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1.
The propagation and termination rate coefficients for bulk polymerization of the butyl acrylate dimer (BA dimer) are determined by pulsed laser techniques. The rate coefficient for propagation, kp, is deduced for temperatures from 20 to 90 °C via the pulsed laser polymerization-size exclusion chromatography (PLP-SEC) method at pulse repetition rates between 1 and 10 Hz. The Arrhenius parameters were found to be: EA(kp) = (34.2 ± 1.0) kJ mol−1 and A(kp)/L mol−1 s−1 = (1.08 ± 0.49) × 107 L mol−1 s−1. The termination rate coefficient, kt, has been measured via SP-PLP-ESR, single pulse-pulsed laser polymerization in conjunction with time-resolved electron spin resonance detection of radical concentration. The resulting Arrhenius parameters as deduced from the temperature range −15 to +30 °C are: EA(〈kt〉) = (22.8 ± 3.7) kJ mol−1 and log(A/L mol−1 s−1) = 10.6 ± 1. The chain-length dependence of kt was studied at 30 °C. For short chains a significant dependence was found which may be represented by an exponent α = 0.79 in the power-law expression kt(i) = kt0i−α.  相似文献   

2.
Hydrogen sulfide (H2S) is currently removed from gaseous effluents by chemical scrubbing using water. Chlorine is a top-grade oxidant, reacting with H2S with a fast kinetic rate and enhancing its mass transfer rate. To design, optimize and scale-up scrubbers, knowledge of the reaction kinetics and mechanism is requested. This study investigates the H2S oxidation rate by reactive absorption in a mechanically agitated gas–liquid reactor. Mass transfer (gas and liquid sides mass transfer coefficients) and hydrodynamic (interfacial area) performances of the gas–liquid reactor were measured using appropriated physical or chemical absorption methods. The accuracy of these parameters was checked by modeling the H2S absorption in water without oxidant. A sensitivity analysis confirmed the robustness of the model. Finally, reactive absorption of H2S in chlorine solution for acidic or circumneutral pH allowed to investigate the kinetics of reaction. The overall oxidation mechanism could be described assuming that H2S is oxidized irreversibly by both hypochlorite anion ClO (k = 6.75 × 106 L mol−1 s−1) and hypochlorous acid ClOH (k = 1.62 × 105 L mol−1 s−1).  相似文献   

3.
The activation-deactivation equilibrium of nitroxide-controlled radical polymerization of styrene at 123 °C was investigated. For this purpose the reaction solution was examined time dependently during the initial phase of the polymerization by using an SEC column combination providing a very good separation of the low-molecular weight species. By time-dependent measurement of the alkoxyamine concentration the activation rate of the alkoxyamines PhEt-TIPNO (N-tert-butyl-N-(2-methyl-1-phenyl-propyl)-O-(1-phenyl-ethyl)-hydroxylamine) kact = 3.2 × 10−3 s−1 and PhEt-BIPNO (N-tert-butyl-N-(1-isopropyl-2-methyl-propyl)-O-(1-phenyl-ethyl)-hydroxylamine) kact = 6.4 × 10−3 s−1 can be determined directly.Considering the Persistent Radical Effect theory, the measurement of the free nitroxide concentration allows to determine the pseudo-equilibrium constant of dissociation/combination between dormant and active species for polystyryl-TIPNO and polystyryl-BIPNO, K = 7.5 × 10−9 mol/L and 1.08 × 10−8 mol/L, respectively.  相似文献   

4.
Cytosine plays an important role in many biological processes since it constitutes the buildings blocks of DNA and RNA. A two-step reduction of Zn2+ ions at the dropping mercury electrode in acetic buffers at pH 4 and 5 in the presence of cytosine was examined. The measurements were performed using an impedance method in a wide potential and frequency ranges.The values of the standard rate constants ks in the both studied system decrease from 3.8 × 10−3 to 2 × 10−3 cm s−1 at pH 4 and from 5.1 × 10−3 to 2.5 × 10−3 cm s−1 at pH 5. The values of the standard rate constants ks1 characterizing the stage of the first electron transfer decrease similarly. However, the values of the standard rate constants ks2 characterizing the stage of the second electron exchange decrease more markedly in the buffer at pH 4 than in the buffer at pH 5.  相似文献   

5.
Boleslav Taraba 《Fuel》2010,89(11):3598-3601
Subaquatic oxidation of two bituminous coals by water-dissolved oxygen was investigated using batch reactor equipped with membrane oxygen sensor. Effects of time, temperature and coal grain size were studied as basic parameters influencing the oxidation process. Obtained results showed the subaquatic coal oxidation can be considered as interaction of the first reaction order with respect to oxygen. From temperature dependence of oxidation rate, activation energies = 72 ± 4 kJ mol−1 and/or 50 ± 4 kJ mol−1 were calculated. For the samples, oxygen consumption RO2 was found to be in the range of 2 × 10−7 mol O2 kg−1 s−1 to 6 × 10−7 mol O2 kg−1 s−1, such values being quite comparable with RO2 for aerial oxidation of bituminous coals.  相似文献   

6.
Samples and fractions of a membrane-forming polymer, poly(1-trimethylsilyl-1-propyne) (PTMSP), were studied by methods of molecular hydrodynamics (velocity sedimentation, translational isothermal diffusion and viscometry) in cyclohexane in the molecular mass range 60<M×10−3 g mol−1<430. The following molecular-mass dependencies of the hydrodynamic characteristics (intrinsic viscosity [η] (cm3 g−1), sedimentation coefficient s0(s) and translational diffusion coefficient D0 (cm2 s−1)) were established: [η]=0.198 M0.50±0.06; s0=8.66×10−16M0.50±0.04; D0=9.30×10−5M−0.50±0.04. On the basis of the hydrodynamics data the equilibrium rigidity and hydrodynamic diameter of PTMSP chains were evaluated. The equilibrium properties of the different disubstituted polyacetylenes molecules are compared on the base of the normalised scaling plots.  相似文献   

7.
Fang Ye  Lishi Wang 《Electrochimica acta》2008,53(12):4156-4160
5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H2SO4 between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s−1. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L−1 phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10−7 mol L−1 to 3 × 10−5 mol L−1. The electrode had a detection limit of 6.0 × 10−8 mol L−1(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s−1, the transfer coefficient α = 0.709, the electron number involved in the rate determining step nα = 0.952, and the diffusion coefficient Do = 3.54  10−5 cm2 s−1 were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation.  相似文献   

8.
Cross-linked polyamides and polyamide gels were prepared from maleimide-containing polyamides and a tri-functional furan compound and showed thermal reversibility in cross-linking behavior and in gel formation through Diels-Alder (DA) and retro-DA reactions. The rate constant k of the DA cross-linking reaction were 1.25-4.83×10−5 dm3 mol−1 s−1 in the temperature range of 20-60 °C with an activation energy of 32.1 kJ mol−1. The cross-linking densities, thermal properties, and thermal reversibility of the polyamides/furan polymers were adjustable with the contents of maleimide groups in polyamides.  相似文献   

9.
A self-assembled bilayer lipid-like membrane (BLM) supported on glassy carbon electrode (GCE) was fabricated using 5,5-ditetradecyl-2-(2-trimethyl-ammonioethyl)-1,3-dioxane bromide (DTDB) for epinephrine (EP) determination in the presence of ascorbic acid (AA). This modified electrode (DTDB/GCE) has strong membrane adsorption accumulation and electrocatalytic ability toward EP and AA. The oxidation of EP was controlled by double step adsorption accumulation process of the DTDB-BLM. The parameters of fitted Langmuir isotherm Γmax, BADS, and ΔGADS values were determined as 1.0×10−11 mol cm−2, 2.04×106 dm3 mol−1, and −45.17 kJ mol−1 for the fist step for EP concentration less than 1 mM, and 4.92×10−11 mol cm−2, 7.35×104 dm3 mol−1, and −37.1 kJ mol−1 for the second step for EP concentration higher than 1 μM. The DPV peaks for EP and AA oxidations were appeared at 0.220 and 0.085 V versus SCE, respectively, allowing the determination of EP in the presence of high concentration of AA. The advantage of DTDB-BLM was demonstrated experimentally in comparison with other three BLMs, and attributed to the dioxane group as well as the suitable length of the carbon chain of DTDB molecule. The current response of the DTDB/GCE was fast and reproducible, suitable for the electrochemical sensing in flow-injection systems. A linear range of 1×10−8 to 1×10−4 M EP was preliminary obtained using a simple setup.  相似文献   

10.
This work reports the electrocatalytic activity of 2,3,5,6-tetrachloro-1,4-benzoquinone (TCBQ)/multi-walled carbon nanotubes (MWCNT) immobilized on an edge plane pyrolytic graphite electrode for nicotinamide adenine dinucleotide (NADH) oxidation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) were used to confirms the presence of chloro after the nanotube modification with 2,3,5,6-tetrachloro-1,4-benzoquinone. The surface charge transfer constant, ks, and the charge transfer coefficient for the modified electrode, α, were estimated as 98.5 (±0.6) s−1 and 0.5, respectively. With this modified electrode the oxidation potential of the NADH was shifted about 300 mV toward a less positive value, presenting a peak current much higher than those measured on an unmodified edge plane pyrolytic graphite electrode (EPPG). Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the NADH oxidation reaction involves 2 electrons and a heterogenous rate constant (kobs) of 3.1 × 105 mol−1 l s−1. The detection limit, repeatability, long-term stability, time of response and linear response range were also investigated.  相似文献   

11.
Thermal hydrocracking and catalytic hydrocracking over NiMo/γ-Al2O3 of a pentane-insoluble asphaltene were conducted in a microbatch reactor at 430 °C. The experimental data of asphaltene conversion fit second-order kinetics adequately, to give the apparent rate constants of 2.435 × 10−2 and 9.360 × 10−2 wt frac−1 min−1 for the two processes respectively. A three-lump kinetic model is proposed to evaluate rate constants of parallel reactions from asphaltenes to liquid oil (k1) and to gas + coke (k3), and consecutive reaction from liquid to gas + coke (k2). The evaluated k1 is 2.430 × 10−2 and 9.355 × 10−2 wt frac−1 min−1, k2 is 2.426 × 10−2 and 6.347 × 10−3 min−1, and k3 is 5.416 × 10−5 and 4.803 × 10−5 wt frac−1 min−1 for asphaltenes hydrocracking in the presence or absence of the catalyst, respectively. Analysis of selectivity shows that the catalytic hydrocracking process promotes liquid production and inhibits coke formation effectively.  相似文献   

12.
Nano-γ-Al2O3 is dispersed onto the glass carbon electrode (GCE) by polishing. This nanostructured modified GCE exhibits a great enhancement to the redox responses of 3-nitrobenzaldehyde thiosemicarbazone (3-NBT). In comparison with bare GCE, 3-NBT gives a more sensitive voltammetric response because of the nanoparticle’s unique properties. The lowest detectable concentration (3σ) of 3-NBT is estimated to be 1.18 × 10−6 M (accumulation for 4 min). The linear relationship between peak current and concentration of 3-NBT holds in the range 1.0 × 10−5 M to 1.0 × 10−4 M (r = 0.9981). The electrochemical properties of 3-NBT on this modified electrode have been investigated with various electrochemical methods. The results indicate that the transference of one electron and one proton involves electrode radical reaction processes I and II, respectively. The coverage value (Γ) of 1.62 × 10−9 mol cm−2 was calculated and the electrochemical parameters, diffusion coefficient D (2.54 × 10−3 cm2 s−1, 2.03 × 10−3 cm2 s−1) and reaction rate constant ks (5.9573 s−1, 7.15 × 10−2 cm s−1) were obtained for quasi-reversible system I and irreversible system II, respectively.  相似文献   

13.
This work evaluates the volumetric mass transfer coefficient (kLa), the gas hold-up (?) and the mixing time (tm) as a function of superficial gas velocity (UG) in a flat-panel photobioreactor (PBR) with high light path. CO2 utilization efficiency and volumetric power consumption (P/V) were also evaluated. A 50 L working volume photobioreactor was developed, 0.67 m in length, 0.57 m in height and 0.15 m in width (light path). The height-width ratio was 3.8, which is lower than reported in most PBRs. Initially, experiments were performed with air and tap water (biphasic system) and, subsequently, using a Spirulina sp. culture (triphasic system: air, culture medium, cells). Minimum and maximum superficial gas velocity values were 5 × 10−5 and 8.4 × 10−3 m s−1, respectively. Maximum values for kLa and ? were 20.34 h−1 (0.0057 s−1) and 0.033 in the biphasic system, and 31.27 h−1 (0.0087 s−1) and 0.065 in the triphasic system. CO2 utilization efficiency was 30.57%. Results indicate that the hydrodynamic and mass transfer characteristics of this photobioreactor are more efficient than those reported elsewhere for tubular and other flat-plate PBRs, which opens the possibility of using PBRs with higher light paths than yet proposed.  相似文献   

14.
A pentane-insoluble asphaltene was processed by thermal cracking and catalytic hydrocracking over NiMo/γ-Al2O3 in a microbatch reactor at 430 °C. Kinetic analysis shows that the first-order kinetics fits the data of conversion in reaction times ≤ 30 min approximately, but deviates from the data of times over 30 min significantly; whereas the second-order kinetics fits the data of the reaction times up to 60 min adequately, to give the apparent rate constants of 1.704 × 10−2 and 9.360 × 10−2 wt frac−1min−1 for the two cracking processes. Furthermore, a three-lump kinetic model is proposed to include parallel reactions of asphaltenes to produce liquid oil (k1) and gas + coke (k3), and consecutive reaction from liquid to gas + coke (k2). The evaluated value of k1 is 1.697 × 10−2 and 9.355 × 10−2 wt frac−1min−1, k2 is 3.605 × 10−2 and 6.347 × 10−3 min−1 , and k3 is 6.934 × 10−5 and 4.803 × 10−5 wt frac−1min−1 for asphaltenes thermal cracking and catalytic hydrocracking, respectively. Selectivity analysis shows that the catalytic hydrocracking process promotes liquid production and inhibits coke formation effectively.  相似文献   

15.
A multi-walled carbon nanotubes (MWCNTs) modified carbon ionic liquid electrode (CILE) was fabricated and used to investigate the electrochemical behavior of guanosine. CILE was prepared by mixing hydrophilic ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4), graphite powder and liquid paraffin together. The fabricated MWCNTs/CILE showed great electrocatalytic ability to the oxidation of guanosine and an irreversible oxidation peak appeared at 1.067 V (vs. SCE) with improved peak current. The electrochemical behavior of guanosine on the MWCNTs/CILE was carefully studied by cyclic voltammetry and the electrochemical parameters such as the charge transfer coefficient (α) and the electrode reaction standard rate constant (ks) were calculated with the result as 0.66 and 2.94 × 10−4 s−1, respectively. By using differential pulse voltammetry (DPV) as the detection method, a linear relationship was obtained between the oxidation peak current and the guanosine concentration in the range from 1.0 × 10−7 to 4.0 × 10−5 mol/L with the detection limit as 7.8 × 10−8 mol/L (3σ). The common coexisting substances showed no interferences to the guanosine detection and the modified electrode showed good ability to distinguish the electrochemical response of guanosine and adenosine.  相似文献   

16.
The interactions of promethazine hydrochloride (PZH) with thiolated single-stranded DNA (HS-ssDNA) and double-stranded DNA (HS-dsDNA) self-assembled on gold electrodes have been studied electrochemically. The binding of PZH with ssDNA shows a mechanism containing an electrostatic interaction, while the mode of PZH interaction with dsDNA contains both electrostatic and intercalative bindings. The redox system belongs to the category of diffusion control approved by cyclic voltammetry (CV). The diffusion coefficients of PZH at the bare, HS-dsDNA and HS-ssDNA modified gold electrodes decrease regularly as 1.34 × 10−3 cm2 s−1, 1.04 × 10−3 cm2 s−1, 7.47 × 10−4 cm2 s−1, respectively. The electron transfer standard rate constant ks of PZH at bare gold, HS-ssDNA and HS-dsDNA modified electrodes are 0.419 s−1, 0.131 s−1, and 0.154 s−1, respectively. The presence of adsorbed dsDNA results in a great increase in the peak currents of PZH in comparison with those obtained at a bare or ssDNA adsorbed gold electrode. The difference between interactions of PZH with HS-ssDNA and HS-dsDNA has been used for hybridization recognition of 14-mer DNA oligonucleotide. The peak current (ipa) of PZH is linearly proportional to the logarithmic concentration of complementary target DNA in the range from 2.0 × 10−9 mol L−1 to 5.0 × 10−7 mol L−1 with the detection limit of 3.8 × 10−10 mol L−1.  相似文献   

17.
The effects of polymerization time and temperature on the molecular weight and molecular weight distribution of polyethylene, produced over homogeneous catalyst bis[N-(3-tert-butyl salicylidene)anilinato]zirconium(IV) dichloride tBu-L2ZrCl2/MAO have been studied. The data on the number of active centers (CP) and propagation rate constants (kP) at different polymerization time have been obtained as well. It was found that at a short polymerization time two types of active centers, producing low molecular weight PE (Mw = (4-10) × 103 g mol−1) are formed. The number of these centers was estimated to be 11% of total zirconium complex and their reactivity is very high (the kP value was found to be 54 × 103 L mol−1 s−1 at 35 °C). High initial activity of the catalyst fell with the increase in polymerization time, whereas the polydispersity values of the resulting PE increase due to formation of new centers, producing high molecular weight PE (Mw = (30-1300) × 103 g mol−1). It was found that the decrease in activity is caused by reducing the initial active centers number and lower reactivity of the new-formed centers (kP = 17 × 103 L mol−1 s−1).  相似文献   

18.
The electrocatalytic oxidation of deoxyguanosine on a ruthenium hexacyanoferrate (RuOHCF) glassy carbon (GC) modified electrode was investigated in acid medium by using rotating disc electrode (RDE) voltammetry. Chronoamperometric experiments allowed information on the charge transport rate through the RuOHCF film and at a very short time window a diffusion-like behavior was observed with a Dct value of 2.7 × 10−11 cm2 s−1 for a film with Γ = 4.47 × 10−9 mol cm−2. The influence of systematic variation of rotation rate, film thickness and the electrode potential indicates that the rate of cross-chemical reaction between Ru(IV) centers immobilized into the film and deoxyguanosine controls the overall electrodic process and the value of the rate constant was found to be 3.2 × 106 mol−1 L1 s−1. The relatively high rate constant of the cross-reaction, the facile penetration of the substrate through the film and the fast transport of electrons suggest that the electrocatalytic process occurs throughout the film layer.  相似文献   

19.
Mutual diffusion coefficients (interdiffusion coefficients) and molar electrical conductivities have been measured for cobalt chloride aqueous solutions in the absence and the presence of saccharose at different concentrations (from 0.01 to 0.3 mol dm−3) and 298.15 K. The diffusion coefficients were measured by using the conductimetric method. For these aqueous solutions, limiting molar conductivity values have been calculated. The value of λ0(Co2+) = 105.36 × 10−4 S m2 mol−1, obtained at 298.15 K in pure water solution, agrees well with that reported in the literature. The Nernst diffusion coefficient values derived from diffusion (1.301 × 10−9 m2 s−1) and from conductance (1.295 × 10−9 m2 s−1) are also in good agreement.The dependence of diffusion coefficients and electrical conductivity of CoCl2 on the concentration of saccharose is discussed by considering the effect of the carbohydrate on the electrolyte dehydration, as well as on the ion-pairs and complexes (CoCl2-saccharose and ions-saccharose) formation.  相似文献   

20.
Electron transfer (ET) kinetics through n-dodecanethiol (C12SH) self-assembled monolayer on gold electrode was studied using cyclic voltammetry (CV), scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). An SECM model for compensating pinhole contribution, was used to measure the ET kinetics of solution-phase probes of ferrocyanide/ferricyanide (Fe(CN)64−/3−) and ferrocenemethanol/ferrociniummethanol (FMC0/+) through the C12SH monolayer yielding standard tunneling rate constant () of (4 ± 1) × 10−11 and (3 ± 1) × 10−10 cm s−1 for Fe(CN)64−/3− and FMC0/+ respectively. Decay tunneling constants (β) of 0.97 and 0.96 Å−1 for saturated alkane thiol chains were obtained using Fe(CN)64− and FMC respectively. Also, it was found that methylene blue (MB) molecules are effectively immobilized on the C12SH monolayer and can mediate the ET between the solution-phase probes and underlying gold substrate. SECM-mediated model was used to simultaneously measure the bimolecular ET between the solution-phase probes and the monolayer-immobilized MB molecules, as well as tunneling ET between the monolayer-immobilized MB molecules and the underlying gold electrode, allowing the measurement of kBI = (5 ± 1) × 106 and (4 ± 2) × 107 cm3 mol−1 s−1 for the bimolecular ET and and (7 ± 3) × 10−2 s−1 for the standard tunneling rate constant of ET using Fe(CN)64−/3− and FMC0/+ probes respectively.  相似文献   

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