Terms Of Reaction Rate Research Articles

Experimentally Closing the Balance of Progress of Reaction in Premixed Turbulent Combustion in the Thin Flame Regime

We investigate the possibility of determining the local turbulent flame speed by measuring the individual terms in the balance of a mean progress of reaction variable for the case of a low turbulence methane-air Bunsen flame in the thin flame regime. Velocity distributions and flame edge positions were measured by particle image velocimetry techniques at 3 kHz for a flame stabilized by a surrounding pilot of the same stoichiometry, for a turbulent Reynolds number around 66 and Karlovitz numbers of the order of 4. The conservation equation for mean progress variable was analyzed along different streamlines as a balance of terms expressed as velocities, including terms for convection, turbulent diffusion, mean reaction, and turbulent and molecular diffusion. Each term was estimated from local velocities and flame locations using a thin flame approximation, and their uncertainty was evaluated based on propagation of experimentally measured statistical correlations. The largest terms were the convective and reaction terms, as expected, with smaller roles for turbulent and molecular diffusion across the flame brush. Countergradient diffusion and transition to gradient diffusion were observed across the flame brush. Closure of the balance of terms in the conservation equations using independently measured terms was not consistently achieved across the flame brush within the reckoned uncertainties, arriving at a balance within 20–30% of the absolute value. Testable hypotheses are offered for the possible reasons for the mismatch, including the role of spatial filtering and 3D effects on the reaction rate term. Finally, the experiments identify the inaccuracies in measuring a true local turbulent flame speed, and suggest a consistent methodology to reduce errors in such estimations. This is the first time such a detailed experimental closure is attempted for any configuration. The results suggest that the significant improvements in spatial resolution are necessary for a full closure.

Facile synthesis of UV-curable fluorosilicone polymers and coatings with good corrosive resistance on account of the reaction of disulfide bonds with vinyl groups

A new UV curing strategy is introduced into the curing field of fluorosilicone polymers. This strategy is predicated on the reaction of sulfur radicals generated from disulfide bonds with vinyl groups under the presence of UV light. Here, we engineered and synthesized a kind of novel fluorosilicone polymers (FS-SS) with disulfide bonds and vinyl groups. The disulfide bonds contained in FS-SS undergo photocleavage under ultraviolet irradiation, generating sulfide radicals, which can interact with vinyl groups to complete the curing reaction. Subsequently, the UV curing behavior of coatings on the basis of the novel polymers and photo-initiator 1173 was investigated by FT-IR spectroscopy and a possible UV-curable reaction mechanism based on disulfide bonds and vinyl groups was proposed. The results showed that curing reactions based on disulfide bonds and vinyl groups can reach a relatively high degree of reaction in a short period of time in terms of reaction rate. However, the lower conversion rate of the reaction may be due to the fact that the sulfur radicals generated by disulfide bonds are more inclined to form disulfide bonds rather than undergo addition reactions with vinyl groups. Subsequently, a series of fluorosilicone coatings with good optical transparency (transmittance above 90 %), good hydrophobicity (the lowest value of surface energy is 21.54 mN/m), lower roughness value (Ra values was in the region of 2.24 nm– 12.2 nm) and high temperature resistance were prepared by utilizing this curing strategy. Furthermore, the applicable experiment of fluorosilicone coatings to protect tinplate as anti-corrosive coatings was also performed. The corrosive resistance results formalize its practical value for possible application as preventive coatings.

A new generation pathway of singlet oxygen in heterogeneous single–atom Mn catalyst/peroxymonosulfate system

The function of heterogeneous catalyst in singlet oxygen (1O2) generation under acidic and neutral conditions and the effect of sulfate radical on the generation of 1O2 is still unclear. This study provided a novel generation pathway of 1O2 in the heterogeneous Mn single − atom catalyst (Mn SAC)/peroxymonosulfate (PMS) system. The MnN4 site with the ideal binding strength promoted the activation of PMS to generate sulfate radical (SO4•–), which would be adsorbed on the carbon/nitrogen sites forming SO4•–(s), reacting spontaneously to produce 1O2. The presence of MnN4 and carbon/nitrogen structure sites could shift the oxidation process from a bulk–phase oxidation to a surface oxidation. This shift has important implications in terms of reaction rate and product distribution, as the dual reaction sites decrease the required migration distance for the active species to form 1O2, avoiding the pointless consumption of active substances.

Geochemistry of neutral mine drainage at sulfide deposits ‒ example of the „Grot“ Pb-Zn mine, South-Eastern Serbia

This study examines the chemistry of mine waters of the ?Grot? Pb? ?Zn mine and identifies the hydrogeochemical factors that influence the formation of mine waters chemical composition. Eleven mine water samples were collected at six locations across the area of Kriva Feja in order to determine their chemical composition. Data analysis revealed that the waters belong to the HCO3 -?SO4 2-?Ca2+ and SO4 2-?Ca2+ water types, with neutral pH values. The concentrations of metals in these waters (zinc, lead, barium, copper, chromium) are generally low, and most of the samples meet drinking water quality criteria (USEPA standards). Modelling using the PHREEQC software indicates that the dominant processes in the formation of the chemical composition of these waters are the dissolution of carbonate minerals and the oxidation of sulphide minerals. Carbonate minerals have a scarcer occurrence compared to sulphide minerals, such as galena, sphalerite and pyrite, which are dominantly distributed. The low intensity of sulphide mineral oxidation is interpreted to result from a rapid water exchange and reduced contact time between the water and the rock. The occurrence of this process is localized only in the ore body zone. This study highlights the importance of kinetics (in terms of the chemical reaction rate) as the main factor influencing the oxidation of sulphide minerals and, subsequently the quality of mine waters.

Influence of geometric shapes of recess on the performance of MR lubricated multi-recessed hybrid spherical thrust bearing

This paper aims to investigate the impact of different geometric shapes of recesses/pockets on the behavior of a multi-recessed hybrid spherical thrust bearing (MHSTB) configuration along with MR (magnetorheological) lubricant behavior. The analysis employs a finite element approach to assess the behavior of MHSTB configurations lubricated with MR fluids, with the MR lubricant's behavior modeled using the Herschel–Bulkley model. The governing equations are solved through Galerkin's discretization method combined with a suitable iterative technique. The study reveals significant variations in bearing performance when altering the magnetic field intensity and axial eccentricity ratio. The study explores various geometric recess shapes (i.e., elliptical, circular, triangular, and square) within the MHSTB configuration while maintaining same bearing operating and geometric parameters. Numerical simulations demonstrate that MHSTB systems operating with MR lubricant exhibit higher fluid film reaction and damping coefficients compared to Newtonian lubricant. Furthermore, it is observed that the elliptical recessed bearing configuration outperforms square, triangular, and circular recessed bearing configuration in terms of fluid film reaction and lubricant flow rate.

Optimization and Enhancement of the Peroxidase-like Activity of Hemin in Aqueous Solutions of Sodium Dodecylsulfate.

Iron porphyrins play several important roles in present-day living systems and probably already existed in very early life forms. Hemin (= ferric protoporphyrin IX = ferric heme b), for example, is the prosthetic group at the active site of heme peroxidases, catalyzing the oxidation of a number of different types of reducing substrates after hemin is first oxidized by hydrogen peroxide as the oxidizing substrate of the enzyme. The active site of heme peroxidases consists of a hydrophobic pocket in which hemin is embedded noncovalently and kept in place through coordination of the iron atom to a proximal histidine side chain of the protein. It is this partially hydrophobic local environment of the enzyme which determines the efficiency with which the sequential reactions of the oxidizing and reducing substrates proceed at the active site. Free hemin, which has been separated from the protein moiety of heme peroxidases, is known to aggregate in an aqueous solution and exhibits low catalytic activity. Based on previous reports on the use of surfactant micelles to solubilize free hemin in a nonaggregated state, the peroxidase-like activity of hemin in the presence of sodium dodecyl sulfate (SDS) at concentrations below and above the critical concentration for SDS micelle formation (critical micellization concentration (cmc)) was systematically investigated. In most experiments, 3,3',5,5'-tetramethylbenzidine (TMB) was applied as a reducing substrate at pH = 7.2. The presence of SDS clearly had a positive effect on the reaction in terms of initial reaction rate and reaction yield, even at concentrations below the cmc. The highest activity correlated with the cmc value, as demonstrated for reactions at three different HEPES concentrations. The 4-(2-hydroxyethyl)-1-piperazineethanesulfonate salt (HEPES) served as a pH buffer substance and also had an accelerating effect on the reaction. At the cmc, the addition of l-histidine (l-His) resulted in a further concentration-dependent increase in the peroxidase-like activity of hemin until a maximal effect was reached at an optimal l-His concentration, probably corresponding to an ideal mono-l-His ligation to hemin. Some of the results obtained can be understood on the basis of molecular dynamics simulations, which indicated the existence of intermolecular interactions between hemin and HEPES and between hemin and SDS. Preliminary experiments with SDS/dodecanol vesicles at pH = 7.2 showed that in the presence of the vesicles, hemin exhibited similar peroxidase-like activity as in the case of SDS micelles. This supports the hypothesis that micelle- or vesicle-associated ferric or ferrous iron porphyrins may have played a role as primitive catalysts in membranous prebiotic compartment systems before cellular life emerged.

Economic comparison of reactive distillation (RD) to a benchmark conventional flowsheet: Regions of RD applicability and trends in column design

A novel methodology for the techno-economic assessment of Reactive Distillation (RD) is presented. The developed methodology benchmarks reactive distillation (RD) to a conventional reactor + distillation train flowsheet (R+D) on a cost-optimized basis, with the optimization being performed on the process unit level (reactor sizing, number of stages, feed point(s)) and the internals level (reactive tray design). This methodology is applied to the ideal quaternary system A+B↔C+D with the conventional boiling point order of TC < TA < TB < TD (αAD = 4, αBD = 2, αCD = 8). From this pool of data, a regime map of RD vs. R+D is established in which the attractive regions of either flowsheet option are identified in terms of the chemical reaction rate and chemical equilibrium. It is found that RD can arise as the cost optimal option for a large range of residence time requirements by virtue of overcoming the external recycle requirements of R+D. This is achieved through optimized reactive tray design. Contrary to conventional distillation design practices, it was found that the preferred use of bubble-cap trays over sieve trays to allow elevated weir heights and designing the column diameter below 80% of flooding become relevant design choices when accommodating high liquid holdup.

Solvent-free synthesis of jasminaldehyde over chitosan–layered double hydroxide catalyst assisted by microwave irradiation

This research paper reports on the use of chitosan-modified layered double hydroxide (LDH) composite catalysts (CS/MgAl–NO3) for the synthesis of jasminaldehyde under microwave irradiation. The catalysts were prepared by co-precipitation in an inert nitrogen atmosphere. The resulting samples were characterized by mean of X–ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric/differential thermal analysis (TGA/DTA), scanning electron microscope (SEM) with energy-dispersive X–ray (EDX), and N2 adsorption/desorption isotherm (BET) analysis. The basicity of each catalyst was determined by the acid-base titration method. The performance of the catalysts was evaluated in the solvent-free synthesis of jasminaldehyde from aldol by condensation reaction between benzaldehyde and 1–heptanal in a microwave oven at P = 100 W and T = 90 °C. The effects of different parameters that are involved in the reaction, such as the catalyst amount and the benzaldehyde to 1–heptanal molar ratio, and reaction temperature, are investigated in detail. The results showed that the CS-functionalization of the catalyst leads to the enhancement of its basic sites making it more efficient than the naked MgAl–NO3 catalyst, in terms of the initial reaction rate, the conversion of the reactants and the selectivity toward the jasminaldehyde. The CS/MgAl–NO3 catalyst was also evaluated in successive regeneration reaction cycles.

Oxidation of Thiols with IBX or DMP: One-Pot Access to Thiosulfonates or 2-Iodobenzoates and Applications in Functional Group Transformations.

o-Iodoxybenzoic acid (IBX) and Dess-Martin periodinane (DMP) are employed for thiol to thiosulfonate conversion at rt. DMP is better than IBX in terms of reaction rate, conversion, and required equivalents. IBX-mediated oxidation of benzyl thiols produced thiosulfonates, whereas DMP afforded O-benzyl esters. The one-pot conversion of a thiol to an ester is unprecedented; this atom-economic transformation has potential for functional group transformations (FGTs), e.g., an alcohol and an aldehyde are accessed from benzyl thiol.

Step-growth polymerization of supracolloidal chains from patchy micelles of diblock copolymers

HypothesisThe formation of supracolloidal chains from the patchy micelles of diblock copolymers bears a close resemblance to traditional step-growth polymerization of difunctional monomers in many aspects, including chain-length evolution, size distribution, and initial-concentration dependence. Thus, understanding the colloidal polymerization based on the step-growth mechanism can offer potential control over the formation of supracolloidal chains in terms of chain structure and reaction rate. ExperimentsWe analyzed the size evolution of supracolloidal chains of patchy micelles of PS-b-P4VP by investigating a large number of colloidal chains visualized in SEM images. We varied the initial concentration of patchy micelles to achieve a high degree of polymerization and a cyclic chain. To manipulate the polymerization rate, we also changed the ratio of water to DMF and adjusted the patch size by employing PS(25)-b-P4VP(7) and PS(145)-b-P4VP(40). FindingsWe confirmed the step-growth mechanism for the formation supracolloidal chains from patchy micelles of PS-b-P4VP. Based on this mechanism, we were able to achieve a high degree of polymerization early in the reaction by increasing the initial concentration and form cyclic chains by diluting the solution. We also accelerated colloidal polymerization by increasing the ratio of water to DMF in the solution and patch size by using PS-b-P4VP with a larger molecular weight.

3D printed polylactide scaffolding for laccase immobilization to improve enzyme stability and estrogen removal from wastewater

This study reports a biocatalytic system of immobilized laccase and 3D printed open-structure biopolymer scaffoldings. The scaffoldings were computer-designed and 3D printed using polylactide (PLA) filament. The immobilization of laccase onto the 3D printed PLA scaffolds were optimized with regard to pH, enzyme concentration, and immobilization time. Laccase immobilization resulted in a small reduction in reactivity (in terms of Michaelis constant and maximum reaction rate) but led to significant improvement in chemical and thermal stability. After 20 days of storage, the immobilized and free laccase showed 80% and 35% retention of the initial enzymatic activity, respectively. The immobilized laccase on 3D printed PLA scaffolds achieved 10% improvement in the removal of estrogens from real wastewater as compared to free laccase and showed the significant reusability potential. Results here are promising but also highlight the need for further study to improve enzymatic activity and reusability.

Effect of Water Deuteration on Protein Electron Transfer

Traditional theories of long-range protein electron transfer describe the reaction rate in terms of the tunneling distance and the reaction free energy. They do not recognize two physical effects: (i) local wetting of the active site by hydration water and (ii) protein identity affecting the rate through dynamics and flexibility. We find, by molecular dynamics simulations, a significant, ∼25 times, slowing down of the rate of protein electron transfer upon deuteration. H/D substitution changes the rate constant pre-exponential factor in the regime of electron transfer controlled by medium dynamics. Switching from light to heavy water increases the effective medium relaxation time. The effect is caused by both a global change in the flexibility of the protein backbone and locally stronger hydrogen bonds to charged residues.

One-step electrodeposition of binder-containing Cu nanocube catalyst layers for carbon dioxide reduction.

To reach industrially relevant current densities in the electrochemical reduction of carbon dioxide, this process must be performed in continuous-flow electrolyzer cells, applying gas diffusion electrodes. Beyond the chemical composition of the catalyst, both its morphology and the overall structure of the catalyst layer are decisive in terms of reaction rate and product selectivity. We present an electrodeposition method for preparing coherent copper nanocube catalyst layers on hydrophobic carbon paper, hence forming gas diffusion electrodes with high coverage in a single step. This was enabled by the appropriate wetting of the carbon paper (controlled by the composition of the electrodeposition solution) and the use of a custom-designed 3D-printed electrolyzer cell, which allowed the deposition of copper nanocubes selectively on the microporous side of the carbon paper substrate. Furthermore, a polymeric binder (Capstone ST-110) was successfully incorporated into the catalyst layer during electrodeposition. The high electrode coverage and the binder content together result in an increased ethylene production rate during CO2 reduction, compared to catalyst layers prepared from simple aqueous solutions.

Synthesis of a graft copolymer of chloroprene rubber with acrylic acid as a shoe adhesive

Synthesized graft copolymers of chloroprene rubber with acrylic acid. A mixture of benzene and dimethylformamide was used as a solvent, and potassium persulfate was used as a polymerization initiator. Based on the dependence of the copolymerization rate on the concentrations of components and temperature, the order of the reaction rate in terms of the concentration of acrylic acid (2.0), potassium persulfate (1.2) and the activation energy of the process (24.4 kJ/mole) were determined. The degree of grafting of polyacrylic acid increases from 2% to 140% with increasing process time, monomer and initiator concentrations. Grafting efficiency is high (70-90%) in a wide range of time and component concentrations. The graft copolymer has high adhesion to the surface of the skin and tissue.

Green heterogeneous catalysts for cleaner solvent-free production of acetates

The development of new chemical synthetic methodologies that transform industrial chemical processes into more sustainable ones, constitutes one of the challenges and objectives of chemical research both in academia and in industry. The use of activated carbons as heterogeneous catalysts represents one of the most beneficial options for process efficiency in terms of reaction rate, yield, and ease of work-up. We have produced six new activated carbons by treatment of three affordable commercial carbons with either nitric acid, or with sulfuric acid. The complete characterization of these nine activated carbons has been carried out through the measurement of nitrogen adsorption capacity, porosimetry, elemental organic analysis, X-ray photoelectron spectroscopy, scanning electron microscopy and determination of the point of zero charge; transmission electron microscopy was also performed on two of them. The catalytic activity of these nine catalysts has been tested in the acetylation reaction of hydroxyl groups, undoubtedly one of the most versatile and widely used chemical transformations both at the laboratory and industrial scale. The results show that by means of a simple and affordable modification of commercial xerogel with sulfuric acid, a more efficient catalyst is formed. Acetylation with the best catalyst is completed in 90 min at room temperature and the product is easily isolated in quantitative yield. The system can be reutilized for five runs with only a small loss of catalytic activity.

Achieving high fuel utilization for microfluidic fuel cell under high flow rate operation

High fuel utilization is highly desirable in microfluidic fuel cell (MFC) operated under high flow rates. This work provides insight into the requirements in geometrical design, electrode material and operation parameter to realize significantly improved fuel utilization under high flow rate operation for the flow-through type MFC. Detailed parametric analyses are performed and corresponding mechanism investigations reveal that the outer part and downstream region of the electrodes contribute much less than their inner and upstream counterparts in terms of reaction rate owing to the increased ohmic resistance. Consequently, simply increasing the electrode width or length cannot bring satisfactory fuel utilization but only results in a reduced current density. Optimized electrode aspect ratio could realize the simultaneous enhancement of fuel utilization and current density, but the increasing extent is still not satisfying. Compared with the geometrical optimization, developing advanced electrode material is more promising. Increasing the specific surface area of the electrode material is demonstrated more effective than electrochemical activity enhancement since the system suffers a severe mass transfer limitation. Besides, low reactant concentration is found not applicable to the high flow rate system owing to the existence of limiting fuel utilization.

“On Water” Effect for Green Click Reaction: Spontaneous Polymerization of Activated Alkyne with “Inert” Aromatic Amine in Aqueous Media

“On Water” Effect for Green Click Reaction: Spontaneous Polymerization of Activated Alkyne with “Inert” Aromatic Amine in Aqueous Media

Insight into the Process and Mechanism of Water-Rock Interaction in Underground Coal Mine Reservoirs Based on Indoor Static Simulation Experiments.

During the storage of underground water reservoirs in coal mines, water–rock interaction occurred between mine water and collapsed rocks, resulting in improved mine water quality, but the water–rock process and mechanism have not been clarified. In this study, six sets of simulated experiments were designed to investigate the water–rock interaction between two types of roof collapse rocks and different water samples in the Daliuta coal mine. The ion ratio method and multivariate statistics are used to reveal the process and mechanism of water–rock interaction during the experimental process from the perspective of input and output water chemical characteristics and rock properties, respectively. The results show that the ion concentration of the effluent water is controlled by water–rock interaction, and the water–rock process mainly involves the dissolution of halite, silicate, pyrite, calcite, dolomite, magnesia chlorite, and gypsum precipitation and is accompanied by ion exchange. Mineral dissolution and precipitation are the most important factors affecting the ion abundance in the effluent. There are differences in the reaction rate, degree of reaction, and dissolution process during the experimental process of fine sandstone and mudstone. Fine sandstone is more reactive than mudstone in terms of reaction rate and degree of reaction, and fine sandstone is dissolved from surface pores to inside and around, while mudstone is generated in new dissolved pores. We found that rock type, ion concentration in the input water, and rock reaction period influence the water–rock interaction during the experiment. The results provide a reference for clarifying the water–rock interaction during the storage of underground water reservoirs in coal mines and predicting the water quality of the effluent.

Mimicking the cementation mechanism of ancient Roman seawater concrete using calcined clays

The negative environmental impacts of Ordinary Portland Cement (OPC)-based materials, including high carbon emission, energy-intensive manufacturing process, and freshwater consumption, can be minimized by capitalizing on the concepts of ancient Roman concrete. Accordingly, this study presents a pathway of producing durable and sustainable seawater concrete by mimicking the cementation of ancient Roman concrete. Calcined clays with blended minerals (kaolinite and montmorillonite), portlandite, and seawater were used to produce these binder mixtures. The evolutions of the reaction products of the seawater-cured paste samples were monitored for up to 56 days using Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Nuclear Magnetic Resonance (NMR), and Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS). Because of the high alkalinity (pH 8.2) of seawater, it acts as an activator for the calcined clay-portlandite mixtures eliminating the need for additional alkali activators. Accordingly, in the presence of seawater, the reaction between calcined clay and portlandite happens relatively rapidly, and compressive strengths of around 17 MPa can be achieved within 7 days. The early age strengths of these samples were primarily attributed to the formation of hydrocalumite. With increasing curing duration, geopolymer gel, C-A-S-H, ettringite, and phillipsite were formed. Both C-A-S-H and phillipsite showed binding of chlorides. Only phillipsite showed sequestration of sulfates in the matrix. The calcined clay blends containing 50 to 75% kaolinite performed better than the samples containing 100% kaolinite in terms of reaction rate and compressive strengths.

Integral equation-based simulation of transient experiments for an [formula omitted] mechanism: Beyond the steady state simplification

Transient electrochemical experiments are usually described theoretically by systems of reaction–diffusion partial differential equations. Converting them to integral equations is a classical and valuable modelling approach. Unfortunately, if any reaction–diffusion equation contains nonlinear reaction rate terms, up to now such a conversion has only been possible by assuming a steady state for the equation. Consequently, only sufficiently fast homogeneous reactions could be handled. In this work a novel integral equation-based modelling approach is described. The steady state assumption is replaced by a two-term singular perturbation expansion of the concentration–flux relationship, recently published by the authors. The expansion is valid for homogeneous reactions of (integer) order m≥1, occurring at planar electrodes. An example simulation of cyclic voltammetry for an EC2 reaction mechanism involving a second order dimerization reaction is performed. It is found that in this way the voltammograms can be satisfactorily simulated for homogeneous reaction rate constants smaller by about one order of magnitude than was previously possible.