tillation Plant for Heavy Water Production,” Proceedings of Symposium on Isotope Separation, Amsterdam, 1957, p. 368. (5) Cohen, K., “Theory of Isotope Separation,” McGraw-Hill, New York, 1951. (6) Dostrovsky, I., “Production and Distribution of Heavy IsotoDes of Oxvcen.” Proceedincs of International Conference on Pkaceful U& of Atomic EGrgy, Geneva, Vol. 4, p. 605, United Nations, 1958. (7) Dostrovsky, I., Raviv, A., “Separation of Heavy Isotopes of Oxygen by Distillation,” Proceedings of Symposium on Isotope Separation, Amsterdam, 1957..~p. 336, North Holland Publishing Cd., Amsterdam, 1958. (8) Garrett, G. A., Shacter, J., “Evaluation of Isotope Separation Process,” Proceedings of Symposium on Isotope Separation, Amsterdam, 1957, p. 17, North Holland Publishing Co., Amsterdam. 1958. (9) London, H., “Isotope Separation by Fractional Distillation,” Ilid., p. 319. (10) Murphy, G. M., ed.; “Production of Heavy LYater,” pp. 120-43, McGraw-Hill, New York, 1955. (11) Nettley. P. T., Cartwright, D. K., Kronberger, H., “Production of 1OBoron by Low Temperature Distillation of BFa,” Proceedings of Symposium on Isotope Separation, Amsterdam, 1957, p. 385.
SUBSCRIPTS act min sq off opt
= actual = minimum = squared off =
optimum
Acknowledgment
-
T h e authors thank Shri H. N. Sethna for his interest in this work. Literature Cited
(1) Akar, P., Simanet, G.. “Industrial Production of Heavy Water by Distillation of Liquid Hydrogen,” Proceedings of International Conference on Peaceful Uses of Atomic Energy, Geneva, Vol. 4,p. 522, United Nations, 1958. (2) Bailey, B. M., “Some Aspects of Heavy \Yater Production by Distillation of Hydrogen,” Proceedings of International Conference on Peaceful Uses of Atomic Energy, Geneva, Vol. 4, p. 557. United Nations, 1958. ( 3 ) Benedict, M., Pigford, T . H., “Nuclear Chemical Engineering,” pp. 378-431, McGraw-Hill, New York, 1957. (4) Casini, R., “Optimum Design Criterion for a Water Dis-
RECEIVED for review September 25, 1961 ACCEPTED June 11, 1962
VAPOR-PHASE HALOGENATION OF BENZENE
B Y CHLORINE TRIFLUORIDE R.
E. BANKS, P E T E R J O H N C O C K ,
R. H . M O B B S , A N D W .
K. R. MUSGRAVE
Chemistry Department, The Citiversity, South Road, Durham, England The vapor-phase halogenation of benzene b y CIF3 is a free radical process unlike the liquid phase reaction which results in electrophilic substitution. It i s possible that free radical substitution occurs first to give chlorobenzene and then chlorofluorobenzene; after this, addition of chlorine and fluorine atoms to the double bonds followed b y more substitution of hydrogen atoms must occur to give fully halogenated and chlorofluorohydrocyclohexanes. To obtain the most extensive halogenation and increase the proportion of fully halogenated cyclohexanes in the product, the volume of nitrogen used to moderate the reaction must be kept as low as possible. This gives a more easily separable and hence more useful product, since the resultant over-all decrease in the number of hydrogen atoms per molecule cuts down enormously the number
of possible isomers in the reaction product. HE HALOGENATION OF BENZESE
and some of its derivatives
C1F3 in the liquid phase, alone and in the presence of catalysts, has been described ( 4 ) . Under the conditions used, the main reaction was one of electrophilic substitution-e.g., CIFa, CoFs
CsH&A@-CsHICIF 00
c.
+
o-
and p-C6H4C12. How-
ever? when the chlorofluorination of benzene is carried out in the vapor phase at 260’ C. the process can best be explained by atomic and free radical reactions which give chlorofluoroand chlorofluorohydrocyclohexanes-e.g., ClF3 + C1F 2F. ;
+
+
CI., F .
ClF + C1. F , ; C8H6--C6HZC1,F,, where x varies from 0 to 6>J and z vary betkveen 0 and 12, and x J t = 12.
+ +
Experimental
Apparatus. T h e apparatus used in this \vork (Figure 1) \vas similar to that described by Musgrave and Smith ( 8 ) ,but the benzene feed was developed from that described by Barbour and others (2). To moderate the reaction between the benzene and the ClFs, these reagents and the nitrogen diluent were introduced into the reactor through a Bigelow “cool flame” burner (73). T h e reactor was packed with copper clippings approximately l:’8 X X l,’loo inch in size (3.5 kg.) and heated by three pairs of semicylindrical section heaters, 262
I&EC PROCESS DESIGN A N D DEVELOPMENT
each of 60-ohm resistance, controlled by variable transformers. No other packing was used on the assumption that although others such as silver- or gold-plated copper clippings ( 8 ) could certainly be found which would increase the yield, they would probably have little effect on the composition of the product. T h e benzene vaporizer and the preheater were wound with 180-ohm and 220-ohm heaters, respectively. and these were controlled by variable transformers so that the benzene vapor and nitrogen entered the reactor at the reaction temperature. T h e reaction products were collected in three brass traps, the first water-cooled and the second and third cooled in solid Con-ethyl alcohol. Procedure, it’hen the heaters had reached the correct temperatures, the apparatus was flushed first with nitrogen and then with C1F3 to remove any grease from the surface of the copper. .4fter flushing again ivith nitrogen. the reactants, diluted with nitrogen, wwe admitted simultaneously. After the first hour, the ClF3feed was closed and the cylinder weighed to check the input rate. T h e reaction was then allowed to proceed; since it was highly exothermic, the voltage to the reactor heaters \vas reduced gradually to keep the reaction temperature constant. After about 70 hours. flow resistance in the reactor increased oiving to the formation of copper halides
Table 1.
a
CsHs, MoleslHr. Flow rate Consumtd Exp. 0.25 0.19 1 0.24 0.12 2 0.11 0.11 3 dii three experiments were carried out at 260".
Reaction Conditions and Over-All Yields"
ClFz, MoleslHr. 0.46 0.48 0.71
and the caking of the copper clippings, and the packing was removed and replaced by fresh clippings. T h e amount of free halogen in the product was negligible, and the contents of the traps were neutralized (water, aqueous N a & 0 3 , and water again) and then dried over anhydrous MgSOd. Trial runs were carried out a t temperatures of approximately 200'> 270"> and 350' C. and with varying flow rates of nitrogen and reactants to determine the limits within which undue decomposition could be avoided. From these, the conditions shown in Table I were chosen for the actual experiments. Separation of Products. EXPERIMEKT 1. A total of 1540 ml. of reaction product was separated into eight fractions, each with a boiling range of about 10" C., and a residue (350 ml.) with a boiling point >166" C. at 760 mm. of Hg using a 15plate fractionating column packed with Fenske helices. These fractions (1190 ml.) were refractionated using a 60-plate concentric tube column (9) to give eight fractions with boiling points
