吸附法碳捕集固体胺吸附剂成型技术研究进展

吸附法碳捕集技术是实现工业过程或大气中CO₂分离与脱除的重要途径之一,高性能吸附剂的开发是该技术的关键。固体胺吸附剂由于其优异的CO₂吸附量、选择性以及较低的再生能耗,近年来受到了广泛的关注,但用于工业的成型吸附剂仍面临机械强度低、稳定性差和胺流失严重等关键难题,难以在工业中大范围的推广应用。本文分析了固体胺成型吸附剂制备面临的主要难题,重点总结了近年来国内外吸附剂成型技术的研发进展,并对固体胺工业吸附剂的发展方向进行了展望。未来固体胺吸附法碳捕集技术的研发重点在于立足吸附反应机理和工业烟气的特性,创新成型固体胺吸附剂制备技术,提升吸附剂的CO₂吸附量、胺效率、机械与循环稳定性,研发低能耗的配套吸附工艺和核心装置。     

Antioxidative degradation mechanism of 2-mercaptobenzimidazole modified TEPA-MCM-41 adsorbents for carbon capture from flue gas

Solid amine adsorbents can efficiently adsorb CO₂, but a significant problem is that amine groups are oxidized. In this research, tetraethylenepentamine-impregnated MCM-41 adsorbents (TEPA-MCM-41) were functionally modified with sulphur-containing antioxidant 2-mercaptobenzimidazole (described as antioxidant MB) and tns-(2.4-di-tert-butyl)-phosphite (defined as antioxidant 168), respectively. The antioxidative degradation mechanism of 8% MB–50% TEPA-MCM-41 was analyzed by in situ diffuse reflectance infrared Fourier transform (in situ DRIFT) spectrum and high-performance liquid chromatography/mass spectrometry (HPLC/mass). The CO₂ adsorption capacity of 50% TEPA-MCM-41 was 4.30 mmol/g under 15% CO₂/85% N₂, but decreased to 1.38 mmol/g after oxidation at 100°C for 42 h under 95% N₂/5% O₂ certain condition. The CO₂ capacity of 8% MB–50% TEPA-MCM-41 reduced from 3.90 to 2.86 mmol/g. After 30 adsorption cycles under 5% O₂/15% CO₂/80% N₂, the capacity of 8% MB–50% TEPA-MCM-41 also only decreased by 16.8%, while 50% TEPA-MCM-41 decreased by 63.2%. The reason for the excellent antioxidant stability of 8% MB–50% TEPA-MCM-41 is that MB scavenged free radicals from amine oxidation and decomposed the hydroperoxides produced by free radical reactions. The hydroperoxides were decomposed into alcohols (non-radical products), which were eventually oxidized to sulphonic compounds. The MB modification inhibited the oxidative degradation of solid amine adsorbents guided for the production of antioxidant-efficient adsorbents.     

Thiol-yne 3D Printable Polymeric Resins for the Efficient Removal of a Model Pollutant from Waters

A new 3D printable resin formulation is developed and optimized from commercially available thiol (pentaerythritol tetrakis(3-mercaptopropionate); PETMP) and alkyne (3-butyn-1-ol; BA) monomers. Printed objects are characterized by Fourier-transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The extraction efficiency of the printed thiol-yne device is then investigated using a model dye – malachite green (MG). The results displayed excellent dye removal efficiency with > 95% MG removed within 5 min. The 3D-printed devices are reusable and show 100% removal over six cycles after washing with deionized water and methanol. The presence of surface hydroxyl groups derived from the BA monomer is shown to enhance dye adsorption in comparison to control materials. The printing procedure and resin formulation are robust and consistent when devices from different resin batches are compared for MG dye removal. The thiol-yne 3D printed devices demonstrated excellent dye removal (> 99%) from water samples collected from a tap and a nearby river source. The successful development of this resin provides a new thiol-yne-based resin system for stereolithography (SLA) 3D printing for the removal of organic dyes from wastewater and presents a potential for broad applications in water treatment.     

Biomimetic Hygroscopic Fibrous Membrane with Hierarchically Porous Structure for Rapid Atmospheric Water Harvesting

Sorption-based atmospheric water generation (SAWG) is a promising strategy to alleviate the drinkable water scarcity of arid regions. However, the high-water production efficiency remains challenging due to the sluggish sorption/desorption kinetics. Herein, a composite sorbent@biomimetic fibrous membrane (PPy-COF@Trilayer-LiCl) is reported by mimicking nature's Murray networks, which exhibits outstanding water uptake performance of 0.77–2.56 g g⁻¹ at a wide range of relative humidity of 30%–80% within 50 min and fast water release capacity of over 95% adsorbed water that can be released within 10 min under one sun irradiation. The superior sorption–desorption kinetics of PPy-COF@Trilayer-LiCl are enabled by the novel hierarchically porous structure, which is also the critical factor to lead a directional rapid water transport and vapor diffusion. Moreover, as a proof-of-concept demonstration, a wearable SAWG device is established, which can operate 10 sorption–desorption cycles per day in the outdoor condition and produce a high yield of clean water reaching up to 3.91 kg m⁻² day⁻¹. This study demonstrates a novel strategy for developing advanced solar-driven SAWG materials with efficient water sorption–desorption properties.     

Tuning the Trade-Off between Ethane/Ethylene Selectivity and Adsorption Capacity within Isoreticular Microporous Metal−Organic Frameworks by Linker Fine-Fluorination

The pore dimension and surface property directly dictate the transport of guests, endowing diverse gas selective adsorptions to porous materials. It is highly relevant to construct metal−organic frameworks (MOFs) with designable functional groups that can achieve feasible pore regulation to improve their separation performances. However, the role of functionalization in different positions or degrees within framework on the separation of light hydrocarbon has rarely been emphasized. In this context, four isoreticular MOFs (TKL-104−107) bearing dissimilar fluorination are rationally screened out and afforded intriguing differences in the adsorption behavior of C₂H₆ and C₂H₄. Ortho-fluoridation of carboxyl allows TKL-105−107 to exhibit enhanced structural stabilities, impressive C₂H₆ adsorption capacities (>125 cm³ g⁻¹) and desirable inverse selectivities (C₂H₆ over C₂H₄). The more modified ortho-fluorine group and meta-fluorine group of carboxyl have improved the C₂H₆/C₂H₄ selectivity and adsorption capacity, respectively, and the C₂H₆/C₂H₄ separation potential can be well optimized via linker fine-fluorination. Meanwhile, dynamic breakthrough experiments proved that TKL-105−107 can be used as highly efficient C₂H₆-selective adsorbents for C₂H₄ purification. This work highlights that the purposeful functionalization of pore surfaces facilitates the assembly of highly efficient MOF adsorbents for specific gas separation.     

In Situ Growth of Cyclodextrin-Based Metal Organic Framework Air Filters for Reusable SO2 Adsorbent Applications

In situ growth of cyclodextrin-based metal-organic frameworks (CD-MOFs) is investigated for the effective fabrication of MOF composites through the vapor diffusion method combined with O₂ plasma treatment. The growth rate of γ-CD-MOFs on poly(ethylene terephthalate) fibers (CD-MOFs–PET) is determined for 136 h, and the CD-MOFs-PET with 24 h growth time shows the highest surface area without crystal deformation. The specific surface area of the CD-MOFs-PET with 24 h growth time is 142.88 m² g⁻¹, which is 235 times higher than the pristine PET fibers. The 24 h CD-MOFs-PET shows removal efficiencies higher than 99% for PM_0.1 and higher than 95% for SO₂ gas. The CD-MOFs-PET demonstrates high recovery of SO₂ adsorption ability by the repeated adsorption-desorption cycles, maintaining up to 90% of initial adsorption performance. This study intends to provide an informative discussion of the applicability of textile-based CD-MOFs and the development of reusable filters for the removal of SO₂.     

Anion-pillared microporous material incorporated mixed-matrix fiber adsorbents for removal of trace propyne from propylene

Separation and purification of light hydrocarbons have been the critical processes for producing basic chemicals and polymers in petrochemical industry. Adsorbents with high performance are highly demanded for the separation of light hydrocarbons. However, the adsorbents filling in the packed bed when evaluated will inevitably induce reduced performance and increased pressure drop that considerably impede their application. Herein, mixed-matrix fiber adsorbents with anion-pillared hybrid microporous materials (SIFSIX-2-Cu-i) embedded within poly (ether sulfone) (PES) are constructed to enable an energy-efficient propylene/propyne separation. Owing to the sufficient binding sites and abundant channels for selective gas transfer, the fiber adsorbents achieve high C₃H₄ uptake capacity of 0.963 mmol g⁻¹ in the propylene/propyne (99/1) mixture breakthrough experiments. Moreover, fiber adsorbents exhibit good tolerance toward high gas velocity and show distinctively low pressure drop, which will be advantageous in industrial applications. This work provides a strategy for fabricating high-performance mixed-matrix fiber adsorbents.     

Fabrication of bimetallic Cu–Zn adsorbents with high dispersion by using confined space for gas adsorptive separation

The number of active components and their dispersion degree are two key factors affecting the performance of adsorbents. Here, we report a simple but efficient strategy for dispersing active components by using a confined space, which is formed by mesoporous silica walls and templates in the as-prepared SBA-15 (AS). Such a confined space does not exist in the conventional support, calcined SBA-15, which does not contain a template. The Cu and Zn precursors were introduced to the confined space in the AS and were converted to CuO and ZnO during calcination, during which the template was also removed. The results show that up to 5 mmol·g^–1 of CuO and ZnO can be well dispersed; however, severe aggregation of both oxides takes place in the sample derived from the calcined SBA-15 with the same loading. Confined space in the AS and the strong interactions caused by the abundant hydroxyl groups are responsible for the dispersion of CuO and ZnO. The bimetallic materials were employed for the adsorptive separation of propene and propane. The samples prepared from the as-prepared SBA-15 showed superior performance to their counterparts from the calcined SBA-15 in terms of both adsorption capacity of propene and selectivity for propene/propane.     

Fabrication and photocatalytic evaluation of functionalized chitosan decorated vanadium pentoxide nano-adsorbents for water remediation

The narrow bandgap and rapid interconversion of the oxidation states of vanadium in vanadium pentoxide makes it an extensively used photocatalyst for the degradation of organic pollutant but inadequate response towards visible spectrum and low quantum yield limits its activity. Here, functionalized chitosan decorated vanadium pentoxide nano-adsorbents are fabricated that exhibited significant sensitivity to visible light absorption and shows more efficient quantum yield by the transformation of absorbed light into radiated light. Further, they were used in the photodegradation of methylene blue under natural conditions. The characterization results demonstrated the presence of chitosan and its derivatives over the surface of nanoparticles. Decorated vanadium pentoxide nano-adsorbents exhibited enhanced surface area and better catalytic properties which increases the photodegradation by lowering the recombination rate of charge and hole. Among the decorated nano-adsorbents, chitosan-anisaldehyde decorated vanadium pentoxide (CHVD₃) possessed wedge-shaped pore that favoured the photocatalytic degradation of methylene blue followed by others synthesized nanoparticles. The degradation rate constant and half life time for CHVD₃ were 3.84 × 10^?3 min^?1 and 18.07 min respectively. Major species responsible for the degradation and the mechanism has been elucidated by taking into consideration the degradation process in absence and presence of various scavengers. The degradation performance of CHVD₃ was severely affected, reducing from 92% to 36% in the presence of the scavenger, where *O₂^? act as a major active species in degradation process.     

Porous alkali-activated material from hypergolic coal gangue by microwave foaming for methylene blue removal

Overall, 100% hypergolic coal gangue (HCG)-based geopolymer foams were produced by a novel saponification-microwave foaming combined route. Microwave foaming with and without expired vegetable oil was first used to produce CG-based geopolymer foams. Macropores were mainly generated by microwave foaming, and mesopores were mainly obtained by the addition of expired soybean oil that underwent a saponification reaction. The effects of the oil content on the density, porosity, pore morphology, compression strength, and methylene blue adsorption properties were studied. High total porosity (85.9–89.0 vol%) and acceptable compression strength (0.46–1.1 MPa) HCG-based geopolymer foams were produced. Foams with 12.59 wt% oil exhibited the best adsorption properties, with an adsorption capacity up to 9.4 mg/g and high removal efficiency of about 95.3%. These solid-waste-based porous components are promising monolithic adsorbents for wastewater treatment.