Hydrocarbon Processing - October 2022 - 52

Catalysts
To adjust the production towards light olefins, FCCUs typically
require a suitable unit design and tailored catalyst technologies
that deliver the required yield profile. Extensive use of
ZSM-5-containing additives that crack olefin molecules from
the gasoline range into liquefied petroleum gas (LPG)-as
well as suitable Y-catalyst properties-are essential to meet the
increased light olefins targets.
Several examples are available in literature that show how an
FCCU can significantly increase its profitability by boosting its
light olefins production.2,3
Studies show that refineries' propylene contribution to
the global supply will continue to play a key role to satisfy the
growing demand for many years to come,4
as that contribution
provides a clear cost-advantage vs. other potential dedicated
technologies, as seen in TABLE 1.
This article details a successful case in which an RFCCU
designed to process one of the heaviest residual feeds worldwide
implemented a catalytic solution to significantly boost
propylene yields and unit profitability by $15.2 MM/yr for the
OQ Sohar Refinery in Oman.
TABLE 1. Economics of various propylene technologies in
US$/MMt [propane dehydrogenation (PDH),
methanol-to-propylene (MTP), coal-to-propylene (CTP)]
Process
FCC
PDH
MTP
Integrated CTP
Feedstock
565
584
510
-20
Utilities
and fixed
53
200
110
350
TABLE 2. Typical feed properties
SG
Nitrogen
Concarbon
Nickel
Vanadium
> 0.92 g/cm3
> 1,500 ppm
> 6.5 wt%
> 12 ppm
> 13 ppm
TABLE 3. Test on incumbent OQ catalyst vs. catalystb
in the absence of ZSM-5 additive
Delta
Conversion, wt% FF
Hydrogen, wt% FF
Dry gas, wt% FF
Propylene, wt% FF
= olefins, wt% FF
C4
Gasoline C5
LCO, wt% FF
-221°, wt% FF
Bottoms, wt% FF
RON
MON
Coke, wt% FF
Incumbent
Base
Base
Base
Base
Base
Base
Base
Base
Base
Base
Base
52 OCTOBER 2022 | HydrocarbonProcessing.com
Catalystb
1.9
-0.06
0.1
0.5
0.1
-1.1
-0.8
0.1
0.3
Base
FIG. 2. Margin comparison between high-propylene FCC vs.
conventional FCC. Source: Wood Mackenzie.
Capital
cost
40
125
106
510
Total
658
909
726
840
High resid-to-propylene catalytic solution implementation
at the OQ Sohar RFCCU. OQ is the national energy
company of Oman, wholly owned by the Sultanate of Oman. In
addition to oil and gas exploration and production, the company
also invests in power generation, energy transportation and
infrastructure, oil refining and petrochemicals manufacturing.
Beginning in 1982 with a single refinery producing gasoline,
the company that is now OQ has built up its downstream offerings
and expanded the Sohar Refinery in 2006 with projects including
the Sohar Refinery Improvement Project (SRIP) and
the Liwa Plastics Industries Complex (LPIC). The complex
now includes a refinery, aromatics plant, steam cracker and
downstream polypropylene and polyethylene plants, making
it one of the best-integrated refinery and petrochemical facility
combinations in the world. The complex enjoys a strategic
location and is able to deliver products to the east or west to
capture market opportunities.
At the heart of the Sohar Refinery is the RFCCU, a primary
conversion unit that converts heavy residue streams into highvalue
products like propylene and clean fuels. The RFCCU
is a side-by-side (SBS) design with a two-stage regenerator,
catalyst cooler, packed stripper and a vortex separation system
(VSS) riser separator system, which allows them to process a
high-Concarbon, high metals-content residual feedstock type.
The RFCCU can process up to 79,000 bpd of one of the most
challenging residual feeds in the industry (TABLE 2).
Propylene is one of the main economic drivers for OQ,
requiring the RFCCU to operate at high severity with a welldesigned
catalyst system to boost light olefins production
within unit constraints-which are typically regenerator temperature
and air blower capacity-while keeping LPG flowrate
at a maximum.
RFCCUs that process residue feedstocks face high intrinsic
coke selectivity (high delta coke), which raises the regenerator
temperature and lowers cat/oil ratio and conversion. Residue
feedstock typically contains high levels of contaminant metals,
which poison the catalyst and can lead to further increase of
regenerator temperature and conversion loss. Maintaining catalyst
activity in this environment is important, as an increased
catalyst deactivation rate requires increased catalyst addition
rates to keep inventory cracking activity.5
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