CO2 Sorption Research Articles

How triazole rings capture carbon dioxide: Energy effects and activation barriers

The interest in carbon dioxide (CO2) sorbents is fostered by the global peril of climate warming. Herein, we examine a new class of potential CO2 scavengers, 1,2,3-triazoles, the current-year Nobel Prize winners. Their affinities to CO2 were characterized in terms of reaction energy profiles, nucleophilicities of the respective in-ring nitrogen atoms, and continuous geometry alterations during the course of the chemical reactions. We computationally revealed varying abilities of 1,2,3-triazoles and the triazolide anion to chemically fix CO2 via the carboxamidation mechanism and linked them to electron density distributions over the triazole rings. The triazolide anions in a dilute solution and ion pairs of tetraethylammonium 1,2,3-triazolide exhibit competitive CO2 sorption capacities, whereas neutral 1,2,3-triazoles were confirmed to be quite weak bases. The presence of an excessive electron in the heterocyclic anion enhances the nucleophilicities of the three nitrogen atoms and, therefore, gives rise to a promising CO2 scavenger. The solvation in water strongly fosters carboxamidation (decreases both the activation barrier and the energetic effect) in most cases thanks to the emergence of polar carboxyl moiety. The reported new knowledge is necessary to rationally rate manifold classes of nitrogen-containing heterocyclic compounds for the sake of searching for chemically robust and economically affordable CO2 scavengers.

Surface functionalization of microporous carbon fibers by vapor phase methods for CO2 capture

The removal of excess CO2 from the atmosphere is expected to play a major role in the mitigation of global warming. Solid-state adsorbents, consisting of CO2-binding functionalities on porous supports, can provide high CO2 capture capacities with low energy requirements. In this contribution, we report on the vapor-phase functionalization of porous carbon fibers with amine functionalities. Functionalization occurs either via direct exposure to cyclic azasilane molecules (2,2-dimethoxy-1,6-diaza-2-silacyclooctane) or by the atomic layer deposition of Al2O3 followed by exposure to azasilane. XPS analysis and SEM/energy-dispersive x-ray spectroscopy (EDX) measurements confirmed Al2O3 deposition and amine functionalization. Yet, the two different functionalization approaches led to different amine loadings and distinct differences in porosity upon functionalization, which affected CO2 capture. Combining Al2O3 and amine functionalization resulted in fast CO2 sorption with superior capturing efficiency. In contrast, direct functionalization resulted in strong reduction of the surface area of the porous support and limited gas exchange. We attribute the superior capture efficiency to the porosity level achieved when combining Al2O3 and amine functionalization demonstrating that this approach might be valuable for compact high-throughput direct air, CO2 capture systems.

Removal of heavy metals from wastewater of textile industry using polymeric nano-adsorbent

Wastewater of textile industry having impurities and heavy metal ions cause problems in human society that can endanger the human health through food chain. Adsorption of heavy metal ions before draining makes wastewater safe for aquatic life and human health. Now a days adsorption of heavy metal through polymeric Nano adsorbent is the emerging technology which is more efficient than conventional adsorbents like activated carbon. The pH 9.0 gave maximum 96% sorption of Co at 1.0 g/L adsorbent dosage, due to increased electrostatic force of attraction produced by the negative charge at the surface of sorbent which is favorable for adsorbing cationic species. In the beginning of 15 minutes retention time, metal ions adsorption was faster due to availability of more number of adsorptive sites but further increase of retention time decreased the sorption due to partial desorption that may occur due to the charge density and diameter of hydrated ions. Similarly in case of Cu, the maximum sorption was 95% at 7.0 pH using 1.0 g/L adsorbent dosage.

Process Simulations of High-Purity and Renewable Clean H2 Production by Sorption Enhanced Steam Reforming of Biogas

Renewable clean H2 has a very promising potential for the decarbonization of energy systems. Sorption enhanced steam reforming (SESR) is a novel process that combines the steam reforming reaction and the simultaneous CO2 removal by a solid sorbent, such as CaO, which significantly enhances hydrogen generation, enabling high-purity H2 production. The CO2 sorption reaction (carbonation) is exothermic, but the sorbent regeneration by calcination is highly endothermic, which requires extra energy. Biogas is one of the available carbon-neutral renewable H2 production sources. It can be especially relevant for the energy integration of the SESR process since, due to the exothermic sorption reaction, the CO2 contained in the biogas provides extra heat to the system, which can help to balance the energy requirements of the process. This work studies different process configurations for the energy integration of the SESR process of biogas for high-purity renewable H2 production: (1) SESR with sorbent regeneration using a portion of the produced H2 (SESR+REG_H2), (2) SESR with sorbent regeneration using biogas (SESR+REG_BG), and (3) SESR with sorbent regeneration using biogas and adding a pressure swing adsorption (PSA) unit for hydrogen purification (SESR+REG_BG+PSA). When using biogas as fuel (Cases 2 and 3), these configurations were studied using air and oxy-fuel combustion atmospheres in the sorbent regeneration step, resulting in five case studies. A thermodynamic approach for process modeling can provide the optimal process operating conditions and configurations that maximize the energy efficiency of the process, which are the basis for subsequent optimization of the process at the practical level needed to scale up this technology. For this purpose, process simulations were performed using a steady-state plant model developed in Aspen Plus, incorporating a complex heat exchanger network (HEN) to optimize heat integration. A comprehensive parametric study assessed the effects of biogas composition, temperature, pressure, and steam to methane (S/CH4) ratio on the process performance represented by the selected key performance indicators, i.e., H2 purity, H2 yield, CH4 conversion, cold gas efficiency (CGE), net efficiency (NE), fuel consumption for the sorbent regeneration step, and CO2 capture efficiency. H2 with a purity of 98.5 vol % and a CGE of 75.7% with zero carbon emissions can be achieved. When adding a PSA unit, nearly 100% H2 purity and CO2 capture efficiency were achieved with a CGE of 77.3%. The use of oxy-fuel combustion during regeneration lowered the net efficiency of the process by 2.3% points (since it requires an air separation unit) but allowed the process to achieve negative carbon emissions.

Sorption as a pre-concentration step for metal ions recovery in multi-elemental systems

Sorption is here proposed as a promising approach for metal pre-concentration and recovery from wastewater. A study was carried out on the simultaneous sorption of Co2+, Cu2+, Ni2+ and Zn2+ on macroalgae, microalgae and cyanobacteria. The effect of pH, initial metal concentration, metal competition and time of contact on metal sorption were evaluated. Metal competition hampers sorption at the studied metal concentration ranges. The metal counterion (sulfate, chloride or acetate) did not influence metal sorption. The brown algae Sargassum sp. was the most promising sorbent (qmax = 0.66 ± 0.03 mmol·g−1), followed by the microalgae Phaeodactylum tricornutum (qmax = 0.36 ± 0.02 mmol·g−1) and the cyanobacteria Spirulina sp. (qmax = 0.216 ± 0.007 mmol·g−1). All biomass samples showed preferential sorption of Cu2+. The experimental kinetic data were well described by Ho’s model, showing chemisorption to be the main sorption mechanism. Ion-exchange of Ca2+, K+ and H+ also played a significant role in metal sorption. After sorption, metal recovery was achieved resorting to incineration. The metal content of the obtained biochar was 4639-fold higher when compared to the initial aqueous solution concentration.

137Cs, 85Sr and 60Co sorption from model solutions of low activity liquid radioactive waste by modified oil shale

The results of the study of cesium, strontium, cobalt radionuclides sorption from model solutions simulating liquid radioactive waste on promising sorbents based on thermally modified oil shale are presented. The dependency of texture parameters obtained from the results of nitrogen adsorption-desorption on the treatment method of oil shale and their relationship to sorption parameters such as distribution coefficient and removal efficiency was discussed. Understanding how pore characteristics affect the sorption activity of such complex systems as sorbents is important for the creation of radionuclide sorption materials with improved characteristics. The efficiency of sorption of cesium, strontium and cobalt radionuclides was rather high for sorbent samples: the distribution coefficient was about 103–104 ml/g with a removal efficiency of more than 66 %. The most effective sorbent was obtained from oil shale with a heating rate of 5 deg/min without subsequent steam treatment, which is recommended to be used for low-active radioactive waste treatment.

Application of isotherms models and error functions in activated carbon CO2 sorption processes

This work is concerned with the calculations using eight different isotherm models (Langmuir, Freundlich, Halsey, Temkin, Toth, Sips, Radke-Prausnitz, and Redlich-Peterson) to fit the experimental isotherm data of CO2 on activated carbon (AC). Moreover, systematic and comprehensive modeling of non-linearized isotherms was performed by developing an algorithm for determining their parameters and analyzing seven error functions. To determine the best-fitted isotherm model and error function, we used the sum of normalized errors (SNE) procedure. The modeling results obtained showed that the Redlich-Peterson, Radke-Prausnitz, and Toth isotherm models are best suited to the empirical data, with relatively high R2 determination coefficients. Finally, the SNE method allowed the selection of the chi-square test (χ2) and the HYBRID error as universal indicators in nonlinear regression to select the set of optimized isotherm parameters. The interpretation of the assumptions of the isotherm models, which featured a strong correlation with the experimental data, allowed a conclusion to be drawn about the sub-monolayer adsorption mechanism on the heterogeneous surface of the AC. The acquired modeling findings are expected to establish a certain theoretical foundation for the characterization of CO2 adsorption equilibrium studies at the interface between porous solid materials and gases.

Sorption of CO2, CH4 and Their Mixtures in Amorphous Poly(2,6-dimethyl-1,4-phenylene)oxide (PPO).

Sorption of pure CO2 and CH4 and CO2/CH4 binary gas mixtures in amorphous glassy Poly(2,6-dimethyl-1,4-phenylene) oxide (PPO) at 35 °C up to 1000 Torr was investigated. Sorption experiments were carried out using an approach that combines barometry with FTIR spectroscopy in the transmission mode to quantify the sorption of pure and mixed gases in polymers. The pressure range was chosen to prevent any variation of the glassy polymer density. The solubility within the polymer of the CO2 present in the gaseous binary mixtures was practically coincident with the solubility of pure gaseous CO2, up to a total pressure of the gaseous mixtures equal to 1000 Torr and for CO2 mole fractions of ~0.5 mol mol-1 and ~0.3 mol mol-1. The Non-Equilibrium Thermodynamics for Glassy Polymers (NET-GP) modelling approach has been applied to the Non-Random Hydrogen Bonding (NRHB) lattice fluid model to fit the solubility data of pure gases. We have assumed here that no specific interactions were occurring between the matrix and the absorbed gas. The same thermodynamic approach has been then used to predict the solubility of CO2/CH4 mixed gases in PPO, resulting in a deviation lower than 9.5% from the experimental results for CO2 solubility.

Insertion of CO2 in metal ion-doped two-dimensional covalent organic frameworks

Carbon capture is one of the essential low-carbon technologies required to achieve societal climate goals at the lowest cost. Covalent organic frameworks (COFs) are promising adsorbents for CO2 capture because of their well-defined porosity, large surface area, and high stability. Current COF-based CO2 capture is mainly based on a physisorption mechanism, exhibiting smooth and reversible sorption isotherms. In the present study, we report unusual CO2 sorption isotherms featuring one or more tunable hysteresis steps with metal ion (Fe3+, Cr3+, or In3+)-doped Schiff-base two-dimensional (2D) COFs (Py-1P, Py-TT, and Py-Py) as adsorbents. Synchrotron X-ray diffraction, spectroscopic and computational studies indicate that the sharp adsorption steps in the isotherm originate from the insertion of CO2 between the metal ion and the N atom of the imine bond on the inner pore surface of the COFs as the CO2 pressure reaches threshold values. As a result, the CO2 adsorption capacity of the ion-doped Py-1P COF is increased by 89.5% compared with that of the undoped Py-1P COF. This CO2 sorption mechanism provides an efficient and straightforward approach to enhancing the CO2 capture capacity of COF-based adsorbents, yielding insights into developing chemistry for CO2 capture and conversion.

Microwave treatment effect on the enhanced basicity of porous clay heterostructured composites derived from Laponite

Porous clay heterostructured composites (PCH) derived from layered hydrous magnesium silicate, Laponite, were functionalized by Fe(NO3)3x9H2O with the use of mechano-chemical impregnation followed by microwave irradiation or hydrothermal treatment to evoke new base properties, active in CO2 sorption. It resulted in the progressive leaching of the Mg2+ from the octahedral sheets of the Laponite structure and their capture on the surface of PCH composites increasing the Mg/Si ratio. The increase of Mg/Si ratio was accompanied by the decline of the (Mg3OH) absorption bands intensity attributed to Laponite and discussed regarding the formation of dispersed nanostructured MgO moieties capable of adsorbing CO2. CO2-TPD temperature-programmed desorption technique revealed that sorption and stabilization of CO2 molecules are related to the coordination of oxygen sites in the formed MgO lattice and that edge and corner sites facilitate the interaction of CO2 molecules with O2− sites on MgO. Doping of PCH resulted also in the nucleation of nanocrystalline α-Fe2O3 able to capture CO2 with strength and stability higher than MgO. Microwave irradiation resulted in significant development of the surface basicity as part of the transformation of clay structure. This study confirms the importance of clay minerals in the uptake and retention of CO2.

Charge-Assisted Hydrogen-Bonded Organic Frameworks with Inorganic Ammonium Regulated Switchable Open Polar Sites.

Surface open polar sites within the voids of porous molecular crystals define the localized physicochemical environment for critical functions such as gas separation and molecular recognition. This study presents a new charge-assisted hydrogen bonding (H-bonding) motif, by exploiting inorganic ammonium (NH4 + ) cations as H-bond donors, to regulate the assembly of C2 -symmetric carboxylic tectons for building robust H-bonded frameworks with permanent ultra-micropores and open oxygen sites. Diverse building blocks are bridged by tetrahedral NH4 + to expand distinctive H-bonded networks with varied pore architectures. Particularly, the open polar oxygen sites can be switched by altering NH4 + sources to tune the deprotonation of carboxyl-containing tectons. The activated porous PTBA·NH4 ·DMF preserves the pore architecture and open polar oxygen sites, exhibiting remarkably selective sorption of CO2 (107.8 cm3 g-1 ,195 K) over N2 (11.2 cm3 g-1 , 77 K) and H2 (1.4 cm3 g-1 , 77 K).

Carbon materials derived from cyano-based IL@ZIF-8 composites for CO2 sorption separation systems

The sorption capacity and selectivity of pre- and post-carbonized cyano-based metal-organic framework (MOF) composite materials (cyano-based IL@ZIF-8) were investigated for the first time. The influence of the ionic liquid (IL) loading and number of cyano groups in the IL anion on a materials gas sorption separation performance was studied. Sorption-desorption equilibrium isotherms of CO2, CH4, and N2 were measured at 303 K in the ZIF-8, cyano-based IL@ZIF-8 composites and their derived carbon materials. The IL loading did not significantly affect the gas uptake of the carbon materials, while for the composites its main contribution was on the increase of the selectivity. The number of cyano groups in the anion played a key role in the sorption capacity and selectivity performance as it directly affects the N content and textural properties. The carbon material obtained from ZIF-8 (C_ZIF-8) precursor showed the best sorption capacity for all gases, just being surpassed by the C_15%[C6MIM][B(CN)4]@ZIF-8 carbon up to 1 bar. In terms of selectivity performance, carbons based on [C6MIM][B(CN)4]@ZIF-8 composites revealed to be equally or more selective than C_ZIF-8, increasing up to 65% between 0 and 1 bar depending on the mixture. The composites produced and their respective carbons demonstrated a promising application as sorbents for post-combustion CO2 separation systems.

Synthesis, structures, and CO2 sorption of a Cu(II) and Zn(II) two-fold interpenetrated pyridyl diimide metal–organic frameworks

Herein we report synthesis, structures and CO2 sorption studies of two 2-fold interpenetrated three dimensional (3D) metal–organic frameworks (MOFs) namely; {[Cu(2,6-NDC)(L1)0.5]·3DMF}n (1) and {[Zn0.5(2,6-NDC)0.5(L2)0.5]·2DMF}n (2) where L1 is 5,5′-carbonylbis(2-(pyridin-3-ylmethyl)isoindoline-1,3-dione, L2 is 2,2′-bis(pyridin-4-ylmethyl)-[5,5′-biisoindoline]-1,1′–3,3′-tetraone, DMF is N,N’-dimethylformamide, and 2,6-NDC is 2,6-naphthalenedicarboxylic acid. The MOFs were synthesized solvothermally and characterized using single-crystal X-ray diffraction (SCXRD), thermogravimetric analysis (TGA), and powder X-ray diffraction (PXRD). SCXRD revealed that 1 and 2 are 3D and possess 33% and 27% of solvent-accessible volumes. Carbon dioxide sorption experiments were conducted at 195 K and 273 K on the desolvated phases of 1 (1-d) and 2 (2-d). 1-d adsorbs 11 cm3 g−1 (STP) at 273 K and 30 cm3 g−1 (STP) at 195 K, while 2-d adsorbs 35 cm3 g−1 (STP) at 273 K and 80 cm3 g−1 (STP) at 195 K.

Fabrication of porous Li4SiO4 ceramic sorbent pebbles with high CO2 sorption capacity via the simple freeze-drying method

At present, the Li4SiO4 ceramic sorbents have displayed a great prospect for CO2 gas removal in the atmosphere owing to their high sorption capacity and stable sorption-desorption property. In this paper, a simple method combining the wet method and freeze-drying method is initially employed to fabricate Li4SiO4 sorbent with rich porosity and direction arrangement channels, which overcomes the dense interior structure, barren porosity, inferior adsorption stability, and costly production described in the previous literature. The effects of freeze way and temperature on the interior structure of Li4SiO4 sorbent were studied respectively. In the freeze-drying process, only the freeze-drying Li4SiO4 cylinder (FSC) green sorbents have columnar ice crystals in the interior owing to the temperature gradient, and the unidirectional alignment of pore channels can be obtained after the vacuum drying process due to the sublimation of ice crystals, which will improve CO2 capture capacity. Moreover, it can be seen from the optical image that the sorbent pebbles have a uniform distribution of diameter and sorbent samples of OSF (fabricated without the freezing process), FSP (fabricated with the freezing process), and FSC show excellent mechanical strength of 37.5 N, 22.5 N, and 0.43Mpa, respectively. Compared with OSP and FSP samples, the FSC sorbent performed superior CO2 sorption capacities (0.305 g CO2/g sorbent) and outstanding stability after 40 times cycles due to its optimal pore microstructure. Therefore, the prominent capture capacity and the satisfying crushing load of the FSC sorbents fabricated via the Freeze-drying method in this paper have promising prospects for CO2 removal.

High-Pressure Adsorption of CO2 and CH4 on Biochar-A Cost-Effective Sorbent for In Situ Applications.

The search for an effective, cost-efficient, and selective sorbent for CO2 capture technologies has been a focus of research in recent years. Many technologies allow efficient separation of CO2 from industrial gases; however, most of them (particularly amine absorption) are very energy-intensive processes not only from the point of view of operation but also solvent production. The aim of this study was to determine CO2 and CH4 sorption capacity of pyrolyzed spruce wood under a wide range of pressures for application as an effective adsorbent for gas separation technology such as Pressure Swing Adsorption (PSA) or Temperature Swing Adsorption (TSA). The idea behind this study was to reduce the carbon footprint related to the transport and manufacturing of sorbent for the separation unit by replacing it with a material that is the direct product of pyrolysis. The results show that pyrolyzed spruce wood has a considerable sorption capacity and selectivity towards CO2 and CH4. Excess sorption capacity reached 1.4 mmol·g-1 for methane and 2.4 mmol·g-1 for carbon dioxide. The calculated absolute sorption capacity was 1.75 mmol·g-1 at 12.6 MPa for methane and 2.7 mmol·g-1 at 4.7 MPa for carbon dioxide. The isotherms follow I type isotherm which is typical for microporous adsorbents.

Mesoporous MgO enriched in Lewis base sites as effective catalysts for efficient CO2 capture

Capturing CO2 has become increasingly important. However, wide industrial applications of conventional CO2 capture technologies are limited by their slow CO2 sorption and desorption kinetics. Accordingly, this research is designed to overcome the challenge by synthesizing mesoporous MgO nanoparticles (MgO-NPs) with a new method that uses PEG 1500 as a soft template. MgO surface structure is nonstoichiometric due to its distinctive shape; the abundant Lewis base sites provided by oxygen vacancies promote CO2 capture. Adding 2 wt % MgO-NPs to 20 wt % monoethanolamine (MEA) can increase the breakthrough time (the time with 90% CO2 capturing efficiency) by ∼3000% and can increase the CO2 absorption capacity within the breakthrough time by ∼3660%. The data suggest that MgO-NPs can accelerate the rate and increase CO2 desorption capacity by up to ∼8740% and ∼2290% at 90 °C, respectively. Also, the excellent stability of the system within 50 cycles is verified. These findings demonstrate a new strategy to innovate MEA absorbents currently widely used in commercial post-combustion CO2 capture plants.

Effect of Surface Characteristics of Graphene Aerogels and Hydrophilicity of Ionic Liquids on the CO2/CH4 Separation Performance of Ionic Liquid/Reduced Graphene Aerogel Composites

Two ionic liquids (ILs) having the same cation with different anions offering opposite hydrophilic/hydrophobic characters, 1-n-butyl-1-methylpyrrolidinium dicyanamide ([BMPyr][DCA]) and 1-n-butyl-1-methylpyrrolidinium hexafluorophosphate ([BMPyr][PF6]), were impregnated onto two different reduced graphene aerogels (rGAs) prepared by the thermal treatment of GAs at 300 and 500 °C to investigate the consequences of the changes in the hydrophilic character of ILs and the reduction temperature of the GAs on the corresponding gas sorption and separation performance of the IL/rGAs. The structural analyses of nanoporous rGAs and IL/rGAs pointed to a change in the quantity of oxygenated functional groups upon thermal treatment and a change in the direct interactions between IL molecules and the host rGA surface upon IL deposition. Single-component CO2 and CH4 sorption measurements were performed for each rGA and IL/rGA composite, and both ideal and mixture CO2/CH4 selectivities were calculated. The samples prepared by reducing the GA at 300 and 500 °C yielded ideal CO2/CH4 selectivities of 3.6 and 18 at 1 mbar and 25 °C, respectively. Among IL/rGA composites, the one prepared at 300 °C displayed a remarkable CO2/CH4 separation performance when combined with the hydrophobic [BMPyr][PF6], offering an ideal selectivity of 450.9 at 1 mbar and 25 °C, whereas the composite prepared with rGA500 yielded a substantially high CO2/CH4 selectivity of 173.5 after the incorporation of the hydrophilic [BMPyr][DCA] at 1 mbar and 25 °C. The ideal CO2/CH4 selectivities of [BMPyr][PF6]/rGA300 and [BMPyr][DCA]/rGA500 surpassed most of the previously reported selectivities of carbon-based materials in the literature. These results demonstrate the broad potential of IL/rGAs in sorption-based gas separations owing to the highly tunable nature of both the structure of IL and the surface characteristics of rGA.

New water-based nanocapsules of poly(diallyldimethylammonium tetrafluoroborate)/ionic liquid for CO2 capture

Encapsulated ionic liquids as green solvents for CO2 capture are reported in this work. We present a novel combination of water-based poly(ionic liquid) and imidazolium-based ionic liquids (Emim[X]). Poly(diallyldimethylammonium tetrafluoroborate)/Emim[X] capsules were developed for the first time using Nano Spray Dryer B-90. Capsules were characterized by FTIR, SEM/EDX, TEM, TGA, DSC, CO2 sorption, and CO2/N2 selectivity, CO2 sorption kinetic and recycling were also demonstrated. Comparing the capsules reported in this work, the combination of poly(diallyldimethylammonium tetrafluoroborate) and the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (P[DADMA]/BF4) showed great potential for CO2 capture and CO2/N2 separation, providing higher results (53.4 mg CO2/g; CO2/N2 selectivity: 4.58).

Enhanced Carbon Storage Process from Flue Gas Streams Using Rice Husk Silica Nanoparticles: An Approach in Shallow Coal Bed Methane Reservoirs

Carbon capture and storage (CCS) is considered a key process to reach net-zero emission by the 2050 aim of limiting global warming. Coal bed methane (CBM) is considered potential geological reservoirs for underground CCS due to the CO2–CH4 exchange feasibility by adsorptive phenomena. Global implementation has been focused only on deep reservoirs to provide methane recovery. Thus, this work proposes a modified CCS process based on silica nanoparticle inclusion for shallow CBM reservoirs (<300 m). The nanomaterials were evaluated at high pressure in two main stages including i) CO2 sorption on a single CO2 stream and ii) CO2 selectivity on a flue gas stream (N2–CO2 mixture). This work includes silica nanomaterial synthesized from rice husk as agro-waste sources with better technical-economic feasibility framed in a circular economy to reduce costs and maximize the use of available resources. Rice husk silica (RSi) nanoparticles were doped with 1.0, 3.0, and 5.0 wt % of urea (Si–U), diethylamine (Si-DE), triethylamine (Si-TE), and ethylenediamine (Si-EM) to enhance the CO2 sorption. First, CO2 sorption was evaluated at 30 °C and between 0.084 and 3 MPa using a CO2 stream to determine the best-doped amount of each N-source. Then, the best nanoparticles were used to impregnate CBM at 10 and 20 wt %, and the subsequent CO2 storage on the flue gas stream (70% v/v N2 and 30% v/v CO2) was done. The results showed that CO2 sorption on RSi increases with the N-group coating in the order RSi-DE < RSi-TE < RSi-U < RSi-EM. Also, the best-doped amount for each N-source was 3 wt %. For CBM impregnation, the nanofluid containing 20 wt % of RSi-EM3 presented the best yield increasing the CO2 sorption from 0.05 to 0.75 mmol g–1, meaning an increase of more than 1000% in the sorption capacity.

Experimental investigations of CO2 adsorption behavior in shales: Implication for CO2 geological storage

Injecting CO2 into shale reservoirs has dual benefits for enhancing gas recovery and CO2 geological sequestration, which is of great significance to ensuring energy security and achieving the “Carbon Neutrality” for China. The CO2 adsorption behavior in shales largely determined the geological sequestration potential but remained uncharted. In this study, the combination of isothermal adsorption measurement and basic petro-physical characterization methods were performed to investigate CO2 adsorption mechanism in shales. Results show that the CO2 sorption capacity increase gradually with injection pressure before reaching an asymptotic maximum magnitude, which can be described equally well by the Langmuir model. TOC content is the most significant control factor on CO2 sorption capacity, and the other secondary factors include vitrinite reflectance, clay content, and brittle mineral content. The pore structure parameter of BET-specific surface area is a more direct factor affecting CO2 adsorption of shale than BJH pore volume. Langmuir CO2 adsorption capacity positive correlated with the surface fractal dimension (D1), but a significant correlation is not found with pore structure fractal dimension (D2). By introducing the Carbon Sequestration Leaders Forum and Department of Energy methods, the research results presented in this study can be extended to the future application for CO2 geological storage potential evaluation in shales.