WO1995033807A1

WO1995033807A1 - Water-in-oil microemulsion

Info

Publication number: WO1995033807A1
Application number: PCT/GB1995/001251
Authority: WO
Inventors: Nissim Garti; Shmaryahu Ezrahi; Abraham Aserin
Original assignee: Yissum Research Development Company Of The Hebrew University Of Jerusalem; Whalley, Kevin
Priority date: 1994-06-03
Filing date: 1995-05-31
Publication date: 1995-12-14
Also published as: IL109893A0; AU2622095A

Abstract

The invention provides a water-in-oil microemulsion having high fire resistance, consisting of mineral oil; at least 50 wt.% water; and at least one polyethoxylated nonionic alcohol surfactant, the alcohol having 12-18 carbon atoms and having attached thereto between 2 and 25 ethoxy groups.

Description

ATER-IN-OIL MICROEMULSION

The present invention relates to a water-in-oil microemulsion. More particularly, the present invention relates to fire-resistant microemulsions useful as hydraulic fluids.

The use of mineral oils as hydraulic fluid involves a grave fire hazard. Fire-resistance may be endowed to the system by adding water and forming a microemulsion through the use of a surfactant and cosurfactant. However, preparing a stable microemulsion that functions as a hydraulic fluid is not a simple task. This is accomplished by incorporating suitable additives in the oil, or sometimes also in the aqueous phase. The selection of an inappropriate additive may, however, cause the breakdown of the microemulsion, especially in the case of high water content. The resulting two phases have a detrimental effect on the hydraulic system; the mineral oil is highly flammable and the water may lead to severe corrosion and other undesirable results.

Another problem that may arise, especially in emulsions having high water content, is the instability of these microemulsions at non-ambient temperatures. There are many instances in which microemulsions separate upon a slight change in their composition or in operational conditions.

In conclusion, although the preparation of a microemulsion per se is not necessarily difficult, the adaptation of a microemulsion for a specific application, such as the preparation of a fire-resistant hydraulic fluid, is far from being simple. The above-mentioned problems and the state of the art are described extensively in European Patent Application No. 069540, which recounts, inter alia, that microemulsions, sometimes referred to as icellar emulsions, soluble oils, swollen micelles, etc., are not new and have been relatively well-discussed in the literature. See, for example, W.C. Tosch, "Technology of Micellar Solutions," Paper No. SPE 1847-b, Society of Petroleum Engineers of AIME (American Institute of Mining, Metallurgical and Petroleum Engineers, Inc., 1967) and Prince, Emulsions and Emulsion Technology, K. Lissant, Ed., Marcell Dekker, Inc., pp. 125-179 (1974).

Water-in-oil microemulsions are typically characterized as clear, bright and transparent, these characteristics being due to the fact that the swollen micelle is typically smaller than the wave length of visible light, and thus diffraction does not occur. If the swollen micelle is large enough, however, diffraction of short wave length, ultraviolet light can be detected instrumentally.

The small size of the . swollen micelles imparts properties to microemulsions that are not found in other fluid systems, particularly microemulsions. Microemulsions are typically less viscous than macroemulsions formed from the same base oil at constant water content; indeed, the viscosity of a microemulsion reflects the viscosity of its base oil, while the viscosity of a macroemulsion is independent of the viscosity of its base oil. Consequently, the viscosity of a macroemulsion can be controlled, at least to some extent, by proper selection of the base oil. This is important in a number of different applications, one of which is hydraulic fluids. As a result of liquid crystals or macroemulsion formation, the addition of water to a microemulsion system considerably increases its viscosity.

In the past, low molecular weight alcohols have been used to destroy lyotropic liquid crystals and to reduce the viscosity of a microemulsion. The alcohol molecules participate with the surfactant in forming an interphase between the water and the oil, and they^' are absorbed through the aid of the surfactant onto the surface of the water. Their inclusion reduces the rigidity of the interphase, thus making the micelles more pliable in reducing the bulk viscosity. Moreover, the presence of the alcohol molecules will prevent or retard the formation of liquid crystals. Alcohols that have been found useful for this purpose include those marketed under the trade names of Cellosolve^CR> , Propasol^CR' and Carbitol^<r , all of which are various forms of glycol ethers. Garner, et al., U.S. Patent No. 2,606,874, teaches the use of 1,2-alkanediols for this purpose. While these alcohols do reduce the viscosity of a microemulsion, they are not completely satisfactory for use in microemulsions designed for fire-resistant hydraulic fluids, because of their poor heat stability.

Fire-resistant hydraulic fluids are used in hot operations such as metal casting, hot forging, steel reduction mills, etc. These fluids are typically circulated under pressure to hot spots in the system, where they absorb heat and the fluid is then returned to a sump, where pressure is released. Flash vaporization of water can occur in release of pressure and high sump temperatures cause rapid water loss. The alcohols presently in use for reducing the viscosity of microemulsions generally cannot tolerate evaporative water loss under thermal stress due to either steam distillation of azeotrope formation. Loss of water under these conditions can destroy the microemulsion and thus also destroy the utility of the fluid for its intended purpose. As a consequence, there is a need to identify a group of alcohols that will form water-in-oil microemulsions which are stable under thermal stress, and to formulate improved fire-resistant hydraulic fluids.

In the above-mentioned European publication, there is described and claimed a water-in-oil microemulsion, comprising an oil phase; an aqueous phase; at least one emulsifier, and at least one aliphatic diol of the formula:

R - CH ^■ (CHR^* ) CH - R" (I) I I OH OH

where R and R" are independently hydrogen or C^-C _a ^■aliphatic groups; each R' is independently hydrogen or a C -C₂₀ aliphatic group; and n is an integer of 1-4, with the provisos that the number of carbon atoms in R is different from the number of carbon atoms in R" , and the total number of carbon atoms in I is from 5 to about 25.

While said publication discusses the possibility of preparing a microemulsion having a water content of between 20-70 wt.% based on total weight of fluid, in fact, in the examples therein, the highest water content achieved was only 40 wt.%. This water content is consistent with other water-in-oil emulsions described in the literature, e.g., in U.S. Patent 3,105,050, from 0.003-30 wt.% H₂0; in U.S. Patent 4,336,147, 50 wt.% water. While publications of course exist relating to oil-in- water microemulsions having much higher water content, e.g., U.S. Patent 4,466,909 describing from 50-99.9 wt.% water, because of the corrosive effect of water, it is undesirable for it to serve as the continuous phase in such microemulsions.

According to the present invention, it has now been found that the use of at least one, and preferably the use of a mixture of at least two, polyethoxylated nonionic alcohol surfactants, enables the formation of a stable, water-in-oil microemulsion having high fire resistance and comprising at least 50 and preferably at least 60 wt.% water in the discontinuous phase.

Polyethoxylated nonionic alcohol surfactants which can be used in the present invention include those designated by the formulas C-.₈.₁(EO)₂; C₁₂(EO)₄; C_18!l(E0)_lo; C ₂(EO)_a; C₁₈.._ι(EO)₂₀ and C_x2(EO)₂₃.

Especially preferred are those polyethoxylated alcohols having between 4 and 10 ethoxy groups attached thereto, e.g., polyoxythylene (10) oleylalcohol [C_18:i(EO)₁₀]; polyoxyethylene (4) laurylalcohol [C_X2(EO)₄], and polyoxyethylene (8) laurylalcohol [C_x2(EO)_B] and mixtures thereof, with each other as well as with other polyethoxylated nonionic alcohol surfactants.

These polyethoxylated alcohols may function both as surfactants and alcohols, i.e., they enable the formation of microemulsions and concommitantly they reduce the viscosity of the system and prevent or retard the formation of liquid crystals. The present investigations have shown that in order to enhance water solubilization, medium-chain alcohols such as butanol or pentanol, or glycol ethers, should be added.

In the more advanced phase of the present research, it has been proven that the combination of an anionic surfactant, such as the sodium salt of 2-ethylhexylsulfo- succinate (AOT) and glycol ethers enables one to fully control the water content of the microemulsion, leading to improved hydraulic fluid.

Thus, the present invention provides a microemulsion having thermodynamic stability and heat stability, while providing the desired viscosity.

Especially preferred embodiments of the present invention further comprise lithium borate, which has been found to inhibit water evaporation and, at the same time, together with other anti-wear agents, to also function as an antioxidant, corrosion inhibitor, and anti-wear agent.

As stated above, the more water a hydraulic fluid contains, the better its fire-resistance will be. Yet, high concentration of water will down-rate the performance of the hydraulic fluid. By judiciously choosing the proper amplitudes for the system, the water content in the microemulsions of the present invention may be altered over a rather wide range without shaking the stability of the system.

Any mineral oil is adequate for use in the present invention, but the paraffin C type is preferable. A typical oil has the following properties: Density at 20°C 0.842 g/cm³

Distillation range 310-384°C

Viscosity index 111

Flash point (open) 156°C

Kinematic viscosity at 40°C 8.37 c St

Kinematic viscosity at 100°C 2.42 c St

Examples of some of the oils which could be used in the present invention include:

Light Hydraulic Oil

Specific gravity at 16°C 0.860-0.876

Viscosity at 37.8°C (SUS) 149-182

Viscosity index (VI) 90

Pour point ( °C) -15

Flash point (°C) 200

Medium Hydraulic Oil

Specific gravity at 16°C 0.868-0.887

Viscosity at 40°C (SUS) 194-236

Viscosity index (VI) 90

Pour point ( °C) -15

Flash point (°C) 200

Heavy-Medium Hydraulic Oil

Specific gravity at 16°C 0.871-0.881

Viscosity at 38°C (SUS) 317-893

Viscosity index (VI) 90

Pour point ( °C) -15

Flash point (°C) 200

Conventional Naphthenic Oil

Specific gravity at 16°C 0.92

Viscosity at 37.8°C (SUS) 110

Viscosity at 100°C (SUS) 38

Pour point (°C) -40 Conventional Midcontinental Oil

Specific gravity at l6°C 0.89

Viscosity at 37.8°C (SUS) 102

Viscosity at 100°C (SUS) 38.9

Pour point (°C) -4

Lube-Base Stock (Paraffinic)

Specific gravity at 16°C 0.862

Viscosity at 37.8°C (SUS) 100

Pour point (°C) -18

Viscosity index (VI) 100

Flash point (°C) 199

Lube-Base Stock (Cycloparaffinic)

Specific gravity at l5.5°C 0.908

Viscosity at 37.8°C (SUS) 100

Pour point (°C) -45.5

Viscosity index (VI) 15

Flash point (°C) 171

As stated above, the compositions of the present invention can preferably contain further co-surfactants. Many alcohols and glycol ethers have been successfully tried. Preferred are l-(2-butoxymethylethoxγ)propanol and l-butoxy-2-propanol.

Applicability Limits of the Present Invention

Component Wt.%

Water 50-75

Mineral oil 10-50

Anionic surfactant, glycol ether, and other 5-50

Additives 0.1-10

While the invention will now be described in connection with certain preferred embodiments in the following examples so that aspects thereof may be more fully understood and appreciated, it is not intended to limit the invention to these particular embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the scope of the invention as defined by the appended claims. Thus, the following examples which include preferred embodiments will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purposes of illustrative discussion of preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of formulation procedures as well as of the principles and conceptual aspects of the invention.

EXAMPLE 1

Component Wt.%

Mineral oil 20.3

Polyoxyethylene (10) oleylalcohol 24.2

Butanol 20.3

Sodium dodecylsulphate 2.7

Water 26.9

Zinc dialkyldithiophosphate 2.5

Other additives 3.1

100.0

EXAMPLE 2

Coπroonent Wt.%

Mineral oil 17.0

Polyoxyethylene (10) oleylalcohol 30.6

Pentanol 16.9

Sodium dodecylsulphate 3.4

Water-ethylene glycol (3:1) 27.1

Zinc dialkyldithiophosphate 2.4

Other additives 2.6

100.0 EXAMPLE 3

Component Wt.%

Mineral oil 24.8

Polyoxyethylene (20) oleylalcohol 33.5

Polyoxyethylene (2) oleylalcohol 23.9

Water 13.2

Zinc dialkyldithiophosphate 2.4

Other additives 2.2

100.0

EXAMPLE 4

Component Wt.%

Dodecane 3.0

Pentanol 3.0

Polyoxyethylene (8) laurylalcohol 6.0

Water 88.0

100.0

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples and that the present invention may be embodied in other specific forms without departing from the essential attributes thereof, and it is therefore desired that the present embodiments and examples be considered in all respects as illustrative and not restrictive, reference being made to the appended claims, rather than to the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

WHAT IS CLAIMED IS:

1. A water-in-oil microemulsion having high fire resistance, comprising a mineral oil; at least 50 wt.% water; and at least one polyethoxylated nonionic alcohol surfactant, said alcohol having 12-18 carbon atoms and having between 2 and 25 ethoxy groups attached thereto.

2. A water-in-oil microemulsion as claimed in claim 1, comprising a combination of at least two polyethoxylated nonionic alcohol surfactants, each of said alcohols having 12-18 carbon atoms and having between 2 and 25 ethoxy groups attached thereto.

3. A water-in-oil microemulsion as claimed in claim 1, comprising at least 60% water.

4. A water-in-oil microemulsion as claimed in claim 1, said polyethoxylated alcohol having between about 4 and about 10 ethoxy groups attached thereto.

5. A water-in-oil microemulsion as claimed in claim 1, further comprising a glycol ether, said microemulsion being stable between 5°C and 60°C.

6. A water-in-oil microemulsion as claimed in claim 1, further comprising lithium borate.