Phase polymerization, advantage

An advantage of this approach to model large-scale fluidized bed reactors is that the behavior of bubbles in fluidized beds can be readily incorporated in the force balance of the bubbles. In this respect, one can think of the rise velocity, and the tendency of rising bubbles to be drawn towards the center of the bed, from the mutual interaction of bubbles and from wall effects (Kobayashi et al., 2000). In Fig. 34, two preliminary calculations are shown for an industrial-scale gas-phase polymerization reactor, using the discrete bubble model. The geometry of the fluidized bed was 1.0 x 3.0 x 1.0 m (w x h x d). The emulsion phase has a density of 400kg/m3, and the apparent viscosity was set to 1.0 Pa s. The density of the bubble phase was 25 g/m3. The bubbles were injected via 49 nozzles positioned equally distributed in a square in the middle of the column. 

S Gas-Phase Polymerization. Not all polymerization reactions are carried out in the liquid phase. Polyethylene, for example, can be polymerized not only in solution as discussed in Section 3.3.2.2, but also through gas-phase polymerization (see Figure 3.28). Significant economic advantage is gained by eliminating costly solvent and catalyst recovery equipment. A fluidized bed reactor is used, into which purified... 

One interesting option towards the reduction of energy consumption comprises the reduction of the amount of solvent to be recycled in the process. In this context the increase of total solids from 20 wt. % commonly used the solution process up to 25-40 wt. % by the application of a slurry technology is particularly advantageous (Sect. 3.1) [517,518]. According to the authors opinion slurry technology avoids the risks associated with the implementation of more advanced technologies such as bulk (Sect. 3.1) or gas-phase polymerization (Sect. 3.2). 

To improve effectiveness of graft-polymerization and to decrease complexity of the lithography method, it is advantageous to use liquid or solid-phase polymerization strategies. One of the solving is to deposit a silicon-containing monomer onto a selectively exposed photoresist and then to heat it. The monomers will polymerize and an excess of them can be removed from the photoresist. The mask obtained can be used for the RIE in... 

The first gas-phase polymerization was first commercialized in Wesseling, Germany by ROW Co. in a joint venture with BASF and Shell companies in 1969. This facility employed the Novolen process for propylene polymerization in the gas phase. UCC and Sumitomo companies later developed fluidized-bed processes for the gas-phase polymerization of propylene. The advantages of this process are its high-effidency catalysis, elimination of residual removal, and elimination of evaporation or centrifugal separation. Its polymer product can be used in almost all applications [12,13,71,72]. 

The sol-gel process performed in low concentrated polymer-solvent solutions is another attractive route to develop hybrid membranes because it allows an in situ dispersion of metal-based nanoparticles within the polymeric matrix, achieving a suitable interfacial morphology between the continuous and the dispersed phase. Silica particles and polyimide have been frequently used to produce these hybrid membranes [107,108]. In general, hydrolysis and condensation reactions are involved in the sol-gel process, when alkoxides are involved in the formation of the dispersed phase. The advantage of using this method is the formation of an inorganic network largely interconnected with the polymeric materials mainly with noncovalent interactions [109]. In Fig. 7.10 a... 

Gas phase polymerization. Compared to the slurry process, polymerization in the gas phase has the advantage that no diluent is used which simplifies the process [74-76]. A fluidized bed that can be stirred is used with supported catalysts. The polymerization is carried out at 2 to 2.5 MPa and 85 to 100 °C. The ethene monomer eireulates, thus removing the heat of polymerization and fluidizing the bed. To keep the temperature at values below 100 °C, gas conversion is maintained at 2 to 3 per pass. The polymer is withdrawn periodically from the reaetor. 

Other initiators that have been used in polymerizing vinyl chloride are diisopropyl peroxydicarbonate, di-5ec-butyl peroxydicarbonate, terUhwiyX peroxypivalate, as well as lauroyl peroxide and benzoyl peroxide. All of these initiators, after allowances are made for variations in their half-lives at a given temperature, behave similarly as far as the two-phase polymerization of vinyl chloride is concerned [79]. There is considerable advantage, from the economic standpoint, in using an initiator such as diisopropyl peroxydicarbonate, which is active at a relatively low temperature. 

Polymerization in droplets has two applications. First, it can be similar to singlephase solution polymerization, yielding a polymer solution compartmentalized in droplets. Second, it can lead to the preparation of polymer particles. For each application, MF polymerization in droplets offers several important advantages. Solution polymerization conducted in droplets (versus a single-phase polymerization) allows the synthesis of polymers that are not soluble in the polymerization medium, which would otherwise lead to polymer precipitation in the microchannels. While in the single-phase MF polymerization the soluble polymer may adsorb to reactor walls and ultimately cause dogging of the reactor, polymerization performed in droplets does not encounter these problems. Similar to other MF reactions carried out in droplets, polymerization in droplets or plugs does not experience the problem of dispersion. Furthermore, an inherent increase in... 

Nanocomposites of conducting polymers exhibit improved physicochemical and biological properties as compared to their individual counterparts. The integration of secondary component within conducting polymer leads to dramatic increase in different properties that are useful from an application point of view. Size, shape and controlled distribution of the dispersed phase are the critical factors to control the desired properties of a nanocomposite. Different approaches such as in situ synthesis, one-pot synthesis, electrochemical polymerization and vapor-phase polymerization have been employed to synthesize the nanocomposites of conducting polymers with metal or metal oxide nanoparticles, carbon-based materials, ternary nanocomposites, etc. All of these methods have certain advantages and drawbacks. Functional nanocomposites synthesized by these methods display many... 

Emulsion polymerization also has the advantages of good heat transfer and low viscosity, which follow from the presence of the aqueous phase. The resulting aqueous dispersion of polymer is called a latex. The polymer can be subsequently separated from the aqueous portion of the latex or the latter can be used directly in eventual appUcations. For example, in coatings applications-such as paints, paper coatings, floor pohshes-soft polymer particles coalesce into a continuous film with the evaporation of water after the latex has been applied to the substrate. 

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