Stoichiometric Factor Research Articles

Eco-friendly procedure for the synthesis of 4-(Phenylamino)pent-3-en-2-one using an heterogeneous catalyst – ZnCl2/Natural phosphate

A new environmentally friendly synthesis of 4-(Phenylamino)pent-3-en-2-one has been developed by condensing aniline with acetylacetone using ZnCl2/Natural Phosphate. The effect of catalyst nature and mass, solvents, reaction time, and temperature on the yield were conducted. The results showed that the condensation reaction was carried out efficiently during 2 h at 35 °C in ethanol. The catalyst could be reused during two cycles without a significant loss in its activity.To investigate the environmental performance of this synthesis, a set of green chemistry metrics has been determined such as atom economy (AE), reaction mass efficiency (RME), stoichiometric factor (SF), and material recovery parameter (MRP). At the same time, we considered the Green Star Metric including simultaneously all of the principles of green chemistry. It appeared from the results that the environmental performance has beensignificantlyimproved when recycling catalyst and solvent, however, the use of less hazardous reagents us well us a renewable raw material is highly recommended to further improve the safety and the greenness of the developed synthesis.

Process optimization, green chemistry balance and technoeconomic analysis of biodiesel production from castor oil using heterogeneous nanocatalyst

In the present work, zinc doped calcium oxide was used as a nanocatalyst for biodiesel production from castor oil. The optimal conditions of biodiesel conversion and green chemistry balance were obtained with response surface methodology. Five green chemistry parameters like carbon efficiency, atom economy, reaction mass efficiency, stoichiometric factor and environmental factor were optimized. The sustainable biodiesel yield 84.9% and green chemistry balance 0.902 was achieved at methanol to oil molar ratio 10.5:1, temperature 57 °C, time 70 min, and catalyst concentration 2.15%. The synthesized biodiesel was characterized by GCMS and FTIR, and physic-chemical properties were determined. Based on experimental study annually 20.3 million kg capacity plant was simulated using SuperPro designer. The sensitivity analysis of oil purchase cost and biodiesel selling price on ROI, payback period, IRR and NPV were investigated. The optimization and technoeconomic analysis provided a sustainable platform for commercial based biodiesel production.

Benchmarking Stochastic and Deterministic Kinetic Modeling of Bulk and Solution Radical Polymerization Processes by Including Six Types of Factors Two

AbstractBulk and solution radical polymerization is important in daily live. A challenge is still to maximize polymerization rate and control over molecular characteristics such as the molar mass distribution. The last decades have made clear that kinetic modeling is indispensable with originally most focus on deterministic implementations such as the method of moments (MoM) and only more recently promising results for event‐driven kinetic Monte Carlo (kMC) simulations that belong to stochastic methods. Computationally, a critical reaction is termination for which one has both distinguishable and nondistinguishable distributed species, which requires a delicate treatment of a stoichiometric factor 2. Proper benchmarking of MoM and kMC simulations demands thus a careful translation of this factor in the Monte Carlo (MC) reaction probabilities. However, limited attention has been paid in the kMC field to the detailed description of such translations. Here, a rigorous derivation is presented on the level of individual termination rates. Emphasis is on termination by recombination and disproportionation. It is highlighted that six types of factor 2 exist that all need to be incorporated with care, including an IUPAC‐based one. The consistency is demonstrated by a successful benchmark of essential modeling results for free radical polymerization of methyl methacrylate.

Optimization and techno-economic analysis of biodiesel production from Calophyllum inophyllum oil using heterogeneous nanocatalyst

The present research work is aimed at reducing the consumption of reactants by process optimization and economic analysis of large-scale commercial plant using techno-economic analysis. The statistical optimization of biodiesel production from Calophyllum inophyllum oil using Zn doped CaO nanocatalyst was used to optimize the conversion efficiency and green chemistry value. The environmental studies on transesterification reaction were done using green chemistry parameters like carbon efficiency, atom economy, reaction mass efficiency, stoichiometric factor and environmental factor. The biodiesel conversion 91.95% was achieved when maintaining the methanol to oil ratio 9.66:1, concentration of catalyst 5% (w/v), time 81.31 min and temperature 56.71 °C with green chemistry value of 0.873. Techno-economic analysis of biodiesel production from Calophyllum inophyllum oil was executed used optimized lab-scale data. The techno-economic analysis of 21 million kg/year biodiesel production plant was investigated. The annual biodiesel revenue of 15,224,000 $/yr and the payback period was about 1.15 years.

Investigation of air-blown two-stage entrained-flow gasification of micronized coal

The aim of this work was to intensify the air-blown conversion of coarse grinding coal into the fuel syngas by means of mechanical activation of some part of the coal without the involvement of other methods of conversion intensification (oxygen enrichment of blast, heating of blast or fuel, etc.). Experimental studies were carried out at the Institute of Thermophysics of the Siberian Branch of the Russian Academy of Sciences (IT SB RAS) using special setup with the two-stage coal and air input. We have performed a comprehensive experimental and computational study of air-blown gasification of coarse coal (Gcoal2) by combustion products of micronized coal (Gcoal1) at the ratio of primary and secondary coal gc = Gcoal1/Gcoal2 = 0.82–0.39 (90/110–90/230 kg/kg), stoichiometric factor α = 1.39–0.51 and the temperature in the flame from 1.200 to 1.300 to 1.500–1.600 °C. It has been found that micronization of primary coal allows maintaining a stable autothermal mode of air-blown gasification of coarse bituminous coal without involving the additional methods of conversion intensification at α = 0.5. The CFD simulation based on experiments determined the conditions for implementation of the investigated process.

Improved Operating Parameters for Hydrogen Peroxide‐Generating Gas Diffusion Electrodes

AbstractThe influence of process parameters on the H2O2 yield of gas diffusion electrodes (GDE) are investigated. The investigated GDEs consist of Vulcan XC72 carbon black and PTFE on gold‐plated nickel wire cloth. An electrolysis cell is used to evaluate the influence of various process parameters, such as temperature, pH value, oxygen pressure and stoichiometric factor, electrolyte flow regime, current density and separator material at steady‐state conditions. It is found that the investigated GDE enables current efficiencies greater than 90 % at up to 2 kA m−2, whereby lower electrolyte temperatures and higher pH values contribute to higher H2O2 yields above 90 % current efficiency.

Reactive Extraction of Levulinic Acid using Tri-n-octylamine in 1-Octanol: Equilibria and Effect of pH

Reactive extraction is a sophisticated separation technique used for the recovery of carboxylic acids from fermentation broth. Levulinic acid is a versatile chemical. A right combination of extractant and diluent will provide a high yield. The reactive extraction of levulinic acid from aqueous solution with tri-n-octylamine (TOA) dissolved in 1-octanol was investigated at room temperature. The effect of pH was studied. From the physical and chemical equilibrium experimental results, the distribution coefficient (KD), extraction efficiency (E%), loading ratio (Z), stoichiometric loading factor (ZS) and modified separation factor (Sf) are calculated. It was found that physical extraction provided less yield compared to chemical extraction. A maximum KD was obtained as 5.248 using 40% TOA (0.9059 mol/L) while 83.99 % of the levulinic acid was extracted. By increasing the initial concentration of levulinic acid increased the concentration of levulinic acid in both the organic phase and aqueous phase. As the concentration of TOA increases from 10 to 40 % (0.2264 mol/L to 0.9059 mol/L), the distribution coefficient and extraction efficiency also increase. By increasing the pH from 3 to 7, the distribution coefficient and extraction efficiency were drastically affected.

Using modeling to select catalyst dilution methods for mass transfer intensification in lab gas–liquid fixed-bed reactors

Heterogeneous catalyst testing methodology at the lab scale must provide intrinsic kinetics data for reactor design purposes as well as the intrinsic activity ranking during catalyst screening in the field of refining and petrochemistry. The significant downscaling of the past century coupled with the increasingly active catalytic formulations may introduce considerable momentum, mass and heat effects in experiments at small scale. Catalyst dilution has emerged as one versatile and robust way to reduce the impact of momentum and heat effects on heterogeneous catalyst testing. This paper presents a methodology based on global phenomena and catalyst dilution modeling to assess and optimize reactor loading techniques for specific problems. More particularly, the aim is to provide catalysts developers and kinetics experts with concrete guidelines for intensifying gas-liquid mass transfer in lab gas–liquid fixed-bed reactors through catalyst dilution. The methodology is applied to the kinetics determination of the oil residue Hydrodemetallation (HDM) and to the screening of catalysts for benzene hydrogenation. Layered dilution, consisting on the split of the catalyst in two beds separated by an intermediate bed containing an inert material of the same size as the catalyst, poorly improves gas–liquid mass transfer. Uniform dilution, based on the direct mixture of catalyst and inert material of the same size, significantly enhances gas–liquid mass transfer as the reactant local consumption per reactor unit volume is strongly reduced. Combinations of both abovementioned dilution techniques can be used with fast and/or high stoichiometric factor chemical systems operated at conversions higher than 70%. A new criterion is proposed to calculate the minimum dilution factor to guarantee negligible gas–liquid mass transfer limitations as a function of conversion, external mass transfer and global pseudo second-order kinetics.

Reactive extraction of levulinic acid using tri-n-octylamine in 1-hexanol

Reactive extraction of levulinic acid using trin- octylamine (TOA) in 1-hexanol was investigated by physical and chemical extractions from aqueous solution at room temperature. Using the equilibrium data, the distribution coefficient (KD), extraction efficiency (E%), loading ratio (Z), stoichiometric loading factor (ZS) and modified separation factor (Sf) are evaluated. It was observed that chemical extraction provided a better yield than physical extraction. A maximum KD was obtained as 10.715 using 40% TOA (0.9059 mol/L) while 91.46% of the levulinic acid was extracted. By increasing the initial concentration of levulinic acid resulted in a decrease of KD and E%. The KD and E% increased by increasing the TOA concentration from 10 to 40% (0.2264 mol/L to 0.9059 mol/L).

Radical-scavenging and Pro-/anti-inflammatory Activity of Tetracycline and Related Phenolic Compounds With or Without Visible Light Irradiation.

Microbial tetracycline (TC) pastes have been employed to treat oral bacterial infection. In the present study, we investigated the kinetic radical-scavenging and pro-/anti-inflammatory activity of TC with or without visible light irradiation (VLI). The radical-scavenging activity of TC and minocycline (MC) was determined by differential scanning calorimetry (DSC). The stoichiometric factor (n) and the rate constant of inhibition and propagation (kinh/kp) were determined. The levels of cyclooxygenase-2 (Cox2), tumor necrosis factor-α (Tnfα) or nitric oxide synthase 2 (Nos2) mRNA in RAW264.7 cells stimulated with lipopolysaccharide (LPS) were investigated using real-time reverse transcriptase-polymerase chain reaction. The n and kinh/kp values for 1 mM TC in 2,2'-azobisisobutyronitrile and benzoyl peroxide systems were 0.1-0.2 and 119-250, respectively, whereas the corresponding values for quercetin (QU) and resveratrol (RE) were 2-4 and 7-15, respectively. In RAW264.7 cells stimulated with LPS, Cox2 and Tnfα mRNA were over-expressed in the presence of TC. MC down-regulated only the expression of Cox2 by about 50% in LPS-stimulated cells. The anti-inflammatory activity determined on the basis of Cox2 inhibition declined in the order QU>RE>MC>TC. Upon application of VLI, only TC down-regulated the expression of LPS-stimulated Cox2 and Tnfα mRNA. After exposure to VLI, TC, but not MC, markedly up-regulated hemoxygenase-1 (Ho-1) expression. TC is a chain-breaking antioxidant with a large kinh Upon activation by VLI, TC may undergo degradation and its degradation products affect pleiotropic mediators such as Cox2, Tnfα and Ho-1. TC may be useful as a local photodynamic therapy for periodontal diseases.

Construction of 3D Antioxidants with Nucleosides as the Core: Inhibition of DNA Oxidation.

We herein attach ferulic and caffeic acids to -OH and -NH2 in cytidine, uridine, adenosine, or guanosine for achieving antioxidative hybrids with three-dimensional (3D) configuration. In the case of molecular docking computation, the nucleoside antioxidants with 3D configuration facilitate to bind with the groove of DNA and to cover the surface of a DNA helix. Experimentally, the antioxidative effects of nucleoside hybrids are measured in the inhibition of DNA oxidation caused by 2,2'-azobis(2-amidinopropane dihydrochloride) (AAPH), and the stoichiometric factor (n, the number of free radical propagations terminated by one molecule of antioxidant) can be selected as a quantitative index for expressing antioxidative effects. It is found that the effect of cytidine tetraferulate against AAPH-induced DNA oxidation is seven times better than that of ferulic acid, even though four ferulic acid moieties are involved and cytidine itself does not exhibit activity. Moreover, the antioxidative effect of cytidine tetracaffeate is almost 20 times higher than that of caffeic acid. The n values of nucleoside antioxidants against AAPH-induced DNA oxidation are found to correlate proportionally with the rate constants for quenching 2,2'-diphenyl-1-picrylhydrazyl and galvinoxyl radicals. Therefore, nucleoside linking with antioxidative carboxylic acid might be a promising way for constructing antioxidants against peroxyl radical-induced oxidation of DNA.

Benefits of Ryegrass on Multicontaminated Soils Part 2: A Green Process to Provide Idrocilamide

A restoration of highly contaminated garden soil is proposed as a greener alternative to the production of vegetables. Depending on potentially toxic elements and their concentration, ryegrass shoots accumulate these elements in sufficient quantity to be used as a catalyst in organic synthesis. The analysis of Cd, Pb, Zn, Cu, Fe, Mn, and Al in ashes issued from the calcination of ryegrass shoots revealed that the concentration of Zn was highest (>7000 mg kg–1). The ratios between potential Lewis acids (Zn, Cu, Fe, Mn, and Al) to carcinogenic metals (Cd or Pb) were 191 ± 7 for LA/Cd and 235 ± 13 for LA/Pb, making the shoots of ryegrass suitable for the production of Zn-rich polymetallic biosourced catalysts. This material was used in the synthesis of idrocilamide under free-solvent condition, providing the drug in a good yield (69.9%). Data show that a limitation of waste, a maximization of the material incorporation in the process, a minimization of the steps, and an optimization of the stoichiometric factor are the main innovative factors in the current process in comparison with those previously reported.

Biodiesel production optimization from waste cooking oil using green chemistry metrics

Biodiesel is a promising alternative to fossil energy, especially when non edible feedstocks are used in the production process. In the present work, biodiesel was produced from university campus restaurants waste frying soybean oil by means of transesterification reaction.The objective of this study was to reduce the energy and reactants consumption and waste generation to achieve a truly green process. For this purpose, a multiobjective optimization using central composite design (CCD) was performed considering three responses: the reaction conversion, the energy consumption and the green chemistry balance. The last two parameters i.e. the energy consumption and the green chemistry balance were considered as responses for the first time, hence an interesting originality. Temperature, KOH catalyst amount and oil to methanol molar ratio were the CCD independent variables.Five green metrics were used to account for the greenness of the reaction, namely: carbon efficiency, atom economy, reaction mass efficiency, stoichiometric factor and environmental factor.The obtained quadratic models for the prediction of the optimum responses fitted reasonably well the experimental data. The results showed a maximum oil conversion of 100%, minimum energy consumption of 2.69 kJ and maximum green chemistry balance of 77.36% at KOH catalyst concentration of 2 wt%, methanol to oil molar ratio of about 4.73 and a minimum temperature of 45 °C.The physicochemical properties of the produced biodiesel agreed well with the international standards ASTM (American Society for Testing and Materials).

Relative Influence of Topology, Dimensionality and Stoichiometry Toward the Properties of Covalent Network Glasses

Trends in density and fragility are analyzed in the Ge-As-Se, As-Se and Ge-Se system for the purpose of identifying correlation with structural characteristics related to topology, stoichiometry and dimensionality. The Ge-As-Se system provides the most revealing testbed as it permits to isolate individual effects. The fragility of Ge-As-Se glasses is clearly controlled by stoichiometric factors while the topological transition at =2.4 is not observed in this system. The density of Ge-As-Se glasses broadly increase with average coordination but show two anomalies centered near = 2.4 and 2.67. These anomalies merge into a single extremum corresponding to stoichiometric compositions when plotted against excess/deficiency in Se, thereby revealing their common link to stoichiometric factors. Nevertheless, when stoichiometric factors are fixed, dimensional effects are revealed in the form of a linear dependence upon content of tetrahedral Ge. Similarly, a diffuse maximum at the topological transition of = 2.4 is observed when only Se-excess compositions are considered. For the As-Se system, a local maximum in fragility is observed at the two dimensional composition As2Se3, contrary to predictions from topological or stoichiometric factors, thereby indicating that dimensional effect control the fragile behavior. Finally, in the Ge-Se system, a topological transition associated with balance of constraints and degrees of freedom is found at = 2.4 when contributions from stoichiometry and dimensionality are absent. In all system, no case is found where topological effects dominate either stoichiometric or dimensional effects, hence it can be concluded that it is the least predominant contribution while stoichiometry is found to be the prevailing effect.

Energy band gaps and excited states in Si QD/SiOx/Ry Oz (R = Si, Al, Zr) suboxide superlattices

X-ray and optical spectroscopies were applied in order to study the band structure and electronic excitations of the SiOx/Ry Oz (R = Si, Al, Zr) suboxide superlattices. The complementary x-ray emission and absorption measurements allow for the band gap values for the SiOx layers to be established, which are found to have almost no dependency on the cation type R. It is determined that, after annealing, the stoichiometric factor x remains near 1.8 in all the systems under study, implying that the silicon quantum dot synthesis reaction is not fully completed. It is shown that the SiOx/Al2O3 multilayer contains octahedral structural motifs (SiO6) usually found in stishovite, whereas SiOx/SiO2 and SiOx/ZrO2 demonstrate an electronic structure similar to conventional silica. The intrinsic electronic excited states are examined by means of synchrotron-excited photoluminescence spectroscopy. Low-energy UV-excited luminescence of SiOx layers is found to have the same spectrum in all of the studied structures, while VUV-excited spectra strongly depend on the cation R. In these measurements, manifestations of ‘slow’ exciton-mediated and ‘fast’ defect-related luminescence are distinguished using nanosecond time resolution. It is shown that both mobile and bounded excitons appear in the suboxide layer under 6.2 eV and 5.8 eV irradiation and then relax radiatively through the triplet-singlet transition of the neighbouring oxygen-deficient centers. The complete picture of the optical excitation and relaxation processes in these materials is illustrated in a general diagram depicting electronic states.

Spectrophotometric determination of trace hydrogen peroxide via the oxidative coloration of DPD using a Fenton system

A low-cost and environmentally-friendly spectrophotometric method for hydrogen peroxide (H2O2) determination based on the oxidative coloration reaction of N,N′-diethyl-p-phenylenediamine (DPD) via the Fenton reactions in aqueous water was established. The generated pink radical cation (DPD+) showed maximum absorption at 551 nm. Importantly, under the optimal conditions (pH 3.0, 20 mM DPD, 1.5 mM Fe(II) and reaction time of 45 s), the increase in absorbance at 551 nm for DPD+ generation was linear with respect to the addition of H2O2 (0–12 μM). The sensitivity and the detection limit of the proposed Fenton-DPD method for H2O2 determination at 551 nm were (2.55 ± 0.01) × 104 M−1 cm−1 and 0.05 μM, respectively. The stoichiometric factor for the reaction of H2O2 with DPD was 1:1.18. The absorbance of the generated DPD+ was found to be stable in different types of water within 20 min. Moreover, the proposed Fenton-DPD method could be used for the analysis of the trace H2O2 in rainwater and determine the rate constants that involved H2O2 with high accuracy.

Synthesis, structure and properties of a calcium oxonitridosilicate phosphor showing green or red luminescence upon doping with Eu2+ or Ce3.

The phase LixCa16-xSi17N32-xO2+x was synthesized by solid-state metathesis at 1050 °C in weld-sealed niobium ampoules. The crystal structure was solved from powder X-ray diffraction data in the space group F4[combining macron]3m (a = 14.7391(1) Å, Z = 4); it is closely related to the previously reported structure of Ca16Si17N34. The structure of LixCa16-xSi17N32-xO2+x is based on a complex network of [SiN4] tetrahedra with interstitial voids filled by Ca ions, partially substituted by Li. This Li substitution is charge-compensated by replacement of N by O in the structure. Theoretical calculations confirm that the unit cell volume decreases with increasing stoichiometric factor x. Europium doped samples of this compound show intense Eu2+ emission at 536 nm on excitation with near-UV or blue radiation at 350-480 nm. Ce3+ doping yields orange to red emission with two broad emission bands at 600 and 665 nm.

An innovative and efficient method to synthesize meloxicam in one-step procedure with respect to the green chemistry

An improved procedure for the synthesis of meloxicam drug (methyl 4-hydroxy-2-methyl-2H-1,2-benzothiazol-2-amine-3-carboxylate 1,1-dioxide) was described in one-step using mainly impregnated montmorillonite K10 (MK10) with ZnCl2 as a heterogeneous catalyst. This innovative method was compared to the last described procedure employed in the manufacture of this anti-inflammatory drug by means of some metrics used in a first step of the evaluation process of the environmental impact of a chemical transformation. Apart from the yield, which was 90%, atom economy, waste, environmental factor, reaction mass efficiency and stoichiometric factor were calculated as 91.6%, 8.4%, 0, 8.1% and 1%, respectively. Interpretation of these metrics was given and highlighted the fact that the strategy used in the current study may be considered as an environmental-friendly and sustainable method that fits well in the green chemistry concepts.

Hybrid of Resveratrol and Glucosamine: An Approach To Enhance Antioxidant Effect against DNA Oxidation.

Resveratrol exhibits various pharmacological activities, which are dependent upon phenolic hydroxyl groups. In this work, glucosamine, lipoic acid, or adamantanamine moiety was applied for attaching to ortho-position of hydroxyl group in resorcinol moiety of resveratrol (known as position-2). Antioxidant effects of the obtained hybrids were characterized using DNA oxidative systems mediated by •OH, Cu2+/glutathione (GSH), and 2,2'-azobis(2-amidinopropanehydrochloride) (AAPH), respectively. The glucosyl-appended imine and amine at position-2 of resveratrol were found to show higher inhibitory effects than other resveratrol derivatives against AAPH-induced DNA oxidation. The antioxidative effect was quantitatively expressed by stoichiometric factor ( n, the number of radical-propagation terminated by one molecule of antioxidant). The stoichiometric factors of glucosyl-appended imine and amine of resveratrol increased to 4.74 (for imine) and 4.97 (for amine), respectively, higher than that of resveratrol (3.70) and glucoside of resveratrol (3.49). It was thereby concluded that the combination of resveratrol with glucosamine at position-2 represented a novel pathway for modifying resveratrol structure in the protection of DNA against peroxyl radical-mediated oxidation.

Direct Coupling of PEM Fuel Cell to Supercapacitors for Higher Durability and Better Energy Management

AbstractA single polymer electrolyte fuel cell has been directly hybridized to a stack of three supercapacitors: the system formed has been investigated in operation in the fuel cell dynamic load cycle, which emulates the energy demand in transported applications. Comparison with regular, non‐hybridized fuel cell operation was analyzed in terms of hydrogen consumption in the case that the gas flow rates are directly controlled by cell current during the cycles with constant gas stoichiometric factors: the smoothening effect of the supercapacitors in the overall circuit leads to more even profiles of the cell current and voltage in the cycle, which allows safer and better hydrogen consumption management in this regime: the average H2 consumption per cycle could be reduced by 16% without change of the overall energy produced. Besides, the runs were conducted over more than 1,300 hours with evaluation of the fuel cell performance and capacity at regular intervals, with or without hybridization. A moderate positive effect of hybridization was observed in the time variations of the voltage‐current curves and the fuel crossover. However, the resistances for ohmic, charge transfer and diffusion phenomena, were not so much improved by the hybridization, in spite of less sharp voltage.