Multi-Stage Membrane Separation for Gas Plasticization
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Solution Overview
Problem
Current glassy polymeric membranes face challenges in organic vapor separations, such as olefin recovery and nitrogen removal from natural gas, due to plasticization issues and low selectivity, especially when exposed to condensable gases or liquids, limiting their performance and durability.
Innovation Solution
A multi-stage membrane process combining glassy polymeric membranes with chemically cross-linked rubbery polymeric membranes or high flux, cross-linked, fumed silica reinforced polyorganosiloxane membranes, which are designed to enhance selectivity and permeance for specific gas separations, including nitrogen and carbon dioxide removal from natural gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If glassy polymeric membranes are used for gas separation, then high selectivity for oxygen/nitrogen separation is achieved, but performance deteriorates when exposed to condensable gases or liquids due to plasticization
Solution Approach 1:
The process is divided into multiple stages with different membrane types (glassy polymeric membrane in first stage, rubbery polymeric membrane in second stage) to handle different separation tasks. This segmentation allows each membrane type to operate in its optimal performance range without being exposed to conditions that cause degradation.
Solution Approach 2:
The rubbery polymeric membrane acts as an intermediary stage between the feed gas and the final product, removing condensable gases and vapors that would otherwise plasticize and degrade the glassy polymeric membrane. This protective intermediary role preserves the long-term performance of the glassy membrane.
2Manufacturing precision
If glassy polymeric membranes are used for high selectivity separations, then capital cost decreases due to smaller membrane area required, but permeation rate is insufficient requiring extraordinarily large membrane surface areas
Solution Approach 1:
The separation process is segmented into two stages: the first stage uses glassy polymeric membrane for high-selectivity separation of permanent gases, while the second stage uses rubbery polymeric membrane for high-permeation rate removal of condensable gases. This segmentation allows the system to achieve both high selectivity and high productivity without requiring extraordinarily large membrane areas.
Solution Approach 2:
The invention merges the advantages of two different membrane types (glassy and rubbery polymeric membranes) into a single multi-stage process. The glassy membrane provides high selectivity for permanent gas separation, while the rubbery membrane provides high permeation rate for condensable gas removal, achieving both goals simultaneously.
3Manufacturing precision
If traditional glassy polymeric membranes are used in presence of heavy hydrocarbons and water, then separation performance is maintained, but condensation within membrane modules occurs and liquid hydrocarbons damage the membrane
Solution Approach 1:
The rubbery polymeric membrane serves as a protective intermediary that removes condensable heavy hydrocarbons and water vapor before they can reach and damage the glassy polymeric membrane. This intermediary layer prevents condensation within the membrane modules and protects against liquid hydrocarbon damage while maintaining separation performance.
Solution Approach 2:
The invention converts the potentially harmful presence of condensable gases and vapors into a beneficial separation opportunity. By using the rubbery polymeric membrane's high permeation rate for these condensables, the system transforms what would be damaging components into a separation target, removing them before they can harm the glassy membrane.
4Quantity of substance
If glassy polymeric membranes are used for nitrogen removal, then nitrogen permeability is higher than methane, but N2/CH4 selectivity is low at less than 5
Solution Approach 1:
The nitrogen removal process is segmented into two stages: the first stage uses glassy polymeric membrane to exploit nitrogen's higher permeability for initial removal, while the second stage uses rubbery polymeric membrane to achieve higher N2/CH4 selectivity. This segmentation allows the system to overcome the low selectivity limitation of single-stage glassy membranes.
Solution Approach 2:
The invention creates a composite membrane system combining glassy and rubbery polymeric membranes with different separation characteristics. The glassy membrane component provides nitrogen permeability, while the rubbery membrane component provides enhanced N2/CH4 selectivity, achieving both objectives through material composition.
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 combined membrane system improves permeance and selectivity over time, maintaining performance even with condensable gases, and achieves higher recovery rates for olefins and nitrogen, addressing the limitations of traditional glassy polymeric membranes.
Implementation Method 1
The separation of a polymeric membrane is based on a solution-diffusion mechanism. This mechanism involves molecular-scale interactions of the permeating gas with the polymer. The mechanism assumes that in a membrane having two opposing surfaces, each component is sorbed by the membrane at one surface, transported by a gas concentration gradient, and desorbed at the opposing surface.
Implementation Method 2
A pressure differential is maintained between the upstream and downstream sides, providing the driving force for permeation. The downstream side can be maintained as a vacuum, or at any pressure below the upstream pressure.
Implementation Method 3
In rubbery polymeric membranes such as polydimethylsiloxane membrane, permeant solubility coefficients are much more important than diffusion coefficient. Thus, these rubbery polymeric membranes preferentially permeate the larger, more condensable gases over the smaller, less condensable gases.
Data Source
AI summary
Combining the features of a glassy polymeric membrane and a rubbery polymeric membrane into a multiple membrane system provides a system having the advantages of both of the types of membranes. The membranes may be in any order in the system and multiple glassy polymeric membranes and multiple rubbery polymeric membranes may be used.