Liquid Butane as Motor Fuel Corrosion Test Methods M. M.HOLM, Standard Oil Company of California, Richmond, Calif.
holder is connected to the vaporizer and the orifice meter. A weighed 75-liter (20-gallon) cylinder of the test fuel is inverted to permit withdrawal of liquid and connection is made to the vaporizer. Steam is turned on and superheated fuel containing the suspected contaminant is passed over the test mirrors. Rate of fuel charge varies from about 5 to 25 k . (10 to 50 pounds) per hour. Total quantity charge may be asqow as 0.5 or 1 kg (1 or 2 pounds), but with most fuels it is desirable to charge 10 kg. (20 pounds) or more. Exact rate and total quantity are governed by the appearance of the mirrors, care being taken to limit any darkening or other evidence of corrosion to metal in the first 7.5- t o 10-cm. (3- or 4-inch) section of the gage glass, For making these adjustments, a control valve is provided in the line between the gage glass and orifice meter. Temperature in the line immediately following the gage glass is maintained at 120" C. (250" F.), control being the steam pressure applied to the vaporizer. After a suitable quantity of fuel has been charged, the feed valve is closed and the cylinder is disconnected and again weighed. The gage glass is then removed from its holder for close inspection of the test mirrors.
SE of liquid butane as motor fuel involves certain problems in refinement and handling not encountered with heavier fuels. Origin of the particular problems pertinent to this discussion centers in the specialized equipment required for proper vaporization and carburetion of the liquefied gas. Conventional equipment for this service comprises a pressure-regulating valve, a heater, and a butane-metering valve. Presence of minute traces of contaminants in the fuel eventually results in improper functioning of this equipment. I n many cases the concentration of interfering material may be so low as to defy detection by ordinary methods of analysis. Contaminants may be grouped conveniently as insoluble scale and dirt : butane-soluble, noncorrosive, nonvolatile material; and material which is corrosive to metal equipment under service conditions. Insoluble scale and dirt present no great problem since they are normally removed by a metal screen placed in the liquid fuel line ahead of the pressureregulating valve. On the other hand dissolved nonvolatile material, such as pipe-threading compounds and valve lubricants, even though not corrosive, has a tendency to collect a t points of low gas velocity in the metering valve, eventually contributing to improper seating. Particularly objectionable is the corrosive type of contaminant, since it not only destroys the equipment but interferes with satisfactory operation before complete failure occurs. Any test procedure for determining quality of a given fuel should be rapid and simple, and give results which can be interpreted in terms of actual service. It is believed that such a procedure has been devised for the specific problem outlined.
Discussion Many fuels are perfectly clean; so when the test is completed the mirrors are bright, showing no evidence of oil, scum, or color change. The nonvolatile, noncorrosive, butanesoluble type of contaminant is readily detected by the appearance of an oil or scum on the mirror surfaces. When the corrosive type of contaminant is present a rapid change in color is noted-for example, darkening is noted in a few minutes with fuel containing 0.000001 per cent of elementary sulfur. mIfIcF METER
Method In principle the method involves inspection of minute quantities of metals which have been exposed to large quantities of the test fuel under conditions representative of, or more severe than, normal service. To facilitate rough visual comparisons and to provide a large contact surface, the metals are prepared in the form of thin copper or silver mirrors on glass, TJse of both types of mirror is usually desirable, the former being representative of the metal in the conventional butane heater and the latter having the advantage of pronounced change in appearance in presence of even the slightest trace of corrosive sulfur. Copper mirrors are prepared by reduction of cupric ammonium hydroxide solution with phenylhydrazine (2). Silver mirrors are prepared by the conventional Brashear formula ( I ) , using sugar as the reducing agent. A sketch of apparatus suitable for contacting the mirrors with the fuel in question is shown in Figure 1. Essential units comprise a steam-heated vaporizer, a 25-cm. (10-inch) section of 1.9-cm. (0.75-inch) gage glass encased in a slotted metal holder, and an orifice gas meter. All parts coming into contact with either liquid or vaporized fuel must be corrosionproof. Chrome-nickel steel is suitable for metal parts. Any gasket material used in making up tight connections should be of such composition that contamination of the fuel is impossible. Asbestos is a satisfactory packing for sealing the gage glass in its metal holder.
FIGURE1
Fuel may usually be rated as satisfactory or unsatisfactory on the basis of mere visual inspection of the test mirrors. In cases where qualitative identification of the contaminant is required, the microanalytical procedure to be followed will naturally depend upon the appearance of the mirrors and any clues provided by previous history of the sample. For example, presence of valve lubricant in some fuel samples has been proved by determining saponification number and wax content of the oily scum. Likewise, with another fuel suspected of sulfur contamination, the suspicion was proved correct by decomposition of the darkened copper mirror with zinc and hydrochloric acid and detection of hydrogen sulfide in the gas evolved. With certain fuels it may be desirable to supplement qualitative identification of the contaminant with critical determination of the quantity present. Such determination is feasible by conventional methods only when the proportion is relatively large-for example, 0.0001 per cent by weight or greater. However, a semi-quantitative index of the concen-
In operation the metal test mirrors, supported, for example, on
glass pearls, are packed into the gage glass, and the gage-glass 299
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tration of the corrosive type of contaminant may be obtained from an estimate of the surface corroded and the known thickness of the mirror. Thickness of mirrors usually varies from about 3 X 10-6 to 20 X 10-6 mm. ( I ) . Obviously no general rule can be laid down as to the depth of film which an unknown corroding agent will penetrate. I n the above-mentioned experiment where sulfur contamination was proved, the copper mirror was about 20 X 10-5mm. thick and average penetration of the corroding agent was to a depth of only 5 X 10-6 mm. It is suggested, therefore, that mirrors of minimum thickness be employed in tests where more than qualitative information is desirable. By use of thin mirrors it is possible to make a semi-quantitative estimate of the concentration of corrosive type of contaminant when the order of magnitude is only 10-7 per cent by weight. Experience with the test procedure outlined indicates that thoroughly satisfactory results with a liquefied gaseous motor fuel will be obtained only if extreme care is taken to avoid contamination in manufacture, transportation, and transfer to customer’s equipment. The following warning instructions are suggested :
1. All fuel tank openings, as well as vapor and liquid transfer hoses, should be capped when not in actual use. 2. When coupling hoses, care should be exercised to prevent entrance of any dust-it may be corrosive. 3. Rubber lining in transfer hoses should be avoided because of possible sulfur leaching. Flexible all-metal hoses or DuPrenelined hoses are preferred. 4. Valve lubricants should not be used. Although certain types are hydrocarbon-insoluble in the usual sense of the term, the solubilities are sufficient to cause trouble in the present service. 5. Welded pipe connections are preferred. In cases where threaded connections are unavoidable, joint dopes should be used sparingly with attention given to prevent them from entering the fuel system.
Literature Cited (1) Bur. Standards, Circ. 389 (1931). (2) Chattaway, Proc. Rou. SOC.(London),80A, 88-92 (1907). R E C E I V ~May D 13, 1936. Presented before the Divisions of Gas and Fuel Chemistry, Industrial and Engineering Chemistry, and Petroleum Chemistry, Symposium on Motor Fuels, at the 91st Meeting of the American Chemioal Society, Kansas City, Mo., April 13 t o 17, 1936.
Modification of the Suspended-Level Viscometer E. H. PAYIVE AND CLARKE C. MILLER, Standard Oil Co. (Indiana), Wood River, 111.
I
(4)published his researches on the development of the suspended-level viscometer, and in 1935 FitzSimons ( I ) described certain changes and accessories which made the instrument more suitable to the particular requirements of the petroleum industry for accurate and speedy viscosity measurements. While this stage of development has been found to be satisfactory, independent study of constructional and operating details by the authors’ laboratory has brought out further modifications in the suspended-level viscometer which have been found advantageous in routine viscosity determinations, as well as research work. It is the purpose of this paper to discuss these features.
bulb, M , the suction is withdrawn, stopcock 3 is opened to the air to form the suspended level, and the flow of oil timed between the two marks x1 and x2 of large bulb A. As many check determinations as desired can be made by repeating the above procedure, without removing the oil from the viscometer. The viscometer is cleaned by draining the oil out through stopcock 6. The entire viscometer is washed out with any suitable low-boiling solvent by filling from the bottom, and using the manifold connections as described. Two washes are sufficient and after the final wash has drained, the entire viscometer is dried out by blowing warm, dry filtered air through all cocks and portions of the viscometer proper.
Modified Suspended-Level Viscometer
and (1) describe the method of calculating a correlation equation for kinematic viscosity in terms of efflux time, based upon accurately measured dimensions of the instrument. However, the authors’ preferred method of calibration is against three or preferably more oils of known and representative kinematic viscosity a t convenient temperatures, the results of which may be correlated in an equation of the form
N 1933 Ubbelohde
The viscometer shown in Figure 1 consists of two pipet-like bulbs, A , connected to two capillaries, B, of different radii and sealed to U-tube oil reservoir C. Tubes D and E serve as air vents for producing the suspended level. Leading into the U-tube oil reservoir, C, is the helical tube, F, through which the viscometer can be filled from the bottom. The entire viscometer is sealed into vapor bath G which is heated by vapors from a pure liquid compound boiling in bulb H . The vapors surround the entire viscometer, maintaining a uniform temperature throughout, Vapors escaping from the vapor bath are condensed in condenser I and returned to bulb H through the line, J. The liquid in bulb H is heated by any convenient means but preferably by an electric heater, K. The temperature of the bath is determined by means of a thermometer (not shown) placed in the vapor space, and the temperature can be regulated and maintained constant at any desired point by either the application of pressure or vacuum. The capillary and air vent tube are connected by means of rubber tubing to a rigid metal manifold, L,which has been found to be advantageous when filling, and cleaning the - operating, . viscometer. OPERATION.All stopcocks on the manifold, L, are closed excent 1 and 2. Gehtle suction is applied at 1, and the clear oil t o be tested is sucked in at the botiom connection, 6, until the U-tube reservoir, C, is about two-thirds full. The bottom connection, 6, is closed, suction is withdrawn from 1, leaving this cock open to the air, and the oil is allowed to come to the temperature of the bath. Tube E is provided with a second thermometer for determining when the oil is at proper temperature for test. Stopcock 2 is closed and the oil drawn into the desired capillary by gentle suction at either 4 or 5. When the oil reaches the small
Calibration of Suspended-Level Viscometers INTERMSOF KINEMATIC VISCOSITY.The literature (4)
kinematic viscosity
=
At
- B/t
(1)
where t equals efflux time in the suspended-level instrument, and A and B are instrumental constants established by collecting sufficient data to cover the desired range of viscosity. Herschel (2) has used a Higgins (3) plot of the variables kinematic 1 versus efflux time (efflux time)2 to arrive a t these constants for the various technical efflux viscometers, and a like procedure may be used here. Alternatively, since it is usually desirable to have the calibration equation fit the low viscosity calibration data most closely, a procedure somewhat resembling the method of least squares may be applied; however, departing from the conventional method in the use of normal equations in the form kinematic efflux time
-A
R + (efflux time12
(2)
