GB2234978A - Fluorosilicone antifoam additive composition for use in crude oil separation - Google Patents

Abstract

An antifoam additive comprises (a) 50-58 (by wt) of a fluorosilicone oil, (b) 1-30% of an aliphatic hydrocarbon, (c) 1-30% of an aromatic hydrocarbon and (d) 1-20% of a chlorofluorocarbon. The additive, which is suitable for use in the separation of crude oil containing associated gas into liquid oil and gas, contains a reduced amount of the environmentally damaging chlorofluorocarbons than similar anti-foam additives.

Description

ANTI-FOAM ADDITIVE This invention relates to an 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 agent such as a polydimethylsiloxane should be added to the crude oil.

Whilst anti-foam agents such as polydimethylsiloxanes can be effective for sweet crude oils, they are not suitable for use with sour crude oils, i.e. crude oils containing appreciable quantites of hydrogen sulphide and mercaptans. This is because they are either unstable, deactivated or solubilised in the presence of hydrogen sulphide.

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 (viscosity > 106 mPa.s) which are too viscous for direct use. Consequently, they require dilution with a suitable solvent so that they may be properly dosed.

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. They are becoming unacceptable because of environmental considerations and industry is being subjected to increasing pressure to limit their use.

Although fluorosilicone oils are insoluble in conventional solvents, such as aliphatic or aromatic solvents; we have surprisingly discovered that by adding a blend of aliphatic and aromatic solvents, the proportion of CFC required to produce a fluorosilicone of usable viscosity can be reduced from 50-70%, as in current practice, to a much lower value, e.g. about 5-10%.

Thus according to the present invention there is provided an anti-foam additive comprising (a) 50-85% (by wt) of a fluorosilicone oil, (b) 1-30% of an aliphatic hydrocarbon, (c) 1-30% of an aromatic hydrocarbon and (d) 1-20Z of a chlorofluorocarbon.

The fluorosilicone oil is preferably present in amount 60 to 75 % (by wt).

The aliphatic hydrocarbon is preferably present in amount 5 to 15%.

The aromatic hydrocarbon is preferably present in amount 5 to 15X.

The chlorofluorocarbon is preferably present in amount 5 to 15%.

It is believed, although applicants do not wish to be bound by this theory, that important parameters in enabling the hydrocarbon blend to reduce the previous reliance on the CFC as the solvent are the presence of both aliphatic and aromatic compounds in the blend and the ratio between one and the other.

This is preferably in the range 0.1 to 5:1, most preferably 0.5 to 3:1.

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+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.

The viscosity of the fluorosilicone oil varies from 400 to 1M cp at 250C Suitable fluorosilicone oils are those disclosed in British patent specification 2196976.

Suitable aliphatic solvents include hexane, heptane, octane, kerosine. The fraction known as "white spirit" is particularly convenient.

The prefered aromatic solvent is toluene.

Suitable chlorofluorocarbons include those which are liquid at ambient temperature such as the ARCTON series of chlorofluorocarbons supplied by ICI.

The additives of the present invention may be prepared by initially mixing the fluorosilicone oil with the chlorofluorocarbon under low shear conditions at ambient temperature followed by addition of the desired mixture of aliphatic/aromatic solvents under the same conditions of both mixing and temperature.

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

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

Additives according to the present invention are stable and can meet viscosity requirements, e.g., a maximum viscosity for pumping of 1000 mPa.s The additives of the present invention may suitably be employed diluted with White spirit.

As previously stated, the additives 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 separation of crude oil containing associated gas into liquid oil and gas wherein the separation is carried out in the presence of an anti-foam additive as hereinbefore described containing an effective amount of fluorosilicone oil.

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

After treatment and following storage and/or transportation, the concentration of active agent may be somewhat less, since some may be lost by adsorption on the walls of containers.

Thus according to yet another aspect of the present invention there is provided a composition comprising degassed crude oil treated with an anti-foam additive as hereinbefore described.

The invention is illustrated with reference to the following examples Examples Example 1 8g of the fluorosilicone oil as disclosed in British patent specification 2196976 and known as C2610 was added to 0.5g Frigane at room temperature. The resultant solution was mixed undo r low shear conditions for between 20-30 secs, as described above, until homogeneous.

A solution of 0.5 g toluene was added to lg of White spirit and the mixture shaken for a few seconds.

The C2610/Frigane mixture was then added to the toluene/White spirit with low shear mixing for approximately 1 minute at ambient temperature.

The resultant solution was clear with a viscosity of 730 mPa.s.

Examples 2-6 Further additives were prepared using the same procedure. For comparison in Example 5 an additive was prepared in the absence of the aromatic solvent and in Example 6 in absence of the aliphatic solvent.

The results set out in the following Table were obtained.

Example Fluorosilicone CFC White Spirit Toluene Viscosity Solution mPa.s Clarity/ stability 1 80 5 10 5 730 Clear 2 80 5 5 10 500 Clear 3 77 3 7 13 810 Cloudy, but stable 4 70 10 10 10 290 Cloudy, but stable 5 70 10 20 0 2 phases Cloudy and unstable 6 85 5 0 10 1450 clear The Examples clearly show that in the presence of both the aliphatic hydrocarbon (White spirit) and the aromatic hydrocarbon (toluene) the resultant additive compositions were stable with usable viscosities. Example 4 (without toluene) and Example 5 (without white spirit) result in additives which are either two-phase and unstable or of high viscosity.

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

Example 7 3ml of Terra Nova crude oil (Canada) 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 45 ml per minute to develop a foam. When the foam had stabilized its height and volume were recorded. The height was recorded as 7 cm and the volume as 12.37 ml. The test was then repeated in the presence of an additive according to the present invention comprising 70Z of the fluorosilicone oil known as C2610, 10% of the chlorofluorocarbon Frigane, 10% toluene and lOX White spirit.

This was diluted with further White spirit until a concentration of 0.3 ppm of the fluorosilicone oil was present as active ingredient.

In the presence of the additive the height of foam was 1 cm giving a volume of 1.767 ml.

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

The anti-foam index (AFI) is then calculated from the following relationship: AFI = FI (no antifoam) - FI (anti-foam) FI (no antifoam) AFI = 1 indicates a perfect anti-foam additive = 0 indicates no activity = a negative value indicates a profoamer Hence from the gas sparging test in the absence of the antifoam additive FI g volume of foam P 12.37 ml = 16.5 secs gas flow rate 0.75 ml sec'l In the presence of the anti-foam additive FI = volume of foam = 1.767 = 2.36 secs gas flow rate 0.75 Hence AFI - 14.4 = 0.86 15.6 Examples 8-9 These examples were performed using the same procedure but varying the amount of active fluorosilicone oil present in the additive.

Examples 10-14 By way of comparison a further series of examples were performed using (a) a commercially available 60,000 cSt polydimethylsiloxane antifoam agent and (b) a fluorosilicone oil as disclosed in British patent specifcation 2196976 and known as C2610 supplied as a solution in the chlorofluorocarbon Frigane.

The results of all the examples are given in the accompanying table.

EXAMPLE ANTIFOAM ADDITIVE | FI | AFI 0.3 ppm C2610 (70Z), Toluene (10X) 2.36 0.86 White spirit (10%), Frigane (10X) 8 0.2 ppm C2610 as above 3.06 0.81 9 0.1 ppm C2610 as above 4.71 0.71 10 1 ppm polydimethylsiloxane 1.18 0.94 11 2 ppm polydimethylsiloxane 0.24 0.98 12 0.1 ppm C2610/Frigane 1.41 0.91 13 | 0.2 ppm C2610/Frigane 0.47 0.97 14 NONE 16.5 =

These examples show that the additives of the present invention are equally as effective as conventional anti-foam agents in suppressing the formation of foam in crude oils.

Claims (11)

Claims

1. An anti-foam additive comprising (a) 50-85% (by wt) of a fluorosilicone oil, (b) 1-30% of an aliphatic hydrocarbon (c) 1-30% of an aromatic hydrocarbon and (d) 1-20% of a chlorofluorocarbon.

2. An anti-foam additive according to claim 1 wherein the fluorosilicone oil is present in amount 60-75% (by wt).

3. An anti-foam additive according to claim 1 wherein the aliphatic hydrocarbon is present in amount 5-15% (by wt).

4. An anti-foam additive according to claim 1 wherein the aromatic hydrocarbon is present in amount 5-15% (by wt).

5. An anti-foam additive according to claim 1 wherein the chlorofluorocarbon is present in amount 5-15% (by wt).

6. An anti-foam additive 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+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.

7. An anti-foam additive according to any of the preceding claims wherein the aliphatic hydrocarbon is White spirit.

8. An anti-foam additive according to any of the preceding claims wherein the aromatic hydrocarbon is toluene.

9. A method for the separation of crude oil containing associated oil and gas wherein the separation is carried out in the presence of an anti-foam additive as hereinbefore described, said additive containing an effective amount of fluorosilicone oil.

10 A method according to claim 9 wherein the fluorosilicone oil is present in amount 0.1 to 20 ppm expressed on the basis of active ingredient.

11. A degassed crude oil treated with an anti-foam additive as defined in any of the preceding claims.