Patent GB-1312353-A (GB)
Title: Process for extracting aromatic hydrocarbons
IPC: C07C7/10
Filed: 1970-07-17
Abstract: 1312353 Separating hydrocarbons by solvent extraction SNAM PROGETTI SpA 17 July 1970 [18 July 1969] 34912/70 Heading C5E A process for extracting aromatic hydrocarbons from a mixture of aromatic and aliphatic hydrocarbons comprises a first stage in which the feed mixture is contacted with a solvent in which aromatic hydrocarbons are soluble, so as to form an extract which contains aromatic hydrocarbons; a second stage in which the extract from the first stage is purified by contact with a countercurrent of a purifying agent comprising a hydrocarbon fraction coming at least in part from a third stage, so as to produce a purified extract; a third stage in which the purified extract is extractively distilled to produce an overhead product of which at least part is used in the second stage; and a fourth stage in which the bottom product of the third stage is rectified so as to separate the dissolved aromatic hydrocarbons from the solvent which is recycled to the first stage: wherein (a) the overhead product from the third stage is separated into a higher boiling fraction and a lower boiling fraction which is passed to the second stage, (b) the rectification in the fourth stage is effected in the presence of water, and (c) the extractive solvent used is selected from sulpholane and its derivatives, N-alkyl-pyrrolidones, dialkylsulphoxides, dialkyl formamides, diacetyl-formamides, methyl carbamide, alkyl derivatives of morpholine, glycols and etherified glycols and can contain up to 30 wt. per cent water. A feed 1 is extracted at 2 and the extract 9 is washed at 10 and extractively distilled at 17 to produce an overhead 18 and a bottoms stream 22 which is rectified at 23 to recover aromatics 29 and the solvent 24. The crosshead 18 containing non-aromatics and light aromatics is condensed and distilled at 19 to produce a lower boiling fraction 20 and a bottoms stream 21, comprising high boiling saturated hydrocarbons and non-aromatics of high polarity, which is recycled to the extraction column 2 at a point between the inlets for the feed and for the solvent stream 3 recycled from the rectification at 23. Water is separated from the overhead aromatic fraction at 28 and in part recycled as the stream 26 to remove solvent from the overhead fraction, in part passed to column 5 to recover extractive solvent from the feed raffinate 4, in part vaporized at 25 and passed into the bottom of column 23, and the remainder passed through line 32 mixing with the aqueous stream 8 and the hydrocarbon streams 14 and 20 to serve as the purification agent used in the extraction column 10. The raffinate 12 from the column 10 is separated in a distillation column 13 into an overhead stream 14 comprising light aliphatic hydrocarbons which is recycled to the column 10 and a bottoms stream 15 which is recycled to the extraction column 2. Instead of recovering the light aliphatic hydrocarbons from the raffinate from column 10 they can be recovered from the raffinate from column 2. The overhead stream 18 can be separated into the fractions 21 and 20 by condensation at different temperatures instead of by distillation at 19 as shown. The aromatic mixture 29 obtained can be further distilled to recover xylenes.