Propylene Yield via Olefin Recycling in Catalytic Cracking
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Solution Overview
Problem
Catalytic cracking units face challenges in maximizing propylene yield due to limitations in recycling processes, particularly in avoiding separation costs and maintaining optimal chemical composition for effective olefin production.
Innovation Solution
Recycling a stream of C4, C5, and C6 olefinic compounds from the interstage of the wet gas compressor upstream of the main reactor, avoiding separation costs and leveraging their high olefinicity to enhance propylene production, while minimizing aromatic content that forms coke and disrupts heat balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gasoline cut is recycled after the separation section, then propylene yield is increased, but separation costs are incurred and aromatic content reduces olefinicity
Solution Approach 1:
The invention takes the recycle stream upstream of the separation section, specifically from the interstage of the wet gas compressor. This preliminary action allows the olefinic cut to be recycled before separation operations, avoiding the need to pay separation costs while still achieving the desired propylene yield enhancement through selective cracking of olefinic compounds.
Solution Approach 2:
The invention extracts the olefinic cut (C4-C6 compounds) from the mixed gas stream at the compressor interstage, separating it by location rather than by chemical separation processes. This extracted olefin-rich stream is then recycled to the cracking unit, avoiding aromatic compounds that would otherwise require separation and reducing overall separation costs.
2Productivity
If temperature at riser outlet is increased to improve propylene selectivity, then propylene yield increases, but coke formation increases and heat balance is disrupted
Solution Approach 1:
The invention applies local quality by directing the recycled olefinic cut specifically to the riser where cracking occurs, rather than mixing it uniformly throughout the system. The olefinic compounds are concentrated in the reaction zone where they undergo selective cracking to propylene, while the aromatic compounds remain in the non-recycled portion, thus localizing the beneficial cracking reaction while minimizing coke formation from aromatics.
3Productivity
If catalyst/charge ratio is increased to enhance propylene production, then propylene yield increases, but operating costs increase
Solution Approach 1:
The invention changes the chemical composition parameter of the recycle stream by selecting olefinic compounds (C4-C6) with high olefinicity from the interstage stream. This parameter change allows for more efficient propylene production because olefins are more reactive and convert to propylene with higher selectivity, thereby reducing the amount of catalyst needed compared to recycling aromatic-rich gasoline cut.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly increases propylene yield by up to 6% compared to conventional recycling methods, while maintaining acceptable levels of dry gases and coke production, thus optimizing the heat balance and enhancing ethylene recovery.
Implementation Method 1
catalytic cracking of petroleum cuts, more particularly so-called 'heavy' cuts
Implementation Method 2
adding to the basic catalytic system a shape-selective zeolite making it possible to improve the selectivity in LPG
Implementation Method 3
The sampling point for the new recycle flow is located at the interstage level of the wet gas compressor
Implementation Method 4
aromatic content that forms coke and thus penalize the heat balance of the unit
Data Source
Figure 1
AI summary
The present invention describes a process for the production of gasoline and co-production of propylene using a catalytic cracking unit having at least one main reactor operating in upflow ("riser") or downflow ("downer"), processing a conventional heavy feed, and in which the main reactor further processes a feed mainly consisting of C4, C5 and C6 olefinic cuts introduced upstream or mixed with said heavy feed, said olefinic feed coming from the interstage of the wet gas compressor, i.e. upstream of the separation section of the catalytic cracking unit.