## Fractionating Column Performance

The design calculations considered in the preceding chapters were based on theoretical plates. In order to complete the design, it is necessary to have the relationship between these idealized values and the actual performance of the contacting device. The vapor and liquid brought into contact with each other in the tower are not at equilibrium, and the rate of mass transfer determines the effectiveness of the unit. This chapter will consider the methods of predicting the effectiveness of the...

## Info

Gadwa (Ref. 12) has studied the plate efficiency in the fractionation of mixtures of (1) benzene-carbon tetrachloride, (2) methanol-iso-butanol, (3) methanol-n-propanol, (4) isobutanol-water, (5) n-pro-panol-water, and (6) methanol-water. A small four-plate column containing one bubble cap per plate was employed. The bubble caps were in. in diameter and 2 in. high containing 38 slots in. wide by in. high per cap. A vapor space of 5 by 5 in. was partitioned off from the overflow pipes, giving a...

## Preface To The First Edition

The subject of fractional distillation has received but scant attention from writers in the English language since Sidney Young published his book Fractional Distillation in 1903 (London). French and German authors have, on the other hand, produced a number of books on the subject, among the more important of which are the following La Rectification et les colonnes rectificatriccs en distillerie, E. Barbet, Paris, 1890 2d ed., 1895. Der Wirkungsweise der Rectificir und Dcstillir Apparate, E....

## Rectification Of Binary Mixtures

The separation of two liquids from each other by fractional distillation may be accomplished in two general ways (1) the batch, or intermittent, method and (2) the continuous method. In the former, the composition and temperature at any point in the system are changing continually in the latter, conditions at any point are constant. It will be recalled that a fractionating column consists of a system up through which vapors are passing and down through which a liquid is running, countercurrent...

## Efficiency Of Packed Towers

The efficiency of packed towers is generally expressed as the height equivalent to a theoretical plate. Most of the reported values of H.E.T.P.'s are for small laboratory columns, since this is one of the largest uses of packed columns. H.E.T.P. is a function of the packing dimension and construction, tower size, vapor velocity, and system being rectified. The efficiency of packed towers may be seriously impaired by the liquid's tending to pass down one side while the vapor flows up the other....

## Relative Volatility Using Partial Pressure

Using T7 31G.4 K., xwp 0.74, and a , 0.9775 gives six equations with six unknown quantities which can be solved to give A 0.206 and B 238. With these constants, the vapor-liquid equilibria were calculated for the system phenol and water at a temperature of 43.4 , and the calculated results are given in Figs. 4-13 and 4-14, labeled Van Laar. It will be noted in this case that the agreement with the experimental results is satisfactory and would be of great utility for actual distillation...

## Vacuum And Steam Distillation

Hg abs., the distillation operation can be carried out in a manner similar to those at higher pressures, and the problems relate to reducing the pressure drop for vapor flow through conventional equipment. The pressure drop of bubble-cap plates can be reduced to the order of 2 mm. Hg per plate (see page 404), and special spray-type plates can give pressure drops as low as 0.5 mm. Hg per plate. With such contacting units it is obvious that even a few plates will...

## Geometric Average For Relative Volatility

And at total reflux the operating-line equation gives yw Xi, giving In some cases the relative volatility does not vary widely, and an average value for the entire column can be used, giving where N is the number of plates in the column. This can be changed to N log x> x)N x xf)w If a total condenser is employed, this becomes N + 1 g(x' x)D(x'7 U (7.53) or, if a partial condenser equivalent to one theoretical plate is employed, N + 2 log These equations offer a simple and rapid means of...

## Multicomponent Mixtures

The state of the art for the batch distillation of multicomponent mixtures is even less satisfactory than for binary mixtures, and except for total reflux, no accurate and practical method is available even without liquid holdup in the column. This difficulty arises from the fact that, starting with a given liquid composition in the still, it is possible to calculate the equilibrium vapor leaving the still, but the composition of the overflow to the still from the first plate cannot be...

## Binary Mixtures

The batch distillation of binary mixtures will be considered fpr the cases of 1 no rectification, 2 rectification without liquid holdup in the column, and 3 rectification with holdup. No Rectification, Batch distillation without rectification corresponds to the simple distillations of Chap. 6, and the calculations of the concentrations as a function of the amount distilled can be made by Eqs. 6-3 and 6-7 . Rectification without Liquid Holdup in Column. Finite Reflux Ratio. In this case, it is...

## Other Types Of Plates

Bubble-cap plates are the most common plate type of contacting device, but other arrangements are used. Perforated or sieve plates are effective vapor-liquid contacting devices and are frequently used for liquids containing suspended solids, such as the beer mashes in alcohol production. At their rated capacity, their efficiency is equal to that of bubble-cap plates, but they have two disadvantages that have limited their utility. 1 Because the pressure drop through the openings of the...

## S

Scatchard equation, 62 Simple distillation, 107 Solution deviations, 46, 65 Sorel-Lewis method, 122 Sorel's method, 118 Steam distillation, 111, 135, 396 Systems, acetic acid-water, 109 acetone-carbon disulfide, 19 acetone-chloroform, 19, 66 ammonia-water, 152 aniline-water, 202 benzene-n-propanol, 51 benzene-toluene, 19 benzene-water, 89, 202 butane-hexane, 80 carbon dioxide-sulfur dioxide, 82 carbon tetrachloride-carbon disulfide, 17 yf x curve, 18 ethanol-benzene-water, 314...

## E

Or reflux from condenser before solvent is added at top Xds, Xrs mol fraction of solvent in distillate and total liquid added to the top of tower, including reflux and solvent Fs solvent added with feed a, a relative volatilities for solvent concentrations above and below feed, respectively If the feed is binary mixture, the terms involving Xdi and xwh are dropped. For certain special cases, simpler equations can be employed. For example, if solvent is added with the feed such that its...

## Liquid Volatility Pa Pb

Assuming that none are reflected, Eq. 15-2 can be used to calculate the. rate of evaporation from a liquid at equilibrium with a vapor. The same relation has been used to predict the rate of evaporation from a liquid even when the vapor is not in equilibrium with a liquid. This may be approximately true for the nonequilibrium case, but there is undoubtedly some interference of the molecules in the vapor with those evaporating, and the use of Eq. 15-3 to calculate the absolute rate of...

## HTU fjj

The transfer unit consists of a step on the operating line such that the change in y or x is equal to the average difference between the equilibrium curve and the operating line over the region of the step. If the equilibrium and operating lines are parallel, the step will be exactly equal to that for a theoretical plate, and the H.T.U. value will equal the H.E.T.P. value. If the slope of the equilibrium curve is less than that of the operating line, the two curves will tend to converge with...

## What The Relative Volatility Of Acetic Acid

Between y and x are known, both the vapor and the liquid compositions can be calculated. In order to determine the equilibrium relationships either the temperature or the total pressure must be known. Given either of these, the other can be determined from the equilibrium relationship for all the components involved. Differential Distillation. This type of distillation is usually carried out as a batch operation although continuous units may also-operate in this manner. Considering first a...

## Example In Lewis Sorel Method

Is assumed where all of the overhead vapor is liquefied, this condensate being divided into two portions, one of which is returned to the column for reffyrc and the other withdrawn as overhead product. The bottoms are of itinuously withdrawn from the still or reboiler. See end of chapter for nomenclature. Consider the region bounded by the dotted line in Fig. 7-1., The only material entering this section is the vapor from the nth plate F , while leaving the section is the distillate D and the...

## Modified Equilibrium Curves And Operating Lines

Several methods have been given which treat a multicomponent mixture as a modified binary mixture of the key components that can be analyzed graphically on a y,x type diagram. Jenny Ref. 10 published a graphical method for multicomponent design calculation. A few plate-to-plate calculations are made at the top and bottom of the column and above and below the feed plate. For the section below the feed plate, a y x diagram is made for the light key component using the calculated values to place...

## Snd

These equations reduce to Eqs. 7-14 , 7-17 , 7-27 , and 7-31 for the special cases considered. Method of Ponchon and Savarit. Ponchon Ref. 14 and Savarit Ref. 15 showed that Eqs. 7-13 and 7-27 , or in general any equation Fia. 7-16. Enthalpy-composition diagram. Fia. 7-16. Enthalpy-composition diagram. of this type, could be easily solved by plotting the enthalpy or other property of the saturated vapor and liquid vs. the mol fraction. For example, in Fig. 7-16, if the value Md for the upper...

## Multicomponent Systems

The ideal solution laws such as Raoult's law and Raoult's law corrected for gas law deviation are applicable to binary or multicompo-nent systems. They treat each component independently of any other component present i.e., the relationship between the mol fraction in the vapor and in the liquid for a given component depends only on the temperature and total pressure. In many cases, these simplified rules are not applicable, and there is interreaction between the various components. It would be...

## Vb w

Rp , CM 12 VB7l X A 32 VB zY V I m 72 -7r 1- A 2- I O-05 XiAn x2 xzAwY x A 12 y B X2 B32 2 X1A12 X2 X3A32 2 In the above equations, the values of A and b are similar to those given for a binary, but in this case, considerable care must be exercised with respect to the subscripts. Thus A12 is equal to amp 1 amp 2, -432 is equal to 63 62, and similarly for other subscripts. It should be pointed out that for a ternary mixture, there are only two independent A terms. Any other A terms can be...

## KA Jyy y y kA xxw x X

Where x'ff y'f are the liquid and vapor compositions in the tower at the level at which the feed is introduced, and x'w is the liquid concentration at the bottom of the packed section. A material balance above the feed gives By assuming values of y, values of x can be calculated by Eq. 7-82 , and these used in Eq. 7-80 together with equilibrium data to evaluate the integrals. A similar material balance below the feed can be used with Eq. 7-81 . The equilibrium curve and the material-balance...

## A 1[2 a 2XF

This arrangement is very similar to that employed in the so-called double towers for the separation of oxygen and nitrogen. In this case the feed is relatively rich in the lower boiling component, nitrogen, and the first tower is used to produce an overhead that contains a high concentration of nitrogen and an impure bottoms containing 40 to 50 per cent oxygen. The liquid nitrogen overhead product from the high-pressure tower is added to the top of the low-pressure tower and serves as the only...

## Ammonia And Water Relative Volatility

Oxygen-Nitrogen and Ammonia-Water Example. Tables 7-3 and 7-4 give similar comparisons for other systems. In Table 7-3 the comparison is for the oxygen-nitrogen system at 10 atm., and again the agreement between the two methods is good. The other data are for ammonia-water at 10 atm., and even in this case the two methods are in fair agreement. Ammonia-Water Example. In order to illustrate the fact that the assumption of constant molal overflow rate is not always justified, consider the...

## Relative Volatility Of Co2

0.4 06 08 Mol fraction COg in liquid 0.4 06 08 Mol fraction COg in liquid 0.2 0.4 06 OB 1.0 Mol fraction COg In liquid Fig. 4-4. a. Vapor-liquid equilibria for CO2-SO2 at constant pressure. 6. Vapor-liquid equilibria for CO2-SO2 at constant temperature. same temperature, but at different total pressures. This is shown in Fig. 4-4 which gives the vapor-liquid equilibrium data for the system carbon dioxide-sulfur dioxide. In general, it is found that the relative volatility decreases as the total...

## F C 221

In the usual vapor-liquid equilibria two phases are involved liquid and vapor. Plowever, in some systems more than one liquid phase may be encountered. For the two-phase system the phase rule states that the degrees of freedom or variance are equal to the number of components. Thus a binary system has two degrees of freedom and can be represented by two variables on rectangular coordinates. Three-component systems involve three degrees of freedom and are usually presented on triangular...