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Jul-2016

Upgrading FCC catalyst performance (TIA)

A US refiner processing crude from the Permian Basin, including both sweet (WTI) and sour (WTS) crude oil, underwent a major FCC turnaround in 2014.

Gary Cheng, Kevin Burton, Kent Turner, Chip Schaeffer and Rosann Schiller
Grace Catalysts Technologies
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Article Summary
Following this major revamp and re-baseline of the unit, the refinery sought to increase profitability via a catalyst change. Unit objectives were: increase LPG olefin yield, preferably C4 olefins; reduce dry gas make; improve slurry upgrading; increase LCO yield; improve coke selectivity; and improve conversion, all at constant fresh catalyst addition rates. An additional operating objective of the refinery is to keep the downstream alkylation unit full year-round, using a combination of FCC operating parameters, an optimised catalyst formulation, and traditional ZSM-5 additive as needed. The FCC feed is comprised primarily of a VGO feedstock, plus a combination of various side streams.

Achieve 400 FCC catalyst
Refiners are continually challenged to respond to changing market dynamics. For example, a common challenge for refiners operating on unconventional feeds, such as shale or tight oil, is a loss of gasoline pool octane, caused by reduced volume of alkylation feedstock. Grace launched the first product in the Achieve series, Achieve 400, to address these octane debits. This breakthrough technology has delivered an economic uplift on the order of $3-7 million/y in multiple commercial applications due to the boost in slurry conversion, FCC naphtha octane, and butylene yield.

During the Achieve R&D programme, five key catalytic functionalities were developed to provide the yield flexibility desired by refiners:
•    Increase distillate yields with high diffusivity matrices
•    Reduce dry gas with advanced metals traps
•    Drive conversion with ultra-high activity zeolites
•    Maximise resid processing with leading coke selectivity
•    Boost refinery octane with dual-zeolite technology.

Achieve catalyst is formulated to include each of these five critical functionalities. High diffusivity matrices maximise distillate yield from the bottom of the barrel and provide resistance to poisoning from unconventional metals. The catalyst can be formulated over a range of activity, rare earth exchange, and isomerisation activities. Grace’s capability to modulate hydrogen transfer activity in self-manufactured zeolites affords each refiner the optimal LPG to gasoline ratio for their operation. Achieve 400 also features multiple zeolites, specifically traditional Y-zeolite and pentasil-type zeolite, to selectively enhance LPG olefinicity by preferentially cracking gasoline olefins at C7 and above into butylenes. 

Incorporation of isomerisation activity into the catalyst particle itself results in a more desirable yield pattern than would be realised by use of a traditional octane boosting FCC additive. Achieve 400 catalyst yields higher octane, with an improved butylenes to propylene ratio when compared to ZSM-5 additives. The zeolite isomerisation activity in the catalyst increases the yield of FCC butylene and iso-butane, keeping the alkylation unit full and maintaining refinery pool octane.

With traditional ZSM-5 technology, cracking of gasoline range olefins continues on into the C6 range, generating a disproportionate amount of propylene relative to butylenes (see Figure 1). Achieve 400 catalyst, however, works to selectively crack gasoline olefins at C7 and above into preferentially more butylene, thus generating a higher ratio of C4 to C3 olefins than separate light olefins additives.
 
US refinery trial
In mid-summer of 2014, the refiner began a trial of Achieve 400 against a traditionally formulated high activity base catalyst. The refinery previously utilised approximately 1.5-3.5 wt% ZSM-5 additive to attain the desired olefinicity and octane shift.

Throughout the catalyst trial, fresh catalyst addition rates were held constant, and Ecat activity remained at 74 wt% on average. Total LPG olefin yield increased by ~3 vol% (see Figure 2). The alkylation unit remained at full capacity, despite a gradual reduction in additions of a separate particle ZSM-5 additive. The site eventually stopped adding ZSM-5 additive and was still able to keep the alkylation unit full.

The constrained downstream alkylation unit benefited from the increased loading of C4 olefins in the 
feed. Moreover, there were minimal increases in C3 
and C4 saturates commensurate with these increases in olefin yield. This can be attributed to the tailored acidity and optimal hydrogen transfer activity of the Achieve catalyst system. LPG saturate yields are shown in Figure 3.

Moving to a low Z/M, high activity matrix catalyst also helped to improve slurry upgrading and increase LCO yield. Slurry yield dropped by ~0.5 vol%, while LCO yield increased by ~0.5 vol% at constant conversion. Plots of these shifts are shown in Figure 4.

Additional benefits included reduced dry gas at comparable metals levels on Ecat, as well as improved overall conversion and volume swell.
 
Results and conclusions
A review of the unit data shows that the refiner was able to significantly improve profitability during the trial. Stated objectives were met, and the refiner obtained an additional benefit of lowering opex by reducing and eventually stopping addition of ZSM-5 additive at full FCC charge rates. Due to the success of the trial, the refiner is still using Achieve technology at this FCC today.

The favourable performance of Achieve 400 has generated an economic uplift of approximately
 $0.70/bbl.

As refiners’ needs continue to become more complex and diverse, FCC catalyst suppliers are continually challenged to respond with new technology to meet these evolving needs. Catalyst technologies must be flexible and adaptable, and continue to fulfill short term refinery objectives. The Achieve series (100, 200, 300, 400, 800) comprises a suite of state-of-the-art catalyst technologies, optimised to meet specific refinery opportunities while not exceeding operating constraints. These FCC catalysts have been applied in 30 commercial applications to date, and have delivered between $0.40-0.95/bbl of incremental value.

This short case study originally appeared in PTQ's Technology In Action feature - Q3 2016 issue.

For more information: Rosann.Schiller@Grace.com
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