A Comprehensive Kinetic Model for the Free-Radical Polymerization of Vinyl Chloride in the Presence of Monofunctional and Bifunctional Initiators (original) (raw)
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Kinetic modelling of free-radical vinyl chloride polymerization with a mixture of initiators
Jurnal Teknologi, 2008
The most critical unit operation in commercial manufacturing of poly(vinyl chloride) (PVC) is the polymerization reactor. Therefore, application of modelling techniques on polymerization reactors is essential to gain a clear understanding on the polymerization kinetics. In this paper, the kinetic behaviour of free-radical vinyl chloride polymerization in a suspension poly(vinyl chloride) (PVC) reactor is described. A kinetic model is used to describe the polymerization reaction. The isothermal model predicts the overall monomer conversion, the polymerization rate, reactor pressure and the monomer distribution in the gas, aqueous, and polymer phases for the polymerization cycle. In commercial reactors, mixtures of initiators are usually added to increase the polymerization rate. The model also explores the effect of initiators onto the polymerization rate and conversion. All algorithms are written in MATLAB 7.1.
Simulation of Pilot and Industrial-Scale Vinyl Chloride Batch Suspension Polymerization Reactors
Industrial & Engineering Chemistry Research, 2007
A complete model for the simulation of vinyl chloride batch suspension polymerization reactors, capable of calculating pilot-scale and industrial-scale reactors, is developed. The model solves the mass balances and moment equations, on one hand, and the energy balances for the suspension, reactor wall, and cooling jacket fluid on the other hand. The controller loop, which determines the flow rate or temperature of the cooling liquid, is also included. The kinetic model is based on calculated diffusional contributions and experimentally estimated intrinsic rate coefficients. [T. De Roo et al., Macromol. Symp. 2004, 206, 215; T. De Roo et al. Polymer 2005, 46, 8340.] This extended set of equations allows calculation of the monomer conversion, the moments of the molecular mass distribution, the reactor temperature and pressure, the cooling agent flow rate and temperature profiles, and possible thermal runaway and/or reactor vessel explosions. Simulated and experimental results for the pilot-scale reactor are in good agreement. a Stage 1: k ) 1; stage 2: k ) 1, 2; stage 3: k ) 2. I1 ) I0, M1 ) M0 at t ) 0; Ri,1, Pi,1 ) 0 at t ) 0; Ri,2, Pi,2 ) 0 at start of stage 2 (that is, monomer conversion X ) 0.1%). I0 and M0 values are taken from Tables 11 and 12.
Chemical Engineering Science, 2001
The industrial manufacturing of poly(vinyl chloride) (PVC) by suspension polymerization is carried out in batch reactors. The productivity increase of these processes is directly related to the reduction of the time required to complete each batch. The reactor cooling system is designed such that it is capable to compensate for the maximum rate of heat release by the exothermic polymerization, so that the reactor cooling capacity is underutilized. An attractive mode of operation is to run the industrial process isothermally and to use a mixture (`cocktaila) of di!erent initiators, which is able to spread the polymerization rate over the batch time. In this work, the optimal formulation of an initiator mixture is studied as a dynamic optimization problem, which makes use of a representative mathematical model for the batch suspension vinyl chloride polymerization process. Results show that by choosing the optimal amounts of initiators in the cocktail, a signi"cant reduction of the total processing time for a given polymer speci"cation can be obtained, as compared to the case in which only one initiator is optimally chosen. : S 0 0 0 9 -2 5 0 9 ( 0 0 ) 0 0 3 1 7 -1
Dynamic Simulation of Industrial Poly(vinyl chloride) Batch Suspension Polymerization Reactors
Industrial & Engineering Chemistry Research, 1997
In the present study a comprehensive mathematical model is developed to simulate the dynamic behavior of industrial poly(vinyl chloride) (PVC) batch suspension polymerization reactors. More specifically, the model predicts the monomer concentration in the gas, aqueous, and polymer phases, the overall monomer conversion, the polymerization rate and polymer chain structural characteristics (e.g., number-and weight-average molecular weights, long-chain branching, shortchain branching, and number of terminal double bonds), the reactor temperature and pressure, and the jacket inlet and outlet temperatures over the whole polymerization cycle. An experimental reactor is employed to verify the theoretical model predictions. It is shown that experimental results on the time evolution of reactor temperature and pressure, the jacket inlet and outlet temperature, and the final conversion and molecular weight averages are in very good agreement with model predictions. The predictive capabilities of the model are also demonstrated through the simulation of experimental data recently reported in the literature. Finally some results on the optimization of the PVC production are presented. IE9604839 X Abstract published in Advance ACS Abstracts, February 15, 1997.
Kinetics and mechanism of vinyl chloride polymerization
Pure and Applied Chemistry, 1981
Kinetic models for formation of CH2C1 branch units based on headto head addition and the first order interruption of the growing chain with formation of Cl. and H. radicals are discussed. Some features of the formation and stabilization of primary particles in bulk and suspension polymerization are reviewed. Different kinetic models for bulk and suspension polymerization are critically reviewed. Particle formation in emulsion polymerization below and above CMC is treated, due consideration being given to the desorption and reabsorption of radicals. The kinetics of emulsion polymerization is discussed in detail. Desorption and reabsorption of radicals are discussed as well as the possibility of termination in the aqueous phase. Steady and non steady state treatments in seed polymerization are discussed. Thermodynamic principles for the formation and stability of monomer emulsions are treated. Initiation in monomer droplets with direct formation of latex particles in the 0.2-1.5 pm range as well as monodisperse particles in the 2-5 pm range are described. Spontaneous emulsification with formation of relatively stable monomer emulsions with different mixed emulsifier systems and subsequent polymerization with initiation in the monomer droplets is discussed. Polymerization under conditions corresponding to sub-saturation pressures can be achieved by addition of a low molecular weight, water insoluble compound to the monomer phase.
Plastics, Rubber and Composites, 2008
A comprehensive multiscale, multiphase dynamic model is developed to simulate heterogeneous vinyl chloride (VCM) suspension polymerisation in industrial batch reactors. From the numerical solution of the proposed integrated model, the evolution of the molecular (i.e. molecular weight distribution, long chain branching, short chain branching, terminal double bonds) and morphological (i.e. particle size distribution, porosity) polymer properties in a PVC batch suspension polymerisation reactor can be predicted. In particular, the polymer molecular properties are determined by employing a kinetic mechanism which describes the VCM free radical polymerisation in both monomer and polymer rich phases. Semi-empirical and phenomenological expressions are used to describe the breakage and coalescence rates of dispersed monomer droplets in terms of the type and concentration of suspending agent, quality of agitation and evolution of the physical, thermodynamic and transport properties of the polymerisation system. The dynamic discretised particle population balance equation (PBE) is solved to calculate the dynamic evolution of the particle size distribution of the produced PVC. Furthermore, the primary particle size distribution (PPSD) inside the polymerising monomer droplets, which influences to a large degree the porosity of the final PVC grains, is determined by the solution of a PBE governing the nucleation, growth and aggregation of the primary particles. Finally, dynamic mass and energy balances are derived to assess the dynamic behaviour of the PVC batch suspension polymerisation reactors. The theoretical model predictions show good agreement with a comprehensive series of experimental data provided by the PVC industry. This verification of the proposed model makes it a powerful tool for the simulation of large scale PVC batch suspension polymerisation reactors.
Journal of Applied Polymer Science, 2000
Monofunctional initiators are extensively used in free radical polymerization. To enhance productivity, a higher temperature is usually used; however, this leads to lower molecular weights. Bifunctional initiators can increase the polymerization rate without decreasing the average molecular weight and this can be desirable. A bifunctional initiator is an important issue to be investigated, and it is of great interest to industries. The objective of this work is to study polymerization reactions with mono-and bi-functional initiators through comprehensive mathematical models. Polystyrene is considered as case study. This work collects and presents some experimental data available in literature for polymerization using two different types of bifunctional initiators. Model prediction showed good agreement with experimental data. It was observed that the initial initiator concentration has a huge impact on the efficiency of initiators with functionality bigger than one and high concentrations of bifunctional initiator make the system behave as if it were a system operating with monofunctional initiator. V
Initiator Feeding Policies in Semi-Batch Free Radical Polymerization: A Monte Carlo Study
Processes, 2020
A Monte Carlo simulation algorithm is developed to visualize the impact of various initiator feeding policies on the kinetics of free radical polymerization. Three cases are studied: (1) general free radical polymerization using typical rate constants; (2) diffusion-controlled styrene free radical polymerization in a relatively small amount of solvent; and (3) methyl methacrylate free radical polymerization in solution. The number- and weight-average chain lengths, molecular weight distribution (MWD), and polymerization time were computed for each initiator feeding policy. The results show that a higher number of initiator shots throughout polymerization at a fixed amount of initiator significantly increases average molecular weight and broadens MWD. Similar results are also observed when most of the initiator is added at higher conversions. It is demonstrated that one can double the molecular weight of polystyrene and increase its dispersity by 50% through a four-shot instead of a ...
Mathematical Modeling and Optimization of a Semi-Batch Polymerization Reactor
IFAC Proceedings Volumes, 2000
This paper concerns mathematical modeling and optimization of a labscale and a pilot-scale semi-batch free-radical homo-polymerization reactors. A firstprinciples mathematical model is developed by using reaction rate laws available in polymerization literature. The model is validated by comparing the model predictions of monomer conversion, polymer mass fraction, number-average molecular weight, weight-average molecular weight, and polydispersity index to off-line measurements taken in pilot-scale and lab-scale polymerization reactors at DuPont's Marshall Laboratory. The validated model is then used to calculate optimal initiator and monomer feed-rate policies which minimize the polydispersity index of the final polymer product, subject to a set of tight operational constraints.