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.