Direct measurements of CO2 capture are essential to assess the technical and economic potential of algal-CCUS

Optimizing biogas methanation over nickel supported on ceria-alumina catalyst: Towards CO2-rich biomass utilization for a negative emissions society

Biogas methanation emerges as a prominent technology for converting biogas into biomethane in a single step. Furthermore, this technology can be implemented at biogas plant locations, supporting local economies and reducing dependence on large energy producers. However, there is a lack of comprehensive studies on biogas methanation, particularly regarding the technical optimization of operational parameters and the profitability analysis of the overall process. To address this gap, our study represents a seminal work on the technical optimization of biogas methanation obtaining an empirical model to predict the performance of biogas methanation. We investigate the influence of operational parameters, such as reaction temperature, H2/CO2 ratio, space velocity, and CO2 share in the biogas stream through an experimental design. Based on previous research we selected a nickel supported on ceria-alumina catalyst; being nickel a benchmark system for methanation process such selection permits a reliable data extrapolation to commercial units. We showcase the remarkable impact of studied key operation parameters, being the temperature, the most critical factor affecting the reaction performance (ca. 2 to 5 times higher than the second most influencing parameter). The impact of the H2/CO2 ratio is also noticeable. The response surfaces and contour maps suggest that a temperature between 350 and 450 °C and an H2/CO2 ratio between 2.5 and 3.2 optimize the reaction performance. Further experimental tests were performed for model validation and optimization leading to a reliable predictive model. Overall, this study provides validated equations for technology scaling-up and techno-economic analysis, thus representing a step ahead towards real-world applications for bio-methane production.

High pressure CO2 adsorption onto Malaysian Mukah-Balingian coals: Adsorption isotherms, thermodynamic and kinetic investigations

CO₂ sequestration into coalbed seams is one of the practical routes for mitigating CO₂ emissions. The adsorption mechanisms of CO₂ onto Malaysian coals, however, are not yet investigated. In this research CO₂ adsorption isotherms were first performed on dry and wet Mukah-Balingian coal samples at temperatures ranging from 300 to 348 K and pressures up to 6 MPa using volumetric technique. The dry S1 coal showed the highest CO₂ adsorption capacity of 1.3 mmol g^-1, at 300 K and 6 MPa among the other coal samples. The experimental results of CO₂ adsorption were investigated using adsorption isotherms, thermodynamics, and kinetic models. Nonlinear analysis has been employed to investigate the data of CO₂ adsorption onto coal samples via three parameter isotherm equilibrium models, namely Redlich Peterson, Koble Corrigan, Toth, Sips, and Hill, and four parameter equilibrium model, namely Jensen Seaton. The results of adsorption isotherm suggested that the Jensen Seaton model described the experimental data well. Gibb's free energy change values are negative, suggesting that CO₂ adsorption onto the coal occurred randomly. Enthalpy change values in the negative range established that CO₂ adsorption onto coal is an exothermic mechanism. Webber's pore-diffusion model, in particular, demonstrated that pore-diffusion was the main controlling stage in CO₂ adsorption onto coal matrix. The activation energy of the coals was calculated to be below -13 kJ mol^-1, indicating that adsorption of CO₂ onto coals occurred through physisorption. The results demonstrate that CO₂ adsorption onto coal matrix is favorable, spontaneous, and the adsorbed CO₂ molecules accumulate more onto coal matrix. The observations of this investigation have significant implications for a more accurate measurement of CO₂ injection into Malaysian coalbed seams.

CO2 bio-mitigation using genetically modified algae and biofuel production towards a carbon net-zero society

CO₂ sequestration carried by biological methodologies shows enhanced potential and has the advantage that biomass produced from the captured CO₂ can be used for different applications. Bio-mitigation of carbons through a micro-algal system addresses a promising and feasible option. This review mostly focused on the role of algae, particular mechanisms, bioreactors in algae cultivation, and genetically modified algae in CO₂ fixation and energy generation systems. A combination of CO₂ bio-mitigation and biofuel production might deliver an extremely promising alternative to current CO₂ mitigation systems. Bio mitigation in which the excess carbon is captured and bio fixation which the carbon is captured by algae or autotrophs and used for producing biofuel. This review revealed that steps for biofuel production from algae include factors affecting, harvesting techniques, oil extraction and transesterification. This review helps environmentalists and researchers to assess the effect of algae-based biorefinery on the green environment.

Maximizing Energy Content and CO2 Bio-fixation Efficiency of an Indigenous Isolated Microalga Parachlorella kessleri HY-6 Through Nutrient Optimization and Water Recycling During Cultivation

An alternative source of energy and materials with low negative environmental impacts is essential for a sustainable future. Microalgae is a promising candidate in this aspect. The focus of this study is to optimize the supply of nitrogen and carbon dioxide during the cultivation of locally isolated strain Parachlorella kessleri HY-6. This study focuses on optimizing nitrogen and CO₂ supply based on total biomass and biomass per unit amount of nitrogen and CO₂. Total biomass increased from 1.23 to 2.30 g/L with an increase in nitrogen concentration from 15.8 to 47.4 mg/L. However, biomass per unit amount of nitrogen supplied was higher at low nitrogen content. Biomass and CO₂ fixation rate increased at higher CO₂ concentrations in bubbling air, but CO₂ fixation efficiency decreased drastically. Finally, the energy content of biomass increased with increases in both nitrogen and CO₂ supply. This work thoroughly analyzed the biomass composition via ultimate, proximate, and biochemical analysis. Water is recycled three times for cultivation at three different nitrogen levels. Microalgae biomass increased during the second recycling and then decreased drastically during the third. Activated carbon helped remove the organics after the third recycling to improve the water recyclability. This study highlights the importance of selecting appropriate variables for optimization by considering net energy investment in terms of nutrients (as nitrogen) and CO₂ fixation efficiency and effective water recycling.

In Situ Dry Chemical Synthesis of Nitrogen-Doped Activated Carbon from Bamboo Charcoal for Carbon Dioxide Adsorption

In this work, nitrogen-doped bamboo-based activated carbon (NBAC) was in situ synthesized from simply blending bamboo charcoal (BC) with sodamide (SA, NaNH₂) powders and heating with a protection of nitrogen flow at a medium temperature. The elemental analysis and X-ray photoelectron spectra of as-synthesized NBAC showed quite a high nitrogen level of the simultaneously activated and doped samples; an abundant pore structure had also been determined from the NBACs which has a narrow size distribution of micropores (<2 nm) and favorable specific surface area that presented superb adsorption performance. The fcarbon dioxide (CO₂) adsorption of the NBACs was measured at 0 °C and 25 °C at a pressure of 1 bar, whose capture capacities reached 3.68–4.95 mmol/g and 2.49–3.52 mmol/g, respectively, and the maximum adsorption could be observed for NBACs fabricated with an SA/BC ratio of 3:1 and activated at 500 °C. Further, adsorption selectivity of CO₂ over N₂ was deduced with the ideal adsorbed solution theory ((IAST), the selectivity was finally calculated which ranged from 15 to 17 for the NBACs fabricated at 500 °C). The initial isosteric heat of adsorption (Qst) of NBACs was also determined at 30–40 kJ/mol, which suggested that CO₂ adsorption was a physical process. The results of ten-cycle adsorption-desorption experimentally confirmed the regenerated NBACs of a steady CO₂ adsorption performance, that is, the as-synthesized versatile NBAC with superb reproducibility makes it a perspective candidate in CO₂ capture and separation application.