Collecting carbon dioxide is important in many commercial applications including the manufacture of fizzy drinks, refrigeration, oil recovery and alkaline water treatment. Membrane gas separation is one method of collecting and storing gases like CO2 from the air.
Due to natural porosity and low cost, metal–organic frameworks (MOFs) have earned a valuable position in membrane gas separation. Unfortunately though, MOFs have a limited performance due to their structure, creating a slow-uptake of the technique throughout the industry, that would bring down the cost for everyone.
In a preliminary investigation at Missouri University of Science and Technology, researchers have used 3D printing to demonstrate the feasibility of alternative MOF composite filters. Though there is still some fine-tuning to be done, the results prove promising for large-scale adoption.
Like for like adsorption
Grown as crystals in controlled thermal conditions, MOFs are composed of clustered metal ions, the likes of which are typically extracted from mineral stones. Instead of absorbing atoms of gas, MOFs adsorb molecules, collecting them on the surface for harvesting or recycling later.
In the Missouri S&T study, two free-standing MOF monoliths were 3D printed to match the physicality and structural make-up of typical powder equivalents: the first named MOF-74(Ni) and the second UTSA-16(Co).
Tested in an enclosed environment both monoliths registered a rate of absorbency comparable to its counterpart – the first achieving 79% of powder capability and the second attaining 87%.
Next generation gas filtration, and rockets into space
The results of Missouri S&T’s study, conducted by Harshul Thakkar, Stephen Eastman, Qasim Al-Naddaf, Ali A. Rownaghi and Fateme Rezaei, are published in the journal ACS Applied Materials & Interfaces.
Conclusions state “we believe this work provides a new proof-of-concept prospect for fabricating MOF monoliths that can be used for various adsorptive-based separation processes.”
Once successful, the structures could present a new wave of gas filtration systems, bringing down the cost of energy generation.
According to a study published in the Journal of Membrane Science, Volume 359, Issues 1–2, on average, conventional gas separation methods costs $40–100 per ton of CO2. By comparison, membrane-based separation is about $23 per ton. The process also requires only 16% of the energy produced by an example coal-fired power plant, whereas the alternative needs around 30%.
Through development, the MOFs studied here could also be tuned to a structure suitable for storing volatile hydrogen gas, which could be useful in the development of advanced space exploration vehicles.
Featured image shows carbonated cola bubbles with ice. Photo via Shutterstock