Lactide Racemization for Purity and Yield Recovery
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing processes for producing lactide and poly(lactic acid) resins face challenges in efficiently separating and recovering meso-lactide, which results in yield losses and increased costs due to impurity concentration and the inability to effectively recycle lactic acid equivalents.
Innovation Solution
A process involving racemization of a lactide composition at up to 180°C in the presence of a catalyst to convert meso-lactide into S,S-lactide and R,R-lactide, allowing for the recovery of lactic acid equivalents in the form of lactide, while minimizing the formation of impurities like lactic acid or oligomers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional separation methods (distillation, melt crystallization) are used to separate meso-lactide from the lactide stream, then the S,S- and R,R-lactide stream is purified, but impurities become concentrated in the meso-lactide stream making it difficult and costly to recover lactic acid equivalents
Solution Approach 1:
Instead of attempting to purify the meso-lactide stream by conventional methods, the invention inverts the approach by using the impurity-concentrated meso-lactide stream as the starting material for racemization. The impurities remain in the stream during racemization, and the resulting racemized lactide is then purified, effectively turning the previously problematic impurity concentration into a manageable situation.
Solution Approach 2:
The invention changes the chemical composition parameter of the meso-lactide stream by subjecting it to racemization conditions (temperature of up to 180°C with a racemization catalyst). This transforms the optically impure meso-lactide into a racemized lactide mixture that can be more easily purified and recycled, converting a waste stream into a valuable product.
2Reliability
If meso-lactide is discarded or used in non-polymer applications to avoid impurity issues, then polymerization quality is maintained, but yield losses increase and process costs increase
Solution Approach 1:
Instead of discarding the meso-lactide stream or using it in low-value applications, the invention recovers lactic acid equivalents from it through racemization followed by purification. This transforms a discarded waste stream into a valuable source of recyclable lactide, improving both yield and process efficiency while maintaining product quality.
3Productivity
If the meso-lactide stream is polymerized directly or in high proportions, then all lactic acid equivalents are utilized, but amorphous polylactide grades are produced with reduced crystalline properties
Solution Approach 1:
The invention performs preliminary racemization of the meso-lactide stream before polymerization. By converting the optically impure meso-lactide into a racemized lactide mixture and then purifying it, the process ensures that the lactide used for polymerization has the appropriate optical composition to produce semi-crystalline or crystalline polylactide grades, rather than amorphous materials.
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 reduces yield losses by recovering lactic acid equivalents as lactide, purifies the lactide product, and concentrates impurities in the remaining meso-lactide stream, enabling more efficient polymerization and recycling within the lactide production process.
Implementation Method 1
subjecting a starting lactide composition to a temperature of up to 180° C. in the presence of a racemization catalyst for a time sufficient to racemize at least a portion of the lactide in the starting lactide composition to form a racemized lactide mixture
Data Source
AI summary
Lactic acid equivalents are recovered from a starting lactide stream by catalytically racemizing a portion of the lactide in the stream at a temperature of 180° C. or below. This increases the proportion of two species of lactide (i.e., at least two of S,S-, R,R- or meso-lactide) at the expense of the third species. The racemized mixture so obtained can be separated to recover some or all of one or more of the lactide species from the remaining lactide species, by a process such as melt crystallization or distillation. Impurities in the starting lactide stream usually are retained mostly in the remaining meso-lactide, so a highly purified S,S- and/or R,R-lactide stream can be produced in this manner. Such a purified S,S- and R,R-lactide stream is suitable for polymerization to form a polylactide.