FCC catalyst for maximum propylene

A case study for boosting unit profitability through FCC catalyst selection for propylene maximisation

Grace Catalysts Technologies
JAVIER LLANO Nogales, BERTA ARAMBURU Lopez-Aranguren and RAFAEL Domingo LARRAZ Mora

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Article Summary

CEPSA’s (Compañía Española de Petróleos SAU) Gibraltar-San Roque refinery operates as a fully integrated refining and petrochemical site. The refinery, originally started up in 1967, is designed to produce a wide range of transportation fuels and petrochemical feedstocks and is strategically located next to the Straits of Gibraltar, supplying local and export markets with a wide range of products. The Gibraltar-San Roque refinery is the largest refinery in the Iberian Peninsula, with a daily crude oil processing capacity of 240 000 b/d.

The fluid catalytic cracking (FCC) unit is the primary hydrocarbon conversion unit in the modern petroleum refinery. It uses heat and catalyst to convert a variety of high molecular weight feeds (for instance, gas oils, cracked gas oils, deasphalted gas oils, and atmospheric/vacuum resids) into lighter, more valuable products such as gasoline, light fuel oil, and petrochemical feedstocks such as propylene and butylenes.1 Rapid growth in demand for propylene in China and the shift to shale gas based ethane cracking in North America have created an acute supply shortage in propylene.2 Several propylene producers have announced capacity expansions utilising new on-purpose technologies such as propane dehydrogenation (PDH). The majority of the capacity expansion will be in the US, China, and the Middle East, increasing the propylene imbalance in Europe. Refiners, particularly those integrated with petrochemical complexes, have the opportunity to increase propylene yield on the FCC and help reduce the supply gap and realise higher FCC product margins.

The FCC unit at CEPSA’s Gibraltar-San Roque refinery is a UOP High Efficiency design with a throughput of approximately 5200-5500 t/d. The FCC unit is a key process unit of the refining complex, upgrading low value feedstock, primarily blends of gas oils – straight run vacuum gas oils (SRVGO) and hydrotreated vacuum gas oils (HTVGO) – with FCC slurry recycle, but also atmospheric residue, furfural extracts and visbreaker naphtha, to deliver higher value alkylate, gasoline and diesel for blending in the refinery fuels pool and to provide aromatic rich feedstock and propylene to the petrochemical site.

After almost 20 years of partnership between Grace and the Gibraltar-San Roque refinery, during which time numerous new catalyst technologies were introduced that delivered successive improvements in FCC unit operating profitability, CEPSA challenged the status quo and implemented back-to-back FCC catalyst trials with Grace and an alternative FCC catalyst supplier.

As will be subsequently discussed, the performance of Grace’s ProgREss-26 FCC catalyst compared to the previous Grace catalyst yielded a considerable improvement in operating profitability for the FCC unit and refinery.

FCC catalyst trial objectives and operating constraints
The refinery defined three primary objectives for the FCC unit to increase the operating profitability of the unit and refinery, as part of CEPSA’s selection of the catalyst technology in unit back-to-back trials:
1. Maximise propylene production
2. Maximise LPG at constant gasoline production
3. Minimise bottoms.

Gibraltar-San Roque refinery’s main FCC unit operating constraints are typically:
1. Wet gas compressor (WGC) capacity
2. Regenerator temperature
3. Regenerator air blower capacity.

ProgREss FCC catalyst technology
The ProgREss FCC catalyst is part of Grace’s propylene maximisation technology for both hydrotreated and non-hydrotreated feed applications. It was initially developed during the period of hyperinflation in rare earth prices, and is a member of a low or no rare earth FCC portfolio, the RepLaCeR catalysts. RepLaCeR catalysts deliver optimum performance at lower rare earth concentrations, minimising refinery exposure to hyperinflated prices. ProgREss FCC catalysts are an extension of the ProtAgon catalyst family and are manufactured using Grace’s EnhanceR technology, the leading manufacturing platform in EMEA. Grace has an extensive catalyst and additive portfolio for increasing propylene yields.

ProgREss-26, designed with an optimised zeolite to matrix ratio and finely tuned rare earth content, provides:
• Low hydrogen transfer activity for enhanced olefins production
• High ZSM-5 activity to selectively crack gasoline range olefins into LPG olefins
• Best in class delta coke and dry gas, allowing the expansion of the FCC unit operating window within the unit operating constraints
• Premium bottoms upgrading with best bottoms to coke selectivity
• Targeted catalytic activity without any increase in catalyst additions.

To maximise propylene in an FCC unit, high ZSM-5 activity and stability are required in the circulating catalyst inventory. The activity of the ZSM-5 must be balanced with sufficient Y-zeolite based FCC technology, to boost LPG olefins production. The ProtAgon family of technologies delivers both of these attributes in a single particle system.

Catalyst retention is critical to the FCC unit’s operation and Grace’s ProgREss-26 catalyst technology provided considerably better attrition resistance compared to the alternative technology trialled. With improved physical properties, Grace helped Gibraltar-San Roque refinery to further minimise catalyst losses (reduce particulate emissions) and hence also improve the reliability of the expander operation.

Laboratory testing
Prior to the FCC catalyst trials, pilot plant testing in CEPSA’s R&D laboratory was conducted to compare FCC catalyst performance for each supplier. The FCC catalysts were steam deactivated to mimic the Ecat properties in the commercial unit, and tested in the DCR circulating riser pilot plant. The testing highlighted the improved performance of Grace’s ProgREss-26 catalyst compared to the alternative catalyst technology trialled in terms of LPG olefins make, the primary objective of the unit for maximum FCC profitability (see Figure 1). Regarding bottoms upgrading capability, the improvements with ProgREss-26 are described in Figure 6, with commercial unit data.

FCC catalyst trial results
As shown in Figures 2 and 3, when comparing Grace’s ProgREss-26 and the incumbent base Grace technology (ProgREss-518), propylene and butylenes yields were boosted significantly at both constant conversion and constant coke yield.

The improvement in LPG olefins make was exhibited over a broad range of operating severity and feedstock quality (see Figure 4). Significant gains in LPG olefins yields, both with propylene and butylenes, were obtained with ProgREss-26 with increasing riser outlet temperature (ROT). This is explained by the optimised, lower hydrogen transfer of the ProgREss-26 catalyst that results in enhanced selectivity and yields of gasoline range olefins, the precursors to LPG olefins.

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