Practical way to determine Order of Reaction in API BULK

ORDER OF REACTION

Order:

This term can be defined as the sum of the powers of the concentrations of the reactants in rate expression. This is what every student know theoretically,

 -r_a =kC_a²C_b

_{So whats the order now,}

_{every one answers the} order is 3,

but when a student enters the professional large scale manufacturing industries, the one should need to apply the theory to the practical cases, but I guarantee you that whatever you studied in the text books is quite different from the practical, as the majority of the problems solved on paper in the engineering classes consists of a common line, “NEGLECT THE LOSSES”, which makes a huge difference, so today lets start to learn how to apply the theory we studied in our books to the large scale, and determine the ORDER OF REACTION.

PRACTICAL  APPROACH  TO  DETERMINE  ORDER  OF  REACTION:

Method 1:

Case study:

Consider a reaction where two components reacts in a solvent medium, for example , the large scale process is,

1)      Charge methanol 2000lts into reactor.

2)      Charge 200kgs of citric acid(X) into reactor, and stir for 25(+/-)5minutes.

3)      Charge 500kgs of Soda Ash(Y) into the reactor.

4)      Maintain the Mass temp 50(+/-)5 for 5hrs(+/-)1hr.

5)      ……..

6)      ……………..

7)      ………………………..

8)      ……………………………………….

9)      …………………………………………………

10)   Unload the residue mass into containers and weigh it, the required product(P)  yield must be 600(+/-)50kgs

So, now this is the case and now first find the KSM(key starting material) , and then what are the reactants, as we here charging methanol, citric acid and soda ash, all the three were not reactants, methanol is just used to provide a medium for reaction, so now the main reactants were citric acid and soda ash,

So to find the order of reaction, just take the each reactant, first lets take citric acid, 200kgs used so find the number of moles,

Number of moles of citric acid= 200/( Mol. Wt. of citric acid) =a say

Number of moles of Soda ash= 500/( Mol. Wt. of Soda ash) = b say.

Now move to the yield we got  i.e., 600kgs, so now find the Product moles,

Number of moles of Product, =600/(Mol. Wt. of Product) =c say

Now write the reaction,  aX +bY  à cP ,

Now find number of moles of citric acid required to produce one mole of product, i.e.,

K=(a/c)*(minimum number of moles of citric acid required to form the product).

Find number of moles of soda ash required to produce one mole of product, i.e.,

L=( b/c)*(minimum number of moles of soda ash required to form product).

So , now write the rate expression,

r_P  = kC_X^KC_Y^L

_{Now find the order, it will be a/c + b/c= (a+b)/c.}

_{Method 2:}

Consider a reaction where two components reacts in a solvent medium, for example , the large scale process is,

1)      Charge methanol 2000lts into reactor.

2)      Charge 200kgs of citric acid(X) into reactor, and stir for 25(+/-)5minutes.

3)      Charge 500kgs of Soda Ash(Y) into the reactor.

4)      Maintain the Mass temp 50(+/-)5 for 5hrs(+/-)1hr.

5)      ……..

6)      ……………..

7)      ………………………..

8)      ……………………………………….

9)      …………………………………………………

₁₀₎           Unload the residue mass into containers and weigh it, the required product(P)  yield must be 600(+/-)50kgs

_{Theoretical combined formula for calculating the order/reaction time/rate constant is,}

(1/C_a)^(1-n) –(1/C_a0)^(1-n) =k(n-1)t

C_a  refers to the final concentration of citric acid, and C_a0  refers to the initial concentration of citric acid, n refers to the order of reaction, k refers to the rate constant, and t refers to the reaction time,

So now to find the order from the above equation we need the rate constant and reaction time, we can get the initial concentration and final concentration from the HPLC/GC reports.

In our case study, its mentioned that the maintainence time is 5hrs, so the sampling to find the Ca, Cao must be done before and after of the maintainence time, and the amount of KSM % i.e., Citric acid percent gives us Ca, Cao. And whenever its mentioned Maintainence time in the procedure, it will be the critical parameter in the process and it will be the reaction time, so now the reaction time is 5hrs.

So now we have to find the rate constant , rate constant characterizes the conversion, means amount of KSM decomposed / disappeared in the particular reaction time, so now lets say 50% decomposed in a whole reaction time of 5 hrs then it will be 200*(50/100) =100kgs. So 100 kgs decomposed in 5 hrs, so Rate constant k will be

i.e.,

=(100/Mol. Wt. of KSM)/ (vol of Reactants*time),

Now substitute and solve the eqn (1/C_a)^(1-n) –(1/C_a0)^(1-n) =k(n-1)t

 for order. That’s it, if you understood it, then say cheers and if you have any queries feel free to comment, sharing is caring, I care for you

About The Author

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Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
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