Patent GB-977294-A (GB)
Title: Decomposition of sulphuric acid waste materials
IPC: C01B17/58
Filed: 1963-02-05
Abstract: <PICT:0977294/C1/1> Sulphuric acid waste material is decomposed to give SO2 and carbon by adding to it such aromatic hydrocarbon material as may be required to bring the mol. ratio of total aromatic and naphthenic hydrogen to sulphuric acid equivalent to a value in the range of 1 : 1 to 6 : 1 and then heating the waste material to a temperature of 150 DEG  to 290 DEG  C. by mixing it with at least 3 times its own weight of hot inert oil in the presence of 6-35% by weight based on the weight of oil, of carbonaceous particles. The total aromatic and naphthenic hydrogen also called the available hydrogen, is determined approximately by dividing the experimentally determined carbon content by 20.  The sulphuric acid equivalent is the sum of the free sulphuric acid plus the actual sulphonic acid content of the sludge, and the latter is obtained as a approximate value by multiplying the difference between the total acidity (as H2SO4) and the free sulphuric acid by 1.65.  The carbonaceous particles are preferably suspended in the hot inert oil before it is mixed with the waste. In the Figure, acid waste material is withdrawn from tank 1 via line 2 and pump 3 and is fed via line 4 into reactor 5 where it is evenly distributed by jacketed spray nozzle 6 over the reaction mixture.  The waste entering reactor 5 is controlled to have a mol. ratio of available hydrogen to sulphuric acid equivalent preferably of 3 : 1 to 5 : 1.  The inert oil enters continuously via pipe 11 and is admixed with the waste from line 4 by agitator 8.  The amounts of reactants entering 5 are controlled so that the weight ratio of oil to sludge is preferably 5 : 1 to 6 : 1.  The temperature of the oil entering is maintained so that the reaction temperature is preferably within the range 215 DEG  to 250 DEG C.  The inert oil which contains preferably 10 to 20% by weight of carbonaceous solids is recycled via line 27, pump tank 26, surge tank 13 and heater 12 back into the process. The sulphur dioxide produced by the decomposition leaves by pipe 19 to condenser 20 which separates the steam content as water and substantially 100% SO2 leaves via pipe 21 for further processing.  The water from 20 goes to water-oil separator 23 and any oil is drawn off via line 25 into pump tank 26. A product stream is withdrawn from 26 by line 30 into classifier 31 where the majority of the steam containing carbon particles of size less than 150, preferably less than 100 Tyler mesh is returned by line 32 to surge tank 13. The remainder of the stream passes into second stage separator 34 where a portion of the carbonaceous solids containing a majority of particles of size greater than 150, preferably greater than 100 Tyler mesh is separated.  The remaining inert oil containing a majority of smaller particles is returned to tank 13.  The product from 34 travels via conveyer 37 to stripper 38 where it is stripped of its remaining oil with steam.  The solid product from 38 goes via conveyer 42 to storage, and the vapours after condensing in 44 are returned to the process in separator 23.