Bulk Polymerization Of Propylene Research Articles

C 1-Symmetric {cyclopentadienyl/indenyl}-metallocene catalysts: synthesis, structure, isospecific polymerization of propylene and stereocontrol mechanism.

A series of new Me2Si-bridged cyclopentadiene/indene proligands {Me2Si(R2',5'2-R3',4'2-Cp)(R2,R4,R5,R6-Ind)H2} (1a-j) with various substitutions both on the indene and cyclopentadiene moieties was prepared. The corresponding C1-symmetric group 4 ansa-metallocene complexes (M = Zr, Hf), namely, {Me2Si(Me4Cp)(Ind)}ZrCl2 (2a-Zr), {Me2Si(Me4Cp)(2-Me,4-Ph-Ind)}MCl2 (2b-M), {Me2Si(Me4Cp)(2-Me,4-Ph,6-tBu-Ind)}ZrCl2 (2c-Zr), {Me2Si(Me4Cp)(2-Me,4-Ph,5-OMe,6-tBu-Ind)}MCl2 (2d-M), {Me2Si(Me4Cp)(2-R',4-(3',5'-tBu2,4'-OMe-C6H2),5-OMe,6-tBu-Ind)}ZrCl2, R' = Me (2e-Zr), R' = Et (2f-Zr), {Me2Si(2,5-Ph2-3,4-Me2-Cp)(2-Me,4-(3',5'-tBu2,4'-OMe-C6H2),5-OMe,6-tBu-Ind)}ZrCl2 (2g-Zr), {Me2Si(Me4Cp)(2-Me,4-(3',6'-tBu2-carbazol-4'-yl)-Ind)}ZrCl2 (2h-Zr), {Me2Si(2,5-Me2,3,4-iPr2-Cp)(2-Me,4-Ph-Ind)}ZrCl2 (2i-Zr), {Me2Si(2,5-Me2,3,4-iPr2-Cp)(2-Me,4-Ph,6-tBu-Ind)}ZrCl2 (2j-Zr) and {Me2Si(Me4Cp)(2-Me-4,5-[a]anthracene-Ind)}MCl2 (2k-Zr) were synthesized and characterized by NMR spectroscopy and mass spectrometry. The solid-state molecular structures of 2b-Zr, 2d-Zr, 2e-Zr, 2f-Zr, 2j-Zr and 2k-Zr were determined by X-ray crystallography. The zirconocene complexes, once activated with MAO in toluene solution, exhibited propylene polymerization activities at 60 °C up to 161 000 kg(PP) mol(Zr)-1 h-1, affording highly isotactic polypropylenes (iPP) with [m]4 up to 96.5% and Tm up to 157 °C. Also, metallocene complexes 2b-e-Zr were supported on SiO2-MAO and evaluated in slurry bulk propylene polymerization at 70 °C, producing iPPs with [m]4 = 91.7-96.6 mol% and low regiodefects (0.2-0.3 mol%) content, with productivities up to 636 000 kg(PP) mol(Zr)-1 h-1. DFT calculations allowed rationalizing a polymerization reaction mechanism occurring through "chain-stationary" enchainment with preference for 1,2-insertions.

Effects of Prepolymerization, Temperature, and Hydrogen Concentration on Kinetics of Propylene Bulk Polymerization Using a Commercial Ziegler-Natta Catalyst

The effects of prepolymerization, temperature, and hydrogen concentration on propylene bulk polymerization with a commercial Ziegler-Natta catalyst were investigated, and the apparent polymerization rate constants were estimated by varying reaction temperatures, hydrogen partial pressures, and polymerization methods. It was shown that prepolymerization has different effects on the polymerization rate and isotacticity of the polymer; without prepolymerization, the polymerization rate and isotacticity reach their maximum at 70°C and 80°C, respectively, whereas the polymerization rate and isotacticity with prepolymerization increase with the polymerization temperature in the range of 50-80°C. Moderate prepolymerization time reduced the fine fraction while increasing polymerization rate and isotacticity. Appropriate prepolymerization technique can increase mass transfer performance and fragmentation, which is a promising way to improve polymerization rate, isotacticity index, and fine fraction. Otherwise, insufficient prepolymerization or excessive prepolymerization causes prepolymer particle fragmentation.

Preparation of MgCl2-Supported Ziegler-Natta Catalysts via New Surfactants Emulsion for Propylene Polymerization

This article describes a MgCl2-supported Ziegler-Natta catalyst for propylene polymerization prepared via an in situ emulsion technique with new surfactants. The effect of preparation conditions such as the TiCl4/toluene molar ratio, TiCl4-contacting temperature, amount of phthaloyl dichloride, stirring rate, mixing time of TiCl4/toluene with the Mg complex, and the n-butyl chloride loading was investigated in detail. Scanning electron microscopy and laser particle size analyzer measurements showed that the catalyst particles exhibit a perfectly spherical shape, narrow particle size distribution, and low fine powder content. Energy-dispersive X-ray spectrometry indicated that the Ti, Mg, and Cl elements were evenly distributed throughout the particles. Powder X-ray diffraction measurements indicated the presence of δ-MgCl2 in the catalyst, and FTIR and GC-MS studies confirmed the presence of in situ formed di(ethylhexyl)phthalate (DEHP). Bulk polymerization of propylene using the catalyst was studied, and it was found that the catalyst displayed high activity, high bulk density with high stereospecificity, and excellent hydrogen sensitivity. The polymer produced by the catalyst has a narrow particle size distribution with a low fine powder content.

Two-phase multi-scale modeling of a tubular loop propylene polymerization reactor

In the present paper a new two-phase multi-scale mathematical model of a tubular loop reactor is presented to describe the bulk polymerization of propylene. The model comprises transient mass and energy balances for the liquid and solid phases and population balance equations to describe the spatio-temporal evolution of the particles size distributions. Particularly, the mathematical modeling approach presented here also takes into account inter-phase transport phenomena for the first time for this class of reactors. As shown through computational simulations, inter-phase mass and energy transport constraints can exert significant influence on the properties of the final product and should not be neglected a priori.

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.

Kinetics of the propylene polymerization with prepolymerization at high temperature using Ziegler‐Natta catalyst

ABSTRACTThe bulk polymerization of propylene in liquid monomers with Ziegler‐Natta catalyst at 95°C is studied, using alkyl aluminum as the cocatalyst and dicyclopentyldimethoxysilane as the external donor. The highest catalyst activity is shown at the cocatalyst/Ti molar ratio of 300, which keeps relatively constant with the molar ratio increasing from 300 to 800. Besides, the catalyst activity is up to 65 kgPP/(gCat*h) in the range of cocatalyst/donor molar ratio from 12 to 16. The polymerization reaction rate curves with and without catalyst precontacting are similar, while the activity with catalyst precontacting are higher than that without precontacting. Furthermore, the kinetics of polymerization with and without prepolymerization are investigated in the range of the polymerization temperature from 70 to 95°C. It shows that at the high temperature, the polymerization rate increases with prepolymerization. Finally, the influence of prepolymerization at 95°C on the polymerization kinetics and particle properties is also described. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41816.

Isospecific Propylene Polymerization Behavior of Lewis Base Functionalized Unbridged Zirconocences under Bulk Conditions

Isospecific propylene polymerization behavior of meta- and para-Lewis base (E) functionalized unbridged zirconocenes (<TEX>$[1-(E_n-Ph)-3,4-Me_2C_5H_2</TEX><TEX>]</TEX><TEX>_2ZrCl_2$</TEX>, E = <TEX>$NMe_2$</TEX>, OMe; n = 1 or 2) was investigated under bulk conditions. Catalytic activity of the zirconocenes, and molecular weight and isotacticity of polypropylenes are found to be dependent on the position and number of the Lewis base functional groups in the zirconocenes. All the crude polypropylenes possess a broad molecular weight distribution and multi-melting transitions, indicating an involvement of multi-catalytic active species in the polymerization. The highest [mmmm] value of an isotactic portion of the polypropylenes reached 89%, which is higher than that (85%) from the well-known <TEX>$C_2$</TEX>-symmetric EBIZr (rac-<TEX>$Et(Ind)_2ZrCl_2$</TEX>) catalyst. These results support that the in situ generated, rigid rac-like cation-anion pair through the Lewis acid-base interactions between the functional groups of zirconocenes and methylaluminoxane anion is effective in the formation of isotactic polypropylene under bulk propylene polymerization conditions.

Characterization of the effects of the C/N mixed external donors on the stereo-defects distribution of polypropylene by successive self-nucleating and annealing and 13C-NMR techniques

As the external donor in Ziegler-Natta catalysts have an important influence on the stereo-defects distribution of polypropylene, the effects of the mixed external donors (the mixture of Donor-C (cyclohexylmethyldimethoxysilane) and Donor-N (n-propyltriethoxysilane) ) on the isotactic sequence length and its distribution of polypropylene prepared by Ziegler-Natta catalyst through propylene bulk polymerization were studied through the Successive self-nucleating and annealing (SSA) and 13C-NMR techniques. The SSA results showed that the relative contents of the highest isotactic component and the lamellar thickness in the polypropylene chain gradually increased with the increase of the relative component of Donor-C in the C/N mixed external donors, indicating the isotactic sequence length of polypropylene got longer, and the lamellar thickness distribution of polypropylene became broader, revealing the isotactic sequence length distribution of polypropylene got broader. In addition, the 13C-NMR results showed that the average meso isotactic sequence length (MSL) of polypropylene gradually increased with the increase of the content of Donor-C in the C/N mixed external donors, which was in good coincident with the results calculated from SSA, showing a good correspondence between the SSA and 13C-NMR techniques.

Bifurcation Analysis of the Bulk Propylene Polymerization in the LIPP Process

AbstractSummary: A dynamic model is built to describe the bulk propylene polymerization in stirred tank reactors (LIPP process), assuming that catalyst deactivation takes place and that the reactor temperature must be controlled with the help of reflux condensers and external heat exchangers. Simulation results show that the dynamic behavior of the LIPP process can be much more complex than described previously, when catalyst deactivation and the performance of the real temperature controller are taken into consideration. Particularly, it is shown that chaotic behavior can be observed in very wide ranges of operation conditions when the more realistic operation conditions are considered.

Study on the sequence length distribution of polypropylene by the successive self-nucleation and annealing (SSA) calorimetric technique

The effect of successive self-nucleation and annealing (SSA) parameters including the annealing time ts, annealing temperature interval and heating and cooling rates on the crystallization properties of polypropylene were researched in detail. Based on those results, the crystallization behavior and the sequence length distribution of polypropylene with different isotacticity and propylene/1-butene copolymer with different 1-butene comonomer content prepared by Ziegler–Natta catalyst were studied through SSA. With the increase of the isotacticity of polypropylene, the sequence length of the polypropylene gradually increases. The polypropylene prepared by propylene bulk polymerization has stronger crystallization ability and longer sequence length than that prepared by propylene sully polymerization. For the propylene/1-butene copolymer, the crystallization ability gradually reduces and the sequence length of each chain segment gradually decreases with the increase of 1-butene content in copolymer. In addition, the polypropylene samples with similar isotactic index prepared by Ziegler–Natta catalyst and metallocene catalyst under similar polymerization condition were also characterized through the SSA technique. The results show that the sequence length of polypropylene prepared by Ziegler–Natta catalyst is far longer than that prepared by metallocene catalyst. The interesting phenomenon that polypropylene prepared by metallocene catalyst has multiple melting peaks after SSA treatment, which is similar to the polypropylene prepared by Ziegler–Natta catalyst, was first reported.

Modeling the Dynamics of the Xylene Soluble Fraction (XS) in a Bulk Propylene Polymerization Process

AbstractA model is built to describe the dynamic trajectories of the xylene soluble fraction (XS) in an industrial bulk propylene polymerization process. Emphasis is given to the coupling between the XS dynamics and the reactor liquid bleed policy. It is shown that cocatalyst recirculation can affect the dynamics of the cocatalyst/donor ratio and consequently the dynamics of XS during polymerization. Simulation results indicate that the effect of the reactor liquid bleed operation and of the cocatalyst/donor ratio upon the XS trajectories can be minimized if PI controllers are designed to control the propane concentration and to increase the speed of the cocatalyst/donor transitions. Finally, it is shown that the model is able to reproduce the dynamic XS profile obtained during a large XS transition at plant site. magnified image

Simultaneous robust data reconciliation and gross error detection through particle swarm optimization for an industrial polypropylene reactor

In a previous study, a nonlinear dynamic data reconciliation procedure (NDDR) based on the particle swarm optimization (PSO) method was developed and validated in line and in real time with actual industrial data obtained for an industrial polypropylene reactor ( Prata et al., 2009, 2008b). The procedure is modified to allow for robust implementation of the NDDR problem with simultaneous detection of gross errors and estimation of model parameters. The negative effects of the less frequent gross errors are eliminated with the implementation of the Welsch robust estimator, avoiding the computation of biased estimates and implementation of iterative procedures for detection and removal of gross errors. The performance of the proposed procedure was tested in line and in real time in an industrial bulk propylene polymerization process. A phenomenological model of the real process, based on the detailed mass and energy balances and constituted by a set of algebraic-differential equations, was implemented and used for interpretation of the actual plant behavior. The resulting nonlinear dynamic optimization problem was solved iteratively on a moving time window, in order to capture the current process behavior and allow for dynamic adaptation of model parameters. Results indicate that the proposed procedure, based on the combination of the PSO method and the robust Welsch estimator, can be implemented in real time in real industrial environments, allowing for the simultaneous detection of gross errors and estimation of process states and model parameters, leading to more robust and reproducible numerical performance.

Effects of external donors and hydrogen concentration on oligomer formation and chain end distribution in propylene polymerization with Ziegler‐Natta catalysts

AbstractThe effect of type and concentration of external donor and hydrogen concentration on oligomer formation and chain end distribution were studied. Bulk polymerization of propylene was carried out with two different Ziegler‐Natta catalysts at 70 °C, one a novel self‐supported catalyst (A) and the other a conventional MgCl2‐supported catalyst (B) with triethyl aluminum as cocatalyst. The external donors used were dicyclopentyl dimethoxy silane (DCP) and cyclohexylmethyl dimethoxy silane (CHM). The oligomer amount was shown to be strongly dependent on the molecular weight of the polymer. Catalyst A gave approximately 50 % lower oligomer content than catalyst B due to narrower molecular weight distribution in case of catalyst A. More n‐Bu‐terminated chain ends were found for catalyst A indicating more frequent 2,1 insertions. Catalyst A also gave more vinylidene‐terminated oligomers, suggesting that chain transfer to monomer, responsible for the vinylidene chain ends, was a more important chain termination mechanism for this catalyst, especially at low hydrogen concentration. Low site selectivity, due to low external donor concentration or use of a weak external donor (CHM), was also found to increase formation of vinylidene‐terminated oligomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 351–358, 2010

Nonlinear dynamic data reconciliation and parameter estimation through particle swarm optimization: Application for an industrial polypropylene reactor

Abstract This work presents a procedure to solve nonlinear dynamic data reconciliation (NDDR) problems with simultaneous parameter estimation based on particle swarm optimization (PSO). The performance of the proposed procedure is compared to the performance of a standard Gauss–Newton (GN) scheme in a real industrial problem, as presented previously by Prata et al. [2006. Simultaneous data reconciliation and parameter estimation in bulk polypropylene polymerizations in real time. Macromolecular Symposia 243, 91–103; 2008. In-line monitoring of bulk polypropylene reactors based on data reconciliation procedures. Macromolecular Symposia 271, 26–37]. Both methods are used to solve the NDDR problem in an industrial bulk propylene polymerization process, using real data in real time for the simultaneous estimation of model parameters and process states. A phenomenological model of the real process, based on the detailed mass and energy balances and constituted by a set of algebraic–differential equations, was implemented and used for interpretation of the actual plant behavior in real time. The resulting nonlinear dynamic optimization problem was solved iteratively on a moving time window, in order to capture the current process behavior and allow for dynamic adaptation of model parameters. Obtained results indicate that the proposed PSO procedure can be implemented in real time, allowing for estimation of more reliable process states and model parameters and leading to much more robust and reproducible numerical performance.

Calculation of Kinetic Parameters and Active Sites Concentration for a New Multiple Site Model in Bulk Propylene Polymerization with the MgCl -Supported Ziegler-Natta Catalyst Using the Genetic Algorithm Method

A comprehensive triple-site-model was studied. This model was based on the new molecular dynamics outcomes obtained from the researchers on the different active sites that exist on the heterogeneous Ziegler-Natta catalyst. The model was composed of high-isospecific site (IS), low-isospecific site (IS), and aspecific site (AS). A transformation occurred on the high isotactic site and a second isotactic site was generated, as the low-isospecific site. The model is able to predict experimental results of bulk propylene polymerization with great accuracy. Moreover, the kinetic parameters and constants for each individual site has an Arrhenius type behavior. These parameters were determined using genetic algorithm adaptation method. The concentration of each type of sites, the isotactic and atactic fraction were determined during the polymerization, per unit mass of catalyst. A very good agreement was found in between the model and reported experimental results.

In‐Line Monitoring of Bulk Polypropylene Reactors Based on Data Reconciliation Procedures

AbstractThe main objective of this work is the implementation of a nonlinear dynamic data reconciliation (NDDR) procedure for the in‐line monitoring of the bulk propylene polymerization, as performed in a real industrial site. Special attention is given to monitoring of the melt flow index (MI) of the polymer product obtained in an industrial extruder at different operating conditions. In order to do that, a model is developed to describe the polymerization process and the controlled degradation of polypropylene in a reactive extruder. The model is implemented in real time, allowing for in‐line and real‐time monitoring of the plant operation.

Porous versus novel compact Ziegler–Natta catalyst particles and their fragmentation during the early stages of bulk propylene polymerization

AbstractThe effect of the porosity of Ziegler–Natta catalyst particles on early fragmentation, nascent polymer morphology, and activity were studied. The bulk polymerization of propylene was carried out with three different heterogeneous Ziegler–Natta catalysts under industrial conditions at low temperatures, that is, with a novel self‐supported catalyst (A), a SiO2‐supported catalyst (B), and a MgCl2‐supported catalyst (C), with triethyl aluminum as a cocatalyst and dicyclopentyl dimethoxy silane as an external donor. The compact catalyst A exhibited no measurable porosity and a very low surface area (&lt;5 m2/g) by Brunauer–Emmet–Teller analysis, whereas catalysts B and C showed surface areas of 63 and 250 m2/g, respectively. The surface and cross‐sectional morphologies of the resulting polymer particles at different stages of particle growth were analyzed by scanning electron microscopy and transmission electron microscopy. The compact catalyst A showed homogeneous and instantaneous fragmentation already in the very early stages of polymerization, which is typically observed for porous MgCl2‐supported Ziegler–Natta catalysts. Moreover, the compact catalyst particles gave rise to almost perfectly spherical polymer particles with a smooth surface. In contrast, the silica‐supported catalyst B gave rise to particles having a cauliflower morphology, and the second reference catalyst C produced fairly spherical polymer particles with a rough surface. All of the three catalysts exhibited similar activities of 450 g of polypropylene/g of catalyst after 30 min of polymerization, and most interestingly, the comparative kinetic data presented indicated that the reaction rates were not influenced by the porosity of the catalyst. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.

Bulk propylene polymerization in the presence of ansa-metallocenes of C 2 and C 1 symmetries: From a rigid thermoplastic to elastomeric stereoblock polypropylene

Bulk propylene polymerization in the presence of ansa-metallocenes with C2 and C1 symmetries has been studied. The catalytic activity, polymerization kinetics, and the molecular weight of polypropylene (PP) depend strongly on catalyst formation conditions. Mixtures of rac and meso isomers of metallocenes make it possible to rapidly produce a high-molecular-weight isotactic PP with high stereoregularity and mechanical characteristics and thus skip the stage of the isolation of pure rac isomer in the catalyst synthesis. The ability of triisobutylaluminum to serve as a cocatalyst is studied for ansa-metallocenes of C1 symmetry. In this case, the molecular weight of PP is higher, indicating that organoaluminum compounds participate in chain termination reactions. An increase in the reaction temperature results in an increase in the stereoregularity and crystallinity of PP. Polypropylene synthesized using ansa-metallocenes of C1 symmetry has good elastomeric properties.

Preparation of porous spherical MgCl2/SiO2 complex support as precursor for catalytic propylene polymerization

AbstractThe MgCl2/SiO2 complex support was prepared by spray drying using alcoholic suspension, which contained MgCl2 and SiO2. The complex support reacted with TiCl4 and di‐n‐butyl phthalate, giving a catalyst for propylene polymerization. The catalyst was spherical and porous with high specific surface area. TEA was used as a cocatalyst, and four kinds of alkoxysilane were used as external donors. The bulk polymerization of propylene was studied with the catalyst system. The effect of the reaction conditions and external donor on the polymerization were investigated. The results showed that the catalyst had high activity, high stereospecificity, and sensitive hydrogen responsibility. Polypropylene has good grain morphology because of duplicating the morphology of the catalyst. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1296–1299, 2005

Steady‐State Behavior of Slurry and Bulk Propylene Polymerization

This paper analyzes the steady‐state behavior of two typical processes to produce poly(propylene): the single‐reactor bulk polymerization process and the slurry polymerization process in a train of continuous stirred tank reactors. The investigation is performed using a commercial process simulator—SIMULPOL 3.0®, and aims at elucidating the general behavior of both processes when subject to perturbations of the input operation variables. Attention is given to the effect of the perturbations upon the polymer properties and to identification of process bottlenecks. Regarding the bulk polymerization process, unstable plant behavior was detected in the absence of a control policy. It was found that multiple steady‐states are possible for this process as a consequence of the recycling of material. As a matter of fact, the reactor recycle flow rate was found to be a fundamental parameter for the bulk process. Unstable behavior can be eliminated with the implementation of classical control strategies.