Technology

The BTX Extraction Unit recovers high-purity Benzene, Toluene, and Xylenes from an aromatics-containing feedstock (such as catalytic reformate, hydrotreated Pygas, or coke oven light oil) by exploiting the difference in relative volatility between aromatic and non-aromatic hydrocarbons in the presence of a selective solvent. Unlike liquid-liquid extraction, this technology performs the separation directly by distillation, using a solvent to alter the relative volatilities of the components rather than relying on boiling point differences alone.

Process Description

General Process Description
The BTX-rich feedstock is fed to an Extractive Distillation Column (EDC), typically at a mid-point, where it contacts a circulating lean solvent introduced near the top of the column. Common solvents include Sulfolane, N-Formylmorpholine (NFM), or Dimethyl Sulfoxide (DMSO), selected for high selectivity toward aromatics, high boiling point, and thermal stability.

Extractive Distillation Column (EDC)
Within the EDC, the solvent selectively absorbs the aromatic compounds, carrying them toward the column bottom, while non-aromatic hydrocarbons are rejected and exit as vapor from the top. A portion of the overhead non-aromatic stream is returned as reflux to wash back any entrained solvent, improving separation efficiency. The non-aromatic overhead product exits as a raffinate stream, often reused as a gasoline blending component or recycled feedstock.

Solvent Recovery Column (SRC)
The aromatics-rich solvent stream from the EDC bottom is routed to a Solvent Recovery Column, typically operated under vacuum to reduce the required boiling temperature and minimize thermal degradation of the solvent. In the SRC, the absorbed aromatics are stripped from the solvent and recovered overhead as a mixed BTX product, while lean solvent exits from the column bottom for recycle back to the EDC.

Solvent Regeneration
A small slipstream of the lean circulating solvent is typically routed through a solvent regeneration step to remove heavy decomposition products and maintain solvent purity and performance over time.

Fractionation
The recovered mixed aromatics stream from the SRC overhead is sent to a downstream Fractionation Unit, where differences in boiling points are used to separate the mixture into high-purity Benzene, Toluene, and Xylene products.

Key Characteristics

Extractive distillation is generally favored over conventional liquid-liquid extraction when feed aromatic concentration is relatively high, since it offers simpler operation and lower energy consumption despite requiring careful solvent selection to balance purity and yield.

Major Equipment List

• Extractive Distillation Column (EDC):
  Main separation column where lean solvent contacts the aromatic feed; typically a trayed or packed column with a rotating disc contactor internal option in some designs.

• Solvent Recovery Column (SRC):
  Vacuum-operated distillation column that strips aromatics from the rich solvent, recovering mixed BTX overhead and lean solvent from the bottom.

• Extractive Stripper:
  Auxiliary column used in some configurations to further strip light non-aromatics from the solvent before it enters the solvent recovery column.

• Water Wash Column:
  Removes traces of entrained solvent from the non-aromatic raffinate stream using water as a wash medium.

• Solvent Regenerator/Reclaimer:
  emoves heavy degradation products and polymeric residues from the circulating solvent to maintain purity and selectivity.

• Reboilers:
  Provide vaporization duty for the EDC, SRC, and water wash/stripper columns (typically steam-heated).

• Condensers/Overhead Coolers:
  ondense vapor streams from column tops (EDC overhead raffinate, SRC overhead BTX product).

• Reflux Drums:
  Hold condensed overhead liquid for reflux and product draw-off from each column.

• Circulation Pumps:
  Solvent circulation pumps (lean/rich solvent), reflux pumps, and product pumps for each column.

• Heat Exchangers:
  Lean/rich solvent exchangers for heat recovery between hot lean solvent and cooler rich solvent streams, plus feed preheaters.

• Decanter/Separator Vessels:
  Used where immiscible liquid phases (e.g., water-hydrocarbon) need to be separated, such as after water wash.

• Storage and Surge Vessels: 
  Solvent storage tank, feed surge drum, and product surge drums for the BTX extract and raffinate streams.

• Filters: Solvent filters to remove particulates and degradation products from the circulating solvent loop.

• Control Instrumentation:
  Level, temperature, pressure, and flow control systems on each column and pump to maintain solvent-to-feed ratio and separation efficiency.

Equipment by Process Section

Exact equipment count and configuration vary by licensor, with some designs consolidating the extractive stripper into the EDC and others using separate vessels.