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Kinetic Modeling - Science topic

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Hello all,
I am developing a kinetic model for a pseudo-homogeneous first-order reaction system and I intend to optimize rate constants. In this regard, I wanted to know if I can use excel for the same and if yes how to do so.
Any help is welcome and much appreciated.
Earnestly looking for insightful answers.
Thanks and regards
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As you know, this is a solved problem. There are many software tools that optimize rate constant values to fit kinetic data (MATLAB, COPASI, SAAM2, ProcessDB, and maybe even CellDesigner, to name a few). Some will offer Nelder-Meade as a choice of the optimization algorithm. To my knowledge, Excel is not in the business of solving ordinary differential equations or optimizing rate constants to fit kinetic data.
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Hello,
I'm looking for some help about the understanding of adsorption kinetics of an adsorbant material (zeolite) towards several chemical pollutants. I saw many papers describing adsorption performance through different kinetics model (Langmuir, Freundlich...) but I am not getting how to model this kinetics onto my data and how to interpret them.
Hoping to be clear enough,
Maurizio
Best regards
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Mehmet Can Dal, I see you don't feel like submitting a counter argument for my post. Do you agree with what I wrote?
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I am working on predicting the nutrition requirement for optimum growth of fish. The available model to do that is using the "5-saturation kinetics model curve calculation". However, details of using this method are not available. Any help will be very appreciated.
Thank you
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You can apply the monod model. The Monod model is mathematically analogous to the famous Michaelis-Menten enzyme kinetic model. You can apply this model to different living forms, from fish growth kinetics to bacterial growth, from algae to plankton.
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In the published literature, it is well established that only 60% of data can be used to fit Korsmeyer-Peppas model.
What about other models like Zero-order, First order, Higuchi, and  Hixson–Crowell.
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Look for publications in the journal in which you will publish the article.
How many models have been applied in articles, do as much.
Generally, 4-5 models are sufficient. If you apply too many models, you can have the study published as two articles. Here is an example:
Modeling of adsorption isotherms of phenol and chlorophenols onto granular activated carbon: Part I. Two-parameter models and equations allowing determination of thermodynamic parameters
Modeling of adsorption isotherms of phenol and chlorophenols onto granular activated carbon. Part II. Models with more than two parameters.
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Hello everyone,
Does anyone have any recommendations on how to calculate a diffusion coefficient from drug release data? I know that I will acquire the drug release over time and with this I can perform a mean least squares test to determine which kinetic model (Korsmeyer-Peppas, ect) is best fitted. This is where I am stuck, how do I get a diffusion coefficient from this kinetic model/data?
This isn't my usual background so I am struggling with this, any help would be greatly appreciated.
Cheers,
Sabrina
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Hello! I have a problem with a reformer kinetic implemented in Aspen Plus. I have a PFR reactor that need to be closed with a recycle. In this recycle there is a very small amount of H2 that invalidate the kinetic and gives me error, this is because in the reaction rate expression, some terms are divided for the partial pressure of H2, and therefor being so small, is like dive everything for zero and that is causing problem in the converge.
Is anyone of you familiar with such problem? There is a way to "eliminate" a component from a stream is present below a certain amount?
Thank you
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Thank you very much for your answer. I am still not practical with Aspen Plus since I focused for a lot of time on Aspen Hysys, I will try to insert the design specification you suggest. I am working at 15bar and 950°C, the molar fraction of hydrogen that i would eliminate is 10^-7.
I will reach you out is any help is needed.
Thank you and wish you the best
Asya
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Can First-order kinetic model be applied to experimental data
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The First-order kinetic model can't be applied to experimental data. Instead, you have to check whether the experimental data are in agreement with the first reaction rate order with respect to A. This is a pretty complex protocol for the reaction with the stoichiometry such as,
aA + bB + cC = xX + yY + zZ
To simplify the procedure, you can use an excess of B and C. Then, you can assume that B and C does not change with time and you can write
dA/dt = F(Ao, Bo, Co) and check if A(t) = Ao(exp(-kt)). If this curve is exponential, you determine an apparent reaction rate constant k. If k does not depend on Ao, then you can say that the reaction is the pseudo first order with respect to A under conditions of your experiment. Pseudo means that k was determined under conditions Ao << Bo and Ao << Co. If you manage to confirm despite all complexity that the reaction is the first order with respect to A under conditions Ao ~ Bo ~ Co, then congratulations. However, to my opinion it would not make much sense for building the kinetic model.
The kinetic model is a sequence of "elementary" uni- and bi-molecular reactions with the rate constants assigned to each step. This model must describe the experimental kinetics in certain range of conditions. Such a model is commonly called the reaction mechanism.
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Kindly suggest the importance of it.
Thank You.
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Adsorption kinetics also controls the rate of adsorption, which determines the time required for reaching equilibrium for the adsorption process.Pseudo kinetic model in adsorption process provide an insight into the adsorption mechanism, surface properties and affinity of the adsorbent.
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Good morning everyone,
I am studying the adsorption of different proteins on nanoparticles and I would like to plot the Langmuir adsorption isotherm.
The Langmuir equation Ce/Qe=1/(QmK)+Ce/Qe. And the isotherm is represented as Ce/Qe vs Ce.
Contrary to the usual set up for Langmuir adsorption isotherm studies, I have a fixed amount of adsorbate (proteins) and increasing amount of adsorbent (nanoparticles).
How to determine Ce, Qe, and plot the Langmuir isotherm?
Thank you for your help. 
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Calculate the uptake (adsorbed amount per unit of adsorbent) then fit your data with adsorption isotherms. For example Langmuir isotherm plot c/q vs c.
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Dear all,
I have planned to do kinetic studies of Dry (CO2) Reforming of Methane experimentally and theoretically for my developed Ni/CeX-Zr1-XO2. I went through some published papers, and they have shown the final kinetics equation based on different kinetic models, which is very difficult for me to understand and perform for my experiment. May I get help from any one of you in this regard or anybody willing to research collaboration with me in these regard?
Thank you in advance for your kind consideration and any valuable supports!
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Okay, thank you Sudesh Kumar !
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How to examine kinetic modelling, thermodynamic and equilibrium calculations in a degradation/absorption or solubility study using response surface methodology (RSM)? Which RSM models are suitable for this?
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As a summary, If you can build a model with R2=1 ( no RSM uncertainty), then yes you can. Otherwise, NO you can't.
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Different researchers are testing new sorbent materials using different methods such as the fixed bed column or batch method, and they use several models to support their results, like Langmuir, Yoon–Nelson, (BDST), Thomas, Elovich equation, the pseudo-first-order equation, the pseudo-second-order equation, and others. So which one is suitable and more important to support and examine the results when testing a new sorbent material?
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When testing new sorbent material, you can use for kinetic modelling : the pseudo second order and intraparticle diffusion. For equilibrium modeling use freundlich, Dubinin raduskevich and sips. For both calculation use the non linear equation for the model.
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I am doing adsorption isotherm studies. I have carried out kinetic modeling with Ce and qe values. However I am stuck in equilibrium studies. I have conducted the experiment for a run of 24 h, which is my equilibrium study time. How do I get the data for making the graph? Are we supposed to use the same data for Ce and qe for experimental study which we used for kinetic study?
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Ce you can measure by an appropiate methode for metal e.g. ICP-OES, for mircopollutants HPCL.
Qe you can measure in case of metals after digestation of the adsorbent, and calculate that from the found concentraion.
Or you calculate Cstart - Ceq = Cadsorbed on adsorbent, now be sure that you know the volume, so that you can calculate to total amount of adsorbate. The total amount of adsorbate you divide by the amount of adsorbent.
If you do a kinetic analysis be sure that you collect enough data from the start of the reaction, if adsorption is fast, it could happend that you have near equilibrium data measured and this leads to a wrong conclusion on the kinetic model. The kinetic models have a big difference in the beginning.
An other point which you should keep in mind is the structure of your adsorbent, does the structure gives the the controling factor for the kinetic? If you got a porous systems the diffision to the adsorption sites will control the kinetic, due to the fact that is the slowest step. A chemisorption is a fast process.
If you look to the isotherm, you take a samples normally after the equilibrium is reached, which is mainyl after 24 h, in this case you change the starting concentration.
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Hello!
Kinetic research in the field of curing process is of great interest for me. It is okay, when some of epoxy resin based systems can be described in terms of usual second (n) order reaction models with additional autocatalysis and/or deceleration terms. Sometime we need to use so called diffusion factor function if reaction is complicated by glass transition temperature and deceleration term in usual from doesn‘t give us a good result of fitting.
I would like to know how do you usually start your model planing? I just interested in the way you calculate you model: directly with all terms or by part.
How can I find the best diffusion factor function?
Very many regards in advance
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I know what the difusion coefficient means, i actually meant the diffusion factor function (f_d) in model based approach for kinetic data estimation! This function equels to unity when there are no diffusion limitaions and approaches to zero if some kind of diffusion limitstions are observed during process.
Authors of some papers use it instead of DiBenedetto equetion which demands to know the exact dependence of glass transition temperature on cure degree.
So, the question is what is the best way to find the function I need to make it possible to describe the kinetic data in terms of diffusion limitation.
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I want to employ the central composite design to optimize 4 parameters with 5 levels. I also would like to fit isotherm/Kinetic models for my batch adsorption experiments
Is it possible to plot isotherm graph from the RSM experimental design results without having to perform the traditional OFAT?
If possible kindly, explain explicitly. thank you for your answers in advance
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What process parameters do you mean and what is the result variable. If the resulting variable is e.g. the adsorbent capacity, and one of the factors is the initial adsorbate concentration, then by registering changes as a function of time (for subsequent samples) you will obtain data sufficient to determine the parameters of the functions describing the kinetics and the equilibrium state.
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According to below articles about kinetic modelling of ODH reactions by G. Che-Galicia and et al. there are some problems need your guidance and advices:
Q.A
  1. According to the nomenclature and equation 13, Kn (absorption equilibrium coefficient) should have the unit of 1 / Pa, but by referring to equation 19 Kn is unitless. why?
  2. According to Equation 18, the first statement in the exp function has the unit of mmol / (g.h), but the second statement is unitless, so we think A' must be outside the exp function. why?
  3. The quantity of Cps (solid heat capacity) and Kez (effective thermal conductivity in axial coordinate) did not reported in the main article and the references mentioned in the context of article. how can we calculate or get this property?
we emailed to authors but don't received any response !
Thank you for the time you spent reading.
Respectfully
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Amir Loghmani i do agree with the expert comments above but I only have to say about that there are many studies available and reports various kinetic modelling of ethane oxidative dehydrogenation under an oxygen free atmosphere employing a catalyst of various percentage and sometimes it might be based on the weight and can from 5-12% wt % of VOx supported on ...... and one can see these studies in the links shared
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It is very easy to specify simple kinetic models, but LHHW is not working for me. It seems that the column (radfrac) does not recognize the existence of this LHHW kinetic model, thus I am unable to set up a heterogeneous catalytic distillation column in aspen plus.
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Hi Zeeshan,
One way you can do is that created the kinetic equations by using FORTRAN and linked with Radfrac modul in Aspen Plus.
Regard,
Ikhsan
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I'm starting to work with kinetic models and I want to insert some reactions into an existing model.
But I arrived at a reaction that the only data available of Vmax comes in micromol.mg-1.min-1, and COPASI only allows me to to use Vmax in mmol.L-1.s-1. Is there any way to convert the units of Vmax into the ones that COPASI requires? The only problem I'm facing is with the grams, since the moles and min units are easy to convert.
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I have also facing the same problem, if I have the Vmax for an enzyme 1.9 µmol/min/mg, How can I convert it to mmole/L/s ?
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Hello everyone,
I have been working on developing a reduced kinetic mechanism for diesel-biodiesel-gasoline mixtures. I have reduced the detailed mechanisms of each individual fuel and combined them to form the final mechanism via Chemkin software.
However, throughout the combining procedure, the Chemkin software does not offer any options to specify a quota for each individual fuel before mixing, so, please kindly guide me on how can I define a specific fraction of each fuel in the final mechanism?
Thanks
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If one go literally to what you wrote, one can think that you mean fuel blending. But, as one know, the rate at which such mixtures are formed does not affect their properties. So you probably mean something else, e.g. the mechanism of the combustion process of fuel mixtures in the engine. You should be clear about this. As for the composition, it is best to use mass fractions here.
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I have applied the Yoon-Nelson kinetic model to the experimental data obtained for CO2 adsorption on solid adsorbents. For the two materials studied, the experimental values of adsorption capacity were found to be 5.9% and 2.3% higher than those of empirical values. However, the R2 values were 0.998 and 0.985 respectively. Now, a journal’s reviewer is expressing disagreement with the values, pointing out that Experimental values are more than empirical values. I feel that high value of R2 and closeness of values (between experimental and empirical) are sufficient to show that the model fits well, as it is only empirical, not theoretical. Please comment on this.
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First, the calculated value (not empirical) can be greater than the experimental value, but it can also be less than or equal to. Secondly, the value of R2 applies to the entire range of changes in the adsorption capacity, not just the end value. Third, ARE can be used in parallel with R2. It's also good to know which form of the Y-N equation you've been using. Explicit with respect to q, or implicit.
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I want to study the effects of some parameters on elution phase of chromatography using lumped kinetic model (LKM) but I have writing the MATLAB code. I want to solve this using finite difference and Euler method. I have attached the equation. Can anyone please help me out?
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I hope it helps you
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I conducted a pesticide dissipation study and the degradation of the compound appeared to me like biphasic. So I tested three kinetic models viz. DFOP, FOMC along with the first order model or SFO in R-Studio and calculated the Chi square error value and Akaike Information Criterion or AIC value for each model to select the best fit one. Based on the calculation, the pesticide followed biphasic DFOP model as I guessed. As I communicated to a journal a comment came like: "Why you have chosen the three models? Briefly discuss their adaptation as well as uncertainty factor". I had answer for the first part but I didn't how to answer the adaptation of the kinetic models I have selected and their uncertainty. So please help..
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Sushovan Das, Well, reviewers have various ideas and they often like to get smart. I have published a lot of work on the kinetics of chemical reactions, but no one has ever asked me about "adaptation" and "uncertinity". One can, of course, try to guess that the reviewer, when writing about "adaptation", had in mind the method of selecting the proper kinetic equation, and when writing about "uncertainty" he/she wanted to know the confidence intervals for the parameters. But it may also be that the meanings of the terms have been confused and the reviewer had in mind the methods of matching when writing about "adaptation".
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i do research about simultaneous photoreduction of Cr(VI) and Fe(III) by TiO2/UV. And I have problem with kinetic model for this reaction. Normally the reaction happens as:
Cr(VI) + H+ +e- --> Cr(III)
Fe(III) + H+ + e- --> Fe(II)
Can I write the overal reaction as:
Cr(VI) + Fe(III) + H+ +ne- --> Cr(III) + Fe(II)
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Ridha Djellabi, Since you've linked your work, here's a quick comment. The most important thing is, of course, the possibility of complete removal of pollutants and the interpretation of the observed phenomena. The mathematical description of the kinetic data is of secondary importance. However, if you choose to do so, do not mislead the reader. There is no evidence in this paper that the processes under investigation are of the first-order. The mere compliance of the empirical exponential function with separate kinetic curves is not enough, and the results presented in Figs. 2 and 4 and in Table 1 even contradict it.
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I am trying to simulate a heterogeneous reaction between two phases in Eulerian multiphase model. I have written a UDF and it compiles and runs well. The reaction is: C+2H2--> CH4. Although my solution shows reasonable values for reactions rates, but I do not see any changes in Hydrogen concentration from the inlet gas. Can anyone where the problem is arising from?
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Hi, I am trying to model gas/solid multiphase granular flow with chemical reactions in Fluent. The solid phase is FCC catalyst together with the coke (hydrogen + carbon) deposited on its surface and the gas phase is oxygen. But I have some problems. 1. When modeling this, should I use both species transport and heterogeneous reactions in multiphase interaction module? 2. How to define solid phase in the materials section as FCC catalyst (granular) together with the coke (hydrogen + carbon) deposited on its surface? Thanks...
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Hello,
I'm looking for someone, who can explain me how to calculate the activation energy of the biomass pyrolysis process. I have a TGA results (mass loss in time and in temperature) with a constant heating rate. And now I don't understand how analyze these data and use the kinetics models for calculation.
Young scientist Tomasz
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Tomasz Noszczyk find attached the chapter 2 of the book Waste Biorefinery-Potential and Perspectives. It discuses extensively how to calculate the kinetics of biomass pyrolysis elaborating on over 20 models that can be used; Diffusion Models, Geometrical Contraction Models, Nucleation or Growth Model, Order Based Models, Single Heating Rate Method, Model Fitting Methods, Isoconversional Methods as well as some other noteworthy methods.
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as mentioned in the following table, how do I arrange those kinetic models for five soils based on the highest determination coefficient( R2) and the lowest root mean square error (RMSE) please?
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Kamal Hama Karim, It's best to start with the physics of the process. Presumably it is about adsorption. It's good if you also include kinetic data along with the adjustments. Information about the numerical methods used would also be useful. On the basis of the attached data, no reliable differentiation between the individual functions is possible.
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Residence time distribution for a tubular reactor follows semi empirical model, I want to know how can I use this RTD for predicting conversion of my system using mass balance equation for the tubular reactor( like axial dispersion model which consider reaction happening in the system as well as axial dispersion).
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Prajakta Gajbhiye, In my opinion, you cannot "incorperate" E(t) into any mass balance equation. However, you can try to modify the mass balance taking into account, apart from longitudinal dispersion, e.g. radial dispersion. The model can also be extended with the dynamics of the catalyst grain. But that's just a guess.
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Based on my reading, initial adsorption rate, ho from PSO kinetic model is always been compared in research to determine which metals will be adsorbed faster or better. How does values of ho related to ionic sizes?
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Good morning Nur ikhsan Bujang
There is no relationship between the initial adsorption rate and ionic radius of adsorbates.
Reg
P.B.Bhagawati
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How can I calculate Kr and Ka for langmuir hinshelwood kinetic model? How the slope of 1/C0 vs 1/r0 plot is related to Ka and Kr?
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Could the presence of ligand on a catalyst surface reduced the reactivity of its surface? If yes/no, please explain why?
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this depends on which type of ligand used
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Do I have to solver-add inn for its calculation?
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If you mean non linear regression, you may use Maltab, polymath and other relevant softwares
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When there is the Thiele modulus and the effectiveness factor to determine the pore resistance in catalysts, why do we need the Wagner modulus?
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Wagner model is a rheological model developed for the prediction of the visco-elastic properties of polymers
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I am trying to develop a mechanistic model for photocatalytic degradation studies of organic compounds. Can somebody help me understand the basics
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Pseudo second order kinetic model.
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we found that the pseudo-first-order model can be described the adsorption process of methylene blue.
What does Pseudo-first-order kinetics model indicate in liquid-solid adsorption system?
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Pseudo second order kinetic model.a complete step by step process...
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How the kinetic models interpret the metal removal process?
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Pseudo first order kinetic model.a complete step by step process..
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to determined pseudo first order i follow this equation log(qe-qt)=log qe-k1t/2.303 but i found qe is lower than qt what can i do to plot log(qe-qt) versus t?
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Pseudo second order kinetic model.a complete step by step process...
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Hi,
I need to develop the kinetic model for the Ping-pong bi-bi mechanism for the lipase-catalyzed synthesis of n-butyl oleate ester according to MM model.
I have the final solution for the rate eq. and the general mechanism (files attached) but all my attempts to develop the rate eq. myself failed.
I'll be happy if you could help and show me the steps for developing the model.
thanks in advence.
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MM model is suitable for enzymatic activity in the bulk, while the hydrolytic activity of lipase occurs at the interface. So, you should use a proper kinetic model.
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I am doing a research on certain kinetic models for predicting methane production. I am having difficulty in finding the input parameters of the Richard's model. How can i find them?
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Maybe you could share your data with responders. Then it is much easier to help. I am also curious why you want to use the Richads' function and not another.
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I am working on color removal from wastewater using AOP and found best fit with exponential decay function 2 and 3 of Origin pro 8.5 . With some literature review some authors suggested the exponential decay function belongs to pseudo first order kinetics model and some suggested second order kinetics model.
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Hello,
I hope the following information is useful.
Lin, J., Wang, L. Comparison between linear and non-linear forms of pseudo-first-order and pseudo-second-order adsorption kinetic models for the removal of methylene blue by activated carbon. Front. Environ. Sci. Eng. China 3, 320–324 (2009). https://doi.org/10.1007/s11783-009-0030-7
Hubbe, M. A., Azizian, S., and Douven, S. (2019). "Implications of apparent pseudo-second-order adsorption kinetics onto cellulosic materials: A review," BioRes. 14 (3), 7582-7626.
Today s. (2004), Citation review of Lagergren kinetic rate equation on adsorption reactions. Scientometrics, 59 (1), 171-177.
Ho, Y.S. (2006), Review of second-order models for adsorption systems. Journal of Hazardous Materials, 136 (3), 681-689.
Regards.
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Development of mathematical and kinetic models would start by matching a categorical example to a closely related reaction to be studied. If the selected example satisfies the characteristics of the proposed reaction having been chosen from the global option, modelling could be executed more precisely.
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As for me, a sequence of proceedings should be as follows. First, stoichiometry, preceded by the development of a chemical model. In turn: Thermodynamic analysis, if necessary preceded by the required tests. Determination of kinetic equations preceded by kinetic tests in a given reactor system and with the elimination, if possible, of undesirable effects and phenomena. Development of a mathematical model whose degree of complexity depends on the adopted assumptions. Finally, there is a validation of the model, although additional checks may be necessary at subsequent stages of its development. This is, in the greatest brief.
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Theoretically, half-life according to first order kinetic model, is independent of concentration, then how the application rate of pesticide in soil is correlated with DT50?
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Lennart Weltje
Sir
Can you elaborate more on the correlation of biodegradation/microorganisms with application rate of pesticides?
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I'm interesting in kinetic model of lignocellulose transform to reducing sugar. Please give suggestion to me.
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Why have you decided that an asking for a clarification of ill formulated question was a personal attack. I explained what is a kinetic model. You suggested to find the reaction rate law, but a kinetic model is not the reaction rate law. Therefore, at least it's not polite from your side to recommend me "render some assistance, if you are disposed?"
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I am doing a kinetic study on an enzymatic reaction which does not follow Michelis-Menten equations.
I am using a model to fit the experimental data, and it can fit the data for each given substrate concentration (mixed with different enzyme concentrations) very well, BUT the rate constant changes by changing the substrate concentration. In other words, the rate constant seem independent of the enzyme concentration, but somehow dependent on the substrate concentration. It should also be mentioned that in all conditions, the substrate is excessive.
I am wondering if this phenomenon is physically possible or something is wrong with the model.
Thanks.
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  • There could be an allosteric effect of the substrate by binding to a second site.
  • The substrate could be contaminated with an alternate substrate or an inhibitor.
  • The substrate may be having a non-specific effect on the enzyme, such as acting as a denaturant, or causing a shift in pH, or increasing the ionic strength.
  • If the reaction is metal ion-dependent and the substrate binds the metal, the concentration of free metal ions may be decreasing as the substrate concentration increases.
  • The substrate could interfere with the method of product detection.
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I'm cultivating a photoautotrophic cyanobacteria (arthrospira platensis) which shows a diauxic growth curve type. What are the most used kinetic models for this kind of curve? Thanks in advance for your answers
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I believe that this phenomenon is related to its inoculum, but we can consider two phases:
i) first exponential growth phase: fragmented cells of A. platensis are reproducing rapidly.
ii) second exponencial growth phase: the fragmented cells of A. platensis now grow in size rather than reproducing, due to some environmental variation (probably lack of nutrient or change in the pH).
Filamentous algae commonly exhibit this behavior. You must know these phases well in order to justify choosing a kinetic growth model.
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Is there any built in equation for Lagergren's 2nd kinetic model in Origin lab? there are other models available but i am unable to find this..thanks
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In addition, I would advise against describing the kinetic data of equilibrium batch adsorption using empirical functions. What will result from this that you will find that the so-called PSO is better than PFO or vice versa. This will probably satisfy the ignorant rewivers. But nothing else.
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I am using magnetite and maghemite nanoparticles (20-80 nm) for anionic gold complex adsorption. I used Pseuso-first-order and second-order models for kinetic data fitting. in order to determine the rate-limiting step, can I use intra-particle diffusion model as my adsorbent is non-porous. this model has been used to fit kinetic data of porous adsorbents in many of the published work. Thank you for your valuable answers.
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Hi@ Laith A. Naji , many thanks for your valuable answer.
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I have tried to do the pseudo-second-order kinetic plot several times using the following equation:
qt = k2*qt^2*t/(1+k2*qt*t),
but every time I am getting a flat line instead of a curve. please help me with this.
Regards.
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I am doing the non-linear plot, that is where I am facing the problem. The linear plots are already done.@Bibek Dash
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I have been working on isoconversional methods for quite a time now. Have used all kinds of methods for kinetic analysis of my pyrolysis data: KAS, FWO, Vyazovkin, Kissinger etc. Going through literature I found, Friedman method has certain advantages over these integral methods (exclude Vyazovkin: it works quite well), but the d(a)/dT (a is normalized conversion) term has to be calculated judiciously. I have tried with forward/backward difference simply in excel ((a2-a1)/T2-T1)) and an almost similar thing in MATLAB too. But the results are not plausible enough.
I haven't tried calculating the slope at the different required points of (alpha) vs T curve, as it makes the whole analysis complex.
So what do I really do with the d(alpha)/dT term to compute kinetic parameters for my data?
An elaborate answer would be highly appreciated.
Thanks!!
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I would like to recommend you the above paper(s) if further query then you can message me.
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Hi all,
I am working on building a kinetic model for lignocellulose decomposition in aspen. I have already defined cellulose as a solid in aspen and completed the drying part of the simulation. But when I enter lumped reaction model for cellulose decomposition in aspen using the kinetics available, it doesn't consider the solid reactions and the inlet and outlet are the same. The simulation doesn't give any errors and I am at loss on what to do. I have already tried all the solid modelling examples available in aspen. I am really hoping anyone of you can give me a clue on how to correct that error.
Thanks
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Thank you Dr. Decker and Dr. Taqvi. Your answers are of great help
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I have a case in which the global equivalence ratio is about 0.5. The fuel is methane. Based on the Kinetic Modelling, the flame temperature of that equivalence ratio should be around 1800 K. However, my CFD simulation showed the flame (max) temperature to be about 2400 K. I used the Flamelet Generated Manifold for the combustion model and GRI Mech 3.0 for the Chemical Mechanism. Both the Kinetic Modelling and the CFD were on the same operating conditions, i.e. pressure ~ 16 bar and initial temperature ~ 673 K.
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In many cases, it is simply because bad mesh quality. I have an experience in simulating reactive distillation of methane, where the maximum temperature is ideally around 400K, but I had observed some locations with the temperature point reaches higher than 700K. Second possibility is that you did not correctly define Cp in the material properties as a function of temperature. Also one need to ensure that the residuals drop to certain levels of tolerance.
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In the kinetics of CO2 methanation or hydrogenation of CO2, how do we determine the term equilibrium constant, Keq. In many kinetic models, rate equations we have the term Keq in the equation, how this constant is found ?
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Open a handbook, find the standard formation Gibbs energies and enthalpies of CH4, CO2 and H2O, use Hess's law to find the standard Gibbs energy and the enthalpy of the reaction, and use van 't Hoff's equation to find Keq at the temperature of interest. If you need it more accurate, correct for the heat capacity of the reaciton via Kirchhoff. Consult any book on chemical thermodynamics for examples; look for equilibria in the gas phase.
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In almost all papers (eg Jacob 1976 10 lump model) discussing Fluidised Catalytic cracking of gas oils/VGO, the starting point is the continuity equation. The equation has a term labeled as Gv , superficial mass flux (kg/m2.s), which is a function of WHSV (weight feed/(weight catalyst*hr)) , catalyst bed density, length of reactor, and the void fraction (the fraction occupied by the vapour phase).
The equation looks like this:
Gv = Sv * RHOcatalyst * L/ epsilon
where
Sv : WHSV
RHOcatalyst : density of catalyst beg
L = reactor length
epsilon = void fraction.
The problem is that no explanation/derivation is provided for this equation. Any help is appreciated.
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Javier Rivera De la Rosa Dear Sir, I went through the Jacob 1976 paper "A Lumping and Reaction Scheme for Catalytic Cracking" and the chapter 5 of Fogler 5th edition which explains gaseous flow in packed beds for a second time.
From what I understood from reading Fogler, there are two kinds of catalyst densities. One is the density of the solid catalyst particles (RHOsolid) and the other is catalyst bulk density, the weight of catalyst per unit volume of riser, which is equal to RHOcatalyst = (1-epsilon)*RHOsolid.
In the Jacob paper the superficial mass flux is given as Gv = Sv * RHOcatalyst * L/ epsilon.
According to my understanding, Gv should be equal to:
Gv = Sv * RHOcatalyst *L
Please comment on this.
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I am doing an experiment on the nutrient release from a compost over time. I have mixed the compost with soil and measure the nutrient concentrations (N, P, K) in this compost mixed soil for 0, 15, 30, 45, 60 and 75 days. Now I want to calculate the rate constant for the nutrient release and fit it to the reaction order kinetic model. How will I do that?
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Let us consider. In your case the nutrient release looks like reaction "Substrate -> N (or P or K)". That is this is first-order reaction, i.e. d[N]/dt=k*[Substrate]. If we will consider the starting concentration of nutrient (N, P or K that will presented here as A) in the initial mix as A0, then d[A]/dt=k*(A0-A(t)). After integration we will obtain A(t)=A0*(1-exp{-k*t}).
This equation may be transformed in linear form ln{(A0-A(t))/A0}=-k*t, that is you can plot the dependence of ln{(A0-A(t))/A0} on time and the slope will be the rate constant.
Best wishes,
Liliya.
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In syngas to olefin coversion, on the basis of catalyst and promotor..can we decide the kinetic model?
Is there any possibility of predicting that which kinetic model will be applicable by knowing the catalyst?
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Hi,
The chemistry of syngas to olefin as a GTL process is very complex in order to high temperature and high pressure in the operation. However, some kinetic models in order to the known mechanism for this reaction over the catslyst are available. You must choose the catalyst and the olefin you want to model them.
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Kinetic and thermo data on binding kinetics of BST DNA Polymerase
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Good question to follow
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Hi science hive mind!
I am running some kinetic simulations to determine the fate of a drug of interest. I am considering reactions with superoxide, hydrogen peroxide, and hydroxil radical. I am considering the Prx as the main H2O2 sink, and SOD the main O2.- target. I found an estimate that Prx can account up to 1% of cell protein, so I'm estimating the Prx molar concentrations as 1E-6. I haven't been able to find estimate for SOD molar concentrations. I am not considering multiple compartments. A range would suffice.
Thanks for your time and expertise
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Hey Edward,
I know Garry R Buettner (https://frrbp.medicine.uiowa.edu/people/garry-r-buettner) at Iowa has had a long-standing interest in quantitative redox biology, including absolute quantification of redox proteins. I agree with Annette that the level will not be stable depending on numerous cellular factors (e.g. stress, cell cycle, oxygen concentration, metabolic state, etc), but Garry may have a good estimate for you since he has spent some time looking into this specific question. Good luck!
~Adam
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Dear all,
I have a sewage wastewater sample with negative zeta potential (-17.1 mV) I had treated this wastewater using a natural anionic flocculating agent and reduction in turbidity, COD, BOD, and TSS were observed. However, there is no change in the zeta potential of wastewater sample after treatment as the value for the same is -17.2 mV.
I had applied intra-particle diffusion kinetic model and it showed positive for this flocculating agent.
Kindly suggest how to describe the mechanism of action of this anionic flocculant on sewage wastewater sample when there is no change in zeta potential value.
thanks and regards
Varsha
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Oh, sorry I forgot to add this to answer your question. In depletion flocculation the particulate species are not changed so their zeta-potential remains the same. The added flocculant will not contribute to the zeta-potential as dissolved polymers scatter far less light than particles, so the effect of their addition you will not see when performing the traditional light scattering micro-electrophoresis (like with a Zetasizer).
If, you add a cationic flocculant it neutralizes the charges on the particles and there you could see a change in zeta-potential.
Kind regards, Leo
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Does anyone know how to fit nonlinear pseudo second order kinetics model using origin software? Please someone help me. I have tried a lot but failed. I want to known programming of origin according to pseudo second order kinetics model.
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I don't know anything about "origin software" but you can fit any equation to any data using the "Solver" Add-In that is distributed as part of Microsoft Excel. Enter your data into an Excel spreadsheet. Each experiment should occupy one row of the spreadsheet with the variables lined up in columns. The last column should contain the "result" of the experiment. Set up a region of the spreadsheet to contain the parameters of the model and enter an initial guess for each parameter. Then enter a column of the spreadsheet next to the "result" containing the "model result" expressed as a function of the variables and parameters. In the next column calculated the difference between the "result and the model result". In the final column calculated the square of the differences and sum that column. Use the Solver to minimize the sum of the squares of the differences. The parameter field will then contain the best fit parameters of the model.
I know nothing about your experiment. Are A, B, C, and D all measured results as a function of time? If so, what are your parameters and what are the equations that express your result values A, B, C, and D as a function of time and the equation parameters?
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I have grown Yeast in synthetic medium. In two days all the substrate were consumed, However, the growth was observed until day 5 and becomes stationary after day 5. What could be the possible explanation?
Also, What will be the mathematical relation of substrate removal and delay in growth?
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Osman Nabayire Kanwugu : Thank you for your response. Your explanation makes sense. Since I don't the access to the publication you refereed. I was not able to read this chapter.
Thank you for explanation
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Im trying to fit multivariables kinetics models for cells growth. Matlab Curve Fitting app only let me introduce one independent variable.
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Neural networks are good alternatives for modelling. I particularly recomend those based of radial functions.
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Actually I am working on catalyst reactor fora ammonia oxidation, whose kinetic model, I want to apply on aspen plus custom model. Needs guidance or if anyone has done similar work on any sort of reactor kindly share.
The reaction is:
4NH3 + 5O2 === 4NO + 6H20
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Do you have a kinetic expression for the primary reaction and side reaction and a good estimate of the rate constants? If so it should be relatively easy to use any kinetic modeling expression and rate constants to model the reaction. Unfortunately I don't have access to Aspen plus but if I can do it in with an excel spreadsheet I would be shocked if you couldn't do it at least as well with Aspen Plus.
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i carried out DSC-TGA for NaN3-KNO3 in nitrogen atmosphere for different heating rates. It has two peaks in DSC plot and there is an initial mass gain in TGA plot. Is it possible t o obtain activation energy (and other kinetic data) of this using models such as Kissinger, OFW, KAS, Coats Redfern etc? if so how?
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Which is the reference value for Tp?
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In my research, I performed batch adsorption experiments of methylene blue on activated carbons. We found the following results:
- Kinetic study showed that the adsorption system followed the pseudo-second-order kinetics model;
- The Freundlich isotherm fits better the experimental data;
the adsorption of methylene blue onto optimal activated carbon was a physisorption process in nature (Thermodynamic study)
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Our understanding of adsorption kinetics is much less than theoretical description ofadsorption equilibrium becuse the kinetics depend on the road to equilibrium. In general, in a well stirred solution three steps can be considered with the adsorption process: (1) film or interparticle diffusion, (2) intraparticle diffusion in pores and (3) surface reactions. In most models only limiting situations that assume that one of these steps is rate controling are considered.
In a paper by Douven et al. (2015) three dimensionless numbers are identified that govern the overall adsorption–diffusion process. The standard models are found to be particular cases of the general adsorption–diffusion model for specific values of the dimensionless numbers.
Reviews that discuss the 1st and 2nd order kinetic equations are presented by Tan and Hameed (2017), Liu & Liu (2008) and Azizian (2004).
S. Douven, C. A. Paez and C. J. Gommes, J. Colloid Interface Sci., 2015, 448, 437–450.
Y. Liu and Y. J. Liu, Sep. Purif. Technol., 2008.61, 229–242.
K. L. Tan and B. H. Hameed, J. Taiwan Inst. Chem. Eng., 2017, 74, 25–48.S. Azizian, J. Colloid Interface Sci., 2004, 276, 47–52.
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Comparing two types of insulin (fast-acting and slow-acting), can we predict which one follows presumably zero-order kinetics model?
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Do you have any kinetic data? Comparison of rates is not enough. In addition, the "order" refers more to the reaction than to the equation. Regards,.
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I have calculated the activation energy from freidman's differential isoconversional method and prexponential function using compensation effect, so I have a unique value for E and A. Now I want to plot a theoretical curve of conversion (Alpha) vs Temperature using the one of the kinetic models in solid state reactions (eg. second order model or Avrami-Erofeev model).
Thank you
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You are welcome, and good luck with your research sir.
Best regards,
BBN
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I would like to know if anyone knows how to plot the surface ([B] vs t vs k1/k2 ) as a numerical solution of the kinetic model of the mechanism A -> B -> C, specifically for the concentration profile of the intermediate specie [B], using any MATLAB ODE solver.
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Hi Enmanuel Duarte, the ODE solver will return a solution set of data points from the universe of discourse. So I think, at most, you can only get the 3-D line plot, not the surface, unless you want to obtain the slope field.
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I put this question, because some researchers believe with no real grounds that this phenomenon is connected with the nonexistent surface heterogeneity of the thermally-stabilized catalyst of NH3 synthesis.
Our answer to this question is simple and unambiguous. Oxygen contaminates Fe catalyst because its heat of chemisorption at Fe is very high (about 670 kJ/mol O2, D. Brennan et al, Proc. Roy. Soc., A256, 1960, 81-105; see also https://www.researchgate.net/publication/235342853_Molar_heats_of_chemisorption_of_gases_at_metals_Review_of_experimental_results_and_technical_problems), while the heat of N2 chemisorption is about 125 kJ/mol only and because the temperature coefficient of chemisorption of two-atomic gases at metals is rather small (R.J. Madix, J. Benziger, Ann. Rev. Phys. Chem., 29 (1978) 285-306; see also https://www.researchgate.net/publication/235799473_Oscillation_theory_of_heterogeneous_catalysis_and_its_use_for_identification_of_the_reaction_scheme_and_kinetics_Catalytic_liquid-phase_benzene-ring_hydrogenation_as_an_example), while the temperature coefficient of the H2 interaction with Fe(Oads) is rather high.
It is shown that the applicability of logarithmic isotherm to some adsorption and catalytic data is explainable by the “pantophagy” of logarithmic functions over some fields of parametric variations; as for linear segments in the galvanometric charging curves obtained in some electrochemical works, there are no independent proofs that they result just from H2 chemisorption and it is not proved that the processes attributed to these segments are the equilibrium ones (https://www.researchgate.net/publication/235342837_Surface_homogeneity_vs_heterogeneity_problem_for_thermally_stabilized_crystalline_bodies_and_the_nature_of_heterogeneous_catalysis, p. 10;
Thus, the return to the opinion on a surface heterogeneity of thermally stabilized catalysts in their catalytic activity has no scientific grounds and sends us back to the erroneous views of the half-century' prescription.
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Read my answer to Miroslaw Crzesik and Peter Broadhurst . My question is not about contamination of the Fe catalysts by O2 but about the problem on the "surface homogeneity vs. heterogeneity" of thermally stabilized catalyzing crystals or poly-crystals by their chemisorption and catalytic activity. You can file your claims not to me but to A. Avetisov, the author of the paper “Mechanism of Oxygen Poisoning of Ammonia Synthesis Catalyst” by the address
https://www.researchgate.net/publication/226288571_Mechanism_of_Oxygen_Poisoning_of_Ammonia_Synthesis_Catalyst and of other papers of this author on the theme of iron contamination in NH3 process by O2, where he consider catalyst surface as the heterogeneous one. As for the phenomenon of contamination of this catalyst by oxygen as such, I agree with you that it has no important practical significance at present time.
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Dear all,
I am in search of such an equation or model which can be used to express relative growth rate or growth kinetics of mushroom.
Your valuable suggestion will be highly appreciated.
Regards
Vinod Kumar
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Relative growth can otherwise be known as exponential growth rate. The following equation can be applied:
RGR =  (ln W2 - ln w1)/(t2 -t1) where,
ln = natural log
t1 = time one (e.g in days)
t2 = time two (e.g) in days)
W1 = size at time one
W2 = size at time two
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The Monod equation is a mathematical model for the growth of microorganisms. But the mushrooms do not follow this trend as they have a phase where spawn running is carried out. Also, the biomass increase is differed from other microbes.
The attached images shows the difference.
Please tell me can we still use Monod equation to to express specific growth rate of mushrooms and substrate utilization?
or which model will be more suitable in my case?
Thanks
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Respected Mirosław Grzesik Sir,
Is it possible to derive a new model in my case, as all mushroom species follow the trends as given in the image above?
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I'm currently working on an adsorption experiment of several dye solutions onto chitosan hydrogel.
In literature, the two most popular kinetic models are Lagergren's pseudo-first-order model and Ho's pseudo-second-order model. By applying this model, we can find out the adsorption rate constant, k.
Based on my experimental data, I found out that changing the adsorbate concentration could change the adsorption modelling result. To be more specific, k would change, too.
However, this seems to be counter-intuitive, especially when we take into account the rate equation. Although the reaction rate could depend on the concentration, the rate constant only depends on the temperature.
I am feeling a bit confused. Does it mean I'm having a misconception about rate constant?
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Thanks everybody. So if I'm correct, in theory constant k should not be affected by initial concentration. But since the kinetic models after all are just empirical models, it may not be truly 100% correct - am I correct?
Also, Mr. Grzesik, thank you very much for your input but I'm not sure I understand what you said in the last message. Are you implying that specialists in the field of sorption would say that rate constant CAN be affected by initial adsorbate concentration?
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I´m currently working with energy storage materials. I want to know how the enthalpy value of this material is affected after several hours under a certain temperature (samples in oven). The models I´ve found so far are related to the heating rate and melting point (Kissinger equation). Since I used the same heating rate to calculate enthalpy for all my samples and the melting point doesn´t change drastically, it´s not so clear how I can use this equation or if in any case I´m using a wrong model. Is there someone who has already worked with something similar? Thank you in advance.
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Look at some of my publications where different models appear.
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I have found the equation as follow:
y = 0.456x + 1.579 R² = 0.914
how can determine the n exponent to determine the mechanism of release ?
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Dr. Grzesik, I may have misunderstood your post. In any case. Dr. Weimer summarized my view succinctly. There a many examples in my work where linearizing an equation leads to poor parameter estimates. Indeed, there is a whole host of statistical issues that were and largely still are common practice that can be done much better now, and often with less effort. I have formulated a graduate statistics course around them. This is probably not the forum for this discussion but I would be happy to learn from others what issues we can improve.
Larry
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To whom it may concern
I'm trying to evaluate the reaction rate, but I don't have typical data.
I have a lot of variables. For example when the temperature is constant, "reactants molar ratio" and "contact time" are different.
One list that has less variables is "conversion-temperature" diagram.
It's my pleasure to get a help from you
best regards
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If "contact time" means a calendar time (batch system), not a residence/space time (flow system), you have, as I guess, a few kinetic curves c =f(t) for T = constant. Do you also have kinetic data for various initial substrate/s concentration/s. If so, you can find the form of the kinetic equation and to determine the value of its parameters. How to do it? Look it up in my comments on RG or in the papers. Regards,
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In the adsorption studies during the determination of equilibrium time, usually the kinetics obey Lagergren pseudo second order model and after calculating the thermodynamic parameters and D-R parameters, physical adsorption is obtained. What could be the possible reason for this? Please attach some reference papers for help. Thank you in advance.
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It may not. The majority just seems to be related to PSO kinetics. Why does it? Because most of the researchers do not apply nonlinear fits to measured adsorption data. If they do apply a nonlinear model, it would not be so much PSO kinetics in literature. Incorrect approach of a linearized model just gives an overestimated R2.
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I was wondering if I could use BOD removal kinetics in my constructed wetland system by the process of phytoremediation.
I have already performed COD removal kinetics. I need some sorts of information like which kinetic model is best suitable for such systems?
I have these variables: Initial COD concentration (three) and retention time (days).
Please give your valuable suggestions.
Thank you.
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Yes, Pl refer to my paper available in RG platform. This was a part of ME dissertation of my student guided by me
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