Description:FIELD OF THE INVENTION
The present invention generally relates to the field of mechanical and chemical engineering and in particularly relates to a process and a system for producing high-purity petrochemical grade from streams of C5-C6 chain.

BACKGROUND OF THE INVENTION

Isopentane is majorly used as a blowing agent in expanded polystyrene production, the purity required for this grade is in the range from 50-80%, however another application of Isopentane is an Induced Condensing Agent (ICA) in polyolefin production process of gas phase polymerization technologies. The typical purity requirement for this application is >95%. The production of high purity isopentane (>95%) is a challenging task. In a typical gas-phase fluidized bed polymerization process, a gaseous stream containing one or more monomers is continuously passed through the fluidized bed under reactive conditions in the presence of a catalyst. The gaseous stream is withdrawn from the fluidized bed and recycled back into the reactor. Generally, the recycled gas stream is heated in the reactor by the heat of polymerization. This heat may be removed in another part of the cycle, so as to maintain the temperature of the resin and gaseous stream inside the reactor below the polymer melting point or the catalyst deactivation temperature.

Polymerization reactions are exothermic in nature, the amount of polymer produced in a fluidized bed polymerization process may be related to the amount of heat that can be withdrawn from the reaction zone. A typical process of gas phase polymerization, the part of recycle stream is cooled down, but could not be decreased below the dew point of the recycle stream without causing problems such as polymer agglomeration or plugging of the reactor system. However, it was found that in some instances a recycle stream may be cooled to a temperature below the dew point in a fluidized bed polymerization process resulting in condensing a portion of the recycle gas stream outside of the reactor. The process of purposefully condensing a portion of the recycle stream is known as “condensed mode” operation. When a recycle stream temperature is lowered to a point below its dew point in condensed mode operation, an increase in polymer production may be possible.
The liquid phase of this two-phase gas/liquid mixture in condensed mode operation is generally entrained in the gas phase of the mixture. Generally, the vaporization occurs when the two-phase mixture enters the fluidized bed, with the resin providing the required heat of vaporization. The vaporization thus provides an additional means of extracting heat of reaction from the fluidized bed. Thereby, the cooling capacity of the recycle gas may be increased further. This can be performed by adding non-polymerizing, non-reactive materials to the reactor, which are condensable at the temperatures encountered in the process heat exchanger. Such materials are collectively known as induced condensing agents (ICA). Increasing concentrations of an ICA in the reactor causes corresponding increases in the dew point temperature of the reactor gas, which promotes higher levels of condensing for higher (heat transfer limited) production rates from the reactor. ICA are usually low molecular weight alkanes, and thus chemically inert. However, in addition to influencing the heat removal capacity, they can also have a significant impact on reaction rate, powder morphology, molecular weight, and other quality related parameters in unexpected ways. Examples of the condensable gas are saturated hydrocarbons including butane, pentane or hexane etc. Chinese Patent Application No. 93105791, further provides examples of volatilizable liquid hydrocarbons in a broader range as the condensing agent,: those selected from saturated hydrocarbons with 2-8 carbon atoms, such as propane, n-butane, iso-butane, n-pentane, iso-pentane, neopentane, n-hexane, iso-hexane and other saturated C6 hydrocarbons, n-heptane, n-octane and other C7 and C8 alkanes or the mixture thereof, among which C5 and C6 are preferred. The other is to control static electricity. The principle is to increase the humidity of the circulating gas, so as to reduce the friction between the powder and the reactor wall, and the excessive static electricity generated by the friction between the powder and the reactor wall, and the static electricity generated by the contact between the wet components and the reactor wall. Among the studied saturates Isopentane is known to have better product performance. This is because it is easier to recover isopentane from the resin produced in the reactor compared to n-hexane. Hence the Isopentane is used as Induced condensing agent in gas phase polymerisation of industrial production of polyethylene (HDPE).

Industrially isopentane is produced by isomerization of n-pentane over the solid acidic catalysts. However, most of the solid catalysts have a problem of rapid deactivation due to the coke formation. In order for researchers to suppress the high deactivation rate, most of the catalysts commercially used are dual function catalysts and are commonly modified by platinum under the presence of hydrogen.

However in refinery operations isopentane is obtained in the isomerization process of light naphtha for high octane gasoline blendstocks, the major challenge lies in the recovery of high purity isopentane stream. There are two possible routes are available industrially to recovery the high purity isopentane. The technologies currently available for isopentane production can be divided into the following:

Conventional distillation techniques: In the crude oil refinery operations, the light naphtha coming from the crude distillation unit or the naphtha hydrotreating unit uses the De-isopentaniser: A deisopentanizer (DIP) column is installed to separate pure isopentane (RON – 92) from light naphtha stream and the column bottoms are sent to isomerization unit in order to produce a stream with RON between 83 to 90.

US patent application no. US5994607A provides further details on the deisopentansier column; in which the feed contained 24.6 wt% isopentane and was fed to a deisopenatniser column at a rate of 93.6 kg/hr. The column has 40 theoretical plates and operates at an overhead pressure of 2 bar with a reflux ratio of 23 with respect to the distillate. The feed was introduced to the column at the 20th plate. 20 kg/h of a liquid distillate which was rich in isopentane (97.95 mole %) and contained about 2 mole % of normal-pentane was extracted overhead and 73.6 kg/h of a liquid effluent comprising 5 mole % of isopentane and 38.6 mole % of normal-pentane was extracted from the bottom, the remaining being constituted by compounds in the feed containing 6 carbon atom per molecule. The column bottom is then passed through the isomerization unit to increase the octane of the stream.
Distillation with molecular sieve adsorption: In another process of refinery production of isopentane, uses a deisopentanizer (DIP) to separate the isopentane from the reactor feed. The DIP column bottoms are routed to the isomerization reactors. The reactor products are separated into isomerate product and normal paraffins in the molecular sieve separation section, which features a novel vapor phase PSA technique. This enables the product to consist entirely of branched isomers with a RON of nearly 90.
US patent application no. US9714390B2 provides further details on the adsorption process. For the adsorption phase, the temperature is in the range from approximately -50° C. to 100° C., preferably in the range 0° C. to 50° C., and the pressure is in the range 10-3 to 10 MPa, preferably in the range 0.1 to 5 MPa. Regarding the regeneration phase, it is preferably carried out at a temperature in the range 100 to 350 °C., preferably in the range 200 to 310 °C, and at a pressure of approximately 10-3 to 10 MPa, more preferably in the range 0.1 to 5 MPa. The adsorbent solids used in the process are selected from metallic oxides (by themselves or mixed with one or more binders or deposited on a support), metallic sulphides (by themselves or mixed with one or more binders or deposited on a support), reduced metals (by themselves or mixed with one or more binders or deposited on a support) which may optionally be doped and/or sulphurized, MOFs (Metal Organic Frameworks) and/or their mixtures. Preferably, they comprise at least one element selected from activated or promoted aluminas, clays, molecular sieves such as zeolites, silica gels, silica-aluminas and activated carbon.
The existing processes have high amounts of impurities (heavier components of naphtha) as compared with the present invention. In the present invention, petrochemical units (i.e., gas phase polymerization of Polyethylene process requires isopentane as a induced condensate agent) which use isopentane with a minimum of 95 wt.%, Isopentane purity along with very stringent requirement of impurities like carbonyls alcohals etc. Further, the existing processes use of DIP (Deisopentaniser) column carries significant risks as the purified isopentane can have impurities such as sulfur and water, which can irreversibly deactivate the catalysts used for petrochemicals production. Furthermore, the existing processes are very complex, thus, a loss of product could occur due to valve malfunction and decrease in purity of isopentane could be obtained in the final product. Therefore, there exists a need to have a better process for the production of high purity isopentane. The present invention has the advantage of using existing processes and only requires installation of new piping to route light isomerate to the HRU Unit; thus being much cheaper than existing processes.

SUMMARY OF THE INVENTION

The present invention generally relates to the field of mechanical and chemical engineering and in particularly relates to a process for producing high-purity petrochemical grade from streams of C5-C6 chain.

In the present invention, the operating conditions of the HRU unit are changed to produce isopentane of suitable concentration. The light isomerate stream from DIH (Deisohexaniser) column top which contanins ~ 40-wt% isopentane is routed to HRU Feed Surge Drum and afterwards enters Naphtha Splitter Column after exchanging heat in Feed Bottoms exchanger. The naphtha splitter column separates the heavier components from C5 components in the naphtha stream. The condensed liquid from the Naphtha Splitter Condenser is collected in the naphtha splitter reflux drum. Part of the condensed liquid is sent to the column as reflux and remaining is sent to the hexane/isopentane column as feed from naphtha splitter reflux pump. The hexane/isopentane column produces the isopentane rich product from the column bottom. The reject streams (Naphtha splitter column bottoms and Hexane/isopentane column top) is then routed to the gasoline pool while the bottom stream from Hexane/isopentane has an isopentane content of ~98 wt%.

In an embodiment, a process for producing high-purity petrochemical grade from streams of C5-C6 chain is provided. The process includes of generating, by a Deisohexanizer (DIH) column, a light isomerate from a stream of straight chain C5 and C6 in isomerisation reactor unit, wherein the light isomerate stream comprising 40wt% of isopentane; connecting top of the Deisohexanizer (DIH) column with a hexane recovery unit (HRU) Feed Surge Drum through a pipe to route the light isomerate stream from top of the Deisohexanizer (DIH) column; routing the light isomerate stream from top of the Deisohexanizer (DIH) column to the HRU Feed Surge Drum through a Deisohexanizer (DIH) pump, wherein the HRU feed Surge Drum is maintained at 1.6 kg/cm2 g pressure; pumping and passing the light isomerate stream from the HRU feed surge drum through feed bottom exchangers to a Naphtha Splitter Column by Naphtha Splitter Feed pumps, wherein heat of the light isomerate stream gets exchanged in the feed bottoms exchangers; separating, by the naphtha splitter column, n-pentane and i-pentane from the light isomerate stream to form a naphtha stream, wherein bottom of the naphtha splitter column is connected with a splitter reboiler through pipe for reboiling the naphtha stream to maintaining column top temperature;passing vapours present in the naphtha stream from top of the naphtha splitter column to a Naphtha Splitter condenser through the pipe for condensing the vapours, wherein top column of naptha splitter column is connected with the Naphtha Splitter condenser through the pipe; collecting condensed liquid from the Naphtha Splitter Condenser in a naphtha splitter reflux drum through the pipe, wherein temperature of the liquid exiting the reflux drum is 33 ?; routing a first part of the condensed liquid back to the naphtha splitter column as reflux by using a naphtha splitter reflux pump and sending a second part of the condensed liquid to a hexane/isopentane column as feed which increases pressure of the stream to 10.5 kg/cm2g, wherein flow of the reflux back to the naphtha splitter column is 20.2 m3/hr; and generating, by the hexane/isopentane column, a high isomerate stream by using naphtha stream, wherein the the high isomerate stream including 95wt% of isopentane.
In anther embodiment, a system for producing high-purity petrochemical grade from streams of C5-C6 chain is provided. The system includes a Deisohexanizer (DIH) column for generating a light isomerate from a stream of straight chain C5 and C6 in isomerisation reactor unit, wherein the light isomerate stream comprising 40wt% of isopentane; a pipe arrangement for connecting top of the Deisohexanizer (DIH) column with a hexane recovery unit (HRU) Feed Surge Drum to route the light isomerate stream from top of the Deisohexanizer (DIH) column, wherein the pipe arrangement is further for routing the light isomerate stream from top of the Deisohexanizer (DIH) column to the HRU Feed Surge Drum through a Deisohexanizer (DIH) pump, wherein the HRU feed Surge Drum is maintained at 1.6 kg/cm2 g pressure; Naphtha Splitter Feed pumps for pumping and passing the light isomerate stream from the HRU feed surge drum through feed bottom exchangers to a Naphtha Splitter Column, wherein heat of the light isomerate stream gets exchanged in the feed bottoms exchangers; the naphtha splitter column for separating n-pentane and i-pentane from the light isomerate stream to form a naphtha stream, wherein bottom of the naphtha splitter column is connected with a splitter reboiler through pipe for reboiling the naphtha stream to maintaining column top temperature; a Naphtha Splitter condenser for condensing vapours present in the naphtha stream from top of the naphtha splitter column, wherein top column of naptha splitter column is connected with the Naphtha Splitter condenser through the pipe; a naphtha splitter reflux drum for collecting condensed liquid from the Naphtha Splitter Condenser through the pipe, wherein temperature of the liquid exiting the reflux drum is 33 ?; a naphtha splitter reflux pump for routing a first part of the condensed liquid back to the naphtha splitter column as reflux and sending a second part of the condensed liquid to a hexane/isopentane column as feed which increases pressure of the stream to 10.5 kg/cm2g, wherein flow of the reflux back to the naphtha splitter column is 20.2 m3/hr; and the hexane/isopentane column for generating a high isomerate stream by using naphtha stream, wherein the high isomerate stream including 95wt% of isopentane.

An objective of the present invention is to to meet the isopentane requirements in the HDPE (High Density Polyethylene) Unit with a minimum isopentane purity of 95 wt%. It requires minimum modifications to ISOM and HRU unit in the Motor Spirit Block (MS-Block) of the refinery.
Another objective of the present invention is to enable production of high-purity isopentane by using light isomerate stream from DIH (Deisohexaniser) column top which contanins ~40 wt% isopentane and subsequent processing in HRU unit using minimal modifications to the existing setup.
Another objective of the present invention is to provide a process, which is much less complex than the existing processes as it, utilize existing equipment of the Isomerisation unit and the HRU unit.
To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF FIGURES
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Figure 1 shows existing deisopentansier column for preparation of isopentane;
Figure 2 shows existing Molecular sieves for preparation of isopentane;
Figure 3 shows a flow chart for a process for producing high-purity petrochemical grade from streams of C5-C6 chain in accordance with an embodiment of the present invention;
Figure 4 shows a block diagram for a system for producing high-purity petrochemical grade from streams of C5-C6 chain in accordance with an embodiment of the present invention;
Figure 5 shows C5/C6 Isomerisation with DIH recycle;
Figure 6 shows Process Flow diagram for the present invention; and
Figure 7 shows PFD of isopentane production simulation in KBC Petro-SIM.
Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present invention. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION:
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises...a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.
Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
Figure 1 shows existing deisopentansier column for preparation of isopentane. The light naphtha coming from the crude distillation unit or the naphtha hydrotreating unit uses the De-isopentaniser: A deisopentanizer (DIP) column is installed to separate pure isopentane (RON – 92) from light naphtha stream and the column bottoms are sent to isomerization unit in order to produce a stream with RON between 83 to 90.

Figure 2 shows existing Molecular sieves for preparation of isopentane. The process of refinery production of isopentane, uses a deisopentanizer (DIP) to separate the isopentane from the reactor feed. The DIP column bottoms are routed to the isomerization reactors. The reactor products are separated into isomerate product and normal paraffins in the molecular sieve separation section, which features a novel vapor phase PSA technique. This enables the product to consist entirely of branched isomers with a RON of nearly 90.

Figure 3 shows a flow chart for a process 300 for producing high-purity petrochemical grade from streams of C5-C6 chain in accordance with an embodiment of the present invention. The claimed process 300 includes of Step 302 of generating, by a Deisohexanizer (DIH) column, a light isomerate from a stream of straight chain C5 and C6 in isomerisation reactor unit, wherein the light isomerate stream comprising 40wt% of isopentane; Step 304 of connecting top of the Deisohexanizer (DIH) column with a hexane recovery unit (HRU) Feed Surge Drum through a pipe to route the light isomerate stream from top of the Deisohexanizer (DIH) column; Step 306 of routing the light isomerate stream from top of the Deisohexanizer (DIH) column to the HRU Feed Surge Drum through a Deisohexanizer (DIH) pump, wherein the HRU feed Surge Drum is maintained at 1.6 kg/cm2 g pressure; Step 308 of pumping and passing the light isomerate stream from the HRU feed surge drum through feed bottom exchangers to a Naphtha Splitter Column by Naphtha Splitter Feed pumps, wherein heat of the light isomerate stream gets exchanged in the feed bottoms exchangers; Step 310 of separating, by the naphtha splitter column, n-pentane and i-pentane from the light isomerate stream to form a naphtha stream, wherein bottom of the naphtha splitter column is connected with a splitter reboiler through pipe for reboiling the naphtha stream to maintaining column top temperature; Step 312 of passing vapours present in the naphtha stream from top of the naphtha splitter column to a Naphtha Splitter condenser through the pipe for condensing the vapours, wherein top column of naptha splitter column is connected with the Naphtha Splitter condenser through the pipe; Step 314 of collecting condensed liquid from the Naphtha Splitter Condenser in a naphtha splitter reflux drum through the pipe, wherein temperature of the liquid exiting the reflux drum is 33 ?; Step 316 of routing a first part of the condensed liquid back to the naphtha splitter column as reflux by using a naphtha splitter reflux pump and sending a second part of the condensed liquid to a hexane/isopentane column as feed from the naphtha splitter reflux pump which increases pressure of the fluid to 10.5 kg/cm2g, wherein flow of the reflux back to the naphtha splitter column is 20.2 m3/hr; and Step 318 of generating, by the hexane/isopentane column, a high isomerate stream by using naphtha stream, wherein the high isomerate stream including 95wt% of isopentane.

In an embodiment, the process of generating a light isomerate from a stream of straight chain C5 and C6 includes of feeding a stream of straight chain C5 and C6 in isomerisation reactor unit with hydrogen gas to form a raw high-octane isomerate; sending stream of the raw high-octane isomerate from the isomerisation reactor unit to a stabilizer column to stabilise the stream; passing the stabilised stream from bottom of the stabilizer column into the DIH column to remove low-octane components resulting in a light isomerate from top and heavy isomerate from bottom of the DIH column.
In another embodiment, the low-octane components are hexane, 2-methylpentane and 3-methylpentane.
In another embodiment, pressure of top and bottom naphtha splitter column are maintained at 1.84 kg/cm2g and 2.68 kg/cm2g pressure respectively, wherein temperature of top and bottom naphtha splitter column are maintained at 58.5 ? and 85.4 ? respectively.
In another embodiment, the process of generating a high isomerate stream by using naphtha stream includes of separating, by the hexane/isopentane column, heavier components isopentane and n-pentane from the naphtha stream to form a high isomerate stream, wherein bottom of the hexane/isopentane column is connected with a hexane/isopentane reboiler through pipe for reboiling the stream to maintaining column top temperature at 58.7 ?; and passing vapours present in the high isomerate stream from top of the hexane/isopentane column to a hexane/isopentane condenser through the pipe for condensing the vapours, wherein top column of high isomerate stream is connected with the hexane/isopentane condenser through the pipe.
In another embodiment, the process of generating a high isomerate stream by using naphtha stream further includes of collecting condensed liquid from the hexane/isopentane Condenser in a hexane/isopentane reflux drum through the pipe, wherein temperature of the liquid exiting the reflux drum is 33 ?; and routing a first part of the condensed liquid back to the hexane/isopentane column as reflux by using a reflux pump and sending a second part of the condensed liquid in form of hexane and isopentane.
In another embodiment, the claimed process includes of routing reject streams from bottom of the Naphtha splitter column and top of the Hexane/isopentane column to a gasoline pool.
In another embodiment, the naphtha splitter column is 36.5 m high column with 55 trays, wherein the light isomerate stream enters at 30th tray of the Naphtha Splitter Column.
In another embodiment, wherein pressure of top and bottom Hexane/Isopentane column are 3.11 and 3.40 kg/cm2g respectively, wherein temperature of the Hexane/Isopentane column top is ~65 ? while maintaining a reflux rate of 9 m3/hr.

Figure 4 shows a block diagram for a system 400 for producing high-purity petrochemical grade from streams of C5-C6 chain in accordance with an embodiment of the present invention. The claimed system includes a Deisohexanizer (DIH) column 402 for generating a light isomerate from a stream of straight chain C5 and C6 in isomerisation reactor unit, wherein the light isomerate stream comprising 40wt% of isopentane.
In an embodiment, the claimed system 400 further includes a pipe arrangement for connecting top of the Deisohexanizer (DIH) column 402 with a hexane recovery unit (HRU) Feed Surge Drum 404 to route the light isomerate stream from top of the Deisohexanizer (DIH) column, 402 wherein the pipe arrangement is further for routing the light isomerate stream from top of the Deisohexanizer (DIH) column 402 to the HRU Feed Surge Drum 404 through a Deisohexanizer (DIH) pump 406, wherein the HRU feed Surge Drum 404 is maintained at 1.6 kg/cm2 g pressure.
In another embodiment, the claimed system 400 further includes Naphtha Splitter Feed pumps 408 for pumping and passing the light isomerate stream from the HRU feed surge drum 404 through feed bottom exchangers 412 to a Naphtha Splitter Column 410, wherein heat of the light isomerate stream gets exchanged in the feed bottoms exchangers 412, wherein the naphtha splitter column 410 for separating n-pentane and i-pentane from the light isomerate stream to form a naphtha stream, wherein bottom of the naphtha splitter column 410 is connected with a splitter reboiler 414 through pipe for reboiling the naphtha stream to maintaining column top temperature.
In another embodiment, the claimed system 400 further includes a Naphtha Splitter condenser 416 for condensing vapours present in the naphtha stream from top of the naphtha splitter column 410, wherein top column of naptha splitter column 410 is connected with the Naphtha Splitter condenser 416 through the pipe arrangment;
In another embodiment, the claimed system 400 further includes a naphtha splitter reflux drum 418 for collecting condensed liquid from the Naphtha Splitter Condenser 416 through the pipe arangment, wherein temperature of the liquid exiting the reflux drum 418 is 33 ?;
In another embodiment, the claimed system 400 further includes a naphtha splitter reflux pump 420 for routing a first part of the condensed liquid back to the naphtha splitter column 410 as reflux and sending a second part of the condensed liquid to a hexane/isopentane column 422 as feed from the naphtha splitter reflux pump 420 which increases pressure of the fluid to 10.5 kg/cm2g, wherein flow of the reflux back to the naphtha splitter column is 20.2 m3/hr, wherein the hexane/isopentane column 422 for generating a high isomerate stream by using naphtha stream, wherein the high isomerate stream including 95wt% of isopentane.

Figure 5 shows C5/C6 Isomerisation with DIH recycle. The isomerization unit (ISOM) processes light naphtha (IBP – 27 ?, FBP – 78 ?) and upgrades it to high-octane isomerate by isomerization reactions of straight chain C5 and C6 components occurring in two reactors in series configuration. The effluent from the reactors is then sent to the stabilizer column for meeting RVP specifications. The stabilizer column bottom stream is then processed in the DIH column which removes low-octane components (primarily hexane, 2-methylpentane and 3-methylpentane) from the raw isomerate (stabilizer column bottom stream) resulting in two streams; light isomerate from the top and heavy isomerate from the bottom. The typical composition and density of light isomerate (DIH column top), heavy isomerate (DIH column bottom) and DIH column recycle streams are given in Table-1. The light isomerate and heavy isomerate streams are combined and sent to the gasoline pool. The table mentions the range of compositions (maximum and minimum) obtained for each stream mentioned below.
Table- 1: DIH Column Stream properties
Property Light Isomerate Heavy Isomerate DIH recycle
2 Methyl Pentane Wt% 12.4 - 16.8 0.01-1.8 1.9 - 28
22 Dimethyl Butane Wt% 12.1 - 16.3 0 - 0.03 0.01 - 3.7
23 Dimethyl Butane Wt% 5.1 - 8.3 0.01 - 0.09 0.2 - 3.8
2-Methyl Hexane Wt% 0.02 - 0.09 2.1 - 3.4 0.2 - 0.5
3 Methul Pentane Wt% 1.8 - 8.2 0.8 - 11.6 6.5 - 54.4
3-Methyl Hexane Wt% 0.03 - 0.04 1.8 - 3 0.1 - 0.4
Benzene Wt% 0 0 0 - 1.2
Cyclo Hexane Wt% 0.02 - 2.3 25.8 - 46.5 2.4 - 14.2
Density at 15°C kg/m³ 636.5 - 648.6 709.3 - 754.2 673.7 - 705.8
Hexane Wt% 0.01 - 3.3 12 - 31.1 13.9 - 38.1
Iso Butane Wt% 0.01 - 1.3 0 0
Iso Pentane Wt% 38.9 - 46 0 0 – 10.2
Methyl Cyclohexane Wt% 0.03 - 3.7 3.4 - 5.8 0.2 - 0.5
Methyl CycloPentane Wt% 0.01 - 2.2 17.2 - 27.9 4 - 36.2
N Butane Wt% 0.2 - 4.6 0 0 - 3.7
n-Heptane Wt% 0 0.8 - 1.3 0.05 - 0.22
n-Pentane Wt% 13.6 - 17.7 0.01 - 0.03 0 - 21.8
Other hydrocarbons Wt% 0 - 2.2 5.6 - 8.8 0.5 - 3.0

The current operation of the hexane recovery unit (HRU) involves the processing of Stabilised Naphtha from NHT unit or DIH recycle stream in two columns: Naphtha Splitter Column which separates C6+ components from the feed stream and Hexane/isopentane Column which produces a C6 rich stream at the bottom of the column. This stream is subsequently desulfurized and hydrogenated to produce a hexane-rich stream called FGH (IBP- 63 ? and 95% recovery in between 64 to 70 ?).
The new modificcation (isopentane mode), processes the Light Isomerate stream of isomerization unit ( from top of deisohexaniser column) in two columns of Hexane Recovery Unit (HRU) to produce an isopentane rich-stream. The Light Isomerate stream has a composition of ~40% wt% isopentane.
Simulation studies:
Prior to conducting experiments, a simulation of the scheme was carried in KBC Petro-SIM. For the simulation, 11.3 m3/hr of Light Isomerate (38.1 wt.% isopentane) from the Isomerisation Unit is distilled in two columns; Naphtha Splitter Column and Hexane/Isopentane Column to obtain isopentane with maximum 98.75 wt% purity. The results of the simulation are tabulated in Table-2.
Table-2: Simulation results
Column Name Column Parameters Isopentane content in distillate (wt%)
80% 85% 90% Max. (94 wt%)
Naphtha Splitter Column Feed Rate (m3/hr) 11.3 11.3 11.3 11.3
Feed Pressure (kg/cm2 g) 2.2 2.2 2.2 2.2
Feed temperature (?) 62 62 62 62
Top Temperature (?) 60.79 60.27 59.77 59.24
Top Pressure (kg/cm2 g) 1.8 1.8 1.8 1.8
Reflux ratio (kg/kg) 3.32 4.71 7.106 18.16
Distillate flow rate (kg/hr) 2500 2500 2500 2500
Reflux temperature (?) 55.17 54.8 54.43 54.14
Bottom Temperature (?) 79.62 79.88 80.15 80.21
Bottom Pressure (kg/cm2 g) 2 2 2 2

Hexane/Isopentane Column Feed Rate (m3/hr) 2500 2500 2500 2500
Top Temperature (?) 68.52 68.29 68.13 68.1
Top Pressure (kg/cm2 g) 3.3 3.3 3.3 3.3
Reflux ratio 3.5 3.89 4.78 4.91
Reflux temperature 60.01 59.81 59.67 59.65
Bottom Temperature (?) 80.53 80.1 79.66 79.28
Bottom Pressure (kg/cm2 g) 3.5 3.5 3.5 3.5
Product flow rate 2100 2100 2100 2100
Isopentane content max. (wt%) 82.33 88.15 94.03 98.75

From the table, it is evident that for naphtha splitter column, maximum isopentane recovery would require a higher reflux rate, implying a lower column top temperature. A higher reflux rate would result in better separation of isopentane and n-pentane from heavier components in the light isomerate stream.It can also be inferred that in order to obtain higher isopentane content at the bottom of Hexane/Isopentane column, a higher isopentane purity would be required in feed to this column. Thus, a higher isopentane purity in feed to the Hexane/Isopentane column would result in higher purity isopentane as indicated in Table-2. For Hexane/Isopentane column, a higher reflux ratio would be required for better separation between two components n-pentane and isopentane as they have close boiling points (36.1 and 27.7 ?). The maximum purity of isopentane obtained from simulation is 98.75 wt%.

Figure 6 shows Process Flow diagram for the present invention. For trial run of the present invention, extensive simulation models are prepared to produce high purity petrochemical grade Isopentane with minimum modifications involved. Piping was installed to connect the light isomerate stream to HRU Feed Surge Drum. Subsequently, the de-inventory of HRU unit columns was done before changing the mode of operation for production of isopentane. The trial run is conducted for a period of 1 week. During the trial run, 12.4 m3 of light isomerate stream from Deisohexanizer light isomerate pump is routed to HRU Feed Surge Drum maintained at 1.6 kg/cm2g pressure. Then this stream is pumped by (Naphtha Splitter Feed pumps) and entered the Naphtha Splitter Column after exchanging heat in Feed Bottoms exchanger. The naphtha splitter column is 36.5 m high column with 55 trays and the feed enters at 30th tray. This column separates heavier components from n-pentane and i-pentane in the naphtha stream. The column top and bottom pressure are maintained at 1.84 kg/cm2g and 2.68 kg/cm2g pressure respectively, whereas the column top and bottom temperature were maintained at 58.5 ? and 85.4 ? respectively. The column bottoms are routed to the gasoline pool as it has high-octane components in the C5-C6 range. The Vapors from the naphtha splitter column are condensed in the overhead condenser. The condensed liquid from the Naphtha Splitter Condenser is collected in the naphtha splitter reflux drum. The temperature of fluid exiting the reflux drum is 33 ?.
Part of the condensed liquid is routed back to the column as reflux and remaining is sent to the hexane/isopentane column as feed from naphtha splitter reflux pump, which increases the pressure of the fluid to 10.5 kg/cm2g. The flow of reflux back to the column was 20.2 m3/hr and the rest is routed to the Naphtha Splitter Column. This stream from naphtha splitter column top enters the Hexane/isopentane Column as feed at 30th tray. The hexane column is 34.85 m tall and has 55 trays. The column top and bottom pressure are maintained at 3.18 kg/cm2g and 3.47 kg/cm2g pressure respectively, whereas the column top and bottom temperature are maintained at 63.3 ? and 78.8 ? respectively.
Figure 7 shows PFD of isopentane production simulation in KBC Petro-SIM. Reflux is increased in Naptha Splitter column from 16.89 m3/hr to 19.62 m3/hr to reduce top temperature from 60 ? to 59.07 ?. This resulted in lesser slippage of heavier compounds (2,2-DMB, 2,3-DMB, 2-MP, 3-MP, nC6) into feed to Hexane/Isopentane Column; leading to higher isopentane purity of column bottom stream ( from 80.2% to 97.2%). Naphtha Splitter Column reflux had been increased to 20.18 m3/hr; but bottom temperature was also increased to 87.58 ? which led to lesser purity of isopentane in the feed stream to Hexane/Isopentane column. The column bottom temperature is kept between 83.3 – 84.6 ? and reflux is marginally increased to 20.55 m3/hr to keep column top temperature at 58.7 ?. This resulted in maximum isopentane content reaching the second column and obtaining a maximum purity of ~99% during the trial. It can be inferred that in order to obtain higher purity of isopentane product from Hexane/Isopentane column; it is necessary to separate heavier components from Naphtha Splitter Feed by changing reflux rate and reboiling for maintaining column top temperature at 58.7 ?. The primary function of the Hexane/isopentane column is to separate isopentane and n-pentane from the feed stream as all the heavier components have been distilled out from the Naphtha Splitter Column. To achieve the highest purity of isopentane, the column top and bottom pressure should be 3.11 and 3.40 kg/cm2g and top temperature should be ~65 ? while maintaining a reflux rate of 9 m3/hr. From both trial run and simulation studies, it can be observed that a isopentane purity of Hexane/Isopentane column bottom is limited by the isopentane content of the feed stream. Hence, it is important to maintain the parameters of the Naphtha Splitter column in order to get maximum isopentane content in the distillate.
Table -3: Plant trial data
Naphtha Splitter Column 18-Dec 19-Dec 20-Dec 21-Dec 22-Dec 23-Dec 24-Dec
Feed Rate (m3/hr) 12.37 12.4 12.67 12.41 12.69 12.31 12.52
Feed Pressure
(kg/cm2 g) 4 4 4 4 4 4 4
Feed temperature
(?) 39.91 38.72 40.54 40.31 40.47 39.98 40.28
Top Temperature
(?) 60 59.07 59.42 59.26 59.18 58.7 59.62
Top Pressure
(kg/cm2 g) 1.84 1.85 1.85 1.85 1.85 1.85 1.85
Reflux flow (m3/hr) 16.89 19.62 20.18 20.2 20.46 20.55 20.03
Distillate flow rate (m3/hr) 2.02 2.92 3.39 2.93 1.39 0.93 1.34
Reflux temperature (?) 32.31 31.96 33.1 34.67 33.72 32.93 33.05
Bottom Temperature (?) 85.96 86.53 87.58 84.45 83.36 84.58 86.1
Bottom Pressure (kg/cm2 g) 2.5 2.69 2.78 2.58 2.68 2.74 2.87

Hexane/
Isopentane Column Feed Rate (m3/hr) 2.02 2.92 3.39 2.93 1.39 0.93 1.34
Top Temperature
(?) 69.89 59.58 61.05 63.92 64.21 65.08 63.09
Top Pressure
(kg/cm2 g) 3.19 3.29 3.25 3.2 3.1 3.12 3.11
Reflux flow (m3/hr) 3.52 7.66 8.57 8.92 9.03 8.6 8.85
Reflux Temperature (?) 34.2 36.67 36.99 37.18 36.62 36.42 36.73
Bottom Temperature (?) 61.53 75.89 74.05 70.92 72.8 73.53 75.58
Bottom Pressure (kg/cm2 g) 3.46 3.58 3.54 3.5 3.39 3.41 3.41
Product flow rate (m3/hr) 1.75 3.1 2.37 2.5 1.94 1.49 1.96
The composition of the Naphtha Splitter column and Hexane/isopentane column feed stream are given in Table-4 and Table-5 respectively. The Hexane/isopentane column bottom product is mainly composed of isopentane (~ 98 wt%) at a flowrate of 1.3 tph; detailed compositions of which are given in Table - 6.
Table- 4: Composition of Naphtha Splitter column feed stream during trial run

Table- 5: Composition of Hexane/Isopentane column feed stream during trial run

Table- 6: Composition of isopentane in Hexane/Isopentane column bottom during trial run

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims. , Claims:1. A process for producing high-purity petrochemical grade from streams of C5-C6 chain, said process comprising:
generating, by a Deisohexanizer (DIH) column, a light isomerate from a stream of straight chain C5 and C6 in isomerisation reactor unit, wherein the light isomerate stream comprising 40wt% of isopentane;
connecting top of the Deisohexanizer (DIH) column with a hexane recovery unit (HRU) Feed Surge Drum through a pipe to route the light isomerate stream from top of the Deisohexanizer (DIH) column;
routing the light isomerate stream from top of the Deisohexanizer (DIH) column to the HRU Feed Surge Drum through a Deisohexanizer (DIH) pump, wherein the HRU feed Surge Drum is maintained at 1.6 kg/cm2 g pressure;
pumping and passing the light isomerate stream from the HRU feed surge drum through feed bottom exchangers to a Naphtha Splitter Column by Naphtha Splitter Feed pumps, wherein heat of the light isomerate stream gets exchanged in the feed bottoms exchangers;
separating, by the naphtha splitter column, n-pentane and i-pentane from the light isomerate stream to form a naphtha stream, wherein bottom of the naphtha splitter column is connected with a splitter reboiler through pipe for reboiling the naphtha stream to maintaining column top temperature;
passing vapours present in the naphtha stream from top of the naphtha splitter column to a Naphtha Splitter condenser through the pipe for condensing the vapours, wherein top column of naptha splitter column is connected with the Naphtha Splitter condenser through the pipe;
collecting condensed liquid from the Naphtha Splitter Condenser in a naphtha splitter reflux drum through the pipe, wherein temperature of the liquid exiting the reflux drum is 33 ?;
routing a first part of the condensed liquid back to the naphtha splitter column as reflux by using a naphtha splitter reflux pump and sending a second part of the condensed liquid to a hexane/isopentane column as feed which increases pressure of the stream to 10.5 kg/cm2g, wherein flow of the reflux back to the naphtha splitter column is 20.2 m3/hr; and
generating, by the hexane/isopentane column, a high isomerate stream by using naphtha stream, wherein the the high isomerate stream including 95wt% of isopentane.
2. The process as claimed in claim 1, wherein process of generating a light isomerate from a stream of straight chain C5 and C6 comprising:
feeding a stream of straight chain C5 and C6 in isomerisation reactor unit with hydrogen gas to form a raw high-octane isomerate;
sending stream of the raw high-octane isomerate from the isomerisation reactor unit to a stabilizer column to stabilise the stream;
passing the stabilised stream from bottom of the stabilizer column into the DIH column to remove low-octane components resulting in a light isomerate from top and heavy isomerate from bottom of the DIH column.
3. The process as claimed in claim 2, wherein the low-octane components are hexane, 2-methylpentane and 3-methylpentane.
4. The process as claimed in claim 1, wherein pressure of top and bottom naphtha splitter column are maintained at 1.84 kg/cm2g and 2.68 kg/cm2g pressure respectively, wherein temperature of top and bottom naphtha splitter column are maintained at 58.5 ? and 85.4 ? respectively.
5. The process as claimed in claim 1, process of generating a high isomerate stream by using naphtha stream comprising:
separating, by the hexane/isopentane column, heavier components isopentane and n-pentane from the naphtha stream to form a high isomerate stream, wherein bottom of the hexane/isopentane column is connected with a hexane/isopentane reboiler through pipe for reboiling the stream to maintaining column top temperature at 58.7 ?; and
passing vapours present in the high isomerate stream from top of the hexane/isopentane column to a hexane/isopentane condenser through the pipe for condensing the vapours, wherein top column of high isomerate stream is connected with the hexane/isopentane condenser through the pipe.
6. The process as claimed in claim 5, the process of generating a high isomerate stream by using naphtha stream further comprising:
collecting condensed liquid from the hexane/isopentane Condenser in a hexane/isopentane reflux drum through the pipe, wherein temperature of the liquid exiting the reflux drum is 33 ?; and
routing a first part of the condensed liquid back to the hexane/isopentane column as reflux by using a reflux pump and sending a second part of the condensed liquid in form of hexane and isopentane.
7. The process as claimed in claim 1, further comprising routing reject streams from bottom of the Naphtha splitter column and top of the Hexane/isopentane column to a gasoline pool.
8. The process as claimed in claim 1, wherein the naphtha splitter column is 36.5 m high column with 55 trays, wherein the light isomerate stream enters at 30th tray of the Naphtha Splitter Column.
9. The process as claimed in claim 1, wherein pressure of top and bottom Hexane/Isopentane column are 3.11 and 3.40 kg/cm2g respectively, wherein temperature of the Hexane/Isopentane column top is ~65 ? while maintaining a reflux rate of 9 m3/hr.
10. A system for producing high-purity petrochemical grade from streams of C5-C6 chain, said system comprising:
a Deisohexanizer (DIH) column for generating a light isomerate from a stream of straight chain C5 and C6 in isomerisation reactor unit, wherein the light isomerate stream comprising 40wt% of isopentane;
a pipe arrangement for connecting top of the Deisohexanizer (DIH) column with a hexane recovery unit (HRU) Feed Surge Drum to route the light isomerate stream from top of the Deisohexanizer (DIH) column, wherein the pipe arrangement is further for routing the light isomerate stream from top of the Deisohexanizer (DIH) column to the HRU Feed Surge Drum through a Deisohexanizer (DIH) pump, wherein the HRU feed Surge Drum is maintained at 1.6 kg/cm2 g pressure;
Naphtha Splitter Feed pumps for pumping and passing the light isomerate stream from the HRU feed surge drum through feed bottom exchangers to a Naphtha Splitter Column, wherein heat of the light isomerate stream gets exchanged in the feed bottoms exchangers;
the naphtha splitter column for separating n-pentane and i-pentane from the light isomerate stream to form a naphtha stream, wherein bottom of the naphtha splitter column is connected with a splitter reboiler through pipe for reboiling the naphtha stream to maintaining column top temperature;
a Naphtha Splitter condenser for condensing vapours present in the naphtha stream from top of the naphtha splitter column, wherein top column of naptha splitter column is connected with the Naphtha Splitter condenser through the pipe;
a naphtha splitter reflux drum for collecting condensed liquid from the Naphtha Splitter Condenser through the pipe, wherein temperature of the liquid exiting the reflux drum is 33 ?;
a naphtha splitter reflux pump for routing a first part of the condensed liquid back to the naphtha splitter column as reflux and sending a second part of the condensed liquid to a hexane/isopentane column as feed which increases pressure of the stream to 10.5 kg/cm2g, wherein flow of the reflux back to the naphtha splitter column is 20.2 m3/hr; and
the hexane/isopentane column for generating a high isomerate stream by using naphtha stream, wherein the high isomerate stream including 95wt% of isopentane.