Kinetic study on bonding reaction of gelatin with CdS nanopaticles by UV–visible spectroscopy

-4- - Reaction Order and Rate Constants

Sugars containing either aldehyde (aldose), ketone (ketose) or hemiacetal groups can be oxidized and are classified as reducing sugars. As oxidation of carbohydrates is widely studied under the field of organic chemistry, the present work deals with the study of the redox reactions between peroxodisulphate and xylose underuncatalyzed and catalyzed conditions. The kinetic study of the above reactions showed that these reactions followed first order with respect to peroxodisulphate and the silver nitrate ion catalyst and a fractional order of (0.2) with respect to xylose. Ag catalyst was used to increase the rate of reaction in case of xylose where reactions proceed very slowly with respect to time as compared to other sugars used. The oxidation showed that configuration of sugars has some bearing on rate of oxidation. At lower concentration of oxidants, the linear dependence of reaction rate tends towards new order at their higher concentration. The rate of reaction was affected at elevated temperature where thermodynamic activation parameters like activation energy (Ea), enthalpy change of activation (∆H#), free energy change of activation (∆G#) and entropy change of activation (∆S#) were determined by Arrhenius and Erying equations. The analysis of the reaction products using IR revealed the presence of formaldehyde and formic acid. A mechanism of the reactions was proposed to explain the experimentally observed rate law and the products.

Trace metal ion speciation in natural waters is often under kinetic control due to slow exchange reactions involving multidentate ligands (both natural and anthropogenic) and constituent ions (e.g. calcium). Incomplete understanding of the kinetic behavior (rates, rate laws, and mechanisms) of multidentate ligand exchange reactions hinders prediction of metal ion bioavailability and mobility in these systems. Here, we aim to improve understanding (1) by examining the mechanism by which calcium suppresses ligand exchange rates and (2) by developing conceptual tools for predicting the kinetic behavior in environmental systems. Using capillary electrophoresis, we examined the effect of calcium concentration on the kinetics of a model disjunctive multidentate ligand exchange reaction between nickel(ii)-nitrilotriacetate (NiNTA) and trans-1,2-cyclohexylenedinitrilotetraacetate (CDTA) at constant temperature (25 °C) and ionic strength (10 mM). Initial NiCDTA formation rates under varying reactant and calcium concentrations were fit with a single disjunctive ligand exchange kinetic model. While the overall reaction pathway is disjunctive under all conditions studied, the presence of calcium causes a non-linear decrease in reaction rates and alters the overall reaction order with respect to free multidentate ligand concentration. The overall rate law is affected by the relative calcium affinity of exchanging ligands, which controls the balance of product formation and reactant reformation rates from the free metal ion intermediate. The log ratio of these rates is proposed as a metric for determining the appropriate simplified form of the rate law for disjunctive ligand exchange reactions. The implications for in situ ligand lability assays and metal ion bioavailability are discussed.

As a promising strategy to remove and recover phosphorus from wastewater, optimization of the struvite (MgNH4 PO4 .6H2 O) precipitation parameters is required to achieve desirable phosphorus removal efficiency. To tackle the challenges upon the precipitation optimization methods as three-level full factorial designs, and central composite design as well, Box-Behnken design was implemented to optimize different reaction parameters for phosphorus removal and recovery during struvite precipitation in the current study. Moreover, the reaction orders and the rate equation were all determined to reveal the reaction kinetics parameters of struvite precipitation. The results showed that the optimal operating parameters of pH, Mg/P ratio and N/P ratio were 9.82, 1.45, and 4.00, respectively, by which more than 95% of phosphorus removal efficiency could be achieved. In addition, it was found that pH and pH/(N/P) had the most influence on phosphorus removal efficiency among different individual factors and interactive items, respectively. The partial orders of PO4 -P, Mg2+ , and in kinetic rate equation were determined as 1.586, 0.930, and 1.236 while the rate constant k was 0.0167±0.0014mM-2.752 per minute by differential method. PRACTITIONER POINTS: Different reaction parameters were optimized by Box-Behnken design. pH and pH/(N/P) had the most influence on phosphorus removal efficiency among different individual factors and interactive items. The reaction orders and the rate equation were all determined to reveal the reaction kinetics parameters.

In the production of boron fibres using the chemical vapor deposition (CVD) technique, boron deposition and dichloroborane formation reactions occurs simultaneously. Boron deposition reaction occurs at the surface, whereas the formation of dichloroborane is the result of both gas phase and surface reactions. A continuous stirred tank reactor (CSTR) type of reactor was designed to investigate the reaction kinetics and kinetic parameters in the gas phase reactions of boron trichloride and hydrogen. It was concluded that reaction rate of the product increased with an increase in the inlet concentration of both reactants (BCl3 and H2) and with an increase in the reactor temperature. While reaction order with respect to BCl3 was almost constant at about 0.5 at each temperature, reaction order with respect to hydrogen increased significantly at temperatures lower than 350°C. A general rate expression was derived for BHCl2 formation from BCl3 and hydrogen. © 2011 American Institute of Chemical Engineers AIChE J, 2012

The advanced oxidation of high purity metoprolol tartrate, extracted from a commercial medicament, with TiO2 and UV light (365 nm) was investigated to determine the effect of initial reactant concentration on the reaction rate and the role of direct photolysis on the photocatalytic process. Analysis of the reaction samples by UV–Vis spectroscopy indicated that metoprolol tartrate is efficiently degraded by photocatalysis via hydroxylation of the aromatic ring. Kinetic studies indicated that the photocatalytic degradation of metoprolol tartrate follows a Langmuir, Hinshelwood, Hougen and Watson (LHHW) mechanism where the reaction order shifts from zero order to first order as the reactant concentration drops. Additional experiments showed that direct photolysis plays a minor role on the photocatalytic oxidation of metoprolol tartrate. Total organic carbon (TOC) studies demonstrated that metoprolol tartrate is transformed to other organic intermediate reaction products before complete mineralization to CO2. The fraction of reactant transformed into intermediate organic products was evaluated by a material balance using the results of analysis of the reaction samples by high performance liquid chromatography and TOC.

Abstract. Parallel reaction is a common reaction of chemical kinetics, and there are two types of parallel reactions according to the reaction orders equivalence: parallel reactions with same reaction orders and parallel reactions with different reaction orders. For the reason that the reaction orders are different, the chemical kinetic numerical computation and kinetic model parameters estimating of parallel reactions with different reaction orders is more complicated than parallel reactions with same reaction orders. In this paper, the 4th order Runge-Kutta method was employed to solve the numerical computation problems of complex ordinary differential equations, which was the chemical kinetic governing equations of parallel reactions with different reaction orders, and also, the Richardson extrapolation and Least Square Estimate were employed to estimate the kinetic model parameters of parallel reactions with different reaction orders. A C++ program has been processed to solve the problem and has been tested by an example of parallel reactions with different reaction orders.

A kinetic study of oxidation of praseodymium oxides: PrO 1.714 + 0.032 O 2 → PrO 1.778

Metal and metal oxide nanoparticles are very suitable for catalytic activities in organic electron transfer processes. Among these, copper is one of the most important materials that have catalytic activity and the synthesis of copper/copper oxide nanoparticles ($$\mathrm{C}\mathrm{u}$$/$${\mathrm{C}\mathrm{u}}_{2}\mathrm{O}$$ NPs) is more cost-effective than other noble metals. In this study, a combination of copper nanoparticles with different degree of oxidation has been synthesized by electrochemical method. The efficiency of synthesized material for the catalytic reduction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride was studied. The morphology, particle size, and crystalline structure of the synthesized catalyst was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. The kinetics of reaction was followed by UV–Visible spectroscopy and the effect of different parameters such as initial concentrations of 4-nitrophenol, sodium borohydride and catalyst dosage on the reaction rate was studied. The recyclability of the prepared catalyst was investigated as well. The reaction order of the catalyst dosage was investigated by graphical analysis method. Finally based on Langmuir–Hinshelwood (L–H) mechanism the rate of reaction was modeled.

Evaluation of the kinetic oxidation of aqueous volatile organic compounds by permanganate

Kinetics and mechanism of micellar catalyzed N-bromosuccinimide oxidation of dextrose in H2SO4 medium was investigated under pseudo-first-order condition temperature of 40°C. The results of the reactions studied over a wide range of experimental conditions show that NBS shows a first order dependence, fractional order, on dextrose and negative fractional order dependence on sulfuric acid. The determined stoichiometric ratio was 1 : 1 (dextrose : N-bromosuccinimide). The variation of Hg(OAC)2 and succinimide (reaction product) has insignificant effect on reaction rate. Effects of surfactants, added acrylonitrile, added salts, and solvent composition variation have been studied. The Arrhenius activation energy and other thermodynamic activation parameters are evaluated. The rate law has been derived on the basis of obtained data. A plausible mechanism has been proposed from the results of kinetic studies, reaction stoichiometry, and product analysis. The role of anionic and nonionic micelle was best explained by the Berezin’s model.

Summary A methodology is presented for determining reaction kinetics from coreflooding: A core is flooded with reactive brine at different compositions with injection rates varied systematically. Each combination is performed until steady state, when effluent concentrations no longer change significantly with time. Lower injection rate gives the brine more time to react. We also propose shut-in tests where brine reacts statically with the core for a defined period and then is flushed out. The residence time and produced brine composition are compared with the flooding experiments. This design allows characterization of the reaction kinetics from a single core. Efficient modeling and matching of the experiments can be performed as the steady-state data are directly comparable to equilibrating the injected brine gradually with time and do not require spatial and temporal modeling of the entire dynamic experiments. Each steady-state data point represents different information that helps constrain parameter selection. The reaction kinetics can predict equilibrium states and time needed to reach equilibrium. Accounting for dispersion increases the complexity by needing to find a spatial distribution of coupled solutions and is recommended as a second step when a first estimate of the kinetics has been obtained. It is still much more efficient than simulating the full dynamic experiment. Experiments were performed injecting 0.0445 and 0.219 mol/L MgCl2 into Stevns Klint (Denmark) and Kansas (USA) chalks at 100 and 130°C (North Sea reservoir temperature). Injection rates varied from 0.25 to 16 pore volume per day (PV/D), while shut-in tests provided equivalent rates down to 1/28 PV/D. The results showed that Ca2+ ions were produced and Mg2+ ions retained (associated with calcite dissolution and magnesite precipitation, respectively). This occurred in a substitution-like manner, where the gain of Ca was similar to the loss of Mg2+. A simple reaction kinetic model based on this substitution with three independent tuning parameters (rate coefficient, reaction order, and equilibrium constant) was implemented together with advection to analytically calculate steady-state effluent concentrations when injected composition, injection rate, and reaction kinetic parameters were stated. By tuning reaction kinetic parameters, the experimental steady-state data were fitted efficiently. The parameters were determined to be relatively accurate for each core. The roles of reaction parameters, pore velocity, and dispersion were illustrated with sensitivity analyses. The determined reaction kinetics could successfully predict the chemical interaction in reservoir chalk and outcrop chalk containing oil with strongly water-wet or mixed-wet state. The steady-state method allows computationally efficient matching even with complex reaction kinetics. Using a comprehensive geochemical description in the software PHREEQC, the kinetics of calcite and magnesite mineral reactions were determined by matching the steady-state concentration changes as function of (residence) time. The simulator predicted close to the identical production of Ca as loss of Mg. The geochemical software predicted much higher calcite solubility in MgCl2 than observed at 100 and 130°C for Stevns Klint and Kansas. The methodology supports reactive flow modeling in general, but especially oil-bearing chalk reservoirs, which are chemically sensitive to injected seawater in terms of wettability and rock strength.

A methodology is presented for determining reaction kinetics from core flooding: A core is flooded with reactive brine at different compositions with injection rates varied systematically. Each combination is performed until steady state, when effluent concentrations no longer change significantly with time. Lower injection rate gives the brine more time to react. We also propose shut-in tests where brine reacts statically with the core a defined period and then is flushed out. The residence time and produced brine composition is compared with the flooding experiments. This design allows characterization of the reaction kinetics from a single core. Efficient modeling and matching of the experiments can be performed as the steady state data are directly comparable to equilibrating the injected brine gradually with time and does not require spatial and temporal modeling of the entire dynamic experiments. Each steady state data point represents different information that helps constrain parameter selection. The reaction kinetics can predict equilibrium states and time needed to reach equilibrium. Accounting for dispersion increases the complexity by needing to find a spatial distribution of coupled solutions and is recommended as a second step when a first estimate of the kinetics has been obtained. It is still much more efficient than simulating the full dynamic experiment. Experiments were performed injecting 0.0445 and 0.219 mol/L MgCl2 into Stevns Klint chalk from Denmark, and Kansas chalk from USA. The reaction kinetics of chalk are important as oil-bearing chalk reservoirs are chemically sensitive to injected seawater. The reactions can alter wettability and weaken rock strength which has implications for reservoir compaction, oil recovery and reservoir management. The temperature was 100 and 130°C (North Sea reservoir temperature). The rates during flooding were varied from 0.25 to 16 PV/d while shut-in tests provided equivalent rates down to 1/28 PV/d. The results showed that Ca2+ ions were produced and Mg2+ ions retained (associated with calcite dissolution and magnesite precipitation, respectively). This occurred in a substitution-like manner, where the gain of Ca was similar to the loss of Mg2+. A simple reaction kinetic model based on this substitution with three independent tuning parameters (rate coefficient, reaction order and equilibrium constant) was implemented together with advection to analytically calculate steady state effluent concentrations when injected composition, injection rate and reaction kinetic parameters were stated. By tuning reaction kinetic parameters, the experimental steady state data could be fitted efficiently. From data trends, the parameters were determined relatively accurate for each core. The roles of reaction parameters, pore velocity and dispersion were illustrated with sensitivity analyses. The steady state method allows computationally efficient matching even with complex reaction kinetics. Using a comprehensive geochemical description in the software PHREEQC, the kinetics of calcite and magnesite mineral reactions were determined by matching the steady state concentration changes as function of (residence) time. The simulator predicted close to identical production of Ca as loss of Mg. The geochemical software predicted much higher calcite solubility in MgCl2 than observed at 100 and 130°C for Stevns Klint and Kansas.

Kinetic studies were made of the reactions between triphenylphosphine 1, dialkyl acetylenedicarboxylates 2 in the presence of NH-acid, such as maleimid (as a protic/nucleophilic reagent) 3. To determine the kinetic parameters of the reactions, they were monitored by UV spectrophotometery. The second order fits were automatically drawn and the values of the second order rate constant (k2) were automatically calculated using standard equations within the program. All reactions were repeated at different temperature range, the dependence of the second order rate constant (ln k2) and (ln k2/T) on reciprocal temperature was in a good agreement with Arrhenius and Eyring equations. This provided the relevant plots to calculate the activation parameters (Ea, H  , S  and G  ) of all reactions. Furthermore, useful information was obtained from studies of the effect of solvent, structure of reactants (dialkyl acetylenedicarboxylates) and also concentration of reactants on the reaction rates. The proposed mechanism was confirmed according to the obtained results and steady state approximation, and the first and third steps (k2, k3) of all reactions were recognized as rate determining and fast steps, respectively on the basis of experimental data.

The liquid–liquid interfacial precipitation method was used to prepare C60 fullerene nanowhisker (FNW)–zeolitic imidazolate framework-67 (ZIF-67) composite from a ZIF-67 solution, C60-saturated toluene, and isopropyl alcohol. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the synthesized C60 FNW-ZIF-67 composite. Its catalytic activity for the reduction of 4-nitrophenol was confirmed by UV–visible (UV-vis) spectroscopy. C60 FNW–ZIF-67 as a catalyst displayed a reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) for 20 min with a rate constant of 1.379 × 10−1 min−1 (at 25 °C), 5.761 × 10−2 min−1 (at 15 °C), and 3.113 × 10−2 min−1 (at 5 °C), respectively. A kinetics study indicated that the hybrid nanocomposite catalyzed the reduction of 4-nitrophenol according to a pseudo-first-order reaction rate equation. The thermodynamic parameters of activation, namely, the enthalpy of activation (ΔH) of 48.966 kJ mol−1, the entropy of activation (ΔS) of −97.479 J mol−1 K−1, and the activation energy (ΔE a) of 51.167 kJ mol−1, were obtained using the Eyring and Arrhenius equations.