Semi batch polymerization

J. W. Wassick, D. Coeeey, B. Calli-HAN, Nonlinear Model Predictive Control of a commercial polymerization semi-batch reactor , presented at the Tutorial on Polymerization Reactor Control, AIChE Annual Meeting, November, 2003. 

A semi-batch reactor has the same disadvantages as the batch reactor. However, it has the advantages of good temperature control and the capability of minimizing unwanted side reactions by maintaining a low concentration of one of the reactants. Semi-batch reactors are also of value when parallel reactions of different orders occur, where it may be more profitable to use semi-batch rather than batch operations. In many applications semi-batch reactors involve a substantial increase in the volume of reaction mixture during a processing cycle (i.e., emulsion polymerization). 

Much has been written on RAFT polymerization under emulsion and miniemulsion conditions. Most work has focused on S polymerization,409-520 521 although polymerizations of BA,461 522 methacrylates382-409 and VAc471-472 have also been reported. The first communication on RAFT polymerization briefly mentioned the successful semi-batch emulsion polymerization of BMA with cumyl dithiobenzoate (175) to provide a polymer with a narrow molecular weight distribution.382 Additional examples and discussion of some of the important factors for successful use of RAFT polymerization in emulsion and miniemulsion were provided in a subsequent paper.409 Much research has shown that the success in RAFT emulsion polymerization depends strongly on the choice of RAFT agent and polymerization conditions.214-409-520027... 

Presented in this paper is a specific example of a semi-batch, free radical, dispersion polymerization. In this example, SimuSolv is used to quantify a Icinetic model derived from free radical polymerization principles and then used to define a new finishing process to reduce residual monomer to an acceptable level. Finally, experimental results are compared with those predicted by the computer simulation. 

MODEL TO PREDICT RESIDUAL MONOMER FOR AN ISOTHERMAL SEMI-BATCH POLYMERIZATION AND AN ISOTHERMAL BATCH FINISHING STEP. 

The various kinetic and thermodynamic factors involved in vinyl free radical polymerization have been considered for the case of a batch (or semi-batch) polymerization being carried out to very high conversion. In particular, computations have been done for the final stage of the reaction when monomer concentration is reduced from approximately 5 volume % to 0.5 volume %. 

In batch or semi-batch polymerization processes it is often desirable to add a "chaser catalyst" towards the end of the reaction to reduce the residual monomer concentration to acceptable levels. The ability of the catalyst to reduce the monomer concentraion to low levels (ca 0.10 vol%) is of considerable importance for economic, envirorunental and physiological reasons. The chaser catalyst addition reduces processing time and increases throughput (Kamath and Sargent (1987)). 

One final note While the techniques used here were applied to control temperature In large, semi-batch polymerization reactors, they are by no means limited to such processes. The Ideas employed here --designing pilot plant control trials to be scalable, calculating transfer functions by time series analysis, and determining the stochastic control algorithm appropriate to the process -- can be applied In a variety of chemical and polymerization process applications. 

Polymerization was performed in a 100 mL glass reactor equipped with a magnetic stirrer and carried out as semi-batch method. First, the reactor was charged with MAO and then 1-hexene in the certain amount was add. Consequently the system was changol to etiiylene atmosphae system. When reaction medium was saturated with ethylme monoma-. 

A way to narrow the MWD and to approach the structure of dendrimers is the addition of a small fraction of a/-functional initiator, to inimers [40,71]. In this process the obtainable degree of polymerization is limited by the ratio of inimer to initiator. It can be conducted in two ways (i) inimer molecules can be added so slowly to the initiator solution that they can only react with the initiator molecules or with the already formed macromolecules, but not with each other (semi-batch process). Thus, each macromolecule generated in such a process will contain one initiator core but no vinyl group. Then, the polydispersity index is quite low and decreases with / M /Mn l-i-l//. (ii) Alternatively, initiator and monomer molecules can be mixed instantaneously (batch process). Here, the normal SCVP process and the process shown above compete and both kinds of macromolecules will be formed. For this process the polydispersity index also decreases with/,but is higher than for the semi-batch process, M /Mn=Pn//. ... 

Theoretical calculations were also conducted on the influence of/-functional initiators on DB in SCVCP [72]. In the semi-batch system, DB is only sHghtly affected by the presence of polyinitiator and is mostly governed by the comonomer content. The calculations are also applied to polymerizations from surface-bound initiators (see later). 

A process for the hydrogenation of adiponitrile and 6-aminocapronitrile to hexamethylenediamine in streams of depolymerized Nylon-6,6 or a blend of Nylon-6 and Nylon-6,6 has been described. Semi-batch and continuous hydrogenation reactions of depolymerized (ammonolysis) products were performed to study the efficacy of Raney Ni 2400 and Raney Co 2724 catalysts. The study showed signs of deactivation of Raney Ni 2400 even in the presence of caustic, whereas little or no deactivation of Raney Co 2724 was observed for the hydrogenation of the ammonolysis product. The hydrogenation products from the continuous run using Raney Co 2724 were subsequently distilled and the recycled hexamethylenediamine (HMD) monomer was polymerized with adipic acid. The properties of the polymer prepared from recycled HMD were found to be identical to that obtained from virgin HMD. 

Polymer production technology involves a diversity of products produced from even a single monomer. Polymerizations are carried out in a variety of reactor types batch, semi-batch and continuous flow stirred tank or tubular reactors. However, very few commercial or fundamental polymer or latex properties can be measured on-line. Therefore, if one aims to develop and apply control strategies to achieve desired polymer (or latex) property trajectories under such a variety of conditions, it is important to have a valid mechanistic model capable of predicting at least the major effects of the process variables. 

Block copolymer synthesis from living polymerization is typically carried out in batch or semi-batch processes. In the simplest case, one monomer is added, and polymerization is carried out to complete conversion, then the process is repeated with a second monomer. In batch copolymerizations, simultaneous polymerization of two or more monomers is often complicated by the different reactivities of the two monomers. This preferential monomer consumption can create a composition drift during chain growth and therefore a tapered copolymer composition. 

A technique is described [228] for solving a set of dynamic material/energy balances every few seconds in real time through the use of a minicomputer. This dynamic thermal analysis technique is particular useful in batch and semi-batch operations. The extent of the chemical reaction is monitored along with the measurement of heat transfer data versus time, which can be particularly useful in reactions such as polymerizations, where there is a significant change in viscosity of the reaction mixture with time. 

Abel, O. A. Helbig W. Marquardt H. Zwick, et al. Productivity Optimization of an Industrial Semi-batch Polymerization Reactor Under Safety Constraints. J Proc Contr 10 351-362(2000). 

T.W. Francisco, S. Yembrick and K.W. Leffew, Semi-batch polymerization analysis by mnlti-point Raman spectroscopy, PAT - J. Process Anal. TechnoL, 3, 13-19 (2006). 

The latexes were prepared using a conventional semi-batch emulsion polymerization system modified for power-feed by the addition of a second monomer tank. Polymerization temperatures ranged from 30-85°C using either redox or thermal initiators. Samples were taken periodically during the polymerization and analyzed to determine residual monomer in order to assure a "starved-feed" condition. As used in this study this is a condition in which monomer feed rate and polymerization rate are identical and residual monomer levels are less than 5%. 

A semi batch reactor comes in two flavors. The first is when some material is fed to the reactor during the batch cycle. There is an initial charge of some of the reactants, but the rest of the reactants or catalysts are continuously fed into the reactor during the cycle. This is called a fed-batch reactor. Many batch polymerization reactors operate in the fed-batch mode, with monomer fed into the reactor during the batch cycle. The fed-batch reactor has the inherent advantage that the concentration of the limiting reactant (or catalyst) can be kept low enough to prevent runaway reactions. 

In Scheme 18 a gas-phase stirred bed reactor for BD polymerization is shown. A 0.25 L semi-batch reactor was used by Ni et al. for studies on the influence... 

To synthesize water-soluble or swellable copolymers, inverse heterophase polymerization processes are of special interest. The inverse macroemulsion polymerization is only reported for the copolymerization of two hydrophilic monomers. Hernandez-Barajas and Hunkeler [62] investigated the copolymerization of AAm with quaternary ammonium cationic monomers in the presence of block copoly-meric surfactants by batch and semi-batch inverse emulsion copolymerization. Glukhikh et al. [63] reported the copolymerization of AAm and methacrylic acid using an inverse emulsion system. Amphiphilic copolymers from inverse systems are also successfully obtained in microemulsion polymerization. For example, Vaskova et al. [64-66] copolymerized the hydrophilic AAm with more hydrophobic methyl methacrylate (MMA) or styrene in a water-in-oil microemulsion initiated by radical initiators with different solubilities in water. However, not only copolymer, but also homopolymer was formed. The total conversion of MMA was rather limited (<10%) and the composition of the copolymer was almost independent of the comonomer ratio. This was probably due to a constant molar ratio of the monomers in the water phase or at the interface as the possible locus of polymerization. Also, in the case of styrene copolymerizing with AAm, the molar fraction of AAm in homopolymer compared to copolymer is about 45-55 wt% [67], which is still too high for a meaningful technical application. 

Chylla, R. W., and Hasse, D. R. (1993),Temperature control of semi-batch polymerization reactors, Comp. Chem. Eng., 17(3), 257-264. 

Batch, semi-batch and continuous emulsion polymerizations are usually carried out in stirred tank reactors, where agitation by a stirrer is necessary. The type of stirrer chosen and its stirring speed can often affect the rate of polymerization, the number of polymer particles and their size distribution (PSD), and the molecular weight of the polymer produced. However, the effect of stirring on emulsion polymerization has never been the main research parameter in research programs [241]. This is probably due to the conflicting results obtained so far by various researchers. 

Figure 12. Degree of polymerization with time in response to step change in monomer ratio in a controlled semi-batch reactor. Key -----, WADP -------, NADP.

Semi-batch epoxy polymerization Simultaneous maximization of number-average molecular weight and minimization of reaction time. NSGA-11 The MOO problem includes a constraint on the desired polydispersity index. Mitnetal. (2004a)... 

Mitra, K., Majumdar, S. and Raha, S. (2004a). Mnlti-objective d3mamic optimization of a semi-batch epoxy polymerization process, Comput. Chem. Eng., 28, pp. 2583-2594. 

You are asked to design a semibatch reactor to be used in the production of specialized polymers (ethylene glycol-ethylene oxide co-polymers). The semi-batch operation is used to improve the molecular-weight distribution. Reactant B (EG) and a fixed amount of homogeneous catalyst are charged initially into the reactor (the proportion is 6.75 moles of catalyst per 1000 moles of Reactant B). Reactant A (EO) is injected at a constant rate during the operation. The polymerization reactions are represented by the following liquid-phase chemical reactions ... 

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