Hydrocarbon Processing - March 2022 - 37

Petrochemical Technology
proposed to find a kind of hydride ion release agent to strengthen
the hydride ion transfer reaction. A large number of experimental
verifications have shown that tetralin and decalin are potential
hydride ion release agents, which can promote 70% of 2-methyl2-butene
to undergo hydrogen transfer to form isopentane. At
the same time, tetralin and decalin are converted to naphthalenes,
and the coke yield of the reaction decreases instead.
Then, the catalytic reaction test of a mixture of olefin-rich
gasoline and tetralin was conducted. As the concentration of tetralin
molecules in the olefin-rich gasoline increases, the yields
of dry gas and coke show a significant decrease. Meanwhile, the
content of olefins gradually decreases-at its lowest, reaching
4%-and the content of paraffins and aromatics increases. This
shows that the reaction between olefins and tetralin molecules
is mainly hydrogen transfer reaction Type I, which produces
paraffins and aromatics, rather than hydrogen transfer reaction
Type II, which produces coke precursors. The role of tetralin
in the reaction process with olefins and its catalytic conversion
path was determined. Only a small part of tetralin undergoes
β-scission reaction (FIG. 6), while most of them form aromatic
hydrocarbons through hydride ion transfer reaction and proton
removal reaction (FIG. 7). In this process, tetralin replaces the
polycyclic aromatic hydrocarbons (PAHs) in the original system
to release hydride ions, thereby inhibiting the condensation
of PAHs to form coke without causing a rapid increase in coke
yield. At the same time, it can significantly promote the hydrogen
transfer reaction of olefin molecules to generate paraffins.
Development of catalytic cracking technology for ultra-low
olefin gasoline. A methodology and mixing ratio of a
hydride ion release agent into the reaction system are proposed
here. The most typical compounds of hydride ion release agents
are tetralins and decalins. FCC light-cycle oil (LCO) contains
many naphthalene compounds. After hydrotreating, naphthalene
compounds become tetralins and decalins. In other words,
these compounds can be derived from hydrotreated FCC LCO.
The hydride ion release agent is similar to a working fluid,
TABLE 1. Industrial operating data before and after ULO
application
Technology
Feedstock properties
Density (20°C)/(kg·m-3
CCR, %
Product distribution, %
Dry gas
LPG
Gasoline
Diesel
Slurry
Coke
Gasoline properties
Olefi ns, %
Aromatics, %
RON
)
MIP
926.7
3.21
3.01
12.03
46.24
25.56
3.84
8.96
24.8
25.5
91.6
ULO
914.5
3.01
3.38
23.27
43.09
16.62
4.55
9
8.5
29.6
92.7
FIG. 7. Schematic diagram of hydride ion release agent promoting
olefin saturation.
Hydrocarbon Processing | MARCH 2022 37
FIG. 6. The β-scission is difficult for a hydride ion release agent.
which circulates between the catalytic cracking unit and hydrotreating
unit to release hydrogen or hydrogenate. The reasonable
way to introduce the hydride ion release agent to the
fresh heavy oil reaction system is to directly mix the hydrogenated
LCO with fresh heavy oil and then introduce the mixture
into the riser reactor. This can significantly improve the physical
properties and chemical reaction performance of the heavy oil.
The mixing ratio of hydrogenated LCO and fresh heavy oil
was systematically studied. It was found that when the mixing
ratio of hydrogenated LCO exceeds 10%, the viscosity of the
heavy oil can be significantly reduced, which can reduce the dry
gas and coke yield in the catalytic cracking process of heavy oil
feedstock. In this process, the hydrogenated LCO itself is a highquality
heavy oil emulsifier. As a result, a catalytic cracking technology
[ultra-low olefins (ULO)] for the production of ultralow
olefin gasoline was developed. Industrial operating data of
ULO technology are shown in TABLE 1.
With the introduction of an external hydride ion release agent,
the contradiction between the deep reduction of gasoline olefins
and the rapid increase in coke yield has been fundamentally resolved.
As shown in TABLE 1, with the introduction of a hydride
ion release agent (mixing ratio of 12%) into fresh heavy oil, gasoline
olefin content decreased to 8.5%. When the conversion rate
40
45
50
20
25
30
35
10
15
5
30
50
70
Conversion, %
FIG. 5. Variation curve of gasoline olefin content and coke yield
with conversion rate.
90
110
14
12
10
8
6
4
2
Olefins in gasoline, %
Coke, %
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