the contact angle. Conversely, gas bubble length and leakage flow decreased. Furthermore, we proposed a new modified model to predict the gas–liquid two-phase mass transfer performance, based on van Baten's and Yao's models. Our proposed model was observed to agree reasonably well with experimental observations.

EKSTRAKSI SAPONIN DARI BUAH LERAK DENGAN PELARUT ETANOL DALAM TANGKI BERPENGADUK

Saponin from Lerak is a type of glicoside and used as washing agent of batik, insecticide, rheumatic medicine, poisoning agent for fish, etc. The most known natural source of saponin is Lerak (Sapindus Rarak D.C.). This research is aimed to have liquid phase volumetric mass transfer • coeficient (kc;B)on the surface of solid as function of the solid diameter and solvent concentration. Lerak is extracted as fine powder. The average diameters of solid sphere are 1,59 mm, 1,02 mm, 0,58 mm and 0,23 mm. Solvent concentrations are 96%, 76, 7%, 48% and 19,2% (wlw). The extractor is a three-cork vessel which is equipp_ed by thermometer, mercury stirrer, electric heater and water cooler. The temperature operation is 75'C and the speed of stirrer is 1000 rpm. Sample is analysed every 15 minutes during 3 hours gravimetrically. The correlation between kc;B and the other variable can be formulated as The error is 4,67%.

Hydrodynamics and gas-liquid mass transfer of CO2 absorption into [NH2e-mim][BF4]-MEA mixture in a monolith channel

This is the first work to investigate the hydrodynamics and gas-liquid mass transfer of carbon dioxide (CO2) absorbed into the amino-functionalized ionic liquid (IL) [NH2e-mim][BF4] and monoethanol-amine (MEA) mixture through a vertical circular monolith channel by means of computational fluid dynamics (CFD). It is shown that there are five flow patterns (i.e., bubbly flow, Taylor flow, slug-bubbly flow, slug-annular flow, and annular flow), and Taylor flow is the main flow pattern. The intrinsic kinetics of CO2 absorbed into the [NH2e-mim][BF4]-MEA mixture was obtained, the reaction orders relative to CO2, [NH2e-mim][BF4], and MEA being 1, and the activation energy Ea (19,313 and 28,991 J•mol−1) and pre-exponential factor k0 (3.34×105 and 7.04×106 mol-1•L•min−1) for CO2 absorbed in [NH2e-mim][BF4] and MEA were derived. After the kinetic parameters were imported into the mass transfer model, it was found that the liquid phase volumetric mass transfer coefficient (kLa) in the presence of a chemical reaction can be improved by three to eight times, indicating that mass transfer can be enhanced remarkably by chemical reaction. Moreover, a correlation formula is developed to predict kLa, which agrees well with the simulation results. This work provides a new way to capture CO2 with the combination of IL and MEA in a monolith reactor.

Adsorption characteristics of phosphoric acid induced activation of bio-carbon: Equilibrium, kinetics, thermodynamics and batch adsorber design

Abstract Activated carbon from Sterculia foetida was prepared using phosphoric acid as activating agent for efficient removal of methylene blue (MB). The effect of different operational parameters like pH (2–12), loading (1–4 g/l), initial dye concentration (50–500 ppm), temperature (298–328 K), and contact time (0–24 h) were investigated for the adsorption of MB. Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models were used to analyse the equilibrium data. The Langmuir model fitted well with maximum monolayer adsorption capacity of 181.81 mg/g. Adsorption kinetics followed pseudo-second order kinetic model. The adsorption process was found to be governed both by intra-particle and film diffusion. Thermodynamic parameters like entropy, enthalpy, and Gibb’s free energy were also evaluated. It was found that the adsorption was spontaneous, endothermic and physisorption in nature. The liquid phase volumetric mass transfer coefficient was found to decrease from 1.03 min−1 to 0.088 min−1 with increase in initial concentration from 50 ppm to 300 ppm. A single-stage batch adsorber design for dye adsorption has been proposed based on the Langmuir isotherm model equation. The reusability study demonstrated that the prepared adsorbent could effectively be used up to 5 cycles without regeneration. The study showed that the activated carbon prepared from Sterculia foetida can be effectively used as an adsorbent for methylene blue removal from aqueous solutions.

Mass transfer in molten salt and suspended molten salt in bubble column

Recently, the practical uses of bubble columns and slurry bubble columns at elevated temperature have attracted much attention. However, there is less knowledge of mass transfer in high temperature slurry bubble column, even though mass transfer data is essential to design bubble column and slurry bubble column. In this study, the CO2 mass transfer in eutectic mixtures of molten carbonate in bubble column at elevated temperature was investigated. CO2 was chosen as gas species, eutectic mixtures of Li2CO3–K2CO3 (38:62mol%) binary molten carbonate and Li2CO3–Na2CO3–K2CO3 (43.5:31.5:25mol%) ternary molten carbonate were used as liquid phase. In those eutectic mixtures, CO2 solubilities were determined at the temperature from 673K to 1173K. The values of solubilities increased with increasing temperature. It was suggested that CO2 dissolved into binary and ternary molten carbonate with chemical interaction, CO2+CO32−↔C2O52−. Increasing the temperature shifted this equation to the right and then more CO2 chemically dissolved into molten carbonates as C2O52−. From the CO2 gas absorption rate in molten carbonates, CO2 liquid phase volumetric mass transfer coefficients, kLa were determined and the influence of temperature and superficial gas velocity on kLa was also investigated. The kLa decreased with increasing temperature. And the kLa increased linearly with increasing superficial gas velocity. Regardless of unusual conditions in molten salt in bubble column at high temperature, where viscosity, surface tension and gas diffusivity were relatively high, it was suggested that the superficial gas velocity was most important operation condition in common with aqueous bubble column at ambient temperature.

Characteristics of gas–liquid dispersion and mass transfer in a multi-plunging jet absorber using gas–liquid two-phase jets

A new type of multi-plunging jet absorber using gas–liquid two-phase jets was devised. The jets were formed through ejector-type nozzles in a sheet of perforated plate. The effects of structural factors of the perforated plate, the number of nozzles and the nozzle arrangement on the product of liquid-phase mass transfer coefficient and gas–liquid interfacial area, the gas holdup, and the penetration depth of bubbles were investigated experimentally. The mass transfer mechanism of the bubble dispersed phase was considered using a coaxial bi-zonal model. The specific gas–liquid interfacial area and the volumetric liquid phase mass transfer coefficient in this absorber were compared with those of other gas–liquid contacting devices. Empirical equations regarding gas holdup and the bubble penetration depth were obtained. The mass transfer mechanism in the multi-plunging jet absorber could be explained by the coaxial bi-zonal model. The multi-plunging jet absorber was found to enhance performance by increasing the number of nozzles.

Discrete system identification and self-tuning control of dissolved oxygen concentration in a stirred reactor

This work presents the applications of discrete-time system identification and generalized minimum variance (GMV) control of dissolved oxygen (DO) level in a batch bioreactor in which Saccharomyces cerevisiae is produced at aerobic condition. Air flow rate and mixing rate were varied to determine the maximum local liquid phase volumetric mass transfer coefficient (KLa). Maximum KLa value was determined at a mixing rate of 600 rpm and air flow rate of 3.4 Lmin−1. For control purpose, manipulated variable was selected as air flow rate due to its effectiveness on the KLa. To examine the dynamic behavior of the bioreactor, various input signals were utilized as a forcing function and three different model orders were tested. A second0order controlled auto regressive moving average (CARMA) model was used as the process model in the control algorithm and in the system identification step. It is concluded that the ternary input is more suitable than the other input types used in this work for system identification. Recursive least squares method (RLS) was used to determine the model parameters. GMV control results were compared with the traditional PID control results by using performance criteria of IAE and ITAE for different types of DO set point trajectories. DO concentration in the batch bioreactor was controlled more successfully with an adaptive controller structure of GMV than the PID controller with fixed parameters.

Steam Stripping of Bromine from Sea Brine: Mass-Transfer Analysis of Randomly Packed Columns

Mass transfer data have been collected on stripping of bromine from aqueous solution at different flow rates of liquid and steam using Rasching and Pall Ring packings randomly packed in glass columns (6.25 to 90 cm diameter) and tower constructed by using granite slabs having square cross-section (25 cm × 25 cm). In the present study, the model proposed by Wagner et al. [1] for distillation considering gas phase resistance as the controlling resistance is modified wherein liquid phase resistance is considered as the controlling resistance for mass-transfer. The modified model and model proposed by Castillo et al. [2] for stripping of volatile organic compounds (VOCs) from water have been successfully applied to the experimental data on debromination of sea brine. Average deviation between observed and calculated value of height of transfer unit based on the modified model of Wagner et al. [1] is 20.9 and 10.7% for bromide-bromate solution and bittern, respectively. The average deviation between observed and calculated overall volumetric liquid phase mass transfer coefficient is 16.62, 15.13 and 84.19% for debromination of bittern using pilot plant data, commercial bromine plants, and sodium bromide-bromate solution, respectively, based on correlations given by Wagner et al. [1]. Similar results based on Castillo et al. [2] model are 34.43, 49.69 and 26.80%, respectively. Volumetric liquid phase mass transfer coefficient for stripping of VOCs from water is in the range of 0.001-0.008 (1/s) whereas in the present study it varies from 0.001 to 0.017 (1/s). In other words, steam stripping of bromine from aqueous systems appears comparatively easier than stripping of VOCs from water.

Self-tuning control of dissolved oxygen concentration in a batch bioreactor

Two different set profiles were used during the dissolved oxygen (DO) level control in a bioreactor in which Saccharomyces cerevisiae NRRL Y-567 was produced under aerobic condition. The performance of self-tuning generalised minimum variance (STGMV) algorithm was observed and compared to conventional PID control performance. Airflow rate and agitation speed were examined as manipulated variables to determine the maximum local liquid phase volumetric mass transfer coefficient ( K L a ). Maximum K L a value was determined at 600 rpm agitation speed and 3.4 L/min airflow rate. An auto regressive moving average with eXogenous (ARMAX) model was used as the process model in the control algorithm and the system identification step. Model and tuning parameters were estimated on-line using recursive least square (RLS) method. Experimental results show that self-tuning DO concentration control by using the set profile which has five step changes performed 90% better than the performance of the same control strategy which utilized the constant set value of DO concentration. In conventional PID control applications, using the set profile which has five step changes brought about 92% decrease in the performance criteria when it is compared with the case using the constant set value of DO concentration.

Toluene removal from nonionic surfactant coacervate phase solutions by vacuum stripping

Cloud point extraction (CPE) has been demonstrated to remove volatile aromatic pollutants from wastewater by using a nonionic surfactant as a separating agent. To make this process economically feasible, the surfactant in the concentrated or coacervate phase containing most of the original pollutant must be recycled and reused. This work proposes a vacuum stripping process to strip the volatile pollutant from the coacervate, leaving the concentrated surfactant solution to be recycled to the CPE process. An acrylic column was packed with glass Raschig rings and operated under rough vacuum in co-current mode to remove toluene from the coacervate phase containing the t-octylphenolpolyethoxylate (OP(EO 7)) nonionic surfactant. Co-current operation is necessary to avoid excessive foaming. In this study, although the apparent Henry's law constant of toluene was drastically reduced due to toluene solubilization in surfactant micelles, up to 90% of toluene was removed from 300 mM OP(EO) 7 surfactant solution using a 30.5-cm long column. The packed column can be operated without flooding and plugging, despite the viscous nature of the coacervate. The toluene removal increases with decreasing liquid loading rate, and column pressure, but with increasing number of distributor holes. The overall liquid phase volumetric mass transfer coefficient is reported for this system.

Gas–liquid mass transfer studies with triple impeller system on a laboratory scale bioreactor

The gas–liquid mass transfer coefficient K L a in a fermentor is known to be a strong function of the mode of energy dissipation and physicochemical properties of the liquid media. Three impeller combinations namely, single, double and triple impellers, respectively have been tested in the laboratory bioreactor (2 l) for their gas–liquid mass transfer performance. The liquid phase physico-chemical properties have been varied using distilled water, aqueous solutions of sodium carboxymethyl cellulose and simulated fermentation medium. The effects of the process variables such as the impeller speed, gas flow rate and the liquid phase physico-chemical properties on the volumetric liquid phase mass transfer coefficient of oxygen, K L a in a stirred bioreactor were investigated by static gassing out method. Correlations have been developed for the predictions of the gas–liquid mass transfer coefficient with liquids having different physico-chemical properties. It has been observed that triple impeller system gave highest values of gas–liquid mass transfer coefficient with the least power consumption.

CFD simulations of mass transfer from Taylor bubbles rising in circular capillaries

Computational Fluid Dynamics (CFD) is used to investigate mass transfer from Taylor bubbles to the liquid phase in circular capillaries. The liquid phase volumetric mass transfer coefficient k L a was determined from CFD simulations of Taylor bubbles in upflow, using periodic boundary conditions. The separate influences of the bubble rise velocity, unit cell length, film thickness, film length, and liquid diffusivity on k L a were investigated for capillaries of 1.5, 2 and 3 mm diameter. The mass transfer from the Taylor bubble is the sum of the contributions of the two bubble caps, and the film surrounding the bubble. The Higbie penetration model is used to describe the mass transfer from the two hemispherical caps. The unsteady-state diffusion model of Pigford is used to describe the mass transfer to the downward flowing liquid film. The developed model for k L a is in good agreement with the CFD simulated values, and provides a practical method for estimating mass transfer coefficients in monolith reactors.

Performance of Multi‐Plunging Jet Absorber Using Liquid Jets Containing Small Solute Bubbles

AbstractThe effects of structural factors in nozzles having a gas sucking type bubble generator and the number of nozzles for a multi‐plunging jet absorber using liquid jets containing small solute bubbles on gas‐liquid interfacial area and mass transfer were investigated. It was found that the volumetric liquid phase mass transfer coefficient (kLa)T of the absorber increased with increasing nozzle number. The mass transfer performance of this absorber was comparable to that of other high performance gas‐liquid contacting devices. A two‐region model was found to be applicable to the mechanism of liquid phase mass transfer in the multi‐plunging jet absorber.

The studies on the oxygen mass transfer coefficient in a bioreactor

The effects of process variables on the volumetric liquid phase mass transfer coefficient of oxygen, k L a, in a stirred bioreactor were investigated by the static gassing-out method. The process variables chosen were impeller speed, air flow rate, temperature, viscosity and loading (%) of biomass support particles (BSP). The k L a value was obtained as 2.766 min −1 in distilled water at process variables such as stirrer speed 300 rpm, air flow rate 0.3 l min −1, temperature 37°C and pH 7. By using the same process conditions, k L a values obtained in glycerol (50%)+distilled water, distilled water containing BSP (loading 25%, particle volume 0.1625 cm 3) and glycerol (50%)+distilled water containing BSP (loading 25%, particle volume 0.1625 cm 3) were 1.383, 0.933 and 0.450 min −1, respectively. The exponents representing dependence of k L a on the process variables were also obtained by using oxygen absorption data, then these values were compared with literature values.

Liquid phase volumetric mass transfer coefficient in dairy effluent stream

The effluent from a dairy cold storage plant was studied for the levels of dissolved oxygen saturation. The effluent to the aerobic digester mainly contains lactose, milk fat, protein and lactic acid. The study was conducted at five different temperatures in a two litre laboratory fermentor. The volumetric liquid phase mass transfer coefficient was correlated to temperature with an average absolute deviation of 6.2%.

Removal of Volatile Organic Compounds from Surfactant Solutions by Flash Vacuum Stripping in a Packed Column

AbstractVolatile organic compounds (VOCs) am be removed from contaminated ground water and subsurface media by surfaclant‐enhanced remediation processes. For the process to be economically competitive it is necessary to recover and reuse the surfactant from this concentrated solution. The VOC can be removed from this concentrated solution by flash vacuum stripping, leaving the surfactant solution for reuse. In this study, the flash vacuum stripping of trichloroethylene (TCE) from an anionic surfactant solution in a co‐current packed column was studied under rough vacuum conditions. The presence of surfactants lead to a reduction in the overall liquid phase volumetric mass transfer coefficient (MTC) of 40 to 95%. depending on flow rate and surfactant concentration at 50°C and 16 kPa. At liquid loading rates of less than 13 cm3/cm2min, the MTC of TCE decreases rapidly with an increase in liquid loading rate, and at liquid loading rates above that, the MTC decreases slightly with an increase in the liquid loading rate. This trend may have been due to foaming. At surfactant concentrations above the critical micelle concentration, the effect of surfactant concentration was not significant at liquid loading rates less than 13 cm3/cm2min. However, beyond that rate, the MTC of TCE decreased drastically with an increase in surfactant concentration. The MTC of TCE increased with an increase in temperature. A large pressure drop (3 to 4 kPa/m) was observed across the packed bed due to foaming.

Gas Holdup and Volumetric Liquid-Phase Mass Transfer Coefficient in a Spout-Fluid Bed.

The effects of gas velocity, liquid velocity and nozzle diameter on the gas holdup and the volumetric liquid phase mass transfer coefficient, kLa, were studied a experimentally in a spout-fluid bed by absorption of oxygen in air into tap water. Gas holdup was found to increase with increasing gas velocity and to decrease with increasing liquid velocity and not to depend on nozzle diameter. kLa was found to increase with increasing gas velocity and liquid velocity and to decrease with increasing nozzle diameter. kLa was found to be strongly dependent on the liquid velocity. Two correlations for gas holdup and kLa in spout-fluid bed were presented with maximum deviation of 8% and 7% respectively.

Gas holdup and volumetric liquid phase mass transfer coefficients in a downjet loop reactor

The gas holdup ϵ and the volumetric liquid phase mass transfer coefficients k La were studied experimentally in a downjet loop reactor via the physical absorption of oxygen in air by tap water. Both ϵ and k La increase with increasing gas and liquid velocities and are larger than those in other types of reactors at the same gas and liquid velocities. At a similar power supply per unit liquid volume, k La also shows greater values than those in an upstream jet loop reactor. On the basis of these observations, empirical equations for ϵ and k La are proposed.

Degradation kinetics of p-nitrophenol ozonation in water

The degradation of p-nitrophenol with ozone in water has been studied. The influence of pH and ozone partial pressure on p-nitrophenol conversion has been observed. The kinetic regime of ozone absorption has been shown to be highly dependent on both variables. Thus, at pH 2 the kinetic regime corresponds to a slow reaction regardless of the ozone partial pressure applied. At pH 6.5 the absorption of ozone develops in the fast kinetic regime the reaction being of pseudo first-order with respect to ozone at ozone partial pressures lower than 500 Pa. Finally, at higher pH (8.5 and 12.4) and ozone partial pressures higher than 2000 Pa, the reaction becomes instantaneous. Under conditions of slow and instantaneous kinetic regimes the liquid phase volumetric mass transfer coefficient, k L a, was calculated. The results are in agreement with those obtained from the absorption of ozone in organic-free water at similar pHs. On the other hand, under the situation of fast pseudo first-order reaction the rate constant for the p-nitrophenol-ozone direct reaction was determined to be 4.5 × 10 6 M −1 s −1. The ozone decomposition reaction develops to some extent only at pH 12.4.

The Use of Surface Renewal and Eddy Diffusivity Theories in the Ozonation of a THM Precursor: 1,3-Cyclohexanedione

Abstract Kinetic equations derived from surface renewal and eddy diffusivity theories for fast and instantaneous kinetic regimes of absorption have been applied to the results of the ozonation of 1,3-cyclohexanedione (CYC) in water. This has allowed the determination of the rate constant of the direct reaction of ozone with CYC and the liquid phase volumetric mass transfer coefficient of the system. The results obtained are close to those reported in the preceding paper (SOTELO et al., 1991) when using the film theory. However, the ozone partial pressure necessary to reach the instantaneous kinetic regime is higher for the case of the theories applied in this work.