D 2879 – 97 R02_RDI4NZK_

Designation D 2879 97 Reapproved 2002 e1 An American National Standard Standard Test for Vapor Pressure-Temperature Relationship and Initial Decomposition Temperature of Liquids by Isoteniscope 1 This standard is issued under the fixed designation D 2879; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon e indicates an editorial change since the last revision or reapproval. e 1 NOTEWarnings were moved from notes to section text editorially December 2002. 1. Scope 1.1 This test covers the determination of the vapor pressure of pure liquids, the vapor pressure rted by mixtures in a closed vessel at 40 6 5 ullage, and the initial thermal decomposition temperature of pure and mixed liquids. It is applicable to liquids that are compatible with borosilicate glass and that have a vapor pressure between 133 Pa 1.0 torr and 101.3 kPa 760 torr at the selected test temperatures. The test is suitable for use over the range from ambient to 748 K. The temperature range may be extended to include tem- peratures below ambient provided a suitable constant- temperature bath for such temperatures is used. NOTE 1The isoteniscope is a constant-volume apparatus and results obtained with it on other than pure liquids differ from those obtained in a constant-pressure distillation. 1.2 Most petroleum products boil over a fairly wide tem- perature range, and this fact shall be recognized in discussion of their vapor pressures. Even an ideal mixture following Raoults law will show a progressive decrease in vapor pressure as the lighter component is removed, and this is vastly accentuated in complex mixtures such as lubricating oils containing traces of dewaxing solvents, etc. Such a mixture may well rt a pressure in a closed vessel of as much as 100 times that calculated from its average composition, and it is the closed vessel which is simulated by the isoteniscope. For measurement of the apparent vapor pressure in open systems, Test D 2878, is recommended. 1.3 The values stated in SI units are to be regarded as the standard. The values in parentheses are for ination only. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use. For specific hazard statements, see 6.5, 6.10, and 6.12. 2. Referenced Documents 2.1 ASTM Standards D 2878 Test for Estimating Apparent Vapor Pres- sures and Molecular Weights of Lubricating Oils 2 E 230 Specification and Temperature Electromotive Force EMF Tables for Standardized Thermocouples 3 3. Terminology 3.1 Definition of Term Specific to This Standard 3.2 ullagethat percentage of a closed system which is filled with vapor. 3.2.1 DiscussionSpecifically, on Fig. 1, that portion of the volume of the isoteniscope to the right of point A which is filled with vapor. 3.3 Symbols C temperature, C, K temperature, K, p pressure, Pa or torr, t time, s, P e experimentally measured total system pressure, P a partial pressure due to fixed gases dissolved in sample, P c corrected vapor pressure, Pa or torr. K 5 C 1 273.15 1 4. Summary of Test 4.1 Dissolved and entrained fixed gases are removed from the sample in the isoteniscope by heating a thin layer of a sample at reduced pressure, removing in this process the minimum amount of volatile constituents from the sample. 4.2 The vapor pressure of the sample at selected tempera- tures is determined by balancing the pressure due to the vapor of the sample against a known pressure of an inert gas. The manometer section of the isoteniscope is used to determine pressure equality. 4.3 The initial decomposition temperature is determined from a plot of the logarithm of the vapor pressure versus the 1 This test is under the jurisdiction of ASTM Committee D02 on Petroleum Products and Lubricants and is the direct responsibility of Subcommittee D02.11 on Engineering Sciences of High Perance Fluids and Solids. Current edition approved April 10, 1997. Published October 1997. Originally published as D 2879 70. Last previous edition D 2879 96. 2 Annual Book of ASTM Standards, Vol 05.01. 3 Annual Book of ASTM Standards, Vol 14.03. 1 Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. reciprocal of absolute temperature. The initial decomposition temperature is taken as that temperature at which the plot first departs from linearity as a result of the decomposition of the sample. An optional provides for the use of isothermal rates of pressure rise for this purpose see Annex A1. These are measured at several temperatures and the logarithm of the rate of pressure rise is plotted versus the reciprocal of absolute temperature. The decomposition temperature of the sample is taken to be that temperature at which the rate of increase of pressure is sufficient to produce a rise of 185 Pa 0.0139 torr/s. NOTE 2Vapor pressures less than 133 Pa 1.0 torr, but greater than 13.3 Pa 0.1 torr at a selected test temperature can be determined directly with reduced accuracy. In some cases the tendency of the sample to retain dissolved or occluded air may prevent direct determinations of vapor pressure in this range. In such cases, data points obtained at higher pressures can be extrapolated to yield approximate vapor pressures in this range. 5. Significance and Use 5.1 The vapor pressure of a substance as determined by isoteniscope reflects a property of the sample as received including most volatile components, but excluding dissolved fixed gases such as air. Vapor pressure, per se, is a thermody- namic property which is dependent only upon composition and temperature for stable systems. The isoteniscope is designed to minimize composition changes which may occur during the course of measurement. 6. Apparatus 6.1 Isoteniscope Fig. 1. 6.2 Constant-Temperature Air Bath Fig. 2 for use over the temperature range from ambient to 748 K, controlled to 62K in the zone occupied by the isoteniscope beyond point “A” Fig. 1. 6.3 Temperature Controller. 6.4 Vacuum and Gas Handling System Fig. 3. 6.5 Mercury Manometer, closed end, 0 to 101.3 kPa 0 to 760 torr range. WarningPoison. May be harmful or fatal if inhaled or swallowed. Vapor harmful; emits toxic fumes when heated. Vapor pressure at normal room temperature exceeds threshold limit value for occupational exposure. See A2.1. 6.6 McLeod Vacuum Gage, 0 to 2.00 kPa 0 to 15 torr, vertical primary standard type. 6.7 Mechanical Two-Stage Vacuum Pump. 6.8 Direct Temperature Readout, either potentiometric or electronic. 6.9 Thermocouple, in accordance with American National Standard for Temperature Measurement Thermocouples ANSI C96.1 from Specification and Temperature Electromotive Force Tables E 230. 6.10 Nitrogen, pre-purified grade. WarningCompressed gas under high pressure. Gas reduces oxygen available for breathing. See A2.2. FIG. 1 Isoteniscope A Dewar, strip silvered, 110 mm ID by 400 mm deep. B Borosilicate glass tube, 90 mm OD by 320 mm long. C Glass rod, 1 8-in. in diameter by 310 mm long. Three of these heater ele- ment holders are fused along their entire length to the outer surface of Tube B at 120-deg intervals. Slots cut into the fused glass rods on 3 8-in. centers serve as guides for the heating wire D. D Resistance wire, B. and S. No. 21 gage, spirally wrapped around Tube B and its attached guides. E Glass wool pad. F Glass wool pad for centering Tube B and sealing annular opening. G Lower plate of insulated isoteniscope holder. Transite disk 1 8 in. thick, loose fit in Tube B. With hole for isoteniscope. H Upper plate of insulated isoteniscope holder. Transite disk 1 8 in. thick, loose fit in Dewar A. With hole for isoteniscope. J Glass wool insulation between plates G and H. K Plate spacer rods. L Heater leads connected to power output of temperature controller. T 1 Temperature-control thermocouple affixed to inside wall of Tube B. T 2 Temperature-indicating thermocouple affixed to isoteniscope. FIG. 2 Constant-Temperature Air Bath D 2879 97 2002 e1 2 6.11 Nitrogen Pressure Regulator, single-stage, 0 to 345 kPa gage 0 to 50 psig. 6.12 Alcohol Lamp.WarningFlammable. Denatured al- cohol cannot be made nontoxic. See A2.3. 7. Hazards 7.1 The procedure requires measuring pressures with de- vices containing mercury WarningSee 6.5. Spillage of this material creates a safety hazard in the of toxic vapor in the room. This can be prevented by use of catchment vessels under the devices. If these fail, and the ventilation of the room during occupancy is below 0.01 m 3 sm 2 ,2ft 3 /minft 2 , thorough cleaning of the floor followed by inspection with a mercury vapor-detecting device is recommended. The follow- ing procedures for floor cleaning have been found effective 7.1.1 A 5 aqueous solution of sodium polysulfide pen- etrates well into porous surfaces, but should not be used on polished metal objects. 7.1.2 Sweeping with flowers of sulfur, or agricultural col- loidal sulfur, is effective on nonporous floors. 7.1.3 Sweeping with granular zinc, about 20 mesh 840 m that has been rinsed in 3 hydrochloric acid, is effective in catching macro-drops. 7.2 The apparatus includes a vacuum system and a Dewar flask constant temperature air bath that is subjected to elevated temperatures. Suitable means should be employed to protect the operator from implosion of these systems. These means include wrapping of vacuum vessels, use of safety shield in front of Dewar flask, and use of safety glasses by the operator. 8. Procedure 8.1 Add to the isoteniscope a quantity of sample sufficient to fill the sample bulb and the short leg of the manometer section WarningPoison. Can be harmful or fatal if inhaled or swallowed. Vapor harmful; emits toxic fumes when heated. Vapor pressure at normal room temperature exceeds threshold limit value for occupational exposure. See A1.1. to point A of Fig. 1. Attach the isoteniscope to the vacuum system as shown in Fig. 3, and evacuate both the system and the filled isoteniscope to a pressure of 13.3 Pa 0.1 torr as measured on the McLeod gage. Break the vacuum with nitrogen WarningCompressed gas under high pressure. Gas reduces oxygen available for breathing. See A1.2.. Repeat the evacu- ation and purge of the system twice to remove residual oxygen. 8.2 Place the filled isoteniscope in a horizontal position so that the sample spreads out into a thin layer in the sample bulb and manometer section. Reduce the system pressure to 133 Pa 1 torr. Remove dissolved fixed gases by gently warming the sample with an alcohol WarningFlammable. Denatured alcohol cannot be made nontoxic. See A2.3. lamp until it just boils. Continue for 1 min. NOTE 3During the initial evacuation of the system, it may be necessary to cool volatile samples to prevent boiling or loss of volatiles. NOTE 4If the sample is a pure compound, complete removal of fixed gases may readily be accomplished by vigorous boiling at 13.3 Pa 0.1 torr. For samples that consist of mixtures of substances differing in vapor pressure, this procedure is likely to produce an error due to the loss of volatile components. Gentle boiling is to be preferred in such cases. The rate of boiling during degassing may be controlled by varying both the pressure at which the procedure is carried out and the amount of heating. In most cases, satisfactory degassing can be obtained at 133 Pa 1 torr. However, extremely viscous materials may require degassing at lower pressures. Samples of high volatility may have to be degassed at higher pressures. In the event that the vapor pressure data indicate that the degassing procedure has not completely removed all dissolved gases, it may be necessary to apply a correction to the data or to disregard data points that are so affected see 8.7. The degassing procedure does not prevent the loss of volatile sample components completely. However, the described procedure minimizes such losses, so that for most purposes the degassed sample can be considered to be representative of the original sample less the fixed gases that have been removed. 8.3 After the sample has been degassed, close the vacuum line valve and turn the isoteniscope to return the sample to the bulb and short leg of the manometer so that both are entirely filled with the liquid. Create a vapor-filled, nitrogen-free space between the bulb and the manometer in the following manner maintain the pressure in the isoteniscope at the same pressure used for degassing; heat the drawn-out tip of the sample bulb with a small flame until sample vapor is released from the sample; continue to heat the tip until the vapor expands sufficiently to displace part of the sample from the upper part of the bulb and manometer arm into the manometer section of the isoteniscope. 8.4 Place the filled isoteniscope in a vertical position in the constant-temperature bath. As the isoteniscope approaches temperature equilibrium in the bath, add nitrogen to the gas-sampling system until its pressure equals that of the sample. Periodically adjust the pressure of the nitrogen in the gas-handling system to equal that of the sample. When the isoteniscope reaches temperature equilibrium, make a final adjustment of the nitrogen pressure to equal the vapor pressure of the sample. Pressure balance in the system is indicated by the manometer section of the isoteniscope. When the liquid levels in the manometer arms are equal in height, balance is indicated. Read and record the nitrogen pressure in the system at the balance point. Use the McLeod gage to measure pressures below 2.00 kPa 15 torr and the mercury manometer for pressures from 2.00 kPa 15 torr to 101 kPa 760 torr. 8.4.1 It is extremely important that adjustments of the nitrogen pressure be made frequently and carefully. If the FIG. 3 Vacuum and Gas Handling System D 2879 97 2002 e1 3 nitrogen pressure is momentarily too great, a bubble of nitrogen may pass through the manometer and mix with the sample vapor. If the nitrogen pressure is momentarily too low, a bubble of sample vapor may escape. If either action occurs, the test is terminated immediately and restarted from 8.3. NOTE 5Because the densities of most samples are very much less than that of mercury, small errors in the final adjustment of the levels of the liquid level in the manometer have a negligible effect on the measured values of vapor pressure above 133 Pa 1 torr. 8.5 Increase the temperature of the constant-temperature bath 25 K. As the temperature rises, maintain pressure bala