High Pressure Polyethylene Flash Separation for Pelletization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High viscosity of polymers such as low density polyethylene homopolymers and copolymers incorporating polar comonomers like vinyl acetate makes pelletization difficult, especially at higher melt indices, due to low heat transfer coefficients and limited temperature reduction using conventional methods.
Innovation Solution
A continuous process for producing high pressure polyethylene involves contacting ethylene, a C2 to C12 modifier, and optionally a polar monomer with an initiator under polymerization conditions, followed by directing the reaction system effluent to a pressure separation unit to remove unreacted monomers, and recycling ethylene to achieve a temperature drop and improved pelletization performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional cooling methods are used to reduce polymer temperature for pelletization, then some temperature reduction is achieved, but the heat transfer coefficients are low and the resulting temperature reduction is limited and unsatisfactory
Solution Approach 1:
The patent extracts and removes unreacted monomer (ethylene and polar comonomer) from the polymer melt before pelletization through a flash separation unit. This extraction of volatile components reduces the monomer concentration in the polymer, which improves heat transfer efficiency during subsequent cooling and enables effective temperature reduction for pelletization of high melt index polymers.
2Manufacturing precision
If production rates are reduced to improve pelletization of high viscosity polymers, then pelletization quality improves, but productivity decreases
Solution Approach 1:
The patent performs preliminary removal of unreacted monomer through flash separation before the pelletization step. By removing volatile monomers in advance, the polymer melt achieves better thermal and rheological properties that enable high-quality pelletization at higher production rates, eliminating the need to reduce production speed for quality reasons.
3Reliability
If extruder and pelletizer conditions are optimized for softer copolymers, then pelletization performance improves, but the range of application is narrow
Solution Approach 1:
The patent changes the compositional parameter of the polymer melt by removing unreacted polar comonomer through flash separation. This parameter change (reducing monomer concentration) improves the melt's thermal and rheological properties, making it suitable for pelletization across a broader range of polymer types and melt indices, including softer copolymers and high melt index polymers that previously could not be pelletized effectively.
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 enhances the purity and pelletization performance of HPPE resin, allowing for increased production rates and improved processability by reducing unreacted monomer concentrations and achieving desired melt indices.
Implementation Method 1
directing an ethylene stream and the reaction system effluent to a pressure separation unit operated at separation conditions thereby removing at least a portion of the unreacted monomer from the reaction system effluent
Implementation Method 2
the ethylene recycle stream being at a temperature sufficient to cause a temperature drop at the pressure separator inlet of from 10.0°C to 140.0°C
Data Source
Figure 1
AI summary
A continuous process for producing high pressure polyethylene is described. The process includes contacting first amounts of ethylene, an optional polar comonomer, and a first C2 to C12 modifier in the presence of a first amount of initiator in a reaction system under polymerization conditions to form a reaction system effluent comprising a first polyethylene resin having a first concentration of unreacted monomer therein; and directing an ethylene stream and the reaction system effluent to a pressure separation unit operated at separation conditions thereby removing at least a portion of the unreacted monomer from the reaction system effluent.