Apparent Kinetics Research Articles

Production of glycerol carbonate using crude glycerol from biodiesel production with DBU as a catalyst

Abstract The biodiesel production technology catalyzed by 1,8-diazabicycloundec-7-ene (DBU) is developed in this work. Crude glycerol containing DBU and DBU/glycerol/CO2 (DGC) ionic compounds reacts directly with dimethyl carbonate (DMC) to produce high value-added glycerol carbonate (GC) catalyzed by DBU and DGC. The catalytic performance of DBU and DGC, as well as the kinetics of the reaction catalyzed by DBU, were investigated. The results show that DGC has a weak catalytic effect on the transesterification of glycerol and DMC. When the temperature is higher than 60 °C, DGC catalyzes the reaction jointly with DBU, which is produced from the decomposition of DGC. DBU has a good catalytic effect on the reaction between glycerol and DMC, with 90% conversion of glycerol and 84% selectivity to GC under the following conditions: DMC-to-glycerol molar ratio of 3:1, 4.0% DBU (based on glycerol mass), reaction time of 60 min, and reaction temperature of 40 °C. The apparent kinetics results show that the activation energies are 30.95 kJ·mol− 1 and 55.16 kJ·mol− 1 for the forward and reverse GC generation reactions, respectively, and the activation energy of the decomposition reaction of GC to glycidol (GD) is 26.58 kJ·mol− 1.

Photoelectrocatalytic oxidation of acid green 50 dye in aqueous solution using Ti/TiO2-NT electrode

To further improve the TiO2 photocatalytic process for water treatment, a nanotube Ti/TiO2 electrode (Ti/TiO2-NT) was prepared by anodizing Ti foil in non-aqueous solution inside the voltage range of 35–55 V. The structural and surface morphology of the Ti/TiO2 electrode were examined by X-ray spectroscopy and scanning electronic microscopy, respectively. The nanotube formation rate was influenced by the anodization voltage which affected its morphology. It was observed that the nanotube formation rate increased by increasing the anodizing voltage. The photoelectrocatalytic (PEC) and photocatalytic (PC) oxidation of acid green 50 (AG50) in aqueous solution using the Ti/TiO2-NT electrode were studied and compared. The results demonstrate that PEC oxidation, at all applied potentials between the Ti/TiO2-NT electrode and carbon graphite electrode, highly enhanced the degradation rate of AG50 compared to PC oxidation. Therefore, the application of a potential in the PC process (PEC) favorably influences the performance of the PC process. The PEC oxidation of AG50 under the application of a potential followed apparent first order kinetics. Nanotube photocatalytic reactivity was influenced by annealing temperature and applied potential at fixed pH of the solution. It was found that the best performance of PEC oxidation was achieved by applying an electrical bias of 1.0 V or 1.2 V.

Geraniol Pharmacokinetics, Bioavailability and Its Multiple Effects on the Liver Antioxidant and Xenobiotic-Metabolizing Enzymes.

Geraniol is a natural monoterpene showing anti-inflammatory, antioxidant, neuroprotective and anticancer effects. No pharmacokinetic and bioavailability data on geraniol are currently available. We therefore performed a systematic study to identify the permeation properties of geraniol across intestinal cells, and its pharmacokinetics and bioavailability after intravenous and oral administration to rats. In addition, we systematically investigated the potential hepatotoxic effects of high doses of geraniol on hepatic phase I, phase II and antioxidant enzymatic activities and undertook a hematochemical analysis on mice. Permeation studies performed via HPLC evidenced geraniol permeability coefficients across an in vitro model of the human intestinal wall for apical to basolateral and basolateral to apical transport of 13.10 ± 2.3 × 10-3 and 2.1 ± 0.1⋅× 10-3 cm/min, respectively. After intravenous administration of geraniol to rats (50 mg/kg), its concentration in whole blood (detected via HPLC) decreased following an apparent pseudo-first order kinetics with a half-life of 12.5 ± 1.5 min. The absolute bioavailability values of oral formulations (50 mg/kg) of emulsified geraniol or fiber-adsorbed geraniol were 92 and 16%, respectively. Following emulsified oral administration, geraniol amounts in the cerebrospinal fluid of rats ranged between 0.72 ± 0.08 μg/mL and 2.6 ± 0.2 μg/mL within 60 min. Mice treated with 120 mg/kg of geraniol for 4 weeks showed increased anti-oxidative defenses with no signs of liver toxicity. CYP450 enzyme activities appeared only slightly affected by the high dosage of geraniol.

Transformation products formation of ciprofloxacin in UVA/LED and UVA/LED/TiO2 systems: Impact of natural organic matter characteristics.

The role of natural organic matter (NOM) in contaminants removal by photolysis and photocatalysis has aroused increasing interest. However, evaluation of the influence of NOM characteristics on the transformation products (TPs) formation and transformation pathways of contaminants has rarely been performed. This study investigated the decomposition kinetics, mineralization, TPs formation and transformation pathways of antibiotic ciprofloxacin (CIP) during photolysis and photocatalysis in the presence of three commercial NOM isolates (Sigma-Aldrich humic acid (SAHA), Suwannee River humic acid (SRHA) and Suwannee River NOM (SRNOM)) by using UVA light emitting diode (UVA/LED) as an alternative light source. NOM isolates insignificantly affected CIP photolysis but strongly inhibited CIP photocatalysis due to competitive radical quenching. The inhibitory effect followed the order of SAHA (49.6%) > SRHA (29.9%) > SRNOM (21.2%), consistent with their •OH quenching abilities, SUVA254 values and orders of aromaticity. Mineralization rates as revealed by F- release were negatively affected by NOM during CIP photocatalysis. TPs arising from hydroxylation and defluorination were generally suppressed by NOM isolates in UVA/LED and UVA/LED/TiO2 systems. In contrast, dealkylation and oxidation of piperazine ring were promoted by NOM. The enhancement in the apparent formation kinetics (kapp) of TP245, TP291, TP334a, TP334b and TP362 followed the order of SRNOM > SRHA > SAHA. kapp values were positively correlated with O/C ratio, carboxyl content, E2/E3 and fluorescence index (FI) of NOM and negatively related with SUVA254 values. The observed correlations indicate that NOM properties are important in determining the fate and transformation of organic contaminants during photolysis and photocatalysis.

Metabolism and pharmacokinetics studies of allyl methyl disulfide in rats

1. Allyl methyl disulfide (AMDS) is one of the main compounds in garlic, whereas its metabolism has not been studied yet.2. In this work, we first identified the metabolites of AMDS in rat erythrocytes and rats using GC–MS. The transformation mechanism study among different metabolites was then conducted. The apparent kinetics of AMDS in rat erythrocytes and pharmacokinetics of AMDS by oral administration in rats were also studied.3. The metabolic pathway study showed that AMDS was mainly metabolized in rats to allyl methyl sulfoxide (AMSO) and allyl methyl sulfone (AMSO2) through mechanisms of reduction, methylation and oxidation. The transformation mechanism study indicated that AMDS was firstly reduced to allyl mercaptan (AM) in rat erythrocytes, and then methylated to allyl methyl sulfide (AMS) by S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH), and finally oxidized to AMSO and AMSO2 by liver microsomes. The half-life of AMDS in rat erythrocytes was 6.285 ± 0.014 min while the half-lives of its active metabolites AMSO and AMSO2 in vivo were 18.17 and 17.50 h, respectively. Also, the large AUCs of the two active metabolites were observed, indicating potential applications of AMDS for certain pharmacological effects.

Slow domain reconfiguration causes power-law kinetics in a two-state enzyme

Protein dynamics are typically captured well by rate equations that predict exponential decays for two-state reactions. Here, we describe a remarkable exception. The electron-transfer enzyme quiescin sulfhydryl oxidase (QSOX), a natural fusion of two functionally distinct domains, switches between open- and closed-domain arrangements with apparent power-law kinetics. Using single-molecule FRET experiments on time scales from nanoseconds to milliseconds, we show that the unusual open-close kinetics results from slow sampling of an ensemble of disordered domain orientations. While substrate accelerates the kinetics, thus suggesting a substrate-induced switch to an alternative free energy landscape of the enzyme, the power-law behavior is also preserved upon electron load. Our results show that the slow sampling of open conformers is caused by a variety of interdomain interactions that imply a rugged free energy landscape, thus providing a generic mechanism for dynamic disorder in multidomain enzymes.

Influence of Cosolvents and Surfactants on the Rate Constant (Log K) of Sparfloxacin

Sparfloxacin, a difluoroquinolone antibacterial agent is clinically used in the treatment of streptococci and community-acquired lower respiratory tract infections. The aim of the present study was to investigate to what extent cosolvents and surfactants could affect sparfloxacin degradation kinetics under acidic condition. The degradation of sparfloxacin in acidic aqueous solution of cosolvents and surfactants at 60 ± 0.2°C was studied. The degradation was determined by UV spectrometry. The degradation was observed to follow apparent first-order rate kinetics and the rate constants for the decomposition were obtained from plots of logarithm percent drug concentration remaining versus time. The reaction was shown to be hydrogen ion catalysed. Significant increase in the stability of sparfloxacin was observed with the cosolvents and surfactants investigated. The study suggests that cosolvents or surfactants at non-toxic concentrations could be incorporated into liquid pharmaceutical dosage forms of sparfloxacin to stabilize the preparations under acidic conditions.

Kinetic study of the photocatalytic degradation of the C-polymorph of a stearic acid microcrystal grown on an amorphous titania surface scattered with anatase microdomains

The photodegradation of a stearic acid (SA) microcrystal on an amorphous titania film surface scattered with submicrometric anatase domains is observed using a Reflected Light – Differential Interference Contrast (RL-DIC) microscopy. The SA microcrystal, grown from a saturated solution, is flat and rhombus-shaped with acute angle of 55° in agreement with the C-polymorph of SA crystal. We observe that the photodegradation initiates at the anatase microdomains under the microcrystal and creates SA holes in the shape of truncated-rhombus or elongated-hexagons having the same orientation and symmetry as the SA microcrystal. The expansion of the SA holes is ascribed to a photodegradation mechanism mediated by the photogeneration and surface diffusion of radical species across the gap between the anatase microdomain and the edges of the SA holes. A detail kinetic study of the SA holes expansion shows that the surface area of the SA holes scales almost linearly with UV exposure time in good agreement with an apparent zero-order kinetics. The morphology and the expansion kinetics of these holes are rationalized through the orientation dependence of the reactivity of the molecules with the radical species.

Diclofenac degradation using mont-La (6%)-Cu0.6Cd0.4S as photocatalyst under NUV–Vis irradiation. Operational parameters, kinetics and mechanism

We report the aqueous photodegradation -under NUV–Vis radiation- of diclofenac, a common non-steroidal anti-inflammatory drug found to be persistent in the environment, using mont-La(6%)-Cu0.6Cd0.4S, a nanocomposite prepared by simple cation exchange and impregnation method. Operational parameters relevant for the process have optimized: amount of catalyst, dissolved oxygen concentration, initial diclofenac concentration and pH. Heterogeneous suspensions of 1gL−1 of mont-La(6%)-Cu0.6Cd0.4S nanocomposite allowed removal of ca. 92% of 10mgL−1 solution of diclofenac at pH=5.9 with natural dissolved oxygen from air within 240min, meanwhile TOC removal was 67%. The photocatalytic process is adequately described by the Langmuir-Hinshelwood kinetic model, following apparent pseudo-first order kinetics. A suitable reaction mechanism has been proposed, based on the available kinetic evidences and the reaction products observed by HPLC–MS analysis.

Emergence of the Reactivity Continuum of Organic Matter from Kinetics of a Multitude of Individual Molecular Constituents.

The reactivity continuum (RC) model is a powerful statistical approach for describing the apparent kinetics of bulk organic matter (OM) decomposition. Here, we used ultrahigh resolution mass spectrometry data to evaluate the main premise of the RC model, namely that there is a continuous spectrum of reactivity within bulk OM, where each individual reactive type undergoes exponential decay. We performed a 120 day OM decomposition experiment on lake water, with an untreated control and a treatment preexposed to UV light, and described the loss of bulk dissolved organic carbon with RC modeling. The behavior of individual molecular formulas was described by fitting the single exponential model to the change in peak intensities over time. The range of the empirically derived apparent exponential decay coefficients (kexp) was indeed continuous. The character of the corresponding distribution, however, differed from the conceptual expectations, due to the effects of intrinsic averaging, overlaps in formula-specific loss and formation rates, and the limitation of the RC model to include apparently accumulating compounds in the analysis. Despite these limitations, both the RC model-simulated and empirical (mass spectrometry-derived) distributions of kexp captured the effects of preexposure to UV light. Overall, we present experimental evidence that the reactivity continuum within bulk OM emerges from a range of reactivity of numerous individual components. This constitutes direct empirical support for the major assumption behind the RC model of the natural OM decomposition.

On the kinetic modeling of biomass/coal char co-gasification with steam

Co-gasification of biomass/coal blends is very promising due to many advantages. Kinetic modeling of the co-gasification process is, however, lagged behind, which is adverse to the development of the co-gasification technology. In this work, a scheme to set up kinetic models for the co-gasification of biomass/coal char blends is proposed. Based on the scheme, a kinetic model for the steam co-gasification of the blended biomass/coal char is built. The intra-particle diffusion, particle structure evolution and peripheral fragmentation are allowed for, and the effects of biomass blending ratio (BBR), gasification temperature, and steam partial pressure on the apparent co-gasfication kinetics are considered. The model prediction is compared against a series of experimental data in literature, and good agreement is achieved. It is concluded that the effects of BBR on the co-gasfication kinetics can be treated as a net increment of the coal char conversion rate, and the net increment can be well predicted by the random pore model. BBR has great impact on the particle structure and composition which greatly affect both the intrinsic kinetics and the intra-particle diffusion.

Synergetic effect of titanium dioxide ultralong nanofibers and activated carbon fibers on adsorption and photodegradation of toluene

Effective adsorption and photodegradation of volatile organic compounds (VOCs) especially for the high concentrations still remained great challenges. Herein, we firstly fabricated ultralong TiO2 nanofiber/activated carbon fiber (TiNF/ACF) porous composites by deposition of TiNFs within ACF felts. The ultralong TiNFs with diameters of 30–100nm and lengths of >200μm were originated from the ordered aggregates of nanocrystals along the [101] direction. The TiNF/ACF porous composites possessed excellent adsorption property for toluene, and the adsorption performances were fit well with pseudo-second-order kinetics model. Their adsorption efficiency reached 98.9% at the toluene concentration of <4600ppm and 85.7% even at the high concentration of 13,800ppm. Moreover, the synergetic effect between the TiNFs and ACFs improved remarkably the photodegradation activity of the composites. The ACFs not only increased the quantum efficiency of TiO2 by hindering the recombination of electron-hole pairs, but also enhanced the light adsorption ability by reducing the TiO2 band gap energy (Eg) to 2.99eV. At the toluene concentrations of 115ppm or 230ppm, the photocatalytic time in which toluene degraded into CO2 and H2O was only 5h or 13h, respectively. The photodegradation kinetics of toluene matched well with the apparent first-order reaction kinetics model at high concentration of 690ppm, while that matched well with the semi-empirical power-law expression equation of CO2 desorption at low concentrations of 115ppm. Hence, the TiNF/ACF porous composites with excellent adsorption and photocatalytic activities had great application potentials for VOC removal.

Application of the aldolization reaction in separating the mixture of ethylene glycol and 1,2-butanediol: Kinetics and reactive distillation

In previous paper, by the thermodynamics investigation, it has been demonstrated that aldolization reaction with acetaldehyde is an effectively way to solve the puzzle of separating ethylene glycol and 1,2-butanediol mixture. In this paper, the reaction kinetics of aldolization was studied and a reactive distillation process was developed. The aldolization reactions were performed in the batch reactor under various conditions, including different temperatures, quantity of the catalyst and feed ratio. The apparent kinetics was correlated with experiment data by a pseudohomogeneous model. Based on the reaction kinetics, an applicable reactive distillation process was developed with a novel reactive distillation column. Simulations were finished by the process simulating software—Aspen Plus V7.3. The result shows that both glycols could be totally converted and their acetals could be easily separated, which shows great industrial application potential in the production of EG.

Kinetics of Catalytic Peroxide Oxidation of Phenol over Three-Dimensional Fractals

The objective of this work was to develop a fractal-like kinetic model for describing hydrogen peroxide oxidation of phenol over Cu/ZSM-5 catalyst of different fractal forms caused by thermal treatment of the catalysts. Pseudo-first-order generalizations of the apparent kinetic rate (Kopelman fractal-like, Brouers–Sotolongo fractal-fractional, Weibull, and stretched exponential models) allowed the kinetics of reaction to be described. These suggested mathematical models of the phenol oxidation plausibly depict the experimental data and correctly reproduce the oxidation process. Fractality of the catalysts exerts a pronounced effect on catalyst activity, as well as on the apparent kinetics of the process. The maximum ability toward phenol oxidation has been detected for the Cu/ZSM-5 catalyst with more fractality.

Degradation of Phenolic Compounds in Aqueous Sucrose Solutions by Ozonation

ABSTRACTThe sugar industry is concerned with color formation due to the oxidation of phenolic compounds in the presence of carbohydrates. In this study, we investigated the ozonation of a mixture of five phenolic compounds in water and aqueous sucrose solution: p-coumaric (p-COU), caffeic (CAF), syringic (SYR), and chlorogenic (CHO) acids, as well as the flavonoid quercetin (QUE). The experiments were carried out in a 3-L glass reactor with magnetic stirring and a diffuser plate at the bottom to feed the ozone-oxygen gas mixture. Initial solution concentrations of 5 mg L−1 of each acid, 15 mg L−1 of quercetin, and 40 g L−1 of sucrose were used. The degradation of phenolic compounds followed apparent first-order kinetics, with rate constants and percent removals decreasing in the presence of sucrose. In water, average consumed ozone dosages of 10.4 and 18.7 mg L−1 were necessary for 50% and 90% removals, respectively, for CHO, CAF, and p-COU; for QUE they were slightly higher (13.9 and 20.5 mg L−1, respectively). At a consumed dosage of 20.8 mg O3 L−1, more than 99% removal was obtained for CHO, CAF, and p-COU, while 96.2% was achieved for SYR. In contrast, QUE revealed to be more recalcitrant during ozonation in the absence of sucrose, with only 70% removal at the highest consumed O3 dosage. The consumed ozone dosages for 50% and 90% removals were higher for CHO, CAF, and p-COU in aqueous sucrose solution, which may impact ozone consumption during real sugarcane juice treatment. Sucrose and t-butanol were the main influential parameters that significantly affected the total amount of phenolic compounds degraded.

Apparent kinetics of the Bunsen reaction in I2/HI solution for the iodine–sulfur hydrogen production process

Massive hydrogen production featuring high efficiency, CO2 free, and cost effectiveness is a crucial challenge for the hydrogen economy. Nuclear hydrogen production through thermochemical iodine–sulfur (IS) process is a potential candidate for this purpose. Chemical reaction kinetics data are indispensable for developing a high-performance reactor as well as the scaling up of the process. The apparent kinetics of the reaction under simulated recycling conditions of IS closed cycle operation was studied by initial rate method. The effects of key parameters, including agitation speed, SO2 partial pressure, I2 concentration, and reaction temperature, on reaction rate, were systematically investigated by measuring the variation in SO2 pressure with reaction time. Initial rate analysis method indicated that the Bunsen reaction rates were 0.23 ± 0.01 and 0.77 ± 0.01 order with respect to SO2 pressure and I2 concentration. The apparent activation energy was 5.86 ± 0.21 kJ/mol. Based on these results, an exponential rate expression of the Bunsen reaction was established. In addition, a simplified method for calculation of kinetics parameters was proposed and compared with conventional techniques. Experimental results provide theoretical basis for design and development of Bunsen reactors and for elucidating the reaction process.

Fast pyrolysis kinetics of alkali lignin: Evaluation of apparent rate parameters and product time evolution

In this study, the apparent kinetics of fast pyrolysis of alkali lignin was evaluated by obtaining isothermal mass loss data in the timescale of 2–30s at 400–700°C in an analytical pyrolyzer. The data were analyzed using different reaction models to determine the rate constants and apparent rate parameters. First order and one dimensional diffusion models resulted in good fits with experimental data with apparent activation energy of 23kJmol−1. Kinetic compensation effect was established using a large number of kinetic parameters reported in the literature for pyrolysis of different lignins. The time evolution of the major functional groups in the pyrolysate was analyzed using in situ Fourier transform infrared spectroscopy. Maximum production of the volatiles occurred around 10–12s. A clear transformation of guaiacols to phenol, catechol and their derivatives, and aromatic hydrocarbons was observed with increasing temperature. The plausible reaction steps involved in various transformations are discussed.

Pyrolysis of sewage sludge in a fixed and a bubbling fluidized bed – Estimation and experimental validation of the pyrolysis time

Pyrolysis of sewage sludge was studied experimentally in a stainless-steel reactor operated as a fixed or fluidized bed. A novel measuring technique, consisting of measuring the mass of the whole reactor and the sample on a scale, was applied. The scale was capable of measuring the whole mass of the reactor with enough accuracy to detect the mass released by the sewage sludge sample during its pyrolysis. This original measuring technique permitted the measurement of the evolution over time of the mass of sewage sludge supplied to the bed in batch during its pyrolysis while moving freely in the bed. From the measurement of the mass of the solid residue remaining in the reactor, the pyrolysis time of the sewage sludge sample can be obtained accurately for each operating condition. Different operating conditions were selected to analyze the evolution with time of the sample mass during the pyrolysis process, including the bed temperature and the velocity of the Nitrogen used as inert gas. An increase of the velocity of Nitrogen from that of a fixed bed (0.8Umf) to that of a low velocity bubbling fluidized bed (2.5Umf) accelerates remarkably the pyrolysis process, i.e. reduces the pyrolysis time, however increasing the Nitrogen velocity further has a slight effect on the characteristic velocity of the pyrolysis process. The pyrolysis process of sewage sludge can also be accelerated by increasing the bed temperature, even though the effect of the temperature is lower than that of the Nitrogen velocity. Furthermore, a mathematical model based on a first order apparent kinetics for the pyrolysis of sewage sludge was proposed. The model was employed to estimate the pyrolysis time for each operating condition, obtaining a proper agreement with the experimental measurements.

Experimental and kinetic study of the nitration of 2-ethylhexanol in capillary microreactors

The nitration process of 2-ethylhexanol (2-EH) with mixed acid was studied in different capillary microreactors. The conversion of 2-EH and selectivity to 2-ethylhexyl nitrate (EHN) were investigated by varying reaction temperature, molar ratio of nitrate to 2-EH, residence time and water content in mixed acid. Under optimized conditions, the conversion of 2-EH and selectivity to EHN could be up to 99% in less than 10seconds, indicating great potential of microreactors in process intensification. Moreover, with an assumption of homogeneous reaction, a kinetic model based on first order kinetics for nitric acid and 2-EH was proposed to determine both the apparent and intrinsic reaction kinetics. By taking into account the activity of solutes that depend on the acidity (Mc), the intrinsic kinetic was obtained, which is independent of the sulfuric acid concentration. The reaction model can well predict the conversion of 2-EH.

Preparation and characterization of highly photocatalytic active hierarchical BiOX (X=Cl, Br, I) microflowers for rhodamine B degradation with kinetic modelling studies

The hierarchical BiOX (X=Cl, Br, I) microflowers were successfully synthesized via simple precipitation method at 160 °C for 24 h and characterized by XRD, SEM, TEM, UV-vis DRS and N2 adsorption-desorption techniques. The as-prepared samples were pure phases and of microflowers composed of nanosheets which intercrossed with each other. The specific surface areas were about 22.9, 17.3 and 16.2 m2/g for BiOCl, BiOBr and BiOI, respectively. The photocatalytic activities of BiOX powers were evaluated by RhB degradation under UV-vis light irradiation in the order of BiOCl > BiOBr > BiOI. Also, the kinetics of RhB degradation over BiOI was selectively investigated, demonstrating that the kinetics of RhB degradation follows apparent first-order kinetics and fits the Langmuir-Hinshelwood model.