JPS61225283A - Foaming suppressing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to bubble suppression methods, and more particularly to methods for controlling bubble formation in hydrocarbon liquids.

When processing, transporting and storing hydrocarbon liquids,
The formation of air bubbles is often observed when transferring from one container to another. For example, when rapidly transferring liquid hydrocarbon fuel to a storage tank, air bubbles can form on the surface of the fuel and are often , the degree of bubbles is significant and persistent enough to require a reduction in the rate of transport of the liquid hydrocarbon fuel to the container. It would be highly desirable to provide a method to suppress bubbles and allow high transport rates.

Various proposals have been made to suppress bubbles in various grades of hydrocarbon liquids by using additives such as silicone products. However, prior to the present invention, a method for reducing foam formation in diesel fuel using very small amounts of ecologically and technically acceptable silicone additives had not been satisfactorily resolved.

U.S. Pat. No. 3,233,986 relates to siloxane polyoxyalkylene block copolymers as anti-foaming agents and discloses the use of various such copolymers to reduce the tendency of organic liquids to form foam. There is. The organic liquids described herein specifically include various hydrocarbon liquids, including liquid hydrocarbon fuels, such as kerosene, gasoline, and diesel fuel. One of the many copolymers described therein is a copolymer containing groups of the general formula set forth below: where Q3
is a group selected from the group consisting of a hydrogen atom and a monovalent hydrocarbon group, G'' is an alkylene group containing at least 2 carbon atoms, G' is a divalent hydrocarbon group, G is a monovalent hydrocarbon radical, n has a value of at least 62, and C has a value of O~2.

US Pat. No. 3,233,986 teaches that at least 60% by weight of the OG'' groups are oxyethylene or oxypropylene groups, and that other oxyalkylene groups can be present in the OG''. It is said that each oxyalkylene block preferably contains from 4 to 30 OG'' groups. It is taught that the moiety attributable to alkylene blocks is not critical and that useful copolymers can contain any relative amounts of siloxane blocks and oxyalkylene blocks.

U.S. Pat. No. 3,233,986 teaches that the amount of copolymer used with the liquid hydrocarbon is not critical, with 5 to 20 parts by weight of copolymer per million parts by weight of liquid hydrocarbon.
00 parts by weight, and it is stated that particularly good results are often obtained when 100 to 500 parts by weight of copolymer are used per million parts by weight of liquid hydrocarbon used.

We now recommend that certain copolymers of the type disclosed in U.S. Pat. It has been found that the tendency of hydrocarbons to form bubbles is increased rather than reduced when used in . We have found that the presence of oxyalkylene groups is critical to the performance of polysiloxane polyoxyalkylene copolymers as foam reducers for hydrocarbon fuels, especially when smaller amounts of copolymer are used.

Hydrocarbon fuels of particular interest in the present invention are diesel fuel and jet fuel.

As used herein, the term "diesel fuel" refers to light household oils, heating oils and diesel fuels, including light oils and fuel oils containing the above-mentioned substances. These materials, whether intended for commercial or other uses, have a viscosity of less than 115 at 38°C and a viscosity of approximately 0.
It is generally characterized by having a boiling point ranging from 0°C to about 380°C. Specifically encompassed by the term "diesel fuel" above are those with viscosities ranging from about 2.9 to about 10.2 centistokes (aS) at 20°C and about 1.2 centistokes (aS) at 38°C.
6 to about 6. Redwood Viscometer Model 1 containing liquid hydrocarbons with viscosities in the range of OcS, viscosity of approximately 30-40 seconds at 38°C, less than 0.2% by weight Conradson residual carbon, 0
．． Water content less than 0.05% by weight, sulfur content less than 1.0% by weight and from about 10100 kcal/kg to about 1030
It is a liquid hydrocarbon with a net calorific value of 0 kcal/kg.

As used herein, the term "jet fuel" refers to kerosene, light oils, and intermediate oils, such as those known as VTUR fuels. ^VTUR fuel is at least 65 at 250°C
% by volume is distilled, has a flash point above 38°C, has a maximum aromatic content of 20% by volume, and has a temperature of 15 cS at -34°C.
, 5
It is an intermediate oil that is distilled at 0-300°C.

One aspect of the present invention is a method for suppressing bubbles in liquid hydrocarbon fuel, in which (i) general formula (ii) general formula RbR'6Siq, where R is a monovalent hydrocarbon group, and the hydrocarbon At least 80% of the groups are methyl groups and R' has the general formula Q (
OA) nOZ (wherein Q is a divalent group bonded to a silicon atom, A is an alkylene group, at least 80% of the OA groups are oxyethylene groups, and Z is a hydrogen atom or an OCR'' group) , where R' is a monovalent group), a is 1, 2 or 3,
b is 0 or 1 or 2, C is 1 or 2, the sum of b and C is 3 or less, and n is 5 to 25. A polysiloxane polyoxyalkylene containing a siloxane unit represented by A copolymer, wherein the polysiloxane polyoxyalkylene copolymer has an average molecular formula such that the OA groups provide 25 to 65% by weight of the calculated molecular weight of the copolymer. The present invention provides a method for suppressing bubbles in a liquid hydrocarbon fuel, characterized in that the liquid hydrocarbon fuel is contained in a liquid hydrocarbon fuel.

In the method of the invention, the hydrocarbon fuel is preferably diesel fuel, which is used as a fuel for motor vehicles, such as private cars and heavy goods transport vehicles, and ships, or jet fuel, such as VTUR, which is used as a fuel for jet engines. . However, the process according to the invention is suitable for other hydrocarbon liquids such as 115
It has also been observed that the present invention can be used, at least to a limited extent, to suppress bubbles in residual fuel oils, light intermediate and heavy naphthas, vaporized oils and motor spirits having a viscosity greater than 1.2 seconds. hydrogen liquids, especially diesel fuels, in the presence of air and possibly water;
It is particularly useful in controlling bubble formation of the hydrocarbon liquids when rapidly pumping from one container to another. Such situations arise during the separation of various grades of hydrocarbon liquids from crude oil, the preparation of various hydrocarbon liquids from selected feedstocks, and the transfer of hydrocarbon liquids from tank trucks to storage tanks. Occurs during the transfer of a substance from one container to another, as is necessary when moving a substance from one container to another.

The polysiloxane polyoxyalkylene copolymers can be used in the process of the invention in any desired amount and can be mixed into the hydrocarbon liquid in any suitable manner. It is preferred to add the copolymers in solution form to the hydrocarbon liquid. Preferred copolymers are hydrocarbon liquids 10
Copolymers that are effective and optimal for reducing the tendency to bubble formation of hydrocarbon liquids when used in amounts of 100 parts per million parts or less, such as in the range of about 1 ppm by volume to about 50 ppm by volume. is effective when used in amounts of 5 to 20 parts by volume of copolymer per 100 parts by volume of hydrocarbon liquid.

The most effective amount of bubble control of the copolymer used depends on the structure of the copolymer. Polysiloxane polyoxyalkylene tripolymers suitable for use in the present invention have the general formula (i) R@S i O・R group is 1
It contains a siloxane unit represented by (which is a valent hydrocarbon group). These units may be present as chain units of the polysiloxane molecule or as terminal groups of the polysiloxane molecule; some R groups may be unsubstituted saturated aliphatic hydrocarbon groups or unsubstituted saturated aromatic groups. Although they can be hydrocarbon groups, more than 80% of these R groups are methyl groups, and optimally each individual R group is a methyl group. The siloxane units according to general formula (i) provide more than half of the units of the polysiloxane molecule, such as from about 65% to about 92%, optimally about 78%, of the polysiloxane units.
~85%.

Polysiloxane polyoxyalkylene copolymers suitable for use in the present invention have the general formula (11) RbR'6
[SiO][In the formula, R4 has the same meaning as above,
R' is a group represented by the general formula Q(OA)nOZ, that is, a group containing an oxyalkylene group, each of the A groups is a divalent hydrocarbon group, and at least 80% of the A groups are ethylene groups, Z is a hydrogen atom or an OCR″ group (R″ is 1
It contains a siloxane unit represented by: Preferably, all A groups are ethylene groups (CH20H*), derived for example from ethylene oxide. If desired, oxyethylene-oxypropylene copolymers can be used, provided that at least 80% of the A groups are ethylene groups.

The polymeric oxyethylene chain can have a random polymer structure or a block polymer structure, i.e. it can have the structure described below: Q (OCxH4)P(OCHaCtH3)QOZoxyalkylene chain is sufficiently stable for the application. It is bonded to the silicon atom of the siloxane chain via a divalent bonding group Q selected so as not to adversely affect the bubble formation control effect of the copolymer. The linking group can be, for example, a substituted or unsubstituted aromatic hydrocarbon, a substituted or unsubstituted cycloaliphatic hydrocarbon, or a substituted or unsubstituted aliphatic hydrocarbon, but also a non-substituted or unsubstituted aliphatic hydrocarbon having from 2 to 8 carbons. Substituted alkylene chains are most advantageous. When oxyalkylene units other than oxyethylene units are present in the oxyalkylene chain, the oxyalkylene groups other than oxyethylene groups can be used to provide up to 20% of the units of the oxyalkylene chain. However, inclusion of units other than oxyethylene units may have an adverse effect on compatibility, and inclusion of units other than oxyethylene units is not preferred.

Suitable copolymers have a value of n between 5 and 25, optimally an n of 5.
It is a copolymer with a value of ~15. Examples of suitable copolymers have an average of 7.5 or about 12 oxyethylene units in each R' group and a linking group Q, as described below.
It contains a -(CHz)3- group.

The terminal group OZ of the R' group is OH or 0OCR" group (in the formula,
R'' can be a monovalent group, for example a lower alkyl group such as methyl, ethyl or butyl; preferred copolymers are those in which the terminal group O2 is a hydroxyl or acetate group. .

For example, the copolymer molecule should have an appropriate balance of lipophilic and lipophobic groups in order for the copolymer to possess desirable properties, including desired compatibility properties.

That is, the copolymer has an average molecular formula such that the OA groups provide about 25% to about 65% by weight of the molecular weight of the copolymer as calculated from the average molecular weight, i.e., the calculated molecular weight. The amount of R' groups present in the copolymer is determined by the individual R' groups used in low concentrations to achieve the desired antifoam properties.
' is selected according to the number of oxyalkylene chain units OA present in the group, ie the value of n. Therefore, n is 5 to 1
With a value of 5, it is preferred that the OA groups provide about 25% to about 55% by weight of the calculated molecular weight of the copolymer.

Further, when n has an average value of about 7.5, the OA groups will be about 30% to about 45% by weight of the calculated molecular weight of the copolymer.
and when n has an average value of about 12, the OA groups account for about 4 of the calculated molecular weight of the copolymer.
It is preferred to provide from 0% to about 55% by weight.

The calculated molecular weight of the copolymer is conveniently in the range 2000-5000, but if higher molecular weight copolymers are used, the amount of OA units is greater than is optimal for lower molecular weight copolymers of similar structure. Or smaller amounts of OA units can be used.

-a units of formula (ii) are from about 8,5% of the siloxane units;
Preferably, it is present in the copolymer in an amount on the order of about 35%. When units according to general formula (ii) are present in an amount greater than about 35% or less than about 8.5% of the siloxane units, the copolymer is added to the diesel fuel or VTUR jet fuel at about 100 parts by volume per million parts by volume. , the copolymer tends to exhibit foam-forming rather than anti-foaming properties. Diesel fuel or VTU
When a smaller amount of said copolymer is mixed into the R jet fuel, such as 50 ppm or less, it is preferred that the copolymer contain from about 11% to about 30% of units of general formula (ii); More preferably, the units of formula (ii) provide from about 15% to about 22% of the units of the copolymer.

Suitable copolymers include those represented by the following average general formula: Me3SiO(Me2SiO)z(MeR'Sin)
ySiM es (in the formula, Me represents a methyl group) *X
:3F ratio can range from 1:1 to 11:1, with a range of 1:1 to 9:1 being preferred. When the copolymer is used as a jet fuel antifoam agent, the x:y ratio is more preferably in the range of 3:1 to 7:1;
A range of 5:1 is optimal. By utilizing a suitable ratio, the copolymer can be added to 10 parts per million parts of hydrocarbon fuel.
When used in amounts of 0 parts or less, for example 40 P9fi or less, good levels of antifoam properties can be achieved.

In the process of the invention it is preferred to add the polysiloxane polyoxyalkylene copolymer in liquid form to the hydrocarbon liquid.Many of the materials suitable for use in the invention are themselves liquids. These materials and non-liquid materials are added diluted with a solvent to facilitate dispersion in the hydrocarbon liquid. No other additives are necessary for the copolymer to be effective as an antifoam agent, and therefore the antifoam agent should be considered to consist essentially of the selected copolymer, since the polysiloxane polyoxyalkylene copolymer is itself a liquid. and 10 at 25°C.
It is suitable to have a viscosity of 0.00 cS or less. Suitable materials have a viscosity of about 200 cS to about 400 cS at 25°C.

The invention also extends to hydrocarbon fuels treated by the method of the invention.

The present invention also provides (i) general formula % formula % (ii) general formula Rb R' c Si O Kounisha 1 formula, where R is a monovalent hydrocarbon group, and at least one of the hydrocarbon groups 80% are methyl groups, and R' has the general formula Q (
OA) nOZ (wherein Q is a divalent group bonded to a silicon atom, A is an alkylene group, at least 80% of the OA groups are oxyethylene groups, and Z is a hydrogen atom or an OCR'' group) , where R' is a monovalent group), Kaede is 1 or 2 or 3, b is O or 1 or 2, C is 1 or 2, and b
and C is 3 or less, and n is 5 to 25], wherein the polysiloxane polyoxyalkylene copolymer contains a siloxane unit represented by Also provided is a liquid hydrocarbon fuel comprising an antifoam agent comprising a polysiloxane polyoxyalkylene copolymer having an average molecular formula providing 25 to 65 weight percent of the calculated molecular weight.

-a Siloxanes having units of formula (i) and (ii) are generally of known types and can be prepared according to methods known in the art, e.g. by condensation and equilibration of the given precursors. By this, the general formula MesS
io +/2, MetSiO and MeHSiO (wherein,
A polysiloxane having a unit represented by Me (Me represents a methyl group) can be obtained. Oxyalkylene substances having olefinic unsaturated bonds, such as vinyl unsaturated bonds or allyl unsaturated bonds, can be prepared by reacting this polysiloxane with a hydrosilylation reaction to form Me3Si.
A polysiloxane polyoxyalkylene copolymer consisting of O+/ units, Me2SiO units and MeR'SiO units (a=3, b=1, c=1) can be obtained.

The examples set forth below are provided to illustrate the invention. In the examples below, selected polysiloxane polyoxyalkylene copolymers were used to control foam formation in diesel or jet fuel.

The symbol Me used in the following examples represents a methyl group.

The first polysiloxane polyoxyalkylene copolymer had the following average composition: MesSiO(MezSiO)s,a(MeR'5iO
) a, 5siHes In the formula, R' is = (CHz) * (OC
HzCH2) + zOH, molecular weight 3124 and 25
6 of the weight of the copolymer and has a viscosity of 400 eS at °C.
It contained 0.9% oxyalkylene groups.

The second polysiloxane polyoxyalkylene copolymer was of the average composition described below: MeaSiO(MezSiO)s,a(MeR' 5i
O) s-ssiHes In the formula, R' is -(CH2)3 (
OCR, C1,)l zOcOcHj, molecular weight 3
It had a viscosity of 250 eS at 275 and 25°C and contained 58% oxyalkylene groups by weight of the copolymer.

General formula He3SiO(He2SiO)X(MeR'Si
O) Still other polysiloxane polyoxyalkylene copolymers, represented by ysiMe3 and characterized in detail in Tables 1 and 1A, were prepared in the following manner.

Average molecular formula MesSiO(Me2SiO)x(HeHS
The copolymer with iO)ysiMei and allyloxyethylene glycol or allyloxyethylene acetate were dissolved in isopropyl alcohol to obtain a solution with a solids content of 75%. The allyloxyethylene compound contained an average of 7,5 oxyethylene units per molecule. This material contains all the S present in the polysiloxane.
A 10% excess amount was used over the calculated amount needed to react with iH. The solution also contained 0.1% of the total solids content of sodium acetate.

The addition reaction involves heating the solution to 70°C and removing the 5iH1 present.
It was induced by adding 10-s mole per mole of secondary chloroplatinic acid.

The reactants were refluxed at about 90°C for 6-12 hours.

The resulting product was cooled, the solvent removed, and filtered. No special step was provided to remove residual allyloxyalkylene glycol.

Plan-yo-person X 9 14 3 6
12 18Y az5aa
aZ Ac Ac Ac Ac
Calculated molecular weight of Ac Ae Ac copolymer (c) 2253 2148 2759 2031
2475 2919 coholimano number average molecule 1 (Mn
) 1710 1862 750 1850 1779
Weight average molecular weight (M-) of 1700 cobo 17mer (c)
Proportion of oxyalkylene groups (wt%) in 41.9 2
9.3 57 46.5 3B, 2 32.4<c>
Proportion (%) of HeR'SiO units in 21.4 11
50 27.3 17.6 13x/y ratio
3 F
0.6 2 4 6 In the above example, Q: (CH2)3.

A: (CHI) 2.

n: 7.5° Ac represents an acetate group.

Stars - 18 - people x 30 9
14 3 22 36Y
3 3 2 5 2
16Z Ac
Calculated molecular weight (c) of HHHAe Ac copolymer
3807 2172 1976 2329 2740
Number average molecular weight (M,) of 10426 copoly 1-3000
1438 1898 721 1800 3F00Cobo lJmer weight average molecular weight (Hw) 8400 eo
i411046 2312 5G4024700(c)
Proportion of oxyalkylene groups (wt%) in 24.8 5
3.7 33.4 70.8 23 48.3(c)
Proportion (%) of MeR'SiO units in 8.6 21.4
H507,729,6x/y ratio
10 3 7 0.611 2.25 In the above example, Q: (CHz):l.

A: -(CH,), -.

n: 7.5° Ac represents an acetate group.

Using test operations intended to simulate the formation of bubbles in hydrocarbon liquids in the field, such as transporting hydrocarbon liquids at high speed (5001/s) from the delivery pipe of a tanker truck to a gas station oil sump. The effects of the first copolymer and the second copolymer as antifoaming agents were evaluated by:

In this test, 10% of the hydrocarbon liquids provided by commercially available diesel fuel purchased as truck fuel were tested.
0 ml was charged into a graduated cylinder with the desired amount of polysiloxane polyoxyalkylene copolymer. Dry nitrogen with a sintered glass bubbler [No. 3-billed end Tatlock (No.

3-B guard and TaLIock)] was bubbled through the liquid for 2 minutes at a rate of 50 rsl per minute.

The bubbler was removed and the gas charging rate was adjusted to 300 ta1/min. Insert the bubbler into the hydrocarbon liquid and
Gas was bubbled through the hydrocarbon liquid at a rate of 300+5ffi/min. During this 2 minute period, the elapsed time when the bubbles successively passed through the 10 ml graduations of the measuring cylinder was recorded. The behavior of the bubbles in the absence of copolymer (blank) and in the presence of various amounts of individual copolymers was evaluated. Each of the copolymers was observed to behave as an antifoam agent, with the second copolymer showing better overall performance.

夾JLLL The first copolymer was tested as described above.

The elapsed time (in seconds) was measured on a blank and on a sample containing 50 pp by volume of the first copolymer. Yui 4j! Lj
B3JL Grade Jl Kokosho J Graduated Cylinder (Brass 1) Blank 50pp So 1m The second copolymer was tested as described above.

Elapsed time (seconds) of blank and second copolymer lpp
Measurements were made on samples containing m and 5 ppm.

11 Measurement cylinder scale (mA') Blank lppm 5 pp
m225' 120 K1jLL The effectiveness of Copolymers 3-14 as antifoaming agents was tested on freshly purchased Shell diesel truck fuel in the following manner. Sample 100 of liquid hydrocarbon fuel
10, 20, 40 and 100 parts by volume of copolymer per million parts by volume of liquid hydrocarbon fuel were added to m1. Copolymers were added as solutions in toluene. Individual samples were loaded into graduated cylinders and dry nitrogen was bubbled through the liquid for 2 min with a sintered glass bubbler (No. 3-billed end Tatlock). The flow rate of dry nitrogen was adjusted to 310 d/min. When the bubbler was removed, the bubbles became smaller.

Insert the bubbler into the hydrocarbon liquid and gas (dry nitrogen)
310mj! Bubbling was carried out through the hydrocarbon liquid for an additional 2 minutes at a rate of 1/min. During this 2 minute period, the volume of bubbles formed was recorded at 15 second intervals.

The maximum volume of air bubbles produced in samples without copolymer (blank) and in samples with various amounts of copolymer were recorded. The maximum volume of bubbles produced in the presence of the copolymer is recorded in Table 2 as a percentage of the maximum volume of bubbles produced in the sample without the copolymer.

As can be observed from Table 2, copolymers 5, 12 and 13 are not effective as antifoam agents and copolymer 9 is not effective as an antifoam agent at low concentrations, while all other copolymers are effective at concentrations between 10 and 100 ppm. It is an effective antifoaming agent.

Also, copolymers 3.7.11 and 14 are effective at various concentrations, whereas copolymers 4.6.8 and 10 must be used in amounts of 40 to 100 pp- to obtain equivalent effectiveness.

E1 The effectiveness of copolymers 3-14 as defoamers was tested on freshly obtained VTUR jet fuel. The method used is to use air instead of dry nitrogen, and the air is 2000 solitre.
The method was similar to that described in Example 3, except that the sample was passed through at a rate of 1/min. The results are shown in Table 3.

As can be observed from Table 3 (due to the nature of the test showing somewhat higher foam height results), copolymers 12 and 13 were not effective as antifoam agents. Copolymers 9 and 13 were the least effective as antifoam agents among the other copolymers, and copolymers 4.8 and 11 were not effective at low concentrations.

Results of bubble formation test of copolymer in diesel fuel (bubble volume as % of bubble volume of blank test) Copolymer Concentration 11-
60 49 '16
97 1713.8
7-U Results of bubble formation test of copolymer in jet fuel (
Bubble volume as % of Bubble volume of blank test)

Claims (1)

[Claims] 1. In a method for suppressing bubbles in liquid hydrocarbon fuel, (i)
General formula RaSiO_(_4_-_a_)_/_2 and (ii)
General formula RbR'cSiO_[_4_-_(_b_+_c_)_
]_/_2 [wherein R is a monovalent hydrocarbon group, at least 80% of the hydrocarbon groups are methyl groups, and R' is of the general formula Q(OA)_nOZ (wherein Q is silicon is a divalent group bonded to an atom, A is an alkylene group, at least 80% of the OA groups are oxyethylene groups, Z is a hydrogen atom or an OCR'' group, where R'' is a monovalent is a substituent group), a is 1 or 2 or 3
, b is 0 or 1 or 2, c is 1 or 2, the sum of b and c is 3 or less, and n is 5 to 25
a polysiloxane polyoxyalkylene copolymer containing siloxane units represented by ], wherein the polysiloxane polyoxyalkylene copolymer has an average molecular formula such that the OA groups provide 25 to 65% by weight of the calculated molecular weight of the copolymer. 1. A method for suppressing bubbles in a liquid hydrocarbon fuel, which comprises incorporating an antifoaming agent made of a polysiloxane polyoxyalkylene copolymer into the liquid hydrocarbon fuel. 2, n has a value in the range of 5 to 15, and the posiloxane polyoxyalkylene copolymer has an OA group of 2 in the copolymer.
The method of claim 1 having an average molecular formula providing 5 to 55% by weight. 3. The method of claim 2, wherein n has an average value of 7.5 and an average molecular formula that provides OA groups less than 45% and more than 30% by weight of the polysiloxane polyoxyalkylene copolymer. . 4. The method of claim 2, wherein n has an average value of 12 and the OA groups provide less than 55% and more than 40% by weight of the polysiloxane polyoxyalkylene copolymer. 5. The polysiloxane polyoxyalkylene copolymer has the average general formula Me_3SiO(Me_2SiO)_x(MeR'Si
O)_ySiMe_3 [where Me is a methyl group,
R' has the general formula Q(OA)_nOZ, where Q is an alkylene group with 2 to 8 carbon atoms, all A's are ethylene, and Z is a hydrogen atom or an OCR'' group, where R'' is a monovalent group, n is a substituent from 5 to 25), and the x:y ratio is in the range of 1:1 to 9:1. The method described in paragraph 1. 6. The method according to claim 5, wherein the x:y ratio is from 3:1 to 7:1. 7. The liquid hydrocarbon fuel is diesel fuel or jet fuel, and the amount of polysiloxane polyoxyalkylene copolymer is 5 to 50 per 1 million parts by volume of the liquid hydrocarbon fuel.
The method according to any one of claims 1 to 6, comprising parts by volume. 8. In a liquid hydrocarbon fuel containing an antifoaming agent made of a polysiloxane polyoxyalkylene copolymer, the polysiloxane polyoxyalkylene copolymer has the general formula (i) RaSiO_(_4_-_a_)_/_2 and (ii)
General formula RbR'cSiO_[_4_-_(_b_+_c_)_
]_/_2 [wherein R is a monovalent hydrocarbon group, at least 80% of the hydrocarbon groups are methyl groups, and R' is of the general formula Q(OA)_nOZ (wherein Q is silicon is a divalent group bonded to an atom, A is an alkylene group, at least 80% of the OA groups are oxyethylene groups, Z is a hydrogen atom or an OCR'' group, where R'' is a monovalent is a substituent group), a is 1 or 2 or 3
, b is 0 or 1 or 2, c is 1 or 2, the sum of b and c is 3 or less, and n is 5 to 25
a polysiloxane polyoxyalkylene copolymer containing siloxane units represented by ], wherein the polysiloxane polyoxyalkylene copolymer has an average molecular formula such that the OA groups provide 25 to 65% by weight of the calculated molecular weight of the copolymer. A liquid hydrocarbon fuel characterized in that it is a polysiloxane polyoxyalkylene copolymer.