October 2022

Catalysts

A successful case of resid-to-propylene maximization using premium catalyst technology

The world has experienced profound changes throughout the global disruption created by the COVID-19 pandemic.

The world has experienced profound changes throughout the global disruption created by the COVID-19 pandemic. The restrictions imposed on travel pushed most people to work remotely, with reduced domestic and international travel. Consequently, oil-derived transportation fuels demand was dramatically reduced, forcing refineries to adjust well-established operating strategies and product slates to maintain profitable operations.

Conversely, the demand for petrochemical products remained strong during the pandemic, which demonstrates the resilience of light olefins and chemicals products. As world markets recover and mobility restrictions lift, demand and margins for transportation fuels have returned to pre-pandemic levels, together with a robust petrochemical market.

Therefore, complex conversion units, including fluid catalytic cracking units (FCCUs), are ramping up feed rates and maximizing conversion of heavy feeds to satisfy this growing demand while adjusting the product slate for maximum profitability. In this environment, the role of premium catalytic solutions is of paramount importance to capture these opportunities and maximize value to the refiner.

The COVID-19 pandemic has also impacted the mid- and long-term view of the oil and gas industry. Many countries are adopting policies and regulations to accelerate the energy transition towards carbon neutrality, and society in general has a heightened environmental awareness. According to analysts, the industry may face a decline of global liquid products demand between 5 MMbpd and 25 MMbpd through to 2050, depending on the pace of the energy transition.1

This transition will not take place evenly across the globe, as mature markets are expected to transition faster than emerging regions. The decline of traditional transportation fuels consumption may lead to a structural low-margin scenario to conventional refining operations, which can be tackled with petrochemical integration and/or bio-feeds processing. The production of petrochemical feedstocks like propylene has a very robust profitability forecast given the expected strong demand vs. gasoline (FIG. 1).

FIG. 1. Global polypropylene demand (left) vs. regional gasoline demand (right) forecast. Source: Wood Mackenzie.
FIG. 1. Global polypropylene demand (left) vs. regional gasoline demand (right) forecast. Source: Wood Mackenzie.

In this environment, conversion units like FCCUs will play a key role in improving a refinery’s profitability by converting low-cost heavy residual stocks into high-value propylene for chemicals production. Analysts are foreseeing a long-term structural margin benefit for those FCCUs incrementally increasing their LPG olefins yield compared to a conventional FCCU product slate (FIG. 2).

FIG. 2. Margin comparison between high-propylene FCC vs. conventional FCC. Source: Wood Mackenzie.
FIG. 2. Margin comparison between high-propylene FCC vs. conventional FCC. Source: Wood Mackenzie.

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.

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 high-value 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 well-designed 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

The proprietary catalyst platforma has led the low coke selectivity market, thanks to its performance demonstrated in more than 260 applications around the world since its commercial launch.

Examples of successful applications can be found in literature1,2 and the catalyst platform RFCC catalysts have proven to deliver:

  • Low delta coke in high metals applications
  • Significant improvement in coke-to-bottoms performance
  • Excellent activity and stability at high contaminant metals levels
  • Increased C3 and C4 olefin yields
  • Opportunities for refiners with the ability to process high-residue feedstock content.

The OQ RFCCU was using a premium coke selective from the authors’ company’s catalyst platforma, along with a competitor’s additive. To further optimize the unit profitability, the Sohar Refinery team conducted a catalyst selection process, targeting the following objectives:

  • Maximum propylene (C3=) production
  • Maximum butylene in LPG
  • Maximum gasoline octane barrels
  • Minimum dry gas
  • Minimum slurry yield.

The authors’ company conducted an extensive internal testing program to determine the best catalytic solution to outperform the incumbent catalyst and additive in the unit based on the unit objectives and constraints.

Among all the solutions tested, a catalystb in combination with a proprietary additivec was the catalytic solution that showed optimum performance.

A first step was made to improve the performance of the Y-zeolite based catalyst, support the lowest delta coke and gas make, increase better light olefins yields and set the stage for an improved efficiency for the ZSM-5 additive to further boost propylene production. The catalystb is a combination of two synergistic technologies that are designed to provide optimum performance benefits. It integrates a proprietary zeolite stabilization in the latest catalyst offeringa to further increase propylene precursors and LPG olefins, as well as decrease the delta coke to process heavier feed in the FCCU.

As seen in TABLE 3, the move from incumbent technology to the new catalystb showed a remarkable gain in conversion of 1.9 wt% with reduced bottoms, and a gain in propylene at constant coke yield.

The next step was to combine the performance of the proprietary catalyst with a high-activity ZSM-5 additive for a final optimal catalytic solution. A study using different amounts of ZSM-5 additive helped the refinery team to assess the potential propylene make for their RFCCU, as well as identify the optimum amount to be blended.

The additivec is one of the authors’ company’s high-activity, commercially available ZSM-5 additives designed for maximum propylene and butylene production, offering high activity per unit of additive.

The levels of ZSM-5 in conventional additives require significantly higher addition rates with the consequential increase in OPEX and manual handling activities. There is also potential to dilute the activity of the circulating catalyst inventory and subsequently deteriorate unit conversion.

As shown in TABLE 4, the inclusion of the high-activity additivec resulted in the expected improvement in propylene and butylenes at the expense of gasoline. As most of the cracked gasoline belongs to the olefinic light naphtha cut, the resulting gasoline octane improved due to aromatics concentration.

These identified performance benefits obtained in the authors’ company’s laboratories were subsequently confirmed in an external independent laboratory using a circulating riser pilot plant, which showed that the proposed catalytic solution outperformed all the other options tested (FIG. 3). Based on the pilot plant results, OQ proceeded with a trial in the industrial unit.

FIG. 3. Propylene yield of different catalysts at an FCC pilot plant (catalystb + additivec labeled as DF1-2 + Z1).
FIG. 3. Propylene yield of different catalysts at an FCC pilot plant (catalystb + additivec labeled as DF1-2 + Z1).

The increase in propylene yield was visible soon after both the incumbent fresh catalyst and the competitor additive solution were replaced, as can be seen in FIG. 4. This catalyst and additive combination, hereinafter named the novel catalyst system, showed intrinsically enhanced selectivity to proylene and light olefins, while preserving bottoms cracking ability (FIGS. 5 and 6) with respect to previous catalysta blended with a competitor ZSM-5 product.

FIG. 4. Catalystd propylene during the industrial trial period.
FIG. 4. Catalystd propylene during the industrial trial period.
FIG. 5. Catalystd light olefins yield at constant conversion.
FIG. 5. Catalystd light olefins yield at constant conversion.
FIG. 6. Catalystd bottoms yield and LCO-share at constant conversion.
FIG. 6. Catalystd bottoms yield and LCO-share at constant conversion.

An additional key performance variable is the ability to produce high-value propylene within wet gas compressor (WGC) limitations. When much higher severity is needed to push for more propylene, there is usually an intrinsic increase of dry gas make due to the enhanced thermal cracking. If this is coupled with non-suitable metals tolerance, it may easily limit the unit as low-value products increase the volumetric flow rather than propylene.

As can be seen in FIG. 7, the novel catalyst system, thanks to its higher crystal activity, was able to produce more propylene per unit of dry gas, which helped the Sohar Refinery to maximize the value of the flowrate coming into the WGC.

FIG. 7. Catalystd propylene vs. hydrogen yields.
FIG. 7. Catalystd propylene vs. hydrogen yields.

To validate both preliminary pilot plant testing and catalystd monitoring, a comparison of normalized data was conducted to assess the performance of both catalyst periods at comparable conditions.

A test run was conducted in the industrial unit to compare both catalytic systems and subsequently normalized using a proprietary FCC SIM softwaref to compare cases at identical conditions. As can be seen in TABLE 5, the new catalytic system increased propylene by 0.9 wt% while improving bottoms cracking at similar coke make.

Due to this optimized catalyst system, OQ improved its position in the FCC industry as one of the best propylene makers processing one of the most challenging residual feedstocks, as can be seen in FIG. 8. A clear improvement in propylene, C4 olefins and octane was achieved, while conversion levels remained unaltered.

FIG. 8. OQ Sohar refinery RFCCU yields vs. industry.
FIG. 8. OQ Sohar refinery RFCCU yields vs. industry.

The authors’ company is continually developing new catalysts and propylene maximization additives. Its latest additiveg, at a constant additive level, shows higher light olefins yields compared to a leading additivec (FIG. 9).

FIG. 9. Propylene yield comparison between the authors’ company’s different ZSM-5 additives.
FIG. 9. Propylene yield comparison between the authors’ company’s different ZSM-5 additives.

Takeaways

OQ conducted a comprehensive and rigorous process to choose a new, higher performing catalytic system that would enable it to boost high-value propylene while reducing bottoms yields in its RFCCU.

The move from a previous-generation catalysta to a new catalystb combined with a high-activity additivec resulted in higher light olefins at much improved bottoms cracking, adding $15.2 MM/yr in profitability.

Although this RFCCU is processing one of the most challenging residual streams in the industry, the authors’ company’s technologies helped position the Sohar Refinery as one of the biggest FCC propylene makers worldwide. The strong resid-to-propylene performance and the unique strategic location of OQ in Oman ensures a tremendous strong profitability position towards the new energy transition era for the FCCU. HP

NOTES

a NEKTOR™ catalyst
b NEKTOR™ SRIP catalyst
c OlefinsUltra® MZ additive
d Ecat ACE™ catalyst
f KBC’s FCC SIM software
g ZAVANTI® additive
h OlefinsUltra®

LITERATURE CITED 

  1. McKinsey & Co, “Global downstream outlook to 2035,” July 2021.
  2. Gonzalez, R., C. Chau, J. Llano, B. Aramburu and R. Larraz, “FCC catalyst for maximum propylene,” PTQ, 4Q 2016.
  3. Serban, S., C. Ekeocha, U. Singh and B. Cipriano, “Maximising yields and profits from the FCC unit,” PTQ, 3Q 2021.
  4. PTQ, 1Q 2019, pp. 61.
  5. Baillie, C. and D. D. McQueen, “Combining mesoporosity with metals tolerance for residue upgrading in FCC,” online: digitalrefining, July 2013.

The Authors

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