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In view of the characteristics and risks of ammonia, its removal is important for industrial production and environmental safety. In this study, viscose-based activated carbon fiber (ACF) was used as a substrate and chemically modified by nitric acid impregnation to enhance the adsorption capacity of the adsorbent for ammonia. A series of modified ACF-based adsorbents were prepared and characterized using BET, FTIR, XPS, and Boehm titration. Isotherm tests (293.15 K, 303.15 K, 313.15 K) and dynamic adsorption experiments were performed. The characterization results showed that impregnation with low concentrations of nitric acid not only increased the surface acidic functional group content but also increased the specific surface area, while impregnation with high concentrations of nitric acid could be able to decrease the specific surface area. ACF-N-6 significantly increased the surface functional group content without destroying the physical structure of the activated carbon fibers. The experimental results showed that the highest adsorption of ammonia by ACFs was 14.08 mmol-L−1 (ACF-N-6) at 293 K, and the adsorption capacity was increased by 165% compared with that of ACF-raw; by fitting the adsorption isotherm and calculating the equivalent heat of adsorption and thermodynamic parameters using the Langmuir–Freundlich model, the adsorption process could be found to exist simultaneously. Regarding physical adsorption and chemical adsorption, the results of the correlation analysis showed that the ammonia adsorption performance was strongly correlated with the carboxyl group content and positively correlated with the relative humidity (RH) of the inlet gas. This study contributes to the development of an efficient ammonia adsorption system with important applications in industrial production and environmental safety. [ABSTRACT FROM AUTHOR]

Granular activated carbon (GAC) has proven to be an effective adsorbent for removing the chemical warfare agent sarin (GB) and simulants like Dimethyl methylphosphonate (DMMP). However, it comes with certain limitations, including inadequate contact efficiency, notable mass transfer resistance, and lower bed utilization efficiency. This study synthesized steel fiber-entrapped activated carbon composites (SFEACs), which exhibited a maximum adsorption capacity of 285.3 mg/g at 303 K. Compared with the packed bed (PB) filled with GAC, while the adsorption capacity of SFEACS decreased, there was a substantial increase in the adsorption mass transfer rate. These SFEACs were combined with GAC to create a structural fixed bed (SFB), which demonstrated excellent performance in DMMP removal. Under identical experimental conditions, the DMMP breakthrough curve of SFB exhibited a steeper profile compared to the packed bed (PB) filled with GAC at the same bed height, and the breakthrough time against DMMP vapor could be extended by 13.8%. Furthermore, the adsorption rate constant of the Yoon-Nelson model increased by more than 17.6%, and the unused bed length, according to the Wheeler–Jonas model, decreased by more than 14%. [ABSTRACT FROM AUTHOR]

[Display omitted] • The experimental and molecular simulation results show that the influence of water vapor on DMMP adsorption equilibrium is small in the range of relative humidity 0–90%. • The adsorption is mainly driven by van der Waals force, and the adsorption potential energy between DMMP molecules and GAC active sites is much higher than that of water molecules. • The presence of polar functional groups, such as hydroxyl, has a significant effect on the adsorption equilibrium of DMMP. • Molecular dynamics simulations revealed that the presence of water had little effect on the diffusion of DMMP molecules in GAC pores. The adsorption behavior of Dimethyl methylphosphonate (DMMP), as a simulant of sarin nerve agent, especially in the presence of water vapor, is crucial for the design of efficient chemical protection equipment. Experimental results reveal DMMP's adsorption isotherm on granular activated carbon (GAC) as a typical type I. The adsorption process was a spontaneous and exothermic physical adsorption process, and the adsorption mechanism was in accordance with Dubinin's micropore filling theory. In the relative humidity range of 10 % ∼ 90 %, the isotherm remained I-type, and the effect of water vapor on the equilibrium adsorption capacity and apparent adsorption rate was weak. Molecular simulations also show that DMMP adsorption on GAC follows a type I isotherm, primarily driven by van der Waals forces of physical adsorption. The adsorption potential energy between DMMP and GAC surpasses that of water molecules, resulting in negligible effects from water vapor on DMMP adsorption equilibrium. Meanwhile, water molecules had minimal effect on the diffusion of DMMP molecules in the GAC pores, and the positional distribution of DMMP multilayer adsorption was consistent under different relative humidity conditions. Furthermore, the presence of polar functional groups such as hydroxyl groups significantly affects the adsorption equilibrium of DMMP. [ABSTRACT FROM AUTHOR]

Composite bed involves an alternative technique in which a layer of micro-fibrous entrapped composite material is added at the downstream end of a conventional fixed bed to strengthen the mass transfer process. In this study, our purpose was to compare the ability of composite beds to remove volatile organic compounds (VOCs) and Freon refrigerants with conventional fixed beds and analyse the effect of relative humidity (RH) on multicomponent organic vapor adsorption on composite beds. This would be used to guide the design of composite beds and their application in air purification. A series of micro-fibrous entrapped activated carbons (MFECs) were prepared using the wet layer paper-making/sintering technologies. The 1,1,1,2-tetrafluoroethane (R134a) and C 6 H 6 breakthrough curves and times on composite beds were systemically evaluated under dry and wet conditions. Results show that under dry condition, due to the enhanced mass transfer, the R134a and C 6 H 6 breakthrough times on composite beds were longer than on fixed beds. Under wet conditions, due to the water vapor competitive adsorption and the difference in organic vapor boiling point, the composite bed prolonged the C 6 H 6 breakthrough time but weakened the R134a breakthrough time. Multicomponent competitive adsorption process (R134a/C 6 H 6) under wet conditions was revealed and divided into six stages including Co-adsorption, H 2 O and R134a breakthrough, R134a desorption, R134a and H 2 O adsorption equilibrium, C 6 H 6 breakthrough, and dynamic adsorption equilibrium. These findings indicated that composite beds may improve the breakthrough time of low-concentration C 6 H 6 and lengthen the service life of conventional fixed beds at any RH, thereby displaying potential for use as an application in air purification. [Display omitted] • A series of micro-fibrous entrapped activated carbons (MFECs) were prepared economically using standard wet layer paper-making/sintering procedures and characterized. • Under dry and wet air conditions, single/double-component breakthrough curves of R134a and C 6 H 6 on composite beds were measured. The influence of relative humidity and organic vapor adsorption ability was first reported. • The competitive process of the R134a, C 6 H 6 , and could be divided into VI Stages. ACF-MFEC entrapped ACP-1 presents better stability and reusability in C 6 H 6 removal. [ABSTRACT FROM AUTHOR]

[Display omitted] • R134a and water vapor adsorption isotherms on AC-2 were measured and investigated via the Single/Dual-site Langmuir-Freundlich model. At the same pressure, the increasing temperature could weaken R134a adsorption capacity. • Under different experimental conditions, R134a breakthrough curves were systemically measured. Due to water vapor competitive adsorption, with increasing relative humidity or moisture content, R134a breakthrough times on AC-2 fixed beds were weakened. • Using the R134a breakthrough curve as the standard, dynamic competitive processes of R134a and water vapor could be divided into four stages: co-adsorption, co-breakthrough, competitive adsorption ("Rolling Up" and "Adsorption Platform"), and dynamic adsorption equilibrium. 1.1.1.2-Tetrafluoroethane (R134a) is developed as a tracer for mechanical leakage detection in military chemistry. Due to the weaker physical adsorption properties, water vapor competitive adsorption limits the use of tracer R134a. Thus, it is urgent to the analyze dynamic competitive adsorption behavior of R134a and water vapor on the activated carbon. In this study, R134a breakthrough curves on the fixed beds packed with activated carbons under different relative humidity and moisture content levels were systematically measured. Combining mass spectrometry, gas chromatography, and a novel fiber Bragg grating temperature sensor, the dynamic competitive adsorption processes and axial temperature of fixed beds were first reported. Interestingly, with increasing moisture content, R134a breakthrough time decreased, but dynamic adsorption capacity increased. This was attributed to the fact that the residual water vapor could increase the specific surface area and pore volume of activated carbon to enhance R134a dynamic adsorption capacity. Using the R134a as the standard, the dynamic competitive adsorption process was first revealed and could be divided into four stages including Co-adsorption, Co-breakthrough, Competitive Adsorption ("Rolling Up" and "Adsorption Platform"), and Dynamic Adsorption Equilibrium. "Rolling Up" and "Adsorption Platform" phenomena are mainly determined by the strength of intermolecular interactions, the concentration difference of adsorbate, and the thermal effect induced by water vapor adsorption/desorption. [ABSTRACT FROM AUTHOR]

A static volumetric method measured the water vapor adsorption isotherms on porous activated carbons (AC and ASC-T) at 278.15 K ～ 308.15 K. Because of the difference in surface oxygen-containing functional groups, a Type-V isotherm represented water vapor adsorption on AC, whereas a Type-IV isotherm characterized ASC-T. The applicability of seven classical adsorption equilibrium models was analyzed and compared systemically. Results show that the Dual-sites Langmuir-Freundlich equation had the lowest residual errors (< 6 ml/g). Further, based on the linearization DA equation, a new partitioned segment-fitting strategy was first developed to describe multi-temperature adsorption isotherms. Two sets of the division points (P/P 0) and parameters (n) were acquired. For AC and ASC-T, the best division point (P/P 0) and parameter (n) were equal to 0.1 and 0.9, 0.2 and 2, respectively. The fitted results of multi-temperature adsorption isotherms show that the R2 values of AC and ASC-T both were bigger than 0.93, showing that the new fitting strategy has very good applicability. It offers the possibility to address the problem of the accurate description for multi-temperature water vapor adsorption data on porous activated carbons. [Display omitted] • Water vapor adsorption isotherms on activated carbons (AC and ASC-T) were measured at 278.15 K ～ 308.15 K using the volumetric method, Adsorption isotherms showed Type-V and Type-IV, respectively. • For the seven classical adsorption equilibrium models, the Dual-site Langmuir-Freundlich equation has a best-fitting result. In the residual range of 0 ml/g to 4 ml/g, the fitted residuals for AC and ASC-T accounted for 85.29% and 100%, respectively. • A new partitioned segment-fitting strategy was developed to use to fit multi-temperature adsorption isotherms. The calculated values of R 2 for AC and ASC-T both are bigger than 0.93 and better than multi-temperature QHR and modified BET equations. [ABSTRACT FROM AUTHOR]

• The single adsorption isotherms of R134a and water vapor on ASZMT were measured and fitted by experiments and adsorption equilibrium models, respectively. • The adsorption selectivity and the binary adsorption equilibrium of water vapor and R134a on ASZMT were investigated via the DIH method and IAST method, respectively. • The different competitive adsorption behavior between R134a and water vapor in different pore size, which is mainly dominated by water vapor concentration, was revealed. • The effect of relative humidity was further examined through R134a breakthrough curves. As an efficient tracer gas of activated carbon filter quality testing, the use of R134a is limited by relative humidity (RH) due to water vapor competitive adsorption. To analyze the competitive effect, the isosteric heats between vapor and ASZMT were calculated by C – C equation, the adsorption selectivity was predicted using the DIH method, and the binary adsorption equilibrium of water vapor and R134a on ASZMT were investigated via IAST model. Results showed that water vapor exhibited a higher isosteric heat than R134a at the same adsorption capacity, indicating a stronger interaction with ASZMT. The water vapor/R134a adsorption selectivity on ASZMT increases from 0 to 6.6, proving that the ASZMT is more selective for water vapor than R134a with water vapor pressure increasing. Besides, with water vapor pressure ratio improving, the R134a adsorption capacity on ASZMT decreases obviously, but water vapor adsorption capacity keeps increasing continuously. R134a breakthrough curves (1000 ppm) also showed that with relative humidity increasing, the R134a breakthrough times and dynamic adsorption capacities both became shorter, from 15 min to 9 min and from 6.68 mg/g to 1.49 mg/g, respectively. It proves that R134a and water vapor have obvious competitive adsorption behavior which is mainly dominated by water vapor concentration. It is necessary for ppm-level R134a to control the lower relative humidity of airflow in application. [ABSTRACT FROM AUTHOR]