GB733336A - Improvements in and relating to the production of lower alkenes - Google Patents

Abstract

Lower alkenes comprising ethylene and propylene are prepared by non-catalytically thermally cracking petroleum feedstocks boiling within the range 100 DEG to 350 DEG C. and containing less than 10 per cent by weight of aromatic compounds, in the vapour phase and in the absence of liquid or semi-liquid substances, under such conditions that at least 20 per cent of the total heat supplied for pyrolysis is absorbed in the reaction at temperatures in ecxess of 700 DEG C., the heat required for thermal cracking being supplied by direct contact with a hot medium. The heat may be supplied by means of steam, a fluidized bed of non-catalytic material such as coke or sand or by means of a pebble heating process in which the pebbles flow counter-current to the hydrocarbon vapours and the pebbles are circulated through the cracking zone and a heating chamber. The hydrocarbons employed may be the usual feed stocks treated by azeotropic or extractive distillation or by liquid / liquid extraction, e.g. with sulphur dioxide to reduce the aromatic content below 10 per cent; kerosenes are mentioned. In the pyrolysis using steam cracking under adiabatic conditions, the inlet temperature should preferably be 800 DEG to 720 DEG C. and the outlet 720 DEG to 640 DEG C.; when using the fluidized bed of non-catalytic material the temperature of the bed should not fall below 700 DEG C., while in the pebble heating process the outlet temperature should not be below 715 DEG C. Examples describe the adiabatic cracking of a preheated light distillate with superheated steam as above, showing the improved yields of ethylene and propylene resulting from reduction of the aromatic content of the feed from 18 per cent to 2.5 per cent; the products also include C4, H8, C4, H6 and methane. Specifications 401,286 and 554,831 are referred to.ALSO:Lower alkenes comprising ethylene and propylene are prepared by non-catalytically thermally cracking petroleum feedstocks boiling within the range 100 DEG to 350 DEG C. and containing less than 10 per cent by weight of aromatic compounds, in the vapour phase and in the absence of liquid or semi-liquid substances, under such conditions that at least 20 per cent of the total heat supplied for pyrolysis is absorbed in the reaction at temperatures in excess of 700 DEG C., the heat required for thermal cracking being supplied by direct contact with a hot medium. The heat may be supplied by means of steam, a fluidized bed of non-catalytic material such as coke or sand or by means of a pebble heating process in which the pebbles flow counter-current to the hydrocarbon vapours and the pebbles are circulated through the cracking zone and a heating chamber. The hydrocarbons employed may be the usual feed stocks treated by azeotropic or extractive distillation or by liquid/liquid extraction, e.g. with sulphur dioxide to reduce the aromatic content below 10 per cent; kerosenes are mentioned. In the pyrolysis using steam cracking under adiabatic conditions, the inlet temperature should preferably be 800 DEG to 720 DEG C. and the outlet 724-640 DEG C.; when using a fluidized bed of non-catalytic material the temperature of the bed should not fall below 700 DEG C., while in the pebble heating process the outlet temperature should not be below 715 DEG C. Examples describe the adiabatic cracking of a preheated light distillate with superheated steam as above, showing the improved yields of ethylene and propylene resulting from reduction of the aromatic content of the feed from 18 per cent to 2.5 per cent; the products also include C4 H8, C4 H6 and methane. Specifications 401,286 and 554,831 are referred to.