Two-Stage Catalytic Cracking for Propylene Yield and Longer Cycles
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Solution Overview
Problem
Existing propylene production processes suffer from low yield and high coke formation on the catalyst, leading to short cycle lengths in reactors.
Innovation Solution
A two-step process involving a low acidic density catalyst for olefins and a high acidic density catalyst for paraffins and naphthenes, with controlled reaction conditions and aromatic addition to minimize coke formation and maximize propylene yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single cracking catalyst is used to convert hydrocarbons to propylene, then the process is simple, but coke formation is high and cycle length is short
Solution Approach 1:
The cracking process is divided into two sequential steps using different catalysts: first a low acidic density catalyst for olefin conversion, then a high acidic density catalyst for paraffin and naphthene conversion. This segmentation allows each catalyst to operate under optimized conditions, reducing coke formation and extending cycle length while maintaining high propylene yield.
2Productivity
If high acidic density catalyst is used to maximize propylene yield, then conversion efficiency is high, but coke formation increases
Solution Approach 1:
The process performs preliminary conversion of olefins to propylene using a low acidic density catalyst before introducing the high acidic density catalyst for paraffin and naphthene conversion. This preliminary action removes the most coke-prone feedstock component, allowing the high acidic density catalyst to operate with reduced coke formation while maintaining high propylene yield from the remaining feedstock.
3Productivity
If reaction temperature is increased to improve conversion, then propylene yield increases, but coke formation on catalyst increases
Solution Approach 1:
The process uses different temperature regimes for the two catalytic steps: the first step with low acidic density catalyst operates at a temperature optimized for olefin conversion with lower coke formation, while the second step with high acidic density catalyst operates at a temperature optimized for paraffin and naphthene conversion. This parameter change allows high conversion efficiency while controlling coke formation through catalyst-specific temperature optimization.
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
The process achieves high propylene yield with reduced coke formation, allowing for extended reactor cycle lengths and improved conversion efficiency.
Implementation Method 1
by contacting the feed with a cracking catalyst in a reactor
Implementation Method 2
feeding the mixture of hydrocarbons optionally in admixture with a recycle stream and having a temperature between 450 and 750° C. to a reactor
Data Source
AI summary
The invention is directed to a process to prepare propylene from a mixture of hydrocarbons having an olefin content of between 5 and 50 wt. % and boiling for more than 90 vol. % between 35 and 280 ?C or from a hydrocarbon feed comprising paraffins, naphthenics and/or aromatics and optionally up to 10 wt. % of olefins, by first contacting the feed with a low acidic density cracking catalyst in a reactor, separating propylene and subsequently contacting the residue with a high acidic density cracking catalyst in a reactor at a more elevated temperature, separating propylene and recycling the residue to first and second cracking reactors. Aromatics may be added to first and second cracking step to improve cycle length.