Kinetic and thermodynamic parameters of volatilization of biodiesel from babassu, palm oil and mineral diesel by thermogravimetric analysis (TG)

The boiling point and volatility are important properties for fuels, as it is for quality control of the industry of petroleum diesel and biofuels. In addition, through the volatility is possible to predict properties, such as vapor pressure, density, latent heat, heat of vaporization, viscosity, and surface tension of biodiesel. From thermogravimetry analysis it is possible to find the kinetic parameters (activation energy, pre-exponential factor, and reaction order), of thermally simulated processes, like volatilization. With the kinetic parameters, it is possible to obtain the thermodynamic parameters by mathematical formula. For the kinetic parameters, the minor values of activation energy were found for mineral diesel (E = 49.38 kJ mol^?1), followed by babassu biodiesel (E = 76.37 kJ mol^?1), and palm biodiesel (E = 87.00 kJ mol^?1). Between the two biofuels studied, the babassu biodiesel has the higher minor value of activation energy. The thermodynamics parameters of babassu biodiesel are, ΔS = ?129.12 J mol^?1 K^?1, ΔH = +80.38 kJ mol^?1 and ΔG = +142.74 kJ mol^?1. For palm biodiesel ΔS = ?119.26 J mol^?1 K^?1, ΔH = + 90.53 kJ mol^?1 and ΔG = +141.21 kJ mol^?1, and for diesel ΔS = ?131.3 J mol^?1 K^?1, ΔH = +53.29 kJ mol^?1 and ΔG = +115.13 kJ mol^?1. The kinetic thermal analysis shows that all E, ΔH, and ΔG values are positive and ΔS values are negative, consequently, all thermodynamic parameters indicate non-spontaneous processes of volatilization for all the fuels studied.     

Removal of uranium(VI) from aqueous solutions using nanoporous ZnO prepared with microwave-assisted combustion synthesis

The adsorption of the uranyl ions from aqueous solutions on the nanoporous ZnO powders has been investigated under different experimental conditions. The adsorption of uranyl on nanoporous ZnO powders were examined as a function of the contact times, pH of the solution, concentration of uranium(VI) and temperature. The ability of this material to remove U(VI) from aqueous solution was followed by a series of Langmuir and Freunlinch adsorption isotherms. The adsorption percent and distribution coefficient for nanoporous ZnO powders were 98.65 % ± 1.05 and 7,304 mL g^?1, respectively. The optimum conditions were found as at pH 5.0, contact time 1 h, at 1/5 Zn²⁺/urea ratio, 50 ppm U(VI) concentration and 303 K. The monomolecular adsorption capacity of nanoporous ZnO powders for U(VI) was found to be 1,111 mg g^?1 at 303 K. Using the thermodynamic equilibrium constants obtained at different temperatures, various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, have been calculated. Thermodynamic parameters (ΔH° = 28.1 kJ mol ^?1, ΔS° = 160.30 J mol^?1 K^?1, ΔG° = ?48.54 kJ mol^?1) showed the endothermic and spontaneous of the process. The results suggested that nanoporous ZnO powders was suitable as sorbent material for recovery and adsorption of U(VI) ions from aqueous solutions.     

Polyvinyl alcohol fibers with functional phosphonic acid group: synthesis and adsorption of uranyl (VI) ions in aqueous solutions

PVA functionalized with vinylphosphonic acid was prepared as a new adsorbent for uranyl (VI) adsorption from aqueous solutions. The vinylphosphonic acid was cografted onto PVA fibers by preirradiation grafting technique. The adsorbent were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The adsorbent was observed to possess a fibrous structure and was bonded with phosphonic acid groups successfully. The adsorbent was used for the adsorption of low levels uranyl (VI) ions from aqueous solutions. The influence of analytical parameters including pH, adsorption time, amount of adsorbent, metal ion concentration, and temperature were investigated on the recovery of uranyl (VI) ion in aqueous solution. The maximum adsorption capacity (32.1 mg g^?1) and fast equilibrium time (30 min) were achieved at pH of 4.5 at room temperature. Thermodynamic parameters (ΔH° = 2.695 kJ mol^?1; ΔS° = 31.15 J mol^?1 K^?1; ΔG° = ?6.748 kJ mol^?1) show the adsorption of an exothermic process and spontaneous nature, respectively. The possible coordination mechanism was illustrated. Adsorption and desorption coexist in aqueous solutions and then the system becomes equilibrium.     

Thermal studies and spectral characterization of the chelate of bis-(η5-cyclopentadienyl titanium(IV) with salicylidene-4-methylaniline

A new chelate (η⁵-C₅H₅)₂Ti(SB)₂, whereSB=O, N donor Schiff base salicylidene-4-methylaniline, was synthesized. The course of thermal degradation of the chelate was studied by thermogravimetric (TG) and differential thermal analysis (DTA) under dynamic conditions of temperature. The order of the thermal decomposition reaction and energy of activation was calculated from TG curve while from DTA curve the change in enthalpy was calculated. Evaluation of the kinetic parameters was performed by Coats-Redfern as well as Piloyan-Novikova methods which gaven=1, ΔH=1.114 kJ·mol^?1, ΔE=27.01 kJ·mol^?1, ΔS=?340.12 kJ·mol^?1·K^?1 andn=1, ΔH=1.114 kJ·mol^?1, ΔE=20.01 kJ·mol^?1, ΔS=?342.60 kJ·mol^?1·K^?1, respectively. The chelate was also characterized on the basis of different spectral studies viz. conductance, molecular weight, IR, UV-visible and¹H NMR, which enabled to propose an octahedral structure to the chelate.     

Chromatographic Framework to Determine the Memantine Binding Mechanism on Human Serum Albumin Surface

In this work, the interaction of memantine with human serum albumin (HSA) immobilized on porous silica particles was studied using a biochromatographic approach. The determination of the enthalpy change at different pH values suggested that the protonated group in the memantine–HSA complex exhibits a heat protonation with a magnitude around 65 kJ mol^?1. This value agrees with the protonation of a guanidinium group, and confirmed that an arginine group may become protonated in the memantine–HSA complex formation. The thermodynamic data showed that memantine–HSA binding, for low temperature (<293 K), is dominated by a positive entropy change. This result suggests that dehydration at the binding interface and charge–charge interactions contribute to the memantine–HSA complex formation. Above 293 K, the thermodynamic data ΔH and ΔS became negative due to van der Waals interactions and hydrogen bonding which are engaged at the complex interface. The temperature dependence of the free energy of binding is weak because of the enthalpy–entropy compensation caused by a large heat capacity change, ΔC _p = ? 3.79 kJ mol^?1 K^?1 at pH = 7. These results were used to determine the potential binding site of this drug on HSA.     

Study of the gadolinium sorption on the C100 ion-exchange resin for the development of the antineutrino detector targets

Adsorption of the gadolinium from H₂O and HCl solutions on the ion-exchange resin C100 is investigated. The experiments were carried out by varying the acidity of the liquid phase, the amount of sorbent, and the temperature. The maximal sorption of the ions Gd³⁺ is observed from the solution 0–0.2 M HCl under optimal conditions, the sorption reaches more than 99.5%. Sorption of Gd³⁺ on C100 from H₂O solution occurs most intensively during the first 3 min then for 30 min the system smoothly comes to equilibrium. The maximal sorption capacity of the resin C100 amounted to 1.2 ± 0.1 mmol g^?1. The thermodynamic parameters of sorption: ΔG = ? 24.20 kJ mol^?1, ΔS = ? 90.27 J mol^?1 K^?1, ?H = ? 50.93 kJ mol^?1 were evaluated. It is shown that the sorption of gadolinium on the ion-exchange resin C100 is described by models of kinetically pseudo-first and pseudo-second order. It is established that the Gd³⁺ sorption on the C100 resin is reversible second order chemical reaction.     

Mechanism of Oxidation of Ketorolac by Hexacyanoferrate(III) in Aqueous Alkali: A Thermodynamics and Kinetics Study

The kinetics of the oxidation of ketorolac by hexacyanoferrate(III) (HCF) in aqueous alkaline medium at a constant ionic strength of 0.75 mol·dm^?3 was studied spectrophotometrically at 300 K. A plausible mechanism was proposed and the rate law was derived. The mechanism of oxidation of ketorolac (KET) in alkaline medium has been shown to proceed via a KET-HCF complex, which decomposes in a slow step followed by other fast steps to give the products. The main oxidative product was identified as (2,3-dihydro-1-hydroxy-1H-pyrrolizin-5-yl-)(phenyl)methanone and is characterized by its LC–ESI–MS spectrum. Thermodynamic parameters of various equilibria of the mechanism were calculated and activation parameters ΔH ^≠, ΔS ^≠, ΔG ^≠ and log₁₀ A were found to be 29.9 kJ·mol^?1, ?220 J·K^?1·mol^?1, 96 kJ·mol^?1 and 2.70 respectively.     

Low-temperature heat capacities, and thermodynamic properties of solid–solid phase change material bis(1-octylammonium) tetrachlorocuprate

A new crystalline complex (C₈H₁₇NH₃)₂CuCl₄(s) (abbreviated as C₈Cu(s)) was synthesized by liquid phase reaction. Chemical analysis, elemental analysis, and X-ray crystallography were applied to characterize the composition and crystal structure of the complex. Low-temperature heat capacities of the complex were measured by a precision automatic adiabatic calorimeter over the temperatures ranging from 78 to 395 K, and two solid–solid phase changes appeared in the heat capacity curve. The temperatures, molar enthalpies and entropies of the two phase transitions of the complex were determined to be: T _{trs, 1} = 309.4 ± 0.35 K, Δ_trs H _{m, 1} = 16.55 ± 0.41 kJ mol^?1, and Δ_trs S _{m, 1} = 53.49 ± 1.3 J K^?1 mol^?1 for the first peak; T _{trs, 2} = 338.5 ± 0.63 K, Δ_trs H _{m, 2} = 6.500 ± 0.10 kJ mol^?1, and Δ_trs S _{m, 2} = 19.20 ± 0.28 J K^?1 mol^?1 for the second peak. Two polynomial equations of the heat capacities as a function of the temperature were fitted by least-square method. Smoothed heat capacities and thermodynamic functions of the complex relative to the standard reference temperature of 298.15 K were calculated based on the fitted polynomial equations.     

Binding interaction and conformational changes of human serum albumin with ranitidine studied by spectroscopic and time-resolved fluorescence methods

This study was designed to examine the interaction of histamine H₂-receptor antagonist drug ranitidine (RTN) with human serum albumin by multi-spectroscopic methods. The experimental results showed the involvement of dynamic quenching mechanism which was further confirmed by lifetime spectral studies. The binding constants (K _a) at three temperatures (288, 298, and 308 K) were 2.058 ± 0.020, 4.160 ± 0.010 and 6.801 ± 0.011 × 10⁴ dm³ mol^?1, respectively, and the number of binding sites (m) were 1.169, respectively; thermodynamic parameters ΔH ⁰ (44.152 ± 0.047 kJ mol^?1), ΔG ⁰ (?26.214 ± 0.040 kJ mol^?1), and ΔS ⁰ (236.130 ± 0.025 J K^?1 mol^?1) were calculated. The distance r between donor and acceptor was obtained (r = 3.40 nm) according to the Förster theory of non-radiative energy transfer. Synchronous fluorescence, CD, AFM and 3D fluorescence spectral results revealed the changes in secondary structure of the protein upon interaction with RTN. A molecular modeling study further confirmed the binding mode obtained by the experimental studies.     

A detailed study of isothermal crystallization of As2Se3 undercooled liquid

Isothermal crystallization of an As₂Se₃ undercooled melt was studied by differential scanning calorimetry and described using the classical theory of nucleation and crystal growth. The maximum rate of nucleation and crystal growth was observed to occur at approximately 235 and 350 °C, respectively. The activation energies of nucleation and crystal growth were determined to be ΔE _D = 311 kJ mol^?1 and ΔE* = 104 kJ mol^?1, respectively. The temperature dependencies of both the activation free energy of nucleation, ΔG*, and the critical diameter, r*, were also calculated.     

Determination of adsorption heats of individual adsorption complex by combination of microcalorimetry and FTIR spectroscopy

Adsorption of CO as a probe molecule on K-FER zeolites differing in Si/Al ratio was investigated. Successful determination of adsorption heats of individual adsorption complexes formed upon adsorption of CO molecules on K-FER zeolites at 300 K by combination of IR spectroscopy with adsorption microcalorimetry is reported. Adsorption heat of bridged carbonyl complexes, where CO molecule interacts with two nearby extraframework K⁺ cations, was experimentally determined for the first time. It was found that bridged complexes on dual cationic sites exhibit adsorption heat of 34.8 kJ mol^?1, whereas monodentate carbonyls on single isolated K⁺ cation exhibit adsorption heat of only 26.2 kJ mol^?1 and adsorption heat of isocarbonyls was 21.5 kJ mol^?1.     

Solid-state studies on crystalline and glassy flutamide

Flutamide usually crystallizes in the orthorhombic non-centrosymmetric space group Pna2₁ (from I) and melts atT _fus =384 K with Δ_fus H=30 kJ·mol^?1. It may be obtained in the glassy state (T _g =272 K) by quenching the melt. Although evidence of polymorphism could not be obtained by means of crystallography, DSC studies of the recrystallization process indicate that a metastable form (form II) occurs first and is transformed into the stable form at room temperature. ΔH for the transition I→II (2.52 kJ·mol^?1) is close to the difference in energy (about 2 kJ·mol^?1) calculated for the two possible conformers of flutamide.     

Thermoanalytical investigation of the synthesis of pyrazine and bipyrazine via the pyrolysis of the bis(pyrazinecarboxylate)copper(II) complex

The pyrolysis of hydrated bis(pyrazinecarboxylate)copper(II) under an argon atmosphere proceeds via the loss of the water molecules at 84–95°C, ΔH=40.4 kJ (mol H₂O)^?1 followed by the thermal decomposition of the complex at 284–325°C, ΔH=97.0 kJ·mol^?1, yielding 0.72 mole of pyrazine, 0.28 mole of bipyrazine, and 2 mole of CO₂ per mole of complex.     

Drug–tea polyphenol interaction

Propericiazine (PCZ) is an antipsychotic agent used for the treatment and the prevention of relapse of schizophrenia. We found that when an oral solution containing PCZ was mixed with a green tea drink, the residual content of PCZ was reduced by forming an insoluble complex between PCZ and tea polyphenol. In this study, the mechanism underlying the incompatibility of PCZ with green tea polyphenol (GTP) in the solution was clarified by isothermal titration microcalorimetry (ITC). Both solutions of 27.4 mM PCZ and 2.2 mM (?)-epigallocatechin gallate (EGCg), which is a main ingredient of GTP, were mixed and then PCZ in the filtrate was reduced to approximately 60 %. According to measurement at 298 K by ITC, PCZ formed an insoluble complex with EGCg at an associate constant (K) of 4.75 × 10² M^?1 exothermically, ΔH = ?40.0 kJ mol^?1. When (?)-epicatechin gallate (ECg) was used as the GTP, PCZ interacted with ECg with K and ΔH values of 3.74 × 10² M^?1 and ?22.1 kJ mol^?1, respectively. On the other hand, little heat of the reaction between PCZ and (?)-epigallocatechin or (?)-epicatechin was observed. The results indicated that the main reason for this incompatibility was the formation of an insoluble complex by PCZ and a gallate-type GTP such as EGCg and ECg in the aqueous solution.     

The research on formation enthalpy of phenanthroline monohydrate and its influence on the growth metabolism of E. coli by microcalorimetry

A precision rotating-bomb combustion calorimeter (thermistor of which was constructed in the laboratory) was calibrated using benzoic acid with purity of 99.999 %. The combustion energy of phenanthroline monohydrate (phen·H₂O) at 298.15 K was determined to be Δ_c U _m ^θ  = ?(5,757.45 ± 2.53) kJ mol^?1. Then, the standard enthalpy of combustion and the standard enthalpy of formation of phen·H₂O were calculated to be Δ_c H _m ^θ  = ?(5,759.93 ± 2.53) kJ mol^?1 and Δ_f H _m ^θ  = ?(391.34 ± 2.98) kJ mo1^?1, respectively. Particularly, the effect of phen·H₂O on growth and metabolism of Escherichia coli (E. coli) was also determined by a TAM air isothermal calorimeter at 37 °C. The thermokinetic parameters, including maximum heat output power (P _max), growth rate constant (κ), generation times (t _G), inhibitive rate (I), and half inhibition concentration (C _I,50), were obtained. The results showed that phen·H₂O possessed the bi-directional biological effect and Hormesis effect, which stimulated the growth of E. coli at lower concentration, but inhibited the growth at higher concentration. The half inhibition concentration C _I,50 of phen·H₂O was found to be 7.31 mg L^?1.     

Thermo-physical characterization of some paraffins used as phase change materials for thermal energy storage

Three phase change paraffinic materials (PCMs) were thermophysically (phase-transition temperatures, latent heat, heat capacity at constant pressure, density, and thermal conductivity) investigated in order to be used as latent heat storage media in a pilot plant developed in Plovdiv Bulgaria. Raman structural investigation probes aliphatic character of the E53 sample, while the E46 and ECP samples contain also unsaturated components due to their Raman features within 1,500–1,700 cm^?1 range. Orthorhombic structure of the three PCMs was evidenced by the Raman modes at the 1,417 cm^?1. The highest latent heat value, ΔH, of phase transitions among the three materials was represented by summation of a solid order–disorder, and melting latent heat was encountered by the E53 paraffin, i.e., 194.32 J g^?1 during a μ-DSC scan of 1 °C min^?1. Conversely, the ECP composite containing ceresin component shows the lowest latent heat value of 143.89 J g^?1 and the highest thermal conductivity of 0.46 W m^?1 K^?1 among the three phase change materials (PCMs). More facile melt-disordered solid transition with the activation energy of 525.45 kJ mol^?1 than the lower temperature transition of disorder–order (E _a of 631.73 kJ mol^?1) during the two-step process of solidification for the E53 melt are discussed in terms of structural and molecular motion changes.     

The thermal decomposition of N,N-dimethyl-3-oxaglutaramic acid and the kinetics of its second-stage thermal decomposition reaction

N,N-dimethyl-3-oxa-glutaramic acid was purified and characterized by ¹H-NMR, Fourier transform infrared spectroscopy (FT-IR) and elemental analysis. The thermal decomposition of the title compound was studied by means of thermogravimetry differential thermogravimetry (TG-DTG) and FT-IR. The kinetic parameters of its second-stage decomposition reaction were calculated and the decomposition mechanism was discussed. The kinetic model function in a differential form, apparent activation energy and pre-exponential constant of the reaction are 3/2 [(1?α)^1/3?1]^?1, 203.75 kJ·mol^?1 and 10^17.95s^?1, respectively. The values of ΔS ^≠, ΔH ^≠ and ΔG ^≠ of the reaction are 94.28 J·mol^?1·K^?1, 203.75 kJ·mol^?1 and 155.75 kJ·mol^?1, respectively.     

Heat capacities and standard molar enthalpy of formation of pyrimethanil maleic salt and pyrimethanil fumaric salt

Novel anilino-pyrimidine fungicides, pyrimethanil maleic salt, and pyrimethanil fumaric salt (C₂₈H₃₀N₆O₄) were synthesized by a chemical reaction of pyrimethanil with maleic acid/fumaric acid. The low-temperature heat capacities of the two compounds were measured with an adiabatic calorimeter from 80 to 350 K. The heat capacities of pyrimethanil fumaric salt are bigger than that of pyrimethanil maleic salt in the measurement temperature range. The thermodynamic function data relative to 298.15 K were calculated based on the heat capacity-fitted curves. The melting points, the molar enthalpies (Δ_fus H _m), and entropies (Δ_fus S _m) of fusion of pyrimethanil maleic salt and pyrimethanil fumaric salt were determined from their DSC curves. The values indicate that pyrimethanil fumaric salt was more thermostable than pyrimethanil maleic salt. The constant-volume energies of combustion (Δ_c U _m ^o ) of pyrimethanil maleic salt and pyrimethanil fumaric salt were measured using an isoperibol oxygen bomb combustion calorimeter at T = (298.15 ± 0.001) K. From the Hess thermochemical cycle, the standard molar enthalpies of formation of the two compounds were derived and determined to be Δ_f H _m ^o (pyrimethanil maleic salt) = ?459.3 ± 4.9 kJ mol^?1 and Δ_f H _m ^o (pyrimethanil fumaric salt) = ?557.2 ± 4.8 kJ mol^?1, respectively. The results suggest that pyrimethanil fumaric salt is more chemically stable than pyrimethanil maleic salt.     

Adsorptive removal of thorium from aqueous solution using diglycolamide functionalized multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were functionalized with diglycolamide (DGA) through chemical covalent route. The adsorption behavior of the DGA-functionalized-MWCNTs (DGA-MWCNTs) towards thorium from aqueous solution was studied under varying operating conditions of pH, concentration of thorium, DGA-MWCNTs dosages, contact time, and temperature. The effective range of pH for the removal of Th(IV) is 3.0–4.0. Kinetic data followed a pseudo-second-order model. The equilibrium data were correlated with the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models. The equilibrium data are best fitted with Langmuir model. The equilibrium Th(IV) sorption capacity was estimated to be 10.58 mg g^?1 at 298 K. The standard enthalpy, entropy, and free energy of adsorption of the thorium with DGA-MWCNTs were calculated to be 8.952 kJ mol^?1, 0.093 kJ mol^?1 K^?1 and -18.521 kJ mol^?1 respectively at 298 K. The determined value of sticking probability (0.072) and observed kinetic and isotherm models reveal the chemical adsorption of thorium on DGA-MWCNTs.