(145a) Delay Coker and Pyrolysis Naphtha Hydrotreating in a Fluidized be Reactor

Delay
Coker and pyrolysis naphtha hydrotreating in a fluidized be reactor.

Roberto Galiasso Tailleur

Simon Bolivar University, Caracas, Venezuela and
Hypro Consultants Orlando Fl 32814

Extended
Abstract

Delay coke (DC) and Pyrolysis
oil from grass (PY) were hydrotreated in presence of straight run naphtha
kerosene cut in a fluidized be reactor pilot plant. Feed were obtained from a
Refinery in the Gulf Coast and characterized by GC-MS and ¹H and ¹³CNMR
analyses. Reactant and product were stored for 20 minutes under hydrogen at 323
K, 1.4 MPa. Feeds and hydrotreated products stored products were filtered and
the gum and solid retained in the filter recovered by CS₂ extraction
and analyzed by GC-MS and ¹H and ¹³CNMR spectroscopies.

The
catalytic tests were performed in a 1 L reactor operating at 423 K, under 1.4
MPa of hydrogen and at residence time of 0.5 h for the feed. The feed contains
either 10% of DC or 10% PY. The operation is in steady state because the catalyst
throughput (SHSV) were adjusted to keep constant the conversion in olefins. Table
1 below shows the properties of the Feed and products obtained (H2-DC and
H2-PY). The catalyst is a PtWNi/TiO₂-Al2O₃, pre-sulphided
at 560 K for 1 hour, and with an average particle diameter of 78 microns [1].  Figure
1 shows the scheme of the pilot plant. The feeds were dilute in straight
run naphtha and kerosene to avoid polymerization [1]

The hydrocarbon
distribution in DC feed was 3.4% of (C₃-C₅), 67.4% of
Naphtha, 29.2 % of kerosene; in PY feed the distribution was: 4.3% of (C₃-C₅),
77.3% of Naphtha, 18.6 % of kerosene.  Properties of the feeds are depicted in Table1.
The feeds characteristics are:

·   
DC-naphtha fraction contained small amounts of benzene
and nitrogen, but medium amount sulfur compounds (thiophene and benzo-thiophene);
its quality is out-of-gasoline specifi- cations. Br number was0.9 and diene
value 0.2 (g I₂/100mL). DC-kerosene fraction had low amounts of
alkyl-diaromatics, alkyl-di-naphthenes and benzo- and dibenzo-thiophenes type
of sulfur. This kerosene is out-of-jet-fuel specification. DC feed do not
contain phenols.

·    PY-naphtha fractions contained low amount of butadiene and sulfur and high
amount of benzene, oxygen, nitrogen and phenols; the quality is out-of-gasoline
specifications. Br number was 5.7 and diene value 1.6 (g I₂/100mL). PY-kerosene
fraction had medium amounts of alkyl-diaromatics, alkyl-di-naphthenes and benzo-thiophenes
type of sulfur. This kerosene is also out-of-jet-fuel specification.

·    There
are different types of olefins and diolefins in DC than in PY feeds. DC
contains more butene (4%), pentenes (5%) and butadiene (-6%), but smaller
amount of styrene (-15%), isoprene (-8%, 3-pentadiene (-2%) and 2,3-pentadiene
(6%) than PY feed, according to GC-MS and liquid ¹³CNMR and ¹HNMR
analyses.

·   
The rate of catalyst deactivation, at the same operating
conditions, is 1.5 higher when using PY instead of DC feed (compare coke
content in spent catalyst in Table 1.) The reason is due to the presence
styrene, phenols and diolefins in the feed. Nitrogen (indole,
quinoline and carbazole) and phenols contribute to the catalyst deactivation. Butadiene, cyclo-pentenes, phenols and styrene are the most
reactive molecules that form coke.

Thermal stability of the
feeds and products. To understand why olefin and diolefins produce important
deactivation, a thermal stability test was developed to measure, in relative
ways, the amounts of gum and solid formed after 20 min storage at different
temperatures under hydrogen 1.4 MPa of pressure and in presence of glass beads of
80 microns (Fig 2a). Fig. 2b shows that the rate of gum and solid
formed (mg/L) during the storage is higher with PY than in DC feed. The higher
the storage temperature, the higher the amounts of gum and solids formed, as
expected base on properties of the feeds. The filter and the solid were washed
with CS₂ to recover the soluble and insoluble gums. They were
measured and analyzed; ratio soluble to insoluble decreases 1.4 times faster
with temperature in PY than in DC feed, as well as the H/C ratio in the solid
formed.

Gum and solid seems to be
formed by polymers of olefins and styrene (MAS 13CNMR Fig. 3.)  Nevertheless,
polymerization reactions involve diolefins and other aromatics molecules.

Both hydrogenated products
present a high relative stability Fig. 2b respect to the feeds. Notice
that all the H2-DC products present higher stability during heating than H2-Py
products; differences are due to the presence of lower alkyl-aromatics and
phenols in the former. The tests confirmed the well-known fact that gum and
solid are built from unsaturated components present in the light fraction of DC
and PY feeds. They make unviable the heating these feeds for any further
processing without a deep hydrogenation. The hydrogenation is difficult because
coke is formed in the external surface of catalyst [1]. Polymerization is
faster than hydrogenation reaction even at 423 K 1.4 MPa. Coke deposition block
the access of the reactants to the inner surface of the catalyst.

Conclusion:  DC and PY feed
are unstable material that need a deep hydrogenation to be used as fuel. Feeds
contain diolefins, olefins, aromatics and phenols that polymerize fast above
303K. They are hydrogenated at expense of high catalyst deactivation.

[1]
Galiasso Tailleur R. “Hydrogenation
and hydrodesulfurization in gas phase of light hydrocarbons from hydrocracking,
desulfurization and delayed coking. I catalyst deactivation” Chem Eng Sci
210(2019) 115195