Batch polymerisation

Fig. 6. Activity and isotacticity vs Al/donor ratio. Batch polymerisation occurs ia diluent hexane at 70°C and 0.7 MPa (7 bar) for 4 h with a superactive...

The value of P for the free running operation of the system is obtained from the batch model equations and deviations from the desired value are used to calculate the required monomer feed volume flow-rate for the semi-batch polymerisation process. 

In batch polymerisation (399), the components of the emulsion are charged into a stirred reactor, which is then heated to begin polymerisation. No material is added or removed during the entire polymerisation. Since most polymerisations are highly exothermal, the rate of heat generation can easily exceed the heat removal capabilities, and a mnaway reaction is possible. The batch polymerisation method offers little or no control over the copolymer composition, but depends upon the comonomer reactivity ratios and the partitioning of the comonomers in the latex particles (288, 340). 

The batch method is quite simple and can be used in many different types of polymerisations, although there is little control beyond the recipe, temperature, and agitation conditions. Because latex particles are usually nucleated in the early stages of a batch polymerisation, they can be made monodisperse, and polystyrene size standard particles have been made using this process. However, significant variations may still exist from batch to batch, making production of a consistent product difficult by the batch process. 

Batch polymerisations are often performed in screening experiments on the laboratory-scale level. However, batch polymerisations are used less often in large-scale, commercial produchon processes than semi-continuous polymerisations because of the inherent limitations in heat transfer and copolymer composition control. 

A monomer preemulsion, used for miniemulsion polymerisation, was prepared by stirring a mixture of epoxy resin, acrylic monomers, surfactants, costabiliser and water. Miniemulsion polymerisation produced the composite latex. Methacrylic acid and/or dimethylaminoethyl methacrylate were added to introduce the functional groups into the composite latices. The functional groups were introduced either by batch polymerisation or two-stage polymerisation, the latex produced by the two-stage polymerisation method had good polymerisation stability, storage stability and solvent resistance. 11 refs. 

Batch polymerisation runs, intended to establish a starting recipe for continuous operation, were carried out with 15% rubber and 85% copolymer. Monomer composition was azeotropic.The reaction was carried out at 70°C and 20% total solids, using standard types of redox initiator, chain-... 

Polyamide 6 can be produced both by batch or continuous polymerisation. Batch polymerisation is preferably used for changing polymer formulations with a wide range of molecular weight, mostly compounding grades. Continuous polymerisation reactors - VK columns (Vereinfacht Kontinuierlich) - have a lower range of product mix but higher productivity and are, i.e. used for the production of textile or industrial fibres. Continuous processes can be operated with one or two reactors in series. 

Batch polymerisation is realised in autoclave reactors which operate on a cycle of phases at increased levels of temperature where the time and pressure parameters are carefiilly adjusted in order to gradually convert the monomer into polymer. The design of the plant is realised in order to optimise the sequences of different autoclaves, giving better continuity to production. The low quantity of product produced per each batch operation and the higher flexibility of the process, make the batch process suitable for the production of speciality polyamides. Batch polymerisation is also suitable for producing copolymers of polyamide 66 and polyamide 6, using partially caprolactam as the raw material together with nylon salt. 

Batch polymerisation is realised in autoclaves. There, the nylon salt solution, transferred from the storage tank, is processed at different temperatures and pressures. The sequence of the operating cycle is set at first to evaporate part of the excess water of the solution (e.g. to a concentration of 70 %). Then, as a consequence of the continuous heat supply, the temperature slowly rises causing the pressure to increase as well. Under these conditions the polycondensation starts. To allow the reaction to proceed, the water is bled off from the reactor in the form of steam, by a control valve that maintains a constant pressure. When the temperature of the mass has reached about 275 °C, the pressure is gradually decreased to atmospheric pressure. The depressurisation rate is a critical parameter and it is fully under the control of dedicated software. 

The simplest polymers to manirfacture are solid grade, or powder products via a batch polymerisation process. This batch process is a one-phase reaction in which all the reactants are added to the vessel prior to the start of the polymerisation process. As the polymerisation progresses the aqueous monomer mix forms into a solid mass. The onset of this gelation occurs at quite low monomer conversion, and manipulation of the polymerisation is not... 

Figure 6.8 Batch polymerisation of powder grade polymer. 

Polymerisation is carried out via a semi-batch (semi-continuous) process that allows reactants to be added during the polymerisation. It is usual for at least one of the redox initiators to be added as a metered feed over the course of the reaction. Other reactants can be added in order to control desired properties such as molecular weight distribution. Temperature control over the course of the polymerisation is also possible, particularly as the oil phase helps to dissipate the heat of polymerisation. Overall the semi-batch polymerisation technique is more versatile than the batch process and, as a consequence, it is possible to better manipulate polymer properties via this route. 

Ponnuswamy S, Shah SL, Kiparissides C. On-hne monitoring of polymer quality in a batch polymerisation reactor. J Appl Polym Sci 1986 32 3239-3246. 

Thus, Z is directly proportional to PC]/Pf and therefore the lower the concentrations of reactants, the lower will be the value of Z and hence the magnitude of co, will be increased. Of course this is only true for a constant ratio of PC] P]. If the ratio of PC] [I] is decreased as the absolute concentrations of reactants in a reactor are decreased, Z could be kept constant. However, a typical feed polymerisation would be designed to operate at standing reactant concentrations of 2-4 orders of magnitude less than the equivalent batch polymerisation. It is therefore highly unlikely that the ratio of pCj. P] in a feed polymerisation could be reduced sufficiently so as to keep Z at the magnitude it would have been in the equivalent batch polymerisation, i.e. 

If a batch polymerisation is performed to high conversion under non-azeotropic conditions, then the monomer feed composition changes and the composition of the copolymer (composition drift) also changes. It is then possible that the copolymer formed initially is no longer miscible in the copolymer formed in a later part of the reaction. Phase separation then occurs and one speaks of heterogeneous copolymers. Such a heterogeneous copolymer has the properties of the different polymers it is composed of (e.g. may have two glass... 

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