GB621873A - Treatment of coke oven gas - Google Patents

Abstract

<PICT:0621873/IV (b)/1> Olefins are separated from coke oven gas containing hydrogen and small amounts of olefins and acetylene by selectively absorbing the olefins and acetylene in an aqueous solution containing 25-35 per cent by weight of silver nitrate, and sufficient ferric nitrate and free nitric acid to keep the silver acetylide complex formed in solution and to prevent precipitation of silver. The preferred solution contains 31 per cent of silver nitrate, 7-13 per cent of free nitric acid, and 10 per cent of ferric nitrate based on the weight of silver nitrate, a suitable solution having the composition: silver nitrate 31, nitric acid 11, ferric nitrate 3.2, and water 54.8 per cent. The olefins are separated from the solution by distilling under vacuum, and the silver acetylide present, whose preparation forms the subject-matter of Specification 616,319, [Group III], precipitated with mercuric nitrate as a mercury-silver acetylide, the preparation of which forms the subject-matter of Specification 616,318, [Group III]. The silver nitrate solution is recycled to the absorption while the precipitate is decomposed by heat and oxidation to recover the mercuric nitrate. Coke oven gas containing ethylene, propylene, acetylene and hydrogen enters at 10 and is compressed to about 150 p.s.i., cooled, and passed up a tower 20 against the absorption solution, exit gas being expanded and burnt. The rich solution passes to expansion chamber 30, released gas being returned to line 10, and thence to stripper 38 with heater 44, olefins being distilled off under a pressure of about 4 1/2 inches of mercury. Lean solution leaving at 49 is largely recycled to the absorber by line 58, while a quantity containing acetylene in amount slightly greater than that absorbed in one pass through absorber 20 is fed by line 66 to precipitator 68 together with a solution of mercuric nitrate and nitric acid from line 70 in amount slightly less than required to precipitate all the acetylene. The precipitate is led by line 72 to a heater 74 while the silver nitrate solution is recycled by line 76 to the absorber. Heater 74 comprises steam coil 82, reflux condenser 86, and air inlet pipe 80. The regenerated mercuric nitrate, in solution with silver nitrate, nitric and nitrous acids, is fed to line 70.