Claims:WE CLAIM:
1. A process for obtaining isoparaffins having low sulphur and nitrogen value from linear hydrocarbons, said process comprising:
i. charging a reactor with said linear hydrocarbons, and at least one hydrotreating catalyst to obtain a first mixture;
ii. introducing hydrogen into said reactor until pressure in said reactor is in the range of 1000 kPa to 10000 kPa to obtain a second mixture;
iii. heating said second mixture at a predetermined temperature to obtain a product mixture comprising n-paraffins, and isoparaffins; and
iv. separating said isoparaffins from said product mixture by passing said product mixture through a bed of molecular sieves to obtain isoparaffins having purity more than 90 %;
wherein the combined content of sulphur and nitrogen in said isoparaffins is below 3 ppm.
2. The process as claimed in claim 1, wherein said linear hydrocarbons comprises n-paraffins in the range of 70 wt% to 80 wt%, n-olefins in the range of 15 wt% to 30 wt%, and isoparaffins in the range of 3 wt% to 10 wt%.
3. The process as claimed in claim 1, wherein the sulphur and nitrogen content in said linear hydrocarbons is in the range of 100 ppm to 500 ppm and 8 ppm to 30 ppm, respectively.
4. The process as claimed in claim 1, wherein said hydrotreating catalyst is at least one selected from the group consisting of Ni-Mo catalyst, Co-Mo catalyst, and Ni-Co-Mo catalyst.
5. The process as claimed in claim 1, wherein said predetermined temperature is in the range of 150 °C to 450 °C.
6. The process as claimed in claim 1, wherein said molecular sieves are 5A type.

, Description:This is an application for a patent of addition to the Indian patent application No. 700/MUM/2014 filed on 27th February 2014, the entire contents of which are specifically incorporated herein by reference.
FIELD
The present disclosure relates to a process for obtaining isoparaffins from linear hydrocarbons.
DEFINITIONS
As used in the present disclosure, the following term is generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
The term ‘Linear hydrocarbon’ for the purpose of the present disclosure refers to a straight chain saturated hydrocarbon.
The term ‘Molecular sieves’ for the purpose of the present disclosure refers to a crystalline substance (as a zeolite) characterized by uniformly sized pores of molecular dimension that can adsorb small molecules and is used especially in separations.
BACKGROUND
A linear hydrocarbon possesses several high value applications such 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 practiced at industrial scales to expedite the extraction/recovery of linear hydrocarbons from crude hydrocarbon feeds.
Urea adduction for separation of n-paraffins from the hydrocarbon stream is a well-known process. The maximum purity of n-paraffin in the urea adduction process is invariably below 98 % as the terminally branched isoparaffins also get adducted along with n-paraffins. Lower adduction temperature improves the yield of n-paraffins, however, it further reduces the purity by facilitating adduction of terminally branched isoparaffins. Molecular sieve based process produces high purity n-paraffins having purity more than 99 %. However, presence of sulfur and nitrogen in the hydrocarbon feed are detrimental to molecular sieves. Therefore, the molecular sieve based process requires stringent feed specifications.
The Indian Patent application No. 700/MUM/2014 discloses a cost effective process for the extraction of linear hydrocarbons from a hydrocarbon feed. The process for extraction of linear hydrocarbons completely eliminates the use of heat energy during solvent recovery, thereby reducing the operation cost involved with the conventional extraction methods. However, the process as disclosed in 700/MUM/2014 does not suggest separation of isoparaffins and n-paraffins from linear hydrocarbons.
Conventionally, isoparaffins are prepared by Fischer–Tropsch process. However, the processes available to prepare and/or separate the isoparaffins are not economical.
Isoparaffins are used in several high value applications in various industries e.g. metal working, paints, inks, dry cleaning, paper, photocopy, sprays, aerosol, fragrant, polishes, detergents, etc. Due to these high value applications isoparaffins are sold at prices higher than that of normal paraffins.
Therefore, there exists a need to develop a process for obtaining isoparaffins.
OBJECTS
Some of the objects of the present disclosure, of which at least one embodiment is adapted to provide, 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.
An object of the present disclosure is to provide a simple and a cost effective process to obtain isoparaffins.
Another object of the present disclosure is to provide isoparaffins having low sulphur and nitrogen value.
Other objects and advantages of the present disclosure will be more apparent from the following description which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to a process for obtaining isoparaffins having low sulphur and nitrogen value from linear hydrocarbons. The process comprises charging a reactor with linear hydrocarbons, and at least one hydrotreating catalyst to obtain a first mixture. Hydrogen is introduced into the reactor until pressure in said reactor is in the range of 1000 kPa to 10000 kPa to obtain a second mixture. The second mixture is heated at a predetermined temperature to obtain a product mixture comprising n-paraffins, and isoparaffins. The isoparaffins are separated from the product mixture by passing through a bed of molecular sieves to obtain isoparaffins having purity more than 90 %. The combined content of sulphur and nitrogen in so obtained isoparaffins is below 3 ppm.
DETAILED DESCRIPTION
Isoparaffins are used in several high value applications in various industries e.g. metal working, paints, inks, dry cleaning, paper, photocopy, sprays, aerosol, fragrance, polishes, detergents etc. Due to these high value applications isoparaffins are sold at prices higher as compared to normal paraffins. However, no commercial process is available to separate these isoparaffins in an economical manner.
The present disclosure envisages a simple and an economical process to obtain isoparaffins.
In accordance with the present disclosure there is provided a process for obtaining isoparaffins having low sulphur and nitrogen value from linear hydrocarbons. The process comprising the following steps:
A reactor is charged with linear hydrocarbons and at least one hydrotreating catalyst to obtain a first mixture.
In accordance with an embodiment of the present disclosure, the linear hydrocarbons comprises n-paraffins in the range of 70 wt% to 80 wt%, n-olefins in the range of 15 wt% to 30 wt%, and isoparaffins in the range of 3 wt% to 10 wt%.
In accordance with an embodiment of the present disclosure, the linear hydrocarbons comprise the sulphur and nitrogen content in the range of 100 ppm to 500 ppm and 8 ppm to 30 ppm, respectively. The linear hydrocarbons are extracted from the hydrocarbon feed by urea adduction process. The adduction process comprises mixing urea with at least one first fluid medium under stirring to obtain a slurry. The hydrocarbon feed is added to the so obtained slurry under stirring to obtain urea-linear hydrocarbon adducts and a raffinate. The so obtained adducts are separated from the raffinate to obtain separated adducts. The separated adducts are washed with at least one second fluid medium, followed by drying to obtain dried adducts. The so obtained dried adducts are mixed with at least one third fluid medium to obtain linear hydrocarbons comprising n-paraffins, n-olefins, and isoparaffins.
The hydrocarbon feed comprises C6 to C60 hydrocarbons which 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.
The first fluid medium is at least one selected from the group consisting of water, methanol, and acetone.
The second fluid medium is at least one selected from the group consisting of methanol, acetone, benzene, toluene, pentane, hexane, heptane, and nonane.
The third fluid medium is at least one selected from the group consisting of water, methanol, acetone, benzene, and toluene.
In accordance with an embodiment of the present disclosure, the hydrotreating catalyst is at least one selected from the group consisting of Ni-Mo catalyst, Co-Mo catalyst, and Ni-Co-Mo catalyst.
Thereafter, hydrogen gas is introduced into the reactor until pressure in the reactor is in the range of 1000 kPa to 10000 kPa to obtain a second mixture.
The second mixture is heated at a predetermined temperature to obtain a product mixture comprising n-paraffins, and isoparaffins.
The hydrogenation reaction is represented by Scheme-I as given below:

n-paraffin n-olefin isoparaffins n-paraffin isoparaffin
wherein, R, R1, R2, and R3 are normal alkanes represented by CnH2n+1, wherein n is an integer in the range of 6 to 58.
The linear hydrocarbons comprising n-paraffins, n-olefins, and isoparaffins are hydrogenated at a predetermined temperature in presence of hydrotreating catalyst to convert n-olefins to n-paraffins, which increases the total amount of n-paraffins from its initial amount. Further, due to catalytic hydrogenation the sulphur and nitrogen content of the linear hydrocarbons gets converted into hydrogen sulphide and ammonia. Hence, the sulphur and nitrogen content of the n-paraffins and isoparaffins are reduced after hydrotreatment process.
In accordance with an embodiment of the present disclosure, the predetermined temperature is in the range of 150°C to 450°C.
The isoparaffins with reduced content of sulphur and nitrogen are separated from the n-paraffins by passing the product mixture through a bed of molecular sieves to obtain isoparaffins having purity of more than 90 %. The so obtained isoparaffins have combined content of sulphur and nitrogen below 3 ppm.
The separation of isoparaffins from the product mixture is represented by Scheme-II as given below:

n-paraffin isoparaffin complex of n-paraffin and isoparaffin
molecular sieves

wherein, R, R2, and R3 are normal alkanes represented by CnH2n+1, wherein n is an integer in the range of 6 to 58; and symbol (:) denotes that the n-paraffins are adsorbed on molecular sieves.
The product mixture comprising n-paraffins and isoparaffins is passed through a bed of molecular sieves which adsorbs n-paraffin on the surface of molecular sieves to obtain isoparaffins.
In accordance with an embodiment of the present disclosure, the molecular sieves are 5A type.
Typically, the product mixture, which comprises 95 wt% to 97 wt% of n-paraffins and remaining 3 wt% to 5 wt% of isoparaffins, obtained by hydrotreating process, is fed to a bed of molecular sieves where the n-paraffins are trapped in the pores of the molecular sieve to obtain isoparaffins. After complete adsorption of n-paraffin in the pores of molecular sieve, the molecular sieve is washed with a washing solvent such as iso-octane to remove any iso-paraffin or other impurities present in the void space. Then the adsorbed n-paraffins are desorbed from the pores of molecular sieve by a desorption solvent such as a mixture of n-pentane and iso-octane.
The high content of sulphur and nitrogen is hazardous to the molecular sieves. The n-paraffins and isoparaffins extracted by the process of the present disclosure have low content of sulphur and nitrogen and hence, the process of the present disclosure to extract isoparaffins is not detrimental to the molecular sieves.
The effectiveness of the extraction process is due to the combination of the process steps such as urea adduction, hydrotreating process, and separation process using a molecular sieve. The urea adduction process is employed for separating linear hydrocarbons such as n-paraffin, n-olefin, and isoparaffin, hydro-treatment of the linear hydrocarbons is employed to convert n-olefin to n-paraffin, and to reduce the sulphur and nitrogen content of the linear hydrocarbons, and separation using a molecular sieve is performed to obtain n-paraffin streams and isoparaffin streams. The combined use of the processes such as urea adduction process, hydrotreating process, and molecular sieve bed separation process synergistically produces high value isoparaffins as by product.
Overall, the process for obtaining high value isoparaffins from linear hydrocarbons is simple and cost effective.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
EXPERIMENTAL DETAILS
Example 1: Process for extracting linear hydrocarbons from a hydrocarbon feed
90 g urea was taken in a three neck 500 ml Round-bottom flask (RBF) fitted with a mechanical stirrer. 140 g methanol and 10 g water (methanol and water mixture) were added to the RBF under continuous stirring at 20 °C for 20 minutes to obtain a slurry. Thereafter, 50 g LLCGO (Light light coker gas oil) was added to the slurry over a time period of 5 minutes to obtain a mixture comprising solid urea-linear hydrocarbon adducts. The so obtained mixture was then stirred at 400 rpm for 30 minutes. The mixture was then allowed to settle for 5 minutes and thereafter transferred to a vacuum filtration assembly to separate the solid urea-linear hydrocarbon adducts from the raffinate comprising un-adducted LLCGO and excess urea in the methanol and water mixture. The solid urea-linear hydrocarbon adducts were washed with 300 g pentane and was filtered to obtain washed solid urea-linear hydrocarbon adducts and the pentane wash. Further, the solid washed urea-linear hydrocarbon adducts were dried to obtain dried solid urea-linear hydrocarbon adducts. The dried solid urea-linear hydrocarbon adducts were then dissolved in 150 g benzene in a closed container in a water bath to decompose the dried solid urea-linear hydrocarbon adducts to obtain a urea slurry and linear hydrocarbons having purity of 97 %. From the analysis of the linear hydrocarbons, it was found that the sulphur content in the linear hydrocarbons was 485 ppm and nitrogen content was 8 ppm.
The Detailed Hydrocarbon Analysis (DHA) of extracted linear hydrocarbons was performed and it was found that the linear hydrocarbons comprised n-paraffins in an amount of 75.5 wt%, n-olefins in an amount of 21.1 wt%, and isoparaffins in an amount of 3.4 wt%.
Example 2A: Process for obtaining high value isoparaffins having low sulphur and nitrogen content from linear hydrocarbons of Example 1
The linear hydrocarbons, comprising n-paraffins, n-olefins, and iso-paraffins, of example 1 were passed through a fixed bed reactor having 8 g hydrotreating catalyst. The hydrogen pressure of the reactor was maintained at 5400 kPa and the temperature was maintained at 330?C to obtain a product mixture comprising n-paraffins and isoparaffins.
The sulphur content and nitrogen content of the n-paraffins and isoparaffins were determined using gas chromatography. The sulphur content and the nitrogen content of the isoparaffins were found to be 1.2 ppm and 1.6 ppm, respectively. The combined sulphur content and the nitrogen content of the isoparaffins were found to be 2.8 ppm.
It is evident from example-2A that the sulphur and nitrogen content of the linear hydrocarbons are reduced due to hydrotreating process of the present disclosure.
Example-2B: Process for separating isoparaffins from n-paraffins using a bed of molecular sieve
The product mixture comprising n-paraffins and iso-paraffins obtained in example-2A was passed through a reactor bed having 5A molecular sieve. The hydrogen pressure of the reactor was maintained at 2500 kPa and the temperature was maintained at 177 °C. The adsorbed n-paraffins of 99.5 % purity were separated with 96.5 % recovery. The raffinate by-product, containing 90 % purity of iso-paraffin and 10 % cycloparaffin, was obtained in 3.5 wt% yield.
It is evident from example 1, example-2A, and example-2B of the present disclosure that the n-paraffins and isoparaffins obtained by the process of the present disclosure have low amount of sulphur and nitrogen content. The high content of sulphur and nitrogen is hazardous to the molecular sieves. Hence, the process of the present disclosure to extract isoparaffins is not detrimental to the molecular sieves.
Further, from example 1, example-2A and example-2B of the present disclosure it is evident that the purity of the isoparaffins obtained by the process of the present disclosure is high. It is observed from example 1, example-2A, and example-2B of the present disclosure that the effectiveness of the extraction of isoparaffins is due to the combination of the process steps such as urea adduction process, hydrotreating process, and separation process using a molecular sieve bed. The combined use of the processes synergistically extracts high value isoparaffins.
Therefore, the process for obtaining high value isoparaffins from the hydrocarbon feed is simple and cost effective.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of:
- a simple and a cost effective process to obtain high value isoparaffins from linear hydrocarbons.
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 disclosure 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 disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
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 disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.