Efficient separation of CO2 and hydrogen with new membrane

Researcher Meixia Shan has developed and tested a new polymer membrane that separates CO₂ and hydrogen very efficiently. On October 24^th Shan, who has already published about this new membrane in Science Advances, defends her PhD-thesis on this subject at TU Delft.

Hydrogen production
The production of hydrogen from hydrocarbons often results in the emission of CO₂. Thus, hydrogen needs to be separated from CO₂. Membrane-based separation has become a promising alternative to traditional separation processes to capture CO₂ owing to the great features such as energy efficiency and environmental friendliness. Among the different membrane materials, polymers are still the most used materials in the membrane market because they are very cheap and easy to process. ‘However, polymer membranes either can’t withstand high temperature or show poor separation performance. These membranes suffer from a trade-off between selectivity and gas permeability’, says Meixia Shan.

POFs and BILP
So called porous organic frameworks (POFs) are an emerging class of microporous polymers that have high CO₂ permeability and selectivity when being processed into membranes due to their intrinsic porosity and strong CO₂ adsorption ability. However, using POFs as membranes are still at the infancy stage due to their insolubility in most common solvents. ‘Now we have developed a new type of POF membrane called BILP (benzimidazole-linked polymer) that combines thermal and chemical stability with narrow pores, which makes it suitable for the separation of small molecules’, says Meixia Shan. ‘This newly developed membrane is synthesized on top of a porous aluminium oxide substrate by a facile interfacial polymerization method. Under high pressure and temperature, the membrane selectively lets small hydrogen molecules pass, but stops most of the carbon dioxide.’

Tests
Meixia Shan has tested the membrane with gas mixtures in the laboratory at 150 degrees Celsius for 800 hours. The selectivity turns out to be double that of existing membranes. ‘Our resulting membrane displays an excellent H₂/CO₂ separation performance. In addition, it is also very stable at high pressures (up to 10 bar) and high temperatures. These conditions are close to the real industrial H₂/CO₂ separation conditions.’

This high H₂/CO₂ separation performance, in combination with long-term stability means that POFs are promising candidates to be applied in membrane fields for CO₂ separation, including biogas upgrading, post-combustion CO₂ capture and pre-combustion capture.