Dispersed Phase Mass Transfer Coefficient Research Articles

Mass transfer performance of pulsed disk and doughnut column (PDDC) in the extraction of active ingredients in peppermint extract obtained by hot percolation

AbstractThe active ingredients in peppermint are widely used in the pharmaceutical, food, cosmetic, and other industries. The traditional methods for producing peppermint extract through hydrodistillation (HD) and percolation are long process with low efficiency. The aim of this study is the improvement of the extraction performance and the efficiency of the extract obtained from hot percolation via pulsed disk and doughnut columns (PDDC), which is one of the most important pieces of liquid–liquid extraction (LLE) equipment. Peppermint extract was used as the continuous phase in the PDDC. n‐Hexane was considered as the dispersed phase in this column. In this study, the effects of three operating parameters were investigated, including the pulse intensity, continuous phase height, and dispersed phase flow rate, on the extraction efficiency of active ingredients in peppermint. The response surface method (RSM) was used to investigate the effect of these parameters on the extraction efficiency. The efficiency of this column in the extracting of active ingredients from peppermint was measured by UV–vis spectrophotometry, via the absorption rate of the main active ingredients of peppermint (menthol) in the samples, and the efficiency was 75% on average. The experimental and theorical of dispersed phase mass transfer coefficient were evaluated and compared. The results showed that the PDDC improved the extraction and mass transfer. By increasing the flow rate of the dispersed phase and the height of the continuous phase, the extraction efficiency and the mass transfer coefficient were increased.

Investigation of the impact of synthesized hydrophobic magnetite nanoparticles on mass transfer and hydrodynamics of stagnant and stirred liquid–liquid extraction systems

The impact of modified magnetite nanoparticles (MMNPs) on hydrodynamics and mass transfer in liquid–liquid extraction process was assessed using a ternary chemical system of toluene-acetic acid–water. The organic phase which contained toluene and acetic acid was dispersed through water, and the mass transfer of acetic acid between two phases was investigated. The hydrophobic modified magnetite nanoparticles (MMNPs) prepared through an optimized in-situ method were added to the dispersed phase at different concentrations (0.001−0.005 wt%). Two separate conditions were provided in the experiments, i.e. stagnant and stirred continuous phase. The latter case was provided by a rotor at two different speeds of 330 and 450 rpm. The effects of nozzle size and acetic acid concentration were also considered. The results showed that the as-prepared MMNPs decreased the terminal velocity and increased the liquid hold-up of the drops. Under the stagnant condition, an enhancement of 103.1% in overall dispersed-phase mass transfer coefficient was achieved at the optimum concentration of 0.001 wt% of MMNPs, whereas under stirred condition, the extraction fraction enhancement was not appreciable.

Investigation the effect of super hydrophobic titania nanoparticles on the mass transfer performance of single drop liquid-liquid extraction process

Hydrophobic titania nanoparticles were synthesized by a novel in situ sol-gel method and applied in a single drop liquid-liquid extraction column to enhance the overall dispersed-phase mass transfer coefficient (Kod). The chemical system of toluene, acetic acid and water was used, and the direction of solute (acetic acid) mass transfer was from dispersed phase, including: toluene and acetic acid to the continuous phase of water. For such system, much of the mass transfer resistance exists in the dispersed phase, which is nonpolar organic liquid. Hence, modified titania nanoparticles (MTNP’s), prepared by sol-gel route, in five different concentrations of 0.001–0.005 wt.% were added in the dispersed phase. Also, the impact of MTNP’s at the different solute concentrations and nozzles was investigated. Results indicated an anomalous enhancement in the overall dispersed-phase mass transfer coefficient at 0.002 wt.% of MTNP’s. A maximum enhancement of 70% in the overall mass transfer coefficient was found in droplets formed from a nozzle of 2.5 mm inner diameter, containing 3 wt.% of solute. Eventually, based on the theoretical model of Newman, a semi-empirical model was presented, that is capable to predict the overall dispersed-phase mass transfer coefficient of nanofluids with an average absolute relative error of 8.6%.

Continuous aqueous two-phase extraction of α-lactalbumin from whey in conventional rotating disc contactor

ABSTRACTThe differential partitioning of α-La to the PEG-rich phase and β-Lg to the salt-rich phase was studied in the continuous extractor, rotating disc contactor (RDC), using polyethylene glycol (PEG) 1000–trisodium citrate system. The performance of the extractor was evaluated in terms of holdup, mass transfer coefficient, extraction efficiency, and recovery by studying the operating variables such as phase velocities and rotor speed. The process conditions for the maximum dispersed phase mass transfer coefficient and recovery of α-La was also obtained and reported.

Investigating the effect of nanoparticles on the dispersed phase mass transfer coefficient in a rotary disc column

In this study, mass transfer performance and static holdup of dispersed phase in a liquid–liquid extraction column with rotating discs is investigated in presence of nanoparticles. The required nanofluid was prepared by dispersing SiO2 nanoparticles in kerosene, as the base fluid, using ultra sonication. The results show that the presence of nanoparticles increases static holdup of the dispersed phase. Moreover, the mass transfer performance was improved 6–45%. At higher rotor speeds, the effect of nanoparticles is reduced. Taking the heat and mass transfer analogy into account, an equation is presented for prediction of effective diffusivity and dispersed phase mass transfer coefficient in terms of nanoparticles content, Reynolds number and Schmidt number. Finally, the mass transfer coefficients obtained via the proposed equation of this work and the equations given by some other researchers have been compared with experimental data.

The Effect of Size and Concentration of Nanoparticles on the Mass Transfer Coefficients in Irregular Packed Liquid–Liquid Extraction Columns

This investigation explored the effects of nanofluids on mass transfer enhancement using an irregularly packed liquid–liquid extraction column and the chemical systems of water–acetic acid–toluene. SiO2 nanoparticles with sizes of 10, 30, or 80 nm are dispersed in toluene–acetic acid to produce nanofluids with different volume fractions of 0, 0.01, 0.05, and 0.1 vol.%. The effects of nanoparticle size and concentration on dispersed phase mass transfer coefficient were discussed based on the experimental data. This is for the first time that the effect of nanoparticle size is studied in liquid–liquid extraction systems. It was found that the mass transfer enhancement was more significant in nanofluids with smaller particles. It was also observed that mass transfer coefficient is larger in nanofluids compared to that in dispersed phase without nanoparticles, with a peak enhancement at a nanoparticle volume fraction of 0.05 vol.% for 10-nm particles and 0.01 vol.% for 30- and 80-nm particles. The maximum mass transfer coefficient enhancement was approximately 42% at 0.05% concentration of nanoparticles using smaller particles (10 nm). Finally, a novel correlation for prediction of effective diffusivity in the presence of nanoparticles has been proposed, which is a function of nanoparticle size and its concentration. The main advantage of this approach is that the principal effect of these two parameters is considered in correlation without which the experimental data could not be fitted with an acceptable accuracy.

Spray and packed liquid–liquid extraction columns: drop size and dispersed phase mass transfer

ABSTRACTThe effects of holdup on Sauter mean drop diameter, D32, and dispersed phase mass transfer coefficient have been studied in the spray and packed extraction columns. For both columns, two well‐defined regions for the dependence of D32 on holdup were observed. D32 increased and decreased with an increase in holdup at low and high levels of holdup, respectively. Changes in dispersed phase mass transfer coefficient against holdup were shown to be similar to D32 for both columns. Moreover, empirical correlations have been derived to predict D32 and dispersed phase mass transfer coefficient for both columns. It has been shown that the derived correlations are in a good agreement with the experimental data. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

Inter-phase mass transfer in turbulent liquid-liquid dispersions: A comparative analysis of models

A comparative evaluation of eight models used to predict the dispersed phase mass transfer coefficient was undertaken using recent drop size and mass transfer data obtained under well known and controlled hydrodynamic conditions encountered in screen-type static mixers. A wide range of experimental conditions were covered ( ɛ = 1.5–117 W/kg, ϕ = 0.1–0.47) thereby allowing for proper assessment of the strength and weaknesses of each model. All models failed to properly predict the experimental results over a wide range of design and operating conditions with the exception of those that contain a system-specific adjustable fitting parameter. Although these models yielded reasonably acceptable order-of-magnitude predictions, they could not accurately account for the variations in the different parameters investigated. This shows that proper understanding of the various factors affecting the dispersed phase mass transfer coefficient is still incomplete and highlights the need for phenomenological models that can account for the various physicochemical and hydrodynamic conditions on the dispersed-phase mass transfer coefficient.

Mass transfer coefficients in a hanson mixer-settler extraction column

The volumetric overall mass transfer coefficients in a pilot plant Hanson mixer-settler extraction column of seven stages have been measured using toluene-acetone-water system. The effects of agitation speed and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The results show that the volumetric overall mass transfer coefficient increases with increase in agitation speed and reaches a maximum. After having reached its maximum, it falls with further increase in agitation speed. It was found that the volumetric overall mass transfer coefficient increases with increase in dispersed phase flow rate, while it decreases with increase in continuous phase flow rate. By using interfacial area, the overall mass transfer coefficients for continuous and dispersed phases are determined from volumetric coefficients. An empirical correlation for prediction of the continuous phase overall mass transfer coefficient is proposed in terms of Sherwood and Reynolds numbers. Also the experimental data of the column investigated are compared with data for various extraction columns. Comparison between theoretical models and experimental results for the dispersed phase mass transfer coefficient shows that these models do not have enough accuracy for column design. Using effective diffusivity in the Grober equation results in more accurate prediction of overall mass transfer coefficient. The prediction of overall mass transfer coefficients from the presented equations is in good agreement with experimental results.

IMPACTS OF PACKING SECTION ON MASS TRANSFER TO DROP SWARMS

Terminal velocity and mass transfer coefficient data for drop swarms were measured in a 0.1 m diameter glass column filled with SMR (Super Mini Ring) packing, using a computerized video imaging system; 30% TBP-Kerosene/acetic acid/water and 50% TBP-Kerosene/acetic acid/water were used as the working systems. A number of techniques for the prediction of the observed mass transfer data were considered, and a new model to predict the mass transfer film coefficient, which accounts for the effects of surface contaminants on the mobility of the interface, is presented and shown to fit the experimental data. The effects of drop size and the presence of packing on overall dispersed phase mass transfer coefficient are presented. It is shown that overall dispersed phase mass transfer coefficient increases with increasing drop diameter, and decreases in the presence of SMR packing.

Correlations for Prediction of Mass Transfer Coefficients in Single Drop Systems and Liquid–Liquid Extraction Columns

Empirical correlations for the prediction of mass transfer coefficients for single drops are presented. Published experimental results for both circulating and oscillating drops are considered. Correlation for the individual continuous-phase mass transfer coefficient, which is based on data from 596 measurements taken from 10 different groups of investigators, reproduces the data with an average absolute error of 14.1%. This is then used to determine a correlating equation for the individual dispersed-phase mass transfer coefficient on the basis of data for overall dispersed-phase mass transfer coefficient taken from 21 sources. The average absolute value of the relative error in the predicted values of overall dispersed-phase mass transfer coefficient from the experimental points by using the correlations for individual mass transfer coefficients is 24.5%. It is further shown that by allowing for the effects of power input per unit mass and dispersed-phase hold-up, the correlations for single drops can be extended to extraction columns. The correction factors required for this purpose have been obtained by using simulated values of overall mass transfer coefficients for pulsed perforated-plate, Karr reciprocating-plate, Kuhni, and rotating disc columns.

Mass transfer coefficients in mixer-settler extraction column.

The volumetric over-all mass transfer coefficient K c a and the volumetric dispersed phase mass transfer coefficient k d a in a mixer-settler extraction column were measured. In the measurement of K c a, iodine was extracted from I 2 -KI aqueous solution into heptane, while iodine was back-extracted from a heptane solution of iodine into sodium thiosulfate aqueous solution to obtain k d a. By using specific interfacial area determined from the estimated Sauter mean diameter of the dispersed drops and the estimated holdup of the dispersed phase, the mass transfer coefficients for the dispersed and the continuous phases were determined from the volumetric coefficients K c a and k d a. The coefficient k d for the dispersed phase coincided with the theoretical value based on diffusion within a rigid sphere using the residence time distribution of dispersed drops. On the other hand, the coefficient k c for the continuous phase agreed well with the correlation of mass transfer around a rigid sphere by assuming that the relative velocity of the dispersed drop to the continuous phase was given by the terminal settling velocity of a rigid sphere having the same diameter and density as the drop.

Intensification of mass transfer in aqueous two‐phase systems

A novel technique which intensifies conventional aqueous two-phase extraction by conversion of dispersed phase into colloidal gas aphrons (CGAs) has been developed for extraction of an enzyme. In the present work, amyloglucosidase (1,4-alpha-D-glucan glucohydrolase) was extracted using a polyethylene glycol-sodium sulfate-water system. The lighter phase, i.e., polyethylene glycol (PEG) rich phase, was converted into CGAs which were then dispersed into a salt rich phase. The effect of type of surfactant and its concentration, dispersed phase velocity, phase composition, and type of sparger on the dispersed phase mass transfer coefficient was investigated. The results suggests 9-16 times higher values of mass transfer coefficient compared to spray column. The multiorifice sparger at concentrations of 0.33 g/L of cetyl trimethyl ammonium chloride yielded best results.

The application of drop size distribution and discrete drop mass transfer models to assess the performance of a rotating disc contactor

AbstractA method has been developed to calculate the overall mass transfer coefficient in an agitated liquid extraction column containing a wide range of drop sizes. The method applied the drop size distribution diagram to estimate the volume percentage of stagnant, circulating, and oscillating drops in the drop population. Individual mass transfer coefficients were then evaluated for the corresponding drop state, using the different single‐drop mass transfer models, after which the overall coefficient Kcal was calculated as the fractional sum of the individual coefficients and their proportion in the drop population. These estimated mass transfer coefficients have been compared with results obtained from a large rotating disc extractor 0.45 m in diameter and 6.75 m high, extracting acetone between water and Clairsol (a parafinic hydrocarbon, principally decane). Good agreement was obtained in the majority of the experiments when the Rose‐Kintner correlation was applied to evaluate the dispersed phase mass transfer coefficient of the oscillating drops. In all experiments agreement between the calculated and experimental overall mass transfer coefficients was improved by evaluating the concentration driving force by applying Simpson's rule, thereby introducing corrections for the variation in flowrate along the column and for possible backmixing.

Mass transfer coefficients—calculation for rigid and oscillating drops in extraction columns

Extraction efficiencies are predicted for rigid, and Handlos-Baron, isolated drops passing countercurrently to a continuous phase in an extraction column. Approximations made in previous theoretical work, in particular the assumption of uniform continuous phase concentrations in calculating the dispersed phase mass transfer coefficient, and the use of average rather than local coefficients, were eliminated to obtain more accurate predictions of mass transfer rates by both models. Significant differences from the approximate solutions previously published were obtained. Preliminary comparisons of theoretical predictions and experimental data are made by applying the isolated drop model predictions to swarms of drops in a Rotating Disc Contactor.

Resistance to mass transfer inside droplets

AbstractAn experimental investigation of the effects of various physical properties on the dispersedphase mass transfer coefficient was carried out for both nonoscillating and oscillating liquid droplets falling in a single stream through stationary continuous liquid phases. The Colburn and Welsh two‐component technique was used to isolate and measure the disperesed‐phase resistance to mass transfer. This technique limited the experimental study to systems with low interfacial tensions, between 2.5 and 5.8 dynes/cm. Solute was transferred into the droplets, and the droplet concentration was measured after droplet‐fall heights ranging from about 2 cm. to 103 cm. Precautions were taken to minimize end effects.The experimental mass transfer rates on nonoscillating droplets in general were greater than that predicted by the Kronig and Brink model for nonoscillating circulating droplets. Experimental Sherwood numbers for four liquid systems were correlated in terms of a relationship involving the dispersed‐phase Schmidt number, the Weber number, and the time group, 4DLtc/d2e, which allows for the time dependency of the transfer mechanism. The data were correlated with an average absolute deviation of 34%. The Kronig and Brink and Newman relations fitted the experimental data for nonoscillating droplets with an average absolute deviation of 46 and 54%, respectively. The experimental results for the oscillating droplets were correlated by two relationships with an average absolute deviation of 10.5%. The Handlos and Baron model fitted the experimental results for oscillating droplets with an average absolute deviation of 38%.