I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
December 1950
of the experimental value, 38.2 cs. The remaining properties may he determined from Figures 1 and 3: niolecular weight, 810; density, 1.904 grams per ml.; and vapor pressure, 14 microns of mercury. The effect of temperature changes on these propert,ies may be determined between 100” and 210” F.
.4dditional work on lubrication properties is impossible a t the preaent time. However, as dctcrmined hy usage these oils compare fdvorably with hydrocarhoii oils.
( 5 ) Ibid., I(-328
2471
(AECU-34) (Doc. 31, 1948).
(6) Ibid., IC-400(AECLJ-300) (hlay 20, 1949). (7) Ibid., I C 4 1 (AECU-241). ( 8 ) Gucker, F. T., Jr., Gagc, F. \V., and Moshcr, C. E., J . A ~ LChem. .
Soc., 60, 2582 (1938). (9) Hanson, W. E., Rept. on Usc of Modified Menaica-Wright Molecular Weight Apparatus, Mellon Institute of Industrial
Research, Pittsburgh, Pa. (September 1945). (10) Hickman, K. C. D., Chem. Rev.,34, 52 (1944). IND. ENG.CHEM.,ANAL.En., 9, 364-7 (11) Hickman, K. C. D., el d., (1937).
RIRLIOGRAFHY
( I ) Am. Scc. Testing Materials, Standards, Part 111-A, p. 325 (2) (3)
(1946). Fawcett, W. M., J . SOC. Chem. Ird. (London).58, 43 (1939). Gabbard, J. L., e t al., Union Carbide and Carbon Corp., Oak Ridge, Tenn., Rcpt. A-3655 (hIDDC-1456) (May 23. 1947).
( 4 ) Ibid.. K-124 ( M D D C - l i 2 4 )
(Jail.
1.5, 1848).
(12) Howat, D. I>., Chem. Age ( L o n d o n ) , 45, 309 (1941). (13) John, K. T.. ./. Rrwcwch Notl. Bur, Standards, 37, 173 (194fi). (14) Vorhoek, F. H . , and Marshall. A . I,., .1. Am, Chem. Soc., 61, 2737
(1939). RECEIVED April
12, lD50. This paper is based on work performed for the At,ornic Energy Cornmiasion h y Carbide & Carbon Chemicals Division. l.nioii C a r h i d e & C’arhon Corporation. Ouk Ridge, T e n n .
Lubricants Produced by Reactions in Glow Discharge R . S. WHITELEY, C. N. KIMBERLIN, G. L. RIATHESON’,
AND R . W.
RICHARDSON
Esso Laboratories, Baton Rouge, La.
B
EFORE World War 11, motor lubricating oils, particularly aviation oils produced by the Volt01 or Electrionprocess, were widelyused in Europe. These oils were in productioll as late as 1940 (gw),and one o f the twoprincipa] lubricants used by the Germ&n Luftwaffe waB a blend of 15y0Voltol concentrate with 85% Edeleanu relined
This report presents studies undertaken to determiric. the type produots which could be made by treating in the glow discharge various raw materials such as fatty oils, acidR and alcohols, esters, lubricating oil fractions, petrolatum, parfin wax, and biphenyl. Polymerization o r condensation was the basic reaction although some hydrogenation and dehydrogenation curre red. Limited data are offered to show that positively charged Particles SUPaviation plied most Of the energy Of reaction. oils were produced from blends of selected mineral oils with “voltolized” rapeseed,,sperm, and other fatty oils. Lubricating oil additives such as pour inhibitors and viscosity index improvers resulted from voltolizing petrolatum and wax. Other interesting products were polyweight alcohols, esters and hasic acids, high ketones, and drying oils. Labratory for conducting liquid-phase reactions under the influence of discharges from either direct or alternating cllrrent is described.
( 4 ). Since the war, Electrion oil is again on the European market and is used for blending with mineral oil base stoclis to produce high quality aviation and automotive lubricants. The process of thickening or polymerizing lubricants by the use of a glow discharge has been known for about 40 years. The process was patented by Alexander de Hemptinne (8) in 1909 and commercial operation was started before 1910 (6). The fact that this process is in use today even on a limited scale is remarkable considering the many advances in petroleum and Iubricarit technology. The de Hemptinne patents (8) were first exploited by the “SociBt6 Anonyme Elektrion.” The product was called “elektrion” and the manufacturing process “elektrionization” (6). These terms are not as familjar as are the German substitutes, “voltol” and “voltolization,” possibly because of the preponderance of German over Dutch or French publications on the subject. Consequently, the more familiar German names are used in this article. Evtensive exploratory research has been carried out to extend de Hemptinne’s early work and to lind other reactions which can be promoted by the electrical glow discharge. Several hundred literature references pertaining tu the effect of the glow disPresent address, Standard Oil Development Company, Elizabeth, N. J.
c*harg:e011 both Ilclulds and gases were found. Interest-
ing descriptions of the foreign commercial installations are available ( 7 , 10, 16, 19, 16), arid adequate bibliographies of the more comprehensive articles are given in several literature surveys (16, 17, 89, 141. This paper is primarily a description of laboratory investigatiom for tho production of lubricating oil additionagents byvoLto1isation. A number Of interesting products Were also formed from high boiling organic materials such as fatty acids, alcohols, esters; aromatic compounds, and p a r a f i i waxes. A liinited amount of information on the mechanism of the reaction was obtained, and the influence of a number of process and electrical variables on the efficiency of the operation and on the quality of the products was determined. The electrical power required to effect a given degree of reaction was measured, and a method of measuring the power consumed is described. REACTIONS LNVOLVED
I n voltolization, as applied commercially to liquid-phase reactions, the apparatus is constructed so t h a t the liquid flows between vertical electrodes which carry opposite charges. In addition to the liquid within the area surrounding the electrodes, a rarefied atmosphere of some gws is maintained. When a suitable voltage is applied to the electrodes, a glow discharge is established. T h e liquid is recycled between the electrodea until the desired product is obtained. The most obvious effect produced by voltolization is a marked increase in Viscosity; however, the over-all reactions are much
INDUSTRIAL AND ENGINEERING CHEMISTRY
2472 HlDH VOLTAGE LEAD,CU WIRE
Vol. 42, No. 12
units simultaneously. The discharge tube is of the ozonizer type-that is, i t has two dielectrics between the electrodes, and the reactants pass between the dielectrics. The discharge tube is 32 inches in length with a 0.6-mm. annular discharge zone. A porous alundum thimble is mounted in the bottom of the larger tube, and gas introduced a t this point lifts the liquid through the voltolization section as a foam. Various gases may be employed to study the effect of the gas phase on the reactions taking place in the liquid. The whole apparatus is placed in a compartment for temperature control. The equipment may be operated continuously or intermittently. The progress of the reaction is followed by measuring the viscosity increase of the charge. Plotted on an A.S.T.M, viscosity chart with power consumption as the abscissa, viscosities give a straight line a t values below about 800 seconds Saybolt a t 210' F. A diagram of the steel trommel apparatus is reproduced in Figure 2. The electrode assembly consists of a series of'electrodes and dielectrics clamped together between two headers. As the assembly is slowly rotated through the liquid reservoir, a film of liquid adheres t o exposed surfaces; this film is subjected to the glow discharge in the area above the liquid. The film is maintained at a relatively uniform depth by a fresh supply of liquid picked u p by cups located on the periphery of the electrode assembly; these cups slowly empty as the electrodes revolve. Temperature is controlled by coils attached to the outside of the vessel below the liquid level. The steel equipment is flexible and easily operated. Its capacity can be changed by increasing or decreasing the number of electrodes in the assembly. ELECTRICAL FACTORS
Figure 1. Glass Tube Voltolizer more complex than simple polymerization (1, 2, 6, 9, 1113, 19.10). The observations made in the Dresent work and the r&ultB of earlier investigations indicate -that several reactions occur concurrently. These reactions may be described as follows: 1. Random polymerization and/or condensation leading to a wide distribution of molecular weights. The mechanism of this molecular weight increase is unknown but i t seems likely t h a t i t involves both simple polymerization at double bonds and a condensation of ions with unsaturates. 2. Hydrogenation and dehydrogenation leading to a n equilibrium unsaturation, the value of which depends on both the starting material and the process variables. D a t a obtained in the present investigation are in agreement with the results of previous workers in showing that of equilibrium is attained. h.!t general destruction of polar groups such as hydroxyl, carboxyl, and carbonyl. Some of these grou s appear much less stable than others to glow i s c h a r g e conditions.
Figure 3 shows the general arrangement of the electrical elements of the trommel voltolizer. When a suitable potential from an alternating current of intermediate frequency-for example, 1000 to 10,000 cycles per second-is applied to the two electrodes in a partially evacuated gas space a glow discharge results. The system then behaves electrically as a condenser
-OIL
CUPS (SYNTHANE)
ALUMINUM ELECTRODES(VARNISH COATED) -HEADER
n
(SYNTHANE)
SHELL (STEEL)
-OUTSIDE
tY
LLECTRODES (GROUNDED)
SPLIT SHELL COPPER BEARING ELECTRICAL INSULATION a SPACERS (MICARTA)
EQUIPMENT
Several types of apparatus for producing the voltolization reaction have been described in the literature ( 2 , 9, 11, 21). I n the present work two types of equipment were used: glass apparatus holding 1 to 2 liters of charge; and somewhat larger steel equipment of the trommel type with 5 to 20 gallons' capacity. A diagram of the glass unit is shown in Figure l. This equipment is simple and one operator has conducted experiments in six to eight
DIE LECTR I C 5 FIBRE BOARD)
GAS INLET-
-
DRAIN
Figure 2. Trommel Voltolizer
T I E R O D 5 (BRASS)
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
December 1950
and a noninductive resistor in series. Thw permits the electrical circuit t o be analyzed by well known mathematical equations, once the factors peculiar to a voltolizer have been experinientnlly determined.
.VACUUM PUMP
VE S S E L
r’RICAL ATlON
INTERMEDIATE
FREQUENCY SOURCE
Figure 3.
Schematic Arrangement of Electrical Elements
The voltolizer itself operates with a leading power factor, the absolute value of which depends on such interrelated variables as pressure, thickness of the dielectrics, distance between the electrodes, and the characteristics of the oil films which flow over the exposed surfaces of the electrodes and dielectrics. The power consumed is the product of power factor, current, and voltage. A high power factor is desirable for the following reasons : 1.
The power is used more efficiently.
2.. The voltage applied to the voltolizer can be reduced to a
minimum.
3. Less inductance must be installed for the correction of the over-all power factor of the circuit so t h a t the frequency changer can operate near its point of maximum efficiency which is a t a power factor of 90 to 95%.
2473
minor importance. From an electrical vieupoirit i t is inore economical to operate a t 120 mm. of mercury ahsolute pressurt tlisn a t 20 mm. Higher voltages are neressary, but higher power factors are obtained. Consequently for a given rlecrrotle area, more power can be applied to the liquid and voltolization procceds niore rapidly. On thr other hand, although pressurcx had no effect on product quality, there was a slight advantage in power consumption for operation a t lower pressures. This is attributed to the f a c t that only a fraction of the energy dissipated in a voltolizer is actually utilized in the polymerization and associated reactions. The remainder is lost as heat. It appears t h a t as the power input is increased heat losses tend to increase faster than the voltolization rate, and the net effert is a greater power consumption per unit of liquid processed. An over-all balance of the various factors involved indicated that 40 to 80 mm. of mercury pressure was the optimum range, and most of the work reported here was performed at about 40 mm No experimental evidence has been obtained to show that voltage had any effect on product quality. From the electrical point of view, increasing the voltage at constant pressure decreases the power factor. Since the voltage drop is primarily across the capacitative portion of the electrical circuit, where it has no beneficial effect, it follows that the system should be operated a t the lowest practicable voltage. ELECTRICAL CIRCUITS A N I ) IN STRUMENTATION
The electrical circuit employed with either the glass or the steel laboratory equipment is illustrated in Figure 4.
INTERMEDIATE F REP U ENCY A . C . SOURCE I15 VOLT
A high power factor in the voltolizer is favored by the use of: 1, The thinnest possible dielectrics 2. The proper spacing of electrodes (which results in a compact electrode assembly) 3. An even distribution of liquid over the electrodes 4. The highest reasonable frequency
The use of high frequency, however, must be consistent with the physical properties of the dielectric material and with the loss in efficiency of the frequency changer which will drop from perhaps 87% a t lo00 cycles per second to about 73% a t 10,000 cycles. High power factors, high frequencies, and the associated low electrode area for a given desired power input result in comparatively high current densities. I n general, variations in current densities in the range of 55 to 155 milliamperes per square foot affected neither the quality of the product nor the course of the reaction under most conditions of voltolization. However, the use of higher current densities did result in a somewhat higher power consumption for a given degree of reaction. I n addition, when the product undergoing treatment reached a high molecular weight there was a tendency toward overpolymerization a t the higher current densities; this resulted in a product t h a t contained lumps of gel-like particles. This could be avoided by slightly reducing the power input as the viscosity of the charge -increased. The more highly unsaturated charge stocks were more susceptible to overpolymeriaation than saturated materials probably because of the higher voltolization rate of the unsaturates. Within the range studied, the pressure of the reaction waa of
LEGEND:
A - AMMETER V = VOLTMETER C i , C p , C 3 - CONDENSE,RS R = STANDARD RESISTANCE
Figure 4. Electrical Circuit Intermediate frequency currents of 1200 to 10,000 cycles per second were obtained from motor-driven frequency changers rated a t 115 volts output. Tapchanging transformers supplied the voltolizer with current between 2500 and 8000 volts. The primary circuit had a high inductance and, consequently, high heat losses because of the excessive current. This undesirable characteristic was corrected by a variable condenser which could be used to increase the power factor to 90 to 95%. The secondary circuit had one leg grounded t o allow the instruments to be operated at low potentials and to reduce safety hazards. Considerable work was required to develop suitable methods of measuring the power consumed by the voltolizer. The system which was finally adopted was both accurate and inexpensive. It is illustrated in Figure 4. The ammeters were hot wire type instruments which could be kept in accurafe calibration by reference to a standard direct current instrument. The voltmeters, which were of the electrostatic type, usually indicated the correct voltage but were periodically checked against 60-cycle instruments. The oscilloscope bridge shown in Figure 4 was used to measure the power factor of the circuit. The hookup is a conventional
INDUSTRIAL AND ENGINEERING CHEMISTRY
2474
Vol. 42, No. 12
cylinder C F R (Cooperative Fuels Research) engines under conditions repreMineral 50% 50% senting varying degrees of severity of Compn. of concentrate oil rapeseed 50% sperm tnenhadan service. In these tests the motor was o.il, 50% oil, 50% blending Rapeseed Sperm oil, 50% stocka oil oil mineral oil mineral oil mineral oil operated at contmlled conditions of Viscosity of concentrate. S.U.S. a t 210° F. 1040 1025 415 1000 400 990 1060 temperature, speed, and power output 10 Concentrate in blend, % None 8.5 8.5 17 10 17 10 for definite intervals of time, usually Inspections of blend Gravity, 'A.P.1. 27.4 26.7 26.9 26.9 26.9 26.8 27.4 27.1 15 hours or multiples thereof. After Flash, F. 500 500 500 500 480 510 510 Viscosity 210° F. 495 124 99 127 125 127 126 131 128 the test the motor was carefully exViscositiindex 97 111 112 110 110 109 110 107 Color (Robinson) 2.5 2.5 2.5 3.25 3 3 2.5 2.5 amined for signs of wear, ring sticking, Pour, F. 20 +15 4-15 +15 +15 4-20 4-10 4-5 varnish and carbon deposits on the Conradson carbon, wt. % 0.80 0.93 0.80 0.78 0.81 0.81 0.90 0.96 pistons, oil deposits in various parts of a Blend of Pennsylvania bright stock with solvent refined mid-continent neutral. the engine, and general over-all cleanliness. Oil consumption and inspections of the used oil were also determined. bridge circuit with a cathode ray oscillosco e substituted for the The oils were rated on a demerit basis using as a reference a galvanometer. With a voltage wave app6ed to the horizontal standard mineral aviation oil, which was assigned a value of 100. deflecting plates of the cathode ray tube in order to get a sweep To ensure against misleading results, which could be caused by and a current wave impressed on the vertical plates, the bridge changes in the mechanical condition of the engine, each fifth or was brought into balance by adjusting the standard variable resistance, R . Attainment of this balance was achieved when sixth test was made on the reference mineral oil. The finding8 the loop trace on the oscilloscope flattened to a line trace. The of these laboratory motor tests were confirmed by a limited power factor could be calculatkd with small error by using the amount of testing in full scale aviation engines, The motor test equation data are too voluminous and their interpretation is too involved Power factor = cos [cot-' 106 to permit a detailed discussion in this report. However, the 2rfCaR over-all conclusion reached was that the voltolized aviation concentrates were of definite value in maintaining engine cleanwhere CSis the capacity in microfarads of the condenser which is in parallel with the resistance, R, in ohms; frequency, f, is exliness, and resulted in a decreased tendency for ring sticking, pressed in cycles per second. The capacit of C3, normally in piston skirt varnish formation, and the deposition of carbonthe range of 0.25 to 1.5 mfd., is a d j u s t e l for frequency and aceous residue. A summary of the conclusions relative to the equipment size to reduce the current through the elements of the effects of raw material quality and manufacturing variables on standard resistance to below the manufacturer's rating. C1 is a condenser of standard capacity, and Cg is a condenser which the quality of aviation concentrates is given in the following is sized to give the desired length of sweep of the electron beam paragraphs. Motor test data furnished the principal basis of across the face of the oscilloscope screen. comparison. The most satisfactory aviation concentrates were produced LUBRICATING OIL ADDITIVES from sperm and rapeseed oils. On the basis of motor tests these The primary purpose in the investigation of the voltol process two oils were approximately equivalent; however, the sperm oil was to produce additives which could be used for the improveconcentrates generally gave slightly better viscosity index imment of lubricating oils. The investigation included two general provement and slightly poorer pour points. Because of their types of products which differed considerably in their effects on low cost a considerable effort was made to produce high quality lubricating oil blends and which could be characterized by the concentrates from various fish oils of which menhaden oil is raw materials used in their preparation: fatty oils or blends typical. Aside from an objectionable fishy odor, the physical of mineral and fstty oils; and oils, waxes, and petrolatums of properties of aviation oils containing menhaden oil concentrates mineral origin. were similar to those containing voltolized rapeseed oil. In Aviation Concentrates. The fatty oil voltok produced spemotor tests, blends containing menhaden oil concentrates which cifically for use in aviation oils were designated &s aviation conhad been voltolized to only 370 to 400 Saybolt viscosity at centrates. A wide variety of fatty oils were studied, but the 210' F. were fairly satisfactory; however, blends containing majority of work was with rapeseed, sperm, and menhaden oils, 1000-viscosity menhaden oil concentrates were considerably inwhich were considered representative of the oil types available ferior to corresponding blends of sperm or rapeseed oil. The for practical use. These were voltolized alone, or in blends oils differed considerably in their rate of voltolization as indicated with an equal volume of mineral oil, to Saybolt viscosities ranging by the following power requirements for voltolizing to 1000 Saygenerally from 370 to loo0 a t 210' F. T o produce a finished bolt viscosity a t 210' F. lubricating oil the concentrates were blended with refined minFatty,Oil eral oils in concentrations of 7 to 17 volume yo. The higher con(in Blend with Equal Vol., SAE-50 Mineral Power Requirement Kw.-Hr./Gallon centrations were generally employed with the lower viscosity Oil) for 1000 ViA./2100 F. voltols. The chief effects of the voltol additive on the usual 19.6 Sperm lubricating oil inspections were: an increase in viscosity; a 4.7 Rapeseed 4.3 Menhaden moderate increase in viscosity index; and generally a lowering of the pour point. Inspections of typical aviation oil blends conAviation concentrates comprising both 100% fatty oils a n d taining various types of concentrates are shown in Table I. blends of equal volumes of fatty and mineral oil were studied. Another important property of the voltolized concentrates is On the basis of motor tests the pure fatty oil concentrates aptheir ability to maintain in a dispersed form the sludge formed peared to be slightly superior to the mixed concentrates when by oxidation of the oil thus leading to an improvement in engine compared on the basis of blends containing equal volumes of cleanliness. The oxidation test (18) results shown in Table I1 concentrates; however, when compared on the basis of blended illustrate this sludge-dispersing property of the voltol blends. oils containing equal quantities of fatty oil the mixed concentrates These tests were conducted on blends with a mid-continent were probably to be preferred. The latter basis of comparison motor oil base since the highly refined aviation base used for the is important because of the relatively high cost of the fatty oils. blends shown in Table I produced very little sludge. An indication of the chemical structure of the two types of conThe motor performance of the blended voltol oils was decentratns is given by the viscosity and neutralization number of termined by laboratory tests in full scale automotive and single
TABLE I. INSPECTIONS OF AVIATION OILS CONTAINING FATTYOIL CONCENTRATES
+
3-
December 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
the free fatty acids which were separated by saponification of concentrates prepared under comparable conditions of voltolization:
-
___
.
Aviation Concentrate -.___--
Composition Rapewed oil (unvoltolized) 10070 Rapeseed ,oil 50% Rapeseed oil, 50% SAE-50 niineral oil 50% Rapeseed oil, 50% SAE-BO mineral oil
-
Free Fatty Aoids Neut. No Saybolt Saybolt mg. KOHY vis., 210' F. vis., 210' F. gram 56 49.3 182 1000 180 74.9
370
114
148
1000
1 59
I29
These viscosities show that the 10004scosity rapeseed oil is less highly polymerized than the fatty component of either the 870- or 1000-viscosity mixed concentrates, The latter concen-
trates probably owe their viscosity chiefly to the highly polymerized condition of their fatty oil content. The neutralization numbers indicate a significant copolymerization of fatty and mineral oils in the mixed concentrates. In the preparation of the mixed fatty-mineral oil Concentrates, two general voltolization techniques were used, In the first technique, which was termed the "initial blending procedure," the fatty and mineral oil starting materials were blended and the mixture was voltolized to the desired viscosity. In the second, termed the "gradual blending procedure," the fatty portion of the concentrate was first voltolized alone to approximately 200 Saybolt viscosity a t 210' F.; then as the voltolization continued the mineral oil was added in increments. Because of the higher rate a t which fatty oils voltolize, as compared with mineral oils, the gradual blending procedure required about one third less pouer than that required by the initial blending procedure to produce a 1000-viscosity concentrizte. This advantage was partly offset by a greater tendency for the gradual blending technique to produce overvoltolized material, which necessitated a reduction in the rate of power input during the latter part of the operation. As might be expected, the concentrates obtained by the gradual blending proredure had a wider range of molecular weights and a lower degree of copolymerization of fatty and niineral oils. The latter fact is illustrated by the following data obtained by saponification of 1000-viscosity, 210" F. concentrates prepared from equal volumes of rapeseed and SAE-40 mineral oils. Blending Procedure Initial Gradual
Cmaponifiables, % ' 29 43
Saponification No Free Fatty. Acids.' 130 161
2475
'viscosity, 210' F. compared to 10$Zo,1000 viscosity, 210' F. concentrate) the lower viscosity concentrates showed an advantage. Mineral oils employed in the production of the 50:50 fattymineral oil experimental aviation concentrates included neutrals, motor oils, and aviation grade oils of various degrees of refinement from Pennsylvania, mid-continent, and coastal crudes. From the manufacturing point of view it appeared t o make no difference what type mineral oil was used, except that the higher viscosity oils required less power for voltolization. The blending characteristics of the concentrates, as measured by laboratory inspections, were likewise independent of the quality of their mineral oil content. In motor tests the effects were not great and were often shielded by other factors. However, i t appeared that the best results were obtained by the use of an oil that had been refined only to a moderate degree-for example, a motor oil of 80 to 90 viscosity index from mid-continent crude. Although it was possible to produce high quality lubricants using the voltolized aviation concentrates, nevertheless, from a practical viewpoint these materials had certain disadvantages. They were essentially high cost products and were not effective unless used in higher concentrations than those generally employed for other types of lubricating oil additives. In addition, the concentrates were not compatible with all types of mineral oil-base stocks, particularly the highly refined neutrals which are generally used in premium quality motor oils. For this reason these materials probably could not be used in a general line of automotive lubricants. The incompatibility was not apparent on the fresh oils, but after the oils had become oxidized in use the concentrates did not remain in solution. Voltolized Waxes and Petrolatums. A second class of lubricab ing oil additives waa produced by the voltolization of mineral oils or waxes and petrolatums obtained from mineral oils. Depending on the manufacturing technique and the particular starting material used, additives were obtained which were effective for viscosity index improvement, pour point reduction, and sludge dispersion. These additives were not so extensively tested in motors as were the aviation concentrates, but in preliminary tests they were effective in maintaining engine cleanliness in automotive and certain Diesel service. The voltolization of low melting point waxes gave products that were fairly effective for the improvement of viscosity index and dispersion of sludge; however, their outstanding characteristic was that of lowering the pour point of oils when blended in low concentrations. Table I11 shows typical results obtained in the reduction of the pour point of two types of lubricating oils. For the production of pour inhibitors the voltolization was generally stopped in the range of 500 to 1000 Saybolt viscosity a t 210' F., although satisfactory inhibitors of higher viscosity could be produced. To avoid cloud formation in the blended oil8 it was necessary to remove'the unconverted wax
The two types of concentrate8 appeared to be equivalent in every way in their effects on the usual physical inspections of lubricating oils in which they were blended. In motor tests, the initially blended concentrates showed a slight advantage over the gradually blended materials. The aviation concentrates were ordinarily voltolized to either 370 to 400 or t o about 1000 Saybolt seconds viscosity a t 210' F. A few samples TABLE 11. INDIANA OXIDATION TESTSON VOLMLIZEDFATTY OIL CONCENTRATE BL~NDS of intermediate viscosity were also prepared. ConMineral centrates of lower viscosity than 370/210° F. Compn. of concentrate oil 50% rapeseed 50% sperm were considered impractical, and those of higher 011, 50% oil. 50% blending Rapeseed Sperm o i l oil mineral oil mineral oil stook" viscosity than about 1000/210' F. proved to be Viscosity of concentrate, difficult to produce because of the formation of S.U.S. a t 210° F. 1040 1025 450 lo00 405 950 None 8.5 8.5 17 17 17 17 Concentrate in blend, 5% overvoltolized material. The higher viscosity Indiana oxidation test, concentrates were superior in the improvement of mg. sludge/lO grams viscosity index; they were also generally better as oil After 24 hours 0 0 0 0 0 0 0 sludge-dispersing agents, although some exceptions After 48 hours 0 0 0 0 0 0 0 After 72 hours 208 0 0 0 0 0 0 to the latter were observed. In comparing avi& After 96 hour8 .. 0 0 0 0 0 0 tion oil blends containing equal volumes of concenAfter 120 houra 0 0 0 n n After 144 hours 680 2 0 0 0 0 trates, the higher viscosity concentrates generally After 168 hours .. . . 2480 2 '1160 1 0 After 192 hours .. .. .. 2480 .. 2280 400 gave better motor performance. However, when used in concentrations that produced the same 4 Conventionally refined SAE-50 mid-continent motor oil. viscosity increase in a given base stock(17%, 370
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2416
Vol. 42, No. 12
viscosity index improvement, these products were generally Saybolt Yield of effective for reducing the pour Pour Points of Blends, F. Vis., 210' F., Extracted Blends in Oil A b Blends in Oil Hb of oils containing bright stocks Starting before Inhibitor? Material Extrsotion % ' 0 . 5 % 0 . 2 % 0 . 1 % 0.06% 0 . 5 % 0 . 2 % 0 . 1 % 0 . 0 5 q but gave only slight pour r e +l5 +15 .. -20 100 +5 1 1 8 O F. m.p. re758 -0 +zo duction in neutral oils. -10 0 o 48 4 -15 -20 -10 fined wax 758 -2 +ij The voltolization of wax813 +15 -15 100 0 +lR 130° F. rn.p.'h re-10 +10 -15 41.3 +5 +i5 -20 o -15 fined wax 813 -15 -io f r e e m i n e r a l o i l s was not Crude scale wax 597 100 - 10 0 +.5 +5 -13 -10 +A studied thoroughly since the -PO --L5 0 0 -20 507 38.7 -10 +;2 0 products obtained did not ap16?)~ E'. ~ n . p .wax 600 100 + 30 +30 .. pear to have any particular (de-oiled petro-' 2000 I00 +3 .. + 30 latii i n ) 2000 50 +a0 , . .. .. +30 .. .. advantage over the voltolized * Unvoltolized wax was removed by extraction with sec-butyl alcohol. wax= and petrolatums. The b Oil A = Pennsylvania neutral dewaxed t o +30° F. pour point: B = blend of Pennsylvania neutral and Pennv o l t o l i a e d o i l s w e r e only sylvania bright stock dewaxed to +30° F. pour. slightly effective for improving viscosity index. They were fairly satisfactory for sludge dispersion but did not equal the voltoliaed p&olatums in from the voltolized product. 'ghis was readily extracted with solvent such as secondary butyl alcohol or liquid propane. The this respect. They did not appear to have any appreciable effect on the pour point ofoils in which they were blended. voltolization of high melting point waxes such as solvent, de-oiled petrolatum resulted in a product that was ineffective as a pour point reducer; however, this material was about as effective as VOLTOLIZED ACIDS, ALCOHOLS, AND ESTERS that produced from low melting point wnses for sludge dispersion To study the effect of voltolixation on functional groups, a or viscosity index improvement. number of organic compounds were treated under glow discharge The most effective materials for dispersion of sludge and imcwnditions, and the products were examined to determine their provement of viscosity index of lubricating oil blends were proproperties. The power requirements for voltolization of several duced by the voltolization of petrolatums. The starting maacids, alcohols, and esters follow : terials were obtained by solvent dewaxing of lubricating oil cuB having Baybolt viscosities at 210' F. generally in the range of 50 to 7 0 ; they contained both oil and high meking waxes. Typical resulk3 or] sludge dispersion and viscosity indes improvrSynthetic" fatty alcohols A75 64 merit by these volt,olized products are shown in Tables IV and \-, Cetyl alcohol 600 36 respectively. The potency of the products for both sludge disLauric acid 633 76 Synthetic'' fatty aC.ii1,. 650 54 pwsioii and viscosit?, index iinprovernent increased. and the Naphthenic acids 720 45 Oleic acid power requirement for a given amount of improvement decreased, 66R 27 Menhaden oil fatty acid8 1400 13 as t,tie viscosity to which the petroiatums were voltolized was inIsopropyl esters of synthetic0 fattv acids 485 100 creaser!. At high viscosity the voltolization became more diffiIsopro"py1 naphthenate 1050 55 Isopropyl oleate IO00 49 cult, so that the optimum viscosity was helieved to be in the Isopropyl esters of menharl(3n rarigc 4000 to 5000 Saybolt sctconds a t 210" F. As with voltolizeti oil acids 17 890 low inelting wises, unconvert.ed material cxould be removed froni the volt olized petrolaturns by solvent ext8ractjion. Of severril solwilts tested the best appeared to be liquid propane. The As in the case of the lubricating oil :tddition agents the power voltolized petrolaturns were ineffective or only moderately effecrequirement for voltolization of the chemical products bore an tive for the reduction I J f pour point whcn used in low concentritinverse relationship t o the degree of unsaturation of the charging \Vilexi used in concentrations of tions of less th:in :illout 0.5";. stock. 2 to 5%,, which were needed for significant sludge clispersiorl nntl Analytical information perhining to both the voltolized and
Saybolt Visoosity of Vultol Vultul a t 210° F. in Blend,
TABIXv.
VISCoSITY 1'ETHOLATUM
"/G
Indiana Oxidation Test M g . Sludge/lO G. Oil 24 hr. 48 hr. 72 hr. 06 hr.
12Thr.
IlvDEX IMPROVEMENT B Y ~ ' O I , T 0 1 ~ I Z E l ) 570 13LENDS I N ( I O A S T A L 0 1 1 , '
Saybolt Viscosity
of Voltolized Petrolatum a t 210° F. Base oil 1,380 4,360 8.720 17,500 4,360 (dewaxed by propane extraction to 51% yield)
.
Blend Vis., 210' F. Viscosity indes ~
R5.6
44
ti4.7 70.6 72.4 81 1
70
100.3
97
70
81
81
unvoltolized products is given in Table VI, There was a general tendency for the polar groups to be destroyed during the voltolization with the alcohol hydroxyl group being the le& st,able of tbosc: investigated. However, the data do indicate that a considerable proportion of polyfunrtional molecules was produced, especially in the case of the acids. In addition t o the general loss of functional groups, the est'ers broke down to yield.small quantit,ies of d d s and appreciable quantities of unsaponifiable material. The voltolized products mere clear, viscous oils which were slightly darker in color t,han the st,arting materials. They could he separated into ftwtions of low and high molecular weight by cstr;u-tion with solvents such as aqueous alcohol. VOLTOLIZEI) DRYING OILS
I'olynierizcd drying oils were prepared by voltolizing tung and linseccl oils to viscosities of 1100 Saybolt at 210' F. The power consumption, 2.2 kw.-hr. per gallon of tung oil and 4.2 kw.-hr. per gallon of linseed oil, indicated that, the process might be economical enough for commercial exploitation. Although the iotiinc nunibers of the voltolized products were lower than those of the original oils, the drying rates were equal, o r perhaps faster, than those of the original oils. Voltolization produced
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1950 no change in the color or other apparent physical properties of these drying oils, except for the increased viscosity.
TABLE VI.
As an example of a pure a r o m a t i c hydrocarbon, biphenyl was subjected to the glow discharge. The properties of the biphenyl did not appear to be a p p r e c i a b l y altered until after the power input had esceeded 25 to 30 kw.-hr. per gallon; but by the time 36 kw.-hr. per gallon had been consumed, the voltolized product had reached a viscosity estimated to be in excess of 1000 Saybolt a t 210' F. The v o l t o l i z e d b i p h e n y l was a tarry material with a dark greenish cast. It r e m a i n e d liquid at room temperature and and in the usual organic solvents.
ANALYTlC.11, INFORMATION ON VOLTOLIZED ORGANIC COMPOUNDS
Saybolt Viscosity, at 210' F. 43 575 39 600 36 637 45 648 43.5 720 42 664 40 1400
Organic Compound Synthetic fatty alcohols" Voltolized Cet lrlcohol <olized Lauric acid Voltolized fatty Voltolized Naphthenic acid Voltolized
VOLTOLIZED AROMATICS
Oleic Voltolized acid Menhaden oil fatty acid Voltolized Isopropyl esters of synthetic fatty acidsa 35 Voltollzad 485 Isopropyl naphthenate Voltoliaed 1050 Isopropyl oleate 33 Voltolized 1092 Isopropyl esters of menhaden oil fatty acid 32 Voltoliaed 890 a From wax oxidation.
WIS
insoluble i n mineral oil
ESTERIFICATION DURING VOLTOLIZATION
A stoichiometric mixture of fatty acids and alcohols was voltoliied to a viscosity of 640 Saybolt a t 210' F., and the product was separated by neutralization and extraction into an acid fraction and an alcohol-ester fraction. The properties of the products are as follows:
--
Neut. No.
Starting mixture (44 vie., 210" F.) Total product (640 vis., 210° F.) .\cid fraction Alcohol-ester fraction
94 50 .5? >
Ester. Hydroxyl No. No. Mg. KOH/G. 114 20 94 94 44 41 106 .. 19 .,
Sapon.
No.
..
I
VACUUM
Ji
___I'I'I' 1000 VOLTS D.C.
Figure 5. Direct Current Glass Cell Voltolizer
2477
.
Average Mol.
Wt. 304 1060
... ... .... ..
251
.742 .. ... ... ... ...
...
310 910
Neut. No. 0.0 0.5 0.0 1.2 265 134 211 147 205 140 187 124 198 157
...
16 27 14 24
...
811
... ...
,..
...
Sapon. NO. 5 7.9 0 6 278 171 250 203 234 160 216 153 256 195 207 159 172 112 177 131
0 1.2
4.2
178 151
Hydroxyl No. 169 73.3 232 94
... ...
... ... ... ... ... ...
...
... ...
17
... ... ... . . 1
Functional Groups Mole 0.92 1.38
... ... .. ..,.
1.1 2.68
... ... ... ... ... ...
1.15 2.59
... ... ...
Ratio, Free to Total COOH/ Mole
...
.. ...
... 0.953 0.784 0.864 0,709 0.874 0.877 0.866 0.810 0.774 0,805
... ... ... ...
...
... ...
... ...
...
... ...
...
As there was little loss of material during voltolization these data indicated that considerable esterification had occurred. .4s usual there was a general loss of functional groups in this experiment. The acid fraction was a dark-red, viscous oil; t,he alcohol-ester portion was a translucent rubbery material. OXIDATION AND CHLORINATION DURING VOLTOLIZATION
A refined 130' F. melting point was was voltolized in t h e Presence of air to a viscosity of GOO Saybolt a t 210' F Anrtlytical (lata obtained on the product were: Neutralization No. 1.4 8.2 Saponification N o . 9.4 Iodine No. Hydroxyl No. 36.8 Carbonyl No. 28.6
These data show that considerable oxidation occurred during the voltolization treatment and that the principal products were alcohols and ketones. The product was quite compatible with mineral oil and showed good pour inhibiting properties. Voltolization of petrolatum in the presence of chlorine resulted in a dark oily polymer containing 9.1% chlorine. Thc product appenred to contain free carbon. MECHANISM OF REACTIONS
The mechanism of the voltolization reaction has been studied extensively. I n some of the more comprehensive studies (3, 1 4 ) the work suggests that most of the energy required for the rcaction is supplied by the positive charged particles in the discharge zone. Additionxl evidence for this concept was obtained by a simple experiment in a direct current, glass-cell voltolizer. The apparatus used is illustrated in Figure 5. A layer of oil was placed beneath the electrode in each leg of the H-tube, which was supported in a vertical position. This arrangement provided for the bombardment of the oil samples beneath the positive and negative electrodcs by electrons and positive ions, respectively. The absolute.pressure in thc vessel was reduced to 4 nun. of mercury and a glow discharge started under the impetus of 1000 volts direct current. The oil layer under the negative electrode warmed u p rapidly. A dark-brown layer formed on the surface, and the entire sample gradually darkened in color and becamp more viscous. On the other hand, the oil layer under the positive electrode did not change color and did not increase appreciably in temperature; increase in viscosity was negligible in comp:tri-
INDUSTRIAL AND ENGINEERING CHEMISTRY
2478
son with the increased viscosity of the oil layer under the negative electrode. Apparently, the bombardment of the oil with positively charged particles caused it to increase in molecular weight, whereas bombardment by electrons alone had little effect. Hydrogenation-Dehydrogenation Reaction. As previously indicated, one of the bmic reactions occurring is a hydrogenationdehydrogenation reaction leading to a condition of constant unsaturation which depends to some extent on the starting materials and also on the conditions of voltolization. Typical results are shown in Figure 6.
I n
Gas Used Hydrogen TIydrogen saturated with water
Air
Vol. 42, No. 12 Relative Power Consumption 100 133
Nitrogen Natural gas
133-150 .~-.. 150
210
When an atmosphere of either ethylene or acetylene was used in the glow discharge ione, the voltolization reaction was greatly inhibited. Comparative data on rapeseed oil are: Power Input Kw.-Hr./Gal.
Gas Phase Hydrogen Ethylene Acetylene
4.6 28
15
Saybolt Viscosity a t 210' F. Initial Final 61 1030 61 63 61 72
The gas phase also influenced the quality of the product to some extent; the best aviation oil blending agents resulted when hydrogen was used as the flushing gas.
40
20
0 30 -~
I
I
,
-
PAR A F F I N WA XI I
,
I l l ,
1
1
251-
,
1000 100 SAYBOLT V I S C O S I T Y , 210 OF.
Figure 6. Effect of Voltolization on Unsnturation
Additional information concerning hydrogenation and dehydrogknation was obtained by measuring the gas which was pumped out of the treating vessel to maintain constant pressure. In one experiment, a blend of equal volumes of rapeseed oil and mineral oil was voltolized to 1050 viscosity, 210" F. without the addition of any flushing gas. The recovered gas consisted almost entirely of hydrogen. Figure 7 shows the gas evolution per kilowatbhour of electricity consumed plotted against viscosity of the voltolizcd material; gas evolution is much greater a t the higher viscosities. This is probably because the fatty oil is highly unsaturated during the early stages of voltolization and retains a great deal of the hydrogen that would otherwise be evolved in the molecular state. As the viscosity of the oil increases the equilibrium unsaturation value is approached, and the full quantity of hydrogen released by ionic impact is removed from the voltolizer. The gas phase in the glow discharge zone appears to have no significant effect on the degree of unsaturation attained, as shown by the following data on blends of rapeseed and mineral oils voltolized to a Saybolt viscosity of 370 a t 210' F. Gaseous Atmosphere above Llquid No flushin gas used, gases produce2 in reaction Low hydrogen flushing rate High hydrogen Bushing rate Natural gas flushing Nitrogen flushing
Iodine No. 31 34 30 29 31
These results indicate that the consumption of molecular hydrogen plays a minor role in establishing the degree of unsaturation nttained. Effect of Gas in Glow Discharge Space. The energy required for voltolization is greatly influenced by the gas that is present in the glow discharge zone. Certain gases such &s chlorine or oxygen react with the product undergoing voltolization, and their effect as ionic media is therefore difficult to determine. I n general, when treating fatty oil-mineral oil blends energy consumption was the lowest in the presence of dry hydrogen. The following tabulation indicates the order of magnitude of the power consumption in the presence of dry hydrogen and several other gases:
SAYBOLT V I S C O S I T Y AT 2 1 O O F .
Figure 7 .
Rate of Gas Evolution with Increasing Viscosity
Effect of Temperature. The effect of the temperature of voltolization on the reaction or on the quality of lubricating oil blending agents was not investigated extensively. However, in the range of 120' to 195' F., the temperature appeared to have no substantial effect. On the other hand, i t is reported (26) that the temperature of the comniercial unite a t Potschappell, Germany, was raised to 305' F. from time to time during the processing of aviation oil additives in order to-destroy the less stable, large molecules. ACKNOWLEDGMENT
The authors wish to thank C. F. Hill and T. R. \I;atts of the Westinghouse Electric and hIaxiufacturing Company, Pittsburgh, Pa., for their assistance and advice in devising the instruments used for measuring power consumption in these investigations. LITERATURE CITED (1) Becker, H., Wiss. Veriifente. Siemens Konzern, 5, 166 (1926). (2) Ibid., 8, NO, 2, 119-217 (1929). (3) Brewer, A. K., a n d Westhaver, J. W., J . Phys. Chern., 33, 833 (1929). (4) B r i t . Intelligence ,Object. Subconim., L o n d o n , H.R.I.S., Final R e p t . 1611, Item 30. (5) D e c a v a l and Rogiers, Chimie & industrie, 25, spec. issue, 4437 (1931): (6) Eichwald, E g o n , Z . Angew. Chem., 35, 505-6 (1922). (7) Friedrich, Ver. deut. Ing., 65, 1171 (1921). (8) Hemptinne, Alexander d e , Brit. P a t e n t 15,748 (1909); G e r m a n Patent 234,543 (1909): U. 6 . P a t e n t 970,473 (1910). (9) Hock, L., Z. Electrochem., 29, 111-19 (1923). (10) Isom, E. C., Oil and Gus J . , 24, 156 (1925).
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
December 1950
(11) Iwamoto, Yoshitora, J . Chem. Ind. Japan, Supp. BZnding, 32,
93B (1929). (12) Zbid., p. 259-60B. (13) Zbid., 33,25-27B (1930). (14) Linder, E. G., and Davis, A. P., J . Phys. C h m . , 35,3649 (1931). (15) Nash, Howard, and Hall, J . Inst. Petroleum Technol.. 20, 1027 (1934). (16) Otto, Petroleum Eng., 2 , 112 (1931). (17) Pritzker, G. G., Petroleum Proc., 2, 291 (1947). (18) Rogers, T. H., and Shoemaker, B. H., IND. ENG.CHEM..ANAL. ED., 6,419 (1934). (19) Swoboda, "Technologie der Technischen Ole und Fette," Stuttgart, Germany, F. Enke (1931).
2419
(20) Technical Oil Mission to Germany. U. S. Dept. Commerce, Washington, D. C.,microfilm reel 60. items 59 and 60, frames 758-83. (21) Ibid., reel 79, item 135. (22) Zbid., reel 179, part 15, item 25, frames 04769-04821. (23) Thomas, Egloff, and Morrell, presented before the Division o f Petroleum Chemistry, 95th Meeting AMERICANCHEMIC. LL SOCIETY, Dallas, Tex. (24) Thomas, Egloff. and Morrell, Chem. Reus., 28, 1-70 (1941). (25) Wolf, Petroleum Z.,25, 95 (1929). RECEIVED April 24. 1950. Presented before the Southwest Regional Meeting. AhlERICAN CHEMICAL SOCIETY, Oklahoma City, Okla., December 9, 1949.
Mode of Action of PhenothiazineTYP e Antioxidants t
C. M. MURPHY, HAROLD R A W E R , AND NATHAN L. SMITH Naval Reseurch Laboratory, Washington, D . C .
T h e oxidation inhibition action of phenothiazine-type compounds on a diester-type lubricating oil has been investigated in a dynamic system over the temperature range 100" to 175" C. in the presence of metal catalysts. Many of the compounds indicated activity a t the higher temperatures. Resonance-stabilized free radicals, capable of reducing peroxides, were postulated to be the actual inhibiting configurations. It was demonstrated that the inhibitors were to some extent regenerative rather than sacrificial. A comparable degree of effectiveness was found to exist in many of the oxygenated derivatives of phenothkzine; this was correlated with their ability to exist as resonance-stabilized free radicals. The ease of bond rup-
ture to form free radicals at the heterocyclic nitrogen is discussed in relation to bond energies. The decreasing effectiveness of phenoselenazine and phenoxazine as mmpared to phenothiazine was ascribed to the lower oxidation potentials. Variations in the antioxidant action of phenothiazine with changes in its molecular configuration are discussed. Some high molecular weight derivatives of phenothiazine with lesser tendency to volatilize were shown to be of the same order of effectiveness as the parent compound. This is of practical importance in such hightemperature applications as lubricants for use in turbinepowered engines and greases for use in silicone-clad motors and gene,rators.
T H E use of phenothiazine
tors less volatile than phenothiazine but with the Itttter'Y desirable features.
H
TIIEORETICA L CONSIDERATIONS
for preventing oxidative changes in polyethylene oils has been reported (10,16). In a recent investigation a t this laboratory on antioxidants for turbo-jet lubricants, phenothiazine exhibited promise for use a t temperatures up to 163" C. It was demonstrated that a pure reference fluid, di-(a-ethylhexyl) sebacate, which has been utilized as a turbo-jet lubricant, could be stabilized with respect to viscosity changes and acid production by the presence of a comparatively low coiicentration of phenothiazine (0.02 to 0.50 weight %, depending upon the temperature). At the upper temperatures, however, there was deposition of lacquer on the oxidation cell wall and on thc metal catalyst strips, and there was also some indication of excessive volatility of the additive. There are numerous applications for high-temperature antioxidants, such as additives to greases for siliconeclad motors and generators and as lubricants for gas turbines and the aforementioned turbo-jet engines. The inhibition activity of phenothiazine was of such high order as to warrant further investigation. Of particular interest were the determination of the practical upper temperature limit of inhibition, the elircidation of the possible mechanisms involved in the inhibition process, the effect of structure on inhibition activity, and the development of inhibi-
OXIDATIONPHENOMENON. It has been generally accepted that the majority of organic oxidation rections proceed by a chain mechanism with hydroperoxide consumption az the ratedetermining step, although other mechanisms have been postulated (If?, 16). The available evidence coxicerning the autoxidation of such compounds as Tetralin (13)indicates that decomposition of the hydroperqide leads to new active molecules which may reinitiate other chains. The over-all process may be demonstrated in the following general fashion: R H +energy (heat, illumination, catalyst) --+R.(free R. R4-0.
+ 01
R-0-0.
+ R H +R-0-0-H 2R.
----f
+ R.
R-R
R. f R-0-0, +R 4 4 - R 2R4-0. --f R - 0 4 - R 0s
rrtdical)(l) (2 ) (3) (4)
(5) (61 Reactions 1 to 3 represent the initiation and subsequent continuation of oxidation by means of the generated free radical, R.. Reactions 4 to 6 represent different methods of terminating the reaction chain. The presence of aldehydes and acids in the oxidation products may be accounted for by the decomposition of the hydroperoxide, R-0-0-H :
+
