Ahmad Shamiri

The extensive amount of available information on global warming suggests that this issue has become prevalent worldwide. Majority of countries have issued laws and policies in response to this concern by requiring their industrial sectors to reduce greenhouse gas emissions, such as CO2. Thus, introducing new and more effective treatment methods, such as biological techniques, is crucial to control the emission of greenhouse gases. Many studies have demonstrated CO2 fixation using… Show more

The extensive amount of available information on global warming suggests that this issue has become prevalent worldwide. Majority of countries have issued laws and policies in response to this concern by requiring their industrial sectors to reduce greenhouse gas emissions, such as CO2. Thus, introducing new and more effective treatment methods, such as biological techniques, is crucial to control the emission of greenhouse gases. Many studies have demonstrated CO2 fixation using photo-bioreactors and raceway ponds, but a comprehensive review is yet to be published on biological CO2 fixation. A comprehensive review of CO2 fixation through biological process is presented in this paper as biological processes are ideal to control both organic and inorganic pollutants. This process can also cover the classification of methods, functional mechanisms, designs, and their operational parameters, which are crucial for efficient CO2 fixation. This review also suggests the bio-trickling filter process as an appropriate approach in CO2 fixation to assist in creating a pollution-free environment. Finally, this paper introduces optimum designs, growth rate models, and CO2 fixation of microalgae, functions, and operations in biological CO2 fixation. Show less

In the present study, experiments have been conducted to measure the surface tension and heat capacity of aqueous mixtures of N-methyldiethanolamine (MDEA) and ionic liquids (ILs) at atmospheric pressure. Two types of ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4] and 1-butyl-3-methyl-imidazolium dicyanamide [bmim][DCA]) were used in these experiments. The surface tension was found to decrease with increasing temperature and ionic liquid concentration. Furthermore, the heat… Show more

In the present study, experiments have been conducted to measure the surface tension and heat capacity of aqueous mixtures of N-methyldiethanolamine (MDEA) and ionic liquids (ILs) at atmospheric pressure. Two types of ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4] and 1-butyl-3-methyl-imidazolium dicyanamide [bmim][DCA]) were used in these experiments. The surface tension was found to decrease with increasing temperature and ionic liquid concentration. Furthermore, the heat capacity of the mixtures increases with decreasing ionic-liquid concentration and increasing temperature. Linear equations were used to correlate the measured surface tension values, quadratic equations were applied to correlate the heat capacity at different compositions and temperatures. Show less

The density and viscosity of aqueous mixtures of N-methyldiethanolamine (MDEA) and the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]), and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([emim][OTf]) were determined. The measurements were carried out at 1 atm pressure and temperatures ranging from (303.15 to 363.15) K. The concentration of MDEA was fixed at (2.0 and 4.0) M, whereas the IL… Show more

The density and viscosity of aqueous mixtures of N-methyldiethanolamine (MDEA) and the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]), and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([emim][OTf]) were determined. The measurements were carried out at 1 atm pressure and temperatures ranging from (303.15 to 363.15) K. The concentration of MDEA was fixed at (2.0 and 4.0) M, whereas the IL concentration was varied from (0.5 to 2.0) M. Both densities and viscosities were increased with increasing IL concentration. Correlation equations of density and viscosity for pure substances and for MDEA and ILs aqueous mixtures as a function of temperature and concentration of MDEA and ILs were also determined. The linear correlation for density had an excellent accuracy with less than 0.98 % deviation for all aqueous mixtures of MDEA and ILs. Meanwhile, the extended Arrhenius equation for viscosity achieved acceptable precision with less than 30 % of deviation from experimental data except for 2.0 M MDEA and 1.5 M [bmim][DCA] mixtures. Show less

A comparative study describing gas-phase propylene polymerization in flui-dized-bed reactors using Ziegler-Natta catalyst is presented. The reactor be-havior was explained using a two-phase model (which is based on principles of fluidization) as well as simulation using the Aspen Polymers process simulator.
The two-phase reactor model accounts for the emulsion and bubble phases which contain different portions of catalysts with the polymerization occurring in both phases. Both models… Show more

A comparative study describing gas-phase propylene polymerization in flui-dized-bed reactors using Ziegler-Natta catalyst is presented. The reactor be-havior was explained using a two-phase model (which is based on principles of fluidization) as well as simulation using the Aspen Polymers process simulator.
The two-phase reactor model accounts for the emulsion and bubble phases which contain different portions of catalysts with the polymerization occurring in both phases. Both models predict production rate, molecular weight, poly-dispersity index (PDI) and melt flow index (MFI) of the polymer. We used both models to investigate the effect of important polymerization parameters, namely catalyst feed rate and hydrogen concentration, on the product polypropylene properties, such as production rate, molecular weight, PDI and MFI. Both the two-phase model and Aspen Polymers simulator showed good agreement in terms of production rate. However, the models differed in their predictions for weight-average molecular weight, PDI and MFI. Based on these results, we propose incorporating the missing hydrodynamic effects into Aspen Polymers to provide a more realistic understanding of the phenomena encountered in fluidized bed reactors for polyolefin production. Show less

The control of a gas phase propylene polymerization model in a fluidized bed reactor were studied, where the rigorous two phase dynamic model takes into account the polymerization reactions occurring in the bubble and emulsion phases. Due to the nonlinearity of the process, the employment of an advanced control scheme for efficient regulation of the process variables is justified. In this case, the Adaptive Predictive Model-Based Control (APMBC) strategy (an integration of the Recursive Least… Show more

The control of a gas phase propylene polymerization model in a fluidized bed reactor were studied, where the rigorous two phase dynamic model takes into account the polymerization reactions occurring in the bubble and emulsion phases. Due to the nonlinearity of the process, the employment of an advanced control scheme for efficient regulation of the process variables is justified. In this case, the Adaptive Predictive Model-Based Control (APMBC) strategy (an integration of the Recursive Least Squares algorithm, RLS and the Generalized Predictive Control algorithm, GPC) was employed to control the polypropylene production rate and emulsion phase temperature by manipulating the catalyst feed rate and reactor cooling water flow respectively. Closed loop simulations revealed the superiority of the APMBC in setpoint tracking as compared to the conventional PI controllers tuned using the Internal Model Control (IMC) method and the standard Ziegler-Nichols (Z-N) method. Moreover, the APMBC was able to efficiently arrest the effects of superficial gas velocity, hydrogen concentration and monomer concentration on the process variables, thus exhibiting excellent regulatory control properties. Show less

An improved model for the production of polypropylene in a gas phase fluidized bed reactor was developed. Comparative simulation studies were carried out using the well-mixed, constant bubble size and the improved models. The improved model showed different prediction characteristics of polymer production rate as well as heat and mass transfer behavior as compared to other published models. All the three models showed similar dynamic behavior at the startup conditions but the improved model… Show more

An improved model for the production of polypropylene in a gas phase fluidized bed reactor was developed. Comparative simulation studies were carried out using the well-mixed, constant bubble size and the improved models. The improved model showed different prediction characteristics of polymer production rate as well as heat and mass transfer behavior as compared to other published models. All the three models showed similar dynamic behavior at the startup conditions but the improved model predicted a narrower safe operation window. Furthermore, the safe ranges of variation of the main operating parameters such as catalyst feed rate and superficial gas velocity calculated by the improved and well mixed models are wider than that obtained by the constant bubble size model. The improved model predicts the monomer conversion per pass through the bed which varies from 0.28 to 5.57% within the practical ranges of superficial gas velocity and catalyst feed rate. Show less

A new model with comprehensive kinetics for propylene homopolymerization in fluidized bed reactors was developed to investigate the effect of mixing, operating conditions, kinetic and hydrodynamic parameters on the reactor performance as well as polymer properties. Presence of the particles in the bubbles and the excess gas in the emulsion phase was considered to improve the two-phase model, thus, considering the polymerization reaction to take place in both the bubble and emulsion phases. It… Show more

A new model with comprehensive kinetics for propylene homopolymerization in fluidized bed reactors was developed to investigate the effect of mixing, operating conditions, kinetic and hydrodynamic parameters on the reactor performance as well as polymer properties. Presence of the particles in the bubbles and the excess gas in the emulsion phase was considered to improve the two-phase model, thus, considering the polymerization reaction to take place in both the bubble and emulsion phases. It was shown that in the practical range of superficial gas velocity and catalyst feed rate, the ratio of produced polymer in the bubble phase to the total production rate is roughly between 10% and 13%, which is a substantial amount and cannot be ignored. Simulation studies were carried out to compare the results of the improved two-phase, conventional well-mixed and constant bubble size models. The improved two-phase and well mixed models predicted a narrower and safer window at the same running conditions compared with the constant bubble size model. The improved two-phase model showed close dynamic behavior to the conventional models at the beginning of polymerization, but starts to diverge with the evolution of time.

Show less

This paper presents a review of studies on mathematical modeling of solid oxide fuel cells (SOFCs) with respect to the tubular and planar configurations. In this work, both configurations are divided into five subsystems and the factors such as mass/energy/momentum transfer, diffusion through porous media, electrochemical reactions with and without CO oxidation, shift and reforming reactions, and polarization losses inside the subsystems are discussed. Using variety of fuels fed to SOFCs is… Show more

This paper presents a review of studies on mathematical modeling of solid oxide fuel cells (SOFCs) with respect to the tubular and planar configurations. In this work, both configurations are divided into five subsystems and the factors such as mass/energy/momentum transfer, diffusion through porous media, electrochemical reactions with and without CO oxidation, shift and reforming reactions, and polarization losses inside the subsystems are discussed. Using variety of fuels fed to SOFCs is issued and their effect on the system is compared briefly. A short review of solid oxide fuel cell configurations and different flow manifolding are also presented in this study. Novel models based on statistical data-driven approach existing in the literatures are considered shortly. Although many studies on solid oxide fuel cells modeling have been done, still more research needs to be done to improve the models in order to predict the fuel cell behaviors more accurately. At the end of this paper the works and studies that can be done for improving the fuel cell models is suggested and pointed by the authors.

Show less

A two-phase dynamic model describing gas phase propylene polymerization in a fluidized bed reactor which considers the polymerization reaction in both phases was used to explore the control of the reactor temperature by manipulating the heat exchanger cooling water flow rate. A model predictive control (MPC) technique is implemented to control of the nonlinear
process and compared its performance with conventional PI controllers tuned using the Internal Model Control (IMC) method as well as… Show more

A two-phase dynamic model describing gas phase propylene polymerization in a fluidized bed reactor which considers the polymerization reaction in both phases was used to explore the control of the reactor temperature by manipulating the heat exchanger cooling water flow rate. A model predictive control (MPC) technique is implemented to control of the nonlinear
process and compared its performance with conventional PI controllers tuned using the Internal Model Control (IMC) method as well as the standard Ziegler-Nichols (Z-N) method. The closed loop simulations revealed that the Z-N PI controller produced oscillatory responses and the MPC and the IMC-Based PI controllers were able to track the changes in the set point. However the quality of the MPC set point tracking was superior to that of the IMC-Based PI controller. Show less

A two-phase model is proposed for describing the dynamics of a fluidized bed reactor used for polypropylene production. In the proposed model, the fluidized bed is divided into an emulsion phase and bubble phase where the bubble phase flow pattern is assumed to be plug flow and the emulsion phase is considered to be perfectly mixed. Similar previous models consider the reaction in the emulsion phase only. In this work the contribution of reaction in the bubble phase is considered and its effect… Show more

A two-phase model is proposed for describing the dynamics of a fluidized bed reactor used for polypropylene production. In the proposed model, the fluidized bed is divided into an emulsion phase and bubble phase where the bubble phase flow pattern is assumed to be plug flow and the emulsion phase is considered to be perfectly mixed. Similar previous models consider the reaction in the emulsion phase only. In this work the contribution of reaction in the bubble phase is considered and its effect on the overall polypropylene production is investigated. The kinetic model combined with hydrodynamic model in order to develop a comprehensive model for gas-phase propylene copolymerization reactor. Simulation profiles of the proposed model were compared with those of well mixed model for the emulsion phase temperature. The simulated temperature profile showed a lower rate of change compared to the previously reported models due to lower polymerization rate. Model simulation showed that about 13% of the produced polymer comes from the bubble phase and this considerable amount of polymerization in the bubbles should not be neglected in any modeling attempt. Show less

A review on surface modification of activated carbon for carbon dioxide adsorption
Abstract
The influence of surface modification of activated carbon with gaseous ammonia on adsorption properties toward carbon dioxide (CO2) was reviewed. It was apparent from the literature survey that the surface chemistry of activated carbon strongly affects the adsorption capacity. In general, CO2 adsorption capacity of activated carbon can be increased by the introduction of basic nitrogen… Show more

A review on surface modification of activated carbon for carbon dioxide adsorption
Abstract
The influence of surface modification of activated carbon with gaseous ammonia on adsorption properties toward carbon dioxide (CO2) was reviewed. It was apparent from the literature survey that the surface chemistry of activated carbon strongly affects the adsorption capacity. In general, CO2 adsorption capacity of activated carbon can be increased by the introduction of basic nitrogen functionalities into the carbon surface. Accordingly, in this review the impact of changes in surface chemistry and formation of specific surface groups on adsorption properties of activated carbon were studied. Two different methods, heat treatment and ammonia treatment (amination) for producing activated carbon with basic surface were compared. Amination was found to be suitable modification technique for obtaining efficient CO2 adsorbents. Finally, the common characterization methods were also mentioned.

Show less

A comparative simulation study was carried out using the improved well-mixed, constant bubble size and well mixed models. These fluidized bed reactor models, combined with comprehensive kinetics for propylene homopolymerization in the presence of a multiple active site Ziegler-Natta catalyst. In the improved model, the effect of the presence of particles in the bubbles and the excess gas in the emulsion phase was taken into account to improve the quantitative understanding of the actual… Show more

A comparative simulation study was carried out using the improved well-mixed, constant bubble size and well mixed models. These fluidized bed reactor models, combined with comprehensive kinetics for propylene homopolymerization in the presence of a multiple active site Ziegler-Natta catalyst. In the improved model, the effect of the presence of particles in the bubbles and the excess gas in the emulsion phase was taken into account to improve the quantitative understanding of the actual fluidized bed process. The superficial gas velocity and catalyst feed rate have a strong effect on the hydrodynamics and reaction rate, which results in a greater variation in the polymer production rate and reactor temperature. At typical operating conditions the improved well mixed and well mixed models were in good agreement. While the constant bubble size model was found to over-predict the emulsion phase temperature and under-predict propylene concentration. Show less

Kinetic modeling of propylene homopolymerization in a gas-phase fluidized-bed reactor
Abstract
A comprehensive mechanistic model describing gas-phase propylene polymerization is developed. The kinetics of polymerization is based on a multiple active site for Ziegler–Natta catalyst. The model considers the polymerization reaction to take place in both bubble and emulsion phases. The developed model was used to predict polymer production rate, number and weight average molecular weights… Show more

Kinetic modeling of propylene homopolymerization in a gas-phase fluidized-bed reactor
Abstract
A comprehensive mechanistic model describing gas-phase propylene polymerization is developed. The kinetics of polymerization is based on a multiple active site for Ziegler–Natta catalyst. The model considers the polymerization reaction to take place in both bubble and emulsion phases. The developed model was used to predict polymer production rate, number and weight average molecular weights, polydispersity index (PDI) and melt flow index (MFI). Results showed that by increasing the superficial gas velocity from 0.1 to 0.7 m/s the proportion of the polymer produced in the bubble phase increases from 7.92% to 13.14% which highlights the importance of considering the existence of catalyst in the bubble phase. Comparing the developed model with published models of the same reactor revealed that the polymer productivity will be higher using the new model at high catalyst feed rate.

Show less