U.S. patent application number 11/988904 was filed with the patent office on 2009-09-17 for process for reducing the cloud point of a base oil.
Invention is credited to Jakob Willem Duininck, Gilbert Robert Bernard Germaine, Wiecher Derk Evert Steenge.
Application Number | 20090230021 11/988904 |
Document ID | / |
Family ID | 35063159 |
Filed Date | 2009-09-17 |
United States Patent
Application |
20090230021 |
Kind Code |
A1 |
Duininck; Jakob Willem ; et
al. |
September 17, 2009 |
Process for reducing the cloud point of a base oil
Abstract
The invention relates to a process for reducing the cloud point
of a base oil feed having a kinematic viscosity at 100.degree. C.
of greater than 10 cSt by separating the molecules inferring the
high cloud point from the base oil by (a) depositing said molecules
on one side of a cooled surface, (b) obtaining a base oil having a
reduced cloud point and (c) melting the deposited molecules and
separating the melted molecules from the surface and reusing said
surface to perform step (a).
Inventors: |
Duininck; Jakob Willem;
(Petit Couronne, FR) ; Germaine; Gilbert Robert
Bernard; (Petit Couronne, FR) ; Steenge; Wiecher Derk
Evert; (Amsterdam, NL) |
Correspondence
Address: |
SHELL OIL COMPANY
P O BOX 2463
HOUSTON
TX
772522463
US
|
Family ID: |
35063159 |
Appl. No.: |
11/988904 |
Filed: |
July 17, 2006 |
PCT Filed: |
July 17, 2006 |
PCT NO: |
PCT/EP2006/064333 |
371 Date: |
January 16, 2008 |
Current U.S.
Class: |
208/27 |
Current CPC
Class: |
C10G 2400/10 20130101;
C10G 31/06 20130101 |
Class at
Publication: |
208/27 |
International
Class: |
C10G 73/32 20060101
C10G073/32 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 18, 2005 |
EP |
05291544.4 |
Claims
1. A process for reducing the cloud point of a base oil feed having
a kinematic viscosity at 100.degree. C. of greater than 10 cSt by
separating the molecules inferring the high cloud point from the
base oil by (a) depositing said molecules on one side of a cooled
surface; (b) obtaining a base oil having a reduced cloud point; and
(c) melting the deposited molecules and separating the melted
molecules from the surface and reusing said surface to perform step
(a).
2. The process according to claim 1, wherein the temperature of the
surface is between the cloud point and the pour point of the base
oil feed.
3. The process according to claim 2, wherein the surface is cooled
at the other side of the surface by a cooling medium.
4. The process according to claim 1, wherein the surface comprises
a substantially vertical oriented tube or arrangement of tubes at
which inner side of the tube or tubes the base oil feed is allowed
to flow and wherein outside of the tube a cooling medium flows.
5. The process according to claim 1, wherein the base oil has a
cloud point greater than 20.degree. C., a saturates content of
greater than 97 wt %, a kinematic viscosity at 100.degree. C. of
greater than 12 cSt, a sulphur content of less than 50 ppm and a
viscosity index of greater than 130.
6. The process according to claim 1, wherein the base oil feed is
prepared from carbon monoxide and hydrogen by (i) contacting carbon
monoxide and hydrogen with a hydrocarbon synthesis catalyst at
elevated temperature and pressure to prepare a substantially
paraffinic hydrocarbon wax; (ii) subjecting the paraffinic wax to a
pour point reducing treatment by means of catalytic
dewaxing/isomerisation; and (iii) isolating by means of
distillation a distillation bottoms fraction as the heavy base
oil.
7. The process according to claim 6, further comprising performing
a hydrocracking/hydroisomerisation step on the paraffinic wax prior
to the pour point reducing treatment.
Description
[0001] The invention is related to a process for reducing the cloud
point of a base oil feed having a kinematic viscosity at
100.degree. C. of greater than 10 cSt.
[0002] WO-A-02070627 describes a process to prepare a base oil
having a kinematic viscosity at 100.degree. C. of 22.9 cSt and a
pour point of +9.degree. C. and a viscosity index of 178. The
process involves the hydroisomerisation of a Fischer-Tropsch
synthesis product boiling from C5 up to 750.degree. C. From the
effluent of the hydroisomerisation a distillation residue boiling
above 370.degree. C. was isolated and catalytically dewaxed. The
dewaxed oil was distilled to obtain as a distillation residue
boiling above 510.degree. C. the base oil as described above.
[0003] WO-A-2004007647 describes a process to prepare a heavy base
oil from a Fischer-Tropsch derived wax. The process involves the
hydroisomerisation of a Fischer-Tropsch synthesis product boiling
from C5 up to 750.degree. C. From the effluent of the
hydroisomerisation a distillation residue boiling above 370.degree.
C. was isolated. This residue was split into a light and a heavy
base oil precursor fraction. By catalytically dewaxing the heavy
base oil precursor fraction a base oil having a pour point of
-15.degree. C., a viscosity index of 157 and a kinematic viscosity
at 100.degree. C. of 26.65 cSt was prepared.
[0004] An advantage of the process of WO-A-02070627 or
WO-A-2004007647 is that base oils are obtained having a high
viscosity and a high viscosity index. A problem is that when the
base oils are obtained by means of a catalytic dewaxing step a hazy
product may be obtained. The hazy product has a high cloud point
resulting in a hazy product at ambient temperature. This property
makes the base oil less suitable for certain applications.
[0005] WO-A-03033622 describes a process to prepare a low haze
heavy base oil from a Fischer-Tropsch derived wax by isolating by
means of deep cut distillation a fraction boiling between 1000 and
1200.degree. F. (538 and 649.degree. C.) and a residue boiling
above 1200.degree. F. The fraction boiling between 1000 and
1200.degree. F. is subjected to a hydroisomerisation step.
According to the specification a base oil having no haze can be
obtained having a pour point of less than +10.degree. C. and a
kinematic viscosity at 100.degree. C. of greater than 15 cSt.
[0006] According to WO-A-03033622 the haze precursors are removed
from the base oil by the deep cut distillation whereby the haze
precursors remain in the residual fraction. A disadvantage of this
process is the deep cut distillation itself. Such a distillation is
difficult to perform. Moreover, because a substantial part of the
feed is recovered as the top product, a substantial amount of
energy will be required for such a distillation. Furthermore
valuable heavy base oil molecules are removed with the distillation
residue. This is disadvantageous for the yield to the heavy base
oils. Moreover the maximum achievable viscosity of the heavy base
oil is limited by this distillation.
[0007] WO-A-0077125 describes a process to remove haze precursors
from a heavy mineral base oil, referred to as Bright Stock, by
contacting the base oil with a solid alumina sorbent.
[0008] EP-A-1548088 describes a process to prepare a haze free base
oil having a cloud point of below 0.degree. C. and a kinematic
viscosity at 100.degree. C. of greater than 10 cSt by
hydroisomerisation of a Fischer-Tropsch synthesis product,
isolating a residue from the effluent of the hydroisomerisation
step, reducing the wax content of the residue to a value of below
50 wt % and finally solvent dewaxing the residue to obtain the haze
free base oil.
[0009] EP-A-1550709 describes a process to prepare a haze free base
oil having a kinematic viscosity at 100.degree. C. of greater than
10 cSt from a Fischer-Tropsch wax feed. The process involves
reducing the wax content in the feed to a value of below 50 wt % by
contacting the feed with a hydroisomerisation catalyst under
hydroisomerisation conditions at a remote location, transporting an
intermediate product having a wax content of below 35 wt % from the
remote location to a location closer to the end user of the haze
free base oil, and solvent dewaxing the transported intermediate
product to obtain the haze free base oil at the location closer to
the end-user.
[0010] A disadvantage of the processes as described in EP-A-1548088
and EP-A-1550709 is that a solvent dewaxing step is performed which
process is considered complex and involving usage of additional
chemicals as ketone and aromatic type solvents.
[0011] The object of this invention is to provide a process to
prepare haze free heavy base oils which is more simple to perform.
The haziness of the base oil is defined as a cloud point of below
15.degree. C.
[0012] This object is achieved with the following process. Process
for reducing the cloud point of a base oil feed having a kinematic
viscosity at 100.degree. C. of greater than 10 cSt by separating
the molecules inferring the high cloud point from the base oil by
(a) depositing said molecules on one side of a cooled surface, (b)
obtaining a base oil having a reduced cloud point and (c) melting
the deposited molecules and separating the melted molecules from
the surface and reusing said surface to perform step (a).
[0013] In step (a) the temperature of the cooled surface is
preferably between the cloud point and the pour point of the base
oil feed. The surface may be cooled by various methods. Suitably
the surface is cooled by contacting the opposite side of the
surface, i.e. the side opposite the side at which the base oils
contacts the surface, with a suitable cooling medium. Examples of
suitable cooling media are evaporating liquids, for example
evaporating ammonia or nitrogen. Nitrogen may be advantageous in
situations wherein liquid nitrogen is available at low cost and
where the nitrogen does not need to be liquefied again. Other
examples are chilled water or other process streams available
having the required temperature and cooling capabilities.
[0014] The design of the surface is not critical. It may be flat,
corrugated or tubular. The design should be such that the surface
can be cooled to the desired temperature for a prolonged period of
time, at least long enough to achieve that at least part of the
molecules inferring the high cloud point solidify and deposit on
said surface. Examples of possible surfaces are double walled,
optionally corrugated, plates. Between the plates the cooling
medium is allowed to flow resulting in a cooled surface at the
opposite, outer, side. One or more of such plates may be submerged
in the base oil as present in a large vessel. In such a
configuration step (a) is preferably performed in a batch operation
mode. After a certain time the oil is removed and the molecules
inferring the high cloud point remain behind on the cooled surface
of the plates. Examples of suitable plate type apparatuses, which
can be used, are described in U.S. Pat. No. 6,074,548 and U.S. Pat.
No. 6,145,340, which publications are hereby incorporated by
reference.
[0015] If a tubular surface is used the cooling medium may pass at
the inside or outside of the tube. In such an embodiment one and
more preferably more tubes are arranged vertically in a vessel. The
vessel is provided with tube sheets and inlets and outlets for
feed, product, cooling medium and used cooling medium. The cooling
medium may be present at the outside of the tubes and the base oil
is present inside the tubes. Such configurations are well known for
de-oiling of wax and are referred to as a so-called "vertical tube
sweating stove" as described in GB-A-1535345 as published in 1978.
In such a vessel the de-oiling is performed in a batch wise
operation. The cooling medium may also be provided inside the tubes
while the base oil flows at the outside of the tubes as for example
described in EP-A-937489 and U.S. Pat. No. 6,024,793. Preferably
step (a) is performed in a semi-continuous type of operation. The
use of a tubular surface as described above makes such a continuous
type of operation possible for the feed of the process of the
present invention. In such an operation the base oil feed is
circulated along or within the tubes while the molecules inferring
the high cloud point are deposited at the opposite surface of the
tubes. Only after reducing the pour point sufficiently a base oil
product is recovered from the circulating stream in step (b).
Examples of possible apparatuses having tubular surfaces and
examples of how to operate said apparatuses are described in
EP-A-937489, U.S. Pat. No. 6,024,793, and U.S. Pat. No. 5,700,435,
which publications are hereby incorporated by reference.
[0016] Both the plate and tubular surface type apparatuses may be
provided with elements to stabilize the layer of solidified haze
inferring molecules. Preferably these elements are positioned near
the cooled surface at the side where the layer will form as
described in EP-A-1216734, which publication is incorporated hereby
by reference. The surface may be further modified by roughing or by
applying a thin layer having a composition similar to the waxy
molecules to be separated. Examples of such materials are poly
olefins, for example polyethylene and polypropylene.
[0017] Step (b) is preferably performed by removing the base oil
product from the vessel after performing step (a). Thus step (b) is
performed after the cloud point of the base oil has been lowered
sufficiently in step (a), also in situations wherein step (a) is
performed by circulating said base oil along the surface as for
example described for the tubular surface above.
[0018] The solidified waxy material may be removed from the surface
in step (c) by passing a hot gas through the vessel at the side at
the waxy material is present. The material will liquefy and may be
separated from the surface by a flow of material due to gravity to
a lower part of the vessel at which it can be removed from the
vessel. Alternatively the temperature of the surface can be
increased by changing the cooling medium for a medium which heats
the surface. This medium may be the same as the cooling medium if
an evaporating medium is used. The heat of condensing may then be
used to increase the temperature of the surface. By operating more
than one vessel a thermal efficient operation can be achieved
wherein one vessel is performing step (a) using a evaporating
cooling medium and another vessel is performing step (c) wherein
said medium condenses as for example described in U.S. Pat. No.
5,700,435, which publication is hereby incorporated by
reference.
[0019] The waxy molecules as obtained in step (c) may be used as a
product as obtained or more preferably are co-fed to a
hydrocracker/hydroisomerisation step or a catalytic dewaxing step
of the process, which prepares the base oil feed of the present
process. Provided of course such process comprises said steps. An
example of a suitable process which does involve these steps is a
process wherein the base oil feed is prepared from a
Fischer-Tropsch wax as will be described in greater detail
below.
[0020] Removing only small quantities of haze incurring molecules
could become difficult because the layer of solidified molecules
would be too small to capture also the remaining haze incurring
molecules. To improve separation the content of molecules incurring
the high cloud point is preferably increased if this content is too
low to form a layer, which is capable of capturing also the last
molecules haze incurring molecules. Increasing this content can be
achieved by adjusting the process, which prepares the base oil
feed, or alternatively by recycling to step (a) any haze incurring
molecules which have been separated from the base oil in an earlier
cycle of the process according the invention.
[0021] The base oil used as feed for the process of the present
invention preferably has a kinematic viscosity at 100.degree. C. of
greater than 10 cSt and more preferably greater than 15 cSt. The
base oil feed preferably has a cloud point greater than 10.degree.
C., more preferably greater than 20.degree. C. The pour point is
preferably smaller than +10.degree. C. and more preferably smaller
than 0.degree. C. The feed may also comprise said base oil, wherein
the desired heavy and non-haze base oil is isolated from the
product of the process of according to the present invention by
separation of lower boiling compounds. Examples of such base oils
are so-called bright stock, which are obtained by de-asphalting the
residue of a vacuum distillation, step of a mineral crude oil. This
de-asphalted fraction is typically subjected to solvent extraction
and solvent or catalytic dewaxing steps and may still contain some
haze. Application of the present invention would remove the haze
problem. Such a mineral oil derived bright stock may even have a
kinematic viscosity at 100.degree. C. of greater than 30 cSt.
[0022] More preferably the base oil is a paraffinic base oil. The
saturates content of the paraffin base oil feed is preferably
greater than 97 wt % and more preferably greater than 99 wt %. The
sulphur content is preferably smaller than 50 ppm. The viscosity
index of the paraffin base oil is preferably greater than 130 and
in most cases smaller than 200.
[0023] Suitably the paraffin base oil feed having the above
properties is the paraffin base oil feed as obtained by
(i) contacting carbon monoxide and hydrogen with a hydrocarbon
synthesis catalyst at elevated temperature and pressure to prepare
a substantially paraffinic hydrocarbon wax; and (ii) subjecting the
paraffinic wax, optionally after performing a
hydrocracking/hydroisomerisation step, to a pour point reducing
treatment by means of catalytic dewaxing/isomerisation and (iii)
isolating by means of distillation a distillation bottoms fraction
as the heavy base oil.
[0024] In step (i) a mixture of H.sub.2 and CO is used. Preferably
the molar H.sub.2/CO ratio of such synthesis gas is between 1.3 and
2.3, preferably between 1.6 and 2.1. This mixture may be made by
gasification or reforming of a carboneous feed, for example coal,
residual oil feeds and natural gas. In case natural gas is used as
carboneous source the synthesis gas is preferably prepared by
catalytic or non-catalytic partial oxidation, autothermal steam
reforming, traditional steam reforming or convective steam
reforming or combinations of said processes.
[0025] The hydrocarbon synthesis catalysts of step (i) are known in
the art and are usually referred to as Fischer-Tropsch catalysts.
Catalysts for use in this process frequently comprise, as the
catalytically active component, a metal from Group VIII of the
Periodic Table of Elements. Particular catalytically active metals
include ruthenium, iron, cobalt and nickel. Cobalt is a preferred
catalytically active metal in view of the heavy Fischer-Tropsch
hydrocarbon that can be made. The catalytically active metal is
preferably supported on a porous carrier. The porous carrier may be
selected from any of the suitable refractory metal oxides or
silicates or combinations thereof known in the art. Particular
examples of preferred porous carriers include silica, alumina,
titania, zirconia, ceria, gallia and mixtures thereof, especially
silica, alumina and titania.
[0026] The amount of catalytically active metal on the carrier is
preferably in the range of from 3 to 300 pbw per 100 pbw of carrier
material, more preferably from 10 to 80 pbw, especially from 20 to
60 pbw.
[0027] If desired, the catalyst may also comprise one or more
metals or metal oxides as promoters. Suitable metal oxide promoters
may be selected from Groups IIA, IIIB, IVB, VB and VIB of the
Periodic Table of Elements, or the actinides and lanthanides. In
particular, oxides of magnesium, calcium, strontium, barium,
scandium, yttrium, lanthanum, cerium, titanium, zirconium, hafnium,
thorium, uranium, vanadium, chromium and manganese are very
suitable promoters. Particularly preferred metal oxide promoters
for the catalyst used to prepare the waxes for use in the present
invention are manganese and zirconium oxide. Suitable metal
promoters may be selected from Groups VIIB or VIII of the Periodic
Table. Rhenium and Group VIII noble metals are particularly
suitable, with platinum and palladium being especially preferred.
The amount of promoter present in the catalyst is suitably in the
range of from 0.01 to 100 pbw, preferably 0.1 to 40, more
preferably 1 to 20 pbw, per 100 pbw of carrier. The most preferred
promoters are selected from vanadium, manganese, rhenium, zirconium
and platinum.
[0028] The catalytically active metal and the promoter, if present,
may be deposited on the carrier material by any suitable treatment,
such as impregnation, kneading and extrusion. After deposition of
the metal and, if appropriate, the promoter on the carrier
material, the loaded carrier is typically subjected to calcination.
The effect of the calcination treatment is to remove crystal water,
to decompose volatile decomposition products and to convert organic
and inorganic compounds to their respective oxides. After
calcination, the resulting catalyst may be activated by contacting
the catalyst with hydrogen or a hydrogen-containing gas, typically
at temperatures of about 200 to 350.degree. C. Other processes for
the preparation of Fischer-Tropsch catalysts comprise
kneading/mulling, often followed by extrusion, drying/calcination
and activation.
[0029] The catalytic conversion process may be performed under
conventional synthesis conditions known in the art. Typically, the
catalytic conversion may be effected at a temperature in the range
of from 150 to 300.degree. C., preferably from 180 to 260.degree.
C. Typical total pressures for the catalytic conversion process are
in the range of from 1 to 200 bar absolute, more preferably from 10
to 70 bar absolute. In the catalytic conversion process especially
more than 75 wt % of C.sub.5+, preferably more than 85 wt %
C.sub.5+ hydrocarbons are formed. Depending on the catalyst and the
conversion conditions, the amount of heavy wax (C.sub.20+) may be
up to 60 wt %, sometimes up to 70 wt %, and sometimes even up till
85 wt %. Preferably a cobalt catalyst is used, a low H.sub.2/CO
ratio is used (especially 1.7, or even lower) and a low temperature
is used (190-240.degree. C.), optionally in combination with a high
pressure. To avoid any coke formation, it is preferred to use an
H.sub.2/CO ratio of at least 0.3. It is especially preferred to
carry out the Fischer-Tropsch reaction under such conditions that
the ASF-alpha value (Anderson-Schulz-Flory chain growth factor),
for the obtained products having at least 20 carbon atoms, is at
least 0.925, preferably at least 0.935, more preferably at least
0.945, even more preferably at least 0.955. Preferably the
Fischer-Tropsch hydrocarbons stream comprises at least 40 wt %
C.sub.30+, preferably 50 wt %, more preferably 55 wt %, and the
weight ratio C.sub.60+/C.sub.30+ is at least 0.35, preferably 0.45,
more preferably 0.55.
[0030] Preferably, a Fischer-Tropsch catalyst is used, which yields
substantial quantities of paraffins, more preferably substantially
unbranched paraffins. A most suitable catalyst for this purpose is
a cobalt-containing Fischer-Tropsch catalyst. Such catalysts are
described in the literature, see e.g. WO-A-9934917.
[0031] The Fischer-Tropsch process of step (i) may be a slurry
Fischer-Tropsch process or a fixed bed Fischer-Tropsch process,
especially a multi tubular fixed bed.
[0032] The paraffinic wax as obtained in step (i) is optionally
subjected to a hydrocracking/hydroisomerisation step. In such a
step the feed is contacted with a suitable hydroconversion
catalyst, which in principle be any catalyst known in the art to be
suitable for isomerising paraffinic molecules. In general, suitable
hydroconversion catalysts are those comprising a hydrogenation
component supported on a refractory oxide carrier, such as
amorphous silica-alumina, alumina, fluorided alumina, molecular
sieves (zeolites) or mixtures of two or more of these. Suitable
catalysts have been found to be those comprising a Group VIII
metal, especially nickel, platinum or palladium and a
silica-alumina carrier as will be described in more detail
below.
[0033] One type of preferred catalysts to be applied in the
hydroconversion step in accordance with the present invention are
hydroconversion catalysts comprising platinum and/or palladium as
the hydrogenation component. A very much preferred hydroconversion
catalyst comprises platinum and palladium supported on an amorphous
silica-alumina (ASA) carrier. The platinum and/or palladium is
suitably present in an amount of from 0.1 to 5.0% by weight, more
suitably from 0.2 to 2.0% by weight, calculated as element and
based on total weight of carrier. If both present, the weight ratio
of platinum to palladium (calculated as element) may vary within
wide limits, but suitably is in the range of from 0.05 to 10, more
suitably 0.1 to 5. Examples of suitable noble metal on ASA
catalysts are, for instance, disclosed in WO-A-9410264 and
EP-A-582347. Other suitable noble metal-based catalysts, such as
platinum on a fluorided alumina carrier, are disclosed in e.g. U.S.
Pat. No. 5,059,299 and WO-A-9220759.
[0034] A second type of suitable hydroconversion catalysts are
those comprising at least one Group VIB metal, preferably tungsten
and/or molybdenum, and at least one non-noble Group VIII metal,
preferably nickel and/or cobalt, as the hydrogenation component.
Usually both metals are present as oxides, sulphides or a
combination thereof. The Group VIB metal is suitably present in an
amount of from 1 to 35% by weight, more suitably from 5 to 30% by
weight, calculated as element and based on total weight of
catalyst. The non-noble Group VIII metal is suitably present in an
amount of from 1 to 25% wt, preferably 2 to 15% wt, calculated as
element and based on total weight of carrier. A hydroconversion
catalyst of this type which has been found particularly suitable is
a catalyst comprising nickel and tungsten supported on fluorided
alumina.
[0035] A preferred catalyst which can be used in a non-sulphided
form comprises a non-noble Group VIII metal, e.g., iron, nickel, in
conjunction with a Group IB metal, e.g., copper, supported on an
acidic support. The catalyst has a surface area in the range of
200-500 m.sup.2/gm, preferably 0.35 to 0.80 ml/gm, as determined by
water adsorption, and a bulk density of about 0.5-1.0 g/ml. The
catalyst support is preferably an amorphous silica-alumina where
the alumina is present in amounts of less than about 30 wt %,
preferably 5-30 wt %, more preferably 10-20 wt %. Also, the support
may contain small amounts, e.g., 20-30 wt %, of a binder, e.g.,
alumina, silica, Group IVA metal oxides, and various types of
clays, magnesia, etc., preferably alumina.
[0036] The preparation of amorphous silica-alumina microspheres has
been described in Ryland, Lloyd B., Tamele, M. W., and Wilson, J.
N., Cracking Catalysts, Catalysis: volume VII, Ed. Paul H. Emmett,
Reinhold Publishing Corporation, New York, 1960, pp. 5-9.
[0037] The catalyst is prepared by co-impregnating the metals from
solutions onto the support, drying at 100-150.degree. C., and
calcining in air at 200-550.degree. C. The Group VIII metal is
present in amounts of about 15 wt % or less, preferably 1-12 wt %,
while the Group IB metal is usually present in lesser amounts,
e.g., 1:2 to about 1:20 ratio respecting the Group VIII metal.
[0038] A typical catalyst is shown below:
TABLE-US-00001 Ni, wt % 2.5-3.5 Cu, wt % 0.25-0.35
Al.sub.2O.sub.3--SiO.sub.2 wt % 65-75 Al.sub.2O.sub.3 (binder) wt %
25-30 Surface Area 290-325 m.sup.2/gm Pore Volume (Hg) 0.35-0.45
ml/gm Bulk Density 0.58-0.68 g/ml
[0039] The hydroconversion conditions applied in such a
hydrocracking/hydroisomerisation step are those known to be
suitable in hydroisomerisation operations. Suitable conditions,
then, involve operating temperatures in the range of from 275 to
450.degree. C., preferably 300 to 425.degree. C., a hydrogen
partial pressure in the range of from 10 to 250 bar, suitably 25 to
200 bar, a weight hourly space velocity (WHSV) in the range of from
0.1 to 10 kg/l/h, preferably 0.2 to 5 kg/l/h, and a gas rate in the
range of from 100 to 5,000 Nl/kg, preferably 500 to 3,000 Nl/kg.
Suitably the conditions are so chosen that the wax conversion be
preferably between 40 and 90 wt % and more preferably between 60
and 90 wt %. In this context of the present invention the wax
content is measured according to the following procedure. 1 weight
part of the to be measured oil fraction is diluted with 4 parts of
a (50/50 vol/vol) mixture of methyl ethyl ketone and toluene, which
is subsequently cooled to -27.degree. C. in a refrigerator. The
mixture is subsequently filtered at -27.degree. C. The wax is
removed from the filter and weighed.
[0040] The optionally partly isomerised paraffinic wax is subjected
in step (ii) to a catalytic dewaxing/isomerisation step. A combined
hydrocracking/hydroisomerisation and dewaxing process may be
performed in series flow wherein the effluent of the first step is
directly subjected to the dewaxing process. In another embodiment
the lower boiling fractions, suitably the boiling fractions that
boil in the middle distillate range and below are first separated
from the effluent before performing the dewaxing step. In another
embodiment also the light base oil precursor fractions are
separated from the effluent before performing the dewaxing step.
The effective cutpoint of such a separation is suitably in the
range of from 400 to 550.degree. C. The effective cutpoint is the
temperature above which at least at least 85% by weight and
preferably at least 90% by weight, of the hydrocarbons present in
this heavy fraction has its boiling point. This separation or
fractionation can be achieved by techniques known in the art, such
as atmospheric and vacuum distillation or vacuum flashing.
[0041] In step (ii) the waxy feed is subjected to a catalytic
dewaxing treatment. In such process step the feed is contacted with
a suitable catalyst under catalytic dewaxing conditions. The
process conditions applied when using such catalysts are preferably
chosen that the resulting base oil feed has a pour point being
substantially lower than its cloud point. The dewaxing catalyst
which may be applied in step (ii) suitably comprises a molecular
sieve and optionally in combination with a metal having a
hydrogenation function, such as the Group VIII metals. Molecular
sieves, and more suitably molecular sieves having a pore diameter
of between 0.35 and 0.8 nm have shown a good catalytic ability to
reduce the pour point of the wax feed. Suitable zeolites are
mordenite, beta, ZSM-5, ZSM-12, ZSM-22, ZSM-23, SSZ-32, ZSM-35 and
ZSM-48 or combinations of said zeolites. Another preferred group of
molecular sieves are the silica-aluminaphosphate (SAPO) materials
of which SAPO-11 is most preferred as for example described in U.S.
Pat. No. 4,859,311. The other molecular sieves are preferably used
in combination with an added Group VIII metal. Suitable Group VIII
metals are nickel, cobalt, platinum and palladium. Examples of
possible combinations are Pt/ZSM-35, Ni/ZSM-5, Pt/ZSM-23,
Pd/ZSM-23, Pt/ZSM-48 and Pt/SAPO-11 or stacked configurations of
Pt/zeolite beta and Pt/ZSM-23, Pt/zeolite beta and Pt/ZSM-48 or
Pt/zeolite beta and Pt/ZSM-22. Further details and examples of
suitable molecular sieves and dewaxing conditions are for example
described in WO-A-9718278, U.S. Pat. No. 4,343,692, U.S. Pat. No.
5,053,373, U.S. Pat. No. 5,252,527, US-A-20040065581, U.S. Pat. No.
4,574,043 and EP-A-1029029.
[0042] The dewaxing catalyst suitably also comprises a binder. The
binder can be a synthetic or naturally occurring (inorganic)
substance, for example clay, silica and/or metal oxides. Natural
occurring clays are for example of the montmorillonite and kaolin
families. The binder is preferably a porous binder material, for
example a refractory oxide of which examples are: alumina,
silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,
silica-beryllia, silica-titania as well as ternary compositions for
example silica-alumina-thoria, silica-alumina-zirconia,
silica-alumina-magnesia and silica-magnesia-zirconia. More
preferably a low acidity refractory oxide binder material, which is
essentially free of alumina, is used. Examples of these binder
materials are silica, zirconia, titanium dioxide, germanium
dioxide, boria and mixtures of two or more of these of which
examples are listed above. The most preferred binder is silica.
[0043] A preferred class of dewaxing catalysts comprise
intermediate zeolite crystallites as described above and a low
acidity refractory oxide binder material which is essentially free
of alumina as described above, wherein the surface of the
aluminosilicate zeolite crystallites has been modified by
subjecting the aluminosilicate zeolite crystallites to a surface
dealumination treatment. A preferred dealumination treatment is by
contacting an extrudate of the binder and the zeolite with an
aqueous solution of a fluorosilicate salt as described in for
example U.S. Pat. No. 5,157,191 or WO-A-0029511. Examples of
suitable dewaxing catalysts as described above are silica bound and
dealuminated Pt/ZSM-5, silica bound and dealuminated Pt/ZSM-35 as
for example described in WO-A-0029511 and EP-B-832171.
[0044] The dewaxing conditions in step (ii) typically involve
operating temperatures in the range of from 200 to 500.degree. C.,
suitably from 250 to 400.degree. C. Preferably the temperature is
between 300 and 330.degree. C. The hydrogen pressures in the range
of from 10 to 200 bar, preferably from 40 to 70 bar, weight hourly
space velocities (WHSV) in the range of from 0.1 to 10 kg of oil
per litre of catalyst per hour (kg/l/hr), suitably from 0.1 to 5
kg/l/hr, more suitably from 0.1 to 3 kg/l/hr and hydrogen to oil
ratios in the range of from 100 to 2,000 litres of hydrogen per
litre of oil.
[0045] From the effluent of step (ii) lower boiling fractions are
suitably separating in step (iii) to obtain a distillation residue
as the base oil feed having the properties as described above.
* * * * *