Polymerization in a slurry

Emulsion polymerization is usually carried out isothermally in batch or continuous stirred-tank reactors. Temperature control is much easier than for bulk or solution polymerization because the small ( 0.5 fim) polymer particles, which are the locus of the reaction, are suspended in a continuous aqueous medium. This complex, multiphase reactor also shows multiple steady states under isothermal conditions. In industrial practice, such a reactor often shows sustained oscillations. Solid-catalyzed olefin polymerization in a slurry batch reactor is a classic example of a slurry reactor where the solid particles change size and characteristics with time during the reaction process. 

Previously Keii and Doi had found, in the case of propylene polymerization in a slurry 98) or in the gas phase 99), a second order decay law ... 

Galli100) found that the kinetic curve, regarding propylene polymerization in a slurry under industrial conditions, can be adequately described by an expression of this type ... 

The first MgCL,-supported catalyst for polypropylene, was developed by Montedison in cooperation with Mitsui Petrochemical. In 1978 it was carried over to an already existing plant for the polymerization in a slurry. Thus, in comparison to the preexisting situation (Fig. 48), it was possible to achieve the first step toward eli-... 

The results mentioned above, referring to polymerization in a slurry, can be further improved by polymerizing in liquid propylene (Figs. 55, 56, 57). 

Propylene is polymerized in a slurry reactor by an equimolar mixture of aluminum triethyl and titanium tetrachloride. The catalyst residue remains with the polymer in a hydrolyzed form. If a customer specifies a maximum ash content of 0.10 wt% in product, what productivity (moles of monomer converted per mole of catalyst) must be achieved Assume that the ash is entirely AI2O3 and Ti02. 

When pure needle-like crystals of -aminobenzoyl chloride are polymerized in a high temperature, nonsolvent process, or alow temperature, slurry process, polymer is obtained which maintains the needle-like appearance of monomer. PBA of inherent viscosity, 4.1 dL/g, has been obtained in a hexane slurry with pyridine as the acid acceptor. Therefore PBA of fiber-forming molecular weight can be prepared in the soHd state. 

Polymerization in a hydrocarbon slurry (usually a light-saturated hydrocarbon) was the first commercial polymerization process to utilize Phillips and Ziegler catalysts. These processes enjoy high popularity because of theit versatihty. 

Slurry (Suspension) Polymerization. This polymerization technology is the oldest used for HDPE production and is widely employed because of process engineering refinement and flexibHity. In a slurry process, catalyst and polymer particles are suspended in an inert solvent, ie, a light or a... 

Polymerization in Hquid monomer was pioneered by RexaH Dmg and Chemical and Phillips Petroleum (United States). In the RexaH process, Hquid propylene is polymerized in a stirred reactor to form a polymer slurry. This suspension is transferred to a cyclone to separate the polymer from gaseous monomer under atmospheric pressure. The gaseous monomer is then compressed, condensed, and recycled to the polymerizer (123). In the Phillips process, polymerization occurs in loop reactors, increasing the ratio of available heat-transfer surface to reactor volume (124). In both of these processes, high catalyst residues necessitate post-reactor treatment of the polymer. 

The effect of physical processes on reactor performance is more complex than for two-phase systems because both gas-liquid and liquid-solid interphase transport effects may be coupled with the intrinsic rate. The most common types of three-phase reactors are the slurry and trickle-bed reactors. These have found wide applications in the petroleum industry. A slurry reactor is a multi-phase flow reactor in which the reactant gas is bubbled through a solution containing solid catalyst particles. The reactor may operate continuously as a steady flow system with respect to both gas and liquid phases. Alternatively, a fixed charge of liquid is initially added to the stirred vessel, and the gas is continuously added such that the reactor is batch with respect to the liquid phase. This method is used in some hydrogenation reactions such as hydrogenation of oils in a slurry of nickel catalyst particles. Figure 4-15 shows a slurry-type reactor used for polymerization of ethylene in a sluiTy of solid catalyst particles in a solvent of cyclohexane. 

As a final example of the application of gas-liquid-particle operation to a process involving a gaseous reactant and a solid catalyst, the possibility of polymerizing ethylene in, for example, a slurry operation employing a metal or metal oxide catalyst can be cited. It has been suggested that the good control of reaction conditions obtained in a slurry-type operation may be of importance in the production of certain types of polyethylene (Rl). 

The homopolymerization and copolymerization of 4-methyl-l-pent-ene is generally carried out in a batch polymerization process (5). Batch polymerization refers to a polymerization method in which a quantity of the monomers are polymerized in a reaction vessel and then the resulting polymer is recovered from that reaction vessel upon the desired level of polymerization of the monomers. It is desirable to carry out such processes under conditions, which result in a slurry of particles of the desired polymer or copolymer in the polymerization diluent rather than a solution of the polymer or copolymer. The formation of such a slurry aids in the separation and purification of the resulting polymer. 

Whatever the merits of each process in a continuous commercial operation, the slurry process is very convenient for batch polymerization studies in the laboratory. The diluent permits precise control of the temperature and serves to dissolve ethylene and other reactants that must contact the catalyst during polymerization. Most of the work reported here was done in a slurry reactor. 

Cr(VI)/Silica develops polymerization activity only gradually when exposed to ethylene at 100°C in a slurry autoclave. An example is shown in Fig. 5, which depicts an experiment in which the catalyst was not immediately active upon introduction into the reactor, but first underwent a dormant period or induction time. The rate of polymerization then increased during the remainder of the experiment. This is thought to be due to the slow reduction of Cr(VI) by ethylene to the Cr(II) active site, or perhaps to the desorption of by-products such as formaldehyde (32). Thus, the concentration of active sites is probably not constant but increases with time. Below 100°C the induction time becomes longer until at about 60°C there is almost no activity. Conversely, increasing the temperature shortens the induction time. At 150°C the catalyst exhibits an immediate and constant activity in solution phase polymerization. 

In PP manufacture, modern bulk (liquid monomer) and gas-phase processes have largely replaced the earlier slurry processes in which polymerization was carried out in hydrocarbon diluent. The most widely adopted process for PP is Basell s Spheripol process.317 Homopolymer production involves a pre-polymerization step at relatively low temperature, followed by polymerization in a loop reactor using liquid propylene random co-polymers are produced by introducing small quantities of ethylene into the feed. The pre-polymerization step gives a pre-polymer particle with the capacity to withstand the reaction peak, which occurs on entering the main loop reactor. The addition of one or two gas-phase reactors for EP co-polymerization makes it possible to produce heterophasic co-polymers containing up to 40% of E/P rubber within the homopolymer matrix. 

Slurry reactors are also used in other situations, such as the polymerization of ethylene or propylene. Here the slurry consists of catalyst particles and a solvent, such as cyclohexane, into which the ethylene or propylene is bubbled and dissolved. Another illustration is the Fischer-Tropsch reaction between hydrogen and carbon monoxide, where these gases are dissolved in a slurry of hydrocarbon oil and catalyst (iron) particles. Catalysis by colloidal metal particles and colloidal enzyme particles are other examples, although not always is one reactant a gas. 

The catalyst and metal alkyl cocatalyst can be brought into contact in a number of ways, depending on the commercial process. In a slurry or solution polymerization process, it is most convenient to simply feed a solution of the cocatalyst directly into the reactor, where it comes in contact with the catalyst in dilute solution and in the presence of ethylene and any comonomer. This procedure allows for continuous adjustment of the cocatalyst concentration for control of polymer properties. 

The next section deals with the development of our alternative process, in which the heat of polymerization is dissipated in a slurry system by the refluxing diluent. Although this process may appear not to be so economically attractive as the bulk route, it offers much more flexibility in the range of molecular weights that can be made. 

Solvents can be eliminated from some reactions by running them in ball mills.57 Methyl methacrylate can be polymerized in a vibratory ball mill using a talc catalyst.58 Ball mills are feasible for reactions on a commercial scale. Huge mills are used by the mining industry in grinding ores before flotation. If the mill is used repeatedly to make the same product, the problem of cleaning it out between runs is eliminated. It is also possible to use an inert liquid diluent in the milling, so that the product can be recovered as a slurry. The preferred diluent would be water if it is inert for the reaction in question. 

Noninterfering anions covalently bound to polymers have been prepared by the AIBN-initiated copolymerization of styrene with trialkylammonium 4-styryltris(pentafluorophenyl)borate (Scheme 30). High-density polyethylene prepared from Cp2ZrCl2— Al(i-Bu)3 and this activator shows no signs of reactor fouling in a slurry polymerization. "... 

Slurry polymerization is often used in the manufacture of polyolefins. Initially, the reaction system consists of the catalyst dispersed (or dissolved as in the case of soluble metallocene catalysts) in a continuous medium, which may be a diluent in which the monomer is dissolved or pure monomer. The polymer is insoluble in the continuous medium, therefore it precipitates on the catalyst forming a slurry. High-density polyethylene (HOPE) is produced in a slurry of isobutane (Chevron-Phillips process) [22 ]. Liquid propylene is used in the Spheripol process to produce i-PP [22]. 

Continuous stirred-tank reactors (CSTRs) are used for large productions of a reduced number of polymer grades. Coordination catalysts are used in the production of LLDPE by solution polymerization (Dowlex, DSM Compact process [29]), of HDPE in slurry (Mitsui CX-process [30]) and of polypropylene in stirred bed gas phase reactors (BP process [22], Novolen process [31]). LDPE and ethylene-vinyl acetate copolymers (EVA) are produced by free-radical polymerization in bulk in a continuous autoclave reactor [30]. A substantial fraction of the SBR used for tires is produced by coagulating the SBR latex produced by emulsion polymerization in a battery of about 10 CSTRs in series [32]. The CSTRs are characterized by a broad residence time distribution, which affects to product properties. For example, latexes with narrow particle size distribution cannot be produced in CSTRs. 

The polymerization of ethylene might be carried out in solution or in a slurry process. But these processes are complicated by the need for a separation step to isolate the resin product from solution. The newer installations favor the gas-phase process that can produce both the low- and high-densily resins. Older plants lack this versatility and are able to produce only either the high-density or the low-density type of polyethylene. 

The polymerization took place in a slurry reactor using hydrocarbon as the suspending medium at near ambient TandP... 

The produced LLDPE had M = 66-234 kg moP and MWD = 2-21. As disclosed in patent (3) the polymerization in a dual reactor may also be carried out in a slurry process, when the polymer is no longer soluble in the solvent... 

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