The kinetics of cyclization reactions on polyaromatics from first principles

Area of Science:

• Computational chemistry
• Chemical engineering
• Materials science

Background:

• Coke formation during hydrocarbon thermal cracking is a significant industrial challenge.
• The process involves complex cyclization reactions of polyaromatic hydrocarbons.
• Understanding the kinetics of these reactions is crucial for process optimization.

Purpose of the Study:

• To investigate the ab initio density functional theory (DFT) calculations on cyclization reactions of polyaromatics during hydrocarbon thermal cracking.
• To elucidate the microscopic mechanisms governing coke formation.
• To establish structure-kinetic relationships for coke formation.

Main Methods:

• Ab initio density functional theory (DFT) calculations were employed.
• Transition State Theory (TST) was used to calculate kinetic parameters.
• Rate constants were computed at various temperatures for industrial cracking conditions.

Main Results:

• The local polyaromatic structure significantly influences activation energy for cyclization.
• The length of the attached alkyl chain affects the frequency factor.
• Coke formation exhibits autocatalytic behavior, with larger polycyclic aromatic hydrocarbons (PAHs) accelerating subsequent reactions.

Conclusions:

• The study provides microscopic insights into coke formation mechanisms.
• Results suggest an autocatalytic nature of coke formation, driven by polyaromatic surface growth.
• This work is a foundational step towards developing predictive models for coke formation kinetics based on local structure.