CA1148834A - Breaking oil-in-water emulsions - Google Patents

Abstract

T I T L E

BREAKING OIL-IN-WATER EMULSIONS

I N V E N T O R

J. Redmond Farnand ABSTRACT OF THE DISCLOSURE
Emulsions of the oil-in-water type, particularly those derived from in situ oil recovery and tar sand processing, can be broken by incorporating an additive comprising (i) formic acid or (ii) a mixture of at least any two of formic acid, oxalic acid and sulfur dioxide, and agitating at an appropriate temperature. The oil phase separates and is recovered. The water phase may be treated to recover formic (and any oxalic) acid, for recycle.

Description

~ 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 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

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 ~13-3a~
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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 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 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 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-

Claims (21)

1. A method of breaking stable oil-in-water emulsions into separate phases, comprising:
(a) incorporating into the emulsion in an amount effective to break the emulsion, an additive comprising one of i) formic acid and ii) a mixture of at least any two of formic acid oxalic acid and SO2;
(b) providing that the emulsion pH is within about 2.8-5;
(c) agitating the treated emulsion until phase separation is at least initiated;
and (d) recovering at least the oil phase.

2. The method of claim 1 wherein formic acid is incorporated in an amount within the range of about 0.01 to 0.5% by wt. based on the emulsion.

3. The method of claim 1 wherein formic acid and an auxiliary acid selected from SO2, oxalic acid, and mixtures thereof, are incorporated.

4. The method of claims 1, 2 or 3 wherein formic acid and SO2 are both incorporated in amounts of about 0.01 to 0.1% by wt formic acid, and up to about 0.5% by wt. SO2, based on the emulsion.

5. The method of claim 1, 2 or 3 wherein oxalic acid and SO2 are both incorporated in amounts of about 0.01 to 0.1% by wt. oxalic acid, and up to about 0.5% by wt. SO2, based on the emulsion.

6. The method of claim 1 wherein SO2 is incorporated, the SO2 being derived from a waste gas.

7. The method of claims 1, 2 or 3 wherein the temperature is elevated to encourage coalescence of the oil phase.

8. The method of claims 1, 2 or 3 wherein a light liquid petroleum fraction is incorporated to facilitate coalescence of the oil phase.

9. The method of claims 1, 2 or 3 wherein the emulsion to be broken has an oil or bitumen content of up to about 50% by wt. and contains emulsion stabilizers.

10. The method of claims 1, 2 or 3 wherein formate or oxalate present in the residual aqueous phase, is recycled after conversion to acid form.

11. The method of claims 1, 2 or 3 wherein the emulsion is derived from an in situ oil recovery process and the residual aqueous phase is recycled for injection in situ, after being made basic with alkali metal bases.

12. The method of claims 1, 2 or 3 wherein a settling period follows the agitation to allow for increased phase separation.

13. The method of claims 1 or 2 wherein excess formic acid sufficient to obviate a settling period, is utilized.

14. A demulsifying agent mixture comprising at least any two of formic acid, oxalic acid and sulfur dioxide.

15. The demulsifying agent mixture of claim 14 in aqueous solution.

16. The demulsifying agent mixture of claim 14 comprising formic acid.

17. The demulsifying agent mixture of claims 14, 15 or 16 comprising formic acid and SO2, the proportion of SO2 ranging up to about 400% by wt. of the formic acid.

18. The demulsifying agent mixture of claims 14, 15 or 16 comprising oxalic acid and SO2, the proportion of SO2 ranging up to about 400% by wt. of the oxalic acid.

19. The demulsifying agent mixture of claims 14, 15 or 16 comprising formic acid and oxalic acid, the proportion of oxalic acid ranging up to about 200% by wt.
of the formic acid.

20. The demulsifying agent mixture of claims 14, 15 or 16 comprising formic acid, oxalic acid and SO2.

21. The demulsifying agent mixture of claims 14, 15 or 16 containing a crude formic acid, with a minor amount of acetic acid present in the formic.