Silane-Crosslinked Polymer Membranes for Gas Separation
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Solution Overview
Problem
Current polymer membranes used for industrial gas separation, particularly cellulose acetate membranes, exhibit low permeability and selectivity, especially when exposed to high concentrations of acid and sour gases, leading to reduced performance over time due to plasticization and pore densification issues during high-temperature crosslinking processes.
Innovation Solution
The development of silane-crosslinked polymer membranes using moderate temperatures below the glass transition temperature of the membrane, employing acid catalysts for grafting and crosslinking, which preserves the porosity and morphology of asymmetric membranes, resulting in membranes with enhanced permeability and selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-temperature crosslinking is used to improve membrane permeability, then gas permeability increases, but pore densification and morphology collapse occur
Solution Approach 1:
The patent changes the temperature parameter from high-temperature crosslinking to moderate-temperature crosslinking (below glass transition temperature), which allows crosslinking to occur without causing pore densification or morphology collapse, thereby maintaining manufacturing precision while achieving improved gas permeability
Solution Approach 2:
The patent introduces silane modifiers to create a composite polymer system where silane groups crosslink with polymer chains, forming a composite structure that enhances gas permeability while maintaining pore morphology through the synergistic combination of polymer and silane components
2Reliability
If high-temperature crosslinking is used to enhance membrane selectivity, then separation performance improves, but non-selective defects are introduced
Solution Approach 1:
The patent changes the temperature parameter to moderate conditions below glass transition temperature, preventing the formation of non-selective defects while still achieving crosslinking that enhances separation selectivity through controlled molecular interactions
3Productivity
If crosslinking is performed above glass transition temperature to improve permeability, then membrane permeability increases, but asymmetric morphology is disrupted
Solution Approach 1:
The patent changes the temperature parameter to operate below the glass transition temperature, which maintains the rigid asymmetric morphology while still enabling crosslinking reactions that improve permeability through enhanced free volume and reduced polymer chain mobility
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 method produces membranes with CO2 permeability up to an order of magnitude greater than unmodified cellulose acetate, maintaining high selectivity and plasticization resistance, with CO2/CH4 selectivities of at least 20 and CO2 permeability of 20-60 Barrer, while avoiding the drawbacks of high-temperature crosslinking such as pore densification and non-selective defects.
Implementation Method 1
employing acid catalysts for grafting and crosslinking
Implementation Method 2
Crosslinking membranes with alkoxysilanes at temperatures significantly above the glass transition temperature of the membrane improves permeability in resulting membranes
Implementation Method 3
Moderate temperatures are elevated temperatures less than a glass transition temperature of the membrane
Implementation Method 4
preserves initial pore morphologies
Implementation Method 5
Polymer membranes are commonly used for gas separation to separate carbon dioxide and hydrogen sulfide out from natural gases
Implementation Method 6
membranes with CO2/CH4 selectivities of at least 20
Data Source
AI summary
Described in the present application are methods of producing silane-crosslinked polymer membranes at moderate temperatures using acid catalysts that, in certain embodiments, result in membranes with unexpectedly high permeabilities and selectivities. In certain embodiments, grafting and crosslinking of the silanes occur by immersing a preformed membrane in a solution comprising a silane and an acid catalyst. Alternatively, in certain embodiments, grafting of silanes to a polymer occurs in the presence of acid catalyst in solution and subsequent casting and drying produces crosslinked membranes. In certain embodiments, an acid catalyst is a weak acid catalyst. Also described in the present application are asymmetric crosslinked polymer membranes with porous layers. In certain embodiments, crosslinked cellulose acetate membranes have permeability up to an order of magnitude greater than the permeability of unmodified cellulose acetate membranes. The membranes have porous layers with a high porosity due to their processing in moderate conditions.