INDUSTRIAL A N D ENGINEERING CHEMISTRY
May, 1926
interested in petroleum chemistry. It is a fact, a matter of the actual experience of those large industries who have carried on research entirely a t their own expense, but on very
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broad lines, that discoveries of greatest industrial value come, not from petty, pot-boiling work hardly deserving the name research, but from the bold delving into fundamentals.
Effect of Pressure and Temperature on Total Volume of Partially Vaporized Midcontinent Crude' By Robert E. Wilson and H. G. Schnetzler STANDARD OIL Co. (INDIANA), WHITING,IND.
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S ORDER to make an intelligent design of a pipe still or
of a series of heat exchangers where a moving stream of liquid is heated and partially vaporized, it is necessary to know approximately the amount of liquid vaporized, or better, the volume of vapor plus liquid, as a function of' temperature and pressure. These data cannot be determined a t all accurately either from an ordinary distillation or from a vapor pressure curve, since it is a complicated function of pressure, temperature, and composition. Attempts to estimate it by conventional methods have been found to give quite inaccurate results. On the other hand, direct measurements to cover the various combinations of pressures and temperatures met in practice are not feasible by the ordinary methods which might be employed for a single determination. This paper describes a method which has been perfected in this laboratory for determining the necessary data and presenting the results in graphical form, and gives the results obtained on a typical Midcontinent crude oil containing various amounts of water. Method
The method consisted essentially in introducing different volumes of the liquid to be tested into a previously evacuated bomb of known volume and measuring the pressures set up a t different temperatures. From the resulting pressuretemperature curves made with different ratios of total volume to cold liquid volume, it is then possible to plot another series of curves showing the ratio of total volume to the volume of the cold liquid as a function of temperature and pressure. In arranging the apparatus it was found necessary to have the pressure gage a t some distance from the bomb in order to prevent its being affected by the temperature. The connecting tube had to be filled with a nonvolatile, oil-insoluble liquid in order to prevent any condensation of vapors therein, while the gage itself was filled with water to prevent mercury from attacking the pressure element. The arrangement of the system is shown in Figure 1. The pressure gage and the system as a whole were found to be substantially correct by measuring the pressure developed by measured amounts of water a t various temperatures. It was desired to make the measurements on samples of Midcontinent crude with several different water contents, covering the range likely to be met with in practice-in other words, up to about 2 per cent by volume of water. The first measurements were therefore made on pipe-line crude containing 0.2 per cent water. Three other sets of measurements were made on samples containing 1 per cent and 1.75 per cent water and on a sample dried by filtering through paper, taking precautions to prevent loss by evaporation. The samples containing 1.0 and 1.75 per cent water were made up by adding measured quantities of the salty water which had separated 1 Received March 23, 1926. Presented before the Divizion of Petroleum Chemistry at the 71st Meeting of the American Chemical Society, Tulsa, Okla., April 5 to 9, 1926.
from crude to the sample of crude containing 0.2 per cent. To prevent any segregation this additional water was measured and introduced into the bomb separately for each charge. Results
The crude used in these tests gave the following Engler distillation (-4. S. T. M. apparatus for gasoline) : Distillation of Midcontinent Crude Water, 0.2 per cent b y volume Gravity, 35.0' A. P. I .
% 08 Initial 10 20 30 40 50 60
70
O
F.
152 252 322 405 473 558 633 690
% 08 6.0
16.0 25.5 27.5 38.0 42.5 55.0 72.0
O
F.
22 1 284 374 392 460 500 600 700
The direct results obtained from each series of measurements are shown in Figure 2 which plots pressure against temperature for different volumes charged to the still. Figure 3 shows plots based on these same results in which the ratio of the volume of vapor plus liquid to the volume of cold liquid is plotted against pressure for different temperatures. The latter figures are more useful in practical design. In considering these figures one is particularly impressed by the large differenceproduced by the variations in the water content of the crude. This is, of course, due to the fact that water
Figure I-Apparatus
because of its very low molecular weight, expands much more in vaporizing than does oil. Thus at 300" F. and 40 pounds pressure dry crude has not expanded over 15 per cent, while crude containing 1.75 per cent water expands 1100 per cent. It is interesting to note that, while 0.2 per cent of water markedly increased the pressure at different temperatures, it does not give the rather striking bulges in the curves which are shown by crude containing 1 per cent and 1.75 per cent of water.
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Vol. 18, No. 5
If the water is all present as a separate phase (emulsified drops) its vapor pressure should merely be added to that of dry crude up to the time it is all vaporized a t the pressure and temperature prevailing. By adding together the vapor pressures measured for dry crude and those calculated for a given amount of water, it is possible to calculate a theoretical vapor pressure curve for wet crude, as has been done in Figure 4 for crude containing 1.75 per cent water, a t 300" F. and varying pressure. It will be noted that the observed curve has the same peculiar shape as the calculated, but is rounded off and is somewhat lower throughout. This discrepancy increases I
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Figure 3-Effect of Temperature a n d Pressure o n t h e Total Volu m e of Partially Vaporized M i d c 0 n t i n e n . t Crude
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
May, 1926
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with increasing total pressure, and also with increased temperatures, and is undoubtedly due in large part to the actual solubility of part of the water in the crude oil. That this may be quite appreciable is shown by the results of Groschuff.2 The increase at higher temperatures and pressures is, of course, characteristic of immiscible liquids. The presence of dissolved salt in the water would also have a slight effect in lowering the observed vapor pressures, especially when the water is nearly all vaporized. At moderate pressures and a t temperatures above 300' F. the volume of vapors produced is so large that it must certainly be taken into account in calculating heat consumption, rates of heat transfer, and pressure drops to be anticipated in all equipment where a moving stream of oil is heated. The serious effect of even small slugs of water or highly emulsified crude is readily apparent from the results on crude containing only 1.75 per cent water as compared with dry crude. 2
Leslie, "Motor Fuels," p. 646; C. A , , I , 2550 (1911).
Power and the Viscosity of Oil' By William F. Parish PARISH & TEWKSBURY, INC., 17
H E interest shown in lubricating oils of late years prompts this author to place in a convenient record some work in Germany, which was reported in part by Philip Kessler before the Verein deutscher Chemiker in 1910. This work was in answer to theories personally advanced by Professors Engler, Holde, Ubelholde, and others, that viscosity was the main characteristic of a lubricant for determining its lubricating power. The popular lubricants for industrial machinery in Germany came from Russia, these oils being the cheapest on the market. In making power tests against these heavy bodied oils and showing very considerable power reductions by the use of American oils, the technical fraternity in Germany became much interested. In certain textile mills power reductions of over 15 per cent were shown through the use of the American oils, resulting in their permanent establishment. One mill required a second demonstration again to supplant Russian oils, which, however, had been mixed to secure lower viscosity, when the power saving with American oils was about 8 per cent. The theory was then advanced that viscosity was the main factor in making power tests. A later examination of the lubricants a t the same mill showed that the viscosity of the mixed local spindle oil was identical with that of the American oil. The author then changed the program of testing and established a method of showing that, irrespective of viscosity, a properly refined and finished oil would wear longer without decomposition than an oil made up by mixing heavy and light distillates to suit a specification based entirely upon viscosity. It is admitted that two oils of the same viscosity in the bearing will show the same coefficient of friction on a handoiled testing machine as long as speed, temperature, and pressure will not allow either oil to decompose or change in the slightest degree. It is only when the more modern methods of severe service and continuous application are used that the oil shows changes in character. These changes are in no way indicated in a preliminary examination of the oil by its viscosity alone. The work done was decisive and has influenced the German technical opinions on the subject. One test was on a ring
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1
Received March 11, 1920.
EAST 4
2
Sr., ~ New ~ YORK,N. Y.
spinning machine in a cotton mill (Chart 1). The power measurements were made with an absorption dynamometer, other measurements by standard instruments of the finest kind. The machine was cleaned in the same manner before each oil was put in. The two new oils were analyzed in the laboratory of an oil company. No. 1 is the American oil and No. 2 is the oil made up locally to duplicate it. The American oil is taken as the basis of performance-power and temperature being increased and speed reduced by use of the mixed oil No. 2. Spinning Frame Test Properties No. 1 No. 2 0.880 0.855 Specific gravity 150' C. 142O C. Flash (Pensky-Martin) Fire 176' C. 166' C. - 8 . 5 ' C. - 7 . 5 ' C . Pour Acidity (SOJ) 0.008 0.02 Natural Mirbane Odor 54 sec. 5 3 . 5 sec. Viscositv. at 40' C. .. Savbolt . Performance Hours run Dynamometer horsepower: Empty machine Machine spinning Speeds per minute: Empty machine' Drum Spindle Ratio Machine ;pinning: Drum Spindle Ratio Relative humidity Temperatures, O C . : Room Spindle base Frictional heat (R-Sb)
348 1.416 2.570
Difference
342 1.517 2.695
0 . 1 0 1 (7.15%) 0.125 ( 4 . 9 % )
810.6 808.7 8863.0 8838.6 10.934 10.929
0.005 (0.05%)
808.0 806.0 8841.2 8784.0 10.942 10.898 71% 73% 26.68 29.87 3.19
25.25 29.48 4.23
0 . 0 4 4 (0.402%)
1 . 0 4 (32.6%)
Another series of tests were made on a cotton twisting machine. This machine has larger and heavier spindles, but the oils were substantially the same as those used on the dynamometer test, though the No. 2 oil was slightly changed. The appearance and odor suggested quite clearly what had been done in blending it, though nothing was shown in the analysis that in any way indicates the peculiarity. The oils were examined in the laboratory of an oil company. Each oil had run in the same machine for four weeks. As before, the American No. 1 oil was taken as the basis of per-
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