CA1160430A

CA1160430A - Method of removing heat from exothermic chemical reactions

Info

Publication number: CA1160430A
Application number: CA000360162A
Authority: CA
Inventors: Fritz Altorfer
Original assignee: Individual
Current assignee: BASF Schweiz AG
Priority date: 1979-09-13
Filing date: 1980-09-12
Publication date: 1984-01-17
Also published as: ES8106054A1; JPS5684626A; ATE1972T1; ES494979A0; JPS6323824B2; EP0028203B1; EP0028203A1; DE3061353D1

Abstract

Case 1-12513/+
Method of removing heat from exothermic chemical reactions Abstract of the Disclosure A method of removing the heat of reaction from continuous exothermic chemical reactions conducted in the liquid phase, which method comprises introducing a fluid which is inert to the reactants, and which is immiscible with the reaction medium, 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, se-parating the emulsion thereby obtained into the phase contain-ing the reaction products and that consisting of the inert fluid. cooling said inert fluid and recycling it to the reactor, such that the inert fluid is able to pass through this circuit as often as desired, and such that a desired stationary temperature is reached in the reactor. The invention also provides an assembly for carrying out this method, consisting of a reactor with feed lines for the starting materials and for the inert fluid necessary for cooling the reaction, a separator which is connected by a line with the reactor and in which the solution containing the reaction products is separated from the inert fluid, and a return line which is provided with a heat exhanger and through which the inert fluid is recycled to the reactor while being cooled.

Description

-) 43(~

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 3 n 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 1 1~l)43() 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 3 1~0~3 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 1 l~V~

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, ~~~`" 1 ~4~n 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.

1 1~t)430 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 3a 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 3~) 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:

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

3,n 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.

v4~n 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 v43n 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.

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.

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,

Claims

What is claimed is:

1. A method of removing the heat of reaction from continuous exothermic chemical reactions conducted in the liquid phase, which method comprises introducing a fluid which is inert to the reactants and which does not dissolve any substantial part of the reactants and reaction products, and which is immiscible with the reaction medium, 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 heated inert fluid, cooling said inert fluid and re-cycling it to the reactor where it can again absorb heat of reaction, such that the inert fluid is able to pass through this circuit as often as desired, and such that a desired stationary temperature is reached in the reactor.

2. A method according to claim 1, wherein the reactor which ensures an intimate mixing of reaction medium and inert fluid is a centrifugal pump, an on-line mixer with feed pump, a static mixer with feed pump, a turbine mixer, or a jet tube reactor.

3. A method according to claim 1, wherein the emulsion issuing from the reactor is passed into a reaction pipe before phase separation takes place, in order to bring the reaction to completion.

4. A method according to claim 3, wherein the reaction pipe is provided with a heat exchanger.

5. A method according to claim 1, wherein the inert fluid used for cooling purely aqueous reaction media is an aliphatic, cycloaliphatic or aromatic hydrocarbon, a halogenated aliphatic or aromatic hydrocarbon, a water-immiscible alcohol, ketone, ester or ether.

6. A method according to claim 1, wherein the reaction from which heat is removed is an exothermic substitution, oxi-dation, reduction, addition, elimination or polymerisation reaction.

7. A method according to claim 6, wherein the reaction from which heat is removed is a nitration, sulfonation, diazotisation, hydrogenation or other reduction reaction.

8. A method according to claim 7, wherein heat of reaction is removed from the nitration of aromatic systems.

9. An assembly for carrying out the method of claim 1 comprising a) a reactor with feed lines for the starting materials and with a feed line for a fluid which is inert to the reactants and is immiscible with the reaction medium, which reactor must ensure an intimate mixing of the reaction medium and the inert fluid, 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 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.

10. An assembly according to claim 9, wherein the reactor is additionally provided with feed lines for solvents in which the reaction is conducted and in which one or more starting materials can be dissolved.

11. An assembly according to claim 9, wherein 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.

12. An assembly according to claim 9, wherein a further reaction zone is provided between the reactor and the separator.

13. An assembly according to claim 12, wherein a part of the line between the reactor and the separator is a reaction pipe in which the reaction is brought to completion.

14. An assembly according to claim 13, wherein the reaction pipe is provided with a heat exchanger.