Sub-Product

A complex combination of hydrocarbons obtained from distillation of aromatic streams. It consists predominantly of aromatic hydrocarbons having carbon numbers predominantly in the range of C₈ through C₁₀ and boiling in the range of approximately 135°C to 210°C (275°F to 410°F)^[1].

A UVCB (Unknown or Variable Composition) substance containing aromatic molecules (one-ring) composed of carbon and hydrogen and consisting of C₉ aromatic hydrocarbons (approximately 90%). The category only includes substances with boiling ranges between ~160°C to ~175°C. The chemical substance definition is a CAS RN definition and reflects a broader boiling range (135°C to 210°C) than the hydrocarbon solvent category member with CAS RN 64742-95-6, which ranges from ~160°C to ~175°C^[2]. 

Trimethylbenzene (TMB) and ethyltoluene (ET) isomers are major constituents in the C₉ aromatic naphtha. The C₉ aromatic naphtha, which was tested under a 1985 U.S. TSCA Section 4 test rule, was required to have a minimum total ET-TMB content of 75%. Commercial C₉ aromatic naphtha typically contains 1,2,4-trimethylbenzene at 20-45%, 1,3,5-trimethylbenzene at 8-15%, and mixed ethyltoluenes at 25-35%^[2].

 The composition of the C₉ aromatic naphtha substance (CAS RN 64742-95-6) will vary somewhat, but generally contains <1% aliphatics and >90% C₉ aromatic hydrocarbons. This substance may contain C₈ and C₁₀ aromatic hydrocarbons, typically in the range 5-10%, though these are not considered impurities, they are constituents of the substance. This substance may contain traces of benzene (<10 ppmv), sulfur (<10 ppmv), and nitrogen (<10 ppmv); however, these chemicals are considered impurities that are intentionally removed during production^[2].

C₉ aromatic naphtha is obtained through several refinery processes^[3]:

• Catalytic Reforming: the process begins with catalytic reforming, where naphtha is converted into a high-aromatic content stream. The reformate produced has a high concentration of aromatics and can be further processed for aromatic extraction.
• Separation Process: After reforming, the aromatic compounds are separated through these steps (Fig. 1):
  • Extraction using a solvent to separate aromatics from non-aromatics.
  • Recovery of aromatics in the solvent recovery column.
  • Fractionation to obtain pure streams.

Figure 1 - Schematic flow diagram for the extraction of BTX aromatics from a catalytic reformate^[4].

Reference

1. ECHA - European Chemicals Agency > Substance Infocard > Solvent naphtha (petroleum), light arom.
2. OECD - Existing Chemicals Database > April 2012, SIDS INITIAL ASSESSMENT PROFILE > C₉ Aromatic Hydrocarbon Solvents Category.
3. Dr. Marcio Wagner da Silva, 24^th Sep 2021, Naphtha to Chemicals Refining Routes, Linkedin.
4. Wikiwand, BTX (Chemistry).