Ethane vapor pressure

EXERCISE 17.6 Arrange the following hydrocarbons in order of increasing vapor pressure ethane, C2H6 propane, C3H8 and butane, C4H10. Explain your answer. 

The Reid vapor pressure is generally barely different from the true vapor pressure at 37.8°C if the light gas content —methane, ethane, propane, and butane— of the sample is small, which is usually the case with petroleum products. The differences are greater for those products containing large quantities of dissolved gases such as the crude oils shown in Table 4.13. 

The Class I binary diagram is the simplest case (see Fig. 6a). The P—T diagram consists of a vapor—pressure curve (soHd line) for each pure component, ending at the pure component critical point. The loci of critical points for the binary mixtures (shown by the dashed curve) are continuous from the critical point of component one, C , to the critical point of component two,Cp . Additional binary mixtures that exhibit Class I behavior are CO2—/ -hexane and CO2—benzene. More compHcated behavior exists for other classes, including the appearance of upper critical solution temperature (UCST) lines, two-phase (Hquid—Hquid) immiscihility lines, and even three-phase (Hquid—Hquid—gas) immiscihility lines. More complete discussions are available (1,4,22). Additional simple binary system examples for Class III include CO2—hexadecane and CO2—H2O Class IV, CO2—nitrobenzene Class V, ethane—/ -propanol and Class VI, H2O—/ -butanol. 

Typically, the liquid out the bottom of the tower must meet a specified vapor pressure. The tower must be designed to maximize the molecules of intermediate components in the liquid without exceeding the vapor pressure specification. This is accomplished by driving the maximum number of molecules of methane and ethane out of the liquid and keeping a.s much of the heavier ends as possible from going out with the gas. 

The first step in a gas processing plant is to separate the components that are to be recovered from the gas into an NGL stream. It may then be desirable to fractionate the NGL stream into various liquefied petroleum gas (LPG) components of ethane, propane, iso-butane, or normal-butane. The LPG products are defined by their vapor pressure and must meet certain criteria as shown in Table 9-1. The unfractionated natural gas liquids product (NGL) is defined by the properties in Table 9-2. NGL is made up principally of pentanes and heavier hydrocarbons although it may contain some butanes and very small amounts of propane. It cannot contain heavy components that boil at more than 375°F. 

Figure 11-30. Vapor pressure curve for ethane refrigerant. (Used by permission Starling, K. E. Fluid Thermodynamic Properties for Light Petroleum Systems, 1973. Gulf Publishing Co., Houston, Texas. All rights reserved.)...

The fact that both heats of formation and equilibrium pressures of the hydrates of spherical molecules correctly follow from one model must mean that the L-J-D theory gives a good account of the entropy associated with the motions of these solutes in the cavities of a clathrate. That the heat of formation of ethane hydrate is predicted correctly, whereas the theoretical value of its vapor pressure is too low, is a further indication that the latter discrepancy must be ascribed to hindered rotation of the ethane molecules in their cavities. 

Systems in which the saturated vapor pressure curve does not cut the critical curve (as in Figs. 7 and 11). Example, ethane + />-dichlorobenzene.74... 

Systems in which the saturated vapor pressure curve cuts a three-phase line of liquid + liquid + gas at a second quaternary point (solid + liquid + liquid + gas). Such systems have the first (or normal) quaternary point (solid + solid + liquid + gas) at lower temperatures and pressures (Fig. 13). Examples, ethane +... 

Silva, A.M., and L. A. Weber, "Ebulliometric Measurement of the Vapor Pressure of 1-Chloro-l,l-Difluoroethane and 1,1-Difluoro Ethane, J. Chem. Eng. Data, 38, 644-646 (1993). 

Vapor Cloud Explosions. Lenoir and Davenport (Ref. 16) have summarized some major VCEs worldwide from 1921 to 1991. The materials involved in these incidents suggest that certain hydrocarbons—such as ethane, ethylene, propane, and butane—demonstrate greater potential for VCEs. Several factors may contribute to these statistics. These materials are prevalent in industry and are often handled in large quantities, increasing the potential for an incident. Certain inherent properties of the materials also contribute to their potential for explosion. These include flammability, reactivity, vapor pressure, and vapor density (with respect to air). 

Carruth, G.F., Kobayashi, R. (1973) Vapor pressure of normal paraffins ethane through n-decanc from their triple points to about 10 mm mercury. J. Chem. Eng. Data 18(2), 115-126. 

The vessel contains volatile liquids (e.g., butanes, propanes, ethanes, etc.) with vapor pressures above atmospheric. 

The amount of ethylene is limited because it is necessary to restrict the amount of unsaturated components so as to avoid the formation of deposits caused by the polymerization of the olefin(s). In addition, ethylene [boiling point —104°C (—155°F)] is more volatile than ethane [boiling point —88°C (—127°F)], and therefore a product with a substantial proportion of ethylene will have a higher vapor pressure and volatility than one that is predominantly ethane. Butadiene is also undesirable because it may also produce polymeric products that form deposits and cause blockage of lines. 

Therefore, the maximum storage pressure (2760 to 32,060 kPag, or 400 to 3200 psig) usually exceeds the vapor pressure of all commonly stored hydrocarbon liquids. Higher-vapor-pressure products such as ethylene or ethane cannot be stored in relatively shallow caverns. 

It was first prepd in 1894 by Nef (Refs 1 2) by nitrating ethane. Accdg to CondChemDict, NEc can be prepd by treating ethane with oxides of nitrogen or with nitric acid under pressure (Ref 9). In die method of prepn listed by Fieser Fieser (Ref 7), vapors of ethane pass together with vapors of nitric acid thru a narrow reaction tube at 420°. 

Vapor pressure of crude oils is primarily influenced by the presence or absence of light and intermediate hydrocarbons, particularly methane. Methane has much more effect than the same quantity of ethane, ethane more than propane, etc. The composition of a crude oil having a vapor pressure of 10 ... 

It can be seen that while this particular crude oil contains over 95t by volume pentanes and heavier, these constituents only contribute about 201 to the vapor pressure. Most of the vapor pressure of this oil is contributed by the propane and butanes, since it contains very little methane and ethane. This oil stream is the product of an extremely selective separation process. Crude oil streams, unless they have "weathered" in an open tank for some period of time,... 

Figure 2-15 shows phase data for eight mixtures of methane and ethane, along with the vapor-pressure lines for pure methane and pure ethane.3 Again, observe that the saturation envelope of each of the mixtures lies between the vapor pressure lines of the two pure substances and that the critical pressures of the mixtures lie well above the critical pressures of the pure components. The dashed line is the locus of critical points of mixtures of methane and ethane. 

The edge of the diagram labeled 100 mole percent methane represents vapor pressures of methane. The edge of the diagram labeled zero mole percent methane gives vapor pressures of ethane. 

When pressure is less than the critical pressures of both components, the bubble-point and dew-point lines join at the vapor pressures of the pure components at either side of the diagram. When the pressure exceeds the critical pressure of one of the components, the bubble-point line and the dew-point line join at a critical point. For instance, a mixture of 98 mole percent methane and 2 mole percent ethane has a critical temperature of minus 110°F at a critical pressure of 700 psia. 

Use the Peng-Robinson equation of state to calculate the vapor pressure of ethane at 32°F. Also, calculate the densities of the liquid and gas at 32°F. Compare your answers with values from Figures 2-7, 2-12, and 3-3. 

Figure 3.12. Fractionator for separating ethylene and ethane with a refrigerated condenser. FC on feed, reflux, and steam supply. LC on bottom product and refrigerant vapor. Pressure control PC on overhead vapor product.

VOLATILE ORGANIC COMPOUNDS. Any hydiocaibon, except methane and ethane, with vapor pressure to or greater than 0,1 inmHg,... 

C2Hg (liq.)- Wiebe, Hubbard, and Brevoort1 measured the heat of vaporization of ethane. Vapor pressure data were reported by Porter,1 Dana, Jenkins, Burdick, and Timms,1 Loomis and Waters,1 Prins,1 Burrell and Robertson,2 Maass and McIntosh,1 Cardoso and Bell,11 Cardoso,1 Kuenen and Robson,1 Kuenen,1 Olszewski,2-11 Hara and Shinozaki,1 Ladenburg and Krugel,2 and Dewar.2... 

Figure 4.2b shows the equivalent of Figure 4.2a to be slightly more complex for systems such as ethane + water, propane + water, isobutane + water, or water with the two common noncombustibles, carbon dioxide or hydrogen sulfide. These systems have a three-phase (Lw-V-Lhc) line at the upper right in the diagram. This line is very similar to the vapor pressure ( V-Lhc) line of the pure hydrocarbon, because the presence of the almost pure water phase adds a very low vapor pressure (a few mmHg at ambient conditions) to the system. 

Figure 5.13 is the equivalent ethane + water pressure versus temperature phase diagram. Note that the Aq-sI-V line intersects the Aq-V-Lhc line at 287.8 K and 35 bar. Due to differences in the volume and enthalpy of the vapor and liquid hydrocarbon, the three-phase hydrate formation line changes slope at high temperature and pressure from Aq-sI-V to Aq-sI-Lhc, due to the intersectiion of Aq-sI-V line with the Aq-V-Lhc line (slightly higher than the ethane vapor pressure). Note that the hydrate formation pressure for ethane hydrates at 277.6 K is predicted to be 8.2 bar. 

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