LDPE Polymerization Monomer Removal via Vacuum Separation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current LDPE polymerization processes face challenges in achieving an unreacted ethylene monomer content below 50 ppm, requiring additional steps like pellet purging and ventilation, which are costly and environmentally undesirable.
Innovation Solution
A three-stage separation system is implemented, with a third separation vessel operating under vacuum pressure and no stripping agent, reducing unreacted ethylene monomer content to below 50 ppm without the need for purging or ventilation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional separation systems are used to remove unreacted ethylene monomer, then the separation process can operate with standard equipment, but the unreacted ethylene monomer content in the LDPE product remains above 50 ppm requiring additional purging steps
Solution Approach 1:
The patent applies parameter changes by operating the third separation vessel under vacuum pressure (reduced pressure parameter) and at elevated temperature, which changes the phase equilibrium parameters to enable more effective monomer removal. This parameter modification allows the separation system to achieve below 50 ppm monomer content without adding complex purging equipment downstream.
2Manufacturing precision
If additional purging and ventilation steps are added downstream to reduce unreacted monomer to below 50 ppm, then the monomer content requirement is met, but process costs increase and safety concerns arise
Solution Approach 1:
The patent applies preliminary action by performing the most effective monomer removal in the third separation vessel under vacuum before the material proceeds to downstream processing and storage. By removing the majority of monomer upfront under controlled vacuum conditions rather than through subsequent purging operations, the system achieves the required <50 ppm level while eliminating the need for dangerous downstream purging and ventilation steps.
3Manufacturing precision
If a third separation vessel operating under vacuum pressure is added to the separation system, then unreacted ethylene monomer content is reduced to below 50 ppm without purging, but the separation system complexity increases
Solution Approach 1:
The patent applies phase transitions by utilizing the vacuum-operated third separation vessel to create conditions where unreacted ethylene monomer transitions from dissolved state in the polymer melt to vapor phase. The vacuum pressure causes the monomer to flash-evaporate and be removed efficiently, achieving <50 ppm content through this phase change mechanism rather than requiring multiple additional separation stages.
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 eliminates the need for costly purging and ventilation steps, improves safety, and achieves the desired low unreacted ethylene monomer levels in the LDPE product, enhancing process efficiency and reducing costs.
Implementation Method 1
a third separation vessel having an operating pressure of less than or equal to 0.05 bar, wherein the third separation vessel produces a separation product comprising LDPE and less than or equal to 50 ppm of the unreacted ethylene monomer
Implementation Method 2
a third separation vessel having an operating pressure of less than or equal to 0.05 bar
Data Source
AI summary
Embodiments of a method for reducing unreacted ethylene monomer in a low density polyethylene (LDPE) polymerization process comprises: delivering a monomer feedstock comprising ethylene monomer to a compressor system to produce a pressurized feedstock having a pressure of at least 2000 bar; passing the pressurized feedstock to at least one free radical polymerization reactor to produce a reactor effluent comprising the LDPE and unreacted ethylene monomer; and delivering the reactor effluent to a separation system comprising a first separation vessel, a second separation vessel, and a third separation vessel in series, the third separation vessel having an operating pressure of less than or equal to 0.05 bar, wherein the third separation vessel produces a separation product comprising LDPE and less than or equal to 50 ppm of the unreacted ethylene monomer, wherein there is no stripping agent added upstream of the third separation vessel.