Development of a hollow fiber membrane micro-reactor for biocatalytic production of formate from CO2

Biocatalytic Membranes for Carbon Capture and Utilization

Innovative carbon capture technologies that capture CO₂ from large point sources and directly from air are urgently needed to combat the climate crisis. Likewise, corresponding technologies are needed to convert this captured CO₂ into valuable chemical feedstocks and products that replace current fossil-based materials to close the loop in creating viable pathways for a renewable economy. Biocatalytic membranes that combine high reaction rates and enzyme selectivity with modularity, scalability, and membrane compactness show promise for both CO₂ capture and utilization. This review presents a systematic examination of technologies under development for CO₂ capture and utilization that employ both enzymes and membranes. CO₂ capture membranes are categorized by their mode of action as CO₂ separation membranes, including mixed matrix membranes (MMM) and liquid membranes (LM), or as CO₂ gas-liquid membrane contactors (GLMC). Because they selectively catalyze molecular reactions involving CO₂, the two main classes of enzymes used for enhancing membrane function are carbonic anhydrase (CA) and formate dehydrogenase (FDH). Small organic molecules designed to mimic CA enzyme active sites are also being developed. CO₂ conversion membranes are described according to membrane functionality, the location of enzymes relative to the membrane, which includes different immobilization strategies, and regeneration methods for cofactors. Parameters crucial for the performance of these hybrid systems are discussed with tabulated examples. Progress and challenges are discussed, and perspectives on future research directions are provided.

Strategies for overcoming the limitations of enzymatic carbon dioxide reduction

The overexploitation of fossil fuels has led to a significant increase in atmospheric carbon dioxide (CO₂) concentrations, thereby causing problems, such as the greenhouse effect. Rapid global climate change has caused researchers to focus on utilizing CO₂ in a green and efficient manner. One of the ways to achieve this is by converting CO₂ into valuable chemicals via chemical, photochemical, electrochemical, or enzymatic methods. Among these, the enzymatic method is advantageous because of its high specificity and selectivity as well as the mild reaction conditions required. The reduction of CO₂ to formate, formaldehyde, and methanol using formate dehydrogenase (FDH), formaldehyde dehydrogenase (F_aldDH), and alcohol dehydrogenase (ADH) are attractive routes, respectively. In this review, strategies for overcoming the common limitations of enzymatic CO₂ reduction are discussed. First, we present a brief background on the importance of minimizing of CO₂ emissions and introduce the three bottlenecks limiting enzymatic CO₂ reduction. Thereafter, we explore the different strategies for enzyme immobilization on various support materials. To solve the problem of cofactor consumption, different state-of-the-art cofactor regeneration strategies as well as research on the development of cofactor substitutes and cofactor-free systems are extensively discussed. Moreover, aiming at improving CO₂ solubility, biological, physical, and engineering measures are reviewed. Finally, conclusions and future perspectives are presented.

Towards Sustainable Oxalic Acid from CO2 and Biomass

To quickly and drastically reduce CO2 emissions and meet our ambitions of a circular future, we need to develop carbon capture and storage (CCS) and carbon capture and utilization (CCU) to deal with the CO2 that we produce. While we have many alternatives to replace fossil feedstocks for energy generation, for materials such as plastics we need carbon. The ultimate circular carbon feedstock would be CO2 . A promising route is the electrochemical reduction of CO2 to formic acid derivatives that can subsequently be converted into oxalic acid. Oxalic acid is a potential new platform chemical for material production as useful monomers such as glycolic acid can be derived from it. This work is part of the European Horizon 2020 project "Ocean" in which all these steps are developed. This Review aims to highlight new developments in oxalic acid production processes with a focus on CO2 -based routes. All available processes are critically assessed and compared on criteria including overall process efficiency and triple bottom line sustainability.

Single-Use Bioreactors for Human Pluripotent and Adult Stem Cells: Towards Regenerative Medicine Applications

Research on human stem cells, such as pluripotent stem cells and mesenchymal stromal cells, has shown much promise in their use for regenerative medicine approaches. However, their use in patients requires large-scale expansion systems while maintaining the quality of the cells. Due to their characteristics, bioreactors have been regarded as ideal platforms to harbour stem cell biomanufacturing at a large scale. Specifically, single-use bioreactors have been recommended by regulatory agencies due to reducing the risk of product contamination, and many different systems have already been developed. This review describes single-use bioreactor platforms which have been used for human stem cell expansion and differentiation, along with their comparison with reusable systems in the development of a stem cell bioprocess for clinical applications.

Polyethylenimine-Modified Membranes for CO2 Capture and in Situ Hydrogenation

Enzymatic CO₂ reduction can provide value-added chemicals from greenhouse gases at ambient temperature and pressure. However, poor solubility of CO₂ results in a low conversion rate. In this work, polyethylenimine (PEI) was attached onto the surface of poly(acrylic acid)-grafted (PAA-grafted) polyethylene membranes, and then, the membranes were used in an integrated process of CO₂ capture and in situ hydrogenation. Modification conditions were optimized with a surface amino group density of PEI-modified membranes as the characteristic parameter, and then, SEM, FTIR, and XPS analyses were conducted. The effect of PEI-modified membranes on enzyme-catalyzed CO₂ conversion to formic acid, regeneration conditions, and reusability were studied. The results show that when the grafting ratio of PAA increased, surface amino group density of PEI-modified membranes increased up to 6.00 × 10^-7 mol/cm² and then kept constant. The optimum modification time, temperature, and PEI concentration were 40 min, 40 °C, and 0.3 wt %. With the same concentration, PEI-1800 could bring more amino groups than PEI-600. SEM, FTIR, and XPS results further confirmed PEI attachment. Introduction of membrane-supported PEI with 5.86 × 10^-6 mol of amino groups facilitated greatly enzymatic CO₂ hydrogenation, and the initial reaction rate increased from 0.280 to 6.90 μM/min. After being regenerated in ammonia, PEI-modified membranes could be reused, and the relative reaction rate was, respectively, 88.0% and 65.7% after 5 and 10 cycles.