640 



Mr. A. F. Dufton on the Separation 



necessary evaporation less 93*5, the heat of evaporation at 

 90° C. of the benzene separated, plus 3 calories, the heat 

 given up by this benzene in cooling to 80 o, 2 C. The loss of 

 this 117*5 calories means the return down the column as 

 liquid of 1*24 gram of benzene. 



Table III. 



C,,H 6 



per cent. 

 in liq. 



100 

 743 

 50 



Grams Vapour 



passing up 



C 6 H 6 +C 7 H 8 = total. 



2-24+0-00= 2-24 

 1-95 +0-33 =228 

 1-66+0-66=2-32 



Temp. 



of 



Vapour. 



o 



80-2 



86-4 



90-0 



Temp. 



of 



Liquid. 



o 



80-2 



84-5 



90-0 



Grams Liquid 



flowing down 



C,H,+C 7 H 8 = total. 



1-24+0-00= 1-24 

 0-95+0-33=1-28 

 0-66+0-66=l-32 



It will be seen that in the middle of the column the vapour 

 is considerably hotter than the liquid. With benzene and 

 toluene, owing to the approximate equality of the latent 

 heats, this method of working gives a practically uniform 

 How throughout the column. 



In the determination of the thermal efficiency of a column 

 used to separate benzene from a mixture of benzene and 

 toluene, calculation must be made of the quantity of heat 

 which would be required if a perfect column were employed. 

 The quantities necessary for different mixtures are given in 

 Table JV. and plotted in fig. 2. 







Table IV. 





Benzene in 



mixture 



100 a per cent. 



Liquid 



evaporate 



grams 



fl+ ] 



d: 



Laient heat 



calculated from 



components. 



Calories required 



to separate 

 1 gm. of benzene. 





(. 1-r a.Jc — 1 









00 





84-0 



X 



5 



15-6 





84-5 



1320 



10 



8-15 





85-1 



698 



20 



4-5 





86-3 



388 



30 



3-29 





87-4 



288 



40 



2-68 





88-6 



237 



50 



2-32 





89-7 



208 



60 



210 





90-9 



191 



70 



1-94 





92-0 



179 



80 



1-81 





93-2 



169 



90 



1-72 





94-3 



162 



100 



1-64 





95-5 



156 



