Nayef Ghasem

Mathematical Model and Advanced Control for Gas-phase Olefin Polymerization in Fluidized-bed Catalytic Reactors

In this study, the developments in modeling gas-phase catalyzed olefin polymerization fluidized-bed reactors (FBR) using Ziegler-Natta catalyst is presented. The modified mathematical model to account for mass and heat transfer between the solid particles and the surrounding gas in the emulsion phase is developed in this work to include site activation reaction. This model developed in the present study is subsequently compared with well-known models, namely, the bubble-growth, well-mixed and die constant bubble size models for porous and non porous catalyst. The results we obtained from the model was very close to the constant bubble size model, well-mixed model and bubble growth model at the beginning of the reaction but its overall behavior changed and is closer to the well-mixed model compared with the bubble growth model and constant bubble size model after half an hour of operation. Neural-network based predictive controller are implemented to control the system and compared with the conventional PID controller, giving acceptable results.

A new correlation for the viscosity of waxy oils

Abstract A number of laboratory and field experiments on the flow behavior of heavy and waxy oils were reported in the literature. These crudes are attractive, from the environmental viewpoint, because of their low sulphur contents. However, handling waxy oils is difficult. The flow of heavy and waxy crudes in pipelines and in reservoir formations is not as easy as light and medium oils. A mathematical correlation has been developed to describe the viscosity of waxy base oil as a function of shear rate, temperature, and wax concentration: μ=A exp (B/T+CW) γ D where μ is viscosity, T is temperature, W is % wax by weight, and γ is the shear rate. The experimental tests were performed by measuring the rheological properties of the waxy oils using rotational viscometer at different temperatures (9, 12, 15, 18, 21, 24°C) and wax concentrations (2%, 4%, 6% and 8% by weight). The proposed correlation was found to fit the experimental data well as demonstrated by high coefficient of correlation—95.71%. A computer program based on the least-square regression on orthogonal functions was used to determine the parameters A, B, C and D.

Effect of Polymer Particle Size and Inlet Gas Temperature on Industrial Fluidized Bed Polyethylene Reactors

Static and dynamic bifurcation behaviors dominate the operation of fluidized bed catalytic reactors for the production of polyethylene (UNIPOL Process) and have important implications on the safe operating temperature and polyethylene production rate. The investigations show that the multiplicity of the steady state phenomenon covers a wide range of parameters together with the phenomenon of periodic oscillations with sharply changing amplitudes with a change of the chosen bifurcation parameter. In some cases, the periodic branches terminate through periodic limit point (PLPs), while in other cases it terminates homoclinically. A detailed parameteric investigation using two-parameter continuation diagrams for the loci of static and Hopf bifurcation points as well as one parameter bifurcation diagrams shows that it is possible to increase the productivity of the unit considerably without exceeding the constraints of the polymer melting point, Gas feed temperature, catalyst feed rate, and polymer particle size distribution are important operating parameters in polyethylene fluidized bed reactors. Gas velocity plays a significant role in keeping the fluidized bed bubbling in addition to the fact that it acts as a cooling media by removing excess heat generated from the polymerization reaction. The kinetic behavior of the catalyst and effect of reactor temperature on product properties require, in some cases, operating just below the softening point of the polymer which requires a suitable controller to avoid polymer melting.

Effect of Polymer Growth Rate and Diffusion Resistance on the Behavior of Industrial Polyethylene Fluidized Bed Reactor

The two-phase model developed for the UNIPOL polyethylene process is improved by introducing polymer diffusion resistance, this means modelling of polyethylene fluidized bed reactors has been examined on two levels, at small scale of individual polymer particle, and macroscale of the whole reactor. The model utilizes the multigrain model that accounts for the reaction rate at catalyst surface to explore the static and dynamic bifurcation behavior of the fluidized bed catalytic reactor. Detailed bifurcation diagrams are developed and analyzed for the effect of polymer growth factor and Thiele modulus (the significance of the porous medium transport resistance is characterized by Thiele modulus) on reactor dense phase monomer concentration and reactor temperature as well as polyethylene production rate and reactor single pass conversion for the safe temperature region. The observations reveal that significant diffusion resistance to monomer transport exists, and this can mask the intrinsic rate constants of the catalyst. The investigation of polymer growth factor indicates that, the nascent stage of polymerization is highly gas phase diffusion influenced. Intraparticle temperature gradients would appear to be negligible under most normal operating conditions.

Dynamic model for polyethylene production in a multizone circulating reactor

The multizone circulating reactor (MZCR) technology is a newly announced reactor design for solid-catalyzed gas-phase polymerization. The process is characterized by two hydrodynamically distinct but interconnecting polymerization zones, thus forming a continuous loop of polymer flow between the said zones. In the present study, a dynamic model for the MZCR reactor is developed to illustrate the basic dynamic behavior of the new reactor design; the model is used to study the copolymerization of ethylene with butene. Several parameter sensitivity analyses are performed to show the computer-simulated time responses for reactor temperature, number-average molecular weight, weight-average molecular weight, catalyst feed rate and the monomer concentration along the reactor length.

Effect of Non-Solvent Additive on Effectiveness of Polyvinylidene Fluoride Membrane Fabricated With Thermal Induced Phase Separation Method for Carbon Dioxide Absorption

In the present work porous poly (vinylidene fluoride) (PVDF) hollow fiber membranes were fabricated via thermally induced phase separation (TIPS) method for the application in gas-liquid membrane contactor. For this purpose long air gap distance was used (90 mm). Scanning electron microscopy (SEM) was used for membrane characterization. Gas permeation test was performed using carbon dioxide as test gas. It was observed that the effective surface porosity and membrane pore size increased with increased glycerol concentration. CO2 absorption using the fabricated hollow fiber membranes were measured in a gas-liquid hollow fiber membrane contactor. The results of the CO2 absorption rate of the tested fibers revealed that complete removal of CO2 was achieved using 7% glycerol added to the casted solution at normal operating conditions for equal gas to liquid volumetric flow rates using sodium hydroxide as absorbent liquid.

Removal of Cadmium from Industrial Wastewater Using Water-Soluble Polymer via Hollow Fiber Membranes

The removal of toxic and polluting metal ions from industrial effluents, water supplies, as well as mine waters is an important challenge to avoid one of the major causes of water and soil pollution. To enable further processing and achieve recovery of metals, separation should be selective. One separation technique, which can meet this requirement, is polymer-enhanced ultra filtration (PEUF). Ultra filtration membranes would only retain macromolecular solutes. PEUF uses water-soluble polymeric agents to complex easily interesting metallic ions and give them a macromolecular size. Binding of metal ions to water soluble polymers enables us to separate them from solution and retain them when they are pumped through an ultra filtration membrane. In the present work Polyetherimide (PEI) is used as water soluble polymer for removal of cadmium ions from waste water via hollow fiber membrane contactor module. Polyvinylidene fluoride (PVDF) hollow fiber membrane contactor is used for this purpose. The PVDF fiber was custom made using thermal induced phase separation techniques. Experimental observations reveal that when PEI concentration increases the percentage removal of Cd (II) also increases. The molecular weight of PEI has positive impact on Cd (II) retention. The pH value of feed has effect on Cd (II) withholding. The percentage of removal increases with solution pH value. Recycling either retentate; the part of a solution that does not cross the membrane; or permeate have no effect on removal. Increase of mixing time before operation increases metal ions removal rate

Enhanced teaching and student learning through a simulator-based course in chemical unit operations design

This paper illustrates a teaching technique used in computer applications in chemical engineering employed for designing various unit operation processes, where the students learn about unit operations by designing them. The aim of the course is not to teach design, but rather to teach the fundamentals and the function of unit operation processes through simulators. A case study presenting the teaching method was evaluated using student surveys and faculty assessments, which were designed to measure the quality and effectiveness of the teaching method. The results of the questionnaire conclusively demonstrate that this method is an extremely efficient way of teaching a simulator-based course. In addition to that, this teaching method can easily be generalised and used in other courses. A students final mark is determined by a combination of in-class assessments conducted based on cooperative and peer learning, progress tests and a final exam. Results revealed that peer learning can improve the overall quality of student learning and enhance student understanding.

Effect of Temperature and Catalyst Concentrations on the Thermal Properties of Polyamide Adhesives at Low Operating Pressure

The polyamides used for hot-melt adhesives were synthesized from C36 dimer fatty acids and ethylenediamine under 200 mmHg and atmospheric pressures. The kinetics of the reaction rate at low pressure and the effect on the thermal properties of the produced polyamide adhesive were experimentally investigated. The effects of reaction temperature and catalyst concentration on polyamide melting point, glass transition temperature, sample weight loss and foaming height were studied. The kinetic rate constants were obtained for polymerization reaction carried out at three different reaction temperatures, 115, 120, and 135 °C, fixed mixing rate of 100 rpm and low operation pressure of 200 mmHg. Polymers produced at atmospheric pressure and reaction temperatures 140, 170, 180, and 190 °C where used to investigate the polyamide thermal properties using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Thermal properties such as melting point, glass transition temperature and the temperature at which 5% and 10% weight loss were recorded by TGA at a heating rate of 10 C/min in N2 atmosphere. The effect of foaming height as a function of reaction temperature and catalyst concentration was measured. The analysis makes known that the reaction temperature and catalyst concentration has a noteworthy impact on the glass transition temperature, foam height and melting point and insignificant effect on the sample weight loss.

Chaotic Behavior of Industrial Fluidized-Bed Reactors for Polyethylene Production

Recent theories of bifurcation and chaos are used to analyze the dynamic behavior of the UNIPOL process for the production of polyethylene in the gas phase using the Ziegler-Natta catalyst. Dynamic behavior covers wide regions of the design and operating parameters domain of this industrially important unit. A conventional proportional-integral (PI) controller was implemented to stabilize the desired operating point on the unstable steady-state branch. The presence of the PI controller stabilized the desired unstable steady-state regions to a certain range of catalyst injection rate, by contrast, it is found out that the controlled process can go through a period doubling sequence leading to chaotic strange attractors. The practical implications of this analysis can be very serious, since chaos is shown to exist right near the desired operating point where high polyethylene production rates can be achieved.