GB1002584A - Improvements in or relating to the manufacture of pure sulphur dioxide - Google Patents

Abstract

<PICT:1002584/C1/1> In manufacturing pure SO2, molten elemental sulphur is introduced into a reactor 1 containing oleum maintained at a temperature below the solidification point of sulphur (120 DEG C.) while subjecting the reaction medium to agitation. Liquid sulphur at 125 DEG to 155 DEG C. is fed continuously at 8 to reactor 1 containing a stirring device consisting of inverted cone 3 and impeller 4. The contents of reactor 1 are maintained at 90 DEG C. by steam jacket 2 and the sulphur is converted into spherules of diameters up to 3 mm. Withdrawal of part of the reaction medium and introduction of SO3-rich oleum are carried out discontinuously and alternately through a filter 5 which is a ring of porous material, e.g. polytetrafluoroethylene. From filter 5 pipe 7 leads to 3-way valve 11. The SO3-rich oleum is introduced by injection under a gaseous SO2 pressure; obstruction of filter 5 caused during previous withdrawal of reaction medium may be cleared partly by the introduction of the SO3-rich oleum and completely by the passage of gaseous SO2 through the filter in the same direction. While liquid is being withdrawn from reactor 1 by pump 12, rich oleum is stored in measuring tank 14 fed through 19 by pump 20 which is stopped by level detector 21 when the liquid in tank 14 reaches a predetermined level 141. When the pressure in SO2 reservoir 16 reaches a predetermined minimum, manometer 22 opens valve 23 to allow compressed SO2 to enter 16 and simultaneously causes valve 11 to rotate so as to allow withdrawal of liquid from the reactor. Valve 23 is closed by the action of manometer 22 when a predetermined maximum pressure is reached in 16. When the level of liquid in 1 falls to the level of probe 10, valve 11 is automatically placed in the position such that rich oleum is admitted from tank 14 to beaker 1. The SO2 which leaves the reactor 1 via pipe 9 is purified and freed from liquid droplets at 24, and is compressed and liquefied at 25. In the example it is stated that the free SO3 content of the oleum in the reactor varies from 13 to 15% during the cycle. The rich oleum contains 35% SO3. About 1/15 of the quantity of SO2 produced is recycled each time, the injection pressure varying between 3 kg./cm.2 and 1.5 kg./cm.2 during the cycle.