Liquid Phase Isomerization Unit for Para-Xylene Yield
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Solution Overview
Problem
Aromatics complexes face yield losses in para-xylene production due to high ortho-xylene levels leading to increased operating temperatures and ring losses in the ethylbenzene isomerization unit, necessitating an improved process to control ortho-xylene feed and enhance para-xylene yield.
Innovation Solution
Integration of a liquid phase isomerization unit in the aromatics complex, where the ortho-xylene rich stream is contacted with an isomerization catalyst in the absence of hydrogen to produce a second isomerization effluent, alongside a para-xylene separation unit using an ethylbenzene isomerization catalyst to optimize para-xylene production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ortho-xylene rich stream is fed to the ethylbenzene isomerization unit, then xylene equilibrium is re-established, but ring losses increase due to higher operating temperatures
Solution Approach 1:
The isomerization process is divided into two separate units: a vapor-phase EB isomerization unit and a liquid-phase xylene isomerization unit. This segmentation allows each unit to operate under optimized conditions, with the liquid-phase unit handling ortho-xylene conversion without contributing to ring losses in the vapor-phase unit.
Solution Approach 2:
A liquid-phase isomerization unit acts as an intermediary between the separation unit and the vapor-phase EB isomerization unit. This intermediary unit converts ortho-xylene to meta-xylene and para-xylene before the stream enters the vapor-phase unit, thereby reducing ortho-xylene content and minimizing ring losses.
2Productivity
If higher operating temperatures are used in the EB isomerization unit, then xylene equilibrium is achieved faster, but ring losses from cracking increase
Solution Approach 1:
The invention changes the physical state parameter of the isomerization process by introducing a liquid-phase unit operating at lower temperatures compared to vapor-phase units. This parameter change enables equilibrium re-establishment without the high temperatures that cause cracking and ring losses.
Solution Approach 2:
The invention utilizes phase transitions by operating one isomerization unit in the liquid phase and another in the vapor phase. The liquid-phase unit operates at lower temperatures to avoid cracking, while the vapor-phase unit handles ethylbenzene conversion. This phase transition strategy resolves the contradiction between productivity and substance loss.
3Productivity
If a vapor-phase isomerization process is used, then EB conversion to xylenes is efficient, but ortho-xylene content must be严格控制 to avoid ring losses
Solution Approach 1:
The liquid-phase isomerization unit automatically handles ortho-xylene conversion without requiring external control mechanisms. It self-regulates by converting excess ortho-xylene to meta-xylene and para-xylene, thereby eliminating the need for complex feed control systems and simplifying operation of the vapor-phase EB isomerization unit.
4Ease of manufacture
If conventional aromatics complex configuration is used, then capital costs are lower, but para-xylene yield is reduced due to ring losses
Solution Approach 1:
The invention merges conventional vapor-phase EB isomerization with a novel liquid-phase xylene isomerization unit in a single integrated complex. This combination allows the facility to maintain cost-effective vapor-phase processing while adding the liquid-phase unit to eliminate ring losses, thereby improving para-xylene yield without prohibitively increasing capital costs.
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 reduces ring losses and improves para-xylene yield by 1 to 2 wt% while operating efficiently with an ortho-xylene lean feed, lowering capital and energy costs.
Implementation Method 1
the isomerization process with EB isomerization type catalyst converts ethyl benzene in the feed to xylenes via a naphthene intermediate pathway
Implementation Method 2
The C8 aromatics stream is contacted with an adsorbent under adsorption conditions to provide a para-xylene stream and a raffinate stream
Data Source
AI summary
Processes and apparatuses for producing para-xylenes are provided. The processes comprises providing a hydrocarbon stream comprising C7+ hydrocarbons. The hydrocarbon stream is separated to provide a C8 aromatics stream and an ortho-xylene rich stream. The C8 aromatics stream is passed to a para-xylene separation unit for separating para-xylene to provide a para-xylene stream and a raffinate stream. At least a portion of the raffinate stream is passed to a first isomerization unit to provide a first isomerization effluent, wherein the first isomerization effluent is produced in the presence of an ethylbenzene (EB) isomerization catalyst. At least a portion of the ortho-xylene rich stream is contacted with an isomerization catalyst in a second isomerization unit in liquid phase at isomerization conditions in substantial absence of hydrogen to produce a second isomerization effluent.