Para-xylene Crystallization with C9+ Removal
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Solution Overview
Problem
Conventional methods for producing para-xylene (PX) face challenges in achieving high purity and efficiency due to the close boiling points of C8 aromatic compounds, requiring significant energy and capital costs, and often involve costly refrigeration and multiple separation steps.
Innovation Solution
A process combining a high selective toluene disproportionation process with a crystallization process to produce a PX enriched stream with a concentration of at least 99.5 wt%, minimizing or eliminating the need for a C9+ separation step, thereby reducing energy consumption and capital costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional fractional distillation is used to separate C8 aromatic compounds, then separation can be achieved, but large equipment, significant energy consumption, and substantial recycles are required
Solution Approach 1:
The patent changes the separation parameter from temperature-based (distillation) to freezing point-based (crystallization). By operating at temperatures below the freezing point of para-xylene (−13.3°C), the process exploits the large freezing point difference between para-xylene and other C8 aromatics to achieve separation without the energy-intensive distillation process
Solution Approach 2:
The patent utilizes the phase transition of para-xylene from liquid to solid at its freezing point (−13.3°C) to separate it from other C8 aromatic compounds that remain liquid at this temperature. This phase change enables efficient separation through filtration or decantation, avoiding the need for large distillation equipment and significant energy input
2Manufacturing precision
If conventional fractional distillation is used to separate C8 aromatic compounds, then separation can be achieved, but large equipment is required
Solution Approach 1:
The patent changes the separation parameter from temperature-based (distillation) to freezing point-based (crystallization). By operating at temperatures below the freezing point of para-xylene (−13.3°C), the process exploits the large freezing point difference between para-xylene and other C8 aromatics to achieve separation without the energy-intensive distillation process
Solution Approach 2:
The patent utilizes the phase transition of para-xylene from liquid to solid at its freezing point (−13.3°C) to separate it from other C8 aromatic compounds that remain liquid at this temperature. This phase change enables efficient separation through filtration or decantation, avoiding the need for large distillation equipment and significant energy input
3Manufacturing precision
If conventional crystallization is used to separate PX, then high PX purity can be obtained, but high utility usage and formation of eutectic between PX and MX require high initial PX concentration
Solution Approach 1:
The patent extracts and removes C9+ hydrocarbons from the C8 aromatic stream before the crystallization step. This pre-treatment eliminates the formation of eutectic mixtures between C9+ compounds and para-xylene, allowing the crystallization process to operate at lower temperatures and achieve high PX purity with reduced energy consumption and utility usage
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 achieves high PX purity with reduced energy and operational costs, and lower environmental emissions, making the PX production process more economically viable and environmentally friendly.
Implementation Method 1
Fractional crystallization in a crystallizer takes advantage of the differences between the freezing points and solubilities of the C8 aromatic components at different temperatures. Due to its higher freezing point, PX is usually separated as a solid in such a process while the other components are recovered in a PX-depleted filtrate.
Data Source
AI summary
A process of producing PX comprising providing a C8+ feedstock, the C8+ feedstock has C8 hydrocarbons and C9+ hydrocarbons, to a crystallization unit under crystallization conditions to produce a PX enriched stream having a PX concentration of at least 99.5 wt % based on the weight of the PX enriched stream, wherein the C8+ feedstock has a PX concentration of at least 70 wt % based on total weight of xylenes in the C8+ feedstock, which the C8+ feedstock having a C9+ hydrocarbons concentration in a range from 1 wppm to 10 wt % based on the total weight of the C8+ feedstock.