Lactide Production via Reactive Distillation and Side-Draw Refluxer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for producing optically pure lactide suffer from lactic acid racemization and contamination with lactic acid oligomers, leading to low molecular weight polylactic acid due to elevated temperatures and subsequent purification challenges.
Innovation Solution
A process involving two reactive distillations, where the first reactive distillation reduces lactic acid racemization and generates lactic acid oligomers, followed by a main distillation column with a vapor side-draw refluxer to purify lactide, minimizing residual impurities and increasing the yield of optically pure L-lactide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If lactic acid is concentrated and pre-polymerized to generate lactic acid oligomers by exposure to elevated temperatures, then the esterification between lactic acid molecules is facilitated and oligomers are generated, but racemization of lactic acid occurs leading to loss of optical purity and increased meso-lactide formation
Solution Approach 1:
The patent employs a reactive distillation process that operates at lower temperatures compared to conventional concentration and pre-polymerization methods. By changing the temperature parameter and using a catalyst system, the process achieves efficient esterification and oligomer generation while minimizing racemization and preserving optical purity of the lactic acid.
Solution Approach 2:
The patent introduces a catalyst as an intermediary substance to facilitate the esterification reaction and oligomer formation at lower temperatures. This catalyst enables the reaction to proceed efficiently without requiring high temperature exposure that would cause racemization, thus resolving the contradiction between productivity and optical purity.
2Quantity of substance
If crude lactide is subjected to conventional distillation to remove impurities, then separation based on volatility differences is achieved, but residual lactic acid and lactic acid oligomers remain contaminating the lactide product
Solution Approach 1:
The patent employs a reactive distillation process that selectively extracts and removes impurities such as residual lactic acid and lactic acid oligomers from the lactide product. The distillation column is designed to separate these components based on their volatility differences, taking them out of the product stream and achieving high lactide purity without requiring additional purification steps.
Solution Approach 2:
The reactive distillation process combines the chemical reaction (esterification and depolymerization) with the separation process in a continuous operation. This continuous useful action allows impurities to be removed as they are formed, preventing their accumulation and ensuring high product purity throughout the process, rather than requiring separate batch purification steps.
3Loss of substance
If lactic acid is exposed to elevated temperatures for concentration and pre-polymerization, then water content is reduced and oligomers are formed, but the residence time at high temperature causes racemization and decreases yield of optically pure L-lactide
Solution Approach 1:
The patent changes the temperature parameter by operating at lower temperatures in the reactive distillation process compared to conventional methods. This parameter change allows efficient water removal through distillation while minimizing the residence time at temperatures that cause racemization, thus preserving optical purity and increasing yield of optically pure L-lactide.
Solution Approach 2:
The reactive distillation process continuously removes water as it is formed during esterification, preventing the need for prolonged high-temperature exposure. This continuous useful action of water removal enables the reaction to proceed efficiently at lower temperatures, minimizing racemization while achieving the desired water content reduction.
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 reduces lactic acid racemization, increases the yield of L-lactide, and produces highly purified lactide free from lactic acid and oligomers, suitable for high molecular weight polylactic acid production without additional purification steps.
Implementation Method 1
The relative order of decreasing volatility of the principal components of the crude lactide is water, lactic acid, meso-lactide, L-lactide and linear lactic acid dimers with boiling points at atmospheric pressure of about 100, 215, 250, 255 and 350° C., respectively
Implementation Method 2
a main distillation column with a vapor side-draw refluxer being connected to
Data Source
AI summary
This invention relates to a process for the continuous production of optically pure lactide from an aqueous solution of lactic acid by means of two reactive distillations followed by a main distillation column with a side-draw refluxer. The first reactive distillation is used for the preparation of lactic acid oligomers and the second reactive distillation used for the depolymerization of the thus obtained lactic acid oligomers to lactide. The crude lactide generated from the second reactive distillation is further purified in the main distillation column with a side-draw refluxer being connected to.