Polymerization in slurry

It has been speculated that, for the case of metallocene catalysts, some of the limitations encountered with slurry reactors (both CSTR and loop) when producing copolymers of lower crystallinity can be minimized or completely eliminated. As discussed above, heterogeneous Ziegler-Natta catalysts produce LLDPE with very broad chemical composition distributions containing low-crystallinity tails. Such low-crystallinity tails are absent in most polyolefins made with metallocene catalysts, thus minimizing the risk of copolymer dissolution during polymerization in slurry reactors. 

We have considered to explain the fast initiation of active sites in low yield gas phase polymerization by a very high rate of diffusion of poisons out of the catalyst. Under slurry process conditions, diffusion coefficient is at least three orders of magnitude lower than for low yield gas phase polymerization. The slow initial polymerization in slurry experiments could perhaps be explained by the slower removal of poisons. 

Yuan, H. G., T. W. Taylor, K. Y. Choi, and W. H. Ray, Polymerization of Olefins Through Heterogeneous Catalysts I. Low Pressure Polymerization in Slurry with Ziegler-Natta Catalysis, J. Appl. Polym. Set, 27, 1691, 1982. 

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 Solution or Slurry. Many hydrocarbon solvents dissolve PE at elevated temperatures of 120—150°C. Polymerization reactions in solution requite, as theit last step, the stripping of solvent. A variety of catalysts can be used in these processes. 

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. 

Some slurry processes use continuous stirred tank reactors and relatively heavy solvents (57) these ate employed by such companies as Hoechst, Montedison, Mitsubishi, Dow, and Nissan. In the Hoechst process (Eig. 4), hexane is used as the diluent. Reactors usually operate at 80—90°C and a total pressure of 1—3 MPa (10—30 psi). The solvent, ethylene, catalyst components, and hydrogen are all continuously fed into the reactor. The residence time of catalyst particles in the reactor is two to three hours. The polymer slurry may be transferred into a smaller reactor for post-polymerization. In most cases, molecular weight of polymer is controlled by the addition of hydrogen to both reactors. After the slurry exits the second reactor, the total charge is separated by a centrifuge into a Hquid stream and soHd polymer. The solvent is then steam-stripped from wet polymer, purified, and returned to the main reactor the wet polymer is dried and pelletized. Variations of this process are widely used throughout the world. 

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. 

Polymerization Processes. Isotactic PB and PMP are produced commercially in slurry processes in Hquid monomers or monomer mixtures (optionally diluted with light inert hydrocarbons) at 50—70°C. The first commercial process for PB production used a highly isospecific... 

If the dissolving of a portion of the polymer takes place, diffusional restriction may occur as a result. Such a case was observed in (98) where a decrease of the polymerization rate (slurry process in cyclohexane) with temperature rise from 75° to 90°C was found despite the increase in the number of propagation centers. At a further increase of the polymerization temperature (>115°C) polymerization becomes a solution process that may also proceed with no diffusional restrictions (94). 

Gas phase olefin polymerizations are becoming important as manufacturing processes for high density polyethylene (HOPE) and polypropylene (PP). An understanding of the kinetics of these gas-powder polymerization reactions using a highly active TiCi s catalyst is vital to the careful operation of these processes. Well-proven models for both the hexane slurry process and the bulk process have been published. This article describes an extension of these models to gas phase polymerization in semibatch and continuous backmix reactors. 

The semibatch model GASPP is consistent with most of the data published by Wisseroth on gas phase propylene polymerization. The data are too scattered to make quantitative statements about the model discrepancies. There are essentially three catalysts used in his tests. These BASF catalysts are characterized by the parameters listed in Table I. The high solubles for BASF are expected at 80 C and without modifiers in the recipe. The fact that the BASF catalyst parameters are so similar to those evaluated earlier in slurry systems lends credence to the kinetic model. 

DSP crystal, a detailed picture of the lattice motion and related displacements was constructed and related to the topochemical postulate and the mechanism of phonon assistance. Holm and Zienty (1972) have measured the quantum yield for the overall polymerization process of a,a -bis(4-acetoxy-3-methoxybenzylidene)-p-benzenediacetonitrile (AMBBA) crystals in slurries and reported it to be 0.7 on the basis of the disappearance of two double bonds ( = 1.4 if assigned on the basis of the number of double bonds consumed). 

FIGURE 5.5 Synthesis schemes for chromatographic stationary phases (a) monomeric synthesis where X represents reactive (e.g., chloro or alkoxy) or nonreactive (methyl) substituents, (b) solution polymerization, in which water is added to the slurry and (c) surface polymerization, in which water is added to the silica surface. 

CA 68, 88704v(1968) [Expl slurries of conventional oxidizers fuels and water which can be gelled by polymerization, in situ, are described. For example, NaN03 14.7,... 

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. 

The discussion above explains why basic information on sorption and diffusion under the reaction conditions, especially at elevated pressures, is required for kinetic and mass- and heat- transfer modelling of catalytic polymerization reactors. If such information is sufficiently available, one should be able, for example, to compare the kinetics of gas-phase and slurry-processes directly by taking into account both gas solubilities in swollen polymers and the hydrocarbons used in slurry processes. 

A variety of technological processes arc used for polyethylene manufacture. They include polymerization in supercritical ethylene at a high ethylene pressure and temperature above the PE melting point (110-140°C), polymerization in solution at 120-150°C or in slurry, and polymerization in the gas phase... 

The majority of literature on Nd-mediated diene polymerization is concerned with polymerization in solution. This technology was developed at an early stage of Nd polymerization technology and many basic principles elaborated for solution processes have been adopted in the development of Nd-BR production. Therefore, the Polymerization in Solution and various aspects associated with it are reviewed first. Other polymerization technologies such as polymerization in bulk (or mass), suspension (or slurry) and gas phase are addressed in separate Sects. 3.1 and 3.2 at a later stage. 

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. 

The manufacture of linear low-density polyethylene (LLDPE) by slurry polymerization in hexane (see Sections 6.2 and 6.8) is carried out by Hoechst, Mitsui, and a number of other chemical manufacturers in a series of continuous stirred tank reactors. The manufacture of butyraldehyde from CO, H2, and propylene using a soluble rhodium phosphine complex (see Sections 5.2 and 5.5) is also carried out in a continuous stirred tank reactor. 

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. 

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