U.S. patent application number 16/621052 was filed with the patent office on 2020-06-25 for process for the removal of nitrogen-containing compounds from a hydrocarbon feed.
The applicant listed for this patent is ExxonMobil Chmical Patents Inc.. Invention is credited to Blaise H. Bridier, Paul Hamilton, John J. Houben, Mechilium J.G. Janssen, Luc R. M. Martens, Pierre J. Osterrieth, Christopher J. Taylor, Gerandine Tosin, Bee N. Yap.
Application Number | 20200199460 16/621052 |
Document ID | / |
Family ID | 59409157 |
Filed Date | 2020-06-25 |
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United States Patent
Application |
20200199460 |
Kind Code |
A1 |
Bridier; Blaise H. ; et
al. |
June 25, 2020 |
Process For The Removal Of Nitrogen-Containing Compounds From A
Hydrocarbon Feed
Abstract
Process for the removal of nitrogen-containing compounds from a
hydrocarbon feed comprising at least one olefin selected from the
C3, C4, C5 and optionally C6 olefins and mixtures thereof
comprising solvent extraction comprising monitoring the degradation
of the solvent.
Inventors: |
Bridier; Blaise H.; (Uccle,
BE) ; Hamilton; Paul; (Spring, TX) ; Janssen;
Mechilium J.G.; (Kessel-Lo, Leuven, BE) ; Osterrieth;
Pierre J.; (Bruxelles, BE) ; Taylor; Christopher
J.; (Southampton, GB) ; Martens; Luc R. M.;
(Vlaams Brabant, BE) ; Yap; Bee N.; (Brussels,
BR) ; Tosin; Gerandine; (Brussels, BE) ;
Houben; John J.; (Rotterdam, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Chmical Patents Inc. |
Baytown |
TX |
US |
|
|
Family ID: |
59409157 |
Appl. No.: |
16/621052 |
Filed: |
June 15, 2018 |
PCT Filed: |
June 15, 2018 |
PCT NO: |
PCT/EP2018/065955 |
371 Date: |
December 10, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10G 2/30 20130101; C10G
50/00 20130101; C10G 2300/202 20130101; C10G 21/28 20130101; C10G
2300/1088 20130101; C10G 2300/4081 20130101; C10G 45/68 20130101;
C10G 29/205 20130101; C10G 21/16 20130101; C10G 21/30 20130101;
C10G 2400/20 20130101; C10G 45/58 20130101; C10G 2300/1092
20130101 |
International
Class: |
C10G 21/16 20060101
C10G021/16; C10G 21/28 20060101 C10G021/28 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2017 |
EP |
17181097.1 |
Claims
1. A Process for the removal of nitrogen-containing compounds from
a hydrocarbon feed comprising at least one olefin selected from the
C3, C4, C5 and optionally C6 olefins and mixtures thereof
comprising the steps of: a) contacting the hydrocarbon feed with an
extracting solvent containing propylene carbonate to obtain a
hydrocarbon phase of reduced nitrogen-containing compounds content
and a solvent phase containing dissolved nitrogen-containing
compounds; b) separating the hydrocarbon phase of reduced
nitrogen-containing compounds content from a solvent phase
containing dissolved nitrogen-containing compounds; c) subjecting
the hydrocarbon phase from step (b) to a distillation step to
separate a heavy phase containing the solvent and optionally heavy
hydrocarbon compounds from a light hydrocarbon fraction containing
the C3, C4 and C5 olefins; d) optionally subjecting the light
fraction to further processing; and e) subjecting the solvent phase
from step (b), optionally with the heavy phase from step (c), to a
regeneration step; and f) recycling the regenerated solvent back to
step (a), said process further comprising monitoring the
degradation of the solvent by keeping the content of the propylene
carbonate present in recycled solvent above 94% by weight relative
to the solvent as measured by gas chromatography; keeping the Total
Acid Number (TAN) of the recycled solvent measured according to ISO
1843/2 below 0.1 mg KOH/g keeping the distribution coefficient of
the nitrogen-containing compounds between the recycled solvent and
the hydrocarbon feed above 50% of the value measured with fresh
solvent; keeping the settling time of the recycled solvent in the
hydrocarbon feed below 200% of the settling time of the raw
propylene carbonate; or maintaining the surface tension of the
recycled solvent as measured by the Ring Tear Off method above 25
mN/m or the interfacial tension measured by the Du Nouy Ring method
above 6 mN/m.
2. The process according to claim 1, wherein the accumulation of
solvent degradation products and heavy hydrocarbons in the
recycling loop can be avoided or at least minimize by one or more
of the following steps filtration of the solvent before feeding it
back to step (a); depending on the monitoring results purging an
appropriate amount of solvent and replacing by fresh solvent;
operating the regeneration step in such a way that the heavy
hydrocarbon compounds and the solvent degradation products are
removed at said regeneration step, for example by decreasing the
reflux ratio in the stripper or adapting the regeneration
temperature; and adding a distillation step between the
regeneration and the extraction steps.
3. The process according to claim 1, wherein the regeneration step
(e) is operated in a stripping column by using an inert gas or a
light hydrocarbon having from 1 to 7 carbon atoms.
4. The process according to claim 1, wherein the solvent comprise
propylene carbonate.
5. The process according to claim 1, wherein the hydrocarbon feed
is a C5 olefin feeds including FCC Light Naphtha streams, steam
cracker C5 rich streams that have been treated for diene removal,
C5 olefin containing streams from Gas to Olefin (GTO) Units, or
Fisher-Tropsch Units.
6. The process according to claim 1, wherein the stripping column
is equipped with an overhead reflux resulting in a column
configuration comprising a stripping portion in the bottom and a
distillation portion at the top.
7. The process according to claim 1, wherein, depending on the
monitoring results, an appropriate amount of solvent is purged at
step (e) and replaced by fresh solvent.
8. A process for converting a hydrocarbon feed comprising at least
one olefin selected from the C3, C4, C5 and optionally C6 olefins
and mixtures thereof contaminated with at least one
nitrogen-containing compound into a hydrocarbon product; said
process comprising the steps of: i) providing a hydrocarbon feed
contaminated with at least one nitrogen-containing compound; ii)
removing the nitrogen-containing compounds from the feed to produce
a hydrocarbon feed stream having a reduced level of
nitrogen-containing compounds; and contacting said hydrocarbon feed
stream having a reduced level of nitrogen-containing compounds with
a catalyst in order to convert the feed stream into a hydrocarbon
product, wherein nitrogen-containing compounds are removed from the
feed by using the process as defined in any one of the preceding
claims.
9. The process according to claim 8 wherein step (iii) is an
isomerization, an alkylation, a hydrogenation, an aromatization or
an oligomerization step.
10. The process according to claim 9, wherein step (ii) is an
oligomerisation step using an oligomerization catalyst comprising a
material selected from the group consisting of zeolites, phosphoric
acids, supported metal oxides and combinations thereof.
11. The process according to claim 10, wherein the oligomerization
catalyst comprises a zeolite, in particular a zeolite selected from
the group consisting of ZSM-5, ZSM-11, ZSM-1, ZSM-18, ZSM-22,
ZSM-23, ZSM-35, ZSM-38, ZSM-48, ZSM-50, ZSM-57, ITQ-39 and mixtures
thereof.
Description
[0001] This invention relates to a process for removing
nitrogen-containing compounds from a hydrocarbon feed, in
particular from a hydrocarbon feed containing C3 to C6 olefins. The
present invention also relates to a process for converting a
hydrocarbon feed contaminated with at least one nitrogen-containing
compound into a hydrocarbon product, said process comprising a step
of removal of nitrogen-containing compounds from the hydrocarbon
feed.
BACKGROUND
[0002] Hydrocarbon feed streams containing light olefins, typically
C3 to C6 olefins, are used in catalytic oligomerisation processes
to obtain oligomers and/or polymers, typically heptenes, octenes,
nonenes and dodecenes. These products may be converted to further
products such as alcohols, plasticisers, adipates, mercaptans and
solvents.
[0003] The hydrocarbon feed steams derive from various sources
including refinery operations such as catalytic or steam cracking
and are known to contain certain amounts of impurities including,
but not limited to, nitrogen-containing compounds such as nitriles.
These impurities may have an adverse effect on the catalysts used
in the oligomerisation process such as phosphoric acid-based
catalyst, zeolite-based catalyst and supported metal catalysts. In
particular, nitrogen-containing compounds may act as catalyst
poisons (contaminants) reducing the activity and life of the
catalyst and/or inducing unsustainable operation conditions and
should be removed from these hydrocarbon feed streams.
[0004] Prior art approaches to remove nitrogen-containing compounds
include removal via liquid-liquid extraction techniques or
adsorption techniques using a so-called guard bed.
[0005] Liquid-liquid extraction is disclosed for example in WO
2009/058229 and WO 2012/078218. The latter document discloses
removal of nitriles and/or pyrroles from a feed stream comprising
olefins and paraffins by contacting the feed stream with a solvent
and removing at least a portion of the nitriles and the pyrroles
from the feed stream. The process conditions are based on the
distribution coefficient of the nitrogen-containing compounds in
the feed stream and the solvent.
[0006] Solvents such as sulfone compounds or alkyl/alkenyl/aryl
carbonates, typically propylene carbonate, are generally used. Such
solvents may be recycled or reused in the extraction process but
generally after a regeneration process such as vacuum and steam
distillation, back extraction, adsorption and anion-cation exchange
resin column. Regeneration processes include contacting the solvent
after use in an extraction process with an inert gas or light
hydrocarbons.
[0007] Continuous solvent recycling will also generate accumulation
in the solvent recycle loop of solvent degradation products as well
as of the heavy hydrocarbon compounds that might be present in the
hydrocarbon feed stream. These components collected in the solvent
recycling loop can also strongly affect the effectiveness of the
removal process and need to be timely removed. These compounds are
not taken into consideration in WO 2012/078218.
[0008] Thus there remains a need for further processes which allow
for an efficient removal of nitrogen-based impurities that can be
run for long periods of time while maintaining good operating
conditions.
SUMMARY OF THE INVENTION
[0009] According to a first aspect, the present invention solves
the above problem(s) by providing a process for the removal of
nitrogen-containing compounds from a hydrocarbon feed, preferably
from a hydrocarbon feed comprising at least one olefin selected
from C3, C4, C5 and optionally C6 olefins and mixtures thereof, the
process comprising the steps of: [0010] a) contacting the
hydrocarbon feed with an extracting solvent containing propylene
carbonate, to obtain a hydrocarbon phase with a reduced
nitrogen-containing compounds content and a solvent phase
containing nitrogen-containing compounds dissolved therein; [0011]
b) separating the hydrocarbon phase with a reduced
nitrogen-containing compounds content from the solvent phase
containing nitrogen-containing compounds dissolved therein; [0012]
c) subjecting the hydrocarbon phase obtained in step (b) to a
distillation step to separate a heavy phase containing the solvent
and optionally heavy hydrocarbon compounds, from a light
hydrocarbon fraction containing the at least one olefin selected
from C3, C4 and C5 olefins and mixtures thereof; [0013] d)
optionally subjecting the light fraction to further processing; and
[0014] e) subjecting the solvent phase obtained in step (b),
optionally with the heavy phase from step (c), to a regeneration
step; and [0015] f) recycling the regenerated solvent back to step
(a), said process further comprising monitoring the degradation of
the solvent by [0016] keeping the content of the propylene
carbonate present in recycled solvent above 94% by weight relative
to the total amount of recycled solvent, as measured by gas
chromatography; or [0017] keeping the Total Acid Number (TAN) of
the recycled solvent measured according to ISO 1843/2 below 0.1 mg
KOH/g; or [0018] keeping the distribution coefficient of the
nitrogen-containing compounds between the recycled solvent and the
hydrocarbon feed above 50% of the value measured for fresh
solvent.
[0019] According to this invention, the degradation of the solvent
may also be monitored by [0020] maintaining the surface tension of
the recycled solvent as measured by the Ring Tear Off method above
25 mN/m; or [0021] maintaining the interfacial tension of the
recycled solvent measured by the Du Nouy Ring method above 6 mN/m;
or [0022] keeping the settling time of the recycled solvent in the
hydrocarbon feed below 200% of the settling time of the raw
propylene carbonate.
[0023] The regeneration step (e) is preferably operated in a
stripping column by using an inert gas such as nitrogen or one or
more of the Group 18 inert gases of the Periodic Table of the
Elements (Wikipedia--2017) or a light hydrocarbon as defined
below.
[0024] According to a second aspect, the present invention relates
to a process for converting a hydrocarbon feed comprising at least
one olefin selected from C3, C4, C5, and optionally C6 olefins and
mixtures thereof, contaminated with at least one
nitrogen-containing compound into a hydrocarbon product, said
process comprising the steps of: [0025] i) providing a hydrocarbon
feed contaminated with at least one nitrogen-containing compound;
[0026] ii) removing the nitrogen-containing compounds from the feed
by using a process in accordance with the first aspect of the
present invention to produce a hydrocarbon feed stream having a
reduced level of nitrogen-containing compounds; and [0027] iii)
contacting said hydrocarbon feed stream having a reduced level of
nitrogen-containing compounds with a catalyst in order to convert
the feed stream into a hydrocarbon product.
[0028] Further and preferred embodiments are disclosed in the
dependent claims and in the following description including the
examples and figures illustrating the present invention.
BRIEF DESCRIPTION OF THE FIGURES
[0029] FIG. 1 is a schematic representation of steps (a) to (e) of
the present invention including monitoring of the solvent
degradation.
[0030] FIG. 2 is a schematic representation of a preferred
distillation column layout used in step (c).
[0031] FIG. 3 shows the content of different nitrogen compounds in
the different process streams in a process according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0032] Before the materials, compounds, components, composition
and/or processes of the present invention are disclosed in more
detail, it is noted that the singular forms "a", "an" and "the"
include plural referents unless otherwise specified.
[0033] Furthermore, the words "comprising" (and any form thereof),
having (and any form thereof), including (and any form thereof) or
containing (and any form thereof) are inclusive or open ended and
do not exclude additional, unrecited elements such as materials,
compounds or compositions or additional process steps.
[0034] Embodiments might be combined and are not separated except
otherwise specified.
[0035] As stated above, according to a first aspect, the present
invention solves the problems of the accumulation of degradation
products and heavy hydrocarbon compound in a solvent recycled loop
by providing a process for the removal of nitrogen-containing
compounds from a hydrocarbon feed, preferably a hydrocarbon feed
comprising preferably at least one olefin selected from the C3, C4,
C5 and optionally C6 olefins and mixtures thereof comprising the
steps of: [0036] a) contacting the hydrocarbon feed with an
extracting solvent containing propylene carbonate to obtain a
hydrocarbon phase of reduced nitrogen-containing compounds content
and a solvent phase containing dissolved nitrogen-containing
compounds; [0037] b) separating the hydrocarbon phase of reduced
nitrogen-containing compounds content from solvent phase containing
dissolved nitrogen-containing compounds; [0038] c) subjecting the
hydrocarbon phase from step (b) to a distillation step to separate
a heavy phase containing the solvent and optionally heavy
hydrocarbon compounds and from a light fraction containing the C3,
C4 and C5 olefins; [0039] d) optionally subjecting the light
fraction to further processing; and [0040] e) subjecting the
solvent phase from step (b), optionally with the heavy phase from
step (c), to a regeneration step; and [0041] (f) recycling the
regenerated solvent back to step (a), said process further
monitoring the degradation of the solvent by [0042] keeping the
content of the propylene carbonate present in the recycled solvent
above 94 wt % by weigh relative to the weight of recycled solvent
as measured by gas chromatography; [0043] keeping the TAN of the
recycled solvent measured according to ISO 1843/2 below 0.1 mg
KOH/g. [0044] keeping the distribution coefficient of the
nitrogen-containing compounds between the recycled solvent and the
hydrocarbon feed above 50% of the value measured with fresh
solvent; [0045] keeping the settling time of the recycled solvent
in the hydrocarbon feed below 200% of the settling time of the raw
propylene carbonate; or [0046] maintaining the surface tension of
the recycled solvent as measured by the Ring Tear Off method above
25 mN/m or the interfacial tension measured by the Du Nouy Ring
method above 6 mN/m.
[0047] Preferably the recycled solvent is stored in a reservoir
located in the solvent recycle loop after its regeneration and
before being recycled to step (a). Preferably such reservoir is
equipped with skimming device to ensure that any accumulation of
hydrocarbons material on the top of said reservoir can be
removed.
[0048] In a preferred embodiment, the accumulation of solvent
degradation products and heavy hydrocarbons in the recycling loop
can be avoided or at least minimized by one or more of the
following steps [0049] 1. filtration of the solvent before feeding
it back to step (a); [0050] 2. depending on the monitoring results,
purging an appropriate amount of solvent and replacing by fresh
solvent; [0051] 3. operating the regeneration step in such a way
that the heavy hydrocarbon compounds and the solvent degradation
products are removed during said regeneration step, for example by
decreasing the reflux ratio in the stripper or adapting the
regeneration temperature; and [0052] 4. adding a distillation step
between the regeneration and the extraction steps.
[0053] According to this invention, degradation of the solvent is
preferably limited by at least one of preventing oxygen and/or air
intake in the equipment used to operate the processes according to
this invention, keeping the water content in the solvent recycle
loop below 1 wt %, more preferably below 0.6 wt %, or operating the
regeneration process at temperature below 140.degree. C.,
preferably below 135.degree. C.
[0054] These operating conditions further limit corrosion of the
equipment.
[0055] The hydrocarbon feed used in this invention can be any
hydrocarbon feed. Preferably the hydrocarbon feed contains at least
one olefin selected from C3, C4, C5 and optionally C6 olefins and
is contaminated with nitrogen-containing compounds. More preferably
the hydrocarbon feed contains at least one olefin selected from C3,
C4, C5 and C6 olefins and nitrogen-containing compounds.
[0056] As used herein, "olefins" refers to any unsaturated
hydrocarbons having the formula C.sub.nH.sub.2n. The feed may also
comprise one or more paraffins. As used herein, "paraffins" refers
to any of the saturated hydrocarbons having the formula
C.sub.nH.sub.2n+2. The paraffins that may be present in the olefin
feed typically have from 1 to 15 carbon atoms, conveniently at
least 3 and no more than 6 carbon atoms. Examples of suitable
paraffins include methane, ethane, propane, butane, pentane,
hexane, isomers thereof and mixtures thereof.
[0057] If present, the paraffin usually acts as a diluent. The
olefin feed may comprise at least 10%, at least 25%, at least 30%,
at least 35%, or at least 40% paraffin, based upon the total volume
of the feed. Alternatively stated, if used, the diluent may be
present in the olefin feed in the range from 10% to 40%,
alternatively, from 10% to 35%, and alternatively, from 20% to 35%
based upon the total volume of the feed. The diluent may also be
fed to the reactor(s) separately from the olefin feed. When fed
separately, the diluent may be fed in amounts equivalent to those
mentioned above, where the diluent is co-fed with the feed.
[0058] The olefin containing feed comprises olefins selected from
propene, butenes, pentenes, optionally hexenes, their isomers, and
mixtures thereof. The process of this invention is especially
useful for the oligomerization of feeds comprising propene,
butenes, pentenes, their isomers, and mixtures thereof. As used
herein, "isomers" refers to compounds having the same molecular
formula but different structural formula.
[0059] Additionally, the feed may comprise an oligomer (higher
olefin), for example, a dimer, such as one provided by recycling a
part of an olefin oligomerization product stream. As used herein,
"oligomer(s)" or "oligomer product" refers to an olefin (or a
mixture of olefins) made from a few light olefins. For example,
oligomers include dimers, trimers, and tetramers, obtained from
two, three or four light olefins of the same number of carbon
atoms, and mixed oligomers, obtained from 2 or more olefins having
different numbers of carbon atoms and mixtures thereof. Typically
oligomers are olefins or mixture of olefins having 20 carbon atoms
or less, alternatively, 15 carbon atoms or less, such as 9 carbon
atoms or less, and conveniently, 8 carbon atoms or less.
[0060] The hydrocarbon feed preferably comprises 30 wt % or more
olefins, such as 40 wt % or more olefins, alternatively, 50 wt % or
more olefins, alternatively, 60 wt % or more olefins,
alternatively, 70 wt % or more olefins, and alternatively, 80 wt %
or more olefins, based upon the total weight of the feed.
[0061] According to the present invention, any of the
above-described feeds may further contain at least one of diolefins
and/or cyclic olefins. Typical cyclic compounds are cyclopentene,
methylcyclohexene, cyclohexene and cycloheptene.
[0062] In any of the olefin oligomerization embodiments described
herein, the feed should be totally free, or at least substantially
free, of aromatic hydrocarbon compounds that consist solely of
hydrogen and carbon atoms. In this context, "substantially free"
means that the olefin feed contains 25 wt % or less, preferably 15
wt % or less, more preferably 10 wt % or less, such as 5 wt % or
less, and most preferably 1 wt % or less aromatic hydrocarbon,
based upon the total weight of the olefin feed.
[0063] Examples of suitable olefin feeds include untreated refinery
streams such as Fluidized Catalytic Cracking (FCC) streams, steam
cracker streams, coker streams, pyrolysis gasoline streams or
reformates.
[0064] Examples of suitable C3 olefin-containing feeds include
untreated C3 rich refinery streams such as "dilute" or "refinery
grade" propylene from a Fluidized Catalytic Cracker (FCC), C3 rich
stream from a steam cracker, from the production of "chemical
grade" or "polymer grade" propylene, from refinery gas recovery
units, from Propane Dehydrogenation Units, from Gas to Olefin (GTO)
Units, or from Fisher-Tropsch Units, and C3 rich return streams
from polypropylene producing units. These C3 streams may contain
for example from 50 to 60 wt % of propylene, or 65 wt % or more, or
70 wt % or above such as 72 wt % or 75 wt % or even up to 79 wt
%.
[0065] Examples of suitable C4 olefin containing feeds include
refinery feeds often referred to as Raffinate-1 (RAF-1),
Raffinate-2 (RAF-2) or Raffinate-3 (RAF-3). Typically, Raffinate-1,
Raffinate-2 and Raffinate-3 may be regarded as streams obtainable
at various stages in the processing of crude C4 streams obtained
from petroleum refining processes. These streams are well known by
the person skilled in the art.
[0066] Examples of suitable C5 olefin feeds include FCC Light
Naphtha streams, steam cracker C5 rich streams that have been
treated for diene removal, C5 olefin containing streams from Gas to
Olefin (GTO) Units, or Fisher-Tropsch Units. In this context,
"Light Naphtha" is understood to mean a stream having a specific
gravity in the range 0.65 to 0.73, An ASTM-D86 boiling point range
between 35 and 125.degree. C. and that contains a range of olefin,
paraffin, diolefins and cyclic hydrocarbon compounds with carbons
numbers typically in the range C5 to C8. More specifically,
according to an embodiment, a so-called Light Light Catalytic
Naphtha (LLCN) stream may be used. Such stream is characterized by
a boiling point range of, for example, from 25 to 70.degree. C. at
atmospheric pressure and a specific gravity between 0.63 and 0.68
and contains at least 60 wt % C5 hydrocarbons.
[0067] The hydrocarbon feed is characterized by comprising a
certain level of nitrogen-containing compounds and, optionally,
certain levels of other compounds such as oxygen-containing
compounds, sulphur-containing compounds, water, diolefins, cyclic
olefins and mixtures thereof. The levels (concentrations) of both
the nitrogen-containing compounds and said other compounds are
usually in a range referred to as impurities or at least as minor
components of the stream. In particular, with regard to nitrogen-
and other heteroatom-containing compounds, the concentrations of
these types of compounds will usually be in the range of from 0.1
to several hundred weight ppm (wt ppm), typically in a range of
from 10 to 500 wt ppm, relative to the total weight of the stream.
With regard to non-heteroatom-containing compounds, such as dienes,
the concentrations of these types of compounds will typically be in
the range of from 0.01 to 5 or 10 weight % (wt %) relative to the
total weight of the feed.
[0068] The process of this invention is capable of reducing the
content of nitrogen-containing compounds in the hydrocarbon feed
from an initial range of from 10 to 500 wt ppm to the range of from
20 to 500 wt ppb relative to the weight of the feed. According to
the present invention, any of the above-described feeds contains
nitrogen-containing compounds and other impurities acting as
catalyst contaminants which must be removed to an acceptable level
before the hydrocarbon feed undergoes a catalyzed reaction.
[0069] In particular, the nitrogen-containing compounds comprise
nitriles, pyrroles or mixtures thereof, typically nitriles. As used
herein, pyrroles are chemical compounds of formula C.sub.4H.sub.5N
optionally substituted by alkyl radical(s) containing from 1 to 3
carbon atoms. As used herein, "nitrile" is any organic compound
that has a nitrile group (or --C.ident.N functional group). As used
herein, "acetonitrile" (ACN) is the chemical compound with formula
CH.sub.3CN. This colorless liquid is the simplest organic nitrile.
As used herein, "propanenitrile", "propionitrile", or "ethyl
cyanide" is a nitrile with the molecular formula C.sub.2H.sub.5CN
and the terms may be used interchangeably. It is also a clear
liquid. Preferably the nitriles removed are a C2 to C5 nitrile. In
the most preferred embodiment the nitrile to be removed is
propionitrile and butyl nitrile, C.sub.3H.sub.7CN. These compounds
are especially toxic to oligomerization catalysts and their removal
leads to significant catalyst life improvement.
[0070] The process of the invention will be further described with
reference to FIG. 1 in which a hydrocarbon feed (1) is introduced
into an extraction separation unit (2) where it is contacted with
an extracting solvent (3) to obtain as overhead stream a
hydrocarbon phase (4) of reduced nitrogen-containing compounds
content and at the bottoms a solvent phase (5) containing dissolved
nitrogen-containing compounds.
[0071] According to this invention the solvent comprises, consist
essentially of propylene carbonate ("PC"). The content of propylene
carbonate in the solvent is of at least 95 wt %, preferably at
least 98 wt %. Content of above 99% are provide good results.
Typically the solvent consists of propylene carbonate comprising
traces of water.
[0072] The extraction is preferably carried out in an extraction
column, more preferably a counter current column. The temperature
and pressure of the extraction column are not critical provided
that they ensure that both the hydrocarbon feed and the solvent
remain in the liquid phase. The temperature is usually between 0
and 90.degree. C., preferably between 10 and 70.degree. C. The
pressure may be between 0 and 10 bara, more preferably between 1
and 5 bara.
[0073] The operating parameters are selected to produce a
hydrocarbon phase containing preferably between 1000 and 15,000 wt
ppm of carbonates, more preferably between 3000 and 10,000 wt ppm
of carbonates.
[0074] The solvent to hydrocarbon feed weight ratio typically
ranges from between 0.05 and 2; preferably this ratio is between
0.1 and 1, more preferably about 0.3.
[0075] The level of nitrogen-containing compounds in the
hydrocarbon phase having a reduced nitrogen-containing compound
content is below 1 ppm, preferably below 0.6 ppm, more preferably
below 0.3 ppm by weight.
[0076] Following the liquid liquid separation, the hydrocarbon
phase (4) having a reduced nitrogen-containing compound content is
transferred to a distillation column (6) in order to separate a
heavy phase (7) containing the solvent and optionally heavy
hydrocarbon compounds present in the feed, including any C6
olefins, if present in the feed, from a light fraction (8)
containing the at least one olefin selected from C3, C4, and C5
olefins and mixtures thereof.
[0077] Heavy hydrocarbon compounds preferably refer to C6 olefins,
C6+ olefins and hydrocarbon compounds with boiling point equal or
above C6 olefin boiling point. Polycarbonate and cyclopentene are
considered as heavy hydrocarbons.
[0078] The distillation is usually carried out through the use of
columns with trays, packed columns including structured packing,
random packing or a combination of both.
[0079] The final boiling point of the light fraction (8) is
preferably below 60.degree. C., more preferably below 55.degree.
C.
[0080] The light fraction (8) may be considered as a clean feed and
may be used in any downstream process. Additional treatments may be
required by said downstream process
[0081] The presence of two liquid phases in the overhead of the
extraction column and in the bottom of the distillation column is
preferably avoided as it potentially leads to process difficulties
such as incorrect instrument readings, unexpected low patterns
and/or accumulation of PC layers stalling of gravity driven heat
exchangers.
[0082] To that effect, reboiler technology is preferably used at
the bottom of the distillation column (6). Also at the top of the
extraction column the level instrument tapping is preferably
oriented to allow free draining of any PC that might be carried
into the pipe work.
[0083] An example of a preferred distillation column layout is
represented in FIG. 2. As shown, the hydrocarbon phase (4) is
preheated before being introduced in a middle zone of the
distillation column (6). The top of the distillation column is
equipped with a condenser (14). A separator (15), typically a
settling tank, at the bottom of the column, separates the heavier
phase from the lighter phase that is sent to a reboiler (16)
optionally after purging. The separator (15) may be replaced by a
pump.
[0084] The solvent phase (7) removed from the distillation column
(6) is subjected to regeneration to remove undesired materials
described hereabove and comprising solvent degradation products
and/or heavy hydrocarbon compounds from the feed before being
returned back to the extraction/separation unit with the
hydrocarbon feed.
[0085] Methods to remove undesired materials from the solvent phase
(7) include but are not limited to, vacuum and steam distillation,
back extraction, adsorption (e.g. using a solid sorbent) and
anion-cation exchange resin columns.
[0086] In this invention, regeneration is preferably performed in a
stripping unit (9), typically a stripping column, by stripping the
solvent phase with a stream of stripping gas (12) whereby the
undesired materials are taken out overhead and regenerated solvent
(10) is taken as bottoms.
[0087] Optionally the solvent phase (5) separated at the bottoms of
the extraction unit is routed to the stripping column as well as
the solvent phase (7) but preferably via a different feed
point.
[0088] According to this invention the stripping gas (12) may be
selected from inert gas, typically nitrogen from light hydrocarbons
having from 1 to 6 carbon atoms, preferably from 1 to 5 carbon
atoms or mixture thereof. The stripping gas is typically free of
nitrogen-containing compounds, i.e. contains preferably less than
0.3, more preferably less than 0.1 wt % of nitrogen-containing
compounds.
[0089] According to a preferred embodiment, the stripping gas
comprises at least 98, preferably at least 99, and more preferably
at least 99.5 wt % of one or more hydrocarbons. The stripping gas
is preferably a fraction of the light fraction (8) produced at step
(c).
[0090] The contacting of the solvent phase with the stripping gas
is preferably carried out at a pressure of from 1 to 5 bars. The
weight ratio of the stripping gas to the crude product is from 50:1
to 125:1 determined at the temperature and pressure used in the
stripping unit.
[0091] Recovery of the undesired materials is maximized by
operating the stripper under high mixing conditions, for example by
minimizing the residence time of the solvent phase inside the
stripper and/or by operating the stripping unit at high load. It is
also preferred that the stripper column includes inert solid
surfaces or trays to facilitate contact between the liquid and gas
phases.
[0092] Removal of undesired materials by stripping the solvent
phase with the stripping gas could result in some entrainment of
solvent into the stripping column overheads.
[0093] According to a preferred embodiment, the stripping column is
equipped with an overhead reflux resulting in a column
configuration comprising a stripping portion in the bottom and a
distillation portion at the top. By using such embodiment the
degradation of the solvent will be limited and the need for
monitoring such degradation is reduced.
[0094] Such configuration also further allows control of the
solvent lost to the stripping tower meaning that the amount in the
overheads could be increased to allow for solvent purging if
required by the overall process. Also such configuration allows for
better separation of the heavy hydrocarbons.
[0095] The reflux rate is usually fixed relative to the net
hydrocarbon feed to the stripping tower, the net hydrocarbon feed
being the sum of the stripping gas with the extractor and
distillation bottoms streams.
[0096] It is recommended that between 2 and 40, preferably 5 and
30% wt being routed back to the tower as reflux.
[0097] The stream (13) recovered at the top of the stripper column
is suitable for Mogas blending.
[0098] After regeneration, the regenerated solvent (10) is
transferred back to the extraction tower, preferably at the top of
the extraction tower (2), thereby closing the solvent recycle
loop.
[0099] According to this invention the accumulation of the
degradation products in the solvent recycle loop is monitored to
control the efficiency of the overall process as described here
above.
[0100] The monitoring is usually carried out by control device (17)
adapted to the analytical method step described below.
[0101] The content of one or more alkyl, alkenyl, or aryl carbonate
is measured by gas chromatography using a 6890 gas chromatograph
from Agilent using a HP-FFAP polyethylene glycol TPA column using
3.3 ml*min of carrier gas. The operating temperature is between
room temperature and 220.degree. C. Flame Ionization Detector (FID)
is used as detector.
[0102] The TAN of the recycled solvent is determined according to
ISO 1843/2
[0103] The distribution coefficient of the nitrogen-containing
compounds between the solvent and the hydrocarbon feed is obtained
by contacting at room temperature equal volumes of the hydrocarbon
feed and solvent and manual shaking the obtained mixture in a
separation funnel at ambient temperature for 1 minute. After
settling, the two phases are separated and the obtained hydrocarbon
phase is further extracted with equal amount of solvent under the
same shaking conditions. This manipulation is repeated at least 3
times under the same conditions and the content of
nitrogen-containing compound in the different phases are measured
by gas chromatography using a Free Fatty Acid Phase (FFAP) column
equipped with a FID detector or with a nitrogen chemo luminescence
detector. The distribution coefficient is the slope of the straight
line obtained by plotting the nitrile concentration in the
hydrocarbon phase versus the one in the solvent.
[0104] The interfacial tension is measured via the Ring Tear Off
(RTO) method BS-EN 14370:2004
[0105] The measurement of surface tension of the solvent is
performed by the Du Nouy Ring method BS-EN 14370:2004
[0106] The settling time is measured on different aged solvent
recycling phase. The settling time of the recycled solvent in the
hydrocarbon feed should be kept below 200% of the settling time of
the raw propylene carbonate, preferably below 150% under the same
settling conditions. The settling time is preferably measured by
mixing 10 ml of the polycarbonate stream with 10 ml of the
hydrocarbon fee during 15 sec at 20.degree. C. The settling time of
recycled solvent measured under these conditions is preferably kept
below 20 s.
[0107] According to a second aspect, the present invention relates
to a process for converting a hydrocarbon feed comprising at least
one olefin selected from the C3, C4, C5 and optionally C6 olefins
and mixtures thereof contaminated with at least one
nitrogen-containing compound into a hydrocarbon product, said
process comprising the steps of: [0108] i) providing a hydrocarbon
feed contaminated with at least one nitrogen-containing compound;
[0109] ii) removing the nitrogen-containing compounds from the feed
by using a process in accordance with the first aspect of the
present invention to produce a hydrocarbon feed stream having a
reduced level of nitrogen-containing compounds; and contacting said
hydrocarbon feed stream having a reduced level of
nitrogen-containing compounds with a catalyst in order to convert
the feed stream into a hydrocarbon product.
[0110] The process for converting the hydrocarbon feed into a
hydrocarbon product concerned by this invention may be an
isomerization, an alkylation, a hydrogenation, an aromatization or
an oligomerization process; preferably such process is an
isomerization or an oligomerization process.
[0111] Typically the process of the present invention is an olefin
oligomerization process. As used herein, "oligomerization process"
refers to any process by which light olefins are linked together to
form the oligomer(s) as defined herein. As used herein, the term
"oligomerization conditions" refers to any and all those variations
of equipment, conditions (e.g. temperatures, pressures, weight
hourly space velocities etc.), materials, and reactor schemes that
are suitable to conduct the oligomerization process to produce the
oligomer(s) as known and applied in the art.
[0112] In a preferred embodiment, the hydrocarbon feed comprises an
olefin, wherein the olefin is preferably selected from the group
consisting of C3, C4, C5 and C6 olefins and mixtures thereof, in
particular C3, C4 and C5 olefins.
[0113] In a preferred embodiment, the hydrocarbon product comprises
an oligomerization product and the catalyst is an oligomerization
catalyst comprising a material selected from the group consisting
of zeolites, phosphoric acids, supported metal oxides and
combinations thereof.
[0114] Preferably, the oligomerization catalyst comprises a
zeolite, in particular a zeolite selected from the group consisting
of ZSM-5, ZSM-11, ZSM-12, ZSM-18, ZSM-22, ZSM-23, ZSM-35, ZSM-38,
ZSM-48, ZSM-50, ZSM-57, ITQ-39 and mixtures thereof.
[0115] Exemplary methods and materials utilized in the
oligomerization process are provided in WO2012/033562, U.S. Pat.
No. 4,973,790 and US-A-2012/0022224.
[0116] The invention is particularly, but not exclusively,
concerned with processes suitable for the production of C5 to C20
olefins boiling in the range of 30.degree. to 310.degree. C.,
preferably 30.degree. to 300.degree. C., more preferably 30.degree.
to 250.degree. C., from propylene and/or butene and/or pentene
containing feedstocks or their mixtures, though ethylene may be
present as well. The oligomer product may be fractionated in a
series of discrete products. In particular the invention is
concerned with the production of the olefins shown in the following
table. Typical values are indicate in table below.
TABLE-US-00001 Distillation Range (.degree. C.) ASTM D1078 Oligomer
Products Initial Boiling Point Dry Point Pentenes 30 Hexenes 63 72
Heptenes 88 97 Octenes 114 126 Nonenes 135 143 Decenes 155 160
Undecenes 167 178 Propylene Tetramers 175 225 or Dodecenes
Tridecenes 204 213
[0117] The oligomer products are useful in many applications and
are the starting material for further processes. For example, the
oligomer product may be polymerized to produce polyolefins that
have application in the plastic industry and synthetic basestocks
for lubricants. The oligomer product may be used in alkylation
reactions for the product of surfactants. The oligomer products may
be reacted with sulphur containing compounds to produce mercaptans.
The oligomer product may undergo hydroformylation and subsequently
hydrogenation to produce alcohols. The alcohols may be used in
industry such as, for example, solvents, or be incorporated into
the production of detergents/surfactants. The alcohols may further
be used in many other areas of industry such as, for example,
undergoing esterification to produce esters that have application
as plasticizers. Oligomer products may be hydrogenated to produce a
predominately paraffin product such as ISOPAR.TM..
[0118] Products could be streams suitable for blending into fuels
dispositions including Mogas, distillate, diesel, jet fuel etc.
from processes like EMOGAS (ExxonMobil Olefins to Gasoline), MODG
(Mobil Olefins to Diesel and Gasoline).
EXAMPLES
[0119] The examples below illustrate some aspects of the present
invention
Example 1
[0120] In this example a LLCN hydrocarbon feed is first sent to an
extraction tower, where it is contacted with PC as extraction
solvent. Any nitriles present in the hydrocarbon feed are absorbed
into the PC phase. The overheads of the extractor tower are routed
to a distillation column where any PC that is present in the
purified hydrocarbon stream is separated into the bottoms along
with any undesired hydrocarbons. The overhead stream is the desired
purified hydrocarbon stream. The bottoms of the distillation are
routed to a stripping tower. The bottom of the extractor is routed
to the same stripping tower as the distillation bottoms, possibly
via a different feed point. In the stripping the stripping medium
is heated pentane coming from higher olefin process which uses the
clean LLCN.
[0121] Any liquid in the overheads of the stripper is condensed and
routed to the refinery mogas pool.
[0122] The data in FIG. 3 demonstrate that the technology achieves
the required separations. Hydrocarbon feed nitrile content is
typically much higher than the nitrogen measured at point 1
(extractor overheads). There are normally very low nitrogen levels
at point 2 (distillation overheads), demonstrating that the cleaned
hydrocarbon is suitable for the downstream acid catalyzed
oligomerization process. The difference in nitrogen content between
points 3 and 4 (stripper top and bottoms), shows that it is being
stripped out from the circulating used PC. The consistent
performance of the extractor to remove nitrogen-containing
compounds from the feed demonstrates that the process works in a
continuous closed loop.
[0123] Also the process according to the present invention can be
operated at low corrosion rate typically less or equal than 2.6
mil/yr allowing low cost carbon steel to be used for the unit
construction.
Example 2
[0124] The data in table 1 represents the model predicted
compositions of the various streams in the process using PRO II
simulation model based on measured physical properties of the
stream components. Key points to note are the very low levels of
nitrile in the clean C5 stream and the high levels of nitrile in
the extractor bottoms and stripper overheads.
[0125] In the example shown in Table 1, some optimization of
conditions has been completed to define allowed preferred operating
ranges to be defined as shown in Table 2.
TABLE-US-00002 TABLE 1 Flow rate, temperature and compositions
generated using PRO 2 for the pilot plant case. The hydrocarbon
feed in this case is LLCN and the stripping gas is pentane. PCN
represents propionitrile and Py is pyrrole. LLCN clean up stream
Stripping C5 stream PC streams Raw Stripper Distillation LLCN
Raffinate Clean C5 Pentane Overheads Solvent Extract Bottom 1 4 8
12 13 3 5 7 Flow rate kg/h 1.63 1.61 1.42 0.71 0.92 0.51 0.53 0.19
Temperature .degree. C. 40 40 33 20 40 40 40 69 Compositions C4-
wt. % 1.1 1.1 1.2 0.0 0.0 0.0 0.1 0.0 C5 sats wt. % 36.6 36.6 40.3
80.4 63.1 0.5 1.6 16.1 C5 olefins wt. % 52.5 51.8 58.5 19.6 19.8
0.2 4.0 14.3 C6+ wt. % 9.9 9.9 0.0 0.0 16.6 0.0 0.5 65.6 PC wt. %
0.0 0.6 0.0 0.0 0.4 99.3 93.8 4.0 PCN wt. % 48.8 0.8 0.5 0.0 80.7
8.2 154.4 2.6 Py wt. % 0.1 0.1 0.0 0.0 0.1 1.4 1.2 0.5
TABLE-US-00003 TABLE 2 Possible operating ranges and preferred
conditions. Parameter Range Preferred Range Extractor Pressure 2-10
barg 2-4 barg Extractor Tem 10-70.degree. C. 40-50.degree. C.
Distillation Pressure 1-5 barg 1.5-3 barg Distillation feed Temp
30-80.degree. C. 40-50.degree. C. Distillation top temp
20-70.degree. C. 45-55.degree. C. Distillation bottom temp
50-100.degree. C. 70-85.degree. C. Distillation reflux flow 1-5
times mass 2-3 times mass feed rate feed rate Stripper feed temp
50-130.degree. C. 95-105.degree. C. Stripper top temp 30-80.degree.
C. 55-65.degree. C. Stripper bottom temp 100-150.degree. C.
125-135.degree. C. Stripper reflux 2-100% of net 25-35% HC feed PC
circulation rate 10-200 wt % of 10-30 wt % of hydrocarbon
hydrocarbon feed rate feed rate Stripping gas rate 10-100 wt % of
70-90 wt % of C5 paraffin C5 paraffin feed feed
Example 3
[0126] This example demonstrates the impact of additional reflux at
the stripper column.
[0127] In table 3 the stripper tower chemical map is shown with a
reflux flow of 34% of net HC feed. There is a concentration of 890
ppmw of PC in the tower overheads. In table 4 the chemical map is
shown with a reflux flow of 17% of the net HC feed and there is a
concentration of 2320 ppm of PC in the tower overheads. However,
the concentration of propionitrile (PCN) in the overheads in table
1 shows that the stripping is no longer effective at this higher
reflux flow. These data points clearly demonstrate the PC content
of the stripper overheads can be tuned based on reflux flow to the
stripper, but the amount of reflux is constrained based on
effective stripping.
TABLE-US-00004 TABLE 3 Stripper stream concentrations with a reflux
of 8T/h- compositions generated using PRO 2 process simulation
software Reflux 34 % of overhead flow wt % Stripper Overheads
Stripper Bottoms PC 0.089 98.414 PCN 0.000 0.014 PYRROLE 0.000
0.000 <C4 0.065 0.000 C5 77.490 1.347 C6+ 22.355 0.225
TABLE-US-00005 TABLE 4 Stripper stream concentrations with a reflux
of 4T/h- compositions generated using PRO 2 process simulation
software Reflux 17 % of overhead flow wt % Stripper Overheads
Stripper Bottoms PC 0.232 98.809 PCN 0.016 0.000 PYRROLE 0.000
0.000 <C4 0.065 0.000 C5 77.384 1.191 C6+ 22.302 0.000
[0128] The data shown in table 5 demonstrates that PC content in
the tower overheads can be tuned using reflux. This also goes some
way to showing the cutoff point beyond which additional reflux flow
will lead to ineffective stripping.
TABLE-US-00006 TABLE 5 Stripper reflux flow versus tower
performance- compositions generated using PRO 2 process simulation
software. Reflux flow as % Stripper Overheads Stripper Bottoms of
overhead flow PC (wt %) PCN (wt %) 0 1.0000 -- 13 0.3342 1.20E-07
17 0.233 2.77E-07 21 0.1628 9.59E-07 25 0.1145 1.78E-05 29 0.0898
0.0109 34 0.0886 0.0155 38 0.0894 0.0307
[0129] The amount of propionitrile in the tower bottoms indicates
the effectiveness of the tower in stripping contaminants whereas
the PC in the overheads demonstrates the effectiveness of the
reflux in limiting PC loss.
* * * * *