Note: Descriptions are shown in the official language in which they were submitted.
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TS 5500
PROCESS FOR THE PREPARATION OF LUBRICATING BASE OILS
The present invention relates to a process for the
preparation of a lubrication base oil, which process
involves two successive hydroconversion stages.
Two stage hydroconversion processes for preparing
lubricating base oils are well known in the art, and
examples of such processes are disclosed in British
Patent Specification No. 1,546,504, European Patent
Application No. 0,321,298 and U.S. Patents Nos.
3,494,854; 3,459,656; 3,974,060 and 4,518,485. From these
disclosures it becomes apparent that the first stage of a
two stage hydroconversion process is usually aimed at
removing nitrogen- and sulphur-containing compounds
present in the hydrocarbon oil feed and to hydrogenate
the aromatic compounds present in the feed to at least
some extent. In the second stage the aromatics content is
subsequently further reduced by hydrogenation and/or
hydrocracking, whilst dewaxing of the effluent from the
first stage by hydroisomerisation of waxy molecules often
takes place as well. The hydroconversion catalysts used
in first and second stage should accordingly be able to
adequately serve their respective purposes. From the
aforementioned prior art documents it becomes clear that
first stage catalysts normally comprise a Group VIII non-
noble metal component and a Group VIB metal component on
a refractory oxide support. First stage catalysts
generally applied, then, include nickel-molybdenum,
nickel-tungsten or cobalt-molybdenum on an alumina,
silica-alumina or fluorided alumina support. Suitable
second stage catalysts comprise a Group VIII noble metal
component, optionally together with a Group VIB metal
component, on an refractory oxide support. As the
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Group VIII metal component platinum and/or palladium,
either in elemental form or as oxide or sulphide, are
disclosed to be useful. As the refractory oxide support
aluminosilicates (zeolitic materials) as well as
inorganic oxides (such as e.g. silica, alumina and
amorphous silica-alumina) or mixtures thereof may be
applied.
Although many of the aforementioned prior art two
stage hydroconversion processes perform satisfactory,
there is always an incentive for further improving the
efficiency of a process. In particular the first stage
operating temperature leaves room for improvement. Due to
the relatively high operating temperature applied in the
first hydroconversion stage, namely, the formation of
polynuclear aromatic compounds in this first stage is
favoured. These polynuclear aromatic compounds formed
must then be removed in the second stage, which implies
that hydroconversion conditions in this second stage
should be sufficiently severe to hydrogenate and/or
hydrocrack said polynuclear polyaromatic compounds. On
the other hand, decreasing the first stage operating
temperature will result in less conversion of the
feedstock into valuable products, which is undesired from
an economic perspective.
The present invention aims to provide a two stage
hydroconversion process for preparing lubricating base
oils, whereby the first stage can be operated at a lower
operating temperature than conventionally applied, whilst
still obtaining products having an excellent viscosity
index at a commercially attractive yield. It will be
evident that such a process will put less stringent
demands on the equipment to be used and hence can be
operated at lower operating costs, whilst still
maintaining a commercially attractive yield. Moreover,
less formation of polynuclear aromatic species also
2 r ?684q.
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implies that less of these species will remain in the
final base oil, which is desired from both environmental
and base oil quality considerations. Thus, the present
invention aims to provide an improved two stage
hydroconversion process for preparing lubricating base
oils. More specifically, the present invention aims to
provide a process for the preparation of a lubricating
base oil, which process allows the production of high
viscosity index lubricating base oils at less demanding
operating conditions, whilst still having a commercially
attractive yield.
These aims have been achieved by selecting a specific
first stage hydroconversion catalyst, which is more
active than the first stage catalysts conventionally
applied and thus allows a lower operating temperature for
obtaining the same yield as with a conventional first
stage catalyst.
Accordingly, the present invention relates to a
process for the preparation of a lubricating base oil
comprising the steps of:
(a) contacting a hydrocarbon oil feed in a first stage
with hydrogen in the presence of a catalyst comprising at
least one Group VIII noble metal component on a
refractory oxide support;
(b) contacting the liquid effluent in a second stage with
hydrogen in the presence of a hydroconversion catalyst
under hydroconversion conditions, and
(c) recovering at least one lubricating base oil having a
viscosity index of at least 80.
Suitable hydrocarbon oil feeds to be employed in
step (a) of the process according to the present
invention are mixtures of high-boiling hydrocarbons, such
as for instance heavy oil fractions. Particularly those
heavy oil fractions having a boiling range which is at
least partly above the boiling range of lubricating base
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oils are suitable as hydrocarbon oil feeds for the
purpose of the present invention. It has been found
particularly suitable to use vacuum distillate fractions
derived from an atmospheric residue, i.e. distillate
fractions obtained by vacuum distillation of a residual
fraction which in return is obtained by atmospheric
distillation of a crude oil, as the feed. The boiling
range of such a vacuum distillate fraction is usually
between 300 and 620 C, suitably between 350 and 550 C.
However, deasphalted residual oil fractions, including
both deasphalted atmospheric residues and deasphalted
vacuum residues, may also be applied, whilst synthetic
waxy raffinates (Fischer-Tropsch waxy raffinates), slack
waxes -particularly those obtained from the dewaxing of
hydrotreated waxy distillates- and hydrocracker bottom
fractions (hydrowax) are also suitable feedstocks to be
used in the process according to the present invention.
Suitable hydrowaxes are those having an effective
cutpoint of 320 C or higher, preferably of 370 C or
higher.
The catalyst to be used in the first hydroconversion
stage is a Group VIII noble metal-based catalyst. If a
hydrocarbon oil feed is used which is not substantially
free of sulphur- and nitrogen-containing compounds, this
catalyst should be sulphided prior to operation in order
to attain optimum catalyst activity and in order to
ensure that the catalyst is sufficiently tolerant towards
the sulphur- and nitrogen-containing compounds present
in the feed. If the catalyst would not be sulphided in
this case, its sulphur-tolerance would be too low under
the operating conditions and the catalyst would
consequently be rapidly poisoned when contacted with the
hydrocarbon oil feed under the operating conditions. Only
in case the hydrocarbon oil feed is substantially free of
any sulphur- and nitrogen-containing compounds, for
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instance when using a synthetic wax as the feed,
sulphiding of the noble metal-based catalyst can be
dispensed with. In most cases, however, the noble metal-
based catalyst must be sulphided prior to operation.
Sulphiding of the catalyst can be achieved by methods
known in the art, such as for instance from European
patent applications Nos. 0,181,254; 0,329,499; 0448,435
and 0,564,317 and from International patent applications
Nos. WO 93/02793 and WO 94/25157. Sulphiding can be
performed either ex situ or in situ by contacting the
unsulphided catalyst with a suitable sulphiding agent,
such as hydrogen sulphide. A hydrocarbon oil containing a
substantial amount of sulphur-containing compounds may
also be used as the sulphiding agent. Such oil is then
contacted with the catalyst at a temperature which is
gradually increased from ambient temperature to a
temperature of between 150 and 250 C. The catalyst is to
be maintained at this temperature for between 10 and 20
hours. Subsequently, the temperature is to be raised
gradually to the operating temperature. Still another
option is to use the hydrocarbon oil feed, which usually
contains a significant amount of sulphur-containing
compounds, as the sulphiding agent. In this case the
unsulphided catalyst may be contacted with the feed under
conditions less severe than the operating conditions,
thus causing the catalyst to become sulphided. Typically,
the hydrocarbon oil feed should comprise at least 0.5% by
weight of sulphur- containing compounds, said weight
percentage indicating the amount of elemental sulphur
relative to the total amount of feedstock, in order to be
useful as a sulphiding agent. From a cost and efficiency
perspective, it is generally preferred to sulphide the
catalyst in situ, i.e. first loading the unsulphided
catalyst into a reactor and thereafter contacting it with
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the sulphiding agent(s) under appropriate sulphiding
conditions.
The refractory oxide support of the first stage
hydrotreating catalyst may be any inorganic oxide,
aluminosilicate or combination of these, optionally in
combination with an inert binder material. Examples of
suitable refractory oxides include inorganic oxides, such
as alumina, silica, titania, zirconia, boria, silica-
alumina, fluorided alumina, fluorided silica-alumina and
mixtures of two or more of these. In a preferred
embodiment an acidic carrier such as alumina, silica-
alumina or fluorided alumina is used as the refractory
oxide carrier. The refractory oxide support may also be
an aluminosilicate. Both synthetic and naturally
occurring aluminosilicates may be used. Examples are
zeolite beta, faujasite and zeolite Y. A preferred
aluminosilicate to be applied is alumina- or silica-bound
zeolite Y.
The Group VIII noble metal component of the first
stage hydroconversion catalyst suitably is a platinum
(Pt) and/or a palladium (Pd) component. If the catalyst
is sulphided prior to operation, the noble metal
component will usually be present as a sulphide during
normal operation, but part of it may very well be present
in elemental and/or oxide form. Beside the Group VIII
noble metal component, a non-noble Group VIII metal
component and/or a Group VIB metal component may be
present as well on the catalyst. Accordingly, nickel
(Ni), cobalt (Co) and/or chromium (Cr), molybdenum (Mo)
or tungsten (W) -suitably in their sulphide form- may
also be present on the catalyst. Of the Group VIB metals,
tungsten and chromium are preferred. Examples of very
suitable first stage catalysts, then, are those noble
metal based-catalysts disclosed in European Patent
Application No. 0,653,242 and International Patent
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Application No. WO 96/03208. Specific examples of
suitable catalysts include PdCr and PdW on silica-bound
zeolite Y, on alumina-bound zeolite Y, on fluorided
alumina-bound zeolite Y, on silica-alumina or on
fluorided alumina. Other examples are Pt on silica-
alumina, PtPd on silica-bound zeolite Y, PtPd on alumina-
bound zeolite Y and PtPd on silica-alumina. All catalysts
mentioned preferably are sulphided prior to operation.
Particularly preferred first stage catalysts are
sulphided PdW on silica- or alumina-bound zeolite Y,
sulphided PdW on silica-alumina and sulphided PdW on
fluorided alumina.
The second hydroconversion stage, i.e. step (b), of
the process according to the present invention may
involve hydrogenation, hydrodesulphurisation,
hydrodenitrogenation, hydroisomerisation of paraffinic
molecules and any combination of two or more of these
processes, depending on the type of hydroconversion
catalyst used. Hydrocracking of paraffinic molecules may
also occur in step (b), but only as a (minor) side
reaction to one or more of the hydroconversion reactions
mentioned above. Accordingly, the hydroconversion
catalyst to be used in step (b) will not be a catalyst
specifically suited for hydrocracking of paraffinic
molecules.
The hydroconversion catalyst used in step (b) of the
process according to the present invention, i.e. the
second stage catalyst, in principle may be any catalyst
known to be active in the hydrogenation,
hydrodesulphurisation, hydrodenitrogenation and/or
hydroisomerisation of the relevant hydrocarbons with the
purpose of manufacturing lubricating base oils.
Accordingly, a first class of suitable second stage
catalysts are the hydrogenation catalysts comprising at
least one Group VIII metal component and optionally at
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least one Group VIB metal component as the hydrogenating
component(s). Such catalysts have hydrogenation activity
and may also have hydrodesulphurisation and/or
hydrodenitrogenation activity. Usually they do not
possess any relevant hydroisomerisation activity.
Suitable Group VIII metal components include both noble
and non-noble metals and/or compounds thereof, usually
oxides and/or suiphides. The second stage catalyst may
accordingly comprise one or more of the non-noble Group
VIII metals nickel (Ni) or cobalt (Co) and/or one or more
of the noble Group VIII metals Pt and Pd. In this
connection it is noted that if a noble metal component is
present on the second stage catalyst, this catalyst is
suitably at least partly sulphided prior to operation in
order to increase its sulphur tolerance. It will be
understood that the extent of sulphidation depends on the
sulphur content of the first stage effluent. At
sufficiently low sulphur content of the first stage
effluent, sulphidation of a second stage noble metal-
based catalyst may be dispensed with.
In addition to the Group VIII metal component, the
second stage catalyst may also comprise a Group VIB metal
component, which may be Cr, Mo and/or W in elemental,
oxide and/or sulphide form. The second stage catalyst
support also is an refractory oxide support and includes
the same supports as listed above for the first stage
catalyst. In case the second stage catalyst comprises a
non-noble Group VIII metal, it may be advantageous to use
phosphorus (P) as a promoter. Examples of suitable second
stage catalysts, then, include NiMo(P) on alumina or
fluorided alumina, CoMo(P) on alumina, NiW on fluorided
alumina, PdW on silica-alumina, fluorided alumina or
silica-bound zeolite Y.
A second class of suitable second stage catalysts are
those catalysts having predominantly hydroisomerisation
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activity. These catalysts are used, if the main objective
of step (b) is to lower the pour point of the first stage
effluent, i.e. dewaxing. Hydroisomerisation catalysts are
well known in the art and usually are based on an
intermediate pore size zeolitic material, suitably
comprising at least one Group VIII metal component,
preferably Pt and/or Pd. Suitable zeolitic materials,
then, include ZSM-5, ZSM-22, ZSM-23, ZSM-35, SSZ-32,
ferrierite, zeolite beta, mordenite and silica-
aluminophosphates, such as SAPO-11 and SAPO-31. Examples
of suitable hydroisomerisation catalysts are, for
instance, described in International Patent Application
No. WO 92/01657. Since hydroisomerisation catalysts
generally are relatively quickly poisoned by sulphur-
containing compounds, the first stage effluent must have
a low sulphur content prior to entry in the second stage.
The amounts of the different metals present on first
and second stage catalyst may vary between wide limits. A
Group VIII noble metal may suitably be present on first
and second stage catalyst in an amount ranging from 0.1
to 10, preferably 0.2 to 5, percent by weight M. wt),
which weight percentage indicates the amount of metal
(calculated as element) relative to total weight of
catalyst. Similarly, a non-noble Group VIII metal may
suitably be present on the second stage catalyst in an
amount of from 1 to 25% wt, preferably 2 to 15% wt,
calculated as element relative to total weight of
catalyst. If present at all, a Group VIB metal is
suitably present on first and second stage in an amount
of from 5 to 30% wt, preferably 10 to 25% wt, calculated
as element relative to total weight of catalyst.
Operating conditions in the first and second
hydroconversion stage are those conventionally applied in
the relevant hydroconversion operations. Accordingly, the
operating temperature may range from 250 to 500 C, the
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operating pressure may range from 10 to 250 bar, the
weight hourly space velocity (WHSV) may range from 0.1 to
kg of oil per litre of catalyst per hour (kg/l.h),
preferably from 0.5 to 5 kg/l.h, and the hydrogen to oil
5 ratio is suitably in the range from 100 to 2,000 litres
of hydrogen per litre of oil. However, as already stated
above, at a given final yield of lubricating base oil,
the first stage catalyst used in accordance with the
present invention allows a lower first stage operating
10 temperature, thus reducing the amount of polynuclear
aromatic species formed in this first hydroconversion
stage and hence allowing less severe conditions in the
second hydroconversion stage. In this connection it is
noted that an activity gain in the first hydrotreatment
stage of only three degrees Celsius may already
significantly reduce the amount of polynuclear aromatics
formed.
Before being subjected to the second stage
hydroconversion, the liquid effluent of the first stage
may first be treated to remove undesired gaseous species,
such as hydrogen sulphide (H2S) and ammonia (NH3).
Particularly for feeds containing substantial amounts of
sulphur- and nitrogen-containing compounds, such as
vacuum distillates derived from an atmospheric residue,
such interstage treatment could be very advantageous. H2S
may, for instance, be removed by absorption in an aqueous
amine solution. A di-isopropanolamine solution is very
useful in this respect. A preferred option, however, is
to remove H2S and NH3 simultaneously from the first stage
effluent by passing said effluent through a high pressure
stripper prior to introduction into the second stage. In
this way the content of both these undesired gases in the
first stage effluent can be effectively reduced to very
low levels, suitably below 10 ppm each. Such low levels
of H2S and NH3 allow the use of second stage catalysts
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which have a higher sensitivity to sulphur and nitrogen,
such as (unsulphided) noble metal-based catalysts. The
use of these kind of catalysts in the second
hydroconversion stage, in return, allows the manufacture
of higher quality base oils, such as technical grade
white oil. Using noble metal-based catalysts in both
hydroconversion stages may even allow the production of
medicinal oil, which must be free of aromatics, nitrogen
compounds and sulphur compounds, if the first stage is
operated at a sufficiently low temperature, thus
preventing the formation of polynuclear aromatics.
Thus, if the liquid effluent of the first
hydroconversion stage is treated to remove H2S and NH3
prior to introduction into the second hydroconversion
stage, the second stage catalyst suitably comprises a Pt
and/or a Pd component as the Group VIII metal component.
This catalyst may further comprise a Group VIB metal
component, preferably based on W or Cr. In this mode of
operation it may be advantageous to use the same noble
metal-based catalyst in the first and second
hydroconversion stage. If, on the other hand, H2S and NH3
are not removed from the first stage effluent, whereas
the feed used is not substantially free of any sulphur-
and/or nitrogen-containing compounds, it is preferred to
use a second stage catalyst comprising a nickel or cobalt
component as the Group VIII metal component and a
molybdenum or tungsten component as the Group VIB metal
component. Suitable examples of any of these catalysts
have already been described above.
Recovery of the lubricating base oil(s) in step (c)
is usually attained by distillation of the second stage
effluent. Each lubricating base oil is then recovered as
a distillate fraction. Suitably the distillation is
carried out under reduced pressure. However, atmospheric
distillation may also be applied. The cutpoint(s) of the
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distillate fraction(s) is/are selected such that each
base oil recovered has the desired viscosity.
If the second stage catalyst is a hydrogenation
catalyst having no or hardly any hydroisomerisation
activity, then a subsequent dewaxing step (d) is required
to obtain lubricating base oils having sufficiently low
pour points. Dewaxing can be achieved by catalytic
dewaxing or solvent dewaxing. Both dewaxing techniques
are well known in the art. For instance, suitable
catalysts for use in catalytic dewaxing include catalysts
based on ZSM-5, ZSM-23 or ZSM-35. Suitable dewaxing
catalysts and dewaxing processes are for instance
described in U.S. Patents Nos. 3,700,585; 3,894,938;
4,222,855; 4,229,282; 4,247,388 and 4,975,177. Solvent
dewaxing is also a well known dewaxing process. The most
commonly applied solvent dewaxing process is the methyl
ethyl ketone (MEK) solvent dewaxing route, wherein MEK is
used as the dewaxing solvent, possibly in admixture with
toluene. For the purpose of the present invention it is
preferred to use the solvent dewaxing route.
If the second stage catalyst is a hydroisomerisation
catalyst, then a separate dewaxing step after step (c)
can be dispensed with. The lubricating base oil(s)
obtained in step (c) in this case meet the specifications
with respect to both viscosity index and pour point and
accordingly no further pour point lowering treatment is
necessary in that case. As already mentioned above, the
first stage effluent must have a sufficiently low sulphur
content before being contacted with a hydroisomerisation
catalyst. If the hydrocarbon oil feed used in step (a) is
a hydrowax or a synthetic waxy raffinate, which usually
have low sulphur and nitrogen contents, then an
interstage treatment for removing H2S and NH3 can be
dispensed with and the first stage effluent can be
directly passed to step (b). If, on the other hand, the
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hydrocarbon oil feed used in step (a) has relatively high
sulphur and nitrogen contents, such as in the case of
vacuum distillates of atmospheric residues, then an
interstage removal of H2S and NH3 is required.
In general, the lubricating base oils eventually
produced using the process according to the present
invention have a viscosity index of at least 80,
preferably at least 90 and more preferably at least 95,
and a pour point of -6 C or lower and preferably -9 C
or lower.
The invention will now be further illustrated by the
following example without restricting the scope of the
invention to this particular embodiment.
Example
A hydrocarbon oil vacuum distillate obtained by
vacuum flashing of an atmospheric residue and having the
properties as indicated in Table I was contacted in a
first step with hydrogen in the presence of a
presulphided catalyst comprising 4.301 wt Pd and 21.9% wt
of W (both calculated as element relative to total weight
of catalyst) on a fluorided alumina carrier (4.4% wt F,
basis total carrier). The effluent of the first step was
subsequently contacted in the second step with hydrogen
in the presence of a conventional NiMoP/alumina catalyst
(3.001 wt Ni, 13.0% wt Mo, 3.2% wt P, all calculated as
element relative to total weight of catalyst). Reaction
conditions applied in both steps and the properties of
the final product after conventional solvent dewaxing at
-20 C are given in Tables II and III, respectively.
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TABLE I Feedstock characteristics
Refractive Index at 70 C 1.5010
Flash Point ( C) 213
Specific Gravity 70/4 C 0.899
Vk80 (cSt)* 28.2
VklOO (cSt)* 14.8
Sulphur (% wt) 2.68
Nitrogen (% wt) 0.13
Hydrogen (o wt) 12.0
C5 asphaltenes (% wt) 0.08
Wax content (% wt) 9.2
* Vk80 and VklOO stand for kinematic viscosity in
centistokes as determined at 80 C and 100 C,
respectively
Comparative Example
The same procedure as described above was repeated,
only this time with a first stage catalyst comprising
5.0% wt Ni and 23.1% wt W on a fluorided alumina carrier
(4.6% wt F, basis total carrier). Process conditions and
properties of the product obtained after conventional
solvent dewaxing at -20 C are listed in Tables II and
III, respectively.
TABLE II Process conditions
Operating Condition Example Comparative
Example
Step 1 Step 2 Step 1 Step 2
Temperature ( C) 380 390 400 390
WHSV (kg/l.h) 1.0 1.0 1.0 1.0
Gas rate (Nl/kg) 1500 1500 1500 1500
Pressure (bar) 140 140 140 140
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TABLE III Product properties
Example Comparative Example
Yield M. wt on 77 72
feed)
VklOO (cSt) 9.55 9.88
VI 95 93
As can be seen from Tables II and III, the process
according to the present invention requires a lower
temperature in the first step, wherein the noble metal-
based catalyst is used, whilst still obtaining a product
having better VI and viscosity at a higher yield.
