1 INTRODUCTION
Due to the heavier tendency of crude oil,1,2 delayed coking based on deep thermal cracking reaction is receiving more and more attention as one of the most important processing technology for heavy oils.3 Free radical chain reaction theory is widely used to explain the mechanism of thermal cracking reaction, includes chain initiation, chain growth and chain termination.4,5 The chain initiation due to the breaking of the C-C bond is usually the control step of the reaction. The chain growth mainly includes the substitution reaction, decomposition reaction, addition reaction and displacement reaction of free radicals. The chain termination refers to the combination of unpaired electrons of free radicals to form stable molecules, which stops the chain reaction.
The analysis and characterization method of heavy oil is far from mature due to the extreme complexity of petroleum composition.6 The application of supercritical fluid extraction and fractionation (SFEF) technology7-9 and Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry technology made breakthroughs in understanding the complex molecular structure of petroleum.10-13 At the same time, the rapidly-developing computing technology greatly promoted the development of petroleum processing models from the traditional multi-lumping models14-17 based on fractions to the molecular-level reaction kinetic models. Representative modeling method for molecular-level reaction kinetic models of refining processes included the structure-oriented lumping (SOL) method,18-20 the modified molecular-type homologous serious (MTHS) representation,21 and Bond-Electron matrix with Monte Carlo simulation and atomic topology.22-25
SOL method has been proved to be effective for heavy oil processing models. ExxonMobil has developed molecular composition fine tuning algorithm, molecular property calculation method, and constructed some molecular-level models of petroleum processing processes based on SOL method. These models could predict the product properties, such as octane number, cetane number, etc.. They have been successfully applied in their refineries. Tian developed a molecular composition matrix calculation model for petroleum,26 and built a kinetic model for steam cracking which could calculate the contents of 132 molecules with reaction conditions.27 Liu and Chen established the molecular-level model for the fluid catalytic cracking process at the molecular level.28 The model introduced feedback of the heat effects to improve the calculation accuracy.
In this paper, the delayed coking reaction kinetic model was built based on the free radical chain reaction mechanism and the SOL method to describe the reaction path of reactant molecules and the generation path of product molecules in the reaction network. The information from the structural vectors in the products especially gasoline and diesel provides reference for the precise control of the delayed coking process at the molecular level.