Theoretical Way to determine the time required for Distillation in Batch Reactor

Hello everyone, Based on requests received asking how to determine the theoretical distillation time cycle in a batch reactor, and today i'm gonna demonstrate you a simple way to determine outta many critical ways to do that,

Today this determination of Time required to carry out distillation is Based upon the Reactor Heat transfer area.








So Please read

How to find heat transfer area before proceeding to determination of distillation time

So, initially we need some of the data regarding

* The reactor mechanical design which includes some parameters like shell thickness, inner dia, length of reactor,

* The batch input details like how much amount of volume we need to handle, how much amount we need to distill out,

* The properties of the material we need to handle like density, specific heat, composition etc, and on the other end we need some properties like thermal conductivity of materials which out heat transfer area is composed off.




Properties of Materials:
Usually for make of Heat Transfer surface we will be usually going for SS316 Grade and for other purposes like for preparing the limpet jacketed coil and the insulation coating, we will be using SS304, and occasionally we will use GLR for Ph sensitive distillation, so below are the thermal conductivities of these materials

Material                Thermal Conductivity,K [W/m.K]
SS304                         10-13
SS316                         13-17
MSGLR                     1.2-1.5





So, after Collecting the required data, we need to calculate the amount of heat needed to perform the distillation operation, 
For the calculation of
* sensible heat we need to take total mass in reactor,
Sh = M * Cp * dT,
M - mass flowrate = Volume * Density
Cp - Specific heat[ usually cp will vary based on temp., so we need to take Cp at distillation temp.]
dT - Distillation temp. - RT temp.
* Latent heat calculation,
Lh = M * Lambda
M - Mass flowrate = volume of distillate * Density
Lambda - latent heat of vapour solvent

After getting the total heat load, we need to calculate the amount of heat that can be transferred through the heat transfer area per sec.
* Amount of heat transferred through the HT area per sec = K * A * dT * ( 1 / X )
K - thermal Conductivity 
A - Heat Transfer Area,
dT - Temp. Difference= Distillation temp. -RT temp.
X - thickness[usually considered as 10mm]

After Getting the heat that can be transferred through out HT area, we need to divide the Overall heat load with the Heat Transfer volume that can be transferred through one Sec,

T= ( ( M * Cp * dT ) + ( M * Lambda ) ) / ( K * A * dT ), Sec





Lemme explain this with a sample calculation,

Need to distill out 1 KL of methanol in a batch reactor GLR of capacity 5 KL, reaction mass volume is 4 KL(i.e., 80% occupancy), now i need to calculate the time for distillation.

Heat transfer area of a 5 KL batch reactor is 12.41 Sq.m, ( Calculate Heat Transfer Area )
Available heat transfer area = ( 4 / 5 ) * 12.41 = 9.93 Sq.m,
Thermal conductivity of a MSGL surface is 1.2 w/m.k = 0.029 KCal/m.Sec.K.

Methanol properties: 



Specific heat = 0.45 KCal/Kg.K, 
Latent Heat = 264 KCal/Kg,
Density = 790 Kg/Cu.m,
Boiling point = 64 degC.

Sensible heat load = M x Cp x dT = 4 x 790 x 0.45 x ( 64 - 25 ) = 56880 KCal,
Latent heat load = M x Lambda = 1 x 790 x 264 = 208560 KCal.

Total Heat load = 265440 KCal.

Amount of heat transfer that a MSGL surface can transfer = K x A x dT = 0.029 x 9.93 x (64-25)

i.e., 11.52 KCal

Time required for distilling out 1 KL methanol is 265440 / 11.52 = 23279 Sec = 388 mins.

i.e., 6.47 hrs. I think this will match with our practical cases.



Thats it, cheers.....


Is any queries, feel free to send me a message or comment here.

Comments are most appreciated.

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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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