Second-order Kinetic Equation Research Articles

Nitrate removal from aqueous solution using fuller’s earth and modified fuller’s earth

ABSTRACT Water, a vital resource for ecosystems and human populations, is facing increasing nitrate contamination due to agricultural runoff, industrial discharge and improper waste disposal. The present study focuses on the efficacy of nitrate removal through adsorption using fuller’s earth (FE) and modified fuller’s earth (acid-treated) (MFE) as adsorbents. The impact of initial pH (2.0–7.0), contact time (5–240 min), adsorbent dosage (1–30 g/L), initial nitrate concentration (50–250 mg/L) and temperature (30–50°C) on nitrate removal using fuller’s earth were studied. The maximum nitrate removal was observed at pH 2.0, and equilibrium was reached in 120 min at 30℃. The Freundlich isotherm best fit the equilibrium data. The maximum nitrate uptake of fuller’s earth and modified fuller’s earth were 84.75 mg/g and 85.47 mg/g, respectively. Nitrate removal by FE and MFE followed a second-order kinetic equation. Thermodynamic studies showed spontaneity and the exothermic nature of the nitrate adsorption process. ∆H° values were −44.96 and −42.63 kJmol−1 for FE and MFE and ΔS° was −85.11 and −74.52 Jk−1mol−1 for FE and MFE, respectively. FE, known for its exceptional adsorption capacity owing to its porous structure and high ion-exchange capacity, has demonstrated a remarkable affinity for nitrate ions in batch studies.

Adsorption of heavy metal ions by carbon-based adsorbent using magnetic nitrogen-doped carbon and graphene oxide

ABSTRACT The adsorption of weighty metal particles from contaminated water sources has garnered significant attention due to its critical role in environmental remediation and ensuring safe drinking water. Heavy metal ions can be removed from water using conventional adsorbents such as activated zeolites; however, these materials have low absorption and slow kinetics. To solve these issues, carbon-based adsorbents that exhibit easy synthesis, high porosity, design ability, and stability have been proposed. In this review, a carbon-based adsorbent, named M-NC, and graphene oxide were created for the particular evacuation of weighty metal particles. To increase the potential for Heavy Metals (HM) immobilization, sulfide-modified biochar was created via a process called synchronous carbon layer epitome. A hypothetical physicochemical and thermodynamic examination of the adsorption of weighty metals Zn2+, Cd2+, Ni2+, Ag2+, Pb2+ and Cu2+ on carbon-based adsorbents was done with factual material science fundaments. The biochar with large surface areas is utilized to eliminate weighty metal particles, quite possibly the most significant heavy metal pollutants, from aqueous solutions. The limit of the adsorbent for eliminating weighty metal ions was concentrated on utilizing Langmuir adsorption isotherm under ultrasound-helped conditions. The Mesoporous Silica Nanoparticles (MNCs) can be applied to the Langmuir model and pseudo-second-order kinetics. It is possible to use the Langmuir and second-order kinetic equations to accurately explain the adsorption method. Thermodynamic limitations were also envisioned because sorption is exothermic when it happens spontaneously. A homogeneous measurable physical science adsorption typically was utilized to describe and analyze the experimental heavy metal removal isotherms at 30°C and pH5 utilizing adsorbents produced by pyrolysis of biomasses (broccoli stalks). The experimental results were investigated in terms of Langmuir and pseudo-2nd-order kinetic equations, Freundlich and isotherm models. The outcome of pH, initial heavy metal ion concentration, contact time, and adsorbent dosage regarding the adsorption capacity and removal efficiency of Pb2+ and Cd2+ on the hydrogel was examined. This study contributes to the advancement of information in the ground of environmentally friendly heavy metal removal techniques, specifically focusing on the usage of biomass-based adsorbents. These findings have the potential to address the need for effective solutions in water purification and environmental cleanup efforts.

Evaluation of Decay Kinetics of Black Elderberry Antioxidants from Fruits and Flowers.

The health-promoting properties of black elderberry are related to its high content of polyphenols (natural antioxidants), which eliminate free radicals and prevent the formation of oxidative stress responsible for many diseases. The aim of this work was to determine, the anti-radical effect of Sambucus nigra infusions based on the reaction with 2,2-diphenyl-1-picrylhydrazyl (DPPH) and galvinoxyl (Glv) radicals and to determine the function describing the disappearance curves of these radicals. The antioxidant properties of infusions obtained from the flowers and fruits of this plant were tested using the modified Brand-Williams method using DPPH and Glv radicals. Higher antioxidant activity towards both the DPPH and Glv radicals was found in flowers compared to fruits. In addition, it was found that the process of quenching radicals in the reaction with Sambucus nigra infusions proceeds in accordance with the assumptions of second-order reaction kinetics. The infusion obtained from flowers quenched radicals faster than fruit infusions. The applied second-order kinetics equation may enable estimation of antioxidants levels in natural sources of radicals.

Factors, Mechanisms, and Kinetics of Spontaneous Emulsification for Heavy Oil-in-Water Emulsions.

In challenging reservoirs where thermal recovery falls short, cold or chemical oil recovery methods are crucial. Spontaneous emulsification (SE), triggered by gentle disturbance, significantly enhances oil recovery. In elucidating SE mechanisms and kinetics, SE processes via direct contact between oil and aqueous phases without stirring were conducted. The effects of temperature, emulsifier concentration, pH, NaCl concentration, and the oil-to-water ratio on SE were investigated through droplet size analysis and turbidity measurements. Furthermore, the emulsification mechanism and derived emulsification kinetics based on turbidity data were obtained. The results underscore the feasibility of SE for oil-water systems, reducing viscous and capillary resistances without agitation. The emulsified oil mass increased with the temperature, pH, and aqueous-to-oil phase volume ratio while decreasing with the NaCl concentration. In this study, for GD-2 crude oil, the optimal emulsified oil amount occurred at a betaine surfactant (BetS-2) emulsifier concentration of 0.45%. Microscopic photo analysis indicated narrow particle size distributions and small droplets, which remained stable over time under various experimental conditions. A combined SE mechanism involving ultralow interfacial tension, interfacial turbulence due to Marangoni effects, and "diffusion and stranding" due to in situ emulsifier hydrophilicity, was speculated. Additionally, an analogous second-order kinetic equation for SE was proposed, indicating exceptional correlation with calculated and experimentally measured values. This study offers theoretical insight for enhancing oil recovery in chemical and cold production of heavy oil in oilfields.

Study on the adsorption of Zn(II) and Cu(II) in acid mine drainage by fly ash loaded nano-FeS

Aiming at the acid mine drainage (AMD) in zinc, copper and other heavy metals treatment difficulties, severe pollution of soil and water environment and other problems. Through the ultrasonic precipitation method, this study prepared fly ash-loaded nano-FeS composites (nFeS-F). The effects of nFeS-F dosage, pH, stirring rate, reaction time and initial concentration of the solution on the adsorption of Zn(II) and Cu(II) were investigated. The data were fitted by Lagergren first and second-order kinetic equations, Internal diffusion equation, Langmuir and Freundlich isotherm models, and combined with SEM, TEM, FTIR, TGA, and XPS assays to reveal the mechanism of nFeS-F adsorption of Zn(II) and Cu(II). The results demonstrated that: The removal of Zn(II) and Cu(II) by nFeS-F could reach 83.36% and 70.40%, respectively (The dosage was 8 g/L, pH was 4, time was 150 min, and concentration was 100 mg/L). The adsorption process, mainly chemical adsorption, conforms to the Lagergren second-order kinetic equation (R2 = 0.9952 and 0.9932). The adsorption isotherms have a higher fitting degree with the Langmuir model (R2 = 0.9964 and 0.9966), and the adsorption is a monolayer adsorption process. This study can provide a reference for treating heavy metals in acid mine drainage and resource utilization of fly ash.

Removal and prediction of chemicals in anaerobic–anoxic–aerobic wastewater treatment system: Case study on organophosphates

Distribution and removal of chemicals in wastewater treatment plants (WWTPs) have mainly relied on mathematical models. Existing exposure assessment models such as SimpleTreat, STPWIN are based on conventional activated sludge processes. There is an urgent need to develop an A2/O-based WWTPs exposure assessment model. Organophosphates (OPEs) have different physical and chemical properties and potential environmental risks. The fate and biodegradation kinetics of three types of OPEs, including alkyl OPEs, chlorinated OPEs and triphenyl ester OPEs, were studied in a laboratory-scale anaerobic/anoxic/aerobic (A2/O) sewage treatment system and batch reactors. The three types of OPEs had different anaerobic, anoxic, and aerobic removal characteristics. A compensation mechanism was found between anaerobic and anoxic/aerobic removal. When the hydraulic retention time decreased from 82 to 20.5 h, the removal efficiencies in the anaerobic unit decreased, while those in the anoxic unit increased; as a result, the total removal efficiencies remained high (>80 %) for all OPEs except triphenyl phosphate (65.5%–75.1 %). The concept of effective sludge concentration (MLSSeff) was proposed to illustrate the compensation mechanism and calibrate the second-order kinetic equation for predicting pollutant removal in the A2/O system: MLSSeff = ken × MLSS, where ken is a constant related to the influent total organic carbon content (TOC). The influent TOC contents of the anoxic and aerobic units affected the value of MLSSeff and OPEs removal. The results are of great significance for assessing OPEs exposure and predicting exposure to emerging micropollutants in sewage treatment systems.

Three-Dimensional Electrode-Enhanced Ozone Catalytic Oxidation for Thiamethoxam Wastewater Treatment: Performance, Kinetics, and Pathway

Thiamethoxam is a second-generation neonicotinoid pesticide that is used worldwide. In this study, a three-dimensional electrode-enhanced ozone catalytic oxidation system (3DE-GAC-O3) was constructed to pretreat thiamethoxam wastewater, with granular active carbon as the particle electrode. The effects of catalytic oxidation time, current density, ozone concentration, initial thiamethoxam concentration, pH, and particle electrode dosage on thiamethoxam degradation were investigated. A response surface method based on the Box–Behnken design was employed to optimize the 3DE-GAC-O3 process. The results revealed that the 3DE-GAC-O3 system exhibited higher efficiency compared with the 3D electrode method, ozone catalytic oxidation, or 2DE-O3. The optimal operating conditions included a particle electrode dosage, ozone concentration, current density, solution pH, catalytic oxidation time, and initial thiamethoxam concentration of 18 g/dm3, 12 g/h, 25 A/m2, 7, 300 min, and 500 mg/dm3, respectively. The corresponding chemical oxygen demand removal rate reached 93.86 ± 0.95%. Thiamethoxam degradation followed a second-order reaction kinetics equation, and the rate constant decreased with increasing the initial thiamethoxam concentration. Free-radical quenching experiments indicated that both O2∙− and ∙OH were present within the 3DE-GAC-O3 system, with ∙OH being the predominant species. A GC-MS analysis revealed the formation of several intermediate products, which were characterized based on the mass fragmentation pattern. Additionally, a probable degradation pathway for thiamethoxam was proposed. Therefore, 3DE-GAC-O3 is an efficient method for the pretreatment of thiamethoxam wastewater.

Dye adsorption onto iron oxide prepared by green method mediated by leaf extract of Falcaria vulgaris

ABSTRACT Iron oxide nanoparticles were green synthesised by Falcaria vulgaris extract. Characterisation of samples was carried out by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). Investigating factors, such as pH, adsorbent dosage, temperature, contact time and the dose effect of the initial concentration of methylene blue dye, was done on adsorption of methylene blue. The synthesised nanoparticles exhibited a relatively spherical and irregular surface, with a size of about 35 nm, a haematite crystal phase and a saturation magnetisation of 8.3 emu/g. The highest adsorption of methylene blue (76%) was achieved at a pH value of 6, with an optimal adsorbent quantity of 0.004 g/L and a starting concentration of 80 mg/L. The adsorption behaviour of synthesised iron oxide nanoparticles follows from Langmuir isotherm and has a maximum adsorption capacity of 49.169 mg/g. The kinetics of methylene blue dye removal using iron oxide nanoparticles followed a second-order kinetic equation. The adsorption activity of iron oxide nanoparticles showed very little change even after two regeneration cycles. Therefore, the obtained adsorbent regained its adsorption capacity with the help of the photo-Fenton process and is reusable again.

Competitive adsorption of copper and zinc ions by Tetradesmus obliquus under autotrophic and mixotrophic cultivation

The competitive adsorption mechanism of Tetradesmus obliquus on copper and zinc ions was explored under varied cultivation conditions. Removal efficiency of Tetradesmus obliquus for these ions was evaluated during autotrophic and mixotrophic cultivation. The results revealed that Tetradesmus obliquus demonstrated achieved removal efficiencies of 74.30 %, 86.48 %, 84.55 %, and 65.33 % for 16 mg/L of Zn2+, Cu2+, and a mixture of Cu2+ and Zn2+, respectively, under autotrophic conditions. Conversely, under mixotrophic conditions, Tetradesmus obliquus demonstrated improved removal efficiencies of 86.90 %, 92.31 %, 92.30 %, and 71.94 % for Zn2+, Cu2+, and a Cu-Zn mixture, along with adsorption capacities of 38.57 mg/g, 43.86 mg/g, 23.15 mg/g, and 15.24 mg/g, respectively. This represents an increase of 46.65 %, 31.16 %, 29.47 %, and 43.50 % compared to the autotrophic group, respectively. The second-order kinetic equation and Langmuir isotherm model, as proposed, successfully fitted the experimental data for kinetics and isotherms of Zn2+ and Cu2+ in the monometallic system. The maximum adsorption capacities were determined to be 43.22 mg/g and 69.41 mg/g, respectively, under mixotrophic cultivation conditions. The Extended Langmuir isotherm model best fit all experimental data in the mixed system. The presence of Cu2+ markedly reduced Zn2+ adsorption, whereas the presence of Zn2+ had no effect on Cu2+ adsorption. The 3D fluorescence results further confirmed that glucose addition stimulates algal cells to produce additional extracellular polymers, consequently enhancing metal adsorption by microalgae. These research findings confirm that culturing Tetradesmus obliquus in a mixed environment enhances heavy metal removal during water treatment, which is of significant importance for environmental remediation and sustainable water purification.

Sulu Çözeltide Tetrasiklin Giderimi için Fındık ve Antep Fıstığı Kabuklarının Eş-karbonizasyonundan Elde Edilen Yeni Hidrokömürün Kullanımı

In present work, the use of a new hydrochar (HSPSHC) produced by the combined hydrothermal carbonization (co-HTC) of hazelnut and pistachio shells (HS and PS) as a sorbent material in tetracycline (TC) antibiotic removal from water was investigated. It was obtained from hydrothermal carbonization of HSPSHC, hazelnut and pistachio shells by mixing 1:1 by mass at 220 oC for 6 h. Mass yield, energy density and higher heating value parameters were calculated for HSPSHC, and the surface chemistry was characterised using Fourier transform infrared spectroscopy (FTIR). TC adsorption on HSPSHC was carried out by kinetic and isotherm studies using batch method. The experimental kinetic results were qualified in pseudo first-order (PFO) and second-order (PSO) kinetic equations and it was observed that the adsorption complied with the PSO kinetics. The experimentally obtained results were applied to Langmuir and Freundlich model equations and isotherm modeling was performed. The adsorption isotherm of TC on the prepared hydrochar was well fitted by the Langmuir equation, which yielded a maximum monolayer adsorption capacity of TC of qm: 137.06 mg/g at 323 K and pH 4.0 on the HSPSHC hydrochar. In addition, thermodynamic studies revealed that the adsorption of TC by HSPSHC is spontaneous and is an endothermic process.

TO ISSUE INCREASING THE EFFICIENCY OF THE MASS TRANSFER PROCESS IN AGITATORS

This study investigates the impact of impeller design on the rate of esterification reaction in a batch reactor. Different impeller designs were tested and compared, including Backswept impeller, C-shaped, Double Blade impeller, and Pitched impeller. The results showed that the choice of impeller design has a significant effect on the rate of esterification reaction, with the Backswept impeller proving to be the most effective. In this work, it is aimed to investigate the esterification of acetic acid and methanol in a batch stirred reactor for the synthesis of methyl acetate. The temperature range of 303.15 K is examined, with sulphuric acid used as the homogeneous catalyst in varying concentrations of 0.0633 mol·L1 to 0.3268 mol·L-1. The feed molar ratio of acetic acid to methanol also varied from 1:1 to 1:4 to observe its influence on the reaction rate. The research delves into the effects of temperature, catalyst concentration, and reactant concentration on the reaction rate. The experimental data is correlated using a second-order kinetic rate equation, and the forward and backward reaction rate constants and activation energies are determined from the Arrhenius plot. The developed kinetic model is compared with previous models in literature. In order to find the most effective impeller for esterification reaction, diameter of impellers was accepted same in the constant volume and dimension of batch reactor. The obtained kinetic equation proves useful for the simulation of a reactive distillation column for the synthesis of methyl acetate. Keywords: the batch reactor, impeller, esterification, effectivity, mass transfer, mixing, mechanical mixers, Logarithmic Shear Rate, Eddy Diffusivity.

The Rainwater Interception Process and Capacity of Urban Tree Organs in Shanghai

The process of rainwater interception by tree organs is crucial in mitigating the impact of intense rainfall on urban drainage systems, particularly in the context of climate change. For this study, we selected ten commonly found tree species in Shanghai, and the main parts of trees, including their leaves, branches, and bark, were collected to analyze their ability to intercept rainwater. The optimized Artificial Rainfall Simulation System (ARSS) was applied to simulate rainfall. The time-changing process of rainwater interception in three organs was measured during a 180 min rainfall event under four different rainfall intensities (4, 8, 12, and 16 mm/h, respectively). Process models of rainwater interception in different organs were fitted with adsorption kinetic equations. The rainwater interception process of tree organs complied with the quasi second-order adsorption kinetic equation. The rainwater interception capacity values of the leaves, branches, and bark of the ten urban tree species ranged from 0.05 to 0.34 mm, 0.13 to 0.24 mm, and 0.29 to 1.22 mm, respectively. The rainwater interception capacity values of the three organs significantly differ (p < 0.05). The results of this study reveal that bark exhibits the greatest rainwater interception ability. Coniferous tree species have a greater ability to intercept rainwater than broad-leaved tree species. There are also differences in the rainwater interception ability of trees in urban and natural areas.

Biosynthesis of iron oxide nanoparticles at different temperatures and its application for the removal of Zinc by plant mediated nanoparticle, as an eco-friendly nanoadsorbent

Surface and underground water sources are threatened by various pollutants every day. Due to the fact that heavy metals do not disappear, their presence in the environment is very dangerous. Therefore, in this study, iron oxide nanoparticles were synthesized using Aloe vera extract and their application for Zinc removal from aqueous solution was studied. Nanoparticles were synthesized in different temperature conditions of 25 °C and 90 °C. The synthesized nanoparticle characteristics were identified using SEM, EDX, XRD, BET surface area, FTIR and UV–visible Spectroscopy. The SEM images indicated that the iron oxide nanoparticles synthesized at 25 °C and 90 °C had spherical morphology with average particle diameter 62.96 nm and 65.34 nm and based on BET results with a specific surface area of 37.450 and 42.520 m2 g−1, respectively. Adsorption of Zn(ΙΙ) in aqueous solution on the surface of synthesized nanoparticles was investigated and the highest adsorption efficiency was obtained at pH = 7, T = 25 °C, adsorbent concentration = 0.3 g/L, contact time = 90 min, adsorbed concentration = 10 mg/L. The adsorption fitted the pseudo second-order kinetic rate equation well, which confirmed that adsorption was via chemisorption. Freundlich model compared to Langmuir model can better describe the adsorption behavior of Zinc with iron oxide nanoparticles. Nanoparticles synthesized at 90 °C had a more uniform structure and higher absorption capacity. The absorption efficiency of 99 % was observed for nanoparticles synthesized.

Reaction mechanism, degradation pathway and toxicity assessment of NH4+ enhanced potassium ferrate removal of levofloxacin

Considering that ammonium ion (NH4+) was widely distributed in natural water and many sewage, it was of great practical significance to study NH4+ enhanced potassium ferrate (Fe(VI)) to rapid removal of levofloxacin (LEV) from water. In this experiment, firstly, the reaction kinetic of NH4+ enhanced Fe(VI) removal of LEV was studied, and the results showed that the enhanced removal reaction conformed to the second-order kinetic equation. When pH ≤ 9, the second-order rate constant kapp was linearly related to NH4+ dosage, but when pH= 10, the above linear relationship was broken, and the slope of the fitting line would change toward a smaller trend. Subsequently, tert-butanol (TBA) and Methyl phenyl sulfoxide (PMSO) were used as probes for·OH and high-valent iron-based intermediate (Fe(V)/Fe(IV)) respectively, which further revealed the reaction mechanism that NH4+ enhanced Fe(VI) to remove LEV as follows: NH4+ could promote Fe(VI) to produce a large amount of Fe(V)/Fe(IV), thus accelerating the degradation of LEV. In addition, 10 degradation intermediates of LEV were identified by quadrupole time-of-flight tandem ultra-performance liquid chromatography mass spectrometer (Q-TOF LC-MS), and then combined with density functional theory (DFT) calculation, two possible degradation pathways were inferred. Through the luminescence inhibition experiment of Vibrio fischeri and the toxicity evaluation of ECOSAR, it could be concluded that in the process of NH4+ enhancing Fe(VI) to remove LEV, the toxicity of the solution showed a trend of increasing first and then decreasing, and its toxicity was effectively improved and reduced after full oxidation. Finally, the experiments in actual water showed that it was feasible to use NH4+ in actual water to enhance Fe(VI) for rapid removal of LEV.

Solvent-free microwave extraction of essential oil and hydrosol from fresh leaves of Cinnamomum burmannii (Nees et T. Nees) Blume after screw extrusion treatment and evaluation of pancreatic lipase inhibitory activities in vitro compared to its main components

One of the most significant sources of commercial camphor oil is the essential oil of Cinnamomum burmannii (Nees et T. Nees) Blume leaves, which has been manufactured using a variety of distillation techniques, including hydrodistillation and microwave-assisted hydrodistillation. In this study, we employed solvent-free microwave extraction (SFME) to recover hydrosol and essential oil from fresh C. burmannii leaves that had undergone screw extrusion. An optimum yield of 12.35 ± 0.62 mL/kg DW of essential oil was obtained by optimizing the major SFME contributing parameters using a face-centered central composite design (FCCCD). By using SFME, the influence of microwave irradiation power on the yield and quality of the essential oil of fresh leaves of C. burmannii was examined. With the aid of first- and second-order kinetic equations, SFME was contrasted with hydrodistillation and dry distillation. A total of 32 components were detected in the essential oil, and 22 components were detected in the hydrosol obtained by SFME under the optimized conditions. The main components of the essential oil were 1,8-cineole (21.67%), borneol (17.37%) and α-terpineol (7.45%), in descending order, and the main components of the hydrosol were trans-2-hydroxycinnamic acid (21.45%), borneol (22.07%), 1,8-cineole (13.65%) and α-terpineol (11.93%). 1,8-Cineole and borneol were the two components with the highest influence on hierarchical clustering, according to principal component analysis and heatmap analysis. Moreover, box-whisker plots were used to determine and compare the inhibitory activities of the essential oil and its three primary constituents against pancreatic lipase. The outcomes demonstrated that 1,8-cineole played a critical role in the essential oil's ability to inhibit pancreatic lipase, and they also demonstrated a positive correlation between the concentration and the amount of inhibition activity.

Transport model simulation prediction and environmental risk assessment of pyrethroid insecticides in urban artificial lakes caused by rainfall: A case study of Cloud Mountain Park in subhumid climate zone

Pyrethroid insecticides are among urban parks' most widely used and harmful insecticides. The advanced prediction method is the key to studying the pollution and diffusion risk of plant conservation insecticides in parks. A two-dimensional advection-dispersion model was established for the North Lake of Cloud Mountain Park in the subhumid area of Hebei Province. The temporal and spatial distribution of lambda-cyhalothrin pollution required by plant growth in artificial lakes under different rainfall intensities and the time of water renewal after rainfall was simulated and predicted. According to the model efficiency (E: 0.98), mean absolute error (MAE: 0.016–0.064 cm), and root mean square error (RMSE: 0.014–0.041 cm), the prediction results showed that the model fits well. The results showed that the concentration of lambda-cyhalothrin in the artificial lake was positively correlated with the increase in rainfall intensity. Under the three scenarios of moderate rain, heavy rain, and rainstorm, the variation of total pollutants into the lake over time conformed to the first-order dynamic equation (R2＞0.97), and the cumulative rates were 0.013 min−1, 0.019 min−1 and 0.022 min−1, respectively. Under light rain, the accumulation rate of lambda-cyhalothrin showed a double-linear relationship, which was in accordance with the second-order kinetic equation (R2＞0.97). The rapid accumulation rate of early-stage rainfall was 0.0024 min−1, and the slow accumulation rate of late-stage rainfall was 0.0019 min−1. The human health risk assessment predicted by the simulation was lower than the hazard value (Rtgn(a-1): 9.65 E−11–1.12 E−10 a-1). However, the potential risk value to aquatic species was higher (RQ: 0.33–23.05). In addition, the increase in rainfall intensity has no significant effect on the acceleration of water renewal time. The two-dimensional dispersion model of pollutants driven by water dynamics provided relevant examples for evaluating the impact of runoff on pesticide scour in parks and supplied scientific support for improving the management of artificial lakes in urban parks.

Efficient synthesis of ethylene carbonate via transesterification of ethylene glycol with dimethyl carbonate over Mg3Al1−xCexO composite oxide

A series of Mg3Al1−xCexO composite oxide catalysts were prepared by co-precipitation for the transesterification of ethylene glycol to ethylene carbonate. The characterization results revealed that the addition of cerium changed the acid-base properties of the catalyst and that the strong basic sites on the catalyst surface played an important role in the reaction. The Mg3Al0.9Ce0.1O catalyst showed the highest catalytic activity (ethylene carbonate yield 98.1%). Compared with pure Mg-Al oxide, the appropriate addition of Ce was conducive to improving the surface basicity and adsorbed oxygen content of the catalyst. Additionally, the reaction process of the formation of ethylene glycol hydroxyl group with the alkoxy anion formed by the catalyst attacking the carbonyl carbon of nucleophilic dimethyl carbonate to form an adsorption intermediate (HEMC) on the catalyst surface for further intramolecular rearrangement to form ethylene carbonate was confirmed by operando infrared spectroscopy. The reaction kinetics shows that the reaction conforms to the second-order kinetic equation, and the activation energy is 53.71 kJ·mol−1. Catalytic stability in a fixed-bed reactor was studied. After a long cycle of use (150 h), the yield of ethylene carbonate was stabilized at about 89.0%.

Direction of changes in porous structure and adsorption capacity during topochemical oxidation of coal activated by alkali

The purpose of the work is to evaluate the influence of topochemical oxidation (H2O2, HNO3) of carbon prepared by alkali activation of coal on porosity and ability to adsorb 4-chlorophenol (CPh), Pb(II) cations and iodine. Carbons were oxidized at the reactant/carbon ratio of 1:1 (mol/mol, 250С, 24 h). Based on nitrogen adsorption-desorption isotherms, the volumes and specific surfaces of ultramicro- (Sumi), supermicro- (Ssmi) and other pores were evaluated. Kinetics and adsorption isotherms (250С) of CPh and Pb(II) were characterized; adsorption capacities of CPh, Pb(II) and I2 were determined. The H2O2-assisted modification was found to significantly increase Sumi (from 615 to 829 m2/g), but decrease Ssmi (from 515 to 494 m2/g). The HNO3-assisted modification slightly increases Sumi (from 615 to 651 m2/g), does not change Ssmi, but forms mesopores. The CPh adsorption is best approximated by the second-order kinetics, and isotherms are well fitted with the use of the Langmuir model. The H2O2 treatment increases the CPh capacity from 314 to 389 mg/g; and the НNO3 modification significantly decreases the CPh capacity (to 189 mg/g). Modifications reduce the iodine capacity by 1.11 times (H2O2) and 2.33 times (HNO3). The Pb(II) absorption was established to describe by the second-order kinetics equation; the adsorption isotherms obey Langmuir (R20.986) and Freundlich (R20.984) models. The Pb(II) capacity slightly increases after H2O2-assisted modification (from 87 to 95 mg/g), but increases sharply (from 87 to 298 mg/g) after HNO3-assisted treatment because of significant increasing OH-acidic groups concentration.

Numerical simulations of the flow of a kerosene gel: Effects of thixotropy and shear-thinning

The ability of a gel to act like a solid-like material at rest and flow like a liquid when sheared can be very useful in propulsion system. Numerical simulation of the flow of gel fuels can be used as a reference to assist experimental studies and applications of these materials. Non-linear rheological effects such as shear thinning, yield stress, thixotropy and viscoelasticity can create difficulties in the formulation and in the numerical investigations. This paper uses a thixotropic shear-thinning constitutive relationship while using a second-order kinetic equation for the structural parameter, where the Carreau–Yasuda model is used for a 5% organic kerosene gel. We study the simple shear flow to verify the accuracy of the numerical method, and the impact of the constitutive parameters on the apparent viscosity as a function of shear rate. To look at the thixotropic flow in more complex flows, we initially study the pipe flow of an organic kerosene gel for different pumping conditions. After performing a parametric study, we find that the thixotropy of the gel strongly affects the shear history, that is, the nonuniform aging distribution. The destruction of the microstructure can be accelerated by adjusting the flow intensity and the model parameters, but it seems that it is difficult to arrive at the equilibrium state within the time scale of the propulsion system; this poses a challenge to the design of the system.

Two-Stage Residual Lifespan Prediction Model for Oil-Paper Insulation Based on Analysis of Furfural and Methanol in Oil

The applicability of existing single aging indicator-based lifespan prediction methods needs further improvement during different aging stages. Considering the aforementioned challenges, this work proposes a two-stage residual lifespan prediction model based on both methanol and furfural. Firstly, the changes in methanol and furfural contents in oil are examined concurrently with the aging duration. The paper insulation's life is divided into different aging stages by using identified two demarcation points according to the indicator's content. By virtue of this, the two-stage residual lifespan model of the insulating paper is obtained by coupling with the second-order aging kinetic equation. Finally, the validity of the proposed model is proved through a comparison to the conventional method of utilizing a single indicator, with a mean absolute percentage error for insulating paper's residual lifespan of 5.6%. In that regard, the research's contribution is to propose an integrated model for predicting the residual lifespan of insulating paper by using methanol and furfural indicators.