GB780802A - Process for cracking and refining synthetic hydrocarbons - Google Patents

Abstract

<PICT:0780802/III/1> In order to prepare motor fuels from hydrocarbon mixtures obtained by the hydrogenation of carbon monoxide, the hydrocarbons boiling above 300 DEG C. are separated from the mixture and subjected to thermal cracking, the cracked vapours are fractionated together at least part of the original synthetic hydrocarbon mixture, hydrocarbons of gasoline boiling range are withdrawn from the fractionating column and are subjected to refining in the presence of a catalyst, such as aluminium silicate at a temperature of about 450 DEG C., the cracked vapours being used to preheat the feed to the refining unit before they are introduced into the fractionating column, and the hot product vapours from the refining unit are passed in heat exchange with an intermediate condensate boiling above 100 DEG C. obtained by fractional condensation of the effluent vapours from the hydrogenation reactor, the intermediate fraction being then passed to the fractionating column. The hot vapours from the hydrogenation reactor are subjected to multi-stage cooling to give four condensates: (a) hot condensate, boiling above 300 DEG C., which is stored in tank 1; (b) intermediate condensate, i.e. hydrocarbons boiling in the range 100 DEG -300 DEG C., stored in tank 5; (c) cold condensate collected at room temperature and stored in tank 9; (d) low temperature condensate stored in tank 11. Hot condesate from tank 1 is heated to 450-500 DEG C. in tubular furnace 2 while maintaining the pressure at such a level that the liquid does not vaporize. The liquid is then released from pressure into vapour-liquid separator 3 where partial vaporization occurs. Steam which has been heated in furnace 2 to about 500 DEG C. is simultaneously passed through line 4 into separator 3. Intermediate condensate from tank 5 is passed through heat exchanger 6, wherein it is heated by the product from refining unit 15a or 15b, and is then introduced into fractionating column 13. The condensates from tanks 9 and 11 are also introduced, via heat exchangers 10 and 12 respectively, into column 13. The bottoms from column 13 are heated to 500-520 DEG C. in furnace 2, and then passed under a pressure of 3-10 kg./sq. cm. into separator 3. The liquid in separator 3 is recycled through the furnace mixed with the feed from tank 1. The hydrocarbon vapours, together with the injected steam, from the separator pass through a cracking-coil heated by radiation in the furnace, and then flow through heat exchanger 7. The uncondensed vapours are introduced into column 13. Part of the liquid condensed in heat exchanger 7 is steam-distilled in column 8, the vapours being introduced into column 13 and the residual liquid (polymers) being withdrawn as bottoms. Hydrocarbon gases and gasoline vapours are withdrawn from the head of column 13, and passed through heat exchanger 12. The condensed gasoline is separated from the gases in separator 14. Part of the gasoline is returned to column 13 as reflux, but the remainder is vaporized and heated to 450 DEG C. in heat exchanger 7 and then passed through one of the alternately-operated refining units 15. The refined product passes out through heat exchangers 6 to a re-run distillation unit (not shown). Hydrocarbons boiling in the diesel oil range are withdrawn from column 13 via stripper 18, and are collected in storage vessel 19. The gases from separator 14 are passed to storage vessel 16, and are then compressed in compressor 17 for recovering C3-C4 hydrocarbons.