FORM-2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION (see section 10 and rule 13) METHOD FOR EXTRACTION OF LINEAR HYDROCARBONS FROM HYDROCARBON FEED RELIANCE INDUSTRIES LIMITED An Indian Company of 3rd Floor, Maker Chamber-IV, 222, Nariman Point, Mumbai-400021, Maharashtra, India. Inventors: 1. BISHTHarender 2. UPADHYAY Alpesh 3. DAS Asit Kumar 4. DONGARARajeshwe 5. MARVE Mahesh G 6. MALVANKER Manthan A 7. CHAKRAVARTHY Ramachandra; 8. MANDAL Sukumar 9. GHOSH Swapan 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 the extraction of linear hydrocarbons from a hydrocarbon feed. BACKGROUND: Linear hydrocarbons possess several high value applications. Some common applications of linear hydrocarbons include their use as solvents, raw materials for the preparation of waxes, poly α-olefins and linear alkyl benzenes (LAB) and the like. In order to meet the increasing demand for linear hydrocarbons, several methodologies have been explored/ practiced at industrial scales to expedite the extraction/recovery of linear hydrocarbons from crude hydrocarbon feeds. EXISTING KNOWLEDGE: Molecular sieve based separation processes are the preferred techniques for commercial scale extraction of linear hydrocarbons, particularly n-paraffms. Molecular sieves provide extracted n-paraffms with high purity and in high yield. However, their sensitivity towards compounds other than n-paraffins such as olefins, sulfur and nitrogen compounds drastically reduce their extraction efficiency for n-paraffins. The use of molecular sieves, therefore, requires extensive pre-treatment of a hydrocarbon feed for removal of such compounds prior to the extraction of n-paraffins, particularly, if the feed contains high amount of olefins, sulfur and nitrogen compounds, for example, coker distillates and the like. Due to stringent feed specifications for olefin, sulfur and nitrogen compounds, a hydrotreating unit constitutes an integral part of commercial units using 5A type molecular sieve for the separation of n-paraffins. During hydrotreating, in addition to sulfur and nitrogen removal, the olefins get converted into their corresponding paraffins. The most common application of n-Paraffms (C10-C14) is in the production of n-olefms for further producing LAB. The n-Paraffms separated by the molecular sieve, are further dehydrogenated to produce n-olefins. The hydrocarbon feed having substantial amount of n-olefins, therefore, does not provide any value addition in molecular sieve based processes. The molecular sieve based processes are known to be carried out under vapor phase as well as under liquid phase. European Patent No. 0004619 discloses a vapor phase process for the extraction of n-paraffins from a hydrocarbon feed by using 5A molecular sieve adsorbent. The vapor phase extraction is carried out at lower pressure and higher temperature. Despite the fact that the vapor phase separation processes are less sensitive to olefins, sulfur and nitrogen compounds, high temperature conditions resulting into high energy requirement and unwanted coke formation further adds to the production cost. United States Patent No. 5510564 discloses a process for liquid phase extraction of linear hydrocarbon by using 5A molecular sieve adsorbent. The liquid phase extraction is usually carried out at considerably higher pressure and lower temperature as compared to the vapor phase extraction process. The major disadvantage allied with the liquid phase extraction process is high sensitivity for olefins, sulfur and nitrogen compounds. Further, the use of de-waxing additives is also reported for the extraction of linear hydrocarbons, for example, in the processes as disclosed in the United States Patent Nos. 7728093 and 7388122. The de-waxing additive selectively crystallizes linear paraffins from a hydrocarbon feed when the hydrocarbon feed mixed with such additives is cooled. The de-waxing additive used in the extraction process remains trapped in the crystalline phase which is difficult to separate from the n-paraffin. Further, the de-waxing additives do not crystallize smaller n-paraffins because of their low crystallization temperature. Use of membranes for the extraction of linear hydrocarbons is also reported, for example, in the process as disclosed in the United States Patent No. 5107059. The aforementioned US patent teaches the use of a microporous membrane for the separation of n-paraffins from iso-paraffins. On one side, the membrane is contacted with the hydrocarbon mixture while on the other side it is contacted with a polar solvent. Iso-paraffins being comparatively more polar than n-paraffins have slightly higher tendency to permeate to the other side of the membrane. Therefore, on one side of the membrane n-paraffins content increases whereas on the other side of the membrane iso-paraffins get concentrated. The use of the membrane however provides only partial separation of n-paraffins. Further to the aforementioned processes the urea adduction is a well-known process for the extraction of linear hydrocarbons from complex hydrocarbon mixtures. However, very few urea adduction commercial units are operating worldwide due to their high operating cost as compared to other commercial processes. One of the most significant contributors to the operating cost is the high energy requirement of the solvent recovery system. Unlike the molecular sieve based process, urea adduction process is tolerant to olefin, sulfur and nitrogen compounds in the hydrocarbon feed, hence, it can be effectively used for extraction of linear hydrocarbons from complex hydrocarbon feeds even without subjecting the hydrocarbon feed to any pre-treatment. Further, the urea adduction process is also capable of extracting both small chain hydrocarbons as well as large chain hydrocarbons. Urea forms hexagonal crystals in the presence of linear hydrocarbons of more than 6 carbon atoms. The tetragonal crystal of urea rearranges into a hexagonal structure in which 6 urea molecules are present in each unit cell. The hexagonal urea crystals form long parallel channels of 5.5A0 diameter in the presence of linear hydrocarbons due to hydrogen bonding between oxygen and NH2 groups of adjacent urea molecules. Long chain linear hydrocarbons facilitate more number of hydrogen bonds, hence, the adduct of urea with long chain linear hydrocarbons is very stable even at higher temperature. Small chain linear hydrocarbons (95% reduction in sulfur and nitrogen content in the extracted hydrocarbons is reported according to the process of the present disclosure. 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. Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application. The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following 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. Example-1: In this example, 100 % water is used as a first solvent and as a decomposition solvent 90g urea was taken in a three neck 500ml round bottom (RB) flask fitted with a mechanical stirrer. 50g water as a first solvent was added to the RB flask under continuous stirring. The temperature while mixing the urea and water was maintained at 20°C for 20 minutes. Thereafter, 50g hydrocarbon feed, for example, light light coker gas oil (LLCGO) was added in the RB flask in 5 minutes duration. The resultant slurry thus obtained was stirred at 400 rpm for 30 minutes. The resultant slurry was then kept for settling for about 5 minutes without stirring. The entire resultant slurry was then transferred to a vacuum filtration assembly to separate the solid urea-linear hydrocarbon adduct and to obtain a raffinate comprising un-adducted LLCGO and excess urea dissolved in water. The solid adduct was then stirred with 300g pentane (second solvent). The slurry thus obtained was subjected to filtration to obtain a washed solid adduct and a second solvent wash. The washed and dried solid adduct was then dissolved in 50g water (decomposition solvent) to decompose the adduct into linear hydrocarbons and urea. 0.4g (0.8 wt %) linear hydrocarbon was recovered from the decomposed urea solution. The purity of the extracted linear hydrocarbons was 38%. The raffinate comprising the un-adducted LLCGO, the excess urea dissolved in water and the second solvent wash were introduced in a separator and mixed together. The resultant mixture thus obtained got separated into two layers under gravity. The bottom layer containing the excess urea dissolved in water was further used for urea-linear hydrocarbon adduct formation. The top layer containing the second solvent wash and the un-adducted LLCGO was sent to a distillation column where it was distilled at 100 °C column bottom temperature. The second solvent wash was recovered in pure form from the top of the distillation column. The un-adducted LLCGO obtained as a bottom stream was used in further application, such as, as a hydrocarbon feed for blending with diesel or kerosene. Example-2: In this example, methanol is used as a first solvent and water is used as a decomposition solvent. 90g urea was taken in a three neck 500ml RB flask fitted with a mechanical stirrer. 150g methanol (first solvent) was added to the RB flask under continuous stirring. The temperature while mixing the urea and methanol was maintained at 20°C for 20 minutes. Thereafter, 50g LLCGO was added in 5 minutes. The obtained resultant slurry was then stirred at 400 rpm for 30 minutes. The slurry was then kept for settling for about 5 minutes without stirring and thereafter transferred to a vacuum filtration assembly to separate the solid urea-linear hydrocarbon adduct and to obtain a raffinate comprising un-adducted LLCGO and excess urea dissolved on methanol. The solid adduct was stirred with 300g pentane as a second solvent and was filtered to obtain washed solid adduct and a second solvent wash. The solid washed adduct was dried. The dried solid adduct was then dissolved in 50g water (decomposition solvent) to decompose the adduct into urea solution and linear hydrocarbon. 10.65g (21.3 wt%) of linear hydrocarbons were recovered from the decomposed urea solution. The purity of the extracted linear hydrocarbons was 96.8%. The raffinate (comprising the un-adducted LLCGO and the excess urea dissolved in methanol) was mixed with the second solvent wash in a separator. The resultant mixture thus obtained got separated into two layers under gravity. The bottom layer contained the excess urea dissolved in methanol and the un-adducted hydrocarbon, whereas, the top layer contained pentane (washing solvent), methanol and also the un-adducted LLCGO. In this example the amount of un-adducted LLCGO was more in the bottom layer and the amount of methanol was more in the top layer due to improper separation of the two layers. The top layer was sent to a distillation column where it was distilled at 100°C column bottom temperature to remove methanol and pentane. The un-adducted LLCGO obtained from distillation column bottom was used as a hydrocarbon feed in further applications including but not limited to blending with diesel or kerosene after hydrotreating. Example - 3: In this example, a mixture of methanol and water is used as a first solvent and water is used as a decomposition solvent. 90g urea was taken in a three neck 500ml RB flask fitted with a mechanical stirrer. 140g methanol and lOg water (methanol and water solution was used as a first solvent) was added to the RB flask under continuous stirring. The temperature of the flask was maintained at 20°C for 20 minutes. 50g LLCGO was then added to the slurry in 5 minutes. The resultant slurry thus obtained was stirred at 400 rpm for 30 minutes. Thereafter, the slurry was kept for settling for 5 minutes without stirring and transferred to a vacuum filtration assembly to separate the solid urea-linear hydrocarbon adduct and to obtain a raffinate comprising un-adducted LLCGO and excess urea dissolved in water and methanol. The solid adduct was then stirred with 300g pentane (second solvent). The slurry thus obtained was subjected to filtration to obtain a washed solid adduct and a second solvent wash. The washed solid adduct was dried and dissolved in 50g water. 10.lg (20.2 wt%) of linear hydrocarbons were recovered from the decomposed urea solution. The purity level of the extracted linear hydrocarbons was 97%. The raffinate comprising the un-adducted LLCGO and the excess urea dissolved in water and methanol solution, and the second solvent wash were introduced in a separator and mixed together. The obtained resultant mixture was then separated into two layers under gravity. The bottom layer comprising the excess urea dissolved in water and methanol solution was further used for urea-linear hydrocarbon adduct formation. The top layer comprising the second solvent wash and the un-adducted LLCGO with some amount of methanol was sent to another separator where it was mixed with water to separate the methanol. The methanol free top layer was then sent to a distillation column where it was distilled at 100°C column bottom temperature. The second solvent wash in pure form (pentane) was recovered from the top of the distillation column. The un-adducted LLCGO obtained as a bottom stream was used as a hydrocarbon feed for other applications like blending with diesel or kerosene after hydrotreating. Example - 4: In this example, a mixture of methanol and water is used as a first solvent and a mixture of benzene and extracted linear hydrocarbon is used as a decomposition solvent. 90g urea was taken in a three neck 500ml RB flask fitted with a mechanical stirrer. 140g methanol and lOg water (methanol and water solution was used as a first solvent) was added to the RB flask under continuous stirring. The temperature of the flask was maintained at 20°C for 20 minutes. 50g LLCGO was then added to the slurry in 5 minutes. The resultant slurry thus obtained was stirred at 400 rpm for 30 minutes. The resultant slurry was kept for settling for about 5 minutes without stirring. The entire resultant slurry was then transferred to a vacuum filtration assembly to separate the solid urea-linear hydrocarbon adduct and to obtain a raffmate comprising un-adducted LLCGO and excess urea dissolved in methanol and water solution. The solid adduct was then stirred with 300g pentane (second solvent). The slurry thus obtained was subjected to filtration to obtain a washed solid adduct and a second solvent wash. The washed solid adduct was dried and mixed with 190 g decomposition solvent (solution of 114g benzene and 76g fluid linear hydrocarbons), and heated to 90°C in a closed container in water bath. The slurry thus obtained was shaken intermittently. The hot slurry was quickly filtered to separate the solid urea and to obtain the fluid linear hydrocarbons dissolved in the decomposition solvent. The solid urea was separated from the decomposition solvent comprising the additional weight fraction of fluid linear hydrocarbon and was washed with n-pentane to recover all benzene and the fluid linear hydrocarbons. The decomposition solvent comprising benzene and the fluid linear hydrocarbons was then subjected to distillation to recover the fluid linear hydrocarbons equivalent to that extracted from the urea-linear hydrocarbon adduct. After separation of benzene, 10.5g (21 wt%)additional fluid linear hydrocarbon (total 86.5g) was recovered. The purity of fluid linear hydrocarbons was 97%. The raffinate comprising the un-adducted LLCGO and excess urea dissolved in water and methanol solution and the second solvent wash were introduced in a separator and mixed together to obtain a resultant mixture. The resultant mixture got separated into two layers under gravity. The bottom layer comprising excess urea dissolved in water and methanol solution was further used for urea-linear hydrocarbon adduct formation. The top layer comprising the second solvent wash and the un-adducted LLCGO along with some amount of methanol was sent to another separator where it was mixed with water to separate the methanol. The methanol free top layer comprising the second solvent wash and the un-adducted LLCGO was then sent to a distillation column where it was distilled at 100°C column bottom temperature. The second solvent wash in pure form (pentane) was recovered from the top of the distillation column. The un-adducted LLCGO obtained as a bottom stream was used as a hydrocarbon feed for other applications like blending with diesel or kerosene after hydrotreating. Analysis of hydrocarbon feed and fluid linear hydrocarbons (n-Paraffin and n-Olefms (nPnO)) extracted by urea adduction process are given in Table - 1. Table-1: Hydrocarbon Feed and nPnO Product Analysis Properties Hydrocarbon Feed Extracted nPnO Remarks Density at 15°C 0.8264 0.759 ASTM D4052 Sulfur, wt% 1.17 0.046 ASTMD4294 Nitrogen, ppm 468 10 ASTM D4629 Color, Saybolt <-16 +18 ASTM D156 Moisture, ppm 274 97 UOP-481 Aromatics, wt% 25.56