GB822912A - Removing cyclopentadiene from hydrocarbon mixtures by distillation - Google Patents

Abstract

<PICT:0822912/III/1> Cyclopentadiene is removed from hydrocarbon feedstocks which contain dicyclopentadiene and other hydrocarbons boiling above the boiling point of cyclopentadiene, such as xylenes, indene and a -methylstyrene, by heating the feedstock to such a temperature, e.g. 300 DEG C., that it is vaporized and the dicyclopentadiene is completely converted into cyclopentadiene, feeding the vapours to or near the base of a fractionating column, supplying hydrocarbon liquid, substantially free of dicyclopentadiene, having a boiling-range lying between 100 DEG and 150 DEG C. as cold reflux into the top section of the column, and withdrawing from the head of the column a vapour mixture containing cyclopentadiene and hydrocarbons boiling below 150 DEG C. A liquid xylene fraction, boiling at about 150 DEG C., may be withdrawn from the column as a sidestream and, after cooling to about 40 DEG C., introduced into the top of the column as reflux. A feedstock derived from the aromatics fraction obtained from the product of a vapour-phase cracking of a petroleum oil is supplied through line 1 into preheater 2. The feedstock next flows through tube still 3 in which it is heated to 300 DEG C. so that it is vaporized, and the dicyclopentadiene is re-dimerized. The vapours are fed via line 4 to one of the plates near the base of column 5. A sidestream comprising xylenes and ethyl benzene is withdrawn from the column, at a temperature of about 150 DEG C., through line 6; this sidestream is cooled to about 40 DEG C. in cooler 7 and then introduced via line 8 on to the top plate of the column. Additional reflux hydrocarbons can, if necessary, be added to the system e.g. by addition to the feed through line 16 or by direct addition to the top of column through line 17. The head of the column is maintained at a temperature between 90 DEG and 110 DEG C.; and a vapour mixture containing cyclopentadiene and xylenes is removed overhead. This vapour is fractionated in column 11 to obtain cyclopentadiene as overhead product, any methyl cyclopentadiene present being removed as a sidestream through line 13, and xylenes being withdrawn as bottoms via line 14. A lower side-stream from column 5, consisting of liquid boiling between 150 DEG and 190 DEG C., is withdrawn through line 10; this liquid contains indene and methyl styrene, but is free from cyclopentadiene. Resins formed from methyl styrene in the side-stream have improved colour and light stability compared with similar resins formed from material produced by fractionation using conventional reflux. In an alternative embodiment, the required reflux can be supplied wholly through line 17, e.g. as a xylenes from an earlier distillation step in the working-up of the aromatics fraction derived from the vapour-phase cracking product. In such case the side-stream comprising xylenes is removed from column 5 via line 18 and is passed via a cooler 19 to storage, while line 6 and cooler 7 are dispensed with. If desired, the cyclopentadiene can be isolated from the overhead from column 5 by condensing the overhead and allowing the cyclopentadiene to dimerize; the resulting dicyclopentadiene is then separated from the lighter hydrocarbons by vacuum distillation. Cyclopentadiene can then be recovered by dedimerization.