Simulated Moving Bed and Distillation Column for Paraxylene Separation
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Solution Overview
Problem
The existing processes for producing high purity paraxylene are complex and costly, requiring multiple separation stages in simulated moving bed adsorption and isomerization steps, which increases investment and energy consumption, and complicates the fractionation process.
Innovation Solution
A process involving a single separation step in a simulated moving bed with a zeolite adsorbent and desorbent, producing three fractions, where the fractions containing ethylbenzene, metaxylene, and orthoxylene are separated and reintroduced into a single distillation column, facilitating raffinate fractionation without increasing complexity or reducing paraxylene yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple separation stages in simulated moving bed adsorption are used, then paraxylene purity is improved, but device complexity and investment costs increase
Solution Approach 1:
The process segments the separation function by using a single simulated moving bed unit that produces three distinct fractions (extract A1 containing paraxylene, and two raffinates A21/A22 with different compositions). This segmentation allows each fraction to be directed to appropriate treatment paths, achieving high purity paraxylene separation without requiring multiple sequential SMB stages.
2Productivity
If multiple separation stages and isomerization steps are implemented, then paraxylene yield is improved, but energy consumption increases
Solution Approach 1:
The process performs preliminary separation in the simulated moving bed to produce two distinct raffinate fractions (A21 and A22) with different compositions before distillation. This preliminary action allows the subsequent distillation column to operate more efficiently by receiving pre-separated feeds, reducing the energy required for fractionation while maintaining high paraxylene yield.
Solution Approach 2:
The two raffinate fractions A21 and A22 are introduced at different feeding points in the distillation column according to their specific compositions. This local quality approach optimizes the distillation process by matching feed composition with column section characteristics, reducing overall energy consumption while achieving effective separation.
3Manufacturing precision
If separate distillation columns are used for treating raffinates, then fractionation efficiency is improved, but device complexity and investment costs increase
Solution Approach 1:
The process merges the treatment of both raffinate fractions A21 and A22 into a single distillation column by introducing them at different feeding points. This consolidation achieves effective fractionation of all C8 aromatics while reducing the number of distillation columns from two to one, thereby lowering investment costs and simplifying the overall process configuration.
Solution Approach 2:
Instead of using multiple columns in parallel, the process introduces a dimensional element by utilizing different vertical feeding points within a single distillation column. This allows simultaneous treatment of multiple raffinate streams with different compositions, achieving the separation efficiency of multiple columns with a single unit.
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 simplifies the fractionation step, reduces energy consumption, and allows for debottlenecking configurations without modifying the paraxylene yield, thereby lowering production costs and thermal loads in the xylene loop.
Implementation Method 1
a single step A of separation in a simulated moving bed of said charge, said step being implemented with a zeolite as adsorbent and a desorbent
Implementation Method 2
step B of fractionation by distillation in a distillation column of fractions A21 and A22 resulting from step A
Data Source
Figure 1a~1b
Figure 2
AI summary
The present invention describes a method for obtaining paraxylene from a feedstock containing xylenes, ethylbenzene and C9+ hydrocarbons, said method comprising: - a single simulated moving-bed separation step A implemented with a zeolite as adsorbent and a desorbent and allowing at least three fractions to be obtained, one fraction A1 comprising a mixture of paraxylene and desorbent, two fractions A21, A22 comprising ethylbenzene (EB), orthoxylene (OX) and metaxylene (MX) and desorbent, said step is carried out at a temperature of 20°C to 250°C, under a pressure between the bubble pressure of the xylenes at the operating temperature and 2.0 MPa, and with a volume ratio of the desorbent to the load in the simulated moving-bed separation unit 2 of 0.4 to 2.5; - a step B of fractionation by distillation in a two-section distillation column of fractions A21 and A22 from step A, in which said fractions are injected separately at separate injection points, allowing the production of a fraction B2 containing ethylbenzene, orthoxylene and metaxylene, and a fraction B42 free of aromatic compounds with eight carbon atoms and containing desorbent.