Catalyst Feed Rate Research Articles

Transient Behavior and Control of Polyethylene Production in a Fluidized Bed Reactor Utilizing Population Balance Model.

In this study, a fluidized bed reactor for polyethylene production was employed using a dry mode approach, where the recycle stream may contain components of a nature that cannot be condensed through standard cooling. To analyze the behavior of the fluidized bed reactors during the copolymerization of ethylene with butene, a dynamic population balance model was employed. The study includes sensitivity analyses through computer simulations to examine the variations in reactor temperature, molecular weights, catalyst feed rate, and monomer/comonomer concentrations in the fluidized bed reactor. It is noteworthy that the reactor exhibits instability under normal operational conditions and is sensitive to changes in the catalyst feed rate and coolant temperature of the heat exchanger. The findings also highlight challenges such as temperature fluctuations above the polymer melting point. This underscores the importance of implementing a temperature control system to prevent issues like reactor shutdown due to elevated temperatures. Dynamic instabilities were observed under specific circumstances and were successfully controlled using Proportional Integral Derivative (PID) control strategies. The population balance model is essential for understanding the complexity of transient polymerization reactions. It enables researchers to simulate and optimize polymerization processes by utilizing the detailed kinetics of the reaction.

Leveraging fuzzy Logic PID controllers for accelerating chemical reactor CFD

A control technique comprising three Fuzzy Logic Proportional Integral Derivative (FLPID) controllers was evaluated to determine their ability to shorten convergence times for the computationally expensive globally unsteady model of a low-density polyethylene reactor. The numerical reactor contained millions of computational elements, a rotating stirrer shaft, intricate near-wall geometry, and highly exothermic polymerization kinetics. Catalyst feed rates were instantaneously increased by 50% to evaluate the FLPID’s performance during a hypothetical process excursion. FLPID achieved quasi-steady state (QSS) 54% faster than conventionally tuned PID controllers. Reducing the percent overshoot of the error and rise time of the controller output, the FLPID demonstrated its ability to lower computational cost. FLPID in CFD offers the potential to improve control methods on actual plant scale processes. In particular, the reduction in error overshoot could reduce the likelihood of reactor overheat events as the temperatures are kept within a tighter operational window.

The toxicity of SiO2 NPs on cell proliferation and cellular uptake of human lung fibroblastic cell line during the variation of calcination temperature and its modeling by artificial neural network.

The online version contains supplementary material available at 10.1007/s40201-021-00663-4.

CFD MODELING OF POLYETHYLENE GAS PHASE FLUIDIZED BED REACTOR WITH INTERNAL CHILLER

Polyethylene production in a gas phase fluidized bed reactor is exposed to unstable temperature behavior, and if not controlled properly the temperature oscillation can cause polymer melting and potential plant shutdown (Ghasem, 1999). Accordingly, the present work improves the previous simple mathematical model by the CFD modelling that addresses the prediction of ethylene concentration and temperature profile in entire reactor of the fluidized bed reactor employed for polyethylene production. The CFD model considers gas phase molecular diffusion in the axial and radial directions. Results revealed that the size of the internal heat exchanger mainly the exchanger heat transfer interface area has strong impact on the temperature contour inside the reactor. Ethylene feed rate and ethylene concentration, catalyst feed rate effect the temperature profile inside the reactor considerably. The increase in ethylene concentration and catalyst feed rate strongly influences the fluidized bed temperature. As ethylene concentration increases reactor temperature increases. Proper temperature control inside the polyethylene gas phase is essential fluidized reactor to maintain the reactor temperature below polymer melting point and hence long term operation of fluidized bed reactor without reactor shutdown and temperature excursion above the polymer melting point.

Modeling and simulation of an industrial slurry phase ethylene polymerization reactor: effect of reactor operating variables

A hierarchical and computationally efficient mathematical model was developed to explain the polymerization of high-density polyethylene (HDPE) in an isothermal, industrial, continuous stirred tank slurry reactor (CSTR). A modified polymeric multi-grain model (PMGM) was used. Steady-state macroscopic mass balance equations were derived for all species (namely, monomer, solvent, catalyst and polymer) to obtain the final particle size and the required monomer and solvent input rates for a given catalyst input and the reactor residence time. The interphase mass transfer coefficients were calculated for the industrial CSTR using the operating data on the reactor. The present model was tuned with some data on an isothermal industrial reactor and the simulation results were compared with data on another set of industrial reactor. The comparison revealed that the present tuned model is capable of predicting the productivity and the polymer yield at various catalyst feed rates and the mean residence times. The effects of variation of two operating variables (catalyst feed rate and mean residence time) on the productivity, the polymer yield, the polydispersity index (PDI) and the operational safety were analyzed. The present study indicated that an optimal value of the reactor residence time (for maximum productivity per catalyst particle) exists at any catalyst feed rate.

Effect of Reaction Time and Catalyst Feed Rate towards Carbon Nanotubes Yields and Purity by using Rotary Reactor

Continuous production of multi-walled carbon nanotubes (MWCNTs) by chemical vapor deposition (CVD) method was investigated in a rotary reactor. The aim of the study was to investigate the effect of catalyst feeding rate and reaction time on the MWCNTs production yield and purity. Bimetallic Co-Mo supported on MgO was used for the growth of MWCNTs and methane gas was used as the carbon precursor. The results indicated that the highest yield of MWCNTs production was attained at the reaction time of 180 min and catalyst feeding rate of 100 mg/min; this sample also had the highest purity (99.16%). SEM and TEM analyses of the synthesized product confirmed that most of the MWCNTs were sinuous and entangled with a uniform diameter. Raman spectroscopy indicated that the as-produced MWCNTs were mostly graphitic with few disordered carbon and impurities. The results highlighted that synthesized MWCNTs were highly pure which eliminates the need for MWCNTs purification process.

Experimental validation of CFD hydrodynamic models for catalytic fast pyrolysis

Hydrodynamics for catalyst fluidization and circulation for Catalytic Fast Pyrolysis (CFP) were investigated using cold flow experiments and used to validate predictions from computational fluid dynamics (CFD) simulations. Proprietary fresh and equilibrium CFP catalyst were tested in lab-scale fixed fluidized bed (FFB) and circulating fluidized bed (CFB) setup. Bed expansion and pressure drop were recorded for fresh catalyst in the fixed fluidized bed setup for a range of gas velocities (0–0.04m/s) which encompassed minimum fluidization and bubbling regimes. Catalyst circulation in the circulating fluidized bed setup on the other hand, was quantified using mass holdup in the mock reactor, particle size distribution for this holdup and pressure profile for a range of transport gas velocities (0.094–0.561m/s, 10–60 SLPM) and catalyst feedrates (3, 6, 12kg/h; G=0.46, 0.92, 1.84kg/m2-s) for a single-inlet and single-outlet mock reactor configuration. Flow patterns and gas jet penetration through the mock reactor provided qualitative observations that were used for evaluating CFD models. CFD code based on CPFD method (Barracuda Virtual Reactor®) was used to simulate these gas-solid fluidized beds based on three-dimensional grids. Grid independence was established for both fixed and circulating fluidized bed models such that an average grid volume of 23–29mm3 was sufficient to effectively predict quantitative and qualitative observables. Several CFD parameter sets were tested to evaluate combinations of drag models, blended acceleration model, particle-wall interactions and collision and stress models. Parker-drag model with blended acceleration and advanced settings for particle-wall interactions, collision and stress parameters is determined to provide the best agreement with experimental results.

Developed Hybrid Model for Propylene Polymerisation at Optimum Reaction Conditions.

A statistical model combined with CFD (computational fluid dynamic) method was used to explain the detailed phenomena of the process parameters, and a series of experiments were carried out for propylene polymerisation by varying the feed gas composition, reaction initiation temperature, and system pressure, in a fluidised bed catalytic reactor. The propylene polymerisation rate per pass was considered the response to the analysis. Response surface methodology (RSM), with a full factorial central composite experimental design, was applied to develop the model. In this study, analysis of variance (ANOVA) indicated an acceptable value for the coefficient of determination and a suitable estimation of a second-order regression model. For better justification, results were also described through a three-dimensional (3D) response surface and a related two-dimensional (2D) contour plot. These 3D and 2D response analyses provided significant and easy to understand findings on the effect of all the considered process variables on expected findings. To diagnose the model adequacy, the mathematical relationship between the process variables and the extent of polymer conversion was established through the combination of CFD with statistical tools. All the tests showed that the model is an excellent fit with the experimental validation. The maximum extent of polymer conversion per pass was 5.98% at the set time period and with consistent catalyst and co-catalyst feed rates. The optimum conditions for maximum polymerisation was found at reaction temperature (RT) 75 °C, system pressure (SP) 25 bar, and 75% monomer concentration (MC). The hydrogen percentage was kept fixed at all times. The coefficient of correlation for reaction temperature, system pressure, and monomer concentration ratio, was found to be 0.932. Thus, the experimental results and model predicted values were a reliable fit at optimum process conditions. Detailed and adaptable CFD results were capable of giving a clear idea of the bed dynamics at optimum process conditions.

Dynamics and stability analysis of gas-phase bulk polymerization of propylene

As one of the most important downstream products of propylene, polypropylene (PP) plays a key role in industrial production and our daily life. In this paper, a detailed mechanism model is built which is derived from practical data and bifurcation diagrams are also obtained to assess an open-loop stability analysis of the reactor, finding out the existence of Hopf point which leads to instability of the open-loop system. Since temperature runaway and oscillations resulted from unstable operation and Hopf point could pose a threat to the safety, productivity and quality of the production process, PI controller is introduced to the system and forms a closed-loop system to improve the stability and controllability of the system. Further calculation shows that, in the case of PI control, the Hopf point, which is the dividing point of the stable and unstable region on the parameter plane, not vanishes but moves to another position with higher catalyst feed rate and the risk of instability still remains. In this situation, appropriate controller parameters can be helpful to avoid unstable operation and expand the range of stable region. Additionally, in the latter part of our work, different closed-loop dynamic simulations are also conducted to show how stability index and the imaginary part of eigenvalues affect the dynamic behaviors of the closed-loop system. In general, this work mainly focuses on the relationship between the process stability and controller parameters and the outcomes are expected to be a guide for industrial operation and design of control system.

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

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.

Comparative simulation study of gas-phase propylene polymerization in fluidized bed reactors using aspen polymers and two phase models

A comparative study describing gas-phase propylene polymerization in fluidized-bed reactors using Ziegler-Natta catalyst is presented. The reactor behavior 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, polydispersity 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.

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.

Dynamic modeling of gas phase propylene homopolymerization in fluidized bed reactors

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.

Kinetic modeling of propylene homopolymerization in a gas-phase fluidized-bed reactor

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.

Broadening the polyethylene molecular weight distribution by controlling the hydrogen concentration and catalyst feed rates

This paper discusses the control of an industrial gas-phase polyethylene reactor to produce a desired molecular weight distribution (MWD) of the polymer. The controller objective is to regulate online the entire molecular weight distribution by either manipulating the hydrogen content inside the reactor or coordinating the feed rates of two different types of catalysts. In this work, the molecular weight distribution is modeled as a function of the reaction kinetics and hydrogen to monomer ratio. Nonlinear model predictive controller (NLMPC) algorithm is used to maintain the desired molecular weight distribution online. The closed-loop simulations indicated the effectiveness of NLMPC to achieve its goal even in the presence of modeling errors. Moreover, the results showed that, altering the hydrogen concentration solely can produce the required polymer quality provided that an efficient mechanism is available to readily alter the hydrogen composition. Alternatively, the desired MWD can also be guaranteed with proper manipulation of the catalyst feed rates while the other process inputs are kept constant.

Dynamics and stability of ethylene polymerization in multizone circulating reactors

Multizone circulating bed reactors (MZCR) have the exclusive characteristics of producing polymers of different molecular weights in a single particle. Traditional fluidized bed reactors, on the other hand, can produce only one kind of molecular weight with relatively narrow distribution. A dynamic model for the MZCR is used to illustrate the basic dynamic behavior of the new reactor design used for polyethylene production. 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/comonomer concentration along the reactor length. At certain operating conditions dynamic instability is observed and the results for the effect of cooling water temperature, catalyst feed rate, monomer and comonomer initial feed concentration on the reactor temperature and polymer molecular weight reveal that the system is very sensitive to disturbances in the heat exchanger coolant temperature. Also, at some operating conditions, the reactor temperature oscillates above the polymer melting temperature. Temperature runaway above polymer softening point is a serious problem which may cause polymer melting and hence reactor shutdown. The oscillatory behavior of the reactor temperature necessitates a suitable temperature control scheme to be installed.

O.606 Bridging face and brain – the view of a neurosurgeon

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.

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.

Development of a multi-scale, multi-phase, multi-zone dynamic model for the prediction of particle segregation in catalytic olefin polymerization FBRs

A comprehensive multi-scale, multi-phase, multi-compartment dynamic model is developed to analyze the extent of particle segregation in catalytic, gas-phase ethylene–propylene copolymerization fluidized bed reactors (FBRs). From the numerical solution of the proposed integrated model, the temporal-spatial evolution of the morphological (i.e., particle size distribution, PSD) and molecular (i.e., molecular weight distribution, MWD) polymer properties in a catalytic polymerization FBR can be predicted. In particular, the polymer molecular properties are determined by employing a generalized multi-site, Ziegler–Natta kinetic scheme. To determine the growth of a single catalyst/polymer particle, the random pore polymeric flow model (RPPFM) is utilized. The RPPFM is solved together with a dynamic discretized particle population balance equation (PBE) to calculate the dynamic evolution of PSD in the various compartments of the FBR. Moreover, overall dynamic mass and energy balances are derived in order to assess the dynamic behavior of catalytic gas-phase FBRs. The effects of various fluidized bed operating conditions (e.g., fluidization gas velocity, temperature and catalyst feed rate) on the morphological and molecular distributed polymer properties are thoroughly analyzed.

Chemical catalysed recycling of waste polymers: Catalytic conversion of polypropylene into fuels and chemicals over spent FCC catalyst in a fluidised-bed reactor

Polypropylene (PP) was pyrolysed over spent FCC commercial catalyst (FCC-s1) using a laboratory fluidised-bed reactor operating isothermally at ambient pressure. The influence of reaction conditions including catalyst, temperature, and ratio of polymer to catalyst feed and flow rates of fluidising gas was examined. The yield of gaseous and liquid hydrocarbon products at 390 °C for spent FCC commercial catalyst (87.8 wt%) gave much higher yield than silicate (only 17.1 wt%). Greater product selectivity was observed with FCC-s1 as a post-use catalyst with about 61 wt% olefins products in the C 3–C 7 range. The selectivity could be further influenced by changes in reaction conditions. Valuable hydrocarbons of olefins and iso-olefins were produced by low temperatures and short contact times used in this study. It is also demonstrated that a post-use catalyst system under appropriate conditions the resource potential of polymer waste can be economically recovered and also can address the recycling desire to see an alternative to solve a major environment problem.