Reaction Mechanisms Research Papers - Academia.edu (original) (raw)

In a nonequlibrium plasma of a gas-discharge HgBr lamp, the terminal electronic state of the HgBr(B–X) radiative transition with a peak wavelength of 502 nm remains populated for a relatively long time and is repeatedly excited to the upper state in collisions with plasma electrons. This transfer of the HgBr molecules from the ground state X to the excited state B is the main mechanism of formation of the light-emitting molecules especially when the lamp is excited by double current pulses. According to our simulations, due to the electron-induced transitions between HgBr(X) and HgBr(B), the output characteristics of the DBD lamp operating in a double-pulse regime are better than those of the lamp operating in a single-pulse regime. In the considered case, the peak power is calculated to increase by a factor of about 2 and the lamp efficiency increases by about 50%.

- by Vadym Naumov and +1
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- Optics, Plasma Physics, Radiation, Laser Physics
- by Maria Kubik
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- Analytical Chemistry, Computational Chemistry, Quantum Chemistry, Inorganic Chemistry
- by Angel Mae Avila
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- Chemistry, Organic Chemistry, Reaction Mechanisms, Catalysis
- by Prashant Deshlahra
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- Reaction Mechanisms, Catalysis, Spectroscopy, DFT calculation
- by Leonardo Dos Santos
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- Reaction Mechanisms, Mass Spectrometry, Polymerization, Microreactors
- by Michelle Coote
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- Quantum Chemistry, Reaction Mechanisms, Modeling, Density Functional Theory
- by Valérie Vallet and +1
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- Thermodynamics, Inorganic Chemistry, Reaction Mechanisms, Structure

In this paper oxychlorination processes were reviewed. We paid special attention to the environmental and ecological aspects of these transformations. Mechanisms of aniline and tert-buthyl ethers oxychlorination were also discussed in... more

- by Maciej Przybyłek
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- Environmental Science, Chemistry, Analytical Chemistry, Organic Chemistry

Despite seven decades of intense research, the generally accepted insertion mechanism (IM) has generated many open questions. It is shown in this paper why IM is incorrect and nonsense. We reexamined the fundamental presumption of this polymerization, evaluated the roles of each basic component and proposed an alternative mechanism by electric charge percolation (CPM).

- by Dragoslav Stoiljkovic
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- Polymer Chemistry, Reaction Mechanisms, Polymers, Polymer synthesis
- by Yong Liu
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- Materials Engineering, Condensed Matter Physics, Thermodynamics, Reaction Mechanisms

Experiments have been performed on a Homogeneous Charge Compression Ignition Engine (HCCI) fuelled with natural gas. The in-cylinder pressure has been measured for different engine speeds and fuel-air ratios. Numerical simulations of the ignition process in the engine have been carried out using a detailed reaction mechanism for butane and lower alkanes. The effects of engine speed an fuel-air ratio on autoignition have been calculated and compared with measurements. In addition, calculations have been made of the ignition delay time sensitivity to initial pressure, initial temperature, and quality of gas fuel. Excellent agreement with single-cycle measurements is obtained for the calculated temperature and pressure profiles. The single-cycle temperature simulations show good agreement with 100 cycle-averaged measurements as well, but cycle-to cycle variations flatten out the averaged profiles, and the need for a PDF-based approach to achieve perfection is evident. Furthermore, it was found that the autoignition process in an HCCI engine is extremely sensitive to variations in initial temperature, whereas changes in pressure, fuel-air ratio and engine speed affects the ignition timing to a much lesser extent.

- by Daniel Nilsson
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- Combustion Science, Combustion Modeling, Reaction Mechanisms, Combustion
- by Antonius Marcelis
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- Reaction Mechanisms, Surface Chemistry, Monolayers, CHEMICAL SCIENCES

Using a very low concentration of potassium persulfate as initiator, acrylamide could be efficiently grafted onto potato starch under microwave irradiation and for the grafting O2 removal from the reaction vessel was not required. Under optimal conditions, grafting and efficiency observed were 160% and 89%, respectively. Grafted starch was characterized by using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). It was observed that the microwave irradiation could significantly accelerate the synthesis of starch-graft-poly(acrylamide), because under identical conditions no grafting was observed in a conventional procedure. Viscosity, shear stability and water/saline solution retention of the microwave-synthesized grafted starch were studied and compared with that of the parent starch.

- by Dr Sadanand Pandey
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- Reaction Mechanisms, Green Chemistry, Starch, Biopolymers

The authors present experimental studies of the deflagration-to-detonation transition (DDT) in tubes with smooth and rough walls in stoichiometric hydrogen-oxygen and ethylene-oxygen mixtures. On the basis of experimental evidence, it is shown that formation of the preheat zone, where reaction is chemically frozen, promotes the transition to detonation if temperature and width of the preheat zone are above certain critical values. A sequence of high-speed Schlieren records permits an accurate determination of the minimal values of temperature and width of the preheat zone, leading to transition to detonation. The experimentally measured critical temperatures and widths of the preheat zone initiating restructuring of the flame and transition to detonation in hydrogen-oxygen and ethylene-oxygen mixtures are consistent with the developed theory.

- by Mike Kuznetsov, PhD
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- Reaction Mechanisms, Combustion, Shock Waves, Chemical Kinetics

Sophomore year laboratory report for the preparation of cyclohexene from cyclohexanol.

- by Mark Ryan Tripole
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- Chemistry, Organic Chemistry, Reaction Mechanisms, Organic Synthesis
- by Mark Ryan Tripole
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- Organic Chemistry, Reaction Mechanisms

The coagulation/flocculation (C/F) processes are mainly due to charge neutralisation (CN) and sweep flocculation (SF) mechanisms. However, the SF mechanism has also its CN property moreover than its well-known weighting characteristic. On this weighting characteristic, the literature has usually focused without taking in consideration the SF’s CN property. This review discusses the implicated mechanisms in destabilisation of colloids and aggregation of flocs. Colloids are very small particles that have extremely large surface area. The consequence of this smallness in size and mass and largeness in surface area is that in colloidal suspensions: gravitational effects are negligible and surface phenomena predominate. Hence, during C/F process, colloids are removed by CN and SF mechanisms which act on the anionic charge of the colloid by its neutralisation prior to its removal by sedimentation/filtration. The sweep flocs can be described as large aggregates of Al(OH)3/Fe(OH)3 that are formed when Al/Fe salt is added to water. Further, sweep flocs are positively charged and the colloids of clay minerals abundantly found in the water are negatively charged. As a result, the colloidal particles are electrostatically attached to the sweep flocs in the neutral pH water as to the hydrolysed metalliccations. Even if researches have greatly elucidated the growth, breaking and the re-growth of flocs, further research is required to understand CN and SF mechanisms and optimise the C/F process at the nano level.

- by Djamel Ghernaout
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- Reaction Mechanisms, Aluminium, Colloid, Coagulation/flocculation

1. Reaksi fermentasi beserta koenzim yang berperan di dalam proses tersebut Jawab : 1. Fermentasi asam laktat Dalam fermentasi asam laktat, piruvat direduksi langsung oleh NADH untuk membentuk laktat sebagai produk limbahnya, tanpa melepaskan CO2. Pada sel otot manusia, fermentasi asam laktat dilakukan apabila suplay oksigen tubuh kurang. Laktat yang terakumulasi sebagai produk limbah dapat menyebabkan otot letih dan nyeri, namun secara perlahan diangkut oleh darah ke hati untuk diubah kembali menjadi piruvat. Bakteri asam laktat mampu mengebah glukosa menjadi asam laktat. Bakeri tersebut adalah Laktobbacillus, Streptococcus, Leuconostoc, Pediococcus dan Bifidobacterium. Ada 2 kelompok fermentasi asam laktat, yaitu homofermentatif dan heterofermentatif. Homofermentatif menggunakan glikolisis melalui jalur EMP dan heterofermentatif menggunakan glikolisis melalui jalur HMP. Proses fermentasi asam laktat dimulai dari lintasan glikolisis yang menghasilkan asam piruvat. Karena tidak tersedianya oksigen maka asam piruvat akan mengalami degradasi molekul (secara anaerob) dan dikatalisis oleh enzimasam laktat dehidrogenase dan direduksi oleh NADH untuk menghasilkan energi dan asam laktat. Secara sederhana reaksi fermentasi asam laktat ditulis sebagai berikut. C6H1206->2CH3CH(OH)COOH+2ATP ASAM LKTAT. Pada manusia, kejadian ini sering temukan ketika seseorang bekerja atau berolahraga berat/keras. Akibat kekurangan oksigen menyebabkan asam piruvat yang terbentuk dari tahapan glikolisis akan diuraikan menjadi asam laktat.yang menyebabkan timbulnya rasa pegal-pegal setelah seseorang bekerja/berolahraga berat/keras. 2. FERMENTASI ALKOHOL Beberapa jasad renik seperti ragi, glukosa dioksidasi menghasilkan etanol dan CO2 dalam proses yang disebut fermentasi alkohol. Jalur metabolisme proses ini sama dengan glikolisis sampai dengan terbentuknya piruvat. Dua tahap reaksi enzim berikutnya adalah reaksi perubahan asam piruvat menjadi asetaldehida, dan reaksi reduksi asetaldehida menjadi alkohol. Dalam reaksi pertama piruvat didekarboksilasi diubah menjadi a setaldehida dan CO2 oleh piruvat dekarboksilase, suatu enzim yang tidak terdapat dalam hewan. Reaksi dekarboksilase ini merupakan reaksi yang tak reversible, membutuhkan ion Mg2+ dan koenzim tiamin pirofosfat.

- by Andri Karina
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- Microbiology, Reaction Mechanisms

This work concentrates on automatic procedures for simplifying chemical models for realistic fuels using skeletal mechanism construction and Quasi Steady-State Approximation (QSSA) applied to detailed reaction mechanisms. To automate the selection of species for removal or approximation, different indices for species ranking have thus been proposed. Reaction flow rates are combined with sensitivity information for targeting a certain quantity, and used to determine a level of redundancy for automatic skeletal mechanism construction by exclusion of redundant species. For QSSA reduction, a measure of species lifetime can be used for species ranking as-is, weighted by concentrations or molecular transport timescales, and/or combined with species sensitivity. Maximum values of the indices are accumulated over ranges of parameters, (e.g. fuel-air ratio and octane number), and species with low accumulated index values are selected for removal or steady-state approximation. In the case of QSSA, a model with a certain degree of reduction is automatically implemented as FORTRAN code by setting a certain index limit. The code calculates source terms of explicitly handled species from reaction rates and the steady-state concentrations by internal iteration. Homogeneous-reactor and one-dimensional laminar-flame models were used as test cases. A staged combustor fuelled by ethylene with monomethylamine addition is modelled by two homogeneous reactors in sequence, i.e. a PSR (Perfectly Stirred Reactor) followed by a PFR (Plug Flow Reactor). A modified PFR model was applied for simulation of a Homogeneous Charge Compression Ignition (HCCI) engine fuelled with four-component natural gas, whereas a two-zone model was required for a knocking Spark Ignition (SI) engine powered by Primary Reference Fuel (PRF). Finally, a laminar one-dimensional model was used to simulate premixed flames burning methane and an aeroturbine kerosene surrogate consisting of n-decane and toluene. In general, detailed calculations of temperature, pressure, concentration and flame velocity show excellent agreement with measurements. Skeletal mechanisms for PRF were constructed for the SI engine case, reproducing autoignition well on removal of reactions pertaining to 15% of the species. QSSA reduction was tested on the staged combustor and the engines, using pure and weighted lifetime indices. Monitoring NO concentrations in the staged combustor and ignition timing in the engines, good reproduction is possible while approximating about 70% of the species. However, some species have to be manually retained for accuracy and numerical stability. For improved ranking, sensitivity was added to the index applied to the premixed flames, in addition to necessary molecular transport information. The maximum atomic mass fraction occupied by a certain molecular species was also constrained to limit the mass and energy deficiency caused by QSSA. For methane, the laminar flame velocities as well as concentration profiles are well predicted by the most strongly reduced mechanism with five global reaction steps. For the kerosene surrogate mechanism, QSSA involving 50% of the species was successfully attempted.

- by Daniel Nilsson
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- Combustion Science, Combustion Modeling, Reaction Mechanisms, Energy Engineering

A comprehensive mechanistic study regarding acetone peroxides reveals that water has a profound effect on the formation of the solid cyclic peroxides, TATP, and DADP. The identification and rate of occurrence of reaction intermediates as well as compositions of the final products offer explanation for previously reported results indicating that acid type and hydrogen peroxide concentration affect the acid catalyzed reaction between acetone and hydrogen peroxide. A kinetics study of the decomposition of TATP revealed the effects of water and alcohols. They generally retard conversion of TATP to DADP and lead to complete decomposition of TATP by acid. A mechanism is proposed for the production of TATP and DADP.

- by Augustus China
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- Reaction Mechanisms, Energetics, Mitigation, Hydrogen Peroxide

This paper presents the results of the theoretical study of the process of low-temperature plasma-assisted reforming of ethanol into molecular hydrogen in the electric discharge in a gas channel with liquid wall (DGCLW) in the regime where the discharge is ignited by the breakdown with the air injection between tubular electrodes and then it burns in the ethanol-water mixture self-sustainingly without air supply. The numerical modeling clarifies the nature of non-thermal conversion and explains the kinetic mechanism of nonequilibrium plasma-chemical transformations in the gas-liquid system and evolution of hydrogen during the reforming as a function of discharge parameters and ethanol-water ratio in the mixture.

- by Vadym Naumov
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- Plasma Physics, Reaction Mechanisms, Hydrogen, Kinetics

A computational fluid dynamics (CFD) methodology for simulating the combustion process has been validated with experimental results. Three different types of experimental setups were used to validate the CFD model. These setups include an industrial-scale flare setups and two lab-scale flames. The CFD study also involved three different fuels: C3H6/CH/Air/N2, C2H4/O2/Ar and CH4/Air. In the first setup, flare efficiency data from the Texas Commission on Environmental Quality (TCEQ) 2010 field tests were used to validate the CFD model. In the second setup, a McKenna burner with flat flames was simulated. Temperature and mass fractions of important species were compared with the experimental data. Finally, results of an experimental study done at Sandia National Laboratories to generate a lifted jet flame were used for the purpose of validation. The reduced 50 species mechanism, LU 1.1, the realizable k-epsilon turbulence model, and the EDC turbulence-chemistry interaction model were usedfor this work. Flare efficiency, axial profiles of temperature, and mass fractions of various intermediate species obtained in the simulation were compared with experimental data and a good agreement between the profiles was clearly observed. In particular the simulation match with the TCEQ 2010 flare tests has been significantly improved (within 5% of the data) compared to the results reported by Singh et al. in 2012. Validation of the speciated flat flame data supports the view that flares can be a primary source offormaldehyde emission.

- by Oscar Ventura
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- Reaction Mechanisms, Density-functional theory, Molecular, DFT

The cytochrome P450 metalloenzyme (CYP) CYP199A4 from Rhodopseudomonas palustris HaA2 catalyzes the highly efficient oxidation of para-substituted benzoic acids. Here we determined crystal structures of CYP199A4, and the binding and turnover parameters, with different meta-substituted benzoic acids in order to establish which criteria are important for efficient catalysis. When compared to the para isomers, the meta-substituted benzoic acids were less efficiently oxidized. For example, 3-formylbenzoic acid was oxidized with lower activity than the equivalent para isomer and 3-methoxybenzoic acid did not undergo O-demethylation by CYP199A4. The structural data highlighted that the meta-substituted benzoic acids bound in the enzyme active site in a modified position with incomplete loss of the distal water ligand of the heme moiety. However, for both sets of isomers the meta-or para-substituent pointed towards, and was in close proximity, to the heme iron. The absence of oxidation activity with 3-methoxybenzoic acid was assigned to the observation that the CeH bonds of this molecule point away from the heme iron. In contrast, in the para isomer they are in an ideal location for abstraction. These findings were confirmed by using the bulkier 3-ethoxybenzoic acid as a substrate which removed the water ligand and reoriented the meta-substituent so that the methylene hydrogens pointed towards the heme, enabling more efficient oxidation. Overall we show relatively small changes in substrate structure and position in the active site can have a dramatic effect on the activity.

- by Lorenza Operti and +1
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- Analytical Chemistry, Reaction Mechanisms, Mass Spectrometry, Metal Ions

Various 2-substituted benzimidazole derivatives have been prepared from o-phenylene diamine and substituted aldehyde in presence of ammonium bromide as catalyst at room temperature. This method was proved to be simple, facile and... more

Various 2-substituted benzimidazole derivatives have been prepared from o-phenylene diamine and substituted
aldehyde in presence of ammonium bromide as catalyst at room temperature. This method was proved to be simple,
facile and ecofriendly with good yield.

- by Dr. Arvind Jadhav
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- Organic Chemistry, Reaction Mechanisms, Room-Temperature

Two new terpenoids, bakayanolide (1) and 2α-hydroxy-3β-methoxy-6-oxo-13α,14β,17α-lanosta -7,24-dien-21,16β-olide (2), together with the known compounds 6β-hydroxy-3-oxo-13α,14β,17α -lanosta-7,24-dien-21,16β-olide (3), sendanolactone (4),... more

- by Rob Capon
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- Analytical Chemistry, Computational Chemistry, Quantum Chemistry, Inorganic Chemistry
- by Shruba Gangopadhyay and +1
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- Quantum Chemistry, Inorganic Chemistry, Reaction Mechanisms, Multireference Methods

Two new synthesized and characterized quinazoline Schiff bases 1 and 2 were investigated for anticancer activity against MCF-7 human breast cancer cell line. Compounds 1 and 2 demonstrated a remarkable antiproliferative effect, with an IC50 value of 6.246×10(-6) mol/L and 5.910×10(-6) mol/L, respectively, after 72 hours of treatment. Most apoptosis morphological features in treated MCF-7 cells were observed by AO/PI staining. The results of cell cycle analysis indicate that compounds did not induce S and M phase arrest in cell after 24 hours of treatment. Furthermore, MCF-7 cells treated with 1 and 2 subjected to apoptosis death, as exhibited by perturbation of mitochondrial membrane potential and cytochrome c release as well as increase in ROS formation. We also found activation of caspases-3/7, -8, and -9 in compounds 1 and 2. Moreover, inhibition of NF-κB translocation in MCF-7 cells treated by compound 1 significantly exhibited the association of extrinsic apoptosis pathway. Acu...

The mechanism of the molybdenum-catalyzed de- oxydehydration (DODH) of vicinal diols has been investigat- ed using density functional theory. The proposed catalytic cycle involves condensation of the diol with an MoVI oxo complex,... more

- by Peter Fristrup
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- Reaction Mechanisms, Density-functional theory, Molybdenum, DFT Calculations
- by Tom Sheppard
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- Reaction Mechanisms, Catalysis, Gold, CHEMICAL SCIENCES
- by Peter Junk
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- Analytical Chemistry, Computational Chemistry, Quantum Chemistry, Inorganic Chemistry
- by Boris E Krisyuk and +2
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- Quantum Chemistry, Organic Chemistry, Physical Chemistry, Atmospheric Science