Note: Descriptions are shown in the official language in which they were submitted.
TREATMENT OF WASTE OILS
The present invention is concerned with the
treatment of waste oils.
S Many produced crude oils contain impurities which
adversely affect refining processes and equipment, and
sometimes the properties of the end product. The most
common impurities are water, salts and clays and they
are usually removed by washing the oil with additional,
low mineral-content water. This procedure often
results in the production of emulsions, from which the
water phase is conventionally separated with the aid of
organic chemical de-emulsifiers and elec-trostatic
coalescers. The washing and water separation steps
together constitute the process known as "desalting".
This process is not sufficient, however, to clean up
some crude oils or crude oil fractions, particularly
from heavy oil production, and these are often disposed
of as waste.
The latter crude oils and fractions are referred
to herein as "normally intractible oils" in that they
resist the conventional puriflcation procedures. These
normally intractible oils contain water and solid
impurities, usually clays which are often complexed
with organic matter, and their intractible nature is
thought to arise from water-in-oil emulsions which are
stabilized by the clay solids.
It has now surprisingly been found that the
addition of calcium hydroxide to normally intractlble
oils enab].es separation of impurities from -the oil to
occur.
In accordance with the present invention,
therefore, there is provided a method of treatment of a
normally intractible oil containing water and solids,
3s which comprises treating the oil with calcium hydroxide
to cause separation of the intractible oil at least
into an oil phase and a water phase.
In the present invention, therefore, a normally
intractible oil containing impurities, mainly in the
form OL w~ter, salts and clays, is treated with calcium
hydroxide. The calcium hydroxide treatment may be
effected by washing the intractible oil with a solution
of calcium hydroxide, preferably a saturated solution,
along with additional solid phase calcium hydroxide, if
desired, at elevated temperatures, preferably about 60
to about 80C, in a procedure analogous to conventional
crude oil washing with water.
The washing o the intractible oil using the
calcium hydroxide solution in accordance with this
invention may be effected in any convenient manner.
For example, the treatment may be effected during
transportation of the intractible oil, for example, by
pipeline, tanker or tank truck, or in a stirred reactor
constructed for the purpose.
The calcium hydroxide treatment may also be
effected by first mixing the intractible oil with a
concentrated slurry of solid calcium hydroxide and
allowing the mixture to stand at elevated temperature,
preferably about 60 to about 80C, for an extended
period of time, usually about 4 to about 24 hours,
prior to any further treatment. In this procedure,
about 0.2 to about 3 g of Ca(OH)2 per kg may be first
mixed with the crude oil or fraction.
Further treatment may then comprise washing with
saturated calcium hydroxide solution, as described
above, or mechanical dewatering, such as by
centrifugation.
The calcium hydroxide treatment surprisingly leads
to separation of the intractible oil, substantially
complete removal of impurities from -the intractible oil
and to readily separable oil and aqueous phases.
Any emulsions which form during the washing step
are very unstable and usually break without the
necessity to use chemical de-emulsifiers.
Electrostatic coalescers also are not required, but
also may be usecl to promote more rapid separation of
the aqueous phase.
Centrifugation of the calcium hydroxide-treated
intractible oil leads to rapid separation into three
phases, namely a clear oil phase, an aqueous phase and
a clay/asphalt (oil sludge) phase. The pre-treatment
with calcium hydroxide is particularly useful in this
procedure, since not only does it aid in the
destabilization of certain of the emulsions, thereby
rendering the centrifugation more efficient, but also
leads to a uniformly limed clay/asphalt phase that ls
more acceptable for road application or landfill, owing
to a decreased possibility of trace metal leaching.
The limed sludge is also more amenable to further
dewatering by freezing and thawing, which may be
effected in western Canada over the winter months in
pits, either at the final disposal site or in a
temporary location prior to transportation to the final
disposal site.
Although other divalent metal compounds are known
to destabilize emulsions, calcium hydroxide (or slaked
lime) is utilized in this invention because of its low
cost and low concentrations precipitate many organic
sur~ace active impurities by an acid-base reaction,
unlike other alkaline reagents or other calcium
compounds, such as calcium chloride. Treatment of many
intractible oils by calcium chloride has no effect on
the ability to separate the components of the oil.
This invention is illustrated further by the
following Examples:
Example l
This Example illustrates the effect of washing a
normally intractible waste oil with saturated calcium
hydroxide solution.
A waste oil sample containing absorbed water and
various other impurities was mixed vigorously for one
minute with an equal volume of saturated calcium
hydroxide solution at about 70C. Excess solid calcium
hydroxide was present in the mixture over and above the
quantity saturating the calcium hydroxide solution at
70C (about 500 mg/1). After standing for four hours
~2~
at about 70C, the aqueous phase had separated in
volume at least equal ~o the volume of solution
originally added. The presence of an intermedia~e
layer of brown, dispersed material indicated that the
upper oil layer had been substantially freed of
impurities and the water associated with them.
Example 2
This Example illustrates the effect of adding a
concentrated calcium hydroxide slurry to a waste oil in
comparison with an ~quivalent amount of calcium
chloride.
Two samples of a normally intractible waste oil
from the Swan Hills area of Alberta, Canada, were
treated wlth 250 ppm and 500 ppm of calcium hydroxide
and calcium chloride respectively, added as a
concentrated suspension or solution in water in the
ratio of 1 part of suspension or solution to 50 parts
of waste oil. After vigorous mixing and standing at
60C, the following observations were made:
20 Time Sample Treatment
(hrs) Ca(OH)2 CaC12
0 immediate signs no sign of
of breakout breakout
lower aqueous no separation
phase separated, observed
9.7% by volume
58 very clear separ- no separation
aration of lower observed
aqueous layer,
8.3% by volume
As may be seen from the results presented above,
the addition of calcium hydroxide was effective in
causing separation of the waste oil while there was no
observed effect with the addition of calcium chloride.
Example 3
This Example illustrates the freeze-thaw
dewatering of an oil sludge treated with Ca(OH)2.
Approximately 150g of a waste oil sludge obtained
from the Brooks area of Alberta, Canada was mixed with
0.9g of hydrated lime at 70C and then frozen to a
temperature of about -10C. After being ~aintained
~2~
frozen for 10 hours, the material was thawed to room
temperature and approximately 50 ml of a water layer
was coll~cted. A small amount of a brlght oil layer
also was observed to form and stick to the sides of the
container.
In a parallel experiment, a further sample of the
waste oil sludge was frozen and then thawed but without
the initial addition of the slaked lime. The
separation of a water layer and an oil layer were not
observed.
In summary of this disclosure, the present
invention provides novel methods for the treatment of
normally intractible oils using calcium hydroxide and
the recovery of useful products therefrom.
Modifications are possible within the scope of this
invention.
