Sep-2024

Refiner and FCC supplier collaborate to improve refining margins

A case study in which a novel catalyst technology was used to improve the profitability of fluid catalytic cracking units at refineries.

Nikolas Larsen and Nicholas Newlon, Marathon Petroleum Corporation
Grant Severyn and Andrew Novotny BASF Corporation

Article Summary

While the petroleum refining industry is well established and highly optimised, significant opportunity still exists to improve performance and profitability for refiners in an increasingly competitive landscape. This article highlights how close collaboration between a refiner and a fluid catalytic cracking (FCC) catalyst supplier results in rapid development and deployment of a novel catalyst technology to improve refining margins. Through open cooperation between the two companies, catalyst design knowledge was integrated with detailed understanding of individual refinery operating limits and overall market drivers.

This article shares three case studies where Marathon Petroleum Corp. (MPC) increased the profitability of its FCC units after upgrading to BASF’s newest iteration of its maximum butylenes (C4=) catalysts, FourtivaTM, from BASF’s current butylenes catalysts, Fourte® and FourtuneTM. These new catalysts synergistically combine BASF’s Multiple Framework Topologies (MFT) with a new Advanced Innovative Matrix (AIM). Together, MFT and AIM target increased butylenes yield and selectivity, which deliver excellent total LPG olefinicity, higher butylene over propylene selectivity, and higher FCC naphtha octane with improved coke selectivity than the incumbent catalysts.

The history
Since being commercialised, BASF catalysts Fourte and Fourtune have delivered value to multiple MPC FCC units. These catalysts use BASF’s MFT technology, which utilises multiple zeolite frameworks and an active matrix to produce a unique balance of low acid site density and high activity to maximise high value product yields. Globally, and especially in North America, market trends continue to show larger spreads for premium high-octane gasoline as motor vehicle engines have been designed for higher fuel efficiencies. FCCs are perfectly suited to take advantage of these market drivers by yielding more butylenes for alkylation units and increasing FCC naphtha octane for gasoline blending. These trends are supported by BASF’s FCC catalyst technology R&D programmes which focus on delivering maximum value to refiners.

Olefin additives (e.g., those containing ZSM-5 zeolite) are available for refiners to increase light olefins from the FCC unit and fill their alkylation capacity. While olefin additives containing ZSM-5 zeolite are highly effective at producing LPG olefins, they more selectively crack light gasoline range molecules into propylene (C3=) and to a lesser extent, butylenes (C4=). In general, C4= alkylate has higher road octane value than C3= alkylate, and C4= alkylate is also less cost intensive to produce. Alkylate made from C3= and isobutane can have a road octane of up to 91, whereas alkylate from C4= can have a road octane of up to 95. Therefore, C4= alkylation is preferred for most refiners operating alkylation units. BASF’s MFT catalysts, and now AIM+MFT catalysts, use holistic catalyst design to increase C4=/C3= selectivity and overcome the existing C4=/C3= limitations of ZSM-5 and other olefin additives.

The path forward
To meet the market demand for light olefins for alkylate production and higher FCC naphtha octane for gasoline blending, BASF delivered the next improvement of its MFT catalysts to MPC to further improve its technology. Fourtiva incorporates an AIM with improved porosity and optimal matrix activity to lower delta coke and minimise saturation reactions. This is combined with the MFT pillars of using multiple zeolite frameworks which have resulted in lower acid site density while maintaining high activity.

Three units are highlighted in this article. All three units historically have used an olefins additive with the objective of maximising light olefins production up to the sites’ alkylation capacities. Comprehensive trial evaluations incorporating operating data analysis, kinetic modelling, and laboratory studies were executed independently by both BASF and MPC. The laboratory studies used equilibrium catalyst (E-cat) samples collected before Fourtiva was introduced to the unit and after the unit’s circulating inventory was fully turned over to Fourtiva. MPC utilises a Davison circulating riser unit (DCR) as a Pilot FCC unit, complimented by an advanced cracking evaluation (ACE) technology® unit with significant accumulated analytical expertise. The overall goal of MPC’s pilot testing programme is to generate measured yield data from commercial materials to minimise the uncertainty surrounding key commercial decisions for each specific application. Pilot unit results have been validated with commercial experience. In addition to predicting commercial FCC performance with the pilot unit, kinetic modelling allows evaluation of product pricing and operational sensitivities to further increase confidence that the trial catalyst will deliver maximum value across multiple scenarios.

The commercial trial results
Based on the comprehensive pilot plant testing and kinetic modelling results of both companies, Fourtiva was selected to be trialled across eight MPC FCC units. Three of those trials are shared in this article. Operating data from trials on units 1, 2, and 3 were gathered throughout the equilibrated period of the incumbent Fourte or Fourtune catalyst and the equilibrated period of the Fourtiva catalyst. The conclusions from the operating and pilot plant data showed excellent agreement with each other. Further, agreement in the observed yield shifts across multiple analysis methods (operations data, E-cat testing, kinetic modelling, and pilot plant post audits) increases confidence that the shifts in operations data are a result of the catalyst technology change and are not due to normal operating variability within the unit.

Unit 1 commercial trial synopsis
The first trial was conducted on a unit that was using the Fourtune catalyst. The objectives were to further improve C4= yield and selectivity, along with increased naphtha octane and improved coke selectivity. The unit uses an olefin additive to increase total LPG olefin production. To accurately analyse the trial performance of Fourtiva, BASF and MPC normalised the olefin additive influence by comparing operating data with the same additive concentration. In Figure 1, the C4= yields and gasoline RONc data for unit 1 is plotted against unit conversion to normalise the effect of the operational differences between the two time periods. At the same olefin additive concentration, Fourtiva demonstrated significant C4= yield (+1 vol%) and gasoline octane (+0.5 RONc) improvement. The new technology also delivered a 9% improvement in delta coke, resulting in a drop in regenerator dense bed temperature of 15°F. Overall, kinetic modelling showed an average economic uplift of US$0.87/bbl for unit 1 across multiple shadow price set sensitivities at optimised conditions.

Unit 2 commercial trial synopsis
On unit 2, MPC was using BASF’s maximum C4= catalyst, Fourte, with an LPG olefin additive. Again, market drivers indicated that increased C4= yield and selectivity over C3= along with increased naphtha octane would be extremely advantageous for the refinery, so Fourtiva was selected as a suitable catalyst. As the unit transitioned to the new catalyst technology, more total feed was being processed by the FCC, which meant it was constrained by mixed C3+C4 product being sent to the alkylation unit. As a result, reactor severity was reduced to the minimum limit and the LPG olefin additive was discontinued. At the higher FCC feed rate, the alkylation unit was maintained at full capacity despite the FCC wet gas compressor operating at its maximum limit. Without using an LPG olefin additive, Fourtiva was able to fill the alkylation unit with more favourable C4=’s due to the LPG selectivity of the new catalyst. The FCC was also able to fill its alkylation capacity while operating at minimum slurry product rundown rates, with minimum riser outlet temperature (ROT). To account for these operational differences, the C4= yields and gasoline RONc data shown in Figure 2 for unit 2 is plotted against reactor severity. The unit was able to achieve increased C4= yield (+1 vol%) and increased naphtha octane (+0.5 RONc) (shown in Figure 2), despite the lower LPG olefin additive in the circulating inventory. Kinetic modelling showed similar yield shifts and an average economic uplift of US$1.40/bbl for unit 2 across multiple shadow price set sensitivities at optimised conditions.