Slurry phase/suspension process

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 (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. 

It is tempting to suggest that polymer processes will gradually evolve toward bulk. Recently, the suspension process for impact polystyrene has been supplanted by the bulk process, and the emulsion process for ABS may similarly be replaced. However, the modern gas-phase process for polyethylene appears to represent an opposite trend. It seems that polymerization technology tends to eliminate solvents and suspending fluids other than the monomers themselves. When the monomer is a solvent for the polymer, bulk processes are preferred. When the monomer is not a solvent, suspension and slurry processes like those for polyethylene and polypropylene are employed. 

The agitated slurry reactors are most commonly used on industrial scales in liquid phase esterification processes. In agitated reactors, the catalyst particles are used in a smaller form and kept in suspension by means of mechanical agitation. Due to smaller catalyst particle size, intraparticle diffiisional effects are negligible in these reactors. Also... 

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations. 

Commerical polymerizations of ethylene, propene, and other a-olefins are carried out as slurry (suspension) and gas-phase processes [Beach and Kissin, 1986 Diedrich, 1975 Lieberman and Barbe, 1988 Magovern, 1979 Vandenberg and Repka, 1977 Weissermel et al., 1975]. Solution polymerization has been used in the past for ethylene polymerization at 140-150°C, pressures of up to 8 MPa (1 MPa = 145 psi = 9.869 atm), using a solvent such as cyclohexane. The solution process with its higher temperatures was employed for polymerization with the relatively low efficiency early Phillips initiators. (Polyethylene, but not the initiator, is soluble in the reaction medium under the process conditions.) The development of a variety of high-efficiency initiators has allowed their use in lower-temperature suspension and gas-phase processes, which are more advantageous from many... 

This term is restricted here to equipment in which finely divided solids in suspension interact with gases. Solids fluidized by liquids are called slurries. Three phase fluidized mixtures occur in some coal liquefaction and petroleum treating processes. In dense phase gas-solid fluidization, a fairly definite bed level is maintained in dilute phase systems the solid is entrained continuously through the reaction zone and is separated out in a subsequent zone. 

The carbamazepine-nicotinamide cocrystal system has been used to illustrate a mechanism for the formation of cocrystals, for which nucle-ation and growth of solid products are determined by the combination of the reactant components to reduce the solubility of the intermolecular complex that eventually becomes crystallized [42], The principles were studied through the use of in situ monitoring of the cocrystallization process in solutions, suspensions, slurries, and wet solid phases of the... 

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. 

The heat of polymerization of ethylene is high (93.6 kJ/mol). Heat removal is thus a key issue in commercial polymerization processes. Polyolefins are produced primarily by suspension (slurry), gas-phase, or solution processes (20). Solution processes have been developed by various companies using hydrocarbons, such as heptane or cyclohexane, or hydrocarbon mixtures as solvents. The reaction temperature is in the range of 200-300°C. An advantage of these processes is that they readily accommodate a wide range of comonomer types and product densities. Like the high-pressure process, which is also a solution process, they are unable to accommodate highly viscous products. 

Synthesis. The early PP plants used a slurry process adopted from polyethylene technology. An inert liquid hydrocarbon diluent, such as hexane, was stirred in an autoclave at temperatures and pressures sufficient to keep 10-20 percent of the propylene monomer concentrated in the liquid phase. The traditional catalyst system was the crystalline, violet form ofTiCl3 and A1C1(C2H5)2. Isotactic polymer particles that were formed remained in suspension and were removed as a 20-40 percent solid slurry while the atactic portion remained as a solution in the liquid hydrocarbon. The catalyst was deactivated and solubilized by adding HC1 and alcohol. The iPP was removed by centrifuging, filtration, or aqueous extraction, and the atactic portion was recovered by evaporation of the solvent. The first plants were inefficient because of low catalyst productivity and low crystalline yields. With some modifications to the catalyst system, basically the same process is in use today. 

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