Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2104~78
A PROC~SS FOR PURIFYING USED LURRICATING OILS
The present invention relates to a process for purifying used
lubricating oils by vacuum distillation and by twice-repeated
secondary treatment of the lubricating oil distillate with finely
divided, non-activated bleaching earth at 260 to 350C.
Each year some one million tonnes of mineral base lubricating
oils are produced in the Federal Republic of Germany alone. Of
this, approximately 500,000 tonnes become used oils, so-called
old oils. Old oil is defined as mineral lubricating or
industrial oil that has become unsuitable for the purpose for
which is was originally intended.
,
Old oil includes used motor oils, gear oils, machine oils,
hydraulic oils, metal-working oils, corrosion protection oils,
etc. Motor oils alone account for more than 40 percent, whereas
the proportion of hydraulic oil is approximately 18 percent.
In addition to mineral-based lubricating oils, lubricating oils
that contain synthetic components are also produced, and there
are also purely synthetic base oils that are used for special
applications. In addition, the use of naturally based
lubricating oils, such as those based on rapeseed oil, is
becoming increasingly important in the area of hydraulic oil.
In the Federal Republic of Germany, old oil has to be disposed of
in accordance with regulations: according to the new waste-
disposal law of 1 November 1986, the owner of the old oil is
himself responsible for disposal according to regulations. The
end user af motor oil and other lubricating oils has the right to
return old oils to the supplier of the lubricating oils without
cost. The material use of the old oil is a primary concern in
the case of disposal. This means that lubricant base oil (second
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raffinate (refined product) is recovered from the old oil by use
of a suitable process, the quality of this corresponding to the
quality of a lubricant base oil that is produced from crude oil.
In the Federal Republic of Germany, the processing of the old oil
is carried out in that the old oil is collected by a pick-up
company, when, for example, engine oil, hydraulic oil, and gear
oil are collected separately from grades of oil such as metal
working oil.
The pick-up company delivers the old oil to old oil reqeneration
plants, so-called second raffihate plants. When this is done,
only old oil that contains no more than 0.2%-wt of chlorine and
not more than 4 ppm polychlorinated biphenyls may be processed in
the second raffinate plants.
Up until the present, the second raffinate process that is
principally used, even outside the Federal Republic of Germany,
iB re-refining with concentrated sulphuric acid and bleaching
earth. In the modern version of this process, the old oil first
has water and low-boiling point components removed from it by
distillation and is then distilled over in a vacuum. The
distillate is treated with concentrated sulphuric acid. So-
called spindle oil is distilled off from the product that has
been 80 treated, over activated bleaching earth. A purely
absorptive secondary treatment with activated bleaching earth at
approximately 120-C can be carried out next (see, for example,
~ltdlverwertuna, Klaus Muller, Erich Schmidt Verlag, Berlin,
Bielefeld, page 104).
From the standpoint of environmental concerns, the sulphuric
acid/bleaching earth process entails the considerable
disadvantage that so-called sludge asphalt is produced, this
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WO 93/13189 PCT/DE92/01074
being a product that forms a sediment as a heavy phase during
treatment of the old oil with concentrated sulphuric acid, cannot
be stored, and is extremely difficult to dispose of. In
addition, considerable quantities of used bleaching earth that is
loaded with sulphuric acid are formed, and this, too, is
difficult to dispose of.
Thus, it can be assumed that new second raffinate plants that
operate using the sulphuric acid/bleaching earth process will no
longer be permitted, at least by the Federal German licensing
authorities.
For years, the professional world has been attempting to develop
new processes that avoid the disadvantages of the sulphuric
acid/bleaching earth process. Examples are the RECYCLON process
(Erdweg, K.J. "RECYCLON-A new process to revert spent oils into
lubricants", Proceedings of the Third International Conference,
Houston, October 16-18, 1987, page 99).
In this process, the old oil is first converted with finely
divided metallic sodium and then distilled over in a vacuum. This
process, too, requires chemical treatment although, however, in
place of concentrated sulphuric acid, highly reactive, finely
divided metallic sodium is used.
A new development, in which metallic sodium in finély divided
form is also used, is the so-called ENTRA process, in which
thermal processing of vapourized lubricating oils is first
carried out in a high vacuum, then activated bleaching earth is
added to the tube reactor that is under a vacuum (ENTRA Engineer
and Handels GmbH, Riderstrasse 6, D-7590 Achern-Sasbachried). An
additional known process for treating old oils is the KTI
process. Here, too, distilled water and volatile components are
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WO 93/13189 PCT/DE92/01074
first removed by distillation. In a second stage the gas/oil
fraction is separated off in a vacuum and in a further stage, the
actual lubricating oil is distilled over in a high vacuum. Then
hydrogenation,treatment is carried out in order to remove
components that contain chlorine, oxygen, phosphorous, and
nitrogen. A process that is carried out in the United States, in
which hydrogenating treatment of the lubricating oil distillate
is also carried out, is the Mohawk process, which that has
essentially higher hydrogenation catalyst dwell times than the
KTI process (Chemical Engineering Partners, 18001 Cowan, Suite
F&G, Irvine, CA 92714, VSA).
In the so-called PROP process, diammoniumphosphate solution is
first added to the old oil. In a second stage of the reaction,
water and highly volatile hydrocarbons are removed by
distillation. Processing is then continued with activated
bleaching earth. Then, hydrogenating refining is carried out.
Bleaching earths have been used for purifying old oils for a
considerable time. These bleaching earths are alluminium-
magnesium-silicates from the bentonite group that contain water
which are activated by boiling in hydrochloric acid: this
releases the soluble base components such as CaO, MgO and Fe2O32
from the raw material and exposes the actual capillary structure
of the adsorption material. These are referred to as walk,
Fuller, or Florida earths or bentonite (Klaus Muller,
Altolverwertuna [Old Oil Use], Erich Schmidt, Verlag GmbH,
Berlin, 1982, page 96).
DE-OS 37 38 391 describes a process for vapourizing old oil in a
vacuum within a special, complicated vapourizing apparatus. The
process comprises two stages, in the second stage the
vapourization of gas oil and spindle oil ovex bleaching earth in
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a vacuum is described. The actual lubricating oil is obtained
from the distillation sump,2cant after the bleaching earth has
been filtered off.
DD-PS 77553 describes the thermal pre-treatment of old oil prior
to hydrogenating refining. Bleaching earth can be added ac a
secondary process material either prior to or after the thermal
treatment.
The listing of these processes, which is not complete, shows that
lt is still a matter of great interest to be able to obtain a
second raffinate in simple and economic process steps without
chemical processing and without the use of costly apparatus, and
which satisfies the demands for use as lubricant base oil. In
this connection, it should be remembered that the use of
activated bleaching earth entails considerable costs.
Most surprisingly, the applicant has succeeded in developing a
process for reprocessing old oils that consist only of simple
distillation steps and a secondary treatment with natural non-
activated bleaching earths. Using this process, it is possible
to treat used oils in a simple and economical manner that has not
been possible up to now, so as to obtain high quality second
raffinate.
The process comprises the purification of old oils by vacuum
distillation, secondary treatment with finely divided solids, and
then separation of these solids, and is characterized in that the
distilled oil is mixed in two stages with a total of 4 to 20%-wt,
preferably 6 to 16%-wt, of non-activated bleaching earths in the
temperature range of 260 to 350-C during a dwell time of 5 to 120
minutes, after which the solids are separated off.
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~0 93/13189 PCT/DE92/01074
First, the low boiling point fractions in the old oil, namely the
low boiling point hydrocarbons, as well as any water that is
still present in the old oil, are distilled off. ~his can be
done under normal pressure, at a sump temperature of
approximately 160-C, for example. However, it is also possible
to work in a low vacuum, for example, at 40 to 100 mbar. Then it
is possible to remove the middle oil [carbolic oil] and the
spindle oil, which is to say the light lubricatinq oil fraction,
similarly in a vacuum, at approximately 5 to 10 mbar and the sump
temperature of 210-C by distillation.
Now, the lubricating oil fraction itself i8 distilled over and
is, in this way, separated from the heavy-volatile additives or
the dissolved solid-like additives that remain in the sump of the
distillation column and which can be drawn off there. In
principle, the vacuum distillation of the lubricating oil can be
carried out in any vacuum distillation apparatuses. There are a
number of distillation columns known in which lubricating oil can
be distilled o,ver gently, for example, short-path vapourizers and
thin-film vapourizers. Generally, the vacuum is of 0.01 mbar to
20 mbar, preferably at 0.05 to 10 mbar.
In the event that the spindle oil is not to be separated ~ff as
already described, it can be distilled off in another way. This
can be done, for example, in that the spindle oil is distilled
off in a vacuum distillation column over the head and the actual
lubricating oil [is drawn off through] a side tap. However,
separation can be effected such that spindle oil is separated off
by distillation in a column, and the actual lubricating oil is
separated off in a further column. As is known, spindle oil is
not used as engine lubricating oil, but is used predominantly in
hydraulic oils. The broad boiling range for lubricating oil lies
approximately between 350-C and 640~C although, however,
2104~78
~ 93/13189 PCT/DE92/01074
fractions with other boiling ranges or viscosities are separated
off, these being, for example, between 360 and 540~C, or 390 and
515-C. Producers of lubricating oil obtain distillation cuts in
such a way that the boiling analysis or viscosity for a specific
application is met.
According to the present invention, the lubricating oil that is
obtained by vacuum distillation now has finely divided non-
activated bleaching earth added to it in a mixing apparatus,
either incrementally or continuously, in two staqes and at 260 to
350 C, preferably at 280 to 3300c, and is thoroughly mixed during
a dwell time of 5 to 120 minutes, preferably from 10 to 70
minutes. Finally, the solid material is separated off.
When this is done, different temperatures and dwell times can be
used in the areas that have been named in the two treatment
stages.
.
Bleaching earths that are based on bentonite are particularly
suitable as solids used for treating the old oil at 260 to 350-C.
It is known that montmorillonite is a main mineral of bentonite.
Beidellite (smectite), nontronite, saponite, or hectorite are~
included among minerals that are suitable according to the
present invention. Mixtures of the above minerals are also
suitable. In addition, iron oxides, e.g., hematite, can also be
used.
Most surprisingly, it has been shown that naturally occurring
bleaching earths, which are only ground and dried after
extraction, are well suited for old-oil purification and can even
be superior to activated bleaching earths; because of its lower
price, which, depending on the supplier, can be approximately
one-tenth the price of activated bleaching earth, these ~ake it
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'~0~78
n~ 93/13189 PCT/DE92/01074
possible to keep the process according to the present invention
more economical than the processes used in the prior art.
Although up to now, expert opinion has been that the described
activation is a prerequisite for purifying old oil, the applicant
has been able to show that, quite unexpectedly for the
practitioner skilled in the art, given the conditions that apply,
outstanding purification results can be obtained with non-
activated bleaching earths.
According to the present invention, the solids that have been
named above can be used either singly or in any combination.
According to the present invention, processing with non-activated
bleaching earths is carried out in two stages. Of course, the
process according to the present invention can be completed in
more than two stages, although the practitioner skilled in the
art will, as far as it is possible, avoid this for reasons of
economy.
One of the stages can also be an addition of non-activated
bleaching earth to a distillation column, provided that the sump
that contains the additives and impurities has been removed. In
addition, the partial addition of bleaching earth falls within
the framework of the present invention, although the practitioner
skilled in the art will avoid this for reasons of economy.
In principle, the grain size of the bleaching earths that are
used do not play a decisive role although finely ground material
is preferred, for example, 30 to 60 mesh. However, the solids
can be used over a very wide range of grain sizes, for example,
between 0.001 mm to 1 mm or larger, in which connection, with a
very fine division, the dwell time can generally be reduced as
can the quantity of solid that is added. Here, the practitioner
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skilled in the art has a great deal of freedom to choose the
grain size. The properties desired according to the present
invention can also be obtained with sizes even smaller than the
grain sizes that have been cited.
Any mixing vessels that are part of the prior art can be used as
the mixing vessel, as can new developments in this area. The
mixing apparatuses can operate either intermittently or
continuously. Stirring or m~xing cascades can be used, as can
simple mixing containers, intensive mixing reactors, with mixing
sections incorporating built-in devices and numerous others.
Here, the practitioner skilled in the art can select any suitable
mixing apparatus, depending on the desired plant size and other
criteria. However, it is important that there be internal
contact between the old oil that is to be purified and the solids
that are used.
The practitioner skilled in the art knows that using additives in
modern lubricants presupposes an extremely complex know-how. It
is necessary to use corrosion inhibitors, surfactants,
dispersants, anti-foaming agents, anti-oxidants, viscosity
enhancers, flow point enhancers, metal deactivators, anti-wear
agents, additives to adjust ignition temperature, and others.
For this reason, an additive packet for a modern high quality -
lubricant consists of a large number of complex chemicals.
Samples of these are fatty acid esters, barium sulphonate,
alkyldithiodizol, alkyl-substituted calcium alylsulphonates,
triphenylphosphorothionate, the amine salts of phosphinic acid
derivatives, aminphosphates, dithiophosphoric acid esters,
sterically inhibited phenol derivatives, naphthalineamine
derivatives, phthalic acid esters, alkylized diphenylamines, 4-
nonyl-phenoxy-acetic acids, polyolefin acid semi esters,
2104~78
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alkylaminotriazol derivatives, polymers with alkyl acid esters,
long chain alcohols, neopentylglycol ester, trimethylolpropane
ester, acelain acid esters, heavy metal compounds such as zinc
compounds, calcium sulfonate, molybdinum sulfide, calcium
carbonate, metallic salts of organic acids, sodium sulfonates,
bernstein acid derivatives, olefin copolymers, styrol-butadiene-
copolymers, and many others.
The above listing makes it clear that the removal of these
multitudinous additives has resulted in the fact that
purification measures have, up to now, been extremely costly. In
particular, it i8 important in this connection that during vacuum
distillation a number of impurities pass out over the head with
the lubricating oil, these being, for example, chlorine
compounds, phosphorous compounds, and colouring agents. This
makes the results obtained according to the present invention,
namely that the twice-repeated secondary treatment with the
bleaching earths that have been cited, under the conditions that
have been quoted, result in a second raffinate of first class
quality, even more surprising.
Table 1 sets out the results obtained according to the present
invention during the purification of three different old oiis I,
II, and III. The analyses and data obtained from a typical old
oil are provided for purposes of comparison.
In each instance, 100 g of old oil distilled over in a vacuum are
stirred in two stirring vessels that are connected in series with
3%-wt I or 5%-wt II and III, respectively, of a dried and ground
untreated bentonite bleaching earth at 300~C for 15 minutes in
each instance.
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The table shows that excellent values can be obtained using the
process accord;ng to the prersent invention with réspeat to
colour, viscosity index, flash point, ash, neutralization
figures, chlorine and phosphorous. The old oils I, II, and III
that are used were taken from ,different old oil pick-up services.
The quality of the old oil corresponds to that described by
legislation with reference to chlorine and PC8 content. The
comparison old oil is a typical old oil of the same categories as
old oils I, II, and III.
In Table 2, old oil III from Table 1 is also used. This was
stirred in two stages, each of 30 minutes, with 6%-wt of
untreated bentonite. The quantities that are cited relate once
again to 100 g of old oil.
The table shows that at 240C it was not possible to obtain
completely satisfactory results.
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~O 93/13189 PCT/DE92/01074
Table 1
Old Oil Ra f f inate Ra f f inate Raffinate
from old from old from old
oil I oil II oil III
Colour (APHA)black 2 2.5 1.5
Viscosity index 135 102 100 99
Flashpoint C 192 >210 >210 >210
Ash ppm 2100 s 2 n.n.
Neutralization
mg KOH/gr 0.33 0.03 <0.05 <0.05
Chlorine ppm 1050 10 6 6
Phosphorous ppm 746 10 11 19
Table 2
Neutralization
number mg KOH/g Colour
,.
240'C
30 minutes . 0.06 2.5
2 x 6 g
Bentonite
280'C <0.06 2
30 minutes
2 x 6 g
Bentonite
300-C
30 minutes <0.05 1.5
2 x 6 g
Bentonite
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WO 93/13189 PCT/DE92/01074
For the practitioner skilled in the art, it was surprising and
impossible to foresee that all norms could be met by using the
process according to the present invention that were required of
the producers of lubricating oil end products.
This can be seen from Table 3. This contains a typical total
analysis of a second raffinate obtained by the process according
to the present invention from an old oil mixture from the Ruhr
area and the Minden area. The excellent oxidization stability
and thermal stability are particularly noteworthy.
Table 3
Viscosity 40-C mm2/s~ 27.10
lOO-C 4.970
Viscosity index Din ISo 2909 108
Pour point C -15
Colour 2.0
Density kg/m3 862.4
Noack g/100 g ~ 14.0
C~ 6.5
C~ 26.5
Cb 67.0
PCB ppm <0.5
PCA ppm 1.4
Oxidation stability minimum 19
Thermal stability C 242
Cl ppm 9
Dialysate 0.2
Dialyse 99.5
Residue C 210
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WO 91/1318~ PCT/DE92/01074
Table 4 shows lubricating oil data from old oil distillates of
variou~ viscosities at 40C and lOO C. Data for the old oil that
is used i8 shown under EP. This is an old oil of French origin.
Distillates 1 and 2 were each treated once and twice, in each
instance with 6%-wt no~-activated bleaching earth at 320~C for a
dwell time of 30 minutes each.
The colour and neutralization fiqures obtained during a single
treatment show that despite the addition of 6%-wt bleaching
earth, no satisfactory results were obtained. Also
unsatisfactory were the results during a single treatment at 10
to 12%-wt (not shown in the table).
~owever, very good results were obtained during a twice-repeated
treatment.
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Table 5 shows the results during treatment of a distillation cut
of 390 to 51S-C from old oil of Spanish origin originating in the
area of Barcelona. A Spanish, non-activated bleaching earth on a
bentonite base was used as the bleaching earth, this containing
saponite and 2 to 3%-wt of hematite.
Sample a) is the untreated cut.
Sample b) is the cut that is treated once with 6%-wt bleaching
earth at 320'C for 30 minutes. The neutralization figure is not
satisfactory. However, very good values were o~tained from a
twice-repeated treatment (sample c). Analogously, in samples d)
and e) 8%-wt bleaching earth was used. Sample f) was treated
once with 8%-wt bleaching earth, which was obtained from the
second treatment stage after filtering off. Neither the colour
figure or the neutralization figure are satisfactory.
Sample g) was treated in the first stage as was sample f) and in
the second stage with 8%-wt fresh bleaching earth. The values
that were obtained are very good. This means that during the use
of fresh bleaching earth in stage 2, the bleaching earth filtered
off from stage 2 in stage 1 very good values are obtained. Good
results were also obtained with 4 to 6%-wt bleaching earth in
this manner.
Generally, the total consumption of bleaching earth can be
reduced in this way.
The figure shows a process flowchart with two solid purification
stages as an example.
The old oil passes through 1, through the filter 2, in order to
separate off coarse impurities. The filtered old oil flows into
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WO 93/13189 210 4 ~ 7 8 PCT/DE92/01074
a stripping column 3 from which a mixture of low-boiling,point
hydrocarbons and water is distilled off over the head. In the
separating container 5, the water flows through 6 out of the
plant whereas the low-boiling point hydrocarbons are collected in
the container 7. The sump 3 flows into the vacuum column 4 in
which lubricating oil is distilled off over the head. 4 can be
operated such that spindle oil i5 separated off over the head and
the actual lubricating oil is drawn off from a side tap.
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wo 93/13189 2104~78 PCT/DE92/01074
Or spindle oil and lubricating oil are distilled off in two
separate vacuum columns. The lubricating oil flows from 4 into
the mixing apparatus 8 in which finely divided, non-activated
bleachinq earth is metered in through 11. Then the mixture of
treated distillate and solids is filtered in 9. The distillate
then flows from the filter into the second mixing stage 10 in
which additional non-activated bleaching earth is metered in
through 12. Now the mixture is filtered once again in 13. The
finished second raffinate base oil is removed through 14. By way
of example, it is shown that one can use the benzene collected in
7 to rinse off oil that adheres to the adsorption agent in the
filters 9 and 3 through 22 and 23, through 15 and 16 into the
container 17 for collection and then return the rinsing fluid in
line 18. This washing circuit is not essential, however, in
particular not in the form that is shown. Washed bleaahing earth
is removed through 19 and 20. The sump from the vacuum
distillation which contains the greatest part of the additives
present in the old oil, is drawn off at 21.
According to the present invention, as has been set out in
detail, used lubricating oils that are mineral based and that can
also contain synthetic oils as well as synthetic lubricating oils
based on hydrocarbons, can be processed to form a high quality
second raffinate.
For use in the present invention, it has been possible to
overcome the opinion of the practitioner skilled in the art to
the effect that if bleaching earths are used to purify old oil
distillates, fractions such as CaO, MgO or Fe2O3 have to be
removed from the raw material in order to expose the capillary
structure of the bleaching earths. The results obtained with the
present invention show that these fractions are an advantage in
conditions according to the present invention.
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