The sorption of propane in slurries of active carbon in water

Application of Nanofluids in CO2 Absorption: A Review

The continuous release of CO2 into the atmosphere as a major cause of increasing global warming has become a growing concern for the environment. Accordingly, CO2 absorption through an approach with maximum absorption efficiency and minimum energy consumption is of paramount importance. Thanks to the emergence of nanotechnology and its unique advantages in various fields, a new approach was introduced using suspended particles in a base liquid (suspension) to increase CO2 absorption. This review article addresses the performance of nanofluids, preparation methods, and their stability, which is one of the essential factors preventing sedimentation of nanofluids. This article aims to comprehensibly study the factors contributing to CO2 absorption through nanofluids, which mainly addresses the role of the base liquids and the reason behind their selection.

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.

Chemical Absorption of CO2 Enhanced by Nanoparticles Using a Membrane Contactor: Modeling and Simulation

In the present work, membrane resistance was estimated and analyzed, and the results showed that total membrane resistance increased sharply when membrane pores were wetted. For further study, a two-dimensional (2D) mathematical model was developed to predict the chemical absorption of CO₂ in aqueous methyldiethanolamine (MDEA)-based carbon nanotubes (CNTs) in a hollow fiber membrane (HFM) contactor. The membrane was divided into wet and dry regions, and equations were developed and solved using finite element method in COSMOL. The results revealed that the existence of solid nanoparticles enhanced CO₂ removal rate. The variables with more significant influence were liquid flow rate and concentration of nanoparticles. Furthermore, there was a good match between experimental and modeling results, with the modeling estimates almost coinciding with experimental data. Solvent enhanced by solid nanoparticles significantly improved the separation performance of the membrane contactor. There was around 20% increase in CO₂ removal when 0.5 wt% CNT was added to 5 wt% aqueous MDEA.

Review of liquid nano-absorbents for enhanced CO2 capture

Liquid nano-absorbents have become a topic of interest as a result of their enhanced mass-transfer performance for CO₂ capture. They are believed to have revolutionized the conventional CO₂ chemisorption process by largely improving CO₂ capture kinetics and reducing the energy requirement for solvent regeneration. Two classes of nanomaterial-based CO₂ capture absorbents, amine-based nanoparticle suspensions (nanofluids) and nanoparticle organic hybrid materials (NOHMs), have been developed, with significant progress achieved in recent decades. This review addresses two key questions for these two state-of-the-art nanomaterials: how are the physical and chemical properties of the prepared liquid nano-absorbents transformed relative to those of the base fluids? And how does the transformation of the properties affect the CO₂ capture behavior? While the current synthesis procedure for liquid nano-absorbents is quite straightforward, more advanced synthesis methods for long-term nanoparticle stability have been suggested for the future. Nanofluids have been shown to increase the CO₂ uptake by over 20% and the CO₂ capture rate by 2-93% compared with the values observed with neat amine solvents. Nanoparticles with catalytic effects on CO₂ capture can significantly increase the CO₂ desorption rate by as high as 4000%. NOHMs exhibit the interesting feature of enhanced mass transfer in CO₂ capture because of the unique pathway network that is created in them for CO₂ to reach specific functional groups. NOHMs promise an effect of combined CO₂ capture and conversion, and can be used especially as electrolytes for CO₂ electro-reduction. However, there are still some challenges for the application of these materials in real life, such as poor stability and high viscosity. Therefore, efficient CO₂ capture processes using these solvents need to be urgently developed and studied in the future.

Absorption and decomposition of ozone in a three-phase split-rectangular airlift reactor under ultrasonic irradiation

Ozone absorption was investigated in a three-phase split-rectangular airlift reactor under ultrasonic irradiation using γ-Al2O3 as catalyst. The reactor consisted of a square column (50 × 50 mm) with the height of 120 mm, divided into a riser and a downcomer by a baffle, 50 mm in width, 4 mm in thickness and 50 mm in total height. An absorption kinetic model was proposed to determine the volumetric mass transfer coefficient of ozone kLaA. The results showed that kLaA increased from 0.409 to 0.712 min(-1) as power density rose from 27.2 to 100.3 W L(-1), comparing with 0.242 min(-1) in the absence of ultrasonic irradiation. The increase in gas flow rate and catalyst loading also favored the increase of kLaA. The degassing effect due to ultrasonic irradiation could be ignored in the ozone absorption process.

Model for a solid-liquid stirred tank two-phase partitioning bioscrubber for the treatment of BTEX

A dynamic mathematical model has been developed to predict the performance of a stirred tank, solid-liquid two-phase partitioning bioreactor (SL-TPPB) for the treatment of benzene, toluene, ethylbenzene and o-xylene (BTEX) contaminated gases. The SL-TPPB system consists of an aqueous phase containing a bacterial consortium and a solid phase of silicone rubber beads (10%; v/v) with a high affinity for BTEX compounds. The silicone rubber beads serve to sequester and release BTEX according to thermodynamic equilibrium, which increases mass transfer from the gas phase and reduces aqueous phase concentrations of these toxic compounds during fluctuating inlet loadings. The model was developed from mass balances on BTEX components in the gas, aqueous and polymer phases, and biomass in the aqueous phase. Dynamic experimental data from this system were used to fit model parameters and to assess the accuracy of the model. A detailed estimability analysis of model parameters and initial conditions was completed to identify uncertain parameters that are most influential for the model predictions and to determine the parameters and initial conditions that should be targeted for estimation using the dynamic data. It was found that the developed model, with estimated parameters and initial conditions, has the ability to predict experimental off-gas BTEX concentrations with reasonable accuracy, which are the outputs of greatest importance.