Naphthene Recycle via Sidedraw Tower and Partial Condensation
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Solution Overview
Problem
Current paraxylene production processes are energy intensive and costly due to the need for separate naphthene towers to recycle C8 naphthenes, which are intermediates in converting ethylbenzene to xylenes, leading to excessive xylene loss and high energy consumption.
Innovation Solution
A process involving a reactor with an ethylbenzene isomerization catalyst, where xylene isomers, ethylbenzene, and C8 naphthenes are reacted, followed by partial condensation and separation to produce a sidedraw stream containing C8 aromatics and naphthenes, which are then recycled using a sidedraw tower apparatus, eliminating the need for a separate naphthene tower.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate naphthene tower is used to recycle C8 naphthenes, then naphthene recycling efficiency is improved, but energy consumption increases
Solution Approach 1:
The patent combines the naphthene separation function with the existing paraxylene recovery section by implementing a sidedraw arrangement. Instead of using a separate naphthene tower, the naphthene-rich stream is withdrawn from a specific tray position in the paraxylene recovery column, merging two separation functions into one unit and eliminating redundant equipment and energy consumption.
Solution Approach 2:
The paraxylene recovery section is designed to perform multiple functions: it recovers paraxylene from the reactor effluent and simultaneously separates and recycles C8 naphthenes through the sidedraw arrangement. This multi-functional design eliminates the need for dedicated naphthene separation equipment and reduces overall energy requirements.
2Manufacturing precision
If traditional separation methods are used for naphthene recycle, then separation effectiveness is improved, but operational cost increases
Solution Approach 1:
The patent merges the naphthene separation operation with the paraxylene recovery process in a single column. The sidedraw arrangement allows simultaneous recovery of paraxylene and separation of naphthenes, reducing the number of separate units and lowering capital and operational costs while maintaining separation effectiveness.
3Manufacturing precision
If conventional fractionation is used for naphthene separation, then separation purity is improved, but energy consumption increases
Solution Approach 1:
The patent applies partial condensation in the overhead condenser system, where only a portion of the overhead vapor is condensed and returned as reflux, while the rest is withdrawn as product. This partial action approach achieves the required separation purity for naphthene recovery while significantly reducing the energy consumption associated with full condensation and re-vaporization cycles.
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 efficiently recycles naphthenes while reducing energy consumption by less than 60% of the traditional energy required for separation, thereby lowering operational costs and preventing xylene loss.
Implementation Method 1
reacting in a reactor a reactor feed stream comprising xylene isomers, ethylbenzene, C8 naphthenes, and hydrogen over an ethylbenzene isomerization catalyst
Implementation Method 2
cooling and separating the reactor effluent stream to form a first condensed liquid stream and a first vapor stream
Implementation Method 3
providing the first condensed liquid stream and the second condensed liquid stream to a sidedraw tower apparatus to produce a sidedraw stream comprising C8 aromatics and a portion of the C8 naphthenes
Data Source
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AI summary
Processes for the energy efficient recycle of naphthenes in a paraxylene manufacturing process comprise partially condensing a reactor effluent and using a sidedraw tower apparatus. The naphthenes are efficiently separated into the sidedraw stream of the sidedraw tower apparatus. At least a portion of the sidedraw stream is directed to a paraxylene recovery section that produces a paraxylene product and a paraxylene lean stream comprising essentially all of the naphthenes in the sidedraw stream directed to the paraxylene recovery section. The paraxylene lean stream is recycled back to the reactor thereby preventing excessive loss of naphthenes from the processes.