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Objective

ERT 316 Reaction Engineering Chapter 5: Collection and Analysis of Rate Data by anis atikah ahmad. Objective. to obtain the rate law for a specific reaction from data collected in experiment ( eg : concentration-time for batch). To find reaction order.

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Objective

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  1. ERT 316 Reaction EngineeringChapter 5: Collection and Analysis of Rate Data byanis atikahahmad

  2. Objective • to obtain the rate law for a specific reaction from data collected in experiment (eg: concentration-time for batch) To find reaction order To find specific rxn rate constant, k

  3. Basic Steps in analysis of rate data

  4. Algorithm for data analysis If 1 of the reactant is in excess, assume its concentration is constant.

  5. Batch Reactor Data 1. Differential method

  6. Batch Reactor Data 1. Determine α 2. Determine β 3. Determine kA :

  7. Batch Reactor Data • How to find since we only have data of concentration and time? 3 Methods:

  8. Graphical Differentiation Plot a histogram

  9. Draw a smooth curve in such a way that: A = B A + C = B + D

  10. Numerical differentiation formulas

  11. Polynomial fit • Fit the concentration-time data to an nth-order polynomial: • Find best value of ai • Differentiate Eq 1 wrt time: Eq 1

  12. Batch Reactor Data Trial & error to find reaction order. If the order is correct, the plot should be linear 2. Integral method (linear plot)

  13. Batch Reactor Data 2. Integral method (linear plot)

  14. Batch Reactor Data 3. Non-linear regression We want to find the parameter values (α,k) for which the sum of the squares of the differences, the measured rate (rm), and the calculated rate (rc) is a minimum. • For conc-time data, we can integrate the mole balance equation to obtain:

  15. METHOD OF INITIAL RATES Determine –rA0 first

  16. METHOD OF HALF-LIVES

  17. Example 5-1 The reaction of triphenyl methyl chloride (trityl) (A) and methanol (B) Trityl (A) + Methanol (B)  Products was carried out in a solution of benzene & pyridine at 25°C. Pyridine reacts with HCl that then precipitates as pyridine hydrochloride thereby making the reaction irreversible. The concentration-time data in table below was obtained in a batch reactor: The initial concentration of methanol was 0.5 mol/dm3 • Determine the reaction order with respect to triphenyl methyl chloride. (At t= 0, CA = 0.05 M

  18. Example 5-1- solution STEP 1 Postulate a rate law. STEP 2 Select reactor type & corresponding mole balance. Batch reactor Since it is a liquid phase reaction, V=V0 STEP 3 Process your data in terms of measured variable (in this case: CA).

  19. Example 5-1- solution STEP 4 Look for simplication. Because the concentration of methanol is 10 times the initial concentration of trityl (excess), its concentration is essentially constant. STEP 5 Determine the reaction order. Taking the natural log; The slope

  20. (2) (1) Find From histogram/finite difference method/polynomial GIVEN!

  21. Graphical Differentiation 3 2.5 2 1.5 1 0.5

  22. Plot Slope= order of reaction ( α )

  23. Find k’ • Substitute the value of into eg,; CA = 22.2 x 10-3 mol/dm3, k’ = 0.125 dm3/mol.min

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