GB815940A - Improvements in or relating to photochemical chlorination apparatus - Google Patents

Abstract

<PICT:0815940/III/1> <PICT:0815940/III/2> <PICT:0815940/III/3> An apparatus suitable for the photo-chemical chlorination of benzene (see Group IV (b)) comprises a pair of parallel transparent tubes each of which is provided with cooling means and surrounded by a source of actinic light, a third tube connecting said pair of tubes at one end thereof and a fourth tube connecting said pair of tubes at their other ends, and a pump rotor in said fourth tube whereby liquid is circulated through said tubes. A plurality of pairs of tubes is preferably used in conjunction with a single pump: thus, in the illustrated apparatus, four pairs of tubes are provided and the reactants are introduced through line 113 into a central vertical well 112 with which each of said tubes communicates. The reactants are pumped by means of a rotor 116 into the upper of each pair of tubes (121, Fig. 1) and return to the well via the lower tubes. Each of the tubes comprises an inner transparent tube 122 containing U-tubes 127 (see Figs. 3 and 4) connected to headers 128 and 129 for circulation of a refrigerant, an outer reflector housing 126, and, between the housing and the inner tube, lamps 125 which supply the desired actinic light.ALSO:<p1> Hexachlorocyclohexane containing at least 20 per cent of the gamma-isomer is continuously produced in a photo-chemical apparatus (see Group III) from an initial mixture of benzene, acetic anhydride, carbon tetrachloride and chlorine at, e.g., 5 to -25 DEG C. As shown in Fig. 5, a reservoir 6, slightly pressurized by argon or helium, is provided for the benzeneacetic anhydride-carbon tetrachloride mixture, make-up quantities of benzene being added through line 8. The mixture passes via line 9 to the continuous reactor 12 together with chlorine from line 16, and circulates at a temperature of -10 DEG C., maintained by a refrigerant entering the apparatus by line 13, under the influence of actinic light. The product is withdrawn to a secondary illuminated reactor 20 where the chlorine is reduced to a trace and thence to a solvent preheater 18, after adding make-up quantities of acetic anhydride. Makeup benzene can also be added to line 25. The preheater 18 is operated at the boiling-point, e.g. 92 DEG C. at atmospheric pressure, and is equipped with a packed column 51 and reflux condenser 19; a small portion of the acetyl chloride and acetic acid formed in the reactors is thus converted to acetic anhydride, and hydrogen chloride is vented. The mixture is then passed to boiler 23 where the unreacted benzene together with acetic anhydride and carbon tetrachloride are volatilized and returned to reservoir 6 via receiver 28 kept under vacuum by a pump attached to line 32. The unvolatilized liquid in boiler 23 is withdrawn into stripper 36 and the product obtained therefrom. Solvent volatilized in the stripper is condensed and collected in evacuated receiver 42 and returned to the boiler. The product is a hot liquid containing acetic anhydride which is removed by stirring vigorously with water; the material obtained is in the form of fine pellets containing 28 per cent of gamma-isomer.