Hypercrosslinked organic polymer networks as potential adsorbents for pre-combustion CO2 capture

Taming structure and modulating carbon dioxide (CO2) adsorption isosteric heat of nickel-based metal organic framework (MOF-74(Ni)) for remarkable CO2 capture

Extended Abstract Integrated Gasification Combined Cycle (IGCC) has been emerged as an efficient alternative to post and oxycombustion systems for power generation with controllable CO2 capture and separation. However, this system operates and requires separation of gases at high pressure prior to combustion which subsequently demands highly stable material for CO2 capture and separation. Pre-combustion flue gas capture has been instigated as an alternative to circumvent the costly procedures of materials regeneration utilized by the energy industry for CO2 capture and separation[1]. Stability of the porous structure and repeated use at high pressure and high temperature are among the essential requirements for the efficient materials to be used for industrial level CO2 separation [2, 3]. Herein we report the CO2 adsorption-desorption performance of nanoporous covalent organic polymers (COPs), which can operate efficiently and repeatedly at elevated pressure of 200 bars and above. Since, pre-combustion capture also requires removal of hydrogen along with CO2; therefore, nanoporous COP was also tested for hydrogen removal at high pressure. COP material prepared with simple technique from building block monomers of cyanuric chloride and linked with 1, 3-bis(4-piperidinyl)propane has enough surface area and pore volume which makes the material capable to store large quantity of syngas at high temperature and pressure. Results indicated that the newly synthesized COP material can adsorbed exceptionally large quantity of CO2 and very little hydrogen at 200 bars and 35 °C. Additionally, the adsorption isotherm was exactly matched with the desorption isotherm, suggesting the material has excellent adsorption-desorption characteristics. Similarly, the material has shown very stable performance when used repeatedly and alternatively for CO2 and hydrogen after regeneration at 50 °C. The capturing performance of material was also investigated for other gases like methane and nitrogen at various pressures and temperatures. Experimental results revealed that COP material has exceptional CO2 adsorption efficiency, very good selectivity, and strong stability and can be manufacture with simple techniques. Upon comparing with other materials like hyper cross-linked polymers, amine modified SBA-15[4], poly-benzimidazole activated carbon, and organic networks[5], it was found that covalent organic polymers presented here has exceptionally high CO2 uptake capacity, release very low heat of adsorption and possess very good mass transfer coefficient[6]. Lastly, material is economically viable when it is compared with the commercially available materials and has exceptional performance contrary to monoethanole amine.

Adsorption behavior of carbon dioxide and methane in bituminous coal: A molecular simulation study

Two representative metal–organic frameworks, Zn4O(BTB)2 (BTB3− = 1,3,5-benzenetribenzoate; MOF-177) and Mg2(dobdc) (dobdc4− = 1,4-dioxido-2,5-benzenedicarboxylate; Mg-MOF-74, CPO-27-Mg), are evaluated in detail for their potential use in post-combustion CO2 capture via temperature swing adsorption (TSA). Low-pressure single-component CO2 and N2 adsorption isotherms were measured every 10 °C from 20 to 200 °C, allowing the performance of each material to be analyzed precisely. In order to gain a more complete understanding of the separation phenomena and the thermodynamics of CO2 adsorption, the isotherms were analyzed using a variety of methods. With regard to the isosteric heat of CO2 adsorption, Mg2(dobdc) exhibits an abrupt drop at loadings approaching the saturation of the Mg2+ sites, which has significant implications for regeneration in different industrial applications. The CO2/N2 selectivities were calculated using ideal adsorbed solution theory (IAST) for MOF-177, Mg2(dobdc), and zeolite NaX, and working capacities were estimated using a simplified TSA model. Significantly, MOF-177 fails to exhibit a positive working capacity even at regeneration temperatures as high as 200 °C, while Mg2(dobdc) reaches a working capacity of 17.6 wt % at this temperature. Breakthrough simulations were also performed for the three materials, demonstrating the superior performance of Mg2(dobdc) over MOF-177 and zeolite NaX. These results show that the presence of strong CO2 adsorption sites is essential for a metal–organic framework to be of utility in post-combustion CO2 capture via a TSA process, and present a methodology for the evaluation of new metal–organic frameworks via analysis of single-component gas adsorption isotherms.

In this study, the adsorption capacity of the low-cost zeolite clinoptilolite was investigated for capturing carbon dioxide (CO2) emitted from industrial processes at moderate temperature. The CO2 adsorption capacity of clinoptilolite (a commercial natural zeolite) and ion-exchanged (with Na+ and Ca2+) clinoptilolite were tested under both dynamic (using a fixed-bed reactor operating with 10% vol. CO2 in N2) and equilibrium conditions (measuring single component adsorption isotherms). The dynamic CO2 adsorption capacity of bare clinoptilolite and ion-exchanged clinoptilolite were evaluated in the temperature range from 293 K to 338 K and the obtained breakthrough curves were compared with those of the commercial zeolite 13X (Z13X). Although the adsorption capacity of Z13X exceeded those of bare clinoptilolite and ion-exchanged clinoptilolite at 293 K, the clinoptilolite exhibited the highest CO2 uptake at a moderate temperature of 338 K (i.e. 25 % higher than Z13X). This feature appears in agreement with the lower isosteric heat of CO2 adsorption on clinoptilolite compared to the other samples. The surface species affecting the qiso and adsorption capacity were investigated through the FTIR spectroscopy using CO2 as probe molecule. As a whole, it has been observed that CO2 forms linear adducts onto K+ and Mg2+ cations of the bare clinoptilolite, and carbonate-like species onto its basic sites. With the Na-exchanged clinoptilolite, Na+ ions led to a decrease in surface basicity and to the formation of both single (Na+···OCO) and dual (Na+···OCO⋯Na+) cationic sites available for the formation of linear adducts.As a result of the remarkable adsorption capacity of clinoptilolite at 338 K, this material appears to be a promising adsorbent for the direct CO2 removal from different flue gases sources operating at such temperatures.

CO2 capture using three-dimensionally ordered micromesoporous carbon

Porous network structures (e.g. metal-organic frameworks, MOFs) show considerable potential in dethroning monoethanol amine (MEA) from being the dominant scrubber for CO2 at the fossil-fuel-burning power generators. In contrast to their promise, structural stability and high-pressure behavior of MOFs are not well documented. We herein report moisture stability, mechanical properties and high-pressure compression on a model MOF structure, MOF-5. Our results show that MOF-5 can endure all tested pressures (0-225 bar) without losing its structural integrity, however, its moist air stability points at a 3.5 hour safety window (at 21.6 °C and 49% humidity) for an efficient CO2 capture. Isosteric heats of CO2 adsorption at high pressures show moderate interaction energy between CO2 molecules and the MOF-5 sorbent, which combined with the large sorption ability of MOF-5 in the studied pressure-temperature ranges show the viability of this sorbent for CO2 capturing purposes. The combination of the physicochemical methods we used suggests a generalized analytical standard for measuring viability in CO2 capture operations.

Graphene-containing microporous composites for selective CO2 adsorption

Activated carbon (AC) supported MgO (MgO@AC) for CO2 capture has been facilely prepared with Mg(NO3)2 as precursor by a solid-state heat dispersion method. The prepared MgO@AC adsorbents with different magnesium loadings were characterized by X-ray diffraction (XRD), N2 adsorption/desorption and scanning electron microscope (SEM), and were investigated for the CO2 adsorption capacity, CO2 adsorption selectivity and cyclic stability. The characterization results reveal that the precursor of Mg(NO3)2 can be highly dispersed on the surfaces of the AC support and converted to MgO during the activation process at high temperatures. The experimental results show that the MgO@AC adsorbent with the MgO loadings of 5 mmol/g AC support achieves a high CO2 adsorption capacity, high CO2/N2 adsorption selectivity and excellent reversibility. Its good adsorption performance and facile fabrication process make it a promising adsorbent for CO2 capture from flue gases. In addition, the isosteric heat of CO2 adsorption on this adsorbent was calculated from the CO2 adsorption equilibrium isotherms at different temperatures using the Clausius–Clapeyron equation, the values are in the range of 45.4–20.1 kJ/mol.

Various cost-effective polycyclic aromatic hydrocarbons (PAHs) were used to fabricate hyper-cross-linked polymers (HCLPs) via an external cross-linker knitting method (ECLKM) followed by N-source impregnation modification. Multiple characterization techniques and thorough tests confirmed that the resultant thermally stable materials featured large specific surface areas (up to 2870 m2 g–1), narrow pore distributions (<0.70 nm), and high pore volumes (up to 1.09 cm3/g). Effects of porosities and N-doping modification ways on HCLPs’ CO2 capture capacities have been fully studied via controlling experiments. Remarkably, HCLP 1 prepared using naphthalene without further modification possessed the highest CO2 uptake capacity (up to 3.8 mmol g–1), indicating that porosities dominated the CO2 uptake process of HCLPs compared with N-doping modification. This study offers a facile strategy to construct HCLPs with great CO2 capture performances using PAHs via a simple one-pot ECLKM.

Porous metal-organic framework [Zn2(ttdc)2(bpy)] (1) based on thieno [3,2-b]thiophenedicarboxylate (ttdc) was synthesized and characterized. The structure contains intersected zig-zag channels with an average aperture of 4 × 6 Å and a 49% (v/v) guest-accessible pore volume. Gas adsorption studies confirmed the microporous nature of 1 with a specific surface area (BET model) of 952 m2·g-1 and a pore volume of 0.37 cm3·g-1. Extensive CO2, N2, O2, CO, CH4, C2H2, C2H4 and C2H6 gas adsorption experiments at 273 K and 298 K were carried out, which revealed the great adsorption selectivity of C2H6 over CH4 (IAST selectivity factor 14.8 at 298 K). The sulfur-rich ligands and double framework interpenetration in 1 result in a dense decoration of the inner surface by thiophene heterocyclic moieties, which are known to be effective secondary adsorption sites for carbon dioxide. As a result, remarkable CO2 adsorption selectivities were obtained for CO2/CH4 (11.7) and CO2/N2 (27.2 for CO2:N2 = 1:1, 56.4 for CO2:N2 = 15:85 gas mixtures). The computational DFT calculations revealed the decisive role of the sulfur-containing heterocycle moieties in the adsorption of CO2 and C2H6. High CO2 adsorption selectivity values and a relatively low isosteric heat of CO2 adsorption (31.4 kJ·mol-1) make the porous material 1 a promising candidate for practical separation of biogas as well as for CO2 sequestration from flue gas or natural gas.

The potential of direct air capture using adsorbents in cold climates.

In this work, the CO2 and N2 adsorption properties of MIL-101 metal-organic framework (MOF) and activated carbon (AC) were investigated using a standard gravimetric method within the pressure range of 0–30 bar and at four different temperatures (298, 308, 318 and 328 K). The dual-site Langmuir–Freundlich (DSLF) model was used to describe the CO2 adsorption behaviors on these two adsorbents. The diffusion coefficients and activation energy Ea for diffusion of CO2 in the MIL-101 and AC samples were estimated separately. Results showed that the isosteric heat of CO2 adsorption on the MIL-101 at zero loading was much higher than that on the AC due to a much stronger interaction between CO2 molecule and the unsaturated metal sites Cr3+ on MIL-101. Meanwhile, the dramatically decreased isosteric heats of CO2 adsorption on MIL-101 indicated a more heterogeneous surface of MIL-101. Furthermore, the adsorption kinetic behaviors of CO2 on the two samples can be well described by the micropore diffusion model. With the increase of temperature, the diffusion coefficients of CO2 in the two samples both increased. The activation energy Ea for diffusion of CO2 in MIL-101 was slightly lower than that in AC, suggesting that MIL-101 was much favorable for the CO2 adsorption. The CO2/N2 selectivities on MIL-101 and AC were separately estimated to be 13.7 and 9.2 using Henry law constant, which were much higher than those on other MOFs.

CO2 capture using mesoporous alumina prepared by a sol–gel process

Experimental and theoretical demonstration of the relative effects of O-doping and N-doping in porous carbons for CO2 capture