Hydrocarbon Processing - March 2022 - 35

Special Focus Petrochemical Technology
X. WANG and Y. XU, Research Institute of Petroleum
Processing, SINOPEC, Beijing, China
New practice of diameter-transformed fluidized
bed reactor in the petrochemical industry
Motor gasoline standards are becoming increasingly stringent-in
particular, the olefins content requirement in motor
gasoline is getting lower and lower. Among these standards, China
standard motor gasoline VI (B) requires that the olefin content
should be < 15 vol%. However, the olefin in China's gasoline
pool is mainly from fluidized catalytic cracking (FCC) gasoline.
Therefore, the production of low-olefin gasoline is a vital issue in
the development of FCC technology.
With the rapid development of the olefin industry, a strong
demand exists for chemical raw materials like ethylene and propylene.
Increasing the production of propylene has become one
of the important tasks of an FCCU. Based on research on the
catalytic reaction pathway and the mechanisms of petroleum
hydrocarbon molecules, the authors' company proposed the
concept of a fluidized bed with a transformed diameter to construct
different reaction zones,1-8
and invented a novel diametertransformed
fluidized bed (DTFB) reactor.9-11
Based on this novel reactor platform, a series of technologies
have been successfully developed: maximizing iso-paraffins in
cracked naphtha (MIP),12,13
ene (CGP),14,15
LCO to gasoline (LTG),16,17
cleaner gasoline and more propyland
integrated technology
of hydrotreating FCC gasoil and highly selective catalytic
cracking for maximizing liquid yield (IHCC),18,19
which have
achieved large-scale applications. These technologies play an
important role in clean fuels production, product structure adjustment
and refining technology upgrading that produce good
social and economic benefits.
DTFB reactors have been applied to more than 100 industrial
catalytic cracking units20
by a patent licensed mode with an annual
processing capacity of more than 120 MMtpy. DTFB reactors
have been developed into an open engineering technology
platform-recently, the catalytic cracking technologies for the
production of ultra-low olefin gasoline and for more propylene
and marine fuel oil components have been developed on this
platform. These new technologies have injected new vitality into
the development of catalytic cracking technology.
What is a DTFB? A DTFB reactor, shown in FIG. 1, is a multiflow,
single-vessel fluidized bed that is organically composed of
a transport bed, a fast fluidized bed and a turbulent fluidized
bed. It mainly includes the first reaction zone (transport bed),
the second reaction zone (turbulent fluidized bed and fast fluidized
bed), the outlet zone (transport bed), transition zone, gassolid
fluidized distributor and spent catalyst circulating pipe (not
shown). A DTFB reactor can not only achieve a low-temperature
(with injection of quench medium or spent catalyst) or high-temperature
(with injection of semi-regenerated catalyst or regenerated
catalyst) environment in the second reaction zone, but also
provides enough time, sufficient space and an abundant amount
of catalyst particles. These favorable conditions can promote gasoline
olefin molecules to undergo secondary reactions, such as
isomerization, selective hydrogen transfer and re-cracking.
Quite different from the conventional riser, a DTFB has the
characteristics of a multi-flow type and multi-temperature zone
that can meet the different requirements of different chemical
pathways of reactants in kinetics and thermodynamics. A DTFB
realizes a new riser temperature distribution, a new catalyst concentration
distribution and a new oil and gas velocity distribution.
A DTFB's reaction mode design. From the viewpoint of FCC
reaction chemistry, hydride transfer reaction plays a key role as it
is not only the elementary reaction of bimolecular cracking reaction,
but also the elementary reaction of the hydrogen transfer
reaction. In the presence of solid acid catalyst, carbenium R2
+
will extract hydride ions from the raw material molecules (e.g.,
alkanes) to undergo a hydride transfer reaction, which converts
itself into product alkanes (R2
molecules form a new R1
H) and makes the raw material
+. After that, the entire catalytic cracking
reaction continues.
Based on the hydride transfer reaction, the bimolecular reaction
evolves into an increasingly complex reaction system as the
reaction depth increases. The optimization of the reaction depth
and the control of the reaction direction are the fundamentals
for achieving directional control of product distribution.
Transport bed
Outlet zone
2nd
reaction
zone
Distributor
1st
reaction
zone
(1-ε)
1-εmf
FIG. 1. The DTFB and its reaction zone with corresponding flow pattern.
Hydrocarbon Processing | MARCH 2022 35
Fast fluidized bed
Turbulent
fluidized bed
Bubbling
fluidized bed
ug
Hydrocarbon Processing - March 2022

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