1,720,984 research outputs found
Investigation of dry reforming of methane over Mo-based catalysts
No full textAn investigation of methane dry reforming over Mo–Ni based catalysts is carried out in a fixed bed catalytic reactor at different temperatures. Two Mo–Ni catalysts supported on alumina are prepared with 20%Mo–10%Ni and 20%Mo–2%Ni, respectively, in which the nickel is used for its highly resistance at high temperature during dry reforming of methane (DRM) reaction. Experimental results shows that an increase in temperature favours the CH4 conversion and determined a higher H2/CO ratio. A small amount of deposited coke is observed because of the abundant presence of CO2 in the reaction medium and only for 2% Ni catalysts. A kinetic model is proposed for the DRM with Mo–Ni based catalysts, in which the reaction mechanism routes and the operating conditions such as the reaction temperature and the CH4/CO2 molar ratio are accounted for. The results of the mathematical model allow a consistent description of the experimental data, in terms of gas outlet composition. The absence of the methane decomposition reaction, responsible of carbon deposition that is known to lead to catalyst deactivation, is the main result that is adequately predicted by the model
Homogenous UV/Periodate Process for the Treatment of Acid Orange 10 Polluted Water
Full text linkThe photoactivated periodate (UV/IO4−) process is used to investigate the degradation of acid orange 10 (AO10) dye. The photodecomposition of periodate ions produces highly reactive radicals (i.e., •OH, IO3•, and IO4•) that accelerate dye degradation. Increasing the initial concentration of periodate to 3 mM enhances the dye removal rate, but over 3 mM periodate, the degradation rate slows down. On the contrary, increasing initial dye concentrations reduces the degradation performance. pH is the most critical factor in AO10 breakdown. Salts slow down the degradation of the dye. However, UV/IO4− is more efficient in distilled water than natural water. Even at low concentrations, surfactants may affect the dye’s decomposition rate. The addition of sucrose reduced the breakdown of AO10. Although tertbutanol is a very effective •OH radical scavenger, it does not affect the dye breakdown even at the highest concentrations. Accordingly, the AO10 degradation is a non-•OH pathway route. According to retrieved data, the photoactivated periodate method eliminated 56.5 and 60.5% of the initial COD after 60 and 120 min of treatment time; therefore, it can be concluded that the UV/IO4− system may treat effluents, especially those containing textile dyes
Physicochemical Properties and Atomic-Scale Interactions in Polyaniline (Emeraldine Base)/Starch Bio-Based Composites: Experimental and Computational Investigations
No full textThe processability of conductive polymers still represents a challenge. The use of potato starch as a steric stabilizer for the preparation of stable dispersions of polyaniline (emeraldine base, EB) is described in this paper. Biocomposites are obtained by oxidative polymerization of aniline in aqueous solutions containing different ratios of aniline and starch (% w/w). PANI-EB/Starch biocomposites are subjected to structural analysis (UV-Visible, RAMAN, ATR, XRD), thermal analysis (TGA, DSC), morphological analysis (SEM, Laser Granulometry), and electrochemical analysis using cyclic voltammetry. The samples were also tested for their solubility using various organic solvents. The results showed that, with respect to starch particles, PANI/starch biocomposites exhibit an overall decrease in particles size, which improves both their aqueous dispersion and solubility in organic solvents. Although X-ray diffraction and DSC analyses indicated a loss of crystallinity in biocomposites, the cyclic voltammetry tests revealed that all PANI-EB/Starch biocomposites possess improved redox exchange properties. Finally, the weak interactions at the atomic-level interactions between amylopectin-aniline and amylopectin-PANI were disclosed by the computational studies using DFT, COSMO-RS, and AIM methods. © 2022 by the authors. Licensee MDPI, Basel, Switzerland
Synthesis and characterization of Layered Double Hydroxides aimed at encapsulation of sodium diclofenac: Theoretical and experimental study
No full textThe main objective of the paper is to study the encapsulation/adsorption of sodium diclofenac (Na-DIC) on hydrotalcite cationic clays (i.e., Layered Double Hydroxides, LDHs) by ion exchange and adsorbent reconstruction mechanisms. The encapsulation/adsorption method is generally used to modify some drugs' physicochemical characteristics, such as unpleasant odors, low solubility, high volatility, etc. LDHs are synthesized and characterized by different techniques (SEM, DRX, FTIR, BET, and ATG). Na-DIC adsorption capacity onto calcined LDH (CLDH) is determined (with maximum value in between 195 and 211 mg/L in the range 25–45 °C), together with the effect of the main operating parameters (adsorbent mass, pH, initial concentration of Na-DIC, and temperature). A statistical physics derived adsorption model allows a correct interpretation of experimental data and indicates that multiple molecules' vertical adsorption per active site occurs. Kinetic tests showed that the Pseudo First order (PFO) model correctly describes the Na-DIC adsorption kinetics on LDH at different temperatures, indicating the pore diffusion as the primary resistance mechanism and an activation energy of +34.56 kJ/mol (physical adsorption). HOMO and LUMO obtained from quantum chemical calculations confirm the ability of Na-DIC to receive electrons from LDH, indicative of polar adsorption (ΔNmax = 1.9). Adsorption is also simulated by Monte Carlo method, which allows determining the Na-DIC/CLDH configuration corresponding to the lowest total energy. The value of the adsorption energy confirms a strong interaction between the DIC and the CLDH. In conclusion, LDH clays show great potential as adsorption support and encapsulation medium, which could be proficiently used also to remove Na-DIC from wastewater. Na-DIC is adsorbed onto calcined hydrotalcite by the reconstruction method, which is explained by the so-called “memory effect” of hydrotalcite
Numerical study of sorption-enhanced methane steam reforming over Ni/Al2O3 catalyst in a fixed-bed reactor
No full textThe present work deals with the Sorption-Enhanced Methane Steam Reforming (SE-MSR), an interesting and energy-efficient hydrogen production route with in situ CO2 capture. A computational fluid dynamics (CFD) model for an industrial-scale fixed-bed reactor, with Ni/Al2O3 as catalyst and CaO as an adsorbent for CO2 capture, is developed taken into consideration also the coke deposition. Temperature is shown to be the key parameter of the SE-MSR chemical process at large scales. H2 production is constant and maximum until the saturation of CaO sorbent occurs, after which the concentrations of all the other compounds start to vary, and the efficiency of the process begins to drop. When the exothermic carbonation reaction stops, an alteration of the thermal regimes is observed. The absence of the contribution of the exothermic carbonation reaction results in a decrease of the temperature, which in turn determines a lower conversion of CH4 and H2O, according to the endothermic reforming reactions. The maximum H2 outlet mole fraction (dry basis) is 0.8, and it occurs in the presence of CO2 sorption; the value drops to 0.42 once the adsorbent reaches its maximum conversion degree. The molar selectivity in hydrogen relative to the quantity of CH4 fed to the reactor is of the order of 1.75 (with CO2-capture) and 0.8 (without CO2 capture). The molar fluxes obtained and the kinetics of the system model show the excellent choice of the operating conditions of the catalyst to produce a large quantity of hydrogen as well as of the adsorbent, which eliminates the CO2 responsible of coke deposition
Theoretical evaluation of the antioxidant activity of some stilbenes using the Density Functional Theory
No full textIn this paper, the antiradical potential of trans-2,4,3′,5′-tetrahydroxystilbene (T-OXY), trans-2,3′,4-trihydroxystilbene (T-RES), cis-2,4,1′,3′-tetrahydroxystilbene (C-OXY) and cis-2,1′,4-trihydroxystilbene (C-RES) is investigated by BDE (E0) and ETS-NOCV calculations, in water, benzene, DMSO, and ethanol. The study of solubility by the COSMO-RS model demonstrates that the compounds are very soluble in DMSO. The hydrogen atom transfer (HAT), sequential proton loss electron transfer (SPLET), and single electron transfer followed by proton transfer (SET-PT) mechanisms are explored as possible oxidation paths of these compounds using the DFT calculations at B3LYP/6-311++G(2d,2p) level of theory in DMSO. For all the studied compounds, the HAT was found to be the thermodynamically dominant mechanism, indicating that the investigated compounds can be classified according to their antiradical activity in the following sequence order T-OXY˃T-RES˃C-OXY˃C-RES. The evaluation of ΔHBDE reaction enthalpies, ΔHIP, and ΔHPA linked to the three mechanisms with certain radicals (HO·, HOO·, CH3O· and CH3OO·, NO·, and NO2·) are determined. The results indicate the HAT and SPLET mechanisms are competitive in inhibiting those species. QTAIM calculations reveal the existence of critical points in the two conformers. The Diels-Alder intramolecular cyclization of (C-OXY) leads to two new tautomers: trans-cycle-OXY (T-CYCLE-OXY) and cis-cycle-OXY (C-CYCLE-OXY) with a significant improvement in the antioxidant activity. In conclusion, T-OXY and T-CYCLE-OXY are identified as the best antioxidant candidates among those tested
In silico drug discovery of Acetylcholinesterase and Butyrylcholinesterase enzymes inhibitors based on Quantitative Structure-Activity Relationship (QSAR) and drug-likeness evaluation
No full textIn the last years, in order to achieve a better treatment of Alzheimer's disease (AD), much focus has been put on the development of cholinesterase (Acetylcholinesterase and Butyrylcholinesterase) inhibitor drugs. Thus, the aim of this study is to discover promising active compounds for Acetylcholinesterase and Butyrylcholinesterase enzymes inhibitors based on QSAR model and drug-likeness evaluation. In this study, a series of DL0410 and its 50 derivatives are accounted for the set up of two QSAR models. This allows an exploration of the main molecular descriptors that control the inhibitory activity of specific compounds towards cholinesterase enzymes: Acetylcholinesterase (AChE) and Butyrylcholinesterase (BuChE). Simultanerously, the models can help to predict the inhibitory activity of new compounds within its applicability domain. A Multiple Linear Regression (MLR) analysis is carried out to derive QSAR models. The results indicate that the QSAR models of Acetylcholinesterase and Butyrylcholinesterase inhibitory activity are robust and have a very good prediction capacity, testified by values of R2 equal to 0.935 and 0.895, respectively. The analysis carried out by adopting the QSAR models succeed in screening 15 potential compounds with higher biological activity. Subsequently, the investigated compounds has been subjected to the drug-likeness evaluation and reactivity study. The results show that most of the compounds do not present any bioavailability problem when administered orally. The results also allow determining the compounds that have not clearance problems, those that are the most stable and the most reactive among those tested. These findings indicate that the newly designed candidate drugs have promising potential toward AChE and BuChE enzyme inhibition and should be experimentally investigated
A strategy for enhancing heat transfer in phase change material-based latent thermal energy storage unit via nano-oxides addition: A study applied to a shell-and-tube heat exchanger
No full textDue to the scarcity of data on the industrial use of energy storage technology based on material phase change (PCM), a complete computational assessment is done in this work, where a nano-PCM technique is used to enhance the thermal energy storage in a big-scale shell-and-tube heat exchanger. Four high thermal conductive nano-oxides (i.e., Al2O3, MgO, SiO2, and SnO2) are added at various concentrations (1–5% v/v) into the PCM (i.e., paraffin RT82). A two-dimensional mathematical model is used to study the produced nano-PCM systems' heat transfer and melting rate. The model accurately predicted the PCM-melting data's observed behavior, showing that it is adequate for simulating PCM problems. The addition of nano-oxides, for up to 5%, in the PCM solid matrix dramatically enhances heat transmission and melting rate during the first melting stage. However, after a long melting period, the melting performance of the nano-PCMs decreased and became equivalent to that of the pure PCM. Furthermore, increasing the concentration of nanoparticles from 1 to 5% did not significantly improve the temperature and liquid fraction evolutions for the four studied nano-PCMs. Therefore, the use of nano-PCMs in the adopted LTES unit can effectively improve heat recuperation and melting rate, but only for a short charging time during which a part (up to 60%) of the PCM's latent heat is recovered. Consequently, the present paper's data is considered a guideline for increasing the efficacy of thermal energy storage in big-scale shell-and-tube heat exchangers using nano-PCM technology
Clorazepate removal from aqueous solution by adsorption onto maghnite: Experimental and theoretical analysis
No full textThe removal of a benzodiazepine (clorazepate, CLZ) from aqueous solution by adsorption onto maghnite clay is investigated supported by theoretical simulations. The Fourier-transform infrared (FTIR), Ultraviolet (UV), X-ray diffraction (XRD), and scanning electron microscope (SEM) analyses were used to characterize the adsorbent. To individuate the optimum conditions for adsorption, equilibrium, and kinetic tests are performed to assess the efficiency of this adsorbent to remove CLZ from polluted water in different operating conditions like pH, initial concentration, adsorbent dosage, and contact time. Adsorption is maximum at low pH, and it is mainly driven by electrostatic interactions between the benzenic ring of CLZ molecule and the montmorillonite layer of maghnite adsorbent. The kinetics obeys to the pseudo-first-order kinetic model, while the Freundlich isotherm model was found to better describe the adsorption equilibrium. The maximum observed adsorption amount of CLZ onto maghnite was about 50 mg g−1 at pH 4.66. A complementary theoretical study is performed to quantify the CLZ/maghnite interactions using Monte Carlo simulations. Interestingly, the results show that the CLZ assumes a horizontal position on the maghnite surface upon adsorption, characterized by high energy adsorption
Effect of the stearic acid-modified TiO2 on PLA nanocomposites: Morphological and thermal properties at the microscopic scale
No full textIn this work, a route is developed to synthesize nanocomposites based on polylactic acid (PLA) and stearic acid-modified TiO2 nanoparticles (TiO2-SA). The nanocomposite is prepared in two steps by solution and melt methods. Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), as well as Thermogravimetric Analysis (TGA) are used to characterize the synthesized materials. Quantum chemical calculations are carried out by means of density functional theory (DFT) calculations, Blends study and AIM analysis, to investigate the role of Stearic Acid (SA) on the nanocomposite PLA/TiO2 at microscopic level. FTIR analysis confirms the functionalization of TiO2 nanoparticles by stearic acid (SA). The DSC results illustrates the overall TiO2 effect in reducing the glass transition temperature Tg (from 58° to 52 °C) and the rise in the crystallinity degree (from 0.19° to 7.18 °C) where the 5% of nanoparticle shows the optimum result. This could be attributed to the fact that TiO2-SA acts as a nucleating agent, as confirmed also by XRD patterns. TGA analysis shows that the thermal stability of PLA decreases by the addition of TiO2-SA and this effect is monothonic with TiO2 content where the 1% nanoparticle shows the most thermally stable formulation. Simulations at atomic level confirmed the dispersion of treated TiO2 in the matrix. In particular, SA plays the role of electron donor with PLA and TiO2, increasing the miscibility between them by a strong hydrogen bond. The main results obtained allow considering SA as a valid option for the functionalization of TiO2 before inclusion in PLA matrix
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