Note: Descriptions are shown in the official language in which they were submitted.
20689~5
80054-3
WASTE LUBRICATING OIL rK~-~K~ATMENT ~AO~C~
This invention relates to re-refining of waste
lubricating oil.
Waste lubricating oil includes such material as used
crankcase lubricating oil from internal combustion
engines of motor vehicles. Such waste oil is often
collected and is subjected to re-refining processes to
remove contaminants and spent additives from the oil in
order to produce a base oil from which new lubricants are
manufactured. Prior methods of re-refining typically
involved the following steps:
1) water removal by atmospheric distillation;
2) precipitation of additives and impurities
as a sludge using a reagent such as sulphuric
acid;
3) removal of sludge;
4) treatment of remaining waste oil with
activated earth with simultaneous steam
stripping; and
5) filtration of the oil.
The aforementioned method has been in use for
decades. However, increasing amounts of additives used
in lubricating oil formulations have made the
aforementioned processes increasingly difficult and
expensive to operate. New methods have evolved that are
aimed at avoiding the production of acid sludge and also
the avoidance of the use of activated earth. For
example, hydro-treatment is used to avoid treatment with
activated earth.
In order to prepare oil for earth treatment or
hydro-treatment, it is necessary to remove the origina
additives present in the oil. The current method of
choice, in place of treatment with a reagent such as
sulphuric acid, is to distil the oil so as to leave the
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additives in the distillation residue. However,
distillation results in thermal decomposition of some oil
additives producing acids and tars or polymers,
particularly in the vapour spaces of the distillation
plant. Wiped-film evaporators using indirect heating,
high turbulence, low residence time and high vacuum have
been used to reduce thermal decomposition of additives.
However it has not been possible to eliminate thermal
decomposition and the consequent production of corrosive
acid compounds and tars when using distillation
procedures on a plant scale.
In most countries where waste lubricating oil is
collected for re-refining, the oils are mixed and stored
in large quantities. When such oil is subjected to high
temperature, for example during distillation of the oil,
the pH of the distillate will be low and the acidic
distillate produced will soon cause corrosion problems in
the plant. In addition tars and polymeric products in
the distillate will cause severe plant fouling. At
laboratory scale, the pH of the distillates can be
measured and the production of tars and polymers may be
monitored by observing a blackening of the laboratory
glassware.
It has been discovered that addition of a base to
waste lubricating oil that is undergoing heat treatment
(such as during distillation) will not necessarily result
in a decrease in the production of acidity in the
distillate. However, pre-treatment of such oil while in
a state when the oil has some water content, with an
alkali metal salt of a weak acid, will result in a
reduction in the acidity of the distillate when the oil
is subsequently subjected to the high temperature.
Accordingly, this invention provides a method of reducing
the acidity of the distillates, and of reducing the
formation of polymers and tars which cause fouling of
2068905
plant equipment, when used oil is distilled, which method
comprises treating said oil while in a state when the oil
has some water content with one or more basic compounds
of an alkali metal.
This invention provides a method to treat waste
lubricating oil cont~;n;ng water to reduce distillate
acidity and formation of fouling compounds during
subsequent distillation of the oil, comprising the
procedures of determining the amount of dibasic metals in
the waste lubricating oil and, reacting one or more basic
compounds of an alkali metal with the oil wherein
sufficient amount of the alkali metal is provided to
substitute for dibasic metals present in the oil. The
basic compound of an alkali metal may be a metal salt of
an acid weaker than sulfonic acid (such as sodium
sulfide, and a carbonate, borate, or an acetate of
sodium, potassium, and lithium). The basic compound of
an alkali metal may also be a hydroxide such as sodium
hydroxide, lithium hydroxide, or potassium hydroxide.
This invention also provides a method to treat waste
lubricating oil cont~;ning at least 1% by weight water
and dibasic metal cont~;ning additives to reduce
distillate acidity and formation of fouling compounds
during subsequent distillation of the oil, comprising:
reacting the oil with one or more basic compounds of an
alkali metal whereby the alkali metal is provided in an
amount between about 70-200% of the stoichiometric
equivalent of the total of calcium, magnesium, and zinc
in the oil. The basic compound of an alkali metal may be
as described above.
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~6~90~
_ - 3a -
Suitable basic compounds for use in the method of
this invention includes basic compounds such as sodium
hydroxide. ~owever, if such a basic compound is injected
into the plant apparatus at the point of di~tillation,
the added compound will not prevent the production of
acidity in the di~tillate or reduce plant fouling.
However, if the basic compound is added to the waste
lubricating oil before distillation and while the oil
still has some water content, it i~ possible to prevent
the production of acidity in the vapour space and
distillates during ~ubsequent distillation. As will be
described in more detail below, the alkalinity of the
reagent used to treat the waste oil is not the important
factor in the process but rather, the reagent used must
be able to provide an alkali metal to substitute for di-
basic metal~ such calcium that are present in certain
lubricating oil additives.
Waste lubricating oil that has not been subjected to
a heat treatment or a drying process will contain some
water. Typically the water content will be at least five
percent by weight. It is preferable that the method of
this invention be carried out that while the waste
lubricating oil subjected to the treatment contains at
least one percent by weight of water.
The alkali metal component of the reagent to be used
in the method of this invention may include sodium,
potassium, and lithium. Generally, the hydroxide, or a
salt of any acid weaker than sulphonic (such as
carbonate, borate, and sulphide, etc.), may be used.
,r~ ~
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It has been found that the pre-treatment process of
this invention is most advantageously carried out if the
alkali metal reagent is added to the waste lubricating
oil in sufficient quantities such that the alkali metal
is present in an amount between 70-200% of the
stoichiometric equivalent of the total amount of calcium,
magnesium, and zinc present in the waste lubricating oil.
The latter metals are the most common di-basic metals
found in waste lubricating oil but there may be others
such as barium. Preferably, the stoichiometric range
employed will be 80-150% of the total calcium, magnesium,
and zinc. Most preferably, the aforementioned
stoichiometric relationship is maintained within the
range 95-105%.
It is possible to carry out the method of this
invention wherein the aforementioned stoichiometric
relationship is less than 70% but an increase in acidity
will be experienced and equipment fouling may occur. It
is also possible to employ the reagent at greater than
200% but generally, a gelling of the distillation residue
will be experienced which may cause other operating
problems.
The amount of time it takes to dry waste lubricating
oil that is subjected to heat varies depending upon the
conditions employed. For example, when such oil is
heated at approximately 100C in laboratory conditions,
it will usually take at least ten minutes to dry the oil.
Under plant conditions, oil may undergo "flash drying"
when plant feed is injected into dried oil maintained at
150C. It is important that the pre-treatment process of
this invention be carried out before the oil is dried so
that the reaction may proceed.
It also been found that the chemical reaction that
takes place in pre-treatment process of this invention is
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time and temperature dependant. Therefore, the pre-
treatment process of this invention may be more quickly
carried out if the temperature is elevated but, it is
necessary that the oil not be dried before the reaction
is complete. The reaction may also be carried out at
room temperature and it has been found that typically,
such reaction will be complete at approximately three
days. At about 60C, approximately one hour is required
for the reaction to be complete. At about 99C, the
reaction will be complete in approximately ten minutes.
This invention is most preferably carried out on a
plant scale by carrying out the pre-treatment process in
a continuous fashion using a large reactor vessel. Such
a vessel may be a tank having a capacity of about 9900
litres. In such a tank a feed rate of approximately 4000
litres per hour will provide a residence time of about
2.5 hours. The level of the contents of the reactor
vessel may be controlled using methods and devices known
in the art for controlling the feed rate to the vessel
and the pumping rate of the contents of the vessel to the
next stage of process. The reactor vessel will
preferably have some agitation means such as a motorized
paddle.
Preferably, the temperature of the aforementioned
reactor vessel will be controlled so that it is
maintained between 60C and the boiling point of water
(for example, at 82C). Methods and devices for
maint~ining the temperature of the reactor vessel are
well known. A circulating pump may be used to circulate
the reactor vessel contents through a heat exchanger and
the pump may be controlled according to the temperature
of the reactor vessel. A recirculation loop through a
heat exchanger will also serve to keep the contents of
the vessel agitated. The reaction vessel may be fully
vented and is operated at atmospheric pressure.
2068905
Preferably, the rate of addition to the oil of the
alkali metal reagent i8 continuou~ly adjusted to maintain
an ideal stoichiometric relationship. For example, the
oil treated in the reactor vessel may be analyzed after
leaving the reactor vessel by ICP emission spectroscopy
for calcium, magnesium, zinc, and sodium content and the
amount of reagent added is adjusted so as to maintain the
desired stoichiometric relationship. Preferably, the
followinq formulae i8 used and the amount of sodium is
adjusted to maintain the relationship within the range
95-105 (all percentages are weight):
Na%xlOO =100
[ zn% + Ca% t Mg~ ]x45.98
65.39 40.08 24.304
The above relationship is for sodium; 45.98 is twice
the atomic weight of sodium. The proportion of each
other element is divided by that element's atomic weight.
It may also be advantageous to carry out the method
of this invention using several reagents. Sodium
hydroxide is often preferred for its availability and low
cost. Bowever, a mixture of sodium hydroxide and sodium
sulphide may also be used with the sodium sulphide being
provided in the re-refining plant as a byproduct of a
hydro-treating step.
The oil that been ~ubjected to the pre-treatment
process of this invention may be distilled and the
distillates therefrom may be subjected to other processes
~uch as hydro-treatment.
The following examples are illu~trative of the
method of this invention.
Example 1
.~i
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500 grams of waste lubricating oil taken from a
large waste oil storage tank was heated, with stirring,
in an open beaker to 150C to remove the water. 250
grams of the aforementioned oil was placed in a 1 litre
flask and a thermometer was used to measure the
temperature of the liquid under distillation while the
oil was heated to a temperature of 385C using a gas
ring. The pH of the distillate was measured to within
one pH unit using pH paper and the flask vapour space and
condenser were ex~mined for tar and fouling deposits.
The distillate was analyzed to determine the identity of
any acid present by water extraction followed by
identification of the acid by the barium chloride
reaction. In this example, it was found that the pH was
<1 and that the glassware was blackened in the neck of
the flask and in the condenser inlet. It was shown that
sulphuric acid was present in the distillate.
Example 2
The method of experiment one was repeated but 2% (by
weight) of a 50% sodium hydroxide solution was added to
the oil before dehydration at 150C. In this example,
the glassware remained clean and the pH of the distillate
was 6-7.
Example 3
The method of example 2 was repeated except that 1%
of calcium hydroxide was added to the oil rather than
sodium hydroxide. In this case, the pH of the distillate
was <1 and the glassware was fouled as in example 1.
Example 4
The method of example 2 was repeated except that a
solution of sodium carbonate was added to the used oil
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(rather than sodium hydroxide) in order to give a 1.33%
(by weight) treatment. In this case, the pH of the
distillate was 6-7 and the glassware remained clear.
This result demonstrates that the functional reagent does
not service to neutralize acidic compounds since calcium
hydroxide in a water suspension is more alkaline than
sodium carbonate.
Example 5
The method of example 1 was attempted on a plant
scale with sodium hydroxide being added to plant feed
oil. The plant feed oil was flash dried at 150C before
entering a wiped film evaporator. However low distillate
pH and plant fouling occurred. When oil from the flash
dehydration unit was taken from the plant and distilled
according to the method in example 1, the resulting pH
was 1-2 and the glassware showed blackening. The
difference in conditions between this example and example
1 was that in this case the oil that was treated with
sodium hydroxide was subjected to flash drying (almost
instantaneous drying) in the plant whilst the oil in
example 1 had been boiled dry over a period exceeding 10
minutes.
That the process of this invention is time and
temperature dependant, is ineffective when a basic
reagent such as calcium hydroxide is used and, requires
the presence of water to proceed, indicates that the
mechanism of this process is not the neutralisation of
sulphuric acid produced in distillation but rather the
prevention of a reaction in which the sulphuric acid is
formed. Detergent additives used in the formulation of
motor oils typically contain di-basic metals (e.g.
calcium, magnesium,and barium salts of aromatic sulphonic
acids of the general formula (using calcium as an
example):
20689~5
g
R R
~ S03 - Ca - S03 ~
When such sulphonate compounds decompose at high
temperature in the presence of available water, the
following reaction occurs:
S03 - Ca - S03 ~ _ _
Ca S04 + 2 ~ + H2 4
When sodium sulphonates decompose under similar
circumstances, sulphuric acid is not produced.
R R
~ S0 Na ~ - ~ + Na HS04
Thus, the process of this invention appears to
involve an ion exchange reaction in which di-basic metal
sulphonates are converted to alkali metal sulphonates.
However, the ideal stoichiometric relationship in this
invention is determined according to the predominant di-
basic metals present in waste oil but not all of such
2~689~
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metals are necessarily present in the form of suphonates.
Various changes and modifications may be made in
practising this invention without departing from the
spirit and scope of the appended claims.
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