Membrane Separation of PF5 and HCl for LiPF6 Synthesis
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Solution Overview
Problem
The separation of phosphorous pentafluoride (PF5) from hydrogen chloride (HCl) in a gaseous mixture is challenging due to their azeotropic nature, making it difficult to achieve high purity streams without introducing additional process chemicals or increasing equipment size.
Innovation Solution
A membrane separation process is used to separate PF5 and HCl by employing a selectively permeable membrane that allows for the separation of azeotropic or near-azeotropic compositions, resulting in enriched streams of PF5 and HCl without the need for additional solvents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a counter-current flow absorption tower is used to remove hydrogen chloride from phosphorous pentafluoride, then hydrogen chloride can be removed from the crude product stream, but the equipment size and liquid solvent inventory must be significantly greater due to the six times higher volumetric flow of the crude gas stream compared to pure phosphorous pentafluoride
Solution Approach 1:
The patent applies preliminary action by performing initial separation of hydrogen chloride from phosphorous pentafluoride through selective absorption before the main distillation process. This pre-treatment step concentrates the phosphorous pentafluoride and removes the bulk of hydrogen chloride, allowing the subsequent distillation column to operate more efficiently with smaller size requirements and achieving the desired high purity product stream
Solution Approach 2:
The patent uses an intermediary absorption step with a suitable solvent that selectively absorbs hydrogen chloride but not phosphorous pentafluoride. This intermediary process acts as a bridge between the crude mixture and the final distillation, enabling the system to handle the azeotropic mixture by first separating one component, thereby reducing the load on the main separation equipment
2Manufacturing precision
If a counter-current flow absorption tower is used to remove hydrogen chloride from phosphorous pentafluoride, then hydrogen chloride can be removed from the crude product stream, but the liquid solvent inventory must be significantly greater due to the six times higher volumetric flow of the crude gas stream
Solution Approach 1:
The absorption tower performs preliminary removal of hydrogen chloride from the crude product stream before distillation. By treating the gas stream in advance to remove the bulk of HCl, the system reduces the solvent inventory needed in subsequent processing steps, as the solvent doesn't need to handle the full volumetric load of the crude mixture
Solution Approach 2:
The patent extracts hydrogen chloride from the crude product stream using a selective absorption process. This extraction step removes the harmful component (HCl) and concentrates the desired product (PF5), allowing the main distillation column to operate with smaller solvent inventory and achieve higher purity more efficiently
3Device complexity
If simple distillation is used to separate phosphorous pentafluoride and hydrogen chloride, then the process would be simple, but separation is not possible because their normal boiling points are less than 1 Kelvin apart and they form an azeotropic mixture
Solution Approach 1:
The patent segments the separation process into two distinct stages: first, selective absorption of hydrogen chloride from the crude product stream to produce a concentrated phosphorous pentafluoride stream, and second, distillation of the enriched stream. This segmentation allows each stage to be optimized independently, achieving high purity separation while managing the azeotropic challenge
Solution Approach 2:
The patent introduces an intermediary absorption step as a mediator between the crude mixture and the final distillation. This intermediary process selectively removes hydrogen chloride using a suitable solvent, creating an enriched phosphorous pentafluoride stream that can then be distilled more effectively, bridging the gap between the azeotropic mixture and the pure product
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 process effectively separates PF5 and HCl, achieving high purity streams with a molar ratio of PF5:HCl suitable for lithium hexafluorophosphate synthesis, while reducing equipment size and operational costs compared to traditional methods.
Implementation Method 1
A membrane separation process is used to separate PF5 and HCl by employing a selectively permeable membrane that allows for the separation of azeotropic or near-azeotropic compositions
Data Source
AI summary
The present invention relates to a process of separating a feed stream comprising HCl and PF5 into a plurality of streams, wherein a first stream is enriched in PFS and a second stream is enriched in HCl, the process comprising the feed stream entering one or more permeable membrane separation modules, wherein the membrane separation module comprises a permeable membrane which is selectively permeable to one of HCl or PF5.