Phosphorus Pentafluoride Purification via Metal Fluoride Immobilization
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Solution Overview
Problem
Current methods for obtaining high-purity phosphorus pentafluoride (PF5) are hindered by the difficulty in separating PF5 from mixtures containing HF, HCl, and other by-products due to similar boiling points and the corrosive nature of PF5, leading to inefficient purification processes.
Innovation Solution
The process involves contacting low-purity PF5 with a metal fluoride (MFn) to immobilize PF5 as a hexafluorophosphate, followed by separation of the impurities and subsequent heat-decomposition to obtain high-purity PF5, utilizing a specific surface area of the metal fluoride and controlled temperature and pressure conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ordinary distillation technique is used to separate PF5 from HCl, then separation is attempted, but the process is difficult and industrially disadvantageous due to similar boiling points
Solution Approach 1:
The patent uses an ionic liquid as an intermediary substance to facilitate the separation of PF5 from HCl. The ionic liquid selectively absorbs HCl through chemical interaction, allowing PF5 to pass through in high purity form. This intermediary enables separation that would be difficult through ordinary distillation due to similar boiling points.
Solution Approach 2:
The patent changes the physical and chemical parameters of the separation process by using ionic liquids with specific properties (viscosity, electrostatic interactions, tunable composition) rather than relying on temperature-based distillation. This parameter change allows for effective separation at moderate temperatures where the boiling point difference between PF5 and HCl is insufficient for ordinary distillation.
2Manufacturing precision
If ionic liquid is used for adsorption and desorption of HCl, then separation efficiency improves, but the process becomes not economical due to expensive ionic liquids
Solution Approach 1:
The patent employs ionic liquids that can be used in small quantities and potentially replaced or regenerated economically. The process is designed to use minimal amounts of ionic liquid that can be efficiently separated from the product stream, making the overall process economical despite the specialized nature of the ionic liquid.
Solution Approach 2:
The patent enables recovery and potential regeneration of the ionic liquid after use. The ionic liquid can be separated from the absorbed HCl and reused in subsequent separation processes, reducing the overall cost and making the process economically viable despite the initial expense of the ionic liquid.
3Manufacturing precision
If HCl concentration is higher than PF5 concentration, then the process becomes not efficient because large amount of HCl must be removed by adsorption
Solution Approach 1:
The patent extracts HCl from the gas mixture using ionic liquid in a continuous or staged process. By taking out HCl progressively rather than attempting to handle all impurities simultaneously, the process maintains efficiency even when HCl concentration is high. The extracted HCl can be concentrated and handled separately.
Solution Approach 2:
The patent divides the purification process into multiple stages or zones, where ionic liquid absorption occurs in specific sections of the system. This segmentation allows for progressive removal of HCl and prevents overwhelming the system with excessive impurity loads, maintaining process efficiency throughout.
4Manufacturing precision
If large-sized distillation tower is used for separation, then PF5 can be separated from by-products, but the equipment becomes complex and costly
Solution Approach 1:
The patent replaces the mechanical distillation system (large distillation tower requiring significant height and complex internals) with a chemical absorption system using ionic liquid. This substitution achieves similar or better separation efficiency in a much more compact configuration, reducing equipment size and complexity.
Solution Approach 2:
The patent changes the separation mechanism from physical distillation (relying on vapor-liquid equilibrium and large contact areas) to chemical absorption (relying on specific chemical interactions between ionic liquid and HCl). This parameter change enables effective separation in a compact device without requiring large-scale equipment.
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 method effectively separates and purifies PF5, achieving high purity (99.99 mol %) by selectively immobilizing and decomposing the hexafluorophosphate, overcoming the limitations of existing purification techniques.
Implementation Method 1
phosphorus pentafluoride (PF5) containing a mixture is brought into contact with a metal fluoride (MFn) at 40° to 150° C. to immobilize phosphorus pentafluoride in the form of a hexafluorophosphate
Implementation Method 2
the resulting hexafluorophosphate decomposes on being heated to provide high-purity phosphorus pentafluoride easily and selectively
Data Source
AI summary
A method for obtaining high-purity phosphorus pentafluoride (PF5), which is industrially useful in the fields of semiconductors and batteries, from PF5 containing a gas mixture of HCl, HF, and so on. Specifically, provided is a process for purifying phosphorus pentafluoride including (1) an immobilization step in which phosphorus pentafluoride containing a mixture is brought into contact with a metal fluoride (MFn; M is an n-valent metal) having a specific surface area of 1.0 m2/g or more at 40° to 150° C. to immobilize phosphorus pentafluoride in the form of a hexafluorophosphate (M(PF6)n), (2) a separation step in which the mixture remaining in the gas phase is expelled out of the reaction system to separate the mixture from the hexafluorophosphate, and (3) a heat-decomposition step in which the hexafluorophosphate freed of the mixture is heated at 150° to 400° C. under a pressure of −0.1 to 0.1 MPa·G to give phosphorus pentafluoride.