Analysis Of Isothermal Data Research Articles

Sulu Çözeltilerden Civa(II) İyonlarının Adsorpsiyonunda Hidroklorik Asit İle Modifiye Edilmiş Kilin Kullanılması

With their natural abundance and minimal processing requirements, clays hold the potential to serve as economical adsorbents for various heavy metals. In this research, the adsorption capacity of hydrochloric acid (HCl) modified clay to adsorb mercury(II) (Hg2+) ions from aqueous solutions was investigated. The parameters affecting the adsorption capacity were determined by studying the initial metal ion concentration, contact time, and temperature effects. For natural clay, an optimal initial concentration of 400 mg/L and a contact time of 50 minutes were identified. Meanwhile, modified clay showed best results with an initial concentration of 400 mg/L and a contact time of 60 minutes for Hg2+ ions. The analysis of isotherm data revealed that the Langmuir isotherm model exhibited the best fit for both materials in Hg2+ ion adsorption. At temperatures of 298 K, 308 K, and 318 K, the adsorption capacity for natural clay and Hg2+ ions were found to be 4.56, 5.01, and 5.08 mg/g, respectively. Meanwhile, the modified clay displayed adsorption capacities of 11.12, 11.37, and 12.30 mg/g for Hg2+ ions at the same temperatures. Additionally, the kinetic analysis determined that the pseudo-second-order kinetic model was the best fit for both materials in Hg2+ ion adsorption. The adsorption experiments investigated the adsorption mechanisms of Hg2+ metal ions on both natural clay and modified clay, with results indicating that the modified clay had a higher adsorption capacity for metal ions compared to the raw clay.

Removal of ammonia and nitrates from contaminated water by using solid waste bio-adsorbents

The presence of pollutants in aqueous solution mainly from hazardous heavy metals and metalloids is creating an environmental and social problem. The ammonia and nitrates are one of the major groundwater contaminants present in the rural areas. A nitrate was regulated in drinking water quality mainly due to excess amounts can cause methemoglobinemia disease. Ammonia in both gaseous and liquid form can be irritating to the eyes, respiratory tract failure and skin due to its alkaline nature. The biological effects of ammonia and nitrates in humans after acute exposures are dose-related depend on their concentration; the amount is taken by the body and duration of exposure. Biosorption is a physiochemical process that occurs naturally in certain biomass which allows it to passively concentrate and bind contaminants onto its cellular structure. It is metabolically passive process not require energy and amount of contaminants in sorbent can remove is dependent on kinetic equilibrium and composition of the sorbents at cellular surface. Every biosorbent had different physical, chemical and biological properties for heavy metals removal by biosorption from the water. The oxygen functional groups are very important characteristics of biosorbents because they measured the surface properties and hence their quality as biosorbents. The analysis of isotherm data by fitting them to different models is important to find a sustainable model that can be used. From the biosorption isotherms describe how the sorbate molecules are distributed between the liquid phase and solid phase when the system reaches equilibrium. The process can be made economical by regenerating and reusing of biosorbent after removing the metals. Various bioreactors can be used in biosorption for the removal of metal ions from large volume of water.

Kinetic and thermodynamic studies on biosorption of Cr(VI) on raw and chemically modified Datura stramonium fruit.

Biosorption of Cr(VI) on sulfuric and phosphoric acid-treated Datura stramonium fruit was investigated in batch mode. The various parameters that influence the biosorption process such as Cr(VI) initial concentration, biosorbent dosage, contact time, temperature, and pH value were optimized. Both linear and non-linear regression analysis of isotherm data suggest that Langmuir isotherm model mimics the behavior of Cr(VI) ion biosorption onto Datura stramonium fruit biosorbent. The maximum Cr(VI) ions adsorption capacity of 138.074mg/g at pH 2 is achieved with phosphoric acid treated Datura stramonium (PDSF). The kinetics of adsorption process is well described by pseudo-second-order model with high R2 and low χ2 value. The estimated activation energy of < 8kJ/mol obtained for both raw and chemically modified adsorbents suggests that the adsorption occurs mainly via physisorption. Besides, thermodynamic results reveal that biosorption of Cr(VI) on both treated and untreated Datura stramonium was endothermic, spontaneous, and randomness in nature.

A Statistical Approach to Determine Optimal Models for IUPAC-Classified Adsorption Isotherms

Adsorption heat transformation (AHT) systems can play a major role in protecting our environment by decreasing the usage of fossil fuels and utilizing natural and alternative working fluids. The adsorption isotherm is the most important feature in characterizing an AHT system. There are eight types of International Union of Pure and Applied Chemistry (IUPAC) classified adsorption isotherms for different “adsorbent-adsorbate” pairs with numerous empirical or semi-empirical mathematical models to fit them. Researchers face difficulties in choosing the best isotherm model to describe their experimental findings as there are several models for a single type of adsorption isotherm. This study presents the optimal models for all eight types of isotherms employing several useful statistical approaches such as average error; confidence interval (CI), information criterion (ICs), and proportion tests using bootstrap sampling. Isotherm data of 13 working pairs (which include all eight types of IUPAC isotherms) for AHT applications are extracted from literature and fitted with appropriate models using two error functions. It was found that modified Brunauer–Emmet–Teller (BET) for Type-I(a) and Type-II; Tóth for Type-I(b); GAB for Type-III; Ng et al. model for Type-IV(a) and Type-IV(b); Sun and Chakraborty model for Type-V; and Yahia et al. model for Type-VI are the most appropriate as they ensure less information loss compared to other models. Moreover; the findings are affirmed using selection probability; overall; and pairwise proportion tests. The present findings are important in the rigorous analysis of isotherm data.

Removal of heavy metal and sulfate ions by cellulose derivative-based biosorbents

A series of environmentally-friendly bagasse pith cellulose-based adsorbents were prepared in an attempt to retain Cu2+ and SO42− from aqueous solutions. The proof of ion adsorption on the biosorbents was identified from Fourier transform infrared spectroscopy and energy-dispersive X-ray spectroscopy-scanning electron microscope. The adsorption capacities were highly dependent on pH and the maximum uptakes of both ions were obtained at pH 5. An increase of solution temperature resulted in decreasing Cu2+ removal but enhancing SO42− adsorption. The kinetic studies showed that the adsorptions of copper and sulfate ions followed the pseudo-second-order kinetics. The analysis of isotherm data indicated that the Langmuir and Freundlich models were in good agreement with the sorptions of Cu2+ and SO42−, respectively. The proportion of carboxylate cellulose and quaternary ammonium-functionalized cellulose in biosorbents influenced on adsorption capacity of the above ions. The adsorption mechanism was mainly governed by ion exchange, complexation and electrostatic association.

NaY zeolite from wheat (Triticum aestivum L.) straw ash used for the adsorption of tetracycline

Converting abundant and renewable wastes to high-value products is important based on economic and environmental viewpoints. In this work, wheat straw ash was used as a precursor for the synthesis of NaY zeolite. The characteristics and effectiveness of NaY as adsorbent for tetracycline (TC) were evaluated. The adsorption behavior of TC–NaY system under different experimental conditions was also illustrated. The Langmuir equation was well applied for the analysis of isotherm data, with maximum equilibrium uptakes of 201.77, 218.51, and 230.69 mg/g at 30 °C, 40 °C, and 50 °C, respectively. Data on TC uptakes versus time followed a pseudo-second order kinetic model. NaY zeolite with a surface area of 657.44 m2/g and pore volume of 0.341 cm3/g could be an efficient adsorbent for the treatment of antibiotic pollutants in wastewater.

Batch adsorption and desorption studies on the removal of lead (II) from aqueous solution using nanochitosan/sodium alginate/microcrystalline cellulose beads

The feasibility of adsorption and desorption behavior of nanochitosan(NCS)/sodium alginate(SA)/microcrystalline cellulose (MC) bead prepared in 2:8:1 ratio for Pb(II) removal has been investigated through batch studies. The proof of adsorption of Pb(II) ions onto NCS/SA/MC beads was identified from FT-IR and EDX-SEM Studies. Studies of the effect of pH, adsorbent dose, metal ion concentration and temperature reveals that the optimum conditions for adsorption was found to be pH:6; adsorbent dose:4g; initial metal concentration: 62.5mg/L and temperature:50°C. Various equilibrium adsorption isotherm models namely Langmuir, Freundlich, Temkin and D-R applied for the analysis of isotherm data indicate that the Freundlich adsorption isotherm model was found to be followed. On the basis of kinetic studies, specific rate constants involved in the processes were calculated and the observed result shows that the pseudo second order kinetics was found to be a better fit. The desorption studies reveals that the recovery of Pb(II) from NCS/SA/MC bead was found to be effective by using 0.1M HCl solution. From the results it was evident that the NCS/SA/MC bead showed better Pb(II) uptake performance and regeneration for further use and hence it was found to be an efficient biosorbent for treating industrial effluent.

A charged metal–organic framework for CO2/CH4 and CO2/N2 separation

A microporous metal–organic framework [InL][(CH3)2NH2]·(H4L=9-(3,5-dicarboxyphenyl)carbazole-3,6-dicarboxylic acid) (1) was hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction and powder X-ray diffraction. The adsorption behavior of 1 has been investigated with respect to CO2, CH4 and N2, and the separation efficiency has been calculated by the Henry’s law analysis of isotherm data. The results indicated that the anionic framework with the inside protonated dimethylamine could enhance its selective adsorption performance for CO2 through strong adsorbent–adsorbate interaction aroused by a strong electrostatic field and pore size effect.

New Insights on the Kinetic Analysis of Isothermal Data: The Independence of the Activation Energy from the Assumed Kinetic Model

Isothermal experiments are widely employed to study the kinetics of solid-state reactions or processes to extract essential kinetic information needed for modeling the processes at an industrial scale. The kinetic analysis of isothermal data requires finding or assuming a kinetic function that can properly fit the evolution of the reaction rate with time, so that the resulting parameters, i.e., the activation energy and pre-exponential factor, can be considered reliable. In the present work, we demonstrate using both simulated and experimental data that the kinetic analysis of a set of isothermal plots obtained at different temperatures, considering a single-step solid-state reaction, necessarily leads to the real activation energy, regardless the mathematical function selected for performing the kinetic analysis. This makes irrelevant the election of the kinetic function used to fit the experimental data and greatly facilitates the estimation of the activation energy for any single process.

Boron Oxide Production Kinetics Using Boric Acid as Raw Material

Boron oxide with a content of 99.93 wt.% from the dehydration of boric acid was synthesized. Conversion of boric acid to boron oxide was completed within 3 days at low temperature range (T < 130 °C) and approximately 30 min at high temperature range (T > 130 °C) for the isothermal dehydration reaction in the temperature range of 80 and 350 °C. Apparent activation energies were 65 and 28 kJ·mol–1 for low and high temperature ranges, respectively. Thermogravimetric analysis (TGA) results showed that the reactions were nearly completed at around 330 °C, and activation energy for the first temperature region was found to be two-thirds of the isothermal value and the same for the second temperature region. Isothermal data analysis revealed that the apparent reaction order value was around 1.0 at low temperature range and decreased to 0.55 with temperature within the high temperature range.

Kinetics of Thermal Decomposition of Iron Carbonate

THE THERMAL decomposition of iron cabonate in air was ……studied by means of DTA-TG, XRD, SEM and Mossbauer measurements. The kinetics of the thermal decomposition process were studied using isothermal and non-isothermal thermogravimetric techniques. The results show that the thermal decomposition proceeds in one step to iron oxide. Kinetic analysis of isothermal data of the decomposition reaction in the light of various solid state reaction models revealed that the reaction is best described by the diffusion models. Kinetic analysis of the dynamic TG curves were discussed with reference to Diefallah’s composite integral method, in comparison with the integral methods due to Coats-Redfern and to Ozawa. The activation parameters were calculated and the results of the isothermal and dynamic integral methods which were compared to each other were discussed.

Kinetic and isotherm studies of the adsorption of Acid Blue 92 using a low-cost non-conventional activated carbon

Abstract Adsorbents prepared from waste plants for the treatment of dyeing effluents have high significance in environmental sustainability. In this research, an attempt is made to analyze the applicability of activated carbon prepared from Euphorbia antiquorum L wood by H 3 PO 4 activation method for the removal of Acid Blue 92 dye. Various kinetic models were used for the analysis of adsorption kinetics and pseudo second-order model fits well for the selected adsorbent–adsorbate system. The moderate rate of dye uptake indicates that the rate-determining step could be physisorption in nature. Langmuir, Freundlich and Dubinin-Raduskevich isotherm models were applied for the analysis of isotherm data. The positive enthalpy of adsorption substantiates that the adsorption process is endothermic in nature.

Gas sorption kinetics by differential closed-loop recycle method: Effect of heat of adsorption

An analytical mathematical model is used to investigate the influence of minute adsorbent temperature changes on the kinetics of sorption of a gaseous adsorbate from mixture with a carrier gas using a differential closed loop recycle method. Isothermal operation may not be achieved even when a very high gas circulation rate is used. Very small changes in the adsorbent temperature during the process can cause substantial departure from isothermal uptake behavior. It is shown that the kinetic process can be assumed to be isothermal only for trace adsorbate concentrations. A criterion for validity of isothermal data analysis is proposed.

Removal of heat of adsorption from adsorbent by forced convection

An analytical mathematical model is used to investigate the effectiveness of forced convection for removal of the heat of adsorption from an adsorbent mass undergoing a differential adsorption process in a flow system. An example of such a process is measurement of gas adsorption kinetics using a differential adsorption bed. Isothermal operation may not be achieved even when a high gas flow rate is used, particularly if the sorption kinetics is relatively fast. Very small changes in the adsorbent temperature can cause significant departure from the isothermal uptake behavior when the heat of adsorption is moderately large. A criterion for validity of isothermal data analysis is given.

Kinetic analysis of the thermal decomposition of pristine and γ-irradiated zinc uranyl acetate

Thermal decomposition of pristine and γ-irradiated zinc uranyl acetate was investigated in air using isothermal and dynamic thermogravimetric techniques. The decomposition proceeded via one major process with the formation of triuranates ZnU3O10 as solid residues. Kinetic analysis of isothermal data, when compared with various solid-state reaction models, showed that the decomposition reaction is best fitted by the phase-boundary model. Kinetic analysis of the dynamic TG curves was discussed with reference to integral methods of modified Coats and Redfern equations. Kinetic and thermodynamic parameters were calculated and evaluated. IR spectroscopy and X-ray powder diffraction techniques were employed to follow the chemical composition of solid residue at different calcination temperatures. The results display that the triuranate ZnU3O10 starts forming by calcination of zinc uranyl acetate at temperatures > 300 °C and undergoes decomposition at higher temperatures (>600 °C) with the formation of U3O8. The results were evaluated regarding the utilization of zinc uranyl acetate as an important source of diuranates and triuranates.

Liquid crystalline thermosets as binder for powder coatings: Thermoanalytical study of the cure characteristics of a carboxylated main chain liquid crystalline oligoester

The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4′-diacetoxybiphenyl and dodecanedioic acid, as a model resin for powder coatings, in presence of triglycidyl isocyanurate (TGIC), as a curing agent, was studied by isothermal differential scanning calorimetry (DSC). The analysis of isothermal data was performed using the model-free isoconversional method. Activation energy as a function of extent of conversion, α, has been calculated by the Friedman technique. It showed an ascending trend from about 133.7 kJ/mol, at α=0.1 to 177.2 kJ/mol, at α=0.4, then it reached approximately a constant value of about 150±5% kJ/mol in the range of 50–90%. The results indicated that the kinetic process does not follow a single-step curing reaction model. To verify the isothermal analysis result, we carried out further, non-isothermal differential scanning calorimetry and depolarizing transmittance measurements on the stoichiometric mixture of LCO/TGIC, at different heating rates. The results of these experiments exhibited that the kinetic process of the investigated system is strongly influenced by curing condition which alters the liquid crystalline state of the sample.

Gamma-radiation effects on the reduction of hematite to iron in the graphite-iron(III) oxide system

The effects of60Co-gamma radiation and of various sample composition on the reduction of hematite to iron in the graphite-iron(III) oxide system in air were studied using isothermal and dynamic TG techniques. Kinetic analysis of isothermal data were performed according to various theoretical models of heterogeneous reactions and the results showed that the three-dimensional phase boundary model gives the best fit of data. Analysis of dynamic TG data were made using Ozawa integral method, Coats-Redfern method and a composite method based on the modified Coats and redfern equation. The activation parameters were calculated and the results of the different methods were compared and discussed. Radiation apparently did not introduce a change in the reaction model or mechanism. However, there is a decrease in activation energy and frequency factor upon irradiation and a decrease in the half-life time of the reaction which is remarkable at the higher temperatures and higher doses.

A simple method for calculating an energy spectrum for defect annealing from a constant heating rate experiment

Abstract A method is presented for deriving the spectrum of activation energies for defect annealing of specimens under linear heating conditions. In analogy with a previously published paper on isothermal data analysis, the basic integral equation is rewritten using a convolution integral, which can be solved using an iterative Fourier analysis. In practical cases, convergence is already reached after a few iterations. The method turns out to be very rapid and efficient; the number of data points processed in the analysis can be made very large. Because the calculated spectrum is the exact solution of the basic integral equation, the energy resolution of the present method is mainly determined by the errors on the experimental data.

Kinetic analysis of thermal decomposition reactions: Part VI. Thermal decomposition of manganese(II) acetate tetrahydrate

The kinetics of the thermal decomposition of manganese(II) acetate tetrahydrate were studied using isothermal and dynamic thermogravimetric techniques. The dehydration of the tetrahydrate proceeds via a two-stage reaction, each stage involving loss of two water molecules, while the thermal decomposition of the anhydrous salt proceeds in one step to MnO. Kinetic analysis of isothermal data of the three decomposition reactions, when compared with the various solid state reaction models, showed that the reactions are best described by the phase boundary and random nucleation models. Kinetic analysis of the dynamic TG curves were discussed with reference to a composite integral method, in comparison with the integral methods due to Coats and Redfern and to Ozawa. The activation parameters were calculated and the results of the isothermal and dynamic integral methods were compared and discussed.

An automated, high precision unit for low-pressure physisorption

A physisorption apparatus with very high sensitivity has been constructed. It is capable of accurately measuring adsorption and desorption isotherms of gases on solids in the pressure range of 10−5–1000 Torr. This is particularly useful for investigating argon sorption on catalysts and catalyst supports, e.g., FCC, reforming and hydroprocessing catalysts; zeolites; and pillared layered materials. The isotherms contain information about micropore and mesopore size distribution, BET surface area, etc. The operation of the unit and the analysis of isotherm data are both fully automated. Details of the equipment and the software are described.