GB1404970A - Process for the separation of cyclopentadiene from cyclopentene and or 1,3-pentadiene - Google Patents

Abstract

1404970 Distilling hydrocarbons NIPPON ZEON CO Ltd 22 Dec 1972 [27 Dec 1971 14 Jan 1972] 59528/72 Heading C5E Cyclopentadiene (CPD) is separated from cyclopentene (CPE), or from 1 : 3-pentadiene (PPL), or from both by azeotropic distillation with n-pentane; the azeotrope of cyclopentadiene and n-pentane boils at a lower temperature than any of the simple hydrocarbons. A ternary mixture of CPD, CPE and PPL is separated by successive steps of azeotropic distillation as above and extractive distillation. Either the CPD is first removed by azeotropic distillation, and the CPE and PPL separated from one another by extractive distillation, or the CPE together with a small proportion of the CPD is first separated from the PPL and the bulk of the CPD by extractive distillation, and the PPL or both fractions then freed of CPD by azeotropic distillation. In either case, if acetylenes are present they will be recovered in the PPL fraction, or can be removed from it by a second extractive distillation, or as a side-stream in the stripping of the extract from the first extractive distillation, or by hydrogenation. The components of the azeotrope may be separated by heating to dimerize the cyclopentadiene, separating the dimer from n-pentane by distillation, and then depolymerizing. The dimer may be separated from the n-pentane by recycling their mixture to the azeotropic distillation. The n-pentane may be supplied as a hydrocarbon mixture containing n-pentane, and may be mixed with the feed before it is distilled, or introduced separately to the middle or lower part of the fractionation column. Specific applications are: (1) a C 5 by-product fraction from hydrocarbon cracking, comprising CPD, isoprene, PPL and CPE (a) is heated to dimerize most of the CPD, (b) the mixture is distilled to a cut point of 50‹ C., (c) the distillate is extracted or extractively distilled to obtain a mixture of isoprene, PPL, CPE and residual CPD, (d) isoprene is removed by distillation, and (e) the residue then sent to the azeotropic distillation; (2) a similar mixture obtained by dehydrogenation of pentanes or pentenes is subjected to steps (c), (d) and (e) of application (1); (3) a C 5 -mixture is distilled to a cut point of 40‹ C., most of the CPD is dimerized by heating, the product distilled to a cut point of 50‹ C., and the distillate from this last step sent to the azeotropic distillation; (4) CPD is partially hydrogenated to a mixture of CPE and CPD, which goes to the azeotropic distillation.