Propanal hydrate

The smaller cavities are distorted pentagon dodecahedra (distance of oxygen atoms to center varies between 3.77 and 3.95 A) their average free diameter is only about 5.0 A. The larger cavities are almost spherical the oxygen atoms lie at the vertices of hexadeca-hedra and their free diameter is 6.7 A. The distances have been calculated on the basis of a unit cell edge of 17.40 A as found for propane hydrate. 

Methane hydrate and propane hydrate crystallize in Structures I and II respectively, their dissociation pressures at — 3°C have been determined and were found to be 23.1 and 1.48 atm. Above a... 

The difference in behavior reported by Von Stackelberg is not thought to be an essential one. Whether decomposition of a hydrate containing two solutes by removal of its vapor through pumping will be a univariant process depends on the number and compositions of the phases formed. In the system of Fig. 10, for instance, a mixed HtS-propane hydrate will exhibit a constant decomposition pressure on pumping at — 3°C if it contains HaS and propane in the azeotropic" ratio of approximately 3 1. 

Projections, linearly independent, 293 Propagation, of polymerization, 158 Propane, hydrate, 10, 33, 43, 46, 47 hydrate thermodynamic data and lattice constants, 8 + iodoform system, 99 Langmuir constant, 47 water-hydrogen sulfide ternary system, 53... 

Lee, J.D. Susilo, R. Englezos, P. (2005c). Methane-ethane and methane-propane hydrate formation and decomposition on water droplets. Chem. Eng. Set., 60, 4203-4212. 

Ngan, Y. T. Englezos, P. (1996). Concentration of Mechanical Pulp Mill Effluents and NaCl Solutions through Propane Hydrate Formation. Ind. Eng. Chem. Res., 35(6), 1894. 

Blockages of valves and pipes can also occur by gas hydrates. Such adducts can be formed by a number of gases with water. In Fig. 7.1-5 the pressure-temperature diagram of the system propane/water with an excess of propane is presented. The line, (g), shows the vapour-pressure curve of propane. Propane hydrate can be formed at temperatures below 5.3°C. At pressures below the vapor pressure of propane a phase of propane hydrate exists in equilibrium with propane gas (Fig. 7.1-5, area b). At higher pressures above the vapor pressure of propane and low temperatures a propane hydrate- and a liquid propane phase were found (area d). In order to exclude formation of gas hydrates these areas should be avoided handling wet propane and other compounds like ethylene, carbon dioxide [14], etc. 

Figure 7.1-5. Pressure-temperature diagram of the system propane/water [13]. a, Propane gas/water b, propane gas/propane hydrate c, propane liquid/water d, propane liquid/propane hydrate e, propane gas/ice f, hydrate curve g, vapor pressure curve of propane.

Two French workers, Villard and de Forcrand, were the most prolific researchers of the period before 1934, with over four decades each of heroic effort. Villard (1888) first determined the existence of methane, ethane, and propane hydrates, de Forcrand (1902) tabulated equilibrium temperatures at 1 atm for 15 components, including those of natural gas, with the exception of iso-butane, first measured by von Stackelberg and Muller (1954). 

Hara et al., 2005). THP, cyclobutanone, and cyclohexane also showed pressure reductions for carbon dioxide hydrate formation (Mooijer-van den Heuvel et al., 2001). THP, cyclobutanone, cyclohexane, and methylcyclohexane all reduced not only the pressure for propane hydrate formation, but also shifted the H-Lw-Lc3H8 line to lower temperature (Mooijer-van den Heuvel et al., 2002). 

Table 2.8 is a slight modification of a microscopic and macroscopic property summary by Davidson (1983) for ice and hydrate structures I and II. Although the values in the table were generally measured or estimated for methane or propane hydrates, the contribution of the guest molecule (other than causing the structure to exist) may be considered small for these properties, to a first approximation. 

Stoll and Bryan (1979) first measured the thermal conductivity of propane hydrates (0.393 Wm-1K-1 at T = 215.15 K) to be a factor of 5 less than that of ice (2.23 Wm-1K-1). The low thermal conductivity of hydrates, as well as similarities of the values for each structure (shown in Table 2.8) have been confirmed from numerous studies (Cook and Leaist, 1983 [0.45 Wm-1K-1 for methane hydrate at 216.2 K] Cook andLaubitz, 1981 Ross et al., 1981 Ross and Andersson, 1982 Asher et al., 1986 Huang and Fan, 2004 Waite et al., 2005). The thermal conductivity of the solid hydrate (0.50-0.58 W m-1 K-1) more closely resembles that of liquid water (0.605 W m-1 K-1). 

X Propane hydrate, Stoll etal., 1979 CH4 hydrate+SDS (unimpacted), Huang etal., 2004... 

Patil (1987) determined the hydrate number of simple propane hydrates to be 18.95 by the de Forcrand method using the Miller and Strong method he obtained hydrate numbers of 19.20,19.95, and 19.89 for NaCl solutions of 3,5, and... 

Section 5.2 shows the prediction method of phase diagrams of the major components of natural gas, namely methane, ethane, and propane hydrates and their mixtures at the common deep-ocean temperature of 277 K. Many of the commonly observed phenomena in natural gas systems are illustrated, while the power of the method is shown to go beyond that of Chapter 4, to illustrate future needs. 

We define the molar volume of the standard hydrates of si and sll as the molar volumes of methane and propane hydrate, respectively. The molar volume of these hydrates, and therefore of the standard states, is well-characterized via diffraction data (Tse, 1990 Huo, 2002). Ballard proposed the following expression for the molar volume of water in hydrates ... 

For example, at 278.2 K, hydrates form at a pressure of approximately 5 bar and dissociate upon pressurization at approximately 600 bar. A more detailed explanation of the pseudo-retrograde hydrate phenomena can be found in the binary hydrates section which follows. Note that the hydrate formation pressure of propane hydrates along the Aq-sII-V line at 277.6 K is predicted to be 4.3 bar. 

Kini, R.A., NMR Studies of Methane, Ethane, and Propane Hydrates Structure, Kinetics, and Thermodynamics, Ph.D. Thesis, Colorado School of Mines, Golden, CO (2002). With permission.)... 

Figure 6.46 Methanol inhibition of simple propane hydrates.

Figure 6.54 Methanol inhibition of methane + propane hydrates.

A spectacular example is the experimental observation of decomposition of solid light alkane hydrates at ambient pressure and temperature —1°C— that is, under conditions of their thermodynamic instability. The final pro ducts are ice (solid) and a hydrocarbon gas. However, the decomposition of, for example, propane hydrate follows the sequence... 

Figure 11. Dissociation pressures of propane hydrate at 273.15 K. Solid line nonspherical and anharmonic, dashed line spherical and harmonic, dash-dot line spherical and vdWP. Horizontal line free energy difference between ice and empty clathrate hydrate II.

---