Ethylene Recovery via Pressure Swing Adsorption
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Solution Overview
Problem
The production of polyethylene is hindered by the high energy costs and capital expenses associated with purifying feedstocks, particularly due to the need for multiple distillation columns and cryogenic temperatures, and conventional methods for recovering unreacted ethylene are energetically unfavorable and costly.
Innovation Solution
A process involving the separation of polymerization product streams into gas and polymer streams, followed by distillation to yield a light hydrocarbon stream, which is then processed using a zeolitic imidazolate framework (ZIF) based purged hydrocarbon adsorber to selectively recover ethylene through pressure swing adsorption, achieving efficient ethylene recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple distillation columns and cryogenic temperatures are used to purify feedstock, then high purity monomer feedstock is achieved, but energy costs and capital expenses significantly increase
Solution Approach 1:
The patent changes the separation parameter from temperature-based distillation to pressure-based adsorption. By using pressure swing adsorption with ZIF-8 at elevated temperatures (20-100°C) and varying pressures (1-100 atm), the process achieves both high purity separation and energy efficiency, resolving the contradiction between purification quality and energy consumption
Solution Approach 2:
The patent replaces the mechanical distillation system with a chemical adsorption system. Instead of using complex mechanical distillation columns operating at cryogenic temperatures, the invention uses ZIF-8 molecular sieves that selectively adsorb ethylene through host-guest chemistry, eliminating the need for energy-intensive cryogenic mechanical systems
2Loss of substance
If conventional purification processes are used to recover unreacted ethylene, then ethylene recovery is achieved, but the process becomes energetically unfavorable and expensive
Solution Approach 1:
The patent changes the recovery parameter from temperature-based distillation to pressure-based adsorption. By operating at elevated temperatures (20-100°C) and varying pressures (1-100 atm), the process achieves high ethylene recovery through selective adsorption followed by pressure-driven desorption, eliminating the need for energy-intensive cryogenic distillation
Solution Approach 2:
The patent implements periodic pressure swing adsorption cycles with multiple beds operating in sequence. Beds are cycled between adsorption (high pressure) and desorption (low pressure) phases, with spent beds being regenerated by switching to the next bed in the sequence. This periodic operation achieves continuous ethylene recovery with minimal energy input compared to conventional continuous distillation
3Manufacturing precision
If multiple distillation columns are operated to produce high purity feedstock, then polymerization-grade monomers are obtained, but the infrastructure complexity and capital cost increase
Solution Approach 1:
The patent changes the separation mechanism from multi-stage thermal distillation to single-stage pressure-swing adsorption. By using ZIF-8's selective adsorption properties at different pressures, the process achieves polymerization-grade purity (≥99.9%) in a single unit operation, eliminating the need for multiple distillation columns and associated complex infrastructure
Solution Approach 2:
The patent extracts the separation function from complex thermal distillation infrastructure to a simpler adsorption-based system. By using ZIF-8 molecular sieves that selectively bind ethylene, the process achieves high-purity separation without requiring the complex network of distillation columns, condensers, reboilers, and cryogenic equipment, thereby reducing capital expenses and infrastructure complexity
Data Source
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AI summary
A process for component separation in a polymer production system comprising: (a) separating a polymerization product into a gas stream and a polymer stream; (b) processing the gas stream in distillation columns to yield a light hydrocarbon stream (LHS) comprising ethylene and ethane; (c) contacting LHS with a purged hydrocarbon adsorber to yield a loaded hydrocarbon adsorber and a non-adsorbed gas stream, wherein ethane is adsorbed by the purged hydrocarbon adsorber at a first pressure to yield adsorbed ethane, and wherein the non-adsorbed gas stream comprises recovered ethylene; (d) contacting the loaded hydrocarbon adsorber with a sweeping gas stream at a second pressure to yield an unloaded hydrocarbon adsorber and a recovered adsorbed gas stream comprising the sweeping gas stream and desorbed ethane; and (e) contacting the unloaded hydrocarbon adsorber with the sweeping gas stream at the first pressure to yield the purged hydrocarbon adsorber and a spent sweeping gas.