CO2 Carrier Research Articles

Biogas purification using cellulose nanocrystals/polyvinyl alcohol coated facilitated transport hollow fiber membranes with L‐arginine as CO2 carrier

AbstractThe composition of biogas consists mainly of CH4 (~60%) and CO2 (40%). To be considered a clean fuel, CH4 concentration in biogas must be increased to over 95%. In this study, membranes which were stacked in a chamber were utilized to purify biogas by passing biogas over them. These membranes were composed of polyethersulfone hollow fiber substrate coated with a “selective layer” made of cellulose nanocrystals (CNC‐0–2 wt) in polyvinyl alcohol (PVA) and l‐arginine as a CO2 carrier. Of the different CNC concentrations in PVA‐LA, CNC1/PVA‐LA (1.0 wt% CNC in PVA‐LA) displayed the lowest water contact angle of 17° (corresponding to higher moisture absorbing ability). With further increase in CNC concentration, even though CNC1.5/PVA‐LA showed the higher crystallinity (66%), and water contact angle increased (20°); reducing the chances of facilitated transport of CO2 through it. Biogas separation experiments were conducted at 90% RH and different feed pressures (0.8–1 bar) for various CNC concentrations. Increasing the CNC concentration led to a thicker selective layer, enhancing the CO2 permeability and selectivity up to CNC1/PVA‐LA. However, with the further addition of CNC, both permeability and selectivity decreased. At 90% RH and 1 bar feed pressure, the CNC1/PVA‐LA setup demonstrated a CO2 permeability of 20,522 Barrer and a selectivity of 33, making it suitable for low‐pressure biogas storage systems with lower energy requirements.

Constructing the high-efficiency “celluveyor conveyor” transport systems in membranes by IL@ZIF-8 for efficient CO2/CH4 separation

Inspired by the high-efficiency transport systems combined the “conveyor” transport pathways with the “celluveyor” transport pathways, the ionic liquid imide modified ZIF-8 (IL@ZIF-8) was prepared as a filler and incorporated into the self-polymerization-confined Pebax/polyethylene glycol methyl ether acrylate matrix (SPM) to prepare mixed matrix membranes (MMMs) for efficient CO2/CH4 separation. The incorporated IL@ZIF-8 can construct the high-efficiency “celluveyor conveyor” transport systems that consisted of the “celluveyor” transport pathways and the “conveyor” transport pathways, and it played important roles in MMMs. Therein, the “celluveyor” transport pathways can be constructed with the help of CO2 carriers (Zn2+) in oriented and ordered pore channels of IL@ZIF-8, contributing to promoting rapid CO2 transport in multiple direction. IL was uniformly distributed on ZIF-8, and it acted as “binder” between adjacent ZIF-8 in IL@ZIF-8. IL in IL@ZIF-8 can adsorb CO2 molecules as a consequence of its strong chemical affinity for CO2, and the “conveyor” transport pathways can be constructed with the help of CO2 carriers ([Tf2N]-) in IL for rapid CO2 transport between the adjacent ZIF-8, improving CO2 separation performance of MMMs. Consequently, it was possible to enhance the performance of CO2 separation by constructing the high-efficiency “celluveyor conveyor” transport systems in SPM/IL@ZIF-8 MMMs. Therefore, SPM/IL@ZIF-8 MMMs were endowed with the excellent CO2 separation performance. It showed an enhanced permeability for CO2, which increased by 96.9 %, and a better CO2/CH4 selectivity, which improved by 56.6 %, when compared to the performance of the pure SPM membrane. It implied that the constructed high-efficiency “celluveyor conveyor” transport systems in MMMs were a promising strategy for efficient CO2 separation.

Carbonation curing of cement-based materials by using potassium glycine solution: Uniformly CO2 sequestration and secondary strengthening

In this research, an internal carbonation curing method was proposed to achieve inside-outside synergistic carbon capture and performance improvement of cement-based materials. Potassium glycine (KG) solution with various concentrations was used as the CO2 carrier. The results indicate that the addition of CO2-rich KG solution increases 7-d and 28-d compressive strength by 29.8% and 16.2%, as well as achieving an overall CO2 uptake of 4∼11% in cement paste. However, at higher KG concentrations, the rapidly generated amorphous calcium carbonate covers the surface of cement particles, which shortens the setting time and inhibits early-age hydration. The presence of carbamate in CO2-rich KG solution improves the stability of metastable CaCO3 polymorphs and prolongs the period of dissolution-recrystallization. Calcite generated by the slowed recrystallization within 14 days having a filling and binding ability in the cement matrix, significantly reducing porosity and providing a secondary strengthening effect.

A potential CO2 carrier to improve the utilization of HCO3– by plant-soil ecosystem for carbon sink enhancement

IntroductionImproving the rhizospheric HCO3– utilization of plant-soil ecosystem could increase the carbon sink effect of terrestrial ecosystem. However, to avoid its physiological stress on the crop growth, the dosage of HCO3– allowed to add into the rhizosphere soil was always low (i.e., <5–20 mol/m3). ObjectivesTo facilitate the utilization of relatively high concentrations of HCO3– by plants in the pursuit of achieving terrestrial carbon sink enhancement. MethodsIn this study, the feasibility of directly supplementing a high concentration HCO3– carried by the biogas slurry to the plant rhizosphere was investigated using the tomato as a model plant. ResultsThe CO2-rich biogas slurry was verified as a potential CO2 carrier to increase the rhizospheric HCO3– concentration to 36 mol/m3 without causing a physiological stress. About 88.3 % of HCO3– carried by biogas slurry was successfully fixed by tomato-soil ecosystem, in which 43.8 % of HCO3– was assimilated by tomato roots for the metabolism, 0.5 ‰ of HCO3– was used by microorganisms for substances synthesis of cell structure through dark fixation, and 44.4 % of HCO3– was retained in the soil. The rest of HCO3– (∼11.7 %) might escape into the atmosphere through the reaction with H+. Correspondingly, the carbon fixation of tomato-soil ecosystem increased by 150.1 g-CO2/m2-soil during a tomato growth cycle. As for the global countries that would adopt the strategy proposed in this study to cultivate the tomato, an extra carbon sink of soil with about 1031.1 kt-C per year (i.e., an additional 0.21 tons of carbon per hectare soil) could be obtained. ConclusionThis would be consistent with the goal of soil carbon sink enhancement launched at COP21. Furthermore, the regions with low GDP per capita may easily achieve a high reduction potential of CO2 emissions from the agricultural land after adopting the irrigation of CO2-rich biogas slurry.

Highly selective production of light aromatics from co-catalytic fast pyrolysis of pre-deoxygenated biomass and hydrogen-rich polyethylene using a dual-catalyst system

Co-catalytic fast pyrolysis of torrefaction deoxygenated pine wood (PW) and high-density polyethylene (HDPE) in dual-catalyst (metal oxidize and zeolite) system is an effective technology to produce renewable bio-aromatics. In this work, the torrefaction deoxygenation pretreatment (TDP) was carried out to remove oxygen element from PW prior to catalytic fast pyrolysis (CFP). 56.90 % oxygen could be removed at TDP temperature of 300 °C, releasing in the oxygen carrier of CO2, CO, H2O, alcohols, acids, phenols, etc. Then, the synergistic effect between the metal oxide and the HZSM-5 in dual-catalyst system was also investigated. Among these metal oxides (Al2O3, MgO, CaO, ZnO, and Fe2O3) and hierarchical HZSM-5, the dual-catalyst of CaO and hierarchical HZSM-5 (treated by 0.2 M NaOH) was the optimal combination. The layout mode between feedstock and dual catalyst was also optimized. The highest yield of aromatics was produced in layout Mode 8, where the CaO was mixed with torrefied PW, but the hierarchical HZSM-5 and HDPE were laid in separated layers. The mixing of CaO and torrefied PW promoted the conversion of the macromolecular oxygenates into micromolecular oxygenates. Then, these small-molecular oxygenates could enter the hierarchical channel of HZSM-5, being converted into aromatics by undergoing the Diels-Alder reaction.

Modeling hydrodynamic and biomass pyrolysis effects of recycled product gases in a bubbling fluidized bed reactor

Fast pyrolysis of biomass in a fluidized bed reactor is typically conducted in a nitrogen gas environment. Recycling product gas can improve the economics of operating such a system by reducing reliance on pure process streams, but much less is known about how recycling pyrolysis product gas may affect fluidization behavior and pyrolysis kinetics. Therefore, gas effects in a fluidized bed biomass pyrolysis reactor were investigated using engineering correlations, low-order models, and CFD simulations for N2, H2, CO, CO2, and CH4 carrier gas mixtures. Our findings reveal viscosity of a gas mixture can be significantly underestimated depending on the model and correlation. Furthermore, fluidization characteristics such as Umf and gas-solid convective heat transfer can be greatly affected by the gas properties. By utilizing H2 as the fluidizing gas (instead of N2), while maintaining a constant fluidization ratio (Us/Umf), the bio-oil yields can be increased ∼5%. This is due to the lower density H2 producing similar hydrodynamics as N2 at higher gas flow rates. These higher flow rates result in shorter gas residence times, and as a result, less secondary reactions that convert bio-oil to light gases and char. Model results also suggest that bio-oil yield is not significantly affected by the type of carrier gas used, with bio-oil yield varying by ∼2% across different gas mixtures while maintaining constant flow rate. This indicates that recycled pyrolytic gas can be used as the carrier gas for biomass pyrolysis.

Advanced process design of subcooling re-liquefaction system considering storage pressure for a liquefied CO2 carrier

Because carbon capture and storage methods are considered greenhouse gas reduction technologies, demand for a large liquefied CO2 (LCO2) carrier to transport captured CO2 to storage sites has arisen. To prevent the emission of boil-off CO2 gas during transport, a CO2 re-liquefaction system would be required. This study suggests a new type of LCO2 subcooling re-liquefaction system for an LCO2 carrier and demonstrates its effectiveness by comparing its performance with that of conventional re-liquefaction systems considering LCO2 storage pressure. The results show that the suggested LCO2 subcooling system has lower specific energy consumption than that of conventional LCO2 re-liquefaction systems, even with a simpler configuration. At 15 bar of storage pressure, the LCO2 subcooling system has a lower specific energy consumption of 176.91 kJ/kgCO2, which is 18.2 and 5.3 % lower than that of the Linde–Hampson cycle and vapor-compression refrigeration cycle using NH3 as a refrigerant, respectively. Additionally, economic benefits can be obtained because the boil-off CO2 compressor is not required in an LCO2 subcooling system. Finally, considering CO2 re-liquefaction performance and the design constraints of the LCO2 carrier, 15 bar LCO2 storage conditions with a subcooling system are considered the most economical LCO2 carrier design.

CO2 Marine Transportation from a Techno-Energetic Perspective

CCUS (Carbon Capture, Utilization, and Storage) is a cornerstone of most proposed carbon dioxide (CO2) emissions strategies, as it is necessary to keep atmospheric CO2 concentrations below 450 parts per million by the year 2100 and, as such, prevent global warming. The Intergovernmental Panel on Climate Change (IPCC) predicts a removal capacity of 12 GtCO2/yr by 2050, whereas the present capability is 41 MtCO2/yr. Decarbonization may not be able to proceed quickly enough to reach net-zero emissions without CCUS technologies. In the maritime sector, CCUS serves a dual purpose: capturing CO2 from fossil fuel combustion and transporting the captured CO2 for its storage or utilization. This paper examines the importance of vessels as liquid CO2 carriers, emphasizing the transportation conditions associated with CO2. A techno-energetic analysis is carried out by studying various combinations of temperature and pressure. From a transport viewpoint, the findings indicate that reducing CO2 pressure is more cost-effective. In terms of pre-processing, higher CO2 pressures may lead to energy and, potentially, cost savings. However, the optimal pressure in the entire logistical chain remains uncertain. Further research is advised to broaden the scope of the chain to be analyzed.

Oxygen-Resistant CO2 Reduction Enabled by Electrolysis of Liquid Feedstocks.

Electrolytic CO2 reduction fails in the presence of O2. This failure occurs because the reduction of O2 is thermodynamically favored over the reduction of CO2. Consequently, O2 must be removed from the CO2 feed prior to entering an electrolyzer, which is expensive. Here, we show that the use of liquid bicarbonate feedstocks (e.g., aqueous 3.0 M KHCO3), rather than gaseous CO2 feedstocks, enables efficient and selective CO2 reduction without additional procedures for removing O2. This effect is made possible because liquid bicarbonate solutions, which serve as a liquid CO2 carrier, deliver high concentrations of captured CO2 to the cathode, while the low solubility of O2 in aqueous media maintains a low O2 concentration at the same cathode surface. Consequently, electrolyzers fed with liquid bicarbonate feedstocks create an environment at the cathode that favors the reduction of CO2 over O2. We validate this claim by electrochemically converting CO2 into CO with reaction selectivities of 65% at 100 mA cm-2 using a 3.0 M KHCO3 solution bubbled with 100% CO2 or 100% O2. Similar experiments performed with a gaseous CO2 feedstock showed that merely 0.5% of O2 in the feedstock reduced CO selectivity by >90% after 1 h of electrolysis. Our findings demonstrate that a liquid bicarbonate feedstock enables efficient CO2 reduction without the need for expensive O2 removal steps.

Electrifying Carbon Capture by Developing Nanomaterials at the Interface of Molecular and Process Engineering.

ConspectusCarbon capture is an indispensable step toward closing the anthropogenic carbon cycle. However, the large-scale implementation of conventional thermochemical carbon capture technologies is hindered by their low energy efficiency, limited sorbent stability, and complexity in infrastructure integration. A mechanistically different alternative, commonly known as electrochemically mediated carbon capture (EMCC), has garnered increasing research traction over the past few years and relies on electrochemical stimuli instead of thermal or pressure swings for the capture and release of carbon dioxide (CO2). Compared to conventional methods, EMCC can be operated under mild conditions driven by intermittent renewable energy sources and has a flexible design to meet the multiscale demands of carbon capture, offering a potentially sustainable, energy-efficient, and cost-effective solution to CO2 concentration from dilute mixtures or the ambient environment.Nanomaterials have played a crucial role in carbon capture research. For instance, nanoporous materials can provide increased free volumes, surface areas, and active sites for carbon capture through physical or chemical adsorption from the gaseous phase. In contrast, EMCC relies on chemical absorption via acid-base interactions using solubilized CO2 in electrolytes. Therefore, most EMCC sorbents and mediators explored so far have been developed as molecules rather than nanomaterials. In recent years, our team has been focusing on electrifying the carbon capture processes at the molecular, materials, and process levels. We seek to address the most pressing issues associated with EMCC, either in fixed-bed or flow systems, that prevent their practical use. These issues include parasitic reactions with molecular oxygen, insufficient electrode capacity utilization, sorbent crossover, etc. To address these problems, there is an urgent need to develop rationally designed nanomaterials at the interface of molecular electrochemistry and device engineering. This Account provides an overview of recent progress on developing new chemistries and engineering batch/continuous processes for EMCC. We discuss the limitations of current EMCC technology and emphasize why nanomaterials are critical for electrifying carbon capture. First, we introduce the design principles for EMCC sorbents based on redox-active organic CO2 carriers and discuss metrics for their performance evaluation. Second, we showcase how molecular design can tackle problems of sorbent solubility, oxygen stability, and electrolyte compatibility in EMCC. Third, we discuss the early results of nanomaterials as solid sorbents in fixed-bed systems, nonswelling membranes for flow systems, and high-surface-area gas-liquid contactors. Finally, building on the foundation we established through our prior work, we offer perspectives on future directions for nanomaterials to help address the challenges in EMCC.

Application of Fuel Cold Energy in CO2 Bog Reliquefaction System on Ammonia-Powered CO2 Carrier

Abstract A CO2 boiled off gas (CO2 BOG) reliquefaction system using liquid ammonia cold energy is designed to solve the problems of fuel cold energy waste and the large power consumption of the compressor in the process of CO2 BOG reliquefaction on an ammonia-powered CO2 carrier. Aspen HYSYS is used to simulate the calculation, and it is found that the system has lower power consumption than the existing reliquefaction method. The temperature of the heat exchanger heater-1 heat flow outlet node (node C-4) is optimised, and it is found that, with the increase of the node C-4 temperature, the power consumption of the compressor gradually increases, and the liquefaction fraction of CO2 BOG gradually decreases. Under 85% conditions, when the ambient temperature is 0°C and the temperature of node C-4 is -9°C, the liquid fraction of CO2 BOG reaches the maximum, which is 74.46%, and the power of Compressor-1 is the minimum, which is 40.90 kW. According to this, the optimum temperature of node C-4 under various working conditions is determined. The exergy efficiency model is established, in an 85% ship working condition with the ambient temperature of 40°C, and the exergy efficiency of the system is the maximum, reaching 59.58%. Therefore, the CO2 BOG reliquefaction system proposed in this study could realise effective utilisation of liquid ammonia cold energy.

Efficient photocatalytic CO2 methanation via promoted conversion of bridge *CO over surface K+ on ultrathin TiO2

The efficient conversion of CO2 to carbon-neural fuels by photocatalysts can effectively address the increasingly prominent challenges of environmental pollution and energy shortage. TiO2 is considered a promising photocatalyst. However, its disadvantages, such as poor adsorption of CO2 and low carrier separation efficiency, inhibit its performance and selectivity in photocatalytic CO2 reduction. Herein, K+-modified anatase TiO2 ultrathin nanosheet photocatalysts were obtained via a reverse etching method using K2Ti8O17 as the precursor. The selectivity of the optimized photocatalyst for methane was 96.02% in a gas–solid system without additives, with an excellent photocatalytic rate of 42.3 μmol·g−1·h−1, which was 3.39 times higher than that of P25. The effects of K+ on photocatalytic behaviors and the selectivity of CH4 was systematically investigated. The test results showed that during treatment with formic acid, a large amount of K+ from the layered K2Ti8O17 were removed and the original structure was destroyed. Therefore, highly dispersed TiO2 nanosheets were obtained, with a small amount of K+ remaining on the TiO2 surface. The well-defined rectangular shapes of TiO2 reduce the transmission distance of photogenerated carriers, whereas the presence of K+ increase the chemisorption of CO2 molecules, thereby activating CO2, promoting the conversion of bridge *CO to -CHO, and increasing CH4 production. This study provides insightful references for the preparation and modification of traditional photocatalysts for photocatalytic CO2 reduction reactions.

Internal carbonation reinforcement of cementitious materials: Mechanism and performance

Cement carbonation technologies are garnering increasing interest, but most CO2 curing methods have limited on-site applications. In this study, a CO2 internal curing route was presented and proven to be feasible. Zeolite NaX was selected as a CO2 carrier due to its good adsorption capacity (16.2 g CO2/100 g drying zeolite) and stability (0.16% weight loss) at room temperature for internal carbonation of cement. CO2-saturated zeolite released the adsorbent once it was exchanged by water molecules during the mixing process, and the dissolved CO2 in the paste solution produced carbonation products. It was discovered that, unlike the main products (calcite polymorphs) in CO2 curing conditions, monocarbonate and calcite were the primary carbonation products in CO2 internal curing cement composites. In addition to accelerating the hydration of C3S, zeolite NaX was found to react with cement systems and facilitate the formation of aluminocarbonates. The resulting composites exhibited quicker and higher strength development, increased modulus, reduced porosity, smaller pore intrusion radius, and minimal volume expansion. Moreover, the formation of monocarbonate was found to be correlated with the volume expansion of the composite system, as determined through thermodynamic calculations and autogenous shrinkage experiments. Finally, the composites exhibited a carbon sequestration capacity of 4.86 g CO2/100 g dry solid composites, with 71% of the CO2 being solidified in minerals.

Supercritical Fluid Nanospray Mass Spectrometry: II. Effects on Ionization.

Nanospraying supercritical fluids coupled to a mass spectrometer (nSF-MS) using a 90% supercritical fluid CO2 carrier (sCO2) has shown an enhanced desolvation compared to traditional liquid eluents. Capillaries of 25, 50, and 75 μm internal diameter (i.d.) with pulled emitter tips provided high MS detection sensitivity. Presented here is an evaluation of the effect of proton affinity, hydrophobicity, and nanoemitter tip size on the nSF-MS signal. This was done using a set of primary, secondary, tertiary, and quaternary amines with butyl, hexyl, octyl, and decyl chains as analytes. Each amine class was analyzed individually to evaluate hydrophobicity and proton affinity effects on signal intensity. The system has shown a mass sensitive detection on a linear dynamic range of 0.1-100 μM. Results indicate that hydrophobicity has a larger effect on the signal response than proton affinity. Nanospraying a mixture of all amine classes using the 75 μm emitter has shown a quaternary amine signal not suppressed by competing analytes. Competing ionization was observed for primary, secondary, and tertiary amines. The 75 and 50 μm emitters demonstrated increased signal with increasing hydrophobicity. Surprisingly, the 25 μm i.d. emitter yielded a signal decrease as the alkyl chain length increased, contrary to conventional understanding. Nanospraying the evaporative fluid in a sub-500 nm emitter likely resulted in differences in the ionization mechanism. Results suggest that 90% sCO2 with 9.99% methanol and 0.01% formic acid yielded fast desolvation, high ionization efficiency, and low matrix effect, which could benefit complex biological matrix analysis.

A new method for carbonating magnesia and its possible application to soil stabilization and CO2 capture

Traditional MgO carbonation (MgO and gaseous CO2) is a promising and sustainable technique in construction fields. However, using this technique to treat in-field soils on a large scale presents problems associated with CO2 diffusion, carbonation conditions, and mixing processes. To address such problems, this study proposed a new method that used NaHCO3 as a CO2 carrier to carbonate MgO, and then the carbonated MgO is applied to treat soils. The engineering properties of the stabilized soil were investigated. A discussion on the technical and economic feasibility of this new method was followed. The results showed that the soil with MgO + NaHCO3 had better mechanical performance than that with OPC due to the formation of various magnesium carbonates. The new method would be more convenient to operate on-site than the traditional carbonation method and presented a strong economic potential for the soda industry. Overall, this method could be an upgrade to MgO carbonation.

Role of CO2 Carriers in Carbon Capture Utilization and Sequestration as A Part of Global Decarbonization Strategy

Abstract: With the world gearing up to cut down carbon emissions to combat the greenhouse effect, a novel method has been introduced to collect and store co2 after pressurizing and liquifying it. carbon sequestered will either be put to use in industries or will be buried deep underground. this concept is highly revered due to its pragmatism and simplicity and is broadly termed as "carbon capture, utilization and sequestration/ storage (ccus)". though it is clear how to capture, utilize and store liquified co2 (lco2), the modus operandi of transportation remains abstruse. though the technical feasibility of this method is still under debate, many shipping companies have set forth to construct liquified co2 (lco2) tankers. ongoing studies are focused on finding the best methods to transport co2 by retrofitting lng ships to better equip them for storing and transporting co2. this paper takes a systematic approach to review the development of lco2 tankers. it discusses the trail of development, major challenges and limitations, technological gaps, and future prospects. it also looks over the economic and ecological aspects of such an endeavor. the paper has also taken care not to be oblivious to other options at hand, including pipelines and railways. it briefly explains the above methods and further discusses their limitations.

NaHCO3 as a carrier of CO2 and its enhancement effect on mineralization during hydrothermal alteration of basalt

Reaction of carbon dioxide (CO2) with minerals to generate stable carbonates, also known as CO2 mineralization, has been regarded as one of the most promising methods for safe and permanent carbon storage. As a promising feedstock, basaltic rock has gained special interest, and elevating basalt carbonation efficiency with the reduction of negative environmental impact is the main challenge for CO2 mineralization system development. Considering multiple potential positive effects of the CO2 carrier, NaHCO3, we conducted this study to experimentally evaluate the CO2 storage efficiency during water-basalt-NaHCO3 interactions under hydrothermal conditions at 200–300°C. The inclusion of NaHCO3 was confirmed to drastically promote the alteration of basalt, especially at higher temperatures. As revealed by experiments conducted at the saturated vapor pressure of water, the carbon storage efficiency at 300°C reached 75 g/kg of basalt in 5 days, which was 12 times higher than that at 200°C. In such hydrothermal systems, basalt was carbonated to generate calcite (CaCO3), where the Ca was mainly from plagioclase; Mg and Fe were incorporated into smectite, and Na in the saline system participated in the formation of Na silicates (i.e., analcime in the case of basalt). Due to the presence of additional Na in solution, all the released elements were consumed quickly with generation of secondary minerals in turn promoted basalt dissolution to release more Ca for CO2 storage. This study illuminated the role of NaHCO3 in basalt carbonation and provided technical backup to the design of advanced CO2 mineralization systems.

In-situ release and sequestration of CO2 in cement composites using LTA zeolites

This paper investigates the impact of in-situ release and sequestration of CO2 on the compressive strength, volume of permeable voids, phase change, hydration reaction, and micro-morphology of cement mortars. Two Linde Type A (LTA) zeolites with micro-pore dimensions of 5 Å and 4 Å (i.e., LTA 5A and 4A zeolites) were employed as CO2 carriers herein. The incorporation of 312 wt% plain LTA 5A and 4A zeolites increases the 1-day compressive strength of the mortars. However, the use of plain LTA 5A zeolite shows marginal contributions to the 7 and 28-day compressive strengths of the mortars, whilst using plain LTA 4A zeolite even deteriorates their 7 and 28-day compressive strengths. The micro-structural analyses reveal that the addition of LTA zeolites promotes the cement hydration and improves the mean chain length (MCL) of calcium aluminosilicate hydrates (C-A-S-H). Nevertheless, this introduces numerous weak points or even a porous structure to the cement matrix. In contrast, in-situ release of CO2 via LTA zeolites significantly enhances the compressive strengths of the mortars at various ages, as this can further facilitate the hydration evolution and improve the MCL of C-A-S-H. Moreover, in-situ release of CO2 brings an incremental content of calcium carbonates. The calcium carbonate contents in the specimens containing 12 wt% LTA 5A and 4A zeolites are increased by 5.3 wt% and 4.8 wt%, respectively. This leads to homogenous distributions of calcite with a grain size of 150600 nm. Thus, LTA 5A zeolite outperforms LTA 4A zeolite with regard to CO2 uptake and the corresponding mechanical properties. This work presents in initial exploration into the application of porous pozzolanic materials in conjunction of CO2 in cement-based materials.

Effect of CO2 capture on the performance of CaO-activated slag pastes and their acid resistance

Carbonation of CaO-activated slag shows great potential in terms of storing CO2, reducing emissions by reducing cement consumption and recycling steel slag. This study investigates the effect of quicklime dosage and CO2 capture time on the performance of CaO-activated slag experimentally. CO2 capture time varies from 0 to 15 min, and the addition of quicklime as CO2 carrier increases from 10 % to 30 %. The fluidity behavior of fresh pastes, and hydration evolution, strength behavior and acid resistance of hardened pastes before and after carbonation were analyzed. The experimental results show that more addition of quicklime and extended CO2 fixation time decrease the fluidity but increase the shear stress and apparent viscosity, which are associated with chemical reaction of quicklime and generation of large amounts of nano-sized CaCO3. Increased addition of quicklime improving the alkaline environment promotes the pozzolanic reaction of CaO-activated slag and enriches the content CO2 carrier. Hence, longer CO2 fixation time improves the filling effect of nanoscale CaCO3 on the hardened matrix obviously, and leads to better mechanical performance. Additionally, both more addition of quicklime and extended CO2 fixation time increase the acid resistance of hardened pastes chemically and physically. Therefore, this study will provide novel carbonated binders, which are benefit to the energy saving, emission reduction and environmental protection.

Diffusion of CO2 in single-step silica nanofluid for subsurface utilization: an experimental study.

This study investigates the role of single-step silica nanofluids as additives to increase CO2 absorption in polymeric solutions for proposed oilfield applications. Using pressure decay approach, the study investigates the applicability of single-step silica nanofluids for CO2 absorption in a high pressure-high temperature (HPHT) cell. Various parameters like nanoparticle size (30-120nm) and concentration (0.1-1 wt%) were investigated to ascertain the absorption performance of the nanofluids and optimization their application in subsurface applications as carrier fluids for CO2. The solutions under observation (deionized water and silica nanofluids) were pressurized under the desired pressure and temperature inside a stirring pot and the decline in pressure was continuously noted. To comprehensively cover the near-reservoir field conditions, the CO2 absorption was investigated in the pressure range of 5-10MPa and at temperatures of 30-90°C. While increasing the nanoparticle concentration (from 0.1 to 1 wt%) increased the CO2 absorption (evident by the sharper decline in pressure), increasing the nanoparticle size reduced the absorption capacity of the nanofluids as a lesser volume of decline in pressure was noted. Furthermore, increasing the temperature of the experimental investigation caused a major reduction (12-19%) in the pressure decay. However, it was also observed that higher pressure (> 7.5MPa) was detrimental for CO2 absorption (due to its supercritical nature). Adding salt (sodium chloride, NaCl) was found to massively lower (up to 33%) while adding surfactant (sodium dodecyl sulfate, SDS) slightly increased the amount of CO2 absorption (in presence of salinity). Based on the observations of this study, the use of single-step silica nanofluids as CO2 carrier fluids is recommended for oilfield conditions where salinity is less than 4 wt%.