Main-Product

During the alkylation of benzene with ethylene to produce ethylbenzene (EB), polyethylbenzenes (PEB) form as byproducts. These consist of benzene rings with multiple ethyl groups attached. The specific constituents include:

Primary PEB Constituents

1. Diethylbenzene (DEB)
   • Structure: Benzene ring with two ethyl groups.Isomers: Ortho-, meta-, and para-diethylbenzene.
   • Role: Dominant PEB byproduct under typical conditions, especially at higher benzene/ethylene ratios
      
2. Triethylbenzene (TEB)
   • Structure: Benzene ring with three ethyl groups.
   • Isomers: Multiple positional isomers (e.g., 1,2,3-; 1,2,4-; 1,3,5-triethylbenzene).
   • Formation: Result of further alkylation of DEB with ethylene
      
3. Tetraethylbenzene (TeEB)
   • Structure: Benzene ring with four ethyl groups.
   • Isomers: Multiple configurations (e.g., 1,2,3,4-; 1,2,3,5-).
   • Occurrence: Forms in smaller quantities, depending on reaction severity
      
4. Higher Ethylated Benzenes
   • Examples:
     • Pentaethylbenzene (PeEB)
     • Hexaethylbenzene (HeEB)
   • Role: Rare, but possible under extreme conditions or prolonged reaction times

Factors Influencing PEB Composition

• Aromatic/Ethylene (A/E) Ratio: Higher ratios favor DEB over heavier PEBs
• Catalyst Type: Zeolite catalysts (e.g., ZSM-5, Beta, MCM-22) influence selectivity and isomer distribution
• Reaction Conditions:
  • Temperature: Higher temperatures (e.g., 220–315°C) increase alkylation rates but may promote heavier PEBs
  • Pressure: Liquid-phase systems (e.g., 500 psig) suppress vapor-phase side reactions

Transalkylation and Byproduct Management

PEBs are typically recycled to a transalkylation reactor, where they react with benzene to regenerate EB. For example:

Heavier PEBs (e.g., TeEB, PeEB) undergo similar transalkylation but require more benzene and energy.

References

1. 18^th Oct 1999, PRODUCTION OF ETHYLBENZENE FROM BENZENE AND ETHYLENE BY LIQUID-PHASE ALKYLATION USING ZEOLITE CATALYSTS, Aspen Model Documentation, PEP Process Module, SRI Consulting.
2. Stephen L. Pohl, US7524467B2, Priority Date 8^th Jun 2006, Process for the production of alkylbenzene, Assignee: Lummus Technology LLC, Status: Expired.
3. Elena Khlebnikova et al., Feb 2017, Modeling of Benzene with Ethylene Alkylation, ijcea, Vol. 8, No. 1, p. 61-66.