Note: Descriptions are shown in the official language in which they were submitted.
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Case 1-12513/+
Method of removing heat from exothermic chemical reactions
The present invention relates to a method of removing heat
from continuous exothermic chemical reactions conducted
in liquid phase, and to an assemb~y for carrying out this
method
The removal of heat from exothermic chemical reactions is
a very important problem in chemical engineering. Dif~erent
solutions to this probl@m are known for reactions
conducted in liquid phase, i.e. in which at least one
liquid phase is present in the reaction space. For example,
in the laboratory the reaction space (reactor) can be put
into a cooling bath that contains a liquid coolant
(e.g. water, oil, organic liquids) or a solid coolant
(ice, dry ice, freezing mixtures`e.g. of ice and salts).
This kind of cooling often has the drawback that it is
difficult to regulate, is cequently unsu~able for
continuous processes, and is too inefficient and
uneconomical (e~g. dry ice). In large-scale production it
is also possible to surround the reaction space with coiled
pipes or a jacket through ~hich a cooling fluid is
circulated, e.g. water, cooling brine (water with salts,
e.g. sodium chloride, calcium chloride, magnesium chloride3,
organic coolants, liquified gases, and also, if appropriate,
fused solids such as liquid salts and metals, If it is
necessary to cool very intensively, it is also possible to
introduce condenser coils into the interior o the
reaction space and then to pass the coolant through them
~xamples o~ special cooling systems that may also be
mentioned here are evaporation coolers and dripping
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coolers. All these various cooling systems referred to
above require fairly elaborate apparatus, are not efficient
enough for all purposes, or are uneconomic to operate.
It is also known to cool an exothermic reaction by introduc-
ing a liquified inert gas (e.g. nitrogen) direct into the
reaction medium. This method, however, is complicated and
uneconomic, for the gas cannot be recovered. Cooling can
also be effected simply by the direct addition of ice or dry
ice to the reaction medium; but in this method it is
difficult to regulate the temperature. Moreover, the use
of ice results in dilution of the reaction medium and this
is often undesired.
Accordingly, it is the object of the present invention to
provide a simple and economic method of removing heat from
continuous exothermic chemical reactions conducted in
the liquid phase, which method does not have the drawbacks of
the known methods and permits the volume of the apparatus
required for the reaction to be kept as small as possible,
and which is advantageous from the point of view of
operational safety.
Surprisingly, the aforementioned object can be attained by
means of the method of this invention which comprises
introducing a fluid which is inert to the reactants and in
which reactants and reaction products are
preferably insoluble or almost insoluble , and
which is immiscible with the reaction medium or with parts
thereof, into a reactor containing the reaction medium and
wherein a homogeneous mixing of reaction medium and inert
fluid that absorbs the heat of reaction must be ensured,
separating the emulsion thereby obtained into the phase
containing the reaction products and that consisting of the ~ated
inert fluid, cooling said inert fluid and recycling lt to
the reactor where it can again absorb heat of reaction,such
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that the inert fluid is able to pass through this cixcuit
as often as desired, and such that a desired stationary
temperature is reached in the reactor.
The method of the present invention is suitable for cooling
all exothermic reactions conducted in the liquid phase. It
will be readily understood that such reactions comprise not
only those in homogeneous liquid phase, but all reactions
in which at least one liquid phase participates. Such
reactions also include those in a solid/Liquid system as
well as those in a liquid/gaseous system. Reactions in
which two liquid phases participate can also be cooled by
the method of the invention, but only if both phases are
immiscible with the inert fluid employed as coolant.
All exothermic reactions of the kind defined above can be
cooled by the method of this invention, provided tha~ the
inert fluid employed as coolant does not participate in
the reaction, that starting materials and reaction productsare
preferab~ in~ e or ~most insoluble therein, and that it is
immiscible with the reaction phase or with one of the
reaction phases. Examples of reactions that can be cooled
in this manner are exothermic substitution, oxidation,
reduction, addition, elimination or polymerisation
reactions. The method of this invention is very
suitable for cooling exothermic nitration, sulfonation,
diazotisation, hydrogenation and other reduction reactions.
It is particularly preferred to use the method of the
invention for removing heat during the nitration of
aromatic systems.
As already mentioned, the inert iluid can be any fluid
that does not particpiate in the particular reaction and
which is immiscible with the reaction
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medium (or parts thereof), and in which the starting
materials and reaction products are preferablyinsolubleor ~mGst
ins~luble. Depending on the intensity o the evolution o~
heat in the reaction which it is desired to cool, or on the
temperature at which the reaction should proceed, it is
necessary to choose fluids having a boiling point above
that temperature in order to prevent the fluid ~rom starting
to boil.
Before entering the reactor, the inert fluid which has been
heated during its previous circuit through the reactor is
cooled. This is done in a conventional cooling device, e.g.
a heat e~changer. The tempera~ure to which the fluid is
cooled depends on the reaction which it is desired to cool
and on the temperature which is to be maintained in the
reactor, as well as on the nature of the fluid itself. For
economic reasons, too low temperatures are not suitable
(high energy costs). The temperature of the coolant can
therefore vary within wide limits, e.g.-from -5~ to +50 C,
with the preferred temperature range being from -20 to
+20C
Another means of influencing the desired temperature in the
reactor is to modify the sojourn time in the reactor by
varying the rate at which the inert fluid circulates through
the cooling circuit. If it is desired to cool more thoroughly
at a given temperature of the inert fluid, the amount of
coolant added to the reactor can be increased. In this
manner it is easily possible to regulate the desired
temperature in the reactor.
Preferred inert ~luids which may conveniently be used for
cooling reactions in aqueous phase are water-immiscible
organic fluids, e.g. conventionaL water-immiscible organic
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solvents such as aliphatic, cycloaliphatic or aromatic
hydrocarbons, halogenated aliphatic or aromatic hydrocarbons,
water-immiscible alcohols, ketones, esters and ethers.
Especially preferred aliphatic hydrocarbons are petroleum
fractions of widely varying boiling ranges (white spirit,
naphtha etc.)~ and paraffin hydrocarbons. The individual
liquid hydrocarbons can, of course, also be used in pure
form.
Examples of suitable cycloaliphatic hydrocarbons are cyclo-
hexane, cyclopentane, methyl cyclohexana, tetralin,
decalin and others. Provided they are immiscible with water,
certain terpene hydrocarbons and terpenoids can also be
used.
..
Examples of aromatic hydrocarbons which may conveniently
employed are: benzene, toluene, xylene, cumene, cymene,
styrene, and mixtures thereof.
Especially preferred halogenated hydrocarbons are chlorinated
hydrocarbons such as methylene chloride, chloroform, carbon
tetrachloride, 1,2-dichloroethane, 1,1,2,2-tetrachloro-
ethane, l,l?l-trichloroethane, 191,2-trichloroethane,
perchloroethylene, propylene chloride, and mixtures
thereo, as well as mono-, di- or trichlorobenzenes and
mono-, di- or tribromobenzenes.
Water-insoluble alcohols which may con~eniently be used as
cooling fluids are e.g. cyclohexanol, methylcyclohexanol,
and fatty alcohols with longer hydrocarbon chain.
Examples of water-insoluble ketones which can be used are:
methyl n-butyl ketone, methyl isobutyl ketone, methyl
n(iso)-amyl ketone, ethyl amyl ketone, di-n-propyl ketone,
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diisopropyl and diisobutyl ketone, mesityl oxide, cyclo-
hexanone, methylcyclohexanone, dimethyl cyclohexanone,
isophorone.
Examples of water-insoluble esters which may be employed
are: n-butyl formate, n-propyl acetate, n-butyl acetate,
isobutyl acetate, n-amyl acetate, isoam~l acetate, hexyl
acetate, cyclohexyl acetate, benzyl acetate, and the
corresponding propionates and butyrates; butyl glycol
acetate, ethyl diglycol acetate, butyl diglycol acetate.
Examples of water-insoluble ethers which can be used are:
diisopropyl ether, dibutyl ether, methyl tert-butyl ether.
In addition, it will be understood that a large number of
other water-immiscible 1uids can also be used, provided
they fulfill the conditions specified above.
If, conversely, a reaction is conducted in an organic
solvent, then it is possible to use, as inert fluid, on
the one hand an organic fluid which is immiscîble with the
solvent of the reaction or, on the other hand, water,
provided the solvent in the reactor is water-immiscible. In-
stead of using water, it is, of course, also possible to
use a salt solution, provided this latter does not influence
the reaction.
To ensure the efficiency of the method, it is necessary that
the reaction medium and the inert cooling fluid are
intimately mixed, so that the area through which the heat
exchange is effected expands and ~e heat transfer takes
place through exceedingly thin layers. As short an exchange
time as possible is thereby achieved.
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This requirement entails the use o a reactor which is able
to ensure such an intimate mixing. The simplest means of
accomplishing this end is to use a conventional reactor
equipped with a high-speed stirrer. However, it is pre-
ferred to use a reactor that makes possible a still better
and more intimate mixing. Examples of such reac-tors are a
ce~hifugal pump reactor, an on-Line mixer with feed pump,
a static mixer with ~eed pump, a turbine mixer, or a jet
tùbe reactor.
The emulsion consisting of reaction medium and inert fluid
formed in the reactor is then passed into a separator in
which both phases are separated, most simply by deposition
of the heavier phase. Other types of ap~aratus for effecting
phase separation can, of course, also be used, e.g. a
centrifugal separator. The phase containing the reaction
products and remaining starting materials (l.e. the
reaction m~xture) is drawn of continuously for further
working up. The inert fluid is passed through a cooler
(heat exchanger) such that it is cooled to the desired
temperature and then recycled to the reactor, so that it
can absorb heat of reaction once more.The above described
mode of carrying out the method of the invention thus
provides a cooling circu~ with a wide-ranging heat
absorption capacity.
If it is necessary or desirable on account of the reaction
conditions of the particular reactio~(e.g. reaction rate,
sojourn time in the reactor, optimum temperature etc.),
a further raaction zone can be provided upstream of the
reactor itself and before the separation of the emulsion,
in order to bring the reaction to completion and thereby
to achieve an increase in yield. This can be expedient in
the case of reactions which proceed slowly and/or of short
sojourn times in the reactor itseli. The further
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reaction zone preferably consists of a reaction pipe which,
whererequired, can also be cooled, i.e. which can be provided
with a heat exchanger, in case the reaction in question
makes it necessary or the yield and quality of the inal
prod~cts is thereby advantageously influenced.
Compared with the known methods, the advantages of the
cooling method of the present invention consist, in particular,
in the fact that the volume of the apparatus required for the
reaction can be kept small, that the operational safety is
greatly increased (intensive cooling direct in the reactor,
no danger of overheating), and that the effici~cy can be
substantially increased by reducing the amount of energy
required.
It is a further object of the inve~ion to provide an
as~embly for carrying out the described method, said assembly
comprising
a) a reactor with feed lines for the starting
materials and, if required, for the solvent or solvents in
which the reaction is conducted and in which one or more
starting materials can be dissolved, and with a feed line
for a fluid ~hich is inert to the reactants and is
immiscible with the reaction medium or parts thereof,
which reactor must ensure an intimate mixing of the reaction
medium and the inert ~luid,
b) a separator which is connected to the reactor by a line
and in which the solution containing the products is
separated from the inert fluid, and
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c) a return line provided with a heat exchanger, which line
connects the separator to the reactor and through which
the inert fluid is recycled to the reactor while being cooled
by the heat exchanger.
A further reaction zone can be provided in the assembly
between the reactor and the separator. Preferably, the line
between reactor and separator is in the form of a pipe in
which the reaction can be brought to completion. If desired,
this latter can be provided with a heat exchanger.
The reactor in the assembly employed in the practice ~ this
invention can be a conventional reactor equipped with a
high-speed stirrer. Preferably, however, the reactor is a
centrifugal pump, an on-line mixer with feed pump, a static
mixer with feed pump, a turbine mixer, or a jet~tube mixer.
It is especially preferred to use a centrifugal pump as
reactor.
The separator employed is preferably one in which both phases
separate by the force of gravity. Other types of apparatus
for effecting phase separation can, of course,b~ used e.g. a
centrifugal separator.
The general mode of operation of the assembly employed in
the practice of this inventiOn may be easily inferred from
the description of the method as outlined above. A preferred
embodiment of the assembly is illustrated by the attached
drawing, wherein the indiv~dualpositions have the following
meanings:
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1 and 3 supply vessels for starting materials, sdutions
of starting materials or solvents
2 and 4 feed pumps
reactor, preferably centrifugal pump reactor
6 reaction pipe for bringing reaction to completion
7 separator
8 receiver for phase containing the reaction
products
9, ~a heat exchanger
Iine for suspension of reaction mixture/inert
fluid
11 outlet for phase containing reaction products
12 return line for the inert fluid
13 metering val~e for inert fluid
For carrying out the method using the assembly illustrated
in the drawing, the inert cooling fluid is~passed from the
line 12 via the reactor 5, the line lO and the separator
7 back into the line 12 ("cooling circuit"). The~reactants
and the solvent in which the reaction is conducted,~are~fed
to the reactor from the suppLy vessels 1 and 3 via the feed
pumps 2 and 4. If, for example, it is desired to carry out
a nitration reaction, the supply vessel 1 contains nltric ~
acid and supply vessel 3 contains the compound to be~nitrated,
e.g. an aromatic carbocyclic compound, optionally dLssolved~
in sulfuric acid. In the reactor 5, which in this~ embodiment
is preferably a centrifugal pump and in which the~reaction
takes place, the reaction mixture is intimately mixed with
the inert fluid which flows into the reactor~and absorbs
the ensuing heat of reaction. After the sojourn time in the
reactor (e.g. after one to several seconds), the emulsion
formed from reaction solution and inert fluid is forced,
under pressure, into the reaction pipe 6 in which the
reaction (e.g. nitration) is brought to compLetion. If it is
necessary for any reason, the reaction pipe 6 can also be
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cooled. The emulsion flows through the connecting pipe 10
into ~e separator 7, in which the phases separate, The
phase which deposits and contains the inaL products (e.g.
nitrating acid in which the nitrated products are dissolved)
is discharged through the line 11 into a receiver 8. The
supernatant inert fluid (the inert fluid employed here has
a specific weight lower than that of the, preferably,
aqueous reaction solution~ passes at its top end into the
pipe 12 which is encased by a cooler (heat exchanger). The
inert fluid is cooled by this cooler to the desired
temperature and, if desired after regulating the rate of
flow by the valve 13, flows back into the reactor. In this
manner the inert fluid flows continuously through the
reactor, absorbs the heat of reaction, and delivers it to
the heat exchanger 9.
The following Examples illustrate the method of the invention
in more detail.
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Example L: Nitration of 4-acetamidoanisole usin~ the
assembly illustrated in the drawin~
The supply vessel 1 is charged with 1900 ml of a 1.579 molar
solution of 4-acetamidoanisole in 93 % sulfuric acid; and
supply vessel 3 is charged with 220 ml o~ 62.58 ~/0 nitric
acid. 2200 ml of a petroleum fraction boiling in the range
from 110-140C are fed into the cooling circuit.The centri-
fugal pump 5 is put into operation and the cooling medium
temperatures of the heat exchangers are regulated to the
following values: heat exchanger 9: -5C, heat exchanger 9a:
-15C. As soon as the petroleum f~action in the circuit has
reached a temperature of -2C, both reactants are fed into
the reactor by means of the pumps 2 and 4. The rate of flow
of nitric acid is 11 ml (0.15 mole) per minute, and that of
4-acetamidoanisole in sulfuric acid is 95 ml (0.15 mole) per
minute. The conditions become stationary after about 4
minutes. A desired discharge temperature from the reactor of
25C is then attained. A too high or too low reaction
temperature can be easily regulated via the cooling of the
heat exchanger 9. The experiment lasts20 minutes. The
aqueous solution of the reaction products which is drawn
off from the separator 7 is then poured into ice-water and
the precipitate is collected by filtration. Yield:
558 g (87.4 % of theory) of 98.7 % 4-acetamido-2-nitroani-
sole.
Example 2
The nitration of Example 1 is repeated, except that 2200 ml
of dichlorobenæene are fed into the cooling circuit. The
rate of flow of nitric acid is 12.8 ml/min., and that of
acetamidoanisole in sul~urc acid is 97.5 ml/min. The total
rate of flow through the circuit is about 1300 ml/min., and
the reaction volume in the pump is 37 ml and that in the
reaction pipe is 14 ml. The sojourn time in the pump is 1.7
seconds, that in the reaction pipe is 0.7 seconds, and the
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conditions become stationary after 4 to 6 minutes. Working up
of the reaction product is as described in ExampLe l,affording,
per m~ute, 28.4 g (88.4 % of theory) of 98 % 4-acetamido-2-
nitroanisole.
Example 3:
4-Propionamidoanisole is nitrated by the methods described
in Examples 1 and 2, affording 4-propionamido-2-nitroanisole
in a yield of c. 90 % of theory.
Exam~le 4:
4-Acetamidoethoxybenzene is nitrated by the methods
described in Examples 1 and 2, affording 4-acetamido-2-
nitroethoxybenzene in a yield of c. 90 % of theory.
Example 5:
2,5-Dichloroacetanilide is nitrated by the methods
described in Examples 1 and 2, affording 2,5-dlchloro-4-
nitroacetanilide in a yield of c. 90 % of theory.
Example 6
4-Chlorobenzoic acid is nitrated by the methods described
in Examples 1 and 2, afording 4-chloro-3-nitrobenzoic acid
in a yield of c. 97 % of theory.
Example 7
Benzoic acid is nitrated by the methods described in
Examples 1 and 2, affording 3-nitrobenzoic acid in a yield
of c. 76 ~/0 o theory.
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Example 8
The supply vessel 1 is charged with 986 ml of
a 1.5 molar soLution of m-toluidine in 98 % suluric
acid, and the supply vessel 3 is
charged with 251 ml of 40 % nitrosylsulfuric acid. 2200 ml
of a petroleum fraction boiling in the range rom
110-140C are fed into the cooling circuit. The centrifugal
pump 5 is put into operation and the cooling medium
temperatur~sof the heat exchangers are regulated to the
following values: heat exchanger 9: 10C, heat exchanger
9a: room temperature. As soon as the petroleum fraction in
the circuit has reached a temperature of 18C, both
reactants are fed into the reactor by means of the pumps
2 and 4. The rate of flow of nitrosyls~f~ric acid is 12.6 ml
~0.075 mole) per minute, and that of m-toluidine~in sulfuric
acid is 49.3 ml (0.075 mole) per minute. The conditions
are stationary after about 2 minutes. A desired d~ischarge
temperature from the reactor of 20C is then attained. A
too high or too low reaction temperature can be easily
regulated via the cooling of the heat exchanger 9~.~The
experiment lasts 20 minutes. The diazo compound, which is
drawn of from the separator, is coupled to phenol and~
the resultant dye is collected by filtration. Yield o~ dye:
~70 g (85 /O of theory).
Example 9:
The supply vessel 1 is charged with 2080 ml of a 1.5
molar solution of l-amino-2-sulfo-4-(4'-aminophenyl)-
aminoanthraquinone in 100 V/o sulfu~cacid; and supply vessel 3
is charged with 277,6 ml of 66 % oleum. 2200 ml of a
petroleum fraction~boiling in the range from 110-140C are
fed into the cooling cycle. The centrifugal pump 5 is put
into operation and the cooling medium temperatures of the
heat exchangers are regulated to the following values:
heat exchanger 9: 10C, heat exchanger 9a: room temperature.
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Both reactants are then fed immediately into the reactorby means of the pumps 2 and 4, The rate of flow o 66 %
oleum is 13,88 ml (0,075 mole) per minute, and that o
l-amino-2-sulo-4-(4'-aminophenyl)aminoanthraquinone in
sulfuric acid is 104 ml (0.075 mole) per minute. The
conditions are stationary after about 2 minutes. ~ desired
reaction temperature of 30C is then attained. A too high
or too low reaction temperature can be easily regulated via
the cooling of the heat exchanger 9. The experiment lasts20
minutes. The aqueous sulfonation mixture is drawn off from
the separator 7 and poured into ice-water. The precipitated
solid is collected by filtration, affording 660.2 g
(90 % of theory) of 1-amino-2-sulfo-4-(2'-su1o-4'-
aminophenyl)aminoanthraquinone,
