Papers by Keyword: Kinetics

Abstract: Magnetized coal fly ash (MCFA) was utilized as a low-cost and eco-friendly adsorbent for the removal of crystal violet (CV) dye from aqueous solution. This study aims to investigate the adsorption behavior of CV onto MCFA through kinetic and isotherm evaluations. The magnetic modification was performed using Fe₃O₄ to enhance the separation efficiency and adsorption performance of raw fly ash. Batch adsorption experiments were conducted to examine the effects of contact time, initial dye concentration, pH, and adsorbent dosage. The kinetic analysis revealed that the adsorption process followed the pseudo-second-order model, suggesting chemisorption as the dominant mechanism. Isotherm modeling showed that the Langmuir model provided the best fit, indicating monolayer adsorption on a homogeneous surface, with a maximum adsorption capacity (q_m) reflecting the strong affinity of CV toward MCFA. The incorporation of magnetic properties significantly improved the adsorbent’s recovery and reusability. Overall, MCFA demonstrated excellent potential as a cost-effective magnetic adsorbent for the remediation of dye-contaminated wastewater.

Abstract: Rice husk ash (RHA), a waste product of the rice mill, is rich in silica. This study aimed to investigate the use of RHA as a potential adsorbent for the removal of free fatty acid (FFA) from the waste frying oil (WFO). Acid pre-treatment of RH prior to combustion using hydrochloric acid (HCl) was proposed to improve its adsorption performance. The synthesized acid-pretreated RHAs were characterized using Fourier Transformed Infrared (FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). It was found that the aRHAs achieved higher silica purity with low levels of organic impurities as compared to untreated RHA. Additionally, aRHAs possessed porous morphology, especially when treated with higher HCl concentration, as revealed by SEM analysis. EDS analysis confirmed the high silica purity with negligible amount of metal impurities for all the RHAs. For adsorption kinetic models and adsorption isotherms, results showed that the intraparticle diffusion model and the Langmuir isotherm gave the best description to the experimental data with the lowest Chi-square values, reported at 0.02 and 5.46, respectively.

Abstract: Refined Coconut oil (RCNO) is the most used feedstock for biodiesel production, which undergoes alkali-catalyzed transesterification to produce fatty acid alkyl esters due to its low free-fatty acids (FFA) content. This study utilized coconut oil fatty acid distillate (COFAD) as an alternative feedstock to RCNO. As it contains high amounts of FFA, it is pretreated through acid-catalyzed esterification to derive fatty acid methyl esters. The kinetics of the hydrochloric acid catalyzed esterification was investigated with the conditions of 10:1 methanol-to-COFAD molar ratio, 5wt% acid catalyst loading (0.4729N with respect to reaction mixture), reaction temperatures at 45°C, 55°C and 65°C, and 2 hours reaction time. It was found that temperature had a positive effect on the reaction. The highest FFA conversion was observed when the reaction temperature was set to 65°C, where it reached 87%, and the activation energy of the reaction was 29690.96 J^.mol^-1. The highest conversion predicted by the kinetic model is approximately equal to 89%. A good fit of the experimental and calculated data was observed with r² > 0.96. Moreover, the spontaneity of the reaction, as well as the effect of water on the reaction, were identified through the determination of thermodynamic parameters. The esterification reaction was found to be spontaneous only at high temperatures.

Abstract: A new degreasing pretreatment technology for quick-drying towels has been developed to solve the environmental pollution caused by a large amount of waste gas during the degreasing process. The optimal deoiling rate of oil extracted from the microfiber surface in supercritical CO₂ fluid is 95.45% when the temperature is 100°C, the pressure is 14 MPa, the time is 60 min, and the CO₂ flow rate is 30 g/min. The implications of various treatment temperatures and times on the effectiveness of oil agent removal are addressed.

Abstract: Experiments were carried out in which the luminescence of color centers in lithium fluoride crystals was excited by two different femtosecond lasers with significantly different energies, durations and pulse repetition rates. It was established that in all experiments the main center, the luminescence of which was excited nonlinearly, was the F₃⁺ color center. Unusual experimental data were obtained; a laser with low pulse energy (4 nJ) excited triplet luminescence of these centers (570 nm) but did not excite singlet luminescence (540 nm). Another laser with a higher pulse energy (0.3 mJ), on the other hand, excited singlet luminescence and did not excite triplet luminescence. A proposed diagram of energy levels and quantum transitions is presented, explaining the possible mechanisms of nonlinear excitation of luminescence in these experiments.

Abstract: Inadequate handling and disposal of contaminated industrial waste significantly contribute to environmental pollution. The presence of pollutants, including dyes, in wastewater necessitates the development of innovative remediation techniques. Metal oxide-catalyzed photodegradation capitalizes on the capacity of a dye to absorb light energy, offering a rapid method to break down the dye into less harmful, colorless byproducts. In this work, bimetallic copper-iron oxides with various copper to iron were synthesized for the photodegradation of fuchsine. The photocatalysts were prepared through oxalate precipitation followed by thermal decomposition. Structural analysis revealed a MOF-like structure of the bimetallic oxalate precursors. Thermal decomposition of the oxalates yielded photocatalytic bimetallic copper-iron oxides. Photodegradation studies demonstrated that the addition of copper-iron oxides accelerated the degradation of fuchsine and a higher concentration of CuO enhances the performance of the photocatalyst. Notably, the copper-iron oxide with a 1:1 (CuFe) ratio proved to be the most effective catalyst for the photodegradation of fuchsine. Furthermore, the photodegradation of fuchsine conforms to a pseudo-first order model and exhibits characteristics of a first-order reaction. Our findings emphasize that simple and high-efficiency bimetallic oxide catalysts can be used for water decontamination applications.

Abstract: The aim of the study is to research of the adsorption properties of heavy metal ions Pb²⁺, Cd²⁺ and Ni²⁺ from industrial wastewater. For the adsorption of heavy metal ions, natural clinoptilolite was used, which belongs to the Ai-Dag deposit of the Tovuz-Kazakh region of Azerbaijan. Isotherms and kinetic curves of adsorption of heavy metal ions Pb²⁺, Cd²⁺ and Ni²⁺ were determined. The dependence of the adsorption of heavy metal ions on the pH value is also shown. It was revealed that the separation process proceeds more intensively at pH values ​​of 5-6. It has been established that the maximum adsorption capacity of the clinoptilolite adsorbent for adsorption of Pb²⁺, Cd ²⁺ and Ni²⁺ ions is 7.5, 6.7 and 5.9 mmol/g, respectively.

Abstract: Arsenic in the water bodies being a serious menace for human and living organisms. To tackle this arsenic contaminant, a series experiments were conducted on biosorption of arsenic using isolated from soil and water sample of Taptapani Hotspring of Odisha, India. Out of the various collected microorganisms three isolates viz. Exiguobacterium sp.(SSB11), Alcaligenesfaecalis DZ2(SSB17) and Lysinibacillussphaericus SI-3(SSB58) possess better affinity towards heavy metals. By exploring this, the consortium of these microorganisms was chosen for bioremediation of As(III) from waste water. As revealed from experiments, the maximum adsorption capacity of the consortium isolates were observed to be 51 g/g. Further, the biosorption kinetics were tested with two robust isotherms viz. Freundlich and Langmuir, thereby revealing better agreement with the Freundlich isotherm.

Abstract: The purpose of this study is to study the kinetics of kaffir lime peel essential oil extraction using microwave assisted hydrodistillation. Extraction was carried out at various powers and the ratios of material to solvent for 1 hour. Soxhlet extraction using n-hexane solvent was also carried out to determine the yield of essential oil. The extraction kinetics was investigated using a mass transfer-controlled approach and expressed by the 1st and 2nd order of reaction rate. The Soxhlet extraction results indicated that the yield of kaffir lime peel essential oil was 5.65% w/w. The higher the microwave power being applied (180, 300, 450, and 600 Watt), the higher the essential oil yielded (2.2; 2.8; 3; and 3.8% w/w), respectively, but at 800 Watt, the yield decreased (3.2% w/w). The smaller the ratio of material to solvent, which means more diluted, the lower the yield of oil were, namely from 4.56; 3.9; and 3.8% w/w, at ratios of material to solvent 1:3, 1:3.5, and 1:4 w/v. Different results were obtained at a ratio of 1:3 (4.56% w/w) which produced a yield greater than the ratio of 1:1.25 (2.88% w/w). Therefore, the optimum conditions for extracting kaffir lime peel essential oil were at 600 Watt and a ratio of material to solvent 1:3 w/w for 56 minutes with a yield of 4.58% and a density of 0.86 g/cm³. The kinetics of the 2nd order of homogeneous model better represented results of the experiments with extraction rate constants at 180, 300, 450, 600, and 800 Watt of 14.89; 14.95; 15.53; 21.32; and 19.85 L.g^-1.min^-1. While the extraction rate constants at the material to solvent ratio of 1:2.5; 1:3; 1:3.5; and 1:4 w/v of 17.38; 19.80; 22.09; and 32.31 L.g^-1.min^-1. The extraction capacity was also affected by the power and the ratio of material to solvent, the extraction capacity were 0.0095; 0.0100; 0.0104; 0.0125; and 0.0106 g.L^-1, at 180, 300, 450, 600, and 800 Watt respectively, and 0.0094; 0.0134; 0.0134; and 0.0118 g.L^-1, at material to solvent ratio of 1:2.5; 1:3; 1:3,5; and 1:4 w/v respectively.

Abstract: The kinetic and isotherm study on the adsorption of crystal violet (CV) on coal fly ash (CFA) has been studied. Before being used as an adsorbent, CFA was characterized with AAS, XRF, FT-IR, and XRD to determine the mineral components in CFA. The adsorption study of crystal violet in water with CFA includes the effects of solution pH, mass adsorbent, crystal violet concentration, and contact time on the adsorption process. The pseudo-second-order kinetic model best expressed the crystal violet adsorption behavior on CFA with the rate constant (k) of 1.24×10^-1 g mg^-1 min^-1. The Langmuir isotherm model was found to be the best model to describe the adsorption, with a maximum adsorption capacity of 10.14 mg g^-1 at room temperature. Based on the value of adsorption energy as well as the best isotherm model, the adsorption of CV on CFA forms a monolayer and can be classified as chemisorption.