Nanocomposite Membrane Containing Bio-nanofibers and Mimic Enzyme for CO2 Separation

NanoMBE project aims to develop a bio-based nanocomposite membrane that can significantly increase the separation performance for CO2 capture from power plant flue gas (CO2/N2 separation) and the upgrading of biogas (CO2/CH4 separation). This nanocomposite membrane is designed to imitate the essential features of biomembranes, for example, the alveolus membrane in human lung. Synthetic bio-catalysts are to be introduced in the membrane to resemble the active site of enzymes in the mammal respiratory system. This type of membranes take advantages of the facilitated transport mechanism, the quick reaction of CO2 promoted by bio-catalysts and the high diffusion rate of gases or ions in water swollen polymers/nanofibers, which is expected to increase the CO2 permanence and selectivity at the same time and to break through the so-called Upper Bound. Specially tailored bio-nanofibers have been developed in this project, which may promote the exploit of bio-product from one of Norway's most important natural resources, i.e. trees. The success of this new technology is expected to reduce the environmental and climate impacts, and also increase the use of biogas as a renewable energy source. In particular, the project has been focused on developing and testing different types of nanocellulose in the application of fabrication CO2 separation membranes as well as investigating fundamental properties of the nanocomposite membrane materials, e.g., polymers, different types of nanocellulose, and their nanocomposites. For example, functionalized nanocellulose has been fabricated by TEMPO-oxidation to form COO- groups and phosphorylation to form O-HPO3-/O-PO3- groups on the surface to improve membrane performance. Polyamines have also attached to the surface aldehyde groups through amine coupling reactions. Nanocomposite membrane containing different types of nanocellulose has been fabricated, characterized and tested for the CO2/N2 and CO2/CH4 separation performance. The swelling and free volume as well as the nano-structures of PVA films and PVA/nanocellulose composites have been studied by various techniques. Free volume has been linked to gas permeation and understanding material structure is important with regards to understanding how the membrane works and can be improved. In addition, several polymers have been tested in order to optimize the polymer matrix for addition of nanocellulose and mimic enzyme. At the later stage of the project, the charge and size distribution of phosphorylated cellulose nanofibrils (P-CNF) have been studied and the effects of these properties on nanocomposite membranes for CO2 separation applications have been investigated. P-CNF of high charge (H-P-CNF) and screened size (H-P-CNF-S) were fabricated and used as nanofillers in the membranes, showing significantly improved separation properties. A transport mechanism is proposed; The addition of nanocellulose redistributes water in the composite to the nanocellulose/PVA interphase. A favorable pathway for CO2 -transport is created, where CO2 molecules can pass more easily due to a less tortuous path with higher CO2 solubility. During the project period, three Ph.D. candidates have defended their thesis, and four master students have completed their scientific training. The international collaboration with the US has been strengthened through exchange of students/researchers, including a 7-month research stay of the Ph.D. student Jonathan Torstensen at the NC State University in 2017 (Raleigh, North Carolina, USA). The research outcomes of the project also include the publication of 12 peer-reviewed scientific articles (e.g., Journal of Membrane Science, Biomacromolecules, Cellulose, and International Journal of Greenhouse Gas Control) and >12 presentations in international conferences (EuroMembranes, TCCS, and MRS).

The outcomes and impacts of the project can be summarized as 1) Advancement of knowledge and competences in the new field of nanocellulose-based membranes for CO2 capture and the mechanism of CO2 transport through this type of membranes with the presence of water vapor. Through communication and dissemination, the outcomes of the project have shown a significant impact in the scientific community, which could be the starting point of future research in several fields, not limited to CO2 capture applications. 2) Education for three Ph.D. students and four master students: The project has given students a high-quality scientific training, and the project results have been taken as examples in the classrooms as teaching materials at NTNU. 3) New project ideas have been derived, including a verification project (Mimic Enzyme Membrane, 2017), a Horizon2020 project entitled NanoMEMC2 (2016-2019), and a new Nano2021 project proposal (NanoHigh5, 2018).

The project entitled ?NanoMBE? ?Nanocomposite Membrane Containing Bio-nanofibers and Mimic Enzyme for CO2 Separation, is aimed to develop bio-based nanocomposite membranes that can significantly increase separation performance for CO2 capture from power p lant flue gas (CO2/N2 separation) and the upgrading of biogas (CO2/CH4 separation). A type of highly efficient nanocomposite membrane is designed using immobilized mimic enzyme with functionalized bio-nanofibers. This membrane takes advantages of the fac ilitated transport mechanism, the quick reaction of CO2 promoted by mimic enzyme and the high diffusion rate of gases or ions in water swollen polymers/nanofibers. The introduction of mimic enzyme (synthetic zinc complexes resembling the active site of C A enzymes) to mimic the bio-catalytic process of the CO2/HCO3- reaction cycle in the membrane is expected to increase CO2 permanence and selectivity of membranes at the same time and to break through the so-called ?upper bound?. The membrane is expected t o reach a high CO2 permeance (>10m3/m2 h bar) with CO2/N2 selectivity (>100) or CO2/CH4 selectivity (>45). Specially tailored bio-nanofibers are to be developed in this project, which may benefits the exploit of bio-product from one of Norway?s most impor tant natural resources, i.e. trees, so as to increases value creation based on natural resources. Despite of all these advantages, reports on such membranes for CO2 separation can barely be found. The success of the proposed new technology can significant ly reduce the environmental and climate impacts and promote the use of renewable energy in Norway.