Note: Descriptions are shown in the official language in which they were submitted.
~ 17~
Backaround of the Invention
Solvent dewaxing of waxy lube oils has long
been known. It has also been known that lighter oils,
oils of lower boiling point and VI of about 90-105/110
are more miscible in dewaxing solvents of a given
composition than are higher boiling-higher VI oils. It
is also widely accepted that good yields of dewaxed
oils are obtained when the dewaxing procedure is
practiced under oil/solvent miscible conditions. To
this end, conditions of solvent to oil ratios, dewaxing
temperatures and solvent/cosolvent ratios have been
adjusted to achieve oil-solvent miscibility at the
dewaxing temperature (filter temperature). All too
often, however, a compromise must be struck between
yield of dewaxed oil and pour point, that is low pour
points are achieved at the expense of product yield or
conversely high yields are achieved at the price of
higher pour point.
U.S. Patent 3,365,390 describes a lube oil
production process involving hydrocracking a heavy oil
feed, separating hydrocracked wax from a hydrocracked
lubricating oil portion of the products and hydroiso-
merizing the hydrocracked wax using an active reforming
catalyst. An isomerized lubricating oil fraction so
produced can be dewaxed separately, to recover ultra
high VI isomerized lube oil, or the isomerized lube oil
fraction is dewaxed in admixture with a hydrocracXed
lubricating oil fraction. When the isomerate is
dewaxed in combination with a hydrocracked lube oil
fraction the wax recovered is a mixture of hydrocracked
wax and isomerized wax and the properties of the
- 2 - 2 ~ -~ 7~ 7 ~
recovered lube oil are upgraded due to the presence of
the isomerate lube oil portion.
High boiling-high VI wax isomerate and
natural waxy oil distillates are difficult to dewax to
achieve pour point in the reg-ion of about -20C and
lower. Such oils when solvent dewaxed to low tempera-
ture typically encounter oil/solvent miscibility
problems resulting in poor dewaxed oil yields.
Descri~tion of the Invention
It has been discovered that high boiling high
VI oils can be solvent dewaxed to low pour point under
miscible conditions when using low miscibility dewaxing
solvents, e.g. C3-C6 ketone based dewaxing solvents
such as methyl ethyl ketone, methyl isobutyl ketone,
acetone, etc. and mixtures thereof such as MEK/MIBK by
combining a quantity of low boiling conventional VI
waxy oil with the high boiling high VI oil and co-
processing the mixture under conventional solvent
dewaxing conditions. The addition of the low boiling
conventional VI waxy oil to the high boiling high VI
oil permits dewaxing to be conducted under miscible
conditions resulting in the production of acceptable
yields of low pour point dewaxed oil. It has further
been discovered that the low pour point dewaxed oil
mixture may be subsequently fractioned into fractions
whose specifications are very close to the parent
materials in terms of boiling point and VI and that
both such fractions possess the low pour point of the
mixture. Upon normalization of yields it has been
discovered that the yield of the low pour-high boiling-
high VI oil fraction achieved by the co-processing
procedure is higher than that achieved when the high
boiling high VI oil is dewaxed by itself.
- 3 - 2~7~
Description of the Figures
Fiaure 1 compares the miscibility of heavy,
high boiling high VI wax isomerate oil to that of a
mixture of said heavy oil with a light oil at a 2/1
ratio in ketone dewaxing solvents of varying propor-
tions at different temperatures.
iaure 2 shows the yield of -21-C pour
dewaxed oil derived from Fischer-Tropsch isomerate, the
yield being normalized to 100 barrels of Fischer-
Tropsch isomerate feed to the dewaxer on the basis of
both neat Fischer-Tropsch isomerate and a Fischer-
Tropsch isomerate/150N blend.
The Invention
Heavy, high boiling, high VI waxy oils, be
they waxy oils obtained by wax isomerization or conven-
tional oils, such as deaspha}ted 600N hydrocracked oil,
or Bright Stocks which are immiscible in typical low
miscibility dewaxing solvents such as C3-C6 ketones at
the low dewaxing temperature used when low pour points
of about -21C are sought can be solvent dewaxed to a
target pour point of about -21-C and lower, preferably
about -24-C, most preferably about -27-C using conven-
tional solvents under miscible conditions (e.g. a
filter temperature of no less than about -35-C so as to
have a pour/filter ~T of about 3-4-C or less) by adding
to the heavy, high boiling, high VI waxy oil a quantity
of lower boil~ng conventional VI waxy oil distillate
and processing this mixture through the solvent dewax-
ing process under miscible conditions.
The light lower boiling conventional VI waxy
oil added to the heavy, high boiling high VI waxy oil
will be such that it can be easily separated from the
_ 4 _ 2 ~ ~ 7 ? ,~
heavy oil by distillation, therefore it will be charac-
terized by possessing a 90% off point about 50-300F,
preferably 50-100F, lower than the 10% off point of
the heavy oil. The bulk of the light oil is substan-
tially lighter and lower boiling than the bulk of the
heavy oil.
The light oil is added to the heavy oil in an
amount sufficient to render the mixture miscible in the
low miscibility dewaxing solvent used at a filter
temperature which permits the waxy oil to possess a
pour point of at least -21~C, preferably about -24C,
most preferably about -27-C. The amount of added light
oil can range between about g to 50% by vol. of the oil
mixture, preferably about 20 to 40 vol.%.
The solvent dewaxing process which is bene-
fited by operating on the dual component waxy feed
stock is any typical solvent dewaxing process including
those identified as dilution indirect chilling process-
es, pre-dilution direct chilling processes or just
direct chilling processes.
Indirect chillinq processes include, for
example, scraped surface chilling processes wherein the
waxy oil charge is diluted with solvent to produce a
solution which is passed through the scraped surface
chiller wherein a refrigerant is passed through the
outer jacket of the heat exchanger while a rotating
scraper blade prevents wax build up in the inner
surface of the chiller.
Direct chilling processes can employ either
no dilution or predilution of the waxy charge. The
waxy charge with or without dilution is then chilled by
the injection of cold solvent directly into the waxy
charge.
- 5 - ~J~
A preferred embodiment of dilution chilling
is the DILCHILL process wherein the waxy charge is
passed through a chilling tower divided into stages and
cold solvent is injected into a number of said stages.
In those stages into which cold solvent is injected, a
high level of agitation is maintained CO that substan-
tially instantaneous mixing of the chilling solvent and
waxy oil is achieved thereby avoiding detrimental shock
chilling. This procedure i8 described in greater
detail in U.S. Patent 3,773,650. In an alternate
embodiment the waxy oil i8 chilled to a temperature
about 35F above the filter temperature in the appara~
tus described above, with chilling down to the filter
temperature being performed in a subsequent scraped
surface chiller. This embodiment is described in U.S.
Patent 3,775,288.
The low miscibility dewaxing solvents which
are typically used in solvent dewaxing processes and
which are the same solvents which are used in the
process of the present invention include C3-C6 ketones
such acetone, methyl ethyl ketone (MEK), methyl
isobutyl ketone (MIBK) and mixtures thereof, such as
MEK/MIBK.
The heavy high boiling high VI waxy oil can
be that material obtained by isomerizing wax either
synthetic wax as is obtained from Fischer-Tropsch
synthesis or natural wax as i8 obtained by dewaxing
hydrocarbon oil8, commonly called slack wax or a
natural petroleum material ~uch as hydrocracked oil,
deasphalted 600N or, Bright Stock oil. When the waxy
oil to be dewaxed is a heavy high boiling high VI wax
isomerate, it is preferred that the total fraction of
oil boiling in the lube oil boiling range (i.e. about
330-C and above preferably about 370C and above) be
the feed to the dewaxing process of the present
- 6 - 2~-17~7~
invention, i.e. utilizes the addition of a light oil
fraction to facilitate dewaxing under miscible condi-
tions. In general heavy-high boiling-high VI materials
be they isomerates natural oils, or hydrocracked oils
are those materials having a viscosity in the range 6
to 12 cSt 0 100C, preferably 8 to 10 cSt ~ 100C, a
mid LV% boiling point of 450 to 5507C, preferably 475
to 525C and a VI of at least 120, preferably at least
140.
The light, lower boiling lower VI oil is one
having a viscosity of about 3 to 7 cSt @ 100C, prefer-
ably about 4 to 6 cSt ~ 100C, a 90% off point about 0
to 300F, preferably about 50 to 100F, lower than the
10% off point of the heavy oil and a VI of less than
about 110, preferably less than about 100.
In the process of the present invention the
heavy oil is mixed with a volume of light oil to permit
operation of the solvent dewaxing process under
miscible conditions at a filter temperature low enough
to produce an oil having a pour point of at least
-21C.
After processing the mixed oil feed through
the solvent dewaxing process the resulting dewaxed oil
product is fractionated into fractions corresponding
very closely to the original parent materials (i.e. a
light oil fraction of conventional VI and a heavy oil
fraction of high VI). Each of these fractions possess-
es a pour point of at lea~t about -21-C, the pour point
of the mixture. The yield of heavy oil of -21C pour
obtained by this co-processing technique is higher than
that achievable by processing the heavy oil by itself.
The wax which is isomerized may come from any
of a number of sources. Synthetic waxes from Fischer-
2 ~ :~ 7~ 7~3
Tropsch processes may be used, as may be waxes recov-
ered from the solvent or autorefrigerative dewaxing of
conventional hydrocarbon oils as well as mixtures of
these waxes. Waxes from dewaxing conventional hydro-
carbon oils are commonly called slack waxes and usually
contain an appreciable amount of oil. The oil content
of these slack waxes can range anywhere from 0 to 45%
or more, usually 5 to 30~ oil. For the purposes of
this application, the heavy waxes recovered from the
dewaxing of Bright Stock and the heavy Fischer-Tropsch
waxes are the feeds of choice.
Hydroisomerization may be performed over any
of the standard hydroisomerization catalysts which
contain a hydrogenation metal selected from Group VIB
and ~roup VIII and mixtures thereof, preferably the
Group VIII metals, more preferably the noble Group VIII
metals, most preferably platinum. Metal loading ranges
between 0.1 to 5.0 wt% metal, preferably 0.1 to 1.0 wt%
metal, most preferably 0.2 to 0.6 wt% metal.
The hydrogenation metal component is support-
ed on a refractory inorganic metal oxide support,
preferably alumina or silica-alumina, most preferably
the transition aluminas, e.g., gamma alumina. Prefer-
ably the support is halogenated. The halogen is
usually chlorine or fluorine or mixture thereof,
preferably fluorine, with net halogen content in the
range 1 to 10 wt%, preferably 2 to 8 wt%.
Isomerization i8 conducted under conditions
of temperature between about 250 to 400C, preferably
270-360~C, pressures of 500 to 3000 psi H2, preferably
1000-1500 psi H2, hydrogen gas rates of 1000 to 10,000
SCF/bbl, and a space velocity in the range 0.1-10
v/v/hr, preferably 1-2 v/v/hr.
- ~ - 2~ ~7~ ~
Preferred catalysts are the subject of u.S.
Patent 4,959,337, U. S . Patent 4,906,601 and U.S. Patent
4,900,707.
The use of these catalysts for the production
of a lube oil base stock or blending stock by the
isomerization of wax is the subject of U.S. Patent
4,929,795, U. S . Patent 4,923,588, and U.S. Patent
4,937,399 respectively.
A most preferred catalyst is the subject of
U.S. Patent 4, 906,601. The use of that catalyst for
wax isomerization is the subject of U.S. Patent
4,923,588.
That catalyst comprises a noble Group VIII
metal on low fluoride content small particle size
refractory metal oxide base. The catalyst is charac-
terized by having a fluoride content in the range of
0.1 to up to but less than 2 wt%, preferably 0.1 to 1. 5
wt%, more preferably 0.2 to 1.0 wt%, a particle diame-
ter of less than 1/16 inch and a preferred noble Group
VIII metal loading in the range of 0.1 to 2.0 wt~. The
preferred small particle æupport is 1/20 inch trilobe
alumina.
As one would expect, noble metal isomeriza-
tion catalysts are extremely susoeptible to deactiva-
tion by the presence of heteroatom compounds (i.e. N, O
or S compound~) in the wax feed 80 care mu~t be exer-
cised to remove such heteroatom materials from the wax
feed charge6. When dealing with high purity waxes such
as synthetic Fischer-Tropsch waxes, such precautions
may not be necessary. In such cases, subjecting such
waxes to very mild hydrotreating may be sufficient to
insure protection for the isomerization catalyst. On
the other hand, waxes obtained from natural petroleum
-- 9 -- 2 ~ ~ r~ ~ r~ ~3
sources contain quantities of heteroatom compounds as
well as appreciable quantities of oil which contain
heteroatom compoundsO In such instances the slack
waxes should be hydrotreated to reduce the level of
heteroatom compounds to levels commonly accepted in the
industry as tolerable for feeds to be exposed to
isomerization catalysts. Such levels will typically be
a N content of about 1 to 5 ppm and a S content of
about 1 to 20 ppm, preferably 2 ppm or less nitrogen
and 5 ppm or less sulfur. Similarly, such slack waxes
prior to hydrotreating should be deoiled to an oil
content in the range of 0 to 35% oil, preferably 5 to
25% oil. The hydrotreating step will employ a typical
hydrotreating catalyst such as Co/Mo or Ni/Mo on
alumina under standard, commercially acceptable condi-
tions, e.g., temperature of 280 to 400C, space veloci-
ty of 0.1 to 2.0 V/V/hr, pressure of from 500 to 3000
psig H2 and hydrogen gas rates of from 500 to 5000
SCF/bbl.
The present invention will be better under-
stood by reference to the following non-limiting
examples.
Figure 1 shows how the miscibility of a
Fischer-Tropsch 8.7 cSt Q100C isomerate fraction
boiling in the 550 to 575C range (about equivalent to
a 250N viscosity grade) can be improved about 10C with
the addition of 33% of a conventional 150N basestock.
Filtration studies were performed with this combined
feedstock and compared with base case evaluation of the
neat Fischer-Tropsch 8.7 cSt ~lOO-C wax isomerate. The
isomerate was made by isomerizing a Fischer-Tropsch 150
wax as feed over an isomerization catalyst comprising
0.6 Pt/5.6% F/A12O3 at a temperature between 365 to
375C, a pressure of 1000 psig, a H2 flow rate of 7500
- lo - 2~.17~7~
SCF H2/bbl and a LHSV of 1. The dewaxing data are
given in Table 1.
In an effort to reach the -21C pour target,
solvent composition of the MEK/MIBK system was lowered
to 10~ MEK and the dewaxing of 100% Fischer-Tropsch 8.7
cSt QlOO-C wax isomerate was performed at a filter
temperature just below miscibility (degrees from
miscibility -3). Typical of immiscible dewaxing, the
process gave a low pour filter temperature spread and
high filter rates. However, as is normally experienced
with immiscible dewaxing, the wash efficiency with two
liquid phases is very poor and the resulting low yield
of 15.7 wt% is unacceptable. Although not measured
directly it is calculated, based on typical immiscible
isomerate dewaxing data that the product had a VI of
about 158, a viscosity at 100C of about 8.0 cSt. It
has been observed that on going from miscible dewaxing
to immiscible dewaxing a viscoæity decrease is common
while VI shows very little change.
Going to miscible dewaxing, as was done in
the second case by raising the filtration temperature,
raised the yields to acceptable levels but the attain-
able pour point was raised to only -lO-C.
Using a blend of conventional 150N oil and
Fischer-Tropsch 8.7 cSt ~lOO-C wax isomerate the Pilter
temperature can be lowered below the target pour
without immiscibility occurring. Low pours ~-21'C)
were achieved at good yields. The lower filtration
rate of 5.2 m3/M2d is not necessarily cause for concern
as plants running 600N stocks are typically designed
for filter rates of 4 to 6 m3/m2d and techniques to
; handle these rates are known.
:
.: . .
2 ~
As one might expect, the product from the
dewaxer is a mixture of conventional and non-conven-
tional lube. Crucial to the process is the successful
separation of the light dewaxed oil from the heavy
dewaxed oil e.g. the light conventional oil from the
heavier isomerate oil. While any separation process
(distillation, extraction, membranes, etc.) could be
considered, the simplest and most straight forward
process is distillation. For that reason low boiling
conventional lubes are co-processed with the relatively
high boiling isomerate oils. It is interesting to note
that this does not imply a wide difference in viscosity
grades. Due to the highly paraffinic nature of the
isomerate oil it has a much higher boiling point than
equivalent viscosity conventional stocks. This differ-
ence in the viscosity/boiling point relationship makes
the separation of a 5.0 cSt 150N oil and a 8.7 cSt
Fischer Tropsch wax isomerate quite feasible as demon-
strated in Table 2.
The dewaxed oil product from the co-process-
ing was cut into fractions which were then reblended to
roughly the same specifications as would be possessed
by individually processed dewaxed oil fractions (See
Table 2).
Using the 40% to Final Boiling Point blend, a
9.2 cSt, 148 VI, -22C pour product was made, leaving a
102 VI, 4.7 cSt, -22-C pour conventional stock. These
specifications are very close to the parent materials.
Surprisingly it has been found that not only is the
dewaxing of the heavy oil fraction made easier by the
procedure of dewaxing a heavy oil/light oil blend, but
also the yield of dewaxed heavy oil is higher. Thus,
while 100 barrels of Fischer-Tropsch isomerate can be
dewaxed to give 15.7 barrels of -21C pour oil (15.7
LV%, see Table 1), when these same 100 barrels of
- 12 -
Fischer-Tropsch isomerates are mixed with 50 barrels of
150N oil (to give a total of 150 barrels of oil to be
dewaxed) a total dewaxed oil yield of 49.3% is obtained
l74 barrels DW0 based on 150 barrels mixture) and upon
fractionation 60% or 44.4 barrels (60% of 74 barrels)
is found to constitute the amount of oil having a VI,
viscosity and pour corresponding to the 15.7 barrels
obtained when the Fischer-Tropsch isomerate was dewaxed
by itself. Thus, yield of the premium quality high VI
oil is increased at the same time the dewaxing is made
easier (See Figure 2).
This yield increase is much greater than
what one would obtain from simply mixing fractions of
separately dewaxed FT isomerate and 150N oil. Linear
blending of such fractions to give a final product with
a ~48 VI would require a mixture of 84 LV% FT
isomerate/16 LV% 150N. This blend would produce a
yield of only 18.7% compared to the about 44% of 148 VI
product obtained by co-processing. The oil product
obtained by linear blending would also be of different
quality. Whereas coprocessing gives a yield of 44.4%
of a 148 VI, 55.21 cSt Q 40-C, 9.19 cSt Q 100C mate-
rial, linear blending would produce an 18.7% yield of a
148 VI, 44.78 cSt 0 40-C, 7.9 cSt Q lOO-C product.
Furthermore, coprocessing followed by fractionation
produces a light oil of 102 VI and 5 Vis which is
obviously superior to the base 150N oil fraction which,
when separately dewaxed produced a DW0 of 90 VI and 5
vis .
- 13 - 2 ~ .~; 7 ~
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