Note: Descriptions are shown in the official language in which they were submitted.
13047
BACKGROUWD OF THE INVE~TI~N
$his invention relates to a process ror the
preparation of alkanolamines and, more particularly, to
a proceRs for preparing alkanolamines with high yiel~s
of monoalkanolamine that may be run continuously by the
reaction of alkylene oxides with a large excess of
ammonia wherein the reaction mixture is maintained in a
ingle phase as a ~upercritical fluid.
' It is known that alkanolamines which are used
in a variety of commercial applications such as
emul~ification agents for soaps and cosmetics and as a
starting material for the proauction of raw materials
for detergents, we~ting agents, emulsifiers, textile
auxiliarie~ and the like can be obtained by ~he reaction
of alkylene oxides with ammonia or amines, the yield of
alkanolamines being a mixture of mono: di-: and
trialXanolamaines with, generally equal relative
proportions of the three alkanolamines being frequently
obtained. The relative proportions of these three
alkanolamines in the product mixture, however, are known
to depend on the relative quantities of alkylene oxide
and ammonia-that are reacted and methods have been used
or suggested for achieving higher yields of one or more
of the alkanolamines in the mixture by varying the
proportion of reactants, such as by increasing the
amount o ammonia rela~ive to the alkylene oxide to
obtain increa~ed yield~ of monoalkanolamine, as well as
by other proce~s changes.
There i8 aiSclo5ea~ for example, in U.S. Patent
~o. 2,196,554 to H. M. Guinot a process for preparing
~ ' ? ` 3 :~
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mono-hydroxylalkylamines with yields of 90%-35~ by
reacting at least 30 parts by weight of ammonia with one
part of alkylene oxide. Relatively dilute aqueous
ammonia solutions are emplo~ed and the patent discloses
that steam generate~ during concentration of the
reaction mixture is used for heating subsequent reaction
mixtures of aqueous ammonia and alkylene oxide to reduce
the heat energy requirements for the process. Another
process for preparing alXanolamines with extremely high
yields of monoalkanolamines and only small amounts of
the di- and trialkanolamines by reacting alkylene oxide
with large excess amounts of ammonia in a liquid phase
reaction system is disclosed in U.S. Patent No.
3,697,598 to Weibull et al. The molar ratio of ammonia
relative to alkylene oxide ~sed in the process is within
the range of 10:1 to 80:1 and the reaction is carried
out in the presence of a cation exchange resin
catalyst. The process of the patent i5 described as
being a continuous process which is capable of being run
isothermally or, preferably, adiabatically at
temperatures in the range of from 20~C~ to 250C. when
pressures are employed that are hi~h enough to keep the
reactants and reaction products in ~he liquid phase
throughout the reaction. ~here is, however, no
disclosure either in the description or in the examples
of the patent which show that high yields of
alkanolamines of any type are obtained when the process
i~ carried out either adiabatically or isothermally
without the use of cation exchange resin catalysts, and
patentees state that without a cation exchan~e catalyst
~Z1~4~z 13047
it i~ not possible 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
liquid phase reaction of ethylene oxide and a large
excess of ammonia, that is mole ratios of ammonia to
ethylene oxide of from 14 to 40 to one. The patent
teache that when the reaction is carried out in the
pre~ence of up to l mole of diethanolamine per mole o'
ethylene o~ide, the product obtained will be a mixture
of only monoethanolamine and triethanolamine with littl~
or no diethanolamine being present. While the process
of the invention is described as being capable of being
run continuously either isothermally or adiabatically,
the ammonia is usually e~ployed in the form of an
aqueous solution, the reaction is carried out in the
liquid phase at temperatures in the range of from 60 to
150~ and pres~ures of from 20 to 120 a~mospheres, and
the monoethanola~ine contsnt of the product mixture
generally does not exceed 70 percent by weight.
While the procesRe~ here~ofore disclosed
5u5ge8t that they are suitable for use in preparing
monoethanolamines in high yields by reacting alkylene
oxides with excess amounts of ammonia, their usefulness
in either batch or continuous operations depends on the
presence of catalysts or ~upplemental proces~ steps~ It
would be highly desirable, however, if a process was
available which coul~ be used to readily prepare
monoalkanolamines at practical reaction rates that did
no~ involve the potential additional problems associated
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with catalysts or costs due to complicated or
supplemental process steps.
SUMMARY OF THE INVENTION
In accordance with the present invention, there
is provided a process for preparing alkanolamines witn
high yields of monoalkanolamine which comprises reacting
an alkylene oxide having from two to four carbon atoms
with ammonia in a molar ratio of ammonia to al~ylene
oxide within the range from about 15:1 to about S0:1 at
temperatures at Which the reaction proceeds above a~out
100C. and at pressures high enough to maintain the
reaction mixture in a single supercritical fluid pnase
to form a product mixture containing predominantly
monoalkanolamine. Unreacted ammonia, wnicA is separated
from the reaction mixture, may be recycled if desired.
The temperatures employed for carrying out tne
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. Tne
pr~ssure should be high enough to maintain the reaction
mixture in a single nomogenous supercritical fluid phase
at any point during the process. The density of the
reaction mixture, which is dependent upon the pressure
employed at the reaction temperature and is an important
consideration as to the rate at wnich the reaction
proceeds, should be maintained as high as possible and
generally should be at least about 15 lbs./cu. ft. (240
kg/cu.~.). The reaction can be carried out batchwise or
~ Z ~ Z 13047
continuously under isothermal or adiabatic conditions
and, while no catalyst i8 required, the presence of a
3mall amount of water in the reaction mixture has an
advantageou~ catalytic effect. The term "supercritical
fluid" as used herein is defined as the physical state
of the reaction mixture wherein either the pressure or
both the temperature and pressure conditions are above
the critical values therefor.
DESCRIPTIO~ OF THE INVENTI~N
.
The process of the invention comprises reacting
an alkylene oxide having from two to four carbon atoms
with Ammonia in a molar ratio of ammonia to alkylene
oxide within the range from about 15-1 to about 50:1 at
a temperature at which the reaction proceeds above about
100C. and at pressures high enough to m~intain the
reaction mixture in a sinqle supercritical fluid phase
for the time necessary to form a product mixture
composed predominately o monoalkanolamine (generally
about 15% ) and small amounts of di-and trialkanolamine
and separating unreacted ammonia therefrom. The mono-
di-, and trialkanolamines can also be separated if
desired.
The alkylene oxides to which the process of the
present invention i applicable is any l,2-alkylene
oxide having from two to four carbon atoms, including
ethylene oxide, propylene oxide, 1,2-butylene oxide,
2,3-butylene oxide, and isobutylene oxide.
In accordance with the present invention, it is
essential that a large excess of ammonia is used in the
z
13047
reaction to obtain yields of monoalXanolamines of at
least 65 weight percent. It is advantageous to use
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 in many ca~es of from about 70 to
80 weight percent. The ammonia shoul~ be added to the
reaction mixture in a liquid state, generally in a
substantially anhydrous condition. The liquid ammonia
and alkylene oxide may be premixed just prior to fee~ing
into the reaction vessel or each may be added separately
to the reactor.
In accordance with the practice of the
invention, it i~ important that the reaction of alkylene
oxide and ammonia be carried out with the reaction
mixture in a homogenous, single supercritical fluid
phase so that the reaction will proceed at a suitable
rate. The reaction can be carried out under isothermal
or adiabatic conditions, The temperature at which the
reaction ahould be carried out is within the range from
about lOO-C. to about 200~C., though the upper limit of
the temperature is not critical. Pre erably, the
reaction temperature is wi~hin the range from about the
critical te~perature of the reaction mixture (generally
'rom about 130-C.) to about 180C. Under isothermal
condi~ion~, since the reac~ion is ~trongly exothermic,
it i5 necessary to withdraw heat from the reaction
mixture to keep the temperature approximately constant.
In the case when the reaction is to be carried
out under adiabatic or nearly a~iabatic conditions, the
reactants are ~reheated ~o from about 100C. to }30C.
~ 2 13047
before ~hey are introduced into the reactor. Because of
the reaction heat involved, any selected initial
reaction temperature i~ rapidly increased and the
initial reaction temperatures shoul~ be chosen so that
the maximum de~ired temperature will be obtained during
the period of residence of the reaction mixture within
the reactor. The preferred maximum temperature is
between about 170~C. and 180~C. though the higher the
reaction te~perature, the higher the pressure that is
necessary to ~aintain the den-Qity of ~he reaction
mixture as high as possible.
At such reaction temperatures, it is essential
that the pres3ures imposed on the system are high enough
to maintain ~he reaction mixture in a single
3upercritical fluid phase. In any case, the reaction
pressure should be at least as high as the critical
pre~sure o~ the reaction mixture at any point
encountered during ~he process. Pre.erably, the
pres~ures impo~ed on the syste~ are within the ran~e
from about 170 to about 240 atmospheres. The 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
phase as a supercritical fluid and that the density
thereof is as high as po~sible so tha~ the reaction will
proceed at a ~uitable rateO The densi~y of the reaction
mixture should be above the critical density and, in
general, at least 15 lb3/cu. ft. (240 kg/cu.m.).
Preferably, the den~ity of the reaction mixture should
be maintained in the range of from a~ou~ 21 to about 28
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lbs/cu. ft. or even higher if practical. The mole ratio
of 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 the reaction mixture is not only
maintained in a single supercritical fluid phase but
that the density of said mixture i5 as high as possible
50 that the reaction will proceed at a practical rate.
While it is not essential that the process of
the invention be carried out in the presence of any
catalyst, advanta~eous embodiments o~ the process of the
invention may be carried out with a small amount of
water incorporated in the reaction mixture along with
the alXylene oxide and ammonia reactants. It ha~ been
found that the presence of ~mall amounts of water in the
reaction mixture has an advantageous catalytic e~Çect on
the reaction rate for forming alkanolamines though it
does not appear to affect the yield of monoalkanola~ine
in the product mixture. The amount of water that is
pre3ent is not critical, and only small amounts of wa~er
may achieve the catalytic affect that is desired~ In
general, from about 0.5 percent up to about 5 percent by
weight of water based on the weight of the reaction
mixture need be present. Amounts of water greatly in
excess of that which may be catalytically u~eful,
however, should be a~oided to limit the energy
require~ents needed to separate water from the product
mixture.
After conclusion of the reaction, substantially
12~ 2 13047
all of the alkylene oxide has been reacted and the
unreacted ammonia may be separated from the product
mixture by any means known in the art, such as by
reducing the pressure to below that at which tne ammonia
is in a gaseous phase, so that the ammonia can be
separated as a gas. Tne ammonia can then be recycled,
if desired, by repressurizing to a liquid phase before
mixing with alkylene oxide. Tne unreacted ammonia may
also be separated from the product mixture by distilling
under pressure. The al~anolamine analogues in the
product mixture may also be separated by known
distillation methods or the product mix~ure may be used
as a starting material for the preparation of other
organic amines.
As pointed out hereinabove, the process of tne
invention may be rarried out batchwise or continuously,
either under isothermal or adiabatic conditions. In an
alternate embodiment of the process of the invention
which is run continuously, tne ammonia and alk~lene
oxide reactants in the molar ratios hereinabove
described are continuously fed, eitner separately or,
preferably, as a mixture, to a ~ubular reactor which is
capable of operating as ef~iciently as possible as a
plug-flow reactor having means for providing the
pressures needed to maintain the reaction mixture in a
single supercritical fluid phase. The reactor may be
carried out isothermally in a tubular reactor having
cooling means or, advantageously, under adiabatic
conditions where the reactants are preneated to a
temperature, for example, between about 100C. to
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~2~ 13047
130C. Small amounts of water may also be added to the
reaction mixture, if desired.
The residence time of the single phase
supercritical fluid reaction mixture in said adiabatic
reactor should be sufficiently high to permit the
reaction to proceed to completion, generally in less
than about 1/2 hour. At the completion of the reaction,
that is generally when all the alkylene oxide has been
reacted, the unreacted ammonia is separated from tne
product mixture as nereinabove described and recycled to
the reactor. The recycled ammonia is pressurized to a
liquid state prior to mixing within tne alkyiene oxide
and fresh make-up ammonia~ The product mixture which is
obtained can be separated into alkanolamine components
by distillation methods known in the art or can be used
as a starting material for the production of materials
such a organic polyamines.
This invention will ~ecome more clear when
considered together with the following examples which
are set forth as being merely iilustrative or the
invention and which are not intended in any manner, to
be limitative thereof. Unless otherwise in~icatea, all
parts and percentages are by weight.
Example 1
A 2 liter (1984 ml.) stainless steel autoclave
having a high speed agitator and equipped with charginy,
sampling, and temperature control means was used in
carrying out the reaction runs of this example. A
series of reactions wexe run using liquid anhydrous
~21~ 13047
ammonia, water, and ethylene oxide in the proportions
reported in Table I. The ammonia and water were charged
to the autoclave which was evacuated to a pressure of
about 1 mm Hg absolute and then witn vigorous agitation
were heated to 170C. The etnylene oxide was then
charged to the autoclave and, with vigorous agitation,
the reaction temperature was maintained at 170C. for 30
minutes. ~ sample of tne reaction mixture was taken
after the time indicated in Table I during each o the
reaction runs of tnis example. After 30 minutes, the
reaction mixture was cooled to below 50C. and unreacted
ammonia was vented from the autoclave until tne pressure
in the autoclave indicated essentially complete removal
of gas. The liquid product mixture was then drained
from the autoclave and the composition thereof was
determined by-gas chromatographic analy~is.
The amount of ammonia and ethylene oxide
reactants used were inten~ea to obtain an average
ammonia to ethylene oxide mole ratio of 25:1 for each of
the reaction runs of this example. The average density
of the reaction mixture during each of the reaction runs
of this example was 24 lbs./cu. ft.
A summary of the proportion of ingredients,
reaction conditions and composition of tne product
mixtures for each of the reaction runs of this example
are reported in Table I.
It is apparent from results shown in Table I
that an alkanolamine mixt~re was prepared with a high
yield of monoal~anolamine during each of the runs of
this example.
- 12 -
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13047
Example 2
Using the apparatus and procedure of Example 1,
a series of reaction runs were carried out to
demonstrate tne effect of reaction product density and
ammonia to ethylene oxide mole ratio on the reaction
rate and distribution of alkanolamines in the product
mixture. Runs l to 8 were carried out with an average
ammonia to etnylene oxiae mole ratio of 30 to 1 ana runs
9 to 12 use a mole ratio of 25 to 1. Runs 1 to 4 and 9
to 12 were carried out at an average density of 22
lbs/cu. ft and Runs 5 to 8 were carried out at an
average density of 24 lbs/cu. ft. A sample of the
reaction mixture was taken from the reactor during each
reaction run.
The proportion of ingredients, temperature and
pressure condition's and analysis results (used
analytical procedures described in example 1) for eacn
of the reaction runs of this Example are summarized in
Table II.
It is apparent from the results shown in Table
II that an alliauolamine product mixture containing high
yields of morroethanolamine was prepared during eacn
reaction run of this example. The reaction rate for
each o the runs would be suitable but the resul~s snow
that the reaction rate for runs 1 to 4 which were
maintained at an average density of 22 lbs/cu. ft. was
somewhat slower than the reaction rate for runs 5 to 8
which were maintained at an average density of 24
lbs/cu.ft.
- 14 -
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13047
Example 3
A mixture of 786.4 grams (46.2 moles) of
ammonia and 15.7 grams of water was charged to tne
stirred autoclave described in Example 1 whicn had
previousl~ been vacuated to about one millimeter of Hg
vacuum. The mixture was heated to 170C. and 3900 psig
with stirring and 54.l grams (1~23 moles) of ethylene
oxide were injected into the stirred mixture. The
density of the reaction mixture was maintained a~ an
average of 27 lbs./cu. ft.
Small samples of the reaction mixture were
periodically removed from the autoclave and analyzed by
mass spectrometry for residual ethylene oxide and tne
sample times and conversion of ethylene oxide are shown
below in Table III.
TABLE III
Time, Minutes ~ Conversion
Sample Number from EO Injection Based on Residual EO
1 3 74.9
2 6 77.2
3 9 92.3
4 24 100.0
After 30 minutes from the time ethylene oxide
was added, the mixture in the autoclave was cooled to
below 50C. and the unreacted ammonia was se~arated from
the product mixture. The liquid product mixture was
discharged from the autoclave and analyzed for
alkanolamine composition by gas chromatography. The
product mixture was determined to contain 84.03 percent
monoethanolamine, 14.36 percent diethanolamine, and 1.60
percent triethanolamine.
F~r comparison purposes, ~ne following reaction
- 16 - -
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13047
run was carried out in the autoclave reactor described
in Example l.
In this control, a mixture of 678 grams (3~.81
moles) of ammonia and 13.57 grams of water was charged
to the evacuated, stirred autoclave of Example l and
heated to 120C. Nitrogen gas was added to the
autoclave until a pressure of 2000 psig was o~tained.
Ethylene oxide ~72.98 grams, 1.659 moles) was injected
into the stirred mixture in the autoclave and tne
temperature was maintained at 120C. during the entire
run. The reaction mixture in the autoclave was a single
phase li~uid.
Small samples were periodically removed from
the autoclave reactor and analyzed by mass spectrometry
for residual ethylene oxide and the results are
summarized in Table V, below.
TABLE V
~ime, Minutes ~ Conversion
Sample Number from EO Injection Based on Residual E9
1 ~ 16.25
2 10 33.00
3 15 35.25
56.00
73.00
6 30 82.75
7 40 92.50
The reaction was continued at 120C. for an
additional 138 minutes after which the mixture was
cooled, unreacted ammonia was separated therefromr and
the liquid product ~ixture was recovered and analyzed by
gas chromatography.
The product mixture was determined to contain
74.44 percent of monoethanolamine, 21.17 percent
- 17 -
~. .
~Z1~4~Z
13047
diethanolamine, and 4.38 percent triethanolamine. While
the liquid phase reaction resulted in nigh yields of
monoethanolamine, the reaction rate was determined slow
to be suitable.
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