scholarly journals (U) SENSMG: First-Order Sensitivities of Neutron Reaction Rates, Reaction-Rate Ratios, Leakage, keff, α, and Subcritical Multiplication Using PARTISN

2019 ◽  
Author(s):  
Jeffrey A. Favorite
Keyword(s):  
Reaction Rate ◽  
Reaction Rates ◽  
First Order ◽  
Neutron Reaction ◽  
Rate Ratios

Bisulfite Degrades Aflatoxin: Effect of Temperature and Concentration of Bisulfite

1978 ◽  
Vol 41 (10) ◽  
pp. 774-780 ◽  
Author(s):  
M. P. DOYLE ◽  
E. H. MARTH
Keyword(s):  
Rate Constant ◽  
Aflatoxin B1 ◽  
Reaction Rate ◽  
Reaction Rates ◽  
Reaction Rate Constant ◽  
Effect Of Temperature ◽  
Kcal Mole ◽  
First Order ◽  
Potassium Acid Phthalate ◽  
Acid Phthalate

Bisulfite reacted with aflatoxin B1 and G1 resulting in their loss of fluorescence. The reaction was first order with rate depending on bisulfite (or the bisulfite and sulfite) concentration(s). Aflatoxin G1 reacted more rapidly with bisulfite than did aflatoxin B1. In the presence of 0.035 M potassium acid phthalate-NaOH buffer (pH 5.5) plus 1.3% (vol/vol) methanol at 25 C, the reaction rate constant for degradation of aflatoxin G1 was 2.23 × 10−2h− and that for aflatoxin B1 was 1.87 × 10−2h− when 50 ml of reaction mixture contained 1.60 g of K2SO3. Besides bisulfite concentrations, temperature influenced reaction rates. The Q10 for the bisulfite-aflatoxin reaction was approximately 2 while activation energies for degrading aflatoxin B1 and aflatoxin G1 were 13.1 and 12.6 kcal/mole, respectively. Data suggest that treating foods with 50 to 500 ppm SO2 probably would not effectively degrade appreciable amounts of aflatoxin. Treating foods with 2000 ppm SO2 or more and increasing the temperature might reduce aflatoxin to an acceptable level.

scholarly journals The Effects of Mixing, Reaction Rates, and Stoichiometry on Yield for Mixing Sensitive Reactions—Part II: Design Protocols

2012 ◽  
Vol 2012 ◽  
pp. 1-13 ◽  
Author(s):  
Syed Imran A. Shah ◽  
Larry W. Kostiuk ◽  
Suzanne M. Kresta
Keyword(s):  
Rate Ratio ◽  
Reaction Rate ◽  
Relative Rate ◽  
Reaction Diffusion ◽  
Reaction Rates ◽  
Reaction Scheme ◽  
Considerable Effect ◽  
Mixing Condition ◽  
Reaction Diffusion Model ◽  
Rate Ratios

Competitive-consecutive and competitive-parallel reactions are both mixing sensitive reactions where the yield of desired product depends on how fast the reactants are brought together. Recent experimental results have suggested that the magnitude of the mixing effect may depend strongly on the stoichiometry of the reactions. To investigate this, a 1D, dimensionless, reaction-diffusion model was developed at the micromixing scale, yielding a single general Damköhler number. Dimensionless reaction rate ratios were derived for both reaction schemes. A detailed investigation of the effects of initial mixing condition (striation thickness), dimensionless reaction rate ratio, and reaction stoichiometry on the yield of desired product showed that the stoichiometry has a considerable effect on yield. All three variables were found to interact strongly. Model results for 12 stoichiometries are used to determine the mixing scale and relative rate ratio needed to achieve a specified yield for each reaction scheme. The results show that all three variables need to be considered when specifying reactors for mixing sensitive reactions.

scholarly journals The Effects of Mixing, Reaction Rates, and Stoichiometry on Yield for Mixing Sensitive Reactions—Part I: Model Development

2012 ◽  
Vol 2012 ◽  
pp. 1-16 ◽  
Author(s):  
Syed Imran A. Shah ◽  
Larry W. Kostiuk ◽  
Suzanne M. Kresta
Keyword(s):  
Rate Ratio ◽  
Reaction Rate ◽  
Model Development ◽  
Reaction Diffusion ◽  
Reaction Rates ◽  
Considerable Effect ◽  
Reaction Diffusion Model ◽  
Effect On Yield ◽  
Reaction Stoichiometry ◽  
Rate Ratios

There are two classes of mixing sensitive reactions: competitive-consecutive and competitive-parallel. The yield of desired product from these coupled reactions depends on how fast the reactants are brought together. Recent experimental results have suggested that the mixing effect may depend strongly on the stoichiometry of the reactions. To investigate this, a 1D, dimensionless, reaction-diffusion model at the micromixing scale was developed. Assuming constant mass concentration and mass diffusivities, systems of PDE's were derived on a mass fraction basis for both types of reactions. Two dimensionless reaction rate ratios and a single general Damköhler number emerged from the analysis. The resulting dimensionless equations were used to investigate the effects of mixing, reaction rate ratio, and reaction stoichiometry. As expected, decreasing either the striation thickness or the dimensionless rate ratio maximizes yield, the reaction stoichiometry has a considerable effect on yield, and all three variables interact strongly.

scholarly journals Kinetic study of HTPB (Hydroxyl Terminated Polybutadiene) Synthesis Using Infrared Spectroscopy

2020 ◽  
Vol 20 (4) ◽  
pp. 919
Author(s):  
Heri Budi Wibowo ◽  
Widhi Cahya Dharmawan ◽  
Ratih Sanggra Murti Wibowo ◽  
Adi Yulianto
Keyword(s):  
Activation Energy ◽  
Infrared Spectroscopy ◽  
Kinetic Study ◽  
Reaction Rate ◽  
Reaction Rates ◽  
Polymerization Kinetics ◽  
Molar Ratio ◽  
First Order ◽  
Initiation Reaction ◽  
Polymer Conversion

A kinetic study of HTPB synthesis by radical polymerization of butadiene with hydrogen peroxide initiator was conducted using infrared spectroscopy. HTPB conversion was determined based on the conjunction termination rate constant, and all polymerization kinetics were evaluated to identify the constant. All polymerization steps (decomposition, initiation, propagation, conjunction, and proportional termination) can be evaluated based on polymer conversion and functionality from data provided by infrared spectroscopy. The investigation variables included the initial molar ratio of initiator to monomer (H2O2/butadiene) and the reaction temperature. These steps were assumed as the first-order reactions, giving constant reaction rates of kd, ka, kp, kt, ktc, and ktd. The reaction rates obtained for these constants were 4.2 × 10–5 sec–1, 8.9 × 10–4, 7.7 × 103, 8.5 × 107, 3.2 × 107 and 5.3 × 107 L mol–1 sec–1, respectively, with activation energy of 7608, 14188, 2247, 105, 87 and 135 kJ mol–1, respectively. The determining step of the reaction rate was identified as the initiation reaction. HTPB conversion can be measured if all polymerization kinetics constants have been evaluated.

EVOLUTION DE L’UREE PLACEE EN BANDES DANS DEUX SOLS ACIDES DU QUEBEC

1981 ◽  
Vol 61 (4) ◽  
pp. 561-570
Author(s):  
M. GIROUX ◽  
D. CARRIER
Keyword(s):  
Moisture Content ◽  
Sandy Soil ◽  
Reaction Rate ◽  
Sandy Loam ◽  
Soil Surface ◽  
Reaction Rates ◽  
Order Reaction ◽  
Urea Hydrolysis ◽  
First Order ◽  
Reaction Rate Constants

The objectives of this experiment were to determine the power of Morin (sand) and Achigan (sandy-loam) soils to hydrolyze urea and to nitrify ammonium. The urea was applied at a rate of 1500 mg N/kg soil in a drill 6 cm below the soil surface. The soils were incubated for 63 days at 20 °C and 25% moisture content (vol/wt) in 2-L containers. The band-applied urea hydrolysis was directly proportional to the logarithm of its remaining concentration in the soil (i.e. first-order reaction). Calculated reaction rate constants were −0.112 and −0.143 per day for the sand and the sandy loam, respectively. The unequal reaction rates were, presumably, related to the different chemical and physical properties of these soils. The rate of urea ammonification was significantly more rapid than the ammonium nitrification. One week after starting the incubation, only 18.3% and 11.5% of the applied urea remained in the Morin and Achigan soils, respectively. However, no nitrification was detected until about the 20th day and it was more active in the sandy soil. Soil pH increased and decreased significantly as ammonification or nitrification progressed, respectively.

Eclogitization kinetics of continental granulites : quantification and implications

2020 ◽  
Author(s):  
Marie Baisset ◽  
Loic Labrousse ◽  
Alexandre Schubnel
Keyword(s):  
Rheological Behavior ◽  
Reaction Rate ◽  
Experimental Studies ◽  
Reaction Rates ◽  
First Order ◽  
Piston Cylinder ◽  
Ductile Flow ◽  
Convergence Zones ◽  
Kinetics Of ◽  
Type Apparatus

<p><span>When implicated in convergence zones, granulites of the lower continental crust are expected to eclogitize at depth.When exposed in the field such units show a bimodal rheological behavior between fracturing of the protolith rock (granulites) and ductile flow of the transformed parts (eclogites). It seems therefore that a competition exists between the rate at which the rocks are loaded in stress and the rate at which they transform, i.e. the overall eclogitization kinetics. The aim of the work presented here is to quantify the kinetics of the metamorphic reactions involved in eclogitization by estimating the reaction rates in plagioclase-bearing assemblages<span>  </span>submitted to different P-T conditions over different time spans. For this, experiments have been performed in piston-cylinder apparatus on aggregates derived from natural granulites. Special attention is paid to the location where nucleation starts and how it propagates in and between the grains. In this prospect, the presence of garnet and cpx in the plagioclase matrix is a first order control on the reaction process. This work follows previous experimental studies (e.g. Shi et al., 2017, Incel et al., 2018) which show that reaction-enhanced embrittlement may be key for fracturing at high pressure. It has been proposed that transient properties of the rocks induced by the very beginning of the reaction (e.g. volume change, small grain size nucleation products) can lead to brittle instabilities. As we assume that the rheological behavior of the crust is controlled by a competition between reaction rate and strain rate, experiments involving deformation of granulites while undergoing eclogitization are required. Preliminary results performed on Griggs-type apparatus, which constitutes the best tool for that, will also be presented.</span></p>

Polyoxometalate (POM) oxidation of lignin model compounds

Holzforschung ◽  
2008 ◽  
Vol 62 (1) ◽  
pp. 38-49 ◽  
Author(s):  
Yong Sik Kim ◽  
Hou-min Chang ◽  
John F. Kadla
Keyword(s):  
Reaction Rate ◽  
Model Compound ◽  
Reaction Rates ◽  
Hydroxyl Group ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Lignin Model Compound ◽  
First Order ◽  
Resonance Stabilization ◽  
Lignin Model

Abstract Various lignin model compounds were oxidized with polyoxometalate (POM), K5[SiVW11O40]·12 H2O, in sodium acetate buffer (I=0.2 M, pH 5.0) and the reaction kinetics were investigated. The reactions were found to have second order reaction rates, first order with regards to both lignin model compound and POM. A dramatic increase in reactivity was observed upon addition of methoxyl groups in ortho-positions to the phenolic hydroxyl group. Syringyl units reacted faster than guaiacyl units. Reaction rates of para-substituted guaiacyl and syringyl model compounds showed a strong dependency on the nature of the substituents. The reaction rate of a 5-5′ dimer lignin model compound was extremely fast. The addition of the ortho-phenol substituent not only increased the electron density of the aromatic ring, but also helped stabilize the intermediate phenoxy radical through resonance stabilization and delocalization.

scholarly journals Kinetics and mechanism of the oxidation of methionine by quinolinium chlorochromate

2005 ◽  
Vol 70 (2) ◽  
pp. 145-151 ◽  
Author(s):  
M. Pandeeswaran ◽  
John Bincy ◽  
D.S. Bhuvaneshwari ◽  
K.P. Elango
Keyword(s):  
Acetic Acid ◽  
Reaction Rate ◽  
Activation Parameters ◽  
Chloroacetic Acid ◽  
Reaction Rates ◽  
Solvation Model ◽  
First Order ◽  
Different Temperatures ◽  
Solute Interactions ◽  
Oxidation Of Methionine

The oxidation of methionine by quinolinium chlorochromate (QCC) has been studied, in the presence of chloroacetic acid, and in water-acetic acid mixtures of varying mole fractions. The reaction is first order with respect to methionine, QCC and acid. The reaction rates were determined at three different temperatures (25, 35 and 45 ?C) and the activation parameters were computed. The reaction rate increased with increasing mole fraction of acetic acid in the mixture and specific solvent-solvent-solute interactions were found to predominate (81 %). A solvation model and a suitable mechanism for the reaction are postulated.

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