COIL TYPE PLUG FLOW REACTOR

1. OBJECTIVE:To study of a non-catalytic homogeneous reaction in a coil type plug flow reactor under ambient conditions.

2. AIM:To determine the rate constants for saponification of ethyl acetate with sodium hydroxide (NaOH) at ambient temperature.

3. INTRODUCTION:Real reactors do not satisfy the idealized flow patterns. Back mix flow or plug flow deviation from ideality can be due to channeling of fluid through the vessel or due to the presence of stagnant region or pockets of fluid in the vessel.In the ideal plug flow reactor (PFR) there is no mixing in the direction of flow and complete mixing perpendicular to the direction of flow. Concentration of the reactant varies along the length of the reactor but not in the radial direction.

4. THEORY

In an ideal plug flow reactor (PFR) there is no mixing in the direction of flow(along the length of the reactor) and complete mixing perpendicular to the direction of flow (in the radial direction).

In case of a COIL, turbulence is introduced due to frequent change in direction of flow and presence of secondary flow, so a higher value of k is expected in case of a COIL type PFR.

PRODUCT

Z

FEED V0, CA0

V is the volume of the reactor; V0 is the volumetric feed rate,CA0 is the feed concentration

of A, and X is the degree of conversion .

For steady state rate operation of a PFTR:

VF A 0

=∫0

XAdx

−rA

.. .

VF A 0

= 1k C2

A0

∫0

XAFdx

(1−X A)2

FA0 = molar flow rate of NaOH

FA0 =V0CA0

V0 = Volumetric flow rate of feed, LPM

VR= Volume of the PFR,L

Or

V R

V 0

= 1k C A0

∫0

XAFdx

(1−X A)2

Or

τ= 1k CA 0

X AF

(1−X AF)

When C A0 and CB0 differ, then:

τ= 1

k CA 0[(CB0

C A 0)−1]

ln(CB0

CA 0)−X A

(CB0

C A0)(1−X A)

X A=CA 0−C A

C A0

C A=Concentration of unreacted NaOH at steady state

k= Reaction rate constant.

This experiment illustrates a bimolecular reaction (reacting species are ethyl acetate and sodium hydroxide): CH3COOC2H5 + NaOH CH3COONa + C2H5OH (1) (B) (A)

-rA= k CACB

where A= NAOH and B = CH3COOC2H5

The initial concentrations of the reacting species are the same CA0= CB0 (neglecting change in density)

-rA = kCA2

CA= CA0 (1- xA)

5. DESCRIPTIONThe reactor is made up of SS tube. The tube is bent in the helical form. The air compressed feed reactants are given through rotameters. The flow rate can be adjusted by operating the needle valve provided on respective rotameter. The compressed air is used for circulation of feed. The concentration of feed and the product coming out from the reactor are analyzed by chemical titration and check the effect and the performance of the reactor.

6. UTILITIES REQUIREDCompressed Air Supply at 2 bar, 0.5 CFMWater SupplyDrainElectricity Supply: 1 Phase, 220 V AC, 0.5 kW

Apparatus: 10 and 20 ml pipettes, 50 cc burette, 6 No.100 cc titration flasks, 6 No. 50 cc graduated cylinder, stop-watch

Chemicals: QuantitySolution of ethyl acetate (N/10) 10 LSolution of sodium hydroxide (N/10) 10 LSolution of hydrochloric acid (N/10) 1LIndicator (phenolphthalein) Few drops

7. EXPERIMENTAL PROCEDURE1) Prepare 10 L of N/10 NaOH solution by dissolving 40 gm of NaOH in 10L of

water.2) Prepare 10 L of N/10 ethylacetate solution by dissolving 88 gm of ethylacetate in

10L of water.

3) Check the drain valves of both feed tanks are closed and pressure regulator reads zero pressure. Fill the tank A and B with appropriate reactants while keeping air releasing valve open. Close the air releasing valves and tank feed inlet valves.

4) Open air inlet valve (from compressor), pull and adjust the pressure regulator to 1kg/cm2.

5) Adjust the rotameter A and rotameter B to adjust the flow rate of the two streams in the feed mixture CA0 = CB0

6) Pass equimolar mixture of Ethylacetate and NaOH into the PFR by allowing equal volumetric feed rates of reactant in to the reactor.

7) After about 10 min or time twice the residence time of the reactor (which ever is greater) i.e. when steady state is achieved, collect exact 10 ml of sample of the liquid at the outlet, in a graduated cylinder that already contains 10 ml of (chilled) N/10 HCl. Transfer this solution (20 ml) in a 250 ml or 100 ml clean and dried titration flask.

8) Titrate this solution against the N/10 solution of sodium hydroxide adding 1 drop of phenolphthalein as indicator. When the endpoint of titration has been reached, read the used volume of NaOH from the burette (VNaOH).

9) Note the volumetric flow rate of liquid at the end of the reactor. Note the reaction temperature.

10) Repeat all the steps for five to seven for different flow rates of feed at the same temperature.

8. SPECIFICATIONReactor: Material stainless steel, capacity 0.7 liters (approx.) (Helical coiled tube type)Feed Tank (2Nos.): Material stainless steel, capacity -20 litersFeed Circulation: By Compressed airFlow Measurement: Rotameter 2 Nos. (One Each for Reactants)Piping: Material stainless steel and PVC Pressure Regulator: 0-2 Kg/cm2

Pressure Gauge: Bourdon type 0-2 Kg/ cm2

Stop Watch: Electronic

9. FORMULAE

a. Degree of Conversion : X A =CA 0−CA

CA 0

b. Residence time τ=VRVo

c. C A=V HCL

N HCL−¿ V NaOH N NaOH

Vsample¿ gmol/L

d. Rate constant k=C A 0−CA

τ CA 0C A

e. K τ CA 0=CA 0−C A

C A

=X A

1−X A

10. OBSERVATION & CALCULATION:

V =……… LCA0 = …….. gmol/LCB0 = …….. gmol/LVHCl =……… mLVsamp =……… mL

Observation Table:

S. No. Vo, LPM VNaOH

123

Calculation Table:

Run No. τ, min CA, gmol/L k, l/(gmol.min)

11. PRECUATIONS & MAINTENANCE INSTRUCTIONSa. Measure the exact volume of water and weigh the chemicals.b. Always use clean water and good quality chemicals and standard solution for

titration.c. Use electronic balance for weighing of chemicals. Don’t mix the droppers of

different chemicals. d. Keep close all the drain valves and vent valve should open while filling the

reactant in feed tanks.e. Flow should not be disturbed during the experiments.f. Handle the chemicals carefully.g. Don’t exceed the pressure above 1 kg/cm2.

12. REFERENCES

H. Scott Fogler “ Elements of Chemical Reaction Engineering” 4th Edition

Octave Levenspiel “chemical Reaction Engineering “ 3rd ed, Wiley,NY,2001

Updated on 10 February 2014