Dispersion of liquid–liquid phase by a jet-induced gas–liquid–liquid mixing column developed for separation of organic pollutants

This article presents the gas and liquid entrainment and its dispersion in a gas–liquid–liquid mixing column. The variations in phase entrainment is observed with the change in the paraffin liquid and kerosene volume fraction from 5% to 35% due to the increase in the flow resistance with increase in the effective viscosity of the liquid–liquid mixture. The degree of dispersion is enunciated based on the axial dispersion model and the flow resistance of the phases in the column. A correlation is proposed to interpret the entrainment of phase as a function of operating variables within the range of experimental conditions.     

Dynamic simulation of liquid—liquid operations using simple non-linear models

In this paper a new method for the dynamic simulation of multistage, multifeed liquid-liquid extraction operations is described. This is achieved by the use of simplified non-linear local models for the equilibrium representation of partially-miscible three-component systems.The probable transient response of the system to perturbations in the input parameters is illustrated. Whilst this has yet to be confirmed experimentally, several examples have been successfully solved and the steady-state results agree with those reported by previous authors.The method, using a simulation language (GEMS), is stable and shows computer requirements well within the range of the steady-state algorithms commonly used for simulation of extraction units.     

Effect of operating factors on liquid–liquid mass transfer and dispersion pattern of sedimentary liquid in a mechanically stirred vessel

Liquid–liquid dispersion and mass transfer were investigated in mechanically stirred vessels without baffles by changing operation factors such as an impeller rotation speed, off-bottom clearance, volumetric liquid ratio, etc. The dispersion regime was categorized into five groups: the sedimentary liquid was kept at the vessel bottom (I), partially elevated without any collision (II), partially dispersed by colliding with the impeller bottom (III), both liquids were partially dispersed by collisions with impeller blades (III’), and the sedimentary liquid was completely dispersed (IV). The dispersion switched to I → II → III → IV with the increasing rotation speed and decreasing off-bottom clearance. The liquid–liquid mass transfer rate was significantly enhanced with the collision of the sedimentary liquid with the impeller bottom, and subsequently increased with the increasing rotation speed, volumetric liquid ratio, and vessel diameter and with the decreasing off-bottom clearance. A multiple regression analysis method was applied to determine the mass transfer rates of III and III’.     

Characteristics of liquid slugs in gas–liquid Taylor flow in microchannels

The hydrodynamics of liquid slugs in gas–liquid Taylor flow in straight and meandering microchannels have been studied using micro Particle Image Velocimetry. The results confirm a recirculation motion in the liquid slug, which is symmetrical about the center line of the channel for the straight geometry and more complex and three-dimensional in the meandering channel. An attempt has also been made to quantify and characterize this recirculation motion in these short liquid slugs (L_s/w<1.5) by evaluating the recirculation rate, velocity and time. The recirculation velocity was found to increase linearly with the two-phase superficial velocity U_TP. The product of the liquid slug residence time and the recirculation rate is independent of U_TP under the studied flow conditions. These results suggest that the amount of heat or mass transferred between a given liquid slug and its surroundings is independent of the total flow rate and determined principally by the characteristics of the liquid slug.     

Desulfurization of liquid hydrocarbon fuels via Cu_2O catalyzed photooxidation coupled with liquid–liquid extraction

By combining the photochemical reaction and liquid–liquid extraction(PODS), we studied desulfurization of model fuel and FCC gasoline. The effects of air flow, illumination time, extractants, volume ratios of extractant/fuel, and catalyst amounts on the desulfurization process of PODS were analyzed in detail. Under the conditions with the air as oxidant(150 ml·min~(-1)), the mixture of DMF–water as extractant(the volume ratio of extractant/oil of 0.5) and photo-irradiation time of 2 h, the sulfur removal rate reached only 42.63% and 39.54% for the model and FCC gasoline, respectively. Under the same conditions, the sulfur removal rate increased significantly up to79% for gasoline in the presence of Cu_2O catalyst(2 g·L~(-1)). The results suggest that the PODS combined with a Cu_2O catalyst seems to be a promising alternative for sulfur removal of gasoline.     

Investigation on characteristics of liquid self-diffusion in slit nanopores using simple quasicrystal model of liquid☆

Dynamical properties of liquid in nano-channels attractmuch interest because of their applications in engineering and biological systems. The transfer behavior of liquid confined within nanopores differs significantly from that in the bulk. Based on the simple quasicrystal model of liquid, analytical expressions of self-diffusion coefficient both in bulk and in slit nanopore are derived from the Stokes–Einstein equation and the modified Eyring's equation for viscosity. The local self-diffusion coefficient in different layers of liquid and the global self-diffusion coefficient in the slit nanopore are deduced fromthese expressions. The influences of confinement by porewalls, pore widths, liquid density, and temperature on the self-diffusion coefficient are investigated. The results indicate that the self-diffusion coefficient in nanopore increaseswith the porewidth and approaches the bulk value as the pore width is sufficiently large. Similar to that in bulk state, the self-diffusion coefficient in nanopore decreases with the increase of density and the decrease of temperature, but these dependences are weaker than that in bulk state and become evenweaker as the porewidth decreases. Thiswork provides a simplemethod to capture the physical behavior and to investigate the dynamic properties of liquid in nanopores.     

Predicting the diameters of droplets produced in turbulent liquid–liquid dispersion

The droplet size distribution in liquid–liquid dispersions is a complex convolution of impeller speed, impeller type, fluid properties, and flow conditions. In this work, we present three a priori modeling approaches for predicting the droplet diameter distributions as a function of system operating conditions. In the first approach, called the two-fluid approach, we use high-resolution solutions to the Navier–Stokes equations to directly model the flow of each phase and the corresponding droplet breakup/coalescence events. In the second approach, based on an Eulerian–Lagrangian model, we describe the dispersed fluid as individual spheres undergoing ongoing breakup and coalescence events per user-defined interaction kernels. In the third approach, called the Eulerian–Parcel model, we model a sub-set of the droplets in the Eulerian–Lagrangian model to estimate the overall behavior of the entire droplet population. We discuss output from each model within the context of predictions from first principles turbulence theory and measured data.     

Prediction of liquid–liquid equilibrium from the Peng–Robinson+COSMOSAC equation of state

An approach combining the Peng–Robinson equation of state and novel solvation free energy calculation is developed here to describe the liquid–liquid equilibria for highly nonideal mixtures. This method has been previously shown to provide reliable vapor–liquid equilibria of pure and mixture fluids. The hydrogen-bonding interaction in this model is refined in order to properly describe the variation in the strength of hydrogen bond between different types of species. This method contains only 15 global parameters and 3 element-specific parameters (one atomic radius and two for the dispersion energy), and can be used to predict the miscibility gap of liquid mixtures and its temperature variations without sacrificing its capability in predicting vapor–liquid equilibria. The overall root-mean-square error in the mutual solubility of 68 binary mixtures predicted from PR+COSMOSAC is 0.0689, compared to those from the Modified UNIFAC 0.0822 and UNIFAC-LLE 0.0697, respectively.     

Salting-out-assisted liquid–liquid extraction and reverse-phase high-performance liquid chromatographic monitoring of thiacloprid in fruits and vegetables

Salting-out-assisted liquid–liquid extraction (SALLE) was developed to extract thiacloprid (THI) from fruits and vegetables. SALLE conditions (NaCl/Na₂SO₄, pH, and solvent polarity) were investigated at various levels for the optimal recovery of THI. Meanwhile, reverse-phase high-performance liquid chromatographic (RP-HPLC) conditions were balanced over 1–100 µg/mL of THI. The optimized SALLE-RP-HPLC method offered 78.33–92.00% recovery of standard THI at an acceptable repeatability 1.81–4.30% and reproducibility 1.08–4.74%. The detection and quantification limits were found to be 0.03 and 0.05 µg/mL, respectively. The real-time analysis verifies its suitability and ease of use for the determination of THI in agricultural commodities.     

Mass transfer behavior of liquid–liquid slug flow in circular cross-section microchannel

An alkaline hydrolysis reaction was used as the model reaction to investigate the performance of liquid–liquid slug flow microchannel. The specific interfacial area was determined through the photographic snapshot method physically by means of measuring the lengths of relevant slugs. The overall volumetric mass transfer coefficients were calculated through the Danckwerts’ model chemically. The influences of various operating conditions on the slug length, the overall volumetric extraction rate and the mass transfer coefficient were investigated quantitatively. A decreasing trend of volumetric mass transfer coefficients along the channel length was found. The linear dependence of the volumetric extraction rate on the volumetric mass transfer coefficient indicates that the overall rate of the process is determined by the mass transfer process. In addition, the volumetric mass transfer coefficients were correlated for different channel lengths.     

CFD modelling of liquid–liquid multiphase microstructured reactor: Slug flow generation

Microreactor technology, an important method of process intensification, offers numerous potential benefits for the process industries. Fluid–fluid reactions with mass transfer limitations have already been advantageously carried out in small-scale geometries. In liquid–liquid microstructured reactors (MSR), alternating uniform slugs of the two-phase reaction mixture exhibit well-defined interfacial mass transfer areas and flow patterns. The improved control of highly exothermic and hazardous reactions is also of technical relevance for large-scale production reactors. Two basic mass transfer mechanisms arise: convection within the individual liquid slugs and diffusion between adjacent slugs. The slug size in liquid–liquid MSR defines the interfacial area available for mass transfer and thus the performance of the reactor. There are two possibilities in a slug flow MSR depending on the interaction of the liquids with the solid wall material: a dispersed phase flow in the form of an enclosed slug in the continuous phase (with film—complete wetting of the continuous phase) and an alternate flow of two liquids (without film—partial wetting of the continuous phase). In the present work, a computational fluid dynamics (CFD) methodology is developed to simulate the slug flow in the MSR for both types of flow systems. The results were validated with the experimental results of Tice et al. (J.D. Tice, A.D. Lyon and R.F. Ismagilov, Effects of viscosity on droplet formation and mixing in microfluidic channels, Analytica Chimica Acta507 (1) (2004), pp. 73–77.).     

Modelling and constraint optimisation of an aromatic nitration in liquid–liquid medium

A methodology, which determines the operating conditions simultaneously optimising the chemical yield and considering the safety aspect, has been developed for a chemical reaction which is carried out batch-wise. To illustrate the methodology, the aromatic nitration of toluene by mixed acid has been chosen as a typical exothermic and non-selective reaction. This reaction takes place in a two-phase medium and, therefore, involves simultaneously chemical reaction and mass transfer phenomena. A kinetic model recently proposed for the slow and fast liquid–liquid reaction regimes was integrated to the mass balance. Nitration experiments were carried out in order to compare experimental composition profiles with simulated ones. Afterwards, an optimisation procedure has been used to maximise conversion, by manipulating the operating conditions subject to safety constraints. The p-nitrotoluene yield was chosen as the criterion to be maximised. Experimental validation for the optimisation procedure has been carried out. A monofluid heating–cooling system controlled by a predictive controller was used for the temperature control of the reactor. Simulation and experimental results are presented, discussed and compared.     

Investigation of vapour—liquid equilibrium of non-ideal multicomponent systems

Fundamentals and computer-aided methods of practice for the calculation and checking of azeotropes, and for the qualitative and rigorous determination of separating spaces for closed distillation are presented, which are valid for non-ideal multicomponent systems. Separating spaces can occur in azeotropic systems only and are decisive for the separability of a system, if distillation is the separation technique. As a prerequisite, a rigorous mathematical model of the vapour-liquid equilibrium is required. The eigenvalues and eigenvectors of the Jacobian matrix of the equilibrium concentrations are the key ingredients of several methods: the eigenvalues describe the asymptotic behaviour of closed distillation profiles, which indicates the order according to which components can be separated; the eigenvalues enter a topological equation for checking the thermodynamic consistency of the azeotropes of a system; the eigenvectors initiate paths connecting azeotropes and pure substances, from the network of which separating spaces can be deduced qualitatively; and eigenvectors are essential to initiate the rigorous profiles of separating spaces.     

An experimental study of immiscible liquid–liquid dispersions in a pump–mixer of mixer–settler

Drop size distribution(DSD) or mean droplet size(d32) and liquid holdup are two key parameters in a liquid–liquid extraction process. Understanding and accurately predicting those parameters are of great importance in the optimal design of extraction columns as well as mixer–settlers. In this paper, the method of built-in endoscopic probe combined with pulse laser was adopted to measure the droplet size in liquid–liquid dispersions with a pump-impeller in a rectangular mixer. The dispersion law of droplets with holdup range 1% to 24% in batch process and larger flow ratio range 1/5 to 5/1 in continuous process was studied. Under the batch operation condition, the DSD abided by log-normal distribution. With the increase of impeller speed or decrease of dispersed phase holdup, the d32 decreased. In addition, a prediction model of d32 of kerosene/deionized system was established as d_(32)/D = 0.13(1 + 5.9φ)We~(-0.6). Under the continuous operation condition, the general model for droplet size prediction of kerosene/water system was presented as d_(32)/D = C_3(1 + C_4φ)We~(-0.6). For the surfactant system and extraction system, the prediction models met a general model as d_(32)/D = bφ~nWe~(-0.6).     

Hydrodynemics of a cocurrent upflow liquid–liquid reciprocating plate reactor for homogeneously base-catalyzed methanolysis of vegetable oils

Hydrodynamics of a continuous cocurrent two-phase upflow reciprocating plate reactor (RPR) for homogeneously base-catalyzed methanolysis of sunflower oil was studied. Here, methanol constituted the dispersed phase and sunflower oil was the continuous phase. The measurements were performed in both the non-reactive (methanol–sunflower oil) and reactive (sunflower oil–methanol–KOH) systems. The main goal was to define the effects of the vibration intensity and the important reaction operating conditions on the pressure fluctuation at the reactor bottom, the power consumption, the dispersed phase holdup, the Sauter-mean drop diameter and the specific interfacial area. The power consumption under batch, single- and two-phase flow was proved to depend on the vibration intensity. The Sauter-mean drop diameter was found to depend on the specific power consumption in accordance with the turbulent model due to the turbulent energy dissipation in well-mixed regions around perforated plates. The simplified correlation of Kumar and Hartland could be used for estimating the Sauter-mean drop diameter. The energy dissipation due to reciprocating plate motion and the superficial dispersed phase velocity affected the dispersed phase holdup and the specific interfacial area. The present results are crucial for designing RPRs for application in continuous base-catalyzed methanolysis of vegetable oils.     

Experimental study and hydrodynamic modeling of countercurrent liquid–solid system with batch liquid

It is known that a transient effluent outlet concentration is obtained with a batch of adsorbent solids in any operation. A preferred steady state outlet concentration can be achieved with a continuous flow of solids. In the present work, information on pressure profiles, the total pressure drop across the column and holdup of solids are experimentally obtained for various solid flow rates, particle sizes and densities in a countercurrent liquid–solid system. These experimental results are compared with the prediction obtained using a phenomenological model containing continuity and momentum balance equations. The dominant drag force term was expressed in terms of various drag equations. The drag expression developed by Foscolo et al. (1983 Foscolo, P. U., Gibilaro, L. G., and Waldram, S. P. (1983). A unified model for particulate expansion of fluidized beds and flow in fixed porous media, Chem. Eng. Sci., 38(8), 1251–1260.[Crossref], [Web of Science ®] , [Google Scholar]) could predict the axial profiles of pressure drop and holdup, and the effect of various parameters on total pressure drop and solid holdup most satisfactorily.     

Selective separation of benzene from hydrocarbon mixtures via liquid–liquid extraction method using aqueous solutions of substituted cyclodextrins

The selective separation of benzene from hydrocarbon mixtures was investigated by way of liquid–liquid extraction using aqueous solutions of unsubstituted α-cyclodextrin (αCD), βCD and seven kinds of substituted CDs. Separation factor for benzene to cyclohexane was evaluated from the extraction of an equimolar mixture of benzene and cyclohexane. Hydroxypropyl-αCD showed the highest selectivity followed by 2,6-di-O-methyl-αCD, hydroxyethyl-βCD, hydroxypropyl-βCD and 2,6-di-O-methyl-βCD. Then, separation selectivity for benzene was compared among the nine kinds of CDs carrying out the extraction from an equimolar mixture of 3-methylpentane, n-hexane, benzene and cyclohexane. Finally, the extraction method was applied to reformate using the aqueous solutions of hydroxypropyl-αCD and hydroxypropyl-βCD. The results suggest that this method is effective for reducing the benzene content in reformate.     

Spray and mixing characteristics of liquid jet in a tubular gas–liquid atomization mixer

For the design and optimization of a tubular gas–liquid atomization mixer,the atomization and mixing characteristics of liquid jet breakup in the limited tube space is a key problem.In this study,the primary breakup process of liquid jet column was analyzed by high-speed camera,then the droplet size and velocity distribution of atomized droplets were measured by Phase-Doppler anemometry (PDA).The hydrodynamic characteristics of gas flow in tubular gas–liquid atomization mixer were analyzed by computational fluid dynamics (CFD) numerical simulation.The results indicate that the liquid flow rate has little effect on the atomization droplet size and atomization pressure drop,and the gas flow rate is the main influence parameter.Under all experimental gas flow conditions,the liquid jet column undergoes a primary breakup process,forming larger liquid blocks and droplets.When the gas flow rate (Q_g) is less than 127 m~3·h~(-1),the secondary breakup of large liquid blocks and droplets does not occur in venturi throat region.The Sauter mean diameter (SMD) of droplets measured at the outlet is more than 140μm,and the distribution is uneven.When Q_g127 m~3·h~(-1),the large liquid blocks and droplets have secondary breakup process at the throat region.The SMD of droplets measured at the outlet is less than 140μm,and the distribution is uniform.When 127Q_g162 m~3·h~(-1),the secondary breakup mode of droplets is bag breakup or pouch breakup.When 181Q_g216 m~3·h~(-1),the secondary breakup mode of droplets is shear breakup or catastrophic breakup.In order to ensure efficient atomization and mixing,the throat gas velocity of the tubular atomization mixer should be designed to be about 51 m·s~(-1)under the lowest operating flow rate.The pressure drop of the tubular atomization mixer increases linearly with the square of gas velocity,and the resistance coefficient is about 2.55 in single-phase flow condition and 2.73 in gas–liquid atomization condition.