Olefin Conversion for FCC Separation Bottlenecks
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Solution Overview
Problem
The challenge in the fluid catalytic cracking (FCC) process is the difficulty in separating olefins from paraffins in product streams, particularly for C4-C7 hydrocarbons, which hinders the efficient recycling and production of light olefins like propylene, as the wide range of boiling points complicates simple separation methods.
Innovation Solution
The process involves converting olefins to larger molecular weight compounds through alkylation with aromatics in dedicated conversion zones, allowing for easier separation of olefin-derived products from paraffins, which are then recycled back to the FCC reactor to enhance light olefin production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If olefins are recycled back to FCC reactor to increase propylene production, then propylene yield is improved, but separation of olefins from paraffins becomes more difficult due to concentration of refractory paraffins in the recycle stream
Solution Approach 1:
The patent applies preliminary action by converting olefins to larger molecular weight compounds (C8+) through oligomerization or alkylation reactions before the separation step. This pre-treatment modifies the olefin properties, making them easier to separate from paraffins in subsequent steps, thus resolving the contradiction between recycling for propylene production and separation difficulty
Solution Approach 2:
The patent changes the molecular weight parameter of olefins by converting them to heavier compounds (C8+) through chemical reactions. This parameter change transforms the separation problem, as the heavier olefin derivatives can be more effectively separated from lighter paraffins using standard fractionation techniques, thereby improving both propylene production and separation efficiency
2Manufacturing precision
If a significant purge is implemented to remove refractory paraffins from the recycle stream, then separation efficiency is improved, but loss of olefins increases
Solution Approach 1:
The patent applies local quality by selectively transforming only the olefin components into heavier compounds through oligomerization or alkylation, while leaving paraffins unchanged. This selective modification creates a local difference in molecular weight and boiling point between olefin derivatives and paraffins, enabling efficient separation with minimal purge and reduced olefin loss
3Reliability
If a large recycle flow rate is used to prevent paraffin concentration, then olefin separation is maintained, but energy consumption increases
Solution Approach 1:
By preliminarily converting olefins to heavier compounds before recycling, the patent reduces the need for large recycle flow rates. The modified olefin derivatives separate more efficiently from paraffins, allowing for lower recycle rates and reduced energy consumption while maintaining separation effectiveness
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 simplifies the separation of olefins from paraffins, enabling more efficient recycling and increased production of light olefins, thereby improving the overall yield and productivity in the FCC process.
Implementation Method 1
to convert the C5-C7 olefins to larger molecular weight C5-C7-derived compounds by the alkylation of C5-C7 olefins with aromatics
Implementation Method 2
Fluid catalytic cracking (FCC) is a catalytic hydrocarbon conversion process accomplished by contacting heavier hydrocarbons in a fluidized reaction zone with a catalytic particulate material
Implementation Method 3
The reaction in catalytic cracking... is carried out in the absence of substantial added hydrogen or the consumption of hydrogen
Implementation Method 4
A high temperature regeneration with oxygen within a regeneration zone burns coke from the spent catalyst which may have been stripped
Implementation Method 5
Spent catalyst may be subjected to stripping by an inert gas such as steam to strip entrained hydrocarbonaceous gases from the spent catalyst
Data Source
AI summary
The process converts FCC olefins to heavier compounds. The heavier compounds are more easily separated from the unconverted paraffins. The heavier compounds can be recycled to an FCC unit or delivered to a separate FCC unit. Suitable conversion zones are oligomerization and aromatic alkylation zones.