Aromatics Recovered from FCC Gasoline – GT-BTX PluS®

FCC Gasoline Desulfurization Technology – GT-BTX PluS

GT-BTX PluS is a variation of GT-BTX® that uses extractive distillation technology for simultaneous recovery of BTX and thiophenic sulfur species from refinery or petrochemical aromatic-containing streams. The technology helps produce low sulfur gasoline meeting the 10 ppm limit of sulfur without change in octane value.  An alternative use of GT-BTX PluS is to generate a large volume of aromatics to produce paraxylene without the requirement of a typical naphtha reformer unit.  The aromatics recovery is especially attractive for use with feedstocks produced from high severity FCC operations.

The process is optimally installed on the FCC mid-cut naphtha stream. GT-BTX PluS removes all thiophenes and some of the mercaptan species from the FCC gasoline feed.  The olefin-rich raffinate can be sent directly to the gasoline pool for blending, or to a caustic treating unit to remove the mercaptan-type sulfur compounds before being sent to the gasoline. The desulfurized aromatics extract stream can be directly fed into petrochemical production units instead of recycling to the naphtha reformer. GT-BTX PluS provides an effective solution for meeting today’s clean gasoline requirements and gives refiners the ability to convert lower-value gasoline components into higher-value petrochemicals.

Process Description

The optimum feed is the mid fraction of FCC gasoline from 70°C to 150°C.  This material is fed to the GT-BTX PluS unit, which extracts the sulfur and aromatics from the hydrocarbon stream.  The sulfur-containing aromatic components are processed in a conventional hydrotreater to convert the sulfur into hydrogen sulfide (H2S).  Because the portion of gasoline being hydrotreated is reduced in volume and free of olefins, hydrogen consumption and operating costs are greatly reduced.  In contrast, conventional desulfurization schemes must process the majority of the gasoline through hydrotreating units to remove sulfur, which inevitably results in olefin saturation, octane downgrade and yield loss.

FCC gasoline is fed to the extractive distillation column (EDC).  In a vapor-liquid operation, the solvent extracts the sulfur compounds into the bottoms of the column along with the aromatic components while rejecting the olefins and non-aromatics into the overhead as raffinate.  Nearly all of the non-aromatics, including olefins, are effectively separated into the raffinate stream.  The raffinate stream can be optionally caustic washed before routing to the gasoline pool or to an aromatization unit to further increase benzene, toluene and xylene (BTX) production.

Rich solvent, containing aromatics and sulfur compounds, is routed to the solvent recovery column (SRC), where the hydrocarbons and sulfur species are separated, and lean solvent is recovered in columns bottoms.  The SRC overhead is hydrotreated by conventional means and either used as desulfurized gasoline or directed to an aromatics plant.  Lean solvent from the SRC bottoms is recycled back to the EDC.

Process Advantages

  • Produces high-quality aromatics from FCC gasoline
  • Reduces the sulfur content of the FCC gasoline fraction being sent to the gasoline pool
  • Reduces H2 consumption, only HDS function is required for thiophenic sulfur
  • No olefin saturation
  • Greater utilization of naphtha reformer compared to units that recycle the cracked gasoline.  Avoids BTX taking a “free ride” through the unit
  • Opportunity to feed more fresh naphtha and generate more hydrogen