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.     

A supporting formulation for introducing gas–liquid reactions

In spite of the widespread industrial application of non-catalytic or homogeneously catalyzed gas–liquid reactions (GLRs), many undergraduate chemical engineering curricula do not include this subject and heterogeneous catalysis provides the only example of a heterogeneous chemical reaction system.Textbooks dealing with GLRs describe and formulate separately the different processes affecting the rate of chemical absorption, without providing a clear picture of the overall problem, which is highly desirable for the identification of effects and understanding of their interplay.As an attempt to provide a different alternative for teaching GLRs, a general approximate formulation for the transport/reaction problem, in terms of a global enhancement factor (GEF) for a single chemically absorbed species, including all possible effects on the basis of the two-film model is presented here.This contribution includes the development of the approximation for the GEF, an analysis of different regimes, which in part can be directly adopted for teaching, and an evaluation of the precision of the GEF estimation, mainly devoted to the lecturer.     

A novel process for scopolamine separation from Hindu Datura extracts by liquid–liquid extraction,macroporous resins,and crystallization

ABSTRACT

An efficient separation method of scopolamine from Hindu Datura extracts was successfully developed by combining liquid–liquid extraction, macroporous resins, and crystallization. First, the extraction solution was successively performed with liquid–liquid extraction by acid water and carbon tetrachloride. Secondly, D151 resin was selected from six tested resins, and the separation parameters were optimized. Finally, scopolamine hydrobromide was obtained after crystallization at ?20°C overnight. Through one run of above combined treatments, the content of scopolamine increased from 3.02% (w/w) to 99.12% (w/w). In addition, the products were assessed by high-performance liquid chromatography (HPLC).     

A continuum model for gas–liquid flow in packed towers

Gas–liquid flow in packed towers is commonly encountered in the chemical and processing industry. A continuum model is developed based on the volume-and-time averaging of multiphase flows in isotropic rigid porous media/packed columns. Closures are presented for the evaluations of the extra surface/intrinsic phase integral terms. Both inertia and inter-phase interactions are retained in the volume averaged (Navier–Stokes) equations. These governing equations are solved for fully-developed axi-symmetric single and gas–liquid two phase flows in highly porous packed towers. It is found that the dispersion term is present in the continuity equation as well as the momentum equations. Numerical simulations with the models show that the volume-and-time averaged equations can predict the velocity, phase hold-up and pressure drop quite well for up to the loading point for gas–liquid counter-current flows.     

A solution strategy for the film model for non-isothermal gas–liquid reactions

A general solution strategy for the film model for gas–liquid reaction has been proposed using the boundary element method (BEM) of discretization over subintervals in gas–liquid films. Non-isothermal effects in the film are included and the associated temperature changes near the gas–liquid interface are computed. The accuracy of the solution procedure is first established using some simple isothermal and non-isothermal benchmark problems and with semi-analytical solutions. Then illustrative results are presented for a non-isothermal series reaction system to illustrate effects of various parameters such as Arrhenius number, solubility changes with temperature, effect of volatility of the liquid phase reactant, etc. The proposed solution method provides fast and accurate values for interfacial fluxes and fluxes into the bulk liquid in addition to concentration profiles. Hence the method is extremely useful for coupling local effects of the film model with global effects based on CFD coupled compartmental model for gas–liquid reactors.     

Numerical simulation and experimental study of gas cyclone–liquid jet separator for fine particle separation

To address the shortcomings of existing particulate matter trapping technology, especially the low separation efficiency of fine particles, herein, a novel gas cyclone–liquid jet separator was developed to research fine particle trapping. First, numerical simulation methods were used to investigate the flow field characteristics and dust removal efficiency of the separator under different working conditions,and to determined suitable experimental conditions for subsequent dust removal experiment...     

Modeling of gas–liquid separation inside a slightly inclined annular duct

Electrical submersible pumping (ESP) is an artificial lift system used in the petroleum industry. ESP skid is an equipment in which the pump is housed inside a pipe forming a slightly inclined annular duct through which two-phase gas–liquid flows from inlet to pump intake. Part of the gas is pulled by the pump and part is separated and flows to the equipment top. This article analyses and models the observed separation process. Experiments showed good qualitative but poor quantitative agreement with literature models. Starting from a two-dimensional drift-flux model, radial and axial slips are modeled through phases' momentum transfer, showing the importance of drag, virtual mass and Basset's forces, leading to a semi-analytical model. As there is no model for such forces for the case of annular duct in the literature, experimental data is used for closure. The proposed model produced satisfactory and physically coherent results.     

A new streamlined bubble-cap distributor for high gas–liquid ratio and the liquid distribution mechanisms

The bubble-cap distributor is the most commonly used and critical internal for trickle bed reactors but holds the inherited disadvantage of liquid central aggregation when operating at a high gas–liquid ratio. A new bubble-cap distributor with a streamlined downcomer was developed in this paper to counter back the liquid aggregation and improve its comprehensive performance. The effect of the streamline parameters of the new distributor on liquid distribution was systematically explored by the coupled Euler–Euler-population balance equation (PBE) model. Compared with the classical and polyline converging–diverging structures, the results showed that the streamlined downcomer was a key to generating radial velocity of two-phase flow and reducing the liquid central aggregation for the bubble-cap distributor. The mechanism of well-distribution was explored for the new distributor. Lower converging and diverging angles enhance the distribution performance. A downcomer with a small converging angle and a 30° diverging angle was recommended for dispersing the central aggregated liquid column and acquiring the high distribution uniformity and spray covering circle. These data would be helpful to the optimal design and scale-up of the bubble-cap distributor in further industrial applications.     

Micro-computed tomography for the investigation of stationary liquid–liquid and liquid–gas interfaces in capillaries

For better understanding and optimization of multiphase flow in miniaturized devices, micro-computed tomography (μCT) is a promising visualization tool, as it is nondestructive, three-dimensional, and offers a high spatial resolution. Today, computed tomography (CT) is a standard imaging technique. However, using CT in microfluidics is still challenging, since X-ray related artifacts, low phase contrast, and limited spatial resolution complicate the exact localization of interfaces. We apply μCT for the characterization of stationary interfaces in thin capillaries. The entire workflow for imaging stationary interfaces in capillaries, from image acquisition to the analysis of interfaces, is presented. Special emphasis is given to an in-house developed segmentation routine. For demonstration purposes, contact angles of water, liquid polydimethylsiloxane, and air in FEP, glass, and PMMA are determined and the influence of gravity on interface formation is discussed. This work comprises the first steps for a systematic 3D investigation of multiphase flows in capillaries using μCT.     

Flow characteristics of gas–liquid two phase plunging jet absorber–gas holdup and bubble penetration depth

A gas-liquid two phase plunging jet is formed through a gas sucking type multi-jet ejector nozzle. In this study, the effects of various conditions in the multi-jet ejector nozzle, the column diameter, and the liquid jet length on penetration depth of air bubblesl _B and gas holdup h_G in a gas-liquid two phase plunging jet absorber were studied experimentally. Consequently, empirical equations concerningl _B and h_G were obtained, respectively. These equations agree with the experimental data with an accuracy of ±20% forl _B and ±25% for h_G.     

A review on single bubble gas–liquid mass transfer

It is common to empirically correlate volumetric mass transfer coefficient k_La for predicting gas–liquid mass transfer in industrial applications, and the investigation of single bubble mass transfer is crucial for a detailed understanding of mass transfer mechanism. In this work, experiments, models and simulations based on the experimental results were highlighted to elucidate the mass transfer between single bubbles and ambient liquid. The experimental setups, measurement methods, the mass transfer of single bubbles in the Newtonian and the non-Newtonian liquid, models derived from the concept of eddy diffusion, the extension of Whitman's, Higbie's and Danckwerts' models, or dimensionless numbers, and simulation methods on turbulence, gas–liquid partition methods and mass transfer source term determination are introduced and commented on. Although people have a great knowledge on mass transfer between single bubbles and ambient liquid in single conditions, it is still insufficient when facing complex liquid conditions or some phenomena such as turbulence, contamination or non-Newtonian behavior. Additional studies on single bubbles are required for experiments and models in various liquid conditions in future.     

Evaporative liquid jets in gas–liquid–solid flow system

Some aspects of the fundamental characteristics of evaporative liquid jets in gas–liquid–solid flows are studied and some pertinent literature is reviewed. Specifically, two conditions for the solids concentration in the flow are considered, including the dilute phase condition as in pneumatic convey and the dense phase condition as in bubbling or turbulent fluidized beds. Comparisons of the fundamental behavior are made of the gas–solid flow with dispersed non-evaporative as well as with evaporative liquids.For dilute phase conditions, experiments and analyses are conducted to examine the individual phase motion and boundaries of the evaporative region and the jet. Effects of the solids loading and heat capacity, system temperature, gas flow velocity and liquid injection angle on the jet behavior in gas and gas–solid flows are discussed. For dense phase conditions, experiments are conducted to examine the minimum fluidization velocity and solids distribution across the bed under various gases and liquid flow velocities. The electric capacitance tomography is developed for the first time for three-phase real time imaging of the dense gas–solid flow with evaporative liquid jets. The images reflect significantly varied bubbling phenomenon compared to those in gas–solid fluidized beds without evaporative liquid jets.     

Solvent-free route for metal–organic framework membranes growth aiming for efficient gas separation

Industrial applications of membranes based on metal–organic frameworks (MOFs) are challenged by their complex fabrication procedures and poor processability, despite their huge potential for efficient gas separation. Especially, the consumption of a large amount of toxic, expensive solvent, and harsh operation by conventional solvothermal growth also make it less attractive for industrial production. Herein, a solvent-free method is proposed to fabricate continuous defect-free MOF membranes on commercial porous stainless steel substrates, where the metal precursors are electrodeposited on the support followed by a heat treatment with the ligand powder via solid-state reaction without using any solvent. This strategy is proven to be applicable for various MOF membranes and it is expected to be a facile, cheap, and environmental friendly way for future large-scale production. © 2018 American Institute of Chemical Engineers AIChE J, 65: 712–722, 2019     

Flow regime transition for cocurrent gas–liquid flow in micro-channels

Experimental investigations of gas–liquid two-phase flow regimes in micro-channels were carried out in this work. Four distinctive flow patterns of slug flow, slug-annular flow, annular flow and parallel stratified flow were captured by a digital video recording (DVR) system and the transitions among different flow regimes were studied. The effect of fluid properties and wetting properties of the channel wall on the flow regime and flow pattern transition were studied as well. Novel empirical correlations for predicting flow pattern transitions during the steady gas–liquid flow in micro-channels have been developed with the fluid properties and the wetting properties of micro-channels incorporated, whereas the traditional flow criteria were based on gas and liquid superficial velocities only. The predictions of the present empirical models agree well with the experimental data.     

Drift-flux model for gas–liquid flow subjected to centrifugal fields

Centrifugal pumps are used in several industrial processes. It is common the operation of this equipment with gas–liquid mixtures, which is the case of the electrical submersible pumping artificial lift method used in the oil industry. The increase of free gas fraction inside the pump may lead to unstable operation and problems such as surging and gas locking phenomena to occur. In this study a drift-flux model is proposed for the gas–liquid flow subjected to centrifugal fields using the impeller as an example. The model is closed with experimental data of bubble diameter, displacements and velocities acquired via high-speed camera at several different rotational speeds and gas mass flow rates using water as the continuous medium. From the modeling and the forces balance in the bubbles, quantitative criteria for the start point of surging and gas locking conditions were proposed.     

Measuring gas hold-up in gas–liquid/gas–solid–liquid stirred tanks with an electrical resistance tomography linear probe

An electrical resistance tomography (ERT) linear probe was used to measure gas hold-up in a two-phase (gas–liquid) and three phase (gas–solid–liquid) stirred-tank system equipped with a Rushton turbine. The ERT linear probe was chosen rather than the more commonly used ring cage geometry to achieve higher resolution in the axial direction as well as its potential for use on manufacturing plant. Gas-phase distribution was measured as a function of flow regime by varying both impeller speed and gas flow rate. Global and local gas hold-up values were calculated using ERT data by applying Maxwell's equation for conduction through heterogeneous media. The results were compared with correlations, hard-field tomography data, and computational fluid dynamic simulations available in the literature, showing good agreement. This study thus demonstrates the capability of ERT using a linear probe to offer, besides qualitative tomographic images, reliable quantitative data regarding phase distribution in gas–liquid systems.     

Review on key issues of an axial gas–liquid separator for ultralow gas content

The separation of gas and liquid is a topic of general interest in science and engineering, for which tremendous efforts are endeavored to develop separators with high efficiency and reliability. However, when it comes to ultralow gas content, some of the separators fail. A special separator finds the potential herein, which consists of a swirl vane, a swirl chamber and a recovery vane. When the gas–liquid mixture goes through the swirl vane, bubbles will be concentrated into the swirl chamber center and evolved into a gas core. However, two key issues need to be addressed for the axial separator before industrial applications. One issue is that all the bubbles must be captured without exception, that is, the separation efficiency is close to 100%. The other issue is the stability of the gas core, the shape of which is sometimes rectilinear and sometimes spiral. A successful separation relies on the rectilinear shaped gas core. Focused on the two issues above, tremendous experimental, numerical and theoretical investigations have been carried out. In this article, the key challenges and solutions for the two issues are summarized.     

Transient gas–liquid mass transfer model for thin liquid films on structured solid packings

This paper describes a model for gas–liquid mass transfer through thin liquid films present on structured packings for gas–liquid operations under dispersed gas flow regime. The model has been derived for two cases: the absorption (or desorption) of a gaseous component into the liquid film and the transfer of the gaseous component through the liquid film to the packing surface where an infinitely fast reaction takes place. These cases have been solved for three bubble geometries: rectangular, cylindrical, and spherical. For Fourier numbers below 0.3, the model corresponds to Higbie’s penetration theory for both cases. The Sherwood numbers for cylindrical and spherical bubbles are 20% and 35% higher, respectively, than for rectangular bubbles. In case of absorption and Fourier numbers exceeding 3, the effect of bubble geometry becomes more pronounced. The Sherwood numbers for cylindrical and spherical bubbles now are 55% and 100% higher, respectively, than for rectangular bubbles. In case of an infinitely fast reaction at the packing surface, the Sherwood number corresponds to Whitman’s film theory (Sh=1$Sh=1$) for all bubble geometries. In this paper also practical approximations to the derived Sherwood numbers are presented. The approximations for both cases and all bubble geometries describe all the model data within an error of 4%. The application of the model has been demonstrated for three examples: (1) gas–liquid mass transfer for a structured packing; (2) gas–liquid mass transfer in a microchannel operated with annular flow; (3) gas–liquid mass transfer in a microchannel with Taylor flow.     

Mechanism and fundamental models of gas–liquid surging for valve columns

The gas–liquid streams in valve columns are likely to surge at low gas velocities, which degrades tray performances and threatens production safety. Therefore, the gas–liquid surging mechanism and vibration properties were investigated in this article. First, the theory of gas–liquid unstable flow at the seal point was proposed based on the principle of lowest energy. Then, the evolution mechanism, gas–liquid flow characteristics, and essential condition of surging are proposed. Meanwhile, experiments were carried out in a Φ580 mm valve column; the frequency spectral and hydraulic characteristics of surging were in accordance with the expected surging mechanism. Moreover, the surging vanish point criterion and safe operating superficial gas velocity for valve columns were advanced. Finally, fundamental models for surging frequency and amplitude were established. The models are in close accordance with the experimental data, which suggests that they could accurately describe the surging behavior.     

Experimental investigation on multiscale hydrodynamics in a novel gas–Liquid–Solid three phase jet-Loop reactor

Multiphase flow hydrodynamics in a novel gas–liquid–solid jet-loop reactor (JLR) were experimentally investigated at the macroscales and mesoscales. The chord length distribution was measured by an optical fiber probe and transformed for bubble size distribution through the maximum entropy method. The impacts of key operating conditions (superficial gas and liquid velocity, solid loading) on hydrodynamics at different axial and radial locations were comprehensively investigated. JLR was found to have good solid suspension ability owing to the internal circulation of bubbles and liquid flow. The gas holdup, axial liquid velocity, and bubble velocity increase with gas velocity, while liquid velocity has little influence on them. Compared with the gas–liquid JLRs, solids decrease the gas holdup and liquid circulation, reduces the bubble velocity and delays the flow development due to the enhanced interaction between bubbles and particles (Stokes number >1). This work also provides a benchmark data for computational fluid dynamics (CFD) model validation. © 2019 American Institute of Chemical Engineers AIChE J, 65: e16537, 2019