Hydrocarbon Processing - March 2022 - 36

Petrochemical Technology
Among them, hydrogen transfer reaction is divided into two
types, as shown in FIG. 2, and the involved chemical bond evolution
includes double bond saturation, aromatization, isomerization,
disproportionation, etc. Therefore, further deep hydrogen
transfer will form coke precursors. The conversion rate is an
indicator of the depth of the reaction, and the direction of the
reaction is to regulate the type of hydrogen transfer reaction, and
then directionally regulate the product distribution and gasoline
composition. Based on these studies, the mechanism and method
for the selective regulation of the bimolecular reaction and
the optimization of the reaction depth by the hydride transfer
reaction were discovered.
If the hydrogen transfer Type I is enhanced, gasoline olefins
are converted into iso-paraffins and aromatics, which are benefiHydrogen
transfer Type I
Hydrogen transfer Type II
cial to increase gasoline octane number. If hydrogen transfer Type
II is enhanced, gasoline olefins are converted into iso-paraffins
with different carbon numbers, but the yield of coke precursors is
also increased. Also, excessive intensification of hydrogen transfer
Type II can easily lead to a substantial increase in the yield of
coke. The relationship between conversion (reaction depth) and
gasoline composition (reaction direction) is shown in FIG. 3.
Conversion rate has a great influence on the composition and
octane number of gasoline and is defined as the mass fraction
of coke, cracked gas and gasoline. FIG. 3 shows PONA data of
gasoline at different conversion rates. When the conversion rate
is < 65%, the gasoline olefin content slowly decreases as the conversion
rate increases, the iso-paraffin content slowly increases,
while aromatic content remains almost unchanged. When the
conversion rate is between 65% and 80%, the olefin content
decreases rapidly, and both iso-paraffins and aromatics increase
significantly. When the conversion rate further increases, the
olefin content continues to decrease but the extent slows down.
Therefore, to further reduce gasoline olefins in an FCC process,
increasing the conversion rate is the main direction for the adjustment
of the reaction mode.
By means of DTFB reaction engineering technology and
FIG. 2. Two types of hydrogen transfer reaction.
60
50
40
30
20
10
30
n-Paraffin
Naphthene
i-Paraffin
Aromatic
Olefin
the structural optimization of molecular sieve catalysts, big data
analyses of all factors affecting conversion rate and transfer reaction
type are carried out-it is found that the reaction temperature
and catalyst activity are the most significant. The reaction
mode between catalyst activity and reaction temperature is established
and a relationship diagram is shown in FIG. 4.
Based on the reaction mode constructed in FIG. 4, the conver50
Conversion,
%
FIG. 3. The relationship between gasoline composition and conversion.
Mode 1-HT II
Mode 3
70
90
sion rate can be adjusted, while the type of hydrogen transfer
reaction can be adjusted-then, the gasoline composition can
be directionally adjusted. From the selective transfer reaction
mode (Mode 2), the reaction temperature and catalyst activity
are further optimized to construct a high-severity reaction mode
(Mode 3 or mode 5), which will increase the conversion rate
and reduce the olefin content of gasoline. Tests have shown that
the olefin content of gasoline in Mode 3 can be reduced to less
than 15%, and the content of iso-paraffins has increased significantly.
Based on the regulation of bimolecular hydrogen transfer
reaction, the concept and method of selective hydrogen transfer
were developed-that is, hydrogen transfer Type I should be
carried out as much as possible to reduce coke formation. This
has laid a solid foundation for the development of corresponding
processes and catalysts.
However, as the olefin content of gasoline is greatly reduced,
Mode 5
the coke yield is greatly increased (FIG. 5), making it difficult to
operate smoothly in Mode 3 and presenting challenges to the
normal operation of the FCCU. The main reason for the substantial
increase in coke yield is that the fused ring aromatics and
olefins continue to undergo hydrogen transfer reaction Type II,
and the condensation reaction produces coke. Therefore, the
contradiction between the deep reduction of olefins and the
rapid increase in coke yield is a scientific problem to be resolved.
Mode 4
Mode 2-HT I
T/°C
FIG. 4. Diagram of the DTFB's reaction mode.
36 MARCH 2022 | HydrocarbonProcessing.com
DTFB to produce ultra-low olefins gasoline: The discovery
of hydride ion release agent and its catalytic conversion
path. Based on the test result that the selectivity of 2-methyl-2-butene's
hydrogen transfer reaction on different spent
catalysts is less than 20%, to further reduce gasoline olefins, it was
MAT, %
PONA, %
Increase in
olefin reduction
Same degree of
olefin reduction
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