High Reaction Rate Constant Research Articles

Investigation of the methylglyoxal scavenging kinetics of different food matrices under simulated intestinal conditions

This study aimed to evaluate the potential roles of different foods to scavenge exogenous dicarbonyl compounds under simulated gastrointestinal conditions. Four food groups having different arginine, creatine, thiol, and flavonoid contents were subjected to simulated gastric and intestinal conditions together with methylglyoxal. In comparison to control, foods from group 1 (chicken, beef and egg), group 2 (walnut, hazelnut, and kidney bean) and group 3 (broccoli, onion, garlic, and cauliflower) caused a significant (p < 0.05) decrease in the concentration of methylglyoxal under gastric conditions. Egg was found as the most efficient methylglyoxal scavenger food under gastric conditions. Changes in the concentration of methylglyoxal were monitored kinetically during the intestinal phase. All foods caused significant (p < 0.05) decreases in the concentration of methylglyoxal under intestinal conditions. Chicken, beef, and broccoli were found to scavenge more than 80% of methylglyoxal during 2 h of intestinal digestion. The reaction of methylglyoxal with scavenging compounds in foods was evaluated using an irreversible bimolecular reaction model. Reaction rate constants and initial reaction rates were calculated for each food. The highest reaction rate constant was estimated as 26.6 ± 1.38 L/mol min for egg, while the highest initial reaction rate was 3.6 ± 0.42 mM/min for chicken. Foods were ranked according to their methylglyoxal scavenging rates under intestinal conditions and their scavenging potential was associated with their scavenging content.

Contrasting hydrogen peroxide- and persulfate-driven oxidation systems: Impact of radical scavenging on treatment efficiency and cost

For the first time, the fate of radicals generated in heterogeneous chemical oxidation treatment systems has been accounted for and used to assess treatment performance in three reaction compartments; reaction with the target compound, rhodamine B (RhB), the aqueous phase scavengers, and the solid phase scavengers. Radicals formed during the ultra-violet (UV) activation of hydrogen peroxide (H2O2) (UV-AHP) and persulfate (S2O82−) (UV-APS) include hydroxyl (•OH) and sulfate radicals (SO4•−), respectively. •OH and SO4•−, used in oxidation treatment systems to degrade a broad spectrum of environmental contaminants, may also react with non-target chemical species (scavengers) that limit treatment efficiency. UV-AHP and UV-APS treatment systems were amended with solid phase alumina to assess scavenging by solid surfaces. The overall rate of reaction and rate of radical scavenging was greater for •OH than SO4•−. Scavenging by dissolved constituents was dominated by the oxidant used (H2O2, S2O82−); and the rate of radical scavenging by alumina was greater than the rate of RhB oxidation in all cases. Treatment efficiency was lower in the UV-AHP than in the UV-APS treatment system and was attributed to greater aqueous and solid phase scavenging rates. The cost of commercially available H2O2 ($0.031 mol−1) and PS ($0.24 mol−1) was used in conjunction with the overall treatment efficiency to assess specific cost of treatment. The specific cost to treat the probe compound with UV-AHP was greater than UV-APS and was attributed to the much lower treatment efficiency with UV-AHP. The much-desired high reaction rate constants between •OH and environmental contaminants, relative to SO4•−, may come at the cost of greater combined scavenging rates, and consequently lower treatment efficiency.

Formation and Oxidation Reactivity of MnO2+(HCO3-)n in the MnII(HCO3-)-H2O2 System.

The MnII(HCO3-)-H2O2 (MnII-BAP) system shows high reactivity toward oxidation of electron-rich organic substrates; however, the predominant oxidizing species and its formation pathways involved in the MnII-BAP system are still under debate. In this study, we used the MnII-BAP system to oxidize As(III) in that As(III), Mn2+, and HCO3- are common components in As(III)-contaminated groundwater. Kinetic results show that MnII(HCO3-)n [including MnII(HCO3)+ and MnII(HCO3)2] is a key factor in the MnII-BAP system to oxidize As(III). Quenching experiments rule out contributions of OH• and 1O2 to As(III) oxidation and reveal that O2•- and the oxidizing species generated from O2•- play predominant roles in the oxidation of As(III). We further reveal that the MnO2+(HCO3-)n intermediate generated in the reaction between MnII(HCO3-)n and O2•-, instead of O2•-, is the predominant oxidizing species. Although CO3•- also contributes to As(III) oxidation, the high reaction rate constant between CO3•- and O2•- indicates that CO3•- is not the predominant oxidizing species in the As(III)-MnII-BAP system. In addition, the presence of Mn(III) further indicates the important Mn(II)-Mn(III) cycling in the MnII-BAP system. We therefore suggest two important roles of MnII(HCO3-)n in the MnII-BAP system: (i) MnII(HCO3-)n reacts with H2O2 to form the MnIII(HCO3)3 intermediate, followed by a subsequent reaction between MnIII(HCO3)3 and H2O2 to produce O2•-; (ii) MnII(HCO3-)n can also stabilize O2•- with the formation of MnO2+(HCO3-)n. MnO2+(HCO3-)n is an electrophilic reagent and plays the predominant role in the oxidation of As(III) to As(V).

Anionic polysaccharide stabilized nickel nanoparticles-coated bacterial cellulose as a highly efficient dip-catalyst for pollutants reduction

This article presents the preparation and catalytic performance of carboxymethyl cellulose stabilized nickel nanoparticles (CMC-Ni) and bacterial cellulose coated with it (CMC-Ni-BC) in the colloidal form and dip-catalyst, respectively. Ni nanoparticles were prepared by mixing nickel chloride and CMC aqueous solutions with reductant followed by quick microwave heating treatment. In a separate experiment, BC was synthesized by Gluconacetobacter xylinum. After purification, the synthesized BC was coated with the prepared CMC-Ni. The CMC-Ni-BC catalytic efficiency was evaluated in anionic 2-nitrophenol (2-NP) and cationic methylene blue (MB) dye reduction reactions by sodium borohydride. While using the similar reaction conditions for the 2-NP reduction, the suspension form of CMC-Ni catalyst showed higher reduction reaction rate constant as compared to the dip-catalyst of CMC-Ni-BC. Similarly, high reaction rate constant was observed for the CMC-Ni in comparison with the CMC-Ni-BC while performing the MB reduction reaction. However, supported type Ni catalyst was easily applied in further reactions without the need of further processing which is needed in the case of colloidal form of the catalyst. Moreover, the CMC-Ni-BC catalyst was also tested in the complex situation using the binary solution of 2-NP and MB for their simultaneous reductions. As high as 7.89 min−1 of reaction rate constant was calculated for the reduction of cationic MB by anionic polysaccharide stabilized Ni nanoparticles-coated BC.

Synergistic effect of metal-organic framework-derived boron and nitrogen heteroatom-doped three-dimensional porous carbons for precious-metal-free catalytic reduction of nitroarenes

We report a scalable and controllable synthesis of metal-organic framework (MOF)-derived three-dimensional boron and nitrogen heteroatom-doped porous carbons (3D-BNPCs) and their synergistic effect for metal-free catalytic 4-nitrophenol (4-NP) reduction. The substitution of boron atoms into zeolitic imidazole framework-8 (ZIF-8)-derived nitrogen-doped porous carbon (B-NPC-1200) significantly improves the electrical conductivity and the catalytic 4-NP reduction. We propose the heteroatom-doping of boron, nitrogen and oxygen in the 3D- B-N PC catalysts creates synergistic effect on 4-NP reduction by creating more catalytically active sites. High-Resolution X-ray Photoelectron Spectroscopy (HR-XPS) and Density Functional Theory (DFT) calculations were carried out to confirm and investigate the role of active sites on adsorption of 4-NP molecules in B-NPC-1200. We find that the strongly active sites can only be created based on the synergistic effect between nitrogen, boron and oxygen atoms, and the increased density of the active sites are responsible for the lowering of the apparent activation energy in B-NPC-1200 structure. As synthesized B-NPC-1200 exhibits superior catalytic activities for 4-NP reduction with a low apparent activation energy of 27.0 kJ/mol and a high reaction rate constant of 2.3*10^−3 (s-1). The catalyst can run five times without decreasing significant catalytic activity. The reduction reactions of various nitroarene compounds have been further tested using the B-N PC-1200 material as the precious-metal-free catalyst.

Metal Nanowire Felt as a Flow-Through Electrode for High-Productivity Electrochemistry.

Flow-through electrodes such as carbon paper are used in redox flow batteries, water purification, and electroorganic syntheses. This work examines the extent to which reducing the size of the fibers to the nanoscale in a flow-through electrode can increase the productivity of electrochemical processes. A Cu nanowire felt, made from nanowires 45 times smaller than the 10 μm wide fibers in carbon paper, can achieve a productivity 278 times higher than carbon paper for mass-transport-limited reduction of Cu ions. Higher increases in productivity were predicted for the Cu nanowire felt based on the mass-transport-limited current, but Cu ion reduction became charge transfer-limited on Cu nanowire felt at high concentrations and flow rates when the mass-transport-limited current became comparable to the charge transfer-limited current. In comparison, the reaction rate on carbon paper was mass-transport-limited under all concentrations and flow rates because its mass-transport-limited current was much lower than its charge transfer-limited current. Higher volumetric productivities were obtained for the Cu nanowire felt by switching from Cu ion reduction to Alizarin Red S (ARS) reduction, which has a higher reaction rate constant. An electroorganic intramolecular cyclization reaction with Cu nanowire felt achieved a productivity 4.2 times higher than that of carbon paper, although this reaction was also affected by charge transfer kinetics. This work demonstrates that large gains in productivity can be achieved with nanostructured flow-through electrodes, but the potential gains can be limited by the charge transfer kinetics of a reaction.

Phenolic composition of rooibos changes during simulated fermentation: Effect of endogenous enzymes and fermentation temperature on reaction kinetics.

Phenolic compounds of Aspalathus linearis (rooibos) are susceptible to oxidation during "fermentation", a process characterized by the formation of a red-brown leaf color. The role of enzymes in this process is not yet understood. An experiment with dried green rooibos plant material pre-treated at 170 °C for 30 min to denature and "inactivate" endogenous enzymes was conducted to confirm the role of oxidative enzymes. The phenolic composition of "enzyme inactivated" plant material was not significantly (p ≥ .05) affected by simulated fermentation, compared to control samples, as determined using piece-wise multivariate analysis of variance for successive time intervals. This proves that rooibos enzymes participate in the oxidation of phenolic compounds during fermentation of the plant material. A kinetic modeling approach was subsequently used to establish reaction kinetic parameters for selected rooibos phenolic compounds. The degradation of aspalathin and nothofagin and formation of eriodictyol glucosides during simulated fermentation at four temperatures from 37 to 50 °C were best described by the fractional conversion model based on first-order kinetics (r2 > 0.98), which allows for non-zero equilibrium concentrations. The extent of degradation for other compounds was too low to enable kinetic modeling. Reaction rates for the degradation/formation of phenolic compounds during fermentation followed the Arrhenius law. Less phenolic degradation (higher equilibrium concentration), but a higher reaction rate constant, was observed at higher temperatures, which could possibly be attributed to inactivation of enzymes.

Antipsychotic drugs scavenge radiation-induced hydroxyl radicals and intracellular ROS formation, and protect apoptosis in human lymphoma U937 cells

Antioxidant activity has been reported for some atypical antipsychotic drugs; however, the detailed mechanism is not well known. Here, we investigated the effects of atypical antipsychotic drugs on •OH radical formation, intracellular reactive oxygen species (ROS), and apoptosis induced by ionising radiation. The reaction rate constants with •OH radicals were determined for five antipsychotic drugs as follows, in descending order: olanzapine, aripiprazole, clozapine, haloperidol, and risperidone. Experiments with aminophenyl fluorescein, a fluorescent dye, showed that olanzapine and clozapine could scavenge intracellular ROS. However, experiments with hydroxyphenyl fluorescein showed that only olanzapine inhibited ROS generation. X-irradiation-induced apoptosis in human lymphoma U937 cells was inhibited by clozapine at relatively low concentrations and by olanzapine at higher concentrations. Clozapine inhibited caspase-8 and caspase-3 activation and prevented loss of mitochondrial membrane potential. In contrast, olanzapine inhibited X-irradiation-induced p-JNK activation. Although the atypical antipsychotic drugs used here have relatively high reaction rate constants with •OH radicals in aqueous solutions, inhibition of intracellular ROS was not due to •OH radical scavenging. In addition, suppression of X-irradiation-induced apoptosis was not directly linked with intracellular ROS scavenging. When apoptosis signalling pathways were studied, clozapine-mediated inhibition of apoptosis was dependent on caspase-3 and caspase-8. In contrast, olanzapine inhibited apoptosis via down regulation of X-irradiation-induced p-JNK. These results suggested that both olanzapine and clozapine have antioxidative and antiapoptotic activities via distinct pathways, and provide useful information for better understanding of drug characteristics.

Solvent-free lipase-catalyzed production of (meth)acrylate monomers: Experimental results and kinetic modeling

This paper gives detailed insight in the solventless synthesis of (meth)acrylate esters catalysed by Novozym 435 with a focus on the quantitative understanding of the reaction kinetics. The (meth)acrylate esters were formed from various (heavy boiling) alcohols by applying methyl (meth)acrylate in excess. Attractive ester titers were obtained (up to 800 g.kg−1 for citronellyl acrylate) combined with a depletion of the (heavy boiling) alcohols, simplifying downstream processing. To study the kinetics, all experimentally obtained progress curves were simultaneously used from every conversion as input for nonlinear regression. The generic developed model based on second order reaction kinetics resulted in a good fit with the experimental data. Higher reaction rate constants were systematically obtained for methyl acrylates (from 0.69 kg/mol/h for 2-hexyl-1-decyl acrylate to 1.69 kg/mol/h for citronellyl acrylate) compared to methyl methacrylate (from 0.35 kg/mol/h for tetrahydrofurfuryl methacrylate to 0.44 kg/mol/h for 4-methoxybenzyl methacrylate). This proves the former to be a better accepted substrate for Novozym 435 compared to the latter.

The Effect of Ingredients Mixing Sequence in Rubber Compounding upon Vulcanization Kinetics of Natural Rubber: An Autocatalytic Model Study

This study examined the effect of ingredients mixing sequence to the vulcanization kinetics of natural rubber. The effects of mixing temperature, vulcanization temperature, and the carbon black type upon the kinetics were also studied by using rheography and an autocatalysis reaction model approach. The results showed that this model is good in providing information on vulcanization reaction kinetics of natural rubber. High vulcanization temperature resulted in high reaction rate constant. The more black carbon mixed at the beginning of the rubber mixing process, the higher reaction rate constant would be. The mixing of carbon black and rubber chemicals mixed into the rubber subsequently resulted in the higher reaction rate constant compared with that of simultaneously.

Production and characterization of hybrid coal using sugar impurities extracted from pitch pine

The main concerns of coal power plants are related to high thermal efficiency and biomass utilization for the reduction of CO2 emissions. In this work, the fuel characteristics of a hybrid coal (HCK) impregnated by sugar impurities extracted from a lignocellulosic biomass were investigated. First, an optimized extraction condition for the sugar impurities was chosen among the various reaction temperatures and times using a hydrothermal pre-treatment (HTP) reactor. The extracted sugar impurities were consisted of 21.76 wt% glucan, 75.88 wt% XMG (xylan + mannan + galactan) and 2.36 wt% arabinan at the optimized reaction condition (190 °C and 30 min). 5 wt% sugar impurities based on the coal weight (dry basis) was used to prepare the HCK and the fuel characteristics were compared. According to the H/C and O/C ratios, raw coals were upgraded. In addition, the calorific value of the raw coals was enhanced by HCK production process. The HCKs had a low moisture re-adsorption rate in an excessive water immersion condition compared to the raw coals. To clarify the combustion behavior of the HCKs, thermogravimetric analysis (TGA) was carried out. The HCKs had a single-stage combustion pattern on the differential thermogravimetric (DTG) curve, even though they were composed of a coal and biomass resource. During the kinetic study of the raw coals and HCKs, a high reaction rate constant (k) and low activation energy (Ea) for the HCKs were identified compared to that of the raw coals.

Synthesis of MoS2-TiO2 nanocomposite for enhanced photocatalytic and photoelectrochemical performance under visible light irradiation

In this work, we have prepared MoS2 nanoflakes modified TiO2 nanoparticles (MoS2-TiO2 nanocomposite) with varying concentration of MoS2 (2.5–10 wt.%) by a two-step hydrothermal synthesis method involving specific preparation conditions for the TiO2 nanoparticles and MoS2 nanoflakes. The prepared samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS) techniques. The photocatalytic activity of the pristine TiO2 nanoparticles and MoS2-TiO2 nanocomposite samples were evaluated by examining the photocatalytic degradation of Rhodamine B (RhB). The photoelectrochemical activity of these samples were measured by performing solar water splitting experiments under visible light irradiation. It was observed that the MoS2-TiO2 nanocomposite with 7.5 wt.% MoS2 exhibits highest photocatalytic and photoelectrochemical activity as it has the optimum amount of MoS2 nanoflakes which probably minimizes the recombination of photogenerated charge carriers as compared to other concentrations of MoS2 in MoS2-TiO2 nanocomposite and pristine TiO2 nanoparticles. In addition, a rather high photocatalytic reaction rate constant was observed for MoS2-TiO2 nanocomposite with 7.5 wt.% MoS2 nanoflakes.

Formation characteristics of calcium stannate from SnO2 and CaCO3 synthesized in CO-CO2 and air atmospheres

Calcium stannate (Ca2SnO4) is a common dielectric ceramic that is generally prepared by a high-temperature solid-state method in an air atmosphere with a roasting temperature of more than 1300 °C. In this study, Ca2SnO4 was much more easily synthesized in a CO-CO2 atmosphere at a relatively low temperature of less than 1000 °C for 30 min. We comparatively investigated the formation behavior and microwave dielectric properties of Ca2SnO4 synthesized from tin dioxide (SnO2) and calcium carbonate (CaCO3) by a solid-state method in air and CO-CO2 atmospheres using X-ray diffraction, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, and vector network analysis. The formation behavior of calcium stannate indicated that the reactions between SnO2 and CaCO3 in CO-CO2 and air atmospheres were both controlled by three-dimensional diffusion. In a CO-CO2 atmosphere, the reaction had a higher reaction rate constant (k) and lower apparent activation energy (E). In addition, Ca2SnO4 was synthesized by a low-temperature solid-state method in a CO-CO2 atmosphere. The results indicated that Ca2SnO4 ceramics had a higher dielectric constant and lower dielectric tangent loss than those synthesized by the high-temperature solid-state method in air. However, the synthesis temperature and time were reduced by more than 300 °C and 8 h, respectively.

Two-dimensional molybdenum disulphide nanoflakes synthesized by liquid-solid phase reaction method: regenerative photocatalytic performance under UV-visible light irradiation by advance oxidation process

Molybdenum disulphide (MoS2) nanoflakes were prepared through liquid-solid phase reaction technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) analysis revealed the formation of pure, polycrystalline, hexagonal phase of MoS2 nanoflakes. The texture coefficient () analysis showed that (100) plane was preferentially oriented. The specific surface area of the nanoflakes was 21 m2 g−1 as determined using Brunaure-Emmett-Teller (BET) technique. A band gap of ∼2.05 eV for MoS2 nanoflakes was estimated from UV-visible spectrum. Regenerative photocatalytic activity of MoS2 nanoflakes was assessed by degrading methylene blue (MB) and safranin-o (SO) dyes under UV-visible light irradiation. Under light irradiation, degradation efficiency for MB was ∼99.58% in 100 min while for SO it was ∼99.89% in 70 min. The MoS2 nanoflakes exhibited excellent photocatalytic performance and good stability in a wide pH range (3–11). MoS2 nanoflakes showed a high reaction rate constant (kapp) for SO ∼ 0.104 49 min−1 and MB ∼ 0.092 18 min−1 as compared to other MoS2 nanostructures. The obtained exceptional photocatalytic performance of MoS2 nanoflakes offers potential applications for the treatment of polluted water as well as in other correlated fields.

Quantum chemical calculation of free radical substitution reaction mechanism of camptothecin

Free radical substitution reaction, which has low energy barrier and takes place in mild reaction conditions, is an important method for camptothecin's modification. The experimental data show that the free radical substitution reaction of camptothecin has high site selectivity, and prefers to take place at site 7. Up to now, few researches focus on the mechanism of it. In this study, the differences of the reaction rate constant (k) for the reactions at different sites, such as site of 7, 9, 10, 11, 12, were investigated with B3LYP of density functional theory at the 6-31+G (d, p) base set level and CPCM aqueous solvent model. It was found that the substitution reaction can be carried out in two steps in acidic condition. First, the methyl radical attacks the corresponding site to form an intermediate having methyl radical combined with the camptothecin skeleton, and then a hydrogen atom was abstracted by the singlet oxygen to form methyl camptothecin, wherein the first step was the rate control step of the reaction. The results show that site 7 has the higherreaction rate constant (k) than other examined sites, indicating that the reaction tends to take place on site 7 position, which is in agreement with the experimental results.

One-step synthesis of flour-derived functional nanocarbons with hierarchical pores for versatile environmental applications

In this study, we develops a one-step and scalable approach to synthesize functional carbons with a tuneable and hierarchically porous structure as well as tailored surface chemistry for environmental applications in CO2 adsorption and carbocatalysis to remove emerging water contaminants. By pyrolyzing a mixture of wheat flour and NaHCO3/Na2CO3/K2CO3 at 700 °C, honeycomb structured carbons (700-PC) with dominant micropores can be formed and exhibit an excellent CO2 storage capacity of 6.8 mmol g−1 at 0 °C and ambient pressure. By including dicyandiamide in the precursors, coralloid carbon skeletons in a micro- and meso-porous texture are selectively formed in the N-doped hierarchical porous carbons (N-PCs). 800-N-PC (N-PCs prepared at 800 °C) with a high surface area of 3041 m2 g−1 shows an enhanced capacity of 19.4 mmol g−1 at 0 °C, 10 bar. For water remediation, 800-N-PC exhibits the most efficient degradation of p-hydroxybenzoic acid (HBA) by advanced oxidation processes (AOPs), with a high reaction rate constant of 0.39 min−1 at 25 °C. In addition, 800-N-PC shows selective adsorption of HBA in a mixed solution of HBA and phenol, while both of them can be effectively degraded by the AOPs. The mechanism of adsorption and catalysis of the newly developed porous carbon is discussed.

Performance evaluation of integrated air pollution control with alkaline waste valorization via high-gravity technology

Abstract In this study, a high-gravity process using alkaline wastes, i.e., petroleum coke fly ash, was proposed for integrated air pollution control, including nitrogen oxides, carbon dioxide and particulate matters. After the control process, the reacted fly ash can be further utilized as supplementary cementitious materials in cement mortar to realize a circular economy. The performance of air pollution control using petroleum coke fly ash in a high-gravity process was evaluated by on-site operations. The results indicated that the removal ratios of nitrogen oxides, carbon dioxide and particulate matters in the flue gas were approximately 99% (in the presence of ozone), 95% and 80%, respectively. In addition, the kinetics of carbon dioxide removal in the high-gravity process was analyzed by a surface coverage model. A high reaction rate constant of 0.27 mol/min/m2 was reached under a liquid-to-solid of 20 mL/g and a rotating speed of 1000 rpm at 20 °C. Furthermore, the performance of reacted fly ash used in blended cement mortar was evaluated. Compared with the pure Portland cement mortar, the compressive strength of cement mortar with reacted fly ash can be increased by 26%. Lastly, a preliminary economic analysis was conducted to estimate the costs and benefits from the process.

Effect of adding Au nanoparticles to TiO2 films on crystallization, phase transformation, and photocatalysis

Abstract

Maximum Current Density in the Reduction of the Bromate Anion on a Rotating Disk Electrode: Asymptotic Behavior at Large Thicknesses of the Diffusion Layer

The reduction of the bromate anion on a rotating disk electrode (RDE) in a steady-state mode due to the catalytic cycle consisting of a reversible bromine/bromide redox pair and irreversible counter-proportionation reaction was studied theoretically. As the cycle is autocatalytic (EC″ mechanism: Electrochim. Acta, 2015, vol. 173, p. 779), at high volume concentrations of bromate the passing current can reach huge values limited by the ultimate diffusion current of bromate through the diffusion layer even at very low volume concentrations of bromine. In contrast to previous theoretical studies of this process, for numerical solution of the set of nonlinear equations with boundary conditions for concentrations we used the COMSOL Multiphysics program package, with which the solution can be found for both the galvanostatic mode (at a given current density) and the maximum current density. This allowed us to study the behavior of the maximum current density for the case of very high thickness of the diffusion layer and very high reaction rate constant. In this mode, the ratio of the maximum current to the limiting diffusion current of the reduction of the bromate anion to bromine was found to exceed not only intuitively anticipated unity, but also the “critical” value of 1.2, which formally corresponds to the limiting diffusion current of its reduction to the bromide anion (though the real end product is bromine), and this limiting value depends on the volume concentrations of both bromate and bromine.

Modeling of a CO2-piperazine-membrane absorption system

CO2 is a main greenhouse gas emission causing global warming and other environmental issues, which is mainly emitted from the fossil fuels combustion or utilization. Membrane absorption is a novel CO2 capture method that combines the advantages of chemical absorption and membrane separation. In this paper, a comprehensive 2D symmetric model for a CO2-piperazine (PZ)-membrane absorption process was proposed. PZ solutions showed high CO2 capture performance due to high chemical reaction rate constant. Decreasing the gas flowrate and increasing the absorbent flowrate promoted the CO2 absorption efficiency. On the other hand, varying the membrane contactor properties could also affect the capture of CO2. 0.28m/s gas velocity, 0.08m/s absorbent velocity, 20% CO2 in gas mixture, and 0.94mol/L PZ were recommended as the optimum conditions after the parametric study. This numerical model is reliable for potential use in CO2-absorbent-membrane absorption systems.