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Simulation of the effect of coke deposition on the diffusion of methane in zeolite ZSM-5

CHEMICAL ENGINEERING JOURNAL 2017年 320卷 458-467页

作者： Li, Yanping Zhang, Chenglong Li, Chengxiang Liu, Zhicheng Ge, Wei Tianjin Univ Sch Chem Engn & Technol Tianjin 300072 Peoples R China Collaborat Innovat Ctr Chem Sci & Engn Tianjin Tianjin 300072 Peoples R China Chinese Acad Sci State Key Lab Multiphase Complex Syst Inst Proc Engn Beijing 100190 Peoples R China Univ Chinese Acad Sci Sch Chem & Chem Engn Beijing 100049 Peoples R China SINOPEC Shanghai Res Inst Petrochem Technol Shanghai 201208 Peoples R China

Coke deposition is one of the main reasons for catalyst deactivation, which is often associated with coverage of the active sites and diffusion restrictions. In this article, the self-diffusion coefficient of methane in ZSM-5 (MFI) with different amounts of coke is studied through molecular dynamics simulation combining hard-sphere and pseudo-particle modeling at a gas loading of 4 molecules per unit cell at 723 K. The T12 tetrahedral sites are considered as the possible coke deposition sites at which the pore is blocked. It is shown that the self-diffusion coefficient of methane in ZSM-5 without coke (D-0) is approximately 7.0 x 10(-9) m(2)/s. Two coke distribution models are proposed to simulate the actual process of coke formation. At the initial stage of coke deposition, the coke with uniform distribution has little influence on the diffusion process. Once the coke deposits are randomly concentrated on some sites and a few pores are therefore completely blocked, the coke has a significant influence on the self-diffusion coefficient, which decreases to 37.0% of D-0 almost linearly with increasing coke amount to 20%. The distribution of coke deposition is the result of the coupling of reaction and diffusion processes. These results may be useful for understanding the reaction-diffusion coupling mechanism of the catalyst deactivation. (C) 2017 Elsevier B.V. All rights reserved.

关键词： Coke deposition Diffusion Molecular simulation Zeolite ZSM-5 pseudo-particle modeling

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Parallelization of pseudo-particle modeling and its application in simulating gas-solid fluidization

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Particuology 2009年第4期7卷 317-323页

作者： Jianxin Lu Jiayuan Zhang Xiaowei Wang Limin Wang Wei Ge Graduate School of Chinese Academy of Sciences Beijing 100049 China State Key Laboratory of Multiphase Complex Systems Institute of Process Engineering Chinese Academy of Sciences Beijing 100190 China

pseudo-particle modeling （PPM） is a particle method proposed by Ge and Li in 1996 [Ge, W., ＆ Li, J. （1996）. pseudo-particle approach to hydrodynamics of particle-fluid systems, in M. Kwauk ＆ J. Li （Eds.）, Proceedings of the 5th international conference on drculating fluidized bed （pp. 260-265）. Beijing： Science Press] and has been used to explore the microscopic mechanism in complex particle-fluid systems. But as a particle method, high computational cost remains a main obstacle for its large-scale application; therefore, parallel implementation of this method is highly desirable. Parallelization of two-dimensional PPM was carried out by spatial decomposition in this paper. The time costs of the major functions in the program were analyzed and the program was then optimized for higher efficiency by dynamic load balancing and resetting of particle arrays. Finally, simulation on a gas-solid fluidized bed with 102,400 solid particles and 1.8 × 10^7 pseudo-particles was performed successfully with this code, indicating its scalability in future applications.

关键词： Parallelization pseudo-particle modeling Gas-solid fluidization Dynamic load balancing

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Numerical study on gas-liquid nano-flows with pseudo-particle modeling and soft-particle molecular dynamics simulation

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MICROFLUIDICS AND NANOFLUIDICS 2008年第5期5卷 639-653页

作者： Chen, Feiguo Ge, Wei Wang, Limin Li, Jinghai Chinese Acad Sci Inst Proc Engn Beijing 100190 Peoples R China Chinese Acad Sci Grad Univ Beijing 100039 Peoples R China

We couple pseudo-particle modeling (PPM, Ge and Li in Chem Eng Sci 58(8):1565-1585, 2003), a variant of hard-particle molecular dynamics, with standard soft-particle molecular dynamics (MD) to study an idealized gas-liquid flow in nano-channels. The coupling helps to keep sharp contrast between gas and liquid behaviors and the simulations conducted provide a reference frame for exploring more complex and realistic gas-liquid nano-flows. The qualitative nature and general flow patterns of the flow under such extreme conditions are found to be consistent with its macro-scale counterpart.

关键词： gas-liquid two-phase flow nano-flow molecular dynamics pseudo-particle modeling

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Numerical study on gas-liquid nano-flows with pseudo-particle modeling and soft-particle molecular dynamics simulation

Numerical study on gas-liquid nano-flows with pseudo-particl...

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第五届全国化学工程与生物化工年会

作者： Chen Feiguo Ge Wei Wang Limin Li Jinghai Institute of Process Engineering Chinese Academy of SciencesBeijing 100190 Graduate University of C Institute of Process Engineering Chinese Academy of SciencesBeijing 100190

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Simulation of particle-fluid systems with macro-scale pseudo-particle modeling

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POWDER TECHNOLOGY 2003年第1-2期137卷 99-108页

作者： Ge, W Li, JH Chinese Acad Sci Multi Phase React Lab Inst Proc Engn Beijing 100080 Peoples R China

pseudo-particle modeling (PPM) is a particle method (PM) proposed in 1996. Though it is effective for the simulation of local phenomena in particle-fluid systems, its application to practical systems is still limited by computational cost. Therefore, macro-scale PPM, or MaPPM is proposed, which combines finite difference (FD) with weighted averaging techniques to upgrade particle interactions to the fluid element level. In this paper, a detailed derivation of the model is presented together with a clearer demonstration of the convergence and accuracy of the model. The approach is then applied to the problem of plane Poiseuille flow and particle-fluid suspension, resulting in a physically reasonable flow pattern. We conclude that MaPPM can be a promising alternative to FD and finite element (FE) approaches whenever multiple moving interfaces are encountered. (C) 2003 Elsevier B.V. All rights reserved.

关键词： computational fluid dynamics particle method multi-phase flow pseudo-particle modeling smoothed particle hydrodynamics

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A new wall boundary condition in particle methods

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COMPUTER PHYSICS COMMUNICATIONS 2006年第5期174卷 386-390页

作者： Wang, LM Ge, W Li, JH Chinese Acad Sci Inst Proc Engn Multiphase React Lab Beijing 100080 Peoples R China Chinese Acad Sci Grad Sch Beijing 100039 Peoples R China

We present a new formulation of the boundary condition for solid walls in particulate fluid flows. It integrates traditional treatments of bounce-back and Maxwellian reflections, and hence ensures both no-slip condition and effective thermostat on the wall. The formulation was validated in a series of simulations with pseudo-particle modeling [W. Ge, J. Li, Chem. Eng. Sci. 58 (2003) 1565-1585]. (c) 2005 Elsevier B.V. All rights reserved.

关键词： boundary conditions plane Poiseuille flow no-slip condition thermostat pseudo-particle modeling

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particle METHODS FOR COMPLEX FLOWS IN CHEMICAL ENGINEERING ——THE pseudo-particle APPROACH

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Particuology 2005年第Z1期 58-59页

作者： Wei GE and Jinghai LI Multi-Phase Reaction Laboratory, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100080, P. R. China

The multi-scale structures of complex flows in chemical engineering have been great challenges to the design and scaling of such systems, and multi-scale modeling is the natural way in response. particle methods (PMs) are ideal constituents and powerful tools of multi-scale models, owing to their physical fidelity and computational simplicity. Especially, pseudo-particle modeling (PPM, Ge & Li, 1996; Ge & Li, 2003) is most suitable for molecular scale flow prediction and exploration of the origin of multi-scale structures; macro-scale PPM (MaPPM, Ge & Li, 2001) and similar models are advantageous for meso-scale simulations of flows with complex and dynamic discontinuity, while the lattice Boltzmann model is more competent for homogeneous media in complex geometries; and meso-scale methods such as dissipative particle dynamics are unique tools for complex fluids of uncertain properties or flows with strong thermal fluctuations. All these methods are favorable for seamless interconnection of models for different scales. However, as PMs are not originally designed as either tools for complexity or constituents of multi-scale models, further improvements are expected. PPM is proposed for microscopic simulation of particle-fluid systems as a combination of molecular dynamics (MD) and direct simulation Monte-Carlo (DSMC). The collision dynamics in PPM is identical to that of hard-sphere MD, so that mass, momentum and energy are conserved to machine accuracy. However, the collision detection procedure, which is most time-consuming and difficult to be parallelized for hard-sphere MD, has been greatly simplified to a procedure identical to that of soft-sphere MD. Actually, the physical model behind such a treatment is essentially different from MD and is more similar to DSMC, but an intrinsic difference is that in DSMC the collisions follow designed statistical rules that are reflection of the real physical processes only in very limited cases such as dilute gas. PPM is idea

关键词： multi-scale method particle method pseudo-particle modeling multi-phase flow

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particle METHODS FOR COMPLEX FLOWS IN CHEMICAL ENGINEERING ——THE pseudo-particle APPROACH

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China Particuology 2005年第1期3卷 58-59页

作者： WeiGE JinghaiLI Multi-PhaseReactionLaboratory InstituteofProcessEngineeringChineseAcademyofSciencesBeijing100080P.R.China

关键词： multi-scale method particle method pseudo-particle modeling multi-phase flow

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