US2211180A - Gasoline antioxidant - Google Patents

Description

Patented Aug. 13, 1940 UNITED STATES GASOLINE ANTIOXIDANT John W. Teter, Chicago, 111., assignor to Sinclair Refining Company, New York, N. Y., a

corporation of Maine No Drawing. Application August 1'], 1937, Serial No. 159,502

11 Claims.

This invention relates to antioxidants for gasoline and more particularly to the use of a mixture of certain compounds for inhibiting the oxidation of gasoline as well as to the gasoline in which such a mixture is incorporated. In its more specific aspect, the invention relates to the incorporation in cracked and polymer gasolines of a partially nitrosated mixture of substituted phenolic compounds.

Cracked gasclines and particularly polymer gasolines contain substantial quantities of unsaturated compounds such as olefins. It is well known that unsaturated compounds have a tendency to oxidize when the gasoline containing them is allowed to stand for an appreciable length of time after its production. There are two salient disadvantages 'which characterize the oxidation or deterioration of cracked and polymer gasolines originally containing substantial amounts of unsaturated compounds. Firstly, gum-like products are formed upon oxidation of these unsaturated compounds. Such solid products may be formed while the gasoline is in storage tanks with the result that the gasoline has a cloudy appearance due to the precipitation of this solid matter. The gum-like product together with additional solid matter formed in the gasoline tank of an automobile, for example, tends to settle out in the gasoline lines and carburetor of the automobile engine. Secondly, the presence of the unsaturated compounds in the gasoline imparts to the gasoline a high-antiknoek rating which is higher in gasolines containing. the larger quantity of these unsaturated compounds. However, when these unsaturated compounds are destroyed by oxidation the antiknock characteristic of the gasoline is seriously lowered.

For these two well recognized reasons therev have been incorporated in cracked and polymer gasolines substances which have the property of effectively inhibiting the oxidation of unsaturated compounds in the gasoline. Besides having this requisite inhibitory effect it is also desirable that the gasoline antioxidants be substantially insoluble in water and highly soluble in the gasoline so that there will be no tendency for the antioxidant to be dissolved out of the gasoline during storage by any moisture in the gasoline.

I have found that a partially nitrosated mixture of substituted phenolic compounds meets the several requirements of a highly desirable gasoline antioxidant. When a small quantity of this mixture is incorporated in cracked or polymer gasoline it exhibits a powerful inhibitory action with respect to oxidation of unsaturated compounds contained in the gasolines. Such a mixture is further characterized by a low solubility in water with ready solubilty in gasoline.

More particularly the novel gasoline antioxidant of my invention comprises a partially nitrosated mixture of coal-tar acids having a boiling range between 200 to 216 C. and comprising cresols, xylenols, etc. This mixture of coal-tar acids having the above characteristics will be referred to hereinafter as lower xylenols.

The lower xylenols mixture may be'nitrosated by subjecting the mixture to the action of sodium nitrite and a mineral acid such, for example, as sulphuric acid. A highly eflicient and inexpensive method of partially nitrosating such a mixture is fully described in my copending application Serial No. 147,870, filed June 12, 1937. This partial nitrosation efiects nitrosation of the most reactive compound or compounds in the mixture, and the nitrosated compound or compounds has the property of being a powerful oxidation inhibitor for gasoline. Inasmuch as the lower xylenols mixture is a comparatively inexpensive source of substituted phenolic compounds, the partially nitrosated mixture is much less expensive than other successful inhibitors now in com- Table I Theoretical Actual ni- Efl'lciency nitrosation trosation of product Percent Percent Percent The inhibitor efliciencies of the partially nitrosated lower xylenols mixture noted in Table I were calculated from the percent of nitrosated substituted phenolic compounds in the mixture determined by analysis of this mixture, the percent of unreacted compounds in the mixture, and the total determined inhibitor efliciencies of these nitrosated and unreacted compounds as well as the partially nitrosated mixture considered as a single inhibitor. It will be readily apparent upon consideration of this table that optimum results are obtained with a mixture which has been nitrosated to the extent of approximately 40% "theoretical nitrosation.

The inhibitor efilciencies of the nitrosated substituted phenolic compounds in the mixture as well as the efliciency of the mixture itself in the foregoing table were determined by the so-called oxygen bomb test on a typical Mid-Continent cracked distillate as the standard of comparison. Samples of the untreated gasolines and of the same gasoline in which small quantities of the various antioxidant mixtures were incorporated were tested for their total induction period. The oxygen bomb test in each case was carried out by placing a 200 c. 0. sample of the gasoline to be tested in a suitable container and then placing the container in a pressure bomb. After sweeping the atmosphere within the sealed bomb with oxygen, the bomb was filled with oxygen at a pressure of lbs. per square inch. The bomb was then placed in a steam bath, heated to 212 F., and maintained at this temperature throughout the test period. The maximum pressure within the bomb was recorded when the temperature thereof reached 212 F. The end of the induction period, that is the point at which the gasoline begins to oxidize, is indicated by a definite and continued drop in the oxygen pressure within the bomb. By noting the time at which this maximum pressure was obtained and the time at which the first appreciable drop in pressure occurred while the contents of the bomb were maintained at 212 R, an induction period was observed which comprises a direct measure of the relative tendency of the various gasoline samples to oxidize during storage.

A small proportion of the novel antioxidant of my invention produces a marked inhibitory effect in gasolines having a tendency to oxidize. For example, the incorporation of 7.8 lbs. of a "lower xylenols" mixture nitrosated to the extent of substantially 40% theoretical nitrosation in about 1,000 barrels (of 42 gallons) of a gasoline having an induction period of 2.0 hours increased the induction period of this gasoline to 6.0 hours in the oxygen bomb tests. The effectiveness of this antioxidant, together with its ready solubility in gasoline, has the salient advantage of markedly inhibiting the oxidation of gasolines and also of dissolving in the gasoline without leaving an insoluble residue therein. The small quantity of this mixture which may be used with effective results has the further advantage of inhibiting oxidation without seriously affecting the colorof the gasoline and without imparting an objectionable odor to the gasoline by the incorporation therein of this novel inhibitor.

The high efficiency of the novel antioxidant of my invention has the further advantage of lowering the cost index of the inhibitor below that of the inhibitors now in commercial use. The cost indices of a lower xylenols mixture nitrosated to the extent of substantially 40% theoretical nitrosation, as compared with two of the most successful commercial oxidation inhibitors now being used, are shown in Table 11 together with the amount of each inhibitor which must be added to 1000 barrels (of 42 gallons) of a typical Mid-Continent gasoline to raise its induction period from 2.0 to 6.0 hours.

The cost index of each inhibitor recorded in Table II was obtained by dividing the cost per unit efficiency of any inhibitor by the cost per unit efllciency of commercial inhibitor "A when each of the inhibitors is used in the same sample of gasoline in such a quantity as to produce a fuel of the same storage stability. The relative cost indices are compared in this table by arbitrarily setting the cost index of commercial inhibitor A at 100. It should be noted in Table II that the cost index of the lower xylenols mixture nitrosated to the extent of substantially 40% theoretical nitrosation is only 47 as compared with 100 and 84 for the two commercial inhibitors. This low cost index is cogent evidence of the advantages to be gained by the use of the inhibitor of my invention.

The novel antioxidant of my invention may be readily incorporated in cracked and polymer gasolines merely by addition of the inhibitor to the gasoline. The relatively high solubility of the unreacted substituted phenolic compounds in the mixture in which the nitrosated compound is dissolved aids in the solution of the nitrosated compounds in the gasoline. For example, a mixture of the antioxidant with some of the gasoline to be treated may be added to a stream of the gasoline as the latter is pumped into a storage tank. In such a case, the rate of addition of the mixture to the stream may be reduced with particular advantage to a rate substantially below that which will give a saturated solution of the antioxidant in the stream before the stream reaches the storage tank. Alternatively, the mixture may be introduced slowly into the low pressure side of a circulating pump associated with the gasoline storage tank, or may be incorporated in the gasoline at the same time, for example, that tetra-ethyl-lead is added to the gasoline. The inhibitors, on the other hand, may be incorporated in the gasoline with advantage by dissolving the inhibitor in a suitable solvent inert with respect to any effect upon the gasoline or the inhibitor. These inert solvents may comprise aliphatic or cyclic alcohols such, for example, as methyl alcohol, ethyl alcohol, butyl alcohol, iso-propyl alcohol, or cyclohexanol. Thus, a concentrated solution of the inhibitor in an appropriate solvent may be prepared and added to the gasoline to be treated.

.As a further alternative, the inhibitor may be incorporated in the gasoline with advantage by dissolving the inhibitor in naphtha or other suitable solvent and subsequently adding the solution to the fuel to be stabilized. This naphtha solution of the partially nitrosated mixture may be obtained directly as the final product in the preparation of the partially nitrosated mixture wherein naphtha, or other suitable solvent, is used for extracting the partially nitrosated mixture from the aqueous reaction solution of the mixture. The solubility of the inhibitor of my invention appears to increase noticeably with an increase in the temperature of the naphtha in which the inhibitor is dissolved. Thus, a concentrated solution of the inhibitor may be readily obtained by dissolving a substantial quantity of the inhibitor in a heated naphtha, or by some equivalent means.

The quantity of the novel antioxidant of my invention which may be used with advantage should not be limited to the quantity used in the foregoing illustrations. The optimum amount of antioxidant which should be used in each case will vary with the characteristics of the gasoline to be treated and will be readily ascertainable by simple tests on the gasoline by one skilled in the art.

I claim:

1. The method of inhibiting the oxidation of gasoline which comprises incorporating in the gasoline an effective amount of a partially nitrosated mixture of substituted phenolic compounds comprising readily nitrosatable phenolic compounds and relatively diflicultly nitrosatable phenolic compounds in which mixture substantially only the readily nitrosatable phenolic compounds are substantially completely nitrosated.

.the range of 200 to 216 C. nitrosated to the extent of substantially 40% theoretical nitrosation of the nitrosatable compounds in the mixture. v

4. An improved motor fuel which comprises gasoline containing an effective amount of a partially nitrosated mixture of substituted phenolic compounds comprising readily nitrosatable phenolic compounds'and relatively difilcultly ultrosatable phenolic compounds in which mixture substantially only the readily nitrosatable phenolic compounds are substantially completely nitrosated.

5. An improved motor fuel which comprises 5 gasoline containing an effective amount of a mixture ofvsubstituted phenolic compounds nitrosated to the extent of between substantially. 25% to 40% theoretical nitrosation of the nitrosatable compounds in the mixture.

6. An improved motor fuel which comprises gasoline containing an efiective amount of a mixture of coal-tar acids boiling within the range of 200 to 216 C. nitrosated to the extent of substantially 40% theoretical nitrosation of 1 the nitrosatable compounds in the mixture.

7. An improved motor fuel which comprises gasoline containing an efiective amount of a mixture of coal-tar acids boiling within the range of 200 to 216 C. nitrosated to the extent an of substantially to theoretical nitrosation of the nitrosatable compounds in the mixture.

8. An oxidation inhibitor for gasoline whic comprises a partially nitrosated mixture of substituted phenolic compounds comprising readily nitrosatable phenolic compounds and relatively difllcultly nitrosatable phenolic compounds in which mixture substantially only the readily nitrosatable phenolic compounds are substantially completely nitrosated.

9. An oxidation inhibitor for gasoline which comprises a mixture of substituted phenolic compounds nitrosated to the extent of substantially 25% to 40% theoretical nitrosation of the nitrosatable compounds in the mixture.

10. An oxidation inhibitor for gasoline which comprises a mixture of coal-tar acids boiling within the range of 200 to 216 C. nitrosated to the extent of substantially 25% to 40% theo- 40 C. nitrosated to