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Your search keyword '"Chew, Jia Wei"' showing total 128 results
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128 results on '"Chew, Jia Wei"'

28. Nucleation of water clusters on functionalised graphite with kinetic Monte Carlo scheme

Author

Tan, Johnathan Shiliang, Do, D. D., Chew, Jia Wei, School of Chemical and Biomedical Engineering, Nanyang Environment and Water Research Institute, and Singapore Membrane Technology Centre

Subjects
Chemical technology [Engineering], General Chemical Engineering, Modeling and Simulation, General Materials Science, Adsorption, Kinetic Monte Carlo, General Chemistry, Condensed Matter Physics, Information Systems
Abstract

Although activated carbon is generally hydrophobic, water can adsorb on its surface due to the presence of functional groups. During the initial interactions between functional groups and water molecules, atoms of the functional groups rotate around the sigma bonds to maximise the electrostatic interactions. This physical process was simulated within the framework of kinetic Monte Carlo (kMC). We extended kMC to account for the rotation of the atoms of functional groups around the sigma bonds by entropic sampling of the orientation space, and tested the modified kMC scheme for adsorption of water on graphite functionalised with either hydroxyl groups or carboxyl groups. Results show that the amount adsorbed is greater when the rotation of atoms around the sigma bonds is allowed. The interspacing of functional groups also affects the adsorbed density. It was found that the optimum distances between hydroxyl groups and carboxyl groups to initiate water cluster are 0.4 and 0.7 nm, respectively, because of the synergistic effect of electrostatic interactions between water molecule and adjacent functional groups. This effect is reduced when the spatial distance is either decreased (because of the increasing importance of the repulsion) or increased (because of the loss of the synergetic effect). Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) This study was supported by A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Pharma Innovation Programme Singapore (PIPS) [A20B3a0070]; A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Individual Research Grant (IRG) program [A2083c0049]; the Singapore Ministry of Education Academic Research Tier 1 [grant numbers 2019-T1-002-065; RG100/19] and the Singapore Ministry of Education Academic Research Tier 2 [grant number MOE-MOET2EP10120-0001].

Published
2022
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31. Reticular materials for wastewater treatment

Author

Mou, Yi, primary, Yuan, Xingzhong, additional, Chen, Haoyun, additional, Yang, Yi, additional, Dai, Huan, additional, Bai, Jing, additional, Chen, Junying, additional, Chew, Jia Wei, additional, Wang, Hou, additional, and Wu, Yan, additional

Published
2023
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47. Solids flux profiles of Geldart Group A particles in high‐velocity circulating fluidized bed risers.

Author

Issangya, Allan S., Karri, S. B. Reddy, Cocco, Ray A., Knowlton, Ted, and Chew, Jia Wei

Subjects
RISER pipe, CATALYTIC cracking, GAS flow, FLUIDIZATION, SOLIDS, PARABOLA
Abstract

Circulating fluidized bed (CFB) risers using Group A particles have traditionally, mostly, been considered to operate in the fast fluidization regime, which consists of a core‐annulus flow profile with solids refluxing in the annulus layer. High gas and solids flow riser studies, however, suggest the existence of additional types of flow behaviours. Therefore, more studies are still needed to help clear uncertainties of local solids flow patterns in CFB risers of Group A particles, especially at gas and solids flow rates at or near those in commercial units. In this study, riser density and local solids flux profiles were measured in 0.3 m diameter risers of three CFB units at gas velocities of 9–16 m/s and solids fluxes of up to 700 kg/s · m2. A variety of radial solids flux profiles were obtained, including a parabolic profile with a peak flux at about the radial centre, a nearly flat profile across the riser cross‐section and an inverted parabola with peak upwards flux near the wall. At high gas velocity and solids flux, risers have no solids downflow at the wall. Multiple fluidization regimes were found to exist in the riser. The bottom dense part of the riser was in the dense suspension upflow regime, and the dilute upper part was in the dilute pneumatic transport regime. With commercial fluid catalytic cracking (FCC) risers operating at nearly similar conditions as tested here, it is likely that they also have one or both fluidization regimes and not the traditional fast fluidization regime. The data in this study fitted well on the Kim et al. fluidization regime map. [ABSTRACT FROM AUTHOR]

Published
2023
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48. Membrane filtration of dextran solutions with water and formamide as solvent.

Author

Yin, Ziqiang, Aggarwal, Siddharth, Yeow, Rique Jie En, Kong, Lingxuan, and Chew, Jia Wei

Subjects
MEMBRANE separation, ULTRAFILTRATION, DEXTRAN, FORMAMIDE, SURFACE charges, SOLVENTS
Abstract

In this study, we investigated and compared the performance (permeate flux, solute rejection and membrane fouling) of an ultrafiltration membrane and a nanofiltration membrane with water and formamide as solvent. The dextran solutions with water as solvent had lower electrical conductivity and usually greater surface charge compared to that in formamide, which facilitated the electrostatic interactions taken place. As a result, faster flux decline and greater fouling resistance were usually observed in water-based solutions in both UF and NF with the same dextran used as solute. In UF, the solute rejection usually increased as the solvent switched from formamide to water, since stronger electrostatic interactions tended to impede the transport of solute through membrane. Opposite trend was found with NF, that formamide usually led to higher solute rejection compared to water as solvent. Despite the differences of surface charge altered the membrane performance prominently, no quantitative correlation was found between permeate flux and zeta potential values. The analysis using a modified Hermia's pore blocking model indicates that the fouling mechanisms could be altered as the change of solute to membrane pore size ratio, surface charge of membranes and solutes, as well as the solvent properties. [ABSTRACT FROM AUTHOR]

Published
2022
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49. Thermochromic Ionogel: A New Class of Stimuli Responsive Materials with Super Cyclic Stability for Solar Modulation

Author

Lee, Heng Yeong, Cai, Yufeng, Velioglu, Sadiye, Mu, Chengzhong, Chang, Chen Jian, Chen, Yi Ling, Song, Yujie, Chew, Jia Wei, and Hu, Xiao Matthew

Abstract

In this work, a new class of polyurethane based ionogels that can respond to external stimulus, e.g., temperature, has been synthesized. The ionogels are mechanically robust and undergo an LCST-type phase transition with no volume change upon heating accompanied by a switching of optical transmittance. The optical switching temperature is tunable within a wide range between subzero to over 100 °C. Molecular dynamic simulation aided molecular design and provided further mechanistic understanding. Apart from the LCST-type transition, these ionogels are absent of freezing point and volatility and demonstrated unprecedented superhigh optical cyclic stability even after 5000 heating–cooling cycles with no detectable liquid leaching. In addition, these ionogels are chemically compatible with a range of additives such as organic dyes and photothermal plasmonic conducting nanoparticles which endow multifunctionality and versatility in terms of applications. A model mini-house affixed with the ionogel-incorporated glazing demonstrates a reduction of indoor temperature by up to 20 °C far superior to state-of-the-art tungstate coated glazing. This new class of ionogels marks an important milestone in smart materials development for a range of applications including autonomous and climate-adaptable solar modulation window.

Published
2024
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50. Fast Pyrolysis of Cellulose, Hemicellulose, and Lignin: Effect of Operating Temperature on Bio-oil Yield and Composition and Insights into the Intrinsic Pyrolysis Chemistry

Author

Ansari, Khursheed B., Arora, Jyotsna S., Chew, Jia Wei, Dauenhauer, Paul J., and Mushrif, Samir H.

Abstract

Fast pyrolysis of biomass produces bio-oil as a dominant product. However, the yield and composition of bio-oil are governed by numerous pyrolysis reactions which are difficult to understand because of the multiphase decomposition phenomena with convoluted chemistry and transport effects at millisecond time scales. In this work, thin-film pyrolysis experiments of biopolymers present in the biomass (i.e., cellulose (∼50 μm), hemicellulose (using xylan as a model biopolymer, ∼12 μm), and lignin (∼10 μm)) were performed over 200–550 °C, to investigate underlying thermal decomposition reactions, based on the product distribution obtained under reaction-controlled operating conditions. Experimental yields of non-condensable gases, bio-oil, and char at different operating temperatures and in the absence of transport limitations were obtained for each biopolymer. Cellulose- and xylan-derived bio-oil comprised of anhydrosugars, furans, and light oxygenates, in addition to pyrans in cellulosic bio-oil and phenols in xylan-derived bio-oil. Lignin pyrolysis bio-oil contained methoxyphenols, phenolic aldehydes/ketones, low-molecular-weight phenols, and light oxygenates. With an increase in the operating temperature, the anhydrosugars, furans (especially HMF and furfural), and pyrans of cellulosic and xylan bio-oils showed further degradation to form light oxygenates and furanic compounds. In the case of lignin, monolignols, initially formed at lower temperatures, further reacted to form low-molecular-weight phenols and light oxygenates with an increase in the operating temperature. In addition, based on the change in bio-oil yield and composition with temperatures, a reaction network/map was proposed for designing the molecular simulation studies of pyrolysis chemistry and developing detailed and accurate kinetics necessary for the bottom-up design of a pyrolysis reactor.

Published
2024
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