Value maximisation in FCC units using multispecialty catalyst formulation
Increasing propylene yields while reducing bottoms production
Somanath Kukade and Pramod Kumar Hindustan Petroleum Corporation Limited
F luid catalytic cracking (FCC) is one of the most impor- tant conversion processes used in petroleum refiner - ies and has existed for over 75 years. It is widely used to upgrade heavier cuts like vacuum gas oil and residues to more valuable petroleum products such as gasoline and light olefins. It can readily adjust to changes in feed quality through modifications in catalyst and operating conditions. Catalysts and additives play important roles with respect to activity and selectivity in FCC units. These units typically produce around 4-6 wt% propylene but can go as high as 12%, depending on feedstock type, operating conditions, such as riser outlet temperature, reactor pressure, catalyst- to-oil ratio, and type of FCC catalysts/additives. A traditional steam naphtha cracker supplies about 57% of global propylene as a by-product of ethylene produc- tion. The FCC unit is also an important source of propylene, producing about 35% of world propylene as a by-product of gasoline production. The remaining 8% is produced by ‘on-purpose’ processes, such as propane dehydrogenation, olefin metathesis, and methanol-to-propylene. However, the shift from naphtha crackers to ethane crackers has seen the gap for propylene increase. Most new steam crackers coming online are designed to use ethane as the primary feedstock, typically producing less than 2% of propylene compared to ethylene production. Propylene demand has increased at an average rate of nearly 4-5% per year. In 2020-21, the propylene growth rate in India stood at 4% CAGR, and polypropylene (PP) at 4% CAGR. Enhancement of the propylene yield from the FCC, from a maximum of 12 wt% to 20 wt%, is one way to meet the growing demand for propylene. Refiners are integrating with petrochemical complexes, so petrochemical rates increase from the current 7% average to 20%. Propylene is perhaps the most versatile building block in the petrochemical industry in terms of its variety of end- use products and many production sources. High demand for PP has been a major driver for the rapid expansion in propylene production processes, and many PP units are added by refineries. Worldwide, approximately two-thirds of propylene is used to make PP. The onus on maximising propylene yields while reduc- ing bottoms warrants a discussion on novel multispecialty catalysts, * such as those formulated and patented by HP Green R&D Centre (HPGRDC). The catalyst formulation is
Activity, selectivity & accessibility
Attrition resistance
Fluidi s ability
Catalyst design
Coke selectivity
Hydrothermal stability
Metals tolerance
Figure 1 Design aspects of FCC catalyst
matrix-based and acts as an additive in conventional FCC units and a standalone catalyst in high olefin FCC units, such as deep catalytic cracking (DCC) units for light olefins maximisation. FCC catalyst design The FCC catalyst is in the form of a powder in Geldart's group A classification of fluidisation and has a particle size of approximately 80 μm. The important FCC catalyst design parameters are shown in Figure 1 . Activity, selectivity, and accessibility convert large feedstock molecules to desired molecules. Attrition resistance is the ability to withstand the impacts of particle-particle and particle-wall colli- sions during circulation. Hydrothermal stability is the abil- ity to withstand temperature and steam deactivation in the regenerator. Metals tolerance is the ability to withstand the effects of Ni, V, Fe, and Na on the feedstock. Coke selec- tivity is the ability to give minimum delta coke and should be fluidisable (Geldart A particle). Binder serves as a glue to hold the zeolites (key ingredient for cracking), matrix, and filler (clay) together by giving them sufficient binding strength. Both clay and binder provide critical FCC param - eters, such as density, attrition resistance, and particle size distribution. Catalyst design for light olefins Catalysts and additives play a vital role in FCC for enhanc- ing light olefins. The proprietary tailor-made catalyst *
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PTQ Q1 2023
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