GB2244279A - Fluorosilicone anti-foam additive - Google Patents

Abstract

A water continuous emulsion suitable for use as an anti-foam additive comprises (a) 85-98% by weight of a fluorosilicone oil and (b) 2-15% by weight of an aqueous surfactant solution. The additive is suitable for use in the separation of crude oil containing associated gas into liquid oil and gas. The additive may be used in both aqueous and non-aqueous systems and allows fluorosilicone oils to be used without the need for environmentally damaging chlorofluorocarbons.

Description

FLUOROSILICONE ANTI-FOAM ADDITIVE This invention relates to a fluorosilicone anti-foam additive, to a method for separating associated gas from crude oil involving the use of the additive and to a stabilised composition containing the same.

When oil is produced from a well, it is forced from the reservoir by pressure up the well to the surface. As the oil rises the pressure becomes less and gas associated with the oil is progressively released from solution.

After emerging from the well, it is usually necessary to treat the mixture of liquid oil and gas to remove free gas and also dissolved gas which is likely to come out of solution when the oil is maintained at about atmospheric pressure, for example, during transport in a tanker.

The separation may be effected near the well head or, alternatively, the oil and gas may be conveyed under high pressure in a pipeline to a different location where the oil and gas are separated.

Sometimes a stable foam is formed as the gas separates from the oil with the result that liquid oil may be lost in the gas stream and the separator ceases to function effectively. To overcome this problem it has been proposed that an anti-foam additive should be added to the crude oil.

One method of administering anti-foam additive is by the formation of emulsions in water or other suitable polar media. In this way a dispersion is formed which can easily be dispersed further in the crude oil.

Fluorosilicone oils are currently used to combat foaming in sour crude oils. Whilst they are stable in the presence of hydrogen sulphide the most efficient fluorosilicones suffer from the disadvantage that in their pure undiluted form they are very viscous materials which are too viscous for direct use.

Unfortunately they are not soluble in conventional solvents and current practice is to use them diluted with a chlorofluorocarbon (CFC). CFC's however are undesirable materials because of their toxicity and cost.

Fluorosilicone oils being insoluble in water should be able to form emulsions. However because of their high viscosity they are difficult to emulsify in water. The high viscosity ratio of the fluorosilicone oil to water favours the formation of water-in-oil emulsions instead of the more suitable oil-in-water emulsions. In the former situation the fluorosilicone oil is not in a dispersed state and the viscosity of the emulsion is higher than that of the fluorosilicone oil itself. In the case of an oil-in-water emulsion however the fluorosilicone oil would be in the form of small droplets and the resultant emulsion would have a viscosity very much lower than that of the fluorosilicone oil itself.

We have now found that fluorosilicone oils may be emulsified in water in the presence of water soluble surfactants to form stable emulsions suitable for use as anti-foam additives.

Thus according to the present invention there is provided a water continuous emulsion, suitable for use as an anti-foam additive comprising (a) 85-98Z (by wt) of a fluorosilicone oil and (b) 2-15X (by wt) of an aqueous surfactant solution.

The aqueous surfactant solution comprises 1-lOZ (by wt) of surfactant, preferably 7-10% (by wt).

Suitable fluorosilicone oils are of formula

wherein R1 is an alkyl or a phenyl radical, R2 is the same as R1 or the radical CnF2n+1(CH2)20 in which n = 4 - 16, and x is in the range 5 to 100, y is in the range 0 to 10, and that a maximum of 90% of R2 is the same as R1.

The viscosity of the fluorosilicone oil varies from 400 to 1M cP at 25-C.

Suitable fluorosilicone oils are those disclosed in British patent specification 2196976.

Suitable surfactants may be either nonionic, cat ionic or anionic surfactants.

Suitable nonionic surfactants include alkyl ethoxylates, alcohol ethoxylates, ethoxy sorbitan esters, amine ethoxylates and alkyl phenyl ethoxylates.

Suitable cat ionic surfactants include quaternary ammonium salts for example cetyl trimethylammonium bromide.

Suitable anionic surfactants include sodium dodecyl sulphate, sodium dodecyl benzene sulphonate and sodium ether sulphonates.

Emulsions according to the present invention may be prepared by directly adding hot fluorosilicone oil to the aqueous surfactant solution, mixing being effected under low shear conditions.

The fluorosilicone oil is added preferably at a temperature in the range 60-80 C.

By low shear conditions we mean mixing at such a rate to produce low shear conditions in the range 10-1,000 preferably 50 to 250 reciprocal seconds.

Suitable mixers include blenders employing propellers, paddles etc or static mixers.

Emulsions according to the present invention are stable in storage.

As previously stated the emulsions of the present invention are suitable for use as anti-foam additives particularly for use in the degassing of crude oil.

Thus according to another aspect of the present invention there is provided a method for the degassing of crude oil containing associated gas into liquid oil and gas wherein the separation is carried out in the presence of a water continuous emulsion containing an effective amount of a fluorosilicone oil as hereinbefore described.

The fluorosilicone oil is suitably employed in amount 0.1 to 20 ppm expressed on the basis of active agent, a reference to the pure fluorosilicone oil in its undiluted state.

The emulsion of the present invention may be diluted to the required active level with clean water.

The emulsion is suitable for use in both aqueous and non-aqueous systems.

Emulsions according to the present invention are stable and can meet viscosity requirements eg a maximum viscosity for pumping of 1000 mPa.s.

Thus according to yet another aspect of the present invention there is provided a composition comprising degassed crude oil treated with a water continuous emulsion as hereinbefore described.

Emulsions of the present invention may also be suitable for use in the brewing, food processing and distillation industries.

The present invention is further illustrated with reference to the following Examples which describe both the preparation of emulsions and their effectiveness as anti-foam additives.

Example 1 The following emulsion was prepared in accordance with the present invention.

19g of a fluorosilicone oil as disclosed in British patent specification 2196976 and known as C2610 was added at 60eC to 0.5 g of a 10% aqueous solution of the surfactant NP20 (nonyl phenyl ethoxylate with 20 moles ethylene oxide). The mixture was emulsified for 30 seconds under low shear conditions using a mini laboratory stirrer operating at 1000 rpm.

The resultant oil-in-water emulsion was homogeneous and contained a mean droplet size of < 20 pm.

The emulsion was then diluted with water to a level suitable for application.

The anti-foam properties of the emulsions of the present invention were tested using the Bikerman gas sparging technique and by comparison with other anti-foam agents.

Example 2 3 ml of Emerald crude oil (North Sea) were placed in a calibrated thermostatted sintered glass tube of 1.5 cm diameter at 250C. Natural gas was sparged through the oil at a flow rate of 30 ml per minute to develop a foam. When the foam had stabilized its height and volume were recorded. The test was then repeated in the presence of an emulsion prepared according to Example 1. The concentration of active ingredient was 0.5 ppm.

The foaminess index (FI) was then calculated from the following relationship: FI (Secs) = volume of foam gas flow rate The lower the value obtained for FI the more effective the anti-foam agent is considered to be.

The anti-foam index (AFI) was then calculated from the following relationship: AFI = FI (no antifoam agent) - FI (anti-foam aRent) FI (no -antifoam agent) AFI = 1 indicates a perfect anti-foam agent = 0 indicates no activity = a negative value indicates a profoamer.

Examples 3 - 4 Example 2 was repeated using varying concentrations of active ingredient.

Examples 5 - 10 By way of comparison a series of tests were performed using (a) a commercially available high molecular weight polydimethylsiloxane anti-foam agent known as SK 3527.

(b) a fluorosilicone oil as disclosed in British patent specification, 2196976 and known as C2610, supplied as a solution in the chlorofluorocarbon Frigane.

The results for Examples 2-10 are given in the accompanying table. For each example both the FI and AFI values were calculated.

From the results it is quite clear that the emulsions of the present invention are comparable with both the commercially available formulations as anti-foam agents. In addition the availability of such emulsions allows fluorosilicone oils to be used effectively in both aqueous and non-aqueous systems without the need for the environmentally damaging chlorofluorocarbons.

Claims (8)

Claims:

1. A water continuous emulsion suitable for use as an antifoam additive comprising (a) 85-98X by weight of a fluorosilicone oil and (b) 2-15% by weight of an aqueous surfactant solution.

2. A water continuous emulsion according to claim 1 wherein the aqueous surfactant solution comprises 1-10% by weight of surfactant.

3. A water continuous emulsion according to claim 2 wherein the aqueous surfactant solution comprises 7-10% by weight of surfactant.

4. A water continuous emulsion according to any of the preceding claims wherein the fluorosilicone oil has the formula:

wherein R1 is an alkyl or a phenyl radical, R2 is the same as R1 or the radical CnF2n+l(CH2)20 in which n = 4 - 16, and x is in the range 5 to 100, y is in the range 0 to 10, and that a maximum of 90% of R2 is the same as R1.

5. A water continuous emulsion according to any of the preceding claims wherein the surfactant is a nonionic surfactant.

6. A method for the degassing of crude oil containing associated oil and gas wherein the separation is carried out in the presence of a water continuous emulsion as hereinbefore described, said emulsion containing an effective amount of fluorosilicone oil.

7. A method according to claim 6 wherein the fluorosilicone oil is present in amount 0.1 to 20 ppm expressed on the basis of active ingredient.

8. A degassed crude oil treated with a water continuous emulsion as defined in any of the preceding claims.