Inert catalyst carriers

A. Characteristics of Ionic Liquid Catalyst Carriers A.l. Inert Catalyst Carriers... 

The Supported Sr-promoted La203 catalysts with different Sr/La ( 0.0, 0.03, 0.3, 2.0, 10.0) ratios and with Sr-La203 loading of 16 1.5 wt% were prepared by impregnating 22-30 mesh size particles of commercial low surface area porous, inert catalyst carrier ( SA-5205 obtained from Norton Co., USA) by the active catalyst mass. The impregnation of mixed nitrates of Sr and La from their aqueous solution on the support particles was done by the incipient wetness technique. The resulting supported catalyst mass was dried at 90°C for 16 h and then calcined in static air at 950°C for 4 h. 

The vanadium generally associated with ashphaltenes, nickel and iron are constituents of the crude oil from which the fiiel oil is derived, whereas the sodium occurs in a brine phase. The silicon and aluminium are present as a result of the refining process, generally derived from inert catalyst carriers. Sulphur is usually present in the form of organic sulphur compounds, the amount depending on the origin of the crude oil from which the fuel oil is obtained. The presence of these "impurities" is the source of fouling from oil combustion. 

The catalyst combines two essential ingredients found in eadier catalysts, vanadium oxide and titanium dioxide, which are coated on an inert, nonporous carrier in a layer 0.02- to 2.0-mm thick (13,16). Other elements such as phosphoms are also used. Ring-shaped supports are used instead of spherical supports to give longer catalyst life, less pressure drop though the reactor, and higher yields (17,18). Half rings are even better and allow more catalyst to be loaded (18). 

The cupric chloride (CuCI2) catalyst (on an inert fixed carrier) may react as... 

When the catalyst is immobilized within the pores of an inert membrane (Figure 25.13b), the catalytic and separation functions are engineered in a very compact fashion. In classical reactors, the reaction conversion is often limited by the diffusion of reactants into the pores of the catalyst or catalyst carrier pellets. If the catalyst is inside the pores of the membrane, the combination of the open pore path and transmembrane pressure provides easier access for the reactants to the catalyst. Two contactor configurations—forced-flow mode or opposing reactant mode—can be used with these catalytic membranes, which do not necessarily need to be permselective. It is estimated that a membrane catalyst could be 10 times more active than in the form of pellets, provided that the membrane thickness and porous texture, as well as the quantity and location of the catalyst in the membrane, are adapted to the kinetics of the reaction. For biphasic applications (gas/catalyst), the porous texture of the membrane must favor gas-wall (catalyst) interactions to ensure a maximum contact of the reactant with the catalyst surface. In the case of catalytic consecutive-parallel reaction systems, such as the selective oxidation of hydrocarbons, the gas-gas molecular interactions must be limited because they are nonselective and lead to a total oxidation of reactants and products. For these reasons, small-pore mesoporous or microporous... 

The key problem here is the preparation of these plates. The plates contained one inert hydrophobic part close to the hydrogen gas side, and another part consisting of a catalytically active metal on various types of carrier powder. The hydrophobic layer was made of 30-50-fjLm nonporous PTFE particles. The catalyst carrier particles were porous (mean pore diameter of 10 nm) with a particle size of about 5 p.m. The catalytic material was of three different types 10% Pd on alumina, 10% Pd on carbon, and 1.9% Pd on Ni0/Si02. In addition to these powder materials, the plates contained nets of nickel wire (0.16 mm) or glass fibers (0.2 mm) as reinforcement. The catalytic plates were prepared... 

Concerning the preparation techniques, there are different approaches from vapor or liquid phase. The critical aspects, that have to be taken into account, are the reliability of the preparation process, the quality of the nanostructures prepared and the integration into final devices. Among the most promising techniques there are catalyst assisted vapor phase transport and thermal oxidation. Vapor phase technique consists in the evaporation of the oxide powder in a furnace with controlled atmosphere. In general the pressure is lower than lOOmbar to ease the vaporization of the oxide powder and an inert gas carrier is used to facilitate the mass transport from the source to the substrates, where the vapors condense in form of nanowires. 

Catalysis in internal nanospaces of liquid catalysis. A catalysis of this sort probably occurs in molten salts carried in pores of inert porous carriers, to increase gas-liquid contact surface areas — vanadium pentoxide catalysts for the oxidation of SO2 to SO3 [5]. Reactants diffuse into the nanolayer below the catalysts surface and the product countercurrently diffuses out. 

The catalyst effectiveness factor rji was calculated from the pore network model of Wood and Gladden [15] under the conditions on which capillary condensation was expected. The pore network model was solved over a range of temperatures from 553 to 580 K and for several pressures in the interval 20-40 bar to create a database of effectiveness factors for input to the macroscopic reactor model. The hydrodesulfurization of 1 mole % diethyl sulfide in an inert dodecane carrier was considered, with a molar gas oil ratio of 4. The catalyst was taken to have a connectivity of 6 and a normal distribution of pore sizes with a mean of 136 A and standard deviation of 28 A. By using the results of the pore network simulation as input to the macroscopic fixed bed reactor model, capillary condensation at the scale of the catalyst pellets was accounted for. 

The large surface area and chemical inertness of CNFs can be applied in catalysis. For example, nanofibers loaded with metallic nanoparticles (Rh, Pt, Pd) are appropriate catalyst carriers for hydrogenation reactions. The elimination and recycling of the catalyst after the reaction is not a problem, nanofibers are very effective in the terms of time and conversion, and they can serve several times without loss of activity [82],... 

Possible temperature gradients along the catalyst bed can be minimized using a single-row Temkin reactor. In such reactors, catalyst beds alternate with the beds of inert heat carrier, so that each catalyst bed is actually a differential reactor. The inert beds serve to remove heat in case of an exothermic reaction. Obviously, the higher the adiabatic heat is expected to rise, the larger number of alternating beds should be used. 

A small amount of a chemical substance is injected into the reactor during a small time interval. In a conventional pulse reactor, the substance is pulsed into an inert steady carrier-gas stream. The relaxation of the outlet composition following the perturbation by this pulse provides information about the reaction kinetics. In the TAP reactor, no carrier-gas stream is used and the substance is pulsed directly into the reactor. Transport occurs by diffusion only, in particular by well-defined Knudsen diffusion. The Knudsen diffusion coefficient does not depend on the composition of the reacting gas mixture. In a thin-zone TAP reactor (TZTR), the catalyst is located within a narrow zone only, similar to the differential PFR. 

Tower Packing. Increased surface area for the reaction, and longer durations, are provided for chemical reactions if the liquid reagents are allowed to trickle down a tower filled with inert shapes of high surface area. Chemical porcelain or other ceramics are frequently used. Such tower packings may also act as CATALYST CARRIERS (q.v.). The ASTM Standard is C515. 

Some effort has been put into achieving economic pathways to imides. Workers at Farbewerke Hoechst A.G. have claimed that the efficiency of thermal dehydration can be increased by the presence of an inert gas carrier, e.g., superheated steam, nitrogen, etc. The reactions were carried out at 220-280°C, in the presence of a catalyst such as phosphoric acid, p-toluene-sulfonic acid, and potassium hydrogen sulfate. Table 3.12 summarizes the best yields obtained. Isolation of the product was reportedly simple. 

As a consequence, operation time of the catalyst increased by 4-5 times and its regeneration was significantly facilitated (heating at 370°C on air for 10 h). The catalyst allows carrying out the dehydrogenation of 4,5,6,7-tetrahydroindole into indole without the use of inert gas carrier only in a solvent vapor flow (toluene) that is important for technology. 

Oxidation of methanol to formaldehyde with vanadium pentoxide catalyst was first patented in 1921 (90), followed in 1933 by a patent for an iron oxide—molybdenum oxide catalyst (91), which is stiU the choice in the 1990s. Catalysts are improved by modification with small amounts of other metal oxides (92), support on inert carriers (93), and methods of preparation (94,95) and activation (96). In 1952, the first commercial plant using an iron—molybdenum oxide catalyst was put into operation (97). It is estimated that 70% of the new formaldehyde installed capacity is the metal oxide process (98). 

The predominant process for manufacture of aniline is the catalytic reduction of nitroben2ene [98-95-3] ixh. hydrogen. The reduction is carried out in the vapor phase (50—55) or Hquid phase (56—60). A fixed-bed reactor is commonly used for the vapor-phase process and the reactor is operated under pressure. A number of catalysts have been cited and include copper, copper on siHca, copper oxide, sulfides of nickel, molybdenum, tungsten, and palladium—vanadium on alumina or Htbium—aluminum spinels. Catalysts cited for the Hquid-phase processes include nickel, copper or cobalt supported on a suitable inert carrier, and palladium or platinum or their mixtures supported on carbon. 

Dry reduced nickel catalyst protected by fat is the most common catalyst for the hydrogenation of fatty acids. The composition of this type of catalyst is about 25% nickel, 25% inert carrier, and 50% soHd fat. Manufacturers of this catalyst include Calsicat (Mallinckrodt), Harshaw (Engelhard), United Catalysts (Sud Chemie), and Unichema. Other catalysts that stiH have some place in fatty acid hydrogenation are so-called wet reduced nickel catalysts (formate catalysts), Raney nickel catalysts, and precious metal catalysts, primarily palladium on carbon. The spent nickel catalysts are usually sent to a broker who seUs them for recovery of nickel value. Spent palladium catalysts are usually returned to the catalyst suppHer for credit of palladium value. 

Pesticides. Many pesticides are highly concentrated and are in a physical form requiring further treatment to permit effective appHcation. Typically carriers or diluents are used (see Insectcontroltechnology). Although these materials are usually considered inert, they have a vital bearing on the potency and efficiency of the dust or spray because the carrier may consist of up to 99% of the final formulation. The physical properties of the carrier or diluent are of great importance in the uniform dispersion, the retention of pesticide by the plant, and in the preservation of the toxicity of the pesticide. The carrier must not, for example, serve as a catalyst for any reaction of the pesticide that would alter its potency. 

Although they are termed homogeneous, most industrial gas-phase reactions take place in contact with solids, either the vessel wall or particles as heat carriers or catalysts. With catalysts, mass diffusional resistances are present with inert solids, the only complication is with heat transfer. A few of the reactions in Table 23-1 are gas-phase type, mostly catalytic. Usually a system of industrial interest is liquefiea to take advantage of the higher rates of liquid reactions, or to utihze liquid homogeneous cat ysts, or simply to keep equipment size down. In this section, some important noncatalytic gas reactions are described. 

A gas-liquid-particle process termed cold hydrogenation has been developed for this purpose. The hydrogenation is carried out in fixed-bed operation, the liquefied hydrocarbon feed trickling downwards in a hydrogen atmosphere over the solid catalyst, which may be a noble metal catalyst on an inert carrier. Typical process conditions are a temperature of 10°-20°C and a pressure of 2.5-7 atm gauge. The hourly throughput is as high as 20-kg hydrocarbon feed per liter of catalyst volume. 

It has been pointed out (S2) that this type of operation might be widely applicable for organic oxidation processes, provided suitable inert carrier liquids can be found. It may be noted in this connection that the liquid must be reasonably resistant against oxidation and that it must not cause catalyst deactivation—for example, by chemisorption. 

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