Liquid Slurry Polymerization

Three types of polymerization processes are used today for low pressure ethylene polymerization these are (a) liquid slurry polymerization, (b) solution polymerization, and (c) gas phase polymerization. A brief description of each follows. 

Liquid Slurry Polymerization with Heterogenized Cp Ti(OCH3)3 Catalyst... 

The kinetic models for the gas phase polymerization of propylene in semibatch and continuous backmix reactors are based on the respective proven models for hexane slurry polymerization ( ). They are also very similar to the models for bulk polymerization. The primary difference between them lies in the substitution of the appropriate gas phase correlations and parameters for those pertaining to the liquid phase. 

Compare and contrast the slurry, gas phase, solution and liquid propylene polymerization methods. 

This raises the question of whether diffusion plays a role in the kinetics of slurry polymerization. Certainly there is no limitation across the gas-liquid interface doubling the catalyst also doubles the polymer yield, but increasing the stirring rate does nothing. Diffusion through the polymer particle is a more troubling issue. There are times when the polymerization clearly becomes diffusion limited, or fouled, due to solvation of the polymer, but this is rarely a problem if the temperature is kept down and the molecular weight up. 

Liquid monomer Polymer swollen with monomer Precipitation or slurry polymerization Polypropylene in a pool of liquid propylene... 

The design of conventional biological reactors is very similar to those of gas-liquid, slurry, and polymerization reactors outlined in other chapters. As a matter of fact, biological reactors are the most versatile of all reactors, since such a reactor can carry two or three phases, the liquid can be Newtonian or non-Newtonian, the solids can be heavy or light, and the reaction mixture can be simple or complex. A biological reactor, however, carries certain distinct features ... 

The Unipol process employs a fluidized bed reactor (see Section 3.1.2) for the preparation of polyethylene and polypropylene. A gas-liquid fluid solid reactor, where both liquid and gas fluidize the solids, is used for Ziegler-Natta catalyzed ethylene polymerization. Hoechst, Mitsui, Montedison, Solvay et Cie, and a number of other producers use a Ziegler-type catalyst for the manufacture of LLDPE by slurry polymerization in hexane solvent (Fig. 6.11). The system consists of a series of continuous stirred tank reactors to achieve the desired residence time. 1-Butene is used a comonomer, and hydrogen is used for controlling molecular weight. The polymer beads are separated from the liquid by centrifugation followed by steam stripping. 

Equipment for heterogeneous reactions is particularly flexible, since each phase can be processed more or less independently. In the fluidized-bed reactor (Fig. 1-4) the reactants flow continuously through and out of the reactor, but the solid-catalyst phase is withdrawn, regenerated, and returned. In the lime kiln (an example of a gas-solid noncatalytic reactor) the two phases pass continuously and countercurrently through the reactor. In heterogeneous liquid-solid polymerization systems the slurry of catalyst and reaction mixture flow together through the reactors. Walas, Brotz, and particularly van Krevelen have summarized the various types of... 

Precipitation polymerization, also known as slurry polymerization, involves solution systems in which the monomer is soluble but the polymer is not. It is probably the most important process for the coordination polymerization of olefins. The process involves, essentially, a catalyst preparation step and polymerization at pressures usually less than 50 atm and low temperatures (less than 100°C). The resultant polymer, which is precipitated as fine floes, forms a slurry consisting of about 20% polymer strspended in the liquid hydrocarbon employed as solvent. The polymer is recovered by stripping off the solvent, washing off the catalyst, and if necessary, extracting any undesirable polymer components. Finally, the polymer is compounded with additives and stabilizers and then granulated. 

Commercial production of crystalline polypropylene (PP) was first put on stream in late 1959 by Hercules in the United States, by Montecatini in Italy, and by Farbenwerke Hoechst AG in Germany. The workhorse process for commercial production of PP has been slurry polymerizations in liquid hydrocarbon diluent, for example, hexane or heptane. These are carried out either in stirred batch or... 

The earliest commercial methods used slurry polymerizations with liquid hydrocarbon diluents, like hexane or heptane. These diluents carried the propylene and the catalyst. Small amounts of hydrogen were fed into the reaction mixtures to control molecular weights. The catalyst system consisted of a deep purple or violet-colored TiCls reacted with diethyl aluminum chloride. The TiCb was often prepared by reduction of TiCU with an aluminum powder. These reactions were carried out in stirred autoclaves at temperatures below 90 °C and at pressures sufficient to maintain a liquid phase. The concentration of propylene in the reaction mixtures ranged between 10-20%. The products formed in discrete particles and were removed at 20-40% concentrations of solids. Unreacted monomer was withdrawn from the product mixtures and reused. The catalysts were deactivated and dissolved out of the products with alcohol containing some HCl, or removed by steam extraction. This was followed by extraction of the amorphous fractions with hot liquid hydrocarbons. 

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]. 

The term fluid covers a wide range of materials—from gases and simple liquids to polymeric materials and semi-solid slurries. Fluids may be classified as either compressible or incompressible. The density of a compressible fluid depends on the pressure. Although this is true for all real fluids, the compressibility of liquids is very small under most conditions and they may be considered incompressible. The flow of gases must usually be treated as compressible unless pressure changes are small. 

Butyl rubber (HR) is an isobutylene-based rubber which includes copolymers of isobutylene and isoprene, halogenated butyl rubbers, and isobutylene/p-methylstyrene/bromo-p-methylstyrene terpoly-mers. HR can be slurry polymerized from isobutylene copolymerized with small amounts of isoprene in methyl chloride diluent at -130 to - 148°F (-90 to - 100°C). Halogenated butyl is produced by dissolving butyl rubber in a hydrocarbon solvent and introducing elemental halogen in gas or liquid state.Cross-linked terpolymers are formed with isobutylene + isoprene + divinylbenzene. 

Propylene polymerization processes, including slurry, gas-phase and liquid pool polymerization, have been reviewed by Lieberman and Barbe [70]. Progress in catalyst development is reflected by significantly simpU-fied polymerization processes and markedly reduced environmental pollution. As is apparent from Figure 18, which displays the general scheme of an olefin polymerization process, in gas-phase and Uquid pool processes hydrocarbon diluents and deactivations as well as polymer purifications steps are eliminated. Reactor granule technology forms... 

The heterogeneous nature of the bulk polymerization of VDC is apparent from the rapid development of turbidity in the reaction medium following initiation. The turbidity results from the presence of minute PVDC crystals. As the reaction progresses, the crystalline phase grows and the liquid phase diminishes. Eventually, a point is reached where the liquid slurry solidifies into a solid mass. A typical conversion-time curve is shown in Figure 1 for a mass polsrmerization... 

Non-Newtonian Flow Behavior. All liquids showing deviations from the behavior above are non-Newtonian. Many liquids encountered in industrial practice, such as paints, emulsions, most mineral slurries, latex, paper pulp, plastic melts, liquid foods, polymeric liquids, and concentrated wastewater sludge, are non-Newtonian. 

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