A New Pulsation Policy in a Disk and Doughnut Pulsed Column Applied to Solid‐Liquid Extraction of Andrographolide from Plants

Classically, sinusoidal oscillations are imposed to enhance mixing and mass transfer between two phases contacted. But, in any case of solid‐liquid contact, it was noticed that this pulsation mode was not efficient enough to allow a controlled behavior of the solid phase. The problem is particularly met during the treatment of raw plants or polydispersed populations with complex physical properties. The objective of this study is to demonstrate the viability of using a nonsinusoidal pulsation in a continuous contactor to replace a traditional batch sinusoidal mode. A review of the different pulsation techniques is firstly presented. The example of solid‐liquid extraction of andrographolide from plants has then been chosen to bring out the advantages of the new pulsation mode. The development of this application as a continuous process in a column has indeed encountered difficulties due to the important heterogeneity of the matter: one of these classes tends to float and the other to sink, which always leads to a definitive flooding in classical operations. Typically, the proposed signal is composed of two different periods: on the one hand, a classical sinusoidal pulsation step used to mix the liquid and solid phases in the active part of the column and allowing an optimal mass transfer and, on the other hand, an impulsion phase, generally used for the transport of solid. The extraction is carried out in a disk and doughnut column of 54 mm in diameter and 3.5 m in height. Liquid and solid are flowing concurrently and downwardly. Experiments have been performed to know the global characteristics of the process in steady state and to suggest some elements for industrial design. The results showed that an optimal tuning of the geometric characteristics of the column, the level of interface and the parameters of the pulsation could increase the operated domain where flooding is avoided.     

Pulsed Disc‐and‐Doughnut Column Performance

Abstract: A study of the hydrodynamic variables, drop size, continuous phase axial dispersion, and mass‐transfer coefficients of a pulsed annular disc‐and‐doughnut liquid extraction column are presented for three different systems. The results indicate that the characteristic velocity plot of Gayler et al. (1953) can be used to describe the variation of holdup with flow rate for a range of pulsation velocities. The existence of several different operating regimes, namely streamline, mixer‐settler, and emulsion regimes, was observed when the input energy was altered. Mass‐transfer data from 72.5 mm i.d. and 2.5 m i.d. columns were interpreted in terms of the differential axial‐dispersion model; the number of transfer units in a unit length of column is proposed as the basis for scale‐up of the mass‐transfer performance. By considering the free areas in the column, a method is proposed for the geometric scale‐up of pulsed disc‐and‐doughnut columns.     

Use of Pulsation to Control Polydispersed Particle Flow in a New Type of Pulsed Column

New internals have been designed and implemented in a semi‐industrial continuous solid‐liquid pulsed column. By coupling these internals with a non‐sinusoidal pulsation, a better control of polydispersed solid particles is achieved. The pulsation is composed of a mixing step during which only the liquid flows through the column and an impulsion step designed to transport the solid phase from stage to stage. Solid and liquid phase behaviors are characterized thanks to residence time distribution measurements. This study demonstrates the strong impact of the pulsation and of the liquid flow rate during the impulsion in reducing particle segregation inside the pilot. The effects of operating parameters on the liquid phase are also investigated and the choice of an operating compromise is discussed to balance the advantages and drawbacks of the process.     

A study on hydrodynamic characteristics in a Φ38 pulsed extraction column by four‐sensor optical fiber probe

Accurate prediction of dispersed phase droplet behavior is crucial to the design and scaling‐up of an extraction column. In this article, the dispersed droplet velocity algorithm and the diameter algorithm in a liquid–liquid two‐phase flow have been developed based on the bubble velocity model in gas–liquid two‐phase flow of Lucas [Measurement Science & Technology. 749, 758(2005)] and Shen [International Journal of Multiphase Flow. 593, 617(2005)]. Hydrodynamic characteristics, including droplet diameter, holdup and droplet velocity, were measured using a self‐made four‐sensor optical fiber probe in a 38 mm‐diameter pulsed sieve‐plate extraction column. Water and kerosene were used as continuous and dispersed phases, respectively. The influences of the pulsed intensity, the continuous and dispersed phase superficial velocities on the hydrodynamic characteristics were investigated. The experimental results show that it is reliable to use a four‐sensor optical probe to measure the hydrodynamic characteristics of a pulsed extraction column. © 2016 American Institute of Chemical Engineers AIChE J, 63: 801–811, 2017     

Modelling of transient mass transfer in liquid and liquid‐solid pulsating systems: Applications and extension to heat transfer

The dynamic surface renewal model of Maucci et al. (2001) is applied to transient mass transfer problems and extended to transient heat transfer measurements in pulsating, two‐phase flows. The model is also used to simulate mass transfer for square‐wave liquid velocity pulses in a liquid‐solid column. Experiments and simulation show that, when flow reversal occurs, the average mass transfer for a pulsating flow can be significantly higher than for steady state flow at the same bulk flow rate. This increase depends mainly on the relative pulse magnitude. The influence of pulse frequency and symmetry is second‐order. Apparent differences between various published studies are resolved.     

Untersuchung der batchweisen Azeotroprektifikation zur Trennung des Gemischs Essigsäure/Wasser

The aim of the present work is to investigate the suitability of the UNIFAC method to properly simulate the batch azeotropic distillation of a mixture of acetic acid, water, and ethyl acetate. A batch distillation including upstream countercurrent liquid‐liquid extraction was performed at pilot scale. A dedicated analytical method for fast and robust determination of top and bottom products was developed and presented. Experimental data were finally used for the validation of numerical predictions. It could be demonstrated that the UNIFAC method is applicable for the simulation of such a complex transient distillation process.     

New Approach in the Prediction of RDC Liquid‐Liquid Extraction Column Parameters

The liquid‐liquid extraction process is well‐known for its complexity and often entails intensive modeling and computational efforts to simulate its dynamic behavior. This paper presents a new application of the Genetic Algorithm (GA) to predict the modeling parameters of a chemical pilot plant involving a rotating disc liquid‐liquid extraction contactor (RDC). In this process, the droplet behavior of the dispersed phase has a strong influence on the mass transfer performance of the column. The mass transfer mechanism inside the drops of the dispersed phase was modeled by the Handlos‐Baron circulating drop model with consideration of the effect of forward mixing. Using the Genetic Algorithm method and the Numerical Analysis Group (NAG) software, the mass transfer and axial dispersion coefficients in the continuous phase in these columns were optimized. In order to obtain the RDC column parameters, a least‐square function of differences between the simulated and experimental concentration profiles (SSD) and 95 % confidence limit in the plug flow number of the transfer unit prediction were considered. The minus 95 % confidence limit and sum of square deviations for the GA method justified it as a successful method for optimization of the mass transfer and axial dispersion coefficients of liquid‐liquid extraction columns.     

Investigation of hydrodynamic and mass transfer of mercaptan extraction in pulsed and non-pulsed packed columns

We investigated the hydrodynamic behavior and mass transfer characteristics of a pilot-scale conventional packed bed extraction column of mercaptan removal from liquid propane. The extraction column was filled with pall rings structured packing where mercaptan was extracted from the continuous phase to the dispersed phase, accompanied by a chemical reaction in propane-mercaptan-caustic system. The pulsing was introduced into the column to enhance the mass transfer rate. Hydrodynamic parameters such as hold up, flooding velocity and mean drop size were studied together with the effect of chemical reaction on increasing mass transfer performance. Finally, the mass transfer and axial mixing coefficients were obtained from the optimization of data by ADM. It was found that at the pulsation intensity from 0.003 to 0.007 m/s, the maximum mass transfer and minimum axial mixing occurred and it can be concluded that pulsation improves the efficiency of mass transfer just at low intensities.     

Analysis of local heat transfer and hydrodynamics in a bubble column using fast response probes

A fast response probe is used to measure local heat transfer in a bubble column. It captured the variations in local heat transfer coefficients due to changes in local hydrodynamic conditions in radial and axial directions. These measurements have been used to identify flow regime transitions, variations in flow patterns and local hydrodynamic structure as obtained with different gas distributors and varying gas velocity. Standard deviations of pressure measurements obtained with a fast response probe have been compared with heat transfer coefficient fluctuations for the first time and the similarities and differences have been pointed out. Variations in average heat transfer coefficients and standard deviations in radial and axial directions point to different hydrodynamic conditions and are compared with literature studies. Relationships between local heat transfer measurements and hydrodynamic conditions are shown.     

Transition from Low Velocity to High Velocity in a Three Phase Fluidized Bed

The onset liquid velocity demarcating the conventional and the circulating fluidization regimes of three‐phase fluidized beds was determined by measuring the time required to empty all particles in a batch fluidized bed at various liquid and gas velocities. Experiments were performed in a gas‐liquid‐solid circulating fluidized bed of 2.7 m in height using glass beads of 0.508 mm in diameter as solid phase and air and tap water as the fluidizing gas and liquid, respectively. The results show that gas velocity is a strong factor on the onset liquid velocity. Higher gas velocity yields a lower onset liquid velocity. It is also demonstrated that the onset liquid velocity has the same value as particle terminal velocity in a gas‐liquid mixture. Within the gas‐liquid‐solid circulating fluidization regime, the solids circulation rate is increased with the total liquid velocity and the auxiliary liquid velocity.     

Gas Sparger Orifice Sizes and Solid Particle Characteristics in a Bubble Column – Relative Effect on Hydrodynamics and Mass Transfer

The relative effects of the size of gas sparger orifices and properties of solid particles on gas‐liquid mass transfer are not yet fully understood. Here, the impact of sparger orifice sizes, solid particle shapes, and their loading amounts in a bubble column reactor on the absorption of oxygen in tap water was investigated. Their influence on the mass transfer coefficient and bubble hydrodynamic parameters was evaluated. The results show that the addition of solid particles can have both positive and negative effects on hydrodynamics and mass transfer, depending on the orifice size of the gas sparger. The introduction of ring‐shaped solid particles can improve the mass transfer rate by up to 28 % without requiring any significant additional power.     

A mass transfer model for the extraction of weak acids/based in emulsion liquid-membrane systems

A mathematical model for analysing the extraction of weak acids and weak bases from aqueous solution by liquid surfactant membrane has been presented. The model assumes that the reactions are reversible and the reaction equilibrium to exist in both the internal phase and the external continuous phase. The scheme for mass transfer analysis is based on an immobilized emulsion globule drop model and the classical film theory, i.e. the overall mass transfer resistance includes that due to the external turbulent boundary layer, the interfacial surfactant layer and the diffusion layer within the emulsion globule. The leakage effect of internal phase due to membrane rupture is also discussed in the mathematical treatment. The proposed model predicts satisfactorily the experimental results of the extraction of weak acids as well as weak bases in a batch separation system as presented in the literature.     

Experimental Investigation and Simulation of a Gas‐agitated Sieve Plate Column

The extraction of hydrogen peroxide by means of deionized water from anthraquinone working solution via anthraquinone process was carried out in a gas‐agitated sieve plate extraction column. The effects of the superficial velocity of air, dispersed phase and continuous phase on the overall plate extraction efficiency have been investigated. The corrections for the prediction of the overall plate extraction efficiency were presented. The correction proposed to predict the overall plate extraction efficiency in the air, water, anthraquinone working solution three‐phase system agreed satisfactory with experimental data with a maximum absolute deviation of 5.6 %. A new design method for gas‐liquid‐liquid three‐phase extractors is developed based on the multistage countercurrent extraction model. The calculated data by the model agreed well with experimental data and the average relative deviation was less than 10 %. Moreover, the model was used to predict a gas‐agitated sieve plate extraction column for industrial production of hydrogen peroxide. The results show that the plate numbers of gas‐agitated sieve plate extraction column are 30–40 % less than that of liquid‐liquid sieve plate column.     

Hydrodynamique et transfert gaz-liquide dans un réacteur verlifix rempli de différents garnissages

This study concerns several Verlifix three phase reactors formed by the association of a jet venturi upper on a column filled with different solid packings. The gas and liquid flows are downstream cocurrent. Four packings are studied: glass Raschig rings, Coming's monolithic ceramics, microporous alumina pellets and glass beads. For these packings and gas and liquid flow rates fixed, we measure the hydrodynamic characteristics (flow regime, liquid dynamic retention, pressure drop) of the fixed bed and gas-liquid mass transfer conductance of the whole reactor, then we specify the influence of the operative conditions and the type of packing.     

Mass transfer in countercurrent and cocurrent bubble columns

The hydrodynamic and mass transfer characteristics in countercurrent, cocurrent and liquid batch operations with various Newtonian liquids were studied experimentally using the same bubble column. Taking the effect of gas sparger geometries, operating variables and liquid properties into account, empirical correlations were obtained for the gas hold-up and the volumetric liquid-phase mass transfer coefficient.     

Flow Regime Identification in a Slurry Bubble Column from Gas Holdup and Pressure Fluctuations Analysis

Analysis of gas holdups and pressure fluctuations are conducted in a slurry bubble column to study changes in flow regimes and comparisons are made with solid‐free bubble column. The pressure fluctuations are measured by fast response pressure transducers mounted on the column wall in the distributor and bulk regions. Air, tap water and 35 micron glass beads are used as the gas, liquid and solid phases respectively. Statistical analysis of pressure fluctuation data combined with gas holdup analysis provided information about flow regime transition and interesting insights into bubble size distributions and changes in flow structure.     

Elimination of Vanadium and Arsenic from VKCs Catalysts

Abstract

Vanadium and arsenic eliminations from an alkaline leaching solution of spent VKCs catalysts were studied. To this end, several commercial resins or polymers synthesized in the laboratory were evaluated in a solid–liquid batch extraction. Conditions for an effective extraction of vanadium and arsenic were determined. An extraction process, using a glass column, is described for the recovery of the vanadium. The elimination of arsenic by precipitation is proposed.     

An Improved Correlation of the Mean Drop Size in a Modified Scheibel Extraction Column

The drop size is of fundamental importance in the design of liquid‐liquid extraction columns, the drop size was measured as a function of the geometry, operating conditions, and physical properties of a liquid‐liquid system with no mass transfer in a five‐stage modified Scheibel extraction column. An improved correlation of the mean drop size in the Scheibel extraction column is presented. The correlation was divided into three sections in terms of the Reynolds number. It could be applied in a wide range and could be further used for the study of mass transfer performance of the modified Scheibel extraction column.     

Continuous alcohol addition in vaporized form and its effect on bubble behavior in a bubble column

This study investigated the effect of alcohol on gas hold-up in two methods to add alcohol into a column. In the first method, a weighed amount of ethanol was poured into the column before the gas hold-up measurement (batch mode). In the second method, we added ethanol continuously in the form of vapor dispersed in the gas phase (continuous mode). The continuous mode was more effective in improving the gas hold-up in a heterogeneous flow regime than the batch mode. On the other hand, it had a negative effect on gas hold-up in a homogeneous flow regime. To investigate these phenomena in more detail, we measured the detachment period, bubble size distribution, and bubble break-up frequency during bubble formation in the continuous mode. When the liquid vapor was highly soluble in the continuous water phase, the detachment period and average bubble size increased and the bubble break-up frequency decreased. On the other hand, when there was little interaction between the liquid vapor and continuous water phase, the effect was negligible. This could be explained by liquid vapor diffusion from the bubble inside into the continuous water phase.     

Extraction of Caprolactam with Toluene in a Pulsed Disc and Doughnut Column–Part III: Mass Transfer Characteristics

Abstract

The mass transfer characteristics of a pulsed disc and doughnut column with a 0.04 m internal diameter and 4.24 m active column length are investigated in order to evaluate its contacting efficiency for caprolactam extraction with toluene. Pilot plant experiments for both the forward and back‐extraction process were performed in order to determine the concentration profile along the column length in both the extract and raffinate phase as a function of the operating conditions. The experimental conditions covered the industrial operating range. Furthermore the dispersed phase hold‐up, average droplet diameter and operating regime were determined and compared with the results obtained for the equilibrium situation, as discussed in Part II.

In the forward extraction process a significant influence of operating conditions was observed, where an increase in the flux decreased the separation efficiency, but an increase in pulsation intensity, temperature, or the addition of ammonium sulphate increased the separation efficiency. In the back‐extraction all concentration profiles were comparable and all caprolactam was extracted after a column length of L/m=2. Compared to the equilibrium situation the drop diameter and pulsation intensity required for the transition of the mixer‐settler to the dispersion operating regime were found to increase under mass transfer conditions, while the hold‐up decreased. HETS values were determined for both the forward and back‐extraction. For the latter HETS=0.28 to 0.41, whereas in the forward extraction HETS=0.32 to 0.67.

The concentration profiles were described with the backflow model, using a constant backflow parameter for the continuous phase and a constant overall mass transfer coefficient. The interfacial area was correlated using drop diameter and hold‐up expressions derived for the equilibrium situation, taking into account the relative effect of mass transfer. Using these expressions the measured data could be correlated and described well.