Lubricating Oils in Contact with Clays Effect of Time at Elevated Temperatures V. A. KALICHEVSKY AND J. W. RAMSAY, Socony-Vacuum Corporation, Paulsboro, N. J.
C
LAYS used for contact filtration of p e t r o l e u m oils vary considerably in ability to d e c o l o r i z e oils and also in regard to the conditions required to bring out their best performance. The determination of the relative efficiency of such clays and the optimum conditions for use are necessary for intelligent purchasing and refinery operation. The character of the reactions between oil and clay complicates the problem of properly evaluating clays of this type to such an extent that, probably, no numerical expression of relative value of various clays, valid for all conditions, may
beyond t h a t required h a d a n unfavorable i n f l u e n c e on the color of the oil. Material used for constructing the apparatus does not appear to influence the color of the oil, provided i t has a reasonably g o o d conductivity to prevent local overheating of the charge. Metal is therefore preferable to glass in order to minimize the p o ss i b i l it i e s of experimental error. The kind of metal does Got seem to influence the results if the air is completely excluded from t h e a p p a r a t u s . As a general precaution, h o w e v e r , the use of comer or s i m i l a r metals, or alloys which have a catalytic effect on oxidation processes, should be avoided. A sketch of the apparatus used in this investigation and embodying the above principles is shown in Figure 1.
A simple laboratory apparatus has been developed and used for int\estigating the effect of time and temperature in decolorizing oils with clays. The time factor was found to be important, and it cannot be neglected in evaluating clay eficiencies. The color of the oil usually improves as the timt. is increased, but, owing to the complicated character of the involved reactions, a reversion in color m a y occur. A simple relationship between the quantity of clay and the equilibrium color, such as Freundlich's adsorption isotherm, probably does not hold strictly for petroleum oils, although there is often a n agreement.
I
be found.
APPARATUS
I
I n developing the contacting apparatus, attention must It consists of a cylindrical vessel which is rounded at the be given particularly t o the degree of agitation if reproducible junction of the walls with the bottom. The vessel is equipped results are t o be obtained. The degree of agitation is de- with a removable cover which makes a practically air-tight conpendent on the design and dimensions of the stirrer, on its nection. The cover has openings for the inlet ( A )and outlet ( B ) relative proportion. with respect to the size of the vessel, steam (or inert gas, such as nitrogen), a mechanical stirrer (C), and on the shape of the vessel, which should kie such as to and a thermometer n ell ( D ) reaching into the main body of the oil. The stirrer, tightly fitted by means of a packing gland, is avoid any settling of the clay. The position of the stirrer operated at a constant speed by means of an electric motor. within the vessel is also important for proper circulation of A weighed amount of oil is introduced into the PROCEDURE. the clay-oil mixture. The stirrer should always deflect the contacting vessel together with a weighed quantity of clay. The oil toward the bottom of the vessel in order t o prevent vessel is closed, agitation started, steam admitted into the air space above the oil level, and heat applied by means of a gas settling. All these variables are evidently interdependent burner. The rate of heating is held uniform in all experiments, and influenced by the relative size of the contacting vessel. although it was found that even rather considerable deviations It was found, however, that, after they were adjusted so as from the standard rate of heating had practically no effect on to obtain the maxinium degree of decolorization in a mini- the color of the treated oil. The maximum temperature and the time of heating the charge at this temperature are the immum length of time, the reproducibility of the results was portant factors governing color. not affected by the size of the apparatus used. After completing the run, the charge is allowed to cool to a Presence of moisture in the clay (determined by drying at temperature a t which it can be filtered free from clay without 220" F. or 104.4' C.) or addition of water t o the oil-clay danger of discoloring by exposure to air. The time of cooling is of practically no importance, provided the surface of the oil mixture influenced the color of the contacted oil if the agita- is protected with steam until the oil has cooled sufficiently. The tion was inadequate. This may possibly be explained by temperature a t which the treated oil can be exposed to air varies the mechanical effect of water vapor which is generated somewhat with the nature of the oil and has to be determined during the treating procedure and which may provide addi- experimentally. Buchner funnels are used for the filtration. tional agitation if the apparatus is not properly designed. COLORMEASUREMENTS S o chemical or other effects of water could be discovered Difficulties were experienced in measuring the color of the with the oils and clays used in this experimental work if suffioil because of various defects in the available color methods. cient agitation was used. Presence of air during contacting is deleterious to the color The NPA, TagRobinson, Lovibond (500 amber series), or of the oil. This mas avoided by using closed vessels and by other scales involving glasses of standard colors, proved maintaining a layer of steam over the surface of the oil as inaccurate because of the difference in hue between the oils soon as heat was applied. B y taking these precautions, i t and the standard glasses. A complete Lovibond color was found that the increase in the violence of agitation beyond analysis permits a n exact expression of the color of oil in a certain point had no influence on the color of the treated terms of three subtractive colors. It is impractical, however, oil, all other conditions being constant. This may be ex- owing to the length of time required to take the readings, plained on the assumption that diffusion of the coloring and to the difficulty of conveniently using the results obmatter through the pores of the individual clay particles, tained. The Duboscq colorimeter was also found to be unand not the renewal of the oil-clay interface, is the controlling satisfactory, as the hue of the oil changes in treating and factor in the rate of decolorizing the oil. I n presence of precludes the possibility of finding a satisfactory standard traces of air, however, a n increase in the degree of agitation for the reasons already mentioned. 941
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I N D U S T R I A L A K D E h-G I K E E R I N G C H E M I S T R Y
The problem was solved by the development of a photoelectric colorimeter and a color intensity scale which have been described in another paper ( 3 ) . This permitted the determination of the oil "colors" with an accuracy which could not be achieved with other colorimeters, and made the present investigation possible, since with the new colorimeter
Vol. 25, No. 8
where the development of new coloring matter, due possibly to polymerization, becomes of greater moment. Finally, cracking reactions overshadow the two other reactions and bring about an improvement in the color of the oil because of decomposition of the polymerized products. It is of considerable interest that the steep portions of most of the time-color intensity curves are between zero and 20 or 30 minutes. These observations emphasize, therefore, the importance of a careful control of the time element.
TABLEI. EFFECTOF TIMEAND TEMPERATURE ON COLOR OF OIL IN CONTACTING ACID-TREATED MIDCONTINENT CYLINDER STOCEWITH ADSORBENT CLAYS ACTIVATED CLAYAa ACTIVATED CLAYBb NATURAL CLAYC Time at Time at Time at Color max. Color max. Color max. temp. intensity temp. intenaihy temp. intensity
TREATINQ
TEMP.
' F.
(" C.)
Min.
Min.
~ - .
zoo 600 (315.6)
FIGURE1. CONTACTIEG APPARATUS any change in color readings could be attributed entirely to the treating procedure.
i25 163 135 112 98 91 84 76 76
0 5 10 20 30 60 120 200
Min.
...
...
...
...
0 5
245 170 153 130 130 92 94
0 10 20 30 45 90 120 200
160 136 125 125 125 10s 105 108
10 20 30 120 200
...
...
OILS Midcontinent cylinder stock of the following characteristics was used: Gravit5 O A . P. I. Flash, F. (" C.) Fire O F. (" C.) Viscbsity at 100' F. (37.8' C.) Viscosity at 210' F. (100" C.) Viscosity index
21.4 515 (268.3) 560 (293.3) 3350 154 75
The stock was first treated with one pound of 98 per cent sulfuric acid per gallon of oil (0.12 kg. per liter). One portion of the stock was then contacted with an acid-treated clay, designated "A," another portion with a n acid-treated clay, designated "B," and a third portion with a natural clay.
TIMEOF CONTACT The experimental data presented in Table I and Figure 2 show the results obtained in contacting acid-treated cylinder stocks with definite amounts of clays for various lengths of time and a t different temperatures. The data show that the time of heating the oil with clay a t the maximum temperature has a decided influence on the color of the finished product. I n general, the color of the oil improves as the time is increased up to a certain maximum, beyond which the color of the oil appears to remain constant. This is particularly true for acid-treated clays A and B, but not necessarily so for the natural clay. The natural clay behaved peculiarly, particularly a t higher contacting temperatures. At 700' F. (371.1' C.) the color of the oil improved as the time of contact was increased up to about 20-30 minutes. On further heating, the color began to darken and reached a maximum after contacting the oil with clay for approximately 60 minutes. On still further heating, the color showed again a n improvement, tending to approach a constant value. These results are probably best explained on the assumption that several simultaneous reactions occur between oil and clay. At first the adsorption of the coloring matter by the clay appears to predominate, but a point is finally reached
3% by weight.
b
4% b y weight.
C
8% by weight.
Although the experimental work shows that the color of the oil contacted with clay reaches a constant value as the time is increased beyond a certain value, this does not preclude the possibility that, by increasing the time beyond the present experimental limits, some other color changes might be observed. There is reason to believe that the time-color intensity curves depend on the quantity of the clay used, but this relationship has not been established definitely. TEhlPERATURE O F
COXTACT
The experimental data show that the maximum temperature a t which the oil is contacted with clay has a considerable influence on the color of the resulting product. Activated clays A and B illustrate this influence particularly well, showing a continued improvement in color of the oil with increased temperature but fixed time of contacting. The natural clay, however, apparently reaches its maximum decolorizing power a t a relatively lower contacting temperature than the two former clays. It is particularly interesting t h a t the 600' and 700' F. (315.6' and 371.1' C.) time-color intensity curves cross each other, probably owing to the changes in the relative velocities of the concurrent reactions already discussed. It is believed that the experimental differences obtained in these tests are beyond the limits of experimental error, since duplicate experiments were in agreement. The experimental data also show that, although the contacting temperature is of considerable importance in obtaining the maximum degree of decolorization, it is frequently possible to obtain an oil of even better color a t lower contacting temperature by properly controlling the time of contact. More time is usually required to reach a constant color value for the oil a t lower than a t higher contacting tempera-
August, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
tures, which would be anticipated from theoretical considerations of reaction velocities. It is evident, however, that the development of a convenient mathematical formula for evpressing the time-temperature relationship for the reactions involved in the decolorization process is particularly difficult, owing to the multiplicity of reactions involved and their probable vaiiations a t different contacting temptlratuIes.
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vated clay A a t 700" F. and 30 minutes of contact was assumed to be 100 per cent. The results show that clay efficiencies generally decrease as the contacting time is shortened or the temperature lon-ered, which is in agreement with the previous discussion. Hon-ever, entirely different results may be obtained if the time of contacting is not
EYALCATIOK OF CLAYEFFICIENCI 300 The usual method of e.caluating the decolorizing efficiency zoo of clays involves determining the quantity of clay required to decolorize a ceitain oil under fixed conditions of temperature and time in comparison with t h a t amount clf a standard clay required to effect the same degree of decolorization under similar conditions. The importance of the temperature factor 400 and its variation with the type of clay used is now being 300 gradually recognized and taken into consideration by petro200 leum chemists in interpreting laboratory results. The time factor, however, has not been sufficiently recognized to include 4 ,oo it in the routine testing of contact clays. 8 60 I n order to show the imDortance of the time> factor in a comprehensive study of clays, the decolorizing efficiency of 300 each of the three clays used was evaluated with respect to time, using a n acid-treated Midcontinent cylinder stock. ZOO The color intensities of the oil contacted with various quantities of clays for 0, 10, and 30 minutes at 500", 600", and IO0 700" F. (260", 315.6", and 371.1" C.) were determined. TIME OF CONTACT AT MAXIMUM TEMPtRATURE (MINUTES) An arbitrary color intensity of 100 was chosen as the referFIGURE 2. EFFECTOFTIMEIN DECOLORIZIVC OILS W I T H ence for evaluating the clay efficiencies. The decolorizing COiYT.4CT CLAYS efficiencies were then determined by dividing the percentage (Midcontinent cylinder stock pretreated with acid). A . Activated of the standard clay required to obtain this color intensity clay A. B. Activated clay B. C. Natural clay by the respective quantity of the unknown clay or of the same standard clay but at diffeient treating contlitions. strictly standardized or if comparisons are made by assigning a 100 per cent efficiency for the clay a t some other temperaTABLE11. DECOLORIZING EFFICIEXCIES OF C L ~ YWITH S ture than 700" F. The change in efficiency in assuming a RESPECTTO ACID-TREATED MIDCONTINENT CYLINDER STOCK AT V.4RIOUS TIMESAND TEMPERBTCRES color intensity other than 100 is frequently considerable, but OF CONTACT^ the importance of this is already well known. EFFICIENCY The above discussion of clay efficiencies refers only to TEMP. TIME Clay A Clay B Natural clay changes in color of the contacted oils and does not take into O F Man. % % 470 account the changes in stability or in viscosity characteristics 700 30 100 69 35 10 94 58 31 of the resulting products, oil losses, etc. All these factors 0 77 40 18 69 36 20 30 600 are also affected by the time as well as by the temperature 61 30 17 10 of contact and cannot be neglected if a true picture of the 47 22 15 0 500 30 42 20 13 commercial value of a clay is desired.
5
10 0
a
Reference color intensity =
100.
39 30
16 12
12
9
I n carrying out these calculations it was found that for a constant time and temperature the plot of the percentage of clay used us. the color intensity of the treated oil is generally, but not always, represented by a straight line on double logarithmic paper. While this would seem to indicate the applicability of Freundlich's adsorption isotherm t o the decolorization of petroleum oils with clay (1, $1, deviations which were observed in some instances and the complicated character of some of the time-color intensity curves leave in doubt the question of whether or not this agreement is accidental. Severtheless, the use of such plots may be recommended, as extrapolations are much easier from straight or only slightly curved lines than from lines with very considerable curvature such as are obtained by using other methods of plotting the experimental data. A few deviations which were found from the straight lines evidently precluded the possibility of expressing efficiencies as a function of color intensity of the treated oil, which should be possible if Freundlicli's isotherm m-ere universally applicable. The relative color efficiencies of clays obtained in this investigation are given in Table 11. The efficiency of acti-
ACKNOWLEDGMENT The authors are indebted to B. W. Story of this laboratory for his many valuable suggestions and constructive criticisms in the course of the work.
LITERATURE CITED (1) Davis, L. L., Refiner Natural GasoZine M f r . , 7, No, 3, 90-1, 100 (1928). (2) Meador, R. O., Ibid., 7, No. 9, 61-4 (1928). (3) Story, B. W., and Kalichevsky, V., IKD. Em+.CHEM.,Anal. Ed., 5 , 214 (1933). RBCEIVEDFebruary 1, 1933. Presented before the Division of Petroleum Chemistry a t the 85th Meeting of the American Chemical Society, Waahington, D. C., March 26 to 31, 1933.
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