GB809635A - Process for upgrading gasoline - Google Patents

Abstract

Gasoline is upgraded by separating into C6 and lighter and C7 and heavier fractions, reforming the latter at 427 DEG to 566 DEG C. and separating the product into C6 and lighter and C7 and heavier fractions, combining both C6 and lighter fractions and subjecting to isomerization and combining at least a portion of the isomerizate with at least a portion of heavier reformate. In a preferred embodiment the gasoline charge having a boiling range of C5 to about 204 DEG C. although it may boil up to 432 DEG C. and which may be a straight-run <PICT:0809635/IV (b)/1> gasoline, or natural gasoline, or cracked gasoline or coker distillate which has been subjected to desulphurization-hydrogenation, is fed to the dehexanizer 2. The bottoms are fed to reforming zone 4 which may comprise a series of reactors wherein the charge is reformed at 427-566 DEG C., 6.8-68 atmospheres and 0.5-10 vol./vol./hr. in the presence of 0.5-20 mols. of hydrogen per mol. of charge. The preferred catalyst contains 0.01 to 5 per cent platinum and alumina with combined chlorine or fluorine in a concentration of 0.2 to 3 per cent. Other supports may be silica, silica-alumina, silica-zirconia, silica-alumina-zirconia, silica-thoria, silica-alumina-thoria, silica-magnesia and silica-alumina-magnesia. Hydrogen is recycled by line 8 and liquid products are debutanized and passed to dehexanizer 13, C6 and lighter being removed by line 14 and C7 and heavier passing by line 15 to blending unit 16. The C6 and lighter fractions from lines 17 and 14 pass by line 18 to depentanizer 20. The pentanes pass to deisopentanizer 23 where n-pentane is recovered as bottoms and isopentanes as overhead pass to blending unit 16. The n-pentane is isomerized in isomerization zone 27 in the presence of hydrogen which may be obtained from the reforming operation. The preferred catalyst is a platinum-containing composite such as the platinum-alumina-halogen catalyst used in reforming. Temperatures of 371-510 DEG C. pressures of 6.8-34 atmospheres, space velocities of 0.5-5 vol. vol./hr. and hydrogen in a mol. ratio to hydrocarbon of 0.5 to 5.0 may be used. Other catalysts such as AlCl3, AlBr3 or ZnCl2 along with the appropriate hydrogen halide and, if desired, composited with alumina, bauxite or clay may be used at 65-149 DEG C. The isomerized fraction is returned to fractionator 23. Hexanes from fractionator 20 pass to deisohexanizer 30, isohexane passing by line 31 to the blending unit and n-hexane by line 32 to isomerization unit 34 operated similarly to unit 27. Once through operation is generally sufficient and the isomerized fraction passes direct to the blending unit. To avoid accumulation of small amounts of hexanes carried over in the overhead from fractionator 20 a drag stream of the bottoms from fractionator 23 is recycled by line 37. Alternative operations include the recycling of isomerized hexanes from zone 34 to fractionator 30 in which case, to avoid build up of any heptanes, a drag stream from the bottoms from 30 is recycled to dehexanizer 2. Also C5's and C6's may be isomerized in a single zone either by passing the feed from line 18 direct to zone 34 or by passing the bottoms from fractionators 23 and 30 through zone 34 and the effluent passed direct to blending or recycled to fractionator 20. To prevent any cyclic compounds formed in zone 34 from hexanes interfering with fractionation in operations involving recycle of isomerized hexanes, the effluent from zone 34 may be solvent extracted to remove cyclic compounds, particularly aromatics, which are directed to the blending zone 16. Butanes and additional isopentanes may be added to the blend to increase volatility. The final product will have a Research leaded octane number of 95-102.