Dynamics of silicate exchange in highly alkaline potassium silicate solutions

1998 ◽  
Vol 76 (2) ◽  
pp. 183-193
Author(s):  
Eva Vallazza ◽  
Alex D Bain ◽  
Thomas W Swaddle
Keyword(s):  
Rate Constants ◽  
Relaxation Times ◽  
Complete Analysis ◽  
True Rate ◽  
Line Shape Analysis ◽  
Cyclic Trimer ◽  
Selective Inversion ◽  
Order Of Magnitude ◽  
Kinetics Of ◽  
Link Formation

The problem of measuring the kinetics of Si exchange between aqueous silicate species by 29Si NMR has been revisited, using highly alkaline KOH solutions (2.8 mol SiIV per kg solvent, [SiIV]/K2O = 0.43) at 60-90°C to minimize the number of silicate species present. Longitudinal 29Si relaxation times T1 and apparent rate constants estimated from line-shape analysis (LSA) varied markedly with the degree of purity of the KOH used, but rate constants k obtained by selective inversion-recovery (SIR) using the CIFIT data-fitting program were independent of the source of KOH and were smaller than those obtained from LSA by at least an order of magnitude. Although only four kinetically significant silicate anions (monomer M, dimer D, linear trimer L, and cyclic trimer C) were present, overlap of the D and L resonances prevented complete analysis of the SIR data. True rate constants could therefore be obtained only for the M-D exchange (for formation of D, k1 (90°C) = 0.13 ± 0.01 kg mol -1 s-1, Δ H1dagger = 67.4 kJ mol-1, Δ S1dagger = -78 J K-1 mol-1; for dissociation of D, k-1 (90°C) = 1.4 ± 0.1 s-1, Δ H-1dagger = 64.7 kJ mol-1, and Δ S1dagger = -66 J K-1 mol-1). Models that included L as the precursor of C (MDLC mechanism) showed, within the limitations imposed by D-L band overlap, that the reactivities of M, D, L, and C in Si-O-Si link formation or dissociation were all roughly comparable. Good fits of the experimental data, however, and equally reliable rate constants for the M-D exchange, could be obtained with models that ignored the presence of L entirely (MDC mechanism). The simple MDC model also provides consistent apparent rate constants kC and k-C for the overall formation of C from M + D and the reverse process, respectively, by SIR of either M or C ( Δ HCdagger = 76.5 kJ mol-1, Δ SCdagger = -57 J K-1 mol-1; Δ H-Cdagger = 88.6 kJ mol-1, and Δ S-Cdagger = -7 J K-1 mol-1).Key words: kinetics, silicates, 29Si NMR.

Faradaic Impedance Study of Mn(II) Reduction Mechanism in NaClO4 and NaCl Solutions on Mercury Electrode

2002 ◽  
Vol 67 (11) ◽  
pp. 1589-1595
Author(s):  
Barbara Marczewska ◽  
Andrzej Persona ◽  
Marek Przegaliński
Keyword(s):  
Electron Transfer ◽  
Rate Constants ◽  
Electrochemical Reaction ◽  
Mercury Electrode ◽  
Reduction Mechanism ◽  
True Rate ◽  
Faradaic Impedance ◽  
Impedance Measurements ◽  
Order Of Magnitude ◽  
Adsorptive Properties

The electrochemical reaction of the Mn(II)/Mn(Hg) system on mercury electrode was studied in 1 M NaClO4 and 1 M NaCl as supporting electrolytes of different complexing and adsorptive properties. The impedance measurements confirmed the two-stage electroreduction of the Mn(II) in investigated solutions. Both the apparent and the true rate constants of the second electron transfer in both supporting electrolytes are lower by one order of magnitude than the rate constant of the first electron transfer. Similar values of corrected rate constants in both electrolytes suggest the similarity in mechanism of the Mn(II) electroreduction.

Elimination rate constants of 36 PCBs in zebra mussels (Dreissena polymorpha) and exposure dynamics in the Lake St. Clair - Lake Erie corridor

1995 ◽  
Vol 52 (12) ◽  
pp. 2574-2582 ◽  
Author(s):  
Heather Morrison ◽  
Rodica Lazar ◽  
G. Douglas Haffner ◽  
Tamara Yankovich
Keyword(s):  
Steady State ◽  
Rate Constants ◽  
Dreissena Polymorpha ◽  
Lake Erie ◽  
Elimination Rate ◽  
Zebra Mussels ◽  
Elimination Kinetics ◽  
Western Lake ◽  
Order Of Magnitude ◽  
Kinetics Of

The elimination kinetics of 36 PCB congeners, ranging in log octanol–water partition coefficients (log Kow) from 5.60 to 7.50, were determined in zebra mussels (Dreissena polymorpha) with shell lengths from 1.0 to 1.5 cm. Elimination rate constants, based on lipid-normalized data, ranged from 0.172 to 0.042 day−1 and exhibited a significant negative regression with log Kow. Time to 95% steady state ranged from 17.5 to 71.0 days and was used to determine the period over which mussels integrated exposure concentrations. Bioavailable PCB congener concentrations, calculated with a steady-state model, were determined from mussels collected offshore of Middle Sister Island in western Lake Erie. Chemical concentrations in water, estimated using mussels, were within an order of magnitude of direct measurements for congeners with log Kow < 6.6. The rapid elimination kinetics of zebra mussels suggests that these organisms can closely track temporal fluctuations in ambient chemical concentrations, and therefore have the potential to regulate contaminant cycling in aquatic ecosystems.

The kinetics of isomeric reactions

1960 ◽  
Vol 257 (1291) ◽  
pp. 541-551 ◽  
Keyword(s):  
Distribution Function ◽  
Rate Constants ◽  
Transition Probabilities ◽  
Relaxation Times ◽  
Careful Consideration ◽  
Time Dependent ◽  
New Method ◽  
Solution Properties ◽  
Reacting Systems ◽  
Kinetics Of

A careful consideration of the kinetics of simple reacting systems near equilibrium shows that the observable relaxation times of the system involve not only transition probabilities (or rate constants) but also the dependence of these quantities on concentrations. By using a new method to describe the kinetics of 2- and 3-state processes (which introduces a time-dependent distribution function for the reaction co-ordinates) it is shown that, under certain conditions, the concentration-dependent terms can be evaluated in terms of the solution properties of the system.

KINETIC STUDIES OF PROTEIN–DYE AND ANTIBODY–HAPTEN INTERACTIONS WITH THE TEMPERATURE-JUMP METHOD

1962 ◽  
Vol 40 (9) ◽  
pp. 1786-1797 ◽  
Author(s):  
A. Froese ◽  
A. H. Sehon ◽  
M. Eigen
Keyword(s):  
Relaxation Time ◽  
Bovine Serum Albumin ◽  
Rate Constants ◽  
Temperature Jump ◽  
Relaxation Times ◽  
Kinetic Studies ◽  
Single Relaxation Time ◽  
Effects Of Temperature ◽  
Arsonic Acid ◽  
Kinetics Of

The kinetics of protein–dye and antibody–hapten reactions were studied with the temperature-jump method. The systems used consisted of (i) bovine serum albumin (BSA) and the dye 1-naphthol-4-[4-(4′-azobenzene azo)phenyl arsonic acid], referred to as N—R′, (ii) BSA and the dye 1-naphthol-2-sulphonic acid-4-[4-(4′-azobenzene azo)phenyl arsonic acid], referred to as NS—R′, and (iii) rabbit antibodies to phenyl arsonic acid [Ab] and the hapten N—R′.Each of the systems exhibited a single relaxation time. From the analysis of the concentration dependence of the relaxation times, it was concluded that each system could be represented by the reactions[Formula: see text]where P refers to BSA or Ab, and D to N—R′ or NS—R′. The following rate constants were calculated for the three systems at 25 °C:[Formula: see text]The effects of temperature and pH on the rate constants of the system BSA – N—R′ are discussed.

Kinetics of biodegradation during remediation of consecutive accidental spills of chlorophenols in a sandy aquifer

2003 ◽  
Vol 47 (9) ◽  
pp. 157-164 ◽  
Author(s):  
B. Antizar-Ladislao ◽  
N.I. Galil
Keyword(s):  
Rate Constants ◽  
Closed Loop ◽  
Polluted Site ◽  
Biodegradation Rate ◽  
First Order ◽  
First Order Kinetics ◽  
Order Of Magnitude ◽  
Configuration System ◽  
Sandy Aquifer ◽  
Kinetics Of

Kinetics of biodegradation of chlorophenols were studied in six sandy aquifer columns (0.06 m I.D.; 1.00 m L). Remediation of chlorophenols was enhanced by using a “closed-loop” configuration system, where local groundwater was recirculated through the polluted site in a controlled manner. Consecutive accidental spills of phenol, 2-monochlorophenol (2-MCP) and 2,4,6-trichlorophenol (2,4,6-TCP) as single pollutants were removed following first order kinetics. The removal of chlorophenols increased by one order of magnitude following consecutive accidental spills demonstrating adaptation of the resident micro flora. The biodegradation rate constants in this study were in the same range and agreed with those reported in the literature for biodegradation in aerobic aquifers. Following the fate of the resident micro flora (enhanced by adding NH4Cl and KH2PO4 at a ratio C/N/P equal to 120:10:1), biomass growth was observed in the sandy aquifer columns and particle size analyses of the aqueous phase recirculated through the polluted site experimentally proved aggregation of cells. Aggregation of cells has been hypothesized as one of the causes for low biodegradation rates found in the field compared to those calculated using biodegradation rate constants determined in batch culture.

scholarly journals Simulation of the kinetics of direct coal hydrogenation

2020 ◽  
Vol 99 (3) ◽  
pp. 110-115
Author(s):  
N.Zh. Balpanova ◽  
◽  
A.M. Gyulmaliev ◽  
Yu.N. Pankin ◽  
F. Ma ◽  
...  
Keyword(s):  
Experimental Data ◽  
Kinetic Parameters ◽  
Rate Constants ◽  
Batch Reactor ◽  
Random Search ◽  
Optimization Method ◽  
Republic Of China ◽  
Search Optimization ◽  
Order Of Magnitude ◽  
Kinetics Of

The kinetics of coal hydrogenation from the Shenghua deposit (People's Republic of China) has been studied. To calculate the kinetic parameters, experimental data on the hydrogenation of coal from the Shenghua field have been used. The hydrogenation process was carried out at a pressure of 5 MPa, at temperatures from 350 to 440 0C using a batch reactor. Tetrahydronaphthalene was used as a solvent and donor in the process of coal hydrogenation. The rate constants were calculated using the random search optimization method and the integral Simpson method. It was found that the previously calculated rate constants of the hydrogenation of Shenghua coal (Runge-Kutt method) differ from our data by one order of magnitude. It is supposed that our calculated values of the rate constants are more reliable and adequate than those obtained by the Runge-Kutt method. The limiting rate of coal hydrogenation is observed for the stage of coal conversion into a mixture of gas and oil.

Condensation of α,ω-siloxane diols with aminoalkyl- (alkoxy)silanes

e-Polymers ◽  
2013 ◽  
Vol 13 (1) ◽  
Author(s):  
Magdalena Lubkowska ◽  
Wlodzimierz A. Stanczyk ◽  
Krystyna Rozga-Wijas
Keyword(s):  
Chain Length ◽  
Silicon Atom ◽  
Rate Constants ◽  
Second Order ◽  
Order Rate ◽  
Siloxane Oligomers ◽  
Order Of Magnitude ◽  
Kinetics Of

Abstract Kinetics of condensation of individual siloxane diols HO[(CH3)2SiO]xSi(CH3)2OH (x=3,5,6 and 9) with aminoalkyl-alkoxysilanes (RO)2SiR’(CH2)3NHR’’ (R = CH3, CH2CH3; R’ = CH3, OR; R’’ = H, (CH2)2NH2) is described. The second order rate constants point to the significant effect of the siloxane diols chain length on reactivity, which increases for higher homologues (almost an order) of magnitude on coming from x=3 to x=9. The role of substituents at silicon atom is discussed. Three novel functional siloxane oligomers (substrates) are described and characterized.

Submerged upflow biotower operation and computer simulation

1994 ◽  
Vol 30 (11) ◽  
pp. 143-146
Author(s):  
Ronald D. Neufeld ◽  
Christopher A. Badali ◽  
Dennis Powers ◽  
Christopher Carson
Keyword(s):  
Computer Simulation ◽  
Benzoic Acid ◽  
Computer Model ◽  
Rate Constants ◽  
Batch Mode ◽  
Operational Conditions ◽  
First Order ◽  
Low Concentrations ◽  
Biological Transformation ◽  
Kinetics Of

A two step operation is proposed for the biodegradation of low concentrations (&lt; 10 mg/L) of BETX substances in an up flow submerged biotower configuration. Step 1 involves growth of a lush biofilm using benzoic acid in a batch mode. Step 2 involves a longer term biological transformation of BETX. Kinetics of biotransformations are modeled using first order assumptions, with rate constants being a function of benzoic acid dosages used in Step 1. A calibrated computer model is developed and presented to predict the degree of transformation and biomass level throughout the tower under a variety of inlet and design operational conditions.

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