GB947923A - Process for the manufacture of olefines - Google Patents

Abstract

<PICT:0947923/C3/1> Olefines containing 2-4 carbon atoms are obtained by the pyrolysis of higher hydrocarbons by contact with a carrier gas comprising superheated steam, the reaction mixture is cooled to 600-150 DEG C. by heat exchange with incoming carrier gas, high boiling hydrocarbons unsuitable for recycle are separated by cooling and removed, other easily liquefiable hydrocarbons are separated by further cooling and recycled to the pyrolysis, the remaining gases are freed from carbon dioxide, sulphur compounds and acetylenes and compressed to 20-30 atmospheres gauge, any hydrocarbons so liquefied being recycled to the pyrolysis, the olefines and carbon monoxide are absorbed in a selective solvent, e.g. a cuprous salt solution, to leave a residual gas of hydrogen, methane and methene homologues and the olefines are isolated by distillation, the heat required for the various separating operations being derived from waste heat from the pyrolysis and, if necessary, by burning the residual gas. Hydrogen is supplied through line 1, and/or if desired residual gas through line 45, and is burned with an equivalent amount of oxygen through line 2. Simultaneously, superheated steam from line 21 obtained from boilers 31, 14 and 17 is introduced through line 4, the temperature being adjusted to not more than 1400 DEG C. Vaporized oil is introduced through line 5, obtained as described below. The reaction mixture is cooled and the steam heated by heat exchange in cooling zone 7, e.g. in single or double cyclones. Further cooling is effected in quenching zone 9 where the effluent is washed in cocurrent with the oil to be pyrolysed which contains some non-volatile material unsuitable for pyrolysis. In the quenching zone the volatile constituents of the oil, introduced through line 10 are vaporized while the residues together with condensed material unsuitable for recycling are withdrawn by line 11 for use as fuel; the quenching oil is circulated through waste heat boiler 14 where the heat is used to evaporate water. Further cooling is effected in cooler 13 by a quenching oil which utilizes its heat in waste heat boiler 17 for producing steam. In cooler 23, cold water is the cooling agent entering by line 25, hot water leaving by line 24 and its heat used before recycling. Liquids condensed in zone 23 pass to separator 27 where oil for pyrolysis is removed by line 29 and evaporated in zone 30 by steam from line 21, the condensate being re-evaporated in boilers 14 and 17 and the oil vapours pass by line 5 to the reactor; water is withdrawn by line 28. Zone 33 is a demisting apparatus and also compresses the gases to about 1 atmosphere gauge. Gas purifier 35 removes CO2 and H2S by washing with aqueous mono- or di-ethanolamine or a salt of an amino-acid or amino-sulphuric acid. The washing liquid is regenerated by steam from line 21, the steam condensate passing by line 38 for evaporation in boilers 14 and 17. Acetylenes are selectively hydrogenated in zone 39 and the gases are then compressed to 10-50 atmospheres gauge. By suitable adjustment of the temperature with water from the water circuit 24-25, C3 and C4 hydrocarbons may be separated and recycled by line 42 to evaporator 30. In washing unit 43 the olefines are absorbed, residual gases being sent by line 45 for burning in the reactor or by line 46 for burning to produce steam, and the absorbed olefines are desorbed by heating with hot water from line 24. The gases are compressed and distilled to separate carbon monoxide by line 49 for use as a fuel and olefines by lines 50, 51 and 52. If the oil to be pyrolysed can be evaporated directly it passes direct to evaporator 30 and quenching zone 9 is replaced by a water cooler.