Vapor-phase compositions involving

THE SUBROUTINE ACCEPTS BOTH A LIQUID FEED OF COMPOSITION XF AT TEMPERATURE TL(K) AND A VAPOR FEED OF COMPOSITION YF AT TVVAPOR FRACTION OF THE FEED BEING VF (MOL BASIS). FDR AN ISOTHERMAL FLASH THE TEMPERATURE T(K) MUST ALSO BE SUPPLIED. THE SUBROUTINE DETERMINES THE V/F RATIO A, THE LIQUID AND VAPOR PHASE COMPOSITIONS X ANO Y, AND FOR AN ADIABATIC FLASHf THE TEMPERATURE T(K). THE EQUILIBRIUM RATIOS K ARE ALSO PROVIDED. IT NORMALLY RETURNS ERF=0 BUT IF COMPONENT COMBINATIONS LACKING DATA ARE INVOLVED IT RETURNS ERF=lf ANO IF NO SOLUTION IS FOUND IT RETURNS ERF -2. FOR FLASH T.LT.TB OR T.GT.TD FLASH RETURNS ERF=3 OR 4 RESPECTIVELY, AND FOR BAD INPUT DATA IT RETURNS ERF=5. 

We will also use these expressions to demonstrate how measurements involving only pressure, temperature, and liquid phase composition - a common experimental technique - can be used to evaluate vapor phase compositions. 

Hermsen and Prausnitz (1963) present the P-Xj data for the system benzene(l)-cyclopentane(2) at 25°C shown in Table 13.E.11. Calculate the values of the vapor phase composition assuming, because of the low pressures involved and the similarity of the two components, ideal vapor behavior. The following Antoine constants are given ... 

The results are summarized in Table 13.7 and suggest no significant impact on the accuracy of the vapor phase composition predictions, until one of the binaries involved is of unacceptable quality. The overall deviation of 0.009 in vapor phase composition for groups A, B, and C, that include 47 multicomponent systems with no unacceptable binaries. 

Because the HPLC mobile phase is a liquid, there are some very obvious differences between HPLC and GC. First, the mechanism of separation in HPLC involves the specific interaction of the mixture components with a specific mobile phase composition, while in GC the vapor pressure of the components,... 

The rate constants involved in the formation of larger clusters are described in terms of the RRK theory, which states that the substimtion reaction rate for the addition of the strongly bound component is much faster than for the addition of the more weakly bound component. This gives rise to the experimental observation that the composition of the clusters does not reflect the composition of the vapor phase from which they are formed. Instead, during the formation stage of the clusters, a non-statistical enrichment toward the more strongly bound species occurs. ... 

Due to the fact that industrial composites are made up of combinations of metals, polymers, and ceramics, the kinetic processes involved in the formation, transformation, and degradation of composites are often the same as those of the individual components. Most of the processes we have described to this point have involved condensed phases—liquids or solids—but there are two gas-phase processes, widely utilized for composite formation, that require some individualized attention. Chemical vapor deposition (CVD) and chemical vapor infiltration (CVI) involve the reaction of gas phase species with a solid substrate to form a heterogeneous, solid-phase composite. Because this discussion must necessarily involve some of the concepts of transport phenomena, namely diffusion, you may wish to refresh your memory from your transport course, or refer to the specific topics in Chapter 4 as they come up in the course of this description. 

There are numerous materials, both metallic and ceramic, that are produced via CVD processes, including some exciting new applications such as CVD diamond, but they all involve deposition on some substrate, making them fundamentally composite materials. There are equally numerous modifications to the basic CVD processes, leading to such exotic-sounding processes as vapor-phase epitaxy (VPE), atomic-layer epitaxy (ALE), chemical-beam epitaxy (CBE), plasma-enhanced CVD (PECVD), laser-assisted CVD (LACVD), and metal-organic compound CVD (MOCVD). We will discuss the specifics of CVD processing equipment and more CVD materials in Chapter 7. 

Evaporation. The primary weathering process involved in the natural removal of oil from the sea is evaporation. It is particularly dominant soon after oil is released. Evaporation involves the transfer of hydrocarbon components from the liquid oil phase to the vapor phase. Estimates from major spills as well as experimental data indicate that evaporation may be responsible for the loss of up to 50% of a surface oil slick s volume during its life. Evaporation rates of oil at sea are determined by wind velocity, water and air temperatures, sea roughness, and oil composition. Some of the light, low-boiling hydrocarbons, such as benzene, toluene, and xylenes, which are rapidly lost through evaporation, are the most toxic. Thus, their removal decreases toxicity to marine life of the oil remaining on the surface. 

The design of a tray tower for gas absorption and gas-stripping operations involves many of the same principles employed in distillation calculations, such as the determination of the number of theoretical trays needed to achieve a specified composition change (see Sec. 13). Distillation differs from absorption because it involves the separation of components based upon tne distribution of the various substances between a vapor phase and a liquid phase when all components are present in both phases. In distillation, the new phase is generated from the original phase by the vaporization or condensation of the volatile components, and the separation is achieved by introducing reflux to the top of the tower. 

Chemical vapor transport is used to synthesize thin films of materials on a substrate. The film can be the same composition as the substrate or different. In order to proceed with chemical vapor transport, the constituent elements of the compound to be deposited as a thin film must be brought into the vapor phase. Given that many of the thin films of commercial importance involve elements with little or no practical vapor pressure, a lot of attention has been focused on preparing volatile compounds that contain the elements needed in thin-film preparations. Most chemical supply companies carry these compounds as stock items. The major classes of compounds include metal alkyl, metal carbonyl, metal alkoxide, metal 3-diketonates, and organometallics. Examples of each are given in Table 3.1. 

Determine the relevant vapor-pressure data. Design calculations involving vapor-liquid equilibrium (VLE), such as distillation, absorption, or stripping, are usually based on vapor-liquid equilibrium ratios, or K values. For the tth species, K, is defined as K, = y, /x, where y, is the mole fraction of that species in the vapor phase and x, is its mole fraction in the liquid phase. Sometimes the design calculations are based on relative volatility c/u], which equals K,/Kj, the subscripts i and j referring to two different species. In general, K values depend on temperature and pressure and the compositions of both phases. 

There are other complications. The salt, besides forming association complexes with solution molecules, possibly could also alter or even destroy already-existing self-interactions of the molecules of a volatile component either with themselves or with those of the other feed component. An example is the associated structure in which liquid water and to a lesser extent some alcohols exist. The effects of salt ions on water-water, water-alcohol, and alcohol-alcohol complexing, for example, must be profound at higher salt concentrations, and will vary in a given system with salt concentration and with alcohol-water proportionality in the liquid. Also, associations of several, rather than just pairs, of liquid-phase species may form. The full complexity of what initially seems to be a rather simple system finally becomes evident when it is considered that the sum of individual effects which make up the overall effect of the salt on the composition of the equilibrium vapor even in a given system are functions of the relative proportions of all components present and vary with liquid phase composition over the entire range involved in the separation. 

The selectivity of activated carbons for adsorption and catalysis is dependent upon their surface chemistry, as well as upon their pore size distribution. Normally, the adsorptive surface of activated carbons is approximately neutral, such that polar and ionic species are less readily adsorbed than organic molecules. For many applications it would be advantageous to be able to tailor the surface chemistry of activated carbons in order to improve their effectiveness. The approaches that have been taken to modify the type and distribution of surface functional groups have mostly involved the posttreatment of activated carbons or modification of the precursor composition, although the synthesis route and conditions can also be employed to control the properties of the end product. Posttreatment methods include heating in a controlled atmosphere and chemical reaction in the liquid or vapor phase. It has been shown that through appropriate chemical reaction, the surface can be rendered more acidic, basic, polar, or completely neutral [11]. However, chemical treatment can add considerably to the product cost. The chemical composition of the precursor also influences the surface chemistry and offers a potentially lower cost method for adjusting the properties of activated... 

In 1990, Xu et al. first reported the transformation of a dry aluminosilicate gel to crystalline MFI by contact with vapors of water and volatile amines, which was named dry gel conversion (DGC).[99] Since then, this method has been extensively studied and a large number of microporous materials with new compositions and structures were prepared. Generally, DGC can be divided into vapor-phase transport (VPT) and steam-assisted conversion (SAC) according to the volatility of the SDAs. For volatile SDAs such as ethylenediamine, a mixture of water and SDA was poured into the bottom of the autoclave and then a dry gel, which does not contain any SDAs, was placed over the liquid surface. Water and SDAs were vaporized at elevated temperature (150 200 °C), reached the dry gel, and initiated the crystallization, which was called VPT. Less volatile SDAs such as tetrapropylammonium hydroxide were usually involved in the dry gel. Only water steam is supplied during the reaction, which was called SAC. 

A conventional bubble point calculation involves the specification of the liquid mole fractions and pressure the subsequent computation of the vapor-phase mole fractions and the system temperature. For a binary system (and only for a binary system) we may specify the temperature and pressure and compute the mole fractions of both phases. Thus, our first step is to estimate the interface temperature T. The second step is to solve the equilibrium equations for the mole fractions on either side of the interface. This step is, in fact, equivalent to reading the composition of both phases from a T-x-y equilibrium diagram. 

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