US 2112735 A
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March 29, 1938. CLARK MINERAL OIL PRODUCT Filed May 19, 1934 V 0 45 T Y m A G D H N W Y r B w a w a A w m 0 A a 2 NIQQ: \Av 583 uh Fig. I.
by His Patented Mar. 29, 1938 MINERAL OIL PRODUCT Frank M. Clark, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application May 19, 1934, Serial No. 726,498
The present invention comprises improved mineral oil compositions.
Crude mineral oils and especially those of the .naphthenic type which are obtained from the Gulf coast and mid-continental petroleum fields contain a high percentage of both unsaturated aliphatic and unsaturated aromatic hydrocarbons.
The formation in mineral oil during use of insoluble gummy and resinous masses (commonly called sludge), and the instability of mineral oil when subjected to heat and exposed to air and light is to be ascribed to the presence in the oil of these unsaturated compounds. It has been the object of refining processes to remove unsaturated compounds as completely as possible.
Heretofore the general practice in the refining of mineral oils has involved initial treatment at high temperatures with concentrated (or fum-' ing) sulphuric acid or else with phosphoric acid. It has also been proposed to associatethe sul- 'phuric acid with boric acid.
Although these prior methods are of value in the treatment of certain types of oils, they all possess certain disadvantages. Mineral -oils treated in accordance with the previously proposed methods are apt to be either under-refined or over-refined and hence not well suited for use in an insulating or dielectric capacity. For example, under-refined oils contain unsaturatedaliphatic hydrocarbons, such as olefin compounds, which by oxidation and polymerization form sludge. When under-refined oil is used in transformers, any sludge which may be formed obstructs the circulation of the oil and reduces the desired cooling effect. A transformer in this condition is easily overheated and caused to fail. Over-refined oils on the other hand contain substantially no unsaturated compounds. Oils of this type, although not subject to sludge-formation, are easily oxidized on exposure to air and soluble products which are highly acidic and corrosive in nature are formed. When such oil isused in a transformer the acid products form permanent emulsions with the oil and water which may be present. Water may be formed by oxidation or may enter thetransformer during operation. Such emulsions hasten electrical breakdown. Under-refined oils and over-refined oils because of the formation of sludge and acid products respectively likewise have been found unsuited for other electrical application, for example, as cooling or dielectric media in cables and capacitors.
When crude oils are refined by treatment with concentrated sulphuric acid alone both aliphatic and aromatic unsaturated compounds are removed. As the sulphuric acid combines with the aliphatic and aromatic unsaturated bodies equally well, it is impossible to remove one type I of unsaturated compounds without also removing the other. Transformeroil in use today refined by the sulphuric acid process is a compromise oil. It contains both the sludge-formingand acid-producing compounds. Oils treated with phosphoric acid are subject to practically the same disadvantage. When the sulphuric acid is associated with boric acid the unsaturated aromatic component of the oil is less attacked but likewise the effect of the sulphuric acid on the aliphatic unsaturated components is reduced. As is well known, transformer and other oils used in an insulating and dielectric capacity commonly have a Saybolt universal viscosity at F. not over about 200 seconds, for example, between about 60 and seconds. In accordance with my present invention I have provided a mineral oil which is particularly well suited for electrical insulating and dielectric purposes containing less. than one per cent by volumaof olefinic (aliphatic) hydrocarbons and containing about 4 to 8 per cent by volume of residual unsaturated aromatic hydrocarbons.
In accordance with my invention an improvedoil product has been produced by the treatment of the crude oil with an acid mixture composed both of sulphuric acid and phosphoric acid. An acid mixture containing the proper amounts of sulphuric acid and phosphoric acid attacks the olefinic constituents preferentially, resulting in a product which contains the minimum of unsaturated olefinic compounds and the desired amount of aromatic unsaturated compounds.
The oil resulting from this treatment is stable,
and is. particularly adapted for insulating and dielectric purposes. It contains a smallamount not exceeding one per cent by volume of olefinic hydrocarbons and about 4 to 8 per cent byvolume of aromatic unsaturated hydrocarbons.
In Fig. 1 of the accompanying drawing, graphs are represented showing the relation of sludge formation when crude mineral oils were treated with varying amounts of difierent refining agents. In Fig. 2 are represented graphs showing the rate ofsludge accumulation in crude oil and in oil refined by various methods.
When in accordance with my invention the oil is treated witha mixture of sulphuric acid 1 and phosphoric acid, the procedure preferred is as follows: 5 pounds of an acid mixture comadded slowly with continuous agitation to 55 gallons of crude mineral oil. The rate 01' addition is such that the temperature will not rise higher thanabout 35? C. Preferably the temperature of the oil-acid mixture should be kept below 25 C. The oil-acid mixture is allowed to stand until 3 The super-.
the resulting sludge'is settled out. natant refined oil is separated, washed with water or with a weak alkaline solution in order to neutralize any free acids left in the oil. A 3 per cent sodium hydroxide solution is preferred for the alkaline wash. Weaker or stronger solutions may be used although the alkaline solution should not be higher than per cent in concentration. The refined oil is dehydrated and then may be subjected to a fullers earth treatment, although the latter treatment is not indispensible.
The oil treated by a properly balanced refining acid mixture as above described is extremely stable and is neither under-refined nor over-refined. An oil which is especially, suited for insulating application shows an aliphatic (olefinic) unsaturation of less than 1 per cent and a much larger amount of aromatic unsaturation, ranging from '4 to 8 per cent. I
The unsaturated aromatic compounds stabilize the oil against oxidation and sludge formation, reduce to a minimum the soluble acidic products of oxidation, and stabilize the oil against ionization eifects when subjected to electric stress which is capable of causing a splitting oil of .hydrogen and the polymerization of the hydrocarbon residue with the formation of insoluble waxy materials. I r
In Figure 1 of the drawing, graph A represents characteristics of oil treated with sulphuric acid, graph B represents characteristics of oil treated with the sulphuric acid-boric acid mixture and graph C represents characteristics of oil treated with the sulphuric acid-phosphoric acid mixture in accordance with, my invention. The percentage of sludge by weight accumulated on the 35th day was determined and plotted as ordinates,
I the amount of refining agent being plotted as abscissae. As shown by graph A increased amounts of sulphuric ,acid produced oil having correspondingly lower sludging characteristics. The best results for the sulphuric acid-,boric acid mixture (graph B) were obtained when lbs. of the acid inixture (containing 2.7% boric acid) were used with 55 gallons of crude oil. As shown by the graph C oil refined by treatment with the sulphuric acid-phosphoric, acid mixture (containing phosphoric acid) resulted in an oil having lower sludging characteristics than oil refined by either of the other two methods. The best results as shown by this graph wereobtained using 5 lbs. of the mixture of sulphuric and phosphoric acids per 55 gallons of crude oil but, as shown in Fig. 1, effective results are also obtained when the oil is treated with the sulphuric-phosphoric acids mixture in the ratio of about 4 to 15 lbs. of said mixture per 55 gallons of crude oil.
Fig. 2 represents by different graphs the percentage of sludge byweight formed during a given time with different refining agents using an optimum amount as indicated in Fig. 1. Graph D represents the sludging charactertistics of, crude oil, graph E represents thatmf oil purified by sulphuric acid (15 lbs. sulphuric acid per 55 gallons of oil) graph F representsfthat of oil purified by a sulphuric acid-boric acid mixture (10 lbs. .acid mixture containing 2.7% boric acid per 55 gallons of oil), and graph G represents the sluding characteristics of oilpurified by a sulphuric acidphosphoric acid mixture (5 lbs. acid mixture containing 15% phosphoric acid per 55 gallons of oil). Crude oil refined by the sulphuric acid-phosphoric acid mixture exhibits superior non-sludging charactertistics although smaller amounts of the refining agent were employed.
The following method was used to determine the sludging characteristics of the various oils represented in the graphs of Figs. 1 and 2. 55 cc; of the oil was placed in a Pyrex test tube containing a copper spiral and heated in an oven at 110 C. The test tubes were removed at definite intervals, the oxidized oil was diluted with an equal amount of naphtha and then was centrifuged.
determined gravimetrically and expressed in per cent by weight of the original oil. As shown in graph G (Fig. 2), oil prepared in accordance with the present invention forms less than five-tenths per cent by weight of sludge when heated for 55 days in the presence of metallic copper as hereinbefore described- 7 By the term "crude mineral oil as used herein '1 mean a non-refined or a semi -refined'oil stock which, when treated as herein described, is adapted for use in an electrical-insulating or dielectric capacity.
Although I have described my invention settingforth the purification and refinement of crude mineral oils in general using specific proportions of my acid mixture, it will be understood by those skilled in the art that some types of crude oils may require modifications in the acid ratio. All modifications of my'product coming within the true spirit and scope of my invention are meant to be covered in the appended claims..
In a divisional application Serial No. 6,189, filed Feb. 12, 1935, I have covered the method feature of the present invention.
What I claim as new and desire to secure by Letters Patent of the United States is:
1. Mineral oil containing a small amount not exceeding one per centv of unsaturated aliphatic hydrocarbons and from about four to eight perbyvolume a small amount not exceeding one per cent of olefinic hydrocarbons and from about 4 to 8 per cent-of residual unsaturated aromatic hydrocarbons, said oil being characterized by greater stability under oxidizing and sludgeforming conditions than mineral oil containing more than one per cent of olefinic hydrocarbons and outside the range of from' about 4 to 8 per cent 01' unsaturated aromatic hydrocarbons.
I mam: M. CLARK.'