Note: Descriptions are shown in the official language in which they were submitted.
~ his inventlon relates to breaking oil-in-water
type emulsions particularly those derived from bitumen (as
in tar sand processing) or from heavy oil reco~ery processes
(as in _ situ injection or flooding).
Many waste water streams or effluents are in
the form of oil-in-water type emulsions some which are very
stable and difficult to break due to dispersants being present.
The dispersed oil phase renders the waste stream unsuitable
for recycle in many cases, and also requires a heavy BOD
(or is a considerable pollutant) if disposed of into the
environment~ Large volumes of these emulsions result from
e.g. tar sand (hot water) processing in situ bitumen
and heavy oil recovery and secondary or tertiary oil well
treatments.
It has been advocated to treat such oil-in-
water emulsions with acids such as sulfuric, to par~ially
break the emulsion to form water~in some cases small amounts
of an oil-in-water phase and a water-in-oil phase, the
latter being ~ery stable. The use of s rong mineral acids
to break emulsions of this type is undesirable since
clay present would be attacked and multivalent cations
released which promote clay flocculation at too early a
stage of the process. Strong mineral acids also react
with some of the organic components of crudes and bitu-
mens to form water-soluble components which lead to losses
in the aqueous phase. Oxidized petroleum acids which may
be formed during some processing steps, may partially break
such oil-in-~water Qmulsions to form a small vol~e of
stable water-in-oil emulsion. Such water-soluble ~itu-
minous acids act also as efficient clay dispersants and
hinder clay separation from aqueous effluent (tailings pond).
See Journ of Can. Petroleum Technology, July-Septenlber
1978 Speight et al p.73-75~ A U.S. Patent 2,678,305
-- 1 --
B~t3~
M~y 11, 1954 Villarreal used gaseous acetic acid in a
carrier such as dry natural gas ~o break an emulsion of
oil and water.
Oil-in-Water emulsions have been broken by other
techniques such as the addition of dense solveJlts as in
Can. Pat. 1,030,090, April 25, 1978 Redford but large
amounts of additive were usually required. These solvents
are usually chlorinated type and would require str,ingent
removal from both the separated water and oil phases. Iron
and aluminum salts have been used to break emulsions, some-
times in conjunction with flotation. However the bulky
sludges these salts produce are difficult to dispose o~.
If the initial emulsion pH is alkaline, the salt requirements
become too high to be practical.
It would be desirable to find an additive
which will br~ak stable oil-in-water emulsions without leaving
residual emulsion or leaving the separated water phase
loaded with divalent or trivalent cations necessitating their
removal before re-cycling the water. This additive should
be effective in relatively small amounts, be readily available
and be economical.
In the course of investigating many additives
I have found that formic acid is peculiarly effective in
hreaking such oil-in-water emulsions wi-thout many of the
undesired side effects mentioned above. Accordingly this
invention provides a method of breaking stable oil-in-water
emulsions into separate phases, comprisiny:
(a~ incorporatiny into the emulsion in an amount ef~ective
to break the emulsion, an additive comprisin~ one o~
(i ) formic acid
and (ii) a mixture of at least any two of formic acid,
oxalic acid and SO
-- 2 --
3~
(b) provi~lng that the emulsion pH is within about 2.8-5;
(c) agitatin~ the treated emulsion until phase separation
is at least in:itiated;
and (d) recoverin~ at least the oil phase.
The invention also includes a demulsifyiny agent
mixture comprisin~ at least any two of formic acid, oxalic
acid and sulfur dioxide, usually in aqueous solution.
The reasons why formic acid is so effective
are not fully understood but a unique combination of proper-
ties appears to be invoLved~
The formic acid used may be a crude byproduct
obtained in the production of petroleum chemicals as a
result of oxidation. ~lso formic acid, contaminated with
minor amounts of acetic acid in the regular industrial
production of the former, could be used without further
purification. In the demulsification experiments below,
it was observed that up to 40~ acetic acid in formic acid
did not prevent a clear water phase from forming. These
crude byproducts have been disposed of as waste in many
instances and should be available at low cost at least in
the case of crude formic acid.
The amount of formic acid (or oxalic) incorporated
into the emulsion should be sufficient to cause the desired
breaking and phase separation. Usually these amounts will
be within the range of about O.Q1 to about 0.5% by wt based
on the emulsion. Where an auxiliary agent is added (as
described below), the amounts of formic acid (or oxalic) can
be well below 0.1%.
It may be desirable for either ef:Eectiveness
economy or both, to incorporate an auxiliary acid part;cularly
at least one of sulfur dioxide and oxalic acid. These
operative acids have at least one dissociation constant
within the range 10 2 to 10 4 (as does Eormic aci~ lowever
not all acids with dissociation constants in this range are
bene~icial. The SO2 may be added to the emulsion in ~aseous
form or in water or formic acid. In some cases tsee tests 52-54
and 63-64) the SO2 has been found to have a synergistic effect.
A suitable source of SO2, or crude mixtures
thereof, for use as auxiliary acid may be waste streams
such as result from the roasting of ores (stack gases) etc.
A preferred source o SO2 is from upgradiny plants and
refineries and where high sulfur coke and coals are used
as fuel. The gas may be bubbled directly into the emulsion
being treated or dissolved in water first. CO2 was found not
effective. The proportion of auxiliary acid relative to the
formic acid may range up to about 500~ by wt.based on the
formic acid, with the preferred range being about 100-~0~.
Test results have indicated that the level of formic acid or
oxalic acid can be reduced to about 0.01 - Ot 05% by wt. based
on the emulsion, in the presence of SO2 within the range given.
Where oxalic is added to formic acid, preferably the amount
is not more than about 200% by wt. of the formic acid.
When the oil phase in the emulsion is a very
viscous bitumen or heavy oil, it has been found desirable
to treat the emulsion at elevated ternperatures where the
viscosity is reduced sufficently to enable the dispersed
bitumen or oil to coalesce into a unitary phase. A preferred
temperature range with tar sand bitumen or heavy oil is about
50-85C This reduction in viscosity can alternatively be
achieved by adding a light ~iquid pekroleum fraction such as ;
toluene, an alipha-tic hydrocarbon solvent mixture, and naphtha, `
thus allowing operation at room temperature. A combination
of these techniques may be used. Coalescence ~s much im-
proved when oil phase viscositv is below ahout 2,~00
centistokes.
~ 3'~
It has been found that the mos-t effective pH
range for breaking ~he emulsion and phase separation and
recovery,is from about 2.8 to 5, preferably 3 to 4.5.
There is usually present in the aqueous phase,
càtions su~ficient to form formate salts. Where it is
desired to recover formic acid for recycle from such formate
solutions this could be accomplished,for instance,by treatment
of the residual aqueous phase with a cation exchange resin in
the H form to give a formic acid solution. The formic acid
(and/or oxalic) may be concentrated or separated for recycle
~y at least one further step such as distillation ! re~erse
osmosis or precipitation.
Alternatively the residual aqueous phase can be
trea-ted with alkali metal hydroxide to convert all residual
acids to desirable peptizing agents for clays and the entire
water phase from the broken emulsion can be reused in in situ
recovery operations. For example, there are at least five
methods being used in Alberta and elswehere to recover in
situ tar sand "oil~' with water. Some methods inject steam
into the depsoit while others use forward combustion followed by
water flooding to enable bitumen recovery. In the latter
system, water is injected into the deposit with alkali and
surface active agents and becomes heated and converted to hot
water or steam down in the deposit where emulsification takes
place. With the method of this invention, the separated
water phase from previously formed in sltu emulsions may
be reused directly without going through any distillation
stage. However, it is important that it contains no ~locculants
for clay as they would interfere with the emulsiication of
in s u oil. Salts containing divalent and trivalent ions,
e.g. calcium, aluminum, iron, etc., would have to be ruled
out since they are flocculants for clay,but salts formed
as a result of adding sodium hydroxide to the clarified water
phases of emulsions broken with formic acid actually peptize
clay and would be desirable additives. Water phases of
emulsions that have been hroken with formic acid could there-
fore be used withou-t removing those impurities providing they
are made basic with alkali containing sodium or potassium
cations (but no divalent or trivalent cations). It follows
that the use of strong mineral acids to break such emulsions
would also be undesirable because these acids would react
with the aluminum constituent in clay to produce aluminum
cations. Tar sand "oil" and crude oils have many functional
groups and polar constituents that are vulnerable to chemical
attac~. Strong mineral acids react with some of these
constituents~ forming water-soluble components which produce
losses to the aqueous phase. In addition, some o these
reaction products are surface active and work in the wrong
direction, e.g. the formation of petroleum sulfonates with
sulfuric acid. For these reasons such strong acids
should not be used on these vulnerable crude oils.
The following Examples are illustrative. An
oil-in-water emulsion obtained by in~situ injection of steam
into heavy oil formation (after separation of the bulk of
the oil phase) was used in most of the tests. This emulsion
contained about 1.1% by wt. of oil phase and was very stable.
The pH was 8.9 and the ash value 0.22%. This ash portion
contained approx. 0.3% V, 0.1~ Ni, 0.03% Mo, 30% Na, 1% Al,
0.3% Ca, 3~ Si and 0~3% Fe~ The latter five consltituents
indicated considerable free alkali as well as clay minerals
and iron compounds. The high alkalinity and the liquid and
solid (clay and silt etc). emulsifiers present all contri-
buted to the high stability. Many different types of additives
~y~
which lowered the pH were tested. In some -tests, where
indicated, oil-in-water emulsi,ons made up from crude oil,
heavy crudes, or t,ar sand heavy oil extracts with various
emulsiiers and pH of 8-9, were used.
The demulsification procedure was to heat the
emulsion to 65-70C, incorporate the additive(s), and
agitate or shake the mixture for up to 10 minute . The
treated emulsions were then held at 65-70C for from 2 - 8
hours to allow phase separation to proceed, and subsequently
examined. In some cases, phase separation was substantially
complete after the agitation steps. Additives were usually
added in solution form, however concentrations are
expressed as wt. ~ named additive based on the oil-in-water
emulsion treated. This concentration represents the minimum
required to give the highest degree of clarity obtaina~le
with the particular additive. The pH obtained at the
additive concentration used is recorded. The results are
summarized in the following Table I. Results are given
for some additives which are unacceptable for various reasons,
for comparison. The "Results" are based on the visual
appearance of the continuous phase using the following
classification:
E (excellent) clear and colourless
G (good) slight cloud
G- considerable cloud
F (fair) deep cloud
P (poor) stable emulsion
Only E is considered a fully satisfactory result.
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In fur-ther tes-ts oil-in-~ater emulsions
were prepared using hi~h shear homogenizing in the presence
of emulsifyin~ agents, and in most cases, clay and alkali,
Aliquots of these emulsions were then treated as described
above~ The emulsions prepared and tested were:
C2 - 1~ Leduc crude + 0.03% Span 85(T~ 0.1% clay -~ NaOH
to pH 8.8
Dl - 1% heavy tar sand oil extract (Fort Mac~urray) + 0.03%
sodium oleate (pH 8.1)
El ~ 1% heavy tar sand oil extract + 0.03% triethanolamine
( T.E.A.)
E2 - 1% heavy tar sand oil extract + 0,03% T.E.A. + 0.1%
clay + NaOH to pH 8.9
G2 - 1~ Leduc crude + 0.03~ sodium dodecyl sulfate -~ 0.1%
clay + NaOH to pH 8.9
Hl - 1% Lloydminster crude + 0.03~ sodium oleate
H2 - 1% Lloydminster crude .+ 0-03% sodium oleate + 0.1% clay
+ NaOH to pH 8.9
~13-
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In tests 1 and 2, only about 0.1% formic
or oxalic acid or mixtures thereof was required to break
the emulsion. The resulting pH (4.5-4.2) should be in the
ran~e where corrosion is minimal. The separated water
phase was clear and colourless. Excellent results were
also obtained with these acids in combination (Test 3).
In test 4, it can be seen that carbonic acid had little
effect in reducing the amount of oxalic acid required. In
tests 5 ~o 12, both mono and dicarboxylic aliphatic acids
with increasing chain lengths were used~ With the
excep~ion of butyric acid, all worked to some extent, but
the requirements were high, and the water phase always
remained sli~htly turbid in~icating ~om~ resi~ual-emulsified
oil. This was pro~ably due to a combination of factors,
e.g. higher molecular weights, weaker dissociation constants
and increased mutual solu~ility of these longer chain acids
with the oil components. Malonic with only one carbon more
than oxalic but with considerably lower dissociation re-
quired more than five times as much acid, and the separated
water phase still possessed a faint cloud. In aqueous
solution decarboxylation starts about 65-70C with this
acid which makes it unacceptable~
The aromatic acids, tests 13 and 14 had
some effect when used in comparatively hi~h concenl:rations,
with terephthalic acid (dicarboxylic) being much more
effective than benzoic acid. Benzene sulfonic acid, test
15, with a high water solubility,produced a clear water
phase but minimum requirements wer~ about our times hi~her
than with formic or oxalic. Toluenesulfonic acid and
phenoldisulfonic, tests 16 and 17, were less effective. Cost
and lesser effectiveness rule out such aromatic acids.
Of the chlorinated and fluorinated acids
tried~ tests 1~-22, only chloroacetic produced an excellent
-15-
334L
xesult: amount required and cost however is less favourable
~or this acid. Chlorobenzoic is probably -too water-insoluble.
Dichloroacetic, trichloroacetic, and trif~uoroacetic are
very strong acids and probably attack asphaltenes and
other oil constituents.
The low molecular weight hydro~y aliphatic
and hydroxy aromatic acids, tests 23-30, wer~ in general
not very effective, especially the weaker ones. Tartaric
and citric, with two and three carboxyl groups respective~y,
produced the best results in this group but an amber colour
in the water phase indicated organic matter was extracted
leading to losses and effluent problems~
No advantages were obtained by introducing
thio and amino groups into the short chain organic acids
(tests 31-35).
Several common inorganic acids were tried,
tests 36-42 for comparison. Boric was ineffectual. The
requirements for sulfuric, nitric, and hydrochloric acids
were comparatively higher and left a slight haze in the
water phase. Phosphoric, being a considerably weaker
acid than the above group, produced better results:
however, the re~uirements were still about three times as
high as formic and oxalic. The hydrofluoric acid requirement
to produce a clear aqueous phase was only about half as
much as for oxalic and formic acids: but toxicity and
efflent problems with HF would be unacceptable. Fluosilicic
acid was also effective but the requirements were somewhat
greater than hydrofluoric because of its higher molecular
weight.
In tests 43-50, it was shown that salts,
especially acid salts, in high amounts only, had considerable
effect on the emulsion.
In test 50, a commercial demulsifying
-16-
8i~33~
a~ent was used wi-th little effect.
While the abo~e experiments were carried
out at 65-70C., in a few random experiments similar results
were obtained at room temperature by diluting the or~anîc
portion two or threefold with a~uitable solvent, e.g.
toluene, and subsequently settling at room temperature.
The reduction in both density and viscosity of the oil
phase permitted the resulting less stable emulsion to
be effectively treated at the lower temperature.
The re~uirements for Al salts were
considered too high to be practical and the~ leave undesired
cations in the water phase. Tests 52 and 53; 63 and 64
show that on some emulsions SO2 has a synergistic effect
with formic acid or vice versa. Test 54 indicates oxalic
is also syneryistic with SO2, the SO2 effecting a reduction
of more than 50% in the amount of oxalic acid required with
this emulsion.
The results indicate that formic acid
is in a class by itself. This acid is water-soluble,
virtually oil-insoluble, and has a dissociation constant
which is most appropriate. It is understood to be less
costly to produce than oxalic acid. Oxalic acid is
considered acceptable as an auxiliary acid with formic acid
or SO2, where large amounts are not required~ Formic acid
has a high affinity for clay, silica and insoluble iron
compounds which ensures wetting and flocculation of these
particles at the interface. Formic acid does not appear
to attack any oil constituents, is relatively inexpensive,
non-toxic in the dilute form used, and is biodegradable.
It has been observed that when about ;`
one third more formic acid than the minimum required, was
used, no set~ing was required since the two phases separated
-17-
immediately after the agitation step.
Where the separated water phase is
distilled, the sodium ~orma-te (or other formates or oxalates)
can be recovered and converted back ~o acid form for recycle.
The oil-in-water emulsions to be treated
may contain up to about 50~ or more of oil phase. The
emulsions most frequently encountered have an oil phase
content within about 0.2-10% by wt.
~18-
