Integrated Capture and Conversion of CO2 to Methane Using a Water-lean, Post-Combustion CO2 Capture Solvent

Glycerol-Derived Water-Lean Amines for Post-Combustion CO2 Capture: The Improvement in Capacity and Viscosity

Water-lean absorbents are regarded as a new generation of post-combustion CO2 capture technology that could significantly relieve those drawbacks posed by traditional aqueous alkanolamines. However, the exponential increase in viscosity during CO2 absorption remains an urgent issue that needs to be resolved before their practical deployment. In this work, novel water-lean amines based on biomass glycerol have been devised as single-component CO2 absorbents with low viscosity (79~110 cP at 25 ∘ C ${{\rm{{^\circ}C}}}$ , 29~39 cP at 40 ∘ C ${{\rm{{^\circ}C}}}$ ) under high capacity (12~18 wt % at 25 ∘ C ${{\rm{{^\circ}C}}}$ , 10~17 wt % at 40 ∘ C ${{\rm{{^\circ}C}}}$ ). The captured CO2 could be smoothly released by thermal desorption. Results from preliminary stability test and 10 absorption-desorption cycles showed that such non-aqueous absorbents had significant structural toughness as well as reusability. Spectroscopic measurements including 13C NMR and in situ FTIR were performed to gain mechanistic insights by monitoring the entire CO2 absorption and desorption process, while DSC, VLE and DFT calculations provided rational interpretation for reaction kinetics and thermodynamics. The synergistic promotion of glycerol ether group on both CO2 chemical and physical absorption was also verified under high pressure conditions.

Novel technologies for CO2 conversion to renewable fuels, chemicals, and value-added products

Population growth, urbanization, industrialization, and increased socioeconomic activities have escalated carbon dioxide (CO2) formation and concentration in the atmosphere. Increased generation and release of CO2 into the atmosphere exacerbates global warming and impedes environmental sustainability. One of the strategies to combat the unpleasant impact of CO2 in the atmosphere is the conversion of CO2 into useful products. This study reviews the benefits, drawbacks, and recommendations for effectively utilizing conventional, hybrid, and novel technologies for converting CO2 into energy and chemical products. The deficiencies noticed with chemical, thermal, biological, and catalytic CO2 conversion technologies (CTs) necessitated the use of hybrid conversion technologies such as biochemical, electrochemical, photocatalytic, and plasma chemical. The study posits that the development and deployment of novel CO2 CTs like bio-electrochemical, photo-electrochemical, and artificial photosynthesis will advance the research domain and revolutionize product formation. The transformation of CO2 into renewable fuels such as methane, syngas, and C2 fuels and chemical products such as methanol, formic acid, dimethyl carbonate, oxygenates, formaldehyde, and hydrocarbons is, eco-friendly, reduces air pollution, mitigates climate change, supports energy security, and provides valuable feedstocks for industries. The study recommends optimization of process parameters and reactor design configurations, increased funding, provision of regulatory framework and support, and partnerships among academia, industry players, and government agencies to achieve cost reduction, reduce environmental impacts, and combat drawbacks associated with CO2 CTs.

Application of Solid-Supported Amines for Thermocatalytic Reactive CO2 Capture

Reactive CO2 capture (RCC) is a promising strategy for process intensification of carbon capture and conversion for production of low-carbon fuels and chemicals. As state-of-the-art sorbent materials in point source and direct air capture systems, solid-supported amines are a natural choice to pair with supported CO2 hydrogenation catalysts (e.g., metallic nanoparticles) for developing high-capacity sorbent-catalyst materials for use in RCC. In this Perspective, we summarize the relevant literature combining solid-supported amines with metallic nanoparticles for thermocatalytic RCC and detail two of our own case studies using RCC to synthesize methane and methanol. Our observations suggest that the temperature mismatch between CO2 desorption and reaction, along with potential catalyst site poisoning by grafted aminosilanes, is a significant obstacle to realizing the potential of amine-based RCC materials in the decarbonization of chemical production. This stands in contrast to literature detailing successful RCC using liquid amines and solid catalysts, which may benefit from more favorable mass transfer dynamics, as well as early stage reports into RCC solid-phase amine-Pd materials, whose findings we were not able to replicate. More judicious reaction selection and synthetic design strategies to match materials with process conditions offer alternative pathways for future research.

Single-Pass Demonstration of Integrated Capture and Catalytic Conversion of CO2 from Simulated Flue Gas to Methanol in a Water-Lean Carbon Capture Solvent

Here, we demonstrate an integrated semibatch simultaneous CO2 capture and conversion to methanol process using a water-lean solvent, N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (2-EEMPA), that serves as both the capture solvent and subsequent condensed-phase medium for the catalytic hydrogenation of CO2. CO2 is captured from simulated coal-derived flue gas at a target >90 mol % capture efficiency, with a continuous slipstream of CO2-rich solvent delivered to a fixed bed catalytic reactor for catalytic hydrogenation. A single-pass conversion rate >60 C-mol % and selectivity >80 C-mol % are observed for methanol at relatively low temperatures (<200 °C) in the condensed phase of the carbon capture solvent. Hydrogenation products also include higher alcohols (e.g., ethanol and propanol) and hydrocarbons (e.g., methane and ethane), suggesting that multiple products could be made offering adaptability with varied CO2-derived products. Catalyst activity and selectivity are directly impacted by the water content in the capture solvent. Anhydrous operation provides high catalyst activity and productivity, suggesting that water management will be a critical parameter in real-world operation. Ultimately, we conclude that the integrated capture and catalytic hydrogenation of CO2 are chemically viable and potentially more energetically efficient and cost-effective than conventional separate capture and conversion approaches.

Tetrameric self-assembling of water-lean solvents enables carbamate anhydride-based CO2 capture chemistry

Carbon capture, utilization and storage is a key yet cost-intensive technology for the fight against climate change. Single-component water-lean solvents have emerged as promising materials for post-combustion CO2 capture, but little is known regarding their mechanism of action. Here we present a combined experimental and modelling study of single-component water-lean solvents, and we find that CO2 capture is accompanied by the self-assembly of reverse-micelle-like tetrameric clusters in solution. This spontaneous aggregation leads to stepwise cooperative capture phenomena with highly contrasting mechanistic and thermodynamic features. The emergence of well-defined supramolecular architectures displaying a hydrogen-bonded internal core, reminiscent of enzymatic active sites, enables the formation of CO2-containing molecular species such as carbamic acid, carbamic anhydride and alkoxy carbamic anhydrides. This system extends the scope of adducts and mechanisms observed during carbon capture. It opens the way to materials with a higher CO2 storage capacity and provides a means for carbamates to potentially act as initiators for future oligomerization or polymerization of CO2.

Fight for carbon neutrality with state-of-the-art negative carbon emission technologies

After the Industrial Revolution, the ever-increasing atmospheric CO2 concentration has resulted in significant problems for human beings. Nearly all countries in the world are actively taking measures to fight for carbon neutrality. In recent years, negative carbon emission technologies have attracted much attention due to their ability to reduce or recycle excess CO2 in the atmosphere. This review summarizes the state-of-the-art negative carbon emission technologies, from the artificial enhancement of natural carbon sink technology to the physical, chemical, or biological methods for carbon capture, as well as CO2 utilization and conversion. Finally, we expound on the challenges and outlook for improving negative carbon emission technology to accelerate the pace of achieving carbon neutrality.

Electrochemical reduction of CO2 in the captured state using aqueous or nonaqueous amines

CO2 capture and its electrochemical conversion have historically developed as two distinct technologies and scientific fields. Each process possesses unique energy penalties, inefficiencies, and costs, which accrue along the mitigation pathway from emissions to product. Recently, the concept of integrating CO2 capture and electrochemical conversion, or "electrochemically reactive capture," has aroused attention following early laboratory-scale proofs-of-concept. However, the integration of the two processes introduces new complexities at a basic science and engineering level, many of which have yet to be clearly defined. The key parameters to guide reaction, electrolyte, electrode, and system design would, therefore, benefit from delineation. To begin this effort, this perspective outlines several crucial physicochemical and electrochemical considerations, where we argue that the absence of basic knowledge leaves the field of designing metaphorically in the dark. The considerations make clear that there is ample need for fundamental science that can better inform design, following which the potential impacts of integration can be rigorously assessed beyond what is possible at present.

Next steps for solvent-based CO2 capture; integration of capture, conversion, and mineralisation

In this perspective, we detail how solvent-based carbon capture integrated with conversion can be an important element in a net-zero emission economy. Carbon capture and utilization (CCU) is a promising approach for at-scale production of green CO2-derived fuels, chemicals and materials. The challenge is that CO2-derived materials and products have yet to reach market competitiveness because costs are significantly higher than those from conventional means. We present here the key to making CO2-derived products more efficiently and cheaper, integration of solvent-based CO2 capture and conversion. We present the fundamentals and benefits of integration within a changing energy landscape (i.e., CO2 from point source emissions transitioning to CO2 from the atmosphere), and how integration could lead to lower costs and higher efficiency, but more importantly how CO2 altered in solution can offer new reactive pathways to produce products that cannot be made today. We discuss how solvents are the key to integration, and how solvents can adapt to differing needs for capture, conversion and mineralisation in the near, intermediate and long term. We close with a brief outlook of this emerging field of study, and identify critical needs to achieve success, including establishing a green-premium for fuels, chemicals, and materials produced in this manner.