Maximising propylene in the FCC unit

Comparative trials with FCC catalyst formulations identified a winner on olefins selectivity and other factors.

Michael Lutz, Harald Zeman, Thomas Krenn, Alexander Mittelmayr
and Ignacio Beltran, OMV
Emmanuel Smaragdis, Matthias Scherer and Christophe Chau, Grace

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Article Summary

Following a trial with a competitor catalyst, the resulting data showed the comparative advantage of Grace’s catalyst system of ProtAgon 4G/OlefinsUltra MZ. The FCC unit’s profitability has been improved due to:
• Higher propylene and isobutylene selectivity
• Improved dry gas selectivity at higher C2= selectivity
• Better bottoms to coke yield
• Improved bottoms upgrading
• Excellent attrition resistance
• Somewhat lower catalyst usage. Moreover, the catalyst change did not affect CO promotion and helped maintain unit particulate and NOx emissions under control. OMV Schwechat refinery decided, based on the comparative results, to continue using Grace’s catalyst technology.

OMV is an integrated international oil and gas company with headquarters in Vienna. It is active in the upstream (exploration and production) and downstream (refining and marketing as well as gas and power) businesses. With group sales of €36 billion, a global workforce of around 25500 and a market capitalisation of €7 billion (end of 2014), OMV is one of the largest listed industrial companies in Austria.

The downstream business division includes the Downstream Oil (including Petrochemicals) and the Downstream Gas businesses. Downstream Oil operates three refineries: Schwechat (Austria) and Burghausen (Southern Germany), both with integrated petrochemical complexes, as well as the Petrobrazi refinery (Romania).

OMV Schwechat refinery is one of the largest and most technologically advanced inland refineries in Europe. The refinery operates integrated petrochemical production facilities, and supplies plastics manufacturer Borealis with petrochemical precursor products, making propylene a key product for the Schwechat refinery.

The fluid catalytic cracking (FCC) unit is the main contributor to the refinery’s production of light olefins, especially propylene, but also gasoline. The FCC unit 
operates at high severity against velocity, air and gas constraints. Therefore any improvement with regard to FCC catalyst optimisation will have to be well thought out and planned. When developed and tuned accordingly, the FCC catalyst plays a significant role in boosting performance, specifically when it comes to yields and thus improvement in profitability. The purpose of this article is to demonstrate how Grace has supported OMV Schwechat refinery in achieving the operating objectives of the FCC unit, as well as how important close unit monitoring of the refinery operation is, in conjunction with pilot plant testing of equilibrium catalyst, for the quantification and verification of actual FCC performance.

FCC unit at Schwechat refinery
The FCC unit at the refinery was built in 1963 and is a UOP high efficiency stacked design with a VSS separation device. The unit has been subject to several technology improvements since it started up, doubling its initial capacity and currently processing 25 500 b/d in full burn combustion. The FCC unit processes hydrotreated VGO at a severity set at around 550°C riser outlet temperature (ROT). The unit is operated using slurry recycle to assist with heat balance closure due to the very light feed processed. It is of paramount importance that the FCC catalyst technology used provides efficient CO burning (high velocity – short residence time) while at the same time maintaining NOx emissions below the limit. The unit objectives are closely linked to market demand for refined petroleum products, with maximum propylene and minimum slurry being the primary targets, while C2= and iC4= are highly desired for petrochemical use and a ETBE etherification unit. C2= produced by the FCC unit supplements ethylene generated by the steam cracker and is beneficial to OMV. After a recent revamp of the gas plant in 2011 to higher capacity, the main FCC unit constraints are CO afterburn and delta coke on the regenerator side, together with ROT, particle emissions and cooling and hydraulic capacity at the gas unit. Maximum light olefin selectivity is therefore of primary importance, while the flexibility to react to market needs regarding C3= production is an essential operating management tool.

The FCC unit switched to Grace’s catalysts and ZSM-5 additive in 2002 and since then, benefiting from continuous catalyst improvements over the years, Grace has been working in close partnership with refinery operations and process teams. Extensive testing was also performed, not only by Grace, but by third party laboratories – Vienna University of Technology (TU Wien) and CPERI in Greece – to ensure the best catalyst formulation for this challenging unit and for evolving refining and petrochemical markets. OMV has consistently targeted improved unit profitability with the best available catalyst technology. With the aim of exploiting new gas plant capacity, Grace and OMV have collaborated to develop a ProtAgon catalyst tailored to OMV’s needs, further boosting C3= yield in the highly constrained Schwechat FCC unit.

During the FCC catalyst bidding process that took place between 2014 and 2015, OMV decided to perform back-to-back trials at the FCC unit in Schwechat between Grace and another supplier.

Grace catalyst technology
Grace has developed ProtAgon 4G (4th generation) technology, the latest catalytic innovation for maximum propylene selectivity based on Grace’s EnhanceR technology platform. ProtAgon FCC catalyst incorporates zeolite-Y and pentasil functionalities as well as an active matrix component to provide maximum propylene yield. The speciality matrix alumina is designed to improve bottoms upgrading. ProtAgon can be formulated for both low and high metal applications. Moreover, in 2015 Grace launched its latest ZSM-5 olefin additive, OlefinsUltra MZ, which is the highest activity olefins additive in the market. To keep up with growing propylene demand, refineries running in maximum propylene mode use significant amounts of olefins additive to boost propylene. High usage of olefins additives in the FCC unit may lead to a loss in conversion, due to dilution of the base catalyst. OlefinsUltra MZ minimises dilution effects in maximum propylene units by providing high ZSM-5 activity, stability and attrition resistance, to deliver 20% higher propylene yield.

OlefinsUltra MZ enables maximum propylene yields while limiting the net additive usage and content in the catalyst inventory, hence limiting dilution compared to conventional and less active ZSM-5 additives.

The combination of ProtAgon 4G as standalone catalyst and OlefinsUltra MZ as an external additive for fine-tuning the propylene yields gives maximum flexibility to the FCC to adjust propylene yield against fluctuating or dynamic propylene demand. Hence, operating at highest C3= selectivity with the catalyst inventory, further optimisation of propylene can be achieved with unit operating conditions.

This FCC catalytic combination of ProtAgon 4G/OlefinsUltra MZ provides the following performance benefits to unit operations and product quality:   
• High propylene yields ex-reactor
• High intrinsic catalyst activity, at hydrogen transfer tailored to customer needs
• Premium bottoms upgrading, at tunable delta coke performance, as needed
• Improved FCC operational flexibility
• Excellent fluidisation properties and catalyst attrition resistance
• Effective CO promotion with minimum effect on NOx emissions.

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