ORTHO XYLENE NITRATION PROCESS AND SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY

The present application claims priority from Indian patent application no. 202221010494 filed on 25 ^th February 2022 and 202221010493 filed on the 25 ^th February 2022, the details of which are incorporated herein by a reference.

TECHNICAL FIELD

The present subject matter described herein, in general relates to a continuous process for the production of mono nitroxylene. In particular, the invention relates to an improved, continuous process for the production of 3-nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX).

BACKGROUND OF THE INVENTION

The process of nitrating benzene or benzenoids e.g., o-xylene is old and well known and has been commercially practiced for many years to yield mono-nitro compounds or generally nitro mass. The produced nitro mass is used, in turn, in the production of corresponding amino compounds. Conventionally, the manufacture of nitro mass comprises the batchwise, stepwise or continuous addition of mixed nitric acid and sulphuric acid to o-xylene.

Since the acid phase and the organic phase are not miscible, the reaction rate and the reaction efficiency between the phases are largely limited by mass transfer; that is, by the ability to expose large interfacial areas of each of the phases to each other. As the interfacial areas are increased, the reaction rate between the phases is enhanced. In conventional nitro mass production facilities, these interfacial areas are normally created by reacting the two phases in one or more agitated vessels where high shear forces are applied to the liquids. In the Chemical Engineering Handbook (Perry), 6th Edition, several methods are proposed to achieve intimate mixing or contact between liquids including, for example, in-line motionless mixers, mechanical agitation, gas agitation, jet mixers, injectors, orifice mixers and nozzle mixers.

None of the aforesaid methods for achieving large interfacial areas of contact between immiscible liquid phases is completely satisfactory nor has any method, other than mechanical agitation, been used commercially to any degree in the manufacture of mono nitro compound. These methods either i suffer from high capital and maintenance costs and high-power requirements, as in the case of agitated vessels, or they are difficult to control in terms of optimum reaction efficiency as in the case of impinging streams or jets.

It is desirable to minimize dinitro formation and/or phenolic impurities since their presence is potentially hazardous. Although phenolic and/or dinitro compounds, for example, may be removed from nitro mass reaction mixtures by a simple alkaline wash, dinitro compound is not so readily removed therefrom. In fact, removal of dinitro compound requires distillation of the product mono nitro compound therefrom, which can lead to high concentrations of dinitro compound in the still bottom, which is a potentially hazardous situation. Similar dinitro compound build-up may occur in any process where mono nitro compound is vaporized. Such build-ups may also occur during use or processing of other mono nitro materials and present a sever risk of explosion or fire whenever they occur.

In the industrial production of nitro compounds, significant amounts of acidic organic by-products are formed. In mono nitroxylene production the main by-product species are nitro xylenols (i.e., an organic acid), in mono nitrobenzene production the main by-product species are nitrophenols, and in nitrotoluene production they are nitro cresols. Other minor organic by-product impurities are also present. In addition to by-products, other impurities present in the nitrated product are sulfuric acid catalyst and unreacted starting reactants such as xylene, benzene, or toluene, in the corresponding nitration processes.

The organic acid by-products present in the crude product stream are particularly undesirable since they can adversely affect later users of the products (i.e., use in other processes, such as in the production of aniline in the case of nitrobenzene). The contaminants are therefore typically removed through a series of process steps. These process steps have been described both in the prior art patents and in the literature, e.g., G. Booth, “Nitro Compounds, Aromatic”, in “Ullmann's Encyclopaedia of Industrial Chemistry, 7th Ed ”, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, (2005).

The steps for removing product impurities from the stream of nitrated product comprise the steps of water washing, alkaline washing and neutral washing. Having removed inorganic acids (i.e., in the water washer), organic acids (i.e., in the alkaline washer) and hydroxyl-nitro-aromatics (i.e., in the neutral washer), the next step is to remove residual organic reactant. Some of the reactions to produce nitroaromatics are run with an excess of the organic feed reactant. For the example of mono nitro-o- xylene, excess o-xylene is used, which remains in the crude product stream. Therefore, the product leaving the washing train is typically sent, directly or indirectly, to either a stripper or a distillation column to recover the excess organic reactant.

A distillation column can also be used instead of a steam stripper to remove excess organic feed reactant from the nitrated product. The main operating difference from steam stripping is that, in a distillation column, heat is introduced indirectly via a reboiler. As a result, no water condensate forms in the column and a “dry” nitrated product are obtained. Without water in the final product, salts that were dissolved in the water entrained with the organic product feed to the column precipitate out, leading to plugging of the column or downstream equipment. Some of this precipitate is carried all the way through with the nitrated product into the downstream process. This problem can be overcome by using an effective neutral washer. After this the crude is stored in a day tank or send to columns for vacuum distillation.

The o-xylenes as employed may be acquired from any convenient source and can be obtained from petroleum reforming [mixed xylenes (ortho, meta and para- xylene)]. The nitrating acid or mixed acid employed in the process of the invention is a mixture employed, to nitrate all of the o-xylene to mono nitroxylene. It has been discovered that when the amount of nitric acid used for this continuous process is more than 1.3 times this theoretical value, the content of by-product di-nitroxylene increases sharply, and when the amount of nitric acid is less than 1 times this theoretical value, the amount of unreacted xylene increases.

So, there is need for an efficient process for the production of mono nitro compounds which are relatively free of contamination with phenolic impurities and/or dinitro compounds, safe and simple to control, and which leads to optimum output of reaction product at least possible cost.

Furthermore, the difference in the boiling points of 3-NoX and 4-NoX is very less. Therefore, a modified vacuum distillation is required for the separation of 3-NoX and 4-NoX. But still there are chances to get a fraction where both 3-NoX and 4-NoX are mixed. So, an improved system is required which is relatively free of contamination, safe and simple to control, and which leads to optimum output of highly pure reaction product with high yield at least possible cost.

OBJECTS OF THE INVENTION The principal object of this invention is to provide a system (100) and a process (500) for the production and separation of mono nitroxylene such as 3-nitro-o-xylene (3-NoX) and 4-nitro-o- xylene (4-NoX).

It is a further object of this invention to provide a system (100) and a process (500) for the safe and environmentally friendly manufacturing process of mono nitroxylene such as 3-nitro-o-xylene (3- NoX) and 4-nitro-o-xylene (4-NoX).

It is an object of the present invention to provide a system (100) and a continuous process (500) for the production of mono nitroxylene containing less amount of the di-nitrated species, by-products and impurities thereof.

It is yet another object of the present invention to provide a process for the removal and recovery of excess organic feed reactant.

It is yet another object of the present invention to provide a process for the separation of 3-NoX and 4-NoX to produce highly pure reaction products with high yield.

SUMMARY OF THE INVENTION

Before the present system and its components are described, it is to be understood that this disclosure is not limited to the particular system and its arrangement as described, as there can be multiple possible embodiments which are not expressly illustrated in the present disclosure. It is also to be understood that the terminology used in the description is for the purpose of describing the particular versions or embodiments only and is not intended to limit the scope of the present application.

This summary is provided to introduce concepts related to a system and process for the production and separation of mono-nitroxylenes such as 3-nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4- NoX). This summary is not intended to identify essential features of the claimed subject matter, nor it is intended for use in determining or limiting the scope of the disclosed subject matter.

In accordance with an embodiment of the present subject matter, a system and a process for the production and separation of mono-nitroxylenes such as 3-nitro-o-xylene (3-NoX) and 4-nitro-o- xylene (4-NoX) is described herein.

In one embodiment, a system for the production and separation of mono-nitroxylenes such as 3-nitro- o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX) is disclosed. The said system may comprise of a first reactor comprising of one or more feed inlets for o-xylene, mixed acid and fresh sulfuric acid formulating a reaction mixture, a product drainpipe enabled for collecting nitro mass from the first reactor, an agitation system comprising of a shaft and one or more pump impellers, and a plurality of baffles. The said system further may comprise of a second reactor comprising a paddle type stirrer. The first reactor and the second reactor are connected via an overflow outlet configured for continuous discharging of the reaction mixture. The said system further may comprise of a high-speed separator (HSS) configured for separation of aqueous layer comprising spent acid and organic layer comprising nitro mass. The said system further may comprise of a fractionation unit comprising of at least two columns (Cl and C2) enabled for the segregation of 3-nitro-o-xylene (3-NoX) and 4-nitro- o-xylene (4-NoX).

In another embodiment, a process for the production and separation of mono-nitroxylenes such as 3- nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX) is disclosed. The said process may comprise a step of formulating a mixed acid by mixing of nitric acid and spent acid. The said process may comprise simultaneous feeding of o-xylene, the mixed acid and fresh sulfuric acid into a first reactor to obtain a reaction mixture. The process may comprise a step of agitating the reaction mixture and simultaneously maintaining a predefined reaction temperature into the said first reactor comprising an agitation system comprising of a shaft and one or more pump impellers and a plurality of baffles. The said process may further comprise a step of continuous discharging overflow of the reaction via the overflow outlet mixture from the first reactor to a second reactor comprising a paddle type stirrer. The said process may further comprise a step of passing the said reaction mixture obtained from the said second reactor to the high-speed separator (HSS) via decanter. The said process may further comprise a step of separating aqueous layer comprising spent acid and organic layer comprising nitro mass from the reaction mixture using the said high-speed separator (HSS). The said process may further comprise a step of washing the organic layer comprising nitro mass in washing system to obtain a washed nitro mass. The said process may further comprise a step of feeding the washed nitro mass to the fractionating unit comprising at least two columns (Cl, C2) enabled to obtain the pure 3- NoX and 4-NoX. The said process may further comprise a step of separating pure 3-NoX from first column (Cl) and pure 4-NoX from second column (C2).

List of Abbreviations

3-NoX- 3 -nitro-o-xylene

4-NoX- 4-nitro-o-xylene

RTDs- resistance temperature detectors HSS- high-speed separator

BRIEF DESCRIPTION OF DRAWINGS

The detailed description is described with reference to the accompanying Figures. In the Figures, the left-most digit(s) of a reference number identifies the Figure in which the reference number first appears. The same numbers are used throughout the drawings to refer like features and components.

Figure 1 illustrates a system (100) for the production and separation of mono nitroxylenes such as 3- nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX), in accordance with an embodiment of the present subject matter.

Figure 2 illustrates implementation (200) comprising a first reactor (101) and second reactor (102) for the production and separation of mono nitroxylenes such as 3-nitro-o-xylene (3-NoX) and 4-nitro- o-xylene (4-NoX), in accordance with an embodiment of the present subject matter.

Figure 3 illustrates the top view of the first reactor (101) showing the arrangement of different inlets, in accordance with an embodiment of the present subject matter.

Figure 4 illustrates the inner bottom view of the first reactor (101) showing the arrangement of propellers (401) and baffles (402), in accordance with an embodiment of the present subject matter.

Figure 5 illustrates the process (500) for the production and separation of mono nitroxylenes such as 3-nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX), in accordance with an embodiment of the present subject matter.

Figure 6 illustrates a high-speed separator (HSS) (106) for the separation of nitro mass, in accordance with an embodiment of the present subject matter.

Figure 7 illustrates a fractionation unit (104) maybe enabled for the separation and purification of 3- nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX), in accordance with an embodiment of the present subject matter.

Figure 8 illustrates integration of simple distillation unit (701) for the separation and purification of 3-NoX and 4-NoX, in accordance with an embodiment of the present subject matter.

Figure 9 illustrates a process (500) comprising step of separating (509) pure 3-nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX) from nitro mass, in accordance with an embodiment of the present subject matter. DETAILED DESCRIPTION

Reference throughout the specification to “various embodiments,” “some embodiments,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments,” “in some embodiments,” “in one embodiment,” or “in an embodiment” in places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

The words "comprising," "having," "containing," and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items or meant to be limited to only the listed item or items.

It must also be noted that, the singular forms "a", "an", and "the" include plural references unless the context clearly dictates otherwise. Although any methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the exemplary methods are described. The disclosed embodiments are merely exemplary of the disclosure, which may be embodied in various forms.

Various modifications to the embodiment may be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. However, one of ordinary skill in the art may readily recognize that the present disclosure is not intended to be limited to the embodiments illustrated but is to be accorded the widest scope consistent with the principles and features described herein. The detailed description of the invention will be described hereinafter referring to accompanied drawings.

The terms a first reactor (Rl) (101) and a second reactor (R2) (102) as used in the present embodiments of the present subject matter maybe alternatively referred to as “reactors” or “reactors (101) and (102)” or “reactor (101) and reactor (102)” or “nitrator reactor” or set of reactors (101, 102) or set of reactors comprising at least two reactors (101, 102). The term column 1 may be alternatively referred to as Cl, column 1 (Cl) and the term column 2 may be alternatively referred to as C2, column 2 (C2).

In accordance with an embodiment of the present subject matter, a system (100) and process (500) for the production and separation of 3-nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX) is described herein.

Figure 1 illustrates a block diagram of a system (100) for the production and separation of 3-nitro-o- xylene (3-NoX) and 4-nitro-o-xylene (4-NoX), in accordance with an embodiment of the present disclosure.

By referring to figure 1, a system (100) for the production and separation of 3-nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX) is described in accordance with the embodiments of the present invention. The said system (100) may comprise of a first reactor (101). The said system (100) further may comprise of a second reactor (102). The first reactor (101) and the second reactor (102) are connected in series with each other to carry out continuous production of and separation of 3-nitro-o- xylene (3-NoX) and 4-nitro-o-xylene (4-NoX). In one embodiment, the reactors such as first reactor

(101) and second reactor (102) are a set of continuous stirred tank reactors (CSTR). The said system

(100) further may comprise of a high-speed separator (HSS) (106).

Referring to figures 2-4, the system (100) comprising said first reactor (101), and the second reactor

(102), comprises one or more components. The first reactor (101) and the said second reactor (102) may comprise of a cylindrical tube equipped with different inlets and outlets. In one embodiment, the first reactor (101) may comprise of a cylindrical tube equipped with one or more inlets, outlets, and vent. The said first reactor (101) comprises inlets such as N1 N2, N3, N4, N5, N6, N8, outlets such as N9, N10, N11, and further a vent N7 at the top end of the said first reactor (101). In an embodiment, the said first reactor (101) may comprise an outlet in form of a product drainpipe (N10) enabled for collecting nitro mass generated from the bottom of the said first reactor (101). The said first reactor

(101) may be equipped with an agitation system comprising of a shaft (202) arranged centrally with a motor unit (201) at the top of the said first reactor (101) and one or more pump impellers (401) enabled for the better heat transfer and turbulent mixing of the reaction mixture. The said pump impellers (401) in the said first reactor (101) may be selected from at least one of open or closed pump impellers. The said first reactor (101) further may comprise a plurality of baffles (402), wherein the said plurality of baffles (402) may be positioned internally, arranged 90°-120° and equally apart from each other.

The said first reactor (101) further may comprise one or more temperature indicator sensors (not shown in figure). The said first reactor (101) further may comprise a temperature gauge (not shown in figure) enabled for local temperature indications. The said first reactor (101) may comprise a jacket along with internal coils (203) enabled for cooling or heating the reaction mixture. The first reactor (101) is enabled for completion of 90-97% of the overall nitration and conversion reaction to obtain nitro mass. By referring to figure 1 and 3, top view of the first reactor (101) is shown which illustrates the different inlet arrangement for all the inputs to the said first reactor (101). It is important to mention that these inlets play the important role in the completion of the reaction. The reaction generally proceeds with the low and fully dissociated nitric acid to nitronium ion and commingling the o-xylene with the said nitronium ion solution so as to provide a fine emulsion. The sulphuric acid and spent acid enable the nitric acid to dissociate into the said nitronium ion. Starting from right side anticlockwise, the inlet N 1 may be a feed inlet for fresh sulfuric acid. The opening N7 may be a vent; the inlet N6 may be enabled for nitrogen gas purging to remove the air/oxygen from outlet N9 the reaction mixture in the first reactor (101). The inlet N5 may be enabled for feeding a mixture of nitric acid and spent acid to the first reactor (101).

In one embodiment, the mixing of nitric acid and spent acid to obtain mixed acid may be done just prior to the feeding point N5 with the help of mixer (not shown), and the inlet N4 may be for feeding the o-xylene to the first reactor (R 1 ) ( 101 ) . The inlet N 3 may be provided for brine supply and removal from the said first reactor (101). An inlet N8 may be provided for feeding the sulphuric acid to the first reactor (R1 ) (101 ).

Again, by referring to figure 2, an inlet N2 may be provided for the feeding of spent acid to the first reactor (Rl) (101). The product drainpipe outlet N10 may be provided for collecting the nitro mass from the first reactor (Rl) (101). The said second reactor (R2) (102) may be enabled for the completion of rest of the 3-10% and preferably 2-5% of the reaction.

Referring to Figure 4, inner bottom view of the first reactor (Rl) (101) and the second reactor (R2) (102) along with the baffles (401) arrangement is shown in accordance with the subject matter of the present invention. The width and thickness of baffles (401) may be adjusted to enable the breaking of the vortex generated due to agitation which ensures the thorough mixing of the reactants and to obtain a reaction mixture. In one embodiment, the said system (100) may comprise metering pumps (not shown) enabled to adjust the rate of flow of each of the reactants such as o-xylene, mixed acid, spent acid and sulphuric acid.

Referring again to Figure 2, the first reactor (101) and the second reactor (102) are connected via an overflow outlet (Ni l or ‘(207)’) configured for continuous discharging of the reaction mixture. The second reactor (102) further may comprise an agitation system comprising of a shaft (204) and a paddle type stirrer (206) enabled for formation and completion of remaining 3-10% of nitration reaction. In one embodiment, the said second reactor (102) may be equipped with temperature indicator sensors. Further, the said second reactor (102) may be equipped with temperature gauge, wherein the said temperature gauge (not shown) maybe enabled for local temperature indications. The said second reactor (102) may be equipped with a jacket along with internal coils (205) enabled for the cooling or heating the reaction mixture. The said second reactor (102) further may comprise a plurality of sensors (not shown in figure) such as resistance temperature detectors (RTDs) enabled for the monitoring and collecting the temperature data. In one embodiment, the said second reactor (102) may be enabled for the nitration of remaining product from the first reactor (101), wherein 3-10% of the reaction maybe completed in the second reactor (102).

By referring to figure 1 and 6, the high-speed separator (HSS) (106) is disclosed in accordance with the embodiment of the present disclosure. The said high speed separator (HSS) (106) may be enabled for the separation of aqueous layer comprising spent acid and organic layer comprising nitro mass. In one embodiment the said high-speed separator (HSS) (106) may be a vertically arranged disc centrifuge enabled to receive nitro mass from the decanter (103). The high-speed separator (HSS) comprises of inlet such as N12, outlets such as N13, and N15, and vent N14. Further referring to Figure 6, the high-speed separator (HSS) (106) is configured for separating the nitro mass and spent acid received from first reactor (101) through outlet N10 and from the second reactor (R2) (102). The high-speed separator (HSS) (106) is further configured for separating the mixture comprising nitro mass and spent acid, wherein the separated nitro mass may be passed through an outlet N13 and remaining mixture of nitro mass and spent acid is passed through an outlet N15. The vent N14 may be provided to the said high speed separator (HSS) (106). The incorporation of high-speed stirrer enabled the overall system to transfer from batch to continuous and online HSS in combination with first and section CSTR reactors (101, 102) was introduced to reduce the previous separation time of up to 7 days.

In one embodiment, the said first reactor (101) and the second reactor (102) are nitrator reactors. In one embodiment, the said inlet (N6) of the first reactor (101) may be configured for nitrogen gas purging the reaction mixture enabled to remove the air/oxygen

The said system further may comprise a washing system (104) enabled for the washing of the organic layer comprising nitro mass obtained from the said first reactor (101) and second reactor (102) and transferred via the high-speed separator (HSS) (106), wherein the said washing system (104) is configured to remove and separate inorganic acids and alkali content from the said organic layer comprising nitro mass. The outlet of the washing system (104) may be connected to the inlet of a fractionation unit (108). Referring to Figure 1 and 7, the said system (100) further may comprise of the fractionation unit (108), wherein the said fractionation unit (108) further may comprise of a simple distillation unit (701) and a vacuum fractionation unit (702), wherein the said vacuum fractionation unit (702) further may comprise of at least two columns (Cl and C2) enabled for the separation of 3-NoX and 4-NoX. In one embodiment, the said fractionation unit (108) may be a distillation unit. In one embodiment, the simple distillation unit (701) may be enabled for the recovery of unreacted o-xylene. In one embodiment, the said fractionation unit (108) may be enabled for the segregation and purification of 3-nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX) from nitro mass.

By referring to figure 5, a process (500) for the production and separation of 3-nitro-o-xylene (3- NoX) and 4-nitro-o-xylene (4-NoX) is described in accordance with the embodiments of the present invention. The said process (500) may comprise a step of formulating a mixed acid by mixing (501) of nitric acid and spent acid. The said process (500) further may comprise a step of simultaneously feeding (502) of o-xylene, mixed acid, and fresh sulfuric acid into a first reactor (101) to obtain a reaction mixture, wherein a ratio mixed acid and fresh sulfuric acid is between 5:1 to 3:1 and preferably 4:1 into the first reactor (101). In one embodiment, wherein the predefined amount of o- xylene and spent acid is within a ratio of 1: 1.5 to 2.5.

The said process (500) further may comprise a step of agitating (503) the reaction mixture and simultaneously maintaining a predefined reaction temperature into the said first reactor (101) comprising an agitation system comprising of a shaft (202) and one or more pump impellers (401) and a plurality of baffles (402).

The said process (500) further may comprise a step of continuous discharging (504) of reaction mixture from the first reactor (Rl) (101) to a second reactor (R2) (102) comprising a paddle type stirrer (204). The said process (500) further may comprise a step of passing (505) the said reaction mixture obtained from the said second reactor (102) to the said high-speed separator (HSS) (106) via decanter (103). The said process (500) further may comprise a step of separating (506) aqueous layer comprising spent acid and organic layer comprising nitro mass from the reaction mixture obtained from the said second reactor (102) in the said high-speed separator (HSS) (106). The said process (500) further may comprise a step of washing (507) the organic layer comprising nitro mass separated from the second reactor (102) and the high-speed separator (HSS) (106) in a washing system (104) to obtain washed nitro mass, wherein the said washing system (104) removes inorganic acids and alkali content from the said organic layer comprising nitro mass separated from the first reactor (101) and the second reactor (102) via the decanter (103) and the high-speed separator (HSS) (106). The said process (500) further may comprise a step of feeding (508) the washed nitro mass obtained in the washing system (104) to the fractionating unit (108) comprising simple distillation unit (701) and vacuum fractionation unit (702), said vacuum fractionation unit (702) comprising at least two columns enabled to obtain the pure 3-NoX and 4-NoX. The said process (500) further may comprise a step of separating (509) pure 3-NoX from first column (Cl) and pure 4-NoX from second column (C2), wherein the said columns are of predetermined length, maintained at predetermined bottom and top column temperature and pressure.

In one embodiment, the said mixed acid comprises of 25.0-35.0 % nitric acid (98%), and not less than about 65.0-75.0% of spent acid. Below 70% spent acid concentration effects in corrosion and selectivity of 3-NoX and 4-NoX is also hampered below 75% of spent acid. Further, for the yield of product also dehydrating value of sulfuric acid is also important. In one embodiment, wherein the dehydration value of reaction mixture is maintained between 2.8 to 3.4 and preferably 3.05.

In one embodiment, the said process (500) may be carried out under atmospheric pressure and the reaction temperatures may be controlled within the range of 20°-25° C.

In one embodiment, o-xylene optionally may be added into a stream of mixed acid. In one embodiment, the arrangement of the stepwise feeding the sulphuric acid, mixture of nitric acid and spent acid and o-xylene may be anticlockwise. Therefore, mixing should be done in anticlockwise. In another embodiment, the feeding arrangement may be clockwise then mixing should be in clockwise direction enabling the generation of nitronium ion before mixing it with o-xylene stream.

In a related embodiment, the nitration reaction conversion is completed to 94-98% i.e., 91-93% conversion in the first reactor (101) and remaining 3-4% conversion in the second reactor (102) keeping 2-6% of the o-xylene unreacted, to avoid dinitro formation in the nitro-mass and to improve selectivity of the 3-NoX and 4-NoX formation. The un-reacted o-xylene from the reaction mixture is recovered from organic layer and distillation and reused as a starting material.

In one embodiment, the said step for the separating (506) of the nitro mass and spent acid involves several sub steps. The step for the separating (506) of nitro mass and spent acid comprises a sub step of providing a mixture comprising nitro mass and spent acid from the second reactor (102) to the said high speed separator (HSS) (106) via the decanter (103). Further, the separating (506) the mixture comprises a sub step of separating the mixture comprising organic layer of nitro mass and aqueous layer of spent acid.

In one embodiment, the predefined amount of 98% sulfuric acid and spent acid may be within a ratio of 0.09:0.25:1. In one embodiment, the said spent acid may be having concentration of > 72% and specific gravity between 1.6-1.65. In another embodiment, the said spent acid may be further recycled in the same reaction.

In one embodiment, the separating (509) of 3-nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX) from nitro mass using the said fractionation unit (108) may comprise of various steps. The step of separating (509) pure 3-nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX) from nitro mass may comprise a sub step of charging (901) the feed of nitro mass from a storage tank to the fractionation unit (108), a sub step of separating (902) the unreacted o-xylene from the rest of the nitro mass in the simple distillation unit (701), a sub step of recycling (903) of the o-xylene to the first nitrator reactor (101), a sub step of storing (904) the remaining nitro mass obtained in simple distillation unit (701) into the o-xylene storage tank (703), a sub step of passing (905) the remaining organic layer of nitro mass from nitro mass storage tank (704) to a column Cl at pre-determined conditions, to obtain 3- NoX, and a sub step of passing (906) the rest of the nitro mass obtained from the column Cl to a column C2 at predefined conditions, to obtain 4-NoX.

In one embodiment, a bottom column temperature of column Cl maybe between 149-153 °C and top column temperature of column Cl may be between 105-109 °C. In still another embodiment, an absolute pressure of column Cl may be between 10-15 mmHg.

In one embodiment, a bottom column temperature of column C2 maybe between 142-148 °C and top column temperature of column C2 may be between 108-111 °C. In still another embodiment, an absolute pressure of column C2 maybe between 5-9 mmHg.

In one embodiment, a feed flow rate to the fractionating unit (108) may be maintained between 500- 600 Kg/hr.

In one embodiment, the % yield of 3-nitro-o-xylene (3-NoX) and of 4-nitro-o-xylene (4-NoX) obtained by the process maybe about 55% and 40% respectively in the overall yield of the nitro mass.

In another embodiment, wherein a conversion of o-xylene to nitro-mass comprising a mixture of 3- nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX) is 1: 1.25 to 1: 1.42.

The instant subject matter is further described by the following examples:

Experimental Details:

Example 1: Again, referring to figure 1 and figure 5, the process (500) of preparation of mono nitroxylene such as 3-nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX) utilizing the system (100) of the invention will now be described. All the reactants may be fed into the said first reactor (101) using respective inlet feed pipes. The rate of flow of each of the reactant o-xylene (flow rate 600-680 kg/hr), mixed acid (2000-2200 kg/hr), spent acid (1300-1350 kg/hr), nitric acid (325-400 kg/hr), and sulphuric acid (375-450 kg/hr) may be controlled by adjusting the operating rates of metering pumps (not shown) so that the reactants are delivered into the said first reactor (101) in slight stoichiometric excess of o- xylene, wherein the reaction temperature is maintained within the range of 18° C- 25° C.

In one embodiment, the data related to temperature optimization for the process (500) of nitration and decrease in the production of impurities is provided as below: It can be evident from the above table that there is decrease in the production of impurities for the reaction temperature between 20°C to 25°C. Impurities are ranging from 0.9-2.5%.

In one embodiment, the said process (500) may comprise steps of purging nitrogen gas through an inlet N6 into the reaction mixture for removing the air/oxygen from the first reactor (101). Further the said process (500) may comprise a step of feeding a mixed acid comprising of nitric acid and spent acid through an inlet N5, wherein the mixing of nitric acid and spent acid may be done just prior to the feeding point N5 with the help of mixer (not shown). Further the said process (500) may comprise a step of feeding the o-xylene to the first reactor (101) through an inlet N4. Further the said process (500) may comprise a step of supplying the brine to the said reaction mixture through an inlet N3, wherein an outlet N3 is supplied for the brine input and removal from the said first reactor (101). Further the said process (500) may comprise a step of feeding the sulphuric acid to the first reactor (101) through an inlet N8. Further the said process (500) may comprise a step of feeding spent acid through an inlet N2 to the first reactor (101) to obtain nitro-mass yield 90-92%. Further the said process (500) may comprise a step of passing the reaction mixture from the first reactor (101) to the second reactor (102) through an overflow outlet (Ni l) or (207) for the completion of the rest of 3- 5% of the reaction which is giving overall yield 95%. The reaction is restricted from completion for safety majors and to reduce accumulation of mono- and di- nitro compounds in the nitro mass mixture.

In another embodiment, the nitrogen gas may be purged to remove all the air/oxygen present in the system (100). The addition of nitrogen gas will help to reduce the oxides of nitrogen (NOx) gases generated which may be scrubbed using a scrubbing system thereby making the said process (500) environment friendly. The mixing of acids is an exothermic reaction, so cooling should be done simultaneously with the help of cooling jacket (203). This cooled solution extends the availability of nitronium ion to react with the fresh stream of o-xylene for the production of mono nitroxylene. The approx. 90-95% and preferably 90-92% reaction may be completed in the first reactor (101). A second reactor (102) similar to first reactor (101) maybe employed in which the product from the first reactor (101) may be subjected to further nitration (up to 3-10% and preferably 3-5%). The balanced reaction may take place in the reactor (102) so that the reaction maybe controlled in a phase manner.

The total residence time for the completion of nitration reaction up to 90-95% and preferably 90-92% maybe approx. 22-24 minutes. The advantage of adding the second reactor (102) to the process (500) is the increase in the production of mixture mono nitroxylenes such as 3-nitro-o-xylene (3-NoX) and 4-nitro-o-xylene (4-NoX) in the nitro mass is near to 98%-99.5% by decreasing the production of dinitro compound impurity. Then nitro mass obtained from the first reactor (101) and/or second reactor (102) is immediately transferred to the separator (may be alternatively referred to as ‘decanter’) (103) to decant the nitro mass and rest of the reaction mixture comprising spent acid. The nitro mass obtained from the said decanter (103) is then subjected to high-speed separator (HSS)

(106) for the separation of aqueous layer comprising spent acid and organic layer comprising nitro mass. The said nitro mass obtained from the high-speed separator (HSS) (106) is then subjected to a washing system (104) for washing (506) the organic layer comprising nitro mass to obtain washed nitro mass, wherein the said washing system (104) removes inorganic acids and alkali content from the said nitro mass obtained from the high-speed separator (HSS) (106). The said organic layer of washed nitro mass obtained from the said washing system (104) is stored in a storage tank (105). The said washed nitro mass obtained from the said washing system (104) is subjected to feeding (507) to the fractionating unit (108) comprising a distillation unit (701) and vacuum fractionation unit (702). The vacuum fractionation unit further comprising at least two columns (Cl and C2) enabled to obtain the pure 3-NoX and 4-NoX.

Example 3:

In one embodiment, referring to Figure 6 a step for the separating (506) aqueous layer comprising spent acid and organic layer comprising nitro mass from reaction mixture obtained from the said second reactor (102) in the said high-speed separator (HSS) (106) via decanter (103) is disclosed. The said step for the separating (506) of the nitro mass and spent acid involves several sub steps. The step for the separating (506) of nitro mass and spent acid comprises a sub step of providing a mixture comprising nitro mass and spent acid from the second reactor (R2) (102) to the said high speed separator (HSS) (106) through an inlet N12. Further the step for the separating (506) comprises a sub step of separating the mixture comprising nitro mass and spent acid, wherein the separated nitro mass may be passed through an outlet N13 and remaining mixture of nitro mass and spent acid is passed through an outlet N15. The vent N14 may be provided to the said high speed separator (HSS) (106).

In another embodiment, the separation of spent acid is performed at 7000 - 8000 RPM with a flow rate of 9000 litters/hr. Further the spent acid separated by HSS (106) may be stored in spent acid tank

(107) for the recycling and further use. The nitro mass may be collected from high-speed separator (HSS) (106) and from decanter (103) may be combined and subjected to further workup.

Example 4: In one embodiment, the effect of the different ranges of the temperature and pressure on the recovery of the nitro mass is illustrated in accordance with the embodiment of the present invention and data is reproduced below. The temperature control is provided by using steam at predetermined flow rate and pressure to maintain the product quality. Table 3: Operating conditional data for the recovery of nitro mass.

It can be evident from the above table that for Cl bottom column temperature is between 149-153 °C, top column temperature is between 105-109 °C, absolute pressure is between 10-15 mmHg and 55% of 3-NOX is obtained. Also, it can be evident from the above table that for C2 bottom column temperature is between 142-148 °C, top column temperature is between 108-111 °C, absolute pressure is between 5-9 mmHg, and 39-40% of 4-NoX is recovered. The feed flow rate was maintained between 500-600 Kg/hr.

Example 5:

In one embodiment, the recovery of unreacted o-xylene and reuse in the process of mono nitro-o- xylene production and separation and purification of 3-NoX and 4-NoX from the nitro mass stream is disclosed in accordance with the embodiment of the present subject matter is described.

By referring to figure 7 and 8 a fractionation unit (108) for the purification of 3-NoX and 4-NoX from the nitro mass stream is disclosed. The said fractionation unit (108) comprises of a simple distillation unit (701) and a vacuum fractionation unit (702), wherein the said vacuum fractionation unit (702) comprises of at least two columns (Cl and C2) enabled for the separation of 3-NoX and 4-NoX.

By referring to figure 9, the process step of separating (509) pure 3-NoX from first column (Cl) and pure 4-NoX from second column (C2) by using the said fractionation unit (108) of downstream nitro mass is disclosed and elaborated further.

The said step of separating (509) pure 3-NoX and pure 4-NoX comprises a sub step of charging (901) the feed of nitro mass from nitro mass storage tank (105) to the simple distillation unit (701) under vacuum, wherein, the bottom temperature of the said simple distillation unit (701) is about 150- 160°C, and top temperature of the said simple distillation unit (701) is about 72-75°C under absolute vacuum pressure of 40 mmHg. Further the said step of separating (509) further comprises a sub step of separating (902) the unreacted o-xylene from the rest of the nitro mass via said simple distillation unit (701). Further the said step of separating (509) further comprises a sub step of storing (903) the separated o-xylene in the o-xylene storage tank (703). Further, the said step of separating (509) further comprises a sub step of recycling (904) of the o-xylene to the first reactor (101). The remaining organic layer of nitro mass is stored in the nitro mass storage tank (704). Further, the said step of separating (509) further comprises a sub step of passing (905) the organic layer of nitro mass from the nitro mass storage tank (704) to the first column Cl having predefined length, bottom temperature 149-150°C, top column temperature 95-100°C and applied bottom vacuum is 18-20 tor (absolute pressure) and top vacuum is 2-3 tor for the vacuum distillation. The output from the first column Cl is 3-NoX, which is stored in the 3-NoX storage tank (705). Further, the said step of separating (509) further comprises a sub step of passing (906) the rest of the nitro mass from Cl to the second column C2 of predefined length enabled for the separation of 4-NoX. The operating conditions of the said column C2 are bottom column temperature 142-145°C, top column temperature 92-95°C and applied vacuum is for bottom 9-10 tor and top value of vacuum is 2-3 tor for the vacuum distillation. The output from the second column C2 is 4-NoX, which is stored in the 4-NoX storage tank (706). The output of the Cl and C2 maybe be subjected to the better separation of the final pure product, i.e., 3- NoX and 4-NoX.

In one embodiment, the process (500), wherein predetermined absolute pressure of column Cl is between 10-15 mmHg, and wherein predetermined absolute pressure of column C2 is between 5-9 mmHg.

The process (500), wherein conversion of o-xylene to nitro-mass comprising a mixture of 3-nitro-o- xylene (3-NoX) and 4-nitro-o-xylene (4-NoX) is 1: 1.25 to 1: 1.42.

Other features of the present invention include selecting the sulfuric acid and spent acid concentration so that the reaction could be carried out at a lower temperature without having a super- atmospheric pressure. Selecting the ratio of nitric acid, spent acid and sulfuric acid so that the nitric acid is preferably low and is substantially fully dissociated to nitronium ion, and commingling the o-xylene with the said nitronium ion solution so as to provide a fine emulsion, whereby the reaction can be carried out at a low temperature and at atmospheric pressure to lower the residence time within the first reactor (101) and second reactor (102) to provide product having only low levels of impurities. It will also be understood that the said process (500) may be applicable to other nitration or other chemical reactions which are mass transfer limited. The advantage of using two similar types of columns for the separation of 3-NoX and 4-NoX is to increase the theoretical plates which ultimately improves the quality of the distilled product. For the safety of the plant the distillation in the column C2 is not done up to 100%. The reason behind that is if the distillation of 4-NoX is 100% then chances of the accumulation of mono- and di- nitro compounds increase, and chances of hazard is more. So, in every run the recovery of 4-NoX is always less than 100%. The residue composition which is left after the distillation comprises reaction residue (solid) and nitroxylene. Specifically, residue composition which is left after the distillation comprises in column C2 is 4NoX: 48-50%, dinitro cresol: 4-5%, dinitro: 30-35%, other phenolic impurities are not more than 9-10%. The embodiments, examples and alternatives of the preceding paragraphs or the description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.