FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
OPTIMIZED FLOW SCHEME FOR SEPARATING AN AROMATIC HYDROCARBON FROM A MIXTURE OF HYDROCARBONS
RELIANCE INDUSTRIES LIMITED
an Indian Company of Maker Chambers IV, Nariman Point, Mumbai - 400021, Maharashtra, India
Inventor:
MARVE MAHESH GOPALRAO
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE DISCLOSURE
The present disclosure relates to a process for separating an aromatic hydrocarbon from a mixture of hydrocarbons.
BACKGROUND
Distillation is a very common approach for solvent recovery employed by a vast majority of industries all over the world. Extractive distillation is a type of distillation in which a high-boiling, relatively non-volatile solvent is used to interact with the components of a mixture which causes the relative boiling points of the components to change. This type of distillation is specifically used for separating components having close boiling points that may not ordinarily be separated by simple distillation. In extractive distillation, the solvent is typically miscible in the mixture, but does not form an azeotropic mixture with either of the components.
Extractive distillation (ED) for the separation or purification of compounds having close boiling points is known in the art. Use of extractive distillation units (EDUs) for the purification of aromatic hydrocarbons in an oil and refinery field is also known. GB 824582 discloses a process that involves co-mingling a hydrocarbon oil charge stream, containing at least 70 % by weight of aromatic hydrocarbons, with a saturated hydrocarbon diluent and boiling below the boiling point of the most volatile aromatic component of the charge stream. The process further involves clay treatment of the aromatic hydrocarbon product.
US 6616831 relates to a process for the separation of aromatic compounds from mixtures of aromatic and non-aromatic compounds using art extractive distillation column and a liquid-liquid extractor. The extractive distillation column operates in parallel with the main extractor, an extractive stripper and the water-wash operations of the process.

US 6781026 describes a process for separating C6-C12 aromatic hydrocarbon from close-boiling non-aromatic hydrocarbons in the presence of a solvent mixture, in an extractive distillation column. The solvent mixture used in the process of US 6781026 is a mixture of sulfolane and 3-methyl sulfolane.
US 5458741 discloses a method for separating benzene from benzene-cyclohexane mixture by using extracting agents such as dimethoxymethane, propyl formate, methyl valerate, l-methoxy-2-propanol, ethyl caproate, methyl caproate, ethyl acetate, ethyl isobutyrate, hexyl acetate, methyl acetoacetate, n-propylcaproate, isopropyl acetate, isobutyl acetate, isoamyl formate, 4-nitro phenol, butyl formate and n-propyl acetate.
The prior art methods, however, involve the use of large quantities of expensive and sometimes even corrosive solvents that increases the operating expenditure (Opex) of the methods. Further, reactors of huge size are also used that result in additional increase in the capital expenditure (Capex). Thus, in spite of various advances in this particular area, the expensive and high maintenance nature of majority of the prior art processes necessitate the development of novel equipment, configurations and methods that are cost-effective and environment friendly.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment is able to achieve, are discussed herein below.
It is an object of the present disclosure to provide a process for separating an aromatic hydrocarbon from a mixture of hydrocarbons.
It is another object of the present disclosure to provide a simple and cost effective process for separating an aromatic hydrocarbon from a mixture of hydrocarbons.
It is yet another object of the present disclosure to provide an environment friendly process for separating an aromatic hydrocarbon from a mixture of hydrocarbons.

It is still another object of the present disclosure to provide a process for separating aromatic hydrocarbons with high purity.
It is yet another object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Other objects and advantages of the present disclosure will be more apparent from the following description and accompanying drawings which are not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure provides a process for separating an aromatic hydrocarbon from a stream of hydrocarbons, said process comprising the following steps:
i. admixing at least one solvent (1) and a stream of hydrocarbons (a) to obtain an admixture and subjecting said admixture to extractive distillation in a first extractive distillation assembly (2) to obtain a first aromatic extract (b), wherein the ratio of said stream of hydrocarbons (a) to said solvent (1) ranges between 1:1 and 1:3 and said stream of hydrocarbons (a) comprises at least one compound selected from the group consisting of aromatic hydrocarbons, aliphatic saturated olefins, aliphatic unsaturated olefins, aliphatic unsaturated di-olefins and contaminants;
ii. hydro-treating said first aromatic extract (b) in a hydro-treater (4) to obtain a second aromatic extract (c);

iii. subjecting said second aromatic extract (c) to extractive distillation in a second extractive distillation assembly (6) to obtain a stream of treated products (d); and
iv. fractionating said stream of treated products (d) in a fractionating column (8), at least once, to obtain an aromatic hydrocarbon (e),
wherein, the purity of said aromatic hydrocarbon (e) ranges between 95% and 99.999%.
Typically, said solvent (1) is at least one selected from the group consisting of aniline, acetonitrile, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide.
Typically, said contaminant is at least one selected from the group consisting of sulfur, nitrogen and oxygenates.
Typically, said aromatic hydrocarbon (e) is selected from the group consisting of benzene, o-toluene, m-toluene, p-toluene, o-xylene, m-xylene, p-xylene, naphthalene, cycloheptatriene, cyclooctatriene, cyclononatriene, cyclodecatriene, cycloundecatriene and cyclododecatriene.
DETAILED DESCRIPTION
Conventionally, single extractive distillation units (EDUs) have been used for separating aromatic hydrocarbons from mixture containing hydrocarbons. As some impurities get entailed along with the aromatic hydrocarbons, single EDUs are supplemented with impurity and contaminant removal steps such as hydro-treatment, clay treatment and contaminant adsorption system. However, such setups make the process large in size and thus expensive. Further, the process of hydro-treatment as

disclosed in the prior art produces hydrogenated products of aromatic hydrocarbons along with saturated aliphatic hydrocarbons. The hydrogenated products of aromatic hydrocarbon prejudice the purity of the final separated aromatic hydrocarbon. In order to overcome the afore-stated drawback, the functioning of the single EDUs in the prior art processes is manipulated in specific ways thereby providing pure aromatic hydrocarbon. A typical manipulation technique includes keeping a high solvent to feed ratio. However, such modifications make the process expensive. Further, it necessitates additional precautions in the hydro-treatment to minimize the formation of hydrogenated products of aromatic hydrocarbons. This concern leads to additional steps of contaminant removal such as clay treatment and adsorption of contaminants to supplement the hydro-treatment; thereby further increasing the cost of the process of aromatic hydrocarbon purification.
The inventors of the present disclosure, in order to overcome the drawbacks associated with the prior art processes, have configured a combination of two extractive distillation units and one hydro-treater in a manner that reduces the equipment size, operating cost and obviates the necessary precautions for monitoring the formation of the hydrocarbon products.
In accordance with one aspect of the present disclosure, there is provided a process for separating an aromatic hydrocarbon (e) from a stream of hydrocarbons (a). Reference is made to Figure 1 that illustrates a flow diagram for the optimized aromatic hydrocarbon extraction process described herein after.
The process initially involves subjecting a stream of hydrocarbons (a) to extractive distillation in a first extractive distillation assembly (2) to obtain a first aromatic extract (b). The raffinate resulting from the first extractive distillation process is removed from the assembly and is represented by (f).
Typically, the stream of hydrocarbons (a) comprises at least one compound selected from the group that includes but is not limited to aromatic hydrocarbons, aliphatic

saturated olefins, aliphatic unsaturated olefins, aliphatic unsaturated di-olefins and contaminants.
The contaminant of the present disclosure includes but is not limited to sulfur, nitrogen and oxygenates.
The solvent (1) used in the step of extractive distillation includes but is not limited to aniline, acetonitrile, dimethyl sulfoxide, dimethyl formamide and dimethyl acetamide.
A ratio ranging from 1:1 to 1:3 is maintained between the stream of hydrocarbons (a) and the stream of solvent (1) for achieving effective extractive distillation. Although the low stream of hydrocarbons to solvent ratio results in higher quantities of impurities to proceed further to the next step, it makes the overall process cost-effective.
The first aromatic extract (b) is men directed to a hydro-treater (4), where the process of hydro-treating takes place to yield a second aromatic extract (c). A hydrogen gas stream (h) is purged in the hydro-treater containing the first aromatic extract (b). The spent hydrogen gas is further removed via stream (g).
The second aromatic extract (c) is further subjected to extractive distillation in a second extractive distillation assembly (6) to obtain a stream of treated products (d). This second step of extractive distillation provides an additional opportunity to remove the impurities which reduces the burden on the step of hydro-treatment to be very selective towards the aromatic hydrocarbon saturation. As a consequence, the additional treatment steps such as clay treatment and contaminant removal by adsorption present in the processes of the prior art can be eliminated; thereby increasing the cost-effectiveness of the process of the present disclosure even further.
In one embodiment, the solvents used in the streams (1) and (m) are the same. In another embodiment, the solvents used in the streams (1) and (m) are different.

The size of the second EDU is always smaller than that of the first EDU and is dependent on the content of the aromatic hydrocarbons in the stream of hydrocarbons (a). Thus, if the concentration of the aromatic hydrocarbons in stream (a) is less, a much smaller second EDU is employed which further reduces the expenditure.
The raffinate of the second extractive distillation, represented by (i), is directed to the raffmate of the first extractive distillation (f).
The stream of treated products (d) is further fractionated, at least once, in a fractionating column (8) to obtain the separated and purified aromatic hydrocarbon (e). The aromatic hydrocarbon (e) of the present disclosure includes but is not limited to benzene, o-toluene, m-toluene, p-toluene, o-xylene, m-xylene, p-xylene, naphthalene, cycloheptatriene, cyclooctatriene, cyclononatriene, cyclodecatriene, cycloundecatriene and cyclododecatriene. The purity of the resultant aromatic hydrocarbon ranges between 95% and 99.999%. The remainder of non-aromatic components after fractional distillation is directed back to the stream of hydrocarbons (a) via stream (k).
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and

range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
TECHNICAL ADVANTAGES AND ECONOMIC SIGNIFICANCE
The present disclosure that relates to a process for the separation of an aromatic hydrocarbon from a mixture of hydrocarbons, has the following technical advantages:
- the process of the present disclosure reduces:
• the quantity of solvent used in the first EDU
• the size of the first EDU, substantially, in comparison with a stand-alone single EDU applications for the same application;
• the extent of solvent circulation required in the first EDU;
• the additional steps for the treatment of impurities and contaminant removal;
and
• the sensitivity to the solvent performance, especially in the first EDU.
- the configuration proposed in the present disclosure makes the performance
relatively insensitive to the type of solvent used in the EDU as any under-
performance of the solvent in the first EDU is compensated by the presence of
second EDU.
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention and the claims unless there is a statement in the specification to the contrary.
While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications in the process or compound or formulation or combination of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.

We claim:
1. A process for separating an aromatic hydrocarbon (e) from a stream of
hydrocarbons (a), said process comprising the following steps:
i. admixing at least one solvent (I) and a stream of hydrocarbons (a) to obtain an admixture and subjecting said admixture to extractive distillation in a first extractive distillation assembly (2) to obtain a first aromatic extract (b), wherein the ratio of said stream of hydrocarbon (a) to said solvent (1) ranges between 1:1 and 1:3 and said stream of hydrocarbons (a) comprises at least one compound selected from the group consisting of aromatic hydrocarbons, aliphatic saturated olefins, aliphatic unsaturated olefins, aliphatic unsaturated di-olefins and contaminants;
ii. hydro-treating said first aromatic extract (b) in a hydro-treater (4) to obtain a second aromatic extract (c);
iii. subjecting said second aromatic extract (c) to extractive distillation in a second extractive distillation assembly (6) to obtain a stream of treated products (d); and
iv. fractionating said stream of treated products (d), at least once, in a fractionating column (8) to obtain an aromatic hydrocarbon(e),
wherein, the purity of said aromatic hydrocarbon (e) ranges between 95% and 99.999%.

2. The process as claimed in claim 1, wherein said solvent (1) is at least one selected from the group consisting of aniline, acetonitrile. dimethyl sulfoxide. dimethyl formamide, dimethyl acetamide.
3. The process as claimed in claim 1, wherein said contaminant is at least one selected from the group consisting of sulfur, nitrogen and oxygenates.
4. The process as claimed in claim 1, wherein said aromatic hydrocarbon (e) is selected from the group consisting of benzene, o-toluene. m-toluene, p-toluene5 o-xylene, m-xylene. p-xylene, naphthalene, cycloheptatriene, cyclooctatriene, cyclononatriene, cyclodecatriene, cycloundecatriene and cyclododecatriene,