Two-Stage Polymerization Reactor for High Viscosity Polylactide
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Solution Overview
Problem
Existing polymerization reactors face challenges in producing homopolymers like polylactide due to high melt viscosities, leading to pressure losses and blockages, which result in costly downtime and inefficiencies, especially when using static mixers as the main polymerization stage.
Innovation Solution
A two-stage polymerization reactor system comprising a stirred vessel or loop-type bubble column as the first stage and a tubular reactor with baffles as the second stage, where the baffles standardize the flow velocity profile across the tubular reactor's cross-section, preventing mixing and reducing flow resistance, thereby allowing for efficient polymerization of high molar mass homopolymers with improved quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a static mixer is used as the main polymerisation stage, then mixing efficiency is improved, but pressure loss increases and blockages occur due to high melt viscosities
Solution Approach 1:
The polymerisation process is divided into two distinct stages: a first stage using a static mixer for initial mixing of monomers, and a second stage using a tubular reactor with flow profile standardisation for completion of polymerisation. This segmentation allows each stage to be optimised for its specific function, avoiding the need for high-mixing-strength equipment in the second stage where viscosity is highest.
Solution Approach 2:
The first polymerisation stage performs preliminary mixing and partial polymerisation before the material enters the second stage. By completing the mixing action and initial polymerisation in the first stage, the second stage receives material that is less viscous and easier to process, preventing blockages in the tubular reactor.
2Stability of the object's composition
If a static mixer is used as the main polymerisation stage, then mixing efficiency is improved, but production downtime increases due to obstructions and blockages
Solution Approach 1:
By segmenting the polymerisation into two stages with different functional requirements, the system avoids the blockage problem that causes downtime. The second stage uses a tubular reactor designed for high-viscosity flow rather than mixing, eliminating the obstruction problem of static mixers in the high-viscosity regime.
Solution Approach 2:
The first stage static mixer is designed for easy cleaning and maintenance. When blockages do occur in the first stage, the system can be quickly cleaned and returned to operation, minimizing production downtime compared to cleaning a tubular reactor.
3Manufacturing precision
If high molar mass homopolymers are produced, then product quality is improved, but melt viscosity increases causing pressure losses and obstructions
Solution Approach 1:
The polymerisation is segmented into two stages where the first stage produces intermediate products with lower viscosity, and the second stage completes the polymerisation to high molar mass homopolymers. This allows the system to handle high-viscosity materials in the second stage without causing blockages, as the tubular reactor is designed for high-viscosity flow.
Solution Approach 2:
The system changes the flow regime parameter between stages: the first stage operates with higher velocity and lower viscosity flow, while the second stage operates with lower velocity and higher viscosity flow. This parameter change allows the system to accommodate high molar mass products without excessive pressure losses.
4Productivity
If flow velocity is increased to improve production rate, then productivity is improved, but shear forces increase causing polymer degradation
Solution Approach 1:
The polymerisation process is segmented into two stages with different velocity profiles. The first stage uses higher velocities for rapid mixing and initial polymerisation, while the second stage uses lower, more controlled velocities to complete polymerisation without degrading the polymer. This segmentation allows high productivity in the first stage while protecting product quality in the second stage.
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 configuration enables reliable and efficient production of high-purity biodegradable polyesters and copolyesters, such as polylactide, by maintaining uniform flow profiles and reducing shear forces, which prevents polymer degradation and obstructions, allowing for continuous operation even at high viscosities.
Implementation Method 1
The baffles according to the invention now exert a flow resistance which is dimensioned specifically in the axial direction so that an almost uniform profile of the flow velocity over the tubular cross-section is attained
Implementation Method 2
A loop-type bubble column is a reactor which enables back mixing of the reaction mixture by guiding in a loop, as a result of which the polymerisation reaction can be facilitated
Implementation Method 3
maintaining uniform flow profiles and reducing shear forces, which prevents polymer degradation and obstructions
Data Source
AI summary
The present invention relates to a polymerization reactor for continuous polymerization, the reactor being constructed in two stages and comprising a prepolymerization stage which is configured as a stirred vessel or as a loop-type bubble column and also a main polymerization stage which is configured as a tubular reactor. Furthermore, the present invention relates to a method for the production of biodegradable polyester, in particular polylactide, the reactor according to the invention being used. Likewise, the invention relates to a polymerization device which comprises further components in addition to the polymerization reactor.