Control of zeolite framework flexibility for ultra-selective carbon dioxide separation

Area of Science:

• Materials Science
• Chemical Engineering
• Separation Science

Background:

• Molecular sieving membranes with uniform pores are crucial for efficient carbon dioxide (CO2) separation.
• All-silica zeolite membranes offer well-defined micropores but suffer from non-selective macropores formed during template removal (detemplation).
• These macropores significantly compromise the size-exclusion effect, hindering CO2 separation performance.

Purpose of the Study:

• To develop an advanced method for preparing ultra-selective all-silica zeolite membranes for CO2/CH4 separation.
• To address the issue of non-selective macropores in zeolite membranes by tuning zeolite flexibility.
• To enhance the practical applicability of all-silica zeolite membranes in gas separation processes.

Main Methods:

• A novel template modulated crystal transition (TMCT) approach was employed to tune the flexibility of Decadodecasil 3R (DD3R) zeolite.
• Instantaneous overheating at 700°C for one minute synchronized template decomposition with structure relaxation.
• Transitional conversion of organic template molecules into stable carbon species, followed by moderate thermal treatment for burnout.

Main Results:

• The developed membranes exhibited high CO2/CH4 selectivity ranging from 157 to 1,172.
• CO2 permeance was recorded between (890–1,540) × 10⁻¹⁰ mol m⁻² s⁻¹ Pa⁻¹.
• Significant CO2 flux (3.6 Nm³ m⁻² h⁻¹) and CO2/CH4 mixture selectivity (43) were achieved at high feed pressure (31 bar).

Conclusions:

• The TMCT approach effectively minimizes non-selective macropores, leading to ultra-selective all-silica zeolite membranes.
• The strategy demonstrates a viable pathway for overcoming limitations in zeolite membrane fabrication for gas separation.
• This method holds promise for the practical application of all-silica zeolite membranes in industrial CO2 capture processes.