Two-step CO2 Research Articles

Enhanced porosity in marine biomass-derived activated carbon via two-step CO2 activation and acidic decontamination

Enhanced porosity in marine biomass-derived activated carbon via two-step CO2 activation and acidic decontamination

Synthesis, characterization, hysteretic two-step CO2 adsorption, and fluorescence properties of two isoreticular mixed-ligand pillared-layer frameworks

Two isostructural and isomorphrous metal–organic frameworks (MOFs), namely [Zn2(Brtpt)2 (bpBTD)]n (1) and {[Zn2 (ntpt)2 (bpBTD)]∙solvent}n (2), where bpBTD = bis(pyridin-4-yl)benzothiadiazole, H2Brtpt = 2-bromoterephthalic acid, H2ntpt = 2-nitroterephthalic acid, with thermal stability of 355 °C for 1 and 265 °C for 2 were hydro (solvo)thermally synthesized in DMF/H2O media at 100 °C. Single-crystal X-ray diffraction analysis revealed that 1 and 2 both possess 2-fold interpenetrating pillared-layer frameworks showing pcu net topology with the point symbol of 41,263. The sufficient extra-framework void spaces are approximately 30.1 % for 1 and 32.0 % for 2 with open channels along the b axis, where the window sizes are ca. 5.51 × 3.15 Å2 in edge for the former and ca. 5.47 × 3.44 Å2 and 3.12 × 3.44 Å2 in edge for the latter. Gas adsorption isotherms revealed that thermally activated 1 and 2 both hardly adsorb N2 with very low N2 uptakes at 77 K. Comparably, the CO2 adsorption isotherms of thermally activated 1 and 2 both revealed gate-opening (two-step) sorption behaviors with an apparent hysteretic adsorption–desorption process, where the maximum uptakes are 135.4 and 171.5 cm3 g−1 STP for 1 and 2, respectively, at 195 K and P/P0 = 1. Photoluminescence studies showed that 1 and 2 both emitted bpBTD-dominated ligand-centered emissions, being as cyan and pearl aqua color fluorescence centered at λem = 467 and 495 nm, respectively, in solid-state and as cyan color fluorescence centered at λem = 455 and 458 nm, respectively, in H2O suspensions.

High-Capacity, Cooperative CO2 Capture in a Diamine-Appended Metal-Organic Framework through a Combined Chemisorptive and Physisorptive Mechanism.

Diamine-appended Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) metal-organic frameworks are promising candidates for carbon capture that exhibit exceptional selectivities and high capacities for CO2. To date, CO2 uptake in these materials has been shown to occur predominantly via a chemisorption mechanism involving CO2 insertion at the amine-appended metal sites, a mechanism that limits the capacity of the material to ∼1 equiv of CO2 per diamine. Herein, we report a new framework, pip2-Mg2(dobpdc) (pip2 = 1-(2-aminoethyl)piperidine), that exhibits two-step CO2 uptake and achieves an unusually high CO2 capacity approaching 1.5 CO2 per diamine at saturation. Analysis of variable-pressure CO2 uptake in the material using solid-state nuclear magnetic resonance (NMR) spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reveals that pip2-Mg2(dobpdc) captures CO2 via an unprecedented mechanism involving the initial insertion of CO2 to form ammonium carbamate chains at half of the sites in the material, followed by tandem cooperative chemisorption and physisorption. Powder X-ray diffraction analysis, supported by van der Waals-corrected density functional theory, reveals that physisorbed CO2 occupies a pocket formed by adjacent ammonium carbamate chains and the linker. Based on breakthrough and extended cycling experiments, pip2-Mg2(dobpdc) exhibits exceptional performance for CO2 capture under conditions relevant to the separation of CO2 from landfill gas. More broadly, these results highlight new opportunities for the fundamental design of diamine-Mg2(dobpdc) materials with even higher capacities than those predicted based on CO2 chemisorption alone.

Ultrastructure, CO2 Assimilation and Chlorophyll Fluorescence Kinetics in Photosynthesizing Glycine max Callus and Leaf Mesophyll Tissues

The ultrastructural and functional features of photosynthesizing callus cells are poorly known. Electron microscopy studies on green, compact Glycine max calluses have shown that they are composed of photosynthesizing cells characterized by clear ultrastructural signs of senescence. Studies on chlorophyll fluorescence and CO2 assimilation kinetics have shown that such cells were still able to maintain photosynthesis but could not compensate for the respiratory CO2 uptake. Having a one-step CO2 assimilation kinetics, photosynthesis in calluses differed from photosynthesis in leaves, which had a two-step CO2 assimilation kinetics. In contrast to leaves, the fluorescence induction curves in G. max calluses strongly differed in shape depending on the color of actinic light (red or blue). Red (in contrast to blue) light excitation did not lead to CO2 assimilation in the calluses, thus suggesting anoxygenic photosynthesis in this case. In particular, the data obtained indicate that the actinic light spectrum should be considered when cultivating calluses for micropropagation of plants and for callus tissue research.

Experimental investigation of bypassed-oil recovery in tight reservoir rock using a two-step CO2 soaking strategy: Effects of fracture geometry

Experimental investigation of bypassed-oil recovery in tight reservoir rock using a two-step CO2 soaking strategy: Effects of fracture geometry

Isotherm modeling and techno-economic analysis of a TSA moving bed process using a tetraamine-appended MOF for NGCC applications

Tetraamine-appended metal-organic frameworks (MOF) are a new family of amine-functionalized MOF materials that show potential for CO2 capture from flue gas conditions relevant to natural gas combined cycle (NGCC) power plants. This work presents isotherm modeling of the tetraamine-appended MOF Mg2(dobpdc)(3-4-3)(dobpdc4−=4,4′-dioxidobiphenyl-3,3′dicarboxylate;3-4-3=N,N′bis(3-aminopropyl)-1,4-diaminobutane), process modeling, scale up, and a techno-economic optimization of a moving bed Temperature Swing Adsorption (TSA) process for carbon capture using this sorbent. This MOF exhibits a unique two-step CO2 adsorption profile in three different pressure ranges. Thus, arctangent-based logistic functions and, quadratic and Langmuir models were employed to represent such isotherm behavior. The results of the isotherm model show good fitting vs the experimental data with an RMSE of 0.41. To model the carbon capture process, the isotherm model was embedded into a moving bed contactor model, and this was used to simulate a TSA CO2 capture cycle and evaluate cost-optimal designs considering flue gas from a -650 MWe NGCC power plant. The capital cost model consists of CAPEX correlations for reactors, compressors, ducting, etc., while the operating costs include steam, water, chemicals, and electricity (following NETL's quality guidelines for energy systems studies). A techno-economic optimization of the capture system was performed by using NETL's Framework for the Optimization and Quantification of Uncertainty and Surrogates tool (FOQUS). Results suggest that a moving bed carbon capture system with tetraamine-appended MOF can be competitive compared to conventional MEA solvent-based capture processes for NGCC plants, when a heat recovery efficiency of at least 40% is achieved, and MOF materials can be produced at a cost below -$9/kg.

A 2D flexible cobalt-MOF: reversible solid-state structural transformation, two-step and gate-opening adsorption behaviours, and selective adsorption of C2H2 over CO2 and CH4.

A new 2D flexible cobalt(II) framework (Co-MOF) exhibits a reversible solid-state structural transformation upon guest molecule removal/uptake. After activation, Co-MOF-α with 1D porous channels transformed into Co-MOF-β (0D voids) accompanied by a shift in metal and carboxylate coordination modes, the rotation of organic linkers and the contraction of interstitial spaces. Gas adsorption experiments reveal that Co-MOF-β exhibits a two-step CO2 adsorption isotherm and close-to-open (type F-IV) isotherms for C2H2, C2H4 and C2H6 at 195 K. Moreover, it shows typical type I adsorption isotherms for the above gases and the selective uptake of C2H2 over CH4 and CO2 at room temperature.

Heterogeneous Hollow Multi-Shelled Structures with Amorphous-Crystalline Outer-Shells for Sequential Photoreduction of CO2.

Constructing delicate nano-/microreactors with tandem active sites in hierarchical architectures is a promising strategy for designing photocatalysts to realize the challenging but attractive CO2 reduction. Herein, hollow multi-shelled structure (HoMS) based microreactors with spatial ordered hetero-shells are fabricated, which achieve two-step CO2 -to-CH4 photoreduction. The multiple inner CeO2 shells increase the number of active catalytic sites to ensure efficient first-step reaction for generating CO, along with enriching the local CO concentration. The second-step CO-to-CH4 reaction is consequently induced by amorphous TiO2 (A-TiO2 ) composites on the adjacent outer-most shell, thus realizing the CO2 -to-CH4 conversion capability using one CeO2 @CeO2 /A-TiO2 HoMS. In-depth explorations in the microreactors provide compositional, structural, and interfacial guidance for engineering HoMS-based microreactors with temporally-spatially ordered shells toward efficient tandem catalysis.

Syngas production from two-step CO2 gasification of low rank coal in an entrained flow reactor

Using CO2 as feedstock for syngas production is one hot topic in the field of clean energy due to the concern of global warming. Hence, two-step gasification (pyrolysis first and then subsequent char gasification) behaviour using CO2 as reactant was investigated under entrained flow conditions for one Inner Mongolia lignite and two Victorian brown coals (Maddingely and Morwell). The effects of CO2 concentration (5–30% CO2) and residence time(0–23 s) were assessed in the low temperature ranges of 700–1000 °C. High temperature improved H2 and CO yield in entrained flow pyrolysis. The higher CO2 concentration and longer residence time enhanced gasification syngas yield and carbon conversion. Three coal chars required around 23 s of residence time for 100% conversion under 20% CO2 and 1000 °C. It indicated that entrained flow gasification of the three chars was preferably performed above 1000 °C for industrial applications. Fe-rich Victorian brown coal achieved better pyrolysis performance than Inner Mongolia lignite because of the inherent catalytic effect of Fe oxides in coal. Morwell coal char achieved the best char-CO2 gasification performance due to higher gasification reactivity and better pore structure. This study provides essential information for the optimization of entrained flow gasifiers toward syngas production using CO2 as feedstock.

A hybrid inorganic–biological artificial photosynthesis system for energy-efficient food production

Artificial photosynthesis systems are proposed as an efficient alternative route to capture CO2 to produce additional food for growing global demand. Here a two-step CO2 electrolyser system was developed to produce a highly concentrated acetate stream with a 57% carbon selectivity (CO2 to acetate), allowing its direct use for the heterotrophic cultivation of yeast, mushroom-producing fungus and a photosynthetic green alga, in the dark without inputs from biological photosynthesis. An evaluation of nine crop plants found that carbon from exogenously supplied acetate incorporates into biomass through major metabolic pathways. Coupling this approach to existing photovoltaic systems could increase solar-to-food energy conversion efficiency by about fourfold over biological photosynthesis, reducing the solar footprint required. This technology allows for a reimagination of how food can be produced in controlled environments.

Microcellular PLA/PMMA foam fabricated by CO2 foaming with outstanding shape-memory performance

Porous shape memory polymers (SMPs) are attracting people's attention due to their extensive application prospect. Herein, a novel and flexible method to produce bio-friendly polylactic acid (PLA)/polymethyl methacrylate (PMMA) shape memory foam by a two-step CO2 microcellular foaming is proposed. The achieved foams exhibit outstanding shape memory performance, such as a maximum shape fixity ratio of 98 %, a maximum shape recovery ratio of 86 %, and further the recovery ratio remaining more than 75 % even after 10 compression-recovery cycles. The additive PMMA phases uniformly disperse with spherical morphology in nanoscale, and they result in the greatly decreased crystallinity and crystal size of PLA. Meanwhile, the extensive interfaces lead to increased crystal density. In this context, more amorphous molecular chains left in the cell wall act as reversible segments, and more numerous denser crystals act as net points, which together can decrease the resistance in the shape memory process, thus, facilitating the significant promotion of shape memory capability of the as-achieved PLA/PMMA foams. Therefore, it exhibits a promising future to produce environmentally friendly SMPs by a simple, cost-efficient, and clean microcellular foaming technology.

A novel carbon cycle process assisted by Ni/La2O3 catalyst for enhanced thermochemical CO2 splitting

Thermochemical two-step CO2 splitting is a potential approach that fixes the sustainable resource into transportable liquid fuels. However, the harsh CO2 splitting conditions, the limited oxygen release kinetics and capacity of metal oxides block further promoted the CO yield and solar-to-fuel energy efficiency. Here, we propose a different carbon cycle assisted by Ni/La2O3 via coupling methane decomposition with thermochemical CO2 splitting, replacing conventional metal oxides cycle. Superior performance was demonstrated with methane conversion reached around 94% with almost pure H2 generation. Encouragingly, CO2 conversion of 98% and CO yield of 6.9 mmol g−1 derived from CO2 were achieved, with peak CO evolution rate (402 mL min−1 g−1) of orders of magnitude higher than that in metal oxide process and outstanding thermodynamic solar-to-fuel energy efficiency (55.5% vs. 18.5%). This was relevant to the synergistic activation of La2O3 and Ni for CO2 in carbon cycle, thus improving CO2 splitting reaction with carbon species.

Two-step CO2 and H2O splitting using perovskite-coated ceria foam for enhanced green fuel production in a porous volumetric solar reactor

Solar thermochemical cycles offer a viable option for the production of green synthetic fuels from CO2 and H2O. Two-step cycles using redox materials consist of a high-temperature reduction creating oxygen vacancies, followed by a re-oxidation step with an oxidant gas (CO2 and/or H2O), resulting in CO and/or H2 production. This study focuses on the thermochemical performance in a solar reactor of a new kind of composite reactive material: reticulated ceria foam with uniform perovskite coating, forming a dual-phase layered heterostructure. La0.5Sr0.5Mn0.9Mg0.1O3 (LSMMg) was selected as perovskite coating due to its high fuel productivity and thermochemical stability upon cycling. The perovskite coating improves the reduction step by increasing the reduction extent reached by the reactive material. The results revealed significant enhancement of oxygen exchange in the dual-phase composite material during reduction compared to individual components. The enhanced reduction extent had a beneficial effect on the oxygen release rate and the total amount of fuel produced by CO2 and H2O splitting, whereas an adverse impact on the peak rate during H2/CO evolution was noticed. Decreasing the reduction pressure allowed enhancing the non-stoichiometric oxygen extent, while the re-oxidation extent increased with the inlet oxidant molar fraction. With suitable operating conditions (reduction at 0.100 bar and oxidation in 100 % CO2), the LSMMg-coated ceria foam produced a higher amount of fuel but with lower fuel production rate in comparison with pure ceria foam. This study points out the beneficial effects of composite redox materials consisting of LSMMg-coated ceria foam in enhancing the oxygen exchange capacity of ceria for solar fuel production.

Rapid CO2 laser processing technique for fabrication of micro-optics and micro-structures on fused silica materials

Micro-optics and micro-structures play important roles in the field of optics. A multi-step processing strategy with the combination of various processing technologies has been applied to fabricate micro-optics and micro-structures. However, the multi-step processing method is complex and expensive. In this work, a rapid CO2 laser processing technique is proposed to fabricate micro-optics and micro-structures on fused silica materials. First, high-power and short-pulse CO2 laser is used to achieve rapid prototyping of micro-optics and micro-structures with pre-designed geometry on fused silica. In this step, a maximum material removal rate of 1.53 mm3/min could be achieved with surface roughness better than 100 nm. Then, using the same CO2 laser source with reduced laser power density, the initially processed fused silica surface could be smoothed to improve the surface quality. By simulating the CO2 laser interaction with fused silica material, the formation mechanism of smooth surface is revealed, and the processing parameters for achieving smooth silica surface are proposed. The surface roughness of finally processed silica surface could reach 10.8 nm. Finally, as an application example of the processed two-step CO2 laser processing method, a micro-structure with special hexagonal shape on fused silica optics is successfully processed. The proposed rapid CO2 laser processing technique for the fabrication of micro-optics and micro-structures on fused silica materials can be realized with only one equipment, which can not only ensure the processing accuracy and efficiency but also reduce the processing cost.

Flexible bifunctional monoethylphosphonate/carboxylates of Zn(ii) and Co(ii) reinforced with DABCO co-ligand: paradigmatic structural organization with pcu topology

The prototypal [M2(EtBCP)2(DABCO)0.5] MOFs, compliant with isoreticular expansion in two-dimensions, show flexibility manifested by a two-step CO2 adsorption isotherm, which might be associated to the “lever-action” of the metal-phosphonate moieties.

Experimental investigation of bypassed-oil recovery via CO2 soaking and huff and puff injection: Effects of miscibility and bypassed-oil size

A series of core-flood tests were performed, together with nuclear magnetic resonance measurements of the initial and residual oil saturation states in the cores, to investigate the recovery and mobilization of bypassed oil using a two-step CO2 soaking and ‘huff and puff’ (huff-n-puff) injection method. Two main factors of interest were focused on: miscibility and size of the bypassed oil. During the initial soaking operation, we found that the ability to remove bypassed oil varies according to the mode used and decreases in the order: first-contact miscibility (FCM), multi-contact (MCM), and immiscibility (IM). The corresponding oil recovery factors are 66.3%, 48.0%, and 28.4%, respectively. FCM also facilitates activation of the bypassed oil to the greatest depth (≥6 cm), followed by MCM (∼3 cm). However, the associated oil recovery factors were found to decrease significantly as the bypassed-oil size was increased from the initial value of 6 cm to 20 cm – where even the FCM mode becomes inefficient. Such size of 6 or 10 cm makes the use of FCM reasonably hopeful (oil recovered: 66.3% and 48.2%, respectively). Smaller ones (6 cm; oil recovery: 48.0%) may be promising for MCM usage (where 3 cm is the best size), but, a size far smaller than 6 cm is needed for IM mode to be effective. Furthermore, in terms of the overall total recovery factor achieved using the two-step soaking and huff-n-puff procedure (bypassed-oil size: 6–20 cm), MCM is the best mode (85.6–86.7%), followed by FCM (69.4–74.0%), and then IM (56.9–59.2%). The size of the bypassed-oil has little effect on the huff-n-puff injection step, which implies this step has a much greater effective activation depth than that of the previous soaking step.

In-situ DRIFTS study of two-step CO2 capture and catalytic methanation over Ru,“Na2O”/Al2O3 Dual Functional Material

Dual Function Materials (DFM) are composed of an alkali or alkaline earth CO2 adsorbent phase and a supported catalyst. It selectively captures CO2 which is then methanated using renewable H2. Both the capture and methanation steps are conducted at about 320 °C so no temperature swings are required allowing for continuous operation using two parallel reactors operating in tandem. This process approaches carbon neutral power generation by recycling the CH4 produced for re-combustion. This two-step process was studied by in-situ DRIFTS at 320 °C over 5%Ru-6.1%“Na2O”/Al2O3 DFM and compared with the 5%Ru/Al2O3 traditional methanation catalyst. In the DFM the Na2CO3/Al2O3 pre-curser is reduced to “Na2O” catalyzed by Ru metal. For both Ru/Al2O3 and DFM CO2 adsorbs on Ru active sites and Al2O3 OH groups during the capture step. For DFM large amounts of CO2 absorb on the Al-O−-Na+ species forming bidentate carbonates. During the H2 reduction step (i.e., methanation step), adsorbed bicarbonates and bidentate carbonates spill over onto the Ru-support interface, where methanation takes place through sequential hydrogenation with formates as reaction intermediaries. Although CO2 was mainly adsorbed on the alkaline support methanation occurs over Ru, supporting the hypothesis that the reaction occurs at the Ru-support interface. Therefore, the multiple adsorption sites over the DFM explain the high CO2 adsorption capacity by the formation of bidentate carbonates that spill over onto the Ru-support interface, during the two-step methanation process.

A 'Fluid' Nickel-Based Ferrite as an Efficient Redox Material for Thermochemical Two-Step CO <sub>2</sub> Splitting

The solar-driven, thermochemical two-step CO2 splitting reaction is essentially hindered by sintering of the redox material, and thermostable supports are often employed to alleviate this issue, although they usually play a limited role due to the harsh thermal condition. Herein, we demonstrate a distinct strategy, by engineering a “fluid” nickel-based ferrite material without using any support. It maintains a steady-state CO yield over 20 cycles, which is up to three times higher than that of the traditional NiFe2O4/ZrO2 material. Characterizations and first principles calculations suggest that its superiority can be attributed to the significantly enhanced flow of Fe cations, dramatically different from the NiFe2O4/ZrO2, where the oxygen ion undertakes the major transport. Such cation diffusion mode in our novel ferrite material provides a more accessible path to the bulk reaction, leading to a fast bulk reaction kinetics in the ferrite. Thus, we developed a new approach to overcome the sintering problem of ferrite materials.

A Two-step CO2 Mineralization Process

This communication briefly highlights our preliminary work on building a lab-scale, two-step CO2 mineralization process plant. Thermally activated serpentine was dissolved in one reactor to release Mg2+ ions without the use of any additive. CO2 from a flue gas (10 mol% CO2 in N2) was transformed into pure synthetic hydromagnesite at 90°C under ambient pressure conditions in a second reactor. A novel design for a solid dosing system was developed that allows for continuous feeding of activated serpentine particles. The operation under ambient pressure conditions, however, was found to be problematic with regards to liquid circulation between the reactors. Nevertheless, the experience from this work has allowed us to design a more robust experimental set-up for CO2 mineralization.

Enhancement of CP-titanum wear resistance using a two-step CO2 laser-sustained plasma nitriding process

In this paper, a method of forming hard, wide-area, crack-free, and wear-resistant nitrided cases on commercially-pure titanium using a 3.5kW CO2 laser-sustained plasma is described. This surface hardening method was comprised of two steps: (1) a laser-sustained nitrogen plasma was first used to nitride the titanium substrate; and (2) a laser-sustained argon plasma was then employed to remelt the nitrided layer deposited in the first step. Previous research using single laser trail experiments had shown that the (second) remelting step can eliminate cracks formed during the (first) nitriding step and homogenize the nitrided layer. In this work, the two-step nitriding-remelting process was extended to wider surface areas by depositing multiple overlapping trails at four different nitriding speeds and a constant remelting speed. The hardened layer was characterized using x-ray diffraction (XRD), optical metallography, and hardness testing. Reciprocating ball-on-flat wear tests were conducted to assess the wear resistance of the nitrided case, with the wear scar being characterized using scanning electron microscopy (SEM) and optical profilometry. Crack-free, hard cases of depths up to 600μm and average hardness values up to 641±86HV0.3 were observed. The LSP nitriding-remelting treatment was found to improve the wear resistance of the base metal (CP-Ti) by up to 80%.