Porous support, liquid distribution

Supported liquid-phase catalysts (SLPCs) combine the salient features of both homogeneous and heterogeneous catalysis for enhanced catalytic and/or process efficiency (337). SLPC catalysts, in which a liquid-phase (homogeneous) catalyst is dispersed within a porous support, have been used in Wacker-type ethylene oxidation for acetaldehyde and vinyl acetate production (337, 338). In the former case, a traditional homogeneous Wacker catalyst (vide supra) consisting of a chlorinated solution of Pd and Cu chlorides retained on a support with monomodal pore size distribution... 

In general, membrane-supported liquid-liquid extraction is offered as a micro-porous hollow fibre module (Fig. 2.23). The membrane contactor contains thousands of micro-porous hollow fibres knitted into an array that is wound around a distribution tube with a central baffle. The hollow fibres are arranged in a uniform open packing allowing the utilisation of the total membrane surface area. The liquid flows over the shellside (outside of the hollow fibre), is introduced through the distribution tube and moves radially across the array of hollow fibres and then around the baffle and is carried out by the collection tube. 

In most of the studies cited above, the drying rate, which is one of the controlling factors, was adjusted through the drying temperature. Another alternative is to vary the capillary flow of the liquid solution. This can be done by changing the viscosity of the liquid solution or by varying the pore size distribution of the porous support. When they studied CuO on a-alumina catalysts, Kotter and Riekert [39, 40] found that the metal distribution changes from egg-shell to uniform when the viscosity of the liquid solvent was increased. 

The FBA reactor design is probably the most peculiar feature of the process, as compared to other solid-based alkylation technologies. The reactor is of fixed bed type, being filled with pellets of the porous support. The supported liquid acid phase is not homogeneously distributed along the reactor bed instead, the acid liquid is confined to a certain so-called reaction zone, which slowly moves downward in the hydrocarbons flow direction, though at a much slower rate. According to the known chemistry for the liquid acid catalyzed alkylation, the ester... 

This review is a survey of the applications and properties of supported liquid phase catalysts (SLP). By a supported liquid phase catalyst is meant the distribution of a catalytically active liquid on an inert porous support and the behaviour of such systems raises many interesting questions on catalyst chemistry, mass transfer in catalysts and reactor design. It is noteworthy thou that such systems have been employed in the chemical industry for many decades - indeed for over a century in the Deacon process for obtaining chlorine from hydrogen chloride - and of almost equally respectable antiquity are the vanadium based catalyst systems used for sulfuric acid manufacture but the recognition of SLP catalysts as possessing features of their own is much more recent. 

The mercury penetration approach is based on the fact that liquid mercury has a very high surface tension and the observation that mercury does not wet most catalyst surfaces. This situation holds true for oxide catalysts and supported metal catalysts that make up by far the overwhelming majority of the porous commercial materials of interest. Since mercury does not wet such surfaces, the pressure required to force mercury into the pores will depend on the pore radius. This provides a basis for measuring pore size distributions through measurements of the... 

Here, following the works of J.H. De Boer (Delft, The Netherlands, see elsewhere [1,2]), by texture one means the individual geometrical structure of catalysts, supports, and other porous systems (PSs) at the level of pores, particles and their ensembles (i.e., on a supramolecular level scale of 1 nm and larger). In a more complete interpretation, texture includes morphology of porous space and the skeleton of a condensed (solid or sometimes liquid) phase, the shape, size, interconnectivity, and distribution of individual supramolecular elements of the system particles and pores (or voids) between particles, various phases, etc. In turn, texturology also involves general laws of texture formation and methods for its characterization [3],... 

As shown in Figure 5, the diffusion media are the porous backings between the catalyst layers and the gas channels. They provide structural support, distribute the reactant gases, and provide a pathway for electrons, gases, and liquid water to move to or from the catalyst layers. The diffusion media are... 

GPC is a further special form of liquid chromatography. The separation column is packed with porous, polymer gels (e.g. polystyrene gel) as stationary phase. The particle size of the packing material and the size distribution of the pores are well defined and uniform. In GPC molecules are separated according to their effective size in solution, i.e., their hydrodynamic volume, and not according to their affinity for the support material. 

The GDL is located on the back of the CL in order to improve gas distribution and water management in the cell. This layer has to be porous to the reacting gases, must have good electronic conductivity, and has to be hydrophobic so that the liquid produced water does not saturate the electrode structure and reduce the permeability of gases. The GDL needs to be resilient and the material of choice for the PEMFC is usually carbon fiber, paper or cloth, with a typical thickness of 0.2-0.5mm [74,75], This macroporous support layer is coated with a thin layer of carbon black mixed with a dispersed hydrophobic polymer, such as P I LL, in order to make it hydrophobic. This latter compound can, however, reduce the electronic conductivity of the GDL, and limit the three-phase boundary access. 

Open tubular columns are simply capillary tubes in which the inside of the column wall is used as the support for the liquid phase. These wall-coated open tubular columns (WCOT) have the stationary phase distributed in the form of a thin film on the inside surface of the open capillary tube, the walls thus serving as the support. In order to reduce the thickness of the liquid phase film, a porous layer may be formed on the inside wall of the capillary tubing and then coated with the liquid phase to produce a support-coated open tubular column (SCOT). Porous-layer open tubular colunms (PLOT) are similar to SCOT colunms, the difference being that in the former, the stationary phase is deposited on fine crystalline particles or glass powder which is adsorbed onto the walls of the tube. In both cases, the available surface area of the wall is increased, and allows an increased amount of liquid phase to be accommodated in the same length and diameter of tubing. The whisker-walled (WW) colunm consists of whiskers chemically etched on the surface of the wall, which also result in a significant increase in the available surface area. Wall-coated, porous-layer, and support-coated capillary columns are all available as whisker-walled, i.e., WWCOT, WWPLOT, and WWSCOT, respectively. 

The support porous structure and the rate of solvent removal from the pores as well as the nature of solvent and metal compound dissolved can considerably influence both the distribution of the active component through the support grain and the catalyst dispersion [163,170-173]. As a rule, the resulting particles size of the active component will be smaller, the more liquid-phase ruptures caused by evaporation of the solvent from the support pores are attained before the solution saturation. Therefore, supports with an optimal porous structure are needed to prepare impregnated Me/C catalysts with the finest metal particles. As a result, carbon supports appropriate for synthesis of such catalysts are very limited in number. Besides, these catalysts will strongly suffer from the blocking effect (see Section 12.1.2) because some of the metal particles are localized in fine pores. 

Chromatography is a separation process in which the sample mixture is distributed between two phases in the chromatographic bed (column or plane). One phase is stationary whilst the other passes through the chromatographic bed. The stationary phase is either a solid, porous, surface-active material in small-particle form or a thin film of liquid coated on a solid support or column wall. The mobile phase is a gas or liquid. If a gas is used, the process is known as gas chromatography the mobile phase is always liquid in all types of liquid chromatography, including the thin-layer variety. 

Chromatographic Silica. Silica particles used for liquid chromatographic supports are generally porous spheres in the diameter range 2-20 pm. Important properties of these particles bearing on chromatographic performance include mean size, size distribution, presence of aggregates and fines, and particle porosity. All these characteristics should be accessible to measurement by FFF most are described later. 

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