Ethane Recovery from Alkylation Vent Gas
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Solution Overview
Problem
Existing processes for producing ethylbenzene using a dilute ethylene feed struggle with low ethylene conversion rates, requiring large amounts of catalyst and resulting in significant loss of ethane in the vent gases.
Innovation Solution
A process involving a reboiled absorber column to absorb ethane and ethylene from a vapor stream, followed by a reaction zone to convert ethylene into ethane and a reaction product, and finally a stripper to separate the ethane from the reaction product, thereby recovering high purity ethane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a catalytic distillation process is used with dilute ethylene feedstock, then ethylbenzene production is achieved, but ethylene conversion is limited to 75-80% requiring large amounts of catalyst
Solution Approach 1:
The process is divided into two distinct stages: a catalytic distillation alkylator for initial ethylene conversion and a separate liquid-phase finishing reactor for complete conversion of unreacted ethylene. This segmentation allows each reactor to be optimized for its specific function, reducing the overall catalyst requirement in the CD alkylator while maintaining high productivity.
Solution Approach 2:
A vent absorber system using benzene as an absorbent acts as an intermediary between the CD alkylator and the finishing reactor. The absorber captures unreacted ethylene from the alkylator overhead and transfers it to the finishing reactor, enabling complete ethylene utilization without requiring excessive catalyst in the first reactor.
2Quantity of substance
If unreacted ethylene is absorbed into circulating benzene and reacted in a finishing reactor, then catalyst requirements are reduced, but ethane is lost in the absorber overhead vent gas
Solution Approach 1:
Instead of discarding the absorber overhead vent gas containing ethane to a fuel header, the process recovers this valuable component through a dedicated ethane recovery system. The vent gas is fed to a separation system that extracts and purifies ethane, which is then recycled to the alkylator feed, eliminating the loss while maintaining reduced catalyst requirements.
3Device complexity
If ethane is sent to fuel gas header, then process simplicity is maintained, but valuable ethane is wasted
Solution Approach 1:
The process implements an ethane recovery system that captures ethane from the absorber overhead vent gas through absorption, stripping, and separation operations. The recovered ethane is purified and recycled to the alkylator feed, transforming what would have been a simple but wasteful process into one that recovers valuable material while adding moderate complexity.
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 purity ethane recovery from vent gases, reducing catalyst requirements and enhancing overall process efficiency by utilizing heat integration and extractive distillation techniques.
Implementation Method 1
a reboiled absorber column to absorb ethane and ethylene from a vapor stream
Implementation Method 2
a reaction zone to convert ethylene into ethane and a reaction product
Implementation Method 3
a stripper to separate the ethane from the reaction product
Implementation Method 4
utilizing heat integration and extractive distillation techniques
Data Source
AI summary
Processes and systems for the production of ethylbenzene using a dilute ethylene feed and subsequent recovery of ethane in the alkylation vent gas.