CSTR LAB MANUAL...
RESULT AND DISCUSSION
OBJECTIVE To carry out a non-catalytic homogeneous reaction of NaOH and ethyl acetate in a series of 3 CSTR’s and i. ii.
To study the performance of a cascade of 3 equal volume CSTR in series. To draw the performance chart for the reactor system and evaluate the reaction rate constant at ambient condition.
APPARATUS REQUIRED Apparatus i. ii. iii. iv. v. vi. vii. viii. ix. x. xi.
Measuring cylinder (1000ml) Measuring cylinder (50ml) Pipette (5ml/10ml) Burette (25ml) Conical flask (100ml) Beaker (100ml) Volumetric flask Bucket Mug Thermometer Conical funnel
REAGENTS REQUIRED Reagents i. ii. iii. iv. v.
NaOH pellets HCl Ethyl acetate Sodium carbonate Phenolphthalein indicator
Quantity 1 1 1 1 4 3 1 2 1 1 1
INTRODUCTION Reactor is one of the most important parts in industrial sector. Reactor is equipment that changes the raw material to the product we want. A good reactor will give a high production and be economical. One of the criterions to choose a good reactor is to know the effectiveness of the reactor itself. One of the most important we need to know in the various chemical reaction was the rate of reaction. By studying the reaction of ethyl acetate and NaOH to form sodium acetate in CSTR, we can evaluate the rate data needed to design in production scale reactor. The main feature of CSTR reactor is that mixing is complete so that the properties such as temperature and concentration of reaction were uniform in all parts of vessel. In experiment, the ethyl and NaOH with equal volume are mixed. Then the experiment is started by mixing them using CSTR. After 5 mins we will take a solution and mix them with HCl, and then it is titrated with NaOH. The amount of NaOH used in titration is taken in the result. The procedure is repeated for the next sample that has been taken after 10,15,20 minutes.
THEORY Ideal steady-state flow reactor is called the mixed reactor, the back mix reactor, the ideal stirred tank reactor, the C* (meaning C-star), CSTR, or the CFSTR (constant flow stirred tank reactor), and, as its names suggest, it is a reactor in which the contents are well stirred and uniform throughout. Thus, the exit stream from this reactor has the same composition as the fluid within the reactor. We refer to this type of flow as mixed flow. Since the composition is uniform throughout, the accounting may be made about the reactor as a whole.
If FA0, = oCAo is the molar feed rate of component A to the reactor, then considering the reactor as a whole we have
Introducing these three terms into balance equation, we obtain
which on rearrangement becomes
where XA and rA are measured at exit stream conditions, which are the same as the conditions within the reactor.
Graphical representation of these CSTR performance equations-
EQUAL SIZE OF CSTR IN SERIES Consider a system of N mixed flow reactors connected in series. Though the concentration is uniform in each reactor, there is, nevertheless, a change in concentration as fluid moves from reactor to reactor. This stepwise drop in concentration suggests that the larger the number of units in series, the closer should the behaviour of the system approach plug flow.
First-Order Reactions. From a material balance for component A about vessel i gives
Because = 0 this may be written in terms of concentrations. Hence
Now the space-time Ʈ (or mean residence time t) is the same in all the equal size reactors of volume Vi. Therefore
Rearranging, we find for the system as a whole
In the limit, for N →∞, this equation reduces to the plug flow equation
Schematic Diagram of 3 CSTR in series
PROCEDURE i. ii. iii. iv. v.
Prepare 10L solution of M/100 NaOH and M/100 ethyl acetate. Fix the flow rate to CSTR’s using rotameter at equimolar reactant flow rate. Switch on the stirrer of the 1st CSTR, when the level of the feed reaches at the stirrer of the impeller level. Similarly switch on the stirrer of the other reactors when the reaction mixture reaches the desired level. Once steady state is obtained, take out a10 ml sample of the reaction mixture using a pipette from the 1st CSTR 5mins after overflow starts and transfer this reaction mixture immediately into a conical flask containing 20ml of N/40 HCl to quench the reaction. Titrate 10 ml of aliquot of the resulting solution against N/100 NaOH. Repeat the process for CSTR no. 2 and 3 in that order. To find out initial concentration CAO transfer 5ml NaOH in a conical flask containing 20ml of N/40 HCl and add 5ml ethyl acetate in it. Titrate 10ml of aliquot of the resulting solution against N/100 NaOH. Carry out steps 1to 6 for another flow rate of reactants.
CALCULATIONS & GRAPHS 1. CALCULATION FOR CA0 (INITIAL CONCENTRATION) Volume of aliquot sample = 30ml Volume of NaOH consumed = 3.7 ml Volume of HCl consumed in titration = V1 ml N1VI = N2V2 V1 = ((40/N)*3.7)/ (100) = 1.48ml Volume of HCl reacted with feed solution V4 = 20-1.48 = 18.52ml So, concentration of solution initially N1V4 = N3V3 N3 = (N/40)*(18.52/10) = 0.0463N Normality = Molarity = 0.0463mol/lit 2. CALCULATION FOR COCENTRATION AT FLOW RATE = 6LPH I. For CSTR 1 Volume of aliquot sample = 30ml Volume of NaOH consumed = 5.2 ml Volume of HCl consumed in titration = V1 ml N1VI = N2V2 V1 = ((40/N)*5.2)/ (100) = 2.08ml Volume of HCl reacted with feed solution V4 = 20-2.08 = 17.92ml So, concentration of solution N1V4 = N3V3 N3 = (N/40)*(17.92/10) = 0.0448N Normality = Molarity = 0.0448mol/lit II. For CSTR 2 Volume of aliquot sample = 30ml Volume of NaOH consumed = 5.4 ml Volume of HCl consumed in titration = V1 ml N1VI = N2V2 V1 = ((40/N)*5.4)/ (100) = 2.16ml Volume of HCl reacted with feed solution V4 = 20-2.16 = 17.84ml So, concentration of solution N1V4 = N3V3 N3 = (N/40)*(17.84/10) = 0.0446N Normality = Molarity = 0.0446mol/lit
III. For CSTR 3 Volume of aliquot sample = 30ml Volume of NaOH consumed = 5.6 ml Volume of HCl consumed in titration = V1 ml N1VI = N2V2 V1 = ((40/N)*5.6)/ (100) = 2.24ml Volume of HCl reacted with feed solution V4 = 20-2.24 = 17.76ml So, concentration of solution N1V4 = N3V3 N3 = (N/40)*(17.76/10) = 0.0444N Normality = Molarity = 0.0444mol/lit Thus for flow rate = 6LPH CA0 = 0.0463 mol/lit CA1 = 0.0448 mol/lit CA2 = 0.0446 mol/lit CA3 = 0.0444 mol/lit
3. CALCULATION FOR COCENTRATION AT FLOW RATE = 9LPH I.
For CSTR 1 Volume of aliquot sample = 30ml Volume of NaOH consumed = 4.2 ml Volume of HCl consumed in titration = V1 ml N1VI = N2V2 V1 = ((40/N)*4.2)/ (100) = 1.68ml Volume of HCl reacted with feed solution V4 = 20-1.68 = 18.32ml So, concentration of solution N1V4 = N3V3 N3 = (N/40)*(18.32/10) = 0.0458N Normality = Molarity = 0.0458mol/lit
For CSTR 2 Volume of aliquot sample = 30ml Volume of NaOH consumed = 4.6 ml Volume of HCl consumed in titration = V1 ml N1VI = N2V2 V1 = ((40/N)*4.6)/ (100) = 1.84ml Volume of HCl reacted with feed solution V4 = 20-1.84 = 18.16ml
So, concentration of solution N1V4 = N3V3 N3 = (N/40)*(18.16/10) = 0.0454N Normality = Molarity = 0.0454mol/lit III.
For CSTR 3 Volume of aliquot sample = 30ml Volume of NaOH consumed = 4.8 ml Volume of HCl consumed in titration = V1 ml N1VI = N2V2 V1 = ((40/N)*4.8)/ (100) = 1.92ml Volume of HCl reacted with feed solution V4 = 20-1.92 = 18.08ml So, concentration of solution N1V4 = N3V3 N3 = (N/40)*(18.08/10) = 0.0452N Normality = Molarity = 0.0452mol/lit
Thus for flow rate = 9LPH CA0 = 0.0463 mol/lit CA1 = 0.0458 mol/lit CA2 = 0.0454 mol/lit CA3 = 0.0452 mol/lit 4. CALCULATION FOR SPACE TIME Space-time Ʈ = V/
ᶹ = Volume of the reactor/Flow rate of fluid (vol.) o
Reactor is cylindrical in shape (V) = 𝜋𝐷2 ℎ/4 = 1.091*10-3 m3 For flow rate 6LPH Total flow rate of fluid = 2*6 = (12*10-3)/3600 m3/s Ʈ = (1.091*10-3*3600)/12*10-3 = 327.31 sec For flow rate 9LPH Total flow rate of fluid = 2*9 = (18*10-3)/3600 m3/s Ʈ = (1.091*10-3*3600)/18*10-3 = 218.06 sec
5. GRAPH BETWEEN (CA)n &(CA)n-1 0.046 0.0458 0.0456
0.0454 0.0452 0.045 0.0448 0.0446 0.0444 0.0442 0.0444
CA(n-1) 6 LPH
6. PERFORMANCE CHART CSTR IN SERIES
Performance Chart 0.046
0.0458 0.0456 0.0454 0.0452
0.045 0.0448 0.0446 0.0444 0.0442 0
TIME (IN SEC) 6 LPH
7. CALCULATION OF RATE CONSTANT For equal size reactor in series we have, 1 k = [(C0/C1)1/N – 1] Ʈ
(According to graph, reaction order is 1st) For flow rate 6LPH Ʈ = 327.31 sec CA0 = 0.0463 mol/lit CA3 = 0.0444 mol/lit So, k = 4.2973*10-5 sec For flow rate 9LPH Ʈ = 218.06 sec CA0 = 0.0463 mol/lit CA3 = 0.0452 mol/lit So, k = 3.69*10-5 sec k (average) = (4.2973*10-5 + 3.69*10-5)/2 = 4*10-5 sec
RESULTS The first order reaction rate is found to have value equal to 4.0*10-5 sec. The performance chart for three CSTR of equal volume connected in series is found as attached graph.
CONCLUSIONS The behaviour of equal volume CSTR connected in series tends to PFR by increasing the same number of reactors. For the same interval of time the conversion is lower from any CSTR for higher feed flow rates.
PRECAUTIONS i. ii. iii.
Wash all the apparatus before and after doing the experiment. Steady state should be obtained before start of sampling time, t=0 and should be assumed carefully after steady state. For NaOH solution after preparing it, it should be titrated with oxalic acid to determine exact normality. Normality is changed due to hydroscopic nature of NaOH. Solution of all components should be prepared accurately. Time measurement and titration should be done accurately.
REFERENCES i. ii.
Octave Levenspiel, Chemical Reaction Engineering., 3rd edition. Jones, R.W., Chemical Engineering Programme., 47,46.