Vaporization-condensation sequence

The structure of the solid determines the mechanism for which internal liquid flow may occur. These mechanisms can include (1) diffusion in continuous, homogeneous solids, (2) capillary flow in granular and porous sohds, (3) flow caused by shrinkage and pressure gradients, (4) flow caused by gravity, and (5) flow caused by a vaporization-condensation sequence. 

The solar condensation sequence The processes of vaporization and condensation are of major importance in the solar nebula. In order to systematize this process, Grossman (1972) used thermodynamic equilibria to calculate the composition of phases in equilibrium with a gas with cosmic element concentrations, at a pressure of 10 3 atm, and as a function of temperature. This work has subsequently been developed by others and is systematized in Lewis (2004). It is worth noting that in detail it is likely that the assumption of equilibrium conditions will not... 

One of the most important operations in a refinery is the initial distillation of the crude oil into its various boiling point fractions. Distillation involves the heating, vaporization, fractionation, condensation, and cooling of feedstocks. This subsection discusses the atmospheric and vacuum distillation processes which when used in sequence result in lower costs and higher efficiencies. This subsection also discusses the important first step of desalting the crude oil prior to distillation. 

The machinery employed in the early refineries was rather small in scale and operated iiiefficieutly. Generally, equipment consisted of a series of shell tubes or stills. These were placed in the horizontal position and were connected one to another from the top through the use of vapor pipes. These pipes directed the vapors from the stills into condensers which cooled the gases and so caused the products to separate out. These products were then collected in sequence, often at one point in the plant, as liquids of varying densities and properties. 

A simple model for side-rectifiers suitable for shortcut calculation is shown in Figure 11.12. The side-rectifier can be modeled as two columns in the thermally coupled direct sequence. The first column is a conventional column with a condenser and partial reboiler. The second column is modeled as a sidestream column, with a vapor sidestream one stage below the feed stage4. The liquid entering the reboiler and vapor leaving can be calculated from vapor-liquid equilibrium (see Chapter 4). The vapor and liquid streams at the bottom of the first column can then be matched with the feed and sidestream of the second column to allow the calculations for the second column to be carried out. 

A direct sequence of two distillation columns produces three products A, B and C. The feed condition and operating pressures are to be chosen to maximize heat recovery opportunities. To simplify the calculations, assume that condenser duties do not change when changing from saturated liquid to saturated vapor feed. This will not be true in practice, but simplifies the exercise. Assume also that the reboiler duty for saturated liquid feed is the sum of the reboiler duty for saturated vapor feed plus the heat duty to vaporize the feed. Data for the two columns are given in Tables 21.7 and 21.8. 

Unlike O, mass dependent fractionation is widespread for Ca in inclusions it ranges from -3.8 to 6.7 %o (Niederer and Papanastassiou 1984) which is about four times the terrestrial range (Schmitt et al. 2003). However, 80% of samples fall within an interval of 2%o. The mass fractionation is the result of complex sequences of condensation and vaporization. The connection to Mg isotopic fractionation is not obvious for these samples as the resolution of Mg measurements is much smaller. 

The temperatures of appearance of various solid phases as a cooling solar gas condenses are illustrated in Figure 7.1. This particular condensation calculation was performed at a pressure of 10 4 atm (thought to be appropriate for parts of the nebula). It is important to note that not every mineral in the sequence actually condenses directly from the vapor. Instead, some minerals form by reaction of previously condensed solids with the vapor. For example, FeS forms by reaction of already condensed Fe metal with sulfur in the gas phase, and olivine first condenses as the magnesium end member forsterite and then becomes progressively more iron-rich by reaction with vapor as temperature decreases. 

The material is substantially constant-boiling as a result of its having been produced by a sequence of fractionating processes involving high-efficiency distillation. Therefore, examination of the boiling point as a function of the percentage of the sample vaporized or condensed will be of little or no value in this connection. 

In this sequence a radical, possibly a btradical derived from unpairing the electrons of the oxazirane oxygen-nitrogen bond, abstracts the a-hydrogen atom of the A -alkyl group to form (XXI) which subsequently isomerizes to (XXII). Alternatively the formation of (XXII) may take place directly by a concerted, reaction. In either event the iminoaikoxy radical (XXII) carries the chain. The ammonia which is formed presumably comes from aldol-like condensations of the imine (XXIV). The fact that vapor-phase pyrolysis does not take this course simply reflects tbo low probability of a chain reaction in the vapor phase. 

From a careful analysis of the condensed- and vapor-phase components in the range 813 to 973 K, Oza and Patel119 deduce the following reaction sequence ... 

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