Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1995-08-03
2001-07-10
Jones, Dwayne C. (Department: 1614)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S932000, C568S927000
Reexamination Certificate
active
06258986
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the production of dinitrotoluene by toluene nitration with nitrating acid under adiabatic conditions.
It is known to convert toluene to dinitrotoluene (DNT) adiabatically (EP-A 597,361). Toluene is reacted adiabatically with at least 2 equivalents of a nitrating acid satisfying specific compositional requirements. A final temperature greater than 120° C. is reached. After phase separation at this temperature, the acid phase is reconcentrated (flash evaporation under vacuum). The heat of the acid phase is used for the reconcentration. The reconcentrated acid is made up with nitric acid and is recycled to the process.
An inherent difficulty in this process is the passage of a certain amount of DNT which is dissolved in the acid with the water which distills off in the flash evaporation. This residual DNT solidifies under the water condensation conditions (the isomer mixture solidifies at approximately 55° C.) and fouls the heat exchanger. There are two possible solutions to this problem.
In one of the possible solutions, staggered heat exchangers may be used. These staggered heat exchangers are operated alternately. When some of the exchangers have been fouled, they are idled and the alternate exchangers are used. The DNT present in the fouled exchangers is then melted off while those exchangers are idle. Fouling of exchange surfaces results in rapid deterioration in cooling performance. Frequent changeovers are therefore necessary. Extra power is required to melt the DNT from the idle condenser (heating up and cooling).
In a second possible solution to the problem of fouling, the heat exchanger, a co-condenser or injection condenser may be used to condense solid-forming exhaust vapors (R. A. Vauck, H. A. Muller,
Grundoperationen chemischer Verfahrenstechnik
[Basic Chemical Process Engineering Operations], 5th edition, VEB Leipzig 1962, p. 447). In this process, the exhaust vapors are introduced into a cold water jet spray and DNT is segregated in finely divided form as a solid. Co-current and counter-current operation are possible. Because of the large volumes of water required in this procedure, the water is circulated in a loop and cooled in the return branch. In order to separate the DNT from the water, a portion of the flow is passed out through a lock. This increases the risk of blocking lines and nozzles with low-melting organic components which tend to adhere to such lines and nozzles. Recovery of DNT in pure form requires a significant amount of energy because the DNT must first be melted down before it is recovered.
A considerably simpler and more elegant solution to the problem of fouled heat exchangers is an isothermal two-stage production of dinitrotoluene such as that disclosed in Ullmann,
Encyklopädie der technischen Chemie
[Encyclopedia of Industrial Chemistry], 4th edition, vol. 17, p. 392, Verlag Chemie, Weinheim (1979). In this two-stage process, an isomeric mixture of mononitrotoluene (MNT) is first prepared. This isomeric mixture is converted in a second, separate process step to an isomeric mixture of dinitrotoluene. The problem of fouling of the heat exchanger when reconcentrating the spent acid under vacuum is eliminated by injecting MNT from the first stage into the exhaust vapors (DE-A 3,409,719). The MNT which is injected lowers the melting point of the DNT thereby ensuring that the exhaust vapors remain fluid even under the water condensation conditions. The organic phase which is isolated by phase separation is recycled into the reaction.
This elegant solution is not useful in a single-stage adiabatic process for toluene dinitration (EP-A 597,361) because there is no freely available MNT present in the single-stage process. MNT is a non-isolatable intermediate product in such a single-stage process.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a continuous, single-stage adiabatic process for the production of dinitrotoluene.
It is also an object of the present invention to provide a single-stage process for the production of dinitrotoluene in which the problem of fouling heat exchangers is avoided.
It is another object of the present invention to provide a single-stage, adiabatic process for the production of dinitrotoluene in which costly process steps and the use of extra energy are avoided.
These and other objects which will be apparent to those skilled in the art are accomplished by nitrating toluene with a nitrating acid composition satisfying specified compositional criteria under adiabatic conditions in a single stage, removing at least 5% by weight of any water present in the reaction mixture and separating the reaction mixture into an acid phase and an organic phase containing the dinitrotoluene. The acid phase may be recycled after sufficient nitric acid has been added to replace that spent in the nitration reaction.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention relates to a process for the continuous production of dinitrotoluene isomer mixtures by toluene nitration. In this process, toluene is reacted under adiabatic conditions in a single stage in a continuously operated reactor with a nitrating acid. This nitrating acid is made up of (a) from about 80 to about 100% by weight (based on total weight of nitrating acid) inorganic materials which include: (i) from about 60 to about 90% by weight (based on the total weight of (a)) of sulfuric acid, (ii) from about 1 to about 20% by weight (based on the total weight of (a)) of nitric acid and (iii) at least 5% by weight (based on the total weight of (a)) of water and (b) from 0 to about 20% by weight (based on the total weight of nitrating acid) of organic materials which include at least 70% by weight (based on total weight of (b)) of dinitrotoluene isomers with the remainder being by-products of the nitration process. The toluene and nitrating acid are used in amounts such that the molar ratio of nitric acid to toluene is at least 1.5:1, preferably at least 1.8:1, most preferably at least 1.9:1. This molar ratio is selected so that small quantities of mononitrotoluene are still present in the reaction mixture after the nitration. At least 5% by weight (based on the total reaction mixture) of the water present in the nitration reaction mixture containing dinitrotoluene is removed. This removal may be achieved by distillation, preferably by flash evaporation, optionally with simultaneous supply of heat. The reaction mixture from which water has been removed leaves the reactor continuously at a temperature of at least 120° C. At this point, up to 0.6 mole, preferably up to 0.3 mole, most preferably up to 0.2 mole, of nitric acid (50 to 100% by weight) may optionally be mixed in the nitration reaction mixture. The nitration reaction mixture from which water has been removed is then separated into an upper product phase and a lower acid phase. The product phase is worked up to recover the product dinitrotoluene. The acid phase may be recycled into the beginning of the process after the addition of nitric acid (50 to 100% by weight nitric acid) to replace the nitric acid used during the nitration reaction.
It has surprisingly been found that condensation of the exhaust vapors may be carried out advantageously if the reaction is conducted in a manner such that small amounts of MNT (minimum 5% by weight based on total weight of reaction product) remain in the reaction product. Separation of the organic phase after acid reconcentration (i.e., removal of at least 5% by weight water) also promotes condensation of the exhaust vapors without solidification of the dinitrotoluene. The reaction product containing small quantities of MNT is subjected to reconcentration (i.e., removal of at least 5% by weight water) immediately after leaving the reactor. The MNT present is distilled off with the water and small quantities of DNT at the top. The ratio of MNT to DNT in the exhaust vapor condensate is from about 10:1 to about 1:5, preferably from about 5:1 to about 1:5. This
Klingler Uwe
Schieb Thomas
Wastian Dietmar
Wiechers Gerhard
Zimmerman Jurgen
Bayer Aktiengesellschaft
Gil Joseph C.
Jones Dwayne C.
Whalen Lyndanne M.
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