U.S. patent application number 09/844478 was filed with the patent office on 2002-01-24 for method for production of ethylene oxide.
Invention is credited to Kakimoto, Yukihiko, Oka, Yoshihisa.
Application Number | 20020010378 09/844478 |
Document ID | / |
Family ID | 18643003 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020010378 |
Kind Code |
A1 |
Kakimoto, Yukihiko ; et
al. |
January 24, 2002 |
Method for production of ethylene oxide
Abstract
In a composite process for subjecting ethylene to catalytic gas
phase oxidation thereby obtaining ethylene oxide and causing this
ethylene oxide to react with water thereby obtaining ethylene
glycol, a method for producing the ethylene glycol is provided
which permits effective utilization of the energy at the step for
dehydrating and concentrating the resultant aqueous ethylene glycol
solution. In the production of ethylene glycol by the supply of the
aqueous ethylene glycol solution to a concentrating treatment at
the multi-effect evaporator, the method contemplated by this
invention for the production of ethylene glycol comprises utilizing
as the source of heating at least one specific step the steam
generated in the multi-effect evaporator.
Inventors: |
Kakimoto, Yukihiko;
(Yokohama-shi, JP) ; Oka, Yoshihisa;
(Chigasaki-shi, JP) |
Correspondence
Address: |
Y. ROCKY TSAO
Fish & Richardson P.C.
225 Franklin Street
Boston
MA
02110-2804
US
|
Family ID: |
18643003 |
Appl. No.: |
09/844478 |
Filed: |
April 27, 2001 |
Current U.S.
Class: |
568/867 ;
549/534 |
Current CPC
Class: |
C07D 301/10 20130101;
C07C 29/106 20130101; C07C 29/106 20130101; C07C 31/202 20130101;
Y02P 20/52 20151101 |
Class at
Publication: |
568/867 ;
549/534 |
International
Class: |
C07C 029/10; C07D
301/10 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2000 |
JP |
2000-134796 |
Claims
What is claimed is:
1. A method for the production of ethylene glycol which in
producing by the catalytic gas phase oxidation of ethylene with a
molecular oxygen containing gas in the presence of a silver
catalyst to obtain ethylene oxide and causing the resultant
ethylene oxide to react with water there by producing an aqueous
ethylene glycol solution and subjecting this aqueous solution to
concentrating operation with a multi-effect evaporator and
dehydrating this aqueous solution and producing ethylene glycol,
which comprises using the vapor generated in the multi-effect
evaporator mentioned above as the source for heating at least one
of the following steps (A)-(H): (A) a step of introducing an
ethylene oxide-containing gas formed by the reaction of catalytic
gas phase oxidation to an ethylene oxide absorber, causing the gas
to contact an aqueous medium absorption solution and form ethylene
oxide-containing bottoms therein, introducing the bottom to an
ethylene oxide stripper, and separating ethylene oxide by heating
the bottoms of the stripper, (B) a step of circulating portion of
the gas from the top of the ethylene oxide absorption column to the
ethyelene oxidation step and introducing the remainder thereof to
the carbon dioxide absorption column and allowing it to contact
with an alkali absorption solution to obtain the carbon
dioxide-containing bottom, and introducing the bottoms to the
carbon dioxide stripper, and heating the bottoms of the stripper
thereby separating carbon dioxide, (C) a step of introducing an
aqueous ethylene oxide solution obtained by concentrating the gas
from the top of the ethylene oxide stripper to the ethylene oxide
dehydration column and heating the bottoms of the dehydration
column thereby separating light end components such as ethylene
oxide, (D) a step of introducing the ethylene oxide-containing
fraction obtained by condensing the gas from the top of the
dehydration column to the light end separation column, heating the
bottoms of this separation column thereby separating the light end
component, and obtaining crude ethylene oxide as the bottoms, (E) a
step of introducing the crude ethylene oxide to the ethylene oxide
rectifying column and heating the bottoms of the rectifying column
thereby obtaining purified ethylene oxide from the top of the
rectifying column. (F) a step of extracting portion of the
absorption solution obtained through the bottom of the ethylene
oxide stripper, introducing it to the by-produced ethylene glycol
concentration column and heating the bottoms of the concentrating
column thereby effecting dehydration and concentration. (G) a step
of introducing the aqueous ethylene glycol solution obtained at the
multi-effect evaporator and concentrated therein to the ethylene
glycol dehydration column, heating the bottoms of the dehydration
column thereby effecting substantial separation of the water
through the top of the column. (H) a step of introducing the
solution of the ethylene glycol dehydration column substantially
deprived of water to the monoethylene glycol distillation column
bottoms, heating the bottoms of the distillation column thereby
separating and obtaining monoethylene glycol from the top of the
column.
2. A method according to claim 1, wherein the number of
multi-effect evaporators to be used is at least three and the steam
to be utilized as the heating source has pressure in the range of
-0.08-1.2 MPa (Gauge).
3. A method according to claim 1, wherein the vapor generated in
the multi-effect evaporator is used as the source for heating of
the step (A).
4. A method according to claim 1, wherein the vapor generated in
the multi-effect evaporator is used as the source for heating of
the step (B).
5. A method according to claim 1, wherein the vapor generated in
the multi-effect evaporator is used as the source for heating of
the step (C).
6. A method according to claim 1, wherein the vapor generated in
the multi-effect evaporator is used as the source for heating of
the step (D).
7. A method according to claim 1, wherein the vapor generated in
the multi-effect evaporator is used as the source for heating of
the step (E).
8. A method according to claim 1, wherein the vapor generated in
the multi-effect evaporator is used as the source for heating of
the step (F).
9. A method according to claim 1, wherein the vapor generated in
the multi-effect evaporator is used as the source for heating of
the step (G).
10. A method according to claim 1, wherein the vapor generated in
the multi-effect evaporator is used as the source for heating of
the step (H).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a method for the production of
ethylene glycol. Particularly this invention pertains, in a
composite process for obtaining ethylene oxide by catalytic gas
phase oxidation of ethylene and causing the ethylene oxide to react
with water thereby obtaining ethylene glycol, to a method for the
production of ethylene glycol by advantageously utilizing in the
composite process mentioned above the vapor generated in the
multi-effect evaporator used in the step for concentrating the
produced aqueous ethylene glycol solution.
[0003] 2. Description of the Related Art
[0004] Ethylene glycol is usually produced by the reaction of
ethylene oxide with water. Then, the ethylene oxide is produced
nowaday by the catalytic gas phase oxidation of ethylene with a
molecular oxygen-containing gas in the presence of a silver
catalyst. The process for the production of ethylene oxide is
roughly as follows.
[0005] The reaction gas containing ethylene oxide formed by the
catalytic gas phase oxidation of ethylene with molecular
oxygen-containing gas on the silver catalyst is introduced to an
ethylene oxide absorber and brought into contact with an absorption
liquid having water as a main component to recover the aqueous
ethylene oxide solution and then forwarded to an ethylene oxide
stripper so as to cause stripping of the ethylene oxide from the
aqueous solution by heating the bottom portion of the ethylene
oxide stripper with steam, the aqueous solution containing
substantially no ethylene oxide and obtained from the bottom
portion of the ethylene oxide stripper is cyclically used as the
absorption liquid, The stripped products such as the ethylene oxide
obtained from the top of the ethylene oxide stripper, water, carbon
dioxide, inert gas (such as nitrogen, argon, methane, and ethane),
such low boiling impurities as formaldehyde, and high boiling
impurities as acetaldehyde and acetic acid are forwarded through
the dehydration step, the light end separation step, and the heavy
end separation step to obtain purified ethylene oxide. Portion of
the gas containing the unreacted ethylene, by-produced carbon
dioxide, and inert gases (such as nitrogen, argon, methane, and
ethane) may be circulated to the ethylene oxidation step. Normally,
it is partially separated and introduced to the carbon dioxide
absorber so that carbon dioxide may be selectively absorbed therein
and the absorbed solution may be treated to recover carbon dioxide
therefrom by stripping.
[0006] The aqueous solution containing monoethylene glycol,
diethylene glycol, triethylene glycol, tetraethylene glycol, and
polyethylene glyol which are obtained by the reaction of purified
or crude ethylene oxide consequently formed with water is deprived
of the water by vaporization as in a multi-effect evaporator. The
concentration consequently obtained is dehydrated to a high degree
and further purified sequentially in a monoethylene glycol
distillation column, a diethylene glycol distillation column, and a
triethylene glycol distillation column to obtain purified ethylene
glycols. Incidentally, in the ethylene oxide absorber even in the
process for the production of ethylene oxide, the reaction occurs
between water with ethylene oxide and forms ethylene glycol.
[0007] The absorbing solution is partly separated and similarly
concentrated in the multi-effect evaporator and/or the dehydration
distillation column to obtain the various ethylene glycol
products(Refer, for example, to "Chemical Process--Fundamentals to
Development of Technique--" compiled by Society of Chemical
Engineering and published by Tokyo Kagaku Dojin on Mar. 25, 1998,
pages 121-128.).
[0008] The production of ethylene glycol from ethylene via ethylene
oxide as described above entails various operations such carbon
dioxide stripping operation, ethylene oxide stripping operation,
dehydrating operation, light end separating operation, an ethylene
oxide rectifying operation, by-produced ethylene glycol
concentrating and dehydrating operation, and further mono-, di-,
and triethylene glycol rectificating operations. Since these
operations consume large amount of heat, they are under obligation
to control supply of the heat volumes efficiently.
[0009] An object of this invention, therefore, is to provide for a
composite process which subjects ethylene to catalytic gas-phase
oxidization and causes the resultant ethylene oxide to react with
water to produce ethylene glycol a method for the production of
ethylene glycol which comprises advantageously utilizing for the
composite process the steam generated at a multi-effect evaporator
used at the step for dehydrating the aqueous ethylene glycol
solution obtained by the composite process.
SUMMARY OF THE INVENTION
[0010] We, after pursuing a diligent study in search of a solution
for the problems mentioned above, have conceived an idea of
advantageously utitilizing the energy of the steam generated from a
multi-effect evaporator serving to evaporate and concentrate the
aqueous ethylene glycol solution obtained by the reaction of
ethylene oxide with water. We have found that the problems
mentioned above are consequently solved. This invention has been
perfected as a result.
[0011] The object of this invention mentioned above is accomplished
by the following item (1) and (2).
[0012] (1) A method for the production of ethylene glycol which in
producing by the catalytic gas phase oxidation of ethylene with a
molecular oxygen-containing gas in the presence of a silver
catalyst to obtain ethylene oxide and causing the resultant
ethylene oxide to react with water thereby producing an aqueous
ethylene glycol solution and subjecting this aqueous solution to a
concentrating operation with a multi-effect evaporator and
dehydrating this aqueous solution and producing ethylene glycol,
which comprises using the vapor generated in the multi-effect
evaporator mentioned above as the source for heating at least one
of the following steps (A)-(H):
[0013] (A) a step of introducing an ethylene oxide-containing gas
formed by the reaction of catalytic gas phase oxidation to an
ethylene oxide absorber, causing the gas to contact an aqueous
medium absorption solution and form ethylene oxide-containing
bottoms therein, introducing the bottom to an ethylene oxide
stripper, and separating ethylene oxide by heating the bottoms of
the stripper,
[0014] (B) a step of circulating portion of the gas from the top of
the ethylene oxide absorber to the ethylene oxidation step and
introducing the remainder thereof to a carbon dioxide absorber and
allowing it to contact with an alkali absorption solution to obtain
a carbon dioxide-containing bottom, and introducing the bottoms to
the carbon dioxide stripper, and heating the bottoms of the
stripper thereby separating carbon dioxide,
[0015] (C) a step of introducing an aqueous ethylene oxide solution
obtained by concentrating the gas from the top of the ethylene
oxide stripper to the ethylene oxide dehydration column and heating
the bottoms of the dehydration column thereby separating light end
components such as ethylene oxide,
[0016] (D) a step of introducing the ethylene oxide-containing
fraction obtained by condensing the gas from the top of the
dehydration column to the light end separation column, heating the
bottoms of this separation column thereby separating the light
weight component, and obtaining crude ethylene oxide as the
bottoms,
[0017] (E) a step of introducing the crude ethylene oxide to the
ethylene oxide rectifying column and heating the bottoms of the
rectifying column thereby obtaining purified ethylene oxide from
the top of the rectifying column,
[0018] (F) a step of extracting portion of the absorption solution
obtained through the bottom of the ethylene oxide stripper,
introducing it to the by-produced ethylene glycol concentration
column and heating the bottoms of the concentration column thereby
effecting dehydration and concentration,
[0019] (G) a step of introducing an aqueous ethylene glycol
solution obtained at the multi-effect evaporator and concentrated
therein to the ethylene glycol dehydration column, heating the
bottoms of the dehydration column thereby effecting substantial
separation of the water through the top of the column, and
[0020] (H) a step of introducing the solution of the ethylene
glycol dehydration column substantially deprived of water to the
monoethylene glycol distillation column bottoms, heating the
bottoms of the distillation column thereby separating and obtaining
monoethylene glycol from the top of the column.
[0021] (2) A method according to claim (1), wherein the number of
multi-effect evaporators to be used is at least three and the steam
to be utilized as the heating source has pressure in the range of
-0.08 to 1.2 MPa (Gauge).
[0022] It has been demonstrated that by partly removing the steam
generated in the top portion of the multi-effect evaporator and
utilizing the removed steam as the source for heating the other
steps, it is made possible to recover the thermal energy possessed
by the steam, attain effective utilization of energy and, with a
smaller consumption of the energy than the total amount of energy
used at the other steps and in the other multi-effect evaporator,
fulfill the distillation at the other steps and the evaporation and
concentration in the multi-effect evaporator.
BRIEF DESCRIPTION OF THE DRAWING
[0023] FIG. 1 is a process flow sheet illustrating the typical
process in working Example 1 and Control 1.
EXPLANATION OF THE PREFERRED EMBODIMENTS
[0024] Now, this invention will be specifically explained below
with reference to preferred mode of embodying this invention
below.
[0025] The reaction of ethylene oxide with water is carried out
under the following conditions. A molar ratio of ethylene oxide and
water, namely ethylene oxide:water, is in the range of 1:7-1:50,
preferably 1:5-1:30. A reaction pressure is in the range of 0.5-3.0
MPa (Gauge), preferably 1.5-2.5 MPa (Gauge), a reaction temperature
is in the range of 120.degree.-250.degree. C., preferably
130.degree.-180.degree. C., and a concentration of the formed
ethylene glycol was in the range of 5-40 mass %. The reaction is
carried out in the batch-wise, the semibatch-wise, or the
continuously, which ever fits the occasion best. The ethylene
glycol thus obtained is supplied to the multi-effect evaporator and
concentrated and dehydrated till a concentration of 40-95 mass % or
over.
[0026] The number of multi-effect evaporators is described in
detail at pages 428-431 of the Handbook on Chemical Engineering
(fourth revised edition, published by Maruzen Publishing Co., Ltd.
on Jan. 20, 1984). The number of multi-effect evaporators ought to
be not less than two and is decided in consideration of the cost of
equipment and the cost of energy to be involved. In this invention,
it is in the range of 3-5. When a first evaporator is supplied with
the initial energy, the interiors of a second and subsequent
evaporators are sequentially concentrated with steam which enters
through the top of the preceding evaporator having a higher
operation pressure. This invention does not need to discriminate
particularly the heat source for initial energy on account of the
kind of initial energy. Preferably, steam or such molten salt as
Dowtherm (a heat transfer medium made and sold by the Dow Chemical
Co.) or niter is used as the heat medium. The pressure in the first
evaporator to which the initial energy is supplied does not need to
be particularly limited. It is decided in due consideration of the
fact that the pressure be effectively utilized for heating the
evaporators to be operated at the subsequent steps. Generally, the
pressure is in the range of 0.20-2.5 MPa (Gauge), preferably in the
range of 0.5-1.2 MPa (Gauge).
[0027] The mode of the multi-effect evaporator is known in three
types, i.e. normal flow, reverse flow, and complex flow. This
invention permits use of any of these types. Further, the
evaporator is in such a style that it may be furnished with a tray
or a packing intended to decrease the amount of a heavy-weight
component which is liable to entrain the steam in flow.
[0028] In this invention, the second and subsequent evaporators are
operated under sequentially lowered working pressures. The pressure
of the steam obtained therefrom is in the range of -0.08 to 1.2 MPa
(Gauge), preferably in the range of -0.05 to 0.5 MPa (Gauge). The
steam of this pressure is utilized advantageously in this
invention. The drainage which is generated from each of the
evaporators has only a small amount of heat and is reclaimed rather
as a raw material for the generation of steam than as a heat
source.
[0029] The amount of heat of the steam which is consequently
obtained as described is effectively utilized at such steps of
producing ethylene oxide and ethylene glycol as described below.
Now, the operating conditions for the component steps defined by
this invention will be specifically described below.
[0030] A: Conditions for ethylene oxide stripper:
[0031] The pressure at the top of the column is in the range of
0.01-0.2 MPa (Gauge), preferably in the range of 0.03-0.06 MPa
(Gauge).
[0032] The temperature of the top of the column is in the range of
85.degree.-120.degree. C., preferably in the range of 90
.degree.-100.degree. C., and the temperature at the bottom of the
column is in the range of 100.degree.-150.degree. C., preferably in
the range of 110.degree.-120.degree. C.
[0033] B: Conditions for carbon dioxide stripper:
[0034] The operation pressure of this column is in the range of
0-0.05 MPa (Gauge), preferably in the range of 0.001-0.02 MPa
(Gauge), and the temperature at the bottom of the column is in the
range of 80.degree.-12020 C., preferably in the range of
100.degree.-110.degree. C.
[0035] C: Conditions for ethylene oxide dehydration column:
[0036] The pressure at the top of the column is in the range of
0-0.5 MPa (Gauge), preferably in the range of 0.01-0.05 MPa
(Gauge).
[0037] The temperature at the top of this column is in the range of
10.degree.-60.degree. C., preferably in the range of
15.degree.-20.degree. C., and the temperature at the bottom of this
column in the range of 10.degree.-130.degree. C., preferably in the
range of 20.degree.-40.degree. C.
[0038] D: Conditions for light end separation column:
[0039] The pressure at the top of this column is in the range of
0.1-1 MPa (Gauge), preferably in the range of 0.3-0.7 MPa
(Gauge).
[0040] The temperature at the top of the column is in the range of
30.degree.-90.degree. C., preferably in the range of
45.degree.-80.degree. C., and the temperature at the bottom of the
column is in the range of 30.degree.-90.degree. C., preferably in
the range of 45.degree.-80.degree. C.
[0041] E: Conditions for ethylene oxide rectification column:
[0042] The pressure at the top of this column is in the range of
0.1-0.8 MPa (Gauge), preferably in the range of 0.2-0.5 MPa
(Gauge).
[0043] The temperature at the top of the column is in the range of
30.degree.-80.degree. C., preferably in the range of
40.degree.-65.degree. C., and the temperature at the bottom of the
column is in the range of 35.degree.-85.degree. C., preferably in
the range of 45.degree.-70.degree. C.
[0044] F: Conditions for by-produced glycol concentration
column:
[0045] The pressure at the top of this column is in the range of
0.08-0.2 MPa (Gauge), preferably in the range of 0-0.15 MPa
(Gauge).
[0046] The temperature at the top of the column is in the range of
60.degree.-150.degree. C., preferably in the range of
70.degree.-110.degree. C., and the temperature at the bottom of the
column is in the range of 70.degree.-200.degree. C., preferably in
the range of 80.degree.-120.degree. C.
[0047] The concentration of ethylene glycol at the bottom of this
column is in the range of 10-90 mass %, preferably in the range of
70-90 mass %.
[0048] G: Conditions for ethylene glycol dehydration column:
[0049] The pressure in this column is in the range of 50-500 hPa,
preferably in the range of 90-140 hPa.
[0050] The temperature at the top of the column is in the range of
30.degree.-80.degree. C., preferably in the range of
45.degree.-55.degree. C. and the temperature at the bottom of the
column in the range of 80.degree.-120.degree. C., preferably in the
range of 90.degree.-110.degree. C.
[0051] H: Conditions for monoethylene glycol distillation
column:
[0052] The pressure in the column is in the range of 10-70 hPa,
preferably in the range of 25-55 hPa.
[0053] The temperature at the top of the column is in the range of
85.degree.-125.degree. C., preferably in the range of
100.degree.-120.degree. C. and the temperature at the bottom of
this column in the range of 90.degree.-130.degree. C, preferably in
the range of 105.degree.-125.degree. C.
[0054] Thus, ethylene glycol is produced from ethylene oxide as the
starting raw material. This ethylene glycol, besides the
monoethylene glycol mentioned above, sequentially forms diethylene
glycol, triethylene glycol, tetraethylene glycol, and polyethylene
glycol by causing the bottom of the distillation column to be
subjected to the subsequent distillation conditions.
[0055] The stripper, dehydration column, separation column,
rectification column, and concentration column which are defined by
this invention are invariably in the type of an ordinary
distillation column and may be furnished with a tray or a packing.
As typical examples of the tray suitably used herein, a bubble cap
tray, a sieve tray, and a ballast tray may be cited. As typical
examples of the packing, Raschig ring, ball rings, saddle rings,
McMahon packing, Interlocks Metal Packing (made by Norton Co. of
U.S.), Merapack (made by Sulzer of Switzerland), and Sulzer BX
Packing (made by Sulzer of Switzerland) may be cited.
[0056] To demonstrate the effect of this invention, the following
working examples and controls will described below. Example 1
(Refer to FIG. 1)
[0057] A gaseous ethylene oxide-containing reaction product
obtained by the catalytic gas phase oxidation of ethylene with a
molecular oxygen-containing gas in the presence of a silver
catalyst was supplied to the lower part of an ethylene oxide
absorber and an absorption solution (water) was introduced from the
upper portion of the absorber and brought into counter flow contact
with the gas reaction product till the ethylene oxide in the
gaseous reaction product was absorbed in the absorption solution
(water). The gas escaping the absorption and emanating from the top
of the absorber was circulated to an ethylene oxide reactor. As
illustrated in FIG. 1, the bottom liquid in the absorber was
supplied to the upper portion of an ethylene oxide stripper 1
having the pressure at the top thereof fixed at 0.045 MPa (Gauge)
and the temperature at the bottom thereof fixed at 115.degree. C.,
portion of the bottom liquid forwarded to a by-produced ethylene
glycol concentration column 2 having the pressure at the top
thereof fixed at 0.076 MPa (Gauge) and the temperature at the
bottom thereof fixed at 122.degree. C., the remainder thereof
circulated to the ethylene oxide absorber (not illustrated), and
the ethylene oxide-containing stripping steam emanating from the
top of the ethylene oxide stripper 1 was condensed in a condenser
7, portion of the condensed vapor was refluxed to the ethylene
oxide stripper 1 and another portion was supplied to an ethylene
oxide dehydration column (not illustrated). The ethylene
oxide-containing vapor emanating from the top of the dehydration
column was condensed in a condenser (not illustrated) and portion
thereof was refluxed to the dehydration column and the reminder
thereof was supplied to the light-end separation column (not
illustrated). The uncondensed steam in the condenser was supplied
to the ethylene oxide reabsorption column (not illustrated). The
steam emanating from the top of the light end separation column was
forwarded to the condenser, the condensate consequently formed was
refluxed to the light end separation column, and the uncondensed
steam in the condenser was supplied to the ethylene oxide
reabsorption column. The bottom liquid in the light end separation
column was forwarded to the ethylene oxide rectification column.
The ethylene oxide vapor emanating from the top of the column was
condensed in the condenser and portion of the condensed vapor was
refluxed to the ethylene oxide rectification column (not
illustrated) and the other portion thereof was extracted as a
product of ethylene oxide. The bottom liquid in the ethylene oxide
rectification column was separated for the purpose of separating
such high-boiling substances as aldehyde and acetic acid.
[0058] Meanwhile, the aqueous solution containing ethylene oxide
was separated from the bottom portion of the ethylene oxide
dehydration column (not illustrated) and was forwarded together
with ethylene oxide as a product to the hydration device, left
reacting therein at a pressure of 1.8 MPa (Gauge) and a reaction
temperature of 150.degree. C. The aqueous ethylene glycol solution
consequently obtained in an amount of 15.2 mass % was forwarded to
a first evaporator 3 operated with the pressure at the top thereof
fixed at 0.41 MPa (Gauge) and the temperature of the interior
liquid at 153.degree. C.
[0059] The bottom liquid in the first evaporator 3 was forwarded to
a second evaporator 4 operated with the pressure at the top of the
column fixed at 0.17 MPa and the temperature in the bottom part
thereof at 136.degree. C., the steam emanating from the top part of
the first evaporator 3 was used as the heat source for the heating
device, the bottom liquid in the second evaporator 4 was forwarded
to the third evaporator 5 operated with the pressure in the top of
the column fixed at 0.07 MPa (Gauge) and the temperature in the
bottom thereof at 124.degree. C., the steam in the top of the
second evaporator 4 was partly used as the heat source for the
heating device of the third evaporator 5, the remainder thereof was
used as the heat source for the heating device for heating the
by-produced ethylene glycol concentration column, and the bottom
liquid in the third evaporator 5 was forwarded to a fourth
evaporator 6 operating with the pressure in the top thereof fixed
at 0.03 MPa (Gauge) and the temperature in the bottom thereof fixed
at 105.degree. C., the steam in the top portion of the third
evaporator 5 was used as the heat source for the heating device of
the fourth evaporator 6, the bottom liquid in the fourth evaporator
6 was forwarded to the ethylene glycol dehydration column and
deprived of the water entrained thereby and then forwarded to the
monoethylene glycol distillation column (not illustrated) till
monoethylene glycol was separated through the top thereof. The
bottom liquid in the monoethylene glycol distillation column was
forwarded to the diethylene glycol distillation column (not
illustrated) to separate diethylene glycol through the top of the
column. The bottom liquid in the column was forwarded to the
triethylene glycol distillation column (not illustrated) to
separate triethylene glycol through the top of the column.
[0060] The procedure described above was repeated for each of the
component steps illustrated in the diagram. The operating
conditions used therefor, the performance of the steam produced,
and the amount thereof consumed are shown in Table 1.
[0061] Control 1
[0062] In the procedure of Example 1, the multi-effect evaporators,
the ethylene oxide stripper, and the by-produced ethylene glycol
concentration column were operated on the condition that all the
steam from the top of the second evaporator 4 would be wholly used
as the heat source for the heating device of the third evaporator
5. The operating conditions used herein, the performance of the
steam produced, and the amount thereon consumed are shown in Table
1.
1 TABLE 1 Example 1 Control 1 Amount of steam used Multi-effect
evaporator ton/hr 28.8 18.1 Ethylene oxide stripper (1) ton/hr 9 26
By-produced ethylene glycol ton/hr 4 12 concentration column Total
ton/hr 41.8 56.1 Operating conditions for multi-effect evaporator
First evaporator (3) Pressure at the top MPa 0.41 0.57 Temperature
at the top .degree. C. 153 163 Temperature in the bottom portion
.degree. C. 159 166 Amount of steam at the top ton/hr 26.7 17.8
Amount of liquid at inlet ton/hr 93.3 93.3 Glycol concentration at
inlet 15.2 15.2 Glycol concentration in bottom 20.8 18.8 portion of
the column Second evaporator (4) Pressure at the top MPa 0.17 0.36
Temperature at the top .degree. C. 130 149 Temperature in the
bottom .degree. C. 136 152 Amount of steam at the top ton/hr 7 18.6
Amount of steam separated to the ton/hr 25 0 other steps Glycol
concentration in bottom 39 24.9 liquid in the column Third
evaporator (5) Pressure at the top MPa 0.17 0.16 Temperature in the
top portion .degree. C. 115 129 Temperature in the bottom portion
.degree. C. 124 135 Amount of steam at the top ton/hr 7.7 19.2
Glycol concentration in bottom 50.2 37.6 liquid of the column
Fourth evaporator (6) Pressure in the top portion MPa -0.03 -0.03
Temperature in the top portion .degree. C. 90 90 Temperature in the
bottom portion .degree. C. 105 105 Amount of steam through the top
ton/hr 7.2 18 Glycol concentration in bottom 72 72 liquid of the
column
[0063] The entire disclosure of Japanese Patent Application No.
2000-134796 filed on May 8, 2000 including specification, claims,
drawings and summary are incorporated herein by reference in its
entirety.
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