INDUSTRIAL AhrD ENGINEERING CHEMISTRY
964
In Figure 6 x has been plotted against fraction of column height for the plate and for the packed columns. It will be noticed that for the plate column the value of x at the point a t which the feed should be introduced is 0.20, whereas for the packed column it is 0.148. For the plate column the feed should be introduced a t a point which is 10/24 of the active height; for the packed column it should be introduced a t a point which is 6.15/24 of the active height.
Vol. 17, No. 9
(27) and
where the primes are used to distinguish the two volatile components and 4V' is a constant similar to M'. These equations cannot in general be exactly integrated as they stand, because both y*' and y*" are functions of both y' and y" and hence the variables are not separated. The relation between y' and y" is obtained by eliminating LE - L A from these equations and is
Unfortunately this relationship cannot in general be expressed in algebraic form, and hence Equations 27 and 28 must be integrated by approximations. The quantities such as M' and R' are measures of the efficiencies from a distillation standpoint of different types of packing for a given height. Figure 6-Comparison
of Plate and Packed Column
In cases in which the driving force of the material transfer is a concentration difference (liquid film controlling) the equation for the rate of material transfer a t any point in the column may be written:
or following the same steps as for the preceding development,
where R' is the average value of tests. dIn V
KGdetermined from column
I n cases where d L is negligible compared with
d In y
Equation 25 becomes
Equations 24 or 25 may be used with Equations 15 and 16 in a manner analogous to the case in which the driving force of the material transfer is represented by a partial pressure difference. When more than two components are present, certain calculation difficulties are met when the methods of this section are applied. This will be shown by briefly considering a three-component mixture in which the driving force of the material transfer for both more volatile components may be represented as a partial pressure difference. For this case equations analogous to (14) would be obtained for both volatile components. These may be written as:
Calculation of Points in the Ethyl Alcohol-Water Distillation Curve By E. Oman and A. Gunnelius [Abstracted by A . R . ROSEfrom Teknisk T i d s k r i f t . 66, 33 (1925)l
OILING points for alcohol in water solution determined within an err01r of * 0.02O C., are given in the following table: Wt.
B. P.
3%
oc.
7c
6.5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 24 23
99.44 98.88 97.88 96.91 96.05 95.18 94.34 93.55 92.83 92.13 91.45 90.82 90.18 89.57 88.97 88.40 87.85 87.34 86.86 86.42 86.03 85.70 85.40 84.90 85.14
25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49
Wt.
B. P. O C .
84.68 84.47 84.27 84.09 83.91 83.73 83.60 83.48 83.28 83.12 82.98 82.84 82.70 82.56 82.43 82.30 82.19 82.08 81.97 81.86 81.76 81.67 81.58 81.49 81.40
Wt.
B. P.
%
c.
50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74
81.31 81.23 81.15 81.07 80.99 80.91 80.83 80.75 80.67 80.58 80.50 80.42 80.34 80.26 80.18 80.10 80.02 79.94 79.87 79.80 79.72 79.64 79.56 79.48 79.41
Wt.
% 75 76 77 78 79 80 81 82 83 34 85
86 87 88 89 90 91 92 93 94 95 96 97 98 49 100
2. P. C.
79.34 79.26 79.18 79.10 70.02 78.95 78.87 78.80 78.72 78.65 78.57 78.50 78.43 78.37 78.30 78.24 78.19 78.14 78.10 78.06 78.04 78.04 78.06 78.08 78.10 78.13
To calculate the alcohol content of any distillation vapor from an alcohol-water mixture: from the composition of the mixture find the boiling point in the table; the temperature being known, get the vapor pressure of water; calculate the molar percentage of the water in the mixture and from this the partial pressure of the water, and by subtraction the partial pressure of the alcohol; the molecular weight of the water and of the alcohol multiplied by their respective partial pressures will give the weights of each in the vapor, from which per cent composition can be calculated. The facts required for the calculation are readily available except the molecular weight of alcohd vapor, and this may be determined from the following: The molecular weight of alcohol in vapor from an aqueous solution having 10 per cent alcohol has been found to be 43.15, and from a 70 per cent solution, 26.05. The variation in molecular weight for 1 per cent alcohol is 0.285.
