Note: Descriptions are shown in the official language in which they were submitted.
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TREATME~T OF SLOP OIL
~he present invention relates to the treatment of
slop oil for the recovery of oil therefrom.
Refinery slop oil, particularly from heavy oil
refineries, typically comprises desalter cuff and
residue from solvent extraction, in the form of a water-
in-oil emulsion, which may range from 10 to 9~% in BS&W
content. Field slop oil i5 similar but tends to have
less calcium soaps. The aqueous component often is in
the form of brine.
Owing to its high viscosity, high BS&W slop oil
cannot be cleaned by centrifugation, even after addition
of as much as 30~ diluent. The stability of the
emulsion is believed to be caused by a significant
content of calcium and possibly iron soap type
surfactants that are probably calcium and iron salts of
asphaltic acids.
In accordance with the present invention, it has
been found possible to invert the water-in-oil emulsion
of slop oils to an oil-in-water emulsion by contacting
the slop oil with at least one non-ionic surfactant.
~ Once inversion of the emulsion has taken place, oil may
; be recovered from the oil-in-water emulsion, for
example, by centrifugation.
It usually also is desirable to raise the pH of the
emulsion following contact with the non-ionic
surfactant, usually to at least about 12, using any
convenient alkalinating agent, such as aqueous sodium
hydroxide. In this way, solid or semi-solid particles
that stabilize the water droplets in the water-in-oil
emulsion become highly negatively charged and disperse
into the continuous water phase of the inverted
emulsion.
Depending on the source of the slop oil, some
pretreatment may be desirable to promote inversion of
the water-in-oil emulsion. For field slop oils, simple
dilution with brine or water is sufficient and may not
be required for dilute slop oils. For refinery slop
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3~
oils, treatment with aqueous sodium carbonate solution
prior to contact with the surfactant, usually at
elevated temperature, promotes the inversion.
It is believed that the sodium carbonate reacts
with calcium soaps in the water-in-oil emulsion to form
calcium carbonate and sodium soaps, driven by the low
solubility of calcium carbonate. The sodium soaps so-
formed tend to stabilize oil-in-water emulsions, so that
the system inverts to a water-thin oil-in-water system.
The washing of the slop oil by the sodium carbonate
solution may be effected in any convenient manner, for
example, by simple mixing of the sodium carbonate
solution and then heating the mixture to an ele~ated
temperature. The temperature generally is above about
60C, typically about 80C.
A preferred procedure involves an initial reaction
of sodium carbonate with the slop oil followed by
triggering inversion to the oil-in-water emulsion by
subsequent addition of water containing a small amount
of surfactant.
The lower viscosity which results when the water-
in-oil emulsion inverts to form the oil-in-water
emulsion enables the emulsion to be centrifuged which,
combined with the lesser effectiveness of the sodium
soaps as emulsifiers, results in the emulsion breaking.
The soap-type materials and any clays and minerals are
removed as a solid phase, which may be further processed
by centrifugation, with or without chemical addition, as
required.
The oil phase can be recovered from the agueous
phase such as by skimming, and subjected to further
cleaning, if necessary or desired, or may be returned to
the refinery stream. The aqueous phase may be disposed
of or reused.
As noted earlier, another procedure which can be
used to separate the oil from the oil-in-water emulsion
is to adjust the pH of the emulsion to a highly alkaline
value, typically about 12, and then permit the emulsion
to stand for an extended period for the oil to separate
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out into a discrete layer. Separation of the discrete
oil layer may be speeded up by centrifugation.
The amount of water added to the slop oil, in the
form of aqueous non-ionic surfactant solution and sodium
carbonate solution depends on the water content of the
slop oil itself and may range from about 10 to about 60
wt.% of the 510p oil.
The amount of surfactant required to form the oil-
in-water emulsion in accordance with the invention
varies depending on the sur~actant used and the quantity
of oil present in the slop oil. Typically, about 0.025
wt.% of non-ionic surfactant is sufficient.
Higher molecular weight members of the alkyl phenyl
polyethoxyethanol series of non-ionic surfactants having
a cloud point above 100C are more effective than lower
molecular weight members. Typical examples of useful
non-ionic surfactants are those sold under the
trademarks Triton X-405 and Igepal C0-897.
The invention is illustrated by the following
Examples:
Example l
200 ml of a refinery slop containing about 70% BS&W
was added to 200 ml of water containing 0.4 g of sodium
carbonate and 0.1 g of Triton X-165. On stirring the
mixture at 80C, an oil-in-water emulsion formed in
about 1 minute. The emulsion was stirred for l hour at
80C and then centrifuged at 1900 g for 30 seconds.
A typical 40 ml quantity produced 2.0 ml of solid
phase, 12 ml of an oil phase and 26 ml of an aqueous
phase. The oil phase was formed to have a BS&W content
of less than 25%. Further centrifugation of the oil at
about 60C at 1900 g for 30 seconds after addition of
20% diluent, decreased the BS&W content to less than
1.0%.
Example 2
400 g of refinery slop oil containing about 70%
BS&W was reacted with 40 ml of a 6~ solution of sodium
carbonate for ~ hour at 80~C with stirring. 160 ml of
water containing 0.1 g of Triton X-405 then was added.
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Upon stirring, the emulsion inverted to an oil-in-water
one. After a further ~-hour stirring, the oil-in-water
emulsion was centrifuged for 30 seconds at 1900 G,
causing separation of a solids phase. The liquid layer
was decanted from the solids and placed in a containment
; vessel where it further separated into an oil layer and
a water layer. After standing for two hours, the oil
layer was found to have a BS&W content of less than 10%.
Example 3
10The procedure of Example 2 was repeated using
Igepal 897 as the non-ionic surfactant. Following
addition of the Igepal 897, the mixture was stirred for
10 minutes and the pH of the oil-in-water emulsion was
adjusted to about 12 with the addition of sodium
hydroxide and stirred for another 10 minutes.
On quiescent standing at 80 to 90C for twelve
hours, the mixture separated to provide greater than 90%
recovery of a clean oil layer ~less than 0.5% BS&W), a
water layer and a solids layer.
Example 4
200 ml of field slop from a heavy oil recovery
project was inverted to an oil-in-water emulsion by
agitation at 80c with an equal volume of 4% brine
containing O.lg of Igepal CO 8~0 surfactant. The pH of
the system was raised to 12 by addition of sodium
hydroxide and agitation was continued for a further two
minutes. Centrifugation of a sample at l900g for 30
seconds then caused separation of a solid phase and two
clearly defined liquid phases. The upper oil phase was
found to contain less than 0.5% BS&W.
In summary of this disclosure, the present
invention provides a novel method of treatment of slop
oils by treatment with non-ionic surfactants to cause
emulsion inversion, followed by oil r~covery from the
resulting less stable oil-in-water emulsion.
Modifications are possible within the scope of the
invention.
