Aromatic Transalkylation Process Hydrogen Purity and Energy Efficiency
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Solution Overview
Problem
The existing aromatic transalkylation processes in aromatics complexes require significant hydrogen makeup gas and consume high-end energy for separation, leading to increased operating costs.
Innovation Solution
The proposed aromatic transalkylation processes eliminate the need for recycle gas purge by maintaining hydrogen purity through recycling and utilize a hot separator and flash drums to enhance energy efficiency, reducing the hydrogen makeup gas requirement and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a significant purge of the recycle stream is performed to maintain hydrogen purity, then hydrogen purity is maintained, but hydrogen is lost and operating costs increase
Solution Approach 1:
The patent extracts and removes light hydrocarbons (C1-C5) from the recycle gas stream using a dedicated extraction column with selective solvent. This targeted removal of contaminants maintains hydrogen purity (75-95 mol%) without requiring purging of the hydrogen-rich stream, thereby eliminating hydrogen loss while achieving the desired purity level.
Solution Approach 2:
The patent introduces a selective solvent as an intermediary substance in the extraction column. This solvent acts as a mediator that selectively absorbs light hydrocarbons from the recycle gas, enabling purification of hydrogen without direct contact between hydrogen and the purge stream, thus maintaining purity while preventing hydrogen loss.
2Manufacturing precision
If the stripper reboiler is used to separate C6 range non-aromatics and benzene from benzene/toluene/xylene products, then separation is achieved, but significant high-end energy is consumed
Solution Approach 1:
The patent segments the separation process into two distinct stages: (1) a flash drum that performs preliminary separation of light hydrocarbons and C6 non-aromatics from the transalkylation effluent, and (2) a benzene/toluene/xylene separation column that focuses only on separating the aromatic products. This segmentation reduces the energy burden on the main separation column while achieving the required manufacturing precision.
Solution Approach 2:
The patent performs preliminary separation of light hydrocarbons and C6 non-aromatics in a flash drum before the main benzene/toluene/xylene separation. This preliminary action removes the most volatile components that would otherwise require significant reboiler energy, thereby reducing high-end energy consumption while maintaining effective separation of the desired aromatic products.
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
These processes achieve recycle gas purity of 75 mole % without purging, significantly reducing hydrogen makeup costs and improving energy efficiency by minimizing fuel consumption in fired heaters.
Implementation Method 1
The reactor effluent is separated in a hot separator into a vapor stream and a liquid stream
Implementation Method 2
a portion of the transalkylation reactor effluent liquid stream is flashed to a low-pressure drum to separate light hydrocarbons, such C1 to C5, as a vapor stream from the aromatics rich liquid hydrocarbons stream
Implementation Method 3
A portion of flash drum liquid is recycled back to a product condenser inlet as a sponge liquid to absorb the light hydrocarbons from the reactor effluent stream
Data Source
AI summary
Aromatic transalkylation processes are described which reduce the hydrogen makeup gas requirement to the aromatic transalkylation unit and improve the energy efficiency of the aromatics complex. The processes may utilize a hot separator, optionally one or more flash drums, and optionally a stripper column. The aromatic transalkylation separator bottom liquid may be preheated and flashed to a low-pressure drum to separate light hydrocarbons, such C1 to C5, as a vapor stream from the aromatics rich liquid hydrocarbons stream. A portion of flash drum liquid may recycled back to a product condenser inlet as a sponge liquid to absorb the light hydrocarbons from the reactor effluent stream and thereby improve the hydrogen purity of the recycle gas (RG) without purging RG.