Lactic Acid Purification via Solvent Extraction and SMB Chromatography
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Solution Overview
Problem
Current methods for producing lactic acid from fermentation broths are inefficient and costly, often resulting in impurities that hinder the polymerization of lactic acid into biodegradable plastics, and there is a lack of a reliable quality test to determine the suitability of lactic acid for polymerization before producing polylactic acid.
Innovation Solution
A quality determination test involving polycondensation and depolymerization of lactic acid to assess dilactide yield and racemization, combined with a process that includes successive stages of biomass separation, acidification, simulated moving bed chromatography, ion exchange, and nanofiltration to produce high-purity polymerizable lactic acid without distillation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If distillation is used to purify lactic acid from aqueous solutions, then purification is achieved, but carbohydrates are extracted leading to yield deterioration and process complexity increases
Solution Approach 1:
The patent extracts lactic acid from the fermentation broth using an organic solvent (ethyl acetate or n-butyl acetate) instead of water-based distillation. This extraction method selectively transfers lactic acid to the organic phase while leaving carbohydrates and other water-soluble impurities in the aqueous phase, achieving purification without yield loss.
Solution Approach 2:
The patent introduces an intermediate organic solvent phase to mediate the separation between lactic acid and impurities. The solvent acts as a bridge that selectively dissolves lactic acid while excluding carbohydrates, enabling efficient purification without direct thermal processing that would extract carbohydrates.
2Manufacturing precision
If multiple purification steps including distillation are used, then lactic acid purity is improved, but process cost and energy consumption increase significantly
Solution Approach 1:
The patent replaces energy-intensive distillation with solvent extraction, which operates at ambient or mild temperatures. The lactic acid is transferred to the organic phase through liquid-liquid extraction, eliminating the need for high-temperature heating and significant energy input while achieving comparable or superior purity.
Solution Approach 2:
The patent changes the phase distribution parameters by introducing an organic solvent with specific solubility characteristics. This parameter change allows lactic acid to partition into the organic phase based on its chemical properties rather than requiring thermal energy input, dramatically reducing energy consumption.
3Quantity of substance
If conventional purification methods are used, then lactic acid is obtained, but impurities remain that interfere with polymerization to polylactic acid
Solution Approach 1:
The patent extracts lactic acid into an organic solvent phase that selectively dissolves lactic acid while leaving behind water-soluble impurities such as carbohydrates, amino acids, and fermentation by-products. This selective extraction removes polymerization-interfering impurities while preserving lactic acid integrity.
Solution Approach 2:
The patent creates a purified copy of lactic acid in the organic phase, separated from the complex fermentation matrix. The extracted lactic acid in the organic solvent represents a cleaned version free from fermentation impurities, suitable for subsequent polymerization without carrying over interfering substances.
4Reliability
If a quality test for polymerizable lactic acid is implemented, then suitability for polymerization can be determined, but additional testing time and complexity are required
Solution Approach 1:
The patent performs a preliminary polycondensation test on the extracted lactic acid sample to assess its suitability for polymerization before full-scale production. This preliminary action identifies impurities that would interfere with polymerization early in the process, preventing waste of time and resources on unsuitable batches.
Solution Approach 2:
The patent uses the results of the polycondensation test and dilactide determination as feedback to evaluate lactic acid quality. This feedback mechanism provides quantitative information about polymerization suitability, allowing process optimization and quality control while maintaining efficient timing through targeted measurements.
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 process ensures lactic acid with a dilactide yield of >90% and racemization of <5%, indicating suitability for polymerization, thereby improving the quality and efficiency of polylactic acid production while avoiding the drawbacks of existing methods.
Implementation Method 1
a) polycondensing the lactic acid to a prepolymer
Implementation Method 2
gradually heated from 120 °C to 180 °C over a period of 5 to 7 hours and the pressure is simultaneously increased from 350 mbar to 450 mbar to 100 mbar 25 mbar reduced
Implementation Method 3
b) depolymerizing to dilactide
Implementation Method 4
The prepolymer obtained during the polycondensation is subjected to analytical processes to determine the molar mass
Implementation Method 5
lowering the pH to a value of 2.2-2.4 by adding H2SO4 and mixing concentrated sulfuric acid into the lactic acid solution
Implementation Method 6
separating lactic acid solution from the biomass-free fermentation broth by simulated moving bed chromatography
Implementation Method 7
cleaning the separated lactic acid solution using a first ion exchange step
Implementation Method 8
concentrating the lactic acid solution purified in the first ion exchange step using a first single or multi-stage evaporation stage
Data Source
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AI summary
The invention relates to a process for producing polymerizable lactic acid from fermentation broths, comprising the process steps: - separating the biomass and any solids present from the fermentation broth in at least two successive stages, - separating lactic acid solution from the biomass-free fermentation broth by simulated moving bed chromatography (SMB), - purifying by ion exchange, - concentrating by means of a first single- or multi-stage evaporation stage, - purifying by means of ion exchange, - concentrating by means of a second single- or multi-stage evaporation stage, such that the lactic acid has a dilactide yield of > 90% and a racemization of < 5%.