Blunt-Edge Mixer Settler for Solvent Extraction Phase Separation
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Solution Overview
Problem
Current solvent extraction (SX) processes face challenges in achieving high-purity products due to phase entrainment issues, where one phase is entrained in the other, leading to contamination and impurities, despite advancements in chemical and hydrodynamic aspects, but lacking specific designs and conditions in mixers and settlers to effectively reduce these issues.
Innovation Solution
The introduction of turbines with blunt-edged blades in mixers and specific internal elements in settlers, such as baffles with and without windows, to reduce shear effects and promote droplet grouping, combined with a decreasing agitation sequence and wide communication channels, facilitates easier phase separation and reduces entrainment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If stirring intensity is increased to improve phase contact and mass transfer, then extraction efficiency is improved, but stable emulsions and small droplets are formed which are easily entrained by the other phase, reducing product purity
Solution Approach 1:
The mixer is divided into multiple compartments (typically 3-5) arranged in series, with each compartment providing a stage of mixing and partial separation. This segmentation allows the mixing process to be distributed, reducing the intensity in each individual compartment while maintaining overall extraction efficiency, and facilitating phase separation between compartments to prevent entrainment.
Solution Approach 2:
A dispersion band formation and breakdown mechanism is introduced as an intermediary process. The mixer is designed to initially form a dispersion band of droplets, then allow this band to break down and coalesce in subsequent compartments or in the settler, acting as a mediator between intense mixing and clean separation, preventing direct entrainment while maintaining mass transfer.
2Area of moving object
If radial agitation with high shear effect is used to reduce droplet size and improve mixing, then contact area is increased, but droplets become too small and difficult to decant, worsening phase separation
Solution Approach 1:
The agitation system is designed to be dynamic rather than static, with multiple compartments providing varying degrees of mixing intensity. The system transitions from higher intensity mixing in early compartments to lower intensity in later compartments, allowing droplets to be broken down initially then allowed to coalesce and separate in subsequent stages, making decantation easier.
Solution Approach 2:
The mixing process is organized as periodic action through the series of compartments, where each compartment provides a cycle of mixing and partial separation. The phases undergo repeated cycles of dispersion and coalescence as they progress through the compartments, ultimately resulting in easier separation in the final settler.
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 significantly enhances the quality of phase separation, reducing entrainment and improving the purity of the end product by minimizing the formation of small droplets and promoting clear decantation, thus achieving higher purity levels in SX processes.
Implementation Method 1
turbines with blunt-edged blades in mixers and specific internal elements in settlers, such as baffles with and without windows, to reduce shear effects and promote droplet grouping
Implementation Method 2
The settler must be capable of re-separating the two components, organic phase and aqueous phase, forming the emulsion
Implementation Method 3
The mixer, which may have several tandem compartments, has the function of dispersing the two phases to be mixed, to form an emulsion in order to favour transfer and obtain equilibrium
Implementation Method 4
The separation conditions depend both on the physical characteristics of the dispersed phases (differences of density, surface tension, viscosity, temperature, acidity, unitary speed)
Data Source
AI summary
The device of the invention includes the following 5 new elements in each mixer-settler: a) agitators with blunt edged turbines, b) decreasing degree of agitation throughout the series of mixing compartments, c) baffle with a central window in the settler interface, located after the flow buffers, and d) baffle without a window, centered in the settler interface, located after the baffle with a window. These elements allow for an operative method which inhibits secondary dispersion, reducing the formation of micro-droplets, without affecting the mass transfer between the phases. Consequently, this obtains a phase separation process with entrainments so small that it is possible to drastically increase the quality of the product, by obtaining an ultra-pure aqueous extract, simultaneously reducing the settling surface required.