Note: Descriptions are shown in the official language in which they were submitted.
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-1-
PROCESS TO MANUFACTURE LOW SULFUR FUELS
FIELD OF THE INVENTION
[0001] The instant invention relates to a process for upgrading of hydrocarbon
mixtures boiling within the naphtha range. More particularly, the instant
invention
relates to a process to produce high octane, low sulfur naphtha products
through the
simultaneous skeletal isomerization of feed olefins and selective
hydrotreating.
BACKGROUND OF THE INVENTION
(0002] Liquid hydrocarbon streams that boil within the naphtha range, i.e.
below
232°C, and produced from the Fluidized Catalytic Cracking Unit ("FCC")
are
typically used as blending components for motor gasolines. Environmentally
driven regulatory pressure concerning motor gasoline sulfur levels is expected
to
result in the widespread production of less than 50 wppm sulfur mogas by the
year
2004. Levels below 10 wppm are being considered for later years in some
regions
of the world, and this will require deep desulfurization of naphthas in order
to
conform to emission restrictions that are becoming more stringent. The
majority,
i.e., 90% or more, of sulfur contaminants present in motor gasolines are
typically
present in naphtha boiling range hydrocarbon streams. However, the naphtha
boiling range streams are also rich in olefins, which boost octane, a
desirable
quality in motor gasolines.
[0003] Thus, many processes have been developed to produce low sulfur
products from naphtha boiling range streams while attempting to minimize
olefin
loss, such as, for example, hydrodesulfurization processes. However, these
processes also typically hydrogenate feed olefins to some degree, thus
reducing the
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-2-
octane number of the product. Therefore, processes have been developed that
recover octane lost during desulfurization. Non-limiting examples of these
processes can be found in United States Patent Numbers 5,298,150; 5,320,742;
5,326,462; 5,318,690; 5,360,532; 5,500,108; 5,510,016; and 5,554,274, which
are
all incorporated herein by reference. In these processes, in order to obtain
desirable
hydrodesulfurization with a reduced octane loss, it is necessary to operate in
two
steps. The first step is a hydrodesulfurization step, and a second step
recovers
octane lost during hydrodesulfurization.
[0004] Other processes have also been developed that seek to minimize octane
lost during hydrodesulfurization. For example, selective hydrodesulfurization
is
used to remove organically bound sulfur while minimizing hydrogenation of
olefins
and octane reduction by various techniques, such as the use of selective
catalysts
and/or process conditions. For example, one selective hydrodesulfurization
process, referred to as SCANfining, has been developed by ExxonMobil Research
& Engineering Company in which olefinic naphthas are selectively desulfurized
with little loss in octane. U.S. Patent Nos. 5,985,136; 6,013,598; and
6,126,814, all
of which are incorporated by reference herein, disclose various aspects of
SCANfining. Although selective hydrodesulfurization processes have been
developed to avoid significant olefin saturation and loss of octane, such
processes
have a tendency to liberate HZS a portion of which may react with retained
olefins
to form mercaptan sulfur by reversion.
[0005] Thus, there still exists a need in the art for a process to reduce the
sulfur
content in naphtha boiling range hydrocarbon streams while minimizing octane
loss
and mercaptan reversion.
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-3-
SUMMARY OF THE INVENTION
[0006] The instant invention is directed at a process for producing low sulfur
naphtha products through simultaneous skeletal olefin isomerization and
selective
desulfurization. The process comprises:
a) contacting a naphtha boiling range feedstream containing organically bound
sulfur and olefins in a reaction zone, operated under effective hydrotreating
conditions and in the presence of hydrogen-containing treat gas, with a
supported catalyst comprising at least one medium pore zeolite selected
from ZSM-23, ZSM-12, ZSM-22, ZSM-57, and ZSM-48, 0.1 to 27 wt.% of
at least one Group VIII metal oxide, and 1 to 45 wt.% of at least one Group
VI metal oxide to produce a desulfurized product.
BRIEF DESCRIPTION OF THE FIGURES
[0007] Figure 1 compares results obtained from the Examples herein at constant
bromine number reduction.
[0008] Figure 2 compares product iso-olefin to n-olefin ratios of products
resulting from the Examples herein.
[0009] Figure 3 compares product iso-paraffin to n-paraffin ratios of products
resulting from the Examples herein.
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-4-
DETAILED DESCRIPTION OF THE INSTANT INVENTION
[0010] It should be noted that the terms "hydrotreating" and
"hydrodesulfurization" are sometimes used interchangeably herein, and the
prefixes
"i-" and "n" are meant to refer to "iso-" and "normal", respectively.
[0011] In the hydrotreating of naphtha boiling range feedstreams, olefins are
typically saturated in the hydrotreating zone resulting in a decrease in
octane
number of the desulfurized product. However, the present invention reduces the
decrease in octane of the desulfurized product through the use of a novel
process
involving contacting a naphtha boiling range feedstream in a reaction zone
operated
under effective hydrotreating conditions. This reaction zone contains a
supported
catalyst comprising at least one medium pore zeolite, 0.1 to 27 wt.% of at
least one
Group VIII metal oxide, and 1 to 45 wt.% of at least one Group VI metal oxide
supported on a suitable substrate.
[0012] The desulfurized product thus obtained has a higher iso-paraffin to n-
paraffin ratio, and thus a higher octane than a desulfurized naphtha treated
by a
selective or non-selective hydrotreating process only, i.e., without an octane
recovery step. The higher octane of the desulfurized product results from the
unexpected finding by the inventors hereof that by operating the reaction zone
under conditions effective for encouraging the skeletal isomerization of n-
olefins to
iso-olefins results in a desulfurized naphtha product having a higher octane
number
than a desulfurized product resulting from a selective hydrodesulfurization
process
only. The inventors hereof have found that the degree of skeletal
isomerization of
n-olefins to iso-olefins benefits the final product because the saturation of
iso-
olefins to iso-paraffins that occurs in the reaction zone herein provides for
less
octane loss in the final product when compared to the saturation of n-olefins
to n-
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-5-
paraffms. It should be noted that iso-paraffins typically have a much higher
octane
than their corresponding n-paraffin. Further, the rate of saturation of iso-
olefins is
typically slower than that of n-olefins. Therefore, by increasing the ratio of
iso-
olefins to n-olefins present in the reaction zone effluent, the resulting
desulfurized
naphtha product exiting the reaction zone also typically has a higher iso-
olefin to n-
olefin ratio as well as a higher olefin content, and thus a higher octane than
a
desulfurized naphtha treated by a selective or non-selective hydrotreating
process
only.
(0013] In the hydroprocessing of naphtha boiling range hydrocarbon
feedstreams, it is typically highly desirable to remove sulfur-containing
compounds
from the naphtha boiling range feedstreams with as little olefin saturation as
possible. It is also highly desirable to convert as much of the organic sulfur
species
of the naphtha to hydrogen sulfide with as little mercaptan reversion as
possible.
By mercaptan reversion we mean the reaction of hydrogen sulfide with olefins
during the hydrotreating to form undesirable alkylmercaptans. The inventors
hereof have unexpectedly found that through the use of the presently claimed
invention, high levels of sulfur can be removed from an olefinic naphtha
stream
without excessive olefin saturation or mercaptan reversion taking place.
[0014] Feedstreams suitable for use in the present invention include naphtha
boiling range refinery streams that typically boil in the range of 50°F
( 10°C) to
450°F (232°C) containing both olefins and sulfur containing
compounds. Thus, the
term "naphtha boiling range feedstream" as used herein includes those streams
having an olefin content of at least 5 wt.%. Non-limiting examples of naphtha
boiling range feedstreams that can be treated by the present invention include
fluid
catalytic cracking unit naphtha (FCC catalytic naphtha or cat naphtha), steam
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-6-
cracked naphtha, and coker naphtha. Also included are blends of olefinic
naphthas
with non-olefinic naphthas as long as the blend has an olefin content of at
least 5
wt.%, based on the total weight of the naphtha feedstream.
[0015) Cracked naphtha refinery streams generally contain not only paraffins,
naphthenes, and aromatics, but also unsaturates, such as open-chain and cyclic
olefins, dimes, and cyclic hydrocarbons with olefinic side chains. The olefin-
containing naphtha feedstream can contain an overall olefins concentration
ranging
as high as 70 wt.%, more typically as high as 60 wt.%, and most typically from
5
wt.% to 40 wt.%. The olefin-containing naphtha feedstream can also have a dime
concentration up to 15 wt.%, but more typically less than 5 wt.% based on the
total
weight of the feedstock. The sulfur content of the naphtha feedstream will
generally range from 50 wppm to 7000 wppm, more typically from 100 wppm to
5000 wppm, and most typically from 100 to 3000 wppm. The sulfur will usually
be present as organically bound sulfur. That is, as sulfur compounds such as
simple
aliphatic, naphthenic, and aromatic mercaptans, sulfides, di- and polysulfides
and
the like. Other organically bound sulfur compounds include the class of
heterocyclic sulfur compounds such as thiophene, tetrahydrothiophene,
benzothiophene and their higher homologs and analogs. Feedstreams suitable for
use herein can also contain nitrogen contaminants that are typically present
in a
range from 5 wppm to 500 wppm.
[0016] The feedstreams used herein are typically preheated prior to entering
the
reaction zone herein and final heating is typically targeted to the effective
hydrotreating temperatures. If the naphtha boiling range feedstream is
preheated, it
can be reacted with the hydrogen-containing treat gas stream prior to, during,
and/or after preheating. At least a portion of the hydrogen-containing treat
gas can
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
_'7_
also be added at an intermediate location in the reaction zone. Hydrogen-
containing treat gasses suitable for use in the presently disclosed process
can be
comprised of substantially pure hydrogen or can be mixtures of other
components
typically found in refinery hydrogen streams. It is preferred that the
hydrogen-
containing treat gas stream contains little, more preferably no, hydrogen
sulfide.
The hydrogen-containing treat gas purity should be at least 50% by volume
hydrogen, preferably at least 75% by volume hydrogen, and more preferably at
least 90% by volume hydrogen for best results. It is most preferred that the
hydrogen-containing stream be substantially pure hydrogen.
[0017] In the reaction zone, the above-described naphtha boiling range
feedstream is contacted with a catalyst comprising at least one medium pore
zeolite. Zeolites are porous crystalline materials, and medium pore zeolites
as used
herein can be any zeolite described as a medium pore zeolite in Atlas of
Zeolite
Structure Types, W.M. Maier and D.H. Olson, Butterworths. Typically, medium
pore zeolites are defined as those having a pore size of 5 to 7 Angstroms,
such that
the zeolite freely sorbs molecules such as n-hexane, 3-methylpentane, benzene
and
p-xylene. Another common classification used for medium pore zeolites involves
the Constraint Index test which is described in United States Patent Number
4,016,218, which is hereby incorporated by reference. Medium pore zeolites
typically have a Constraint Index of 1 to 12, based on the zeolite alone
without
modifiers and prior to treatment to adjust the diffusivity of the catalyst.
Preferred
medium pore zeolites for use herein are selected from ZSM-23, ZSM-12, ZSM-22,
ZSM-57, and ZSM-48, with ZSM-48 being the most preferred.
[0018] Another means of describing zeolites is alpha value or number. Alpha
value, or alpha number, is a measure of zeolite acidic functionality and is
more
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
_g_
fully described together with details of its measurement in United States
Patent
Number 4,016,218, J. Catalysis, 6, pages 278-287 (1966) and J. Catalysis, 61,
pages 390-396 (1980), which are all incorporated herein by reference.
Generally
the alpha value reflects the relative activity with respect to a high activity
silica-
alumina cracking catalyst. To determine the alpha value as used herein, n-
hexane
conversion is determined at 800°F. Conversion is varied by variation in
space
velocity such that a conversion level of 10 to 60 percent of n-hexane is
obtained
and converted to a rate constant per unit volume of zeolite and compared with
that
of the silica-alumina catalyst, which is normalized to a reference activity of
1000°F.
Catalytic activity is expressed as a multiple of this standard, i.e. the
silica-alumina
standard. The silica-alumina reference catalyst contains 10 wt.% A1203 and the
remainder is Si02. Therefore, as the alpha value of a zeolite catalyst
decreases, the
tendency towards non-selective cracking also decreases. Zeolites suitable for
use
herein have an alpha value of up to 20, preferably between 0.1 and 20, more
preferably 1 to 19, and most preferably between 10 and 20.
(0019] The medium pore zeolites used herein are typically combined with a
suitable porous binder or matrix material. Non-limiting examples of such
materials
include active and inactive materials such as clays, silica, and/or metal
oxides such
as alumina. Non-limiting examples of naturally occurring clays that can be
composited include clays from the montmorillonite and kaolin families
including
the subbentonites, and the kaolins commonly known as Dixie, McNamee, Georgia,
and Florida clays. Others in which the main mineral constituent is halloysite,
kaolinite, dickite, nacrite, or anauxite may also be used. The clays can be
used in
the raw state as originally mixed or subjected to calcination, acid treatment,
or
chemical modification prior to being combined with the medium pore zeolite.
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-9-
[0020] It is preferred that the porous matrix or binder material comprises
silica,
alumina, or a kaolin clay. It is more preferred that the binder material
comprise
alumina. In this embodiment the alumina is present in a ratio of less than 15
parts
zeolite to one part binder, preferably less than 10, more preferably less than
5, and
most preferably 2.
[0021] The catalysts used herein also comprises 0.1 to 27 wt.% of at least one
Group VIII metal oxide and 1 to 45 wt.% of at least one Group VI metal oxide.
The at least one Group VIII metal oxide concentration of the catalysts used
herein
is preferably 0.1 to 10 wt.%, more preferably 1 to 8 wt.%, and most preferably
1 to
wt.%, and the at least one Group VIII metal oxide concentration of the
catalysts
used herein is preferably 1 to 30 wt.%, more preferably 1 to 20 wt.%, and most
preferably 2 to 10 wt.%. Preferred Group VIII metal oxides are those selected
from
Fe, Co and Ni, more preferably Co and/or Ni, and most preferably Co. Preferred
Group VI metal oxides are those selected from Mo and W, more preferably Mo.
The at least one Group VIII metal oxide and the at least one Group VI metal
oxide
can be incorporated onto the above-described supported medium pore zeolite by
any means known to be effective at doing so. Non-limiting examples of suitable
incorporation means include incipient wetness, ion exchange, mechanical mixing
of
metal oxide precursors) with zeolite and binder, or a combination thereof.
(0022] The reaction zone used herein can be comprised of one or more fixed bed
reactors or reaction zones each of which can comprise one or more catalyst
beds of
the same or different catalyst. Thus, it is within the scope of the instant
invention
that catalysts comprising different zeolites, different Group VIII and Group
VI
metal oxides, and mixtures thereof be used in the same reaction vessel.
Although
other types of catalyst beds can be used, non-limiting examples of suitable
bed
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-10-
types include fluidized beds, ebullating beds, slurry beds, and moving beds.
Preferred are fixed catalyst beds. Interstage cooling or heating between
reactors or
reaction zones, or between catalyst beds in the same reactor, can be employed
since
some olefin saturation can take place, and olefin saturation and the
desulfurization
reaction are generally exothermic. A portion of the heat generated during
hydrodesulfurization can be recovered. Where this heat recovery option is not
available, conventional cooling may be performed through cooling utilities
such as
cooling water or air, or through use of a hydrogen quench stream. In this
manner,
optimum reaction temperatures can be more easily maintained.
[0023] As stated above, the above-defined naphtha boiling range feedstream
containing organically bound sulfur and olefins is contacted with the
supported
catalyst described herein in a reaction zone operated under effective
hydrotreating
conditions. By effective hydrotreating conditions, it is meant those
conditions that
provide for the skeletal isomerization of at least 20 wt.% of the n-olefins
present in
the feedstream to iso-olefins, preferably at least 40 wt.%, more preferably at
least
50 wt.%. By skeletal isomerization, it is meant the reorientation of the
molecular
structure of the normal olefins (n-olefins) with a preference for branched
chain iso-
olefins over straight. Thus, skeletal isomerization, as used herein, refers to
the
conversion of a normal olefin to a branched olefin or to the rearranging or
moving
of branch carbon groups, which are attached to the straight chain olefin
molecule,
to a different carbon atom, and non-skeletal isomerization can be described as
the
rearranging of the position of the double bond within the straight chain or
branched
olefin molecule.
[0024] By effective hydrotreating conditions, it is also meant those
conditions
chosen that will achieve a resulting desulfurized naphtha product having less
than
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-11-
100 wppm sulfur, preferably less than 50 wppm sulfur, more preferably less
than
30 wppm sulfur. Typical effective hydrotreating conditions will be those that
include temperatures ranging from 150°C to 425°C, preferably
200°C to 370°C,
more preferably 230°C to 350°C. Typical weight hourly space
velocities
("WHSV") range from 0.1 to 20hr-1, preferably from 0.5 to Shr 1. Any effective
pressure can be utilized, and pressures typically range from 4 to 70
atmospheres,
preferably 10 to 40 atmospheres. In a most preferred embodiment, the effective
hydrotreating conditions are selective hydrotreating conditions configured to
achieve a sulfur level and degree of skeletal isomerization within the above-
defined
ranges, most preferably the conditions are selected such that the desulfurized
naphtha product has a sulfur level sufficiently low to meet current regulatory
standards in place at that time. By selective hydrotreating conditions, it is
meant
conditions such as those contained in U.S. Patent Nos. 5,985,136; 6,013,598;
and
6,126,814, all of which have already been incorporated by reference herein,
which
disclose various aspects of SCANfining, a process developed by the ExxonMobil
Research and Engineering Company in which olefinic naphthas are selectively
desulfurized with little loss in octane.
[0025) As previously stated, the desulfurized product thus obtained will
typically have a higher iso-paraffin to n-paraffin ratio, and thus a higher
octane than
a desulfurized naphtha treated by a selective or non-selective hydrotreating
process.
Typical iso-paraffin to n-paraffin ratios in the desulfurized product
resulting from
the present process are greater than l, preferably 2, more preferably 3. Thus,
compared to selective hydrodesulfurization catalyst systems, the processing of
the
naphtha boiling range feedstream over the present catalyst system results in a
desulfurized naphtha product with a higher octane at constant olefin
saturation even
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-12-
when both catalyst systems maintain similar desulfurization/olefin saturation
selectivity.
[0026] In one embodiment of the instant invention, the nitrogen content of the
naphtha boiling range feedstreams is reduced in a feed pre-treatment step
because
catalytic treatments are impeded by nitrogen-containing compounds present in
the
feedstream. Thus, one embodiment of the instant invention involves treating
the
naphtha boiling range feedstream with an acidic material to reduce the
nitrogen
content of the feedstreams. Non-limiting examples of suitable acidic materials
include sulfuric acid, Amberlyst, alumina, spent sulfuric acid obtained from
an
alkylation unit, and any other material known to be effective at reducing the
nitrogen concentration of a naphtha boiling range feedstream. Preferred acidic
materials are Amberlyst and alumina. In the feed pretreatment step, the
naphtha
boiling range feedstream can be contacted with the acidic material under
conditions
effective for removing at least a portion of the nitrogen-containing compounds
present in the naphtha boiling range feedstream. By at least a portion, it is
meant at
least 10 wt.% of the nitrogen-containing compounds present in the feedstream.
Preferably, at least that amount of nitrogen-containing compounds that will
result in
a first reaction zone effluent containing less than 50 wppm total nitrogen,
based on
the first reaction zone effluent. More preferably the first reaction zone
effluent
contains less than 25 wppm total nitrogen, most preferably less than 10 wppm
nitrogen, and in an ideally suitable case, less than 5 wppm total nitrogen.
Thus, by
"conditions effective for removal of at least a portion of the nitrogen-
containing
compounds", it is meant those conditions under which the first reaction zone
effluent will have the above described total nitrogen concentrations, i.e., 10
wt.%
removal, etc. It should be noted that if sulfuric acid or spent sulfuric acid
obtained
from an alkylation unit is used, the acid concentration should be adjusted by
adding
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-13-
a diluent before either is contacted with the naphtha boiling range feedstream
to
avoid polymerizing olefins.
[0027] The above description is directed to several embodiments of the present
invention. Those skilled in the art will recognize that other embodiments that
are
equally effective could be devised for carrying out the spirit of this
invention.
[0028] The following examples will illustrate the effectiveness of the present
invention, but is not meant to limit the present invention in any fashion.
EXAMPLES
EXAMPLE 1 - CATALYST PREPARATION
[0029] A base ZSM-48 catalyst comprising 65% ZSM-48 / 35% Alumina was
used to prepare a catalyst as contemplated herein. The properties of the base
catalyst are given in Table 1 below.
[0030] 100 grams of the base catalyst was charged to a rotary cone for
impregnation with Mo. The Mo solution used for impregnation was prepared by
dissolving 22.6 grams of ammonium heptamolybdate in a quantity of water
sufficient to completely wet it. The Mo solution was sprayed onto the base
catalyst
and the resulting catalyst was dried at 250°F for 12 hours. The Mo
containing base
catalyst was calcined in a tube furnace for 3 hours at 1000°F using an
air circulation
rate of 5 vol. air/vol. catalyst.
[0031] The Mo impregnated catalyst was again charged to the rotary cone for
impregnation with Co. The Co solution used for impregnation was prepared by
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-14-
dissolving 18.3 grams of cobalt nitrate in a quantity of water sufficient to
wet the
entire cobalt nitrate solid. The Co solution was sprayed onto the base
catalyst and
the resulting catalyst was dried at 250°F for 12 hours. The Co/Mo
containing base
catalyst was calcined in a tube furnace for 3 hours at 1000°F using an
air circulation
rate of 5 vol. air/vol. catalyst.
[0032] The finished catalyst contained 2.59 wt.% Co and 9.51 wt.% Mo.
TABLE 1
BASE CATALYST PROPERTIES
A1 ha 20
Surface Area 224 mZ/
Densit 0.66 /cc
Water so tion 8.8 wt.%
Hexane so tion 8 wt.%
Cyclohexane sorption 9 wt.%
EXAMPLE 2
[0033) An FCC naphtha was treated at ambient conditions and liquid hourly
space velocities ("LHSV") of 2-3 hr' with Amberlyst-15 to reduce the nitrogen
content of the feed to 3wppm. The feed having the properties described in
Table 2
below was then contacted with the catalyst described in Example 1 above. The
contacting conditions included various temperatures within the range of 480-
650°F,
i.e. 480, 482, 400, S 18, 525, 536, 552, 624, 649°F, hydrogen treat
rates of
2000scf/bbl of 100% pure hydrogen, pressures of 250psig, and LHSV of 2hr-'.
The
results of this experiment are described in the Figures below.
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-15-
EXAMPLE 3 - COMPARATIVE (I)
[0034] An FCC naphtha was treated at ambient conditions and liquid hourly
space velocities ("LHSV") of 2-3 hr' with Amberlyst-15 to reduce the nitrogen
content of the feed to lwppm. The feed having the properties described in
Table 2
below was then contacted with a commercial hydrotreating catalyst having 1.2
wt.% Co0 and 4.2 wt.% MoO. The contacting conditions were selected from those
known in the art to be "selective" and included various temperatures within
the
range of 450-600°F, i.e. 480, 503, 421, 537, and 557°F hydrogen
treat rates of
2000scf/bbl of 100% pure hydrogen, pressures of 250psig and LHSV of 4hr-1. The
results of this experiment are described in the Figures below. The
concentration of
mercaptans produced in this Example was also compared to the concentration of
mercaptans produced in Example 2 at 525°F. These results are contained
in Table
3 below.
EXAMPLE 4 - COMPARATIVE (II)
[0035] An FCC naphtha feed having the properties described in Table 2 below
was contacted with a commercial hydrotreating catalyst having 1.2 wt.% Co0 and
4.2 wt.% MoO. The contacting conditions included a temperature of
525°F,
hydrogen treat rates of 3000scf/bbl of 100% pure hydrogen, pressures of
170psig
and LHSV of 2.3hr'. The results of this experiment are described in the
Figures
below. The concentration of mercaptans produced in this Example was also
compared to the concentration of mercaptans produced in Example 2 at
525°F.
These results are contained in Table 3 below.
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-16-
TABLE 2
FEED PROPERTIES
Exam le Exam le Exam le
2 3 4
API Gravi 56.6 56.7 57.1
Total S, w m 711 603 735
Nitro en, w 3 1 48
m
Bromine Number 69.8 70.2 71
H dro en 13.27 13.29 13.23
Road Octane 92.2 92.5 93.5
Number "RON"
Paraffins wt.%
n-Paraffins 3 3.22 3.02
iso-Paraffins 21.91 23.22 22.08
Total Paraffins24.91 26.43 25.11
Na hthenes 8.42 8.37 9.28
Aromatics 28.44 29.69 25.19
Olefins wt.%
n-Olefins 12.6 11.95 12.83
iso-Olefins 17.68 17.35 17.01
Other olefins 7.91 6.2 10.61
Total olefins 37.97 35.5 40.43
Distillation
F ASTM D2887
5% 95 90 85
10% 109 107 105
50% 230 228 222
90% 350 346 341
95% 373 371 365
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-17-
TABLE 3
Feed Treat Total iso Product Mercaptan/
S, Gas Pressure,to S, Bromine Number
wppm scf/bblsi n-olefinwppm Ratio
ratio
Exam le 2 711 2000 250 2.9 30 0.24
Exam le 3 603 2000 250 1.5 100 0.4_1
Exam le 4 735 3000 170 N/A 30 0.63
[0036] As described above, mercaptans are generally formed by the reversion
reaction of olefins with hydrogen sulfide. Thermodynamics for model compounds
show that mercaptan reversion equilibrium for branched olefins, i.e. iso-
olefins, is
lower than that for normal olefins. Consequently, the isomerization of n-
olefins to
iso-olefins can give a lower mercaptan concentration at constant bromine
number.
This benefit is readily illustrated by comparing mercaptan/bromine number
ratios at
constant temperature. Thus, by comparing the mercaptan/bromine number ratios
of
the products produced at 525°F in Examples 2, 3, and 4, the results
contained in
Table 3 show that the catalyst used in Example 2 above produced less
mercaptans
that the catalysts used in Examples 3 and 4. It should be noted that the
mercaptanlbromine number ratio is sensitive to the equilibrium constant for
feeds
with similar sulfur concentrations subjected to catalysis with similar treat
gas rates,
which is a function of the ratio of iso to n-paraffins.
[0037] Figure 1 shows that at constant bromine number reduction, the octane
loss was much lower for Example 1 than for the comparative Examples. The
reduction in bromine number was measured according to ASTM 1159.
CA 02533354 2006-O1-19
WO 2005/012459 PCT/US2004/024128
-18-
[0038] Figure 2 shows that at constant bromine number, the catalyst of Example
1 provided a higher iso-olefin to n-olefin ratio than the catalysts of the
comparative
Examples. Higher branched olefin concentrations, i.e. iso-olefins, results in
higher
octane at constant bromine number since octane numbers for branched olefins
are
typically higher than those for normal olefins.
[0039] Figure 3 shows that the catalysts of the catalyst of Example 1, one
contemplated by the instant invention produced a product having a higher iso-
paraffin to n-paraffin ratio. A higher iso-paraffin to n-paraffin ratio in a
product
will result in a product having a higher octane than a product with a lower
ratio.
