FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
1. Title of the invention: METHODS AND ASSEMBLY FOR IMPROVING OCTANE
NUMBER IN GASOLINE BLENDS
2. Applicant(s)
NAME NATIONALITY ADDRESS
BHARAT PETROLEUM CORPORATION LTD. Indian Bharat Bhavan, 4 & 6 Currimbhoy Road, Ballard Estate, Mumbai, Maharashtra 400001, India
3. Preamble to the description
COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it
is to be performed.

TECHNICAL FIELD
[0001] The present subject matter relates generally to gasoline blends and
in particular to methods for improving octane number in gasoline blends.
BACKGROUND
[0002] Hydrocarbons generally having 4-12 carbon atoms and a boiling
point in the range of about 35-200 °C are commercially sold as gasoline. Gasoline is typically a blend of several streams produced in a petroleum refinery with certain specifications according to performance requirements and government regulations. Modern gasoline engines require high octane gasoline. In addition, over the years, environmental concerns have led to more stringent specifications on gasoline. For example, the United States already requires aromatics levels of less than 30 vol% and benzene at less than 0.8 vol%. So, today refineries have to produce high octane gasoline with minimum aromatic and benzene content.
BRIEF DESCRIPTION OF DRAWINGS
[0003] The detailed description is described with reference to the
accompanying figures. In the figures, the left-most digit(s) of a reference number
identifies the figure in which the reference number first appears. The same numbers
are used throughout the drawings to reference like features and components where
possible.
[0004] Fig. 1 illustrates a typical process scheme employed to produce
isomerization product and gasoline blending components.
[0005] Fig. 2 illustrates a schematic process flow of an example method for
improving octane number in gasoline blends, in accordance with an embodiment of
the present subject matter.
[0006] Fig. 3 illustrates a schematic process flow of another example
method for improving octane number in gasoline blends, in accordance with an
embodiment of the present subject matter.

[0007] Fig. 4 illustrates a schematic of an exploded view of an example
divided wall column naphtha splitter, in accordance with an embodiment of the
present subject matter.
[0008] Fig. 5 illustrates a schematic process flow of another example
method for improving octane number in gasoline blends, in accordance with an
embodiment of the present subject matter.
[0009] Fig. 6 illustrates a schematic process flow of another example
method for improving octane number in gasoline blends, in accordance with an
embodiment of the present subject matter.
DETAILED DESCRIPTION
[0010] The present subject matter relates to methods and assembly for
improving octane number in gasoline blends in refinery operations. Generally, the
octane number of gasoline blends is monitored in terms of octane barrels. Octane
barrels relates to the number of barrels of gasoline of a particular octane number
produced in a day. Commercial gasoline is generally a blend of low boiling
hydrocarbons, such as hydrocarbons with 4-12 carbon atoms. These hydrocarbons
may be produced by various hydroprocessing reactions, such as separating of crude
oil fractions. Various types of gasoline blends may be used for different applications
depending upon gasoline engine design and climate conditions. In addition,
commercial gasoline should meet all safety and environmental regulations.
[0011] One component of gasoline performance is the octane number, with
higher octane number gasoline giving higher performance. Catalytic reforming and isomerization are widely used processes for improving the octane number of naphtha boiling range components, i.e., the C5 to C12 components. The isomerization process is generally used for increasing the octane number of C5 and C6 paraffin components. The octane number is increased because of the rearrangement of the structure of straight chain paraffins into branched chain paraffins, referred to as isomerization reaction. Isomerization is an equilibrium driven reaction and lower temperatures are favorable for driving the forward reaction.

[0012] In catalytic reforming, the paraffins and naphthenes are passed
through a reformer to form higher octane aromatics. Catalytic reforming converts low octane paraffins to naphthenes, naphthenes are converted to higher octane aromatics, and aromatics are left unchanged. Catalytic reforming is generally used for converting C7 and higher components into their aromatics. However, lower boiling components, such as C6 components require severe operating conditions compared to those for C7 and higher components. The severity of operating conditions leads to more benzene production in the reformate and high coke formation on the catalyst surface. In addition, it also reduces hydrogen/feed production because C6 paraffins contribute very little hydrogen.
[0013] Even though both isomerization and catalytic reforming units are
used for increasing the research octane number (RON) of hydrocarbons, catalytic reforming depends on aromatics production for increasing RON while isomerization maximizes iso-paraffins by converting normal paraffins. Thus, the isomerization unit product contains negligible aromatic content, but its Reid vapor pressure (RVP) is higher compared to that of the reformer product. Maximization of RON of isomerization product while minimizing RVP is important to maximize the octane barrels in refinery.
[0014] Light naphtha isomerization is a process that significantly improves
octane in light gasoline fractions. It is a particularly important process step in petroleum refineries typically employed to meet the most stringent gasoline specifications, such as those for reducing benzene, aromatics and sulfur content in the gasoline pool. However, many of these regulatory mandates have the undesirable side effect of reducing octane barrels production in refineries. The refining industry is thus under constant pressure to reduce operating and capital expenses.
[0015] Light naphtha typically contains C5 to C9 components and is
produced in refineries from different sources, such as from an atmospheric crude distillation column, hydrocracker unit, diesel hydrotreating unit, and delayed coker unit. Light naphtha is primarily separated into isomerization unit feed and catalytic reforming unit feed through distillation. The number of separation columns and

degree of separation depends on the individual refinery configuration. The ideal components for isomerization are n-pentane, n-hexane, 2-methyl pentane, and 3-methyl pentane. However, obtaining 100% of the desired components in an isomerization feed is not possible as close boiling components such as iso-pentane, cyclopentane, cyclohexane, benzene, and C7 isomers boil at a similar temperature range and form azeotropes. Details of undesired components in an isomerization feed and their effect is provided in Table 1. Minimization of undesired components will have a positive effect on isomerate yield and hydrogen consumption.
Table 1: Undesirable components in isomerization feed and their effect.

S.no Undesirable component Effect on isomerization
1 iso-pentane • Does not participate in reaction
• Inhibits n-pentane isomerization
due to equilibrium reaction
• Underutilization of isomerization
unit capacity
2 Cyclopentane • Does not participate in reaction
• Underutilization of isomerization
unit capacity
3 C7 isomers and paraffins • Leads to production of off gas and lighter components due to cracking
4 Benzene • Inhibits catalyst performance
• Consumes high amount of
hydrogen for saturation
[0016] Isomerization converts normal paraffins into iso-paraffins.
Isomerization reaction is an equilibrium reaction; the equilibrium of iso- and normal paraffins will be reached at the reactor effluent. When this equilibrium is reached, an equilibrium product ratio will be obtained. Further attempts to exceed the equilibrium product ratio for increasing iso-paraffins in the reactor effluent will only result in less iso-paraffin yield and an increase in propane and lighter components yield because of cracking. An example isomerate product composition along with their boiling points is provided in Table 2.

Table 2: Isomerization reaction products

S.No Component Boiling
point
°C RON Remarks
1 Iso-pentane 27.84 92.3 High RON blending component, subjected to RVP of total gasoline pool produced in refinery
2 n-pentane 36.07 61.7 Low RON blending component, can be recycled subjected to RVP of total gasoline pool produced in refinery and Isomerization unit capacity
3 Cyclopentane 49.25 100.1 High RON blending components for gasoline
4 2,2 dimethylbutane 49.73 91.8

5 2,3 dimethylbutane 57.98 100.3

6 2-methyl pentane 60.26 73.4 Low RON component, can be recycled to isomerization unit subjected to required RON of isomerate and isomerization unit capacity
7 3-methyl pentane 63.27 74.5

8 n-hexane 68.73 24.8

9 Methyl cyclopentane 71.81 91.3 Good RON components, can be blended directly in gasoline pool
10 2,2 dimethylpentane 79.19 92.8

11 2,4 dimethylpentane 80.49 83.1

12 Cyclohexane 80.72 83.9

13 2-methyl hexane 90.05 42.4 Low RON, prone to cracking, not desirable in isomerization feed
14 3-methyl hexane 91.85 52

[0017] Each molecule in the isomerate product has distinct properties, and
the routing of each molecule depends on the required RON, RVP, isomerization unit configuration and other available sources of octane barrels in refinery and their properties. Iso-pentane is a high RON component but has a high RVP. Presence of iso-pentane is attributed two sources, one is carryover of iso-pentane present in light naphtha due to improper separation and another source is the isomerization of n-pentane in the isomerization reactor. n-Pentane in the isomerization product is the unreacted fraction inside the isomerization reactor because of equilibrium limitation. Its RON is low compared to that of iso-pentane.

[0018] Conventionally, n-pentane is minimized in the isomerization
product by removing the maximum amount of possible n-pentane in a fractionator prior to isomerization. However, because of this approach, iso-pentane, which is relatively easy to produce compared to other high octane components, is prevented from being produced because of a lack of n-pentane in the feed, which leads to a loss in the production of octane barrels.
[0019] Cyclopentane, 2,3 dimethylbutane and 2,2 dimethylbutane are good
sources of RON improvers in a gasoline blend. 2-Methylpentane, 3-methyl pentane, and n-hexane are low RON components. Typically, these components are separated in an isomerization product separator and recycled to the isomerization reactor for further RON improvement of the isomerate product. Other heavy components shown in Table 2 are low RON components, but their percentage in the isomerization product depends upon the isomerization feed composition, and usually their fraction is insignificant.
[0020] A typical isomerization unit complex includes a naphtha splitter, a
pentane removal unit, a benzene saturation reactor, an isomerization reactor, a stripper, and an isomerization product fractionator. The naphtha splitter, pentane removal unit, and isomerization product fractionator are distillation units. Typically, low RON components such as normal paraffins and single branch isomers are recycled back to isomerization reactor for increasing the isomerate yield with higher RON. The design and operation of these units is important in producing high number of octane barrels with desired specifications while using minimum energy.
[0021] The most energy intensive separations are the distillation processes
that separate components or fractions based on boiling point and relative volatility. Closer the boiling point higher the energy requirement for separation, in particular, the separation of dimethyl butane from methyl pentane from the isomerization product and the separation of iso-pentane from n-pentane in the isomerization feed require large energy inputs to the respective distillation column reboilers to perform the desired separations.

[0022] Fig. 1 illustrates a typical process scheme employed to produce
isomerization product and gasoline blending components. Light naphtha feed 102 enters a naphtha splitter column 104. After separation in the naphtha splitter 104, a naphtha splitter first top cut 108, rich in mixed pentanes and C6 paraffins is sent to a separator 112 for removing mixed pentanes or iso-pentanes. A naphtha splitter first bottom cut 116 rich in C7+ components is sent to a catalytic reforming unit 122. The reformation products 126 from the catalytic reforming unit 122 are then sent to a gasoline blending pool 132. A naphtha splitter mid cut 142 rich in benzene and cyclohexane is removed from the naphtha splitter column 104 and sent for further processing.
[0023] A separator top cut 144 rich in mixed pentanes or iso-pentane is sent
to a flow splitter 148 from which a portion of the separator top cut 144 is sent to the gasoline blending pool 132. A separator bottom portion 152 rich in n-pentane and C6 hydrocarbons is sent to the isomerization unit 156. Isomerization is performed in the isomerization unit 156 and the isomerization products 160 are sent to a stripper 164. Light components are removed from the stripper 164 as a top product. The stripper bottom product 168 is sent to an isomerization product separator 172. The isomerization product separator 172 separates a separator top cut 174 rich in pentanes and dimethyl butanes and it is sent to the gasoline blending pool 132. The separator bottom cut 178, which is heavy isomerate product is sent to the gasoline blending pool 132. A stream 182 rich in n-hexane and methyl pentanes is recycled back to the isomerization unit 156 for isomerization.
[0024] This conventional process has several disadvantages. It uses more
columns and consumes very high energy. For example, naphtha splitters play an important role in providing quality feed to downstream isomerization and reforming units. To achieve this objective, naphtha splitters are often designed with higher reboiler and condenser duties. When designed with less energy usage for saving energy, naphtha splitters provide low quality feedstock to downstream units because of their poor separation efficiency. In particular, isomerization feed quality reduces, and the feed has a lot of undesirable components as shown in Table 1. The presence of the low RON light component n-pentane in the isomerate product limits

the blending percentage of light isomerate in the gasoline blending pool. There is
underutilization of the isomerization unit capacity. There are undesirable benzene
precursors in the reformate feed, which results in increasing benzene production
and underutilization of the reactor capacity. These lead to a decrease in octane
barrels production and have a high energy consumption for the separation
processes. To avoid the disadvantages of poor separation, naphtha splitters are often
designed with higher reboiler and condenser duties. Thus, in view of the importance
of energy reduction for separation and the demand for high octane gasoline, there
is a need of a process for producing high octane gasoline with minimum aromatics.
[0025] The present subject matter overcomes these and other disadvantages
and relates to a method for improving octane number in gasoline blends. The method comprises receiving a light naphtha feed by a naphtha splitter and splitting the naphtha feed into a first top cut, a first side cut, a second side cut, and a first bottom cut. The first side cut from the naphtha splitter is received by an isomerization unit for isomerization of the first side cut feed in isomerization unit to produce an isomerization reaction product. The isomerization reaction product produced by the isomerization unit is received by an isomerization product stripping unit. A stripper bottom product is received by a first column separator. Products are separated in the first column separator and a heavy isomerate product from the first column separator is sent to a gasoline blending pool. A first separator top cut is sent to one of the gasoline blending pool or a second column separator. The second column separator receives the first separator top cut and the first top cut from the naphtha splitter. Low RON components are removed in the second column separator and the products are sent to the gasoline blending pool. A second separator bottom cut is removed from the second column separator and sent into the gasoline blending pool.
[0026] The present subject matter also relates to an assembly for producing
high octane barrels. The assembly comprises a naphtha splitter, an isomerization unit to receive the first side cut from the naphtha splitter, an isomerization product stripping unit to receive isomerization reactor product, a first column separator for separating isomerization product and to receive stripper bottom product, a second

column separator for removing low RON components and to receive the first
separator top cut from the first separator and the first top cut from the naphtha
splitter, a gasoline blending pool, a catalytic reforming unit, and a benzene
saturation and cyclohexane recovery unit to receive a second side cut from the
naphtha splitter. The first and the second column separators and the naphtha splitter
may individually be selected from a distillation column or a divided wall column.
[0027] The method and assembly of the present subject matter improves the
octane barrels produced with minimum capital and operating cost. The use of a
divided wall naphtha splitter allows separating various components, such as iso-
pentane-rich stream, n-pentane and n-hexane rich stream, benzene rich stream, and
C7+ components in a single divided wall column. The top cut from the naphtha
splitter may be directly added to the gasoline blending pool. In addition, removal
of benzene and aromatics in the naphtha splitter allows for reduced aromatics in
gasoline, providing a simple way of removing aromatics from gasoline.
[0028] The first column separator allows for separating the products from
the isomerization unit. A side cut from the first column separator rich in n-hexane and methyl pentanes may be recycled back to the isomerization unit for further isomerization. In another example, a mid cut from the first column separator may be recycled back to the naphtha splitter. This may also allow heat exchange. This stream may act as an additional reflux for the naphtha splitter, which minimizes benzene and C7+ components in the first side cut. The reduced amount of benzene reduces hydrogen consumption in a benzene saturation reactor because of the reduction in benzene content in the isomerization feed. The reduction in C7+ components minimizes off gas and light gas production. Light components iso-pentane, n-pentane will evaporate and will be obtained in the first top cut, which is routed to the gasoline blending pool. This may also reduce condenser duty in the naphtha splitter. Furthermore, the separation of iso-pentane, n-pentane, cyclopentane, and dimethyl butanes by the second column separator allows for removing low RON, high RVP n-pentane that limits the blending percentage of light isomerate in the gasoline blending pool, increasing RON and improving RVP. Thus, the method and assembly of the present subject matter allows for integrating

separation columns, feed and product schemes, and reactors for improving RON of octane barrels and producing high octane barrels with the flexibility to control the RVP of the gasoline blending pool and operate according to the gasoline blending requirements.
[0029] The use of a divided wall column as the first and/or second column
separator provides greater energy efficiency and improved product yields compared
to a distillation column separator. The size of a divided wall column separator will
be smaller compared to a distillation column to achieve the same level of separation.
Furthermore, depending on the components to be separated, a distillation column
may be not able to separate close-boiling components. The use of a divided wall
column also prevents feed contamination when a side cut is removed close to the
feed inlet and prevents intermixing or back mixing of the separated components
with the inlet feed, leading to greater energy efficiency in the separation process.
[0030] Aspects of the present subject matter are further described in
conjunction with the appended figures. It should be noted that the description and figures merely illustrate the principles of the present subject matter. It will thus be appreciated that various arrangements that embody the principles of the present subject matter, although not explicitly described or shown herein, can be devised from the description and are included within its scope. Moreover, all statements herein reciting principles, aspects, and implementations of the present subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof.
[0031] Fig. 2 illustrates a schematic process flow of an example method for
improving octane number in gasoline blends, in accordance with an embodiment of the present subject matter. A light naphtha feed 204 is received by a naphtha splitter 208. In an example, the naphtha splitter 208 may be a divided wall unit where a divided wall may be disposed in a middle portion of the naphtha splitter 208. The naphtha splitter 208 splits the feed stream into a first top cut 212, a first side cut 216, a second side cut 220, and a first bottom cut 224. The first top cut 212 is rich in iso-pentane and may be sent to a gasoline blending pool 230 via a flow splitter 234. The flow splitter 234 allows a part of the first top cut 212 to be sent to the

gasoline blending pool 230 and another part to be used for other processing such as feed to hydrogen generation unit and as a naphtha product depending upon refinery product slate requirement.
[0032] The first side cut 216 rich in n-hexane, 2-methyl pentane, and 3-
methyl pentane may be sent to an isomerization unit 238. The first side cut 216 may be isomerized in the isomerization unit 238 to produce isomerization reaction product 242. The isomerization reaction product 242 may be received by an isomerization product stripping unit 246. Light components 250 may be removed from the top of the isomerization product stripping unit 246. A stripper bottom product 254 may be received by a first column separator 258, for example a divided wall column separator. The first column separator 258 allows for simple separation of the stripper bottom product 254 and use of a divided wall column makes it less energy intensive compared to conventionally used distillation processes. In an example, a divided wall may be disposed in a middle portion of the first column separator 258. A first separator bottom cut 262, comprising heavy isomerate product may be sent to the gasoline blending pool 230. A first separator top cut 266, rich in mixed pentanes and methyl butanes may be sent to the gasoline blending pool 230. Gasoline blending pool 230 receives different streams of refinery products, such as hydrocracker naphtha, fluid catalytic cracking unit gas oil, and any other streams that meet the gasoline specifications criteria, for blending with gasoline. Ratio of each stream in the gasoline blending pool 230 depends on the individual stream properties and the required gasoline specifications. In another example, the first separator top cut 266 may be sent to a second column separator (not shown in Fig. 2).
[0033] From the first column separator 258, first separator side cut 270, rich
in n-hexane and methyl pentanes may be recycled back to the isomerization unit 238. In an example, this recycle may be done with or without heat exchange. The second side cut 220, comprising mainly cyclohexane and aromatics, such as benzene, may be received by a benzene saturation and cyclohexane recovery unit 268, where the second side cut 220 may be hydrotreated for benzene saturation and the saturated product is separated into a cyclohexane-rich stream 272 and a leftover

product stream 274, from where they may be sent for further processing as required, such as feed to hydrogen generation unit and as a naphtha product depending upon refinery product slate requirement. The first bottom cut 224 from the naphtha splitter 208 may be received by a catalytic reforming unit 278. After reformation reaction, a high octane number reformate 282 may be sent to the gasoline blending pool 230.
[0034] The use of a divided wall column as naphtha splitter 208 allows
separating various components, such as iso-pentane rich stream, n-pentane and n-hexane rich stream, benzene rich stream, and C7+ components in a single divided wall column. This reduces the number of separators, reducing costs and improving operating efficiency. The first top cut 212 from the naphtha splitter 208 may be directly added to the gasoline blending pool. In addition, removal of benzene and aromatics in the naphtha splitter allows for reduced aromatics in gasoline, providing a simple way of removing aromatics from gasoline.
[0035] Fig. 3 illustrates a schematic process flow of another example
method for improving octane number in gasoline blends, in accordance with an embodiment of the present subject matter. In the example process shown in Fig. 3, a second column separator 310 is provided after the first column separator 258 of Fig. 2. In an example, the second column separator 310 may be a distillation column. In another example, the second column separator 310 may be a divided wall column in which a divided wall may be disposed in a middle portion of the column. In yet another example, the divided wall may be disposed on a top portion of the second column separator 310. In an example, the first separator top cut 266 rich in mixed pentanes and methyl butanes may be received by the second column separator 310. The second column separator 310 may also receive the first top cut 212 from the naphtha splitter 208. The second column separator 310 is for removing low RON components before blending into the gasoline blending pool 230 for increasing the overall RON of the gasoline blending pool 230 or to increase the gasoline blending pool 230 total octane barrels at a particular RON. In an example, the low RON components may be iso-pentane, n-pentane, 2,2 dimethyl butane, and

2,3 dimethyl butane. As the second column separator 310 helps to increase the RON, it may also be called a RON Maximizer.
[0036] The second column separator 310 separates the feed into a second
separator top cut 320, a second separator bottom cut 330, and an n-pentane-rich stream 340. The second separator top cut 320 is rich in iso-pentane and may be sent to the gasoline blending pool 230. The second separator bottom cut 330 may comprise cyclopentane, double branched C6 paraffins, and dimethyl butanes and may be sent for mixing with the gasoline blending pool 230. The n-pentane-rich stream 340 may be sent for further processing as required. The separation of the different components in the second column separator 310 allows for removing low RON, high RVP n-pentane, which limits the blending percentage of light isomerate in the gasoline pool. In an example, if the RVP is highly limiting, only dimethyl butanes may be blended in the gasoline blending pool 230.
[0037] The use of a second column separator 310 for separating iso-pentane
and n-pentane further allows removal of low RON components before mixing with the gasoline. This helps increasing the RON of the gasoline or total octane barrels produced in an efficient manner leading to reduced operating costs. In addition, it provides flexibility to control RVP and RON of the streams depending on the requirement.
[0038] Fig. 4 illustrates a schematic of an exploded view of an example
divided wall column naphtha splitter, in accordance with an embodiment of the present subject matter. The naphtha feed 204 enters the naphtha splitter 208. The first top cut 212 is rich in iso-pentane and may also comprise n-pentane. The first top cut 212 may be sent to the gasoline blending pool 230. The first side cut 216 is rich in C5 and C6 components and may comprise n-pentane, n-hexane, 2-methyl pentane, and 3-methyl pentane. The first side cut 216 may be sent to the isomerization unit 238. The second side cut 220 is rich in C6 cyclics and aromatics, such as cyclohexane and benzene. The second side cut 220 may be sent to the benzene saturation and cyclohexane recovery unit 268. The first bottom cut 224 comprises mainly heavy hydrocarbons, such as C7+ components, and may be sent to the catalytic reforming unit 278.

[0039] Fig. 5 illustrates a schematic process flow of another example
method for improving octane number in gasoline blends, in accordance with an embodiment of the present subject matter. In the example shown in Fig. 5, a mid cut 510 is removed from the first column separator 258 of the example process of Fig. 3. In an example, the mid cut 510, which is rich in n-hexane and methyl pentanes, may be removed from the first column separator 258 and sent to the naphtha splitter 208 above the first side cut 216. The mid cut 510 may act as an additional reflux for the naphtha splitter 208, which minimizes benzene and C7+ components in the first side cut 216, better hydraulic control, reduction in condenser duties, and decrease in column operating pressure. In addition, this may allow reduced hydrogen consumption in a benzene saturation reactor because of reduction in benzene content in the isomerization feed. Reduction in the C7+ components minimizes off gas and light gas production. Light components iso-pentane, n-pentane will evaporate and will be obtained in first top cut 212, which is routed to the gasoline blending pool 230. Furthermore, there may be a reduction in the naphtha splitter 208 condenser duty. In another example, the n-pentane stream 340 may be separated from the second column separator 310 and sent to the isomerization unit 238. This allows for further improving the RON or octane barrels of the gasoline blending pool 230. In an example, the naphtha splitter 208, the first column separator 258, and the second column separator 310 may be one of a distillation column separator, divided wall column separator, or a combination thereof.
[0040] Fig. 6 illustrates a schematic process flow of another example
method for improving octane number in gasoline blends. In an example, the second column separator 310 may comprise a dividing wall 610 so that the dividing wall 610 divides a top portion of the second column separator 310. The feed, which may be the first separator top cut 266 and the first top cut 212 from the naphtha splitter 208, enters on one side of the dividing wall. The second separator top cut 320 rich in iso-pentane is drawn from the same side as that of the feed. The n-pentane-rich stream 340 rich in n-pentane is recovered from a second side of the dividing wall 610.

[0041] The present subject matter also relates to an assembly for improving
octane barrels. The assembly comprises the naphtha splitter 208, the isomerization unit 238 to receive the first side cut 216 from the naphtha splitter 208, the first column separator 258, the gasoline blending pool 230, the catalytic reforming unit 278, and the benzene saturation and cyclohexane recovery unit 268. The assembly further comprises a second column separator 310 for removing low RON components and to receive a first separator top cut 266 from the first column separator 258 and the first top cut 212 from the naphtha splitter 208.
[0042] In an example, the low RON components rich in n-pentane is
separated as n-pentane stream 340 in the second column separator 310. The second
separator bottom cut 330 may comprise cyclopentane and double branched C6
paraffins and the second separator top cut 320 may comprise iso-pentane.
[0043] In an example, the gasoline blending pool 230 may receive different
cuts from one or more of the second column separator 310, the bottom cut 262 of the first column separator 258, the first top cut 212 of the naphtha splitter, and from the catalytic reforming unit 278.
EXAMPLES
[0044] The disclosure will now be illustrated with working examples,
which are intended to illustrate the working of disclosure and not intended to take
restrictively to imply any limitations on the scope of the present disclosure. Unless
defined otherwise, all technical and scientific terms used herein have the same
meaning as commonly understood to one of ordinary skill in the art to which this
disclosure belongs. Although methods and materials similar or equivalent to those
described herein can be used in the practice of the disclosed methods and
compositions, the exemplary methods, devices and materials are described herein.
It is to be understood that this disclosure is not limited to particular methods, and
experimental conditions described, as such methods and conditions may apply.
[0045] To compare the methods of the present subject with conventional
methods, the process was simulated using an example feed composition shown in Table 3.

Table 3: Feed composition used for simulating method of improving octane number

Mass flow tons/hr 50
i-pentane wt% 6.5
n-pentane
11.7
C6 paraffins
21.5
Benzene
2.5
C7+ components
51.0
[0046] Table 4 shows an example composition of the first side cut 216 sent
to the isomerization unit 238. Scheme 1 uses the first column separator 258 and Scheme 2 uses the first column separator 258 and the second column separator 310. Isomerization feed quality is comparatively better in the schemes of the present subject matter compared to those of prior arts. High amounts of undesired components cyclohexane and C7+ components were obtained in the isomerization feed of prior art. In contrast, in the method of the present subject matter, good quality isomerization feed was obtained as divided wall column was able to separate out the undesirable components efficiently compared to the conventional prior art scheme.
Table 4: Composition of isomerization unit feed

ISOM feed (Combined)
Prior art Scheme 1 Scheme 2
Mass flow tons/hr 27.0 27.0 27.0
i-pentane wt% 0.2 3.1 3.1
n-pentane
8.8 9.7 9.7
CP and MCP
6.6 9.7 9.7
C6 double branch iso paraffins
10.2 6.4 6.4
C6 single branch isomers
42.7 41.8 41.8
n-hexane
18.3 22.3 22.3
Benzene and Cyclohexane
7.8 5.9 5.9

C7+ components 5.4 1.0 1.0
Reboiler duty
Number of columns for
naphtha splitting Gcal/hr Base 2 0.76* Base
1 Base 1
[0047] Table 5 shows the isomerization reaction product obtained from the
isomerization unit 238. The isomerate is richer in iso-paraffins compared to the isomerate obtained using conventional processes. In the prior art process, the amount of C7+ components is high because of inefficient separation of light naphtha in the isomerization feed. Table 5: Total isomerate composition

Isomerate product
Prior art Scheme 1 Scheme 2
Mass flow tons/hr 27.0 27.0 27.0
i-pentane wt% 6.8 9.8 9.8
n-pentane
2.1 3.1 3.1
CP and MCP
8.1 8.7 8.7
C6 double branch iso paraffins
28.5 28.2 28.2
C6 single branch isomers
35.4 35.2 35.2
n-hexane
7.3 7.2 7.2
Cyclohexane
6.4 7.1 7.1
C7+ components
5.4 0.7 0.7
[0048] Table 6 shows an example composition of the gasoline blending
pool originating from the isomerization unit and first top cut 212. Reformate unit products are excluded in octane blending pool. Table 7 shows the total energy and number of theoretical stages used in the proposed schemes. The gasoline of the present subject matter has higher amounts of high RON components, leading to an increase in the RON value compared to that obtained using conventional processes. The amount of single branch isomers is reduced in the schemes of the present subject matter as the first column separator 258 can concentrate single branch isomers in the first separator side cut 270. A high concentration of single branch isomers in the recycle stream is converted into double branch isomers that have a

high RON compared to single branch isomers. Subsequently, the amount of double branch isomers is increased in the total octane blending pool. The RON obtained using scheme 1 is increased 3 units and consumes 22% less energy compared to the prior art scheme. In addition to the energy savings, scheme 1 can achieve RON improvement with a minimum number of trays, 35 trays less in an example, compared to the prior art scheme, when using a divided wall column. The RON obtained using scheme 2 improved 4 points compared to the prior art scheme. In scheme 2, the energy and number of trays used for separation are same as those in the prior art scheme. Table 6: Composition of gasoline blending pool

Octane barrels
Prior art Scheme 1 Scheme 2
Mass flow tons/hr 16.9 16.5 16.5
i-pentane wt% 19.4 22.0 25.6
n-pentane
12.0 13.2 9.2
CP and MCP
8.6 4.5 4.4
C6 double branch iso paraffins
32.1 38.5 38.2
C6 single branch isomers
7.3 10.0 10.5
n-hexane
6.1 0.8 1.1
Cyclohexane
7.7 9.9 9.9
C7+ components
7.0 1.1 1.1
RON Base Base+3 Base+4
No. of distillation columns 4 2 3
[0049] Table 7 shows a comparison of the energy consumption for
conventional process and the process of the present subject matter and the number
of theoretical stages used in the proposed scheme. The process of the present subject
matter uses less energy for reboiler and condenser compared to that of conventional
processes.
Table 7: Comparison of energy consumption

Energy comparison
Parameter units Prior art Scheme 1 Scheme 2
Total Reboiler duty Gcal/hr Base Base-4 Base

Total condenser duty Gcal/hr Base Base-4 Base
No. of theoretical stages Base Base-35 Base
[0050] Thus, the process and assembly of the present subject matter allows
for increasing the octane barrels without increasing capital or operation costs. Furthermore, the present subject matter provides for a flexible process for obtaining the desired RON value in gasoline blends that also consumes lesser energy than conventional processes.
[0051] Although embodiments for the present subject matter is described in
language specific to structural features, it is to be understood that the specific features and methods are disclosed as example embodiments for implementing the claimed subject matter.

I/We Claim:
1. A method for improving octane number in gasoline blends, the method
comprising:
receiving a light naphtha feed (204) by a naphtha splitter (208);
splitting of the light naphtha feed (204) into a first top cut (212), a first side cut (216), a second side cut (220), and a first bottom cut (224);
receiving by an isomerization unit (238) the first side cut (216) from the naphtha splitter (208);
isomerization of the first side cut (216) in the isomerization unit (238) to produce an isomerization reaction product (242);
receiving the isomerization reaction product (242) produced by the isomerization unit (238) by an isomerization product stripping unit (246);
receiving a stripper bottom product (254) by a first column separator (258);
separating products in the first column separator (258) and sending heavy isomerate product to a gasoline blending pool (230);
sending a first separator top cut (266) to one of the gasoline blending pool (230) or a second column separator (310); and
obtaining gasoline blends of desired octane number from the gasoline blending pool (230).
2. The method as claimed in claim 1 comprising receiving, by the second
column separator (310), the first separator top cut (266) and the first top cut
(212) from the naphtha splitter (208);
removing low RON components in the second column separator (310) and sending the products to the gasoline blending pool (230); and
separating a second separator bottom cut (330) from the second column separator (310) and blending it into the gasoline blending pool (230).
3. The method as claimed in claim 1 comprising receiving the second side cut
(220) from the naphtha splitter (208) by a benzene saturation and
cyclohexane recovery unit (268), wherein the second side cut (220)
comprises benzene and cyclohexane.

4. The method as claimed in claim 1 comprising receiving the first bottom cut (224) from the naphtha splitter (208) by a catalytic reforming unit (278).
5. The method as claimed in claim 1 comprising separating n-hexane and methyl pentanes in the first column separator (258) and sending them to the isomerization unit (238).
6. The method as claimed claim 1 comprising separating n-hexane and methyl pentanes in the first column separator (258) and sending them to the naphtha splitter (208).
7. The method as claimed in claim 1, wherein the low RON components in the second column separator (310) comprise n-pentane.
8. The method as claimed in claim 1, wherein the second separator bottom cut (330) comprises cyclopentane and double branched C6 paraffins.
9. The method as claimed in claim 1 comprising separating an n-pentane stream (340) from the second column separator (310) and sending it to the isomerization unit (238).
10. The method as claimed in claim 1 comprising separating an iso-pentane-rich stream as a second separator top cut (320) and sending the second separator top cut (320) to the gasoline blending pool (230).
11. The method as claimed in claim 1 comprising removing a mid cut (510) from the first column separator (258) and sending the mid cut (510) to the naphtha splitter (208).
12. An assembly for improving octane number in gasoline blends, the assembly comprising:
a naphtha splitter (208);
an isomerization unit (238) to receive a first side cut (216) from the naphtha splitter (208);
an isomerization product stripping unit (246) to receive isomerization reaction product (242);
a first column separator (258) to receive stripper bottom product (254) for separating isomerization reaction product (242);

a gasoline blending pool (230) to receive different streams for blending with gasoline;
a catalytic reforming unit (278) to receive a first bottom cut from the naphtha splitter (208) for reformation of a feed; and
a benzene saturation and cyclohexane recovery unit (268) to receive a second side cut (220) from the naphtha splitter (208) for separating cyclohexane and aromatics.
13. The assembly as claimed in claim 12 comprising a second column separator (310) to receive a first separator top cut (266) from the first column separator (258) and the first top cut (212) from the naphtha splitter (258) for removing low RON components.
14. The assembly as claimed in claim 12, wherein,
low RON components removed in a second column separator (310) comprise iso-pentane, n-pentane, 2,2 dimethyl butane, and 2,3 dimethyl butane;
a second separator bottom cut (330) comprises cyclopentane and double branched C6 paraffins; and
a second separator top cut (320) comprises iso-pentane.
15. The assembly as claimed in claim 12, wherein the gasoline blending pool (230) is to receive different cuts from one or more of a second column separator (310), a first separator bottom cut (262) of the first column separator (258), a first top cut (212) of the naphtha splitter (208), and from the catalytic reforming unit (278).
16. The assembly as claimed in claim 12, wherein a second column separator (310) comprises a dividing wall (610) to separate a top portion of the second column separator (310), wherein a second column separator (310) is to receive a first separator top cut (266) and a first top cut (212) from the naphtha splitter (208) on one side of the dividing wall (610), and wherein a second separator top cut (320) rich in iso-pentane is to be drawn from the same side as that of the feed and n-pentane-rich stream (340) rich in n-pentane is to be recovered from a second side of the dividing wall (610).

17. The assembly as claimed in claim 12, wherein the naphtha splitter (208), the first column separator (258), and a second column separator (310) are individually selected from a distillation column and a divided wall column.