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Papers by mahmoud parvazinia
Catalysis Research, 2023
In this review article, the main methods of synthesizing and applications of hypercrosslinked ma... more In this review article, the main methods of synthesizing and
applications of hypercrosslinked materials are studied. Porous
structure, high specific surface area, and pore volume make
these materials an excellent choice for different applications
including gas storage, carbon capture, and molecular
separation, removal of pollutants, catalysis, and drug delivery
and sensing. In this review article, catalytic applications are
particularly considered.
Annals of Chemical Science Research
International Journal of Chemical Kinetics
Catalysts
In this study, a mathematical model for the time evolution of molecular weight distribution (MWD)... more In this study, a mathematical model for the time evolution of molecular weight distribution (MWD) was developed. This temporal model is based on the well-known Ziegler–Natta polymerization mechanism and reaction kinetics by the parametric solving of related differential equations. However, due to the generality of the reactions involved, the model can be extended to the other type of catalysts, such as metallocenes, Phillips, etc. The superiority of this model lies in providing the possibility of a more precise prediction over the active sites and kinetic parameters using a simple mathematical equation, which leads to improved reactor design in large-scale production. The model uses a function to develop a methodology for MWD calculations. In this way, the transient response is limited to the first few minutes of the reaction; however, it is important as it demonstrates the establishment of the final MWD. According to the results, almost for practical conditions with negligible tran...
Finite Element Modeling of Multiscale Transport Phenomena, 2010
Proceedings of the 1998 American Control Conference. ACC (IEEE Cat. No.98CH36207), 1998
In a batch reactor for the methyl methacrylate polymerization (MMA), temperature control was stud... more In a batch reactor for the methyl methacrylate polymerization (MMA), temperature control was studied. Three methods of heat-release estimation (HRE), namely, kinetic model (KM), online energy balance (OLEB) and calorimetric-state estimator (CSE) were investigated. The following three criteria were used to assess these methods: (i) Ability to adjust kinetic errors. (ii) Ability to adjust against dynamic errors. (iii) Sensitivity to temperature noises. The results indicate that the CSE method has a better performance with respect to kinetic and dynamic errors. Additionally, by using this method, the temperature control design becomes self-tuning
Finite Elements in Analysis and Design, 2012
ABSTRACT A method for the stable-accurate solution of convection–diffusion and diffusion-reaction... more ABSTRACT A method for the stable-accurate solution of convection–diffusion and diffusion-reaction equations is proposed to produce a solution similar to highly refined meshes for any level of discretisation. The method is applied on finite element and finite difference methods. The idea is based on the analytical or numerical solutions of the governing equation in a test domain and then determining the level of adjustment in an element with length l by solving the global system of equations in the test domain. The adjustment can be done either on the coefficients of the equation or enrichment of normal shape functions in the Galerkin finite element scheme. The numerical experiments are performed in one and two dimensional cases. Different mesh schemes and boundary conditions are used. To validate the approach, the numerical results obtained for a benchmark problem are compared with the analytical solution in a wide range of Damköhler and Peclet numbers.
The Brinkman equation is used to model the isothermal flow of the Newtonian fluids through highly... more The Brinkman equation is used to model the isothermal flow of the Newtonian fluids through highly permeable porous media. Due to the multiscale behaviour of this flow regime the standard Galerkin finite element schemes for the Brinkman equation require excessive mesh refinement at least in the vicinity of domain walls to yield stable and accurate results. To avoid this, a multiscale finite element method is developed using bubble functions. It is shown that by using bubble enriched shape functions the standard Galerkin method can generate stable solutions without excessive near wall mesh refinements. In this paper the performances of different types of bubble functions are evaluated. These functions are used in conjunction with bilinear Lagrangian elements to solve the Brinkman equation via a penalty finite element scheme.
Finite Element Modeling of Multiscale Transport Phenomena, 2010
A two-dimensional (2D) single particle model for the copolymerization of propylene-ethylene with ... more A two-dimensional (2D) single particle model for the copolymerization of propylene-ethylene with heterogeneous Ziegler-Natta catalyst is developed. The model accounts for the effects of the initial shape of the catalyst and carck/ pore patterns on the copolymer composition, polymerization rate and the average molecular weight properties. The spherical and oblate ellipsoidal shapes of catalyst particle and four different pattern distributions of cracks and pores in a growing particle are studied in this simulation. It is assumed that the diffusion coefficient of monomers in the cracks/pores is 10 times higher than the compact zone of the particle.In other word, the cracks are distinguished from parts with higher monomer diffusion coefficient.The dynamic 2D monomer diffusion-reaction equation is solved together with a two-site catalyst kinetic mechanism using the finite element method. Simulation results indicate that the initial shape of catalyst changes the average copolymer composi...
The main focus of the present research work has been the development of a multi-scale finite elem... more The main focus of the present research work has been the development of a multi-scale finite element modelling technique for transport phenomena. Initially the isothermal steady flow of a Newtonian fluid through highly permeable porous media has been modelled and then the method is extended to more complex problems such as the convection–diffusion equation. The standard Galerkin method is used to model the flow in highly permeable porous media and, considering the disadvantages of this method the focus of study is moved to methods which can deal with multi-scale problems. Two-dimensional models based on both the continuous penalty method and the mixed method using the Taylor–Hood element are applied. The Brinkman model together with the continuity equation are used to simulate the flow in highly permeable porous media. In addition to the no-slip wall boundary conditions, the Navier's slip wall boundary conditions has been used in conjunction with the Brinkman equation to make it...
Atwo-dimensional single particle finite element model was used to examine the effects of particle... more Atwo-dimensional single particle finite element model was used to examine the effects of particle fragmental pattern on the average molecular weights, polymerization rate and particle overheating in heterogeneous Ziegler-Natta olefin polymerization. A two-site catalyst kinetic mechanism was employed together with a dynamic two-dimensional molecular species in diffusion-reaction equation. The initial catalyst active sites distribution was assumed to be uniform, while the monomer diffusion coefficient was considered to be different inside the fragments and cracks. In other words, the cracks were distinguished from fragments with higher monomer diffusion coefficient. To model the particle temperature a lumped heat transfer model was used. The fragmentation pattern was considered to remain unchanged during the polymerization. A Galerkin finite element method was used to solve the resulting two-dimensional (2-D) moving boundary value, diffusion-reaction problem. A two-dimensional polymer...
Gas phase polymerization of propylene was carried out in a semi-batch minireactor using a commerc... more Gas phase polymerization of propylene was carried out in a semi-batch minireactor using a commercially supported Ziegler–Natta (ZN) catalyst. The influence of variables including monomer partial pressure, external electron donor, reaction temperature and time on the particle morphology and size distribution was investigated. Generally, more uniform fragmentation and particle densities were obtained at lower reaction rates. Monomer partial pressure showed a significant role of particle size and its distribution, the higher the monomer partial pressure, the broader particle size distribution was obtained. Polymerization pressure had a significant role on the morphology of particles. Wider cracks and more porosity were resulted from the polymerizations at higher pressures. Furthermore, a broader particle size distribution was obtained from the polymerization at higher pressures. The particle size analysis revealed the monomer partial pressure as the most effective parameter on the dist...
Iranian Polymer Journal, 2017
Catalysis Research, 2023
In this review article, the main methods of synthesizing and applications of hypercrosslinked ma... more In this review article, the main methods of synthesizing and
applications of hypercrosslinked materials are studied. Porous
structure, high specific surface area, and pore volume make
these materials an excellent choice for different applications
including gas storage, carbon capture, and molecular
separation, removal of pollutants, catalysis, and drug delivery
and sensing. In this review article, catalytic applications are
particularly considered.
Annals of Chemical Science Research
International Journal of Chemical Kinetics
Catalysts
In this study, a mathematical model for the time evolution of molecular weight distribution (MWD)... more In this study, a mathematical model for the time evolution of molecular weight distribution (MWD) was developed. This temporal model is based on the well-known Ziegler–Natta polymerization mechanism and reaction kinetics by the parametric solving of related differential equations. However, due to the generality of the reactions involved, the model can be extended to the other type of catalysts, such as metallocenes, Phillips, etc. The superiority of this model lies in providing the possibility of a more precise prediction over the active sites and kinetic parameters using a simple mathematical equation, which leads to improved reactor design in large-scale production. The model uses a function to develop a methodology for MWD calculations. In this way, the transient response is limited to the first few minutes of the reaction; however, it is important as it demonstrates the establishment of the final MWD. According to the results, almost for practical conditions with negligible tran...
Finite Element Modeling of Multiscale Transport Phenomena, 2010
Proceedings of the 1998 American Control Conference. ACC (IEEE Cat. No.98CH36207), 1998
In a batch reactor for the methyl methacrylate polymerization (MMA), temperature control was stud... more In a batch reactor for the methyl methacrylate polymerization (MMA), temperature control was studied. Three methods of heat-release estimation (HRE), namely, kinetic model (KM), online energy balance (OLEB) and calorimetric-state estimator (CSE) were investigated. The following three criteria were used to assess these methods: (i) Ability to adjust kinetic errors. (ii) Ability to adjust against dynamic errors. (iii) Sensitivity to temperature noises. The results indicate that the CSE method has a better performance with respect to kinetic and dynamic errors. Additionally, by using this method, the temperature control design becomes self-tuning
Finite Elements in Analysis and Design, 2012
ABSTRACT A method for the stable-accurate solution of convection–diffusion and diffusion-reaction... more ABSTRACT A method for the stable-accurate solution of convection–diffusion and diffusion-reaction equations is proposed to produce a solution similar to highly refined meshes for any level of discretisation. The method is applied on finite element and finite difference methods. The idea is based on the analytical or numerical solutions of the governing equation in a test domain and then determining the level of adjustment in an element with length l by solving the global system of equations in the test domain. The adjustment can be done either on the coefficients of the equation or enrichment of normal shape functions in the Galerkin finite element scheme. The numerical experiments are performed in one and two dimensional cases. Different mesh schemes and boundary conditions are used. To validate the approach, the numerical results obtained for a benchmark problem are compared with the analytical solution in a wide range of Damköhler and Peclet numbers.
The Brinkman equation is used to model the isothermal flow of the Newtonian fluids through highly... more The Brinkman equation is used to model the isothermal flow of the Newtonian fluids through highly permeable porous media. Due to the multiscale behaviour of this flow regime the standard Galerkin finite element schemes for the Brinkman equation require excessive mesh refinement at least in the vicinity of domain walls to yield stable and accurate results. To avoid this, a multiscale finite element method is developed using bubble functions. It is shown that by using bubble enriched shape functions the standard Galerkin method can generate stable solutions without excessive near wall mesh refinements. In this paper the performances of different types of bubble functions are evaluated. These functions are used in conjunction with bilinear Lagrangian elements to solve the Brinkman equation via a penalty finite element scheme.
Finite Element Modeling of Multiscale Transport Phenomena, 2010
A two-dimensional (2D) single particle model for the copolymerization of propylene-ethylene with ... more A two-dimensional (2D) single particle model for the copolymerization of propylene-ethylene with heterogeneous Ziegler-Natta catalyst is developed. The model accounts for the effects of the initial shape of the catalyst and carck/ pore patterns on the copolymer composition, polymerization rate and the average molecular weight properties. The spherical and oblate ellipsoidal shapes of catalyst particle and four different pattern distributions of cracks and pores in a growing particle are studied in this simulation. It is assumed that the diffusion coefficient of monomers in the cracks/pores is 10 times higher than the compact zone of the particle.In other word, the cracks are distinguished from parts with higher monomer diffusion coefficient.The dynamic 2D monomer diffusion-reaction equation is solved together with a two-site catalyst kinetic mechanism using the finite element method. Simulation results indicate that the initial shape of catalyst changes the average copolymer composi...
The main focus of the present research work has been the development of a multi-scale finite elem... more The main focus of the present research work has been the development of a multi-scale finite element modelling technique for transport phenomena. Initially the isothermal steady flow of a Newtonian fluid through highly permeable porous media has been modelled and then the method is extended to more complex problems such as the convection–diffusion equation. The standard Galerkin method is used to model the flow in highly permeable porous media and, considering the disadvantages of this method the focus of study is moved to methods which can deal with multi-scale problems. Two-dimensional models based on both the continuous penalty method and the mixed method using the Taylor–Hood element are applied. The Brinkman model together with the continuity equation are used to simulate the flow in highly permeable porous media. In addition to the no-slip wall boundary conditions, the Navier's slip wall boundary conditions has been used in conjunction with the Brinkman equation to make it...
Atwo-dimensional single particle finite element model was used to examine the effects of particle... more Atwo-dimensional single particle finite element model was used to examine the effects of particle fragmental pattern on the average molecular weights, polymerization rate and particle overheating in heterogeneous Ziegler-Natta olefin polymerization. A two-site catalyst kinetic mechanism was employed together with a dynamic two-dimensional molecular species in diffusion-reaction equation. The initial catalyst active sites distribution was assumed to be uniform, while the monomer diffusion coefficient was considered to be different inside the fragments and cracks. In other words, the cracks were distinguished from fragments with higher monomer diffusion coefficient. To model the particle temperature a lumped heat transfer model was used. The fragmentation pattern was considered to remain unchanged during the polymerization. A Galerkin finite element method was used to solve the resulting two-dimensional (2-D) moving boundary value, diffusion-reaction problem. A two-dimensional polymer...
Gas phase polymerization of propylene was carried out in a semi-batch minireactor using a commerc... more Gas phase polymerization of propylene was carried out in a semi-batch minireactor using a commercially supported Ziegler–Natta (ZN) catalyst. The influence of variables including monomer partial pressure, external electron donor, reaction temperature and time on the particle morphology and size distribution was investigated. Generally, more uniform fragmentation and particle densities were obtained at lower reaction rates. Monomer partial pressure showed a significant role of particle size and its distribution, the higher the monomer partial pressure, the broader particle size distribution was obtained. Polymerization pressure had a significant role on the morphology of particles. Wider cracks and more porosity were resulted from the polymerizations at higher pressures. Furthermore, a broader particle size distribution was obtained from the polymerization at higher pressures. The particle size analysis revealed the monomer partial pressure as the most effective parameter on the dist...
Iranian Polymer Journal, 2017