Question
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What is the best route for maximum propylene from a resid feed to the FCC?
Jun-2021
Answers
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Charlie Chou, Sulzer Chemtech, Charlie Chou@Sulzer.com
The FCC heavy naphtha/gasoline portion actually has a lot of olefins that can be re-cracked in the FCC for propylene. However, the FCC heavy naphtha/gasoline also has significant aromatics which is not preferred in the FCC. GTC offers a GT-BTX PluS technology that utilises a simple extraction process to extract aromatics from FCC heavy naphtha/gasoline to produce high-purity BTX (extract) as petrochemical products; and the remaining FCC heavy naphtha/gasoline (raffinate) would be non-aromatics and rich in olefins, which would be an ideal stream to recycle back to the FCC to crack for additional propylene. By doing this, the propylene yield can increase by 2-6% if there is a second riser to be recycled to (or to add a second riser), or increase by absolute 1-3% if recycling to the only/first riser together with resid feed.
Jun-2021
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Carel Pouwels, Albemarle, Carel.Pouwels@Albemarle.com
Producing propylene from a resid feed is not as easy as processing the VGO fraction. Propylene make is governed by the ability to create and preserve gasoline olefins, the potential of which is reduced when processing higher boiling fractions. Nevertheless, it is certainly a profitable route given the lower price of resid feed. The choice of the residue, however, is important. The less refractory the feed, the more conversion can be obtained, thereby more gasoline olefins. Gasoline olefins are the precursors for the generation of propylene. It is thus key to maximise these by maximising conversion. While the crackability of the feed is of paramount importance, unit limitations ultimately determine how severely an operation can be pushed. In resid applications, this often comes down to regenerator temperature, air rate, and the maximum duty of a cat cooler, if present.
Several options are available to maximise propylene from an FCC unit, all related to the requirements the client has and the starting point. Considering a completely new FCC unit begins with the process technology. Process licensors are the right partners to work with to determine the best choices for strategic and economic long-term solutions. One can choose from conventional process designs that yield between 10 wt% and 12+ wt% of propylene. There are also several high severity applications that target propylene yields in the 15-20 wt% range. These applications commonly operate at 550-600 oC with cat-to-oil ratios about double those of conventional FCC operations.
In the case of an existing FCC unit where debottlenecking downstream units is considered, or where hardware changes to the FCC unit are feasible, process licensors are again good partners. They can suggest various scenarios and help customers make the right choices for their goals.
When the refiner is not planning an overhaul of the FCC unit or its downstream units, the options to maximise propylene are restricted to process conditions, the choice of feed, and catalyst design. The catalyst supplier can be consulted to provide good insight into the optimal operation combined with the best catalyst technology and design for customer goals.
Albemarle provides such expertise and offers maximum propylene catalysts AFX and DENALI AFX. Both are proven in all current process technologies offered by licensors today. While a good catalyst technology is a prerequisite, more important is catalyst application knowledge. At Albemarle, using collected data from all our industrial applications, our Technical Services, Applications, Modelling Department, and R&D teams work together to build deeper understanding of catalysis in relation to process conditions and catalyst technology.
Jun-2021
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