US2951751A - Hydrocarbon oils having improved electrical properties - Google Patents

Description

Patented Sept. 6, 1960 HYDROCARBON OILS HAVING IMPROVED ELECTRICAL PROPERTIES John P. McDermott, Springfield, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed 'July 30, 1958, Ser. No. 751,848 9 Claims. (Cl. 52-45) The present invention relates to hydrocarbon oils havmg improved electrical properties and more particularly relates to petroleum products such as turbo-jet engine fuels, naphthas, gasolines, kerosenes, heating oils, solvents and similar liquid hydrocarbons boiling in the range between about 75 F. and about 750 F. to which have been added certain tetraalkyl ammonium salts of hydroxy carboxylic acids which greatly reduce the tendency of such oils to generate and accumulate electrical charges which can liberate suflicient energy to ignite the hydrocarbon vapors in air during handling and storage.

Considerable attention has been focused in recent years upon the electric properties of hydrocarbon oils as a result of explosions which have occurred during the handling of such oils. It has been established that these explosions have probably been due to tribo-electric discharges. Although most such explosions have taken place while turbo-jet aircraft fuels were being transferred from one tank to another, there have been instances of explosions occurring during the handling of gasolines, kerosenes, solvents and other hydrocarbon products boiling between about 75 and about 750 F. when the ambient temperatures were slightly above-the flash points of the products. Turbo-jet engine fuels are particularly hazardous because their volatility is such that their vapors form explosive mixtures with air over a relatively Wide temperature range.

The mechanisms involved in explosions of hydrocarbon oils attributed to tribo-electricity are not fully understood; but it is believed that ionic contaminants present in the hydrocarbons in very small concentrations play an important role. Studies have shown that electricity is rapidly generated when hydrocarbons containing small amounts of materials capable of undergoing charge separation flow past a solid or liquid interface. Electrical potentials of several thousand volts can readily be built up in this manner. When such a potential reaches a sufficiently high level, electrical energy is discharged and may ignite hydrocarbon vapors present in admixture with air to cause an explosion. This is, of course, only one explanation of the phenomenon and there may be other mechanisms involved.

The contaminants in hydrocarbons which undergo charge separation as described above influence the conductivity of the hydrocarbon stream. When the con-.

centration of materials capable of undergoing charge separation in the hydrocarbons is low, conductivity is low. As the concentration of materials capable of undergoing charge separation increases, conductivity also increases. Since increased conductivity tends to permit .and accumulate electrical charges to a dangerous degree.

It has been suggested in the past that the danger of explosions of hydrocarbons could be abated by adding .to the hydrocarbons certain polyvalent metal soaps,

magnesium oleate and related metallic compounds, for example, which would increase the specific conductivity of the hydrocarbons to a value greater than about 1X10 mho/cm. Mixtures of such compounds have been said to be particularly effective. Although such additives do markedly increase the conductivity of hydrocarbons, it has been found that their usefulness is generally limited to a very narrow concentration range. If the concentration of such an additive in an oil is inadvertently reduced, there may be greater danger of an explosion than if no additive were present at all. For this reason, the additives suggested for use heretofore have generally proved inadequate.

The present invention provides a new and improved class of additives for use in hydrocarbon oils boiling in the range between about F. and about 750 F. that afiords substantially greater protection against explosions due to tribe-electric discharges than compounds of the prior art. In accordance with the invention, it has been found that certain tetraalkyl ammonium salts of hydroxy carboxylic acids are surprisingly eifective for this purpose when added to turbo-jet engine fuels, gasolines, kerosenes, heating oils, solvents and similar hydrocarbon oil products. The additives of the invention markedly increase the specific conductivity of such products and furthermore, as shown hereinafter, decrease the amperage of streaming current and the number of high voltage discharges which occur while the products are being pumped, even when the additives are present in only extremely low concentrations. The additives employed in accordance with the invention are tet-raalkyl ammonium salts of hydroxy carboxylic acids containing from 2 to 10 carbon atoms per molecule. Examples of such hydroxy carboxylic acids which may be employed in preparing the additives of the invention include glycolic acid, lactic acid, hydracrylic acid, 3-hydroxybutyric acid, 2-hydroxybutyric acid, l-hydroxybutyric acid, glyceric acid, erythric acid, arabitic acid, mannitic acid, gluconic acid, galacturonic acid, tartronic acid, malic acid, tartaric acid, trihydroxyglutaric acid, saccharic acid, citric acid, mandelic acid, phenyl-lactic acid, tropic acid and gallic acid. The additives thus include tetraalkyl ammonium salts of both aliphatic and cyclic carboxylic acids containing from 2 to 10 carbon atoms per molecule. The acids must contain at least one hydroxy group as well as one carboxyl group. They may, however, contain up to 5 hydroxyl groups and up to 4 carboxyl groups. Salts of the aliphatic hydroxy carboxylic acids containing from 2 to 6 carbon atoms per molecule are preferred. Tetraalkyl ammonium salts of malic acid and gluconic acid, wherein one hydroxyl group and one carboxyl group are attached to a carbon atom in common, have been found preferred.

The tetraalkyl ammonium salts of the acids set forth in the preceding paragraph may readily be prepared by treating a quaternary ammonium hydroxide with the desired hydroxy carboxylic acid and then removing the water formed by means of an azeotropic distillation employing a solvent such as benzene or toluene. Suitable tetraalkyl ammonium hydroxides for use in this reaction are those having alkyl groups of from 1 to 24 carbon atoms in length. Examples of such quaternary ammonium hydroxides include tetrapropyl ammonium hydroxide, ethyl tributyl ammonium hydroxide, butyltrihexyl ammonium hydroxide, dimethyl dihexadecyl ammonium hydroxide, tetraheptadecyl ammonium hydroxide and the like. Quaternary ammonium hydroxides prepared from naturally occurring materials such as coconut oil, tallow fat and soy bean oil are widely available on the commercial market and are preferred. A typical mixture of such commercial quaternary ammonium hydroxides is trimethyl soya ammonium hydroxide. The soya group is derived from soy bean oil and is composed of 8% C 91% C and 1% C alkyl chains. Similar mixtures 'are derived from Lorol alcohols, which are mixtures of primary alcohols containing from 10 to 18 carbon atoms prepared by the hydrogenation of coconut oil. Such mixtures are described in US. Patent No. 2,560,588. Quaternary ammonium hydroxides having 1 or more such mixed alkyl groups may be employed.

The tetraalkyl ammonium salts of hydroxy carboxylic acids described above are, in accordance with the invention, incorporated into hydrocarbon oils boiling in the range between 75 F. and about 750 F. in concentrations ranging from about 0.00005% to about 0.5% by weight. Concentrations between about 0.0025 and about 0.05% are generally effective and are preferred.

The hydrocarbon oils in which the additive of the invention may be employed are those boiling between about 75 and about 750 F., particularly petroleum distillate fuels boiling in that range. Such fuels include gasolines, aviation turbo-jet fuels, kerosenes, diesel fuels and heating oils. Gasolines as referred to herein are mixtures of volatile hydrocarbons boiling between about 75 F. and about 450 F. as determined by ASTM D-8656 and are defined by ASTM Specifications D9l0-56 and D439-56T. Such gasolines may contain various beneficial additives such as anti-knock agents, scavenging agents, antioxidants, dyes, anti-icing agents and solvent oils in total additive concentrations up to about by weight. Aviation turbo-jet fuels comprise mixtures of volatile hydrocarbons boiling in the range between about 100 F. and about 600 F. and are defined by US. Military Specifications MIL-F-5616, MIL-F- 5624C, MlLF25524A, and MIL-F-25558A. Diesel fuels as referred to in connection with the invention in general boil. between 250 F. and 750 F. and are covered by ASTM Specification D97553T. Heating oils as the term is used herein include both kerosenes and burner fuels falling within grades 1 and 2 of ASTM Specification D39648T. As pointed out heretofore, the additives of the invention are particularly effective in turbo-jet aviation fuels. They may, however, also be employed in solvents, naphthas, transformer oils and other hydrocarbon oils boiling between about 75 F. and about 750 F.

The exact nature and objects of the invention may be fully understood by referring to the following examples.

EXAMPLE 1 In order to determine the effectiveness of the addition agents of the invention, the specific conductivities of samples of a turbo-jet aviation fuel containing various amounts of the additives were determined. The fuel employed was representative of the W4 fuels defined by US. .Military Specification MIL-F-5624C and had an API gravity of 48.7, a Reid vapor pressure of 2.5

4 lbs/sq. in. and a to 520 F. boiling range. Specific conductivities were measured by applying a fixed direct current voltage to a Balsbough type 2TN50 conductivity cell containing the sample. The cell was connected in series with an accurate standard high resistance. Current flowing in the circuit was determined by measuring the voltage across the standard resistance with a Keithley electrometer and applying Ohms law. Knowing the voltage drop across the conductivity cell and the current flowing in the circuit, the resistance of the sample was calculated. This resistance,'multiplied by the cell constant, gave the specific resistance. The specific conductivity is the reciprocal of the specific resistance and has the dimensions, mho/cm. The specific conductivity values thus obtained are shown in the following table.

Table l SPECIFIC CONDUCTIVITIES 0F FUELS CONTAINING QUATERNARY AMMONIUM SALTS OF HYDROXY OAR- BOXYLIC ACIDS Specific Fuel Conductivity mho/cm.

1 .l'P-4+No additive 6X10- 2 JP4+0.01 wt. percent Mono-(Trlmethylsoyaammonium) malate 1.0)(10- 3 JP4+0.01 wt. percent Di-(Trimethylsoyaammonium) malate 1.9)(10' 4 JP4+0.01 wt. percent Trimethylsoyaammomum glycolate LOXIO- 6 JP4+0.01 wt. percent Mono-(Trimethylsoyaammonium) tartrate 2. 4X10- 6 JP-4+0.01 wt. percent Trimethyls lactate 1. 5X10'" 7 JP-4-l-0.01 wt. percent Dimeth nium gallate 2.2X10" 8 J'P4+0.01 wt. percent Trimethylsoyaammoninm g8 ate 1.6)(10' 9 IPA-+0.01 wt. percent Mono-(Trtmeth lsoyaammonium) citra 1. 4X10- 10 JP4+0.005 wt. percent Dimethy monium gluconate 1. 4X10-" 11 IPA-+0.01 wt. percent Trimethylsoyaammoninm gluconate 3.0X10- 12 JP1+0.05 wt. percent Trimethylsoyaammonium gluconate 1.7X10' 13-.- JP-4+0.01 wt. percent Dimethyldisoyaammonium gluconate 3.1)(10 QUATERNARY AMMONIUM SLATS OF STRAIGHT CARBOXYLIO ACIDS 14 JP4+0.01 wt. percent Di-(Dimethyldisoyaammonium) sebacate B.4 10-" 15 J P4+0.0l wt. percent Trimethylsoyaammom'um caproate v4.3)(10- From the above table it can be seen that the additives of the invention increased the specific conductivity of the turbo-jet aviation fuel from the initial value of Samples of a turbo-jet aviation fuel of the JP-4 type to which had been added quaternary ammonium salts of hydroxy carboxylic acids were subjected to a labo ratory pumping test designed to demonstrate the effectiveness of the additives in decreasing electrical discharges when the fuel was pumped over a solid having a large surface area. The test was carried out by pumping the liquid through a glass tube containing glass wool as a charge separating surface and measuring during a ten-minute interval the number of discharges across a calibrated spark gap connected between the glass wool and ground. The liquid was pumped from a reservoir through a rotameter and then passed downwardly through a one inch internal diameter glass pipe 15 inches 55 long, after which it was returned to the reservoir. The glass pipe contained 3 grams of Corning Pyrex Filtering Fiber glass wool which was wound around a removable rack. The rack was made of glass rods and had cross pieces to support the glass wool. The pump was an Eastern Industries Centrifugal pump Model B-1 and the rotarneter Was a Brooks Tru Taper, #615-2. The equipment Was joined with mm. internal diameter glass tubing having ball joints to facilitate dismantling. Half-inch Lucite was used for the base and for the bracket which supported the glass pipe. A tungsten probe was passed through the glass pipe to make contact with the lower portion of the glass wool. The probe was connected to an adjustable spark gap, the other side of the gap being grounded. The gap was adjusted to 0.064 so that it would spark at 7,000 volts. Sparks across the gap were detected by noting deflections of the pointer of a Keithley Model 200 electrometer fitted with a Keithley Model 2005 detector, the latter placed so that it pointed at the insulated side of the spark gap. The entire apparatus was enclosed in a humidity cabinet constructed of Lucite.

Before each test, the unit was taken apart, washed with chloroform, dried with nitrogen and reassembled with a fresh hat of glass wool wound on the glass rack. Lucite parts were cleaned by washing with ethanol. A 500 cc. sample of the fuel to be tested was placed in the reservoir, the relative humidity in the cabinet was adjusted to a value between and at 70 F. by a stream of nitrogen, the pump motor was adjusted by means of a Variac to give a flow rate of 1500 cc. per minute as measured by the rotameter and the number of 7000 kilovolt sparks produced during 10 minutes of pumping was recorded. The data obtained in this manner, together with specific conductivity data obtained as described in Example 1, are set forth in Table II.

Table II EFFECTIVENESS OF ADDITIVES FOR REDUCING -ELEO- gglgll AL DISCHARGES IN THE LABORATORY PUMPING No. of 7 kv. Specific Con- Fuel Discharges/ duetivity .TP-4 32 1. 2X10- .TP-4+0.005% Dimethyldisoyaarnmonium Gluconate 0 1. 3X10- .TP4+0.01% Dimethyldiso aarnmoniurn Gallate 0 1. 6 10- EXAMPLE 3 In order to aiford a comparison between the eifectiveness of the additives of the invention and additives proposed in the past for reducing the accumulation and discharge of electricity in hydrocarbons, streaming cur-rent tests were carried out on samples of a fuel containing varying amounts of trimethylsoyaammonium malate and samples of the same fuel containing a mixture of 61 parts of chromium dioctyl salicylate and 39 parts of calcium dioctyl sulfosuccinate. These tests were similar to the test described in the preceding example except that the equipment was modified by substituting a stainless steel pipe for the glass pipe previously used to hold the glass wool filter. This pipe was insulated from the 6 receiving tank and was grounded. Streaming currents were measured with a Keithley micro-microammeter connected between the tank and ground. Data as to the specific conductivity and number of 7 kilovolt discharges during a 10 minute interval as described in Examples 1 and 2 were also obtained. The results of these tests are shown in Table III.

Table III COMPARISON OF THE EFFECTIVENESS OF ADDITIVES OF THE INVENTION AND PRIOR ART ADDITIVES 1 Additive A-Mixtnre of 61 parts of chromium dioctyl salicylate and 39 parts of calcium dioctyl suliosuccinate.

2 Additive BDimethyldisoyaammonium malate.

The data set forth in Table III above show that the additive of the invention, the trimethylsoyaammonium malate, while less potent for increasing specific conductivity than the additive of the prior art was much more potent for decreasing the streaming current and the number of high-voltage discharges, even when it was used in extremely low concentrations. It is evident that the decreasing of flow of current and of high voltage discharges under conditions of pumping is more indicative of practical utility of the additives than an increase in conductivity measured under stationary conditions in a cell.

EXAMPLE 4 Further tests were carried out to determine the comparative effectiveness of the additives of the invention and other additives by pumping heating oil samples containing the various additives through a glass wool filter and a plastic pipe into the open top of a tank. The heating oil employed had a 32 API gravity and a 347 to 660 F. boiling range. Analyses showed that this heating oil contained traces of asphaltic impurities.

The apparatus employed in the test comprised a 13 gallon tank to which the heating oil was pumped at a rate of 3 gallons per minute through the glass wool filter and a /2" diameter polyethylene pipe. The tank wall was grounded. It was found that when this heating oil containing traces of asphaltic impurities was pumped through the filter and pipe into the tank, a streaming current of 3X10 amperes was generated. The streaming potential was 9000 volts per inch 3 inches from the glass Wool and the potential between the tank and ground, when the tank was not grounded, built up to 40,000 volts. Brilliant discharges 8 to 10 inches in length occurred repeatedly in the polyethylene pipe when a grounded probe was contacted with the pipe. These localized discharges may constitute a pronounced hazard in the handling of fuels, solvents and similar hydrocarbon oils.

Similar tests were then carried out using samples of the heating oil containing trimethylsoyaammonium gluconate, di-(trimethylsoyaammonium) malate, which are additives in accordance with the present invention, and those other additives which have been proposed by the prior art, namely calcium sulfonate, commercial additive D, and a mixture of these last two. The localized discharges obtained with samples of the heating oil containing each of these additives during a 10 minute period were measured. The results obtained are shown in Table IV.

7 Table IV LOCALIZED DISCHARGES WITH ADDITIVE BLENDS IN HEATING OIL Localized Discharges/10 Minute Period Di-(trimethylsoya ammonnium) Malate Calcium Sulfonate Mixed with Oommercial Additive Additive, Wt

percent Trimethylsoyaamm onium Gluconate Commercial Additive Calcium Sulfonate The data set forth in Table IV demonstrate that the trimethylsoyaammonium gluconate and the di-(trimethylsoyaammonium) malate, quaternary ammonium salts of hydroxy carboxylic acids are much more effective for reducing localized discharges than the calcium sulfonate, the Commercial Additive D or the mixture of the calcium sulfonate and the Commercial Additive D. No localized discharges at all occurred with the samples containing the malate in concentrations greater than 0.0005 wt. percent. The gluconate was slightly less effective than the malate but was much better than the sulfonate and the Commercial Additive D alone or in combination.

It will be understood that the additives of the present invention may be incorporated into fuels, solvents and other hydrocarbon oils boiling in the range between about 75 F. and 750 F. in conjunction with other additives intended to improve other properties of such oils. Such other additives include, for example, stabilizing agents, haze inhibitors, dyes, dye stabilizers, rust inhibitors and the like.

What is claimed is: p

1. A hydrocarbon oil boiling in the range between about F. and about 750 F. having incorporated. therein from about 0.00005 to about 0.5% by weight of a tetraalkyl ammonium salt of a C to C unsubsti-' tuted hydroxy carboxylic acid, the alkyl groups of said salt each containing from 1 to about 24 carbon atoms.

2. An oil as defined by claim 1 wherein said salt is a tetraalkyl ammonium salt of a C to C aliphatic hydroxy carboxylic acid.

3. An oil as defined by claim 1 wherein said salt is present in a concentration of from about 0.0025% to about 0.05% by weight. a

4. A liquid hydrocarbon fuel boiling in the range between about 75 F. and about 750 F. to which has been added from about 0.0025% to about 0.05% by weight of a tetraalkyl ammonium salt of a C to C unsubstituted aliphatic hydroxy carboxylic acid, the alkyl groups of said salt each containing from 1 to about 24 carbon atoms.

5. A fuel as defined by claim 4 wherein said salt is a References Cited in the file of this patent UNITED STATES PATENTS 2,113,606 Taub et a1. Apr. 12, 1938 2,288,413 Morgan June 30, 1942 2,295,773 Chenicek Sept. 15, 1942

Claims (1)

1. A HYDROCARBON-OIL BOILING IN THE RANGE BETWEEN ABOUT 75*F. AND ABOUT 750*F. HAVING INCORPORATED THEREIN FROM ABOUT 0.00005% TO ABOUT 0.5% BY WEIGHT OF A TETRAALKYL AMMONIUM SALT OF A C2 TO C10 UNSUBSTITUTED HYDROXY CARBOXYLIC ACID, THE ALKYL GROUPS OF SAID SALT EACH CONTAINING FROM 1 TO ABOUT 24 CARBON ATOMS.