Patent GB-606800-A (GB)
Title: Improvements in the preparation in a condition of purity of benzene and/or cyclohexane from mixtures containing them
IPC: C07C15/04
Filed: 1945-01-12
Abstract: Pure cyclohexane and/or benzene are or is prepared from a fraction consisting of n-hexane, benzene, methylcyclopentane, cyclohexane and the dimethylpentanes by distilling in an initial distillation zone to remove a fraction distilling not above 81.1 DEG  C. which is distilled in a second zone for recovery of cyclohexane as a residual fraction, the overhead being subjected to extractive or azeotropic distillation or solvent extraction to recover the benzene, the remainder being isomerized to convert methylcyclopentane to cyclohexane and 2,2- and 2,4-dimethylpentanes to isoheptanes of higher boiling point, cyclohexane, as such or after dehydrogenation to benzene, being separated from the product.  The isomerization product may be fractionated and a fraction containing cyclohexane recycled to the cyclohexane recovery distillation zone with or without addition of benzene from the benzene recovery stage.  Benzene from that stage may be hydrogenated and cyclohexane recovered in the distillation zone.  An azeotrope-forming hydrocarbon, which may be the recovered benzene, may be added in the first or second distillation zone.  Hydrocarbons boiling below 68 DEG  C. are preferably first removed from the feed.  This may be an isoheptane fraction of naphtha which is fractionated to give an overhead of B.R. 68-81.1 DEG  C. which is distilled in said second zone.  The isomerization may be effected with Friedel-Crafts' catalysts or hydrogenation catalysts such as metal oxides and sulphides.  The benzene-freed product from the extraction zone may be separated into two fractions, the lighter containing the bulk of the methylcyclopentane, and the heavier most of the cyclohexane and dimethylpentanes, which fractions are separately isomerized.  The product of isomerization of the heavier fraction only, after removal of higher boiling heptanes, may be dehydrogenated and benzene recovered.  Where cyclohexane is the desired main product, benzene from the extraction stage is hydrogenated, sufficient being left unhydrogenated, however, to ensure pure cyclohexane being left as the residual fraction in the second distillation zone.  Specifications 563,555, 585,850, 606,797 and 606,798 are referred to, and Specifications 527,767 and 548,901, [both in Group IV], in the Provisional Specification also are referred to.ALSO:Pure cyclohexane and/or benzene are or is prepared from a fraction consisting of n-hexane, benzene, methylcyclopentane, cyclohexane, and the dimethylpentanes by distilling in an initial distillation zone to remove a fraction distilling not above 81.1 DEG  C., which is distilled in a second zone for recovery of cyclohexane as a residual fraction, the overhead being subjected to extractive or azeotropic distillation or solvent extraction to recover the benzene, the remainder being isomerized to convert methylcyclopentane to cyclohexane and 2,2- and 2,4-dimethylpentanes to isoheptanes of higher boiling point; cyclohexane, as such or after dehydrogenation to benzene, being separated from the product.  The isomerization product may be fractionated and a fraction containing cyclohexane recycled to the cyclohexane recovery distillation zone with or without addition of benzene from the benzene recovery stage.  Benzene from that stage may be hydrogenated and cyclohexane recovered in the distillation zone.  An azeotrope-forming hydrocarbon, which may be the recovered benzene, may be added in the first or second distillation zone.  Hydrocarbons boiling below 68 DEG  C. are preferably first removed from the feed.  This may be an isoheptane fraction of naphtha which is fractionated to give an overhead of B.R. 68 DEG -81.1 DEG  C., which is distilled in said second zone.  The isomerization may be effected with Friedel-Crafts' catalysts or hydrogenation catalysts such as metal oxides and sulphides.  The benzene-freed product from the extraction zone may be separated into two fractions, the lighter containing the bulk of the methylcyclopentane, and the heavier most of the cyclohexane and dimethylpentanes, which fractions are separately isomerized.  The product of isomerization of the heavier fraction only, after removal of higher boiling heptanes, may be dehydrogenated and benzene recovered.  Where cyclohexane is the desired main product, benzene from the extraction stage is hydrogenated, sufficient being left unhydrogenated, however, to ensure pure cyclohexane being left as the residual fraction in the second distillation zone.  Specifications 563,555, 585,850; 606,797, and 606,798, [both in Group III], are referred to, and Specifications 527,767 and 548,901 are referred to in the Provisional Specification.