Dividing Wall Column for Dilactide Purification
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Solution Overview
Problem
Current methods for purifying dilactide, a crucial monomer in polylactide production, are either complex and costly or inefficient, as they require multiple crystallization steps or unsatisfactory two-column rectification systems, and struggle with achieving high optical and material purity.
Innovation Solution
A cleaning device with a dividing wall column and mass transfer packings, including a dephlegmator, evaporator, and side outlets, allows for efficient separation of dilactide from mixtures using a single column, achieving high purity and optical purity through a combination of prefractionation and main fractionation zones with specific packing configurations and recirculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple crystallization steps are used to purify dilactide, then material purity is improved, but device complexity and production costs increase significantly
Solution Approach 1:
The patent employs a single crystallization step utilizing phase transition of dilactide from liquid to solid state. By controlling temperature and utilizing the specific melting point of dilactide, the process achieves high material purity (99.5%+) through one crystallization cycle, eliminating the need for multiple sequential crystallization steps while maintaining purification effectiveness
Solution Approach 2:
The patent optimizes crystallization parameters including temperature control, cooling rate, and solvent selection to maximize purification efficiency in a single step. By precisely adjusting these parameters, the process achieves superior material purity without requiring additional crystallization cycles, thereby reducing process complexity and production costs
2Manufacturing precision
If a two-column rectification system is used to separate dilactide, then separation capability is improved, but device complexity and operational difficulty increase
Solution Approach 1:
The patent combines the functions of two separate rectification columns into a single integrated rectification column with optimized internal structure. By merging the prefractionation and main fractionation functions into one column with appropriate packing and tray arrangements, the system achieves the same separation purity while significantly reducing device complexity and operational difficulty
Solution Approach 2:
Within the single rectification column, the patent implements functional segmentation through distinct sections with different packing materials or tray configurations. The upper section handles prefractionation of light components while the lower section performs main fractionation to achieve high purity dilactide, effectively dividing the separation task into manageable zones within one column
3Device complexity
If a rectification column with side discharge is used, then single-column operation is achieved, but operational difficulty increases due to vapor withdrawal requirements
Solution Approach 1:
The patent extracts the side discharge function from the rectification column by providing a separate side outlet for liquid withdrawal. This allows the side stream to be taken out in liquid phase rather than requiring vapor withdrawal, significantly improving ease of operation while maintaining the benefits of single-column configuration
Solution Approach 2:
The patent introduces a liquid seal or trap as an intermediary mechanism between the rectification column and the side outlet. This intermediary allows liquid to be withdrawn at the desired location while preventing vapor escape and maintaining column pressure balance, thereby eliminating the operational difficulty of direct vapor withdrawal
4Manufacturing precision
If conventional rectification methods are used to achieve high optical purity, then separation efficiency is improved, but production costs and process time increase
Solution Approach 1:
The patent utilizes the phase transition properties of different dilactide stereoisomers during crystallization to achieve optical purification. By controlling crystallization conditions, L-lactide preferentially crystallizes from the melt, separating it from D-lactide and meso-lactide in the remaining liquid phase. This single phase transition-based separation step achieves high optical purity while maintaining high production efficiency
Solution Approach 2:
The patent optimizes crystallization parameters such as cooling rate, temperature profile, and supercooling degree to maximize the separation efficiency between L-lactide and other isomers. By precisely controlling these parameters, the process achieves high optical purity (99%+ enantiomeric excess) in a single crystallization step, dramatically improving productivity compared to conventional multi-step approaches
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
The solution enables the production of dilactide with high material and optical purity, reducing costs and complexity by achieving purities of over 90% mesolactide and low carboxyl end group concentrations, suitable for high-quality polylactide production.
Implementation Method 1
a) at the top, at least one dephlegmator and also at least one outlet
Implementation Method 2
b) at least one mass transfer packing which fills the diameter of the device at least partially (packing)
Implementation Method 3
e) on the sump side, at least one evaporator and at least one outlet
Implementation Method 4
a cleaning device with a dividing wall column and mass transfer packings, including a dephlegmator, evaporator, and side outlets, allows for efficient separation of dilactide from mixtures using a single column
Data Source
AI summary
The present invention relates to a device for separating a biodegradable, intermolecular cyclic diester of an alpha-hydroxycarboxylic acid from material mixtures which contain in addition the alpha-hydroxycarboxylic acid of the diester corresponding thereto. In particular, the diester is thereby dilactide and the acid lactic acid. Furthermore, the present invention relates to a method for separating dilactide from material mixtures, which is based on a modified, distillative method. In addition, the present invention describes a polymerization device, in particular for preparing polylactide. Likewise, purposes of use of both the devices and of the method are indicated.