Low-Racemization Lactide Production Through Step-Controlled Depolymerization
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Solution Overview
Problem
The existing methods for synthesizing lactide in polylactic acid (PLA) production face challenges such as high racemization, low yield, and instability in the depolymerization process, leading to reduced optical purity and mechanical properties of PLA due to the formation of meso-lactide (m-lactide), which complicates the separation process and increases economic inefficiency.
Innovation Solution
A multi-stage cascade depolymerization process with step control is employed, utilizing depolymerization reactors and circulation tanks to regulate molecular weight, combined with protonated solvents, to reduce racemization and coking, ensuring continuous and stable operation, and improving the conversion rate and yield of lactide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If traditional depolymerization process is used to prepare lactide, then the process can be carried out under high-temperature and high-vacuum conditions, but the racemization of lactide increases significantly leading to low optical purity
Solution Approach 1:
The patent changes the reaction parameters from traditional high-temperature and high-vacuum conditions to moderate temperature (160-240°C) and atmospheric or mild pressure conditions, combined with a specific catalyst system, to reduce racemization while maintaining depolymerization efficiency
Solution Approach 2:
The patent introduces a catalyst as an intermediary substance to facilitate the depolymerization reaction under milder conditions, replacing the need for extreme temperature and vacuum conditions that cause racemization
2Productivity
If excessive catalyst or high temperature is used to accelerate depolymerization, then the reaction rate increases, but the racemization reaction is accelerated leading to meso-lactide formation
Solution Approach 1:
The patent optimizes the catalyst concentration to a specific range (0.1-5 wt%) and controls the reaction temperature (160-240°C) to achieve both high reaction rate and high optical purity, avoiding the need for excessive catalyst or high temperature
Solution Approach 2:
The patent monitors the reaction progress and adjusts catalyst concentration and temperature dynamically to maintain optimal conditions that prevent racemization while ensuring complete depolymerization
3Manufacturing precision
If conventional purification processes are used to remove m-lactide, then the separation can be attempted, but the process is difficult and the overall yield is only 40%-60%
Solution Approach 1:
The patent takes preliminary action by preventing racemization during the depolymerization process through optimized catalyst and temperature control, rather than attempting to remove m-lactide after formation, thereby achieving both high purity and high yield
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 method achieves a lactide conversion rate of 97.0% or more, reduces racemization by over 50%, and enhances the stability and efficiency of the depolymerization process, resulting in a crude lactide product with improved quality and yield.
Implementation Method 1
reacting a lactic acid oligomer and a depolymerization catalyst in a first depolymerization reaction unit to obtain a first liquid-phase material
Implementation Method 2
A multi-stage cascade depolymerization process with step control is employed, utilizing depolymerization reactors and circulation tanks to regulate molecular weight
Data Source
AI summary
Disclosed are a method and a system for continuously preparing lactide by step control. The method includes the steps of (1) reacting a lactic acid oligomer and a depolymerization catalyst in a first depolymerization reaction unit to obtain a first liquid-phase material; (2) circulating the first liquid-phase material in a second depolymerization reaction unit for reaction until the molecular weight of the liquid-phase material is higher than 6,000 to obtain a second liquid-phase material; (3) circulating the second liquid-phase material in a third depolymerization reaction unit for reaction until the molecular weight of the liquid-phase material is higher than 10,000; and (4) collecting gas-phase crude lactide from the first depolymerization reaction unit, the second depolymerization reaction unit and the third depolymerization reaction unit, and then purifying same.