Lactic Acid Purification via Multi-Stage Distillation
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Solution Overview
Problem
Current methods for purifying lactic acid from fermentation sources fail to effectively remove both non-volatile and volatile impurities, leading to suboptimal polymerization conditions and catalyst deactivation, resulting in lower purity and increased color during polylactic acid production.
Innovation Solution
A two-stage process involving concentration of lactic acid to 85-95% and subsequent multi-stage column distillation with three zones, minimizing residence time and thermal degradation, to separate lactic acid and impurities in a single step.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple distillation steps are used to purify lactic acid, then purity of lactic acid is improved, but energy consumption and operating costs increase significantly
Solution Approach 1:
The distillation column is divided into three functional zones (rectification zone, stripping zone, and intermediate zone) with different operating conditions. The rectification zone operates at lower pressure to remove volatile impurities, the stripping zone operates at higher pressure to remove non-volatile impurities, and the intermediate zone connects these zones. This segmentation allows simultaneous removal of both volatile and non-volatile impurities in a single pass, eliminating the need for multiple sequential distillation steps and significantly reducing energy consumption.
2Manufacturing precision
If multiple distillation steps are used to purify lactic acid, then purity of lactic acid is improved, but investment costs increase
Solution Approach 1:
Multiple distillation functions (removal of volatile impurities, removal of non-volatile impurities, and concentration of lactic acid) are merged into a single distillation column through the three-zone configuration. This integration reduces the number of separate columns and associated equipment (pumps, heat exchangers, control systems), thereby reducing capital investment costs while achieving the same purification effect that would require multiple sequential columns.
3Quantity of substance
If conventional distillation is used, then lactic acid is concentrated, but volatile impurities remain in the purified product
Solution Approach 1:
The rectification zone is specifically designed with optimized packing or trays and operating conditions (lower pressure, higher reflux ratio) to maximize the removal of volatile impurities. This localized optimization ensures that volatile components are effectively separated in this specific zone, while other zones handle different separation tasks, achieving comprehensive purification that conventional uniform distillation cannot accomplish.
4Quantity of substance
If conventional distillation is used, then lactic acid is concentrated, but non-volatile impurities are not effectively removed
Solution Approach 1:
The stripping zone is specifically designed with optimized conditions (higher pressure, different liquid-vapor contact patterns) to maximize the removal of non-volatile impurities. This localized optimization ensures that heavy components are effectively separated in this specific zone, while other zones handle different separation tasks, achieving comprehensive purification that conventional uniform distillation cannot accomplish.
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 significantly improves the purity and color of lactic acid, reducing thermal and chemical degradation, and enhances the yield, resulting in better polymerization conditions and higher quality polylactic acid production.
Implementation Method 1
b. Distillation in a multi-stage column comprising three zones and allowing the separation in a single step of lactic acid, volatile compounds and heavier impurities
Implementation Method 2
a. Concentration of the lactic acid solution to a concentration between 85 and 95%, preferably between 90 and 95%, i.e. 15 to 5% free water or preferably 10 to 5% free water
Data Source
Figure 1~2(D)
AI summary
The present invention concerns a method for purifying an aqueous lactic acid solution, obtained from a fermentation medium or from any other source previously cleared of solid substances and/or of biomass that may be present and ionic substances, characterised in that it comprises the two following steps: a. Concentration of the lactic acid solution until a concentration of between 85 and 95% is reached, preferably of between 90 and 95%, i.e. between 15 and 5% free water or preferably between 10 and 5% free water; b. Distillation in a multi-stage column comprising three areas and allowing the separation, in a single step, of the lactic acid, volatile compounds and the heaviest impurities.