Catalyst pelleted

Although mote expensive to fabricate than the pelleted catalyst, and usually more difficult to replace or regenerate, the honeycomb catalyst is more widely used because it affords lower pressure losses from gas flow it is less likely to collect particulates (fixed-bed) or has no losses of catalyst through attrition, compared to fiuidized-bed and it allows a mote versatile catalyst bed design (18), having a weU-defined flow pattern (no channeling) and a reactor that can be oriented in any direction. 

One of the reasons for developing the parallel plate catalyst was to reduce the pressure drop across the catalyst bed and consequently to reduce power costs for circulating the recycle gas. For pressure drop measurements across the 2-ft long catalyst beds, see Table X. These data show that the pressure drop across the parallel plates is about 1/15 of that across the pelleted catalyst bed. 

Heat-exchanger type PROX system with non-pellet catalyst... 

A small-scale PROX system was manufactured in a type of heat exchanger using non-pellet catalyst. Pt-Ru catalyst screened was impregnated on the support sheet. The support sheet was made by coating y-AlaOs on porous SUS-mesh plate (thickness 1.0 mm). The surface area of the catalyst sheet was 96 mVg. The catalyst sheet was applied to a heat exchanger type reactor of PROX as shown in Fig. 2. The PROX reactor was manufactured as a unit module and tested. Fig. 3 is the test-set of the PROX. Air was applied as the coolant. 

Rajanikanth, B.S. and Ravi, V. (2002) Pulsed electrical discharges assisted by dielectric pellets/catalysts for diesel engine exhaust treatment, IEEE Trans. Diel. El. Insul. 9, 616-26. 

Catalytic coal liquefaction processes do not specifically use hydrogen donor solvents although coal is introduced into the liquefaction reactor as a slurry in a recycle liquid stream. Catalyst is used as a powder or as granules such as pellets or extrudates. If powdered catalyst is used, it is mixed with the coal/liquid stream entering the reactor. Pelleted catalyst can be used in fixed bed reactors if precautions are taken to avoid plugging with solids or in fluidized bed reactors. In the latter case, the reacting system is actually a three phase fluidized bed, that is, catalyst particles and coal solids, as well as liquid, are fluidized by gas. 

Fluidized catalytic processes, in which the finely powdered catalyst is handled as a fluid, have largely replaced the fixed-bed and moving-bed processes, which use a beaded or pelleted catalyst. A schematic flow diagram of fluid catalytic cracking (FCC) is shown in Fig. 4. 

The optimization of the catalyst formulation is relevant not only to the active species but also to the structure of the support. Indeed, structured catalysts in the form of monolith or foam offer great advantages over pellet catalysts, the most important one being the low pressure drop associated with the high flow rates that are common in environmental applications. 

In order to set up the ATR reactor, a commercial pelletized catalyst, 0.3%Pt/Al2O3 (Engelhard), was used. 

These cracking and H-addition processes also require catalysts, and a major engineering achievement of the 1970s was the development of hydroprocessing catalysts, in particular cobalt molybdate on alumina catalysts. The active catalysts are metal sulfides, which are resistant to sulfur poisoning. One of the major tasks was the design of porous pellet catalysts with wide pore structures that are not rapidly poisoned by heavy metals. 

Pellet. Catalyst pellets for fixed bed reactors are typically 1.5 - 10 mm in diameter. 

The heat curves, themselves, are informative. The kaolin-based pellet catalyst has a few more active sites then attapulgite, but its site activity decreases rapidly and to values only about 3 kcal./mole above the heat of liquefaction of the liquid at maximum coverage. Obviously, a distinction cannot be made between physical adsorption and chemisorption for some of the amine adsorbed at full coverage on the cracking catalyst. On the other hand, attapulgite has a much narrower distribution of adsorption energies, and the lowest heats are about double the heat of liquefaction of butyl amine. Therefore, it appears safe to conclude that the amount remaining after evacuation at 25° is chemisorbed. 

Catalytic materials can be physically supported on either pelleted or monolithic substrates. In the case of the pelleted catalyst, the support is an activated alumina. A typical monolithic catalyst is composed of a channeled ceramic (cordierilc) support having, for example. 300 to 400 square channels per square inch on which an activated alumina layer is applied. The active agents (platinum, palladium, rhodium, etc.) arc then highly dispersed on the alumina. 

In the case of pelleted catalyst, the pellets are confined by screens (Fig. 11 the monolithic-lype catalyst (Fig. 2) being a single rigid material. 

Activated Layer Loss. Loss of the catalytic layer is the third method of deactivation. Attrition, erosion, or loss of adhesion and exfoliation of the active catalytic layer all result in loss of catalyst performance. The monolithic honeycomb catalyst is designed to be resistant to all of these mechanisms. There is some erosion of the inlet edge of the cells at the entrance to the monolithic honeycomb, but this loss is minor. The pelletted catalyst is more susceptible to attrition losses because the pellets in the catalytic bed mb against each other. Improvements in the design of the pelletted converter, the surface hardness of the pellets, and the depth of the active layer of the pellets also minimize loss of catalyst performance from attrition in that converter. 

The amount of catalyst used per vehicle depends on engine size, catalyst location, desired efficiency, and several other considerations. Since it is necessary to relate the amount of catalyst to that of the poison which may come in contact with it, we indicate that on a typical U. S. eight-cylinder vehicle, made in 1977, two monolithic catalysts, each weighing about 1 kg, are employed. The weight of a pelleted catalyst on a similar vehicle is of the order of 3 kg. Furthermore, the pelleted catalysts... 

When varying the temperature of the catalyst, while keeping all other variables constant, it was noticed in laboratory devices (30), burning iso-octane containing TEL, that the retention of lead on monolithic catalysts does increase with temperature (10) in the 350°-760°C range. In burner experiments with monolithic base metal catalysts (21) lead retention doubled when the temperature was increased from 600° to 850°C. In dynamometer studies of pelleted catalysts, again, a temperature increase from 550° to 750°C caused a sevenfold increase in lead retention (23). 

If one assigns, after Yao (38), the area occupied by a surface sulfate group as 30 A2, and if the sulfur content and the BET area are known, it is possible to estimate whether, indeed, sulfur retention is kept below one monolayer. Table VI shows a compilation of sulfur retention, recalculated as number of monolayers. The buildup of sulfur at a given temperature takes place during relatively short exposures to the exhaust, typically of the order of a few thousand miles of vehicle operation. When the temperature is changed, the extent of retention will change. Thus, a certain pelleted catalyst (42) accumulated in 3000 miles about 0.5% of sulfur,... 

Not surprisingly, all the data pertaining to axial distribution of contaminants in the bed were obtained for monolithic catalysts, where such determination is performed simply by successive sectioning (see Fig. 3) and analysis of each separate section. In pelleted catalysts there is considerable spatial mixing of the pellets during operation, and the sampling is also difficult. 

The distribution of contaminants within the porous layer again has to be considered separately for monolithic and pelleted catalysts. Gradients of the contaminant concentration in both cases can be very steep or relatively flat. Some inferences on the poison-carrying species can be deduced from such gradients. 

The evidence that phosphorus in fuel is detrimental to the oxidation activity of noble metal catalysts is quite convincing. Data from engine dynamometer runs with pelleted catalysts (28) show that raising the level of phosphorus from 60 to 130 mg/gal (added as cresyl diphenylphosphate, CDP) at a low concentration of lead, markedly suppresses the oxidation of hydrocarbons and of carbon monoxide. The effect on the oxidation of... 

Commonly used levels of decomposition are catalyst surface, single catalyst pellet, catalyst bed, reactor including heat exchangers, mixing and distributing devices, and an entire unit with the catalytic reactor as one of its elements. Each lower element is a component of the higher level. It is invariable to the dimension of an upper element and can be studied separately. 

In the past, laboratory batch reactors (which are still our workhorses) with powder catalysts were applied and somehow showed their limitations with pellet catalysts. 

---