Copolymers, production reactor

Olefin Block Copolymer Production in a Continuous Reactor. 89... 

Sauter mean diameter, 11 795, 13 135, 23 186, 188, 189, 190-191 Sauter mean drop diameter, 10 755, 756 Savannah River production reactors, 17 583 Savard/Lee gas-shielded tuyere, 16 151 Savard-Lee injectors, 14 741 Savory, 23 171 Saybolt color scale, 7 310 Saybolt Universal Seconds (SUS), 15 207 Saytex HP-7010, 11 474 S-B-S block copolymers, 24 706 S-B-S polymers, 24 713-714, 715 SC9... 

A single reactor system is used to make olefin homopolymers and random copolymers. Two reactors are operated in series for the production of block copolymers (impact copolymers). An inert conveying gas (nitrogen) is used to maintain the fluidised bed in the reactor for impact copolymerisation [43,51]. 

For impact copolymer production, a second reactor (4) in series is required. A reliable and effective gas-lock system (3) transfers powder from the first (homopolymer) reactor to the second (copolymer) reactor, and prevents cross contamination of reactants between reactors. This is critically important when producing the highest quality impact copolymer. In most respects, the operation of the second reactor system is similar to that of the first, except that ethylene in addition to propylene is fed to the second reactor. Powder from the reactor is transferred and depressurized in a gas/powder separation system (5) and into a purge column (6) for catalyst deactivation. The deactivated powder is then pelletized (7) with additives into the final products. 

In the process, homopolymer and random copolymer polymerization occurs in the loop-type reactor (or vessel-type reactor) (1). For impact copolymer production, copolymerization is performed in a gas-phase reactor (2) after homopolymerization. The polymer is discharged from a gas-phase reactor and transferred to the separator (3). Unreacted gas accompanying the polymer is removed by the separator and recycled to the reactor system. The polymer powder is then transferred to the dryer system (4) where remaining propylene is removed and recovered. The dry powder is pelletized by the pelletizing system (5) along with required stabilizers. 

Copolymer composition is a third area of contrast. Copolymer composition in a batch reactor tends to change with time. The first polymer formed is rich in the more reactive monomer and the final polymer contains more of the least reactive monomer. This drift in composition can lead to polymer particles with nonuniform composition in the radial dimension. The copolymer product formed in a single CSTR, however, should be relatively uniform in composition if the reactor is operated at steady state. If several CSTRs are connected in series, polymers of several different... 

The reactor can also yield monomodal homo- and random copolymer products by operating the sections under the very same conditions. In this case, the lack of the... 

One might suppose that the lower temperatures required to make copolymers would also lower the MW of the polymer, making control more difficult. Fortunately, the incorporation of comonomer also tends to accelerate termination (raise the MI), which usually compensates for the required lower temperature. Consequently, when Cr/silica is the catalyst there is not usually a substantial difference in MI potential in homopolymer- versus copolymer production. However, variations to this general rule are possible, because some catalysts can be more sensitive to comonomer than others. For example, when 1-hexene is added to the reactor with a Cr/silica-titania catalyst, the polymer MI tends to rise more than with Cr/silica. 

Particles of polypropylene are continuously formed at low pressure in the reactor (1) in the presence of catalyst. Evaporated monomer is partially condensed and recycled. The liquid monomer with fresh propylene is sprayed onto the stirred powder bed to provide evaporative cooling. The powder is passed through a gas-lock system (2) to a second reactor (3). This acts in a similar manner to the first, except that ethylene as well as propylene is fed to the system for impact copolymer production. The horizontal reactor makes the powder residence time distribution approach that of plug-flow. The narrowness of residence time distribution contributes to higher product quality. 

Copolymer product formed in a series of CSTRs will, in the absence of intermediate feeds, be mixtures of molecules with distinct compositions, i.e. that formed in the first reactor, second reactor, etc. The coupling of this phenomena with residence time distributions will produce particles in die final effluent stream with different compositions even if they are the same size. In a three-reactor series, for example, product particles of the same size are likely to have spait different times in the three reactors. 

Even though tubular reactors are not used industrially for the production of impact copolymers, some reactor technologies (such as gas phase horizontal reactors) were developed to narrow the reactor residence time distribution and, consequently, produce impact copolymer with narrower homopolymer/copolymer distributions. 

There are many parallels between polypropylene and polyethylene manufacturing processes. The reactor configurations are similar, but, due to the different requirements of the polymer, it will be seen that there are significant differences between the processes as well. While propylene homopolymer can be produced in reactors of various configurations, for impact copolymer production, gas phase is the reactor of choice because of the stickiness of the polymer and the solubility of the copolymer in the monomer and diluent. 

The dominant process in this market segment is the Spheripol process by Basell. Similar to the dominance achieved by the Phillips process in HOPE, roughly one-third of the world s polypropylene is produced using the Spheripol process. The Spheripol process uses loop reactors. A small loop reactor is used to prepolymerize the catalyst the main polymerization, for homopolymer or random copolymer, takes place in one or two loop reactors. For impact copolymer production, a gas-phase reactor is required after the loop reactor because of the limited solubility of ethylene in liquid propylene. A typical flow diagram of the Spheripol process is shown in Figure 2.40. 

The Unipol process, initially developed for polyethylene production, was later extended to polypropylene manufacture. The process consists of a large fluidized-bed gas-phase reactor for homopolymer and random copolymer production, and a second smaller reactor for impact copolymer production. The second reactor is smaller than the first one because only 20% of the production comes from the second reactor. This reactor typically has a lower pressure rating as copolymerization is usually carried out at lower temperatures and pressures. Condensed mode operation is used in the homopolymer reactor but an inert diluent is not required because propylene is partially fed as a liquid. The copolymerization reactor is operated purely in the gas phase. The Unipol process has a unique and complex product discharge system that allows for very efficient recovery of unreacted monomer, but this does add complexity and capital cost to the process. 

Micromrxers in conjunction with serial microreactors can also be used effectively for LRP reactions, particularly for mixing viscous living polymer melts with non-viscous monomer for block copolymer production. For example, poly(n-butyl acrylate) can be synthesized in a microtube reactor via an N M P reaction, then the viscous homopolymer melt can be efficiently mixed with low-viscosity styrene monomer via a micromixer [90]. This can then be followed by N M P of the styrene on to the poly (w-butyl acrylate) chains in a second microtube reactor, thus creating a block copolymer. This technique gives a narrower molecular weight distribution product than comparable batch reactions. 

Since cyclohexane is a solvent for PS at the operating temperature of 80 C, the conversion is more moderate than the system that only had MAA as second-stage monomer charge. The final product from the 300-ml Parr reactor system was dried out and a dry sample was dissolved in THF. Water was added in as precipitant for the purified block copolymer. The unprecipitated block copolymer was called the raw product. In Fig. 3.2.2, size exclusion chromatography data are shown for the intermediate PS, raw block copolymer product, and purified copolymer product. 

Attempts were made to carry out C-NMR spectroscopy of monomeric components, intermediate, and final copolymer products. Problems include long NMR runs (8-12 h per sample) and the difficulty in completely dissolving the VDC segments of the copolymer samples. Still, it was possible to conclude that the second-stage monomers were incorporated into the intermediate copolymer radicals from the Stage 1 reactor (Fig. 4.3.6). 

The feed preparation and reactor sections of thermoplastic block copolymer production process are similar to the solution SBR process (36,39,40,42-45). Styrene, butadiene, and solvent are purified by distillation, followed by passing the reactants and solvent over alumina columns and molecular sieves (Fig. 8). 

The Borstar PP process is based on the Borstar PE process described in Section 3.2.3.3. When homopol5miers and random copol5miers are produced, the reactor configuration consists of a propylene bulk loop reactor and a fluidised bed gas phase reactor operated in series. During heterophasic copolymer production, the polymer from the first gas phase reactor is transferred into a second smaller gas phase reactor where the mbbery copolymer is made. 

Swing reactor operation, where the operating conditions are changed to make different polymers, have been considered theoretically but do not appear to have been used in practice. Dual reactors in series have been used for impact polypropylene copolymer production (Burdett, 1992). 

The power feed addition strategy is also conducted under monomer starved conditions but aiming at producing a copolymer with varying composition, see Basset and Hoy (1981). In this case a heterogeneous copolymer composition distribution, that is, a copolymer product with a predefined composition distribution, is sought. This is obviously achieved by varying the ratio of the monomer flow rates into the reactor continuously with time. 

The enthalpy of the copolymerization of trioxane is such that bulk polymerization is feasible. For production, molten trioxane, initiator, and comonomer are fed to the reactor a chain-transfer agent is in eluded if desired. Polymerization proceeds in bulk with precipitation of polymer and the reactor must supply enough shearing to continually break up the polymer bed, reduce particle size, and provide good heat transfer. The mixing requirements for the bulk polymerization of trioxane have been reviewed (22). Raw copolymer is obtained as fine emmb or flake containing imbibed formaldehyde and trioxane which are substantially removed in subsequent treatments which may be combined with removal of unstable end groups. 

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