C =
Low yields of LPG including C = and C =
LCO C 12 –C 20
ZSM-5 Zeolite
C =
Feedstock Vacuum gas oil or resid (C –C )
Naphtha C 5 –C (includes C =, C= and C=)
Y - zeolite, metals traps, optimi s ed unit cell size + matrix
Higher octane
Coke
Bottoms
Catalyst technology Preserve activity in presence of metals, minimise hydrogen transfer, minimise dry gas
ZSM-5 t echnology
Figure 4 Roles of Y-zeolite-based catalyst and ZSM-5 technology in the generation of propylene and butylene
diet, and product values. The catalyst for the FCC is therefore designed to aid a refiner by minimising crude and operat - ing expense while maximising the value of all products and throughput. The catalyst for an FCC that seeks to maximise (or increase propylene) is formulated considering the follow - ing aspects: • Unit feed type: resid and/or VGO • Desired product yield slates • Unit constraints, such as max regenerator temperature or max catalyst circulation, among others. In general, to maximise propylene and FCC gasoline RON, the selected catalyst generates and preserves the maximum yield of gasoline range olefins so that these can be further cracked by ZSM-5 into propylene. The concept is well illus - trated in Figure 4 , showing the catalytic approach to maxi - mise LPG olefins from the FCC. ZSM-5 technology is key to increasing C3= yield from the FCC. This shape-selective zeolite cracks gasoline range mol - ecules into predominantly LPG olefins. ZSM-5 additives are available from many suppliers but range widely in activity. For applications targeting the most demanding propylene yields, highest activity ZSM-5 additives allow the refiner to capture the most value. The main benefit of using the high - est activity ZSM-5 vs a lower activity ZSM-5 is that it results in minimal ZSM-5 additions. This results in minimal dilution of the base catalyst activity and, as a result, affords flexibil - ity to employ catalysts with low hydrogen transfer, which boosts C3 = yield even further. The high-activity ZSM-5-based additives currently in the Grace portfolio include the proprietary OlefinsUltra MZ tech - nology and the latest ZAVANTI additive, intended for the applications with the highest C 3 = yields. Case study: medium-sized US Midwest refinery It is not unusual to see a refiner’s interest towards increasing propylene production peak during spot opportunities when economics are favourable. However, these events typically come and go for refiners not positioned to quickly make more propylene, resulting in a lost profit opportunity. After identifying multiple opportunities for improved FCC margin, a medium-sized US Midwest refinery decided to explore the use of the high-activity OlefinsUltra MZ additive as an opportunity to increase propylene. For this first-time
user, several elements of planning were required to cross the finish line and utilise OlefinsUltra MZ additive when the eco - nomics prompted usage. This refinery started planning in Q1 to be ready for the next spot opportunity anticipated in Q4. The following are several items considered by the refinery in preparation for usage of OlefinsUltra MZ additive: • Injection system : Use of an injection system affords the refinery flexibility to add ZSM-5 additive when propylene economics are strong as opposed to including the additive pre-blended in its catalyst. The refinery has an additive loader on site that is leased from a competitor. The refin - ery is charged a lease fee when an additive not supplied by said competitor is injected through this additive loader. However, the refinery owns a separate loader with an open port that can be used to add additive. Therefore, this refin - ery is free to use the best additive technology available irre - spective of the supplier. • Evaluating yield shifts : The refinery involved its planning team early in the process to vet the economics and worked on the back end after the trial to add shift vectors into its LP model. An additional area to understand is the decay of additive activity. Commercial data were leveraged to better understand the lasting yield effect of the additive once addi- tions to the FCC were stopped. • Inventory : Opportunities when propylene economics are strong can occur on short notice, so having inventory on hand to base load and achieve desired yields within a short number of days is desirable. The refinery team agreed to buy additive ahead of time and hold enough inventory to basel - oad and not have to wait for delivery lead time to maximise value from opportunities when they arise. After successful implementation of the trial, both propyl - ene and RON increased (as shown in Table 1 and Figures
Yield shifts for OlefinsUltra MZ additive
Additive addition rate (relative to fresh catalyst), wt%
Delta C3=, vol% Delta (R+M)/2
OlefinsUltra MZ shift to baseline
3.0
2.75
3.2
Table 1
33
Catalysis 2023
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