U.S. patent application number 16/812284 was filed with the patent office on 2021-09-09 for process for increasing the concentration of normal hydrocarbons in a stream.
The applicant listed for this patent is UOP LLC. Invention is credited to Ernest J. Boehm, Gregory Funk, Mark P. Lapinski, Marina S. Minin, Cora Wang Ploentham, David J. Shecterle.
Application Number | 20210277316 16/812284 |
Document ID | / |
Family ID | 1000004812202 |
Filed Date | 2021-09-09 |
United States Patent
Application |
20210277316 |
Kind Code |
A1 |
Funk; Gregory ; et
al. |
September 9, 2021 |
PROCESS FOR INCREASING THE CONCENTRATION OF NORMAL HYDROCARBONS IN
A STREAM
Abstract
A process increases the concentration of normal paraffins in a
feed stream comprising separating a naphtha feed stream into a
normal paraffin rich stream and a non-normal paraffin rich stream.
The non-normal paraffin rich stream is isomerized over a first
isomerization catalyst to convert non-normal paraffins to normal
paraffins and produce a first isomerization effluent stream. An
iso-C4 stream is separated from the first isomerization effluent
stream and isomerized over a second isomerization catalyst to
convert iso-C4 hydrocarbons to normal C4 hydrocarbons and produce a
second isomerization effluent stream. The normal paraffin rich
stream, the normal paraffins in the first isomerization effluent
stream and/or the second isomerization effluent stream may be fed
to a steam cracker.
Inventors: |
Funk; Gregory; (Carol
Stream, IL) ; Ploentham; Cora Wang; (Elk Grove
Village, IL) ; Minin; Marina S.; (Lake Forest,
IL) ; Lapinski; Mark P.; (Aurora, IL) ;
Shecterle; David J.; (Arlington Heights, IL) ; Boehm;
Ernest J.; (Hanover Park, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UOP LLC |
Des Plaines |
IL |
US |
|
|
Family ID: |
1000004812202 |
Appl. No.: |
16/812284 |
Filed: |
March 7, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10G 2300/1044 20130101;
C10G 61/06 20130101; C10G 63/04 20130101 |
International
Class: |
C10G 63/04 20060101
C10G063/04; C10G 61/06 20060101 C10G061/06 |
Claims
1. A process for increasing the concentration of normal paraffins
in a feed stream comprising: separating a naphtha feed stream into
a normal paraffin rich stream and a non-normal paraffin rich
stream; isomerizing the non-normal paraffin rich stream over a
first isomerization catalyst to convert non-normal paraffins to
normal paraffins and produce a first isomerization effluent stream;
separating an iso-C4 stream from said first isomerization effluent
stream; isomerizing said iso-C4 stream over a second isomerization
catalyst to convert iso-C4 hydrocarbons to normal C4 hydrocarbons
and produce a second isomerization effluent stream; and feeding
said second isomerization effluent stream to a steam cracker.
2. The process of claim 1 further comprising separating a C4 stream
from said first isomerization effluent stream and separating said
C4 stream into said iso-C4 stream and a normal C4 stream.
3. The process of claim 2 further comprising feeding said normal C4
stream to said steam cracker.
4. The process of claim 2 further comprising feeding said normal C4
stream to the step of separating a normal paraffins stream from
non-normal paraffins stream and desorbing normal paraffins from an
adsorbent.
5. The process of claim 2 further comprising feeding said normal-C4
stream and said desorbed normal paraffins to a steam cracker
together.
6. The process of claim 2 further comprising feeding said second
isomerization effluent stream to the step of separating said C4
stream into an iso-C4 stream and a normal C4 stream.
7. The process of claim 1 further comprising: separating said first
isomerization effluent stream to produce a C3 stream and further
converting said C3 stream into an olefinic stream.
8. The process of claim 1 further comprising separating a C5 and C6
paraffins stream from said first isomerization effluent stream and
recycling the C5 and C6 paraffins stream to the step of separating
the naphtha feed stream into the normal paraffin rich stream and
the non-normal paraffin rich stream.
9. The process of claim 1 wherein the step of separating the
naphtha feed stream into the normal paraffins stream from the
non-normal paraffins stream comprises extracting said normal
paraffins by use of an adsorbent.
10. The process of claim 1 further comprising separating cyclic
hydrocarbons from said non-normal paraffin stream before
isomerizing the non-normal paraffins stream.
11. A process for increasing the concentration of normal paraffins
in a feed stream comprising: separating a naphtha feed stream into
a normal paraffin rich stream and a non-normal paraffin rich
stream; separating the non-normal paraffin rich stream to provide
an iso-C6 paraffin rich stream and C6 cyclics rich stream; and
isomerizing the iso-C6 paraffin rich stream over a first
isomerization catalyst to convert non-normal paraffins to normal
paraffins and produce an isomerization effluent stream.
12. The process of claim 11 further comprising separating a C4
paraffin rich stream from said first isomerization effluent stream
and separating said C4 paraffin rich stream into said iso-C4
paraffin rich stream and a normal C4 paraffin rich stream;
separating an iso-C4 paraffin rich stream from said first
isomerization effluent stream; isomerizing said iso-C4 paraffin
stream over a second isomerization catalyst to convert iso-C4
paraffins to normal C4 paraffins and produce a second isomerization
effluent stream; and feeding said second isomerization effluent
stream to a steam cracker.
13. The process of claim 11 further comprising separating a C5 and
C6 paraffin stream from said first isomerization effluent stream
and recycling the C5 and C6 paraffin stream to the step of
separating the naphtha feed stream into the normal paraffin rich
stream and the non-normal paraffin rich stream.
14. The process of claim 11 further comprising feeding said normal
paraffin rich stream to a steam cracker.
15. The process of claim 12 further comprising separating a C4
paraffin rich stream from said first isomerization effluent stream
and separating said C4 paraffin rich stream into said iso-C4
paraffin rich stream and a normal C4 paraffin rich stream.
16. The process of claim 15 further comprising feeding said normal
C4 paraffin rich stream to said steam cracker.
17. The process of claim 12 further comprising feeding said normal
C4 paraffin rich stream to the step of separating the naphtha feed
stream into the normal paraffin stream and the non-normal paraffin
stream and desorbing normal paraffins from an adsorbent and feeding
said normal-C4 paraffin rich stream and said desorbed normal
paraffin stream to a steam cracker together.
18. The process of claim 12 further comprising: separating said
first isomerization effluent stream into a C3 paraffin rich stream
and further converting said C3 stream into an olefinic stream.
19. The process of claim 12 wherein the step of separating the
normal paraffins stream from the non-normal paraffins stream
comprises extracting said normal paraffins by use of an
adsorbent.
20. A process for increasing the concentration of normal
hydrocarbons in a feed stream comprising: separating a naphtha feed
stream into a normal paraffins stream and a non-normal paraffins
stream; isomerizing an iso-C4 paraffin rich stream over an
isomerization catalyst to convert iso-C4 paraffins to normal C4
paraffins and produce an isomerization effluent stream; separating
a normal C4 paraffin rich stream from said isomerization effluent
stream; and feeding said normal C4 paraffin rich stream to the step
of separating a normal paraffins stream from non-normal paraffins
stream and desorbing normal paraffins from an adsorbent.
Description
FIELD
[0001] The field is processes for increasing the concentration of
normal hydrocarbons in a feed stream and specifically separating
out various fractions of a naphtha stream to convert iso-paraffins
into normal paraffin in an isomerization zone for producing a feed
stream for a steam cracker.
BACKGROUND
[0002] Ethylene and propylene are important chemicals for use in
the production of other useful materials, such as polyethylene and
polypropylene. Polyethylene and polypropylene are two of the most
common plastics found in use today and have a wide variety of uses.
Uses for ethylene and propylene include the production of vinyl
chloride, ethylene oxide, ethylbenzene and alcohol.
[0003] The great bulk of the ethylene consumed in the production of
the plastics and petrochemicals such as polyethylene is produced by
the thermal cracking of higher molecular weight hydrocarbons. Steam
is usually mixed with the feed stream to the cracking reactor to
reduce the hydrocarbon partial pressure and enhance olefin yield
and to reduce the formation and deposition of carbonaceous material
in the cracking reactors. The process is therefore often referred
to a steam cracking or pyrolysis.
[0004] The composition of the feed to the steam cracking reactor
affects the product distribution. A fundamental basis of this is
the propensity a some hydrocarbons to crack more easily than
others. The normal ranking of tendency of the hydrocarbons to crack
to ethylene is normally given as: normal paraffins; iso-paraffins;
olefins; naphthenes, and, aromatics. Benzene and other aromatics
are particularly resistant to steam cracking and undesirable as
cracking feed stocks, with only the alkyl side chains being cracked
to produce the desired product.
[0005] The feed to a steam cracking unit is also normally a mixture
of hydrocarbons varying both by type of hydrocarbon and carbon
number. This variety makes it difficult to separate less desirable
feed components, such as naphthenes and aromatics; from the feed
stream by fractional distillation. The normal paraffins and the
non-normal paraffins can be separated by an adsorption process.
Increasing the concentration of normal paraffins in a stream can
improve the quality of a feedstock to the steam cracking unit.
[0006] Common feeds to steam crackers include light naphtha, which
is concentrated in C5-C6 hydrocarbons, and LPG, which comprises
C3-C4 hydrocarbons. Light naphtha streams typically contain a
mixture of n-paraffins, iso-paraffins, naphthenes and aromatics. It
is generally not possible to procure light naphtha streams that are
concentrated in n-paraffins. Similarly, LPG streams typically
contain a mixture of n-butane, iso-butane, and propane; but streams
concentrated in n-butane are not commonly available.
[0007] One way to upgrade light naphtha is first to separate the
naphtha into a normal paraffin rich stream and a non-normal
paraffin rich stream; and subsequently convert a substantial amount
of the non-normal paraffin stream in an isomerization zone in the
presence of a catalyst into normal paraffins.
[0008] An efficient process for separating and converting the
iso-paraffins in light naphtha to normal paraffins would
significantly increase the profitability of steam cracking
operations by increasing the yield of high value ethylene and
propylene.
BRIEF SUMMARY
[0009] A process increases the concentration of normal paraffins in
a feed stream comprising separating a naphtha feed stream into a
normal paraffin rich stream and a non-normal paraffin rich stream.
The normal paraffin rich stream may be fed to a steam cracker. The
non-normal paraffin rich stream is passed over a first
isomerization catalyst to convert non-normal paraffins to normal
paraffins and produce a first isomerization effluent stream. An
iso-C4 stream is separated from the first isomerization effluent
stream and isomerized over a second isomerization catalyst to
convert iso-C4 hydrocarbons to normal C4 hydrocarbons and produce a
second isomerization effluent stream. The second isomerization
effluent stream may be fed to a steam cracker.
[0010] Alternatively, after separating a naphtha feed stream into a
normal paraffin rich stream and a non-normal paraffin rich stream,
the process comprises separating the non-normal paraffin rich
stream to provide an iso-C6 paraffin rich stream and a
methylcyclopentane or C6 cyclic rich stream; and passing the iso-C6
paraffin rich stream over a first isomerization catalyst to convert
non-normal paraffins to normal paraffins and produce an
isomerization effluent stream.
[0011] In a further alternative, after separating a naphtha feed
stream into a normal paraffins rich stream and a non-normal
paraffins rich stream; isomerizing an iso-C4 paraffin rich stream,
which may be derived from other petrochemical complex streams or
derived from the non-normal paraffins rich stream, over an
isomerization catalyst to convert iso-C4 paraffins to normal C4
paraffins and produce an isomerization effluent stream. A normal C4
paraffin rich stream is separated from the isomerization effluent
stream and the normal C4 paraffin rich stream is fed to the step of
separating a normal paraffins stream from non-normal paraffins
stream and desorbing normal paraffins from an adsorbent.
[0012] Additional details and embodiments of the invention will
become apparent from the following detailed description of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The FIGURE is a schematic view of a conversion unit.
DESCRIPTION OF THE INVENTION
[0014] The present disclosure endeavors to separate normal
paraffins from a light naphtha stream for ideal steam cracker feed.
The process employs a normal paraffin-non-normal hydrocarbon
separation to extract normal paraffins from the light naphtha
stream and transports the normal paraffins to a steam cracking
unit. Furthermore, the non-normal hydrocarbons are converted to
normal paraffins and transported to a steam cracking unit. The
non-normal hydrocarbons, which include iso-paraffins, naphthenes
and aromatics, can optionally undergo an additional separation to
remove the C6 cyclics and any C7+ components from the C5 and C6
iso-paraffins. The C6 cyclics include methylcyclopentane (MCP),
cyclohexane and benzene. The C5 and C6 iso-paraffins can be
isomerized to increase the concentration of normal paraffins and
then subjected to separation. The C5+ paraffins can be recycled
back to the normal-non-normal separation while C4 hydrocarbons can
be further separated to remove normal C4 paraffins for feed to the
steam cracking unit. Separated iso-C4 paraffins can be reverse
isomerized to equilibrium concentrations of normal-C4 paraffins
which can be removed and forwarded to the stream cracking unit.
Normal C4 hydrocarbons can be used to desorb normal paraffins in
the normal-iso paraffin separation. The entire desorbent stream
comprising C4-C6 normal paraffins with perhaps some normal C7
paraffins can be fed to the stream cracking unit.
[0015] The term "C.sub.X" is to be understood to refer to molecules
having the number of carbon atoms represented by the subscript "x".
Similarly, the term "C.sub.X-" refers to molecules that contain
less than or equal to x and preferably x and less carbon atoms. The
term "C.sub.X+" refers to molecules with more than or equal to x
and preferably x and more carbon atoms.
[0016] The naphtha feed stream is preferably a hydrotreated light
naphtha stream comprising substantially C5 and C6 hydrocarbons
having a T90 between about (60.degree. C.) and about 90.degree. C.
The end point is taken to minimize the presence of hydrocarbons
with more than six carbon atoms in the feed. No more than about 30
wt % C7+ hydrocarbons, preferably no more than about 20 wt % C7+
hydrocarbons and more preferably no more than about 10 wt % C7+
hydrocarbons can be present in the light naphtha feed stream. The
naphtha feed stream may comprise normal paraffins, iso-paraffins,
naphthenes, and aromatics.
[0017] We have found that normal paraffins are more prone to crack
to olefins in a steam cracking unit. Hence, it is desired to
increase the concentration of normal paraffins in the feed stream
10. The first step in the process is a step of separating the
naphtha feed stream into a normal paraffin-rich stream and a
non-normal paraffin-rich stream. Normal molecules are defined to
mean straight chain molecules such as normal butane, normal hexane,
and normal pentane. The most efficient process for such a
separation utilizes adsorption. In an aspect, an adsorbent
separation unit 12 is used to separate normal paraffins from
non-normal paraffins.
[0018] As used herein, the term "a component-rich stream" means
that the rich stream coming out of a vessel has a greater
concentration of the component than the feed to the vessel. As used
herein, the term "a component-lean stream" means that the lean
stream coming out of a vessel has a smaller concentration of the
component than the feed to the vessel.
[0019] The naphtha feed stream is delivered to the process in a
feed line 10 and passed to the adsorbent separation unit 12. The
feed stream in feed line 10 is passed through a valve 101 in the
adsorbent separation unit 12 which delivers the feed to an
appropriate bed in an adsorbent vessel 46.
[0020] The feed stream in feed line 10 is separated into a normal
paraffins stream and a non-normal paraffins stream. Straight chain
normal paraffins of the naphtha mixture selectively enter or
occlude into the porous structure of the adsorbent components but
branched or cyclic non-normal chain paraffins do not enter the
pores. The non-normal paraffins exit the process as a raffinate
stream. In order to provide a useful method for separation of
normal from non-normal paraffins, it is necessary to desorb the
occluded normal paraffins. In the disclosed process, normal butane
will be abundantly available and can be used as a desorbent to
desorb normal paraffins in an extract-desorbent stream. If the
normal paraffins are to be sent to a steam cracking unit, there is
efficiently no need to separate the desorbent normal butane from
the extract normal paraffins.
[0021] The adsorbent used in the adsorption vessel preferably
comprises aluminosilicate molecular sieves having relatively
uniform pore diameters of about 5 Angstroms. The preferred
adsorbent is provided by commercially available type 5A molecular
sieves produced and sold by UOP LLC.
[0022] The adsorbent vessel 46 may comprise a series of vertically
spaced, separate beds interconnected by a pipe between the bottom
of one bed and the top of its upstream adjacent bed. The valve 101
may comprise a manifold arrangement or a rotary valve for advancing
the points of inlet and outlet of respective streams in a
downstream direction. The adsorbent vessel 46 operates in an upflow
mode, although downflow may be suitable. The adsorbent vessel 46 is
shown to have four beds I-IV for simplicity, but it may have more
beds such as eight, twelve or twenty-four beds.
[0023] The feed stream is introduced through feed line 10 through
valve 101 which is positioned to send the feed stream through line
17 into the adsorbent bed I. The extract and desorbent is withdrawn
from a top of the desorption bed III in line 33, transported
through the valve 101 in an extract line 20 to either a separation
vessel to separate desorbent from extract or as feed to a steam
cracking unit 150. The desorbent is introduced through desorbent
line 45 through valve 101 which is positioned to send the desorbent
through line 45 into the bottom of the desorbent bed III. The
raffinate is withdrawn from a top of the adsorption bed I through
raffinate line 23, through valve 101 and to the raffinate
fractionation column 24.
[0024] Simulated countercurrent flow is achieved by periodically
advancing downstream the point of introducing the feed stream and
the desorbent while simultaneously and equally advancing downstream
the point of withdrawal of raffinate and extract. The adsorbent bed
I is defined as the zone bounded between the feed stream inlet and
the raffinate outlet; the primary rectification bed II is defined
as the zone bounded between the raffinate outlet and the desorbent
inlet; the desorption bed III is defined as the zone bounded
between the desorbent inlet and the extract outlet; and the
secondary rectification bed IV is defined as the zone bounded
between the extract outlet and the feed stream inlet. Typical
liquid phase operation is preferred, for example, at temperatures
of the from about 50.degree. C. to about 300.degree. C., and more
particularly no more than about 260.degree. C., and pressures of
from slightly superatmospheric to about 30 atmospheres.
[0025] Relatively less adsorbed raffinate is withdrawn from the
adsorption vessel 46 in the raffinate line 23 through the valve 101
and enters the raffinate fractionation column 24. Since it is
desired to obtain a normal paraffin product, the raffinate
fractionation column 24 is operated to separate two fractions, a
raffinate overhead stream rich in normal paraffin desorbent
comprising, in an embodiment, C4- normal paraffins and a bottoms
stream rich in non-normal paraffin raffinate comprising C5+
paraffins. The raffinate overhead stream is withdrawn from the
raffinate fractionation column 24 in an overhead line 28, condensed
in a cooler 29 and fed to a separator 30. A portion of the
condensed raffinate overhead is recycled to the raffinate
fractionation column 24 as reflux through a reflux line 31 and the
remaining portion of the condensed raffinate overhead is withdrawn
through a net raffinate overhead line 32. The raffinate overhead
stream comprises normal paraffin desorbent which can be recycled to
the adsorption vessel 46 in desorbent line 45. Another portion of
the raffinate overhead stream in line 48 can be recovered or taken
as steam cracker feed and fed to the steam cracker unit 150 in
lines 48, 20 and 110.
[0026] The term "column" means a distillation column or columns for
separating one or more components of different volatilities. Unless
otherwise indicated, each column includes a condenser on an
overhead of the column to condense and reflux a portion of an
overhead stream back to the top of the column and a reboiler at a
bottom of the column to vaporize and send a portion of a bottoms
stream back to the bottom of the column. Feeds to the columns may
be preheated. The top pressure is the pressure of the overhead
vapor at the vapor outlet of the column. The bottom temperature is
the liquid bottom outlet temperature. Overhead lines and bottoms
lines refer to the net lines from the column downstream of any
reflux or reboil to the column. Stripper columns may omit a
reboiler at a bottom of the column and instead provide heating
requirements and separation impetus from a fluidized inert media
such as steam. Stripping columns typically feed a top tray and take
main product from the bottom.
[0027] As used herein, the term "separator" means a vessel which
has an inlet and at least an overhead vapor outlet and a bottoms
liquid outlet and may also have an aqueous stream outlet from a
boot. A flash drum is a type of separator which may be in
downstream communication with a separator that may be operated at
higher pressure.
[0028] The raffinate bottoms stream is withdrawn from raffinate
fractionation column 24 through a bottoms line 25 where a portion
of the raffinate bottoms flows through a reboiler line 26, reboiler
heater 49 and returns heated to the raffinate fractionation column
24. The remaining portion of said raffinate bottoms flows through
line 27 as a non-normal paraffin rich stream, particularly rich in
non-normal C5 and C6 paraffins. The raffinate fractionation column
24 operates in bottoms temperature range of about 199 to about
221.degree. C. and an overhead pressure of about 276 to about 552
kPa (gauge).
[0029] The desorbent displaces the selectively adsorbed normal
paraffins from the solid adsorbent in desorbent bed III of
adsorbent vessel 46. The desorbent and extract are withdrawn in
line 33 through the valve 101. Normally, the desorbent and the
extract are separated to recycle the desorbent stream back to the
adsorption vessel. However, in an embodiment, sufficient desorbent
is produced later in the process as will be explained hereinafter.
Moreover, the normal C4 desorbent is an excellent steam cracker
feed. So, the normal C5 and C6 paraffin extract desorbed from the
adsorbent by the normal C4 paraffin desorbent may all be fed
together to the steam cracking unit 150 to produce a higher
selectivity to C3 olefins. Hence, in the process 2, an
extract-desorbent column may be obviated.
[0030] The non-normal paraffin rich stream particularly rich in
non-normal C5 and C6 paraffins can be isomerized to increase the
concentration of normal C5 and C6 paraffins to equilibrium levels.
However, it has been discovered that the conversion to normal
paraffins in an isomerization zone can be increased by removing a
portion of the C6 cyclic hydrocarbons, such as cyclohexane,
methylcyclopentane, and benzene, in the isomerization feed stream
passing into the isomerization zone. Specifically, when the
concentration of C6 cyclic hydrocarbons in the stream has been
reduced, disproportionation reactions occur which lead to increased
amounts of valuable C3 paraffins and C4 paraffins, as well as
increases in the per pass conversion of the iso-paraffin
hydrocarbons in the feed to normal paraffins. The products from the
disproportionation reactions undergo isomerization reactions
leading to an increase in yields of normal paraffins. Furthermore,
additional conversion to C2 to C4 normal paraffins in the
non-normal paraffin rich stream is accomplished via hydrocracking
reactions.
[0031] In an embodiment, the process locates a raffinate splitter
column 50 downstream of the adsorbent vessel 46 to separate C6
cyclic hydrocarbons and any C7+ hydrocarbons from isoparaffins in
the non-normal paraffin rich stream in line 27. Since the
non-normal paraffin rich stream in line 27 does not contain
n-hexane with a normal boiling point of 69.degree. C. because it is
removed in the adsorption vessel 46, the separation of C6 cyclics
from iso-paraffins is simplified. The lightest C6 cyclic
hydrocarbon is methylcyclopentane having a normal boiling point of
72.degree. C. whereas iso-C6 paraffins normally boil at
50-64.degree. C. Hence, the proper ordering of separation steps
obviates a difficult split between normal hexane and
methylcyclopentane that would be capital and operationally
intensive and result in a loss of much of the normal hexane, which
is a valuable steam cracker feed.
[0032] The raffinate splitter column 50 separates C6 cyclic
hydrocarbons and C7+ hydrocarbons from the non-normal paraffin
stream in line 27. The raffinate splitter overhead stream in the
raffinate splitter net overhead line 56 is rich in C5 and C6
iso-paraffins and can be termed as an iso-C6 paraffin rich stream,
an iso-C5 paraffin rich stream, a non-normal, non-cyclic paraffin
rich stream or an iso-paraffin rich stream. The non-normal paraffin
stream is withdrawn in a raffinate splitter overhead stream from
the raffinate splitter column 50 in an overhead line 52, through a
cooler 53 and into a separator 54. A portion of said raffinate
overhead stream is recycled to the raffinate fractionation column
50 as reflux through a reflux line and the remaining portion of the
raffinate splitter overhead stream is withdrawn in net raffinate
splitter overhead line 56. The raffinate splitter overhead stream
is an iso-C6 paraffin rich stream and is also an iso-C5 paraffin
rich stream which can be termed a non-normal, non-cyclic paraffin
rich stream or an iso-paraffin rich stream. The non-normal,
non-cyclic paraffin rich stream may be fed to an isomerization unit
60 in the net splitter overhead line 56 to increase its
normal-paraffin concentration. The raffinate splitter column 50
operates in bottoms temperature range of about 124 to about
154.degree. C. and an overhead pressure range of about 0 to about
138 kPa (gauge).
[0033] The raffinate splitter bottoms stream is withdrawn from
raffinate splitter column 50 through a bottoms line from which a
portion of the raffinate splitter bottoms flows through a reboiler
line 59, a reboiler heater 57 and returns to the raffinate splitter
column 50. The remaining portion of the raffinate splitter bottoms
stream flows through a net splitter bottoms line 64 as a cyclic
hydrocarbon stream rich in cyclic C6 hydrocarbons and benzene and
particularly rich in methyl cyclopentane. The cyclic paraffins
stream in the net splitter bottoms line 64 can be taken to a
reforming unit to produce aromatic hydrocarbons or sent to the
steam cracker.
[0034] The non-normal, non-cyclic paraffin rich stream in the net
raffinate splitter overhead line 56 may be combined with a hydrogen
stream in a first hydrogen line 62 and heated by heat exchange with
reactor effluent and fed to higher isomerization unit 60. In the
higher isomerization unit 60, the iC5 hydrocarbons and the iC6
hydrocarbons, in the presence of hydrogen provided by hydrogen line
62 and a higher isomerization catalyst, are converted to increase
the concentration of normal paraffins: ethane, propane, normal
butane, normal pentane and normal hexane. Three reactions promote
the production of normal paraffins iso-paraffin disproportionation
reactions, reverse isomerization of iso-paraffins, and paraffin
hydrocracking reactions.
[0035] Cracking of some of the paraffins can occur in the higher
isomerization unit 60 to produce C4- paraffins. Moreover, the
conversion of iC5 and iC6 paraffins increases significantly via
disproportionation reactions due to the fact that the non-normal,
non-cyclic paraffin rich stream in the net splitter overhead line
56 is passed into the higher isomerization unit 60 lean in cyclic
C6 hydrocarbons. It is believed that the paraffin
disproportionation reactions occur by the combination of two
iso-paraffin paraffins followed by scission into one lighter
hydrocarbon and one heavier hydrocarbon. For example, two iC5
paraffins can combine and form an iC4 paraffin and an iC6 paraffin
in the presence of hydrogen. The iC4 paraffins can further react
via disproportionation to form a C3 paraffin and an iC5 paraffin. A
significant portion of the produced iC4 paraffins also converts to
normal C4 paraffins via isomerization reactions in the
isomerization zone. Production of C3 and C4 normal paraffins via
disproportionation and isomerization reactions occurs with low
production of low-value undesired methane as a cracked product.
Thus, there is an increase in the overall yield of the normal
paraffins in the first isomerization unit 60.
[0036] In the higher isomerization unit 60, hydrocracking of the C5
and C6 components occurs to produce methane, ethane, propane, and
isobutane. The isobutane can further react via disproportionation
reactions and/or isomerization to further produce normal paraffins.
For embodiments that include a lower isomerization unit 120, the
isobutane produced in the higher isomerization unit 60 can be
separated and fed to the lower isomerization unit to convert the
isobutane to normal paraffins. In this respect, the isobutane that
is produced in the higher isomerization unit 60 is considered a
desired product in addition to the C2 to C6 normal paraffin
products.
[0037] The higher isomerization catalyst in the higher
isomerization unit 60 may include chlorided alumina, sulfated
zirconia, tungstated zirconia or zeolite-containing isomerization
catalysts. The higher isomerization catalyst may be amorphous,
e.g., based upon amorphous alumina, or zeolitic. A zeolitic
catalyst would still normally contain an amorphous binder. The
catalyst may comprise a sulfated zirconia and platinum as described
in U.S. Pat. No. 5,036,035 and European patent application 0 666
109 A1 or a platinum group metal on chlorided alumina as described
in U.S. Pat. Nos. 5,705,730 and 6,214,764. Another suitable
catalyst is described in U.S. Pat. No. 5,922,639. U.S. Pat. No.
6,818,589 discloses a catalyst comprising a tungstated support of
an oxide or hydroxide of a Group IVB (IUPAC 4) metal, preferably
zirconium oxide or hydroxide, at least a first component which is a
lanthanide element and/or yttrium component, and at least a second
component being a platinum-group metal component. These documents
are incorporated herein for their teaching as to catalyst
compositions, isomerization operating conditions and techniques. An
advantage of a non-chlorided catalyst, such as a sulfated zirconia
catalyst, is the absence of chloride omitting further treatment of
the effluent streams from the isomerization unit 60. If chlorided
alumina catalyst is used as the isomerization catalyst, a
chloriding agent will be added to the higher isomerization feed
stream 61.
[0038] The higher isomerization process conditions in the higher
isomerization unit 60 include an average reactor temperature
usually ranging from about 40.degree. to about 250.degree. C.
Reactor operating pressures generally range from about 100 kPa to
10 MPa absolute. Liquid hourly space velocities (LHSV) range from
about 0.2 to about 25 volumes of hydrocarbon feed per hour per
volume of catalyst. Hydrogen is admixed with or remains with the
higher isomerization feed to the higher isomerization unit to
provide a mole ratio of hydrogen to hydrocarbon feed of from about
0.01 to 20. The hydrogen may be supplied totally from outside the
process or supplemented by hydrogen recycled to the feed after
separation from higher isomerization reactor effluent.
[0039] Contacting within the higher isomerization unit 60 may be
effected using the higher isomerization catalyst in a fixed-bed
system, a moving-bed system, a fluidized-bed system, or in a
batch-type operation. The reactants may be contacted with the bed
of higher isomerization catalyst particles in upward, downward, or
radial-flow fashion. The reactants may be in the liquid phase, a
mixed liquid-vapor phase, or a vapor phase when contacted with the
higher catalyst particles, with a mixed phase or vapor phase being
preferred. The higher isomerization unit 60 may be in a single
reactor 66 or in two or more separate higher isomerization reactors
67, 68, and 69 with suitable means therebetween to ensure that the
desired isomerization temperature is maintained at the entrance to
each zone.
[0040] The reactions in the higher isomerization unit 60 generate
an exotherm across the reactors so the higher isomerization
effluent streams need to cooled between reactors. For example, a
first higher isomerate stream from a first isomerization reactor 67
may be heat exchanged with the higher isomerization feed stream in
the higher isomerization feed line 61 comprising the non-normal,
non-cyclic paraffin rich stream mixed with hydrogen to cool the
higher isomerate and heat the higher isomerization feed stream.
Moreover, a second higher isomerate stream from a second higher
isomerization reactor 68 may be heat exchanged with the higher
isomerization feed stream comprising the non-normal, non-cyclic
paraffin rich stream mixed with hydrogen upstream of the heat
exchange with the first higher isomerate steam to cool the higher
isomerate stream and heat the higher isomerization feed stream.
Additionally, a third isomerate stream from the third isomerization
reactor 69 may be heat exchanged with the higher isomerization feed
stream comprising non-normal, non-cyclic paraffin rich stream mixed
with hydrogen upstream of the heat exchange with the second higher
isomerate stream to cool the higher isomerate and heat the higher
isomerization feed stream. Since hydrocracking reactions are very
exothermic, two to five higher isomerization reactors in sequence
enable improved control of individual reactor temperatures and
partial catalyst replacement without a process shutdown. A first,
higher isomerization effluent stream comprising an increased
concentration of normal paraffins exits the last higher
isomerization reactor 69 in the higher isomerization unit 60 in a
higher isomerization effluent line 65.
[0041] A debutanizer column 70 separates a first isomerization
effluent stream into a debutanizer overhead stream comprising C4-
paraffins and a debutanized bottoms stream comprising C5+
paraffins. The debutanizer overhead stream is withdrawn from the
debutanizer column 70 in a debutanizer overhead line 72 and
condensed in a cooler and passed into a separator 74. A portion of
the condensed debutanizer overhead stream is recycled to the
debutanizer column 70 as reflux through a reflux line and the
remaining portion of the condensed debutanizer overhead stream is
withdrawn in line 76 and fed to a deethanizer splitter column 80. A
debutanizer off gas stream is taken from the separator overhead in
line 73. The debutanizer off gas in the net overhead line 73 may be
scrubbed (not shown) to remove chlorine if a chloride isomerization
catalyst is in the isomerization unit 60 and passed to fuel gas
processing or sent to a steam cracking unit 150 for further
recovery of hydrogen and ethane that can be used as steam cracking
feed.
[0042] The debutanized bottoms stream is withdrawn from the
debutanizer column 70 through a bottoms line from which a portion
of the debutanized bottoms stream flows through a reboiler line 77,
a reboiler heater and returns to the debutanizer column 70. The
remaining portion of the debutanized bottoms flows through a net
debutanized bottoms line 79 rich in normal and iso C5-C7 paraffins,
is cooled by heat exchange with the first isomerization effluent
stream in the first isomerization effluent line 65 and is recycled
to the feed line 10 to the adsorption separation unit 12 for
separation of the normal paraffins from the non-normal paraffins.
The debutanizer column 70 operates in bottoms temperature range of
about 153 to about 188.degree. C. and an overhead pressure range of
about 1.3 to about 1.5 MPa.
[0043] The deethanizer column 80 separates the condensed
debutanizer overhead stream in the line 76 into a deethanizer
overhead stream rich in C2- hydrocarbons and a deethanized bottoms
stream rich in C3 and C4 paraffins. The deethanizer overhead stream
is withdrawn from the deethanizer column 80 in a deethanizer
overhead line 82 and condensed in a cooler and passed into a
separator 84. The condensed deethanizer overhead stream is recycled
to the deethanizer column 80 as reflux through a reflux line and
the uncondensed off gas is removed in a deethanizer net overhead
line 83. The deethanizer off gas in the net overhead line 83 may be
scrubbed to remove chlorine if a chloride isomerization catalyst is
in the higher isomerization unit 60 and passed to fuel gas
processing. The debutanizer off gas stream in the debutanizer
overhead in line 73 may also be processed with the deethanizer off
gas stream in the deethanizer net overhead line 83. The deethanizer
and debutanizer off gas may both be subjected to contact with
sponge oil taken from the debutanized bottoms stream to absorb
heavy paraffins entrained in the off gas streams to preserve them
for use more valuable than fuel. The deethanizer column 80 operates
in bottoms temperature range of about 100 to about 130.degree. C.
and an overhead pressure range of about 210 to about 300 kPa
(gauge).
[0044] The deethanized bottoms stream is withdrawn from the
deethanizer column 80 through a bottoms line from which a portion
of the deethanized bottoms stream flows through a reboiler line 87,
a reboiler heater and returns to the deethanizer column 80. The
remaining portion of the deethanized bottoms flows through a net
deethanized bottoms line 89 comprising C3 and C4 paraffins and is
fed to a depropanizer column 90.
[0045] The depropanizer column 90 separates the deethanized bottoms
stream into a depropanizer overhead stream comprising propane and a
depropanized bottoms stream comprising C4 paraffins. The
depropanizer overhead stream is withdrawn from the depropanizer
column 90 in a depropanizer overhead line 92 and fully condensed in
a cooler and passed into a separator 94. A portion of the condensed
depropanizer overhead stream is recycled to the depropanizer column
90 as reflux through a reflux line and the remaining condensed
depropanizer overhead stream is taken as a C3 stream in a
depropanizer product line 95 which may be further upgraded such as
by steam cracking or dehydrogenation to make an olefinic C3
stream.
[0046] The depropanized bottoms stream is withdrawn from the
depropanizer column 90 through a bottoms line from which a portion
of the depropanized bottoms stream flows through a reboiler line
97, a reboiler heater and returns to the depropanizer column 90.
The remaining portion of the depropanized bottoms stream comprising
C4 paraffins flows through a net depropanized bottoms line 99.
Thus, a C4 paraffin rich stream is separated from the first, higher
isomerization effluent stream in the first, higher isomerization
effluent line 65.
[0047] The C4 paraffin rich stream has a large concentration of
normal C4 paraffins which make an excellent steam cracker feed. So,
separation of the normal C4 paraffins from the non-normal
C4-paraffins may be performed to produce steam cracker feed.
[0048] In an embodiment, the C4 paraffin rich stream is fed to a
deisobutanizer column 100 to separate the C4 stream into an iso-C4
paraffin rich overhead stream and a normal C4 paraffin rich bottoms
stream. The deisobutanizer overhead stream rich in isobutane is
withdrawn from the deisobutanizer column 100 in a deisobutanizer
overhead line 102 and fully condensed in a cooler and passed into a
separator 104. A portion of the condensed deisobutanizer overhead
stream is recycled to the deisobutanizer column 100 as reflux
through a reflux line and the remaining condensed deisobutanizer
overhead stream is taken as an isobutane rich stream in a
deisobutanizer net overhead line 105. The isobutane stream may be
fed to a butane isomerization unit 120 to increase the
concentration of normal butane paraffins in the isobutane stream in
the deisobutanizer net overhead line 105.
[0049] The deisobutanized bottoms stream is withdrawn from the
deisobutanizer column 100 through a bottoms line from which a
portion of the deisobutanized bottoms stream flows through a
reboiler line 107, a reboiler heater and returns to the
deisobutanizer column 100. The remaining portion of the
deisobutanized bottoms flows through a net deisobutanized bottoms
line 109 which is rich in normal butane. Thus, a normal butane rich
stream is separated from the first, higher isomerization effluent
stream in the first higher isomerization effluent line 65. The
normal butane rich stream is an excellent steam cracker feed, so a
portion of the normal butane rich, deisobutanized bottoms stream
may be fed in a steam cracker feed line 110 to the steam cracking
unit 150. The other portion of the normal butane rich,
deisobutanized bottoms stream in a replenish desorbent line 112 may
be used to replenish desorbent in the desorbent line 45. The
deisobutanizer column 100 operates in bottoms temperature range of
about 60 to about 80.degree. C. and an overhead pressure range of
about 517 to about 758 kPa (gauge).
[0050] The isobutane rich stream in the deisobutanizer net overhead
line 105 may be combined with a hydrogen stream in a hydrogen line
113 and optionally a fresh isobutane stream in fresh isobutane line
114 to provide a second, butane isomerization feed stream in butane
isomerization feed line 116. The butane isomerization feed stream
is heated by heat exchange with a butene isomerization effluent
stream and isomerized in a second, butane isomerization unit 120.
In the butane isomerization unit 120, the isobutane paraffins, in
the presence of hydrogen provided by hydrogen line 113 and a butane
isomerization catalyst, are converted into normal butane to attain
equilibrium levels of normal butane.
[0051] In addition to isobutane-normal butane isomerization, the
conversion of isobutane via disproportionation reactions can also
occur. The iC4 hydrocarbons can react via disproportionation to
form a C3 hydrocarbon and an iso-C5 paraffin. The iso-C5 paraffins
can also isomerize to equilibrium forming normal pentane. Thus,
there is an increase in the overall yield of the normal paraffins
to propane, normal butane and normal pentane in the butane
isomerization unit 120.
[0052] The butane isomerization catalyst may include chlorided
alumina, sulfated zirconia, tungstated zirconia or
zeolite-containing isomerization catalysts. The butane
isomerization catalyst may be amorphous, e.g., based upon amorphous
alumina, or zeolitic. A zeolitic catalyst would still normally
contain an amorphous binder. The catalyst may comprise a sulfated
zirconia and platinum as described in U.S. Pat. No. 5,036,035 and
European patent application 0 666 109 A1 or a platinum group metal
on chlorided alumina as described in U.S. Pat. Nos. 5,705,730 and
6,214,764. Another suitable catalyst is described in U.S. Pat. No.
5,922,639. U.S. Pat. No. 6,818,589 discloses a catalyst comprising
a tungstated support of an oxide or hydroxide of a Group IVB (IUPAC
4) metal, preferably zirconium oxide or hydroxide, at least a first
component which is a lanthanide element and/or yttrium component,
and at least a second component being a platinum-group metal
component. These documents are incorporated herein for their
teaching as to catalyst compositions, isomerization operating
conditions and techniques. An advantage of a non-chlorided
catalyst, such as a sulfated zirconia catalyst because it does not
contain chloride omitting further treatment of the effluent streams
from the second, butane isomerization unit 120. If chlorided
alumina catalyst is used as the isomerization catalyst, a
chloriding agent will be added to the second, butane isomerization
feed stream 116.
[0053] The butane isomerization conditions in the butane
isomerization unit 120 include reactor temperatures ranging from
about 40.degree. C. to about 250.degree. C., preferably at reactor
temperatures ranging from 90.degree. C. to 204.degree. C. Reactor
operating pressures generally range from about 100 kPa to 10 MPa
absolute. LHSV range from about 0.2 to about 25 volumes of
hydrocarbon feed per hour per volume of catalyst. Hydrogen is
admixed with or remains with the butane isomerization feed to the
butane isomerization unit to provide a mole ratio of hydrogen to
hydrocarbon feed of from about 0.01 to 20. The hydrogen may be
supplied totally from outside the process or supplemented by
hydrogen recycled to the feed after separation from butane
isomerization reactor effluent.
[0054] Contacting within the isomerization unit 120 may be effected
using the catalyst in a fixed-bed system, a moving-bed system, a
fluidized-bed system, or in a batch-type operation. The reactants
may be contacted with the bed of catalyst particles in upward,
downward, or radial-flow fashion. The reactants may be in the
liquid phase, a mixed liquid-vapor phase, or a vapor phase when
contacted with the catalyst particles, with a mixed phase or vapor
phase being preferred. The butane isomerization unit 120 may be in
a single reactor 122 or two or more separate reactors 122 and 124
with suitable means therebetween to ensure that the desired
isomerization temperature is maintained at the entrance to each
zone. Since the main reaction in the butene isomerization unit is
isomerization of isoparaffins to normal paraffins which is
endothermic, the temperatures across the reactors decline.
Consequently, the butene isomerization effluent needs to be
reheated before going to the downstream reactor. For example, a
first butane isomerate stream from a first butane isomerization
reactor 122 may be heated by heat exchange and fed to a second
butane isomerization reactor 124. Moreover, a second butane
isomerate stream from the second butane isomerization reactor 124
may be heat exchanged with the butane isomerization feed stream
comprising an isobutane-rich stream mixed with hydrogen to cool the
second butane isomerate and heat the butane isomerization feed
stream. Two or more reactors in sequence enables improved
isomerization through control of individual reactor temperatures
and partial catalyst replacement without a process shutdown. A
second, butane isomerization effluent stream comprising increased
normal paraffins exits the last reactor in the butane isomerization
unit 120 in a second, butane isomerization effluent line 126.
[0055] A stabilizer column 130 separates the butane isomerization
effluent stream into a stabilizer overhead stream comprising C3-
hydrocarbons and a stabilized bottoms stream comprising C4+
paraffins. The debutanizer overhead stream is withdrawn from the
stabilizer column 130 in a stabilizer overhead line 132 and
condensed in a cooler and passed into a separator 134. A condensed
stabilizer overhead stream is recycled to the stabilizer column 130
as reflux through a reflux line and the uncondensed gases are taken
as a butane isomerization off gas in a stabilizer net overhead line
136. The stabilizer off gas in the stabilizer net overhead line 136
may be scrubbed to remove chlorine if a chloride isomerization
catalyst is in the butane isomerization unit 120 and passed to fuel
gas or other processing.
[0056] The stabilized bottoms stream comprising C4+ paraffins is
withdrawn from the stabilizer column 130 through a bottoms line
from which a portion of the stabilized bottoms stream flows through
a reboiler line 137 and a reboiler heater and returns to the
deisobutanizer column 130. The remaining portion of the stabilized
bottoms flows through a net stabilized bottoms line 139 comprising
a mixed butanes stream comprising normal butane and isobutane. The
mixed butanes stream is fed back to the deisobutanizer column 100
to separate isobutanes from normal butanes. Thus, the second,
butane isomerization effluent stream is fed to the step of
separating the C4 stream into an isobutane stream and a normal
butane stream. The stabilizer column 130 operates in bottoms
temperature range of about 110 to about 130.degree. C. and an
overhead pressure range of about 2.1 to about 2.5 MPa.
SPECIFIC EMBODIMENTS
[0057] While the following is described in conjunction with
specific embodiments, it will be understood that this description
is intended to illustrate and not limit the scope of the preceding
description and the appended claims.
[0058] A first embodiment of the invention is a process for
increasing the concentration of normal paraffins in a feed stream
comprising separating a naphtha feed stream into a normal paraffin
rich stream and a non-normal paraffin rich stream; isomerizing the
non-normal paraffin rich stream over a first isomerization catalyst
to convert non-normal paraffins to normal paraffins and produce a
first isomerization effluent stream; separating an iso-C4 stream
from the first isomerization effluent stream; isomerizing the
iso-C4 stream over a second isomerization catalyst to convert
iso-C4 hydrocarbons to normal C4 hydrocarbons and produce a second
isomerization effluent stream; and feeding the second isomerization
effluent stream to a steam cracker. An embodiment of the invention
is one, any or all of prior embodiments in this paragraph up
through the first embodiment in this paragraph further comprising
separating a C4 stream from the first isomerization effluent stream
and separating the C4 stream into the iso-C4 stream and a normal C4
stream. An embodiment of the invention is one, any or all of prior
embodiments in this paragraph up through the first embodiment in
this paragraph further comprising feeding the normal C4 stream to
the steam cracker. An embodiment of the invention is one, any or
all of prior embodiments in this paragraph up through the first
embodiment in this paragraph further comprising feeding the normal
C4 stream to the step of separating a normal paraffins stream from
non-normal paraffins stream and desorbing normal paraffins from an
adsorbent. An embodiment of the invention is one, any or all of
prior embodiments in this paragraph up through the first embodiment
in this paragraph further comprising feeding the normal-C4 stream
and the desorbed normal paraffins to a steam cracker together. An
embodiment of the invention is one, any or all of prior embodiments
in this paragraph up through the first embodiment in this paragraph
further comprising feeding the second isomerization effluent stream
to the step of separating the C4 stream into an iso-C4 stream and a
normal C4 stream. An embodiment of the invention is one, any or all
of prior embodiments in this paragraph up through the first
embodiment in this paragraph further comprising separating the
first isomerization effluent stream to produce a C3 stream and
further converting the C3 stream into an olefinic stream. An
embodiment of the invention is one, any or all of prior embodiments
in this paragraph up through the first embodiment in this paragraph
further comprising separating a C5 and C6 paraffins stream from the
first isomerization effluent stream and recycling the C5 and C6
paraffins stream to the step of separating the naphtha feed stream
into the normal paraffin rich stream and the non-normal paraffin
rich stream. An embodiment of the invention is one, any or all of
prior embodiments in this paragraph up through the first embodiment
in this paragraph wherein the step of separating the naphtha feed
stream into the normal paraffins stream from the non-normal
paraffins stream comprises extracting the normal paraffins by use
of an adsorbent. An embodiment of the invention is one, any or all
of prior embodiments in this paragraph up through the first
embodiment in this paragraph further comprising separating cyclic
hydrocarbons from the non-normal paraffin stream before isomerizing
the non-normal paraffins stream.
[0059] A second embodiment of the invention is a process for
increasing the concentration of normal paraffins in a feed stream
comprising separating a naphtha feed stream into a normal paraffin
rich stream and a non-normal paraffin rich stream; separating the
non-normal paraffin rich stream to provide an iso-C6 paraffin rich
stream and C6 cyclics rich stream; and isomerizing the iso-C6
paraffin rich stream over a first isomerization catalyst to convert
non-normal paraffins to normal paraffins and produce an
isomerization effluent stream. An embodiment of the invention is
one, any or all of prior embodiments in this paragraph up through
the second embodiment in this paragraph further comprising
separating a C4 paraffin rich stream from the first isomerization
effluent stream and separating the C4 paraffin rich stream into the
iso-C4 paraffin rich stream and a normal C4 paraffin rich stream;
separating an iso-C4 paraffin rich stream from the first
isomerization effluent stream; isomerizing the iso-C4 paraffin
stream over a second isomerization catalyst to convert iso-C4
paraffins to normal C4 paraffins and produce a second isomerization
effluent stream; and feeding the second isomerization effluent
stream to a steam cracker. An embodiment of the invention is one,
any or all of prior embodiments in this paragraph up through the
second embodiment in this paragraph further comprising separating a
C5 and C6 paraffin stream from the first isomerization effluent
stream and recycling the C5 and C6 paraffin stream to the step of
separating the naphtha feed stream into the normal paraffin rich
stream and the non-normal paraffin rich stream. An embodiment of
the invention is one, any or all of prior embodiments in this
paragraph up through the second embodiment in this paragraph
further comprising feeding the normal paraffin rich stream to a
steam cracker. An embodiment of the invention is one, any or all of
prior embodiments in this paragraph up through the second
embodiment in this paragraph further comprising separating a C4
paraffin rich stream from the first isomerization effluent stream
and separating the C4 paraffin rich stream into the iso-C4 paraffin
rich stream and a normal C4 paraffin rich stream. An embodiment of
the invention is one, any or all of prior embodiments in this
paragraph up through the second embodiment in this paragraph
further comprising feeding the normal C4 paraffin rich stream to
the steam cracker. An embodiment of the invention is one, any or
all of prior embodiments in this paragraph up through the second
embodiment in this paragraph further comprising feeding the normal
C4 paraffin rich stream to the step of separating the naphtha feed
stream into the normal paraffin stream and the non-normal paraffin
stream and desorbing normal paraffins from an adsorbent and feeding
the normal-C4 paraffin rich stream and the desorbed normal paraffin
stream to a steam cracker together. An embodiment of the invention
is one, any or all of prior embodiments in this paragraph up
through the second embodiment in this paragraph further comprising
separating the first isomerization effluent stream into a C3
paraffin rich stream and further converting the C3 stream into an
olefinic stream. An embodiment of the invention is one, any or all
of prior embodiments in this paragraph up through the second
embodiment in this paragraph wherein the step of separating the
normal paraffins stream from the non-normal paraffins stream
comprises extracting the normal paraffins by use of an
adsorbent.
[0060] A third embodiment of the invention is a process for
increasing the concentration of normal hydrocarbons in a feed
stream comprising separating a naphtha feed stream into a normal
paraffins stream and a non-normal paraffins stream; isomerizing an
iso-C4 paraffin rich stream over an isomerization catalyst to
convert iso-C4 paraffins to normal C4 paraffins and produce an
isomerization effluent stream; separating a normal C4 paraffin rich
stream from the isomerization effluent stream; and feeding the
normal C4 paraffin rich stream to the step of separating a normal
paraffins stream from non-normal paraffins stream and desorbing
normal paraffins from an adsorbent.
[0061] Without further elaboration, it is believed that using the
preceding description that one skilled in the art can utilize the
present invention to its fullest extent and easily ascertain the
essential characteristics of this invention, without departing from
the spirit and scope thereof, to make various changes and
modifications of the invention and to adapt it to various usages
and conditions. The preceding preferred specific embodiments are,
therefore, to be construed as merely illustrative, and not limiting
the remainder of the disclosure in any way whatsoever, and that it
is intended to cover various modifications and equivalent
arrangements included within the scope of the appended claims.
[0062] In the foregoing, all temperatures are set forth in degrees
Celsius and, all parts and percentages are by weight, unless
otherwise indicated.
* * * * *