Slurry-phase polymerization

The Phillips-type catalyst can be used in solution polymerization, slurry polymerization, and gas-phase polymerization to produce both high density polyethylene homopolymers and copolymers with olefins such as 1-butene and 1-hexene. The less crystalline copolymers satisfy needs for materials with more suitable properties for certain uses that require greater toughness and flexibiUty, especially at low temperatures. 

EP2 A process for polymerizing olefins in the slurry phase. Developed by Borealis. 

Slurry phase (or suspension) process. The uniquedooldng equipment in Figure 23—5 is a loop reactor. This process also takes place in a solvent (in this case, normal hexane, isobutane, or isopentane) so that the mixture can be pumped continuously in a loop while the polymerization is taking place. Feeds (the solvent, comonomer if any, ethylene and Ziegler-Natta catalyst) are pumped into the loop and circulated. Polymerization rakes place continuously at temperatures below the melting point of the polyethylene allowing solid polymer particles to form enough to form slurry. The reaction takes place at 185—212°F and 75—150 psi. A slurry of HOPE in hexane is drawn off continuously or intermittently. 

Gas-phase fluidized bed polymerization, solution polymerization, slurry polymerization, and polymerization in melt under high ethylene pressure... 

Continuous stirred tank reactors are also widely used for hexane slurry ethylene polymerization by many manufacturers. In the Hoechst process, the reaction is carried out in four CSTRs arranged in series such that the slurry phase and the vapor phase move in concurrent flow. Polymerization occurs at 100 psig and 85 C with 98% conversion of ethylene. The residence time in the reactor is about 2.7 hr. The product slurry is pumped into centrifuges, which separate the bulk of the hydrocarbon diluent liquid from the polymer fluff. 

The different polymerization classes discussed above can be implemented in several ways bulk polymerization, solution polymerization, gas-phase polymerization, slurry polymerization, suspension polymerization and emulsion polymerization. 

LLDPEs from tubular or cascade loop reactor have fewer LCB and broader MWD than autoclave products. Modeling of an industrial slurry-phase olefin catalytic polymerization of two loop reactors in series was carried out by U. Thessaloniki and Total Petrochemicals... 

V. Touloupides et al.. Modeling and simulation of an industrial slurry-phase catal dic olefin polymerization reactor series, Chem. Eng. Sci., 65, 3208-3222 (2010)... 

Ethylene and comonomer are purified, then dried and fed with recycled diluent with a catalyst slurry to a double loop continuous reactor. Polsrmer forms as discrete particles on catalyst grains and is allowed to settle briefly at the bottom of settling legs to increase concentration from about 40% in main loop to 50-60% in the product discharge (77). Reactor temperatures are usually 70-110°C and reactor pressures are between 3 and 5 MPa (450 and 720 psi). Diluent and residual monomers are flashed off for recycle and polymer is conveyed for pelletization. Production of low density pol5uners was not practicable due to solubility of low density/low molecular weight polymer molecules in the diluent, but the use of chromox catalysts that produce broad molecular weight LLDPE and metallocene catalysts that produce mLLDPE have broadened the product portfolio for slurry-phase polymerization. 

In general, we can distinguish homogeneous and heterogeneous polymerization processes. Homogeneous processes take place within the substance in question (with the monomer or the formed polymer acting as reaction medium) or in a solvent. Heterogeneous processes include precipitation, slurry phase, suspension, emulsion, or gas-phase polymerizations. 

Slurry-phase polymerization involves a solid from the beginning of the polymerization process. An important example is the production of high-density polyethylene (HOPE) using immobilized, solid Ziegler-Natta catalysts in a solvent (typically liquid alkanes). Slurry phase polymerization is carried out in stirred tank reactors or loop reactors where the three-phase system is pumped with high flow velodties to reduce the probability of reactor fouling (for details see Section 6.20). 

Figure 3. Ethylene polymerization activity in gas-phase and slurry reactors. [SMHNT catalyst gas-phase, 90 C, Pcair =0.4 MPa slurry phase, 70 C, Po,f =0.1 MPa].

Slurry-phase processes may involve either an inert diluent such as iso-butane or heptane, or condensed monomer such as propylene. In either case the catalyst particles are suspended and well mixed in the liquid medium. Monomer concentrations are high and the liquid provides good removal of the heat produced by the polymerization of the polymer particles. The two main reactors for slurry-phase olefin polymerization are the loop reactor and continuous-stirred tank. Slurry-phase processes are very attractive for high crystalline homopolymer products such as polypropylene and polyethylene. 

Cp Ti(OCH3)j catalyst can also be supported onto silica particles and activated by MAO for slurry-phase polymerization of styrene [6,7], Figure 8.3 illustrates the polymerization rate profiles with time and the initial polymerization rates at four different monomer concentrations at 70... 

The change in the slurry phase volume in SPS polymerization can be calculated using a simple mass balance model. We first consider a mass balance for the entire slurry phase ... 

Choi, K. Y., Chung, J. S., Woo, B. G., Hong, M. H. Kinetics of slurry phase polymerization of styrene with pentamethyl cyclopentadienyl titanium trimethoxide and methyl aluminoxane. I. Reaction rate analysis. J. Appl. Polym. Sci., 88, 2132-2137 (2003). 

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