Para-Xylene Adsorption Segregation for Ethylbenzene Management
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Solution Overview
Problem
The existing methods for maximizing para-xylene (PX) production from C8 aromatic streams are limited by the presence of ethylbenzene (EB), which competes with PX for adsorption capacity and reduces the efficiency of PX recovery, especially in adsorptive separation and isomerization processes.
Innovation Solution
The process involves segregating hydrocarbon feeds with differing EB contents for separate PX adsorption and isomerization, using a divided wall raffinate column to separate EB-rich and EB-depleted streams, and applying vapor phase and liquid phase isomerization to enhance PX concentration, thereby optimizing the efficiency of PX recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single adsorption unit is used to treat C8 aromatic streams containing both PX and EB, then the process is simpler, but the adsorption capacity for PX is reduced due to competition from EB
Solution Approach 1:
The invention divides the adsorption process into two separate adsorption units: a first adsorption unit that treats feeds with higher EB content, and a second adsorption unit that treats feeds with lower EB content. This segmentation allows each unit to be optimized for its specific feed composition, preventing EB from competing for adsorption capacity in the PX-recovery unit, thereby resolving the contradiction between process simplicity and adsorption efficiency.
2Quantity of substance
If EB-rich streams are subjected to isomerization, then PX concentration can be increased, but the presence of EB reduces isomerization efficiency
Solution Approach 1:
The invention extracts or removes EB-rich streams from the isomerization feed stream by using the first adsorption unit to treat EB-containing feeds separately. This allows the isomerization process to operate on EB-depleted feeds, maximizing isomerization efficiency while still achieving increased PX concentration through the combined operation of both adsorption units.
3Productivity
If PX recovery is maximized from equilibrium C8 streams, then PX yield is limited by the original PX concentration, but additional processing steps increase complexity
Solution Approach 1:
The invention applies preliminary action by using the first adsorption unit to pre-treat feeds with higher EB content, removing a portion of the EB before the streams are combined and treated by the second adsorption unit. This preliminary removal of EB from feeds allows the system to achieve higher overall PX recovery from equilibrium C8 streams without requiring excessive processing steps, as the preliminary treatment prepares the feed for more efficient final recovery.
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 increases the overall efficiency of PX adsorption and isomerization, leading to higher PX concentrations and improved energy management by minimizing EB's impact on the adsorption capacity and isomerization processes.
Implementation Method 1
a first hydrocarbon feed comprising xylenes and ethylbenzene is provided to a first para-xylene adsorption section, where a first PX-rich stream and a first PX-depleted stream are recovered from the feed
Implementation Method 2
The first and second PX-depleted streams are then separated into an EB-rich stream and an EB-depleted stream in a divided wall raffinate column
Implementation Method 3
at least part of the EB-rich stream is then fed to a xylene isomerization unit where the EB-rich stream is isomerized to produce a first isomerized stream having a higher PX concentration
Data Source
AI summary
The present invention is an improved process and apparatus for producing para-xylene, particularly with respect to a process that involves the methylation of toluene and/or benzene to selectively produce para-xylene, wherein streams having differing amounts of ethylbenzene are separately treated in the recovery of para-xylene. A first hydrocarbon feed comprising xylenes and ethylbenzene is provided to a first para-xylene adsorption section, and a second hydrocarbon feed comprising xylenes and less EB than the first hydrocarbon feed is provided to a second para-xylene adsorption section. Segregating the feeds with differing ethylbenzene contents increases the overall efficiency of the adsorption of para-xylene by the adsorption units. Efficiency and energy savings may be further improved by subjecting the lower-content ethylbenzene stream to liquid phase isomerization.