US3066018A - Fuel oils having improved burning characteristics - Google Patents

Description

United States Patent Ofiice 3,066,018 Patented Nov. 27, 1962 3,056,018 FUEL OILS HAVING EMPRQVED EURNINQ CHARACTERKSTEQ "Robert J. McGuire, Monroevilie, Pa, assignor to Gulf Research & Deveiopment @ornpany, Fittshurgh, Pa, a corporation of Delaware No Drawing. Filed June 6, 196%, 5131. No. 33,933 it Claims. (Cl. 44-66) heavier fuel oils that can be burned in fuel burners, such as those of the atomizing type and of the rotary wall flame type, with little or no accompanying formation of smoke or soot. Oils that are normally burned in oil burners of the types indicated are those of No. 2 grade or heavier, although somewhat lighter oils can be used.

.Although some smoke and soot formation may accompany combustion of any hydrocarbon oil where less than optimum combustion conditions are used, the problem is serious in the case of oils having an API gravity of less than 34, as substantial smoking and soot formation will occur during combustion of such oils even when favorable combustion conditions are employed. The poor combustion characteristics of such oils are considered attributable to the relatively high proportion of aromatic components contained therein. Fuel oils having an API gravity of less than 34 will normally contain in excess of about 20 percent aromatics, for example, 25, 40, or even-6t) percent or more of aromatic components, whereas lighter fuel oils will normally contain a substantially lower proportion of -aromatics, for example, 15 percent orless. In the case of distillate oils, a high aromatics content usually signifies a large proportion of cracked distillates, as the latter are relatively rich in aromatics. The proportion of catalytically cracked distillate fuel oils in commercially marketed fuel oils has increased in recent years notwithstanding the relatively inferior burning qualities of such oils, because the demand for fuel oils or comparable boiling range has exceeded the available supply of straight-run oils.

Not only do low-gravity distillate oils containing large proportions of cracked. distillate, that is, oils rich in aromatics, form greater quantities of soot during combustion than straight-run, high-gravity distillate oils, or similar oils low in aromatics,but also such oils form soot of different quality. Soot formed from the latter oils is a loosely deposited, low-density material having a low coefficient of heat transfer, whereas soot from the former oils is resinous, much denser and has a higher coetficient of heat transfer.

While the problem of obtaining clean combustion is especially'serious in the case of distillate fuels, where fuel quality is of major importance, a combustion problem also exists in the case of residual fuel oils. Residual fuels, similarly as middle distillate fuel oils, have an API gravity less than 34 (API gravity for typical No. 6 fuel oils varies in the range of about to 15), and they also frequently contain exceptionally large proportions, for example 60 percent or more, of aromatic components. Residual fuels can contain relatively low-boiling aromatic components as well as higher boiling materials, as they are frequently diluted or cut back with lower boiling cracked distillate oils in order to reduce the viscosity of the heavier oils.

Although the combustion of fuel oils having an API gravity of less than 34, and consequently a' relatively large proportion of aromatics, will tend to produce soot and smoke in atomizing type burners, that is, burners in which the fuel oil is burned in the form of a spray of liquid droplets after mixture with air, combustion of such oils in rotary wall-flame type burners constitutes an especially severe problem. In the latter instance the fuel oil is burned in vapor form after vaporization of the fuel by impingement thereof on a hot metal surface.

The present invention relates to the improvement'of hydrocarbon fuel oil compositions that normally tend to form smoke and soot during combustion, whereby such oils are rendered more suitable for use as fuels in domestic oil burners of various types such as heating furnaces of the atomizing or rotary, wall-flame type, combustion gas turbine engines, and the like. It has now been found that such improved fuel compositions can be obtained by incorporating in a fuel oil of the type described a small amount of a triester of a hexitan and a fatty acid containing 12 to 20 carbon atoms per molecule,- or a polyoxyethylene derivative of a partial ester of a hexitan and a fatty acid containing 12 to 20 carbon atoms per molecule. sorbitan is the preferred hexitan for purposes of the present invention as are faty acids containing 18 carbon atoms per molecule. It is preferred to employ polyoxyethylene derivatives that contain a total of about 3 to 9 ethoxy groups per molecule, but other polyoxyethylene derivatives can be used. Thus, there can be used polyoxyethylene derivatives that contain a total of about 3 to 30 ethoxy groups per molecule. Specific examples of preferred materials included by this invention are sorbitan trioleate and a polyoxyethylene derivative of sorbitan nonooleate containing a total of six ethoxy groups per molecule. However, other materials disclosed herein can be used. Examples of such other materials are mannitan trioleate, dulcitan trioleate, and polyoxyethylene derivatives of sorbitan monooleate, sorbitan monostearate, sorbitan monopalmitate, and sorbitan monolaurate containing 3, 6, or 21 ethoxy groups per molecule, and polyoxyethylene derivatives of sorbitan trioleate and sorbitan tristearate containing 2 or 6 ethoxy groups per molecule. The hexitan esters and polyoxyethylene derivatives thereof disclosed herein are preferably employed in the fuel oil compositions of this inveintion is proportions in the range of 0.01 percent to 0.1 percent by weight of the composition, but other proprtions can be used.

The exact mechanism by which the hexitan esters and polyoxyethylene derivatives thereof of the herein-disclosed class function to reduce smoke and soot forming tendencies of fuel oils has not been definitely determined, and accordingly, it is not intended that the present invention be limited to any particular theory of operation. It has been hypothesized that the hexitan esters and polyoxyethylene derivatives thereof Whose use is included by this invention possess a critical balance of surface-active properties such as to promote a reduction in the size of the fuel droplets sprayed into the combustion zone of the burner and/0r such as to promote an improvement in the spray pattern. This view is more or less supported by the fact that compounds bearing a close chemical similarity to the materials disclosed herein have been found to be substantially less efiective in reducing the smoke and soot forming tendencies of fuel oils. However, the above-indicated hypothesis would appear to'be somewhat negatived by the fact that the combustion characteristics of fuel oils in rotary, wall-flame burners that do not involve spraying the fuel are also improved by the herein-disclosed materials.

As disclosed above, the materials found effective for the purposes of this invention include triesters of hexitans and higher fatty acids that contain 12 to 20 carbon atoms 3. per molecule, and polyoxyethylene derivatives of partial esters of hexitans and fatty acids containing 12 to 20 carbon atoms per molecule. Best results are obtained when the triesters or polyoxyethylene derivatives disclosed herein are liquids having a viscosity not greater than 600 centipoises at 25 C.

The esters referred to herein are, as indicated, derived from higher fatty acids containing 12 to 20 carbon atoms per molecule, representative members of which are lauric, palmitic, oleic, and stearic acids. Esters derived from oleic acid are preferred for the purposes of this invention by reason of their low viscosity and fluidity, whereby formation of homogeneous mixtures with fuel oil is facilitated.

The polyoxyethylene derivatives of the hexitan fatty acid partial esters whose use is included by the present invention can be represented by the general formulas:

and No. 6 fuel oils, and the use of such oils is included by the present invention. Fuel oils of these grades are defined in the ASTM Standards on Petroleum Products and Lubricants under the ASTM Specification D396. The invention is especially important in connection with fuel oils having an API gravity of less than 34, particularly when these oils contain an excess of about percent aromatic hydrocarbons, as such oils involve serious smoke and soot forming problems.

In order to demonstrate the effectiveness of the materials of the class disclosed herein, representative members of such class were incorporated in samples of No. 2 fuel oil and the thus-compounded fuel oils were subjected to a full scale, one day smoke test in a domestic oil burner (Timken Model OBC-llO, Oil-boiler). Conventional burner controls were associated with the test apparatus in conjunction with electrical timer relays to provide I I RCO 0 CHQOHCHO (CHzCHzO) XHCHO (CH2CH20)yHCHO (CHzCHzO) lHGH:

where R is the hydrocarbon radical component of a higher fatty acid, and x, y, and z are like or unlike numbers of 1 to 10, preferably, 1 to 3. An example of a preferred polyoxyethylene hexitan partial ester is one of the formula indicated above where R is a 17 carbon atom alkenyl substituent and x, y, and z are each 2.

The hexitan esters and derivatives employed in this invention need not be pure and commercial materials can be used. Examples of such materials are sorbitan trioleate, the polyoxyethylene sorbitan monostearate, and the polyoxyethylene sorbitan monooleate marketed, respectively, as Span 85, Tween 60, and Tween 81.

The hexitan esters and polyoxyethylene derivatives thereof disclosed herein can be employed in fuel oils in any proportion that will reduce the smoke and soot forming tendencies of the oils. The optimum proportion in any given case can vary in accordance with the individual addition agent and in accordance with the nature of the fuel oil, as all of the materials disclosed herein are not exactly equivalent in their ability to improve the combustion characteristics of fuel oils, and as all fuel oils are not equally responsive to such materials. Normally, some improvement in the combustion characteristics of fuel oils of the kind disclosed herein can be obtained by the use of as little as 0.01 percent of the materials disclosed herein. A major improvement is normally obtainable by the use of proportions in the range of about 0.03 to 0.07 percent by weight of the fuel oil. Normally no additional advantage with respect to smoke and soot formation during combustion is obtained by the use of amounts in excess of about 0.1 percent by weight of the fuel oil. In fact, it has been found that amounts in excess of about 0.1 percent, although still effective to reduce smoke and soot formation, actually can be less beneficial from the standpoint of smoke and soot reduction than amounts of 0.1 percent or less.

The hexitan esters and polyoxyethylene derivatives thereof disclosed herein can be added to fuel oils whose combustion characteristics are to be improved either as such or in the form of concentrated solutions in solvents such as kerosene or toluene. If desired, the esters and derivatives disclosed herein can also have included therewith other addition agents designed to improve one or more properties of the fuel oil. Some agitation will normally be desirable when mixing the herein-disclosed materials with fuel oil in order to facilitate rapid formation of a homogeneous mixture, but agitation is not essential.

As indicated, the hexitan esters and polyoxyethylene derivatives thereof disclosed herein are useful in conjunction with any fuel oil that normally tends to form 20-minute on and IO-minute off cycles of burner operation. After permitting a warm-up of at least one 20-minute on cycle of burner operation with maximum combustion air, smoke spot number and carbon dioxide content readings were taken on the flue gas at the middle of the on phases for several cycles using different air gate settings to regulate the quantity of combustion air. Changes of gate setting were made during burner oiF phases of the cycle. Smoke spot readings were obtained by withdrawing flue gas from a sampling probe installed in the chimney pipe through a disc of a No. 4 Whatman filter paper one inch in diameter for two minutes. A vacuum pump was used to maintain a pressure differential of 2% inches Hg across the disc. The smoke spot rating was determined by means of a photo-cell meter that had been calibrated by a Bacharach-Shell smoke spot chart graduated in increasing shades of black ranging from 0 (clean disc) to 9 (black disc) as the standard. CO readings were obtained by withdrawing flue gas through a sampling probe installed in the chimney pipe in accordance with the United States Department of Commerce Bulletin CA104-46, and by analyzing the thus-withdrawn flue gas for percent CO in an Orsat-type flue gas analyzer.

Two different fuel oils were employed in the abovedescribed tests. The first oil, hereinafter referred to as Base Fuel A, was a blend of 35 percent by volume West Texas straight-run and 65 percent by volume fluid catalytically cracked No. 2 fuel oil distillate having an API gravity of 29.3 and an aromatics content of 45.0 percent by weight. The other fuel oil employed in the test, hereinafter referred to as Base Fuel B, was a blend of 17.5 percent by volume of a mildly hydrogenated West Texas straight-run and 82.5 percent by volume of a fluid catalytically cracked No. 2 fuel oil distillate having an API gravity of 29.6 and an aromatics content of 42 percent by weight.

The materials employed in the tests included Span 85, Tween 60, and Tween 81. Span is a commerical sorbitan trioleate that is normally in the form of an amber, thin, oily liquid having a viscosity in the range of about to 250 centipoises at 25 C., a specific gravity of about 0.92-0.98, a flash point of about 500 F. and a fire point of about 570 F. Tween 60 is a commercial polyoxyethylene sorbitan monostearate that is normally in the form of a lemon-orange, oily liquid having a viscosity in the range of 400 to 600 centipoises at 25 C., specific gravity of about 1.05-1.10, a flash point of about 545 F., and a fire point of about 635 F. Tween 81 is a commercial polyoxyethylene sorbitan monooleate that is normally in the form of a lemon-colored, oily liquid having a viscosity in the range of about 350 to 550 centipoises at 25 C., a specific gravity of about 1.00-1.05,

5 a flash point of about 550 F. and a fire point of about 600 F. The material employed in the tests had an absolute viscosity of 456.8 centipoises at 77 F. and an average molecular weight of 722. The latter value corresponds to an average of about 6.6 ethoxy groups per molecule.

The smoke spot numbers obtained in the above-described tests when the CO content of the flue gas was 12 percent, that is, the level at which minimum smoke and soot was produced by the uninhibited fuel oil, are presented below.

Table A Additive Propor- Smoke Make-Up tion, Spot N Percent 12% CO2 by Wt.

Base Fuel A- 1. 25 +Sorbitan Trioleate 0.06 1. 0 +Polyoxyethylene Sorbitan Monostearate. 0. 06 0. 95

Base fuel B 2. 2 +Polyoxyethylene Sorbitan Monooleate 0.05 1. 95 +Polyoxyethylene Sorbitan Monooleate- 0.5 2.0

The results set forth in the preceding table clearly demonstrate the effectiveness of the hexitan esters and polyoxyethylene derivatives thereof of the class disclosed herein to reduce smoke and soot formation in actual operation in domestic fuel oil burners. The results set forth in the preceding table also demonstrate the especial effectiveness of proportions in the range of 0.01 to 0.1 percent by weight of the fuel oil composition.

'It will be understood that the specific embodiments set forth hereinabove are illustrative only and that the invention is not limited to the use of the specific materials or proportions disclosed therein, and that good results can be obtained by the substitution in the foregoing embodiments of other fuel oils disclosed herein and by the substitution in the same or equivalent amounts of other hexitan triesters or other polyoxyethylene derivatives of hexitan fatty acid partial esters disclosed herein.

Examples of other compounded fuel oils containing materials of the type whose use is included by the present invention are indicated in the following table:

Table B Addition Agent; Concentration, Percent by Wt.

Base Fuel 0.06 Base Fuel A.

Polyoxyethylene Sorbitan Dllaurate 0. 06 Base Fuel B Polyoxyethylene Sorbitan Trloleate Gravity.

The term hexitans is employed herein in its conventional sense to indicate the intramolecular anhydrides derived from hexitols such as sorbitol, mannitol and dulcitol. These anhydrides are normally considered to comprise a mixture of inner anhydrides containing 5- and 6-membered, oxygen-containing, heterocyclic rings.

If desired, the fuel oil compositions of this invention may contain in addition to the compounds previously disclosed herein oxidation inhibitors, corrosion inhibitors, antifoam agents, sludge inhibitors, color stabilizers, and/or other addition agents adapted to improve the oils in one or more respects.

Obviously, other modifications and variations of the invention as herein-described may be resorted to without departing from the spirit or scope hereof. Therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A fuel oil composition comprising a major amount of a hydrocarbon fuel oil that normally tends to form smoke and soot during combustion, and a small amount, sufficient to reduce the smoke and soot forming tendencies of the oil, of a member selected from the group consisting of a triester of a hexitan and a fatty acid containing 12 to 20 carbon atoms per molecule and a polyoxyethylene derivative of a partial ester of a hexitan and a fatty acid containing 12 to 20 carbon atoms per molecule, where said polyoxyethylene derivative contains 3 to 30 ethoxy groups per molecule, said small amount being in the range of about 0.01 to 0.1 percent by weight.

2. The fuel oil composition of claim 1 where said hydrocarbon fuel oil is a distillate fuel oil 3. The fuel oil composition of claim 1 where said hydrocarbon fuel oil has an API gravity less than about 34.

4. The fuel oil composition of claim 1 where said small amount is in the range of about 0.03 to 0.1 percent by weight.

5. The fuel oil composition of claim 1 where said member is an oily liquid having a viscosity not greater than about 600 centipoises at 25 C.

6. A fuel oil composition comprising a major amount of a hydrocarbon fuel oil that normally tends to form smoke and soot during combustion, and a small amount, sufiicient to reduce the smoke and soot forming tendencies of the oil, of a triester of a fatty acid containing 12 to 20 carbon atoms per molecule, said small amount being in the range of about 0.01 to 0.1 percent by weight.

7. A fuel oil composition comprising a major amount of a hydrocarbon fuel oil that normally tends to form smoke and soot during combustion, and a small amount, suificient to reduce the smoke and soot forming tendencies of the oil, of sorbitan trioleate, said small amount being in the range of about 0.01 to 0.1 percent by weight.

8. A fuel oil composition comprising a major amount of a hydrocarbon fuel oil that normally tends to form smoke and soot during combustion, and a small amount, sufficient to reduce the smoke and soot forming tendencies of the oil, of a polyoxyethylene derivative of a partial ester of a hexitan and a fatty acid that contains 12 to 20 carbon atoms per molecule, where said polyoxyethylene derivative contains 3 to 30 ethoxy groups per molecule, said small amount being in the range of about 0.01 to 0.1 percent by weight.

9. A fuel oil composition comprising a major amount of a hydrocarbon fuel oil that normally tends to form smoke and soot during combustion, and a small amount, sufiicient to reduce the smoke and soot forming tendencies of the oil, of a polyoxyethylene derivative of a partial ester of a heXitan and a fatty acid that contains 12 to 20 carbon atoms per molecule, where said polyoxyethylene derivative contains 3 to 9 ethoxy groups per molecule, said small amount being in the range of about 0.01 to 0.1 percent by weight.

10. A fuel oil composition comprising a major amount of a hydrocarbon fuel oil that normally tends to form smoke and soot during combustion, and a small amount, sufficient to reduce the smoke and soot forming tendencies of the oil, of a polyoxyethylene derivative of sorbitan monooleate containing about six ethoxy groups per molecule, said small amount being in the range of about 0.01 to 0.1 percent by weight.

References Cited in the file of this patent UNITED STATES PATENTS Caron et a1 Apr. 10, 1951 Rogers Feb. 12, 1952 OTHER REFERENCES

Claims (1)

1. A FUEL OIL COMPOSITION COMPRISING A MAJOR AMOUNT OF A HYDROCARBON FUEL OIL THAT NORMALLY TENDS TO FORM SMOKE AND SOOT DURING COMBUSTION, AND A SMALL AMOUNT, SUFFICIENT TO REDUCE THE SMOKE AND SOOT FORMING TENDENCIES OF THE OIL, OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF A TRIESTER OF A HEXITAN AND A FATTY ACID CONTAINING 12 TO 20 CARBON ATOMS PER MOLECULE AND A POLYOXYETHYLENE DERIVATIVE OF A PARTIAL ESTER OF A HEXITAN AND A FATTY ACID CONTAINING 12 TO 20 CARBON ATOMS PERMOLECULE, WHERE SAID POLYOXYETHYLENE DERIVATIVE CONTAIN 3 TO 30 ETHOXY GROUPS PER MOLECULE, SAID SMALL AMOUNT BEING IN THE RANGE OF ABOUT 0.01 TO 0.1 PERCENT BY WEIGHT.