GB830574A - Process of producing acetylene and ethylene - Google Patents

Abstract

<PICT:0830574/IV (b)/1> In a process for the production of a desired hydrocarbon, particularly acetylene and/or ethylene, by the pyrolysis of a suitable feedstock wherein the feedstock is heated to above 800 DEG C. in a regenerative furnace to produce an off-gas containing the desired hydrocarbon, tars in a gaseous state and other gases, and the off-gas is quenched to a temperature at which the desired hydrocarbon is stable but above the dew point of the tars, and removed from the furnace at such temperature, the off-gas is suddenly cooled to condense the tars which are then removed and the desired hydrocarbon is subsequently recovered. Two regenerative furnaces 11 and 12 are used, each containing three masses forming two spaces; they are alternately heated and used for pyrolysis. Thus, furnace 12 is heated by passing fuel from line 47b (obtained within the process) into the first space of the furnace while air or other oxygen-containing gas is passed into the end from line 48. Combustion occurs heating the central and later masses and the flue gases leave through lines 52a and 54c. Simultaneously furnace 11 is on a make period; steam (line 45), fresh feed propane (line 46a) and recycle feed (line 126) are passed by line 51 into the end of the furnace in the opposite direction to the flow of gases in the previous heating period. The feed is pyrolysed in the first and central masses and quenched in the third and the off-gas formed is removed by lines 52 and and 54a. A stream of liquid, mostly water, at about 140 DEG F. is sprayed from line 73 into the off-gas vaporizing the liquid and cooling the gas which passes into tar separator 13. Water and tar collect in the bottom of this and tar passes down into the collector 14. The gas entering the separator passes downwardly through an inner cylindrical chamber at the bottom of which, just above the collected liquid, it changes direction and moves upwardly through the annular space between the inner and outer chambers. It is then scrubbed with water and washed with cold water supplied by line 69 before leaving by line 61. It is joined by water from lines 74 and 75 and is passed into the scrubber 15 where it is scrubbed by cold water from line 69 and warm water from line 77. Water collecting in the bottom of the scrubber is passed to line 73 and by line 64 to the pond 20 where it is cooled before re-use. A certain amount of light oil is collected by this water and this assists in keeping the tar separated in separator 13 liquid. The gases then pass through pump 19 which maintains a subatmospheric pressure of about 15 inches of mercury back to the furnaces and now brings the gas to atmospheric pressure. The gas is cooled by cold water from line 69 thereby condensing all steam and then passes through electrostatic precipitator 21 before being collected in storage vessel 22. As illustrated in Figs. 2b and 3 (not shown), the gas is treated as follows. It is first treated with a selective solvent, e.g. acetone, acetonyl acetone or more preferably dimethyl formamide, to dissolve out diacetylene and some acetylene; these are then stripped from the solvent and recycled to the furnace by line 126. Further treatment with more of the same solvent removes all acetylene plus a small amount of other gases. Acetylene is obtained from this mixture by fractionation fore-runnings being recycled by line 108a, acetylene passing to storage by line 114 and the remainder being recycled by line 126. The acetylene may be washed just before leaving its column with cold solvent to remove final traces of more soluble contaminants. Ethylene is then separated from the remaining gas by fractionation. Remaining gases are used in the process, e.g. for stripping solvent in which case they are eventually recycled by line 126 or are led back by line 161 for use as a fuel for compressors or heating the furnaces.