CA1275022A - Emulsions - Google Patents

Abstract

ABSTRACT

An emulsifier for producing heat-stable emulsions of water in a fuel oil comprises an admixture of 93-97 wt %
of a sorbitan fatty acid monoester and 3.7 wt % of polysorbate-80. The preferred composition comprises an admixture of Span-80 and Tween-80.

Description

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The presen-t invention rela-tes to an emulsifier for producing heat-stable emulsions oE wa-ter in fuel oil, and to the emulsions themselves and their p:roduction. In particular the emulsions may be preheated prior to combus-tion.
I-t is well }cnown that the addition of water to liquid hydrocarbon fuels so as -to form an emulsion can have a number of beneficial effects as regards the combustion of the fuel. During combustion, the tiny droplets of wa-ter vaporise explosively within the fuel itself and lead -to excellen-t atomisation of the fuel and improve combus-tion efficiency. Although the addition of the water detracts from the overall calorific value of the fuel, nevertheless small savings in overall fuel consumption can be achieved. Furthermore, the presence of -the water tends -to reduce the overall flame temperatures leading to lower nitrogen oxide emisions.
The cleaner combustion also results in less emission of unburnt fuel components and carbon monoxide. Indeed, in the case of heavy fuel oils, the cleaner combustion of emulsified fuels may lead to substantial savings in furnace maintenance costs.
Hi-therto, emulsified fuels have been burned in diesel engines by mechanically emulsifying the water wi-th the oil shortly prior to combustion. Such emulsions are not s-table over long periods and each engine must be fitted with its own emulsifier. Separate storage and handliny systems must also be provided for the fuel and water respectively.
Stable emulsions of w~ter in petroleum frac-tions ob-tained using an emulsifier are known from U.S. pa-tent 3 876 391 and U.K. pa-tent 2 066 288. U.S. paten-t 3 876 391 discloses in Table 3 the use of an emulsifier blend of Tween-80* and Span-80* to produce emulsions of water in JP4 aviation fuel. U.K. pa-tent

2 066 288 discloses in Example 1 -the use of sorbitan monoolea-te (a Span) and ethoxyla-ted sorbitan monooleate a Tween ) to emulsiEy water in a mixture of * '['rade Mark 2 ".
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light fuel oil and methanol. ~owever, these prior disclosures are concerned only with light petroleum fract;ons which do not require preheating to lower their viscosity prior to combustion.
Fuel oils require preheating (e,g, to ~0 50 C for a fuel oil of 200cS viscosity) prior ~o combustion.
Often the fuel oil may be heated and cooled a number of times hefore combustion. This poses a problem since such heating generally causes water-in-oil emulsions to separàte. By the term "fuel oi1" we include fuel oil having a viscosity of 200-380cS and heavy fuel oils having nominal viscosities of 1000, 2000 and 6000 cS.
Lighter fractions which do not require preheating, such as gasoline, automotive diesel fuel, gasoil, and industrial diesel fuel (light fuel oil of viscosity less than 200 cS), are excluded.
It is an object of the present invention to provide an emulsifier capable of producing a heat stable emulsion of water in a fuel oil.
The present invention provides an emulsifier for producing heat-stable emulsions of water in a fuel oil, which comprises an admixture of (i) 93-97 ~t~ of a sorbitan fatty acid monoester, and (ii) 3-7 wt~ of polysorbate-80.
Typically, the fatty acid is lauric, palmitic, stearic or oleic acid. The sorbitan monoester is yreferably sorbitan monooleate (a~ailable under the trade name Sean-80).
Polysorbate-80 is a widely used term for the oleate ester of sorbitol copolymerised with approximately ~0 moles of e~hylene oxide for each mole of sorbitol.
The ratio of components (i) and ~ii) is in the region 93-97:3-7~ by weight. If too much component (ii) is used, the emulsion becornes too viscous. This advantageous ratlo is not disclosed in the prior art yatent specieications discussed above.

- 3 ~7~i~2~, The two components must be mixed together to provide the emulsifier before addition of water. Generally, the emulsifier is mixed with the water prior to addi~ion of the hydrocarbon, Usually, emulsifier will be added in an S amount of 0.02-1~ by volume based on the hydrocarbon content, The water content may be up to 70~ by volume of the hydrocarbon content. For normal use in an hydrocarbon fuel, the water content will usually be in the range 5-20%, However, where a particularly cool flame is required, for example in the flare stacks of drilling rigs, larger amounts of water e.g. up to 25% may be used.
The raw emulsion is then preferably passed through a centrifugal colloid mill in order to break up the water droplets.
In general, the water droplet si~e in the emulsion will be less than 100 microns. The drop size distribution generally varies dependent on the amount of water present. For example, in a typical 5% water emulsion, the majority of the water by volume was in drops be~ween 10 and 25 microns in diameter, although a large number of much smaller drops were also present, For a 15% wa~er emulsion, most of the water volume lay in drops in the region 50-100 microns.
The water--in-oil emulsion so produced is heat--stable over the long term and handles in a similar fashion to the hydrocarbon itself. In general, it is found that boiliny and centrifuging do not substantially effect the emulsion.
Embodiments of the invention will now be described by way of example only wi~h reference to the accolnpanying drawing and Examples.

Exam~le 1 - Production of Water/Oil Emulsion Figure 1 shows a continuous blending systern wherein emulsifier E is introduced ~rom tank 4 into a water flow W in a predetermined amount. The mixture of water and emulsifier is then rmixed with oil O prior to pass;rlg into .. ~I

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a premixer tank 5 equipped with a vane mixer. The premixed emulsion is then passed into a centrifugal colloid mill 6 set at a 0.003 inch (0.008 cm) spacing so as to produce a water-in-oil emulsion.
The various flows are monitored as shown in the drawing and the data fed into a central controller 7, which in turn controls water/emulsifier flow valve 1, oil flow valve 2 and the emulsifier dosing pump 3 via the dosing pump control 8. Transducers 9, 10 and 11 respectively monitor the water/emulsifier flow in line 13, emulsifier flow in line 19, and oil flow in line 15, Flow rate information from transducers 10 and 11 is fed in the controller. Ratio bias 12 allows the water/oil ratio to be set. Warning lights Il, I2, I3, show if "no additive". "high additive" and "low oil"
conditions respectlvely occur. From the colloidal mill, the water-in-oil emulsion passes to a storage tank where it is usually preheated in a recirculating system before being combusted.
The emulsifier consisted of a mixture of 95% by volume sorbitan monooleate (Span 80 from Atlas Chemicals - a Trade Mark) and 5~ by volume polysorbate-80 (Tween 80 - a Trade Mark).
The emulsifier content of the emulsion was 0.04 volume per cent based on the oil, For the purposes of the following tests, emulsions of 5%, 10~ and 15~ v/v water content were prepared. The oil was a heavy fuel oil.
For the 5~ water emulsion. most of the water was in drops between 10 and 25 microns in diameter, with a large number (but small volume) of very small drops from 1-2 microns. For the 10% water emulsion, the very small drops were again observed, bu~ the size range of drops was extended up to about 75 microns. For the 15% water emulsion, the very small drops were once again observed, with the larger drops extending in size up to about lO0 microns and most of the water volume in drops from 50-100 microns.

The emulsions produced were opaque dark coffee-coloured liquids which were stable indefinitely.

Exam~_2 - Combustion of Emulsions S Inclependent tests were carried out by the University o~ Newcastle, New South Wales into a comparison of the combustion and heat transfer characteristics of hea~y fuel oi1 with the water-oil emulsions as produced in Example l.
lQ A special experimental furnace was constructed which allowed measurement of fuel flow, flue gas composition, flue gas temperature, flame and radiation temperatures, heat absorption (by a water-cooled coil) and flame visualisation. This way it is possible to construct an overall heat balance.
Photograph of flames of neat oil, 5%, 10% and 15~
v/v water in oil showed qualitatively that the water/oil emulsion fuels produced shorter, more intense flames with a higher peak flame temperature. This was confirmed by measurements of flame radiation with optical and total radiation pyrometers.
Measurements of the heat absorbed by the water-cooled coil surrounding the flame showed that the increased flame temperatures resulted in higher heat transfer rates and higher furnace thermal efficiencies.
The greatest increase in efficiency was achieved with a 10% water in oil emulsion. and this also led to an increase in peak flame temperature of about 50 C.
The results of the heat balance on the furnace are 3Q given in the Table, which shows the percentage of heat absor~ed in the water-cooled loop which is a measure of the heat produced in the flame. It can be seen that the amount of heat produced in the flame is generally gceatec for the wa~er-in-oil emulsions, particularly ~or the lO~
water content. However, it is generally noted that at the lower water contents (e.g. S~) there is a reduction in heat output, pre&umably due to the ceduction in calorific value of the fuel exceeding the increase in combustion efficiency.

able Water ontent ~_v~v Thermal input ~ 100 100 100 100 Heat absorbed in water--cooled loop %38 35 4~ 41 Flue gas loss ~ 43 42 4g 44 Wall loss % 10 11 10 10 Unaccounted loss % 9 12 2 5 Exa~y~e 3 - Comparison of Emulsion stabilities A) Emulsions of water in heavy fuel oil were prepared using the following emulsifier blends falling outside the scope of the present invention i) sorbitan monooleate + Tween 20 ii) sorbitan monooleate + Tween 81 iii) dioctyl sodium sulfosuccinate ~ Tween 80 iv) dioctyl sodium sulfosuccinate + Tween 81 v) dioctyl sodium sulfosuccinate + Tween 20 In each blend the two components were varied from 5/95 ~t% to 95/5 wt~ in increments of 10 wt~.
In some cases stable water--in-oil emulsions resulted, but these emulsions separated once heated to 45 C. In no case did a heat-stable emulsion result.
B) Emulsions of water in heavy fuel oil were prepared using an emulsifier blend of sorbitan monooleate + Tween 80 in varying proportions from 5/95 wt% to 95/5 wt% in increments of 5 wt~. It was found that the following blend 9S wt~ sorbitan monooleate ~ 5 wt% Tween 80 ;ave the best results in terms of producing a heat--stable water-in--oil emulsion.

Claims (7)

The embodiments of an invention in which an exclusive property or privilege is claimed are defined as follows:

1. An emulsifier for producing heat-stable emulsions of water in a fuel oil, which comprises an admixture of (i) 93-97 wt% of a sorbitan fatty acid monoester, and (ii) 3-7 wt% of polysorbate-80.

2. An emulsifier according to claim 1, wherein the monoester is sorbitan monooleate.

3. A heat-stable emulsion of water-in-fuel oil which comprises a) fuel oil, b) 0.02-1% by volume of an admixture of (i) 93-97 wt% of a sorbitan fatty acid monoester, and (ii) 3-7% wt% of polysorbate-80; and c) water.

4. The emulsion of claim 3 wherein the monoester is sorbitan monooelate.

5. The emulsion of claim 3 or 4 wherein the water content is 5-20% by volume based on the volume of the fuel oil.

6. The emulsion according to claim 3 or 4 wherein substantially all the water particles have a size less than 75 microns.

7. An emulsion according to claim 3 or 4 wherein the water content is 5-20% by volume based on the volume of the fuel oil and wherein substantially all the water droplets have a size less than 75 microns.

9.