Lean Solvent Washing Zone for Aromatic Hydrocarbon Purity
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Solution Overview
Problem
Existing extractive distillation processes face challenges in removing contaminants from the lean aromatic selective solvent stream, which affects the purity and recovery of desired aromatic hydrocarbons, especially when the feed stream has a wide boiling range and introduces contaminants through mechanical leaks or solvent degradation.
Innovation Solution
The apparatus includes an extractive distillation zone, a second distillation zone, and a lean solvent washing zone, where a portion of the lean solvent stream is washed with a non-aromatic hydrocarbon stream to remove contaminants, producing a clean solvent stream that can be recycled, and an optional by-product washing zone to further process the by-product stream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a wide boiling range feed stream is processed in the extractive distillation column, then the separation difficulty increases, but the aromatic recovery and purity requirements must still be met
Solution Approach 1:
The process is divided into multiple zones within the distillation column: an extractive distillation zone for initial separation, a second distillation zone for further purification, and a lean solvent washing zone for final contaminant removal. This segmentation allows each zone to handle specific separation tasks, enabling the system to manage wide boiling range feeds while maintaining high aromatic purity and recovery
Solution Approach 2:
A non-aromatic hydrocarbon washing stream is introduced as an intermediary substance in the lean solvent washing zone. This washing stream selectively removes heavy aromatic contaminants from the lean solvent without affecting the desired aromatic products, thus maintaining purity requirements while handling complex feed compositions
2Ease of operation
If contaminants are not removed from the lean solvent stream, then the process operation is simpler, but contaminants accumulate and degrade solvent performance
Solution Approach 1:
The lean solvent washing zone is positioned before the solvent is recycled back to the extractive distillation column. Contaminants are removed in advance through washing with non-aromatic hydrocarbon, preventing their accumulation in subsequent process cycles and maintaining consistent solvent performance without requiring complex online remediation systems
Solution Approach 2:
Contaminants are extracted from the lean solvent stream using a non-aromatic hydrocarbon washing stream. The washing stream selectively dissolves and removes heavy aromatic contaminants and other impurities, separating them from the lean solvent that is then recycled, thus maintaining solvent reliability while keeping the overall process relatively simple
3Reliability
If additional solvent regeneration steps are implemented, then contaminant removal is improved, but the device complexity and operational costs increase
Solution Approach 1:
The lean solvent washing zone serves multiple functions simultaneously: it removes heavy aromatic contaminants from the lean solvent, recovers some solvent from the by-product stream, and prepares the washed solvent for recycling without requiring separate regeneration units. This multi-functionality improves contaminant removal while limiting increases in device complexity
Solution Approach 2:
The washing function is merged directly into the existing distillation column structure as a third zone, rather than requiring a separate washing column or regeneration unit. The non-aromatic hydrocarbon washing stream is introduced and contacted with the lean solvent within the same equipment, combining separation and washing operations to reduce overall device 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
This approach effectively reduces contaminant levels in the lean solvent stream, improving the separation efficiency and reducing the need for additional solvent regeneration, thereby enhancing the purity and recovery of aromatic hydrocarbons while minimizing solvent loss and operational costs.
Implementation Method 1
a portion of the lean solvent stream is washed with a non-aromatic hydrocarbon stream to remove contaminants
Implementation Method 2
the hydrocarbon feed stock can be contacted with an aromatic selective solvent, in an extractive distillation column (ED column)
Implementation Method 3
The rich solvent phase is separated in a second distillation column, which may include the presence of water, to produce an extract overhead stream of the desired aromatic hydrocarbon components and a lean solvent stream
Data Source
AI summary
The invention is a process and apparatus for removing a contaminant from an aromatic selective solvent. A feed stream comprising an aromatic hydrocarbon and a non-aromatic hydrocarbon is contacted with the aromatic selective solvent in an extractive distillation zone to produce a raffinate stream comprising the non-aromatic hydrocarbon, and a rich solvent stream comprising the aromatic hydrocarbon and the solvent. The rich solvent stream is separated in a second distillation zone to produce an extract stream comprising the aromatic hydrocarbon, and a lean solvent stream comprising the contaminant and the aromatic selective solvent. At least a portion of the lean solvent stream is washed with a non-aromatic hydrocarbon to produce a clean solvent stream, at least a portion of which is passed to at least one of the extractive distillation zone and the second distillation zone.