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tinuous Laboratory T H. T. RALLAND H. M. SMITH,U. S. Bureau of Mines, Petroleum Experiment Station, Bartlesville, Okla. tionating tower &, which is also packed with No. 18 jack chain. Here the heavier fractions of the distillates are separated and washed back, while the vapors pass to condenser R where they liquefy, the condensate collecting in the receiver, S. The gas passes through flask X and line T to the vacuum pump and thence to the atmosphere. It is essential that receiver 8 be kept cold enough so that the vapor pressure of the distillate will be negligible. For the same reason condenser R must be cold enough to liquefy all vapors.
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NVESTIGATIONS concerned with the character and composition of the less volatile constituents of petroleum should be conducted with material as little changed from the original as possible. This means that the more volatile components of a crude oil must be removed under such conditions that there is only a minimum opportunity for decomposition to occur. In several projects a t this station there has been need for a continuous topping method that would remove gasoline, kerosene, and gas oil from petroleum without decomposition either of the tops or of the residuum. In two of these investigations (1, 6) the gasoline was removed a t 100' C. by distillation with natural gas, and the kerosene and gas-oil fractions were subsequently removed by steam distillation in a gas-fired still. However, this necessitates heating the ail to several hundred degrees Centigrade, and even with steam there is considerable possibility for decomposition where the oil is in contact with the hot still walls, particularly with certain types of crude oil. I n connection with some work now under way, it seemed advisable to develop means of topping that would remove all of the lighter constituents up to oil having a viscosity of about 50 seconds Saybolt without heating the crude above 150" C. The fundamental principle used to accomplish this was that of isothermal evaporation from a thin, heated film of oil at pressures of 2 to 5 mm. of mercury. A few experiments indicated that, in addition, a short fractionating column and the sweeping action of a small stream of inert gas would help considerably in obtaining the desired objectives. The fractionating column virtually eliminated overlap between distillate and residuum, while the small gas stream, countercurrent to the oil flow, besides substantially reducing the effective evaporation pressure of the oil, continuously removed the more or less stagnant layer of heavy vapors formed by evaporation from the oil film.
The operating procedure is as follows : The entire topping system is evacilated to a constant minimum pressure which should be 2 mm. or less.' Nitrogen or natural 1 If the apparatus is absolutely free of leaks and of material having a measurable vapor pressure a t the temperature of the manometer, the pressure indication should be zero. I n practice these conditions are not completely fulfilled.
DESCRIPTION OF APPARATUS As a result of several experiments the apparatus shown in Figure 1 was developed. It consists essentially of two independent parts, the heating circuit and the topping system The heat needed by the process is supplied by the hot vapors of a liquid boiling in the flask, A . These vapors ascend through line B, enter the outside chamber of isothermal heating unit C at the top, and pass through the chamber and out at the bottom to D, where they are condensed and returned to the boiler, completing the circuit for the heating medium. The temperature of the vapor leaving the bottom of the still is determined by thermometer E. In practice, the vapor stream should have a velocity and volume sufficient to maintain this temperature constant, whether or not the topping section is being used. The topping system may be considered conveniently by following first the ath of the crude oil through the apparatus and then the course ofthe gas and vapors. The crude oil to be topped is poured into storage flask F through strainer G and drawn by the vacuum in the system through line H and control cock I into degasser and foam breaker J. The crude then enters the top of the isothermal heating chamber C through stopcock K and dripper L. The heating chamber is simply an eight-bulb condenser; the four top bulbs are packed with No. 18 steel jack chain, and the four bottom bulbs are empty. The chain provides much surface and serves as a heat reservoir to heat the cool, incoming crude oil quickly. The oil passes downward through the still and eventually runs out of dripper M into topped-oil receiving flask N . By proper manipulation of stopcock 0, flask N may be removed, emptied, and reevacuated without stopping the distillation. While the crude oil is flowing downward through the heater, a small stream of inert gas is admitted in the center of the bottom bulb at P. This gas rises countercurrent t o the descending oil film and carries the vapors evaporated from the crude-into frac373
u
FIGURE 1. ISOTHERMAL CRUDEOIL TOPPING UNIT
A N A L Y T I C A L EDITION Vol. 6, No. 5 gas is then admitted until the manometer remains constant at TABLEI. VACUUMDISTILLATION AT 40 MM. PRESSW~ the working pressure, generally 8 to 20 mm. of mercur dependORIQINAL TOPPEID ing upon the extent of to ping desired. This gas suppr; is easily CRUDJJ CRUDJJ~ Initial temp., C. 114 194 controlled by a fine neeie valve which has a constant pressure 1.35 0.0 of one ound r square inch (0.07 kg. per sq. cm.) gage on the 8.80 0.0 inlet d e , so t%t in effect the needle valve acts as a flowmeter, 15.70 0.0 and, once the initial evacuation ressure and working pressure 28.20 1.2 35.75 11.5 have been fixed, there will be no gctuation unless leaks develop. 43.55 21.0 There will be small amounts of dissolved gas evolved from the a Topped at 158; C. (boiling turpentine) and 19 mm. total pressure with crude, but, if the pump has ample capacity and the crude input about 18 mm. partial Dressure of natural 888. to the degasser is kept reasonably constant, these gases will not A four-unit apparatus has also been constructed, in which the units are connected in parallel to the crude-oil source, topped-oil receiver, gas inlet, distillate receiver, and vacuum pump. Topped oil from this apparatus, using nitrogen as the inert gas and a temperature of 158’ C., shows virtually the same characteristics as that given in Table I. There is a small gap between the topped oil and the distillate, as shown in Figure 2, where distillation curves for the crude oil, topped oil, and distillate are given. These are all made with a standard Engler apparatus. The curves indicate that the separation is fairly sharp. The apparatus described is very flexible from an operating standpoint. Liquids covering a wide range of boiling points may be used as the heating medium, and pressures may be VOLUME DISTILLED, PER CENT varied over a considerable latitude. The partial pressures FIGURE2. ENGLER DISTILLATION CURVES of the gas used may also be changed to suit conditions, as may the kind of gas used. It is obvious that the capacity of such appreciably affect the pressure. A flowmeter couldibe inserted advantageously in the gas supply line t o afford visual evidence an apparatus is small. The four-unit set-up has a capacity of the amount of gas entering. After a constant working pres- of 200 to 300 grams of topped oil per hour when used with sure has been set, the crude is allowed to enter slowly until tem- the crude oil mentioned above under conditions removing perature equilibrium in the fractionating tower is attained, when about 21 per cent of the crude. The apparatus may be conthe rate of crude input is fixed t o maintain the desired temperature at the top of the fractionator, as indicated by the copper- structed readily from materials usually available in the laboraconstantan thermocouple, W. If the entire ap aratus is well tory. insulated, uniformly reproducible results shoufd be possible LITERATURE CITED since the following factors, which also control the reflux, are fixed: total and partial pressure, heat input, and crude input. (1) Smith, H. M., Bureau of Mines, Tech. Paper 428 (1928). (2) Smith, H. M., et al., Ibid., 477 (1930). This apparatus has been used for topping a crude oil from RJJCJJIV~D May 25,1934. Presented before the Division of Petroleum Chemthe Port Neches Field, Texas. The characteristics of the iatry at the 12th Midwest Regional Meeting of the American Chemical original crude and of the topped oil, as indicated by vacuum Society, Kansaa City, Mo., May 3 to 8 , 1934. Published by permission of distillation at 40 mm. pressure, are shown in Table I. S. Bureau of Mines. (Not subject to copyright.) 374
Determination of Phosgene by the Soda Method I
Effect of Fire-Extinguisher Chlorinated Hydrocarbons MARYAN P. MATUSZAK,~ U.S. Bureau of Mines, Pittsburgh, Pa.
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T HAS been claimed (6) that values obtained by the U. S. Bureau of Mines with the alcoholic soda method (2,S),for phosgene produced by oxidation of carbon tetra-
chloride, were too high because of “hydrolysis of carbon tetrachloride and other chlbrinated hydrocarbons.” That no error due to the presence of carbon tetrachloride was found in blank determinations made under the specified conditions of analysis was confirmed by a tube experiment (2, Table 111), in which three determinations showed no phosgene whatever, although a concentration of carbon tetrachloride of 14,000 p. p. m. was present. In several similar blank determinations the writer has likewise failed t o detect any error due to absorption and saponification of carbon tetrachloride, even when using a more sensitive technic (4) in the Mohr titration than the earlier workers. It is not implied that carbon tetrachloride cannot be Present address, 301 South Creek Ave., Bartlesville, Okla.
saponified by alcoholic soda. But if the conditions of analysis used in the earlier work-absorption, a t 0.5 liter per minute, of 4 or 5 liters of air Containing carbon tetrachloride up to 5850 p.p.m., or of 0.5 to 1 liter containing up to 14,700 p. p. m., by a petticoat-bubbler ahsorber containing 50 cc. of N sodium hydroxide in 85 per cent alcohol-are maintained, and if neutralization is not unreasonably delayed, no error due to this compound is present. Chloroform, the next most abundant component of commercial fire-extinguisher liquids, saponifies more readily than carbon tetrachloride (6). Hence, experiments were made to determine the concentration a t which it causes a detectable error under the conditions of analysis. Chloroform-containing air samples, 5.08 liters in volume, were absorbed by 50 cc. of N sodium hydroxide in 85 per cent alcohol in a petticoat-bubbler absorber during 10.5 minutes. The Mohr determinations were made with great care. Neutrali-
