Azeotropic water vapors

Anhydrous hydrazine, required for propellant appHcations and some chemical syntheses, is made by breaking the hydrazine—water azeotrope with aniline. The bottom stream from the hydrate column (Fig. 4) is fed along with aniline to the azeotrope column. The overhead aniline—water vapor condenses and phase separates. The lower aniline layer returns to the column as reflux. The water layer, contaminated with a small amount of aniline and hydrazine, flows to a biological treatment pond. The bottoms from the azeotrope column consist of aniline and hydrazine. These are separated in the final hydrazine column to give an anhydrous overhead the aniline from the bottom is recycled to the azeotrope column. 

At atmospheric pressure, sulfuric acid has a maximum boiling azeotrope at approximately 98.48% (78,79). At 25°C, the minimum vapor pressure occurs at 99.4% (78). Data and a discussion on the azeotropic composition of sulfuric acid as a function of pressure can also be found in these two references. The vapor pressure exerted by sulfuric acid solutions below the azeotrope is primarily from water vapor above the azeotropic concentration S03 is the primary component of the vapor phase. The vapor of sulfuric acid solutions between 85% H2S04 and 35% free S03 is a mixture of sulfuric acid, water, and sulfur trioxide vapors. At the boiling point, sulfuric acid solutions containing <85% H2S04 evaporate water exclusively those containing >35% free S03 (oleum) evaporate exclusively sulfur trioxide. 

This study was undertaken to obtain the necessary vapor-liquid equilibrium data and to determine the distillation requirements for recovering solvent for reuse from the solvent-water mixture obtained from adsorber regeneration. Previous binary vapor-liquid equilibrium data (2, 3) indicated two binary azeotropes (water-THF and water-MEK) and a two phase region (water-MEK). The ternary system was thus expected to be highly nonideal. 

The extrapolation is to what is called pervaporation, where the feed mixture is a liquid, but the permeate vaporizes during permeation, induced by the relatively low pressure maintained on the permeate side of the membrane. Accordingly, the reject or retentate remains a liquid, but the permeate is a vapor. Thus, there are features of gas permeation as well as hquid permeation. The process is eminently apphcable to the separation of organics and to the separation of organics and water (e.g., ethanol and water). In the latter case, either water vapor may be the permeate, as in dehydration, or the organic vapor may be the permeate. The obvious, potential application is to the separation of azeotropic mixtures and close-boiling mixtures—as an alternative or adjunct to distillation or liquid-liquid extraction methods. 

A paper by the China Petrochemical Dev Co [3h] reported that the use of pure oxygen for cyclohexane oxidation leads to an increased yield and selectivity to Ol/One with respect to the traditional air-based technology, under inherently safe conditions. The latter are achieved by the addition of water, which avoids the formation of flammable mixtures in the overhead vapor space and in the vapor bubbles. In fact, cyclohexane and water form a minimum-boiling azeotrope, the vapor pressure of which is higher than that of cyclohexane. The increased vapor pressure acts as an inert component. 

Clearly, the azeotrope has vapor pressure characteristics of a single component. It is also clear that pressure has an effect on the location of the azeotrope, and this pressure influence is used commercially to make separations (see reference 23). In some cases, a change in pressure can cause the azeotrope to disappear for ethanol-water, distillation at a pressure of 75 mm Hg or less results in an azeotrope-free operation. 

At the top of the absorption column the water vapor is condensed and recycled into the column. To increase the liquid reflux in the column some external water is fed into the column serving as washing agent. The operating line of column C-1 hes above the equilibrium line which is characteristic of absoibers. The azeotrope (maximum azeotrope) does not hinder the absorption process. 

Consider Tables 22.1 and 22.2. A crystal of sodium chloride, NaCl, is exposed to an air sample that has water vapors, ethanol vapors, and diethyl ether vapors. (Water, ethanol, and diethyl ether are all liquids at room temperature.) Ignoring the possibility of minimum-energy interactions between the three vapors (that is, azeotropes and the like), what would you predict to be the true surface structure of NaCl (Ignore interactions between the NaCl and the vapors.)... 

Regardless of the way fatty acids are incorporated, the main step of alkyd synthesis is the polyesterification. This process is quite similar to the process for saturated polyester resin production, and actually more or less the same equipment can be used (Figure 16.3). The polyesterification of the alkyd raw materials normally proceeds at 240°C with the aid of xylene as a mode of transportation of the water, by forming a binary azeotrope with it. The xylene and water vapors rise through the column on top of the reador and are condensed on top of a separator. The xylene is pumped back into the reador and the water is removed. Because of... 

Isopropyl alcohol and water form a minimum boiling point azeotrope at 88 wt% isopropyl alcohol and 12 wt% water. Vapor-liquid equilibrium (VLE) data are available from several sources and can be used to back-calculate binary interaction parameters or liquid-phase activity coefficients. The process presented in Figure B.3 and Table B.6 was simulated using the UNIQUAC VLE thermodynamics package and the latent heat enthalpy option in the CHEMCAD simulator. This package correctly predicts the formation of the azeotrope at 88 wt% alcohol. 

Figure 8.8c shows that for liquid isopropanol concentrations less than the azeotrope (which corresponds to Xa = 0.685), the vapor contains a higher percentage of isopropanol than the liquid, while at liquid isopropanol concentrations greater than the azeotrope the vapor contains less isopropanol than the liquid. At the azeotrope (where the equilibrium curve crosses the reference curve) the vapor and liquid have the same composition, and the boiling-point temperature of this mixture, 80.4°C, is less than the boiling point of either pure species or of any mixture of them with a different composition (at 1.00 atm). This type of azeotrope is common, and makes separation by distillation difficult. If we start with a liquid mixture of, say, 10 mol% isopropanol and attempt to separate it into pure isopropanol and pure water by distillation, we find that it is easy to get practically... 

The reactor effluent, containing 1—2% hydrazine, ammonia, sodium chloride, and water, is preheated and sent to the ammonia recovery system, which consists of two columns. In the first column, ammonia goes overhead under pressure and recycles to the anhydrous ammonia storage tank. In the second column, some water and final traces of ammonia are removed overhead. The bottoms from this column, consisting of water, sodium chloride, and hydrazine, are sent to an evaporating crystallizer where sodium chloride (and the slight excess of sodium hydroxide) is removed from the system as a soHd. Vapors from the crystallizer flow to the hydrate column where water is removed overhead. The bottom stream from this column is close to the hydrazine—water azeotrope composition. Standard materials of constmction may be used for handling chlorine, caustic, and sodium hypochlorite. For all surfaces in contact with hydrazine, however, the preferred material of constmction is 304 L stainless steel. 

Pervaporation is a relatively new process with elements in common with reverse osmosis and gas separation. In pervaporation, a liquid mixture contacts one side of a membrane, and the permeate is removed as a vapor from the other. Currendy, the only industrial application of pervaporation is the dehydration of organic solvents, in particular, the dehydration of 90—95% ethanol solutions, a difficult separation problem because an ethanol—water azeotrope forms at 95% ethanol. However, pervaporation processes are also being developed for the removal of dissolved organics from water and the separation of organic solvent mixtures. These applications are likely to become commercial after the year 2000. 

Alkan olamines have high boiling points and under normal ambient conditions their vapor pressures are low. Only DMAMP (see Table 2) forms an azeotrope with water, which boils at 98.4°C and contains 25% by weight of DMAMP. According to current DOT regulations, AMP, AMP-95, DMAMP, DMAMP-80, AEPD, and AB are all classified as combustible Hquids. 

Vinyl acetate is a colorless, flammable Hquid having an initially pleasant odor which quickly becomes sharp and irritating. Table 1 Hsts the physical properties of the monomer. Information on properties, safety, and handling of vinyl acetate has been pubUshed (5—9). The vapor pressure, heat of vaporization, vapor heat capacity, Hquid heat capacity, Hquid density, vapor viscosity, Hquid viscosity, surface tension, vapor thermal conductivity, and Hquid thermal conductivity profile over temperature ranges have also been pubHshed (10). Table 2 (11) Hsts the solubiHty information for vinyl acetate. Unlike monomers such as styrene, vinyl acetate has a significant level of solubiHty in water which contributes to unique polymerization behavior. Vinyl acetate forms azeotropic mixtures (Table 3) (12). 

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