Mass transfer from nanofluid drops in a pulsed liquid–liquid extraction column

CFD comparison of water based SiO2 nanofluid with benchmark MEA amine solution for CO2 capture through porous membrane contactor

Abnormal emission of environmentally-hazardous greenhouse pollutants (mainly CO2) to the atmosphere have motivated global researchers to develop green, affordable and effective techniques to maximize their separation from different feed. To reach this aim, application of more effective and greener absorbing solutions is of great importance to decrease the harmful disadvantages of benchmark amine solutions like corrosion, eco-detriment and complexity of operation. In the current decades, nanofluids have shown great ability of application in membrane-based separation industries owing to their outstanding privileges like high specific surface area, great stability and feasibility of employment in both hydrophilic and hydrophobic membranes. The main novelty of this scientific investigation is the efficiency comparison of SiO2-based nanofluid with monoethanolamine (MEA) benchmark solution for CO2 capture in gas-liquid membrane contactor (MC) using CFD approach. Analysis of the results showed the approximately similar performance of SiO2-based nanofluid compared to MEA for separating CO2 (98.8% using SiO2-based nanofluid VS 99.5% using MEA). Despite lower efficiency, SiO2-based nanofluid can be well identified as an environmentally-friendly and efficient alternative absorbent for use in CO2-separation industries instead of chemically-detrimental MEA solutions. Additionally, effects of some membrane/module parameters like number of fibers, module length and gas velocity on the separation of CO2 are explained, comprehensively.

Molecular simulation of liquid-liquid extraction of acetic acid and acetone from water in the presence of nanoparticles based on prediction of solubility parameters

In this work, molecular dynamics simulation (MD) was used for studying the liquid-liquid extraction of acetic acid and acetone from water in the presence of nanoparticles. In the next step, the solubility parameter of acetic acid and acetone were predicted at 1 atm and different temperatures along with the solubility parameter of solvents and water at 25 °C and 1 atm. Three pure systems and three systems with different concentration of nanoparticles were investigated to show the effect of cell size or number of molecules on the solubility parameter. With the addition of SiO2 nanoparticles to the solvents, at low concentrations of nanoparticles (0.01-0.1 vol%), the solubility parameter is increased due to the Brownian motion. With the further increase concentration of the nanoparticles, the solubility parameter decreases due to the accumulation of nanoparticles. The difference between the solubility parameter of benzene and acetone was 0.414 (J/cm3)0.5 and 3.13 (J/cm3)0.5, with and without the presence of SiO2 nanoparticles, respectively. Finally, toluene was found to be the best solvent for acetone and acetic acid at silica nanoparticles concentration of 0.062 vol%.

Mass transfer intensification for carbon quantum dot nanofluid drops under pulsed electric fields

Simultaneous use of carbon quantum dot (CQD) nanofluids and pulsed electric fields exhibits amazing mass transfer intensification in liquid-liquid extraction of circulating drops. Here, the chemical system of kerosene-acetic acid-water with mass transfer resistance in the organic phase was used in which organic nanofluid drops contained CQD or modified CQD-Fe. These products with extremely small sizes of 7.2 and 13.4 nm were synthesized and characterized by DLS, Zeta potential, XRD, EDS and SEM techniques. To find optimum conditions, CQD concentrations within (0.0005-0.003) wt%, electric field frequencies within (50-550) Hz and electric field strengths to 16 V/cm were examined. From hydrodynamic point of view, the flow pattern of drops was in circulating mode, and that terminal velocity of drops correctly followed the Grace model. The substantial effect of pulsed electric field on the CQD and CQD-Fe nanofluids, brought about mass transfer enhancements to 263.5 and 291.6%. This can be attributed to the electro-induced motion of global CQDs with pulsed electric fields. For the aim of modelling, the adapted Kumar and Hartland equation with a developed correlation of the enhancement factor versus involved dimensionless variables were satisfactory to reproduce the mass transfer coefficient data.

Intensification of CO2 absorption using MDEA-based nanofluid in a hollow fibre membrane contactor

Porous hollow fibres made of polyvinylidene fluoride were employed as membrane contactor for carbon dioxide (CO₂) absorption in a gas–liquid mode with methyldiethanolamine (MDEA) based nanofluid absorbent. Both theoretical and experimental works were carried out in which a mechanistic model was developed that considers the mass transfer of components in all subdomains of the contactor module. Also, the model considers convectional mass transfer in shell and tube subdomains with the chemical reaction as well as Grazing and Brownian motion of nanoparticles effects. The predicted outputs of the developed model and simulations showed that the dispersion of CNT nanoparticles to MDEA-based solvent improves CO₂ capture percentage compared to the pure solvent. In addition, the efficiency of CO₂ capture for MDEA-based nanofluid was increased with rising MDEA content, liquid flow rate and membrane porosity. On the other hand, the enhancement of gas velocity and the membrane tortuosity led to reduced CO₂ capture efficiency in the module. Moreover, it was revealed that the CNT nanoparticles effect on CO₂ removal is higher in the presence of lower MDEA concentration (5%) in the solvent. The model was validated by comparing with the experimental data, and great agreement was obtained.

Molecular investigation into the effect of carbon nanotubes interaction with CO2 in molecular separation using microporous polymeric membranes

The use of nanofluids has been recently of great interest to separate acidic contaminants such as CO₂. The main objective of this research is to assess the influence of carbon nanotubes (CNTs) addition to distilled water on enhancing the CO₂ molecular separation through a porous membrane contactor (PMC). For this aim, a comprehensive model is developed based on non-wetted and counter-current operational modes to evaluate the principal mass and momentum transport equations in tube, membrane and shell compartments of PMC. Consequently, a CFD-based axisymmetrical simulation is implemented according to finite element technique (FET) to prognosticate the results. It is found from the results that the addition of 0.1 wt% carbon nanotubes (CNTs) particles to water significantly enhances the mass transfer and consequently the CO₂ molecular separation efficiency from 38 to 63.3%. This considerable enhancement can be justified due to the existence of two momentous phenomena including Brownian motion and Grazing effect, which enhance the mass transport of CO₂ molecules in the PMC. Moreover, the effect of CNTs concentration, some membrane's parameters such as number of hollow fibers and porosity and also some module's design parameters including module radius and length on the CO₂ separation performance are investigated in this paper as another highlight of the current work.

Compensating effect of ultrasonic waves on retarding action of nanoparticles in drops liquid-liquid extraction

The influence of ultrasonic waves on liquid-liquid extraction of circulating drops and in the presence of magnetite nanoparticles was investigated. Experiments were conducted in a column equipped with an ultrasound transducer. The frequency and intensity of received waves, measured by the hydrophone standard method, were 35.40 kHz and 0.37 mW/cm², respectively. The recommended chemical system of cumene-isobutyric acid-water was used in which mass transfer resistance lies in the aqueous phase. Nanoparticles, within concentration range of (0.0003-0.0030) wt%, were added to the aqueous continuous phase. The presence of nanoparticles and ultrasonic waves provided no sensible change in drop size (within 2.49-4.17 mm) and measured terminal velocities were close to Grace model. However, presence of nanoparticles, caused mass transfer to decrease. This undesired effect was significantly diminished by using ultrasonic waves so that mass transfer coefficient increased from (73.0-178.2) to (130.2-240.2) µm/s, providing a 55.6% average enhancement. It is presumably due to disturbing the accumulated nanoparticles around the drops. The current innovative study highlights the fact that using ultrasonic waves is an interesting way to improve liquid-liquid extraction in the presence and absence of nanoparticles.

Experimental studies on the effect of ultrasonic waves on single drop liquid-liquid extraction

The influence of ultrasonic waves on hydrodynamics and mass transfer of circulating drops in liquid-liquid extraction process was studied. The recommended chemical systems of toluene-acetic acid-water with mass transfer resistance mainly in the organic phase, and cumene-isobutyric acid-water in the aqueous phase were used. An extraction column, equipped with an ultrasonic emitter of 35.40kHz real frequency and 0.37mW/cm² intensity, was employed. The ultrasound properties were measured using the hydrophone standard method. Drops terminal velocity was comparable with the Grace model. In mass transfer study, significant enhancement was revealed in overall mass transfer coefficient for different drop sizes and for the both mass transfer directions by using ultrasonic waves. The average and maximum enhancements were, respectively, 20.8 and 31.7% for toluene-acetic acid-water, and 40.3 and 55.1% for cumene-isobutyric acid-water. Small drops exhibited a higher enhancement percentage. Regarding the mass transfer direction, the system of cumene-isobutyric acid-water with continuous to dispersed phase direction, was benefited more as the consequence of creating effective agitation in continuous phase than in dispersed phase.

Influence of silica nanoparticles on mass transfer in a membrane-based micro-contactor

Experiments were performed in a membrane based micro-contactor The results showed that nanoparticles are more effective on mass transfer at lower flow rates.