Estimation of Effective Moisture Diffusivity in Starchy Materials Following Hydrothermal Treatments

2011 ◽  
Vol 312-315 ◽  
pp. 364-369 ◽  
Author(s):  
Seyed Amir Bahrani ◽  
Catherine Loisel ◽  
Jean Yves Monteau ◽  
Sid Ahmed Rezzoug ◽  
Zoulikha Maache-Rezzoug
Keyword(s):  
Reaction Rate ◽  
Effective Diffusivity ◽  
Moisture Diffusivity ◽  
Reaction Model ◽  
Reaction Rate Constant ◽  
Diffusivity Coefficient ◽  
Maize Starch ◽  
First Order ◽  
Melting Phenomenon ◽  
Treatment Processes

Two hydrothermal treatment processes (DV-HMT and DIC treatment) were investigated on standard maize starch for three processing temperatures; 100, 110 and 120°C. The gravimetric change of starch powder during the treatment was analyzed by a simultaneous water diffusion and starch reaction model. The effective diffusivity coefficient (Deff) and reaction rate constant (k) were estimated by minimizing the error between experimental and analytical results. The values of Deff and k clearly increased with temperature. The degree of starch melting was evaluated for the two treatments using the first-order reaction model as a function of processing time. The results suggest that the absorption process is controlled by water–starch reactivity that induces melting phenomenon of starch crystallites, which progresses when temperature increases. The two hydrothermal treatments considerably differ: DIC being more prone to water absorption as demonstrated by the values of Deff and k.

scholarly journals Determination of exothermic batch reactor specific model parameters

2019 ◽  
Vol 292 ◽  
pp. 01063
Author(s):  
Lubomír Macků
Keyword(s):  
Rate Constant ◽  
Reaction Rate ◽  
Batch Reactor ◽  
Specific Model ◽  
Reaction Rate Constant ◽  
Order Reaction ◽  
First Order Reaction ◽  
Model Parameters ◽  
Reactor Model ◽  
First Order

An alternative method of determining exothermic reactor model parameters which include first order reaction rate constant is described in this paper. The method is based on known in reactor temperature development and is suitable for processes with changing quality of input substances. This method allows us to evaluate the reaction substances composition change and is also capable of the reaction rate constant (parameters of the Arrhenius equation) determination. Method can be used in exothermic batch or semi- batch reactors running processes based on the first order reaction. An example of such process is given here and the problem is shown on its mathematical model with the help of simulations.

scholarly journals The alcoholysis of 1,2,2-trimethylpropyl-methylfluorophosphonate

2000 ◽  
Vol 65 (12) ◽  
pp. 857-866
Author(s):  
Mladjen Micevic ◽  
Slobodan Petrovic
Keyword(s):  
Kinetic Data ◽  
Reaction Rate ◽  
Frequency Factor ◽  
Reaction Rate Constant ◽  
Order Reaction ◽  
Activation Entropy ◽  
Second Order Reaction ◽  
Third Order ◽  
First Order ◽  
Kinetics Of

The alcoholysis of 1,2,2-trimethylpropyl-methylfluorophosphonate (soman) was examined with a series of alkoxides and in corresponding alcohols: methanol, ethanol, 1-propanol, 2-propanol, 2-methoxyethanol and 2-ethoxyethanol. Soman reacts with the used alkoxides in a second order reaction, first order in each reactant. The kinetics of the reaction between 1,2,2-trimethylpropyl-methylfluorophosphonate and ethanol in the presence of diethylenetriamine was also examined. A third order reaction rate constant was calculated, first order in each reactant. The activation energy, frequency factor and activation entropy were determined on the basis of the kinetic data.

scholarly journals Impact of citric acid on the drying characteristics of kiwifruit slices

2020 ◽  
Vol 42 ◽  
pp. e40570
Author(s):  
Ibrahim Doymaz
Keyword(s):  
Regression Analysis ◽  
Citric Acid ◽  
Effective Diffusivity ◽  
Type Equation ◽  
Moisture Diffusion ◽  
Moisture Diffusivity ◽  
Diffusivity Coefficient ◽  
Drying Time ◽  
Drying Temperature ◽  
Drying Behaviour

Kiwifruit slices were dried at four different air drying temperatures of 50, 55, 60 and 70ºC and at 2 m s-1 air velocity by using a cabinet dryer in this study. The drying, rehydration and colour characteristics were significantly influenced by pretreatment and drying temperature. The drying time decreased with the increase in drying temperature. The drying rate curves showed that the entire drying process took place in the falling rate period. Five well-known thin-layer models were evaluated for moisture ratios using nonlinear regression analysis. The results of regression analysis indicated that the Midilli & Kucuk model the best to describe the drying behaviour with the lowest c2 and RMSE values, and highest R2 value. The effective moisture diffusivity of the dried kiwifruit slices was calculated with Fick’s diffusion model, in which their values varied from 4.19×10–10 to 6.99×10-10 m2 s-1 over the mentioned temperature range. The dependence of effective diffusivity coefficient on temperature was expressed by an Arrhenius type equation. The calculated values of the activation energy of moisture diffusion were 10.37 and 19.08 kJ mol-1 for citric acid and control samples, respectively

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.

Mathematical modeling and simulation of hexane degradation in fungal and bacterial biofilters: effective diffusivity and partition aspectsThis article is one of a selection of papers published in this Special Issue on Biological Air Treatment.

2009 ◽  
Vol 36 (12) ◽  
pp. 1919-1925 ◽  
Author(s):  
Sonia Arriaga ◽  
Sergio Revah
Keyword(s):  
Mathematical Modeling ◽  
Kinetic Constant ◽  
Effective Diffusivity ◽  
Reaction Model ◽  
Small Error ◽  
Bacterial Biofilm ◽  
Order Kinetic ◽  
Biofilm Thickness ◽  
First Order ◽  
Superficial Area

Mathematical modeling in the biofiltration of volatile organic compounds is a valuable tool for performance prediction and in scaling up. Majority of the published models include parameters obtained from fitting experimental data, thus masking their real influence as they are lumped generally. The present work aims to evaluate experimentally some of the most relevant parameters including kinetic constant, partition coefficient in the biofilm, biofilm thickness, superficial area, and effective diffusivity. For the fungal biofilm, all the parameters mentioned above were obtained experimentally; and for the bacterial biofilm, the biofilm thickness and some intrinsic parameters used to obtain the first-order kinetic constant were taken from the literature. These parameters were then incorporated in a mathematical model to describe the steady-state degradation of hexane in bacterial and fungal biofilters operating under continuous mode. Experimentally, the dimensionless partition coefficients (mG) indicated that hexane was 4 and 35 times more soluble in the bacterial (mG = 9.14) and fungal (mG = 0.88) biofilters, respectively, than in water (mG = 30.4). Comparison of model estimates with experimental concentration profiles of the pollutant along the height of the biofilters proves that the first-order limited by reaction model was appropriate to interpret the experimental results with a small error of ∼1%.

scholarly journals Effects of HRT on the efficiency of denitrification and carbon source release in constructed wetland filled with bark

2017 ◽  
Vol 75 (12) ◽  
pp. 2908-2915 ◽  
Author(s):  
Yinghe Jiang ◽  
Yao Li ◽  
Ying Zhang ◽  
Xiangling Zhang
Keyword(s):  
Carbon Source ◽  
Removal Efficiency ◽  
Constructed Wetland ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Municipal Sewage ◽  
First Order ◽  
N Removal ◽  
Carbon Release ◽  
The Relationship

Constructed wetland is widely used to treat municipal sewage. However, lack of carbon source always constraints the application of constructed wetland in advanced tailwater treatment process. Bark was used as the filler and external carbon source of constructed wetland in the study, and the effects of hydraulic retention time (HRT) on NO3−−N removal efficiency and carbon release velocity were explored. Results showed that the NO3−−N removal process was steady in the constructed wetland filled with bark without additional carbon source. The NO3−−N removal efficiency and NO3−−N concentration presented a first-order reaction. The reaction rate constant k was 0.4 day−1. The relationship between NO3−−N removal efficiency (η) and HRT (t) was η = 1-e−0.4t, and η was increased with increasing of HRT. η reached a maximum of 77% at HRT of 4.48 days. η obtained the minimum of 20% at HRT of 0.75 days. The relationship between the carbon source releasing velocity (v) by bark and HRT was v = 0.53(1.62/t-1/t2) + 0.32. v increased first and then decreased with HRT increasing. The maximum v was detected at t = 1.12 days.

The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

1999 ◽  
Vol 77 (5-6) ◽  
pp. 530-536 ◽  
Author(s):  
Juan Crugeiras ◽  
Howard Maskill
Keyword(s):  
Rate Constant ◽  
Perchloric Acid ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Ion Pair ◽  
Ion Concentration ◽  
Forward Rate ◽  
First Order ◽  
Hydronium Ion ◽  
Carbenium Ion

We have studied the equilibration shown in eq. [3] of 4,4prime-dimethoxytrityl alcohol in aqueous perchloric and nitric acids containing low proportions of acetonitrile using stopped-flow kinetics techniques. The rate constants for the overall progress to equilibrium, kobs, have been resolved into forward and reverse components using the equilibrium UV absorbance and a value for the molar absorptivity of the 4,4prime-dimethoxytrityl carbenium ion determined in concentrated aqueous perchloric acid. The forward reaction (rate constant kf) is first order in both the alcohol and the acid concentrations; the reverse reaction (rate constant kr) is pseudo first order with respect to the carbocation. At constant hydronium ion concentration, the forward rate constant increases linearly with the concentration of electrolyte, whereas the reverse rate constant decreases. These effects depend upon the nature of the anion, but not the cation, and are not ionic strength effects. At constant anion concentrations, kf in both acids, and kr in perchloric acid, are independent of hydronium ion concentration; however, kr decreases with increasing hydronium ion concentration at constant nitrate concentration. At nonconstant ionic strength, changes in kf and kr observed in increasing concentrations of perchloric acid are attributable wholly to changes in perchlorate concentration. A mechanism is proposed which involves pre-equilibrium protonation of the alcohol, heterolysis of the protonated alcohol to give a 4,4prime-dimethoxytrityl carbenium ion - water ion-molecule pair, then conversion of this into a dissociated carbenium ion in equilibrium with ion pairs. To account for the strong effects of perchlorate and nitrate upon the forward rate constants, it is proposed that these anions provide additional reaction channels from the ion-molecule pair. However, we find no evidence of acid catalysis in the reaction of the ion-molecule pair (in contrast to our finding for the reaction of the corresponding ion-molecule pair formed from dimethoxytritylamine in acidic media). Some of the elementary rate and equilibrium constants of the proposed mechanism have been evaluated.Key words: trityl, carbenium ion, stopped-flow, ion pair, ion-molecule pair.

scholarly journals Immobilized rGO/TiO2 Photocatalyst for Decontamination of Water

Catalysts ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 708 ◽  
Author(s):  
Radek Zouzelka ◽  
Monika Remzova ◽  
Jan Plsek ◽  
Libor Brabec ◽  
Jiri Rathousky
Keyword(s):  
Photocatalytic Degradation ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Tio2 Photocatalyst ◽  
Limited Effect ◽  
Environmental Application ◽  
First Order ◽  
Beneficial Effects ◽  
Low Concentrations ◽  
Reduced Graphene

The preparation of immobilized graphene-based photocatalyst layers is highly desired for environmental applications. In this study, the preparation of an immobilized reduced graphene oxide (rGO)/TiO2 composite by electrophoretic deposition (EPD) was optimized. It enabled quantitative deposition without sintering and without the use of any dispersive additive. The presence of rGO had beneficial effects on the photocatalytic degradation of 4-chlorophenol in an aqueous solution. A marked increase in the photocatalytic degradation rate was observed, even at very low concentrations of rGO. Compared with the TiO2 and GO/TiO2 reference layers, use of the rGO/TiO2 composite (0.5 wt% of rGO) increased the first-order reaction rate constant by about 70%. This enhanced performance was due to the increased formation of hydroxyl radicals that attacked the 4-chlorophenol molecules. The direct charge transfer mechanism had only limited effect on the degradation. Thus, EPD-prepared rGO/TiO2 layers appear to be suitable for environmental application.

Drying Kinetic Simulation of Clay Tiles Made from the Raw Material Having Less Clay Fraction

2014 ◽  
Vol 1036 ◽  
pp. 3-8
Author(s):  
Miloš Vasić ◽  
Zagorka Radojević
Keyword(s):  
Clay Fraction ◽  
Effective Diffusivity ◽  
Moisture Diffusivity ◽  
Effective Moisture Diffusivity ◽  
Diffusivity Coefficient ◽  
Moisture Movement ◽  
Effective Moisture ◽  
Drying Kinetic ◽  
Clay Tiles

In order to describe the internal moisture rate and to take all different mechanisms of moisture movement into account, it is suitable to use effective diffusivity as a measure of moisture rate, irrespectively of the mechanisms really involved. This means that all different mechanisms and driving forces for internal moisture transport are lumped together and introduced into effective moisture diffusivity. Hence, diffusion equations are retained and reused with the effective diffusivity coefficient as a measuring parameter of internal moisture ratio. In our previous studies we have presented the calculation method which assumed constant diffusivity. The next goal was to estimate effective diffusivity at various moisture contents, in a real case of non-linear drying curves, and to predict drying kinetic. In our last study we have developed a model for determination of the variable effective diffusivity and identification of the exact transition points between possible drying mechanisms. In this paper we have tried to develop more accurate tool for determination of time dependent effective moisture diffusivity. An analytical model and computing procedure were developed to evaluate mass transfer properties and describe drying kinetic of clay tiles having less clay fraction. The proposed procedure was validated with experimental drying data. Presented results have demonstrated that the proposed dying model can be applied for the accurate description of experimental drying kinetics and a reliable estimation of effective diffusivity.

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