CL-402: Chemical Process Technology
July-November Session, 2016
7th semester, Department Of Chemical Engineering
Indian Institute Of Technology Guwahati, Guwahati
Assignment-3
Use Aspen Plus V8.8 for process design.
Total Marks: 70
Mono Ethylene Glycol Production
Mono Ethylene Glycol (MEG) is used as a raw material in the manufacturing of Polyester Staple
Fibres, Polyester Filament Yarns and Polyethylene Terepthalate & Biaxially Oriented Polyethylene Terepthalate films. MEG also finds vast application as coolants, brake fluids, antitfreeze
Alkyd Resin, Unsaturated Polyester Resin etc.
Problem 1: Commercially, ethylene glycol is produced from ethylene oxide (EO) through a
reaction with water. The steps involved in the production of ethylene glycol are:
step 1. Ethylene oxide reacts with water according to the following liquid-phase reaction and
yield the main product ethylene glycol:
C2 H4 O + H2 O −−→ C2 H6 O2
Ethylene glycol further reacts with unreacted ethylene oxide to produce diethylene glycol (DEG)
, a byproduct.
C2 H6 O2 + C2 H4 O −−→ C4 H10 O3
Both the reactions are irreversible.The rates of production of ethylene glycol in the main reaction
and diethylene glycol in the secondary reaction are given by the following relations:
9547.7
rEG = exp 37.0 −
xEO xw
T
9547.7
rDEG = exp 37.3 −
xEG xEO
T
Generally, excess of water is used which helps in reducing the by-product formation.
step 2. The reactor oulet stream contains ethylene glycol, di-ethylene glycol and water. The
products from the reactor is sent to multieffect evaporators train for removal of the water in
three successive stages.
step 3. After removing major quantity of water in evaporators, glycols are sent to fractionator to
remove the remaining quantity of water. Thereafter, it is sent to another fractionator to separate
MEG from DEG.
Assignment-3
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Based on the above answer the following:
a. In reactor, conversion of ethylene oxide to ethylene glycol depends on three variables: reactor temperature, reactor pressure and water to ethylene oxide ratio. Study the effect of these
variables on ethylene glycol and di-ethylene glycol production and draw graphs to show these
effects.
b. Based on the study in part a, select optimum parameters and develop a process for the production of 12.0 million metric tonnes per annum (MMTPA) of ethylene glycol with minimum
95 mol% purity (± 1% is allowed in mass balance). What is the specific energy requirement for
the production of ethylene glycol in terms of Kcal/Kg?
Problem 2: Reactive distillation (RD) is a process in which a chemical reaction and distillation
occur simultaneously in one single apparatus. Reactive distillation belongs to the so-called
“process intensification technologies”. The most important advantage of this technology for
equilibrium-controlled reactions is the elimination of equilibrium limitation of conversion by
continuous removal of products from the reaction mixture.
The conventional method for the production of ethylene glycol using a reactor and followed by
a series of evaporators/fractionators is very complex. This process can be replaced by reactive
distillation. Therefore, develop a flowsheet (design a reactive distillation column) for the production of 12.0 million metric tonnes per annum (MMTPA) of ethylene glycol with minimum
95 mol% purity (± 1% is allowed in mass balance) based on the following data:
Column Specification:
column pressure, kPa
101.3
total stages
10
reaction stages
stages 2-6
effective liquid holdup per stage, m3
0.5
This column produces no distillate products,instead, the vapor leaving the top tray is condensed
completely and recycled. Water enters onto the top tray of the column.
Case 1. 27.56 kmol/h of ethylene oxide enters the column at stage 6.
Case 2. Total feed of 27.56 kmol/h of ethylene oxide is equally distributed among trays 2-6.
In both cases, plot temperature profile and mole fraction profile of components along the column. What is the specific energy requirement for the production of ethylene glycol in terms
of Kcal/Kg? What is your observation regarding the reactive distillation compared to conventional process.
Note: you may add/remove equipments as per your requirement. if you are increasing the
pressure, use pump/compressor. similarly if you are increasing/reducing the temperature, use
heat exchangers.
Assignment-3
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