Browsing by Author "Xing, Yi"

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A numerical modelling study of SO2 adsorption on activated carbons with new rate equations
(2018-12-01)
Li, Ziyi
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Liu, Yingshu
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Wang, Haihong
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Tsai, Chuen-Jinn
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Yang, Xiong
Modelling dynamic adsorption of sulfur dioxide (SO2) on activated carbons (ACs) is significant in guiding practical desulphurization processes and making highly efficient use of adsorbents in terms of the adsorption rate which largely depends on particle size. In this work, models derived from the Vermeulen and an improved linear driving force (LDF) rate equation were studied for the first time on SO2 adsorption over AC particles with different sizes. For larger particles (>= 3 mm), breakthrough curves predicted by the Vermeulen equation showed good agreement with experimental data, demonstrating that intraparticle diffusion resistance varied with particle size, feed concentration, adsorption time and location. For smaller particles (1 mm), a correction on the volume-averaged adsorption capacity as a function of adsorption time and saturation in the rate equation was developed to avoid the underestimation of adsorption rate due to the inappropriate parabolic concentration profile inherent in the conventional LDF model. By providing a concentration gradient and adsorption rate closer to actual values, the improved LDF equation was confirmed to provide excellent prediction results on 1-mm particles. Different modelling characteristics of the two models indicates varying effects of intraparticle diffusion on adsorption rate with particle size regarding the specificity of SO2 physisorption on ACs.
Adsorption phenomena and related mechanisms of airborne nanoparticles on porous materials
(2018-08-19)
Li, Ziyi
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Liu, Yingshu
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Tsai, Chuen-Jinn
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Xing, Yi
;
Lu, Pei
Desorption of Polycyclic Aromatic Hydrocarbons on Mesoporous Sorbents: Thermogravimetric Experiments and Kinetics Study
(2016-02-10)
Li, Ziyi
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Liu, Yingshu
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Yang, Xiong
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Xing, Yi
;
Tsa, Chuenjinn
The desorption performances of naphthalene and pyrene on mesoporous MCM-41, SBA-15, and CMK-3 sorbents are studied on the basis of temperature-programmed desorption experiments over the temperature range of 350-800 K at different heating rates. The kinetic parameters for each sorbate sorbent pair are determined with combined model-fitting methods. The data for naphthalene and pyrene are best fitted with the same kinetic models on MCM-41 (with 1D mesopore channels), in contrast to those on SBA-15 and CMK-3, which have micropore mesopore structures, leading to different desorption mechanisms for these two sorbates. SBA-15 with interconnectivity between adjacent mesopores not only shows high sorption capacities but also offers diffusion advantages in desorption, which contributes to the order of the degree of ease in desorption: SBA-15 > MCM-41 > CMK-3. CMK-3, with higher microporosity and hydrophobicity, shows stronger binding with the adsorbates while still benefiting in pyrene desorption from the consecutive mesoporosity.
Experimental research on purifying ultrafine nanoparticle by SBA-15 and its filtration mechanism
(2018-05-01)
Xing, Yi
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Yu, Han
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Lu, Pei
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Li, Ziyi
;
Liu, Yingshu
Airborne ultrafine nanoparticle (UFNP) is a key factor causing heavy haze pollution in Beijing-Tianjin-Hebei, which is very harmful to human health and the environment. Removal of environmental UFNPs by porous material is an important method of air purification treatment. However, the specific mechanism by which porous material filters UFNPs is not clear. In this study, UFNPs with 2-10 nm diameter were removed by SBA-15 mesoporous silica molecular sieves with different pore sizes, and the filtration mechanism was analyzed using transmission electron microscopy (TEM), specific surface area tests (BET), and X-ray photoelectron spectroscopy (XPS). The analyses showed a distinctive filtration of UFNPs over the interior mesopore channels. The removal efficiencies of SBA-15 with different pore sizes were also compared, demonstrating the influence of the pore size and structure on most penetrating particle size (MPPS). The UFNP filtration efficiency of SBA-15 increased with the increase of pore size. Moreover, SBA-15-14.6 could effectively purify UFNPs, and it had the highest fractional diffusive filtration efficiency of 98.79% and a total efficiency of 92.58% for UFNPs. This study provides a technical basis for the filtration of UFNPs using mesoporous materials. (C) 2018 Elsevier B.V. All rights reserved.
Getting insight into the influence of coexisting airborne nanoparticles on gas adsorption performance over porous materials
(2020-03-15)
Xing, Yi
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Cui, Yongkang
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Li, Ziyi
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Liu, Yingshu
;
Bao, Danqi
Adsorption as one of the most important air cleaning methods has been extensively applied during which the coexisting airborne nanoparticles (NPs) with sizes close to adsorbent pore sizes could inevitably influence gas adsorption processes. In this work, the influence of sub-20 nm NPs on toluene adsorption on ZSM-5 zeolites exchanged with different cations (Li+, Na+ and K+) were studied based on gas-and-particle coexisting adsorption/filtration tests. Affinities for both toluene and NPs on adsorbents follow Li-ZSM-5 > Na-ZSM-5 > K-ZSM-5 regarding the orders of charge density, pore size, and internal and external specific surface areas. The toluene adsorption was shown to be impaired by coexisting NPs from perspectives of thermodynamics and kinetics. For Li-ZSM-5, Na-ZSM-5 and K-ZSM-5, significant relative reductions of 10.4 %, 10.5 % and 16.0 % in toluene adsorption capacity at the lower feed concentration, and of 20.3 %, 15.2 % and 2.3 % in mass transfer coefficient at the higher feed concentration were observed, respectively. The influential mechanisms regarding competitiveness between toluene and NPs in interaction with cationic and porous surfaces were accordingly proposed, which are of practical significance for selecting robust adsorbents under realistic harsh air conditions.
Novel Wire-on-Plate Electrostatic Precipitator (WOP-EP) for Controlling Fine Particle and Nanoparticle Pollution
(2015-07-21)
Li, Ziyi
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Liu, Yingshu
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Xing, Yi
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Thi-Minh-Phuong Tran
;
Thi-Cuc Le
A new wire-on-plate electrostatic precipitator (WOP-EP), where discharge wires are attached directly on the surface of a dielectric plate, was developed to ease the installation of the wires, minimize particle deposition on the wires, and lower ozone emission while maintaining a high particle collection efficiency. For a lab-scale WOP-EP (width, 50 mm; height, 20 mm; length, 180 mm) tested at the applied voltage Of 18 kV, experimental total particle collection efficiencies were found as high as 90.9-99.7 and 98.8-99.9% in the particle size range of 30-1870 nm at the average air velocities of 0.50 m/s (flow rate, 30 L/min; residence time, 0.36 s) and 0.25 m/s (flow rate, 15 L/min; residence time, 0.72 s), respectively. Particle collection efficiencies calculated by numerical models agreed well with the experimental results. The comparison to the traditional wire-in-plate EP showed that, at the same applied voltage, the current WOP-EP emitted 1-2 orders of magnitude lower ozone concentration, had cleaner discharge wires after heavy particle loading in the EP, and recovered high particle collection efficiency after the grounded collection plate was cleaned. It is expected that the current WOP-EP can be scaled up as an efficient air-cleaning device to control fine particle and nanopartide pollution.
Performance of mesoporous silicas (MCM-41 and SBA-15) and carbon (CMK-3) in the removal of gas-phase naphthalene: adsorption capacity, rate and regenerability
(2016-01-01)
Liu, Yingshu
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Li, Ziyi
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Yang, Xiong
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Xing, Yi
;
Tsai, Chuenjinn
The adsorption isotherms of naphthalene on three typical mesoporous adsorbents, mesosilicas MCM-41 and SBA-15, and mesocarbon CMK-3 were determined by column tests at 125 degrees C, with feed concentrations ranging from 7.63 x 10(-5) to 4.64 x 10(-2) mol m(-3) (1.88 to 1140 ppm). The Langmuir model and constant-pattern wave propagation model were found to well fit the isotherms and the breakthrough curves, respectively. Regenerabilities of the mesoporous samples and a benchmark activated carbon (AC) were characterized based on thermogravimetric analysis (TGA). The results show mesoporosity significantly reduced the internal mass-transfer resistance, contributing to facile desorption and to fast adsorption kinetics shown by high overall mass-transfer rate coefficient following the order of: CMK-3 > SBA-15 > MCM-41. Micropore-mesopore coexisting structures present in CMK-3 and SBA-15 facilitated the adsorption at very low concentrations due to micropore-filling, while greater surface hydrophobicity and micropore abundance on CMK-3 exhibited larger affinity for nonpolar naphthalene, rendering the highest adsorption capacity (1.014 mol m(-3)) among all sorbents including ACs. SBA-15 showed higher regenerability with a desorption temperature below 440 K, owing to the weaker binding and diffusion advantages contributed by the interconnectivity between primary mesopores.
Performance of mesoporous silicas and carbon in adsorptive removal of phenanthrene as a typical gaseous polycyclic aromatic hydrocarbon
(2017-02)
Li, Ziyi
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Liu, Yingshu
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Yang, Xiong
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Xing, Yi
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Tsai, Chuen-Jinn
Adsorptive removal of the predominant polycyclic aromatic hydrocarbons (PAHs), represented by phenanthrene, from hot gases using mesoporous adsorbents (mesosilicas MCM-41 and SBA-15, and mesocarbon CMK-3) has been studied through tests of column adsorption and temperature programmed desorption (TPD). Adsorption equilibria on MCM-41 and CMK-3, and on SBA-15 were well described by Langmuir and Freundlich models, respectively, showing the order of adsorption capacity of CMK-3 > SBA-15 > MCM-41 originated from different geometrical structures and texture properties. Adsorption dynamics based on breakthrough fitting by the constant-pattern wave propagation model showed that mesoporosity contributed to fast overall adsorption kinetics by reducing the internal resistance as being the predominant mass-transfer step, particularly on SBA-15 with a 2-D cross-linked structure. The TPD tests revealed the order of ease of desorption of SBA-15 approximate to MCM-41 > CMK-3, where the structural advantage on SBA-15 dominated the strong site binding as indicated by the intrinsic activation energy and exponential factor obtained by TPD models. Results from different TPD models showed that re-adsorption effect during desorption increased with decreasing dimension of adsorbent structure and that the utilization of the simplified linear TPD model could be violated by the strong sorbate-sorbent binding. Comparisons with traditional adsorbents and with the removal of naphthalene by these mesoporous adsorbents were made, showing higher applicability of CMK-3 for phenanthrene regarding stronger adsorption affinity and capacity as well as decreased disadvantages in regenerability relative to mesosilicas. (C) 2016 Elsevier Inc. All rights reserved.
Removal of ultrafine particles by porous nanomaterials with varied morphologies
(2019-01-15)
Yin, Likun
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Yang, Xiong
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Xing, Yi
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Lu, Pei
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Tsai, Chuen-Jinn
The removal characteristics of sub-25 nm ultrafine particles (UFPs) by different porous nanomaterials with different morphologies were studied based on efficiency curves obtained with specially designed filtration system. The material morphological effects on UFPs collection were investigated. The results demonstrate a complex and synergic mechanism of material structural framework, pore size distribution, and porosity order in terms of diffusion and interception dependent on flow velocity. Both porosity and fiber-like tubular structures promoted the UFPs removal. Microporosity and disordered mesoporosity could enhance the roughness of the internal surface and intensify the interaction with UFPs. Specifically, the large and ordered mesoporosity was able to render selectivity for UFPs at certain sizes and exhibited the best particle collection performance which can be largely associated with significant pore size and volume. The dependence of the ratio of diffusion to interception on flow velocity and the comparison of different pores in terms of the matching sizes with particles derived from single sphere efficiency model fitting results were also discussed. This work is significant to deeper understanding of interactions between airborne nanoparticles and porous surfaces. (C) 2018 Published by Elsevier B.V.
Research Progress of Gaseous Polycyclic Aromatic Hydrocarbons Purification by Adsorption
(2019-04-01)
Yang, Xiong
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Li, Ziyi
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Liu, Yingshu
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Xing, Yi
;
Wei, Jinchao
Gaseous polycyclic aromatic hydrocarbons (PAHs) are carcinogenic and mutagenic pollutants and also able to promote the growth of secondary particulate matters, which have attracted great attention in recent years. Control of PAHs emissions in exhaust gases using different techniques has been hot topics in the atmospheric environment field. Adsorption is one of the most effective ones and is well accepted by industries in gaseous pollutant removal in which the adsorbent characteristics play critical roles. In this paper, the latest advances in the field of PAHs adsorption are critically reviewed with special emphasis on adsorption-desorption characteristics and related applications. Studies on adsorption equilibrium, kinetics, and desorption properties of PAHs as special low-volatile gases on conventional activated carbons and novel mesoporous adsorbents are summarized and compared, showing the advantages of mesoporous adsorbents over traditional adsorbents in terms of the fast adsorption and facile desorption. The significant factors on the optimal balance between adsorption and desorption as well as the corresponding adsorbent materials are discussed in detail. This work can be a reference for further studies on adsorptive purifications of PAHs and other low-volatile gases.