DESC:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
[See section 10, Rule 13]

A PROCESS FOR PREPARATION OF NITROTOLUENES;

DEEPAK NITRITE LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956 WHOSE ADDRESS IS 9/10, KUNJ SOCIETY, ALKAPURI, VADODARA, GUJARAT 390007, INDIA

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

Field of Invention
The present invention relates to a process for the preparation of nitrotoluenes, more particularly a mixture of mono nitrotoluenes.
Background of the invention:
Toluene Nitration is an important chemical reaction producing commercially valuable intermediates such as nitrotoluene and dinitrotoluene. The mononitration products of toluene are ortho, meta, paraisomers. Such products act as useful starting materials for industries such as pharmaceutical, agro, dye andpigment.
The widely used method of industrial nitration occurs in a mix acid of concentrated solution of nitric acid and sulfuric acid at 30°C -70°C in a Continuously Stirred Tank Reactor (CSTR). Conventionally, the large scale process of preparation of mononitro toluenes involves the reaction of toluene and a mixed acid which is a mixture of nitric acid, sulfuric acid and water. The resultant product obtained is a mixture of isomeric mononitrotoluenes and dinitrotoluenes and irrespective of the reaction conditions, the ratio is fairly constant of about 60% orthonitrotoluene, about 35% of the paranitrotoluene and about 5% of the metanitrotoluene. This is then followed by separation techniques such as distillation and crystallization. However, such process of preparation of mononitrotoluene generates a large amount of spent sulfuric acidwaste. If said spent sulfuric acidwaste is discharged without proper treatment it leads to environmental problems such as soil acidification and ecosystem damage. Conventionally known techniques used for the recovery of sulfuric acid from such industrial waste acid is neutralization or reconcentration of the acid in order to achieve targeted strength of sulfuric acid before being recycled. The process such as that of re-concentration increases the cost and utility.
Thus, there exists a need for a process which is a cost effective continuous process for preparing mononitrotoluenes using processed spent sulfuric acid obtained fromvariousnitration processes. Further, there exists a need of a process which will reduce the cost of production, avoid the waste of resources and reduce the environmental pollution and impact on the environment.
Summary of Invention
Accordingly, an embodiment of the present invention discloses a process for preparing nitrotoluene, the process comprising:
providing spent acid that comprises a mixture of sulfuric acid and nitric acid;
steaming said spent acid to reduce the amount of nitric acid in said spent acid to obtain a recycled spent sulfuric acid;
feeding said recycled spentsulfuric acid to a mixture of toluene and nitric acid where said recycled spentsulfuric acid, toluene and nitric acid react to form a reaction mass; and
separating the reaction mass into a first phase comprising nitro toluene and a second phase comprising waste acid.
In the aforesaid embodiment the spent acid is obtained from nitration of monohydric alcohol or a mixture of monohydric alcohols such as amylalcohols, hexanols, heptanols and octanols, their isomers and mixtures.
Detailed description of the invention:
The present invention discloses an eco-friendly improved continuous process for the preparation of nitrotoluene more particularly a mixture of mono nitrotoluenes of ortho –para -meta nitro toluene by the nitration of toluene using a processed spent acid obtained from another nitration process.
Further, the present invention discloses a process for the manufacture of mono nitrotoluenes while ensuring the important characteristics of specific to isomer ratio such as that of 57-60% ortho-nitrotoluene, 37-40% para- nitrotoluene and 3-4% of meta- nitritoluene, cresol impurities of less than 0.1%, purity as per application standard are retained.
An embodiment of the present invention discloses a process for preparing nitrotoluene, the process comprising
providing spent acid that comprises a mixture of sulfuric acid and nitric acid;
steaming said spent acid to reduce the amount of nitric acid in said spent acid to obtain a recycled spent sulfuric acid;
feeding said recycled spentsulfuric acid to a mixture of toluene and nitric acid to a reactor where said recycled spentsulfuric acid, toluene and nitric acid react to form a reaction mass; and
separating the reaction mass into a first phase comprising nitro toluene and a second phase comprising waste acid.
The spent acid comprising a mixture of sulfuric acid and nitric acid is obtained from another nitration process namely nitration ofmonohydric alcohol or a mixture of monohydric alcohols such as amylalcohols, hexanols, heptanols and octanols, their isomers and mixtures preferably but not limited2-ethyl hexanol. Said mixture of the spent acid comprises of 80-82%w/w sulfuric acid and 3%w/w -5% w/w of impurities of nitric acid is then subjected to steam distillation at 100°Cfor 4hours-5hours to obtain recycled spent sulfuric acid. Steaming of the spent acid comprising of a mixture of sulfuric acid and nitric acid reduces the amount of nitric acid impurities to less than 0.2% w/w and a recycled spent sulfuric acid of strength of 80-82%w/w is obtained.
The recycled spent sulfuric acid, a mixture of toluene and fresh nitric acid of strength 98%w/w is then fed to a continuously stirred tank reactor CSTR (R1) already containing said recycled spent sulfuric acid of strength 80%w/w -82%w/w. The molar ratio of the toluene to the nitric acid is greater than 1.The temperature maintained in the continuously stirred tank reactor CSTR (R1) in the range of 50°C-55°C.Said recycled spent sulfuric acid, nitric acid, toluene and the already present said recycled spent sulfuric acid react to form a reaction mass. On completion of the reaction, the reaction mass formed overflows from the first Continuously Stirred Tank Reactor (CSTR) (R1) to the second Continuously Stirred Tank Reactor (CSTR) (R2) for organic and aqueousphase separation and finally to the third Continuously Stirred Tank Reactor(CSTR) (R3)for washing of organic phase using water, alkali and finally followed by water at room temperature.
The said reaction massformed is transferred to second CSTR (R2)where it is separated into a first phase which is an organic phase comprising of crude nitro toluene and a second phase comprising of waste acid. Separation of said first phase of crude nitro toluene and said second phase of waste acid is based on specific gravity difference. The first phase of crude nitro toluene comprises a mixture of mononitrotoluenes of orthonitrotoluene, metanitrotoluene and paranitrotoluene. The waste acid comprises of 70-72%w/w of aqueous sulfuric acid, less than 1% w/w nitric acid and other impurities such as 2,6-dinitro-p-cresol, 2,4-dinitro-o-cresol-p-nitophenol, 2,4- dinitrophenol, 3-nitro-4-hydroxy benzoic acid.
The organic mass of crude nitro toluene obtained is transferred into a third CSTR (R3) where it is subjected to aqueous washing with water followed by alkaline washing with alkali such as5-10% Caustic lye, soda ashand neutralization using water at room temperature to obtain impurity free crude nitro toluene. This final impurity free crudenitro toluene organic mass obtained was then followed by recovery of unreacted toluene and moistureusing atmospheric distillation. This step is then followed by vacuumdistillation to separate ortho-nitrotoluene followed by fractional crystallization to separate meta-nitrotoluene and para-nitrotoluene. The final products of ortho-nitrotoluene, para-nitrotoluene and meta-nitrotoluene is 99.5%.
Thus, an advantage of the present invention is that recycled spent sulfuric acid is used in the process to prepare nitro toluene instead of fresh sulfuric acid, thus making the process of the present invention cost effective. Use of recycled spent sulfuric acid wherein the impurities have been reduced by steaming reduces the cost of the process in comparison to processes such as re-concentration of an acid to achieve a desired concentration.
Example
1. Steam distillation is carried out for 4 hours at a temperature of 100°C on400 gm of spent acid comprising a mixture of sulfuric acid and 2.5%w/w of nitric acid impurities obtained from 2-ethyl hexanol nitration. Steaming of said spent acid is carried out to reduce the amount of nitric acid in said spent acidto obtain395gms recycled spent sulfuric acid. 319 gm of 80%w/w of recycled spent sulfuric acid, a mixture of 215gm of 98%w/w nitric acid and 270gm toluene were fed into aContinuously Stirred Tank Reactor(CSTR R1) already containing of 319 gm of 80%w/w recycled spent sulfuric acid and the temperature was maintained at 50°C. Said recycled spent sulfuric acid, toluene and nitric acid react to form a reaction mass. On completion of the reaction, said reaction mass overflows from the firstContinuously Stirred Tank Reactor(CSTR-R1) to the secondContinuously Stirred Tank Reactor(CSTR -R2) where the reaction mass is separated based on specific gravity difference in to a first organic phase comprising of crude nitrotoluene and a second phase comprising of 715gm 70%waste acid. The organic phase i.e.375gmof crude nitrotoluene is then fed to the third Continuously Stirred Tank Reactor (CSTR -R3) where it was washed with 350 ml fresh water followed by alkaline washing with 350ml 10% caustic lye solution and neutralizationusing 700ml water at room temperature. 315gmof final crude nitrotoluene obtained was followed by recovery of unreacted toluene and moistureusing atmospheric distillation which is the followed by vacuumdistillation to separate ortho-nitro toluene followed by fractional crystallization to separate of meta-nitro toluene and para-nitro toluene.
The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the disclosure.

,CLAIMS:We claim:
1. A process for preparing nitrotoluene, the process comprising
providing spent acid that comprises a mixture of sulfuric acid and nitric acid;
steaming said spent acid to reduce the amount of nitric acid in said spent acid to obtain a recycled spent sulfuric acid;
feeding said recycled spent sulfuric acid to a mixture of toluene and nitric acid where said recycled spent sulfuric acid, toluene and nitric acid react to form a reaction mass; and
separating the reaction mass into a first phase comprising nitro toluene and a second phase comprising waste acid.
2. The process as claimed in claim 1, wherein the spent acid is obtained from nitration ofmonohydric alcohol or a mixture of monohydric alcohols such as amylalcohols, hexanols, heptanols and octanols their isomers, mixtures preferably 2- ethyl hexanol.
3. The process as claimed in claim 1, wherein the recycled spent sulfuric acid is of strength 80-82% weight by weight.
4. The process as claimed in claim 1, wherein the first phase of nitro toluene comprises of a mixture of ortho nitro toluene, para nitro toluene and meta nitro toluene.
5. The process as claimed in claim 1, wherein the second phase of waste acid comprises of 70% -72% aqueous sulfuric acid, less than 1% nitric acid and impurities.
6. The process as claimed in claim 1, wherein the recycled spent sulfuric acid is fed to a reactor already having said recycled spent sulfuric acid of strength 80%-82% weight by weight.
7. The process as claimed in claim 1, wherein the said recycled spent acid, toluene and nitric acid are reacted at 50°C to 55°C.
8. The process as claimed in claim 1 or 4, wherein the nitro toluene obtained is crude nitro toluene.
9. The process as claimed in claim 8, wherein the process further comprises of washing the crude nitrotoulene followed by neutralization, distillation and fractional crystallization to separate the nitrotoulene into ortho nitro toluene, para nitro toluene and meta nitro toluene.