Abstract:
Novel insulating oil compositions comprising a major amount of an insulating oil and a minor amount of a diarylalkane.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to novel insulating oil compositions comprising a major amount of an insulating oil and a minor amount of a diarylalkane. 
     2. Description of the Prior Art 
     Insulating oils, for example, transformer oils, are required to have low power factors and high dielectric strengths, and to be able to maintain thermal and oxidative stability toward degradation and oxidation and to possess minimum tendency toward the formation of gas while in use. See, for example, U.S. Pat. No. 3,549,537 to Brewster et al. Insulating oils composed largely of naphthenes and/or highly-branched, non-cyclic, paraffins can be used satisfactorily as transformer oils, for example, but unfortunately, they possess the tendency to produce gas during service. 
     SUMMARY OF THE INVENTION 
     We have found that the gassing characteristics of insulating oils composed largely of naphthenes and/or highly-branched, noncyclic paraffins can be greatly decreased by the addition thereto of a selected amount of specific diarylalkanes. 
     BRIEF DESCRIPTION OF NOVEL INSULATING OIL COMPOSITIONS 
     The insulating oils used herein can be obtained from any naphthenic and/or paraffinic origin. By &#34;naphthenic and/or paraffinic oils&#34; we mean to include naturally-derived, or synthetic, stocks containing largely one-ring structures, such as cyclopentane and cyclohexane derivatives, two-ring structures, such as decalin and dicyclohexyl derivatives, three-, four-, and five-membered ring structures, which may be part of the same or different molecule and their mixtures, etc. The paraffinic oils are defined as being largely of highly-branched, non-cyclic, compounds. A more useful conventional definition is that developed by E. C. Lane and E. L. Garton in the &#34;Bureau of Mines Report of Investigations No. 3279&#34;, September, 1935, and reported in &#34;Petroleum Refining Processes&#34; by M. M. Stephens and O. F. Spencer, 4th Edition, The Pennsylvania State University Press, University Park, Pa., 1958, page 38, in which classification is based on the gravity of the first two distillation cuts. Typical naphthenic crudes include those from Huntingdon Beach, San Joaquin, Coastal B-1, etc. Typical paraffinic crudes are the Poza Rica, Kuwait, Grand Bay/Quarantine Bay, Ordovician Crudes, etc. In addition these oils can be synthetic oils, such as those obtained as the result of the oligomerization of 1-olefins having from six to 14 carbon atoms, preferably from eight to 12 carbon atoms, such as 1-decene, mixtures of 1-decene and 1-octene, 1-dodecene, etc., as described, for example, in U.S. Pat. No. 4,045,507 to Cupples et al. Mixtures of naphthenic and paraffinic oils, including mixtures of natural and synthetic oils, can also be used, for example, in weight ratios of about 99:1 to about 1:99, preferably about 90:10 to about 10:90. In general the insulating oil used herein can be defined in accordance with the parameters set forth in Table I. 
     
                       TABLE I______________________________________                    Preferred          Broad Range                    Range______________________________________Specific Gravity, 60°/60° F.            0.75 to 0.91                        0.79 to 0.91(15.5°/15.5° C.)Viscosity, SUS:s (ASTM D-2161)(100° F. or 37.8° C.)            40 to 70    50 to 70(210° F. or 98.9° C.)              30 to 36.5                          32 to 36.5Viscosity, Kin: cSt(100° F. or 37.8° C.)             4 to 13     6 to 13(210° F. or 98.9° C.)            1.5 to 3.1    2 to 3.1Pour Point, (ASTM D-97)°F.       -120 to -40 -100 to -40°C.       -80 to -40  -73 to -40Flash Point, (ASTM D-92)°F.       293 to 500  293 to 400°C.       140 to 260  140 to 204Weight Percent TotalParaffin* Content             80 to 100   90 to 100Weight Percent AromaticContent           0 to 20     0 to 10Interfacial Tension, mN/m,(ASTM D-971)     40 to 80    40 to 60______________________________________ Highly-branched, noncyclic paraffins, highlybranched cyclic paraffins and/or their mixtures. 
    
     The diarylalkane that is added to the above insulating oils to reduce their gassing tendencies of such insulating oils can be defined by reference to the following structural formula: ##STR1## wherein R 1  can be hydrogen or an alkyl group having from one to 12 carbon atoms, preferably from one to eight carbon atoms, such as methyl, ethyl, propyl, n-heptyl, dodecyl, etc.; R 2  and R 3 , the same or different, can be an alkyl group having from one to six carbon atoms, preferably from one to three carbon atoms, such as methyl, ethyl, propyl, n-hexyl, etc.; and n is an integer, the same or different, from 0 to 5, preferably 1 to 2. Examples of diarylalkanes that can be used are di(4-methylphenyl) methane, 4-methylphenyl-2-methylphenyl methane, 1,1-di(4-methylphenyl)ethane, 1,1-di(3,4-dimethylphenyl)ethane, 1,1-di(3,4-dimethylpheny)heptane, 1,1-di(3,4-dimethylphenyl)decane, 1-(4-methylphenyl)-1-(phenyl)hexane, 1-(3,4-diethylphenyl)-1-(4-methylphenyl)ethane, 1,1-di(3,4-diethylphenyl)ethane, etc. Preferred diarylalkanes are the 1,1-diarylalkanes, 1,1-di(4-methylphenyl)ethane and 1,1-di (3,4-dimethylphenyl)ethane. The above diarylalkanes can be used alone or as mixtures. Additionally, a hydrocarbon stream containing one or more of the diarylalkanes identified above can also be added to insulating oils to obtain the desired beneficial results. 
     The amounts of diarylalkane added to the insulating oil to inhibit the gassing tendency thereof can be varied over a wide limit, but, in general, the amount present, based on the weight of the final insulating composition, will be in the range of about five to about 20 weight percent, preferably about five to about 15 weight percent. Since the insulating oil and the diarylalkane are both hydrocarbons and therefore completely miscible one in the other, mixing of the two at ambient temperature and ambient pressure until a homogeneous solution is obtained will suffice. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following Table II compares the properties of the naphthenic base oil employed herein with the ASTM D-3487 insulating oil specifications for Type I Oil. The naturally-derived base oil (naphthenic) was obtained from Interprovincial Pipeline No. 1 and was a mixture of low sulfur, low pour point crudes. After conventional distillation, the fraction consisting of a 50:50 mixture of light vacuum and heavy vacuum oils (Gravity °API 25) was subjected to hydrotreating following the conditions in U.S. Pat. No. 3,764,518. The purpose of this treatment was to upgrade the product through hydrocracking, isomerization and saturation. After the first stage hydrotreatment, the product was then subjected to a second stage hydrotreatment following the conditions in Canadian Pat. No. 978,881, wherein the primary purpose of such treatment is to saturate aromatic structures with hydrogen. The product from the two stage hydrotreatment has the properties shown in Table II. The synthetic base oil was prepared in accordance with the procedure of Example 1 of U.S. Pat. No. 4,045,507 of Cupples et al, employing 1-decene as feedstock. The product from this oligomerization, after stripping off unreacted 1-decene, indicated 53 percent conversion, and was found to contain 24 weight percent dimer, the remainder being the trimer, tetramer and pentamer of 1-decene. The total product was then passed over a commercial nickel catalyst (NiO104T, 1/8-inch pellets having a surface area of 125 square meters per gram) at 165° C. and 600 pounds per square inch guage (41 kilograms per square centimeter) of hydrogen pressure at a rate sufficient of effect stabilization of the product through hydrogenation. Distillation under vacuum afforded the synthetic base oil used herein, a dimer fraction boiling in the temperature range of 160°-168° C. at five millimeters of mercury. 
     
                                           TABLE II__________________________________________________________________________                           ASTM D-3487,       Naturally-derived                 Synthetic Insulating OilDescription Base Oil (Naph-                 Base Oil  Specificationsor Test     thenic)   (Paraffinic)                           Type I Oil__________________________________________________________________________Gravity: °API(ASTM D-1298)       34        46.5        --Specific Gravity,(ASTM-D941)60°/60° F.(15.5°/15.5° C.)       0.8550    0.7949    max 0.91Viscosity, SUV: s(ASTM D-2161)37.8° C. (100° F.)       59.5      42.6      max 7098.9° C. (210° F.)       34.7      31.6      max 36.5Viscosity, Kin: cSt37.8° C. (100° F.)       10.17     5.06      max 13.098.9° C. (210° F.)       2.55      1.65      max 3.1Interfacial Tension:mN/M (ASTM D-971)       55        50        min 40Flash, COC: °F. (°C.)(ASTM D-92) 350 (177) 315 (157) min 293 (145)Fire, COC: °F. (°C.)(ASTM D-92) 370 (188) 345 (174)   --Pour Point: °F. (°C.)(ASTM D-97) -55(-48)  below -100 (-73)                           max -40 (-40)Appearance (Visual)       bright    water white                           clear &amp; brightColor, (ASTM D-1500)       L 0.5     L 0.5     max 0.5Corrosive Sulfur,(ASTM D-1275)       Non-corrosive                 Non-corrosive                           Non-corrosiveWater PPM(ASTM D-1315)       24        15        max 35NeutralizationNo., (ASTM D-974)Total Acid No.       &lt;0.03     &lt;0.03     max 0.03Aniline Point,(ASTM D-611):°F. (°C.)       204 (95)  215 (102) 145-172 (63-78)Power Factor,(ASTM D-924):Percent25° C. (77° F.)       0.002     0.002     max 0.05100° C. (212° F.)       0.065     0.05      max 0.30Dielectric Strength:Kv (ASTM D-877)       47        46        min 30Oxidation Test,(ASTM D-2440)(0.075 PercentDBPC*)72 HourSludge: Percent       0.008     0.001     max 0.15Total Acid No.       0.10      0.06      max 0.5164 HourSludge: Percent       0.009     0.003     max 0.3Total Acid No.       0.10      0.10      max 0.6Rotary Bomb Oxida-tion:Min (0.075 PercentDBPC)(ASTM D-2112), 140° C.       125       480+        --Analysis, Weight Per-centAromatics   0.4       0.0Saturates   99.6      100 Percent                 Branched                 IsoparaffinsMass Spec Analysis,Weight Percent       Alkanes              24.0                 Average Mol.                 Weight = 280       1-Ring       Cycloalkanes              27.3       2-Ring       Cycloalkanes              18.7       3-Ring       Cycloalkanes              13.7       4-Ring       Cycloalkanes              12.0       5-Ring       Cycloalkanes               4.2       Aromatics               0.1Gassing Tendency;(ASTM D-2300),mm.sup.3 /minProcedure B,80° C.50 Minutes UsingHydrogen asSaturant Gas       +38.5     +32.0       --__________________________________________________________________________ *2,6-ditertiarybutyl-p-cresol 
    
     Three blends were prepared for testing, one containing 11 weight percent, based on the final product, of 1,1-di(3,4-di- methylphenyl)ethane (DXE) [Blend No. 1], the second containing 13 weight percent, based on the final product, of DXE [Blend No. 2], and the third containing 121/2 weight percent, based on the final product of DXE [Blend No. 3]. The remainder in each blend was naphthenic-base oil in Table II. The incorporation of DXE in the naphthenic-base oil was easily effected by physical blending. The results obtained are tabulated below in Table III. 
     
                       TABLE III______________________________________Description       Blend   Blend   Blendor Test           No. 1   No. 2   No. 3______________________________________Gravity: °API (ASTM D-1298)                             31.5Specific Gravity, 60°/60° F.(15.5°/15.5° C.)(ASTM D-941)                      0.8681Viscosity, SUV: s(ASTM D-2161)37.8° C. (100° F.)  58.498.9° C. (210° F.)  34.5Viscosity, Kin: cSt37.8° C. (100° F.)  9.8598.9° C. (210° F.)  2.50Flash, COC: °F. (°C.)(ASTM D-92)                       325 (163)Fire, COC: °F. (°C.)(ASTM D-92)                       370 (188)Pour Point: °F. (°C.)                             below(ASTM D-97)                       -65 (-54)Appearance (Visual)               brightCorrosive Sulfur                  Non-(ASTM D-1275)                     corrosiveWater: ppm (ASTM D-1315)          48Neutralization No.(ASTM D-974)Total Acid No.                    &lt;0.03Aniline Point(ASTM D-611)°F. (°C.)           182 (83.5)Power Factor (ASTM D-924):Percent25° C. (77° F.)     0.002100° C. (212° F.)   0.065Dielectric Strength: kV(ASTM D-877)                      44Oxidation Test(ASTM D-2440)(0.30 Percent DBPC*)72 HourSludge: Percent   0.001   0.002   0.001Total Acid No.    0.05    0.05    0.11164 HourSludge: Percent   0.012   0.008   0.002Total Acid No.    0.11    0.11    0.11Rotary Bomb Oxidation:Min (0.3 Percent DBPC*)(ASTM D-2112), 140° C.     300 °+Analysis, HPLC:Weight PercentAromatics                         14.4Saturates                         85.6Gassing Tendency: mm.sup.3 /minProcedure B, 80° C.50 minutes (ASTM D-2300)             +5.1    -2.8    -7.5Using Hydrogen asSaturant Gas______________________________________ *2,6-ditertiarybutyl-p-cresol 
    
     Since the primary criteria for the transformer fluids reside in having excellent oxidation stability and low gassing tendencies, each of Blends Nos. 1 and 2 were tested for these properties and found to be acceptable. Thereafter, Blend No. 3 was tested for the same properties and was also found to be acceptable. Blend No. 3 was further tested for other properties and found to be compatible for the required specifications for transformer fluids. 
     The data in the above table clearly show the advantages resulting from the claimed invention. The base oil alone had a tendency to give off much gas. The mere addition of DXE to the base oil in fact not only greatly reducted gassing tendency of the oil but resulted in a blend having gas absorption properties. Note, too, the particularly surprising fact that the addition of inherently unstable additive to a base oil did not adversely affect the sludge and acid number and that the number of minutes when such blends were subjected to the rotary bomb oxidation tests was actually extended from 125 to above 300. This is most unusual in light of the data in Table IV, below, which shows that DXE alone, 1,1-di(4-methylphenyl)ethane[DTE] alone or 1,1-di(4-methylphenyl)heptane[DTH] alone gave poor results when subjected to the Oxidation Test ASTM D-2440 and Rotary Bomb Oxidation Test ASTM D-2112. Other data in Table III show that a combination of base oil and DXE not only gives good oxidative stability and low gassing tendencies, but that components in the mixture are compatible with each other as physical properties show. 
     
                                           TABLE IV__________________________________________________________________________Description or Test            DXE      DTE    DTH__________________________________________________________________________Specific Gravity (ASTM D-941)60°/60° F. (15.5°/5° C.)            0.9790   0.9752 0.933Boiling Point, °C.            315-317  298-300                            330-350Molecular Weight (m/e)            238      210    280Viscosity, Kin: cSt(ASTM D-2161)100° F. (37.8° C.)            12.45    3.88   13.54210° F. (98.9° C.)            2.43     1.32   2.54Flash Point COC: °F. (°C.)(ASTM D-92)      325 (163)                     327 (164)                            --Fire Point, °F. (°C.)(ASTM D-92)      380 193) --     --Pour Point: °F. (°C.)(ASTM D-97)      -30 (-34)                     -70 (-57)                            -65 (-54)Refractive index, n.sub.D.sup.20            1.5637   1.5608 --Interfacial Tension,mN/m (ASTM D-971)            37       --     --Color, ASTM D-1500            L 0.05   --     --Water: ppm (ASTM D-1315)            29       --     --Neutralization No.,(ASTM D-974)Total Acid No.   &lt;0.03    --     --Aniline Point, °F.(ASTM D-611) (°C.)            29 (-1.6)                     --     --Dielectric Constant,(ASTM D-924)     2.5      2.5    --Dielectric Strength, kV:(ASTM D-877)     46       --     --Power Factor, Percent:(ASTM D-924)77° F. (25° C.)            0.005    0.006  --212° F. (100° C.)            0.27     0.20   --Rotary Bomb Oxidation,min (ASTM D-2112), 140° C.,            105      118    --(0.29 Percent DBPC)Oxidation Test,(ASTM D-2440)72 Hour          (0.075 Percent                     (0.29 Per-            DBPC*)   cent DBPC*)Sludge: Percent  0.84     Nil    --Total Acid No.   9.08     0.47   --164 HourSludge: Percent  1.14     0.42   --Total Acid No.   11.40    7.88   --Gassing Tendency: mm.sup.3 /minProcedure, B, 80° C.50 min (ASTM D-2300)            -105     --     --Using Hydrogen asSaturant Gas__________________________________________________________________________ *2,6-ditertiarybutyl-p-cresol 
    
     Additional tests were carried out wherein DXE added to the naphthenic oil was also added to the synthetic oil defined above. For this purpose three blends were prepared, Blend. No. 4 containing eight weight percent DXE, Blend No. 5 containing 11 weight percent DXE and Blend No. 6 containing 10 weight percent DXE. The results obtained are set forth in Table V below. 
     
                       TABLE V______________________________________              Blend   Blend   BlendDescription or Test              No. 4   No. 5   No. 6______________________________________Gravity: °API (ASTM D-1298)              --      --      42.2Specific Gravity, 60°/60° F.(15.5°/15.5° C.) (ASTM D-941)              --      --      0.8146Viscosity, SUV: s (ASTM D-2161)37.8° C. (100° F.)              --      --      43.798.9° C. (210° F.)              --      --      --Viscosity, Kin: cSt37.8° C. (100° F.)              --      --      5.4198.9° C. (210° F.)              --      --      1.71Interfacial Tension: mN/m(ASTM D-971)       --      --      --Flash, COC: °F.) (°C.)              --      --      315 (157)(ASTM D-92)Fire, COC: °F. (°C.)              --      --      360 (182)(ASTM D-92)Pour Point: °F. (°C.)              --      --      below - 65 (- 54)(ASTM D-97)Apperance (Visual) --      --      water                              whiteCorrosive sulfur (ASTM D-1275)              --      --      non-                              corrosiveWater: ppm (ASTM D-1315)              --      --      49Neutralization No.(ASTM D-974)Total Acid No.     --      --      &lt;0.03Aniline Point, (ASTM D-611):°F. (°C.)              --      --      198.5 (92.5)Power Factor, (ASTM D-924):Percent25° C. (77° F.)              --      --      0.002100° C. (212° F.)              --      --      0.03Dielectric Strength: kV(ASTM D-877)       --      --      44Oxidation Test, (ASTM D-2440)(0.30 Percent DBPC*)72 HourSludge: Percent    0.002   0.001   0.001Total Acid No.     0.05    0.05    0.16164 HourSludge: Percent    0.004   0.004   0.003Total Acid No.     0.11    0.09    0.63Rotary Bomb Oxidation:min (0.30 Percent DBPC*)(ASTM D-2112) 140° C.              --      --      300+Gassing Tendency; mm.sup.3 /minProcedure B, 80° C.50 minutes (ASTM D-2300)              +1.1    -10.8   -7.9Using Hydrogen asSaturant Gas______________________________________ *2,6-ditertiarybutyl-p-cresol? 
    
     The data in Table V show that a blend of DXE and a paraffinic base oil has acceptable oxidative stability, very low gassing tendency, and that the two fluids in a mixture are compatible with each other as physical properties show. 
     Obviously, many modifications and variations of the invention as hereinabove set forth, can be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.