mô phỏng, tính toán cân bằng nhiệt lượng thiết bị sản xuất EG từ EO

PRODUCTION OF ETHYLENE GLYCOL
Manufacturing process Discrimination
The different processes followed for the production of ethylene glycol includes:
Ethylene carbonate process:
In this method, ethylene oxide is converted to an intermediate, ethylene carbonate, by
reaction with carbon dioxide, which is then hydrolyzed by water to give ethylene glycol.
This process was in use in the 1970s, but this process was replaced later by combined
ethylene oxide-glycol plants.
Halcon Acetoxylatin Process:
Two reaction steps were used in the Oxirane plant. In the first, ethylene glycol
diacatate is obtained by the oxidation of ethylene in an acetic acid solution, catalyzed by
tellurium and a bromine compound.
The reaction complex, which is quite complicated, proceeds via a tellurium-
bromoethylene complex. The oxidation, which is carried out at 90-200 °C and 20-30 atm
pressure, results in a mixture of acetates due to partial hydrolysis of the diacetate.
The reaction liquid effluent is withdrawn and processed to recover glycol acetates and
glycol and provide the recycle streams back to oxidation.
In the second step of the process, the glycol acetates are hydrolyzed to ethylene
glycol and acetic acid.
The process is obviously relatively more complex and will amount to huge capital
cost and Literature also shows that it has operating difficulties. A plant started at
Channelview in United State to produce 800 million lb/yr of ethylene glycol was shut down
after difficulties in start up.
Esterification:
Ethylene glycol can be produced by reaction of formaldehyde with carbon monoxide.
This route first produces glycolic acid which is converted by esterification and
hydrogenolysis to ethylene glycol.
HCHO +CO + H
2
0 HOCH
2

COOH
HOCH
2
COOH +ROH HOCH
2
COOR + H
2
0
HOCH
2
COOR + 2H
2
HOCH
2
CH
2
OH + ROH
Teijin Oxychlorination Process:
This process produces ethylene glycol by the reaction of ethylene with thallium salts
in the presence of water and chloride or bromide ions. A redox metal compound (such as
copper) oxidizable with molecular oxygen is added to the reaction medium to permit the
regeneration of the thallium salt. The Teijin process is still in the works and yet to be
commercialized.
Union Carbide Syngas Process:
The following process developed by Union Carbide, Inc. Uses synthesis gas for the
production of ethylene glycol. Glycerol and propylene oxide are the major byproducts.
Methanol, methyl formate and water are also produced as shown below.
2CO + 3H
2
→ HOCH

2
CH
2
OH

An expensive rhodium based catalyst catalyzes the reaction. The process is yet to be
commercialized. Union Carbide has already started work on a modified process in association
with Ube Industries. It plans to set up a commercial scale plant soon.
Oxidation of Ethylene:
This process involves the oxidation of ethylene to ethylene glycol in an aqueous
medium using an iron copper catalyst to produce Ethylene Glycol as represented in the
reaction below.

Fe-Cu
CH
2
=CH
2
+ ½ O
2
+ H
2
0 HOCH
2
CH
2
OH
Hydrolysis of Ethylene Oxide:
The reaction chemistry is quite simple; it is either acid or thermally catalyzed. It is
summarized as follows: ethylene oxide reacts with water to form ethylene glycol, and then

further reacts with ethylene glycol and higher homologues in a series of consecutive reactions
as shown in the following equations:
CH
2
CH
2
O + H
2
O → HOCH
2
CH
2
O
ethylene glycol
2CH
2
CH
2
O + H
2
O → HOCH
2
CH
2
OCH
2
CH
2
OH
diethylene glycol

3CH
2
CH
2
O + H
2
O → HOCH
2
CH
2
OCH
2
CH
2
OCH
2
CH
2
O
triethylene glycol
Production Process Description
In the process either a 0.5 to 1.0% sulphuric acid (H2SO4) catalyst is used at 50 to
70oC for 30 minutes or, in the absence of the acid, a temperature of 195oC and 185 psi for 1
hour will form the diol. The formation of higher glycols is inevitable because ethelene oxide
reacts faster with ethylene glycols faster than with water. The most important variable is the
water-to-oxide ration, and the production of diethylene glycol (DEG) and triethylene glycol
(TEG) can be reduced by using a large excess of water. A 90 percent yield is realized when
the ethylene oxide/water molar ratio is 1:5-8.
The advantage of the acid-catalyzed reaction is no high pressure, however the thermal
reaction needs no corrosion resistance and no acid separation step.

The crude glycols are dehydrated and then recovered individually as highly pure
overhead streams from a series of vacuum-operated purification columns. Ethylene glycol
(boiling point: 197.6oC) is readily vacuum distilled and separated from the diethylene glycol
(boiling point: 246oC, density: 1.118, flash point: 124oC) and triethylene glycol (boiling
point: 288oC, density: 1.1274, flash point: 177oC).
Since ethylene glycol is produced in relatively high purity, differences in quality are
not expected. The directly synthesized product meets the high quality demands (polyester
grade glycol).
Other Alternatives:
Other Possible catalyst for this reaction includes quaternary ammonium and
phosphonium salts. A more recently developed catalyst system is based on use of Pd (II)
complexes. A mixture of PdCl2, LiCl and NaNO3 in acetic acid and acetic anhydride has
been shown to give a 95% selectivity
During this process, Pd(II) is reduced to Pd(0). If PdCl
2
-CuCl
2
-CuOCOCH
3
is used,
reaction proceeds under mild conditions without formation of a precipitate. A yield of over
90% is obtained.
ETHYLENE GLYCOL PRODUCTION
The production of ethylene glycol by the hydrolysis of ethylene oxide has been
selected in the following Design Thesis because it is by far the most widely used method for
the production of ethylene glycol. It is relatively economical, simple reliable and can be used
in plants that manufacture ethylene oxide and glycol together.
For this Project design there is a modification to the common Flow sheet used for the
Hydrolysis of Ethylene Oxide process that has been shown above. This modified unit
arrangement will still achieve the production of Ethylene Glycol at a lower Capital cost.

As stated above this reaction can be acid or based catalysed but for this work a choice
of a neutral and high pressure and temperature reaction is made because it has the economic
advantage of having no need for corrosion resistance and no acid separation step.
The chemistry of the reaction is summarized as follows: ethylene oxide reacts with
water to form ethylene glycol, and then further reacts with ethylene glycol and higher
homologues in a series of consecutive reactions as shown in the following equations:
Step 1
CH
2
CH
2
O + H
2
O → HOCH
2
CH
2
O
ethylene glycol
Step 2
2CH
2
CH
2
O + H
2
O → HOCH
2
CH
2

OCH
2
CH
2
OH
diethylene glycol
Step 3
3CH
2
CH
2
O + H
2
O → HOCH
2
CH
2
OCH
2
CH
2
OCH
2
CH
2
O
triethylene glycol
The aim of this work is the yield of Ethylene Glycol not those of higher glycol does
this reaction is modified in such a way as to favour reaction step one and disfavour the other
two steps and this is achieved by using excess of water for the reaction to dilute the

concentration of the ethylene glycol produced to discourage the formation of higher glycols.
Production Process Description
Ethylene Oxide and water a passed into a Continous Stirring Tank Reactor which
operates a temperature of 195oC and pressure 185 psi for 1 hour will form the diol. Since the
formation of higher glycols is inevitable because ethelene oxide reacts faster with ethylene
glycols faster than with water then the water-to-oxide ration must be manipulated to reduce if
not eliminate the production of diethylene glycol (DEG) and triethylene glycol (TEG). This is
done by using a large excess of water. In this work, the ethylene oxide/water molar ratio is 1:
7 and the yield of Ethylene glycol is 90%. This Plant is designed to produced 10000kg/yr of
Ethylene Glycol.
The crude Ethylene produced from the reactor is dehydrated and recovered as highly
pure overhead stream from a distillation column with a partial condenser. The Distillate from
the partial condenser is mainly water and is recycled back to the reactor and mixed with
incoming water. The flow sheet for this sequence is shown below
P
Fig: Shows the Flow sheet for the Production of Ethylene Glycol Simulated on Aspen
Hysis
MATERIAL BALANCE FOR THE REACTOR
Reaction Stoichiometry:
CH
2
CH
2
O + H
2
O → HOCH
2
CH
2
O

ethylene glycol
Molecular weight of Species:
CH
2
CH
2
O = (12x2+1x4+16) = 44kg/kmol
HOCH
2
CH
2
O = (12x2+1x6+16x2) =62kg/kmol
Material Balance for Ethylene Oxide:
The target is 10,000kg/yr
10,000kg/yr of HOCH
2
CH
2
O = 10,000/62 = 1612.9kmol/yr = 5.33x10
-5
kmol/sec
HOCH
2
CH
2
O
The Ethylene glycol/Water splitter column can only achieve a 99% separation for the
ethylene glycol thus 5.33x10
-5
/0.99 = 5.38x10

-5
kmol/sec of ethylene glycol must be produced
from the reactor to be feed into the column.
From Literature, the yield of Ethylene Glycol in the reactor is 90%
Yield of 90% implies
Moles of ethylene oxide used up in the reaction/total moles of ethylene Oxide = 90/100
5.38x10
-5
kmol/moles of ethylene oxide = 0.9
Therefore, moles of ethylene oxide = 5.38x10
-5
/0.9 = 5.97x10
-5
kmol of ethylene Oxide is
used up during the reaction but 5.97x10
-5
/0.9 = 6.63x10
-5
kmol/sec of Ethylene is actually feed
into the reactor
Mass of ethylene Oxide required per second = 44kg/kmol x 6.63x10
-5
kmol = 2.92x10
-3
kg
Unreacted Ethylene oxide = 6.63x10
-5
kmol/sec - 5.38x10
-5
kmol/moles = 6.6x10

-6
kmol/moles
Material balance for Water:
From Literature,
Since the feed ratio is 1: 7 therefore the moles of water feed = 7 x 6.63x10
-5
kmols = 4.64x10
-
4
kmols
Mass flow rate of water required = 18kg/kmols x 4.64x10
-4
kmol = 8.35x10
-3
kg/sec
Taking density of water = 1000kg/m
3

The volume of water required per year = 8.35x10
-3
/1000 = 8.35x10
-6
m
3
/sec of water
Unconverted Water
The reacting moles are same for water and ethylene oxide, therefore the amount of water
reacting = amount in moles of ethylene oxide=5.97x10
-5
kmol.

Therefore
Amount of water left unconverted = Total Water fed – Amount that took part in the reaction
= 4.64x10
-4
kmol – 5.97x10
-5
kmol = 4.04x10
-4
kmol
=4.04x10
-4
kmol x 18kg/kmols = 7.27x10
-3
kg/sec of Water
=7.27x10
-3
/1000 = 7.27x10
-6
m
3
/sec of Water
ENERGY BALANCE FOR THE REACTOR
Equation of the reaction
C
2
H
4(g)
+ H
2
0

(g)
= C
2
H
6
O
2(l)
Standard Heat of formation data for this condition
Ethylene Oxide = -52.6kj/mol
Water = -241.8kj/mol
Ethylene glycol = - 460kj/mol
Heat of reaction = Summation of the heat of formation for product – summation of the heat of
formation of the reactants
= (1 x -460) – ((1 x -52.6) + (1 x -241.8)) = -165.6kj/mol
Therefore –DH
R
(Heat of the reaction) = +165.6kj/mol
The reaction is exothermic so a cooler is incorporated take out the heat produced/mol as the
reaction progresses.
Heat generated by the reaction (Q) = Heat taken by cooling water (Q)
Q = mCPDT of water
Heat generated by the reaction (Q) = 165.6 x 5.38x10
-5
(moles of Ethylene oxide produced) =
8.91x10
-3
kj/s
Where
Where 25
0

c – the Temperature of water available
Degree of approach is taken as 10
0
c
CP of water = 4.180kj/kgk
Thus
8.91x10
-3
kj/s = mCPDT = m x 4.180 x (35-25) +273k
Where 25
0
c – the Temperature of water available
Degree of approach is taken as 10
0
c
CP of water = 4.180kj/kgk
m = 8.91x10
-3
/ 1162.04= 7.67 x 10
-6
kg/s
Thus 7.67 x 10
-6
kg/s of water must be feed into the cooler system around the reactor to
maintain at operational temperature.
MATERIAL BALANCE FOR THE DISTILLATION COLUNM
Ethylene Glycol has a boiling point of 197.6
0
c while water has a boiling point of
100

0
c showing that water will boil over first leaving the Ethylene glycol in the bottoms.
From Literature, Relative volatility of Ethylene glycol versus water α = 15.1
Specification for the column
Feed rate=F=Amount of water unconverted + Unreacted Ethylene oxide + Ethylene glycol
F=4.04x10
-4
kmol/s+6.6x10
-6
kmol/s+5.38x10
-6
kmol/s=4.64x10
-4
kmol/s
Which implies that
Water – 0.87 moles
Ethylene Glycol – 0.12 moles
Ethylene Oxide – 0.01 moles
Bottoms (B)
Specification
99% Ethylene Glycol with flow rate of 5.38x10
-5
x0.99 = 5.33x10
-5
kmol/s
1% water with flow rate of 4.04x10
-4
x0.01 = 4.04x10
-6
kmol/s

Therefore
Bottoms (B) = 5.33x10
-5
kmol/s + 4.04x10
-6
kmol/s = 5.734x10
-5
kmol/s
Distillate (D)
Specification
100% Water
Distillate (D) = F – B = 4.64x10
-4
kmol/s - 5.734x10
-5
kmol/s = 4.07x10
-4
kmol/s
L+D=T
Where
L=Flow of Condensate returned to the column
D=Flow of condensate taken out as Distillate
T=Flow of vapour leaving the first stage of the column
Reflux Ration = L/D
At 2.5reflux, L/D=2.5
L=2.5D = 2.5x4.07x10
-4
kmol/s = 1.02x10
-3
kmol/s

T=2.5D+D=3.5D=1.4x10
-3
kmol/s
At total Reflux; the theoretical number of trays can be calculated with relative volatility of
Ethylene glycol versus water α = 15.1
Using Fenske’s Equation
N
m
+1 = log (X
D
/1-X
D
1-X
B
/X
B
)/logα
=log(0.98/0.12 x 0.99/0.01)/log15.1
N
m
= (2.908/1.178) – 1 = 2.46 – 1 =1.46
Using Gillilands rule of thumb, the actual number of tray = 2.5xNm = 2.5x1.46 =3.65trays
Correcting for Tray Efficiencies assuming the efficiency to be 60% = 3.65/0.60 = 6.108= 7
trays
SIMULATION OF THE DISTILLATION COLUNM
The column was simulated using ASPEN HYSIS with the main aim of obtaining the
energy balance of the system and the reboiler and condenser duties. The above calculated
value for the Feed rate and mole composition of the species, reflux ratio, Distillate flow rate,
and number of trays were inputed into the software. Peng Robinson was used as the fluid
package and the specification of the composition of ethylene glycol in the bottoms was

specified as 0.99. It was noted that the HYSIS Estimate of the other Distillate flow, Bottoms
flow etc were very close to the manual calculations made for them. The result of the
simulation is shown below along with the condenser and heater duties.
ETHYLENE GLYCOL/WATER SPLITTER FLOW
SHEET
SPECIFICATION FOR THE REACTOR EFFLUENT
(COLUMN INPUT)


DISTILLATE ESTIMATE
BOTTOMS ESTIMATE