Process for producing alkenes, dialkenes and aromatics

摘要

The invention relates to a combined process for producing lower alkenes, dialkenes and monocyclic aromatics from hydrocarbon fractions whose main constituents boil above 200 DEG C, by a hydrogenation treatment and subsequent pyrolysis. While dispensing with the technologically expensive deep hydrogenation of the polycyclic aromatic raw material fractions, a hydrogenation product suitable for the pyrolysis can be made available which gives a quantity of cracked gas comparable with naphtha pyrolysis without increased occurrence of low-hydrogen carbon compounds. According to the invention, the bicyclic and oligocyclic aromatics are converted over NiO-WO3 catalysts on alkalysed alumosilicate by selective hydrogenation and mild hydrocracking of the cycloalkenobenzenes, which are partially formed as intermediates, into monocyclic aromatics alkylated up to 5-15% by mass. In the downstream pyrolysis, this hydro treated hydrocarbon mixture gives high total yields, specific to the raw material, of the target products, with only a little coke and tar deposits in the condensation zone of the pyrolysis furnace, it being possible to influence the ratio in which olefins and C6/C8 aromatics arise. Owing to their reduced content of sulphur compounds and nitrogen compounds, the liquid pyrolysis products have a high value in use.