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Adsorption is a potential technology that is expected to meet NOx ultra-low emission standards and achieve the recovery of NO2. In this study, the adsorption/desorption behavior of NOx with competitive gases (e.g., H2O(g) and CO2) was studied on MFI zeolites with different Si/Al ratios and under different relative humidity (0~90% RH). Sample characterization of self-synthesizing zeolites was conducted by means of X-ray diffraction, Ar adsorption-desorption, and field emission scanning electron microscopy. The results showed that low-silica HZSM-5(35) showed the highest NOx adsorption capacity of 297.8 μmol/g (RH = 0) and 35.4 μmol/g (RH = 90%) compared to that of other adsorbents, and the efficiency loss factor of NOx adsorption capacity at 90%RH ranged from 85.3% to 88.1%. A water-resistance strategy was proposed for NOx multicomponent competitive adsorption combined with dynamic breakthrough tests and static water vapor adsorption. The presence of 14% O2 and lower adsorption temperature (25 °C) favored NOx adsorption, while higher CO2 concentrations (~10.5%) had less effect. The roll-up factor (η) was positively correlated with lower Si/Al ratios and higher H2O(g) concentrations. Unlike Silicalite-1, HZSM-5(35) exhibited an acceptable industrial desorption temperature window of NO2 (255~265 °C). This paper aims to provide a theoretical guideline for the rational selection of NOx adsorbents for practical applications. [ABSTRACT FROM AUTHOR]

A small scale (~270 Nm3·h−1) vacuum pressure swing adsorption (VPSA) air separation system was established in Qinghai Province (in China) with an altitude of 3800 m, which was used to supply oxygen for relieving the hypoxia. The effects of adsorption and desorption time, purge and pressure equalization step and feed temperature on the performance of the process were investigated by performing experiments under plateau special conditions. Results showed that pressure equalization and intermittent purge steps could effectively improve the performance of the VPSA process. The system could produce 270 Nm3·h−1 of 90% O2 with 62.6% oxygen recovery from compressed air. The maximum productivity and minimum energy consumption with pressure ratio of 160:42 for ~90% O2 were 121.7 L·h−1·kg−1 and 0.55 kWh·Nm−3, respectively. [ABSTRACT FROM AUTHOR]

Naphthalene (NAP) is a typical gaseous polycyclic aromatic hydrocarbons (PAHs) pollutant that displays toxicological effects on biosystems. Ordered mesoporous carbon has relatively adequate adsorption capacity; however, the attached hydrophilic functional groups were proven to affect the adsorption performance in the presence of moisture. In this paper, trimethylchlorosilane (TMCS) is used to carry out the hydrophobic modification of ordered mesoporous carbon FDU-15, and the adsorption and desorption properties of FDU-15 were studied. Furthermore, the adsorption isotherms of naphthalene on FDU-15 and modified FDU-15 were fitted by L-F equation, and the kinetic parameters of desorption of naphthalene on modified FDU-15 were analyzed based on the method of temperature programming desorption (TPD). The results showed that the micropore volume and specific surface area of FDU-15 were significantly increased after hydrophobically modified by TMCS, and the polar functional groups of the hydrophobically modified FDU-15 were significantly reduced. Furthermore, the adsorption of naphthalene by FDU-15 before and after modification conformed to the L-F equation (R2 > 99%), and the adsorption of naphthalene by modified FDU-5 at low concentration was significantly improved due to the increase of micropores. Based on desorption kinetic performance study of modified FDU-15, it can be seen that the adsorption kinetic characteristics of naphthalene on the modified FDU-15 conform to the mechanical function of the JMA equation. When the mass ratio of TMCs to FDU-15 is 1:10 in the modification process, the pore structure and surface hydrophobicity of the modified FDU-15 reach an excellent balance. At this time, the adsorbent had the optimum desorption performance under experimental conditions, and the desorption activation energy was decreased from 60.98 kJ/mol of FDU-15 to 50.28 kJ/mol. [ABSTRACT FROM AUTHOR]

Adsorption as an air purification method is widely employed to remove volatile organic compounds with low concentration using zeolites. In this study, ZSM-5 and LSX zeolites modified by alkali metal cations (Li+, Na+ and K+) were used as adsorbents for the abatement of toluene. The adsorption behaviors of toluene onto adsorbents with different pore sizes and cation contents were evaluated systematically based on the experiments of adsorption equilibrium, kinetic diffusion and desorption. Besides, Langmuir and Freundlich model, constant-pattern wave propagation model and Kissinger method were applied to fit with the above experimental data. The adsorption amount followed the sequence of Li-LSX > Na-LSX > K-LSX > Li-ZSM-5 > Na-ZSM-5 > K-ZSM-5 obtained from equilibrium isotherms. LSX zeolites showed twice adsorption capacity on unit volume compared to ZSM-5. The mechanisms of steric hindrances and electrostatic interactions controlling the diffusion rate under high and low concentrations were proposed, respectively. At relatively low loadings of toluene, the diffusion resistances were primarily affected by electrostatic interaction due to preferential adsorption of toluene on cationic sites. While at relatively high loadings, the diffusion resistance was mainly restricted by steric effect because of saturated cationic sites. The strength of adsorbate-adsorbent interactions was assessed by temperature programmed desorption experiments. It showed that both adsorption sites and microporous walls contributed to the desorption energy. [ABSTRACT FROM AUTHOR]

[Display omitted] • Comparisons of NO x adsorption and desorption among series of zeolites are conducted. • Effects of zeolite structures, cations, SiO 2 /Al 2 O 3 ratios on NO x sorption are shown. • H-typed 10-membered-ring straight-channel zeolite is selected as preferred sorbent. • Importance of kinetics of NO oxidation-NO 2 physisorption process is revealed. • Accessibility of Brønsted acid sites that drives NO-NO 2 catalytic cycle is discussed. Adsorption is a promising technology for deep purification of nitrogen oxides (NO x) from flue gases and simultaneously recycling NO 2 as an economically valuable chemical. Zeolite as a robust NO x adsorbent provides the key step for success in practical applications, of which the screening remains challenging regarding the NO-NO 2 oxidation and adsorption combined process. In this work, experimental evaluations on practical NO x sorption performances on series of zeolites were conducted. Effects of the zeolite typological structure, compensating cation, and SiO 2 /Al 2 O 3 ratio on deep purification efficacy, water resistance, and regenerability at varying humidity were obtained, revealing the importance of kinetics of the NO oxidation and NO 2 physisorption consecutive process. The H-typed 10-membered-ring straight-channel zeolites (MFI and FER) were demonstrated to be the preferred NO x adsorbents qualified for industrial needs, as compared to other caged-channel, hybrid-channel, larger-sized straight-channel, or Na-typed counterparts. Deeper insights into the key role of Brønsted acid sites (BAS) in driving the NO-NO 2 catalytic cycle and promoting the adsorption competitiveness of NO x over water vapor were revealed based on in-situ diffuse reflectance Fourier transform infrared spectroscopy characterizations. The MFI zeolite with improved performance at the low-silica version could benefit from the efficient utilization of BAS within the highly accessible medium-sized straight channel, while the FAU zeolite (representative caged-channel zeolite) requiring appropriate SiO 2 /Al 2 O 3 ratio for optimal BAS utilization may suffer from the limited site accessibility. The findings clarify the relationships between NO x oxidative adsorption performances and zeolite properties, which provides a fundamental perspective and scientific screening strategy for NO x adsorbents. [ABSTRACT FROM AUTHOR]

The kinetics of the thermal desorption of CO2 adsorbed on zeolite 13X were obtained using a differential thermogravimetric analyser under two different carrier gas conditions. The varying heating rates were set as 8, 12, 16, and 20 K min−1, respectively. The desorption activation energy of the physisorption sites for this experiment evaluated by an integral method without prediction of the reaction order ranged from 12.15 to 14.12 kJ mol−1 (CO2 as the carrier gas) and 43.32 to 50.42 kJ mol−1 (Ar as the carrier gas), respectively. The desorption activation energy of the chemisorption sites ranged from 57.95 to 58.53 kJ mol−1 (CO2 as the carrier gas) and 74.02 to 79.92 kJ mol−1 (Ar as the carrier gas), respectively. [ABSTRACT FROM AUTHOR]

Adsorption is a promising technology for simultaneously capturing nitrogen oxides (NO x) from flue gases and recycling NO 2 as a profitable chemical, for which a robust and efficient adsorbent provides the key step for success in practical applications. This work reports the enhancement of NO x adsorption performances with less cost of desorption energy on Cu-ZSM-5 zeolites prepared by a facile and rapid (690 s) modification method, the incipient-wetness impregnation coupled with microwave drying (IM). In comparisons to H-ZSM-5, Na-ZSM-5 and conventionally liquid-phase ion-exchanged counterparts under sub-1000 ppm NO x feed concentrations and room temperature, the IM sample renders a record NO x adsorption capacity (q t,NOx) of 0.878 mmol/g from dry gas stream on zeolites, and an applicable q t,NOx of 0.1 mmol/g from wet gas stream with a proper copper loading (2.1 wt%). The temperature programmed desorption of NO x on the optimal IM sample saturated with NO x from wet gas stream exhibit primary peak temperature lower than reported Cu-ZSM-5 and significant NO 2 proportion (72.6 %) in desorbed NO x. Deeper insights into advantageous NO x oxidative adsorption over the properly-loaded Cu-ZSM-5 in terms of diverse adsorbate states and competitiveness towards H 2 O were gained, showing IM method a promising sorbent improvement strategy for practical use. [Display omitted] • Cu-ZSM-5 is prepared by incipient-wetness impregnation coupled with microwave drying. • A record NO x adsorption capacity at sub-1000 ppm dry gas feed on zeolites is obtained. • Applicable NO x adsorption capacity at wet feed is gained on properly-loaded Cu-ZSM-5. • Lower NO x desorption temperature and higher NO 2 proportion in desorbed gas are shown. • Advantageous NO x oxidative adsorption competing with H 2 O on Cu-ZSM-5 is revealed. [ABSTRACT FROM AUTHOR]

Capturing and recovering naphthalene as a profitable chemical from hot flue gas are of significance in terms of environmental protection with economic benefits, for which the adsorption technology using high-performance sorbents provides the key step for success in practical applications. Carbonaceous materials with hydrophobic natures have been shown to render high affinities with non-polar naphthalene, but remain challenging due to difficulties in tackling the trade-off between adsorption and desorption. This work reports a systematic investigation with deeper insights into adsorption equilibria, kinetics and regenerabilities of gaseous naphthalene on typical carbonaceous sorbents originated from different texture properties, including ordered mesoporous carbons (CMK-3, CMK-5 and FDU-15), carbon nanotubes (SWCNT and MWCNT) and a coconut-shell-based activated carbon (AC). The adsorption isotherm and breakthrough curves at wide feed concentration ranges and temperature programmed desorption curves for each sorbent were obtained along with series of theoretical model fitting. FDU-15 and CMK-5 were demonstrated as superior sorbents with high maximum adsorption capacities (1.13 and 1.735 mmol/g) and low desorption activation energy (62.66 and 72.68 kJ/mol), respectively exhibiting advantages of the 3-dimensional diffusion-controlled desorption upon a hexagonal pore arrangement and the efficient adsorption upon a reasonable mesopore-micropore hierarchical structure, in contrast to poor kinetics on pure microporosity (AC) and 1-dimensional topologies (CNTs). Deeper insights into the morphology-affinity relationship revealed advantageous naphthalene transport behaviors over 3-dimensional ordered mesoporosities with appropriate coexisting microporosities and narrower primary size (2–5 nm) or diverse forms of mesopore, which contribute toward reaching comprehensive balances of sorption performances. [Display omitted] • Adsorption equilibria of gaseous naphthalene on carbonaceous sorbents are obtained. • Regenerability with desorption kinetic triplet for each sorbent is quantified. • Ordered mesoporous carbons, FDU-15 and CMK-5, are demonstrated as superior sorbents. • 3-dimensional ordered mesoporosities with narrower primary size (2–5 nm) are favored. • Micropore-mesopore hierarchical structure gives high adsorption/desorption kinetics. [ABSTRACT FROM AUTHOR]