Methane vapour pressure

Methane, See also Liquefied natural gas Natural gas, 41, 47, 258, 291, 484 physical properties, 295 vapour pressure, 294 Micro-organisms, 1, 138 Mineral acids, 27, 28 Mineral oils, 15, 159, 166 Mists, See also Aerosols definition, 14 origin, 51... 

The temperatures in the troposphere allow methane to reach its saturated vapour pressure and hence the potential to condense and produce precipitation. This suggests that regions of the surface may be covered with liquid methane or, more... 

Liteanu et al. [75] studied the isothermal dehydration of (NH4)2HP04 in a fluidized bed. The ar-time curves were fitted by the contracting volume equation, and the rate of dehydration in air increased with decreasing particle size. For a fixed particle size, the reaction rates and apparent values of increased with variation in carrier gas in the sequence air < methane < hydrogen. The apparent values of E were 80 4,93 3 and 104 3 kJ mol", respectively. The reaction rate also increased with water vapour pressure in the air, but E decreased from 84.5 0.5 in dry air to 64.0 0.5 kJ mof when the water vapour pressure was 17.7 Torr. Water vapour on the grain surfaces promoted dissociation ... 

To avoid the contamination of the samples with tungsten atoms emitted from the hot filament the latter was carbonized in situ in the vacuum chamber in a methane atmosphere for 20 min. The layer of tungsten carbide formed has a much lower vapour pressure compared to metallic tungsten within the temperature range of the filament chosen (1800-2500°C). Figure 3.6 shows an SEM micrograph of a carbonized filament. 

In some cases, in order to apply the theory, it is necessary to extrapolate the vapour pressure of the liquefied gas beyond the critical point. For example, suppose that it is desired to estimate the ideal solubility of methane at a temperature of 25 C, which is far above critical. If the observed vapour pressures are extrapolated by means of the Clausius-Clapeyron equation, the estimated value of p at 25 is found to be 289 atm— but of course this does not correspond to a stable state of gas-liquid ecjuUibrium. The ideal solubility of methane at 25 is therefore 1/289=0.0035. Some of the observed solubilities, as quoted by Hildebrand and Scott, are given in the table. 

Recently the DFT method combined with SAFT equations of state has been used to predict the interfacial properties of real fluids. LDA methods are accurate enough to treat liquid-liquid and liquid-liquid interfaces where the density profiles are usually smooth functions, and have been used in combination with the SAFT-VR approach to predict the surface-tension of real fluids successfully. The intermolecular model parameters required to treat real substances are determined by fitting to experimental vapour-pressure and saturated liquid density data in the usual way (see section 8.5.1) and the resulting model is found to provide accurate predictions of the surface tension. A local DFT treatment has also been combined with the simpler SAFT-HS approach, but in this case only qualitative agreement with experimental surface tension data is found due to the less accurate description of the bulk properties provided by the SAFT-HS equation. Kahl and Winkelman" have followed a perturbation approach similar to the one proposed with the SAFT-VR equation and have coupled a local DFT treatment with a Lennard-Jones based SAFT equation of state. They predict the surface tension of alkanes from methane to decane and of cyclic and aromatic compounds in excellent agreement with experimental data. 

Air Obviously, more volatile chemicals such as halo-methanes will partition primarily into air because of their high vapour pressure. Indeed, vapour pressure is really solubility in air in disguise. The common vapour pressure P2 (superscripts designating saturation or maximum value) being convertible into a concentration by dividing P by the gas constant temperature product RT. 

The vapour pressure and density affect the substances rate of reaction (the amount and rate of atoms/molecules escaping) and where/what level the gas will be found (hydrogen sulphide heavier than air, methane lighter than air). This information will enable a variety of differing control measures to be considered. 

The feed methane gas, under operating pressure, was saturated with water vapour in a saturator by bubbling the gas through liquid water before entering the feed side of the permeation cell. The saturator was kept at room temperature. A heating system was added to the saturator so that the water vapour pressure could be adjusted to different values within the operating temperature range of the VPS. 

The density of a vapour or gas at eonstant pressure is proportional to its relative moleeular mass and inversely proportional to temperature. Sinee most gases and vapours have relative moleeular masses greater than air (exeeptions inelude hydrogen, methane and ammonia), the vapours slump and spread or aeeumulate at low levels. The greater the vapour density, the greater the tendeney for this to oeeur. Gases or vapours whieh are less dense than air ean, however, spread at low level when eold (e.g. release of ammonia refrigerant). Table 6.1 ineludes vapour density values. 

Since few chemicals (e.g. hydrogen, methane, ammonia) have a molecular weight less than that of air, under ambient conditions most gases or vapours are heavier than air. For example, for common toxic gases refer to Table 3.1 for flammable vapours refer to Table 5.1. At constant pressure the density of a gas or vapour is, as shown, inversely proportional to the absolute temperature. As a result ... 

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