Note: Descriptions are shown in the official language in which they were submitted.
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131~0
BA~KGR3UND OF THE IN~ENTION
This invention relates to a process ror the
preparation of alkanolamines and, more particularly, to
a continuous process for preparing alkanolamines with
high yields of monoalkanolamine by the reaction of
alkylene oxides with a large excess of ammonia wherein
the reaction mixture is maintained in a single phase as
a supercriti~-al fluid.
It is known that alkanolamines, which are used
in a variety of commercial applications such as
emulsification agen~s ror soaps and cosmetics and as a
starting material for the production of raw materials
for detergents, wetting agen~s, emuLsifiers, textile
auxiliaries and the like, can be obtained by the
reaction of alkylene oxides with ammonla or amlnes, the
yield of alkanolamines being a mixture of mono; di-; and
trialkanolamine with, generally e~ual relative
proportions of the ~hree alkanolamines being frequently
ootained. Th~ relative proportions of these three
alkanolamines in the product mixture, however, are known
to depend on the relative quantities o~ alkylene oxide
and ammonia that are reacted and processes have
heretofore been used or suggested for achieving higher
yields of one or more of the alkanolamines in the
mixture which involve varying the proportion of such
reactants, such aSs increasing the amount of ammonia
relative to the alkylene oxide to ob~ain increased
yields of monoalkanolaminet as well as by other process
changesO
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13150
There is disclosed, for example, in U.S. Patent
No. 2,196,55~ to H. M. Guin~t a process for preparing
mono-hydroxylalkylamines with yields of 90%-95~ by
reacting at least 30 parts by weight of ammonia with one
part of alkylene oxide in a liquid phase reaction.
Rela~ively dilute a~ueous ammonia solutions are em~loyed
and the patent discloses that steam generated during
conoentration of the reaction product mixture is used
for heating subsequent reaction product mixtures to
sapara~e a~nonia gas thererrom, thus reducing tne neat
energy requirements for the process. Another process
for preparing al~anolamines with extremely high yields
of monoalkanolamines and only small amounts of the di-
and trialkanolamines oy reacting alkylene oxide witn
large excess amounts of ammonia in a li~uid phase
reaction sys~em is disclosed in U.S. Patent No.
3,697,598 to Weibull et al. The molar ratio of ammonia
relative to al~ylene oxide used in the process is within
the range of 10:1 to 80:1 and tha reaction is carried
out in tne presence of a cation excAange resin
catalyst. The process o~ the patent is described as
being a continuous process whicn is capable of being run
isothermally or, preferably, adiabatically at
temperatures in the range of from 20C. to 250C. when
pressures are employed that are hi~h enough to keep the
.,
reactants and reaction products in the li~uid phase
throughout the reaction. There is, however, no
disclosure either in the description or in the examples
o~ the patent which show that high yields of
alkanolamines of any ty~e are obtained when the process
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13150
is carried out either adiabatically or isothermally
without the use of cation exchange resin catalysts, and
patentees state tnat without a cation exchange catalyst
it is not possiDle to realize an adiabatic reaction
because it is too slow. Further, in U.S. Patent No.
3,723,530 to Goetze et al., there is also disclosed a
process for preparing a mixture of alkanolamines by the
li~uid phase reaction of ethylene oxide ana a iarge
excess of ammonia, that is mole ratios of ammonia to
ethylene oxide of from L~ to ~0 to one. The patent
teaches that when the reaction is carried out in the
presence of up to 1 mole of dietnanolamine per mole of
ethylene oxide, the product obtained will be a mixture
of only monoethanolamine and triethanolamine witn little
or no diethanolamine being present. The process of the
invention is described as being capaole of being run
continuously, either isothermally or adiabatically.
When operated continuously, the reaction is carried out
in the liquid phase at temperatures in the range of from
60 to 150C and pressures of from 20 to 120
atmospheres, and the monoethanolamine content of the
product mixture yenerally does not exceed 7Q percent by
weight. A continuous embodiment of the process which is
descrlbed as being preferred is directed to initially
reacting ethylene oxide with an excess of ammonia in a
li~uid phase to ~repare a mixture of alkanolamines from
which diethanolamine is separated and recycled. The
recycled dietnanolamine, when added to fre~h ammonia an~
ethylene oxide starting reactan~s i Q the proportions
describ~d, results in t~e net formation of reduced
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amounts of die~hanolamine. This proce3s, how~ver,
re~uires the coneinuous se~aration of dietnanolamine
from the product mix~ure and is operated in the liquid
phase .
In Canadian patent application S.N. 408,545-1,
filed July 30, 1982, ~here is disclosed a process for
preparing alkanolamines with high yield~ of
monoalkanolamines by reacting ~lkylene oxide with a
large ~xcess of ammonia in a single supercritical fluid
phase. The process disclosed therein is described as
being capable o running batcnwise or continuously under
isothermsl or adiabatic condi~ions. When the process is
run continuously, a reactor which is capable of
operating as efficiently as possibl@ as a "plug-flow~
reactor may ~e employe~ for carryin~ out the reaction.
The present invention is dir~cted to preferrea
e~bo~im~n~s of the continuously run processes described
in said copending application.
SU~ARY OF T~E I~V~NTION
.
In accordance with the present invention, there
is ~rovi~ed a continuous p~oces~ for preparing
alkanolamines with high yields of monoalkanolamine which
comprises continuously reacting a flo~ing stream of a
homogeneou~ mixture o~ an alkylene oxide having from two
to four c~rbon atoms ana ammonia in a molar ratio o~
ammonia to alkylene oxide within ~he range from about
15:1 to about 50:1 maintained in a ~ingle supercritical
fluid pha~e in a plug-flow reac~or at ~emperatures at
which the reaction proceeds above about 100C. ana at
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13150
pressures high enough to maintain the reaction mixture
in a single supercritical fluid phase having a density
at least about 15 lbs/cu.ft. (240 kg/cu.m.) for the time
necessary to form an alkanolamine proauct mixture
containing predominately monoalkanolamine. Unreacted
ammonia may be separated from the pro~ucc mixture and
recycled while the alkanolamine product mixture is
recovered, or the prcduct mixture may be used in the
preparation of further amine products, if desired.
The temperatures employed for carrying out the
reaction are preferably as high as possible so that the
reaction will proceed at a suitable rate and
temperatures above the critical temperature of the
reaction mixture may be advantageously used. The
pressure should be high enough to maintain the reaction
mixture in a single nomogeneous pnase as a supercritical
fluid at any point during the reaction. The density of
the supercritical fluid reac~ion mixture is an important
consideration as to the rate at which the reaction
proceeds and should be maintained as hign a possible
throughout the reaction and generally at least about 15
lbs./cu. ft. 12~0 kg/cu.m.). Tbe reaction can be
carried out under isothermal or, preferably adiabatic
conditions and, while no cata~yst is required, tne
presence of a small amount of water in the reaction
mixture ha~ an advantayeous catalytic effect. The term
"supercritical fluid" as used herein is defined as the
physical state oE tne reaction mixture wherein eitner
the pressure or both the temperature and pressure
conditions are above tne critical vaLues therefor. The
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term "plug-flow reactor" as used herein is defined as a
reactor in which there is no mixing of a stream of
fluids in the direction of the flow thereof through the
reactor. Such plug-flow reactors may oe non-adiaoatic
tubular or adiabatic pipe.
DESCRIPTION OF T~ INVENTIO~
. . . ~ _ .
The process of the invention comprises
continuously reacting a homogeneous flowing stream of a
mixture of alkylene oxide having from two to four carbon
atoms and ammonia in a molar ratio of ammonia to
alkylene oxide within the range from about 15:1 to about
50:1 which is maintained in a single, nomogeneous phase
as a supercritical fluid at temperatures at which the
reaction proceeds a~ove aDout 100C. and at pressures
high enough to maintain the reaction mixture in a
supercritical fluid phase having a ~ensity of at least
15 lbs/cu~ft. for the time necessary to form a product
mixture composed predominately of monoalkanolamine
(generally about 75%) and small amounts of di-and
trialkanolamine. If desired, unreacted a~nonia can be
separated from said product mixture at the completion of
the reaction with alkylene oxide and recycle~ while tne
alkanolamine product mixture is recovered. The mono-, -
di-, and trial~anolamines can also be separatea, if
de~ired. The pro~uct mixture, including unreacted
ammonia, may also ~e used in the preparation of other
amine product~.
~ he alkylene oxides to which the process of the
present invention is applicable is any alkylene oxide
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131~0
having from two to four carbon atoms, including ethylene
oxide, propylene oxide, l,2-butylene oxide, 2,3-butylen~
oxide, and isobutylene oxide.
In accordance with the present invention, it is
essential that a large excess of ammonia relative to the
alkylene oxide is used in tne reaction ~o obtain yields
of monoalkanolamines of at least 65 weight percent. It
is advantageous to use from about 15 to about 50 moles,
and preferably from about 20 to about 35 moles, of
ammonia for each mole of alkylene oxide to obtain yields
of monoalkanolamine in many cases of from about 70 to 85
weight percent.
It is essential that the reac~ion of alkyLene
oxide and ammonia be carried out in a homogeneous,
single supercri~ical fluid phase so tnat tne reaction
will proceed at a suitable rate. The reaction can be
carried out under isothermal or, preferably, adiabatic
conditions. The temperature at which the reaction
should be carried out i5 within the range from a~out
100C. to about 200C., though the upper limit of the
temperature is not critical. Pre~erably, the reaction
tempera~ure is within the range from about the critical
temperature o~ tne reaction mixture (generally from
about 130C.) to about 180C. Under isothermal
conditions, since tne reaction is strongly exotner;nic,
it is necessary to withdraw heat from the reaction
MixtUre ~o keep the temperature approximately constant.
In the case when the reaction is to be carried
out under adiaDatic or nearly adiabatic conditions, the
reactants are preheated, preferably to a temperature in
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131~0
the range from about 100C. to about 160C.j before the~
are introduced into ~he reactor. Because of the
reaction heat involved, any selected initial reaction
temperature rapidly increases and the initial reaction
temperatures should be chosen so that the maximum
desired temperature will be obtained during the period
of residence of the reaction mixture within the
reactor. The preferred maximum temperature is between
about 170C. and 180C., though the higher the reaction
temperature, the hiyher the pressure that is necessary
to maintain the density of the reaction mixture as high
as possible.
At sucn reaction temperatures, it is essential
that the pressures imposed on the system are high enough
~o maintain tne reaction mixture in a single
supercritical fluid phase. In any case, the reaction
pressure shouia be at least as nigh as tne criticai
pressure of the reaction mixture at any poin~
encountered during the process. Preferably, tne
pressures imposed on the system are within the range
from about 170 to about 240 atmospheres. TAe latter is
a practical upper limit and is not critical.
As pointed out hereinabove, it is important
that the reaction mixture is maintained in a single
homogeneous phase as a supercritical ~luld and that the
density thereof is as high as possible so that the
reaction will proceed at a suitable rate. Tne density
of the reaction mixture should be above its critical
density and, in general, at least 15 1DS/CU. ft. ~240
kg/cu.m~). Preferably, the density of the reaction
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mixture should be maintained in the range of from about
21 to about 28 lbs/cu. ft. or even higher, if
practical. The mole ratio of the ammonia and alkylene
oxide reactants and the reaction temperature have a
significant effect on the density of the reaction
mixture. It is important, therefore, that the reaction
pressures are maintained as high as is practical so that
tne reaction mixture is not only maintained in a single
supercritical fluid phase but that the density of said
mixture is as high as possible.
While it is not essential that the process of
the invention be carried out in the presence of any
catalyst, advantageous embodiments of the process of the
invention may be carried out with a small amount of
water incorp~rated in the reaction mixture along with
the alkylene oxide and a~nonia reactants. It has been
found that the presence of small amounts of water in the
reaction mixture has an advantageous catalytic effect on
the reaction rate for forming alkanolamines though it
does not appear to affect the yield of monoalkanolamine
in the product mixture. The amount of water that is
present is not critical, and onLy small amounts of water
will achieve the catalytic affect ~hat may be desired.
In general, from about 0.5 percent to about 5 percent by
weight of water based on the weight of the reaction
mixture may be present. Amounts of water greatly in
excess of that which may be catalytically useful,
ho~ever, should be avoided to limit the energy
requirements needed to separate water from the product
mixture.
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1315~
In accordance with the present invention the
process may be carried out continuously under isothermal
or, preferably, adiabatic conditions in a plug-flow
reactor or series of reactors which have a small
cross-section in comparison to their length. A
turbulent plug-flow reactor allows for tne
unidirectional flow of a process stream of reactants
that minimizes back-mixing (axial mixing) within the
reactor. The reactor may be provided with heat exchange
means to maintain the temperatura of the flowing
reaction mixture at desired levels but such temperature
control means would not be needed if the reaction is
carried out under adiabatic conditions.
In the continuous reaction process of the
invention, a liquid mixture of the ammonia and alkylene
oxide reactants in the molar ratios hereinabove
described, preferably with a small amount of water
admixed therewith, is preheated and then fed to the
reactor through an inlet section therein where a
swirling motion is imposed on the feed stream. When a
tubular reactor (non-adiabatic) i5 employed, the
reaction may be controlled to proceed within a
relatively narrow temperature range such as, for
example, about 20C. though the temperature of tne feed
mixture may be varied over a wide temperature range,
such as, for example, from about 20 to about 100C.
Under adiabatic conditions, the mixture of reactants
should be preheated to a temperature, from between about
100C to about 1~0C, so that the maximum desired
reaction temperature (generally from about 170 to 200)
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13150
will be attained during the period of residence of the
reaction mixture wi~nin the reactor or series of
rea~tors. The pressure within the reac~or shall be high
enough so that the reaction mixture is maintained in a
single, homogeneous phase as a supercritical fluid
having the highest possible density at any point within
the reactor.
The throughput rate of tne reaction mixture
should be chosen to provide a residence ~ime within the
reactor or reaccors sufficient to permit the reaction to
proceed to completion, generally less than about 1/2
hour. In an adiabatic reactor having the inlet feed
configuration herein described, a velocity of from about
0.15 to about 0.5 feet/second or even nigher of the
fluid stream may be advantageously employed to permit
plug-flow operation. At the completion of the reaction,
that is generally when all the alkylene oxide has b~en
reacted, the unreacted ammonia can be separated from the
product mixture by means known in the art, such as by
reducing the pressure on the product mixture to below
that at which the ammonia is in a gaseous phase or by
distilling under pressure, and the alkanolamine proauct
mixture may be recovered. The unreacted, separated
ammonia can then be recycled, if ~esired, by
repressurizing or condensing to a liquid state prior to
mixing with ~re~A alkylene oxide. The alkanolamlne
analogues in the product mixture may also be separated
by known distillation methods. Tne product mixture
obtained during the continuous reaction process may also
be used without further treatment as a starting material
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for the preparation of other organic amines.
The present invention will be further described
with reference to the accompanying drawing in which:
Fig. l is a schematic showing of a typical
adiabatic reaction system for use in the invention.
Fig. 2 is a schematic illustration of an
adiabatic plug flow reactor suitable for use in the
invention.
Referring to Fig. l of the drawing, li~uid
ammonia and alkylene oxide are blended in the
proportions herein described in the feed pipe 1. Small
amounts of water may also be added, if desired. The
mixture of reactants is pumped througn line 2 to a
preheater 3 where the mixture is heated to a temperature
in the range from about 100C to about 160C and tnen
fed through an axial inlet pipe 4 to the adiabatic
reactor. The adiabatic reactor may be a single
plug-flow reac~or or, as shown, a series of plug-flow
reactor stages 5a, 5b, and 5c, each of which has an
20~ axial inlet pipe. Means are provided for imposing a
swirling motion on the reaction mixture feed stream
entering each reactor stage to mïnimize thermal
stratification therein witnout increasing axial-mixing.
The pressure within each of the reactor stage is
maintained in the range, in general, from about 170 to
240 atm by a pressure control valve 6 so that the
reaction mixture stream is in a single supercritical
fluid phase at any point within the reactor and has a
density of at least 15 l~/cu. ft..
The number of reactor stages employed may vary
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depending on the amount of product to be produced, the
total length of reactor re~uired to achieve the desired
production rate, the feasible length for any reactor
stage, and similar considerations. A typical system may
comprise from 1 to 6 reactor stages of up to 100 feet or
more in length with 3 to 5 reactor stages being
generally advantageously employed.
The product mixture in which all or
substantially all of the alkylene oxide has been
converted to alkanoiamines is fed from tne last
adiabatic reactor stage 5c through pressure control
valve 6 and line 10, where the proauct mixture stream is
depressurized to between about atmospheric pressure and
40 a~m, and then fed immediately into a flasn separator
11. In the flash separator 11 a substantial amount of
tbe unreacted ammonia rapidly separates from the product
mixture as a gas which escapes at ~he top of the
separator 11 in gaseous form and is recycled via line 12
through a compressor or condensor 13. The alkanolamine
product mixture is drawn from the bottom of tAe
separator 11 through line 1~ for refining, if desired.
Fig. 2 illustrates an adiabatic reactor 5
typical of the reactor stages 5a, 5b, or Sc of Fig. 1
having an axial inlet pipe 4 into a generally
cylindrical hollow body 7 having a small cross-section
in comparison to its length which def~nes an internal,
longitudinally extending passageway. Mounted within the
inlet end 20 thereof are a pair of opposed, semi-
elliptically shaped baffles 21 which impose a swirling
motion to the reaction mixture fed therethrough to
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13150
achieve a swirling plug-flow regime for the reactor.
~ntermediate the inlet pipe 4 and the opposed baffles 21
in the inlet end 20 of said reactor 5 is mounted a
perforated plate 8 which serve to distribute and
straighten the flow of fluid entering the cylindrical
body 7 of said reactor 5. The semi-elliptically snape~
baffles 21 which impose a swirling motion to the flowing
stream of fluid wit~in the reactor Inay be prepared from
semi-elliptic plates having ratios of major to minor
axis of from about 1.25:1 ~o about 2.0:1. Other means
for imposing a swirling ~otion to the flow of fluid
tnrough the reactor may also be used such as, for
example, baffles with varying configurations, spacing,
numbers, size, and metnod of mounting within the inlet
end of the reactor, the cross-section and length of the
reactor, the velocity of flow t'nrough tne reactor and
the like being factors which must be considered in
choosing the particular configuration desired.
In a typical embodiment of the processs of the
invention, liquid ethylene oxide and a,nmonia in a molar
ratio of ammonia to ethylene oxide of 30:1 are blended
in feed pipe 1 along with 3 percent by weight of water.
The mixture of reactants is pumped through line 2 to a
preheater 3 where the mixture is heated to a temperature
of about 130~C. and then fed to adiabatic plug-flow
reactor stage 5a, a reactor having an outer diameter of
30 inches and a length of 100 feet at a velocity of 0.3
ft./séc. The reaction mixture is subsequently fed at
such velocity to 3 successive adiabatic plug-flow
reactor ~tages of similar dimensions and inlet
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configuration. The pressure in the reactor stages is
controlled by pressure control valve 6, hign enough to
maintain the reactant mixtures in a single, homogenous
phase as a supercritical fluid naving a density of 2~
lbs./cu.ft. at any point therein, generally about 200 to
210 atmospheres. After a total residence time in the
reactor of about 25 to 30 minutes, the product mixture
exits from the last reactor stage at a temperature o~
about 175C. and is fed through pressure control valve 6
and line lO to flash separator ll. The product mixture
passing through line lO is depressurized to about 20
atmospheres an~ when the product Inixture enters the
flash separator ll, unreacted ammonia is rapidly
separated tnerefrom and exits fro~ the top of the
separator through line 12. The unreacted ammonia is then
condensed to a li~uid in condenser 12 and recycled.
The alkanolamine product mixture is fed from
tne bottom of separator ll through line L4, rerined by
known distillation techniques and recovered.
This invention will become more clear when
considered together with the following examples which
are se~ forth as being merely iLlustrative of tne
invention and which are not intended in any manner, to
be limitative tnereof. Unless otherwise indicated, all
parts and percentages are by weight.
s
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EX~MPLE 1
A reaction system ana apparatus similar to that
shown in the drawlng (Fig. 1 and Fig. 2) except that the
adiabatic plug-flow reactor is comprised of 4 reactor
stages, each of which are 30 inches in diameter and lO0
feet long, was used in a continuous run in which
ethylene oxide was reacted with ammonia. In this run a
liquid ethylene oxide feed of 5000 pounas per hour was
mixed with a liquid ammonia-water mixture feed of 90,000
pounds per nour (96 percent NH3, 4 percent water) to
give an ammonia to ethylene oxide mole ratio of 45:1.
The mixed ammonia an~ ethylene oxide feed was preheated
to a temperature of about 150C. and then pumped into
the rirst reactor stage at a velocity of about 0.21
feet/sec. The pressure in the reactor stages was
controlled to maintain the flowing stream in a single
supercritical fluid phase having an average reaction
mixture density of about 21.5 lbs./cu.ft. The pressure
at the outlet of the final reactor stage was about 2700
psig (about 184 atm.) and the temperature vf tne praduct
mixture at the outlet of the fourth reactor stage was
about 170C. after a residence time witnin the reactor
stages of 28 min~tes. The product mixture from the
final reactor stage was depressurized to about 400 psig
(27 atm.) in the line leading to a flash-tank separator
and substantiallySall the unreacted ammonia separated
from the product mixture in ~he flash-tank separator.
The separated ammoniat-COMMAND-)001 from the top of the
separator and passed through a condenser where it was
condensed to a li~uid and then was recycled.
13150
The product mixture was recovered from the
bottom of the flash-tank separator, refined to remove
the small amount of unreacted ammonia that was entrained
therewitn, and then collected. The composition of the
product mixture was determined by gas chromatographic
analysis to contain 80 percent by ~eight of
monoethanolamine, 17.5 percent by weight of
diethanolamine, and 2.5 percent by weight of
triethanolamine. No measurable amount of unreacted
ethylene oxide was found.
EXAMPLE 2
Using the reaction systeJQ and apparatus of
Example 1, a continous run was made in which a liquid
ethylene oxide feed of 5200 pounas per hour was mixed
with a liquid ammonia-water mixture feed of ~0,000
pounds per nour (97 percent NH3 and 3 percent water)
to give an ammonia ~o ethylene oxide mole ratio of
44:1. Tne mixed ammonia and ethylene oxide feed was
preheated to a temperature of about 154Co and pumped
into the first reactor stage at a velocity of about 0.26
ft./sec. The pressure in the reactor stages was
controlled to maintain tne flowing stream o~ reactants
in a single supercritical fluid phase having an average
reaction mixture density of about 22.5 lbs./cu.ft. The
pressure at the outlet of the final reactor stage was
about 3000 psig (204 atms.) and the temperature of tne
product mixture at the outlet of the final reactor stage
was about 174.5C. a~ter a residence time of 2g
minutes.
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The temperature of the reaction mixture at the outlet of
eacA of the reactor stages was found to be:
at the outlet of the first reactor stage - 166C.
at the outlet of the second reactor stage - 169.6C.
at the outlet of the third reactor stage - 174.8C.
The product mixture from the final rea~tor
stage was depressurized to about 400 p5i9 and fed to a
flash-tank separator wAere substantially all the
unreacted ammonia rapidly separated from the product
mixture and was then taken from the top of the
separator, condensed to a liquid and recycled.
The product mixture recovered rrom the bo~tom
of the separator was collected and determined to have
the following composition:
83 percent by weight monoethanolamine
15 percent by weight diethanolamine
2 percent by weight triethanolamine
No measurable amount of unreacted ethylene
oxide was found in the product mixture.
EXAMPLE 3
Using the reaction system and apparatus of
Example 1, a continous run was made in whic~ a liquid
ethylene oxide feed of 10,000 pounds per hour was mixed
with a liquid ammonia-water mixture feed of 11~,000
pounds per hour (97.5 percent NH3, 2.5 percent water)
to give an ammonia to ethylene mole ratio of 29:1. The
reactant mixture was preheated to a temperature of a~out
150C. and pumpPd into the first reactor stage at a
velocity of 0.33 ft./sec. The pressure in tne reactor
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stages was controlled to maintain the reactant mixture
in a single supercritical fluid pnase having an average
rea~tion mixture density of about 23 lbs./cu.ft.
The pressure at the outlet of tAe final reactor
was about 3,000 psig (204 atms.) and the temperature of
the product mixture at the outlet of the final reactor
stage was about 180C. after a residence time of 23
minutes.
Analysis of tne product mixture after
scparating unreacted ammonia was determined to be:
76.2 percent by weight of monoethanolamine
20.8 percent by weight of diethanolamine
3.0 percent by weight of ~riethanolamine
It was also determined tAat 0.1 percent
unreacted ethylene oxide was present in the produc~
mixture.
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