Development of Activated Carbon Fibers from Wool Felts as Carbon Dioxide Adsorbents

In this study, activated carbon fibers (ACFs) were produced from mechanically recycled acrylic (PAN) and cotton (CO) fibers and their blend (PAN/CO) in felt form as an adsorbent for carbon dioxide capture. For this purpose, stabilization, carbonization, and chemical activation processes were applied consecutively. The effects of recycled fiber type, carbonization temperature, and activation agent impregnation ratio were investigated. The resultant ACFs were characterized by elemental analysis, SEM, FTIR, XPS, and BET analyses, and carbon dioxide adsorption capacity was tested. It was observed that the fibrous structure of all samples was preserved at all stages, although the fiber diameters were reduced. The maximum quantity of adsorbed CO2 was found to be 3.79, 3.47, and 3.28 mmol CO2/g for recycled PAN, CO, and PAN/CO based samples, respectively, at 298 K at a relative pressure of 0.989. It was conducted that the carbon dioxide adsorption performance was affected by both the ACF surface area and the nitrogen content in the structure. It was concluded that recycled fiber‐based ACFs as CO2 adsorbents could be successfully produced with reasonable adsorption performance as a sustainable alternative.Highlights Activated carbon fibers were produced from recycled acrylic and cotton fibers Fibrous structure was preserved, but fiber diameters decreased Reasonable carbon dioxide adsorption capacity was attained Recycled fiber‐based ACFs could be a sustainable alternative to CO2 adsorbents

Porous hyper-cross-linked aromatic polymers are one ofthe emergingclasses of porous organic polymers with the potential for industrialapplication. Four different porous polymeric materials have been preparedusing different precursors (indole, pyrene, carbazole, and naphthalene),and the composition and textural properties were analyzed. The materialswere characterized in detail using different physicochemical techniqueslike scanning electron microscopy, transmission electron microscopy,nitrogen adsorption at 77 K, Fourier transform infrared spectroscopy,X-ray diffraction, etc. The effect of textural properties and nitrogenspecies on carbon dioxide and nitrogen adsorption capacities and selectivitywas studied and discussed. The carbon dioxide and nitrogen adsorptioncapacities were measured using a volumetric gas adsorption system.The adsorption data were fitted into different adsorption models,and the ideal absorbed solution theory was used to calculate adsorptionselectivity. Among the studied samples, POP-4 shows the highest carbondioxide and nitrogen adsorption capacities. While POP-1 shows maximumCO2/N2 selectivity of 78.0 at 298 K and 1 barpressure. It is observed that ultra-micropores, which are presentin the prepared materials but not measured during conventional surfacearea measurement via nitrogen adsorption at 77 K, play a very importantrole in carbon dioxide adsorption capacity and determining the carbondioxide selectivity over nitrogen. Surface nitrogen also increasesthe CO2 selectivity in the dual mode by increasing carbondioxide adsorption via the acid–base interaction as well asby decreasing nitrogen adsorption due to N–N repulsion.

Polyacrylonitrile-based activated carbon fibers (ACFs), modified using potassium hydroxide (KOH) or tetraethylenepentamine (TEPA), were investigated for carbon dioxide (CO2) adsorption, which is one of the promising alleviation approaches for global warming. The CO2 adsorption isotherms were measured, and the values of isosteric heat of adsorption were calculated. The results showed that the KOH-modified ACFs exhibited a great deal of pore volume, and a specific surface area of 1565 m2/g was obtained. KOH activation made nitrogen atoms easily able to escape from the surface of ACFs. On the other hand, the surface area and pore volume of ACFs modified with TEPA were significantly reduced, which can be attributed to the closing or blocking of micropores by the N-groups. The CO2 adsorption on the ACF samples was via exothermic reactions and was a type of physical adsorption, where the CO2 adsorption occurred on heterogeneous surfaces. The CO2 uptakes at 1 atm and 25 °C on KOH-activated ACFs reached 2.74 mmole/g. This study observed that microporosity and surface oxygen functionalities were highly associated with the CO2 uptake, implying the existence of O-C coordination, accompanied with physical adsorption. Well cyclability of the adsorbents for CO2 adsorption was observed, with a performance decay of less than 5% over up to ten adsorption-desorption cycles.

Influence of nickel oxide on carbon dioxide adsorption behaviors of activated carbons

Activated carbon fiber (ACF) is widely used sorbent material for wastewater treatment. Three natural cellulosic fibres (kapok, cotton, and ramie) and three regenerated cellulosic fibres (bamboo fiber, viscose, and lyocell) are used to prepare ACFs using chemical activation. These ACFs are characterized using scanning electron microscope, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) testing, elemental analysis, adsorption property and nitrogen adsorption–desorption. XRD and FTIR spectrum of all six cellulosic ACFs are almost similar showing that ACFs have almost same chemical and physical composition. All cellulosic ACFs are constituted of C, H, ash and O, but C content is higher in natural cellulosic fibres. Surface morphology and surface area of cellulosic ACFs play the basic role in adsorption. The 2nd order pseudo kinetic model is fitted for all cellulosic ACFs as R2 > 0.99 and adsorption controlling process is chemical sorption. The adsorption capacity of the kapok-based ACFs is best, owing to their hollow structure, the micropores on surface and high specific surface area. Bamboo, ramie and cotton based ACFs also have high adsorption but they need more time to adsorb impurities than kapok based ACFs. Viscose based ACFs shows moderate adsorption, while the least adsorption is shown by the lyocell based ACFs because of their smooth and uniform structure. Adsorption analysis and other properties evaluation show that kapok fiber is the best precursor than other five cellulosic fibres.

Pitch‐based activated carbon fibers were prepared for application to methane storage. Chemical activation was accomplished by treatment with potassium hydroxide and heat, leading to increased specific surface area and micropore volume. Structural properties and morphology were evaluated by X‐ray diffraction and scanning electron microscopy, respectively. Textural properties and microporosity were determined from N2 /77 K adsorption–desorption isotherms using the Brunauer–Emmett–Teller equation and the Horvath–Kawazoe method. The methane storage capacity is influenced by activation time. This is attributed to the creation of a narrow distribution of micropores, which is a factor closely related to the methane storage capacity. This indicates that the methane storage behavior depends on the pore volume. Although a large pore volume is desirable for methane storage, the size of the pores in the activated carbon fibers that facilitate the activation process is also a significant factor.

Selective adsorption of supercritical carbon dioxide and methane binary mixture in shale kerogen nanopores

To promote the adsorption and activation of carbon dioxide in the dry reforming of methane (DRM), Ni and Al2O3 were coprecipitated on activated carbon fibers (ACF). Various characterization methods were adopted in order to investigate the surface characteristics of different catalysts. Chemisorption characterization results, such as H2-temperature programmed reduction (H2-TPR), H2-temperature programmed desorption (H2-TPD), and CO2-temperature programmed desorption (CO2-TPD) illustrated that ACF in a nickel-based catalyst could enhance the basic sites and improve the metal dispersion on a catalyst surface, which is beneficial for the adsorption and activation of feed gas. The coprecipitated coating on ACF proved by scanning electron microscope (SEM) can prevent the carbon of ACF from participating in the reaction, while retain good surface properties of carbon fibers. X-ray diffraction (XRD) patterns illustrated that the ACF in a nickel-based catalyst could decrease the crystallite size of the spinel NiAl2O4, which is beneficial for methane reforming. In addition, the Fourier transform infrared spectroscopy (FTIR) of different catalysts revealed that the added ACF could provide abundant functional groups on the surface, which could be the intermediate product of DRM, and effectively promote the reaction. Different to the catalyst supported on single alumina, the performance evaluation and stability test proved that the catalyst added with ACF exhibited a better catalytic performance especially for CO2 conversion. Moreover, based on the characterization results as well as some related literature, the dry reforming mechanism over optimum catalyst was derived.

Climate change, global warming, and rise in water levels are environmental problems caused by the high emissions of greenhouse gases, and the most harmed one is carbon dioxide. Biochar is a material produced by thermochemical conversions with oxygen-depleted conditions of organic materials, and this process calls pyrolysis. Recently, it has been evaluated as a carbon dioxide capture, and its porous structure, structural properties, and production methods are easy. Al Ghaf (Prosopis cineraria) tree is one of the United Arab Emirates’ national trees with a wide range of intriguing properties, including high nutritional value, medicinal/pharmaceutical potential, and biosorption. This paper focuses on the biochar synthesized from three parts of the Al Ghaf tree: leaves, roots, and branches, to determine which part can achieve the maximum carbon dioxide capture. The ability of the produced biochar to capture carbon dioxide was tested through direct gas–solid​ interaction inside an integrated fluidized bed reactor. The carbon dioxide adsorption capacity was expressed by two methods related to (a) the loaded biochar mass and (b) the total amount of carbon dioxide fed to the reactor. The carbon dioxide adsorption capacity results concerning the loaded mass were 6.88%, 5.50%, and 3.63% for leaves, roots, and branches, respectively. At the same time, the results based on the total amount of carbon dioxide fed were 65.5%, 58.7%, and 37.7% for leaves, roots, and branches, respectively. Such results were confirmed by the physicochemical characteristics of the synthesized biochar using Scanning Electron Microscopy with Energy Dispersive X-ray Analysis, Thermogravimetric analysis (TGA), and X-ray diffraction analysis. Al Ghaf tree requires further study and inquiry to identify the most appropriate applications.

In order to investigate the adsorption characteristics of activated carbon fibers (ACFs) with improved surface morphologies towards volatile organic compounds (VOCs), a commercial low-grade ACF was surface modified by successive surface treatment (ST) and chemical activation (CA) process. O3 was used as an ST agent for the formation of oxygen-containing functional groups on the carbon matrix of ACFs. CA was carried out after ST, using a KOH solution. After the successive ST-CA process, Brunauer-Emmett-Teller (BET) surface area and average pore diameter of ACFs were increased from 1483 m2/g to 2743 m2/g and enlarged from 1.931 nm to 2.512 nm, respectively. The successive ST-CA process also resulted in the adsorption capacities of benzene, toluene, and xylene of the ACFs to increase from 0.22 g−Ben./g−ACFs, 0.18 g−Tol./g−ACFs, and 0.19 g−Xyl/g−ACFs up to 0.37 g−Ben./g−ACFs, 0.35 g−Tol./g−ACFs, and 0.38 g−Xyl/g−ACFs, respectively.

Surface thermodynamics of hydrocarbon vapors and carbon dioxide adsorption on shales

Activated carbons derived from viscose fibers were prepared using potassium hydroxide, carbon dioxide, or water vapor as activation agents. The produced activated carbon fibers were analyzed via scanning electron microscopy and energy dispersive X-ray spectroscopy, and their porosity (specific surface area, total pore volume, and pore size distribution) was calculated employing physisorption experiments. Activated carbon fibers with a specific surface area of more than 2500 m2 g−1 were obtained by each of the three methods. Afterwards, the suitability of these materials as electrodes for electrochemical double-layer capacitors (supercapacitors) was investigated using cyclic voltammetry, galvanostatic measurements, and electrochemical impedance spectroscopy. By combining CO2 and H2O activation, activated carbon fibers of high purity and excellent electrochemical performance could be obtained. A specific capacitance per electrode of up to 180 F g−1 was found. In addition, an energy density per double-layer capacitor of 42 W h kg−1 was achieved. These results demonstrate the outstanding electrochemical properties of viscose-based activated carbon fibers for use as electrode materials in energy storage devices such as supercapacitors.

Carbon fibers and activated carbon fibers are materials of high industrial interest. When presented as a felt, its use becomes easier and more practical. This work aims to study the conditions for obtaining and characterizing an activated carbon felt, using sheep wool as a precursor. The wool felt was oxidized, carbonized in nitrogen atmosphere and activated in water vapor. The working temperatures were selected through thermogravimetric analysis. The products and intermediates were characterized through thermogravimetric analysis, infrared spectroscopy, scanning electron microscopy, Raman spectroscopy and nitrogen adsorption-desorption. The products were assessed as potential sorbents for methane-carbon dioxide separation by adsorption kinetics measurements at different pressures. Results revealed a high influence of the carbonization temperature on the physicochemical and textural properties of the products. The adsorption kinetics and capacities of the gases showed that selectivities in separation were related to both felt carbonization temperature and gas pressure. This work revealed that activated carbon wool felts are a good alternative to synthetic fibers felt and they can be used for methane/carbon dioxide separation.

Activation of coal tar pitch carbon fibres: Physical activation vs. chemical activation

Adsorption technology has emerged as a viable approach to reducing CO2 emissions. Generally, activated carbons-based adsorbents, in particular, are promising due to their abundant availability, tunable physicochemical properties, and suitability over a wide temperature range. In this study, activated carbons (ACC) modified with magnesium oxide (MgO) was evaluated for carbon dioxide capture in an adsorption process. ACC, the feedstock, was produced using the fast pyrolysis of Astragalus. The availability and cheapness of the Astragalus material next to MgO led to the synthesis of a new compound called ACC/MgO. The aim of this new synthetic compound was to achieve a cost-effective approach to carbon dioxide adsorption. This approach somehow shows the innovation of the work. Another innovation is adsorbent moulding (monolith) and its industrialisation. The synthetic material underwent various analyses, including FTIR, XRD, SEM, BET, and EDX. Fifteen experiments were designed using the response surface methodology-Box-Behnken (RSM-BBD) design to determine the maximum carbon dioxide adsorption capacity (ADC). One of the optimal points, with the highest carbon dioxide ADC (1.355 mmol/g), was determined at an initial MgO loading of 13.26 wt.%, an average ACC particle size of 0.58 mm, and a Polyvinyl alcohol (PVA) content of 6.34 wt.%. Kinetic models and isotherm models were employed to analyse the adsorption data. The findings indicated that the entire adsorption range could be described by employing the fractional-order model. Investigation into the diffusion mechanism revealed that both film diffusion and intraparticle diffusion predominantly governed the rate-limiting steps. The adsorbent exhibited favourable regeneration at lower temperatures and demonstrated consistent regenerability following seven cycles of adsorption and regeneration. This research demonstrated that ACC modified with MgO is a suitable adsorbent due to its high capacity and efficiency in carbon dioxide capture.