Pellets, properties shape

Commercial zeolites are usually mixed with a binder such as y-alumina and shaped into pellets. The shaping procedure causes changes in binder porosity to give zeolites with different physical properties. 

The building and construction industry commonly uses polyolefin microcomposite and nanocomposite as reinforcement materials to enhance the physical properties (tensile strength, modulus, and damping) of POCs. There are many current and future applications of POCs in constmction including walling, roofing, outdoor furniture, and timber. These composites can be molded into sheets, frames, pellets, structural shapes, and others [77]. 

When the step change in trace species is made to the left hand side of the cell the shape of the resiMnse on the opposite, i.e. right hand side, is more dependent on the pellet properties than that on the left hand side the latter tends to be dominated by the mixing characteristics within volume V. The transfer function relating Cp(s) to C (s) can be shown to be of the form given in equation 11. 

DRI can be produced in pellet, lump, or briquette form. When produced in pellets or lumps, DRI retains the shape and form of the iron oxide material fed to the DR process. The removal of oxygen from the iron oxide during direct reduction leaves voids, giving the DRI a spongy appearance when viewed through a microscope. Thus, DRI in these forms tends to have lower apparent density, greater porosity, and more specific surface area than iron ore. In the hot briquetted form it is known as hot briquetted iron (HBI). Typical physical properties of DRI forms are shown in Table 1. 

The activity, which may be defined as the net rate of S02 oxidation in moles/s/m3 catalyst according to reaction (1), depends on the intrinsic activity of the catalyst material, the diffusion properties of the catalyst material, the size of the catalyst pellets, and the shape of the pellets. 

The catalyst activity depends not only on the chemical composition but also on the diffusion properties of the catalyst material and on the size and shape of the catalyst pellets because transport limitations through the gas boundary layer around the pellets and through the porous material reduce the overall reaction rate. The influence of gas film restrictions, which depends on the pellet size and gas velocity, is usually low in sulphuric acid converters. The effective diffusivity in the catalyst depends on the porosity, the pore size distribution, and the tortuosity of the pore system. It may be improved in the design of the carrier by e.g. increasing the porosity or the pore size, but usually such improvements will also lead to a reduction of mechanical strength. The effect of transport restrictions is normally expressed as an effectiveness factor q defined as the ratio between observed reaction rate for a catalyst pellet and the intrinsic reaction rate, i.e. the hypothetical reaction rate if bulk or surface conditions (temperature, pressure, concentrations) prevailed throughout the pellet [11], For particles with the same intrinsic reaction rate and the same pore system, the surface effectiveness factor only depends on an equivalent particle diameter given by... 

For application in flow reactors the nanocarbons need to be immobilized to ensure ideal flow conditions and to prevent material discharge. Similar to activated carbon, the material can be pelletized or extruded into millimeter-sized mechanically stable and abrasion-resistant particles. Such a material based on CNTs or CNFs is already commercially available [17]. Adversely, besides a substantial loss of macroporosity, the use of an (organic) binder is often required. This material inevitably leaves an amorphous carbon overlayer on the outer nanocarbon surface after calcination, which can block the intended nanocarbon surface properties from being fully exploited. Here, the more elegant strategy is the growth of nanocarbon structures on a mechanically stable porous support such as carbon felt [15] or directly within the channels of a microreactor [14,18] (Fig. 15.3(a),(b)), which could find application in the continuous production of fine chemicals. Pre-shaped bodies and surfaces can be... 

Polymer processing can be defined as the process whereby raw materials are converted into products of desired shape and properties. Thermoplastic resins are generally supplied as pellets, marbles, or chips of varying sizes and they may contain some or all of the desired additives. When heated above their Tg, thermoplastic materials soften and flow as viscous liquids that can be shaped using a variety of techniques and then cooled to lock in the micro- and gross structure. 

The physical properties of pellets have been widely used to determine an acceptable yield of pellets. These include shape indices, size and size distribution, densities, pore volume and distribution, flow properties, and friability. Of course, drug release from the pellets is a critical parameter to be monitored in order to ensure potency and uniformity of drug distribution. 

Thiele(I4>, who predicted how in-pore diffusion would influence chemical reaction rates, employed a geometric model with isotropic properties. Both the effective diffusivity and the effective thermal conductivity are independent of position for such a model. Although idealised geometric shapes are used to depict the situation within a particle such models, as we shall see later, are quite good approximations to practical catalyst pellets. 

For the purpose of this text, only conventional projectiles are considered in detail. Conventional projectiles for firearms are bullets, pellets, and slugs, each of which may differ from others of the same kind in size, shape, weight, composition, and physical properties. 

So far we have examined the essence of polymers, both natural and synthetic. We have looked at a variety of ways that they are synthesized and studied some of their properties. In this chapter we will find out how we can convert a polymer sample that might be in powder or pellet form into some useful object. This is largely the realm of the engineers, who design the processing equipment and determine the conditions that produce polymeric products with optimum properties. These objects take a wide variety of shapes, including films, fibers, solid parts, hollow containers such as bottles, and foamed objects. 

The nature of the polymerization reactor also depends upon the desired form of the product (pellet, powder, bead, etc.). For example, extruder reactors (Stuber and Tirrell, 1985) are best suited to producing pellets, sheets, and coatings. The beads that may be directly useful in processing are best produced by the suspension polymerization process. The round beads, however, may not have suitable bulk-flow properties and are dangerous if spilled. Alternate shapes and the appropriate methods of production are, therefore, often employed. 

Catalysts may be porous pellets, usually cylindrical or spherical in shape, ranging from 0.16 to 1.27 cm (Vm to Vi in) in diameter. Small sizes are recommended, but the pressure drop through the reactor increases. Among other shapes are honeycombs, ribbons, and wire mesh. Since catalysis is a surface phenomenon, a physical property of these particles is that the internal pore surface is nearly infinitely greater than the outside surface. 

Catalysts are formed by a variety of methods depending on the rheology of the materials. The products of different processes have been compared in general terms in Table 3.2. The choice of the method depends on the size, shape and density of the catalyst particle required, on the strength required and on the properties of the starting material. The three main processes used in catalyst manufacture to make conveniently sized particles from powders are pelletizing, extrusion and granulation. 

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