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 a-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-paraffins. Molecular sieves provide extracted n-paraffins 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-Paraffins (C ₁₀ -C ₁ 4) is in the production of n-olefins for further producing LAB. The n-Paraffins 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 suggests 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 suggests 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 suggests 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, urea adduction is a well-known process for the extraction of linear hydrocarbons from complex hydrocarbon mixtures. However, urea adduction processes involve high operating cost as compared to other commercial processes. One of the significant contributors to the operating cost is the high energy requirement of the solvent recovery system.

Unlike the molecular sieve based process, the 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, 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 5.5 A 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 (<C ₆ ) facilitate less number of hydrogen bonds which make the adduct unstable above 25 °C.

United States Patent No. 5847209 suggests a urea adduction process for the removal of unwanted branched products, aromatic and sulfur compounds from petroleum refinery streams. The urea adduct is decomposed further into solid urea and linear hydrocarbons by mechanical shearing. The recovered solid urea is reused in the urea-adduction formation.

Indian Patent No. 162876suggests a urea adduction process for the separation of linear hydrocarbons from coker kerosene. Dichloromethane is used as a solvent for the urea-adduct formation and water is used to decompose the urea adduct product.

Further, United States Patent No. 3247177 suggests a continuous process for the extraction of linear hydrocarbons to decrease the freezing point of jet fuels. The process mentioned in the aforementioned US patent uses water as a solvent; methyl isobutyl ketone as a promoter; and alkyl benzene sulfonate as an emulsifying agent. Further, the process as mentioned in the aforementioned US patent uses a reactor containing granular particles of 4-20 mesh size for separation of urea-adduct from the un-adducted hydrocarbon and urea solution.

Therefore, there is felt a need to provide a process for the extraction of linear hydrocarbons wherein the problem of high operating cost associated with the conventional processes for extraction of linear hydrocarbons is minimized to a significant extent. OBJECTS

Some of the objects of the present disclosure are described herein below:

It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.

Another object of the present disclosure is to provide a process for the extraction of linear hydrocarbons from a hydrocarbon feed.

Still another object of the present disclosure is to provide a process for the extraction of linear hydrocarbons from a hydrocarbon feed that completely eliminates the use of heat energy during solvent recovery, thereby minimizing the high operation cost involved with the conventional extraction methods.

Yet another object of the present disclosure is to provide a process for the extraction of linear hydrocarbons from a hydrocarbon feed wherein some of the solvents used in the extraction process are used further without being subjected to any recovery methods.

A further object of the present disclosure is to provide a process for the extraction of linear hydrocarbons from a hydrocarbon feed wherein some of the solvents used in the extraction process are recovered by distillation using low temperature waste heat available from refineries.

A still further object of the present disclosure is to provide a process for the extraction of linear hydrocarbons from a hydrocarbon feed wherein some of the solvents used in the extraction process are recovered without requiring any heat energy and are used further in the extraction of linear hydrocarbons.

A yet further object of the present disclosure is to provide a simple and a cost efficient process for the extraction of linear hydrocarbons that provides extracted linear hydrocarbons with high purity and in high yield.

Other objects and advantages of the present invention will be more apparent from the following description when read in conjunction with the accompanying figure, which are not intended to limit the scope of the present invention. SUMMARY

In accordance with the present disclosure there is provided a process for the extraction of linear hydrocarbons from a hydrocarbon feed, the process comprising the following steps: i. admixing the hydrocarbon feed with a urea slurry, the urea slurry comprising urea dissolved in at least one first fluid medium, under constant agitation to form a first mixture comprising urea-linear hydrocarbon adduct;

ii. filtering the first mixture to obtain a first filtrate and a first residue comprising the urea-linear hydrocarbon adduct;

iii. washing the first residue with a first washing medium to obtain a first washed residue containing the urea-linear hydrocarbon adduct;

iv. treating the first washed residue with a decomposition medium comprising a mixture of at least one second fluid medium and at least one linear hydrocarbon to obtain a second mixture;

v. filtering the second mixture to obtain a second filtrate and a second residue containing a solid de-adducted urea;

vi. washing the second residue with a second washing medium to remove traces of hydrocarbons from the second residue to obtain washed urea;

vii. recycling a first portion of the second filtrate to the process step (iv) to be part of the decomposition medium; and

viii. distilling a second portion of the second filtrate to obtain a plurality of fractions of linear-hydrocarbons.

In accordance with the present disclosure, the solid de-adducted urea obtained in the process step (v) is recycled and/or reused in the process step (i).

In accordance with the present disclosure, the process for the extraction of linear hydrocarbons from a hydrocarbon feed further comprises the following steps so as to recover and reuse said first and second fluid media used during the extraction of linear hydrocarbons: i. mixing said urea-linear adduct and said first washing medium obtained after washing of the first residue in step (iii) to obtain a resultant mixture and separating said resultant mixture under gravity into a top layer and a bottom layer; ii. separating said top layer comprising the un-adducted hydrocarbon feed and said first washing medium, and the bottom layer comprising the excess urea slurry and traces of the un-adducted hydrocarbon feed;

iii. distilling said top layer to recover said first washing medium and the un-adducted hydrocarbon feed;

iv. recycling said first washing medium recovered at the end of process step (iii) to the process step of washing the urea-linear hydrocarbon adduct; and

v. recycling said bottom layer comprising the excess urea slurry and traces of the un- adducted hydrocarbon feed to the process step of urea-linear hydrocarbon adduct formation.

Further, the un-adducted hydrocarbon feed recovered at the end of process step (iii) is used in further applications including, but not limited to, blending with diesel or kerosene after hydrotreating.

In accordance with one embodiment of the present disclosure, the hydrocarbon feed comprises to Ceo hydrocarbons.

In accordance with one embodiment of the present disclosure, the linear hydrocarbon is at least one selected from the group consisting of hydrocarbons from to Ceo-

In accordance with one embodiment of the present disclosure, the first fluid medium is at least one selected from the group consisting of water, methanol, acetone, and mixtures thereof.

In accordance with one embodiment of the present disclosure, the amount of urea in said urea slurry ranges from 20 wt% to 80 wt%.

In accordance with one embodiment of the present disclosure, the second fluid medium is at least one selected from the group consisting of methanol, acetone, benzene, toluene, pentane, hexane and heptane.

In accordance with one embodiment of the present disclosure, the amount of the second fluid medium in said decomposition medium ranges from 30 wt% to 100 wt%

In accordance with one embodiment of the present disclosure, the amount of said linear hydrocarbon in said decomposition medium ranges up to 70 wt%. BRIEF DESCRIPTION OF THE ACCOMPNAYING DRAWING

Figure 1 of the accompanying drawings illustrates a flow diagram for the process for the extraction of linear hydrocarbons from a hydrocarbon feed, in accordance with the present disclosure.

DETAILED DESCRIPTION

The description herein after and 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.

Accordingly, the disadvantages allied with the extraction of linear hydrocarbons from a complex hydrocarbon mixture, as identified in the above described prior-art and other related references, such as high energy requirement, poor solvent recovery and high operation cost are minimized to a significant extent in the present disclosure by providing a process for the extraction of linear hydrocarbons from a hydrocarbon feed wherein solvents along with other reagents used in the extraction process are recovered considerably in high weight proportions without demanding any heat energy, and are recycled in the further extraction of linear hydrocarbons.

The process for the extraction of linear hydrocarbons from a hydrocarbon feed in accordance with present disclosure is described in detail below:

The separation of linear hydrocarbons from a hydrocarbon feed in accordance with the process of the present disclosure is based on the formation of urea-linear hydrocarbon adduct when a hydrocarbon feed comprising a complex mixture of linear and branched hydrocarbons of different carbon contents is admixed with urea. The linear hydrocarbons present in the hydrocarbon feed selectively form an adduct with urea and get separated from the hydrocarbon feed.

The process for the extraction of linear hydrocarbons in accordance with the process of the present disclosure comprises the method steps of admixing the hydrocarbon feed with urea slurry to form a first mixture comprising urea-linear hydrocarbon adduct, wherein the urea- slurry comprises urea dissolved in at least one first fluid medium; filtering the first mixture comprising the urea-linear hydrocarbon adduct to obtain a first filtrate and a first residue comprising the urea-linear hydrocarbon adduct; washing the first residue with a first washing medium to obtain a first washed residue containing the urea-linear hydrocarbon adduct; and treating the first washed residue with a decomposition medium that comprises a mixture of at least one second fluid medium and at least one linear hydrocarbon to obtain a second mixture, wherein the decomposition medium decomposes the first washed residue containing the urea- linear hydrocarbon adduct to obtain the linear hydrocarbons in substantially pure form.

In accordance with the present disclosure, the urea-slurry used herein is prepared by uniformly mixing a pre-determined weight proportion of urea in a first fluid medium. Urea is typically mixed in an excess amount varying from 20 to 80 wt%. The first fluid medium suitable for preparing the urea slurry includes at least one fluid medium that is selected from the group consisting of water, methanol and acetone.

In accordance with one of the embodiments of the present disclosure, the first fluid medium is a mixture of water and methanol in a weight proportion varying from 0 to 30 wt% and 70 to 100 wt , respectively.

The urea slurry is admixed with at least one hydrocarbon feed under constant agitation to obtain a resultant slurry. The agitation of the resultant slurry is continued for a predetermined period to obtain urea-linear hydrocarbon adduct. The agitation of the resultant slurry is typically accomplished at a temperature varying from 20 to 25°C at atmospheric pressure for a time period varying from 20 to 30 minutes.

The hydrocarbon feed used for the process of the present disclosure comprises to Ceo hydrocarbons and includes at least one hydrocarbon feed selected from the group consisting of light coker gas oil (LCGO), light light coker gas oil (LLCGO), heavy coker gas oil (HCGO), coker naphtha, FCC gas oil, FCC naphtha, straight run gas oil, and straight run naphtha. In accordance with one of the embodiments of the present disclosure, the hydrocarbon feed is a light light coker gas oil (LLCGO) comprising Cs to C ₂₂ hydrocarbons. In addition, the light coker gas oil comprises 5 to 50 wt% olefins, 0.5 to 3 wt% sulfur and 100 to 1000 ppm nitrogen.

As compared to the conventional processes, the process for the extraction of linear hydrocarbons according to the present disclosure is tolerant to olefin, sulfur and nitrogen compounds. The process of the present disclosure therefore advantageously eliminates the need for pre-treating the hydrocarbon feed.

While admixing the hydrocarbon feed and the urea slurry together, the linear hydrocarbons present in the hydrocarbon feed form a solid adduct with the urea. Some weight fractions of the linear hydrocarbons and all non-linear hydrocarbons (branched) remain in un-adducted form. Therefore, the resultant slurry comprising the urea-linear hydrocarbon adduct also comprises un-adducted hydrocarbons and excess urea slurry at the end of the run. The urea- linear hydrocarbon adduct thus formed is then separated from the resultant slurry. The separation of the urea-linear hydrocarbon adduct is typically accomplished either by filtration or centrifugation. In accordance with one of the embodiments of the present disclosure, the resultant slurry is subjected to filtration to obtain the urea-linear hydrocarbon adduct and to obtain a first filtrate and a first residue comprising the urea-linear hydrocarbon adduct. The first residue comprising the urea-linear hydrocarbon adduct in accordance with the present disclosure comprises the un-adducted hydrocarbons. The first residue comprising the urea- linear hydrocarbon adduct is further processed to recover the linear hydrocarbons.

The first residue comprising the urea-linear hydrocarbon adduct is then washed with a first washing medium to remove impurities present therein. The first washing medium used for washing the urea-linear hydrocarbon adduct typically includes a low boiling point fluid. Examples of first washing medium that are suitable for the process of the present disclosure include at least one fluid medium selected from the group consisting of methanol, acetone, benzene, toluene, pentane, hexane and heptane. In accordance with one of the embodiments of the present disclosure, the first washing medium is pentane. The first washing medium and the urea-linear hydrocarbon adduct are preferably mixed under constant stirring for a predetermined period at room temperature and atmospheric pressure. The slurry thus formed is then subjected to either filtration or centrifugation to separate the washed urea-linear hydrocarbon adducts and to collect the used first washing medium. The inventors of the present disclosure suggest multistage washing of the urea-linear hydrocarbon adduct for maximum removal of the impurities present therein.

The next process step includes a de-adduction step wherein the linear hydrocarbons are separated from the washed urea-linear hydrocarbon adduct. Separation of the linear hydrocarbons is typically accomplished by decomposing the urea-linear hydrocarbon adduct. The decomposition of the adduct in accordance with the process of the present disclosure typically involves dissolution of the adduct in a decomposition medium. The inventors of the present disclosure advantageously use a fluid medium as the decomposition medium that has high solubility for linear hydrocarbons.

Conventional methods reported hitherto mainly comprise the use of water for decomposition of the urea adduct, as water possess high solubility for urea. Also, the aqueous urea solution is easily separable from the linear hydrocarbons. The aqueous urea solution comprises excess of water, which needs to be completely removed before the urea is recycled. Nevertheless, the removal of excess amount of water requires high amounts of heat energy, which further adds to the operating cost. Therefore, in order to dissipate the heat energy requirement, the inventors of the present disclosure advantageously use a mixture of aromatic fluids and fluid linear hydrocarbons as a decomposition medium to decompose the urea-linear hydrocarbon adduct. The decomposition medium used for the process of the present disclosure has high solubility for linear hydrocarbons as compared to the urea.

The washed residue comprising the urea-linear hydrocarbon adduct in accordance with the process of the present disclosure is then mixed with a decomposition medium comprising a mixture of at least one second fluid medium and at least one linear hydrocarbon. At least one second fluid medium includes at least one fluid medium selected from the group consisting of water, methanol, acetone, benzene and toluene.

In accordance with one of the embodiments of the present disclosure, the decomposition medium is a mixture of benzene and the fluid linear hydrocarbon in a weight proportion varying from 30 to 100 wt% and 0 to 70 wt , respectively. In accordance with one of the embodiments of the present disclosure, the weight fraction of benzene and the fluid linear hydrocarbon is 60 wt% and 40 wt , respectively.

The first residue comprising the urea-linear hydrocarbon adduct when mixed with the decomposition medium, decomposes into urea and at least one linear hydrocarbon. The de- adducted urea thus obtained is in solid form and remains insoluble in the decomposition medium, whereas the at least one linear hydrocarbon extracted from the urea-linear hydrocarbon adduct get dissolved in the decomposition medium. The linear hydrocarbon(s) extracted from the hydrocarbon feed in accordance with the present disclosure are in the form of liquid or solid, and has good solubility in the decomposition medium. The decomposition medium thus obtained at the end of the de-adduction step comprises a mixture of benzene and the linear hydrocarbon(s).

The de-adducted urea being in solid form is then separated from the decomposition medium. The separation of the de-adducted urea from the decomposition medium is carried out either by centrifugation or vacuum filtration. The separated (in case of filtration the second residue) de-adducted urea is further washed with a second washing medium to remove traces of hydrocarbons, if any, and recycled to the urea-linear hydrocarbon adduct formation step for adduct formation with a fresh hydrocarbon feed.

The decomposition medium collected (as a second filtrate) after separating the solid de- adducted urea comprises additional weight fraction of the linear hydrocarbon(s) equivalent. The total weight proportion of the fluid linear hydrocarbon(s) in the decomposition medium, after separating the solid de-adducted urea (residue), ranges from 5 to 70 wt%.

A first portion of the decomposition medium that comprises benzene and the fluid linear hydrocarbon(s) is then recycled to the de-adduction method step whereas a remaining second portion is directly sent to an alkylation reactor where both benzene and the fluid linear hydrocarbon(s) such as n-olefins react to form linear alkyl benzene. Alternatively, the second portion is sent to a distillation column to recover the fluid linear hydrocarbon(s) that is extracted from the urea-linear hydrocarbon adduct and are used for washing the solid de- adducted urea, respectively. If the former process step is used, there is no need to have a distillation column and this further reduces the operating cost. However, in the latter process step, the amount of benzene and the fluid linear hydrocarbon(s) requiring distillation is significantly small. A small portion of the recovered fluid linear hydrocarbon(s) is used for washing the solid de-adducted urea and the remaining portion is sent as a final product.

The weight fraction of the first portion and the second portion of the decomposition medium typically varies from 30 to 100 wt% and 0 to 70 wt , respectively. The first portion of the decomposition medium, which is recycled to the method step of de-adduction is a mixture of benzene and fluid linear hydrocarbon(s).

In accordance with the present disclosure, the fluid linear hydrocarbon(s) comprise to Ceo hydrocarbons.

The process in accordance with the present disclosure further comprises the steps of recovering and re -using the first and second fluid media used in various process steps during the extraction of linear hydrocarbons. The first washing medium obtained by washing the first residue in accordance with the process of the present disclosure is mixed with the urea- linear adduct and the excess urea dissolved in the first fluid medium. The obtained resultant mixture is then introduced in a separator where the resultant mixture gets separated into a top layer and a bottom layer. The separation of the resultant mixture into two layers is accomplished under gravity and without requiring any heat energy. The bottom layer consisting of the excess urea first fluid medium slurry and traces of the un-adducted hydrocarbons is recycled to the process step of urea-linear hydrocarbon adduct formation for adduct formation with a fresh hydrocarbon feed and the recycled solid de-adducted urea. The top layer consisting of the un-adducted hydrocarbons and the first washing medium is sent to a distillation column maintained at low re-boiler temperature. The distillation of the top layer separates a majority of the first washing medium from the un-adducted hydrocarbons via column top. The heat requirement during distillation of the top layer is fulfilled either by low pressure (LP) steam or by various refinery streams, which have waste heat in the temperature range of 100 - 150°C. Heat recovery from these streams is not economical due to their lower temperature and generally, these streams are cooled by fin fan coolers in the refinery, which consumes electric energy. The first washing medium, recovered in pure form from the top of the distillation column, is used as the first washing medium for washing the urea-linear hydrocarbon adduct. The bottom stream comprising the un-adducted hydrocarbons is used as a hydrocarbon stream in further applications including but not limited to blending with diesel or kerosene after hydrotreating.

In one particular embodiment, the process of the present disclosure is further illustrated in Figure- 1 of the accompanying drawings. The stream of hydrocarbon feed containing linear hydrocarbons 1, such as n-paraffin and n-olefins, is charged into a reactor (R-01) containing an aqueous methanolic solution of urea (mixture of water and methanol represents the first fluid medium). The temperature of the reactor (R-01) is maintained at 20 -25°C. The urea solution together with the hydrocarbon feed is intimately mixed under continuous agitation by a mechanical agitator (M-01) to obtain a first mixture. After certain time, a solid adduct product of urea and linear hydrocarbon starts forming. As the adduct forms in the reaction, viscosity of the first mixture increases. The total residence time of the first mixture in the reactor (R-01) is in the range of 20-30 minutes. Thereafter, the first mixture comprising the adduct is discharged via stream 2 and pumped by a pump (P-01) to a pressure tight rotary drum filter (F-01) for separation. The first mixture is filtered to isolate the adduct (first residue) and to obtain a first filtrate (or raffinate). The so obtained first filtrate consisting of un-adducted hydrocarbons and excess urea dissolved in the aqueous methanolic solution is discharged via stream 4. The first filtrate is then conveyed to a first separator vessel (S-01) at its inlet (20).

The isolated solid adduct (first residue) is discharged from the drum filter (F-01) via stream 3 and conveyed by means of a belt (Belt - 1) to a first washing reactor (R-02) where it is washed with a first washing medium to remove the un-adducted impurities present therein. The washed first residue can be directly used. However, for maximum removal of un- adducted impurities the inventors of the present disclosure suggest two stage washing and filtration. However, in order to minimize the consumption of the first washing medium in two stage washings, the first stage washing is typically accomplished by re-using the first washing medium obtained after washing the first residue. The adduct received in the first washing reactor (R-02) is homogenously stirred with the first washing medium for 10 minutes by means of a mechanical agitator (M-02) at room temperature and atmospheric pressure. The first mixture thus formed is discharged via stream 5 and pumped by a pump (P-02) to a pressure tight rotary filter (F-02). The first mixture is filtered to isolate the first stage washed adduct (first residue) and to obtain a first filtrate. The first filtrate of first stage washing is discharged from the rotatory filter (F-02) via stream 7 and conveyed to the first separator (S- 01) at its inlet 20 for further processing. The first stage washed solid adduct (first residue) is discharged from the rotatory filter (F-02) via stream 6. The stream 6 is conveyed by means of a belt (Belt - 2) to a second washing reactor (R-03). The washed adduct (first washed residue) is again washed for 10 minutes in the second washing reactor (R-03) with the first washing medium received from distillation columns C-02 and C-03. The washed adduct is homogenously stirred with the first washing medium in the second washing reactor (R-03) by means of a mechanical agitator (M-03).The intermediate mixture formed in the second washing reactor (R-03) is discharged via stream 8 and pumped by a pump (P-03) to a pressure tight rotary filter (F-03). In the rotary filter (F-03) the intermediate mixture is filtered to isolate a solid adduct (intermediate residue) and to obtain the intermediate filtrate. The intermediate filtrate is discharged from the rotary filter (F-03) via stream 9. This first washing medium is returned to the first washing reactor (R-02) along with fresh first washing medium stream 30 via stream 31 for the first stage washing of the adduct product.

The second stage washed solid adduct (intermediate residue) is discharged from the rotary filter (F-03) via stream 10 and conveyed by means of a belt (Belt -3) to a de-adductor reactor (R-04). The second stage washed solid adduct is homogenously mixed by means of a mechanical agitator (M-04) with a hot solution of benzene and first fluid linear hydrocarbons (n-paraffin and n-olefin) (hereinafter refer as a decomposition medium) in the de-adductor reactor (R-04). The benzene and the linear hydrocarbon are admixed in the weight proportion of 60 wt% and 40 wt , respectively, to obtain the first decomposition medium. Upon mixing with the decomposition medium, the adduct de-adducts/decomposes into solid urea and linear hydrocarbons. Since urea is insoluble in the decomposition medium, the entire de-adducted urea remains in solid phase. The solid de-adducted urea along with the decomposition medium is discharged via stream 11 and pumped by means of a pumping means (P-04) to a centrifuge (F-04), where the solid de-adducted urea is separated from the decomposition medium. The solid de-adducted urea is then washed with a second washing medium (that in present case can be a hot fluid linear hydrocarbons recovered from the bottom of distillation column (C-01) through stream 18), to remove all benzene. The washed solid urea (second residue) is discharged via stream 13 and conveyed by means of a belt (Belt - 4) to the reactor (R-01). The washed solid urea is recycled for forming adduct with fresh hydrocarbon feed. The decomposition medium (second filtrate) is discharged via stream 12 and collected in a vessel (V-01). The decomposition solvent (second filtrate) is pumped from the vessel (V-01) by means of pumping means (P-05). A first portion 15 of the decomposition medium from the centrifuge (F-04) is recycled to the de-adductor reactor (R-04) via stream 19 by pumping means (P-06) for de-adduction/decomposition of another batch of adduct product. A second portion 14 of the decomposition medium is conveyed to the distillation column (C-01) via a heat exchanger (E-02) to recover the linear hydrocarbons that are extracted from the adduct in the decomposition step in the de-adductor reactor (R-04) and are used for washing the solid de-adducted urea, respectively. The linear hydrocarbons stream 16 discharged from the bottom of the column (C-01) is pumped by the pumping means (P-07) through the heat exchanger (E-02). A small weight fraction 18 of the recovered fluid linear hydrocarbons stream 16, equivalent to the amount of the third fluid linear hydrocarbons, is conveyed to the centrifuge (F-04) for washing the solid de-adducted urea. The remaining portion of the recovered linear hydrocarbon is discharged via the heat exchanger (E-02) as a final product. The distillate stream 17 from the distillation column (C-01) is combined with the second fluid medium stream 15 and conveyed to the de-adductor reactor (R-04).

Alternatively, a small fraction of the decomposition medium from centrifuge (F-04) is directly sent to an alkylation reactor for conversion of the fluid linear hydrocarbons (linear olefins) into linear alkyl benzene. If this route is followed, the requirement of distillation column (C-01) is eliminated and hence the operating cost of the process is reduced.

The first residue from the drum filter (F-01) (obtained via the stream 4) and the first washing medium of first stage washing from the rotary filter (F-02) (obtained via the stream 7) are mixed in the first separator (S-01). The resultant mixture thus obtained is then separated into two layers under gravity. The bottom layer containing the excess urea dissolved in the aqueous methanolic solution (urea slurry) and trace amounts of un-adducted hydrocarbons is recycled to the reactor (R-01) via the stream 21 by means of a recycle pump (P-08) for further adduct formation with fresh hydrocarbon feed and the recycled solid de-adducted urea from the centrifuge (F-04). The top layer containing the first washing medium of first stage washing and the un-adducted hydrocarbons with some amount of methanol is discharged via outlet 22. The top layer from the first separator (S-01) is conveyed to a second separator (S- 02) by pumping means (P-09). In the second separator (S-02), the top layer is mixed with small amount of water (received through stream 23) to separate the methanol. The water methanol mixture thus obtained is similar to the solvent required in adduct formation in the reactor (R-01), this mixture is discharged via stream 24 and pumped by pumping means (P- 10) to a collection tank,(not shown) for use as make-up for solvent loss. The mixture of methanol free un-adducted hydrocarbons and the first washing medium of first stage washing is discharged via stream 25, and is then conveyed to the distillation column (C-02) via a heat exchanger (E-01). The mixture is distilled to recover a majority of the second solvent wash of the first stage washing at ~100°C column bottom temperature. In this column, the inventors of the present disclosure have tried to minimize the bottom temperature so that low temperature waste heat from a refinery can be used. The first washing medium of first stage washing is recovered in pure form from the top of the column (C-02) via stream 27 to be conveyed to the second washing reactor (R-03) for second stage washing of the first stage washed solid adduct. The bottom layer 26 from the column (C-02) containing the un- adducted hydrocarbons and small amounts of the first washing medium of the first stage washing is conveyed to another distillation column (C-03) where the remaining first washing medium of the first stage washing is recovered from the top of the column (C-03) via stream 28. The bottom layer 29 is discharged from the bottom of the column (C-03). The streams 27 and 28 are combined into a stream 30, which is fed to the second washing reactor (R-03) for second stage washing of the first stage washed adduct. The stream 29 containing the un- adducted hydrocarbons is discharged via the heat exchanger (E-01). The cooled un-adducted hydrocarbons stream 31 obtained from the heat exchanger (E-01) can be pumped by pumping means (P-ll) for use in further applications including but not limited to blending with diesel or kerosene after hydrotreating.

The process for the extraction of linear hydrocarbons in accordance with the present disclosure is typically accomplished under very mild operating conditions, for example, at near atmospheric pressure and temperature <100°C. Further, the process of the present disclosure does not require any specialized and costly hardware for high pressure, high temperature and high complexity processes. This makes the process of the present disclosure superior to other commercial processes in terms of capital expenditure.

The linear hydrocarbons extracted in accordance with the process of the present disclosure are analyzed for purity level measurement. The purity of fluid linear hydrocarbons extracted from the hydrocarbon in accordance with the process of the present disclosure does not get affected by olefin, sulfur and nitrogen contents present in the feed. In fact, >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, 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 fluid medium 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 filtrate comprising un-adducted LLCGO and excess urea dissolved in water. The solid adduct was then stirred with 300g pentane (first washing medium). The slurry thus obtained was subjected to filtration to obtain a washed solid adduct (first residue) and a second solvent wash (first filtrate). The washed and dried solid adduct (first residue) was then dissolved in 50g water (decomposition medium) 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 filtrate comprising the un-adducted LLCGO, the excess urea dissolved in water and the first washing medium after 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 first wash medium after wash and the un- adducted LLCGO was sent to a distillation column where it was distilled at 100 °C column bottom temperature. The first wash medium after 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 (residue) and to obtain a filtrate comprising un-adducted LLCGO and excess urea dissolved on methanol. The solid adduct was stirred with 300g pentane as a first washing medium and was filtered to obtain washed solid adduct and the first washing medium after wash. The solid washed adduct was dried. The dried solid adduct was then dissolved in 50g water (decomposition medium) 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 filtrate (comprising the un-adducted LLCGO and the excess urea dissolved in methanol) was mixed with the first washing medium after 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 medium), 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 (first residue) and to obtain a first filtrate 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 first washing medium. 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 filtrate comprising the un-adducted LLCGO and the excess urea dissolved in water and methanol solution, and the first washing medium after 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 fluid medium and a mixture of benzene and extracted linear hydrocarbon is used as a decomposition medium.

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 (residue) and to obtain a filtrate comprising un-adducted LLCGO and excess urea dissolved in methanol and water solution. The solid adduct was then stirred with 300g pentane (first washing medium). The slurry thus obtained was subjected to filtration to obtain a washed solid adduct (second residue) and a used first washing medium. 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 linear hydrocarbons dissolved in the decomposition medium. The solid urea was separated from the decomposition medium comprising the additional weight fraction of a linear hydrocarbon and was washed with n-pentane to recover all benzene and the fluid linear hydrocarbons. The decomposition medium comprising benzene and the at least one linear hydrocarbon 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 filtrate comprising the un-adducted LLCGO and excess urea dissolved in water and methanol solution and the used first washing medium 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 used first washing medium 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 used first washing medium and the un-adducted LLCGO was then sent to a distillation column where it was distilled at 100°C column bottom temperature. The used first washing medium 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-Olefins (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 ASTM D4294

Nitrogen, ppm 468 10 ASTM D4629

Color, Saybolt <-16 +18 ASTM D156

Moisture, ppm 274 97 UOP-481

Aromatics, wt% 25.56 <lwt% IP-391

nPnO, % 24.5 96.6 DHA ASTM

D6730

Initial Boiling 134.4 55.8

point

1% 142.3 146.3 High temperature

5% 167.1 172.4 Simulated

10% 176.6 186.5 distillation

20% 192.2 196.4 analysis

30% 200.4 209.3 ASTM D7169

40% 211.6 216.6

50% 218.8 218.5 60% 228.0 235.4

70% 235.8 236.8

80% 246.7 254.1

90% 256.5 263.4

95% 264.5 271.1

98% 269.7 272.2

99% 276.0 289.6

Final Boiling 298.9 319.8

Point

Detailed Hydrocarbon Analysis (DHA) of hydrocarbon feed and nPnO recovered by urea adduction process are given in Table - 2. The hydrocarbon feed used in the processes of examples- 1, 2, 3 and 4 contained 24.44% total nPnO. The total nPnO in the extracted product were 96.6%.

Table - 2: DHA analysis of Hydrocarbon Feed and nPnO

In examples 1, 3 and 4, the resultant mixture comprising the filtrate (mixture of the un- adducted LLCGO and the excess urea dissolved in the first solvent) and the used first washing medium does not need any distillation to separate the excess urea dissolved in the first solvent from the un-adducted LLCGO. The un-adducted LLCGO having more affinity for the used first washing medium (pentane) compared to the first fluid medium (water/water- methanol solution) got extracted into the used first washing medium. Since, the used first washing medium comprising the extracted un-adducted LLCGO and the aqueous/aqueous methanolic solution of urea are immiscible, therefore the resultant mixture got separated into two layers under gravity and does not require any heat energy. The bottom layer containing aqueous/aqueous methanolic urea solution is directly recycled back for adduction of fresh hydrocarbon feed.

In examples- 1, 2 and 3, the energy requirement for removal of decomposition solvent (water) is very high whereas, in example 4 the energy requirement for removal of decomposition medium (Benzene + nPnO mixture) is significantly reduced which can be further minimized if the benzene and nPnO mixture is directly sent for alkylation.

Table 3 gives a comparison of yield, purity and energy requirement per ton of nPnO.

Table - 3: Comparison of yield, purity & energy requirement for Example 1 - 4

Example nPnO nPnO Energy requirement for Energy Remarks No. Yield, Purity separation of excess urea requirement for

wt% wt% dissolved in distillation of

water/methanol/water- decomposition

methanol solution from a solvent ,

mixture of un-adducted GCal/Ton of

LCGO and used first nPnO

washing medium,

GCal/Ton of nPnO

Yield and! purity are

Example - 1 0.8 38.0 very low;

high energy requirement

Highest

Example - 2 21.3 96.8 energy

requirement

Example - 3 20.2 97.0 High energy requirement

Lowest

Example- 4 21.0 97.0 0 0.5 energy

requirement

Thus, example-4 requires lowest amount of energy for obtaining nPnOin high yield and with high purity.

TECHNICAL ADVANCEMENT

The present disclosure related to "a method for extraction of linear hydrocarbons from a hydrocarbon feed" has following technical advancements:

• Simple and cost efficient process for extraction of linear hydrocarbons from hydrocarbon feed.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a statement in the specification specific to the contrary.

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.