Final report from Call 1 Project: Mixed matrix membranes for post-combustion capture

Written by Dr Maria-Chiara Ferrari, Lecturer at the University of Edinburgh. Principal Investigator on Call 1 Project: Mixed matrix membranes preparation for post-combustion capture

Membrane processes are considered as a promising alternative to the more classical post-combustion capture technologies due to the reduced maintenance of the process, the absence of dangerous solvents and their smaller footprint.

What progress has taken place since the last blog?

This project focussed on developing composite materials with polymers and fillers in order to control the properties of the membrane and understand what happens when you try to mix two different phases. Theoretically the mixed matrix should have enhanced properties in terms of separation but problems at the interface can nullify the improvements. What the project investigated is what happens when you mix two different phases in different quantities and how this affects the separation that we can obtain.

Composite materials of a commercial polymer (PEBAX) and a zeolitic imidazolate framework (ZIF8) have been prepared. PEBAX is easy to handle and form as a membrane and ZIF8 is used to tailor the properties to the specific CO₂/N₂ separation. After some optimisation of the preparation procedure we were able to form the membranes with different amount of ZIFs.

The materials were characterised looking at the difference in transport of CO₂ and nitrogen. For post combustion application, we want a material that lets carbon dioxide through preferentially, i.e: high permeability for CO₂, but also to hinder the transport of nitrogen, i.e: high selectivity.

Since the interaction between the two phases is crucial, we also took images of all the sample with a Scanning Electron Microscope (SEM) to look at the morphology of the composites.

What have the results shown?

Several mixed matrix materials have been prepared and tested. The results show that we were able to improve the permeability of the membranes for CO₂ while we were hindering the transport of nitrogen, creating composites with characteristics desired for a membrane separation process.

The images have shown that the nanoparticles embedded in the polymer can aggregate and form clusters during the drying of the membranes. This affects the final separation performance of the composite materials and it is the key parameter to control to obtain the desired properties.

What will happen next?

The results of the project have been published in a report to the UKCCSRC, and will be presented at the AIChE Annual meeting in November 2016. Nicholas Bryan is using the protocols and results from the project to obtain further improved mixed matrices in his PhD research. The understanding of the interactions between the 2 phases is crucial to develop new materials that can make CCS more economically viable.

The collaboration with Johnson Matthey is continuing through their support in the Advisory Board of several other projects.