Gas–liquid flows through porous media in microgravity: Packed Bed Reactor Experiment-2

Modifications were made to the Packed Bed Reactor Experiment (PBRE) and flown on the International Space Station as PBRE-2 to eliminate external pressure oscillations at higher liquid flow rates and the packing diameter was reduced to increase the pressure gradient for lower flows. It is found that gas hold-up is a function of bed history at low liquid and gas flow rates whereas higher gas hold-up and pressure gradients are observed for the test conditions following a liquid only pre-flow compared to the test conditions following a gas only pre-flow period. Over the range of flow rates tested, the capillary force is the dominant contributor to the pressure gradient, which is found to be linear with the superficial liquid velocity but is a much weaker function of the superficial gas velocity and varies inversely with the particle diameter.     

Experimental Investigation of Pressure Drop Hysteresis in a Cocurrent Gas–Liquid Upflow Packed Bed

Extensive experimental work on hysteresis in a cocurrent gas–liquid upflow packed bed was carried out with three kinds of packings and the air–water system. However, only when packed with small glass beads (f1.4 mm) was the bed pressure drop hysteresis observed. Two more liquids with different liquid properties were employed to further examine the influence of parameters on pressure drop hysteresis. The similarity of pressure drop hysteresis in packed beds was concluded in combination of experimental evidence reported in literature.     

Numerical simulation of fine particle liquid–solid flow in porous media based on LBM-IBM-DEM

Fine particle liquid–solid flow in porous media is involved in many industrial processes such as oil exploitation, geothermal reinjection, and filtration systems. It is of great significance to master the behaviours of the fine particle liquid–solid flow in porous media. At present, there are few studies on the influences of the migration of fine particles on the flow field in porous media, and the effects of the porosity of porous media and inlet fluid velocity on the migration behaviours of fine particles in porous media. In this paper, a liquid–solid flow model was established based on the lattice Boltzmann method (LBM)-immersed boundary method (IBM)-distinct element method (DEM) and verified by the classical Drag Kiss Tumble (DKT) phenomena and flow around a cylinder successfully. In this model, the interaction between solid particles is analyzed using the distinct element method, and the interaction between fine particles and flow field is handled by IBM. Then, the migration and blockage of fine particles in porous media was studied using this model. It is found that, in addition to the blockage, a large amount of blocked-surface sliding-separation occur in fine particles. At the same time, the decrease in porosity increases the damage degree of fine particles on the permeability. The porosity exerts great influence on the penetration rate and dispersion behaviour of fine particles. The inlet fluid velocity mainly affects the residence time of fine particles and the average velocity of motion in the direction perpendicular to the main flow direction.     

SO2 Removal by Seawater in a Packed–Bed Tower: Experimental Study and Mathematical Modeling

Flue gas desulfurization of industrial plants using seawater is studied experimentally and theoretically in a counter–current packed–bed tower. Experiments are carried out based on a 16–run orthogonal array of the Taguchi method (five factors, four levels) and ANOVA table created to determine the most significant controlling factors on SO₂ removal efficiency. Liquid flow rate (1.5–4 l/min), gas temperature (50–350°C), gas flow rate (8–20 m³/h), and SO₂ concentration (500–2000 ppmv) are revealed as important factors, while the pH of seawater (8–9.5) is not significant. Experimental results show that an increase in gas temperature causes a decrease in the removal efficiency. A mathematical model is developed for the removal of SO₂ by seawater for non-isothermal operating conditions. In the modeling procedure the equilibrium reactions of eight dissolved species within the liquid phase are considered to calculate the kinetic of reaction correctly. The results of this study confirm the capability of seawater for SO₂ removal in packed-bed towers.     

Gas—liquid interfacial area in stirred vessels: The effect of an immiscible liquid phase

The presence of an inert immiscible organic phase in gas—liquid dispersions in stirred vessels influences the interfacial area in a more complex fashion than hitherto reported. As the organic phase fraction is increased, the interfacial area expressed on the basis of a unit volume of dispersion or aqueous phase, first increases, passes through a maximum and then decreases. This trend is observed irrespective of whether the area is determined by chemical means or by physical method.It is found that for low values of inert phase fraction, the average bubble size decreases whereas the gas holdup increases, resulting in increased interfacial area. The lower average bubble size is found to be due to partial prevention of coalescence as the bubbles size generated in the impeller region actually increases with the organic phase fraction. The actual values of interfacial areas depend on the nature of the organic phase.It is also found that the organic phase provides a parallel path for mass transfer to occur, when the solubility of gas in it is high.     

Process intensification in vapor–liquid mass transfer: The state-of-the-art

The concept of process intensification(PI) has absorbed diverse definitions and stays true to the mission—"do more with less", which is an approach purposed by chemical engineers to solve the global energy environment problems. To date, the focus of PI has been on processes mainly involving vapor/liquid systems. Based on the fundamental principles of vapor–liquid mass transfer process like distillation and absorption, there are three strategies to intensify interphase mass transfer: enhancing the overall driving force, improving the mass transfer coefficient and enlarging the vapor–liquid interfacial area. More specifically, this article herein provides an overview of various technologies to strengthen the vapor–liquid mass transfer, including application of external fields, addition of third substances, micro-chemical technology and usage of solid foam, with the objective to contribute to the future developments and potential applications of PI in scientific research and industrial sectors.     

Dynamics of Mobile Concentration Fronts in Gas–Liquid Reaction Systems: Analysis and Numerical Experiment

Theoretical Foundations of Chemical Engineering - A mathematical model has been developed for the process of chemosorption with the moving front of an instantaneous irreversible reaction at small...     

Bed expansion of binary mixtures of irregular particles in solid–liquid fluidization: Experimental,empirical correlation,and GA-ANN modelling

Expansion behaviour for a bed of binary mixture of the irregularly shaped particle in Newtonian liquid was measured in two different circular columns. Variations in the physical parameters on the expansion behaviour have been reported. Bed expansion increases with an increase in liquid velocity and a decrease in particle diameter. Static bed height and expansion of the bed are low for higher diameter columns. An empirical correlation has been developed for predicting the ratio of bed height at the fluidized condition to the initial bed height as a function of the physical and dynamic variables related to the system for the binary particle mixtures. The correlation coefficient and variance of the estimate are 0.9299 and 0.0013, respectively, which is acceptable statistical accuracy. A hybrid of the genetic algorithm and neural network modelling for the prediction of the same has also been attempted where the input parameters are optimized using the Levenberg–Marquardt algorithm. With a relative error of 1.46%, the genetic algorithm performed well. So, the modelling has successfully predicted the bed height ratio at fluidized conditions to the initial bed height.     

Gas–liquid mass transfer in periodically operated trickle-bed reactors: Influence of the liquid-phase physical properties and flow modulation

The influence of periodic operation on trickle-bed reactor (TBR) hydrodynamics and gas–liquid mass transfer was investigated. Two-phase pressure drop, dynamic liquid hold-up and gas–liquid mass transfer coefficient (k_La) were determined at various liquid flow rates and for different modes of liquid flow variation (increasing and decreasing liquid flow rate). The results reveal the considerable influence of type of liquid flow rate modulation on k_La values (deviations of up to 80% in k_La). Simulation studies on gas-limited reaction in a periodically operated TBR indicate that an enhancement in conversion of about 14% can be expected from an appropriate selection of the operating mode, thus clearly demonstrating the quantitative process intensification feasible through increased gas–liquid mass transfer.     

Phase formation in porous liquid phase sintered silicon carbide: Part III: Interaction between Al2O3–Y2O3 and SiC

The structure and phase formation of porous liquid phase sintered silicon carbide (porous LPS-SiC), containing yttria and alumina additives have been studied. The present paper is focused on the system Y–Al–Si–C–O. The systems Al–Si–C–O and Y–Si–C–O have been studied in previous papers [J. Eur. Ceram. Soc. (in press) parts I and II].The reaction products of the interaction of Al₂O₃/Y₂O₃ with SiC and resulting microstructures were analysed by model experiments. The influences of different sintering atmospheres, namely argon and Ar/CO and different temperatures have been investigated. Thermodynamic calculations and sintering experiments reveal that silicides or carbides can be formed in addition to stable oxides. The main parameters controlling the formation of the different reaction products are the free carbon content, the oxygen activity and the temperature.Using CO containing atmospheres, the decomposition of the oxide additives can be effectively suppressed and stable porous LPS-SiC can be produced.     

The Selectivity and Sustainability of a Pd–In/γ-Al2O3 Catalyst in a Packed-Bed Reactor: The Effect of Solution Composition

This study tested the selectivity and sustainability of an alumina-supported Pd–In bimetallic catalyst for nitrate reduction with H₂ in a continuous-flow packed-bed reactor in the presence of: (i) dissolved oxygen (DO), an alternative electron acceptor to nitrate, (ii) variable NO₃ ^?:H₂ influent loadings, and (iii) the presence of a known foulant, sulfide. The sustainability of the catalyst was promising, as the catalyst was found to be stable under all conditions tested with respect to metal leaching. The presence of DO at concentrations typical of treatment conditions will increase H₂ demand for NO₃ ^? reduction, but has no negative impact on the selectivity of the catalyst. Under optimal conditions, i.e., a pH of 5.0 and a high NO₃ ^?:H₂ influent loading, low NH₃ selectivity (5%) was achieved for extended periods (36 days), resulting in sustained levels of NH₃ that approached the European legal limit. The biggest challenge to the sustainability of the catalyst was the addition of sulfide, that initially increased NH₃ selectivity and ultimately resulted in complete deactivation of the catalyst. Further work is required to identify regeneration methods to restore sulfide-fouled catalyst activity and selectivity; however, the most effective use would be to remove sulfide prior to catalytic treatment.     

Electrochemical reduction of 2-ethyl-9,10-anthraquinone (EAQ) and mediated formation of hydrogen peroxide in a two-phase medium Part II: Production of alkaline hydrogen peroxide by the intermediate electroreduction of EAQ in a flow-by porous electrode in two-phase liquid–liquid flow

Hydrogen peroxide production by the intermediate electroreduction of the 2-ethyl–9,10-anthraquinone (EAQ) was carried out in a flow-by cell and a two-phase electrolyte formed by a mixture of tributylphosphate (TBP) and diethylbenzene (DEB) as the organic phase, and a solution of NaOH as the aqueous phase. The cathode used was a reticulated vitreous carbon (RVC) foam. We have examined the following process variables: electrolysis current (0.3–3.1A), catholyte flow rate (470–1630mlmin–1), EAQ concentration in the organic phase (0.21–0.42m), organic/aqueous phase volume ratio (1/9–4/6) and grade of porosity of the RVC (20–45ppi). The electrolyses can be carried out in the presence or absence of oxygen gas. The first method is the so-called one-step electrolysis and the second method is the two-step electrolysis. In the second method, the disodium salt of the hydroquinone (EAQNa2) is electrochemically formed in the absence of oxygen. The second step consists of the chemical reaction of this salt with oxygen to form hydrogen peroxide. We obtained a hydrogen peroxide concentration of 0.8m after 10Ah with an electrolysis current of 1.55A and a current efficiency of 70%.