Ahmad Shamiri

The Influence of Ziegler-Natta and Metallocene Catalysts on Polyolefin Structure, Properties, and Processing Ability

50 years ago, Karl Ziegler and Giulio Natta were awarded the Nobel Prize for their discovery of the catalytic polymerization of ethylene and propylene using titanium compounds and aluminum-alkyls as co-catalysts. Polyolefins have grown to become one of the biggest of all produced polymers. New metallocene/methylaluminoxane (MAO) catalysts open the possibility to synthesize polymers with highly defined microstructure, tacticity, and steroregularity, as well as long-chain branched, or blocky copolymers with excellent properties. This improvement in polymerization is possible due to the single active sites available on the metallocene catalysts in contrast to their traditional counterparts. Moreover, these catalysts, half titanocenes/MAO, zirconocenes, and other single site catalysts can control various important parameters, such as co-monomer distribution, molecular weight, molecular weight distribution, molecular architecture, stereo-specificity, degree of linearity, and branching of the polymer. However, in most cases research in this area has reduced academia as olefin polymerization has seen significant advancements in the industries. Therefore, this paper aims to further motivate interest in polyolefin research in academia by highlighting promising and open areas for the future.

A review of CO2 capture by absorption in ionic liquid- based solvents

Abstract Concern has increased about climate change caused by carbon dioxide (CO2) emissions through human activities in recent years. The Intergovernmental Panel on Climate Change predicts a 1.9°C rise in temperature by the year 2100, and this means a reduction in CO2 is vital for human beings and all other life on earth. Therefore, there is an urgent need for the development of CO2 separation processes to mitigate this potential problem. Post-combustion power plants can employ various types of separation technology. Among them, chemical absorption using aqueous amine is more developed and more reliable. The conventional solvents used in the chemical absorption process together with the use of absorbents, ionic liquid, alkanolamines and their blended aqueous solutions are reviewed in this work. Different ionic liquid-based solvents for CO2 absorption and the most effective parameters on mass transfer phenomena between CO2 and solvent are reviewed. The major concerns for this technology, including the physiochemical properties of ionic liquid-based solvents, Henry’s constant and mass transfer coefficient and their correlations, and various factors for effective CO2 absorption, are addressed.

An overview of biological processes and their potential for CO2 capture.

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.

Dynamics and Predictive Control of Gas Phase Propylene Polymerization in Fluidized Bed Reactors

Abstract A two-phase dynamic model, describing gas phase propylene polymerization in a fluidized bed reactor, was used to explore the dynamic behavior and process control of the polypropylene production rate and reactor temperature. The open loop analysis revealed the nonlinear behavior of the polypropylene fluidized bed reactor, justifying the use of an advanced control algorithm for efficient control of the process variables. In this case, a centralized model predictive control (MPC) technique was implemented to control the polypropylene production rate and reactor temperature by manipulating the catalyst feed rate and cooling water flow rate respectively. The corresponding MPC controller was able to track changes in the setpoint smoothly for the reactor temperature and production rate while the setpoint tracking of the conventional proportional-integral (PI) controller was oscillatory with overshoots and obvious interaction between the reactor temperature and production rate loops. The MPC was able to produce controller moves which not only were well within the specified input constraints for both control variables, but also non-aggressive and sufficiently smooth for practical implementations. Furthermore, the closed loop dynamic simulations indicated that the speed of rejecting the process disturbances for the MPC controller were also acceptable for both controlled variables.

Improved single phase modeling of propylene polymerization in a fluidized bed reactor

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.

A review of different solvents, mass transfer, and hydrodynamics for postcombustion CO2 capture

Abstract There is a growing environmental concern regarding carbon dioxide (CO2) emissions from human activities that result in global warming or climate change. To tackle this potential problem, it is crucial to develop CO2 capture technologies. This paper reviews the current status of postcombustion carbon capture by absorption in packed column using different solvents. The major concerns with the selection of absorbent, such as absorption rate, CO2 absorption capacity, CO2 solubility, environmental cost, and toxicity, are discussed. The hydrodynamics and mass-transfer performance of CO2 absorption in a packed column are reviewed. The determinant factors of CO2 absorption, including effective interfacial area and mass-transfer coefficients in different contactors, are discussed. Liquid holdup and pressure-drop models are investigated.

Two Phase Dynamic Model for Gas Phase Propylene Copolymerization in Fluidized Bed Reactor

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.

Evaluation of hydrodynamic behavior of the perforated gas distributor of industrial gas phase polymerization reactor using CFD-PBM coupled model

Abstract A 2D computational fluid dynamics (Eulerian–Eulerian) multiphase flow model coupled with a population balance model (CFD-PBM) was implemented to investigate the fluidization structure in terms of entrance region in an industrial-scale gas phase fluidized bed reactor. The simulation results were compared with the industrial data, and good agreement was observed. Two cases including perforated distributor and complete sparger were applied to examine the flow structure through the bed. The parametric sensitivity analysis of time step, number of node, drag coefficient, and specularity coefficient was carried out. It was found that the results were more sensitive to the drag model. The results showed that the entrance configuration has significant effect on the flow structure. While the dead zones are created in both corners of the distributors, the perforated distributor generates more startup bubbles, heterogeneous flow field, and better gas–solid interaction above the entrance region due to jet formation.

A review on modeling and control of olefin polymerization in fluidized-bed reactors

Abstract This is a detailed review on olefin polymerization models, and the most recent process control approaches used to control these nonlinear systems are presented. Great focus has been given to the various approaches of fluidized-bed reactor (FBR) modeling. Currently, there has yet to be a single model that blends these modeling aspects together into one single formulation. In this article, the classification of models works by looking at their assumption in considering the phases inside the system. Researchers have been unraveling vast information to narrate in detail the relations between various variables that can be found in FBRs. Although it is not difficult to understand about the basics of modeling polymer properties, a gap exists for future researchers to justify in detail the phenomena and reduce the gap between model predictions and the actual data. The various controlling approaches to control these FBRs have also been reviewed and categorized depending on the method they used to control significant parameters of this nonlinear system. The progress that can be expected in this field leads to the creation of more efficient reactors and minimizing waste.

Different hydrodynamic model for gas-phase propylene polymerization in a catalytic fluidized bed reactor

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 homo-polymerization 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.