Finishing Membrane Unit for Olefin Purification
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Solution Overview
Problem
Systems combining a C3/C4 splitter with membrane technology for producing polymer grade propylene often fall short of meeting product specifications due to limitations in controlling the purity of the overhead stream and feed, requiring slow and complex adjustments in reflux ratios and permeate pressure, which are not always feasible.
Innovation Solution
A membrane system that includes a main membrane unit and a finishing membrane unit, where the finishing membrane unit enhances propylene purity by adjusting the split stream flow and composition, using facilitated transport membranes with nanoporous support membranes and hydrophilic polymers, and metal salts to achieve a product stream with 99.5% or higher propylene concentration, while sharing compression systems for cost and space efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single membrane unit is used to produce polymer grade propylene, then the system complexity is reduced, but the product purity cannot meet specifications
Solution Approach 1:
The membrane separation system is divided into two distinct units: a main membrane unit for initial separation and a finishing membrane unit for final purification. This segmentation allows each unit to perform its specific function optimally, with the main unit handling bulk separation and the finishing unit achieving the required 99.5%+ purity, thereby resolving the contradiction between system simplicity and product purity.
2Manufacturing precision
If reflux ratio and permeate pressure are adjusted to meet product specifications, then product purity is improved, but the adjustment process becomes slow and complex
Solution Approach 1:
The main membrane unit performs preliminary separation to produce a permeate stream that is already close to specification (95-99.5 mol% propylene). This preliminary action reduces the burden on the finishing unit and allows the system to reach final specifications more quickly without requiring complex adjustments of reflux ratio and permeate pressure, as the two-unit configuration inherently provides better control.
3Device complexity
If a C3/C4 splitter is eliminated in favor of membrane-only separation, then the number of equipment items is reduced, but the ability to achieve carbon number separation is lost
Solution Approach 1:
The system merges the C3/C4 splitter with a two-stage membrane separation system. The membrane units are integrated into the existing distillation framework, where the main membrane unit handles olefin/paraffin separation and the finishing unit achieves final purification. This combination allows the system to maintain carbon number separation capability while reducing reliance on additional membrane equipment, thereby balancing equipment reduction with functional adaptability.
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 system effectively produces a high-purity propylene stream by cascading control from the main product stream to the split stream, ensuring the final product meets specifications with improved operational efficiency and reduced complexity, while also optimizing equipment usage and plot space.
Implementation Method 1
using facilitated transport membranes with nanoporous support membranes and hydrophilic polymers
Implementation Method 2
A permeate stream with a composition of 95 to 99.5 mol % propylene is then compressed
Implementation Method 3
facilitated transport membranes with nanoporous support membranes
Data Source
AI summary
A process and system to control the final product quality in a system for separating olefins and paraffins in a membrane system. A small finishing membrane stage is added to an existing membrane system that takes a slip stream from the product, purifies it to a very high concentration of propylene and blends it back into the product stream.