Investigation of the effects of nanoparticle size on CO2 absorption by silica-water nanofluid

Experimental study and analysis of CO2 and SO2 absorption in various water-based nanofluids by response surface methodology

The absorption of acidic gases in the oil and gas industries is important due to their toxicity and corrosive effects. Recently, the application of nanofluids based on aqueous or organic solvents as absorbents has been examined by a variety of researchers. In this study, a single bubble column was exploited to study the effect of water-based nanofluids on the absorption processes of SO2 and CO2 using response surface methodology (RSM) based on Box-Behnken three-level experiment design. With this in mind, CO2 and SO2 are separately injected at the bottom of a bubble column filled with one of the nanofluids: Al2O3-water, SiO2-water, or ZnO-water for each experiment. Then, the rate of SO2 or CO2 absorption in the nanofluids has been elucidated. The effect of important parameters including the weight fraction of the nanoparticles (NPs) (0.01, 0.055, and 0.1 wt.%), gas-liquid contact time (150, 300, and 450 s), and the diameter of nozzle for gas injection (0.46, 0.57, and 0.68 mm) have been studied. Results revealed that the maximum molar flux of both gases was observed in the ZnO-water nanofluid, followed by the SiO2-water nanofluid. In addition, increasing the nanoparticle mass fraction and the bubble size causes the molar flux to rise. However, increasing the gas-liquid contact time causes the molar flux of the mentioned gases to decrease. Finally, a set of the accurate equations has been proposed to predict the molar flux of SO2 and CO2 in the various nanofluids assessed in this work.

Diffusion of CO2 in single-step silica nanofluid for subsurface utilization: an experimental study

This study investigates the role of single-step silica nanofluids as additives to increase CO₂ absorption in polymeric solutions for proposed oilfield applications. Using pressure decay approach, the study investigates the applicability of single-step silica nanofluids for CO₂ absorption in a high pressure-high temperature (HPHT) cell. Various parameters like nanoparticle size (30-120 nm) and concentration (0.1-1 wt%) were investigated to ascertain the absorption performance of the nanofluids and optimization their application in subsurface applications as carrier fluids for CO₂. The solutions under observation (deionized water and silica nanofluids) were pressurized under the desired pressure and temperature inside a stirring pot and the decline in pressure was continuously noted. To comprehensively cover the near-reservoir field conditions, the CO₂ absorption was investigated in the pressure range of 5-10 MPa and at temperatures of 30-90 °C. While increasing the nanoparticle concentration (from 0.1 to 1 wt%) increased the CO₂ absorption (evident by the sharper decline in pressure), increasing the nanoparticle size reduced the absorption capacity of the nanofluids as a lesser volume of decline in pressure was noted. Furthermore, increasing the temperature of the experimental investigation caused a major reduction (12-19%) in the pressure decay. However, it was also observed that higher pressure (> 7.5 MPa) was detrimental for CO₂ absorption (due to its supercritical nature). Adding salt (sodium chloride, NaCl) was found to massively lower (up to 33%) while adding surfactant (sodium dodecyl sulfate, SDS) slightly increased the amount of CO₂ absorption (in presence of salinity). Based on the observations of this study, the use of single-step silica nanofluids as CO₂ carrier fluids is recommended for oilfield conditions where salinity is less than 4 wt%.

Intelligent modelling for the elimination of lanthanides (La3+, Ce3+, Nd3+ and Eu3+) from aqueous solution by magnetic CoFe2O4 and CoFe2O4-GO spinel ferrite nanocomposites

In this research, a novel CoFe₂O₄-GO (Graphen Oxide) resulting from the combination of high applicable magnetic and organic base materials and synthesized with a simple and fast co-precipitation route was synthesized for the REEs (Rare Earth Elements) extraction. This adsorbent could remove the La³⁺, Ce³⁺, Nd³⁺ and Eu³⁺ by maximum adsorption capacity of 625, 626, 714.2, 1111.2 mg/g at optimized pH = 6, respectively. A data-driven model was obtained using Group Method of Data Handling (GMDH)-based Neural Network to estimate the adsorption capacity of these LREEs as a function of time, pH, temperature, adsorbent ζ (zeta)- potential, initial concentration of lanthanides ions, and ε which is defined by the physico-chemical properties of lanthanides. The results clearly indicated that the model estimate the experimental values with good deviation (mostly less than 10%) and it can be used for the prediction of the results from other similar researches with less than 25% deviation. The results of sensitivity analysis indicated that the adsorption capacity is more sensitive to pH of the solution, temperature, and ε. Finally, the desorption studies showed an excellent removal efficiency (97%) at least for three adsorption-desorption cycles. These results claimed that the CoFe₂O₄-GO is a highly efficient adsorbent for the REEs extraction.

A cleaner approach for high-efficiency regeneration of base and precious metals from waste printed circuit boards through stepwise oxido-acidic and thiocyanate leaching

This work evaluated a green route for developing an eco-friendly flowsheet to regenerate base and precious metals from waste printed circuits boards (WPCBs). Copper (as nanoparticles with an average diameter of 50 nm) and other base metals were extracted via oxidative acid leaching with high efficiency. Thiocyanate was employed for the first time as a green and economical reagent for the extraction of gold from pretreated WPCB. The effect of various parameters, including reagent dosage and temperature, was evaluated on the gold leaching rate, and 100% gold dissolution was achieved at the optimal condition. It was found that ferric iron concentration as the gold leaching oxidant has a notable effect on gold extraction. Also, at temperatures above room temperature, the recovery rate increases in a short period and then decreases continuously. The activation energy of the optimum gold thiocyanate leaching was found to be 42.84 kJ/mol, indicating chemical reaction to be the rate-controlling step. Gold extraction from the thiocyanate medium was carried out by employing activated carbon, where 100% gold adsorption was achieved in 2 h. Toxicity assessment of final residue revealed that it could be categorized as an environmentally safe waste with negligible risk.

Experimental Investigation of Mass Transfer Intensification for CO2 Capture by Environment-Friendly Water Based Nanofluid Solvents in a Rotating Packed Bed

In this research, two intensification approaches for CO2 capture via a rotating packed bed (RPB) and nanofluids were examined simultaneously to maximize the experimental mass transfer coefficient. The two intensification approaches were done by using water as a green, environmentally friendly absorption solvent and as the base fluid for preparing nanofluids and also by using centrifugal acceleration in an RPB. Physicosorption of CO2 in an RPB was carried out by applying Al2O3, TiO2, and SiO2 nanofluids to intensify the mass transfer in water, and the operation parameters such as the angular speed of the rotor, concentration and type of nanoparticles, gas and liquid flow rates, and CO2 concentration in mass transfer intensification were evaluated and several nanofluids were selected to survey investigate how they affect the mass transfer at low pressure. The results show that the Al2O3 nanofluid was more effective than other nanofluids and that the 40 nm nanofluid of this type was more efficient than the 20 nm size. Therefore, a correlation is proposed in this paper for liquid volumetric mass transfer coefficient prediction that includes the microconvection of nanoparticles and surface tension.

A Review on Enhancing Solvent Regeneration in CO2 Absorption Process Using Nanoparticles

The employment of nanoparticles in solvents is a promising method to reduce the energy consumption during solvent regeneration. Numerous experimental and theoretical studies have been conducted to investigate the remarkable enhancement of nanoparticles. Yet, there are limited reviews on the mechanistic role of nanoparticles in enhancing the solvent regeneration performance. This review addresses the recent development on the employment of various nanoparticles, which include metals oxides, zeolites and mesoporous silicas, to enhance the mass and heat transfer, which subsequently minimize the solvent regeneration energy. The enhancement mechanisms of the nanoparticles are elaborated based on their physical and chemical effects, with a comprehensive comparison on each nanoparticle along with its enhancement ratio. This review also provides the criteria for selecting or synthesizing nanoparticles that can provide a high regeneration enhancement ratio. Furthermore, the future research prospects for the employment of nanoparticles in solvent regeneration are also recommended.

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.

The effect of ZIF-67 nanoparticles on the desulfurization performance of deep eutectic solvent based nanofluid system

The nanoparticles of zeolitic imidazolate framework (ZIF-67) were synthesized and added to ethanolamine/deep eutectic solvent solution to form nanofluid system. The dynamic removal performance of prepared nanofluid system for hydrogen sulfide was investigated. For the system based on choline chloride and urea, the introduction of nanoparticles showed significant enhancement effect on the desulfurization performance. The optimal mass fraction of nanoparticles in nanofluid systems were identified as 0.1%. Besides, the experimental results showed that the prepared nanofluid systems have high regeneration performance, and the presence of moderate moisture is beneficial to the regeneration process. The absorbents and nanoparticles before and after absorption were characterized by Fourier transform infrared spectra, nuclear magnetic resonance, scanning electron microscope, energy dispersive spectrum, X-ray diffraction and X-ray photoelectron spectroscopy. The characterization results showed that the surface of nanoparticle was covered by CoS₂ after absorption.

Superadsorbent Fe3O4-coated carbon black nanocomposite for separation of light rare earth elements from aqueous solution: GMDH-based Neural Network and sensitivity analysis

A series of nanocomposites adsorbents with different magnetite/carbon black ratios were synthesized by using the co-precipitation method and used for separation of LREEs (Ce, La, and Nd) from aqueous solution. The adsorption efficiency of nanocomposites is strongly dependent on both pH and the loading carbon on nanocomposite. The maximum adsorption capacity (370 mg/g) was reported by nanocomposite with 20% Fe3O4 and 80% carbon in pH 7 for LREE initial concentration of 250 ppm. Results revealed that the LREEs adsorption behavior of the optimal adsorbent fits well with Langmuir isotherm and pseudo-first-order kinetic model. Moreover, the average values of thermodynamic parameters suggest the endothermic and irreversible chemisorption mechanism. An empirical correlation was obtained by using GMDH (Group Method of Data Handling)-based Neural Network to predict the adsorption kinetics of LREEs as a function of ion's electronegativity, molecular weight, and initial concentration. The results showed that the correlation can predict the experimental data mostly lower than 12.5% and it can predict the results of other researches with similar conditions with up to 25% from the experimental values. Finally, the results of sensitivity analysis revealed that the adsorption of LREEs is more sensitive to ions electronegativity and molecular weight at equilibrium conditions.

Cellulose nanocrystals coated with a tannic acid-Fe3+ complex as a significant medium for efficient CH4 microbial biotransformation

Microbial biotransformation of CH₄ gas has been attractive for the production of energy and high-value chemicals. However, insufficient supply of CH₄ in a culture medium needs to be overcome for the efficient utilization of CH₄. Here, we utilized cellulose nanocrystals coated with a tannic acid-Fe³⁺ complex (TA-Fe³⁺CNCs) as a medium component to enhance the gas-liquid mass-transfer performance. TA-Fe³⁺CNCs were well suspended in water without agglomeration, stabilized gas bubbles without coalescence, and increased the gas solubility by 20 % and the k_La value at a rapid inlet gas flow rate. Remarkably, the cell growth rate of Methylomonas sp. DH-1 as model CH₄-utilizing bacteria improved with TA-Fe³⁺CNC concentration without any cytotoxic or antibacterial properties, resulting in higher metabolite production ability such as methanol, pyruvate, formate, and succinate. These results showed that TA-Fe³⁺CNCs could be utilized as a significant component in the culture medium applicable as a promising nanofluid for efficient CH₄ microbial biotransformation.

Environmental impacts of nanofluids: A review

Nanofluids (NFs) have been expanding their applications in many areas as high-performance heat transfer fluid (HTF) for heating and cooling purposes. This is mainly due to the improved thermophysical properties relative to the base fluid (BF). The addition of nanoparticles (NPs) to BF, to obtain NFs, increases the thermal conductivity, hence better heat transfer properties and thermal performance. The properties of NFs can be considered somehow intermediate between those of the BF and the added solid NPs. The improved heat transfer using NFs results in increased energy conversion efficiency, which results in reduced energy consumption for heating or cooling applications. BF and their environmental impacts (EIs) have been widely discussed within the scope of their applications as a HTF, with most of the attention given to the improved energy efficiency. The IEs of NPs and their toxicity and other characteristics have been extensively studied due to the widespread applications on newly engineered NPs. However, with the evolution of expanding the applications of NFs, the different EIs were not well addressed. The discussion should consider both the base fluid and NPs added in combination as the NF constitutes. The current work presents a brief discussion on the EIs of NFs. The discussion presented in this work considers the NPs as the primary contributor to the EIs of different NFs. It was found that the EIs of NFs depend significantly on the type of NP used, followed by the BF, and finally, the loading of NPs in BF. The use of non-toxic and naturally occurring NPs at lower NPs loading in water as NF promises a much lower EIs in terms of toxicity energy requirements for production, and other EIs, while still maintaining high thermal performance. The production methods of both NPs, i.e., synthesis route, and NF, i.e., one-step or two-step, were found to have a significant effect on the associated EIs of the produced NF. The simpler NP synthesis route and NF production will result in much lower chemicals and energy requirements, which in turn reduce the EIs.

CFD simulation of CO2 absorption by water-based TiO2 nanoparticles in a high pressure stirred vessel

This work presents the modeling and simulation of CO₂ capture by a water-based Titanium dioxide (TiO₂) solid nanoparticle in a stirred high-pressure vessel at a constant temperature. Photocatalytic material such as TiO₂ has excellent properties, namely it is nontoxic, inexpensive, and non-polluting. CFD model equations are developed and solved using COMSOL software package. The effect of the concentration of a solid nanoparticle in a water-based TiO₂ solution, the size of TiO₂ nanoparticles and the rate of mixing on the CO₂ absorption rate is investigated. A 2D mathematical model considers both shuttle and micro-convention mechanisms. Results reveal that the best TiO₂ concentration range is between 0.5 and 1 kg/m³ and that a particle size of 10 nm is more efficient than higher particle sizes. A moderate mixing rate maximizes the CO₂ removal rate. The theoretical predictions are validated using lab experimental data and those in the available literature. Results confirm that the model calculations match with the experimental results. Accordingly, the model successfully predicts the experimental data and can be used for further studies.

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.

The Effect of Various Nanofluids on Absorption Intensification of CO2/SO2 in a Single-Bubble Column

Application of nanoparticles in aqueous base-fluids for intensification of absorption rate is an efficient method for absorption progress within the system incorporating bubble-liquid process. In this research, SO2 and CO2 were separately injected as single raising bubbles containing nanofluids to study the impact of nanoparticle effects on acidic gases absorption. In order to do this, comprehensive experimental studies were done. These works also tried to investigate the effect of different nanofluids such as water/Al2O3 or water/Fe2O3 or water/SiO2 on the absorption rate. The results showed that the absorption of CO2 and SO2 in nanofluids significantly increases up to 77 percent in comparison with base fluid. It was also observed that the type of gas molecules and nanoparticles determine the mechanism of mass transfer enhancement by nanofluids. Additionally, our findings indicated that the values of mass transfer coefficient of SO2 in water/Al2O3, water/Fe2O3 and water/SiO2 nanofluids are, respectively, 50%, 42% and 71% more than those of SO2 in pure water (kLSO2-water=1.45×10-4 m/s). Moreover, the values for CO2 in above nanofluids were, respectively, 117%, 103% and 88% more than those of CO2 in water alone (kLCO2-water=1.03×10-4 m/s). Finally, this study tries to offer a new comprehensive correlation for mass transfer coefficient and absorption rate prediction.