Heterogeneous catalyst particles

As with organic solvents, proteins are not soluble in most of the ionic liquids when they are used as pure solvent. As a result, the enzyme is either applied in immobilized form, coupled to a support, or as a suspension in its native form. For production processes, the majority of enzymes are used as immobilized catalysts in order to facilitate handling and to improve their operational stability [24—26]. As support, either inorganic materials such as porous glass or different organic polymers are used [27]. These heterogeneous catalyst particles are subject to internal and external... 

However, these techniques may not detect important phenomena taking place on the surface of or within the interior of individual Inm-to Ipm-diameter inorganic particles that are s3rnthesized specifically for their catalytic activity. AEM is an extremely useful technique for analysis of the individual heterogeneous catalyst particle and its relationship to various supporting materials. Structural and chemical analyses can be obtained from specimen regions nearly 1000 times smaller than those studied by conventional bulk analysis techniques. This high lateral spatial... 

In addition to the general improvement of transfer in micro reactors, there is evidence that the voltage of electroosmotic flow (for EOF see [14]) in combination with the large internal surface area in glass chips can induce hydroxide ion formation [6]. Concerning catalyst loss, there is no obvious direct correlation rather, micro reactors can act as mini fixed beds fixing heterogeneous catalyst particles. 

Analytical Electron Microscopy of Heterogeneous Catalyst Particles... 

The heterogeneous catalyst particles in the reactor are surrounded by a boundary layer of gas or liquid, which can be considered as a static him around the particle. A reactant molecule has to diffuse through this boundary layer via film diffusion (1). As most catalysts have pores, the reactant molecule also has to diffuse through the pores in order to approach the active site, the pore diffusion process (2). Inside the pores, the reactant molecules adsorb at or near the active center and react (3, 4). The resulting product molecules desorb (5) and return back into the fluid phase via pore diffusion (6) and film diffusion (7). Further details on this can be found in general textbooks [1-3]. 

The process of formation of the crystalline state is controlled by the kinetics of nucleation and this may arise in a number of ways. Primary nucleation in a quiescent state must be associated with foreign bodies such as deliberately added nucleating agents, such as fine talc particles, or residual impurities such as heterogeneous catalyst particles followed by spherulite growth. The plot of extent of crystallinity, (p, as a function of time is sigmoidal in nature and follows an Avrami equation of the form... 

Two types of mass- transfer can be distinguished for catalysis with heterogeneous catalyst particles. External mass transfer refers to molecular transport between the bulk reaction mixture and the surface of the enzyme particle through a boundary layer. Internal mass transfer is the molecular transport inside the solid enzyme phase. Internal mass transfer occurs within the pores of the catalyst particle to and from the particle surface. Figure 4.9-4 illustrates the definitions of external and internal mass transfer. 

Supported Single-Site Catalysts Catalysts supporting is considered a prerequisite for the application of most coordination catalytic systems. The most important polymerization methods (slurry and gas phase) require the use of supported or heterogenized catalysts. Particle morphology and bulk density are the main physical features of a supported catalytic system, determining its application in commercial processes [49]. 

The novel and perspective field of tubular turbulent apparatus application is the carrying out of fast chemical processes with formation of solid phase. This provides wide possibilities for modification of metal-complex Ziegler-Natta catalytic systems at the expense of hydrodynamic influence on disperse structure of micro-heterogeneous catalysts particles, receipt of high-effective anti-agglomerates for synthetic rubbers, etc.. 

The polymerization of olefins with coordination catalysts is performed in a large variety of polymerization processes and reactor configurations that can be classified broadly into solution, gas-phase, or slurry processes. In solution processes, both the catalyst and the polymer are soluble in the reaction medium. These processes are used to produce most of the commercial EPDM rubbers and some polyethylene resins. Solution processes are performed in autoclave, tubular, and loop reactors. In slurry and gas-phase processes, the polymer is formed around heterogeneous catalyst particles in the way described by the multigrain model. Slurry processes can be subdivided into slurry-diluent and slurry-bulk. In slurry-diluent processes, an inert diluent is used to suspend the polymer particles while gaseous (ethylene and propylene) and liquid (higher a-olefins) monomers are fed into the reactor. On the other hand, only liquid monomer is used in the slurry-bulk pro-... 

A closely analogous system is the vapor-phase fluidized beds used for polypropylene (PP) manufacturing, but in that case, the monomer can be kept in the vapor phase and does not need to be added as a liquid. This also allows one to use the propylene monomer vapor as a means to remove the heat of polymerization. PP also requires the addition of seed heterogeneous catalyst particles. 

In most cases, the catalyst in a reactor is in the form of particles. Figure 9-2 shows some different kinds of heterogeneous catalyst particles. 

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