Enhanced CO2 Uptake Research Articles

Functionalization of pyrolyzed hydrochar with nitrogen containing deep eutectic solvent for carbon capture at low and high pressure

The purpose of this research is to evaluate the effectiveness of pyrolyzed hydrochar functionalized with nitrogen containing deep eutectic solvent (DES) in the absorption of CO2 under low- and high-pressure conditions. Pyrolyzed hydrochars were synthesized by hydrothermally carbonizing pine at the temperature of 200°C and 260°C, followed by pyrolysis at 600°C. These pyrolyzed hydrochars were impregnated with 3 different nitrogen containing DES namely choline chloride: urea, choline chloride: glycerol, and tetrabutylammonium bromide: glycerol all in 1:2 molar ratio. It was found that the functionalized pyrolyzed hydrochars were enhanced with nitrogen and oxygen functionalities (N-H, C-N, and CO). The results also show a substantial reduction in surface area for the functionalized pyrolyzed hydrochars, ranging from 10.19 to 227.74 m2g−1, compared to the surface areas of pyrolyzed hydrochars of 306–337 m2g−1. On the other hand, an increase in N content up to 38 % was identified after functionalization of pyrolyzed hydrochars. Upon conducting CO2 uptake at low (0.1–1 bar) and high (2.5–3.5 bar) pressure, the functionalized pyrolyzed hydrochars exhibited an CO2 uptake of up to 9.5 mmol/g at high pressure, which was attributed to the increased total nitrogen content, enhanced surface functionalities, and available micropore volume. The low-pressure isotherm for functionalized pyrolyzed hydrochars showed Langmuir-type isotherm, suggesting a monolayer adsorption. In contrast, the high-pressure isotherms were better fitted to the Freundlich isotherm, suggesting a multilayer adsorption behavior. It was concluded that the enhanced CO2 uptake is the result of the combined impact of increased surface functionalities and porosity, which results in improved physical and chemical adsorption mechanisms at the high pressure.

Tetraphenylanthraquinone and Dihydroxybenzene-Tethered Conjugated Microporous Polymer for Enhanced CO2 Uptake and Supercapacitive Energy Storage.

Conjugated microporous polymers (CMPs) feature extended excellent porosity properties and fully conjugated electronic systems, making them highly effective for several uses, including photocatalysis, dye adsorption, CO2 capture, supercapacitors, and so on. These polymers are known for their high specific surface area and adjustable porosity. To synthesize DHTP-CMPs (specifically TPE-DHTP CMP and Anthra-DHTP CMP) with abundant nitrogen (N) and oxygen (O) adsorption sites and spherical structures, we employed a straightforward Schiff-base [4 + 2] condensation reaction. This involved using 2,5-dihydroxyterephthalaldehyde (DHTP-2CHO) as the primary building block and phenolic OH group source, along with two distinct structures: 4,4',4″,4"'-(ethene-1,1,2,2-tetrayl)tetraaniline (TPE-4NH2) and 4,4',4″,4"'-(anthracene-9,10-diylidenebis(methanediylylidene))tetraaniline (Anthra-4Ph-4NH2). The synthesized Anthra-DHTP CMP had a remarkable BET surface area (BETSA) of 431 m2 g-1. Additionally, it exhibited outstanding thermal stability, as shown by a T d10 of 505 °C. Furthermore, for practical implementation, the Anthra-DHTP CMP demonstrates a significant capacity for capturing CO2, measuring 1.85 mmol g-1 at a temperature of 273 K and 1 bar. In a three-electrode test, the Anthra-DHTP CMP has a remarkable specific capacitance of 121 F g-1 at 0.5 A g-1. Furthermore, even after undergoing 5000 cycles, it maintains a capacitance retention rate of 79%. Due to their outstanding pore characteristics, abundant N and O, and conjugation properties, this Anthtra-DHTP CMP holds significant potential for CO2 capture and supercapacitor applications. This work will pave the way for the development of materials based on DHTP-CMPs and their postmodification with additional groups, facilitating their use in photocatalysis, photodegradation, lithium battery applications, and so on.

Efficient carbon dioxide capture using biodegradable surfactants in form of clathrate hydrate: New eco-friendly approach

CO2 hydrate formation kinetics are relatively slow, hindering large-scale implementation for carbon capture and storage. Amino acids have been widely investigated as green promoters for CO2 hydrate formation due to their potential in the CO2 uptake capacity. However, there is still a limited number of studies focusing on the application of biosurfactants for CO2 hydrate formation. In this study, four biodegradable surfactants (BSs), derived from castor oil, were investigated as efficient promoters for CO2 hydrate formation. BSs provided the highest promotion efficiency, enhancing CO2 uptake by 10 times and achieving a 50.19 % conversion degree compared to 6.45 % in pure water. An important characteristic of BSs is their high biodegradability, as demonstrated by a BOD/COD ratio of 52.2 % after 28 days. The combination of promotion power, non-foaming properties, and biodegradability makes BSs unique candidates for addressing the challenges associated with CO2 capture and storage using hydrate-based sequestration strategies.

Ultrafine Cu-Pd bimetallic clusters enhance asymmetric electron distribution to boost C-C coupling in photothermal CO2-to-ethanol conversion

Converting CO2 to ethanol through photothermal catalysis faces significant challenges due to it involves multi-electron reduction and kinetically sluggish C-C coupling process. Here, copper and a minor quantity of palladium are encapsulated within the cage of UiO-66 using a dual-solvent-sonication method to form ultrafine Cu2O/Cu-Pd clusters. The Cu-Cu2O serves as an electron center to enhance CO2 uptake and activation, while the incorporation of Pd accelerates H2 activation. Due to differences in electronegativity, electrons tend to transfer from Cu to Pd, which reduces the electrostatic repulsion between intermediates and facilitates the coupling of *CO and *CHO. The photothermal ethanol yield of Cu6Pd@UiO-66 reached 1077.69 μmol·gcat–1·mL–1 with a selectivity of 94.62%, representing an 11.64-fold increase over the non-illumination, and a 3.11-fold enhancement compared with Cu6@UiO-66. This study offers evidence supporting the promotion of C-C coupling through an asymmetric electron distribution, potentially advancing the conversion of CO2 to liquid products.

A general Energy-Efficient strategy for optimizing CO2 Capture: Designing and harnessing the rapid adsorption kinetics of Amine-Impregnated adsorbents

This study aims to optimize the performance of amine-impregnated CO2 adsorbents for both direct air capture (DAC) and point source CO2 capture (PSC) applications. The main objective of this study is to investigate the relationship between the weight fraction of amine loading and the efficiency of CO2 uptake on the designated support, aiming to find a straightforward method to design effective amine support materials. To this end, a composite material denoted as PEI/CNT@ZIF-8 has been developed. This composite is comprised of polyethylenimine (PEI), multi-walled carbon nanotubes (CNTs), and zeolitic imidazolate frameworks (ZIF-8). CNTs offer several advantages for enhancing CO2 uptake, including rearranging the ZIF-8 particles to facilitate PEI loading, creating strong electrostatic interaction for amine anchoring, and establishing CO2 diffusion channels to improve CO2 capture kinetics. In DAC scenarios, with a CO2 concentration of 400 ppm balanced with N2, the 25.0 wt% PEI/CNT(1)@ZIF-8(5) demonstrates superior CO2 uptake, achieving 4.08 mmol g−1 within a one-hour interval by harnessing the rapid kinetic region and exhibiting a low desorption energy of 55.8 kJ mol−1 for releasing CO2. In PSC scenarios, with a CO2 concentration of 15 vol% under both dry and wet conditions, the 37.5 wt% PEI/CNT(1)@ZIF-8(5) exhibits excellent CO2 uptake of 2.21 and 2.58 mmol g−1, respectively, at 50 ℃. The findings suggest that adjusting the balance between CO2 uptake and adsorption kinetics by considering the amine weight fraction can optimize the performance of solid amine CO2 adsorbents across diverse operational conditions. Furthermore, rather than relying on a single support material, this study reveals the potential of combining CNTs with materials such as SiO2 nanoparticles, Al2O3, or metal–organic frameworks (MOFs) to enhance CO2 capture performance. This approach holds promise as an effective and straightforward strategy.

Unusually large microporous HKUST-1 via polyethylene glycol-templated synthesis: enhanced CO2 uptake with high selectivity over CH4 and N2.

Porous solids with highly microporous structures for effective carbon dioxide uptake and separation from mixed gases are highly desirable. Here we present the use of polyethylene glycol (20,000g/mol) as a soft template for the simple and rapid synthesis of a highly microporous Cu-BTC (denoted as HKUST-1). The polyethylene glycol-templated HKUST-1 obtained at room temperature in 10min exhibited a very high Brunauer-Emmett-Teller (BET) surface area of 1904 m2/g, pore volume of 0.87 cm3/g, and average micropore size of 0.84nm. However, conventional HKUST-1 exhibits a BET surface area of 700-1700 m2/g confirming the advantages of using this method. X-ray powder diffraction and electron microscopy analysis confirm the formation of highly crystalline and uniform octahedral particles with sizes ranging from 100nm to 120µm. Adsorption isotherms recorded at temperatures between 273 and 353K and pressures up to 40bar revealed a more favorable adsorption capacity of HKUST-1 for CO2 vs. CH4 and N2 (708mg (CO2)/g, 214mg (CH4)/g and 177mg (N2)/g at 298K and 40bar). The Langmuir, isotherm model, and isosteric heats of adsorption were evaluated. The CO2 interaction at PEG-templated HKUST-1 is physical, exothermic, and spontaneous with DH° = - 6.52kJ/mol, DS° = - 13.72J/mol, and DG° = - 2.43kJ/mol at 298K at 40bar. The selectivities in equimolar mixtures were determined as 53 and 24, respectively, for CO2 over N2 and CH4. CO2 adsorption-desorption tests reveal high adsorbent reusability. The cost-effective and quickly prepared PEG-templated HKUST-1 demonstrates high efficacy as a gas adsorbent, particularly in selectively capturing CO2.

Analysis of the Impact of Nanofluids on the Improvement in CO2 Absorption using Taguchi Method

Capturing Carbon dioxide (CO2) has been the most crucial issue due to the dangerous impact of emissions of CO2 on the warming of globe and climate change. A novel class of solvent has been effectively employed in absorption technology in recent decades to eliminate CO2. The process of employing nanofluids to enhance CO2 uptake is receiving a lot of attention. However, other studies are needed to enhance the nanofluid absorption rate. The purpose of this study was to use nanofluid (based on amines) to optimize the absorption process for CO2 from flue gas. The technique was designed to extract CO2 from exhaust gas. This paper discusses the removal of CO2 from flue gas and parameter adjustments that increase overall removal efficiency. The nanoparticle concentration, stirring speed, and nanoparticle size were all varied during the tests. The experimental design using Taguchi method was applied to determine the optimal conditions of nanofluid for the process of absorption. Taguchi experimental design to investigate the perfect setting for the highest possible rate of CO2 absorption. The best settings were found to be a nanoparticle beginning concentration of 0.01 vol%, a stirrer speed of 4 rpm, and a nano size of 60 nm, according to the results of multiple regression and signal to noise ratio (S/N). Additionally, the analysis of variance (ANOVA) was used to determine the relative significance of each factor. The results show that the proportion of contributions were as follows: mixing speed (rpm) 46.56%, nano concentration (vol.%) 4.33%, and nano size (nm) 43.18%. The most useful parameter was the mixing speed (rpm). The experimental and anticipated values agreed well with regression analysis (R2=97.26%), and the findings of the confirmation test demonstrated that the CO2 absorption rate was 0.0029 g/s; a success that is highly advantageous for industrial uses.

Enhanced CO2 uptake of the coastal ocean is dominated by biological carbon fixation

Observational reconstructions indicate a contemporary increase in coastal ocean CO2 uptake. However, the mechanisms and their relative importance in driving this globally intensifying absorption remain unclear. Here we integrate coastal carbon dynamics in a global model via regional grid refinement and enhanced process representation. We find that the increasing coastal CO2 sink is primarily driven by biological responses to climate-induced changes in circulation (36%) and increasing riverine nutrient loads (23%), together exceeding the ocean CO2 solubility pump (41%). The riverine impact is mediated by enhanced export of organic carbon across the shelf break, thereby adding to the carbon enrichment of the open ocean. The contribution of biological carbon fixation increases as the seawater capacity to hold CO2 decreases under continuous climate change and ocean acidification. Our seamless coastal ocean integration advances carbon cycle model realism, which is relevant for addressing impacts of climate change mitigation efforts.

Active Learning-Based Guided Synthesis of Engineered Biochar for CO2 Capture.

Biomass waste-derived engineered biochar for CO2 capture presents a viable route for climate change mitigation and sustainable waste management. However, optimally synthesizing them for enhanced performance is time- and labor-intensive. To address these issues, we devise an active learning strategy to guide and expedite their synthesis with improved CO2 adsorption capacities. Our framework learns from experimental data and recommends optimal synthesis parameters, aiming to maximize the narrow micropore volume of engineered biochar, which exhibits a linear correlation with its CO2 adsorption capacity. We experimentally validate the active learning predictions, and these data are iteratively leveraged for subsequent model training and revalidation, thereby establishing a closed loop. Over three active learning cycles, we synthesized 16 property-specific engineered biochar samples such that the CO2 uptake nearly doubled by the final round. We demonstrate a data-driven workflow to accelerate the development of high-performance engineered biochar with enhanced CO2 uptake and broader applications as a functional material.

Direct CO2 capture from simulated and Ambient Air over aminosilane-modified hierarchical silica

Aminosilane-modified Hierarchical silica, HSA and HST-based adsorbents were synthesized by aminosilanization using Hierarchical silica (HS) with 3-aminopropyltriethoxysilane (APS) and N1-(3-trimethoxysilylpropyl)diethylenetriamine (TMPTA), respectively, and characterized to establish their physicochemical, structural, morphological, and porosity properties. Their CO2 adsorption performance was evaluated under direct air capture (DAC) conditions: 1) simulated air with CO2 concentration of 400 ppm in helium (He) at 30 °C and 2) indoor air with CO2 concentration ≥400 ppm at 30 °C, where HSA and HST modified with 70 wt% of respective aminosilanes outperformed others. The modified HS adsorbents showed an increase in kinetics, CO2 uptake under dry and humid conditions, stable cyclic adsorption-desorption performance, moderate enthalpy of desorption indicating a dominant chemisorption mechanism. Under dry and humid simulated air conditions (400 ppm CO2 in He), HSA-70 displayed a CO2 uptake of 0.82 mmol/g and 1.70 mmol/g, respectively, while HST-70 exhibited enhanced CO2 uptake of 1.54 mmol/g and 2.08 mmol/g, respectively. Cyclic stability of HSA-70 and HST-70 was confirmed through five thermal swing adsorption (TSA) cycles. In addition to this, their use for indoor air CO2 capture was also explored through ten short TSA cycles. Developed HSA-70 and HST-70 adsorbents exhibited more selectivity for CO2 over water, demonstrating their usage in practical direct air CO2 capture application.

Tuning the CO2 selective adsorption performance in MOFs by incorporating functional groups on the isophthalate skeleton

By introducing functional groups into the isophthalate ligand to decorate the pore of the MOFs, gas adsorption and separation performance can be tunable. In this paper, two isostructural 2D Co-MOFs, [Co(5-MIA)(bpy)]·H2O (1) and [Co(5-EIA)(bpy)]·H2O (2) (5-H2MIA = 5-methoxyl-isophthalic acid; 5-H2EIA = 5-ethyoxyl-isophthalic acid; bpy = 4,4′-bipyridine), with different functionalized pore surfaces and channel sizes were designed and constructed. The structures and performance of the two Co-MOFs were analyzed by SCXRD, PXRD, IR, TGA, and gas sorption (CO2, C2H2, CH4, CO, and N2). Attributed to the methoxyl of isophthalate skeleton, 1a (activated 1) shows enhanced CO2 uptake over other gases. In spite of decreased pore sizes (3.49 Å) compared with 2a (4.38 Å), the CO2 uptake of 1a (43.41 cm3 g−1) is larger than that of 2a (22.39 cm3 g−1) at 298 K and 100 kPa. Compound 1 incorporates methoxyl groups into the narrow channel, and exhibits the cooperative effect of CO2-preferential due to adsorbent-adsorbate coactions and size sieving. GCMC simulation has been used to explore the adsorption coactions of CO2 and 1, and the results confirmed that the methoxyl groups in the channel are the main binding sites of CO2. At ambient temperature and 100 kPa, the IAST selectivities of CO2/C2H2 (1:1), CO2/CH4 (1:1), C2H2/CH4 (1:1), CO2/CO (1:2) and CO2/N2 (15:85) on 1a were 2.6, 39.3, 13.3, 282 and 1433, respectively. The easy activation and regeneration, excellent thermal and humidity stability, and good reusability, make 1a hopeful adsorbent for adsorption and separation of CO2.

Electrochemical ocean alkalinity enhancement using a calcium ion battery

The oceans play a major role in moderating atmospheric CO2 levels. Enhanced CO2 uptake into ocean waters can be achieved by the provision of appropriate cations to the surface ocean, an approach known as ocean alkalinity enhancement (OAE). Here, we present a calcium ion battery approach that enhances alkalinity via electrochemical manipulation of seawater calcium concentrations. We demonstrate the efficacy of this approach using a potassium barium iron cyanide [K2BaFe(CN)6] (PBFC) electrode, a Prussian blue analogue, to move calcium ions from one reservoir of seawater to another. Using material and electrochemical characterization of the Ca2+ ion insertion and expulsion properties of PBFC in synthetic seawater, we determine the repeatability of Ca2+ ion insertion and expulsion from the PBFC electrode. Our analyses prove a 2.75 % increase in seawater alkalinity via the PBFC electrode, which yields 2.64 mg CO2 (0.72 mg C) uptake per liter of seawater. This proof-of-concept method offers a unique, low-cost, energy efficient electrochemical approach for atmospheric carbon dioxide removal that can combine with marine-based renewable energy to enable a new family of effective, scalable climate change solutions.

Construction of three-dimensional porous organic polymers with enhanced CO2 uptake performance via solid-state thermal conversion from tetrahedral benzoxazine-linked precursor

Porous organic polymers (POPs) with three-dimensional (3D) linkages have drawn great interest due to their potential applications in separation, adsorption, and sensing fields. Herein, a new 3D benzoxazine (BZ)-linked porous organic polymer (TPM-BZ-Py POP) was synthesized by linking a tetrahedral benzoxazine (TPM-BZ-Br4) with tetraethynylpyrene (Py-T) via Sonogashira coupling. Specifically, the synthesis of the tetrahedral benzoxazines with four oxazine rings in a single monomer involved the utilization of Schiff base formation, NaBH4 reduction as well as Mannich condensation reactions. To confirm the chemical structure of the benzoxazine monomers and their corresponding polybenzoxazines, Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H NMR), and carbon nuclear magnetic resonance (13C NMR) spectroscopy techniques were employed. The pore volume and specific surface area of the 3D TPM-BZ-Py POP were determined through N2 adsorption/desorption isotherms, and they were found to be 0.52 cm3/g and 185 m2/g, respectively. In addition, the solid-state chemical transformation occurred during thermal ring-opening polymerization (ROP), and the resulting 3D poly(TPM-BZ-Py) POP displayed higher CO2 capture ability (1.81 mmol/g) compared with TPM-BZ-Py POP (0.60 mmol/g) at room temperature. Such enhancement observed in poly(TPM-BZ-Py) POP was proposed to be caused by the formation of phenolic units and Mannich bridges within the polymer network by taking into consideration the structural transformation during the ring-opening polymerization (ROP). The functionalities in poly(TPM-BZ-Py) have great potential to interact with CO2 molecules through strong intermolecular hydrogen bonding or acid/base interactions, which further supports the benefit of incorporating oxazine rings into POP frameworks.

PCO2 decrement through alkalinity enhancement and biological production in a shallow-water ecosystem constructed using steelmaking slag

Ocean-based carbon dioxide removal has gained immense attention as a countermeasure against climate change. The enhancement of ocean alkalinity and the creation of new blue carbon ecosystems are considered effective approaches for this. To evaluate the function of steelmaking slag from the viewpoints of CO2 reduction and creation of new blue carbon ecosystems, we conducted a comparative experiment using two mesocosms that replicated tidal-flats and shallow-water ecosystems. Initially, approximately 20 seagrasses (Zostera marina) were transplanted into the shallow-water area in the mesocosm tanks. The use of steelmaking slag is expected to increase the pH by releasing calcium and mitigate turbidity by solidifying dredged soil. In the experimental tank, where dredged soil and steelmaking slag were utilized as bed materials, the pH remained higher throughout the experimental period compared with the control tank, which utilized only dredged soil. As a result, pCO2 remained consistently lower in the experimental tank due to mainly its alkaline effect (March 2019: −10 ± 6 μatm, September 2019: −130 ± 47 μatm). The light environment in the control tank deteriorated due to high turbidity, whereas the turbidity in the experimental tank remained low throughout the year. The number of seagrass shoots in the experimental tank was consistently approximately 20, which was higher than that in the control tank. Additionally, more seaweed and benthic algae were observed in the experimental tank, indicating that it was more conducive to the growth of primary producers. In conclusion, tidal-flat and shallow-water ecosystems constructed using dredged soil and steelmaking slag are expected to enhance CO2 uptake and provide a habitat for primary producers that is superior to those constructed using dredged soil only.

Influence of Polyethylenimine (PEI) in enhancement of microstructure and surface morphology of recycled construction and demolition waste aggregate in concrete by carbonation

This investigation explores the influence of Polyethylenimine (PEI) on the improvement of carbon dioxide (CO2) uptake, surface texture, and pore structure of construction and demolition waste (CDW) through carbonation. The study focuses on the coarser fraction of CDW (10 mm), which is pre-treated with varying concentrations of PEI before being carbonated. The resulting changes in pore structure, mineralogical composition, physical properties, and surface morphologies of the CDW are characterized using various techniques. The study also evaluates the impact of carbonated CDW on compressive strength. The results indicate that PEI modification of CDW enhances carbonation efficiency by reducing pores more effectively than non-treated CDW. This microstructural refinement is possible due to the formation of calcite and its products, facilitated by PEI adsorption into CDW, enhanced CO2 uptake, and formation of calcite products through carbonation. Additionally, PEI modification results in the formation of undulated plate-like structures that enhance surface morphology and compressive strength when used in concrete. The carbonation behavior of PEI-modified CDW in concrete was also investigated by analyzing carbonation depth and pH value. The results reveal that the optimal PEI concentration for enhancing the performance of CDW is 0.2. Overall, the study highlights the potential of PEI modification as an effective approach to improve the properties of CDW and its potential as a sustainable construction material.

A computational investigation on the roles of binding affinity and pore size on CO2/N2 overall adsorption process performance of MOFs through modifying MIL-101 structure

To develop an appropriate metal-organic framework to capture CO2 from dry flue gas, understanding the roles of structural modifications, location of primary adsorption sites and underlying adsorption mechanisms is crucial. Herein, effects of type, position and concentration of nitrogen-containing functional groups and C/N-substituted ligands are investigated on overall CO2/N2 adsorption process performance and mechanism of pristine and metal-substituted MIL-101 MOFs. In this investigation, density functional theory computations, grand-canonical Monte-Carlo, and molecular dynamics simulations are applied. Taguchi-based overall evaluation criteria objective function is also used to assess the overall adsorption performances of these MIL-101 MOFs in terms of CO2 uptake capacity, CO2/N2 selectivity, isosteric heat of adsorption and mass transfer resistance. The PBE/DZVP computations resulted in the CO2-framework binding energies ranging from −3.85 to −21.01 kJ/mol implying an acid-base type of physisorption. A correlation is introduced to estimate the CO2 uptake capacity from binding affinity and pore diameter of these MIL-101 MOFs. Mechanistic investigations show that to enhance CO2 uptake capacity and CO2/N2 selectivity, functionalization of the linker ligands is more successful than functionalization of the open metal sites having strong interactions with CO2 molecules. Results also showed that the best possible scenario to improve the overall adsorption process performance of MIL-101 is to substitute the C atom(s) of the BDC ligands with the N atom(s), regardless of the central metal atom type. The comprehensive molecular design approach introduced in this work can be used as a methodology by scientists for the development of new MOFs for practical CO2 capture applications.

High temperature CO2 capture in lithium orthosilicate packed fluidized bed: Gamma ray densitometry based numerical model and its experimental validation

BackgroundLithium orthosilicate (Li4SiO4) is steadily emerging as the default solid sorbent for high temperature CO2 capture in industrial settings. Li4SiO4 is also one the few materials qualified to serve as both catalyst and sorbent in sorption enhanced steam reforming process for high purity carbon neutral H2 production. Application of packed fluidization technique to enhance CO2 uptake in packed bed of pure Li4SiO4 particles has not been reported until now. MethodsGamma ray densitometry (GRD) technique is employed to non-intrusively obtain average voidage of Li4SiO4 packed fluidized bed as a function of operating time and axial bed coordinate. Based on the experimental results of GRD technique, a numerical model is developed to obtain the transient cross-sectional profiles of internal bed temperature and gas phase CO2 concentration as high temperature carbonation of Li4SiO4 progresses in packed fluidized bed. The numerical model is validated using experimentally obtained internal bed temperature and breakthrough curves. Temporal variation of bed effective thermal conductivity has been evaluated from model temperature profiles. FindingsIt was observed that the time averaged effective thermal conductivity and net solid weight gain of packed fluidized bed is around 1.7–2.3 and 1.1–1.3 times that of unary packed bed respectively at specified process parameters for high temperature CO2 capture.

Enhanced CO2 uptake is marginally offset by altered fluxes of non-CO2 greenhouse gases in global forests and grasslands under N deposition.

Despite the increasing impact of atmospheric nitrogen (N) deposition on terrestrial greenhouse gas (GHG) budget, through driving both the net atmospheric CO2 exchange and the emission or uptake of non-CO2 GHGs (CH4 and N2 O), few studies have assessed the climatic impact of forests and grasslands under N deposition globally based on different bottom-up approaches. Here, we quantify the effects of N deposition on biomass C increment, soil organic C (SOC), CH4 and N2 O fluxes and, ultimately, the net ecosystem GHG balance of forests and grasslands using a global comprehensive dataset. We showed that N addition significantly increased plant C uptake (net primary production) in forests and grasslands, to a larger extent for the aboveground C (aboveground net primary production), whereas it only caused a small or insignificant enhancement of SOC pool in both upland systems. Nitrogen addition had no significant effect on soil heterotrophic respiration (RH ) in both forests and grasslands, while a significant N-induced increase in soil CO2 fluxes (RS , soil respiration) was observed in grasslands. Nitrogen addition significantly stimulated soil N2 O fluxes in forests (76%), to a larger extent in grasslands (87%), but showed a consistent trend to decrease soil uptake of CH4 , suggesting a declined sink capacity of forests and grasslands for atmospheric CH4 under N enrichment. Overall, the net GHG balance estimated by the net ecosystem production-based method (forest, 1.28 Pg CO2 -eq year-1 vs. grassland, 0.58 Pg CO2 -eq year-1 ) was greater than those estimated using the SOC-based method (forest, 0.32 Pg CO2 -eq year-1 vs. grassland, 0.18 Pg CO2 -eq year-1 ) caused by N addition. Our findings revealed that the enhanced soil C sequestration by N addition in global forests and grasslands could be only marginally offset (1.5%-4.8%) by the combined effects of its stimulation of N2 O emissions together with the reduced soil uptake of CH4 .

Enhanced ethanol-driven carboxylate chain elongation by Pt@C in simulated sequencing batch reactors: Process and mechanism

Carboxylate chain elongation can create value-added bioproducts from the organic waste. The effects of Pt@C on chain elongation and associated mechanisms were investigated in simulated sequencing batch reactors. 5.0 g/L of Pt@C greatly increased the synthesis of caproate, with an average yield of 21.5 g COD/L, which was 207.4% higher than the trial without Pt@C. Integrated metagenomic and metaproteomic analyses were used to reveal the mechanism of Pt@C-enhanced chain elongation. Pt@C enriched chain elongators by increasing the relative abundance of dominant species by 115.5%. The expression of functional genes related to chain elongation was promoted in the Pt@C trial. This study also demonstrates that Pt@C may promote overall chain elongation metabolism by enhancing CO2 uptake of Clostridium kluyveri. The study provides insights into the fundamental mechanisms of how chain elongation can perform CO2 metabolism and how it can be enhanced by Pt@C to upgrade bioproducts from organic waste streams.

N-doped sponge-like biochar: A promising CO2 sorbent for CO₂/CH₄ and CO2/N₂ gas separation

Sponge-like biochar sorbents were prepared from the dissolution of chitosan followed by freeze-drying methodology and pyrolysis at three different temperatures (400, 600, and 800 °C) to produce sustainable N-enriched carbon materials with enhanced CO2 uptake from CO2/CH4 and CO2/N2 gas mixtures. The pyrolysis process was reproduced by operando TGA-IR to study the gas evolved from the pyrolysis process. It was found that the pyrolysis temperature highly influences the textural properties of the chitosan sponge-like biochar materials, impacting mainly the amount and type of the N-species on the sample but also at the microporosity. XPS revealed the transformation of the amino groups from chitosan into pyridinic-N, pyrrolic-N, graphitic center-N, and graphitic valley-N or pyridine-N oxide species during the pyrolysis process. Increasing the pyrolysis temperature enhanced the quantity of the latter two N-type species. All sponge-like biochars adsorbed higher amounts of CO2 compared with CH4 and N2 gases, with maximum CO2 uptake (∼1.6 mmol⋅g−1) at 100 kPa and 25 °C for the sample pyrolyzed at 600 °C (named CTO_P600). Biochar produced at 800 °C showed no longer adsorption capacity for CH4 and N2, having the highest selectivity value for CO2/N2 separation under continuous flux conditions among all prepared biochar sorbents. Isobaric CO2 adsorption measurements on the CTO_P600 sorbent revealed that physisorption phenomena predominantly governed the CO2 adsorption process, which was confirmed by its consistent adsorption capacity after 10 consecutive adsorption–desorption cycles. Moreover, the biochar exhibited tolerance to water vapor adsorption, indicating its suitability to work under moisture-rich conditions.