Polymerisation reactors

Fig. 2. Emulsion polymerisation plant. A, Emulsion feed tank B, polymerisation reactor C, dmmming tank E, filter M, meter P, pressure gauge T,...

Figure 5.107. The polymerisation reactor with cooling and bursting disc.

A polymer is produced by the emulsion polymerisation of acrylonitrile and methyl methacrylate in a stirred vessel. The monomers and an aqueous solution of catalyst are fed to the polymerisation reactor continuously. The product is withdrawn from the base of the vessel as a slurry. 

Fig. 1 Polymerisation reactor with its cooling unit and bursting disc.

Polymer synthesis is not difficult today. To synthesise a polymer we only need an appropriate quantity of the monomer and the catalyst and a suitable polymerisation reactor and we can obtain a polymer of our choice in terms of the required Molecular weight, structure, crystallinity, etc. 

In a typical polymerising experiment, a mixture of monomer, solvent and initiator is allowed to feed into a chain of three polymerising reactors. The first reactor is having three heating zones. 

Most polymerisation reactions occur via a complex reaction scheme. Relatively few reactant species are involved (sometimes only one) and these are usually well-defined. However, the reaction products can be described in a number of ways. The polymer molecules produced in these reactions vary in size in some cases the size distribution can be very wide. In effect, a polymerisation reaction produces a large number of reaction products and reaction selectivity requires special treatment. For some purposes, the polymer molecules can be treated as a combined group which is referred to generally as polymer . However, the physical properties of any given type of polymer depend on its molecular weight distribution. Therefore, it is often necessary to obtain a quantitative description of the product size distribution. This will depend on both the kinetic scheme for the polymerisation reaction and the mixing conditions in the polymerisation reactor. 

HA Duxbury, The Sizing of Relief Systems for Polymerisation Reactors", The Chemical Engineer 31-37, January 1980... 

Set point changes. These are deliberate changes in the operating conditions, such as a change in polymer grade for a polymerisation reactor, change in distillate composition for a distillation column, etc. 

Kiparissides, C., Daskalakis, G., Achilias, D. S., Sidiropoulou, E., Dynamic simulation of polyvinylchloride batch suspension polymerisation reactors, Ind. Eng. Chem. Res., 1997, 36, 1253-1267... 

Alternating copolymers may be considered as homopolymers with a structural unit composed of the two different monomers. Random copolymers are obtained from two or more monomers, which are present simultaneously in one polymerisation reactor. In graft polymerisation a homopolymer is prepared first and in a second step one or two monomers are grafted onto this polymer the final product consists of a polymeric backbone with side branches. In block copolymerisation one monomer is polymerised, after which another monomer is polymerised on to the living ends of the polymeric chains the final block copolymer is a linear chain with a sequence of different segments. 

The formation of polymer build-up in polymerisation reactors and the routes towards minimising polymer buildup are described. The antifouling action of Evicas 90, a naphthol/formaldehyde condensate, is demonstrated and the main factors influencing the formation of polymer build-up and the effectiveness of antifouling agents are outlined. 10 refs. 

Many aspects of homopolymerisation reaction engineering have been studied in recent years (1-4). Much attention has been given the nature of the dependence of the polymer molecular weight (MW) and molecular weight distribution (MWD) on the operating conditions of the polymerisation reactor. 

Alongside the growth of understanding of the complex inter-relationship between the reaction and reactor dynamics there has been rapid increase in the application of computers for polymerisation reactor control (5). 

In contrast to the requirements for homopolymerisation processes, the parameters needed to fully describe copolymerisation processes are more numerous. Molecular features such as the copolymer composition, composition distribution and chain sequence structure and their variation with conversion are compounded with those of copolymer MW and MWD. To understand copolymerisation processes, it is desirable to decouple as many of these molecular parameters as possible and study the influence of polymerisation reactor conditions on each. As yet there have been relatively few reports on the detailed behaviour of copolymerisation reactors (6-9 ). This work forms part of a wider range of investigations which are being carried out in our laboratories of control methods for the production of speciality polymers. 

Zeaiter, J. Romagnoli, J.A. Gomes, V.G. Gilbert, R.G. Operation of semi-batch emulsion polymerisation reactors modelling, validation, and effect of operating conditions. Chem. Eng. Sci. 2002, 57, 2955-2969. 

All the reaction constants discussed in this book have relative values and not absolute values, because the PO anionic polymerisation is strongly diffusion dependent and each polymerisation reactor has specific hydrodynamic properties. 

One of the most common technologies for the synthesis of polymer polyols by a radical mechanism is based on the stepwise addition of a mixture of vinylic monomers (polyether polyol, initiator, transfer agent (mixture I)) to a second mixture (mixture II) of polyether polyol (identical with the polyether used for mixture I) and NAD (macromer or nonreactive NAD) under a nitrogen protective atmosphere, in the polymerisation reactor at 115-... 

Polyether polyols for rigid PU foams are obtained in the same type of polymerisation reactors as those used for high molecular weight polyether polyols, i.e., in stainless steel loop reactors, with an external heat exchanger, preferably with the possibility of generating a large surface of the liquid reaction mass, by a spray technique or by an ejector technique... 

In order to decrease the total reaction time, a small reactor, with a stirrer, is linked to the polymerisation reactor, for the preparation of the initial starters - catalyst mixture. In this reactor, there are 1-3 polyols used as starters, the catalyst (KOH, NaOH or a tertiary amine) and sometimes, for solid polyols, an initial liquid medium (for example a part of an intermediary or final polyether polyol called heel , or an inert solvent). Generally, in the synthesis of polyether polyols for rigid foams it is preferred to avoid the utilisation of inert solvents, which need recycling and a more complicated installation. 

The mixture of starters and catalyst (especially with solid starters, such as sucrose or pentaerythritol) is stirred for 1-2 hours, under nitrogen at 80-100 °C, to obtain a thermodynamic equilibrium (partial solid solubilisation, solvation of solid surfaces and so on). All these preparations can be made in the small reactor simultaneously with the PO polymerisation reaction. After the polymerisation step and after final polyether evacuation, the prepared mixture of starters with catalyst is added to the polymerisation reactor and the polymerisation reaction begins immediately. Of course, the catalyst can be added separately, directly into the reactor, after charging the starter mixture. After the creation of an inert atmosphere of nitrogen and the increase of reaction temperature... 

The polymerisation reactor is charged with a polyol - catalyst mixture and, under an inert atmosphere of nitrogen, PO (or EO) is added at the polymerisation temperature, preferable 105-125 °C for KOH or NaOH catalysts and 80-95 °C for tertiary amines. 

The AR method has been extended to more complex system, as non-isothermal reactions, catalytic reactions, polymerisation reactors, or combination with separations. Other important applications of Attainable Region are in the field of optimisation and planning of experiments. More information can be found by consulting the above cited website. 

In a polymerisation reactor, a monomer/polymer solution is to be agitated in a baffled mixing vessel using a double turbine (6 fiat blades) impeller, with the configuration B-B in Table 8.1, at a rotational speed of 2Hz. The solution exhibits power-law behaviour with n = 0.6 and m = 12 Pa-s° . Estimate the power required for a 300 mm diameter impeller. The density of the solution is 950kg/m. ... 

Thus, using small-scale tubular turbulent divergent-convergent-type reactors at the stage of uniform gas-liquid mixture formation, prior to feeding this mixture into a stirred tank polymerisation reactor, results in a notable (virtually hy one order of magnitude) increase in the phase contact surface. A developed phase interface facilitates the uniform saturation of liquid products with monomers and hydrogen. In this case, it allows improved performance characteristics of the EPR in contrast to stirred tank reactors. 

Moreover, step-by-step preparation of the liquid-gas mixture in tubular turbulent divergent-convergent-type reactors, as well as the mixture feed distribution for parallel polymerisation reactors, using a tubular turbulent spider-type distribution device, allowed copolymers with the same properties to be produced in different polymerisation reactors, run in parallel (Table 3.5). 

Table 3.5 Effect of homogeneous liquid-gas mixture feed distribution for polymerisation reactors run in parallel on EPDM rubber uniformity ...

Liquid-gas mixture feed method Polymerisation reactors run in parallel Mooney viscosity... 

The raw polymer as produced leaves the polymerisation reactor in a form not readily marketable. 

Figure 6.3 One litre suspension polymerisation reactor. Note teflon bearings at the top and bottom of the stainless steel impeller-type stirrer, and stainless steel baffles, to optimise stirring and hence suspension.

Core-shell latexes with a poly(butyl methacrylate) (PBM A) core and a polypyrrole (PPy) shell were prepared by chemically polymerising pyrrole in the presence of a PBMA latex, different shell thicknesses being obtained by varying the concentration of the PBMA latex in the polymerisation reactor. At low PPy concentrations, the shell was smooth and the conductivity correlated with the PPy content, with a percolation threshold of 0.25 wt% PPy, giving a theoretical shell thickness of 0.6 nm. At higher PPy concentrations, different morphologies were formed and the conductivity was almost independent of the PPy content. 4 refs. Presented at the International Conference on Science and Technology of Synthetic Metals (ICSM 98), Montpellier, France, 12-18 July 1998. 

The application of ultrasonics to the monitoring of emulsion polymerisation reactors is considered. The use of acoustic speed measurements to monitor conversion is demonstrated by its apphcation to the control of the emulsion copolymerisation of styrene and butyl acrylate. The potential of acoustic attenuation for the measurement of particle size is discussed and applied to the determination of the particle size distribution of PVC and PTFE latices. 27 refs. 

INVESTIGATION ON PRODUCTION OF CARBOXYLATED STYRENE-BUTADIENE RUBBER LATEX IN DIFFERENT POLYMERISATION REACTORS... 

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